Direct Reprogramming of Mouse Fibroblasts into Melanocytes
Summary
Here, we describe an optimized direct reprogramming system for melanocytes and a high-efficiency, concentrated virus packaging system that ensures smooth direct reprogramming.
Abstract
The loss of function of melanocytes leads to vitiligo, which seriously affects the physical and mental health of the affected individuals. Presently, there is no effective long-term treatment for vitiligo. Therefore, it is imperative to develop a convenient and effective treatment for vitiligo. Regenerative medicine technology for direct reprogramming of skin cells into melanocytes seems to be a promising novel treatment of vitiligo. This involves the direct reprogramming of the patient’s skin cells into functional melanocytes to help ameliorate the loss of melanocytes in patients with vitiligo. However, this method needs to be first tested on mice. Although direct reprogramming is widely used, there is no clear protocol for direct reprogramming into melanocytes. Moreover, the number of available transcription factors is overwhelming.
Here, a concentrated lentivirus packaging system protocol is presented to produce transcription factors selected for reprogramming skin cells to melanocytes, including Sox10, Mitf, Pax3, Sox2, Sox9, and Snai2. Mouse embryonic fibroblasts (MEFs) were infected with the concentrated lentivirus for all these transcription factors for the direct reprogramming of the MEFs into induced melanocytes (iMels) in vitro. Furthermore, these transcription factors were screened, and the system was optimized for direct reprogramming to melanocytes. The expression of the characteristic markers of melanin in iMels at the gene or protein level was significantly increased. These results suggest that direct reprogramming of fibroblasts to melanocytes could be a successful new therapeutic strategy for vitiligo and confirm the mechanism of melanocyte development, which will provide the basis for further direct reprogramming of fibroblasts into melanocytes in vivo.
Introduction
Vitiligo is a skin disease that seriously affects the physical and mental health of the affected individuals. For various reasons, including metabolic abnormalities, oxidative stress, generation of inflammatory mediators, cell detachment, and autoimmune response, the functional melanocytes are lost, and the secretion of melanin is stopped, leading to the development of vitiligo1,2. This condition occurs widely and is particularly problematic on the face. The main treatment is the systemic use of corticosteroids and immunomodulators. Phototherapy can be used for systemic or local diseases, and there are surgical treatments, such as perforated skin transplantation and autologous melanocyte transplantation3,4,5. However, patients who use drug therapy and phototherapy are prone to relapse, and these treatments have poor long-term therapeutic effects. Surgical treatment is traumatic and only moderately effective2,6. Therefore, a new and effective therapeutic strategy is needed for vitiligo.
The reprogramming of induced pluripotent stem cells (iPSCs) reverses these cells from their terminal state to a pluripotent state, a process mediated by the transcription factors, Oct4, Sox2, Klf4, and c-Myc7. However, due to the possibility of tumorigenicity and the long production time, this technology has been met with skepticism when applied to clinical settings8. Direct reprogramming is a technology that makes one type of a terminal cell transform into another type of a terminal cell9. This process is achieved by suitable transcription factors. Various cells have already been directly reprogrammed successfully, including cardiomyocytes10, neurons11, and cochlear hair cells12. Some researchers have even reprogrammed skin tissue directly in situ, which can be used for wound repair13. The advantages of direct reprogramming include reduced wait times and costs, lower risk of cancer, fewer ethical problems, and a better understanding of the mechanism underlying cell fate determination9.
Although the direct reprogramming method is widely used, there is currently no definite method for the direct reprogramming of skin cells into melanocytes, especially because of the numerous transcription factors to be considered14,15. The transcription factors, Mitf, Sox10, and Pax3, have been used for direct reprogramming of skin cells into melanocytes14. In contrast, the combination of MITF, PAX3, SOX2, and SOX9 has also been used for direct reprogramming of skin cells into human melanocytes in another study15. In this protocol, despite the use of a different screening method, the same result was obtained with the combination of Mitf, Sox10, and Pax3 for direct reprogramming of skin cells into melanocytes as described previously14. Developing a system to generate melanocytes from other skin cells can provide a scheme for transforming other skin cells of vitiligo patients into melanocytes. Hence, it is crucial to construct a simple and efficient method for this direct reprogramming to generate melanocytes successfully.
