Name: mapping metabolism: monitoring lactate dehydrogenase activity directly in tissue
Uploaded: 2018-06-21T14:00:00
Description: Watch this Scientific Journal Video about Mapping Metabolism: Monitoring Lactate Dehydrogenase Activity Directly in Tissue at JoVE.com

HAC was the Milton E. Cassel scholar of the Rita Allen Foundation (http://www.ritaallenfoundation.org). This work was funded by grants to HAC from National Institute of General Medical Sciences R01 GM081686, R01 AR070245, National Institute of General Medical Sciences R01 GM0866465, the Eli &#38; Edythe Broad Center of Regenerative Medicine &#38; Stem Cell Research (Rose Hills and Hal Gaba awards), the Iris Cantor Women&#8217;s Health Center/UCLA CTSI NIH Grant UL1TR000124, the Leukemia Lymphoma Society, Impact awards from the Jonsson Comprehensive Cancer Center to WEL and HAC. Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number P50CA092131. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. HAC is a member of the Eli &#38; Edythe Broad Center of Regenerative Medicine &#38; Stem Cell Research, the UCLA Molecular Biology Institute, and the UCLA Bioinformatics Interdepartmental Program.

All experiments described were approved by the Animal Care Committee at the University of California, Los Angeles.
1. Generate Slides of Frozen Mouse Skin
<ol>
	<li>Euthanize mice in accordance with institution policy. 
	Note: Follow institutional policy for protective clothing. All protocols involving animals must be approved by the Institutional Animal Care Committee.</li>
	<li>Remove the mouse&#8217;s hair with an animal hair trimmer.</li>
	<li>Make incisions in the skin using scisso...

