Name: visualizing angiogenesis by multiphoton microscopy in vivo in genetically modified 3d-plga/nhap scaffold for calvarial critical bone defect repair
Uploaded: 2017-09-07T12:30:00
Description: Watch this Scientific Journal Video about Visualizing Angiogenesis by Multiphoton Microscopy In Vivo in Genetically Modified 3D-PLGA/nHAp Scaffold for Calvarial Critical Bone Defect Repair at JoVE.com

This study was supported by the Shenzhen Peacock Program, China (No. 110811003586331), the Shenzhen Basic Research Program (No. JCYJ20150401150223631, No. JCYJ20150401145529020, and No. JCYJ20160331190714896), the Guangdong Public Research and Capacity Building Special Program (No. 2015A020212030), the National Natural Science Foundation of China (No. 81501893), the National Major Basic Research Program of China (2013CB945503), and the SIAT Innovation Program for Excellent Young Researchers (Y5G010).

The animal care was in compliance with the Guide for the Care and Use of Laboratory Animals of Guangdong Province. All procedures were performed under the supervision and approval of the Ethics Committee for Animal Research, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences.
1. Lentiviral (LV) Production
<ol>
	<li>Clone the pdgf-b cDNA into a lentiviral expression vector (pLenti6/5-eGFP or LV-eGFP) at a custom multiple-cloning site downstream of the cytomegalov...

<ol>
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E., Mosheiff, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+engineering+approaches+for+bone+repair:+concepts+and+evidence.">Tissue engineering approaches for bone repair: concepts and evidence.</a> Injury. 42 (6), 609-613 (2011).</li><li>Chiarello, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=allograft+and+bone+substitutes+in+reconstructive+orthopedic+surgery.">allograft and bone substitutes in reconstructive orthopedic surgery.</a> Aging Clin Exp Res. 25, S101-S103 (2013).</li><li>Elangovan, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+enhancement+of+bone+regeneration+by+gene+activated+matrix+encoding+for+platelet+derived+growth+factor.">The enhancement of bone regeneration by gene activated matrix encoding for platelet derived growth factor.</a> Biomaterials. 35 (2), 737-747 (2014).</li><li>Bouyer, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+delivery+of+tunable+doses+of+BMP-2+from+an+adaptable+polymeric+scaffold+induces+volumetric+bone+regeneration.">Surface delivery of tunable doses of BMP-2 from an adaptable polymeric scaffold induces volumetric bone regeneration.</a> Biomaterials. 104, 168-181 (2016).</li><li>Rezwan, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biodegradable+and+bioactive+porous+polymer/inorganic+composite+scaffolds+for+bone+tissue+engineering.">Biodegradable and bioactive porous polymer/inorganic composite scaffolds for bone tissue engineering.</a> Biomaterials. 27 (18), 3413-3431 (2006).</li><li>Burg, K. J., Porter, S., Kellam, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomaterial+developments+for+bone+tissue+engineering.">Biomaterial developments for bone tissue engineering.</a> Biomaterials. 21 (23), 2347-2359 (2000).</li><li>Xiao, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modifications+of+collagen-based+biomaterials+with+immobilized+growth+factors+or+peptides.">Modifications of collagen-based biomaterials with immobilized growth factors or peptides.</a> Methods. 84, 44-52 (2015).</li><li>Chen, G., Lv, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immobilization+and+Application+of+Electrospun+Nanofiber+Scaffold-based+Growth+Factor+in+Bone+Tissue+Engineering.">Immobilization and Application of Electrospun Nanofiber Scaffold-based Growth Factor in Bone Tissue Engineering.</a> Curr Pharm Des. 21 (15), 1967-1978 (2015).</li><li>Kofron, M. D., Li, X., Laurencin, C. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein-+and+gene-based+tissue+engineering+in+bone+repair.">Protein- and gene-based tissue engineering in bone repair.</a> Curr Opin Biotechnol. 15 (5), 399-405 (2004).</li><li>Chen, F. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+insights+into+and+novel+applications+of+release+technology+for+periodontal+reconstructive+therapies.">New insights into and novel applications of release technology for periodontal reconstructive therapies.</a> J Control Release. 149 (2), 92-110 (2011).</li><li>Winn, S. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+therapy+approaches+for+modulating+bone+regeneration.">Gene therapy approaches for modulating bone regeneration.</a> Adv Drug Deliv Rev. 42 (1-2), 121-138 (2000).</li><li>Chang, P. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adenovirus+Encoding+Human+Platelet-Derived+Growth+Factor-B+Delivered+to+Alveolar+Bone+Defects+Exhibits+Safety+and+Biodistribution+Profiles+Favorable+for+Clinical+Use.">Adenovirus Encoding Human Platelet-Derived Growth Factor-B Delivered to Alveolar Bone Defects Exhibits Safety and Biodistribution Profiles Favorable for Clinical Use.