The author wishes to thank Annette Blak Rasmussen and Kristine Moeller for their technical support

The collection of skin samples from healthy adult volunteers undergoing plastic surgery requires approval from the ethical committee in the host institutions. This protocol was approved by the Regional Ethical Committee of Region Midtjylland, Denmark (M-20110027). The method described here is derived from similar studies by Maciaq et al.10 and Liu and Karasek11.
1. Isolation of Keratinocytes from Human Skin
<ol>
	<li>Start by making the following solutions: 50 mL solution of 0.25% trypsin and 0.1% glucose in DPBS. Mix and filter sterilize (0.2 &#181;m) the solution. Prepare 10 mL of RPMI-1640 + 2% FBS solution, 50 mL of DPBS and keratinocyte serum-free medium (KSFM). Add KSFM supplements and 250 &#181;L of gentamycin to 500 mL of KSFM. Pre-warm the solutions to 37 &#176;C before use.</li>
	<li>Collect skin from healthy adult volunteers undergoing plastic surgery. The skin samples used are approximately 10 cm x 15 cm, but can vary in size. Keep the skin cool under transportation by transporting the skin samples in a Styrofoam box containing a cooling element. If necessary, the skin sample can be stored at 4 &#176;C overnight.</li>
	<li>Remove fat from underneath the skin section using sterilized scissors, scalpels, and forceps.</li>
	<li>Buckle out the skin section (approximately 10 cm x 15 cm) on a sterile cover on top of a plate using needles. First, clean the skin with a dry sterilized gauze pad. Then clean the skin using a sterilized gauze pad with 70% ethanol.</li>
	<li>Using a foot planer, cut of the upper layer (epidermis) of the skin section and put it in a 9 cm Petri dish. Then, immediately add 25 mL of the DPBS/trypsin/glucose solution (prepared in step 1.1) to the Petri dish. Incubate for 30 min at 37 &#176;C.</li>
	<li>Using a pipette remove the DPBS/trypsin/glucose solution from the Petri dish and add 10 mL of RPMI-1640 + 2% FBS to inactivate the trypsin.</li>
	<li>Using two forceps, now release the epidermal cells into the medium by gently scraping and agitating both the epidermal and the dermal compartment of the skin sections.</li>
	<li>Filter the epidermal cell suspension through a metal filter (1 mm hole size), and collect in a 50 mL tube. Add the remaining skin sections to a 50 mL tube containing 10 mL of RPMI-1640 without FBS and vortex for 10 s. Filter the suspension through the metal filter into a 50 mL tube containing the epidermal cell suspension. Add DPBS to a total volume of 50 mL.</li>
	<li>Centrifuge the cell suspension for 10 min at 450 x g at room temperature.</li>
	<li>Remove the supernatant and resuspend the epidermal cell pellet in approximately 10 mL of 37 &#176;C KSFM depending on the size of the cell pellet. Count the cells using the Trypan Blue staining method under microscope. The number of cells obtained from a 10 cm x 15 cm skin section is approximately 50 - 100 x 106 cells. To each 75 cm2 culture flask, transfer 8 x 106 cells together with 12 mL of 37 &#176;C KSFM. Gently shake the culture flasks to ensure uniform distribution of the cells.</li>
	<li>Incubate the keratinocytes in a 37 &#176;C incubator with 100% humidity and 5% CO2. Change the medium after 2 days and three times weekly. Passage cells when the culture is 70 - 80% confluent, which takes approximately 2 weeks depending on the proliferation rate of the keratinocytes.</li>
</ol>
2. Passaging of Keratinocytes
<ol>
	<li>Heat the appropriate amount of 0.05% Trypsin-EDTA solution to 37 &#176;C in an incubator. Use 4.5 mL of 0.05% Trypsin-EDTA solution for a 75 cm2 culture flask.</li>