<ol>
	<li>Boonacker, E., Van Noorden, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enzyme+cytochemical+techniques+for+metabolic+mapping+in+living+cells,+with+special+reference+to+proteolysis.">Enzyme cytochemical techniques for metabolic mapping in living cells, with special reference to proteolysis.</a> J Histochem Cytochem. 49, 1473-1486 (2001).</li><li>Seidler, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+tetrazolium-formazan+system:+Design+and+histochemistry.">The tetrazolium-formazan system: Design and histochemistry.</a> Prog Histochem Cytochem. 24, 1-86 (1991).</li><li>Van Noorden, C. J. F., Frederiks, W. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Enzyme Histochemistry: A Laboratory Manual of Current Methods. , (1992).</li><li>Winzer, K., Van Noorden, C. J., Kohler, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+cytochemical+analysis+of+glucose-6-phosphate+dehydrogenase+activity+in+living+isolated+hepatocytes+of+European+flounder+for+rapid+analysis+of+xenobiotic+effects.">Quantitative cytochemical analysis of glucose-6-phosphate dehydrogenase activity in living isolated hepatocytes of European flounder for rapid analysis of xenobiotic effects.</a> J Histochem Cytochem. 49, 1025-1032 (2001).</li><li>Negi, D. S., Stephens, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+improved+method+for+the+histochemical+localization+of+glucose-6-phoshate+dehydrogenase+in+animal+and+plant+tissues.">An improved method for the histochemical localization of glucose-6-phoshate dehydrogenase in animal and plant tissues.</a> J Histochem Cytochem. 25, 149-154 (1977).</li><li>Boren, 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=In+situ+localization+of+transketolase+activity+in+epithelial+cells+of+different+rat+tissues+and+subcellularly+in+liver+parenchymal+cells.">In situ localization of transketolase activity in epithelial cells of different rat tissues and subcellularly in liver parenchymal cells.</a> J Histochem Cytochem. 54, 191-199 (2006).</li><li>Miller, A., 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=Exploring+metabolic+configurations+of+single+cells+within+complex+tissue+microenvironments.">Exploring metabolic configurations of single cells within complex tissue microenvironments.</a> Cell Metab. , (2017).</li><li>Shen, 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=Prognostic+value+of+serum+lactate+dehydrogenase+in+renal+cell+carcinoma:+a+systematic+review+and+meta-analysis.">Prognostic value of serum lactate dehydrogenase in renal cell carcinoma: a systematic review and meta-analysis.</a> PLoS One. 11, e0166482 (2016).</li><li>Zhang, X., 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=Prognostic+significance+of+serum+LDH+in+small+cell+lung+cancer:+A+systematic+review+with+meta-analysis.">Prognostic significance of serum LDH in small cell lung cancer: A systematic review with meta-analysis.</a> Cancer Biomark. 16, 415-423 (2016).</li><li>Petrelli, 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=Prognostic+role+of+lactate+dehydrogenase+in+solid+tumors:+a+systematic+review+and+meta-analysis+of+76+studies.">Prognostic role of lactate dehydrogenase in solid tumors: a systematic review and meta-analysis of 76 studies.</a> Acta Oncol. 54, 961-970 (2015).</li><li>Valvona, C. J., Fillmore, H. L., Nunn, P. B., Pilkington, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+regulation+and+function+of+lactate+dehydrogenase+A:+Therapeutic+potential+in+brain+tumor.">The regulation and function of lactate dehydrogenase A: Therapeutic potential in brain tumor.</a> Brain Pathol. 26, 3-17 (2016).</li><li>Markert, C. L., Shaklee, J. B., Whitt, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+of+a+gene:+Multiple+genes+for+LDH+isozymes+provide+a+model+of+the+evolution+of+gene+structure,+function+and+regulation.">Evolution of a gene: Multiple genes for LDH isozymes provide a model of the evolution of gene structure, function and regulation.</a> Science. 189, 102-114 (1975).</li><li>Read, J. A., Winter, V. J., Eszes, C. M., Sessions, R. B., Brady, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+basis+for+altered+activity+of+M-+and+H-isozyme+forms+of+human+lactate+dehydrogenase.">Structural basis for altered activity of M- and H-isozyme forms of human lactate dehydrogenase.</a> Proteins. 43, 175-185 (2001).</li><li>Holness, M. J., Sugden, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+pyruvate+dehydrogenase+complex+activity+by+reversible+phosphorylation.">Regulation of pyruvate dehydrogenase complex activity by reversible phosphorylation.</a> Biochem Soc Trans. 31, 1143-1151 (2003).</li><li>Yi, W., 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=Phosphofructokinase+1+glycosylation+regulates+cell+growth+and+metabolism.">Phosphofructokinase 1 glycosylation regulates cell growth and metabolism.</a> Science. 337, 975-980 (2012).</li><li>Fan, 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=Tyrosine+phosphorylation+of+lactate+dehydrogenase+A+is+important+for+NADH/NAD(+)+redox+homeostasis+in+cancer+cells.">Tyrosine phosphorylation of lactate dehydrogenase A is important for NADH/NAD(+) redox homeostasis in cancer cells.</a> Mol Cell Biol. 31, 4938-4950 (2011).</li><li>Zhao, 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=Lysine-5+acetylation+negatively+regulates+lactate+dehydrogenase+A+and+is+decreased+in+pancreatic+cancer.">Lysine-5 acetylation negatively regulates lactate dehydrogenase A and is decreased in pancreatic cancer.</a> Cancer Cell. 23, 464-476 (2013).</li><li>Vanderlinde, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+total+lactate+dehydrogenase+activity.">Measurement of total lactate dehydrogenase activity.</a> Ann Clin Lab Sci. 15, 13-31 (1985).</li><li>Nelson, S. 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=Metabolic+imaging+of+patients+with+prostate+cancer+using+hyperpolarized+[1-(1)(3)C]pyruvate.">Metabolic imaging of patients with prostate cancer using hyperpolarized [1-(1)(3)C]pyruvate.</a> Sci Transl Med. 5, 198ra108 (2013).</li><li>Flores, A., 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=Lactate+dehydrogenase+activity+drives+hair+follicle+stem+cell+activation.">Lactate dehydrogenase activity drives hair follicle stem cell activation.</a> Nat Cell Biol. , (2017).</li><li>Fischer, A. H., Jacobson, K. A., Rose, J., Zeller, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cryosectioning+tissues.">Cryosectioning tissues.</a> CSH Protoc. 2008, (2008).</li><li>Espada, 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=Non-aqueous+permanent+mounting+for+immunofluorescence+microscopy.">Non-aqueous permanent mounting for immunofluorescence microscopy.</a> Histochem Cell Biol. 123, 329-334 (2005).</li><li>Hisada, R., Yagi, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=1-Methoxy-5-methylphenazinium+methyl+sulfate.+A+photochemically+stable+electron+mediator+between+NADH+and+various+electron+acceptors.">1-Methoxy-5-methylphenazinium methyl sulfate. A photochemically stable electron mediator between NADH and various electron acceptors.</a> J Biochem. 82, 1469-1473 (1977).</li></ol>

The method described here can be used to monitor the activity of lactate dehydrogenase or other metabolic enzymes that generate NADH or NADPH, in different cell types within a tissue or within different portions of a tissue over time. Lactate dehydrogenase is an important enzyme for understanding the biology of stem cells and tumors, and the ability to monitor lactate dehydrogenase activity in individual cells is likely to provide important insights into the function of this enzyme.
One import...

