Compartmentation of Mitochondrial and Oxidative Metabolism in Growing Hair Follicles: A Ring of Fire

The study investigated the energetics of growing hair follicles, focusing on the mitochondrially abundant bulb. Using multiphoton and light sheet microscopy on cultured bovine hair follicles and plucked human hairs, researchers assessed mitochondrial membrane potential (ΔΨ), cell viability, reactive oxygen species (ROS), and secretory granules. They found that lower bulb epithelial cells had high viability and polarized mitochondria, with most ROS co-localizing with these mitochondria. An abrupt transition to a nonfluorescent core was observed, where ΔΨ disappeared, and ROS and ΔΨ increased near this transition, forming a circumferential paraxial ring at sites for outer cortex/cuticle formation. Dermal papillar fibroblasts produced minimal ROS. Similar patterns were observed in plucked hairs, indicating that hair movement out of the follicle occurred independently of follicular bulb bioenergetics, likely through a tractor mechanism involving the inner and outer root sheaths.