	<li>Remove medium from the cells, and add 4.5 mL/75 cm2 culture flask pre-warmed 0.05% Trypsin-EDTA solution to the cells. Place the culture flask in the incubator (37 &#176;C) and after approximately 5 min, check under the microscope if the cells have started loosening.</li>
	<li>When approximately 50% of the cells have loosened, gently hit the culture flask against the hand to loosen the remaining cells. Then, to inactivate the trypsin, add 6 mL of RPMI-1640 + 2% FBS (37 &#176;C) to the 75 cm2 culture flask and transfer the cell suspension to 50 mL tubes.</li>
	<li>Rinse the culture flasks with 3 mL of RPMI 1640 + 2% FBS and add to the 50 mL tubes. Centrifuge cells for 10 min at 450 x g at room temperature.
	<ol>
		<li>Resuspend the pelleted cells in 10 mL of KSFM (37 &#176;C). Count the cells and transfer 3 x 106 cells to a 150 cm2 culture flask together with 20 mL of KSFM (37 &#176;C). Gently shake the culture flask to ensure uniform distribution of the cells. Freeze the cells when the culture is 80 - 90% confluent, which takes approximately 4-6 days depending on the proliferation rate of the keratinocytes (see Section 3, freezing protocol below). Expand the keratinocytes to generate appropriate frozen stocks.</li>
	</ol>
	</li>
</ol>
3. Freezing of Keratinocytes
<ol>
	<li>Heat the appropriate amount of 0.05% Trypsin-EDTA solution to 37 &#176;C in an incubator. Use 9 mL of 0.05% Trypsin-EDTA solution for a 150 cm2 culture flask.</li>
	<li>Remove medium from the cells, and add 9 mL/150 cm2 culture flask pre-warmed 0.05% Trypsin-EDTA solution to the cells. Place the culture flask in the incubator (37 &#176;C) and after approximately 5 min, check under the microscope if the cells have started loosening.</li>
	<li>When approximately 50% of the cells have loosened, gently hit the culture flask against the hand in order to loosen the remaining cells. Then, to inactivate the trypsin, add 12 mL of RPMI-1640 + 2% FBS (37 &#176;C) to the 150 cm2 culture flask and aspirate the cell suspension to 50 mL tubes.</li>
	<li>Rinse the culture flasks with 6 mL of RPMI 1640 + 2% FBS and add to the 50 mL tubes. Centrifuge the tubes for 10 min at 450 x g at 4 &#176;C. Prepare ice-cold cell freezing medium (KSFM + 10% DMSO).</li>
	<li>Resuspend the cell pellet in KSFM + 10% DMSO, count the cells, and freeze cells at a density of 6 x 106 cells/mL using standard slow-freezing cryopreservation methods12.</li>
	<li>Store the keratinocytes in liquid nitrogen (vapor phase) until ready to use.</li>
</ol>
4. Thawing and Culturing Frozen Keratinocytes
<ol>
	<li>Rapidly thaw the appropriate frozen vials in a 37 &#176;C water bath. Use 70% ethanol to clean the outside of the cryovial. Transfer the appropriate number of cells (approximately 15,000 cells/cm2) to a culture flask and immediately add pre-warmed growth medium (KSFM) to the culture flask. 
	Any size of culture flasks can be used depending on the setup of the experiment.</li>
	<li>Use 5 mL culture medium for a 25 cm2 culture flask. The number of cells added the culture flask might vary because the growth of the cells varies from donor to donor. Incubate cells in a 37 &#176;C incubator with 100% humidity and 5% CO2.</li>
	<li>Change the medium after 2 days and three times weekly using fresh pre-warmed KSFM. 
	Note: Our data have demonstrated that on average 95% of the cells isolated by the protocol described here are positive for the keratinocyte-marker cytokeratine-1413.</li>
</ol>

