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Kidney Week

Abstract: PO1992

Tropomyosin Isoforms Play a Role in Healthy and Injured Kidney Podocytes

Session Information

  • Podocyte Biology
    October 22, 2020 | Location: On-Demand
    Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

  • 1204 Podocyte Biology

Authors

  • Hammad, Dina, Washington University in Saint Louis School of Medicine, Saint Louis, Missouri, United States
  • Miner, Jeffrey H., Washington University in Saint Louis School of Medicine, Saint Louis, Missouri, United States
  • Suleiman, Hani, Washington University in Saint Louis School of Medicine, Saint Louis, Missouri, United States
Background

The podocytopathies are a group of glomerular diseases that affect the kidney’s ability to filter the blood, and often lead to kidney failure. Healthy podocytes cover the glomerular capillaries with thousands of extensions called foot processes that interdigitate with one another and maintain their elaborate cell shape by tightly regulating their actin cytoskeleton. Podocytes respond to insults in a typical fashion by undergoing foot process effacement (FPE), a dramatic shift in podocyte morphology and the disappearance of the intricate foot processes. Tropomyosins (Tpms) are coiled-coil dimers that form co-polymers along actin filaments and change the filaments’ biophysical properties. Over 40 different Tpm isoforms have been identified as the gene products of 4 Tpm genes: Tpm1, 2, 3 & 4. Various Tpm isoforms target to different locations inside cells and change the type of actin cables assembled in those locations. We hypothesize that podocyte shape is controlled by a specific set of Tpm isoforms that regulate actin cytoskeletal dynamics. Changing the tropomyosin isoforms after injury might be linked to changing podocyte shape and the FPE phenomenon.

Methods

To test our hypothesis, we used RT-PCR and RNAseq (Illumina and PacBio) to identify the whole array of Tpm isoforms that are enriched in podocyte and in isolated healthy glomeruli. Using different mouse models for podocyte injury (i.e., Cd2ap KO, Lamb2 KO, Col4a3 KO & Adriamycin-nephropathy (AdrN)), we identified a change in Tpm isoforms in the glomeruli isolated from these mice.

Results

RNAseq results from WT glomeruli show a different pattern of Tpm expression than the injured glomeruli counterparts, with the most significant changes occurring in Tpm 1.7 & Tpm 3.4. PacBio data also showed an interesting novel Tpm-related gene product only in injured glomeruli. We isolated RNA from WT and AdrN glomeruli and compared them to primary podocytes taken from podocyte-specific translating-ribosome-affinity-purification (“TRAP”) mice. This system allowed us to purify podocyte mRNA for RNAseq, away from that in other glomerular cell types. Comparing the isolated RNA from WT-TRAP & AdrN-TRAP mice, we are able to identify the podocyte-specific Tpm isoforms that are associated with injury.

Conclusion

This study suggests roles for tropomyosin isoform changes in regulating podocyte shape in health and injury conditions.

Funding

  • Private Foundation Support