Fig 2: Expression of the ABCA4 gene at mRNA (A) and protein (B) levels after 24 h of hair follicle stem cells treatment with calcium ions (1.2 µM). ns: not significant.

Fig 3: Expression of the ABCA4 gene at mRNA and protein levels in keratinocytes treated with vitamin A derivatives. ABCA4 gene expression after 24 (A) and 48 h (B) of treatment with 10 µM all-trans-retinal and 1 µM retinoic acid, assessed by qRT-PCR. Western Blot analysis of ABCA4 protein expression after 48 h treatment with 10 µM all-trans-retinal (at-RAL) and 1 µM retinoic acid (RA) (C). The plot of the correlation between ABCA4 gene expression and Involucrin (INV) (D) or KRT5 gene (E). ABCA4 gene expression: **** p-value < 0.0001 after 24 h of cell culture and ** p-value of 0.005 after 48 h of cell culture; INV expression: ** p-value of 0.0014 after 24 h of cell culture.

Fig 4: The effect of at-RAL concentrations (2.5, 5, 10, 15 µM) on cell viability (A) and ABCA4 gene expression in human hair follicle stem cells (B) and keratinocytes (C). Human hair follicle stem cells: * p-value of 0.0196 (control vs. 10 µM) and 0.0465 (control vs. 15 µM). Keratinocytes: **** p-value < 0.0001.

Fig 5: Effect of at-RAL treatment on proliferation, viability rate and ABCA4 gene expression in human hair follicle stem cells. Cell proliferation rate (A) and viability (B) of human hair follicle stem cells after 24 h of incubation with at-RAL (10 µM) or retinoic acid (1 µM). Hair follicle stem cells proliferation rate (C) and viability (D) after 24 h of incubation with the ABCA4 gene silencers (siABCA4) followed by 24 h treatment with at-RAL (10 µM). ABCA4 gene expression in human hair follicle stem cells after 24 h of incubation with ABCA4 gene silencers (siRNA) (E) followed by 24 h treatment with at-RAL (10 µM) (F). Proliferation rate: ns—not significant, * p-value of 0.0267, ** p-value of 0.0022, *** p-value of 0.0003; Viability rate: ns—not significant, * p-value of 0.0476, ** p-value of 0.0062; ABCA4 gene expression: ** p-value of 0.0018 after 24 h of cell culture and ** p-value of 0.0076 after 48 h of cell culture.