</a> Hum Gene Ther. 20 (5), 486-496 (2009).</li><li>Phipps, M. C., Xu, Y. Y., Bellis, S. 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C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=PDGF-B+gene+therapy+accelerates+bone+engineering+and+oral+implant+osseointegration.">PDGF-B gene therapy accelerates bone engineering and oral implant osseointegration.</a> Gene Ther. 17 (1), 95-104 (2010).</li><li>Javed, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Significance+of+the+platelet-derived+growth+factor+in+periodontal+tissue+regeneration.">Significance of the platelet-derived growth factor in periodontal tissue regeneration.</a> Arch Oral Biol. 56 (12), 1476-1484 (2011).</li><li>Murali, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomimetic+hybrid+porous+scaffolds+immobilized+with+platelet+derived+growth+factor-BB+promote+cellularization+and+vascularization+in+tissue+engineering.">Biomimetic hybrid porous scaffolds immobilized with platelet derived growth factor-BB promote cellularization and vascularization in tissue engineering.</a> J Biomed Mater Res A. 104 (2), 388-396 (2016).</li><li>Andrae, J., Gallini, R., Betsholtz, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+platelet-derived+growth+factors+in+physiology+and+medicine.">Role of platelet-derived growth factors in physiology and medicine.</a> Genes Dev. 22 (10), 1276-1312 (2008).</li><li>Wosnitza, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasticity+of+human+adipose+stem+cells+to+perform+adipogenic+and+endothelial+differentiation.">Plasticity of human adipose stem cells to perform adipogenic and endothelial differentiation.</a> Differentiation. 75 (1), 12-23 (2007).</li><li>Hankenson, K. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Angiogenesis+in+bone+regeneration.">Angiogenesis in bone regeneration.</a> Injury. 42 (6), 556-561 (2011).</li><li>Schmidt, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+three-dimensional+quantification+of+VEGF-induced+scaffold+neovascularisation+by+microcomputed+tomography.">Rapid three-dimensional quantification of VEGF-induced scaffold neovascularisation by microcomputed tomography.</a> Biomaterials. 30 (30), 5959-5968 (2009).</li><li>Perng, C. 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C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+critical+size+defect+as+an+experimental+model+to+test+bone+repair+materials.">The critical size defect as an experimental model to test bone repair materials.</a> J Craniofac Surg. 1 (1), 60-68 (1990).</li><li>Hollanders, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bevacizumab+Revisited:+Its+Use+in+Different+Mouse+Models+of+Ocular+Pathologies.">Bevacizumab Revisited: Its Use in Different Mouse Models of Ocular Pathologies.</a> Curr Eye Res. 40 (6), 611-621 (2015).</li><li>Gao, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=QSIM:+quantitative+structured+illumination+microscopy+image+processing+in+ImageJ.">QSIM: quantitative structured illumination microscopy image processing in ImageJ.</a> Biomed Eng Online. 14, 4 (2015).</li><li>Kobat, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deep+tissue+multiphoton+microscopy+using+longer+wavelength+excitation.">Deep tissue multiphoton microscopy using longer wavelength excitation.</a> Opt Express. 17 (16), 13354-13364 (2009).</li><li>Lohmann, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bone+regeneration+induced+by+a+3D+architectured+hydrogel+in+a+rat+critical-size+calvarial+defect.">Bone regeneration induced by a 3D architectured hydrogel in a rat critical-size calvarial defect.</a> Biomaterials. 113, 158-169 (2016).</li><li>Lv, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+angiogenesis+and+osteogenesis+in+critical+bone+defects+by+the+controlled+release+of+BMP-2+and+VEGF:+implantation+of+electron+beam+melting-fabricated+porous+Ti6Al4V+scaffolds+incorporating+growth+factor-doped+fibrin+glue.">Enhanced angiogenesis and osteogenesis in critical bone defects by the controlled release of BMP-2 and VEGF: implantation of electron beam melting-fabricated porous Ti6Al4V scaffolds incorporating growth factor-doped fibrin glue.</a> Biomed Mater. 10 (3), (2015).</li><li>Guldberg, R. 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Bone is a highly vascularized tissue with a unique capacity to continuously heal and remodel throughout the lifetime of an individual1. The level of vascularization is important for osteogenesis and defect repair. Low vascularization limits the wide clinical application of tissue-engineered bone. Constructing a highly vascularized tissue-engineered bone according to the theory of biomimetics has become a tool for repairing large segment bone defects. Various kinds of scaffolds have been successful...

