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Abstract: PO1721

A New View of Macula Densa Cell Protein Synthesis

Session Information

Category: Glomerular Diseases

  • 1201 Glomerular Diseases: Fibrosis and Extracellular Matrix

Authors

  • Shroff, Urvi Nikhil, University of Southern California, Los Angeles, California, United States
  • Gyarmati, Georgina, University of Southern California, Los Angeles, California, United States
  • Riquier-brison, Anne, University of Southern California, Los Angeles, California, United States
  • Izuhara, Audrey, University of Southern California, Los Angeles, California, United States
  • Peti-Peterdi, Janos, University of Southern California, Los Angeles, California, United States
Background

Macula densa (MD) cells, a chief regulatory cell type in the kidney, have prominent protein synthetic organelles. mRNA translation and protein synthesis are tightly regulated processes and the mTOR and Wnt signaling pathways play a central role in regulating this activity. The present study aimed to examine the role of Wnt/mTOR in regulating MD protein synthesis.

Methods

Changes in bulk protein synthesis activity were quantitatively visualized using an OPP-incorporation based fluorescence assay in a new mouse MD cell line (mMDGeo) treated with low salt medium or the GSK3b inhibitor lithium to activate MD cells. For studies in vivo, MD-Wntgof and MD-mTORgof mice were developed using a nNOS-Cre inducible system with Wnt and mTOR gain-of-function, respectively, to upregulate signaling specifically in MD cells. MD gene profiling validated by data from Human Protein Atlas (HPA) was used to confirm the expression of various pathways and regulators of protein synthesis and vesicular exocytosis.

Results

OPP experiments in mMDGeo cells in vitro showed that low salt (5.98 ± 1.15) and lithium (5.67 ± 0.24) treated cells had significantly higher protein synthetic activity as compared to control (3.13 ± 0.15). Similarly, MD cells in vivo in wildtype mice on a low salt (2.59 ± 0.26) or lithium diet (2.00 ± 0.26) had significantly higher OPP fluorescence as compared to control diet (1.16 ± 0.18). Upregulation of MD-Wnt signaling in MD-Wntgof mice (1.36 ± 0.04) also resulted in a significant increase in MD protein synthesis as compared to control (1.16 ± 0.06). The expression of MD-enriched secreted proteins (Ccn1, Pappa2, Nov, Cxcl14) was enhanced in activated MD cells. Finally, results from MD gene profile analysis with HPA validation showed high and MD-specific expression of several pathways involved in mRNA translation (p70S6K, eIF3C, eEF2), chaperones (HSP90AB1) along with certain elements of regulated vesicular exocytosis.

Conclusion

In summary, the unique MD microanatomy and cell-specific protein synthetic machinery support the robust synthesis and secretion of a diverse array of tissue remodeling and angiogenic proteins which are regulated by mTOR and Wnt signaling in these cells. The regulatory pathways MD protein synthesis and secretome may be targeted to enhance endogenous glomerular and vascular tissue remodeling and repair.

Funding

  • NIDDK Support