Thrombospondin-1 Plays a Critical Role in the Induction of Hair Follicle Involution and Vascular Regression During the Catagen Phase.

Hair growth is associated with pronounced vascular-endothelial-growth-factor-induced perifollicular angiogenesis, whereas the catagen regression phase is characterized by apoptosis-driven blood vessel regression. The biologic relevance of endogenous inhibitors of angiogenesis in the control of hair cycling, however, has remained unknown. We studied the expression and biologic role of the angiogenesis inhibitor thrombospondin-1 (TSP-1) during the induced adult hair follicle cycle in wild-type, TSP-1 deficient, and TSP-1 overexpressing transgenic mice. TSP-1 expression was absent from hair bulb and dermal papilla cells during early to mid-anagen but was highly upregulated throughout the catagen involution phase. In TSP-1 deficient mice, the follicle growth phase was significantly prolonged, associated with increased perifollicular vascularization and vascular proliferation. Conversely, hair follicle growth was delayed in K14/TSP-1 transgenic mice that expressed high levels of TSP-1 in outer root sheath keratinocytes, associated with reduced perifollicular vascularization. These effects were most probably mediated via its antiangiogenic effects because TSP-1 did not affect the growth of cultured murine vibrissae in the absence of a functional vascular system. These results identify a critical role of TSP-1 in the induction of anagen follicle involution, with potential implications for the therapeutic modulation of hair follicle growth. [ABSTRACT FROM AUTHOR]