Molecular mechanisms underlying renal lipotoxicity and DKD progression

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Project Summary Diabetic kidney disease (DKD), the leading cause of chronic and end stage renal disease, is characterized by excessive urinary albumin excretion followed by loss of kidney function. In DKD, over- reabsorption of filtered albumin and/or albumin-bound palmitic acid (PA), the most abundant saturated fatty acid (FA) in human urine, could lead to tubular cell injury and activation, which may be involved in the induction of interstitial fibrosis and chronic reduction of renal function. However, the molecular link between tubular and interstitial cells during DKD progression is not clear. Kidney injury molecule-1 (KIM- 1) is a noninvasive biomarker for renal proximal tubule (PT) damage and has been identified as a scavenger receptor for epithelial phagocytosis of lipoproteins and apoptotic cells. We hypothesize that KIM-1 interacts with STAT3 to amplify PA-albumin reabsorption capacity and promote lipotoxicity- induced tubulointerstitial fibrosis in progressive DKD. The hypothesis will be pursued with the following specific aims: Aim I will in vivo determine the role of KIM-1 in tubular lipid accumulation, STAT3 activation, and tubulointerstitial fibrosis during DKD onset and progression. Systematic studies will be conducted to 1) conduct spatiotemporal analysis of KIM-1 expression, lipid accumulation, STAT3 activation, and associated lipotoxicity and fibrosis in early, middle and advanced stages of DKD in wild- type and eNOS-/- mice and 2) determine the effects of KIM-1 deficiency on tubular lipid accumulation, STAT3 activation, and tubulointerstitial inflammation and fibrosis in high-fat diet-fed diabetic KIM-1- deficient (Kim-1-/-) and Kim-1-/-/eNOS-/- mice. Aim II will in vitro determine the role and regulation of KIM- 1 and STAT3 in primary cultured cells and mature proximal tubuloids in response to different FA-albumin overload. We will delineate the differential effects of different FA-bound albumin on KIM-1, p-STAT3, and lipotoxicity by evaluating cell ATP depletion, intracellular lipid deposition, autophagy activity and ER stress, cell death, and lysosomal oxidative stress in both 2D cell culture and stable human tubuloids. In addition, we will examine if KIM-1 or STAT3 inhibition or overexpression would affect PA-albumin overload-induced lipotoxicity and STAT3 activation in both 2D cell cultures and 3D organoids. Upon completion of these experiments we are hopeful that KIM-1 will emerge as a druggable target for the prevention and treatment of DKD.