Abstract: FR-PO0655
RhoA and Its Downstream Effectors ROCK/Cofilin and Formin Trigger Mitochondrial Fragmentation in PKD
Session Information
- Cystic Kidney Diseases: Basic and Translational Research
November 07, 2025 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Genetic Diseases of the Kidneys
- 1201 Genetic Diseases of the Kidneys: Monogenic Kidney Diseases
Authors
- Kapus, Andras, St Michael's Hospital Keenan Research Centre for Biomedical Science, Toronto, Ontario, Canada
- Harikumar, Rohankrishna, St Michael's Hospital Keenan Research Centre for Biomedical Science, Toronto, Ontario, Canada
- Lichner, Zsuzsanna A, St Michael's Hospital Keenan Research Centre for Biomedical Science, Toronto, Ontario, Canada
- Tuo, Chen, St Michael's Hospital Keenan Research Centre for Biomedical Science, Toronto, Ontario, Canada
- Wei, Kuiru, St Michael's Hospital Keenan Research Centre for Biomedical Science, Toronto, Ontario, Canada
- Szaszi, Katalin, St Michael's Hospital Keenan Research Centre for Biomedical Science, Toronto, Ontario, Canada
Background
Polycystic kidney disease (PKD) is the most prevalent genetic renal disorder, caused by the loss/loss of function of polycistin-1 (PC1) or 2 (PC2), and characterized by excessive cyst formation and fibrosis. A key cellular feature of PKD is the fragmentation of mitochondria, but the underlying mechanism is unknown. Our previous studies have shown that PC loss induces RhoA- dependent nuclear translocation of myocardin-related transcription factor, leading to fibrogenesis. Based on this scenario, we asked whether PC1/2 loss-induced mitochondrial fragmentation might also be a mediated by RhoA.
Methods
Mitochondrial morphology was quantified by volumetric confocal microcopy in mitoRFP-transfected LLC-PK1 tubular cells. RhoA activity was measured by RhoA G-LISA. The manipulation of expression/activation of proteins is described at the corresponding results.
Results
RhoA activation by constitutively active RhoA or RhoA II activator toxin induced robust mitochondrial fragmentation. Importantly, PC1 or PC2 silencing triggered RhoA activation and mitochondrial fragmentation, which was prevented/reversed by downregulation/inhibition of RhoA (siRNA, dominant negative (DN) RhoA, or C3 toxin). Fission was catalyzed by dynamin-related protein 1 (Drp1), as a) PC loss promoted RhoA-dependent mitochondrial Drp1 translocation; and b) fragmentation was prevented/reversed by Drp1 silencing or inhibition (mDivi or DN-Drp1). PC loss provoked cofilin phosphorylation (inhibition) via Rho kinase (ROCK) and its target LIM kinase. Inhibition of ROCK or LIMK reduced fragmentation. Mitochondrial fission also required the other major RhoA effector pathway, the activation of formins. Mitochondrially targeted active formins, like DIAPH3, but not its actin polymerization-deficient mutant induced fission, while the pan-formin inhibitor SMIFH2 abolished PC loss-provoked fragmentation. Importantly, the human PKD cell line WT 9-12 exhibited fragmented mitochondrial network, which was restored by SMIFH2. Fragmentation facilitated PC1/2 loss-induced fibrogenic gene expression.
Conclusion
Thus, PC1/2 loss leads to mitochondrial fragmentation by activation of RhoA and its effectors, which promote F-actin polymerization by decreased severing (cofilin inhibition) and increased assembly (formin activation).