Bone is a highly vascularized tissue that continues to remodel during the lifetime of an individual1. The rapid and effective bone regeneration of large bone defects resulting from trauma, nonunion, tumor resections, or craniofacial malformations is a complex physiological process. Traditional therapeutic approaches used for bone defect repair include autograft and allograft implantation, but their use involves several problems and limitations, such as limited availability, significant donor site morbidity, a high risk of infection, and host immune rejection2,3. However, artificial bone grafts offer an efficient alternative to alleviate these limitations. They can be made from biodegradable materials, are easy to be fabricate with a suitable pore size, and can be genetically modified4,5.
Currently, various tissue engineering scaffolds have been employed in the development of tissue-engineered bone6,7. To induce bone repair and regeneration more effectively, engineered biomaterials combined with growth factors have emerged and achieved good results8,9. Unfortunately, the short half-life, easy-to-lose activity, and supraphysiological dosage of growth factors for therapeutic efficacy limit their clinical application10. To overcome these problems, the delivery of growth factor genes instead of growth factors has been demonstrated as an effective approach to sustain bioactivity for the treatment of osseous defects and diseases11,12. Viral vectors are promising delivery tools for tissue regeneration due to their high expressing efficiency13.
Among growth factors, platelet-derived growth factor (PDGF-BB) was selected in this study because it is not only a mitogen and chemoattractant for mesenchymal and osteogenic cells, but also a stimulant for angiogenesis14,15. Previous preclinical and clinical studies showed that PDGF-BB could safely and effectively promote bone repair in periodontal osseous defects16,17. Recent studies revealed that PDGF-BB stimulates angiogenesis by motivating endothelial cell migration and proliferation in vivo18,19. Furthermore, PDGF-BB can also render mesenchymal stem cells (MSCs) capable of differentiating into endothelial cells20, and this further highlights the potential role of MSCs in neovascularization. Therefore, inducing the de novo formation of vasculature in scaffolds with PDGF-BB is an important step for the repair of tissue grown into scaffolds in bone tissue engineering.
Bone defect healing is a dynamic tissue morphogenetic process that requires coordinated osteogenesis and angiogenesis at the repairing positions21. Neoangiogenesis into implanted tissue-engineered scaffolds is an essential pre-requisite for supplying cells with nutrients and oxygen for growth and survival and for removing metabolic waste. Commonly used imaging methods, including X-ray micro-computed tomography (microCT), magnetic resonance imaging (MRI), scanning electron microscopy (SEM), optical coherence tomography (OCT), and confocal laser scanning microscopy, are applied instead of histological examination to obtain angiogenesis information22,23. However, these methods face various obstacles in visualizing and measuring neovasculature in 3D scaffolds in bone tissue engineering. Multiphoton microscopy (MPM) is a comparatively novel bio-imaging technique that has the distinct advantage of simultaneously visualizing cells, extracellular matrix, and surrounding vascular networks in vivo. It possesses an inherent three-dimensional imaging capability for deep tissue penetration and causes low photodamage. Hence, in the last decade, MPM has gained much attention in biomedical studies24, including in neuroscience, immunology, and stem cell dynamics. However, it is barely used in orthopedic research.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Poly(D,L-lactide-co-glycolide) (PLGA)</td>
			<td>Sigma</td>
			<td>P1941</td>
			<td>L/G ratio 75:25, MW 66000-107000</td>
		</tr>
		<tr>
			<td>Hydroxyapatite nanoparticles</td>
			<td>Sigma</td>
			<td>702153</td>
			<td>Average diameter &#60; 200nm</td>
		</tr>
		<tr>
			<td>Chloroquine diphosphate salt</td>
			<td>Sigma</td>
			<td>C6628</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC-conjugated 250-kD dextran</td>
			<td>Sigma</td>
			<td>FD250S</td>
			<td></td>
		</tr>
		<tr>
			<td>1,4-dioxane</td>
			<td>lingfeng,Shanghai</td>
			<td></td>
			<td>0.45 micron</td>
		</tr>
		<tr>
			<td>Stericup filters</td>
			<td>Merck Millipore Corporation</td>
			<td>SLHV033RB</td>
			<td></td>
		</tr>
		<tr>
			<td>PDGF-BB Cdna</td>
			<td>Sino Biological, Inc</td>
			<td>MZ50801-G</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-PDGF-BB mouse polyclonal antibody</td>
			<td> BioVision, Inc</td>
			<td>5489-30T</td>
			<td></td>
		</tr>
		<tr>
			<td>PDGF-BB recombinant protein</td>
			<td></td>
			<td>4489-50</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium-phosphate transfection solution</td>
			<td>Promega Corporation</td>
			<td>E1200</td>
			<td></td>
		</tr>
		<tr>
			<td>L-DMEM</td>
			<td>Hyclone</td>
			<td>SH30021.01</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>Hyclone</td>
			<td>SH30028.01</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin, Liquid</td>
			<td>Thermo Fisher Scientific</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Thermo Fisher Scientific</td>
			<td>10099-141</td>
			<td></td>
		</tr>
		<tr>
			<td>Transwell </td>
			<td>Corning</td>
			<td>3422</td>
			<td></td>
		</tr>
		<tr>
			<td>Male BALB/c mice</td>
			<td>Guangdong Medical Laboratory Animal Center </td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sodium pentobarbital </td>
			<td>Merck</td>
			<td>1063180500</td>
			<td></td>
		</tr>
		<tr>
			<td>multiphoton microscopy</td>
			<td></td>
			<td></td>
			<td>A homemade in Shenzhen Institutes of Advanced Technology to detect two-photon excited fluorescence (TPEF) and second harmonic generation signal (SHG).</td>
		</tr>
		<tr>
			<td>isoflurane</td>
			<td>Keyuan, Shandong</td>
			<td>401750169</td>
			<td></td>
		</tr>
		<tr>
			<td>TRIzol reagent</td>
			<td>Invitrogen</td>
			<td>15596018</td>
			<td></td>
		</tr>
		<tr>
			<td>PrimeScript RT Master Mix (Perfect Real Time)</td>
			<td>Takara</td>
			<td>RR420B</td>
			<td></td>
		</tr>
		<tr>
			<td>SYBR Premix Ex Taq (Tli RNaseH Plus)</td>
			<td>Takara</td>
			<td>RR036B</td>
			<td></td>
		</tr>
		<tr>
			<td>Hematoxylin and eosin</td>
			<td>Beyotime</td>
			<td>C0105</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin</td>
			<td>Leica </td>
			<td>RM2235</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultracentrifuge OPtima L-100XP</td>
			<td>Beckman Coulter</td>
			<td>L-100XP</td>
			<td></td>
		</tr>
		<tr>
			<td>Low-temperature printer </td>
			<td>Tsinghua university</td>
			<td></td>
			<td>A homemade in Tsinghua university</td>
		</tr>
		<tr>
			<td>LightCycler 480 instrument </td>
			<td>Roche</td>
			<td>5815916001</td>
			<td></td>
		</tr>
		<tr>
			<td>microCT</td>
			<td>Bruker</td>
			<td>1176</td>
			<td></td>
		</tr>
		<tr>
			<td>commercial software</td>
			<td>Bruker</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

