Molecular mechanism of dynamic regulation of the proNGF/NGF ratio in controlling hair follicle cycle transition in liaoning cashmere goats

Background Nerve growth factor (NGF) and its precursor proNGF exert opposing biological functions in cell proliferation and apoptosis through distinct receptor systems—TrkA versus p75NTR/Sortilin. This study aimed to investigate whether dynamic changes in the relative ratio of proNGF to NGF regulate hair follicle cycle transition in Liaoning cashmere goats (Capra hircus) via the dynamic balance of the TrkA/p75NTR signaling axis, and to elucidate the underlying molecular mechanisms Methods Skin samples from Liaoning cashmere goats were collected during the telogen (March), anagen (September), and catagen (January) phases. Histological structures of hair follicles were examined via hematoxylin and eosin (H&E) staining. The mRNA and protein expression levels of NGF, proNGF, TrkA, p75NTR, and Sortilin across distinct hair follicle cycle stages were assessed using quantitative real-time PCR (qRT-PCR) and Western blotting. In vitro , rat hair follicle stem cells (rHFSCs) and human dermal papilla cells (hDPCs) were employed as cellular models and subjected to 11 different treatment conditions, including NGF alone, proNGF alone, combined treatments with varying proNGF/NGF ratios, and intervention with the TrkA inhibitor K252a. Cell proliferation and apoptosis were evaluated via CCK-8 assay and flow cytometry. Differential ratio groups (control, high-ratio, and low-ratio groups) were selected for transcriptomic sequencing to analyze differentially expressed genes (DEGs) and their enriched signaling pathways. Results H&E staining revealed the highest secondary hair follicle activity during the anagen phase. qRT-PCR and Western blot analyses showed that NGF and TrkA expression levels were significantly elevated in anagen (P < 0.05), whereas proNGF, p75NTR, and Sortilin exhibited significantly increased expression in catagen (P < 0.05). The proNGF/NGF protein expression ratio was lowest in anagen (0.56), highest in catagen (1.89), and intermediate in telogen (1.56). CCK-8 assay results indicated that NGF treatment alone significantly promoted the proliferation of both rHFSCs and hDPCs (P < 0.05), an effect that was completely abrogated by K252a; proNGF treatment alone exerted no significant effect on proliferation. At proNGF/NGF ratios of 1.56 and 1.89, cell proliferation rates were significantly lower than those in the NGF-alone group (P < 0.05), whereas at a ratio of 0.56, the proliferation rate showed no significant difference from the NGF-alone group but was significantly higher than that of the control group. Flow cytometry confirmed that proNGF treatment alone and high proNGF/NGF ratios (1.56 and 1.89) significantly induced apoptosis. Transcriptomic sequencing revealed that, in the high-ratio group (proNGF/NGF = 1.89) compared with the low-ratio group (0.56), DEGs were significantly enriched in pathways related to “regulation of apoptotic process” and “steroid hormone biosynthesis,” with notable downregulation of the anti-apoptotic molecules Faim2 and Naip5. Conclusion The dynamic changes in the proNGF/NGF ratio serve as a critical molecular determinant governing hair follicle cycle transition in cashmere goats. During the anagen phase, the NGF/TrkA pro-survival signaling predominates, driving follicular growth; conversely, during the catagen phase, the proNGF/p75NTR/Sortilin pro-apoptotic system prevails, inducing follicular regression. The proNGF/NGF ratio may serve as a novel molecular biomarker for hair follicle cycle status. Targeting this balance could offer new therapeutic strategies for regulating cashmere growth in cashmere goats and for treating human hair follicle-related disorders.