Chronic kidney disease (CKD) is a world-wide problem that results from the damage of renal structures progressing to the complete loss of kidney function also known as end-stage renal disease (ESRD). Estimations indicate that more than 15% of adults in United States have CKD. There is no cure for ESRD and current therapies include hemodialysis and kidney transplant which are expensive and place a significant burden on the quality of life. Fibrosis is central to the pathologic manifestations associated with the progression of CKD to ESRD. Kidney function declines progressively as results from the accumulation of insoluble collagen and other ECM proteins in the renal parenchyma. Pharmacological blockade of the renin-angiotensin system slows down renal function decline, but it does not necessarily stop fibrosis progression, manifesting the urgent need for new antifibrotic therapies. Lysyl oxidase like-2 (LOXL2) has emerged as an attractive pharmaceutical target in renal fibrosis because it is an ECM-remodeling enzyme that crosslinks collagen regulating its deposition and degradation. However, the cellular and molecular mechanism by which LOXL2 contributes to kidney fibrosis and CKD progression are not well understood. In this proposal, we show that LOXL2 is upregulated in human kidney biopsies and experimental mouse models of kidney disease. Our pilot studies showed that inhibition of LOXL2 significantly ameliorated kidney function decline and renal fibrosis in diabetic mice. In vitro studies exploring molecular mechanism of LOXL2 expression suggest that profibrotic transforming growth factor beta (TGF-?) and hypoxia are key regulators in the glomerulus and tubulointerstitium, respectively. Moreover, we show that extracellular LOXL2 directly activates renal cortical fibroblasts, suggesting a novel pathogenic function of LOXL2 that may further contribute to renal fibrosis. Based on these findings, we hypothesize that LOXL2 contributes to the pathogenesis of CKD both by promoting collagen crosslinking and by activating renal fibroblasts. We will test this hypothesis by 1) using genetic and pharmacological approaches combined with injury mouse models of CKD, 2) exploring cellular and molecular mechanism in in vitro systems, and 3) using state of the art mass spectrometry technologies to elucidate biochemical changes of collagen in renal fibrosis. Thus, in this project we propose 3 specific aims: to determine the biochemical mechanism of LOXL2-catalyzed collagen crosslinking (Aim 1); to determine the pathogenic role of LOXL2 in glomerulosclerosis (Aim 2) and tubulointerstitial fibrosis (Aim 3). The knowledge gained from these studies will not only serve as a foundation to better understand the role of LOXL2 in renal fibrosis, but also contribute to the development of novel, effective therapies to stop the progression of CKD.
Diabetes is the leading cause of end-stage renal disease (ESRD) in the U.S. This work will improve our knowledge of how patients with diabetes develop kidney fibrosis and generate new targets for its treatment.
