Fig. 4From: Functional complexity of hair follicle stem cell niche and therapeutic targeting of niche dysfunction for hair regenerationSympathetic nerves relay external light signals to HFSCs. Sympathetic nerves are a gateway for the communication between internal HFSC niche and external environment. Intense light irradiation to eyes promotes HFSC activation through an ipRGC-SCN-sympathetic nervous circuit. Increased norepinephrine release from cutaneous sympathetic nerves facilitates HFSC activation by upregulating hedgehog signalingBack to article page