Non-apoptotic role for caspase-7 in hair follicles and the surrounding tissue.

Hair follicles are unique organs undergoing regular cycles of proliferation, differentiation, and apoptosis. The final step of apoptosis is, in general, mediated by executioner caspases comprising caspase-3, -6 and -7. Despite their commonly accepted apoptotic function, executioner caspases also participate in non-apoptotic processes. In the present study, we investigated activation (cleavage) of caspase-7 in mouse hair follicles and surrounding tissue during embryonic development into adulthood. Casp7 (-/-) mice were examined to understand the effect of caspase-7 deficiency in the skin. The activated form of caspase-7 was observed during embryonic hair follicle development, as well as in the first hair cycle. In general, activation of caspase-7 did not correlate with apoptosis and activation of caspase-3, except during physiological hair follicle regression. Notably, cleaved caspase-7 was observed in mast cells and its deficiency in the adult skin resulted in increased mast cell number. Our study shows for the first time activated caspase-7 in hair follicles and mast cells and indicates its non-apoptotic roles in the skin.