visualizing angiogenesis by multiphoton microscopy in vivo in genetically modified 3d-plga/nhap scaffold for calvarial critical bone defect repair

The reconstruction of critically sized bone defects remains a serious clinical problem because of poor angiogenesis within tissue-engineered scaffolds during repair, which gives rise to a lack of sufficient blood supply and causes necrosis of the new tissues. Rapid vascularization is a vital prerequisite for new tissue survival and integration with existing host tissue. The de novo generation of vasculature in scaffolds is one of the most important steps in making bone regeneration more efficient, allowing repairing tissue to grow into a scaffold. To tackle this problem, the genetic modification of a biomaterial scaffold is used to accelerate angiogenesis and osteogenesis. However, visualizing and tracking in vivo blood vessel formation in real-time and in three-dimensional (3D) scaffolds or new bone tissue is still an obstacle for bone tissue engineering. Multiphoton microscopy (MPM) is a novel bio-imaging modality that can acquire volumetric data from biological structures in a high-resolution and minimally-invasive manner. The objective of this study was to visualize angiogenesis with multiphoton microscopy in vivo in a genetically modified 3D-PLGA/nHAp scaffold for calvarial critical bone defect repair. PLGA/nHAp scaffolds were functionalized for the sustained delivery of a growth factor pdgf-b gene carrying lentiviral vectors (LV-pdgfb) in order to facilitate angiogenesis and to enhance bone regeneration. In a scaffold-implanted calvarial critical bone defect mouse model, the blood vessel areas (BVAs) in PHp scaffolds were significantly higher than in PH scaffolds. Additionally, the expression of pdgf-b and angiogenesis-related genes, vWF and VEGFR2, increased correspondingly. MicroCT analysis indicated that the new bone formation in the PHp group dramatically improved compared to the other groups. To our knowledge, this is the first time multiphoton microscopy was used in bone tissue-engineering to investigate angiogenesis in a 3D bio-degradable scaffold in vivo and in real-time.

Cylindrical Porous PLGA/nHAp scaffolds 0.6 mm in height and 4 mm in diameter were fabricated with a 3D printer. The morphologies of the scaffolds were analyzed via scanning electron microscopy and microCT. Figure 1A shows the photograph of the implanted scaffold. MicroCT scanning revealed that more than 85% of the pores had sizes ranging from 200 to 400 &#181;m (Figure 1B). SEM imaging demonstrated that the surface of the scaffold had a rough microtopogra...

Watch this Scientific Journal Video about Visualizing Angiogenesis by Multiphoton Microscopy In Vivo in Genetically Modified 3D-PLGA/nHAp Scaffold for Calvarial Critical Bone Defect Repair at JoVE.com

Visualizing Angiogenesis by Multiphoton Microscopy In Vivo in Genetically Modified 3D-PLGA/nHAp Scaffold for Calvarial Critical Bone Defect Repair

Here, we present a protocol to visualize blood vessel formation in vivo and in real-time in 3D scaffolds by multiphoton microscopy. Angiogenesis in genetically modified scaffolds was studied in a murine calvarial critical bone defect model. More new blood vessels were detected in the treatment group than in controls.

Visualizing Angiogenesis by Multiphoton Microscopy In Vivo in Genetically Modified 3D-PLGA/nHAp Scaffold for Calvarial Critical Bone Defect Repair

The reconstruction of critically sized bone defects remains a serious clinical problem because of poor angiogenesis within tissue-engineered scaffolds ...

