Fig. 5: Stem cell-mediated corpse clearance protects the niche for tissue homeostasis.
From: Stem cells tightly regulate dead cell clearance to maintain tissue fitness
a, Model for HFSC sensing of corpses. b, Left, multiplexed immunofluorescence of Rxra wild-type versus catagen-specific Rxra-cKO hair follicles (strategy as in Fig. 2d). Cell-type markers: CD68, monocytic phagocytes; CD206, mature macrophages; langerin, epidermal-resident macrophages; ITGA6, epidermal progenitors; F4/80, pan-macrophage; MHCII, pan-immune cells. Right, quantification (top; F4/80, n = 4 mice per genotype); (bottom; MHCII, n = 3 mice per genotype) per dermal area. Scale bars, 50 μm. c, Percentage of unengulfed corpses per hair follicle and immune response (MHCII+ cells per dermal area). n = 3 (CatII) and n = 4 (CatVI, CatVII) mice per genotype. Shaded area represents 95% confidence interval. d, Immunofluorescence showing stress factors (cJun and FosB) and DNA damage (TUNEL). P-cadherin (PCAD) is a hair germ marker. Asterisk highlights hair shaft autofluorescence. cJun: n = 26 hair follicles (4 wild-type mice), n = 29 hair follicles (3 Rxra-cKO mice); FosB: n = 26 hair follicles per genotype (3 mice per genotype). Scale bars, 10 μm. e, Left, strategy to ablate Rxra at catagen entry and analyse subsequent telogen and anagen periods (top) and quantification (bottom) of hair cycle stage. n = 6 wild-type and n = 7 cKO mice. Right, strategy (top) to inhibit corpse clearance by HX531 (RXR inhibitor, left) or annexin V (to mask phosphatidylserine, right) versus contralateral vehicle in catagen, and quantification (bottom) on subsequent hair cycle stage. n = 4 mice per experimental condition. Inhib, inhibitor. f, Top, schematic of experiment to expose HFSCs to necrotic debris by blocking engulfment with annexin V or using necrotic-conditioned medium. Bottom, quantification of stress factors after exposure. n = 4 experiments per condition (averaged duplicates). g, Top, experimental design to repeatedly expose naive HFSCs to necrotic debris. Bottom left, quantification of HFSCs over time (one of three independent experiments shown). n = 3 replicates per condition per time point. Shaded area represents 95% confidence interval. Bottom right, colony-forming efficiency (middle) and size (right) upon passage of HFSCs exposed to repeated damage. n = 6 experiments per condition. CM, conditioned medium. Quantifications, multiple pairwise independent two-sided Student’s t-tests, P values indicated. NS, not significant (P > 0.05). In box plots, the centre line is the median, box edges delineate first and third quartiles and whiskers extend to 1.5× the inter-quartile range. Further details on statistics and reproducibility in Methods. See also Extended Data Fig. 10 for additional supporting experiments.
