#4947 LMO7 IN URINE AS A SPECIFIC MARKER OF COMPROMISED RENAL EPITHELIAL INTEGRITY
Authors: Chen Hung-Chun , Zhen Yen-Yi 
Published: June 2023

Abstract

Background and Aims
Renal epithelial barrier (REB) are the physical isolator as well as physiological interface mediating body fluid and electrolytes homeostasis. Maintaining epithelial integrity is tightly related to REB biological function. LMO7 (LIM domain only 7) is a protein associated with the cell–cell junctional complex and is predominantly distributed in renal tubular epithelial cells. Previously, we reported that the LMO7 is associated with the maintenance of renal epithelial integrity, and that LMO7 releases to conditioned medium when the epithelial integrity was lost. In this study, we attempt to characterize roles of LMO7 and its functional interacting protein in maintaining epithelial integrity, and relevance of the LMO7 released from plasma membrane and the loss of tubular epithelial integrity.

Method
Renal ischemia-reperfusion injury (IRI) in mice as a model of acute kidney injury (AKI) were settled as a platform to investigate the the roles of LMO7 and its functional interacting protein in the pathological progression of compromised tubular epithelial integrity. Additionally, renal epithelial cells cultured in hypoxia as the pathogenic condition equivalent to AKI were also employed to investigate the role of LMO7. We also search the STRING database with LMO7 as query to find out its functional interacting proteins. Pathological pattern associated with LMO7 and its functional interacting protein in mice suffering from AKI as well as loss of tubular epithelial integrity were examined by immunofluorescent visualization. The LMO7 in urine as well as in conditioned medium derived from medium of hypoxia culture were quantified by Western blot analysis.

Results
Renal damage in IRI mice showed loss of epithelial integrity by histochemical staining, presence of LMO7 in urine, and high serum creatinine on the third day post IRI. Under the periodic acid-schiff (PAS) staining, loss of epithelial integrity is visible in proximal tubules, Henle's loops, and collecting ducts at the third day after reperfusion, and brush border impairment is observed in the outer stripe of the outer medulla. Most severe damages in renal tubules are present in Henle's loops where the epithelia express abundant LMO7. In the AKI mice, the LMO7 in renal tubules was apparently lower in Henle's loops. Additionally, the VANGL1, a LMO7 interacting protein participated in epithelial integrity and planar cell polarity in kidney, is also absent in Henle's loop of AKI mice. Hypoxia and glucose deprivation in cultured renal epithelial cells resulted in loss of epithelial integrity, and down-regulation of LMO7 and VANGL1. LMO7 was also identified in conditioned medium in which cells exposed to hypoxia but not normoxia. Additionally, the LMO7 was detected in urine of some patients with chronic kidney disease.

Conclusion
Presence of LMO7 in urine has been promising in experimental models holding compromised epithelial integrity. These approaches identified the role of LMO7 in maintaining epithelial integrity and that LMO7 being released into urine after renal epithelial damage as a novel marker for loss of REB.