Fig 2: Expression of the ABCA4 gene at mRNA and protein levels after treatment of hair follicle stem cells (HHF-SCs) with vitamin A derivatives: 10 µM all-trans-retinal (at-RAL) and 1 µM retinoic acid. ABCA4 gene expression was assessed by qRT-PCR for HHF-SCs after 24 and 48 h of treatment with vitamin A derivatives (A). * p-value of 0.0157. Analysis of ABCA4 protein expression assessed by Western Blot for HHF-SCs after 24 and 48 h of treatment with 10 µM all-trans-retinal (B,C) and 1 µM retinoic acid (D). Relative densities of Western Blot bands for ABCA4 and Involucrin proteins after 24 and 48 h of treatment of HHF-SCs with 10 µM all-trans-retinal (E,F, respectively) and 1 µM retinoic acid (G). **** p-value < 0.0001.

Fig 3: 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.

Fig 4: Experimental timeline of the ABCA4 gene silencing.

Fig 5: Effect of treatment with vitamin A derivatives on proliferation, viability rate, and ABCA4 gene expression in normal human keratinocytes. Cell proliferation rate (A) and viability (B) of keratinocytes after 24 h of incubation with at-RAL (10 µM) or retinoic acid (1 µM). Proliferation rate (C) and viability (D) of keratinocytes 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 keratinocytes after 24 h of incubation with ABCA4 gene silencers (siRNA) (E) followed by 24h treatment with at-RAL (10 µM) (F). Proliferation rate: ns – not significant, * p-value of 0.0265 and 0.0223, respectively; ABCA4 gene expression: ** p-value of 0.0072 and **** p-value < 0.0001 after 48 h of cell culture; INV gene expression: **** p-value < 0.0001 after 48 h of cell culture; KRT5 gene expression: ** p-value of 0.0061 and *** p-value of 0.0007 after 48 h of cell culture.