Insulin-activated store-operated Ca2+ entry via Orai1 induces podocyte actin remodeling and causes proteinuria

Abstract

Podocyte, the gatekeeper of the glomerular filtration barrier, is a primary target for growth factor and Ca2+ signaling whose perturbation leads to proteinuria. However, the effects of insulin action on store-operated Ca2+ entry (SOCE) in podocytes remain unknown. Here, we demonstrated that insulin stimulates SOCE by VAMP2-dependent Orai1 trafficking to the plasma membrane. Insulin-activated SOCE triggers actin remodeling and transepithelial albumin leakage via the Ca2+-calcineurin pathway in podocytes. Transgenic Orai1 overexpression in mice causes podocyte fusion and impaired glomerular filtration barrier. Conversely, podocyte-specific Orai1 deletion prevents insulin-stimulated SOCE, synaptopodin depletion, and proteinuria. Podocyte injury and albuminuria coincide with Orai1 upregulation at the hyperinsulinemic stage in diabetic (db/db) mice, which can be ameliorated by the suppression of Orai1-calcineurin signaling. Our results suggest that tightly balanced insulin action targeting podocyte Orai1 is critical for maintaining filter integrity, which provides novel perspectives on therapeutic strategies for proteinuric diseases, including diabetic nephropathy.

Enhanced Orai1-mediated store-operated Ca2+ channel/calpain signaling contributes to high glucose-induced podocyte injury

“…Thus, Ca 2+ signals from different sources in podocytes may interact with each other at a site of a particular signaling pathway. Another example is the finding from a recent study that Orai1-mediated SOCE induces podocyte actin remodeling by activation of calcineurin pathway (11), a pathway also activated by TRPC6-mediated Ca 2+ signals (50,51). One advantage of sharing the same effector among different Ca 2+ pathways is that the Ca 2+ signals from different sources converge on one molecule where all signals are integrated to a final message delivered to next event.…”

“…It should be noted that store-operated Ca 2+ signalinginduced cell responses can be mediated by multiple signaling pathways, such as calcineurin (11) and TGF-β1/Smad (20,54,55) pathways. Our findings in this study do not exclude a possible involvement of a calpain-independent mechanism in SOCE-induced podocyte injury.…”

“…In this regard, the importance of transient receptor potential canonical (TRPC) 5 and TRPC6 channels in maintaining podocyte function and structure has been widely studied (5)(6)(7)(8)(9)(10). Although a recent study by Kim et al reported a contribution of store-operated calcium channel (SOC) to podocyte injury (11), the function of the channel in podocytes and the downstream mechanism mediating the channel function is, at a large extent, not known. SOC is activated upon depletion of the endoplasmic reticulum (ER) Ca 2+ .…”

Ion channels as a therapeutic target for renal fibrosis

“…The renoprotective effect of Orai1 deficiency was similarly confirmed in vitro experiments in UUO mice and high-fat fed ApoE −/− mice ( Mai et al, 2016 ). Studies on podocytes from diabetic nephropathy mice suggest that specific Orai1 deletion prevents insulin-stimulated SOCE, slit-diaphragm disruption and proteinuria, possibly due to chronic stimulation of Orai1 activation or aberrant Ca 2+ signaling, which in turn activates Ca 2+ -regulated phosphatases leading to remodeling of the actin cytoskeleton ( Kim et al, 2021 ). Furthermore, using siRNA to down-regulate STIM1 expression in cultured podocytes from diabetic nephropathy rats serum could reverse the decrease in autophagy and inhibit EMT by restoring Ca 2+ homeostasis ( Jin et al, 2018b ; Jin et al, 2019 ).…”

Phenotypic Transition of Vascular Smooth Muscle Cells Induced by Endothelial TIE2 Mutations in Venous Malformations

“…Cell contraction assay was performed via Cell Contraction Assay Kit (CBA-201, Cell Biolabs, USA) [17].…”