Protocol
Representative Results
Discussion
The quality of the virus is crucial for the success of direct reprogramming to melanocytes in this protocol. The method of packaging and concentrating viruses in this protocol is simple and easy to repeat and does not rely on any other auxiliary concentrated reagent. This protocol can be followed successfully in most laboratories. To ensure the quality of the concentrated virus, the following points need special attention. One is the cell status of HEK-293T. Although HEK-293T cells are immortalized cells, the cells used …
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
This study was partially supported by grants from the National Natural Science Foundation of China (82070638 and 81770621) and the Natural Science Foundation of Jiangsu Province (BK20180281).
Materials
| 0.05% Trypsin-EDTA | Gibco | 25300-062 | Stored at -20 °C |
| 0.45 μM filter | Millipore | SLHVR33RB | |
| 5 mL polystyrene round bottom tube | Falcon | 352052 | |
| 95%/100% ethanol | LANBAO | 210106 | Stored at RT |
| Adenine | Sigma | A2786 | Stock concentration 40 mg/mL Final concentration 24 µg/mL |
| Alexa Fluor 555 Goat anti-Mouse IgG2a | Invitrogen | A21137 | Dilution of 1:500 to use |
| Antibiotics(Pen/Strep) | Gibco | 15140-122 | Stored at -20 °C |
| Anti-TRP1/TYRP1 Antibody | Millipore | MABC592 | Host/Isotype: Mouse IgG2a Species reactivity: Mouse/Human Dilution of 1:200 to use |
| Anti-TRP2/DCT Antibody | Abcam | ab74073 | Host/Isotype: Rabbit IgG Species reactivity: Mouse/Human Dilution of 1:200 to use |
| CHIR99021 | Stemgent | 04-0004 | Stock concentration 10 mM Final concentration 3 μM |
| Cholera toxin | Sigma | C8052 | Stock concentration 0.3 mg/mL Final concentration 20 pM |
| Cy3 Goat anti-Rabbit IgG (H+L) | Jackson Immunoresearch | 111-165-144 | Dilution of 1:500 to use |
| DMEM (High glucose) | HyClone | SH30243.01 | Stored at 4 °C |
| DMSO | Sigma | D2650 | Stored at RT |
| FBS | Gibco | 10270-106 | Stored at -20 °C Heat-inactivated before use |
| Gelatin | Sigma | G9391 | Stored at RT |
| GFP-PURO plasmids (Mitf, Sox10, Pax3, Sox2, Sox9 and Snai2) | Hanheng Biological Technology Co., Ltd. | pHBLPm003198 pHBLPm001143 pHBLPm002968 pHBLPm002981 pHBLPm004348 pHBLPm000325 | Stored at -20 °C |
| Hematoxylin | Abcam | ab220365 | Stored at RT |
| Human EDN3 | American-Peptide | 88-5-10A | Stock concentration 100 μM Final concentration 0.1 μM |
| Hydrocortisone | Sigma | H0888 | Stock concentration 100 µg/mL Final concentration 0.5 µg/mL |
| L-DOPA | Sigma | D9628 | Stored at RT |
| Lipofectamine 2000 | Invitrogen | 11668-019 | Transfection reagent, stored at 4 °C |
| Masson-Fontana staining kit | Solarbio | G2032 | Stored at 4 °C |
| Neutral balsam | Solarbio | G8590 | Stored at 4 °C |
| Paraformaldehyde | Sigma | P6148 | Stored at RT |
| PBS (-) | Gibco | C10010500BT | Stored at RT |
| Phorbol 12-myristate 13-acetate (TPA) | Sigma | P8139 | Stock concentration 1 mM Final concentration 200 nM |
| Polybrene | Sigma | H9268 | cationic polymeric transfection reagent; Stock concentration 8 μg/µL Final concentration 4 ng/µL |
| Puromycin | Gibco | A11138-03 | Stored at -20 °C |
| Recombinant human bFGF | Invitrogen | 13256-029 | Stock concentration 4 μg/mL Final concentration 10 ng/mL |
| Recombinant human insulin | Sigma | I3536 | Stock concentration 10 mg/mL Final concentration 5 µg/mL |
| Recombinant human SCF | R&D | 255-SC-010 | Stock concentration 200 μg/mL Final concentration 100 ng/mL |
| RPMI-1640 | Gibco | 11875-093 | Stored at 4 °C |
| Xylene | Sigma | 1330-20-7 | Stored at RT |
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