Experimental Design
The aim of this study was to understand the biological function of keratin in hair growth. Firstly, to determine the activity of hair growth, back-skin hairs in mice were removed, and hair follicle formation and hair regrowth was evaluated after intradermal injection of hair-derived keratin (Fig. 1A-F). Next, to define cellular interaction of keratin with major cells participating in hair growth, cellular behavior such as DP cell condensation and germ formation was studied by treating keratin in in vitro DP cell and ORS cell culture (Fig. 1G-H, Fig. 2 and Fig. 3). From the results (Fig. 1-3), it was hypothesized that keratin-induced hair growth could be closely related to a biological cascade happened during hair cycle with regards to the exposure of keratin from TGF-b2-induced apoptotic ORS cells at stages of anagen-catagen transition. To characterize keratin release or deposit from apoptotic ORS cells, apoptosis of ORS cells and its following keratin release and deposit from TGF-b2-treated ORS cells were evaluated, and then DP cell condensation was observed by the direct co-culture with TGF-b2-treated ORS cells and the DP cell culture in conditioned medium collected from TGF-b2-treated ORS cell culture to evaluate the effect of released or deposited keratin from apoptotic ORS cells on DP cell condensation (Fig. 4). Following DP cell condensation induced by released and deposited keratin from apoptotic ORS cells, apoptosis-related caspase 3 and caspase 6 expressions and caspase-mediated keratin degradation were characterized, and the release and deposit of keratin through caspase-mediated keratin degradation in TGF-b2-treated apoptotic ORS cells and its effect on DP cell condensation were evaluated by in vitro siRNA-mediated silencing of caspase 6 mRNA expression in TGF-b2-treated apoptotic ORS cells (Fig. 5). To confirm the effect of keratin released from TGF-b2-treated apoptotic ORS cells on DP cell condensation, the keratin were eliminated from conditioned medium collected from TGF-b2-treated cell culture by immunodepletion, and DP cell condensation was evaluated with DP cell culture in the keratin-eliminating conditioned medium collected from TGF-b2-treated apoptotic ORS cells (Fig. 6A-C). In company with proving the effect of keratin released from TGF-b2-treated apoptotic ORS cells on DP cell condensation, mRNA expressions of keratin 31 (KRT31) and keratin 34 (KRT34) were silenced in ORS cells by in vitro KRT31/KRT34 siRNA transfection, and then P-cadherin expressing germ formation of ORS cells was observed in KRT31/KRT34-silenced ORS cell culture in the presence of TGF-b2 to evaluate the effect of keratin spatially deposited from TGF-b2-treated apoptotic ORS cells on germ formation (Fig. 6D). Finally, to study the role of keratin in hair follicle formation and hair growth in vivo, KRT31/KRT34 silencing was processed by Invivofectamine KRT31/KRT34 siRNA transfection to mice (Fig. 7).
Cell Culture
Human outer root sheath cells (ORS; CEFO, CB-ORS-001) and human dermal papilla cells (DP; CEFO, CB-HDP-001) were purchased and expanded in each human outer root sheath cell growth medium (CEFO, CB-ORS-GM) and human dermal papilla growth medium (CEFO, CB-HDP-GM) at 37oC in a humidified atmosphere containing 5 % CO2 according to the manufacturer's instructions. Cultures were fed every two days and passaged by treatment with 0.25 % trypsin/EDTA (Gibco, 25200056), and the expanded DP cells within 5 passages and ORS cells within 3 passages were used in this study.
Human Hair Keratin Extraction
Human hair keratin was extracted by slightly modified Sindai method, as reported previously 12, and kindly provided by Gapi Bio. Detail methods of microwell fabrication are available in Supplementary Methods.
Human Hair Keratin-mediated Hair Growth Test in Mice
For in vivo studies, male C57BL/6 mice were used, which were purchased from YoungBio (Samtako, 1404957265). The mice were housed under controlled condition at a temperature of 23 ± 2°C, humidity of 50 ± 5%, and light-dark cycle of 12 h. Mice were provided with a laboratory diet and water ad libitum. All animal experiments were approved by the Institutional Animal Care and Use Committee of Konkuk University (KU18159, KU19066), and procedures on animals were performed in accordance with the relevant guidelines and regulations. The hair on the dorsal skin of mice was shaved repeatedly using an electric clipper to synchronize the hair follicle cycle. Before treatment, the dorsal hair was completely removed using the commercial hair removal cream Veet® (Reckitt Benckiser, 62200809951).