<ol>
	<li>Barker, J. N., Mitra, R. S., Griffiths, C. E., Dixit, V. M., Nickoloff, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keratinocytes+as+initiators+of+inflammation.">Keratinocytes as initiators of inflammation.</a> Lancet. 337 (8735), 211-214 (1991).</li><li>Nickoloff, B. J., Turka, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keratinocytes:+key+immunocytes+of+the+integument.">Keratinocytes: key immunocytes of the integument.</a> Am J Pathol. 143 (2), 325-331 (1993).</li><li>Fuchs, E., Raghavan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Getting+under+the+skin+of+epidermal+morphogenesis.">Getting under the skin of epidermal morphogenesis.</a> Nat Rev Genet. 3 (3), 199-209 (2002).</li><li>Bos, J. D., Kapsenberg, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+skin+immune+system+Its+cellular+constituents+and+their+interactions.">The skin immune system Its cellular constituents and their interactions.</a> Immunol Today. 7 (7-8), 235-240 (1986).</li><li>Nestle, F. O., Di Meglio, P., Qin, J. Z., Nickoloff, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+immune+sentinels+in+health+and+disease.">Skin immune sentinels in health and disease.</a> Nat Rev Immunol. 9 (10), 679-691 (2009).</li><li>Albanesi, C., Scarponi, C., Giustizieri, M. L., Girolomoni, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Keratinocytes+in+inflammatory+skin+diseases.">Keratinocytes in inflammatory skin diseases.</a> Curr Drug Targets Inflamm Allergy. 4 (3), 329-334 (2005).</li><li>Gilliet, M., Lande, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antimicrobial+peptides+and+self-DNA+in+autoimmune+skin+inflammation.">Antimicrobial peptides and self-DNA in autoimmune skin inflammation.</a> Curr Opin Immunol. 20 (4), 401-407 (2008).</li><li>Rohani, M. G., Pilcher, B. K., Chen, P., Parks, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cdc42+inhibits+ERK-mediated+collagenase-1+(MMP-1)+expression+in+collagen-activated+human+keratinocytes.">Cdc42 inhibits ERK-mediated collagenase-1 (MMP-1) expression in collagen-activated human keratinocytes.</a> J Invest Dermatol. 134 (5), 1230-1237 (2014).</li><li>Meephansan, J., Tsuda, H., Komine, M., Tominaga, S., Ohtsuki, M. <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+IL-33+expression+by+IFN-gamma+and+tumor+necrosis+factor-alpha+in+normal+human+epidermal+keratinocytes.">Regulation of IL-33 expression by IFN-gamma and tumor necrosis factor-alpha in normal human epidermal keratinocytes.</a> J Invest Dermatol. 132 (11), 2593-2600 (2012).</li><li>Maciag, T., Nemore, R. E., Weinstein, R., Gilchrest, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+endocrine+approach+to+the+control+of+epidermal+growth:+serum-free+cultivation+of+human+keratinocytes.">An endocrine approach to the control of epidermal growth: serum-free cultivation of human keratinocytes.</a> Science. 211 (4489), 1452-1454 (1981).</li><li>Liu, S. C., Karasek, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+growth+of+adult+human+epidermal+keratinocytes+in+cell+culture.">Isolation and growth of adult human epidermal keratinocytes in cell culture.</a> J Invest Dermatol. 71 (2), 157-162 (1978).</li><li>Naaldijk, Y., Friedrich-Stockigt, A., Sethe, S., Stolzing, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+different+cooling+rates+for+fibroblast+and+keratinocyte+cryopreservation.">Comparison of different cooling rates for fibroblast and keratinocyte cryopreservation.</a> J Tissue Eng Regen Med. 10 (10), E354-E364 (2016).</li><li>Otkjaer, 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=IL-20+gene+expression+is+induced+by+IL-1beta+through+mitogen-activated+protein+kinase+and+NF-kappaB-dependent+mechanisms.">IL-20 gene expression is induced by IL-1beta through mitogen-activated protein kinase and NF-kappaB-dependent mechanisms.</a> J Invest Dermatol. 127 (6), 1326-1336 (2007).</li><li>Watt, F. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Involucrin+and+other+markers+of+keratinocyte+terminal+differentiation.">Involucrin and other markers of keratinocyte terminal differentiation.</a> J Invest Dermatol. 81 (1 Suppl), 100s-103s (1983).</li><li>Boyce, S. T., Ham, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium-regulated+differentiation+of+normal+human+epidermal+keratinocytes+in+chemically+defined+clonal+culture+and+serum-free+serial+culture.">Calcium-regulated differentiation of normal human epidermal keratinocytes in chemically defined clonal culture and serum-free serial culture.</a> J Invest Dermatol. 81 (1 Suppl), 33s-40s (1983).</li><li>Hennings, H., 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=Calcium+regulation+of+growth+and+differentiation+of+mouse+epidermal+cells+in+culture.">Calcium regulation of growth and differentiation of mouse epidermal cells in culture.</a> Cell. 19 (1), 245-254 (1980).</li><li>Carlson, M. W., Alt-Holland, A., Egles, C., Garlick, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+tissue+models+of+normal+and+diseased+skin.">Three-dimensional tissue models of normal and diseased skin.</a> Curr Protoc Cell Biol. , (2008).</li><li>Kamsteeg, 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=Type+2+helper+T-cell+cytokines+induce+morphologic+and+molecular+characteristics+of+atopic+dermatitis+in+human+skin+equivalent.">Type 2 helper T-cell cytokines induce morphologic and molecular characteristics of atopic dermatitis in human skin equivalent.</a> Am J Pathol. 178 (5), 2091-2099 (2011).</li><li>van den Bogaard, E. H., 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=Crosstalk+between+keratinocytes+and+T+cells+in+a+3D+microenvironment:+a+model+to+study+inflammatory+skin+diseases.">Crosstalk between keratinocytes and T cells in a 3D microenvironment: a model to study inflammatory skin diseases.</a> J Invest Dermatol. 134 (3), 719-727 (2014).</li><li>Raaby, L., 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=Langerhans+cell+markers+CD1a+and+CD207+are+the+most+rapidly+responding+genes+in+lesional+psoriatic+skin+following+adalimumab+treatment.">Langerhans cell markers CD1a and CD207 are the most rapidly responding genes in lesional psoriatic skin following adalimumab treatment.</a> Exp Dermatol. , (2017).</li></ol>

