Deletion of exocyst component 5 suppresses repair of injured kidney by limiting cell proliferation.

Impaired cell proliferation causes fibrotic changes in tissues, leading to loss of function. Although exocyst component 5 (Exoc5), a central component of the eight-protein exocyst complex, regulates the targeting and docking of intracellular vesicles which are essential for cell proliferation, its role in tissue regeneration remains to be defined. Here, we investigated the role of Exoc5 in the repair of kidney injury induced by ischemia-reperfusion (I/R) using proximal tubule cell (PTC)-specific Exoc5 knockout (Exoc5KO) mice generated by crossing Exoc5f/f with PEPCK-cre mice. Exoc5KO and wild-type (Exoc5WT) mice were subjected to either bilateral kidney I/R or sham surgery. I/R induced functional and structural kidney damage in both Exoc5KO and Exoc5WT mice, as evidenced by increased plasma creatinine and BUN, decreased glomerular filtration rate, and histological damage. Kidney function and structure gradually improved in both Exoc5KO and Exoc5WT mice over time; however, neither group fully recovered normal function, and the recovery was less pronounced in Exoc5KO than in Exoc5WT mice. Twenty-one days after I/R, Exoc5KO mice showed greater collagen deposition and α-smooth muscle actin (α-SMA) and vimentin expression compared to Exoc5WT mice, whereas E-cadherin expression was lower. Post-I/R PTC proliferation in Exoc5KO mice was significantly lower than in Exoc5WT mice. In contrast, post-I/R induction of paired box 2 (Pax2) was greater in Exoc5KO than in Exoc5WT mice. In HK-2 cells, a human PTC line, Exoc5 downregulation by siRNA increased Pax2 expression and further increased N-cadherin, phosphorylated-Smad3 (p-Smad3), and α-SMA expression compared to control cells following TGF-β treatment. Collectively, these findings indicate that loss of Exoc5 impairs PTC regeneration and exacerbates fibrosis in the injured kidney, suggesting its therapeutic potential in preventing the transition from acute kidney injury (AKI) to chronic kidney disease (CKD).