Summary Background The absence of melanocytes poses a challenge for long‐term tissue homeostasis in vitiligo. Surprisingly, while individuals with Fitzpatrick phototypes I–II (low melanin content) have a higher incidence of melanoma and nonmelanoma skin cancer, people with vitiligo are at a decreased risk for the same. Objectives To understand the molecular mechanisms that protect vitiligo skin from ultraviolet (UV)‐induced DNA damage by (i) characterizing differentially expressed microRNAs in lesional vs. nonlesional epidermis and (ii) identifying their upstream regulators and downstream gene targets. Methods Genome‐wide microRNA profiling of nonlesional and lesional epidermis was performed on five individuals with stable nonsegmental vitiligo using next‐generation RNA sequencing. The relevance of the upstream regulator and downstream target gene of the most differentially expressed microRNA was studied. Results Our study found sirtuin1 (SIRT1), an NAD‐dependent deacetylase, to be a direct target of miR‐211 – the most significantly downregulated microRNA in lesional epidermis. Inhibition of SIRT1 with EX‐527 downregulated keratin 10 and involucrin, suggesting that SIRT1 promotes keratinocyte differentiation. Overexpression of miR‐211 mimic led to a significant increase in γ‐H2AX positivity and cyclobutane pyrimidine dimer (CPD) formation, hallmarks of UVB‐mediated DNA damage. These effects could be ameliorated by the addition of resveratrol, a SIRT1 activator. Furthermore, a long noncoding RNA, MALAT1, was identified as a negative upstream regulator of miR‐211. Overexpression of MALAT1 resulted in increased expression of SIRT1 and a concomitant removal of UVB‐induced CPDs in primary keratinocytes. Conclusions These findings establish a novel MALAT1–miR‐211–SIRT1 signalling axis that potentially confers protection to the ‘amelanotic’ keratinocytes in vitiligo.

The loss of melanocytes in vitiligo is associated with architectural, transcriptional, and cellular perturbations of keratinocytes and manifests as a reduced proliferation potential in vitro and delayed re‐epithelialization in vivo. To understand the molecular mechanisms underlying this delay, microRNA (miRNA) profiling was performed on split skin biopsies collected on Day 1 (basal level) and Day 14 (wound re‐epithelialization) from nonlesional (NL) and lesional (L) skin of five subjects with stable nonsegmental vitiligo and 129 miRNAs were found to be differentially regulated between the NL and L healed epidermis. miR‐21‐5p, expressed at comparable levels on NL and L Day 1 samples, demonstrated significant upregulation during re‐epithelialization. However, the extent of its upregulation was relatively lower in L (10 times compared to Day 1) as compared to NL skin (17 times compared to Day 1). The overexpression of miR‐21 in keratinocytes led to a significant increase in the expression of proliferation markers (Ki67 and MCM6 messenger RNA, Ki67 positivity), along with an increase in keratinocyte migration. Using a small interfering RNA mediated knockdown approach, we further demonstrated that miR‐21‐5p mediates its effects by suppressing the expression of programmed cell death 4 (PDCD4) and mammary serine protease inhibitor (Maspin), both tumor‐suppressor genes. Investigation of clinical samples corroborated the lower miR‐21 levels and a higher expression of PDCD4 and Maspin in L Day 14 compared to the NL Day 14 epidermis. In conclusion, this study revealed that a relatively lower upregulation of miR‐21‐5p in L skin leads to significantly higher levels of PDCD4 and Maspin, delaying wound re‐epithelialization by reducing the proliferation and migration of keratinocytes.

Vitiligo, one of the most common acquired disorders of pigmentation, is characterized by the absence of melanocytes. 1 The loss of melanocytes, cells which produce melanin and constitute less than 5% of the epidermis, leads to pervasive changes in keratinocytes at both architectural 2,3 as well as molecular levels. 3 Despite the absence of melanin, the risk of developing nonmelanoma skin cancers (NMSC) like squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) is significantly lower in people with vitiligo as compared to ethnicity-matched controls. 4,5 We hypothesized that the pervasive perturbations reported in the transcriptome and miRnome of vitiligo skin could help resolve this conundrum. microRNAs (miRNAs), 22-nucleotide long, non-coding RNA molecules, repress protein translation by destabilizing their target mRNAs 6,7 and have emerged as key post-transcriptional regulators of gene expression. 8 While miRNAs regulate important functions in cell development, homeostasis, growth and survival, 8 aberrantly