.The author has no conflict of interest.

Here, we describe how to easily isolate primary human keratinocytes from adult skin, and how to culture them in vitro. This model can have a broad application for investigation of epidermal cell biology, and can be useful for researchers interested in studying cutaneous diseases.
Some of the advantages of the protocol described here is that in contrast to keratinocytes isolated from neonatal foreskin obtained from newborn males undergoing circumcision, primary human keratinocytes from...

The skin is the biggest organ of the human body and serves as a protective barrier against the external environment. The skin is composed of two main layers: the dermis and the epidermis, where the epidermis constitutes the outermost layer of the skin. The most abundant cell type in the epidermis is the keratinocytes comprising more than 95% of the cell mass1,2. The keratinocytes are maintained at various stages of differentiation in the epidermis and are organized into basal, spinous, granular, and cornified layers that correspond to specific stages of differentiation3. The primary function of keratinocytes is to provide the structural integrity of the epidermis, thereby producing an intact barrier to the outside world.
The keratinocytes also represent the first line of defense against pathogens in the skin, and therefore play an important role in the innate immune response4,5. Exposure of the keratinocytes to external stimuli leads to activation of intracellular signaling pathways and subsequently, production of a number of various inflammatory mediators including cytokines, chemokines, and antimicrobial peptides. These keratinocyte-derived proteins participate in the inflammatory response by recruiting and activating immune cells such as dendritic cells, neutrophils, and specific T cells6,7. Thus, because keratinocytes play a crucial part in numerous biological processes, the rationale behind the technique presented here was to generate an in vitro model to study skin biology. Primary keratinocyte cultures obtained from neonatal foreskin are often used to study skin biology8,9. However, with the technique described here, keratinocytes from both genders are obtained resulting in a higher biological diversity of the cells.
Here, we present a detailed protocol for the isolation and generation of primary human keratinocytes from adult skin, including maintenance and freezing of the keratinocytes. The overall goal of this method is to generate primary human keratinocytes that can be used as a model to study cutaneous biology in vitro.

<table><tbody><tr><td>KSFM</td><td>ThermoFisher Scientific</td><td>17005-034</td><td>Cell culture medium</td></tr><tr><td>KSFM supplements</td><td>ThermoFisher Scientific</td><td>37000-015</td><td>Supplements for KSFM</td></tr><tr><td>DPBS</td><td>ThermoFisher Scientific</td><td>14190-144</td><td>DPBS without Calcium and Magnesium</td></tr><tr><td>DMSO</td><td>Sigma-Aldrich</td><td>D8418</td><td>Dimethyl sulfoxid</td></tr><tr><td>Gentamycin</td><td>ThermoFisher Scientific</td><td>15710-049</td><td>Cell culture medium additive</td></tr><tr><td>Sterilization filter</td><td>Sartorius</td><td>16534</td><td>Syringe filter with a pore size of 0.2 &amp;micro;m</td></tr><tr><td>Trypsin</td><td>Sigma-Aldrich</td><td>T7409</td><td>Used to trypsinize cells</td></tr><tr><td>Glucose</td><td>Sigma-Aldrich</td><td>G7528</td><td>-</td></tr><tr><td>RPMI-1640</td><td>ThermoFisher Scientific</td><td>61870-010</td><td>-</td></tr><tr><td>FBS</td><td>ThermoFisher Scientific</td><td>16000044</td><td>Used to inactivate trypsin</td></tr><tr><td>Forceps</td><td>-</td><td>-</td><td>Forceps from any company can be used</td></tr><tr><td>Scissors</td><td>-</td><td>-</td><td>Scissors from any company can be used</td></tr><tr><td>Scalpel</td><td>Swann Morton</td><td>0501</td><td>Scalpels from any company can be used</td></tr><tr><td>70% ethanol</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Gauze pads</td><td>NOBAMED</td><td>875420</td><td>Gauze pads from any provider can be used</td></tr><tr><td>Foot planer</td><td>Credo Solingen</td><td>1510</td><td>Foot planer from any provider can be used</td></tr><tr><td>Petri dishes</td><td>TPP</td><td>93100</td><td>Petri dishes from any provider can be used</td></tr><tr><td>Metal filter</td><td>-</td><td>-</td><td>In-house 1 mm hole size metal filter</td></tr><tr><td>75 cm&lt;sup&gt;2&lt;/sup&gt; culture flasks</td><td>NUNC</td><td>156499</td><td>-</td></tr><tr><td>150 cm&lt;sup&gt;2&lt;/sup&gt; culture flasks</td><td>TTP</td><td>90151</td><td>-</td></tr><tr><td>0.05% Trypsin-EDTA solution</td><td>ThermoFisher Scientific</td><td>25300-062</td><td>Used to trypsinize cells when passaging</td></tr></tbody></table>