The overall goal of this experiment is to visualize In Vivo blood vessel formation in three dimensional scaffolds in real time by multi photon microscopy. These measured are key question in bone generating field such as how to neutralize and trick in vivo blood vessel formation in three dimensional scaffolds in real time. The one advantage of this technique is that it enables to simultaneously neutralize CERES, extracellular metrics and surrounding molecular networks in vivo.To begin, prepare a homogenous solution containing 20 grams of PLGA and 20 milliliters of 1, 4 dioxane. Then, add two grams of powdered nHAP to the solution. Using a magnetic stirrer, mix the suspension vigorously at 1500 rpm at room temperature for 16 hours to form a uniform paste that will be used for printing porous PLGA NHAP scaffolds.Once printed, freeze dry the scaffolds for 48 hours to completely remove any solvent. And then sterilize them in 75 percent ethanol for one hour. Afterward, lifalyze them once more to obtain neutral, antiseptic material.Next, add four point five times 10 to the fifth of lentiviral particles to each scaffold and allow the particles to absorb in a humidified incubator maintaining 37 degrees celsius for two hours. Now that lentiviral particle's absorbed on the scaffolds, wash the scaffolds twice with two milliliters of PBS to remove any unbound residues. Snap freeze the washed scaffolds in liquid nitrogen.And after lifalyzing once again, store them at minus 80 degrees celsius for further studies. Transfer 3d scaffolds previously coated with four point five times ten to the fifth lentiviral particles carrying green fluorescent protein in two point zero milliliter cryogenic vials filled with one milliliter of complete DMEM and incubate them at 37 degrees celsius with shaking for five days. Every twelve hours of incubation, collect one milliliter samples of the media containing lentiviral particles released from the scaffolds, and replace them with one milliliter of fresh media.To transduce HEK293T cells, first remove the medium from HEK293T cells cultured in a 12 well plate and wash the cells twice with PBS. Then, add one milliliter of the previously collected media to the washed HEK293T cells and incubate the plate for 48 hours at 37 degrees celsius in a humidified incubator. After 48 hours of incubation, measure the number of GFB positive HEK293T cells by flow cytometry to determine the number of bioactive lentiviral particles.To begin, randomly divide C57 black six mice into three treatment groups:control, PH, and PHp of 14 animals each. Shave the skin on the head of an anesthetized mouse and disinfect the surface with an iodine tincture and then 75 percent alcohol solution. Place the head of the mouse in a stereotactic instrument and size the skin with a scalpel and then using scissors, make a one centimeter linear cut.Using a sterile cotton swab, scrape the periosteum off the cranial bone to reveal it's surface. Then, on the left side of the skull, create with a trephine bur a four millimeter diameter critical size defect. Transplant the scaffold into the side of the bone defect.Use ophthalmic forceps to gently cover the surgical site with the periosteum. Afterward, close the wound by applying three stitches per each centimeter of incision. Finally, administer the analgesic buprenorphine to control post-operative pain and keep the animal on a heating pad to maintain it's body temperature until it wakens.When the mouse regains consciousness, provide it with food and water and monitor it's everyday activity until the end of the experiment. After assembling the multi photon microscopy system for TPEF and SHG imaging, tune the femtosecond titanium sapphire laser to 860 nanometers. To visualize newly formed blood vessels, inject the mouse intravenously with 200 microliters of a 10 milligram per milliliter dextran solution in saline, then, using the stereotactic instrument, immobilize the anesthetized animal on a heating plate to maintain it's body temperature at 37 degrees celsius.Inject the mouse with 200 microliters of saline intraperitoneally to prevent dehydration. Finally, provide the animal with a three percent mixture of isoflurane in 100 percent oxygen to maintain sufficient anesthesia and analgesia during imaging. To begin imaging, scan a pair of galvo mirrors to create a 512 by 512 micrometer sampling area.Then, using an NA one point O water immersion objective lens, focus the excitation beam on the sample and collect the back scattered TPEF HSG signal. Set the field of view so that it covers the normal bone area and the edge of the defect in the control group, but only the implanted scaffold when imaging the animal from PH or PHp group. Then, scan five different sites of the defect.Acquire image stacks every 12 seconds over a two hour imaging period. Presented here is a photograph of the scaffold prepared with the 3d printing technique, along with a micro-CT image showing the overall porosity of the prepared material. The microporous structure of the scaffold is shown in an SEM image acquired at 5000 times magnification.As shown, HEK293T cells treated with media containing lentiviral particles released from the scaffolds efficiently expressed the green fluorescent protein. As estimated by flow cytometry, the total number of the released particles reached approximately 40 percent. The most robust release effect was observed within the first 24 hours of the study, and gradually decreased over time, confirming that lentiviral particles coated on the scaffolds maintain their biological activity for up to 96 hours.In vivo analysis of the blood vessels formed within a calvarial bone defect showed that new blood vessels, while undetectable in the control group of mice, were clearly visible in both PH and PHp groups eight weeks after scaffold transplantation. Additionally, while in both PH and PHp groups many collagen deposition sites were detected, only in the PHp group an increasing number of smaller vessels growing into scaffolds could be observed and the overall blood vessel area was significantly different. Once mastered, this technique can be done in two hours if it is performed properly.While attempting this procedure, it's important to remember to immobilize the head of the mouse to keep it still during scanning to avoid any artifacts. Following this procedure, other methods such as photoacoustic imaging can be performed in order to provide additional data such as deep tissue images. After its development, this technique paved the way for researchers in the field of bone regeneration to investigate angiogenesis in transplants.After watching this video, you should have a good understanding of how to visualize in vivo plasma formation in 3d scaffolds in real time, and microphoton microscopy.

visualizing-angiogenesis-multiphoton-microscopy-vivo-genetically

Research

JoVE Journal

Bioengineering

Visualizing Proteins and Macromolecular Complexes by Negative Stain EM: from Grid Preparation to Image Acquisition

Single particle electron microscopy (EM), of both negative stained or frozen hydrated biological samples, has become a versatile tool in structural biology 1. In recent years, this method has achieved great success in studying structures of proteins and macromolecular complexes 2, 3. Compared with electron cryomicroscopy (cryoEM), in which frozen hydrated protein samples are embedded in a thin layer of vitreous ice 4, negative staining is a simpler sample preparation method in which protein samples are embedded in a thin layer of dried heavy metal salt to increase specimen contrast 5. The enhanced contrast of negative stain EM allows examination of relatively small biological samples. In addition to determining three-dimensional (3D) structure of purified proteins or protein complexes 6, this method can be used for much broader purposes. For example, negative stain EM can be easily used to visualize purified protein samples, obtaining information such as homogeneity/heterogeneity of the sample, formation of protein complexes or large assemblies, or simply to evaluate the quality of a protein preparation.
In this video article, we present a complete protocol for using an EM to observe negatively stained protein sample, from preparing carbon coated grids for negative stain EM to acquiring images of negatively stained sample in an electron microscope operated at 120kV accelerating voltage. These protocols have been used in our laboratory routinely and can be easily followed by novice users.

Visualizing protein samples by negative stain electron microscopy (EM) has become a popular structural analysis method. It is useful for quantitative structural analysis, such as calculating a 3D reconstruction of the molecules being studied, and also for qualitative examination of the quality of protein preparations. In this article we present detailed protocols for preparing the EM grids, staining the sample and visualizing the sample in an electron microscope. Novice users can follow these protocols easily and to utilize negative stain EM as a routine assay, in addition to other biochemical assays, for evaluating their protein samples.

Single particle electron microscopy (EM), of both negative stained or frozen hydrated biological samples, has become a versatile tool in structural ...