Understanding the locations within tissues in which enzymes have high or low activity is essential for understanding development and physiology. Transcript or protein levels are often used as surrogates for enzymatic activity. While such studies can be informative, they do not provide information that can be critical for determining an enzyme&#39;s activity, such as post-translational modifications, the presence of protein complexes, or the enzyme&#39;s subcellular localization. When enzymatic activity is directly measured, it is often monitored in homogenized protein lysates that no longer contain information about individual cells within the mixture or the spatial distribution of the cells with high or low activity within a tissue.
We provide here a detailed protocol for mapping the spatial distribution of enzymatic activity within a tissue sample. The methodology is based on earlier studies demonstrating that tetrazolium salts can be used to localize the activity of dehydrogenases, reductases, and oxidases in frozen tissue1. With these methods, a water-insoluble formazan is formed when protons are transferred to a tetrazolium salt2,3. Glucose-6-phosphate dehydrogenase generates NADPH and a proton, and has been detected with tetrazolium activity. Glucose-6-phosphate dehydrogenase has been monitored in in European flounder hepatocytes4, in alveolar type 2 cells of the lungs5 and nephrons of the kidney5. Tetrazolium salts have also been used to monitor transketolase activity in frozen tissue6. A similar approach was recently&#160;used to monitor the activity of multiple dehydrogenases in the same tissue on adjacent slides7.
We describe here a method to use tetrazolium salts to monitor the spatial distribution of lactate dehydrogenase activity (Figure 1). Lactate dehydrogenase can convert pyruvate generated by glycolysis to lactate, and the reverse reaction. Lactate dehydrogenase activity is consequently an important determinant of pyruvate&#39;s entrance into the tricarboxylic acid cycle versus its secretion as lactate. Lactate levels in the blood are often used to diagnose a range of diseases, including cancer8,9,10, because it can signal that illness or injury has damaged cells and the enzyme has been released.
There are four lactate dehydrogenase genes: LDHA, LDHB, LDHC, and LDHD11. LDHA and LDHB are thought to have arisen from duplication of an early LDHA gene12. LDH is active as a tetramer and LDHA and LDHB can form homotetramers and heterotetramers with each other. LDHA is reported to have higher affinity for pyruvate, while LDHB is reported to have higher affinity for lactate, and to preferentially convert lactate to pyruvate13. The LDHA promoter contains binding sites for the HIF1&#945;, cMYC and FOXM1 transcription factors11. In addition, like many other glycolytic enzymes14,15, LDH can be modified by post-translational modifications. Fibroblast growth factor receptor 1 can phosphorylate LDHA at Y10, which promotes tetramer formation, or Y83, which promotes NADH substrate binding16. LDHA can also be acetylated17. For these reasons, a complete understanding of LDH activity requires monitoring not only LDH protein levels, but the enzyme&#39;s activity as well.
In addition to the method we present here, other approaches have been used to monitor lactate dehydrogenase activity. Lactate dehydrogenase activity can be monitored spectrophotometrically in homogenized protein lysate. The generation of NADH as lactate is converted to pyruvate can be measured based on absorbance at 340 nm, while the disappearance of NADH can be monitored as pyruvate is converted to lactate18. Lactate dehydrogenase activity has also been monitored with magnetic resonance imaging (MRI). 13C- pyruvate can be administered and the conversion of pyruvate to lactate can be monitored as the ratio of [1-13C]lactate/[1-13C]pyruvate. Elevated ratios of [1-13C]lactate/[1-13C]pyruvate have been observed in cancer tissue19. While MRI-based approaches can provide information on lactate dehydrogenase activity in normal and disease tissues, the methodologies do not have the resolution needed to determine the activity level in specific cells. The methodology provided here can provide information on lactate dehydrogenase activity in tissue areas and even in single cells.
Using in situ activity assays, we found that the activity of lactate dehydrogenase is high in the hair follicle stem cells of mouse skin20. We also used the method to monitor the activity of lactate dehydrogenase in cultured embryonic stem cells and found the activity is higher in the stem cells than the feeder layer. Finally, we monitored the activity of lactate dehydrogenase in fresh mouse aorta and observed staining in smooth muscle cells. We describe here a detailed protocol for monitoring lactate dehydrogenase activity in frozen mouse skin.

<table border="0" cellpadding="0" cellspacing="0" style="width:815px;" width="814">
	<tbody>
		<tr height="43">
			<td height="43" style="height:43px;width:312px;">Surgical instruments</td>
			<td style="width:164px;"></td>
			<td style="width:121px;"></td>
			<td style="width:217px;">For collecting skin from euthanized mice</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Tissue-tek cryomold 25 mm x 20 mm x 5 mm</td>
			<td style="width:164px;">Fisher Scientific</td>
			<td style="width:121px;">NC9511236</td>
			<td style="width:217px;">For freezing mouse skin</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Tissue-Tek O.C.T. compound</td>
			<td style="width:164px;">Fisher Scientific</td>
			<td style="width:121px;">NC9638938</td>
			<td style="width:217px;">For mounting cryomolds</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Ice bucket</td>
			<td style="width:164px;">Fisher Scientific</td>
			<td style="width:121px;">07-210-106</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Dry Ice</td>
			<td style="width:164px;"></td>
			<td style="width:121px;"></td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Polysine Adhesion Slide</td>
			<td style="width:164px;">Fisher Scientific</td>
			<td style="width:121px;">12-545-78</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">4% formalin</td>
			<td style="width:164px;">Fisher Scientific</td>
			<td style="width:121px;">23-245-684</td>
			<td style="width:217px;">Dilluted in water</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">phosphate buffered saline, pH 7.4</td>
			<td style="width:164px;"></td>
			<td style="width:121px;"></td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">vortex</td>
			<td style="width:164px;"></td>
			<td style="width:121px;"></td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Tris base</td>
			<td style="width:164px;">Fisher Scientific</td>
			<td style="width:121px;">23-245-684</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">NAD</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:121px;">N7004</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Phenazine methosulfate</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:121px;">P9625</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:312px;">Nitrotetrazolium blue chloride</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:121px;">N6876</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Lithium L-lactate</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:121px;">L2250</td>
			<td style="width:217px;">Substrate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">37&#176;C incubator (or tissue culture incubator)</td>
			<td style="width:164px;"></td>
			<td style="width:121px;"></td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Braziliant! Counter stain</td>
			<td style="width:164px;">Anatech</td>
			<td style="width:121px;">861</td>
			<td style="width:217px;">Counter stain</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Mounting medium</td>
			<td style="width:164px;">Vector Laboratories</td>
			<td style="width:121px;">H-5000&#160;</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Cover slips for slides</td>
			<td style="width:164px;">Fisher Scientific</td>
			<td style="width:121px;">12-544D</td>
			<td style="width:217px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:312px;">Light microscope</td>
			<td style="width:164px;"></td>
			<td style="width:121px;"></td>
			<td style="width:217px;"></td>
		</tr>
	</tbody>
</table>