generation and culturing of primary human keratinocytes from adult skin

The main function of keratinocytes is to provide the structural integrity of the epidermis, thereby maintaining a mechanical barrier to the outside world. In addition, keratinocytes play an essential role in the initiation, maintenance, and regulation of epidermal immune responses by being part of the innate immune system responding to antigenic stimuli in a fast, nonspecific manner. Here, we describe a protocol for isolation of primary human keratinocytes from adult skin, and demonstrate that these cells respond to calcium-induced terminal differentiation, as measured by an increased expression of the differentiation marker involucrin. In addition, we show that the isolated keratinocytes are responsive to IL-1&#946;-induced activation of intracellular signaling pathways as measured by the activation of the p38 MAPK pathway. Taken together, we describe a method for isolation and culturing of primary human keratinocytes from adult skin. Because the keratinocytes are the predominant cell type in the epidermis, this method is useful to study molecular mechanisms in cutaneous biology in vitro.

Calcium-induced Terminal Differentiation 
Human keratinocytes undergo terminal differentiation upon treatment with calcium14,15,16. Primary human keratinocytes were isolated and cultured as described in the above protocol. When approximately 50 - 60% confluent, the cells were stimulated with calcium (1.2 mM) or vehicle and pictures of the cells were taken on day 0, 1, and 2. Figure 1</s...

Watch this Scientific Journal Video about Generation and Culturing of Primary Human Keratinocytes from Adult Skin at JoVE.com

Generation and Culturing of Primary Human Keratinocytes from Adult Skin

The human skin acts as a first line of defense against the external environment. We present a method for isolating primary human keratinocytes from adult skin. These isolated keratinocytes are useful in numerous experimental setups, and are a highly suitable model for studying molecular mechanisms in cutaneous biology in vitro.

The main function of keratinocytes is to provide the structural integrity of the epidermis, thereby maintaining a mechanical barrier to the outside world. ...

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16.3K Views.  Aarhus University Hospital. The human skin acts as a first line of defense against the external environment. We present a method for isolating primary human keratinocytes from adult skin. These isolated keratinocytes are useful in numerous experimental setups, and are a highly suitable model for studying molecular mechanisms in cutaneous biology in vitro.

Video: Generation and Culturing of Primary Human Keratinocytes from Adult Skin

Generation of Genetically Modified Organotypic Skin Cultures Using Devitalized Human Dermis

Organotypic cultures allow the reconstitution of a 3D environment critical for cell-cell contact and cell-matrix interactions which mimics the function and physiology of their in vivo tissue counterparts. This is exemplified by organotypic skin cultures which faithfully recapitulates the epidermal differentiation and stratification program. Primary human epidermal keratinocytes are genetically manipulable through retroviruses where genes can be easily overexpressed or knocked down. These genetically modified keratinocytes can then be used to regenerate human epidermis in organotypic skin cultures providing a powerful model to study genetic pathways impacting epidermal growth, differentiation, and disease progression. The protocols presented here describe methods to prepare devitalized human dermis as well as to genetically manipulate primary human keratinocytes in order to generate organotypic skin cultures. Regenerated human skin can be used in downstream applications such as gene expression profiling, immunostaining, and chromatin immunoprecipitations followed by high throughput sequencing. Thus, generation of these genetically modified organotypic skin cultures will allow the determination of genes that are critical for maintaining skin homeostasis.