Video-rate Scanning Confocal Microscopy and Microendoscopy

Confocal microscopy has become an invaluable tool in biology and the biomedical sciences, enabling rapid, high-sensitivity, and high-resolution optical sectioning of complex systems. Confocal microscopy is routinely used, for example, to study specific cellular targets1, monitor dynamics in living cells2-4, and visualize the three dimensional evolution of entire organisms5,6. Extensions of confocal imaging systems, such as confocal microendoscopes, allow for high-resolution imaging in vivo7 and are currently being applied to disease imaging and diagnosis in clinical settings8,9.
Confocal microscopy provides three-dimensional resolution by creating so-called "optical sections" using straightforward geometrical optics. In a standard wide-field microscope, fluorescence generated from a sample is collected by an objective lens and relayed directly to a detector. While acceptable for imaging thin samples, thick samples become blurred by fluorescence generated above and below the objective focal plane. In contrast, confocal microscopy enables virtual, optical sectioning of samples, rejecting out-of-focus light to build high resolution three-dimensional representations of samples.
Confocal microscopes achieve this feat by using a confocal aperture in the detection beam path. The fluorescence collected from a sample by the objective is relayed back through the scanning mirrors and through the primary dichroic mirror, a mirror carefully selected to reflect shorter wavelengths such as the laser excitation beam while passing the longer, Stokes-shifted fluorescence emission. This long-wavelength fluorescence signal is then passed to a pair of lenses on either side of a pinhole that is positioned at a plane exactly conjugate with the focal plane of the objective lens. Photons collected from the focal volume of the object are collimated by the objective lens and are focused by the confocal lenses through the pinhole. Fluorescence generated above or below the focal plane will therefore not be collimated properly, and will not pass through the confocal pinhole1, creating an optical section in which only light from the microscope focus is visible. (Fig 1). Thus the pinhole effectively acts as a virtual aperture in the focal plane, confining the detected emission to only one limited spatial location.
Modern commercial confocal microscopes offer users fully automated operation, making formerly complex imaging procedures relatively straightforward and accessible. Despite the flexibility and power of these systems, commercial confocal microscopes are not well suited for all confocal imaging tasks, such as many in vivo imaging applications. Without the ability to create customized imaging systems to meet their needs, important experiments can remain out of reach to many scientists.
In this article, we provide a step-by-step method for the complete construction of a custom, video-rate confocal imaging system from basic components. The upright microscope will be constructed using a resonant galvanometric mirror to provide the fast scanning axis, while a standard speed resonant galvanometric mirror will scan the slow axis. To create a precise scanned beam in the objective lens focus, these mirrors will be positioned at the so-called telecentric planes using four relay lenses. Confocal detection will be accomplished using a standard, off-the-shelf photomultiplier tube (PMT), and the images will be captured and displayed using a Matrox framegrabber card and the included software.

The complete construction of a custom, real-time confocal scanning imaging system is described. This system, which can be readily used for video-rate microscopy and microendoscopy, allows for an array of imaging geometries and applications not accessible using standard commercial confocal systems, at a fraction of the cost.

Confocal microscopy has become an invaluable tool in biology and the biomedical sciences, enabling rapid, high-sensitivity, and high-resolution optical ...

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to evaluate new strategies that aim at improving vascularization, reliable methods are required to make the in-growth of new blood vessels into bio-artificial scaffolds visible and quantify the results. Over the past couple of years, our group has introduced a full skin defect model that enables the direct visualization of blood vessels by transillumination and provides the possibility of quantification through digital segmentation. In this model, one surgically creates full skin defects in the back of mice and replaces them with the material tested. Molecules or cells of interest can also be incorporated in such materials to study their potential effect. After an observation time of one&#8217;s own choice, materials are explanted for evaluation. Bilateral wounds provide the possibility of making internal comparisons that minimize artifacts among individuals as well as of decreasing the number of animals needed for the study. In comparison to other approaches, our method offers a simple, reliable and cost effective analysis. We have implemented this model as a routine tool to perform high-resolution screening when testing vascularization of different biomaterials and bio-activation approaches.

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Vascularization is key to approaches in successful tissue engineering. Therefore, reliable technologies are required to evaluate the development of vascular networks in tissue-constructs. Here we present a simple and cost-effective method to visualize and quantify vascularization in vivo.

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to ...

Assessing Leukocyte-endothelial Interactions Under Flow Conditions in an Ex Vivo Autoperfused Microflow Chamber Assay

Leukocyte-endothelial interactions are early and critical events in acute and chronic inflammation and can, when dysregulated, mediate tissue injury leading to permanent pathological damage. Existing conventional assays allow the analysis of leukocyte adhesion molecules only after the extraction of leukocytes from the blood. This requires the blood to undergo several steps before peripheral blood leukocytes (PBLs) can be ready for analysis, which in turn can stimulate PBLs influencing the research findings. The autoperfused micro flow chamber assay, however, allows scientists to study early leukocytes functional dysregulation using the systemic flow of a live mouse while having the freedom of manipulating a coated chamber. Through a disease model, the functional expression of leukocyte adhesion molecules can be assessed and quantified in a micro-glass chamber coated with immobilized endothelial adhesion molecules ex vivo. In this model, the blood flows between the right common carotid artery and left external jugular vein of a live mouse under anesthesia, allowing the interaction of native PBLs in the chamber. Real-time experimental analysis is achieved with the assistance of an intravital microscope as well as a Harvard Apparatus pressure device. The application of a flow regulator at the input point of the glass chamber allows comparable physiological flow conditions amongst the experiments. Leukocyte rolling velocity is the main outcome and is measured using the National Institutes of Health open-access software ImageJ. In summary, the autoperfused micro flow chamber assay provides an optimal physiological environment to study leukocytes endothelial interaction and allows researchers to draw accurate conclusions when studying inflammation.

