Melanogenesis markers expression in premature graying of hair- a cross-sectional study

Background: Studies on mice and aging human hair follicles provide compelling evidence that graying of hair results from premature differentiation of Melanocyte stem cells (MeSC) in the niche/bulge. Objective: To analyze whether differentiation of melanocyte stem cells is responsible for premature graying of hair (PGH). Methods: Twenty- five patients of PGH (n=25) attending dermatology department were recruited. Five unpigmented and five pigmented hairs were obtained per patient by separating individual follicles by 1 mm punch biopsies. The hairs were dissected at a distance of 2 mm from the bulb to separate the stem cells (upper segment) (US) from the melanocytes (lower segment) (LS). RNA was extracted from hair follicle segments US and LS, and expression of GP100, Tyrosinase (TYR) and Tyrosinase related protein-1 (TYRP1) genes was quantified using Qiagen one-step RT-PCR kit. Results: We found melanogenesis gene expression in both temporary (US) and permanent (LS) segments of unpigmented and pigmented hair follicles. When compared between the US and LS of white hair, the expression of TYR and GP100 was much higher in US than LS, suggestive of melanogenesis in the bulge. Similarly, when compared between white and black US, the expression of all three genes was higher in white US than black US, although not statistically significant. Limitations: Low samples size and lack of data pertaining to the expression of genes at protein level are the limitations of current study. Conclusion: Even though this pilot study data yielded key information about the expression of GP100, TYR and TYRP-1 at mRNA level, further studies quantifying the expression of these genes at protein level are needed to provide additional clues to further address the results in detail.

Chronic overexpression of neuropeptide Y in the skin is sufficient to induce inflammation and epidermal and dermal pathology

Neuropeptide Y (NPY) is a pleiotropic peptide produced in the central nervous system and peripheral organs. Despite conjectures that NPY may have a role in skin physiology and pathology, the effects of NPY in this organ remain poorly understood. We reported that a knock-in mouse with entopic NPY overexpression exhibits significantly elevated NPY in the skin, accompanied by premature and progressive hair graying secondary to depletion of melanocyte stem cells within hair follicles. However, the question remains as to whether NPY overexpression in the skin can induce non-melanocyte pathology. In this study, we employed this mouse to investigate the consequences of skin-specific overexpression of NPY. Our findings show that chronic NPY overexpression in the skin induces dermal fibrosis and epidermal hyperkeratosis. Additionally, NPY overexpression induces significant accumulation of macrophages and regulatory T cells in the dermis. RNA sequencing of whole skin from NPY-overexpressing mice further reveals NPY-mediated transcriptional changes consistent with inflammatory processes and inflammation-associated skin changes and highlights novel cell types involved in the NPY-mediated response in the skin. Together, these results provide long-awaited evidence of NPY’s involvement in skin pathology, providing a background for defining the precise role of NPY in the regulation of cutaneous homeostasis and disease.

Aldh2 dependent formaldehyde metabolism fuels purine demands in melanocyte stem cells

ABSTRACTAldehyde-processing enzymes are viewed as essential clearing agents that rapidly deactivate harmful aldehydes. In the bone marrow, two specific enzymes, aldehyde dehydrogenase (ALDH) 2 and alcohol dehydrogenase (ADH) 5, were previously reported to protect hematopoietic stem cells from endogenous formaldehyde accumulation. Unexpectedly, we found that melanocyte stem cells (McSCs) in zebrafish depend on formate, an Aldh2-generated reaction product, to drive regeneration. Activated McSCs require Aldh2 (but not Adh5) to generate differentiated progeny, and by using scRNA-sequencing analysis, we identified a de novo purine biosynthesis program that is uniquely present in activated McSCs. Consistent with formate serving as one-carbon units for nucleotide biosynthesis, we found that purine supplementation (but not pyrimidine supplementation) was able to restore melanocyte regeneration in the absence of Aldh2. This work shows that Aldh2 enzymes generate reaction products that are needed to meet metabolic demands in regeneration.

Complementary In Vivo Approaches Reveal Quiescent Melanocytes in Anagen Outside the Hair Follicle Bulge

ABSTRACTMelanocyte stem cells (McSCs) are key components of the hair follicle (HF) stem cell system that are derived from neural crest during embryogenesis and are responsible for regeneration of differentiated melanocytes during successive HF cycles. Our previous research has shown presence of two subsets of phenotypically and functionally distinct McSCs exist in murine telogen HFs, CD34+ McSCs in the bulge/lower permanent portion (LPP) and CD34− McSCs in the secondary hair germ (SHG). Whether these subsets are maintained independently or exist in a developmental hierarchy is not yet known. Using Dct-H2BGFP mice, we analyzed the quiescent and proliferative properties of McSCs and melanocytes in anagen and telogen. We found unexpectedly that Kit+Nestin− quiescent melanocytes are maintained outside of the bulge/LPP region throughout anagen in addition to the Kit+Nestin+ quiescent melanocytes of the bulge/LPP. Both subpopulations express lower levels of melanocyte differentiation markers Mitf, Pax3, Dct, Tyrp1 and Tyr compared to differentiated melanocytes of the HF bulb/matrix. These results suggest that quiescent melanocytes localized in the outer root sheath, both in and below the bulge/LPP) retain the stem cell phenotype observed in quiescent McSCs during telogen. This finding has implications for maintenance of distinct subsets of McSCs throughout successive HF cycles.