Shp2-mediated MAPK pathway regulates ΔNp63 in epithelium to warrant corneal innervation and homeostasis

Corneal nerve fibers serving sensory, reflex and neurotrophic functions sustains the corneal homeostasis and transparency to warrant the normal visual function. It remains unknown whether corneal epithelium is also reciprocally important for the corneal innervation. Herein, we generated a compound transgenic mouse strain, K14rtTA;tetO-Cre (TC);Shp2(flox/flox), in which Shp2 was conditionally knocked out from the K14-positive cells including corneal epithelium (Shp2(K14ce-cko)) upon doxycycline (dox) administration. Our data revealed that Shp2(K14ce-cko) resulted in corneal denervation. More specifically, the corneal epithelium thickness and corneal sensitivity reduced dramatically in Shp2(K14ce-cko) mice. In addition, corneal epithelial debridement wound healing was delayed substantially in the mutant mice. These defects manifested in Shp2(K14ce-cko) mice resemble the symptoms of human neurotrophic keratopathy. Our In vitro study unveiled that neurite outgrowth of the mouse primary trigeminal ganglion cells (TGCs) was inhibited as co-cultured with mouse corneal epithelial cells (TKE2) transfected by Shp2-, Mek1/2-, or ∆Np63-targeted siRNA but not by Akt1/2-targeted siRNA. Furthermore, ∆Np63 RNA interference down-regulated Ngf expression in TKE2 cells. More interesting, co-transfection experiments revealed that Shp2 tightly monitored ΔNp63 protein level in HEK293 and TKE2 cells. Taken together, our data suggested that Shp2-mediated MAPK pathway regulated ΔNp63, which in turn positively regulated Ngf in epithelium to warrant corneal innervation and epithelial homeostasis