Along with one of the highest rates of obesity in the country, hypertension, frequently associated with obesity, is highest in West Virginia, occurring in 41% of adults. Important in the pathogenesis of hypertension is altered handling of salt by the kidney. It appears that tight junctions (TJ) have an important role in our body?s handling of salts. In the kidney, the molecular composition of TJ determines the permeability and ion selectivity of different nephron segments. In particular, the TJ in the proximal tubular segment are quite permeable to Na+ and more ?leaky? than TJ in the distal tubular segment. These differences in permeability are consequences of the specific expression of different claudin isoforms. While proximal tubules express claudin 2, distal nephrons have claudin 4 as their major claudin isoform. Interestingly, changes in claudin expression are noted in renal tubules from salt- sensitive hypertensive animals. Consistently, knockout of claudin 4 causes hypotension. Clearly, properly controlled expression of claudins is essential for the intact animal to express maximal natriuresis, and impairment of this regulatory process contributes to salt-sensitive hypertension. However, little is known about what controls the composition of TJ along the nephron. Preliminary studies have shown that the signaling function of Na/K- ATPase (NKA) is a key to this regulation, and thus a key to paracellular selectivity and permeability in renal epithelial cells. The signaling NKA works through the activation of Src, feed forward amplification of ROS (reactive oxygen species), and downstream regulation of other protein and lipid kinase pathways. We have also learned that NKA and Src are highly expressed, and form a protein complex in renal epithelial cells. Moreover, we have demonstrated a dysregulation of this pathway in animal models of obesity and hypertension. On this scientific premise, we propose to test our central hypothesis that NKA regulates the selective permeability of TJ by altering the expression of claudins through its interaction with Src. We further contend that this NKA-mediated regulation is altered in salt-sensitive hypertension, resulting in changes in TJ structure and function in renal tubules. Therefore, Aim 1 will test the hypothesis that NKA regulates TJ permeability, complexity and ion selectivity through a specific Src-caveolin-claudin pathway in renal epithelial cells.
Aim 2 will assess whether NKA differentially regulates the expression and trafficking of claudin isoforms.
Specific Aim 3 will evaluate human relevance and assess the potential role of NKA-mediated regulation of TJ in hypertension by studying the differentiated kidney organoids from human iPS cells with NKA point mutation generated through the CRISPR technology, and nephron segments derived from animal models of salt-sensitive hypertension. Once completed, the proposed studies will provide novel molecular insight into NKA-mediated regulation of paracellular transport activity in kidney. The finding may lead to novel therapeutic options for hypertension. Finally, participation in the COBRE will provide the necessary enhanced career and scientific mentoring to become a successful independent scientist.