The goal of this paper is to provide a comprehensive and detailed protocol on how to generate genetically modified human organotypic skin from epidermal keratinocytes and devitalized human dermis.

Organotypic cultures allow the reconstitution of a 3D environment critical for cell-cell contact and cell-matrix interactions which mimics the function ...

A Simplified and Efficient Method to Isolate Primary Human Keratinocytes from Adult Skin Tissue

Primary human keratinocytes isolated from fresh skin tissues and their expansion in vitro have been widely used for laboratory research and for clinical applications. The conventional isolation method of human keratinocytes involves a two-step sequential enzymatic digestion procedure, which has been proven to be inefficient in generating primary cells from adult tissues due to the low cell recovery rate and reduced cell viability. We recently reported an advanced method to isolate human primary epidermal progenitor cells from skin tissues that utilizes the Rho kinase inhibitor Y-27632 in the medium. Compared with the traditional protocol, this new method is simpler, easier, and less time-consuming, and increases epithelial stem cell yield and enhances their stem cell characteristics. Moreover, the new methodology does not require the separation of the epidermis from the dermis, and, therefore, is suitable for isolating cells from different types of adult tissues. This new isolation method overcomes the major shortcomings of conventional methods and is more suitable for producing large numbers of epidermal cells with high potency both for laboratory and for clinical applications. Here, we describe the new method in detail.

Here we present a protocol to efficiently isolate primary human keratinocytes from adult skin tissues. This method simplifies the conventional procedure by using the ROCK Inhibitor Y-27632 in the inoculation medium to spontaneously separate epidermal cells from dermal cells.

Primary human keratinocytes isolated from fresh skin tissues and their expansion in vitro have been widely used for laboratory research and for clinical ...

Establishing a High Throughput Epidermal Spheroid Culture System to Model Keratinocyte Stem Cell Plasticity

Epithelial dysregulation is a node for a variety of human conditions and ailments, including chronic wounding, inflammation, and over 80% of all human cancers. As a lining tissue, the skin epithelium is often subject to injury and has evolutionarily adapted by acquiring the cellular plasticity necessary to repair damaged tissue. Over the years, several efforts have been made to study epithelial plasticity using in&#160;vitro and ex vivo cell-based models. However, these efforts have been limited in their capacity to recapitulate the various phases of epithelial cell plasticity. We describe here a protocol for generating 3D epidermal spheroids and epidermal spheroid-derived cells from primary neonatal human keratinocytes. This protocol outlines the capacity of epidermal spheroid cultures to functionally model distinct stages of keratinocyte generative plasticity and demonstrates that epidermal spheroid re-plating can enrich heterogenous normal human keratinocytes (NHKc) cultures for integrin&#945;6hi/EGFRlo keratinocyte subpopulations with enhanced stem-like characteristics. Our report describes the development and maintenance of a high throughput system for the study of skin keratinocyte plasticity and epidermal regeneration.

Here we describe a protocol for the systematic cultivation of epidermal spheroids in 3D suspension culture. This protocol has wide-ranging applications for use in a variety of epithelial tissue types and for the modeling of several human diseases and conditions.

Epithelial dysregulation is a node for a variety of human conditions and ailments, including chronic wounding, inflammation, and over 80% of all human ...

