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Abstract: TH-PO783

The Role of DDR1 in Podocyte Lipotoxicity and Progression of Alport Syndrome

Session Information

Category: Glomerular Diseases

  • 1201 Glomerular Diseases: Fibrosis and Extracellular Matrix

Authors

  • Kim, Jin Ju, University of Miami, Miami, Florida, United States
  • Molina David, Judith T., University of Miami, Miami, Florida, United States
  • Varona Santos, Javier T., University of Miami, Miami, Florida, United States
  • Merscher, Sandra M., University of Miami, Miami, Florida, United States
  • Miner, Jeffrey H., Washington University School of Medicine, St. Louis, Missouri, United States
  • Fornoni, Alessia, University of Miami, Miami, Florida, United States
Background

The glomerular basement membrane (GBM) is primarily composed of laminin and Collagen type IV. De novo production of the α1 chain of collagen type I (Col I) has been observed mouse models of Alport Syndrome (AS, Col4a3KO). Discoidin domain receptor 1 (DDR1) is a unique receptor tyrosine kinase that is activated by collagens. Deletion of the DDR1 in Col4a3KO mice was shown to improve survival and renal function. However, how DDR1 activation by aberrant collagen production contributes to podocyte injury and proteinuria is poorly understood. I test the hypothesis that aberrant Col I induced podocyte injury via DDR1-dependent lipotoxicity.

Methods

Differentiated human podocytes were serum starved, followed by 18hrs treatment with 50ug/mL Col I (Corning). Following collagen treatments, podocyte lipid content was determined by BODIPY 493/503 and Cell Mask Blue staining. Free Fatty acid (FFA) uptake assessed using a fluorometric free fatty acid uptake kit (abcam). Mice in which exon 5 of a3 chain of collagen type IV is deleted (Col4a3KO), a model for AS, were obtained from the Jackson Laboratory for the determination of kidney cortex DDR1 phosphorylation

Results


DDR1 phosphorylation was increased in kidney cortex from Col4a3KO mice and the degree of DDR1 phosphorylation correlated with blood urine nitrogen (BUN, R2 =0.7, p<0.01). In vitro, DDR1 was phosphorylated by collagen type I (50µg/mL, 18hr) in cultured human podocytes. Increased intracellular lipid accumulation (p<0.05), Free fatty acid (FFA) uptake (p<0.01) and intracellular triglyceride level (p<0.01) were also observed in Col I treated podocytes. DDR1 dominant active (DA) transfected HEK293 cells showed increased expression of CD36, a protein involved in FA uptake, and increased FFA uptake compared to cells transfected with DDR1 WT and dominant negative (DN, p<0.05). siRNA knock down of CD36 reduced FFA uptake when compared to scramble siRNA control (p<0.05). Col I induced DDR1 activation is associated with podocyte lipotoxicity, FFA uptake and intracellular lipid droplet deposition. Glomeruli isolated from Col4a3KO mice showed increased lipid content and increased expression of CD36.

Conclusion

Our data suggest that Col I-induced/DDR1-mediated lipotoxicity may represent a novel mechanism leading to podocyte injury in AS.

Funding

  • NIDDK Support