Role of BK Channel in Chronic Kidney Disease

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Project Summary Chronic kidney disease (CKD) affects 26–30 million U.S. adults and remains a major public health problem (1; 2). Renal fibrosis is the inevitable consequence of almost every type of CKD regardless of underlying etiology, and leads to progressive renal failure and end-stage of renal disease (ESRD) (1). Thus, preventing renal fibrosis may in turn prevent progression of CKD and ESRD. While there is compelling literature suggesting many potential therapeutic targets for treating renal fibrosis, very few have advanced to the initial phase of clinical trials (3; 4), and none have shown efficacy in the treatment of renal fibrosis (4). Thus, it is crucial to continue to discover and test novel potential therapeutic targets for renal fibrosis. Unilateral ureteral obstruction (UUO) is a common and well-validated renal fibrosis experimental model. Transforming growth factor-beta (TGF-β) isoforms are multifunctional cytokines that play a central role in driving fibrosis in most, if not all, forms of CKD (5). Big potassium (BK) channels (also called Big-K, Maxi-K or Slo1 channels) are K+ channels and may be one novel target that plays a major role in renal fibrosis. BK channels consist of the α-subunit (BKα), which functions as a channel independently, β-subunits (β1-4), and the γ-subunit (6; 7). A recent study reported that BK channel β1-subunit deficiency exacerbates vascular fibrosis and remodeling in high-fat fed obesity mice, suggesting that reduced BKα sensitivity and activity caused by β1 deficiency (8) leads to vascular fibrosis (9). We have compelling preliminary evidence that shows for the first time that BKα also plays a critical role in renal fibrosis. While BKα knockout (KO) mice were prone to developing more severe fibrosis after UUO (Figure 1), pre-treatment with the BK channel opener, BMS191011 (Sigma-Aldrich, SML0866), that can activate BK channels (10), protected mice from developing renal fibrosis in wild-type (WT) UUO mice (Figure 2) by suppressing TGF-β1 signaling pathway (Figures 3-4). These data suggest that the BK channel plays an important role in the development of renal fibrosis. Thus, elucidating the mechanisms underlying the role of BK channel in the pathogenesis of renal fibrosis is of utmost clinical importance. Our overall hypothesis is that BK channel deficiency is prone to developing renal fibrosis via activating the TGF-β signaling pathway in renal fibrotic mouse models. In this application we will propose three specific aims to test our overall hypothesis: Specific Aim 1: To validate the role of the BK channels in the development of renal fibrosis in different renal fibrosis mouse models. Specific Aim 2: To investigate the molecular mechanisms underlying the BK-mediated development of renal fibrosis. Specific Aim 3: To translate the experimental findings by examining whether BK expression levels are correlated with the severity of renal fibrosis in CKD patients. SA3.1. Determine whether BK expression levels are quantifiably correlated to the severity of renal fibrosis in kidney biopsy samples from CKD patients with diabetic nephropathy and focal segmental glomerulosclerosis (FSGS). Elucidation of the molecular mechanisms underlying the BK-mediated development of renal fibrosis will provide novel insights into whether BK channels can be utilized as a potential therapeutic target for treating CKD patients and preventing them from progressing to ESRD.