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Abstract: FR-OR38

mTOR Activity of Macula Densa (MD) Cells Is a Major Determinant of Glomerular Structure and Function

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
  • 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 are paracrine regulators of renal hemodynamics and renin and were recently reported to feature a high rate of protein synthesis. Since the central regulator of protein synthesis is the mTOR pathway, the purpose of the present study was to examine the role of MD mTOR signaling in the maintenance of glomerular structure and function.

Methods

Inducible MD-specific mTOR gain-of-function (MD-mTORgof) mice were generated by crossing nNOS/CreERT2-mTmG and TSC2/fl mice. Protein synthesis activity in vivo at the single-cell level was quantified using O-propargyl-puromycin (OPP) fluorescence imaging and histological analysis in Sox2-tdTomato and MD-GFP mice. Glomerular filtration rate (GFR) was measured via transdermal detection of FITC-sinistrin plasma decay (MediBeacon) and renal blood flow (RBF) was quantified via intravital microscopy.

Results

Sox2-tdTomato mice and the OPP assay showed the highest protein expression in the MD among all renal cell types. Immunolabeling validated MD-specific TSC2 KO and upregulated pS6K in MD-mTORgof mice. MD-mTORgof significantly increased the overall rate of protein synthesis in MD cells (1.300±0.057) vs control (0.944±0.039). Physiological activation of MD cells by low salt diet further enhanced MD protein synthesis in both WT (1.365±0.055) and MD-mTORgof (1.482±0.056) mice, which was blocked by Rapamycin treatment. MD-enriched proteins such as CCN1, CCN3, Pappa2 and CxCl14 had significantly higher expression in response to MD-mTORgof. GFR was significantly elevated in MD-mTORgof mice compared to WT (1981±121.30 vs 1444±99.48 μL/min/100 g BW) with similar changes observed with respect to RBF based on single afferent (AA)/efferent arteriole (EA) blood flow, vessel diameter and glomerular tuft area measurements. COX2, mPGES1, renin, the length of basal MD cell processes (maculapodia) and MD cell number/plaque were also significantly increased in MD-mTORgof vs WT mice.

Conclusion

mTOR signaling is an important regulator of MD cell protein synthesis, proliferation, differentiation and paracrine signaling to the glomerulus via classic hemodynamic and novel, non-traditional glomerular tissue remodeling elements that may be therapeutically targeted to increase RBF, GFR and endogenous tissue remodeling in kidney diseases.

Funding

  • NIDDK Support