Deciphering the Role of Slit-Diaphragm Interactors in Podocyte Integrity and Glomerular Diseases

Background: Renal filtration is determined by the slit-diaphragm (SD), a cell-cell junction between the foot processes of renal podocytes. Through an unbiased screening approach, we have identified several interaction partners of the SD core proteins Nephrin, Neph1 and Podocin. Here, we investigate the role of two of them: the natriuretic peptide receptor 3 (NPR3), a member of the ANP Receptors, and MER Proto-Oncogene, Tyrosine Kinase (MERTK), a member of the TAM receptor tyrosine kinases. Methods: Podocyte specific knockout C57BL/6 mice (NPR3-/-) and (MERTK -/-) were used. NPR3-/- and WT mice (n=54) were exposed (or not) to unilateral nephrectomy followed by Deoxycorticosterone acetate (DOCA) high salt hypertension model. After weekly measurements of blood pressure (BP) and albuminuria (6 weeks), the kidneys and blood were harvested for functional and tissue assessment. Next NPR3-/- and WT mice (n=20) were subjected to the Adriamycin nephropathy model, 10 days’ post treatment, urine, blood and kidney were collected for analysis. Lastly, MERTK-/- and WT mice (n=26) were exposed to nephrotoxic serum induced nephritis (NTN) model, with the assessment of albuminuria and glomerular damage 4 and 8 days’ post-treatment. Results: Following DOCA administration, the systolic BP, kidney weight, glomerular tuft volume, and albuminuria were increased in treated animals compared to controls (p<0,01), NPR3-/- mice showed intermedium profile between WT and controls. Adriamycin treatment induced a mild albuminuria in WT, unlike NPR3-/- mice (p<0,05). Blood Urea Nitrogen (BUN) was not different. Following NTN treatment, albuminuria levels and glomerular damage were increased in both genotypes, yet this phenotype was significantly more severe in MERTK -/- mice compared to WT animals. Conclusion: Given that both NPR3 and MERTK are involved in cellular signaling, these results suggest a potential role of these interactors in the dynamic adaptation of podocyte and/or SD function. The molecular mechanisms behind these dynamic changes are currently being deciphered. Funding: Government Support – Non-U.S.