mapping metabolism: monitoring lactate dehydrogenase activity directly in tissue

Mapping enzymatic activity in space and time is critical for understanding the molecular basis of cell behavior in normal tissue and disease. In situ metabolic activity assays can provide information about the spatial distribution of metabolic activity within a tissue. We provide here a detailed protocol for monitoring the activity of the enzyme lactate dehydrogenase directly in tissue samples. Lactate dehydrogenase is an important determinant of whether consumed glucose will be converted to energy via aerobic or anaerobic glycolysis. A solution containing lactate and NAD is provided to a frozen tissue section. Cells with high lactate dehydrogenase activity will convert the provided lactate to pyruvate, while simultaneously converting provided nicotinamide adenine dinucleotide (NAD) to NADH and a proton, which can be detected based on the reduction of nitrotetrazolium blue to formazan, which is visualized as a blue precipitate. We describe a detailed protocol for monitoring lactate dehydrogenase activity in mouse skin. Applying this protocol, we found that lactate dehydrogenase activity is high in the quiescent hair follicle stem cells within the skin. Applying the protocol to cultured mouse embryonic stem cells revealed higher staining in cultured embryonic stem cells than mouse embryonic fibroblasts. Analysis of freshly isolated mouse aorta revealed staining in smooth muscle cells perpendicular to the aorta. The methodology provided can be used to spatially map the activity of enzymes that generate a proton in frozen or fresh tissue.

We have previously reported results for in situ activity assays in mouse skin20. As shown in Figure 3, we observed high levels of lactate dehydrogenase activity in the hair follicle stem cells at the base of the hair follicle when the procedures described above were followed. These findings were corroborated by fluorescence activated cell sorting of skin for hair follicle stem cells and confirming high lactate dehydrogenase ac...

Watch this Scientific Journal Video about Mapping Metabolism: Monitoring Lactate Dehydrogenase Activity Directly in Tissue at JoVE.com

Mapping Metabolism: Monitoring Lactate Dehydrogenase Activity Directly in Tissue

We describe a protocol for mapping the spatial distribution of enzymatic activity for enzymes that generate nicotinatmide adenine dinucleotide phosphate (NAD(P)H) + H+ directly in tissue samples.

Mapping enzymatic activity in space and time is critical for understanding the molecular basis of cell behavior in normal tissue and disease. In situ ...

