Abstract: SA-OR009

COSMC, the Molecular Chaperone of O-Linked Glycosylation, Is Essential for Podocyte Function

Session Information

  • A View on the Glomerulus
    November 04, 2017 | Location: Room 294, Morial Convention Center
    Abstract Time: 06:06 PM - 06:18 PM

Category: Glomerular

  • 1002 Glomerular: Basic/Experimental Pathology

Authors

  • Stotter, Brian Ross, Div of Nephrology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, United States
  • Talbot, Brianna, Div of Nephrology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, United States
  • Schlondorff, Johannes S., Div of Nephrology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, United States
Background

Proper podocyte function is required to maintain the glomerular filtration barrier. Many podocyte proteins undergo post-translational O-linked glycosylation (OLG), which requires T-synthase and its molecular chaperone Cosmc. Prior studies have shown that global COSMC knockout produces immature glycoproteins that express Tn antigen. We hypothesize that podocyte-specific COSMC deletion causes albuminuria, renal failure, and glomerulosclerosis due to aberrant OLG.

Methods

Male podocin-Cre mice were bred with female COSMCfl/fl mice to produce males devoid of COSMC in podocytes (Podo-COSMCY/fl) and females with mosaic COSMC loss in podocytes (Podo-COSMC+/fl). Serum creatinine (SCr) and urine albuminuria were measured at 1 and 2 months of life for experimental and control mice. Kidneys were harvested for histology, immunofluorescence (IF), electron microscopy (EM), and biochemical analysis. Immature OLG was detected by staining for Tn antigen with lectin HPA.

Results

Podo-COSMCY/fl males have heavy albuminuria by 1 month, with mesangial expansion and glomerulomegaly on histology and diffuse foot process effacement by EM. By 2 months, SCr is elevated compared to controls and histology shows extensive glomerulosclerosis, interstitial fibrosis, and tubular atrophy. Podo-COSMC+/fl females have mosaic glomerular Tn antigen expression, mild albuminuria, and normal SCr by 1 and 2 months. Podo-COSMC+/fl females have normal histology at 1 month but both rare segmental sclerosis and foot process effacement by 2 months. IF shows diffuse lectin HPA staining in Podo-COSMCY/fl male podocytes and mosaic staining in Podo-COSMC+/fl female podocytes. Podocalyxin, an O-linked podocyte glycoprotein, is normally expressed in 1 month Podo-COSMCY/fl males and 1 and 2 month Podo-COSMC+/fl females, but is lost in 2 month Podo-COSMCY/fl males. In contrast, staining of O-linked glycoprotein podoplanin is reduced in COSMC-deficient podocytes by 1 month, confirmed by Western blot of glomerular lysates.

Conclusion

Loss of COSMC in podocytes causes albuminuria and renal failure with glomerulosclerosis, interstitial fibrosis, and tubular atrophy. This phenotype is most severe in male mice that have complete COSMC excision, and less severe in mosaic females. The mechanism of podocyte injury may be due to aberrant function of podocalyxin, podoplanin, and other O-linked glycoproteins.

Funding

  • NIDDK Support