NRSA for Nina Cintron Pregosin: nvestigating podocyte-parietal epithelial cell communication through intercellular bridges in kidney disease

Abstract/Project Summary Chronic kidney disease (CKD) affects more than 37 million adults in the United States. However, as many as 9 in 10 adults with CKD are not even aware that they have it. If left untreated, CKD can progress to End Stage Kidney Disease (ESKD), which results in the need for dialysis or kidney transplantation. There are currently more than 90,000 Americans on the kidney transplant waitlist, and 13 people die each day while waiting for a kidney transplant. Podocytes are highly specialized terminally differentiated cells that are critical for the filtration of blood into urine, therefore podocyte loss is often one of the first steps in the process that leads to CKD. The prevalence of CKD is expected to increase in the next decade, therefore it is important to understand mechanisms of podocyte injury and investigate potential methods of recovery. Injured podocytes trigger the activation and proliferation of neighboring parietal epithelial cells (PECs) which line the bowman’s capsule. Novel intercellular bridges were observed between injured podocytes and activated PECs, suggesting a direct mechanism of physical communication between the two cell types. Intercellular bridges are thin, actin-based structures that directly connect the cytoplasms of two cells. Similar bridge-like structures have been studied in other cell types such as neuronal, epithelial, and immune cells. Due to their ability to transport materials such as proteins, organelles, viruses, and prions, intercellular bridges can be pathological or physiological. However, the role of intercellular bridges between podocytes and PECs is unknown. Therefore, this study aims to investigate the functional role of intercellular bridges between podocytes and PECs. Preliminary studies have shown that intercellular bridges form in response to podocyte injury induced by podocyte-specific loss of the pro-differentiation transcription factor Klf4 or treatment with nephrotoxic serum (NTS). Interestingly, no intercellular bridges were observed in a slower model of injury, mice with diabetic kidney disease, leading to the hypothesis that intercellular bridges form in response to rapid podocyte loss. Immunofluorescence staining revealed that intercellular bridges contain actin, BIRC3, RAB8A, and RAB11A. Vesicle-like structures were also observed within the bridges, supporting the hypothesis that intercellular bridges may be used to directly transport materials between two cells. To better understand the role of intercellular bridges, their formation in vitro will be investigated using a coculture of mouse podocytes and PECs. To test the function of these bridges will also be investigated by testing whether intercellular bridges are required to trigger PEC activation and proliferation by disrupting bridge formation using pharmacological inhibitors of actin polymerization. The long term goal of this proposal is to investigate the therapeutic potential of intercellular bridges to promote podocyte recovery. This would also be the first study, to date, to investigate the mechanistic role for these intercellular bridges between injured podocytes and activated PECs in proliferative glomerulopathies.