This method can help answer key questions in the biology field such as activity of enzymes at different locations within tissues. The main advantage of this technique is that it allows the researcher to detect enzymatic activity directly in the tissue samples. To begin this procedure, remove the mouse's hair with an animal hair trimmer.Make an incision on the skin of the back using scissors. Then, lift the skin up and cut it away. Next, fill the Cryomold with freezing reagent compound.Using needle nose forceps, place the skin sections into the field's Cryomold. Orient the skin sections so that the cross section of the skin from the epidermis to the dermis, hypodermis and muscle is visible. If possible, mount the experimental and control mice together in the same Cryomold, so they can be sectioned on to the same slide and processed together.Take care not to create bubbles. Place the Cryomold on a flat surface of a block of dry ice in an ice bucket. For storage, transfer the Cryomold into a negative 80 degree Celsius freezer.Samples can be maintained in the freezer for approximately three months without significant loss of enzymatic activity. For sectioning, using a cryostat set at negative 20 degree Celsius, slice the tissue to create seven to 10 micrometer-thick sections for the best skin morphology. In this procedure, establish the set of slides to be tested, which includes a control slide on which NAD will be withheld, another control slide on which the substrate lactate will be withheld, and a positive control slide from a frozen tissue block previously investigated.Briefly fix the slides containing the skin sections with 4%formalin for five minutes. Then, wash the slides with PBS. Next, vortex the reagents, including the NADP, PMS, nitrotetrazolium blue chloride, and lactate together for lactate dehydrogenase activity staining in an appropriately sized tube.Next, prepare a second solution in which all reagents are present except NAD. Subsequently, prepare a third solution in which all reagents are present except lactate. To incubate the slides and staining solution or control solutions, dip them into the solution at the same time.Then, incubate them in a humidified environment at 37 degree Celsius in the dark. Monitor the conversion of the staining solution from clear to blue. When the samples have reached the desired level of blueness, stop the reaction by removing the staining solution and rinsing them with PBS.Afterward, a counterstain on to the slides when the slides have reached an appropriate level of blueness. Counterstains that turn the nuclear red or green will provide good contrast with the blue created by the Formosan precipitant. Then, mount the slides with aqueous or non-aqueous mounting medium.One to three drops of mounting medium is sufficient depending on the size of the cover slip. Subsequently, image the slides under a light microscope. Take photographs of experimental and control samples, and all negative controls at 10X, 20X, and 40X magnification.The intensity of staining will increase over time as the same is incubated with the staining solution. As shown here, high levels of lactate dehydrogenase activity were observed in the hair follicle stem cells at the base of the hair follicle. Control samples that did not receive the lactate substrate did not show staining.These findings were corroborated by fluorescent activated cell sorting of skin for hair follicle stem cells and confirming high lactate dehydrogenase activity in the stem cell compartment with activity on sorted cells. Based on the findings that hair follicle stem cells have high lactate dehydrogenase activity, cultured embryonic stem cells were tested. Mouse embryonic fibroblast serving as a feeder layer were analyzed in the presence of embryonic stem cells or alone.High lactate dehydrogenase activity was observed in the embryonic stem cells as compared with the mouse embryonic fibroblast as shown in different time points. The staining protocol was also applied to freshly isolated tissue. Mouse aortas were dissected.Samples were incubated with Hank's balanced salt solution containing 0.5%Triton X for 10 minutes. Then, with the lactate dehydrogenase staining solution for 10 minutes. The images here show lactate dehydrogenase solution with and without lactate.While attempting this procedure, it's important to remember to use frozen tissue slices with intact enzymatic activity and the frozen blocks should not be too old. If prepared sections are being stored, the sections should not be allowed to dry out. After watching this video, you should have a good understanding of how to visualize lactate dehydrogenase activity in the mouse skin.

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Biochemistry

A Method for Measuring Metabolism in Sorted Subpopulations of Complex Cell Communities Using Stable Isotope Tracing

Mammalian cell types exhibit specialized metabolism, and there is ample evidence that various co-existing cell types engage in metabolic cooperation. Moreover, even cultures of a single cell type may contain cells in distinct metabolic states, such as resting or cycling cells. Methods for measuring metabolic activities of such subpopulations are valuable tools for understanding cellular metabolism. Complex cell populations are most commonly separated using a cell sorter, and subpopulations isolated by this method can be analyzed by metabolomics methods. However, a problem with this approach is that the cell sorting procedure subjects cells to stresses that may distort their metabolism.
To overcome these issues, we reasoned that the mass isotopomer distributions (MIDs) of metabolites from cells cultured with stable isotope-labeled nutrients are likely to be more stable than absolute metabolite concentrations, because MIDs are formed over longer time scales and should be less affected by short-term exposure to cell sorting conditions. Here, we describe a method based on this principle, combining cell sorting with liquid chromatography-high resolution mass spectrometry (LC-HRMS). The procedure involves analyzing three types of samples: (1) metabolite extracts obtained directly from the complex population; (2) extracts of "mock sorted" cells passed through the cell sorter instrument without gating any specific population; and (3) extracts of the actual sorted populations. The mock sorted cells are compared against direct extraction to verify that MIDs are indeed not altered by the cell sorting procedure itself, prior to analyzing the actual sorted populations. We show example results from HeLa cells sorted according to cell cycle phase, revealing changes in nucleotide metabolism.

This article describes a method for studying cellular metabolism in complex communities of multiple cell types, using a combination of stable isotope tracing, cell sorting to isolate specific cell types, and mass spectrometry.

Mammalian cell types exhibit specialized metabolism, and there is ample evidence that various co-existing cell types engage in metabolic cooperation. ...

Defining Hsp33's Redox-regulated Chaperone Activity and Mapping Conformational Changes on Hsp33 Using Hydrogen-deuterium Exchange Mass Spectrometry

Living organisms regularly need to cope with fluctuating environments during their life cycle, including changes in temperature, pH, the accumulation of reactive oxygen species, and more. These fluctuations can lead to a widespread protein unfolding, aggregation, and cell death. Therefore, cells have evolved a dynamic and stress-specific network of molecular chaperones, which maintain a "healthy" proteome during stress conditions. ATP-independent chaperones constitute one major class of molecular chaperones, which serve as first-line defense molecules, protecting against protein aggregation in a stress-dependent manner. One feature these chaperones have in common is their ability to utilize structural plasticity for their stress-specific activation, recognition, and release of the misfolded client. 
In this paper, we focus on the functional and structural analysis of one such intrinsically disordered chaperone, the bacterial redox-regulated Hsp33, which protects proteins against aggregation during oxidative stress. Here, we present a toolbox of diverse techniques for studying redox-regulated chaperone activity, as well as for mapping conformational changes of the chaperone, underlying its activity. Specifically, we describe a workflow which includes the preparation of fully reduced and fully oxidized proteins, followed by an analysis of the chaperone anti-aggregation activity in vitro using light-scattering, focusing on the degree of the anti-aggregation activity and its kinetics. To overcome frequent outliers accumulated during aggregation assays, we describe the usage of Kfits, a novel graphical tool which allows easy processing of kinetic measurements. This tool can be easily applied to other types of kinetic measurements for removing outliers and fitting kinetic parameters. To correlate the function with the protein structure, we describe the setup and workflow of a structural mass spectrometry technique, hydrogen-deuterium exchange mass spectrometry, that allows the mapping of conformational changes on the chaperone and substrate during different stages of Hsp33 activity. The same methodology can be applied to other protein-protein and protein-ligand interactions.