To examine the hair growth promoting effect of keratin, 1.0 (w/v)% keratin in phosphate buffered saline (PBS; Gibco, 10010023) was used. 10-week old mice were shaved repeatedly to synchronize the hair cycle and randomly assigned to three groups: Neg. Con group; 3% Minoxidil group with daily topical application of 100 μL of 3% Minoxidil (Minoxyl® 3%; Hyundai Pharm, Co., Seoul, Korea); 1.0 (w/v)% Keratin group with intradermal injection of 100 μL of 1.0 (w/v)% keratin once. The mice were sacrificed after 2 weeks.
Detail methods of the hair growth promoting effect of keratin according to keratin concentration are available in Supplementary Methods.
Interaction Assay of DP Cells with Keratin
DP cells were seeded at a density of 2x104 cell/cm2 on 12 well and 6 well non-treated tissue culture plate (SPL LIFE SCIENCES, 32012, 32006). The DP cells were adjusted to be stable for 1 day in human dermal papilla growth medium (CEFO, CB-HDP-GM) at 37oC in a humidified atmosphere containing 5 % CO2 prior to keratin treatment. After 1 day of adjustment, DP cells were cultured in human dermal papilla growth medium containing 1.0(w/v)% keratin or not. The morphological change of DP cells in the presence of keratin was observed under inverted fluorescent microscopy (Olympus IX71), and the number of condensed DP cell aggregates was counted. Cell proliferation upon keratin treatment was measured using Cell Counting Kit-8 (Dojindo Molecular Technologies, CK04-20). DP cells were seeded on 12 well non-treated tissue culture plate (SPL LIFE SCIENCES, 32012) at a seeding density of 1 × 104 cells/cm2, and cultured in human dermal papilla growth medium (CEFO, CB-HDP-GM) containing 1.0(w/v)% keratin or not in a humidified atmosphere of 5% CO2 at 37°C, and the medium was refreshed every two days. At specific time points (1, 3 and 5 days), each well had 10 μL of the Cell Counting Kit-8 solution added and then was incubated at 37°C for 2 h. Cell proliferation assays were performed in a 96-well plate reader by measuring the absorbance at a wavelength of 450 nm.
For DP cell condensation assay according to different cell seeding density, DP cells were seeded at a seeding density of 5x103 cell/cm2, 1x104 cell/cm2 and 2x104 cell/cm2 on 6 well non-treated tissue culture plate (SPL LIFE SCIENCES, 32006). The DP cells were adjusted to be stable for 1 day in human dermal papilla growth medium (CEFO, CB-HDP-GM) at 37oC in a humidified atmosphere containing 5 % CO2 prior to keratin treatment. After 1 day of adjustment, DP cells were cultured in human dermal papilla growth medium containing 1.0(w/v)% keratin or not. The number of condensed DP cell aggregates was counted using inverted fluorescent microscopy (Olympus IX71).
Detail method of interaction assay of DP cells with keratin on Matrigel is available in Supplementary Methods.
Interaction Assay of ORS Cells with Keratin
ORS cells were seeded at 2x104 cell/cm2 on 12 well and 6 well tissue culture plate (SPL LIFE SCIENCES, 30012, 30006). The ORS cells were adjusted to be stable for 1 day in human outer root sheath cell growth medium (CEFO, CB-ORS-GM) at 37oC in a humidified atmosphere containing 5 % CO2 prior to keratin treatment. After 1 day of adjustment, ORS cells were cultured in human dermal papilla growth medium containing 1.0(w/v)% keratin or not. The morphological change of ORS cells in the presence of keratin was observed under inverted fluorescent microscopy (Olympus IX71) and time-lapse images were captured. Cell proliferation upon keratin treatment was measured using Cell Counting Kit-8 (Dojindo Molecular Technologies, CK04-20). ORS cells were seeded on 12 well tissue culture plate (SPL LIFE SCIENCES, 30012) at a seeding density of 1 × 104 cells/cm2, and cultured in human outer root sheath cell growth medium (CEFO, CB-ORS-GM) containing 1.0(w/v)% keratin or not in a humidified atmosphere of 5% CO2 at 37°C, and the medium was refreshed every two days. At specific time points (1, 3 and 5 days), each well had 10 μL of the Cell Counting Kit-8 solution added and then was incubated at 37°C for 2 h. Cell proliferation assays were performed in a 96-well plate reader by measuring the absorbance at a wavelength of 450 nm.
RNA Extraction and Sequencing
To perform transcriptome sequencing (RNA-Seq) analysis of DP cells and ORS cells, total RNA was extracted from the ORS and DP cells in the absences of keratin and in the presence of keratin. Detail methods of RNA extraction, sequencing and differential gene expression analysis are available in Supplementary Methods.
