The aim of this study was conducted to investigate the effect of heat stress on the hair follicle population and related signalling pathways in rex rabbits. Forty‐eight rabbits were randomly divided into two groups: one group in a high ambient environment (32 ± 2°C, heat stress) and the other group with normal temperature (20 ± 2°C, control). The results show that heat stress decreased the body weight gain and feed conversion rate, rabbit hair length and hair follicle density (p < 0.05). Besides, heat stress suppressed the gene expression of noggin, insulin‐like growth factor 1 (IGF‐1) and IGF‐1 receptor and protein expression of phosphorylated mechanistic target of rapamycin (mTOR) in rabbit skin (p < 0.05), while stimulated significantly the gene expression of bone morphogenetic protein 2 (BMP2) and BMP4 (p < 0.05). Heat exposure did not alter significantly the gene expression of alkaline phosphatase, versican and hepatocyte growth factor compared with the control (p > 0.05). In conclusion, noggin‐BMP, IGF‐1 and mTOR signalling pathways may be associated with the process of heat stress‐repressing hair follicle development.

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Background Hair follicles are an appendage of the vertebrate epithelium in the skin that arise from the embryonic ectoderm and regenerate cyclically during adulthood. Dermal papilla cells (DPCs) are the key dermal component of the hair follicle that directly regulate hair follicle development, growth and regeneration. According to recent studies, miRNAs play an important role in regulating hair follicle morphogenesis and the proliferation, differentiation and apoptosis of hair follicle stem cells. Results The miRNA expression profile of the DPCs from Rex rabbits with different hair densities revealed 240 differentially expressed miRNAs (|log2(HD/LD)| > 1.00 and Q-value≤0.001). Among them, ocu-miR-205-5p was expressed at higher levels in DPCs from rabbits with low hair densities (LD) than in rabbits with high hair densities (HD), and it was expressed at high levels in the skin tissue from Rex rabbits (P < 0.05). Notably, ocu-miR-205 increased cell proliferation and the cell apoptosis rate, altered the progression of the cell cycle (P < 0.05), and modulated the expression of genes involved in the PI3K/Akt, Wnt, Notch and BMP signalling pathways in DPCs and skin tissue from Rex rabbits. It also inhibited the phosphorylation of the CTNNB1 and GSK-3β proteins, decreased the level of the noggin (NOG) protein, and increased the level of phosphorylated Akt (P < 0.05). A significant change in the primary follicle density was not observed (P > 0.05), but the secondary follicle density and total follicle density (P < 0.05) were altered upon interference with ocu-miR-205-5p expression, and the secondary/primary ratio (S/P) in the ocu-miR-205-5p interfered expression group increased 14 days after the injection (P < 0.05). Conclusions In the present study, ocu-miR-205 promoted the apoptosis of DPCs, altered the expression of genes and proteins involved in the PI3K/Akt, Wnt, Notch and BMP signalling pathways in DPCs and skin from Rex rabbits, promoted the transition of hair follicles from the growth phase to the regression and resting phase, and altered the hair density of Rex rabbits.

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