Assessing Leukocyte-endothelial Interactions Under Flow Conditions in an Ex Vivo Autoperfused Microflow Chamber Assay

Here, we present a protocol that allows the investigator to assess leukocyte recruitment dynamics ex vivo by connecting a chamber coated with endothelial-derived adhesion molecules to the circulatory system of a mouse. This method offers significant advantages since it allows for leukocyte assessment under relative biological conditions.

Leukocyte-endothelial interactions are early and critical events in acute and chronic inflammation and can, when dysregulated, mediate tissue injury ...

Distinctive Capillary Action by Micro-channels in Bone-like Templates can Enhance Recruitment of Cells for Restoration of Large Bony Defect

Without an active, thriving cell population that is well-distributed and stably anchored to the inserted template, exceptional bone regeneration does not occur. With conventional templates, the absence of internal micro-channels results in the lack of cell infiltration, distribution, and inhabitance deep inside the templates. Hence, a highly porous and uniformly interconnected trabecular-bone-like template with micro-channels (biogenic microenvironment template; BMT) has been developed to address these obstacles. The novel BMT was created by innovative concepts (capillary action) and fabricated with a sponge-template coating technique. The BMT consists of several structural components: inter-connected primary-pores (300-400 &#181;m) that mimic pores in trabecular bone, micro-channels (25-70 &#181;m) within each trabecula, and nanopores (100-400 nm) on the surface to allow cells to anchor. Moreover, the BMT has been documented by mechanical test study to have similar mechanical strength properties to those of human trabecular bone (~3.8 MPa)12.
The BMT exhibited high absorption, retention, and habitation of cells throughout the bridge-shaped (&#928;) templates (3 cm height and 4 cm length). The cells that were initially seeded into one end of the templates immediately mobilized to the other end (10 cm distance) by capillary action of the BMT on the cell media. After 4 hr, the cells homogenously occupied the entire BMT and exhibited normal cellular behavior. The capillary action accounted for the infiltration of the cells suspended in the media and the distribution (active migration) throughout the BMT. Having observed these capabilities of the BMT, we project that BMTs will absorb bone marrow cells, growth factors, and nutrients from the periphery under physiological conditions.
The BMT may resolve current limitations via rapid infiltration, homogenous distribution and inhabitance of cells in large, volumetric templates to repair massive skeletal defects.

A step-by-step generic process to create a bone-like template with engineered micro-channels is presented. High absorption and retention capabilities of the template are demonstrated by capillary action via micro-channels.

Without an active, thriving cell population that is well-distributed and stably anchored to the inserted template, exceptional bone regeneration does not ...

Production of Genetically Engineered Golden Syrian Hamsters by Pronuclear Injection of the CRISPR/Cas9 Complex

The pronuclear (PN) injection technique was first established in mice to introduce foreign genetic materials into the pronuclei of one-cell stage embryos. The introduced genetic material may integrate into the embryonic genome and generate transgenic animals with foreign genetic information following transfer of the injected embryos to foster mothers. Following the success in mice, PN injection has been applied successfully in many other animal species. Recently, PN injection has been successfully employed to introduce reagents with gene-modifying activities, such as the CRISPR/Cas9 system, to achieve site-specific genetic modifications in several laboratory and farm animal species. In addition to mastering the special set of microinjection skills to produce genetically modified animals by PN injection, researchers must understand the reproduction physiology and behavior of the target species, because each species presents unique challenges. For example, golden Syrian hamster embryos have unique handling requirements in vitro such that PN injection techniques were not possible in this species until recent breakthroughs by our group. With our species-modified PN injection protocol, we have succeeded in producing several gene knockout (KO) and knockin (KI) hamsters, which have been used successfully to model human diseases. Here we describe the PN injection procedure for delivering the CRISPR/Cas9 complex to the zygotes of the hamster, the embryo handling conditions, embryo transfer procedures, and husbandry required to produce genetically modified hamsters.

Pronuclear (PN) injection of the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein-9 nuclease (CRISPR/Cas9) system is a highly efficient method for producing genetically engineered golden Syrian hamsters. Herein, we describe the detailed PN injection protocol for the production of gene knockout hamsters with the CRISPR/Cas9 system.

The pronuclear (PN) injection technique was first established in mice to introduce foreign genetic materials into the pronuclei of one-cell stage embryos. ...

Rigid Embedding of Fixed and Stained, Whole, Millimeter-Scale Specimens for Section-free 3D Histology by Micro-Computed Tomography

For over a hundred years, the histological study of tissues has been the gold standard for medical diagnosis because histology allows all cell types in every tissue to be identified and characterized. Our laboratory is actively working to make technological advances in X-ray micro-computed tomography (micro-CT) that will bring the diagnostic power of histology to the study of full tissue volumes at cellular resolution (i.e., an X-ray Histo-tomography modality). Toward this end, we have made targeted improvements to the sample preparation pipeline. One key optimization, and the focus of the present work, is a straightforward method for rigid embedding of fixed and stained millimeter-scale samples. Many of the published methods for sample immobilization and correlative micro-CT imaging rely on placing the samples in paraffin wax, agarose, or liquids such as alcohol. Our approach extends this work with custom procedures and the design of a 3-dimensional printable apparatus to embed the samples in an acrylic resin directly into polyimide tubing, which is relatively transparent to X-rays. Herein, sample preparation procedures are described for the samples from 0.5 to 10 mm in diameter, which would be suitable for whole zebrafish larvae and juveniles, or other animals and tissue samples of similar dimensions. As proof of concept, we have embedded the specimens from Danio, Drosophila, Daphnia, and a mouse embryo; representative images from 3-dimensional scans for three of these samples are shown. Importantly, our methodology leads to multiple benefits including rigid immobilization, long-term preservation of laboriously-created resources, and the ability to re-interrogate samples.