DP Cell Spheroid Formation and Maintenance assay of the replated DP Cell Spheroids
For DP cell spheroid formation, cell spheroids as a micro tissue unit were generated by docking DP cells into polyethylene glycol (PEG) microwell array with 450 µm in diameter. PEG microwells were fabricated by microfabrication procedures, reported previously30. Detail methods of DP cell spheroid formation and maintenance assay are available in Supplementary Methods.
TGFb2-mediated ORS Cell Apoptosis and Co-culture with DP Cells
ORS cells were seeded at 2x105 cell/cm2 on 12 well tissue culture plate (SPL LIFE SCIENCES, 30012) to make confluent ORS cell layer. The ORS cells were adjusted to be stable for 1 day in human outer root sheath cell growth medium (CEFO, CB-ORS-GM) at 37oC in a humidified atmosphere containing 5 % CO2. After 1 day of adjustment, ORS cells were cultured in human dermal papilla growth medium containing 100ng/ml TGFb2 (PeproTech, 100-35B) for 5 days, and the media was refreshed every day. Detail methods of DP cell condensation in direct co-culture of DP cells and TGFb2-treated ORS cells, and under conditioned media from TGFb2-treated ORS cell layer are available in Supplementary Methods.
Immunodepletion Study
To study the role of keratin released from TGFb2-induced apoptotic ORS cells in DP condensation and germ formation of ORS cells, the released keratin in conditioned media from TGFb2-treated ORS cell layer culture was removed by immunodepletion method. First, antibodies-conjugated beads were prepared as follows; 150ml of nProtein A Sepharose (GE Healthcare, 17528001) was incubated with 400ml of guinea pig anti-Type I+II Hair Keratins antibody (PROGEN, GP-panHK) or guinea pig normal IgG (Sigma-Aldrich, I4756), as another negative control, for 18 h at 4°C. Non-specific binding was prevented with blocking buffer containing 1% bovine serum albumin (BSA; Sigma-Aldrich, A9418) in TBS (Tris-Buffered Saline; Biosesang, TR2005-000-74) with 0.1% Tween 20 (Duchefa Biochemie, P1362.1000) for 3 h at 4°C. The conditioned media were collected from TGFb2-treated ORS cell layer cultured for 5 days, and 30ml of the conditioned media were mixed with 75ml antibodies-conjugated beads, and then incubated with gentle shaking overnight at 4°C. After incubation, antibodies-conjugated beads were removed by passing the mixture through a Centrifuge Columns (Thermo Scientific, 89898). Detail methods of DP cell condensation and P-cadherin expressing germ formation of ORS cells under keratin-removed conditioned media are available in Supplementary Methods.
Caspase-3 and Caspase-6-mediated Hair Keratin Digestion Assay
1(w/v)% hair keratin was dissolved in the reaction solution composing of 50mM HEPES (Gibco, 15630-080), 50mM NaCl (JUNSEI CHEMICAL, 19015-1250), 0.1% CHAPS (Sigma-Aldrich, C3023), 10mM EDTA (Sigma-Aldrich, 03609), 5% glycerol (SAMCHUN CHEMICALS, G0274) and 10mM DTT (Sigma-Aldrich, 43815) at pH 7.2. 5U/ml Casase-3 (Enzo, ALX-201-059) or 5U/ml Casase-6 (Enzo, ALX-201-060) was added to the reaction solution containing hair keratin and incubated at 37oC for 0, 1, 3 and 24 hrs. After the reaction, samples were denatured on 70°C for 10 min in LDS sample buffer (Invitrogen, B0007). Equal amounts of denatured samples were loaded in pre-casted 4-12% Bis-Tris Plus Gels (Invitrogen, NW04120BOX), and the electrophoresis was done by running at 200 V for 22 min. The gel was rinsed three times with distilled water for 5 min each and stained by SimplyBlue SafeStain (Invitrogen, LC6060). After 1 hr of staining, the gel was rinsed using distilled water until the background was removed thoroughly, and then images of the gel was obtained using a commercialized scanner (Canon, TS8090).
In Vitro Caspase-6 Gene Silencing Study
To evaluate the effect of caspase-6 mediated keratin degradation during TGFb2-induced ORS cell apoptosis on keratin release or deposition and DP condensation, caspase-6 gene expression in ORS cells was silenced by caspase-6 siRNA transfection. Detail methods of in vitro caspase-6 gene silencing study are available in Supplementary Methods.