One of the most challenging stress conditions that organisms encounter during their lifetime involves the accumulation of oxidants. During oxidative stress, cells heavily rely on molecular chaperones. Here, we present methods used to investigate the redox-regulated anti-aggregation activity, as well as to monitor structural changes governing the chaperone function using HDX-MS.

Living organisms regularly need to cope with fluctuating environments during their life cycle, including changes in temperature, pH, the accumulation of ...

Small-Scale Colorimetric Assays of Intracellular Lactate and Pyruvate in the Nematode Caenorhabditis elegans

Lactate and pyruvate are key intermediates of intracellular energy metabolic pathways. Monitoring the lactate/pyruvate ratio in cells helps to determine whether there is an imbalance in age-related energy metabolism between mitochondrial oxidative phosphorylation and aerobic glycolysis. Here, we show the utilization of commercial colorimetric assay kits for lactate and pyruvate in the model organism C. elegans. Recently, the sensitivity and accuracy of the colorimetric/fluorimetric assay kits have been improved greatly by the research and development conducted by reagent manufacturers. The improved reagents have enabled the use of small-scale assays with a 96-well plate in C. elegans. In general, a fluorimetric assay is superior in sensitivity to a colorimetric assay; however, the colorimetric approach is more suitable for the use in common laboratories. Another important issue in these assays for quantitative determination is protein precipitation of homogenized C. elegans samples. In our protein precipitation method, common precipitants (e.g., trichloroacetic acid, perchloric acid and metaphosphoric acid) are used for sample preparation. A protein-free assay sample is prepared by directly adding cold precipitant (final concentration of 5%) during homogenization.

Small-Scale Colorimetric Assays of Intracellular Lactate and Pyruvate in the Nematode Caenorhabditis elegans

We describe a modified small-scale extraction and colorimetric assays of lactate and pyruvate in the nematode C. elegans. When utilizing commercial assay kits, the technical development of their sensitivity and accuracy is important. Protein precipitation in extraction is the most critical step for the quantitative determination of intracellular metabolites.

Lactate and pyruvate are key intermediates of intracellular energy metabolic pathways. Monitoring the lactate/pyruvate ratio in cells helps to determine ...

Quantification of Hypopigmentation Activity In Vitro

This study presents laboratory methods for the quantification of hypopigmentation activity in vitro. Melanin, the major pigment in melanocytes, is synthesized in response to multiple cellular and environmental factors. Melanin protects skin cells from ultraviolet damage, but also has biophysical and biochemical functions. Excessive production or accumulation of melanin in melanocytes can cause dermatological problems, such as freckles, dark spots, melasma, and moles. Therefore, the control of melanogenesis with hypopigmentation agents is important in individuals with clinical or cosmetic needs. Melanin is primarily synthesized in the melanosomes of melanocytes in a complex biochemical process called melanogenesis, which is influenced by extrinsic and intrinsic factors, such as hormones, inflammation, age, and ultraviolet light exposure. We describe three methods to determine the hypopigmentation activity of chemicals or natural substances in melanocytes: measurement of the 1) cellular tyrosinase activity and 2) melanin content, and 3) staining and quantifying cellular melanin with image analysis.
In melanogenesis, tyrosinase catalyzes the rate-limiting step that converts L-tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA) and then into dopaquinone. Therefore, the inhibition of tyrosinase is a primary hypopigmentation mechanism. In cultured melanocytes, tyrosinase activity can be quantified by adding L-DOPA as a substrate and measuring dopaquinone production by spectrophotometry. Melanogenesis can also be measured by quantifying the melanin content. The melanin-containing cellular fraction is extracted with NaOH and melanin is quantified spectrophotometrically. Finally, the melanin content can be quantified by image analysis following Fontana-Masson staining of melanin. Although the results of these in vitro assays may not always be reproduced in human skin, these methods are widely used in melanogenesis research, especially as the initial step to identify potential hypopigmentation activity. These methods can also be used to assess melanocyte activity, growth, and differentiation. Consistent results with the three different methods ensure the validity of the effects.

We describe three experimental methods for evaluating the hypopigmentation activity of chemicals in vitro: quantification of 1) cellular tyrosinase activity and 2) melanin content, and 3) measurement of melanin by cellular melanin staining and image analysis.

This study presents laboratory methods for the quantification of hypopigmentation activity in vitro. Melanin, the major pigment in melanocytes, is ...

