Expression analysis of melanocyte stem cells from Mitfmi-vga9/+ mice reveals a role for MITF in the transcriptional regulation of innate immune gene expression
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ABSTRACT: Melanocyte stem cells (McSCs) and mouse models of hair graying serve as useful systems to uncover mechanisms involved in stem cell self-renewal and the maintenance of regenerating tissues. Interested in assessing genetic variants of hair graying, we found that the Mitfmi-vga9/+ strain of mice is susceptible to loss of McSC maintenance via ectopic McSC differentiation. Based on transcriptome and molecular analyses of Mitfmi-vga9/+ mice we report a novel role for MITF in the regulation of systemic innate immune gene expression. We also demonstrate that viral mimic (poly I:C) is sufficient to expose genetic susceptibility to hair graying. These observations point to a critical suppressor of innate immunity and the consequences of its dysregulation, and for melanocytes, both may have particular implications for the autoimmune, depigmenting disease vitiligo.
Project description:A better understanding of human melanocyte and melanocyte stem cell (McSC) biology is essential for treating melanocyte-related diseases. This study employed an inherited pigmentation disorder carrying the SASH1S519N variant in a Hispanic family to investigate the SASH1 function in melanocyte lineage and the underlying mechanism for this disorder. We used a multidisciplinary approach, including clinical exams, human cell assays, yeast two-hybrid screening, and biochemical techniques. Results linked early hair graying to the SASH1S519N variant, a previously unrecognized clinical phenotype in hyperpigmentation disorders. We identified SASH1 as a novel regulator in McSC maintenance and discovered that TNKS2 is crucial for SASH1’s role in vitro. Additionally, the S519N variant is located in one of multiple tankyrase binding motifs and alters the binding kinetics and affinity of the interaction. In summary, this disorder showcases accelerated aging in human McSC, linking both gain and loss of pigmentation to McSC dysfunction in the same individuals. The findings offer new insights into the roles of SASH1 and TNKS2 in McSC maintenance and the molecular mechanisms of pigmentation disorders. We propose that a comprehensive clinical evaluation of patients with skin disorders should include an assessment and history of hair pigmentation loss.
Project description:Cellular quiescence is a reversible and tightly regulated stem cell function that is essential for healthy aging. However, the control elements of tissue-specific renewal, quiescence, and aging remain poorly understood. Using melanocyte stem cells (McSCs) to model and test the regulation of tissue-specific quiescence, we find that stem cell quiescence is neither a singular nor static process. McSCs display remarkable heterogeneity, with a fraction expressing the immune checkpoint protein PD-L1. Differential gene expression profiling identifies tissue-specific control of this immune privilege, specifically during melanocyte stem cell dormancy. In vitro quiescence assays confirm that inducing quiescence is sufficient to drive PD-L1 expression in melanoblasts and PD-L1 subsequently regulates aspects of melanoblast cell cycling. In vivo, a portion of McSCs appear to leverage this immune checkpoint as a key aspect of their dynamics during the dormant stage of the hair cycle. With age, this dynamic becomes unbalanced, tipping towards a higher proportion of PD-L1-expressing McSCs and a more deeply quiescent McSC pool. Collectively, these findings demonstrate that immune checkpoint expression is a physiological attribute of McSC quiescence and offer PD-L1-expressing quiescent stem cells as molecular targets for potential reactivation in regenerative and gerontological medicine.
Project description:Through recurrent bouts synchronous with the hair cycle, quiescent melanocyte stem cells (McSCs) become activated to generate proliferative progeny that differentiate into pigment-producing melanocytes. The signaling factors orchestrating these events remain incompletely understood. Here, we use single cell RNA-sequencing with comparative gene expression analysis to elucidate the transcriptional dynamics of McSCs through quiescence, activation, and melanocyte maturation. Unearthing signs of increased WNT and BMP signaling along this progression, we endeavored to understand how these pathways are integrated during differentiation. Employing conditional lineage-specific genetic ablation studies in mice, we find that loss of BMP signaling in the lineage leads to hair graying due to a block in melanocyte maturation. We show that interestingly, BMP signaling functions downstream of activated McSCs and maintains WNT effector, transcription factor LEF1. Employing pseudotime analysis, genetics, and promoter analyses, and chromatin landscaping, we show that following WNT-mediated activation of McSCs, BMP and WNT pathways collaborate to trigger the commitment of proliferative progeny by fueling LEF1 and MITF-dependent differentiation. Our findings shed light upon the signaling interplay and timing of cues that orchestrate melanocyte lineage progression in the hair follicle and underscore a key role for BMP signaling in driving complete differentiation.
Project description:To elucidate mechanisms governing McSC self-renewal and differentiation we analyzed individual transcriptomes from thousands of melanocyte lineage cells during the regeneration process. We identified transcriptional signatures for McSCs, deciphered transcriptional changes and intermediate cell states during regeneration, and analyzed cell-cell signaling changes to discover mechanisms governing melanocyte regeneration.
