Figure 2.

Impact of excessive and insufficient GHR stimulation on human scalp HFs: (A) HPS axis in the case of absent GH signaling, like Laron’s syndrome, leading to almost absent levels of IGF-1 due to absent GHR stimulation. Clinical findings include alopecia, frontal hairline recession, and structural defects. (B) HPS axis in the case of GH excess, like acromegaly, which upregulates both IGF-1, an anagen promoter, and TGF-β, a catagen promoter. Clinically, acromegaly patients show increased hair growth and hirsutism.