Measuring and Interpreting Oxygen Consumption Rates in Whole Fly Head Segments

Regulated metabolic activity is essential for the normal functioning of living cells. Indeed, altered metabolic activity is causally linked with the progression of cancer, diabetes, neurodegeneration, and aging to name a few. For instance, changes in mitochondrial activity, the cell&#39;s metabolic powerhouse, have been characterized in many such diseases. Generally, the oxygen consumption rates of mitochondria were considered a reliable readout of mitochondrial activity and measurements in some of these studies were based on isolated mitochondria or cells. However, such conditions may not represent the complexity of a whole tissue. Recently, we have developed a novel method that enables the dynamic measurement of oxygen consumption rates from whole isolated fly heads. By utilizing this method, we have recorded lower oxygen consumption rates of the whole head segment in young versus aged flies. Secondly, we have discovered that lysine deacetylase inhibitors rapidly alter the oxygen consumption in the whole head. Our novel technique may therefore aid in uncovering new properties of various drugs, which may impact metabolic rates. Furthermore, our method may give a better understanding of metabolic behavior in an experimental setup that more closely resembles physiological states.

Measuring alterations in metabolic rates is central to understanding the progression of various diseases and aging. Here, we present a novel technique to measure whole head oxygen consumption that more closely resembles the physiological state and may aid in revealing novel drugs that modify mitochondrial activity.

Regulated metabolic activity is essential for the normal functioning of living cells. Indeed, altered metabolic activity is causally linked with the ...

SUMO-Binding Entities (SUBEs) as Tools for the Enrichment, Isolation, Identification, and Characterization of the SUMO Proteome in Liver Cancer

Post-translational modification is a key mechanism regulating protein homeostasis and function in eukaryotic cells. Among all ubiquitin-like proteins in liver cancer, the modification by SUMO (Small Ubiquitin MOdifier) has been given the most attention. Isolation of endogenous SUMOylated proteins in vivo is challenging due to the presence of active SUMO-specific proteases. Initial studies of SUMOylation in vivo were based on the molecular detection of specific SUMOylated proteins (e.g., by western blot). However, in many cases, antibodies, generally made with non-modified recombinant protein, did not immunoprecipitate SUMOylated forms of the protein of interest.&#160;Nickel chromatography has been the other approach to study SUMOylation by capturing histidine-tagged versions of SUMO molecules. This approach is mainly used in cells stably expressing or transiently transfected with His-SUMO molecules. To overcome these limitations, SUMO-binding entities (SUBEs) were developed to isolate endogenous SUMOylated proteins. Herein, we describe all the steps required for the enrichment, isolation, and identification of SUMOylated substrates from human hepatoma cells and hepatic tissues from a liver cancer mouse model by using SUBEs. Firstly, we describe methods involved in the preparation and lysis of the human hepatoma cells and liver tumor tissue samples. Then, a thorough explanation of the preparation of SUBEs and controls is detailed along with the protocol for the protein pull-down assays. Finally, some examples are provided regarding the options available for the identification and characterization of the SUMOylated proteome, namely the use of western-blot analysis for the detection of a specific SUMOylated substrate from liver tumors or the use of proteomics by mass spectrometry for high-throughput characterization of the SUMOylated proteome and interactome in hepatoma cells.

SUMO-Binding Entities SUBEs as Tools for the Enrichment, Isolation, Identification, and Characterization of the SUMO Proteome in Liver Cancer

Here, we present a protocol to enrich, isolate, identify, and characterize proteins modified by SUMO in vivo both from human hepatoma cells and liver tumors obtained from mouse models of hepatocellular carcinoma by using SUMO-binding entities (SUBEs).

Post-translational modification is a key mechanism regulating protein homeostasis and function in eukaryotic cells. Among all ubiquitin-like proteins in ...

Rapid and Cost-Effective RNA Extraction of Rat Pancreatic Tissue

Regardless of the extraction method, optimized RNA extraction of tissues and cell lines are carried out in four stages: 1) homogenization, 2) effective denaturation of proteins from RNA, 3) ribonuclease inactivation, and 4) removal of contamination from DNA, proteins, and carbohydrates. However, it is very laborious to maintain the integrity of RNA when there are high levels of RNase in the tissue. Spontaneous autolysis makes it very difficult to extract RNA from pancreatic tissue without damaging it. Thus, a practical RNA extraction method is needed to maintain the integrity of pancreatic tissues during the extraction process. An experimental and comparative study of existing protocols was carried out by obtaining 20-30 mg of rat pancreatic tissues in less than 2 minutes and extracting the RNA. The results were assessed by electrophoresis. The experiments were carried out three times for generalization of the results. Immersing pancreatic tissue in RNA stabilization reagent at -80 &#176;C for 24 h yielded high integrity RNA, when the RNA extraction reagent was used as the reagent. The results obtained were comparable to the results obtained from commercial kits with spin column bindings.

The purity and integrity of the isolated RNA is a vital step in RNA dependent assays. Here, we present a practical, rapid, and inexpensive method to extract RNA from a small quantity of undamaged pancreatic tissue.

Regardless of the extraction method, optimized RNA extraction of tissues and cell lines are carried out in four stages: 1) homogenization, 2) effective ...

