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Abstract: TH-PO772

Identification of Circular Dorsal Ruffles as Signal Platforms for the AKT Pathway in Glomerular Podocytes

Session Information

Category: Glomerular Diseases

  • 1403 Podocyte Biology

Author

  • Yoshida, Sei, Nankai University, Tianjin, Tianjin, China
Background

Circular dorsal ruffles (CDRs) are rounded membrane ruffles induced by growth factors to function as precursors of the large-scale endocytosis called macropinocytosis. In addition to their role in cellular uptake, recent research using cell line systems has shown that CDRs/macropinocytosis regulate the canonical AKT/mTORC1 growth factor signaling pathway. However, as CDRs have not been observed in tissues, their physiological relevance has remained unclear. Here, we first report that CDRs are expressed in glomerular podocytes ex vivo and in vivo, and we visually captured the transformation process to macropinocytosis.

Methods

Ultra-high resolution scanning electron microscopy (SEM) and confocal microscopy were used to see if CDRs are expressed at the surface of mouse glomerulus and isolated glomeruli. Podocyte cell line MPC5 was used for further imaging analysis as well as biochemical assays to test if CDRs regulate the Akt/mTORC1 pathway.

Results

High-resolution SEM of mouse kidney tissue showed that glomerular podocytes displayed CDR-like structures in vivo (Fig. 1A, arrows). In total, 21 glomeruli from five mice were examined using SEM. CDR-like structures formed in 25.38% of the podocytes (n=528). Moreover, epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) induced CDRs in MPC5 cells. Inhibition of CDRs significantly mitigated GF-induced AKT phosphorylation and attenuated mTORC1 activation in cells. Confocal microscopy showed that AKT signaling components localized to CDRs. Importantly, we utilized isolated mouse glomeruli for ex vivo experiments and found that podocytes express CDRs as macropinocytic cups after EGF stimulation (Fig. 1B, arrows), regulating the AKT pathway.

Conclusion

Our results demonstrate the physiological role of CDRs as signal platforms for the AKT/mTORC1 pathway in podocytes at the tissue level. As mTORC1 plays critical roles in podocyte metabolism and aberrant activation of mTORC1 triggers podocytopathies, the outputs from this study strongly suggest that targeting CDR formation could represent a potential therapeutic approach for these diseases.

Funding

  • Government Support – Non-U.S.