Hair Cycle-Specific Immunolocalization of Retinoic Acid Synthesizing Enzymes Aldh1a2 and Aldh1a3 Indicate Complex Regulation

The study investigated the synthesis of retinoic acid in hair follicles by examining the expression of enzymes Aldh1a2 and Aldh1a3 in adult C57BL/6J mice. It found that Aldh1a2 was consistently expressed in the outer root sheath and basal/spinous layer across all hair cycle stages, and in the bulge area during anagen and early catagen phases. Aldh1a3, on the other hand, was primarily found in the dermal papilla, pre-cortex, and hair shaft during the mid to late anagen phase. These findings suggest that Aldh1a2 and Aldh1a3 are involved in different aspects of epithelial proliferation and differentiation within the hair follicle, indicating a complex regulation of retinoic acid synthesis that may affect hair growth and cycling.