Disrupted Cholesterol Biosynthesis and Hair Follicle Stem Cell Impairment in the Onset of Alopecia

Background: Hair follicle cycle and the functioning of stem cells in alopecia are influenced by the suppression of cholesterol synthesis and the accumulation of sterol intermediates. Objective: This investigation aims to elucidate the regulatory function of disrupted cholesterol homeostasis in the functioning of hair follicle stem cells (HFSCs) and the cycling of hair follicles. Additionally, it seeks to provide an understanding of the fate of stem cells in primary cicatricial alopecia (PCA). Methods: To evaluate the influence of cholesterol on the functionality of hair follicles, a study was conducted to analyse gene expression and pathways associated with hair follicle stem cell markers in scalp samples affected by PCA (LPP, FFA, CCCA, DC, DF, TF). To assess the influence of disrupted cholesterol homeostasis on HFSCs, we conducted experiments involving the administration of 7-dehydrocholesterol (7DHC) and BM15766 (Pharmacological inhibitor of cholesterol biosynthesis), to Human Hair Follicle Outer Root Sheath Cells (HORSCs), as well as C57BL/6 mice, and hair follicle organoid cultures. The study utilised reverse transcription polymerase chain reaction (RT-PCR) to assess gene expression, while immunofluorescence was employed to analyse protein expression. The tracking of stem cell fate was accomplished through the utilisation of a BrdU pulse-chase experiment, while the verification of apoptotic consequences was established by utilising the TUNEL assay. A statistical analysis was conducted to assess the statistical significance of the data. Results: There was a notable decrease in the expression of HFSC marker genes among patients afflicted with PCA. In vitro data further confirmed the cholesterol inhibition and sterol intermediate accumulation in stem cells, leading to stem cell characteristics' disruption. The experimental group of mice exposed to 7DHC and BM15766 also exhibited a notable inability to initiate hair regrowth. Consequently, this deficiency in hair regrowth resulted in the activation of apoptosis, specifically in the stem cells. Additionally, our confirmatory analysis, which was performed utilising organoid culture, consistently yielded comparable results. The results as mentioned above emphasise the significant importance of cholesterol production in preserving the integrity and functionality of HFSCs, hence providing novel insights into the progression of alopecia. Conclusion: Individuals with aberrant cholesterol production, particularly those afflicted with PCA, experience a persistent impairment in hair regrowth due to the irreversible destruction of their hair follicles. The observed phenomenon is hypothesised to be attributed to the loss of hair follicle stem cells. Our study presents additional findings that elucidate the previously unknown involvement of sterol intermediates in regulating hair follicle cycling and stem cell function in PCA. The regulation of cholesterol production and the buildup of sterol intermediates have an impact on the hair follicle cycle and the role of stem cells in alopecia. ### Competing Interest Statement The authors have declared no competing interest.