Role of proteolytic suPAR fragment in insulin dependent diabetes and kidney disease

The global epidemic of chronic kidney disease (CKD) is progressing at an alarming rate. CKD affects an estimated 37 million people in the U.S. (15% of the adult population; more than 1 in 7 adults), and this number has more than doubled in the last two decades. Kidney-related diseases are rapidly eluding present treatment options and resources. The three common causes of CKD are diabetes mellitus, hypertension, and glomerulonephritis. We and others have implicated soluble urokinase activating receptor (suPAR) as one of the significant risk factors for both, the onset as well as the progression of CKD, regardless of its etiologies. In addition to its role as a biomarker, we and others have suggested that suPAR is a pathogenic/scarring factor that underlies podocyte injury by activating v3 integrin on podocytes. Podocytes are terminally differentiated cells essential for maintaining the specificity of the kidney filter. Our preliminary data suggest that the presence of the proteolytic fragment of suPAR, D2D3 fragment, in the plasma induces glomerular injury by activating v3 integrin on podocytes. In addition, and highly unexpectedly, our preliminary studies suggest that the D2D3 fragment also injures -cells of the pancreas. Together, these insights suggest a hypothesis that circulating D2D3 fragment simultaneously causes injury to two organs, the kidney and pancreas. We test this hypothesis in 3 Specific Aims. In Specific Aim 1, we define the physiological mechanisms by which D2D3 induces kidney and pancreas injuries by examining organ functions in D2D3-Tg mice on regular- and high-fat- diet challenged by nephrotoxic serum or Adriamycin. In addition, we will cross D2D3-Tg mice with Non-Obese Diabetic (NOD) mice to examine synergy upon pancreas injury. Anti-suPAR antibodies and small molecules that target regulatory GTPases (dynamin, Cdc42, Rac1), whose roles will be elucidated in Aims 2 and 3, will be tested as potential therapeutics. As D2D3-Tg mice exhibit dual organ injury, combination treatments targeting diverse pathways in distinct cell types will also be investigated. In Specific Aim 2, we examine the effects of the D2D3 fragment on the actin cytoskeleton, regulatory GTPases, mitochondrial function, and gene expression in terminally differentiated and primary podocytes in the presence and absence of lipotoxic stimuli or high glucose levels. We focus on the effects of D2D3 on a feedback loop between the actin cytoskeleton and mitochondrial function, and its modifications by changes in podocyte physiology. In Specific Aim 3, we examine the effects of D2D3 on glucose uptake, intracellular Ca2+ dynamics, cytoskeleton dynamics, and gene expression in -cells, isolated mouse islets, and tissue slices. The proposed study, delineating molecular mechanisms and the physiological relevance of dual organ injury, is a critical step in developing novel mechanism-specific therapeutics for CKD and insulin-dependent diabetes mellitus.