The Role of Trio, a Rho Guanine Nucleotide Exchange Factor, in Glomerular Podocytes

Abstract

Nephrotic syndrome is a kidney disease featured by heavy proteinuria. It is caused by injury to the specialized epithelial cells called “podocytes” within the filtration unit of the kidney, glomerulus. Previous studies showed that hyperactivation of the RhoGTPase, Rac1, in podocytes causes podocyte injury and glomerulosclerosis (accumulation of extracellular matrix in the glomerulus). However, the mechanism by which Rac1 is activated during podocyte injury is unknown. Trio is a guanine nucleotide exchange factor (GEF) known to activate Rac1. By RNA-sequencing, we found that Trio mRNA is abundantly expressed in cultured human podocytes. Trio mRNA was also significantly upregulated in humans with minimal change disease and focal segmental glomerulosclerosis, two representative causes of nephrotic syndrome. Reduced expression of Trio in cultured human podocytes decreased basal Rac1 activity, cell size, attachment to laminin, and motility. Furthermore, while the pro-fibrotic cytokine, transforming growth factor β1 increased Rac1 activity in control cells, it decreases Rac1 activity in cells with reduced Trio expression. This was likely due to simultaneous activation of the Rac1-GTPase activation protein, CdGAP. Thus, Trio is important in the basal functions of podocytes and may also contribute to glomerular pathology, such as sclerosis, via Rac1 activation.

Rho GTPase regulatory proteins in podocytes

“…68 TRIO mRNA was abundantly expressed in cultured human podocytes and was upregulated in glomeruli from patients with minimal change disease and FSGS, significantly albeit modestly, in the Nephroseq database (1.18-fold and 1.24-fold increase from healthy controls, respectively). 69 In cultured mouse podocytes, TGFβ1 activated TRIO and Rac1 while gene deletion of TRIO by CRISPR suppressed Rac1 activity, reduced cell size, and impaired cell attachment and migration. 69 These findings suggest that TRIO is important for basal podocyte functions and may also contribute to glomerular pathology via Rac1 activation but in vivo confirmation has not been reported.…”

“…69 In cultured mouse podocytes, TGFβ1 activated TRIO and Rac1 while gene deletion of TRIO by CRISPR suppressed Rac1 activity, reduced cell size, and impaired cell attachment and migration. 69 These findings suggest that TRIO is important for basal podocyte functions and may also contribute to glomerular pathology via Rac1 activation but in vivo confirmation has not been reported.…”

Ras-Related C3 Botulinum Toxin Substrate 1 Combining With the Mixed Lineage Kinase 3- Mitogen-Activated Protein Kinase 7- c-Jun N-Terminal Kinase Signaling Module Accelerates Diabetic Nephropathy

“…Diabetic nephropathy (DN), the most common microvascular complication of diabetes, occurs in approximately 40% of diabetics and has become a leading cause of end-stage renal disease globally ( Zhang et al, 2019 ; Chang et al, 2020 ; Martinez-Moreno et al, 2020 ). Published studies suggest that activation of Ras-related C3 botulinum toxin substrate 1 (RAC1) induces renal damage and plays an important role in the pathogenesis and progression of DN ( Lin et al, 2015 ; Maier et al, 2018 ).…”

Podocyte RhoGTPases: new therapeutic targets for nephrotic syndrome?

“…SLIT-ROBO pGTPase-activating protein 2a (SRGAP2a) suppresses podocyte motility through inactivating RhoA and Cdc42 and is downregulated in patients with kidney disease 34 . Trio, a GEF for Rac1, is expressed in podocytes and is significantly upregulated in glomeruli of patients with FSGS 35 . Human FSGS-causing mutations in anillin have been shown to induce hyperactivation of both Rac1 and mTOR in podocytes 36 .…”