Isolation and Culture of Adult Epithelial Stem Cells from Human Skin

The homeostasis of all self-renewing tissues is dependent on adult stem cells. As undifferentiated stem cells undergo asymmetric divisions, they generate daughter cells that retain the stem cell phenotype and transit-amplifying cells (TA cells) that migrate from the stem cell niche, undergo rapid proliferation and terminally differentiate to repopulate the tissue.
Epithelial stem cells have been identified in the epidermis, hair follicle, and intestine as cells with a high in vitro proliferative potential and as slow-cycling label-retaining cells in vivo 1-3. Adult, tissue-specific stem cells are responsible for the regeneration of the tissues in which they reside during normal physiologic turnover as well as during times of stress 4-5. Moreover, stem cells are generally considered to be multi-potent, possessing the capacity to give rise to multiple cell types within the tissue 6. For example, rodent hair follicle stem cells can generate epidermis, sebaceous glands, and hair follicles 7-9. We have shown that stem cells from the human hair follicle bulge region exhibit multi-potentiality 10.
Stem cells have become a valuable tool in biomedical research, due to their utility as an in vitro system for studying developmental biology, differentiation, tumorigenesis and for their possible therapeutic utility. It is likely that adult epithelial stem cells will be useful in the treatment of diseases such as ectodermal dysplasias, monilethrix, Netherton syndrome, Menkes disease, hereditary epidermolysis bullosa and alopecias 11-13. Additionally, other skin problems such as burn wounds, chronic wounds and ulcers will benefit from stem cell related therapies 14,15. Given the potential for reprogramming of adult cells into a pluripotent state (iPS cells)16,17, the readily accessible and expandable adult stem cells in human skin may provide a valuable source of cells for induction and downstream therapy for a wide range of disease including diabetes and Parkinson's disease.

A rapid, robust way of isolating viable adult epithelial stem cells from human skin is described. The method utilizes enzymatic digestion of skin collagen matrix , followed by plucking of hair follicles and isolation of single cell suspensions or tissue fragments for cell culture.

The homeostasis of all self-renewing tissues is dependent on adult stem cells. As undifferentiated stem cells undergo asymmetric divisions, they generate ...

Biology

Cultivating a Three-dimensional Reconstructed Human Epidermis at a Large Scale

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process and the characterization of the model is described. Neonatal primary keratinocytes are grown submerged on permeable polycarbonate inserts and lifted to the air-liquid interface three days after seeding. After fourteen days of stimulation with defined growth factors and ascorbic acid in high calcium culture medium, the model is fully differentiated. Histological analysis revealed a completely stratified epidermis, mimicking the morphology of native human skin. To characterize the model and its barrier functions, protein levels and localization specific for early-stage keratinocyte differentiation (i.e., keratin 10), late-stage differentiation (i.e., involucrin, loricrin, and filaggrin) and tissue adhesion (i.e., desmoglein 1), were assessed by immunofluorescence. The tissue barrier integrity was further evaluated by measuring transepithelial electrical resistance. Reconstructed human epidermis was responsive to proinflammatory stimuli (i.e., lipopolysaccharide and tumor necrosis factor alpha), leading to increased cytokine release (i.e., interleukin 1 alpha and interleukin 8). This protocol represents a straightforward and reproducible in vitro method to cultivate reconstructed human epidermis as a tool to assess environmental effects and a broad range of skin-related studies.

This protocol describes a straightforward method to cultivate three-dimensional reconstituted human epidermis in a reproducible and robust manner. Additionally, it characterizes the structure-function relationship of the epidermal barrier model. The biological responses of the reconstituted human epidermis upon proinflammatory stimuli are also presented.

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process ...

Bioengineering

Generating Primary Cultures for Keratinocyte Live Cell Imaging

Tracking stem cells and committed progenitor behavior at the single-cell level in human skin has been challenging both in vivo and in vitro.&#160;Live-cell imaging has allowed for significant advances in the ability to identify differences between keratinocyte stem cells and committed progenitor behavior. Live-cell imaging is an evolving and somewhat challenging method to study keratinocyte behavior in vitro. This protocol has been developed to culture keratinocytes at low seeding density, enabling relatively long-term time-lapse photography and monitoring of individual cell behavior. Passage 0 keratinocytes are grown at clonal density, and time-lapse photography allows documentation of individual cell divisions and the time of their occurrence. For maximum biological relevance, freshly isolated human keratinocytes are placed in vitro. This approach focuses on proliferation. However, this protocol can be adapted for use in other live cell imaging applications measuring individual cell behavior, such as measuring cell migration, wound healing, and motility.

This protocol outlines the culture of freshly obtained (passage 0) keratinocytes for use in live cell imaging.

Tracking stem cells and committed progenitor behavior at the single-cell level in human skin has been challenging both in vivo and in ...