We developed protocols and designed a custom apparatus to enable embedding of millimeter-scale specimens. We present sample preparation procedures with an emphasis on embedding in acrylic resin and polyimide tubing to achieve rigid immobilization and long-term storage of specimens for the interrogation of tissue architecture and cell morphology by micro-CT.

For over a hundred years, the histological study of tissues has been the gold standard for medical diagnosis because histology allows all cell types in ...

Visualizing Adhesion Formation in Cells by Means of Advanced Spinning Disk-Total Internal Reflection Fluorescence Microscopy

In living cells, processes such as adhesion formation involve extensive structural changes in the plasma membrane and the cell interior. In order to visualize these highly dynamic events, two complementary light microscopy techniques that allow fast imaging of live samples were combined: spinning disk microscopy (SD) for fast and high-resolution volume recording and total internal reflection fluorescence (TIRF) microscopy for precise localization and visualization of the plasma membrane. A comprehensive and complete imaging protocol will be shown for guiding through sample preparation, microscope calibration, image formation and acquisition, resulting in multi-color SD-TIRF live imaging series with high spatio-temporal resolution. All necessary image post-processing steps to generate multi-dimensional live imaging datasets, i.e. registration and combination of the individual channels, are provided in a self-written macro for the open source software ImageJ. The imaging of fluorescent proteins during initiation and maturation of adhesion complexes, as well as the formation of the actin cytoskeletal network, was used as a proof of principle for this novel approach. The combination of high resolution 3D microscopy and TIRF provided a detailed description of these complex processes within the cellular environment and, at the same time, precise localization of the membrane-associated molecules detected with a high signal-to-background ratio.

An advanced microscope that permit fast and high-resolution imaging of both, the isolated plasma membrane and the surrounding intracellular volume, will be presented. The integration of spinning disk and total internal reflection fluorescence microscopy in one setup allows live imaging experiments at high acquisition rates up to 3.5 s per image stack.

In living cells, processes such as adhesion formation involve extensive structural changes in the plasma membrane and the cell interior. In order to ...

A Reliable and Reproducible Critical-Sized Segmental Femoral Defect Model in Rats Stabilized with a Custom External Fixator

Orthopedic research relies heavily on animal models to study mechanisms of bone healing in vivo as well as investigate the new treatment techniques. Critical-sized segmental defects are challenging to treat clinically, and research efforts could benefit from a reliable, ambulatory small animal model of a segmental femoral defect. In this study, we present an optimized surgical protocol for the consistent and reproducible creation of a 5 mm critical diaphyseal defect in a rat femur stabilized with an external fixator. The diaphyseal ostectomy was performed using a custom jig to place 4 Kirschner wires bicortically, which were stabilized with an adapted external fixator device. An oscillating bone saw was used to create the defect. Either a collagen sponge alone or a collagen sponge soaked in rhBMP-2 was implanted into the defect, and the bone healing was monitored over 12 weeks using radiographs. After 12 weeks, rats were sacrificed, and histological analysis was performed on the excised control and treated femurs. Bone defects containing only collagen sponge resulted in non-union, while rhBMP-2 treatment yielded the formation of a periosteal callous and new bone remodeling. Animals recovered well after implantation, and external fixation proved successful in stabilizing the femoral defects over 12 weeks. This streamlined surgical model could be readily applied to study bone healing and test new orthopedic biomaterials and regenerative therapies in vivo.

In vivo mammalian models of critical-sized bone defects are essential for researchers studying healing mechanisms and orthopedic therapies. Here, we introduce a protocol for the creation of reproducible, segmental, femoral defects in rats stabilized using external fixation.

Orthopedic research relies heavily on animal models to study mechanisms of bone healing in vivo as well as investigate the new treatment techniques. ...

In Vivo Two-Color 2-Photon Imaging of Genetically-Tagged Reporter Cells in the Skin

Fibroblasts are mesenchymal cells that change their morphology upon activation, ultimately influencing the microenvironment of the tissue they are located in. Although traditional imaging techniques are useful in identifying protein interactions and morphology in fixed tissue, they are not able to give insight as to how quickly cells are able to bind and uptake proteins, and once activated how their morphology changes in vivo. In the present study, we ask 2 major questions: 1) what is the time-course of fibroblast activation via toll-like receptor-4 (TLR4) and lipopolysaccharide (LPS) interaction and 2) how do these cells behave once activated? Using 2-photon imaging, we have developed a novel technique to assess the ability of LPS-FITC to bind to its cognate receptor, TLR4, expressed on peripheral fibroblasts in the genetic reporter mouse line; FSP1cre; tdTomatolox-stop-lox&#160;in vivo. This unique approach allows researchers to create in-depth, time-lapse videos and/or pictures of proteins interacting with live cells that allows one to have an increased level of granularity in understanding how proteins can alter cellular behavior.

Morphological changes occur in immune responsive fibroblast cells following activation and promote alterations in cellular recruitment. Utilizing 2-photon imaging in conjunction with a genetically engineered Fibroblast-specific protein 1 (FSP1)-cre; tdTomato floxed-stop-floxed (TB/TB) mouse line and green fluorescently tagged lipopolysaccharide-FITC, we can illustrate highly specific uptake of lipopolysaccharide in dermal fibroblasts and morphological changes in vivo.

Fibroblasts are mesenchymal cells that change their morphology upon activation, ultimately influencing the microenvironment of the tissue they are located ...