Spectrophotometric Methods for the Study of Eukaryotic Glycogen Metabolism

Glycogen is synthesized as a storage form of glucose by a wide array of organisms, ranging from bacteria to animals. The molecule comprises linear chains of &#945;1,4-linked glucose residues with branches introduced through the addition of &#945;1,6-linkages. Understanding how the synthesis and degradation of glycogen are regulated and how glycogen attains its characteristic branched structure requires the study of the enzymes of glycogen storage. However, the methods most commonly used to study these enzyme activities typically employ reagents or techniques that are not available to all investigators. Here, we discuss a battery of procedures that are technically simple, cost-effective, and yet still capable of providing valuable insight into the control of glycogen storage. The techniques require access to a spectrophotometer, operating in the range of 330 to 800 nm, and are described assuming that the users will employ disposable, plastic cuvettes. However, the procedures are readily scalable and can be modified for use in a microplate reader, allowing highly parallel analysis.

Techniques to measure the activity of key enzymes of glycogen metabolism are presented, using a simple spectrophotometer operating in the visible range.

Glycogen is synthesized as a storage form of glucose by a wide array of organisms, ranging from bacteria to animals. The molecule comprises linear chains ...

Monitoring Protein Aggregation Kinetics In Vivo using Automated Inclusion Counting in Caenorhabditis elegans

Protein aggregation into insoluble inclusions is a hallmark of a variety of human diseases, many of which are age-related. The nematode Caenorhabditis elegans is a well-established model organism that has been widely used in the field to study protein aggregation and toxicity. Its optical transparency enables the direct visualization of protein aggregation by fluorescence microscopy. Moreover, the fast reproductive cycle and short lifespan make the nematode a suitable model to screen for genes and molecules that modulate this process.
However, the quantification of aggregate load in living animals is poorly standardized, typically performed by manual inclusion counting under a fluorescence dissection microscope at a single time point. This approach can result in high variability between observers and limits the understanding of the aggregation process. In contrast, amyloid-like protein aggregation in vitro is routinely monitored by thioflavin T fluorescence in a highly quantitative and time-resolved fashion.
Here, an analogous method is presented for the unbiased analysis of aggregation kinetics in living C. elegans, using a high-throughput confocal microscope combined with custom-made image analysis and data fitting. The applicability of this method is demonstrated by monitoring inclusion formation of a fluorescently labeled polyglutamine (polyQ) protein in the body wall muscle cells. The image analysis workflow allows the determination of the numbers of inclusions at different timepoints, which are fitted to a mathematical model based on independent nucleation events in individual muscle cells. The method described here may prove useful to assess the effects of proteostasis factors and potential therapeutics for protein aggregation diseases in a living animal in a robust and quantitative manner.

Monitoring Protein Aggregation Kinetics In Vivo using Automated Inclusion Counting in Caenorhabditis elegans

Here, a method is presented for the analysis of protein aggregation kinetics in the nematode Caenorhabditis elegans. Animals from an age-synchronized population are imaged at different time points, followed by semiautomated inclusion counting in CellProfiler and fitting to a mathematical model in AmyloFit.

Protein aggregation into insoluble inclusions is a hallmark of a variety of human diseases, many of which are age-related. The nematode Caenorhabditis ...

Identifying G-Quadruplexes in a DNA Template Using Chemical Mapping

In Vitro Chemical Mapping of G-Quadruplex DNA Structures by Bis-3-Chloropiperidines

G-quadruplexes (G4s) are biologically relevant, non-canonical DNA structures that play an important role in gene expression and diseases, representing significant therapeutic targets. Accessible methods are required for the in vitro characterization of DNA within potential G-quadruplex-forming sequences (PQSs). B-CePs are a class of alkylating agents that have proven to be useful chemical probes for investigation of the higher-order structure of nucleic acids. This paper describes a new chemical mapping assay exploiting the specific reactivity of B-CePs with the N7 of guanines, followed by direct strand cleavage at the alkylated Gs. 
Namely, to distinguish G4 folds from unfolded DNA forms, we use B-CeP 1 to probe the thrombin-binding aptamer (TBA), a 15-mer DNA able to assume the G4 arrangement. Reaction of B-CeP-responding guanines with B-CeP 1 yields products that can be resolved by high-resolution polyacrylamide gel electrophoresis (PAGE) at a single-nucleotide level by locating individual alkylation adducts and DNA strand cleavage at the alkylated guanines. Mapping using B-CePs is a simple and powerful tool for the in vitro characterization of G-quadruplex-forming DNA sequences, enabling the precise location of guanines involved in the formation of G-tetrads.

Author Spotlight: Characterizing DNA G-Quadruplex by Bis-3-Chloropiperidine Based Chemical Mapping 

Bis-3-chloropiperidines (B-CePs) are useful chemical probes to identify and characterize G-quadruplex structures in DNA templates in vitro. This protocol details the procedure to perform probing reactions with B-CePs and to resolve reaction products by high-resolution polyacrylamide gel electrophoresis.

G-quadruplexes (G4s) are biologically relevant, non-canonical DNA structures that play an important role in gene expression and diseases, representing ...