Hair Follicles Employ a Two-Dimensional Healing Strategy to Repair Three-Dimensional Injuries

The study investigated how 3-dimensional injuries in hair follicles (HFs) are repaired, focusing on the post-radiation anagen hair follicle repair (AHFR) process. Researchers used multiphoton intravital imaging to observe that after radiation-induced damage, which caused germinative/matrix cells to become apoptotic, the normally immotile basal outer root sheath cells/lower proximal cup cells became motile to regenerate internal structures. These cells moved along the outer cylindrical surface plane of the HF towards the injury, independently and stochastically, rather than taking a direct route through the internal layers or moving collectively. The study found that this 3-dimensional regeneration could be mapped onto a 2-dimensional plane, similar to conventional 2-dimensional healing, and mathematical modeling suggested this strategy allows for long-range cell communication and maintenance of the 3-dimensional organ architecture, enabling timely regeneration without resetting the hair cycle.