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Abstract: FR-PO694

SMPDL3b Regulates Proteinuria in Experimental Alport Syndrome via Sphingosin-1-Phosphate

Session Information

Category: Glomerular Diseases

  • 1304 Glomerular Diseases: Podocyte Biology

Authors

  • Mitrofanova, Alla, University of Miami School of Medicine, Miami, Florida, United States
  • Pamreddy, Annapurna, The University of Texas Health Science Center at Houston, Houston, Texas, United States
  • Fontanella, Antonio Miguel, University of Miami School of Medicine, Miami, Florida, United States
  • Tolerico, Matthew, University of Miami School of Medicine, Miami, Florida, United States
  • Mallela, Shamroop Kumar, University of Miami School of Medicine, Miami, Florida, United States
  • Gurumani, Margaret Zvido, University of Miami School of Medicine, Miami, Florida, United States
  • Molina David, Judith T., University of Miami School of Medicine, Miami, Florida, United States
  • Kim, Jin Ju, University of Miami School of Medicine, Miami, Florida, United States
  • Burke, George William, University of Miami School of Medicine, Miami, Florida, United States
  • Merscher, Sandra M., University of Miami School of Medicine, Miami, Florida, United States
  • Sharma, Kumar, The University of Texas Health Science Center at Houston, Houston, Texas, United States
  • Fornoni, Alessia, University of Miami School of Medicine, Miami, Florida, United States
Background

Alport Syndrome (AS) is caused by mutations in the gene coding for type IV collagens and is characterized by progressive loss of kidney function, where podocytes play the central role. We previously reported that cholesterol and sphingolipids are major determinants of podocyte function, and that sphingomyelin phosphodiesterase acid-like 3b (SMPDL3b), a lipid raft associated protein, plays an important role in podocyte survival and regulates the availability of bioactive sphingolipids such as sphingosine-1-phosphate (S1P). We tested the hypothesis that altered podocyte SMPDL3b expression affects the generation of S1P thus contributing to the renal failure in AS.

Methods

Illumina sequencing RNA data analysis, qRT-PCR and Western blot analysis were used to characterize differentiated immortalized murine podocytes isolated from AS mice. Kidney cortices from 8-week-old AS mice were used for LC-MS analysis. Kidneys from 20-weeks-old podocyte-specific Smpdl3b deficient AS mice (DKO) mice and their controls were processed for in-depth phenotypical analysis, including urinary albumin-to-creatinine ratio (ACR) and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). 16-weeks-old AS and DKO mice were intraperitoneally injected with 100 nM S1P for 4 weeks. Two-tailed t-test or One-Way ANOVA followed by Tukey’s post-test were used to detect statistical changes.

Results

SMPDL3b expression is significantly higher in isolated podocytes and in kidney cortices from AS mice. Moreover, decreased expression of S1P phosphatase 1, an enzyme that catalyzes S1P dephosphorylation, in isolated podocytes was observed in association with S1P and ceramide accumulation in kidney cortices from AS mice. Podocyte specific SMPDL3b deletion in DKO mice resulted in decreased ACR levels and increased number of podocytes foot processes. S1P injections in DKO mice caused worsened albuminuria.

Conclusion

Our data indicate that SMPDL3b expression may affect availability of S1P, thereby regulating proteinuria levels in experimental AS. Thus, targeting SMPDL3b expression levels in the podocytes may represent a novel approach to improve renal outcomes in patients with AS.

Funding

  • NIDDK Support