Hair cycle and wound healing in mice with a keratinocyte-restricted deletion of FAK

Focal adhesion kinase (FAK) is a critical component in transducing signals downstream of both integrins and growth factor receptors. To determine how the loss of FAK affects the epidermis in vivo, we have generated a mouse model with a keratinocyte-restricted deletion of fak (FAKK5 KO mice). FAK(K5 KO) mice displayed three major phenotypes--irregularities of hair cycle, sebaceous glands hypoplasia, and a thinner epidermis--pointing to defects in the proliferative capacity of multipotent stem cells found in the bulge. FAK-null keratinocytes in conventional primary culture undergo massive apoptosis hindering further analyses, whereas the defects observed in vivo do not shorten the mouse lifespan. These results suggest that the structure and the signaling environment of the native tissue may overcome the lack of signaling through FAK. Our findings point to the importance of in vivo and three-dimensional in vitro models in analyses of cell migration, proliferation, and survival. Surprisingly, the difference between FAKloxP/+ and FAKK5 KO mice in wound closure was not statistically significant, suggesting that in vivo loss of FAK does not affect migration/proliferation of basal keratinocytes in the same way as it affects multipotent stem cells of the skin.