Coordination of LMO7 with FAK Sustains Epithelial Integrity in Renal Epithelia Exposed to Osmotic Pressure

Abstract

In kidney, epithelial barrier has diverse functions in body fluid and electrolyte homeostasis, and urine production. Maintaining epithelial integrity fundamentally builds up physiological functionality of the renal epithelial barrier (REB). Specially, the REB) states regularly in osmotic dynamics. The osmotic dynamics gives rise of osmotic pressure that is a physical force. Overloading of osmotic pressure can crack epithelial integrity and damage REB. How REB endures the osmotic pressure force yet remains enigmatic. LMO7 (LIM domain only 7) is a protein associated with cell-cell junctional complex and cortical F-actin. LMO7 upregulation was observed in cells cultured in hypertonic condition. In kidney, LMO7 predominantly distributes in epithelial cells in renal tubules. Hypertonic stimulation leads to assembly of LMO7 and F-actin in cortical stress fibers in renal epithelial cells. Hypertonic-isotonic alternation as pressure force pushing plasma membrane inward/outward was set as osmotic disturbance and was applied to test FAK signaling and LMO7 functioning in maintaining junctional integrity. Along with junctional integrity, LMO7 depleted cells resulted in loss of junctional integrity in the epithelial sheet cultured hypertonic medium or hypertonic-isotonic alternation. On the other hand, FAK inhibited by PF-573228 leads to failure in robust cortical F-actin assembly and association of LMO7 with cortical F-actin in epithelial cells responding upon hypertonic stress. Epithelial integrity in context of osmotic stress, LMO7 and FAK signaling both involves in assembling robust cortical F-actin and maintaining junctional integrity. The LMO7 elaborately manages FAK activation in renal epithelial cells, which was evidently demonstrated in NRK-52E cells who have excessive FAK activation and lost epithelial integrity when cells with LMO7 depletion exposed to hypertonic environment. Our data suggests that LOM7 manages FAK activation and is responsible for maintaining REB under osmotic disturbance.