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Kidney Week

Abstract: FR-PO1015

Loss of Podocyte-Specific SGPL1 Results in Albuminuria and Focal Segmental Glomerulosclerosis in Hypertensive Mice

Session Information

Category: Genetic Diseases of the Kidney

  • 1002 Genetic Diseases of the Kidney: Non-Cystic

Authors

  • Hodgin, Jeffrey B., The University of Michigan, Ann Arbor, Michigan, United States
  • Zhao, Piming, Children''s Hospital Oakland Research Institute, Oakland, California, United States
  • Luo, Jinghui, University of Michigan, Ann Arbor, Michigan, United States
  • Yang, Yingbao, University of Michigan, Ann Arbor, Michigan, United States
  • Saba, Julie D., Children's Hospital Oakland Research Institute, Oakland, California, United States
Background

Steroid-resistant nephrotic syndrome (SRNS) often manifests as focal segmental glomerulosclerosis (FSGS), has no efficient treatment, and carries a high risk of relapse after transplant. Inactivating SGPL1 mutations cause a familial form of SRNS, but the cellular and molecular mechanisms are unknown. SGPL1 encodes sphingosine phosphate lyase (SPL), an enzyme responsible for the irreversible degradation of sphingosine-1-phosphate (S1P). S1P is a bioactive lipid that ligates to a family of G protein-coupled receptors (S1PRs) whose signaling regulates cell survival, migration and immune cell trafficking. Because whole body SGPL1 knockout mice die in the perinatal period, and most monogenic causes of SRNS result from recessive or dominant mutations in genes localized to the podocyte, we focused on podocyte-specific SGPL1.

Methods

We generated conditional knockout mice lacking SGPL1 expression in podocytes (SPLPodo_KO). Hypertension was induced in wild-type (WT) and SPLPodo_KO mice by nephrectomy, implanted osmotic minipumps releasing angiotensin II (AngII, 1.2 µg/kg/min), and 1% NaCl in the drinking water. Blood pressure was measured by tail-cuff, 24-hr-urine was collected, and kidneys harvested at 4 weeks for histology. SPL-deficient cultured human podocytes were generated by CRISPR/Cas9, assayed for S1P levels, and treated with AngII. Autophagy was assayed by Western blotting of LC3A-I and -II.

Results

SPLPodo_KO mice had no spontaneous phenotype. Compared to WT mice (n=6), hypertensive SPLPodo_KO mice (n=8) had elevated albumin-to-creatinine ratio (ACR g/g) (2.7+/-1.8 vs 0.5+/-.1 at 2 wks and 8.1+/-5.7 vs 1.93+/-3.7 at 4 wks; both P<0.05). In addition, the % glomerulosclerosis in hypertensive SPLPodo_KO was more than double than WT mice (1.51+/-0.71% vs 0.70+/-0.21%; P<0.05). In vitro studies revealed undetectable SPL expression and activity and sphingolipid accumulation in SGPL1-KO vs WT human podocytes. In addition, SGPL1-KO human podocytes showed increased autophagy with AngII exposure, indicating increased sensitivity to injury.

Conclusion

We found that SPLPodo_KO mice are profoundly sensitive to glomerular stress, indicating a prominent role for this signaling pathway in FSGS. Therapeutic targeting of S1P signaling, such as with the S1PR antagonist FTY720, which is already FDA approved for use, may be beneficial.

Funding

  • NIDDK Support