Isolation, Culture, and Characterization of Primary Schwann Cells, Keratinocytes, and Fibroblasts from Human Foreskin

This protocol describes isolation methods, culturing conditions, and characterization of human primary cells with high yield and viability using rapid enzymatic dissociation of skin. Primary keratinocytes, fibroblasts, and Schwann cells are all harvested from the human newborn foreskin, which is available following standard of care procedures. The removed skin is disinfected, and the subcutaneous fat and muscle are removed using a scalpel. The method consists of enzymatic and mechanical separation of epidermal and dermal layers, followed by additional enzymatic digestion to obtain single-cell suspensions from each of these skin layers. Finally, single cells are grown in appropriate cell culture media following standard cell culture protocols to maintain growth and viability over weeks. Together, this simple protocol allows isolation, culturing, and characterization of all three cell types from a single piece of skin for in vitro evaluation of skin-nerve models. Additionally, these cells can be used together in co-cultures to gauge their effects on each other and their responses to in vitro trauma in the form of scratches performed robotically in the culture associated with wound healing.

The study of wound healing associated with musculoskeletal injury often requires the assessment of in vitro interactions between Schwann cells (SCs), keratinocytes, and fibroblasts. This protocol describes the isolation, culturing, and characterization of these primary cells from the human foreskin.

This protocol describes isolation methods, culturing conditions, and characterization of human primary cells with high yield and viability using rapid ...

Neuroscience

Isolation and Culture of Primary Mouse Keratinocytes from Neonatal and Adult Mouse Skin

The keratinocyte (KC) is the predominant cell type in the epidermis, the outermost layer of the skin. Epidermal KCs play a critical role in providing skin defense by forming an intact skin barrier against environmental insults, such as UVB irradiation or pathogens, and also by initiating an inflammatory response upon those insults. Here we describe methods to isolate KCs from neonatal mouse skin and from adult mouse tail skin. We also describe culturing conditions using defined growth supplements (dGS) in comparison to chelexed fetal bovine serum (cFBS). Functionally, we show that both neonatal and adult KCs are highly responsive to high calcium-induced terminal differentiation, tight junction formation and stratification. Additionally, cultured adult KCs are susceptible to UVB-triggered cell death and can release large amounts of TNF upon UVB irradiation. Together, the methods described here will be useful to researchers for the setup of in vitro models to study epidermal biology in the neonatal mouse and/or the adult mouse.

Epidermal keratinocytes form a functional skin barrier and are positioned at the front line of host defense against external environmental insults. Here we describe methods for isolation and primary culture of epidermal keratinocytes from neonatal and adult mouse skin, and induction of terminal differentiation and UVB-triggered inflammatory response from keratinocytes.

The keratinocyte (KC) is the predominant cell type in the epidermis, the outermost layer of the skin. Epidermal KCs play a critical role in providing skin ...

Isolation and Culture of Primary Oral Keratinocytes from the Adult Mouse Palate

For years, most studies involving keratinocytes have been conducted using human and mouse skin epidermal keratinocytes. Recently, oral keratinocytes have attracted attention because of their unique function and characteristics. They maintain the homeostasis of the oral epithelium and serve as resources for applications in regenerative therapies. However, in vitro studies that use oral primary keratinocytes from adult mice have been limited due to the lack of an efficient and well-established culture protocol. Here, oral primary keratinocytes were isolated from the palate tissues of adult mice and cultured in a commercial low-calcium medium supplemented with a chelexed-serum. Under these conditions, keratinocytes were maintained in a proliferative or stem cell-like state, and their differentiation was inhibited even after increased passages. Marker expression analysis showed that the cultured oral keratinocytes expressed the basal cell markers p63, K14, and &#945;6-integrin and were negative for the differentiation marker K13 and the fibroblast marker PDGFR&#945;. This method produced viable and culturable cells suitable for downstream applications in the study of oral epithelial stem cell functions in vitro.

The present protocol describes the isolation and culture of oral keratinocytes derived from the adult mouse palate. An evaluation method using immunostaining is also reported.

For years, most studies involving keratinocytes have been conducted using human and mouse skin epidermal keratinocytes. Recently, oral keratinocytes have ...

Human Skin Keratinocyte Isolation: A Method to Culture Primary Keratinocytes from Skin Samples

Johansen, C. et al. <a href="https://www.jove.com/v/56863"> Generation and Culturing of Primary Human Keratinocytes from Adult Skin</a>. J. Vis. Exp. (2017)
This video describes the isolation of keratinocytes&#8212;the most prominent cells of human skin&#39;s epidermal layer, by employing a combination of enzymatic digestion and mechanical disruption methods. This method helps in the preferential growth of keratinocytes over other skin cell types using a selective growth medium.

Johansen, C. et al.  Generation and Culturing of Primary Human Keratinocytes from Adult Skin. J. Vis. Exp. (2017)
This video describes the isolation of ...