Revealing the Role of Renin-Angiotensin System Signaling in Parietal Epithelial Cells

Introduction:. The Bowman's capsule surrounds the kidney's glomerular tuft; it consists of a single layer of parietal epithelial cells (PECs) that serve as a crucial barrier between the urinary space and the renal interstitium. Under pathological conditions, PECs shift from a resting state to one of increased proliferation and migration toward the glomerular tuft, contributing to glomerular injury. Activation of PECs is implicated in proteinuric kidney diseases, but the mechanisms regulating receptor signaling in these cells remain incompletely understood. The renin-angiotensin system (RAS) is a critical regulator of kidney function and has been implicated in a variety of renal pathologies. However, its role in PECs, especially in relation to intracellular signaling pathways that could drive glomerular dysfunction, remains poorly defined. We hypothesize that components of the RAS are present in PECs and that the associated intracellular signaling pathways play a role in driving glomerular dysfunction. Methods: The vibrodissociation technique was employed to isolate Bowman’s capsules containing PECs from discarded adult male and female human transplant tissues, as well as from 12-week-old male and female Wistar rats. Changes in intracellular Ca 2+ concentration (Fluo8) and nitric oxide (NO; DAF-FM) levels in response to acute Ang II application were monitored using live confocal microscopy. To identify the functional receptor mediating Ang II signaling in PECs, cells were preincubated with specific blockers of AT1R or AT2R (Losartan and PD123319, respectively). Scanning electron microscopy (SEM) was employed to assess the structural morphology of PECs. Statistical analysis was performed using one-way ANOVA (OriginPro). Results: SEM analysis confirmed the structural integrity of PECs in the isolated Bowman capsules, showing surfaces lined with cilia, and revealed a significant age-related decline in cell numbers in humans. Acute Ang II peptide administration triggered a rapid increase in NO production as shown by an increase in the amplitude of the fluorescent response in PECs (n≥62 cells for rats (N=5), n≥23 cells for humans (N=3), p<0.01). Of note, no significant intracellular Ca 2+ influx was observed in response to Ang II; instead, a rapid decline in cytosolic Ca 2+ levels was detected, which returned to baseline within 8 minutes. Our results indicate that Ang II induces NO production primarily through AT2R activation (n≥36 cells for rats (N=3), p<0.01), a mechanism that was consistent for both males and females and across the rat and human species. Conclusion: This study provides new insights into the role of Ang II-mediated signaling in PECs, revealing for the first time a direct connection between Ang II and redox homeostasis in these cells. Our findings underscore the importance of AT2R activation in driving NO production and highlight the potential of targeting this pathway to modulate PEC activation in kidney diseases. Future investigations will be essential to further delineate PEC involvement in glomerular dysfunction and develop therapeutic strategies aimed at mitigating PEC hyperplasia in kidney disease. Funding Sources: Supported by the National Institutes of Health DK129227 (to OP) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.