In Vitro KRT31/KRT34 Gene Silencing Study
To evaluate the effect of KRT31/KRT34 gene silencing during TGFb2-induced ORS cell apoptosis on keratin release or deposition and germ formation of ORS cells, KRT31 and KRT34 gene expressions in ORS cells were silenced by KRT31/KRT34 siRNA transfection. Detail methods of in vitro KRT31/KRT34 gene silencing study are available in Supplementary Methods.
Apoptosis and Growth Factor Antibody Array
TGFb2-induced ORS cell apoptosis was evaluated by comparative analysis using human apoptosis antibody array (Abcam, ab134001), and the comparative analysis of growth factors present in the conditioned medium collected from TGFb2-treated ORS cell culture in immunodepletion study were done using human growth factor antibody array (Abcam, ab134002) according to manufacturer’s instructions. Detail methods of apotosis array and growth factor antibody array analysis are available in Supplementary Methods.
Western Blot Analysis
Molecular expressions of KRT34 and b-catenin in hair keratin-treated ORS cells, keratin content at protein level in conditioned medium collected from TGFb2-treated ORS cell culture, the keratin content in keratin-removed condition medium collected from TGFb2-treated ORS cell culture in immunodepletion study, keratin content at protein level in conditioned medium collected from KRT31/KRT34-silenced ORS cell culture or molecular keratin expression in KRT31/KRT34-silenced ORS cell, molecular expressions of caspase 6 in TGFb2-treated ORS cells and keratin content at protein level in conditioned medium collected from caspase 6-silenced ORS cell culture were evaluated by western blot analysis. Detail method of western blot analysis is available in Supplementary Methods.
Real Time Quantitative Polymerase Chain Reaction (RT-qPCR)
The gene expressions indicative of DP cell’s intrinsic property and TGFb2 gene expressions of DP cell spheroids and the replated DP cell spheroids were evaluated by RT-qPCR. Detail method of RT-qPCR analysis is available in Supplementary Methods.
Indirect Enzyme-Linked Immuno-Sorbent Assay (ELISA)
The molecular expressions indicative of DP cell’s intrinsic property from the replated DP spheroids cultured in the presence of keratin were evaluated by ELISA. Detail method of ELISA is available in Supplementary Methods.
In Vivo KRT31/KRT34 Gene Silencing Study
To confirm the effect of keratin on hair growth, KRT31/KRT34 were silenced by lipofectamine-mediated delivery of KRT31/KRT34 siRNAs. First, Invivofectamine complex for KRT31/KRT34 siRNA delivery was prepared as follows; siRNAs of KRT31 (Bioneer, 16660-1), KRT34 (Bioneer, 16672-1) and negative control (Bioneer, SN-1003) were purchased, and siRNAs of KRT31 and KRT34 were dissolved in RNase-free water as each 24 mg/ml concentration respectively. The two solutions, KRT31 siRNA and KRT34 siRNA, were combined as 1:1 volume ratio to be 12 mg/ml of final concentration. 12 mg of negative control siRNA was also dissolved in 1 ml of RNase-free water. siRNAs-Invivofectamine (Thermo Fisher Scientific, IVF3005) complex was prepared by the manufacturer's instruction, and 0.5 mg/ml of complex was prepared finally prior to injection to mice. For in vivo study, 6-week-old mice were shaved repeatedly to synchronize the hair cycle and randomly assigned to three groups: Con group with IV injection of 200 μl of negative control siRNA injection; siRNA group with IV injection of 200 μL of KRT31/KRT34 siRNA injection; siRNA+Keratin group with KRT31/KRT34 siRNA injection (IV, 200 μl) and intradermal injection of total 100 μl of keratin a day after first siRNA injection. For each group, mice were sacrificed at either day 7 or day 14. Pictures of the back skin were taken at day 3, 7, 10, and 14 to examine the hair growth. The silencing of KRT31/KRT34 gene expressions was confirmed by RT-qPCR. Detail method of RT-qPCR analysis is available in Supplementary Methods..
Histological Analysis
The skin tissues were fixed with 10% neutral-buffered formalin (BBC Biochemical, 0141). The tissues were embedded in paraffin and sectioned at 4 μm thickness, followed by staining with hematoxylin and eosin for histological analysis. The number of hair follicles in each cycle and diameter of anagen hair follicles were quantified in multiple fields on perpendicular sections at ×100 magnification.
Immunocytochemical and Immunohistochemical Staining
Detail methods of immunocytochemical and immunohistochemical staining are available in Supplementary Methods.
Statistical Analysis
All values obtained from in vitro and in vivo analysis are presented as the mean ± standard deviation (SD). Statistically significant differences were identified by two-sided Student’s t-test or one-way ANOVA parametric test. A P-value of less than 0.05 was considered significant.