Project description:Adult tissue stem cells protect their long-term potential by exerting precise control over their transitions between quiescence, activation, and differentiation. Through cyclic bouts synchronous with the hair cycle, quiescent melanocyte stem cells (McSCs) become activated to generate proliferative progeny that differentiate to produce and transfer pigment to hair cells. The signaling factors orchestrating this process are still poorly understood. Here, we use single cell RNA-sequencing with pseudotime analysis to elucidate the transcriptional trajectory of McSCs through quiescence, activation, and differentiation into mature melanocytes. Unearthing signs of increased WNT and BMP signaling along this progression, we lineage-ablate either pathway and see hair graying. We show that BMP signaling functions downstream of McSCs but upstream of WNT signaling through LEF1. After stem cell activation, the two pathways trigger committed, proliferative progeny to fuel MITF-dependent differentiation. Analyses of the promoters required for melanosome maturation suggest a specific reliance upon MITF and LEF1 transcription factors, which we show are dampened without BMP signaling. Our findings shed light upon the signaling interplay that orchestrates the melanocyte lineage. Moreover, the block in differentiation and enhanced proliferation observed in the absence of BMP signaling raises the disconcerting possibility that BMP may harbor not only tumor promoting but also tumor suppressing activity in melanoma.
Project description:We sorted melanocyte nuclei from quiescent (telogen) skin, skin actively producing hair shafts (anagen), and skin exposed to UVB. With these sorted nuclei, we then utilized single-nucleus assay for transposase-accessible chromatin with high-throughput sequencing (snATAC-seq) and characterized three melanocyte lineages: quiescent McSCs (qMcSCs), activated McSCs (aMcSCs), and differentiated melanocytes (dMCs) that co-exist in all three skin conditions. Furthermore, we successfully identified differentially accessible genes and enriched transcription factor binding motifs for each melanocyte lineage. Our findings reveal potential gene regulators that determine these melanocyte cell states and provide new insights into how aMcSC chromatin states are regulated differently under divergent intrinsic and extrinsic cues. We also provide a publicly available online tool with a user-friendly interface to explore this comprehensive dataset, which will provide a resource for further studies on McSC regulation upon natural or UVB-mediated stem cell activation.
Project description:Adult tissue stem cells protect their long-term potential by exerting precise control over their transitions between quiescence, activation, and differentiation. Through cyclic bouts synchronous with the hair cycle, quiescent melanocyte stem cells (McSCs) become activated to generate proliferative progeny that differentiate to produce and transfer pigment to hair cells. The signaling factors orchestrating this process are still poorly understood. Here, we use single cell RNA-sequencing with pseudotime analysis to elucidate the transcriptional trajectory of McSCs through quiescence, activation, and differentiation into mature melanocytes. Unearthing signs of increased WNT and BMP signaling along this progression, we lineage-ablate either pathway and see hair graying. We show that BMP signaling functions downstream of McSCs but upstream of WNT signaling through LEF1. After stem cell activation, the two pathways trigger committed, proliferative progeny to fuel MITF-dependent differentiation. Analyses of the promoters required for melanosome maturation suggest a specific reliance upon MITF and LEF1 transcription factors, which we show are dampened without BMP signaling. Our findings shed light upon the signaling interplay that orchestrates the melanocyte lineage. Moreover, the block in differentiation and enhanced proliferation observed in the absence of BMP signaling raises the disconcerting possibility that BMP may harbor not only tumor promoting but also tumor suppressing activity in melanoma.
Project description:Vitiligo is an autoimmune skin disease caused by cutaneous melanocyte loss. Although phototherapy and T cell suppression therapy have been widely used to induce epidermal re-pigmentation, full pigmentation recovery is rarely achieved due to our poor understanding of the cellular and molecular mechanisms governing this process. Here, we identify unique melanocyte stem cell (McSC) epidermal migration rates between male and female mice, which is due to sexually dimorphic cutaneous inflammatory responses generated by ultra-violet B exposure. Using genetically engineered mouse models, and unbiased bulk and single-cell mRNA sequencing approaches, we determine that manipulating the inflammatory response through cyclooxygenase and its downstream prostaglandin product regulates McSC proliferation and epidermal migration in response to UVB exposure. Furthermore, we demonstrate that a combinational therapy that manipulates both macrophages and T cells (or innate and adaptive immunity) significantly promotes epidermal melanocyte re-population. With these findings, we propose a novel therapeutic strategy for repigmentation in patients with depigmentation conditions such as vitiligo.
Project description:Vitiligo is an autoimmune skin disease caused by cutaneous melanocyte loss. Although phototherapy and T cell suppression therapy have been widely used to induce epidermal re-pigmentation, full pigmentation recovery is rarely achieved due to our poor understanding of the cellular and molecular mechanisms governing this process. Here, we identify unique melanocyte stem cell (McSC) epidermal migration rates between male and female mice, which is due to sexually dimorphic cutaneous inflammatory responses generated by ultra-violet B exposure. Using genetically engineered mouse models, and unbiased bulk and single-cell mRNA sequencing approaches, we determine that manipulating the inflammatory response through cyclooxygenase and its downstream prostaglandin product regulates McSC proliferation and epidermal migration in response to UVB exposure. Furthermore, we demonstrate that a combinational therapy that manipulates both macrophages and T cells (or innate and adaptive immunity) significantly promotes epidermal melanocyte re-population. With these findings, we propose a novel therapeutic strategy for repigmentation in patients with depigmentation conditions such as vitiligo.
Project description:In the McSC lineage in zebrafish, Aldh2 activity is an important source of formate through its metabolism of its substrate formaldehyde. This formate is required as input into the folate cycle, in particular de novo purine biosynthesis. This scRNA-seq experiment was conducted to investigate the global effects of Aldh2 inhibition on the transcriptomes of isolated McSCs.