Expression of transforming growth factor β isoforms and their receptors during hair growth phases in mice

Transforming growth factor β (TGF-β) is a family of potent growth inhibitor proteins, often produced as a precursor and often secreted in a complex with the latent TGF-β binding protein (LTBP). We investigated the expression of TGF-β1, -β2, -β3, LTBP, TGF-β receptor proteins type I and type II (TβR-I and -II) during induced hair growth in C57 BL-6 mice. We here demonstrated that TGFβs and TβR-I are expressed in hair follicle epithelium and have found a positive reactivity for LTBP and TβR-I in sebocytes. Dermal tissue was weakly stained for LTBP and TGF-β3. In early anagen the inner hair root sheath epithelium expressed TGF-β1, whereas outer hair root was positive for TβR-I during anagen/catagen switch. TβR-II found in sebaceous glands without significant variations during the hair cycle. We may conclude that in follicle epithelium TGF-β1 is not produced in a complex together with LTBP. On the other hand, it is possible that other types of LTBP, like LTBP-2 and LTBP-3, are present, which are not detected by the antibody we used. Furthermore, a very rapid secretion of LTBP from producing cells may prevent immunohistochemical detection. TGF-β1 released by inner hair root sheath may regulate outer root sheath growth. A bidirectional interaction of sebocytes and hair follicle epithelium in the TGF-β/LTBP seems possible. Sebocytes can be considered to be a target for TGFs since they express both TβR-I and -II. The general properties of TGF-β as a growth inhibitor of epithelial cells may suggest a possible involvement in either the abrogation of extensive growth at the end of anagen or the initiation of catagen for the follicle epithelium as well as growth control for sebaceous glands.