The β isoform of GSK3 mediates podocyte autonomous injury in proteinuric glomerulopathy

Abstract

Converging evidence points to glycogen synthase kinase (GSK) 3 as a key player in the pathogenesis of podocytopathy and proteinuria. However, it remains unclear if GSK3 is involved in podocyte autonomous injury in glomerular disease. In normal kidneys, the β isoform of GSK3 was found to be the major GSK3 expressed in glomeruli and intensely stained in podocytes. GSK3β expression in podocytes was markedly elevated in experimental or human proteinuric glomerulopathy. Podocyte specific somatic ablation of GSK3β in adult mice attenuated proteinuria and ameliorated podocyte injury and glomerular damage in experimental adriamycin (ADR) nephropathy. Mechanistically, actin cytoskeleton integrity in podocytes was largely preserved in GSK3β knockout mice following ADR insult, concomitant with a correction of podocyte hypermotility and lessened phosphorylation and activation of paxillin, a focal adhesion associated adaptor protein. In addition, GSK3β knockout diminished ADR induced NFκB RelA/p65 phosphorylation selectively at serine 467, suppressed de novo expression by podocytes of NFκB dependent podocytopathic mediators, including B7-1, cathepsin L and MCP-1, but barely affected the induction of NFκB target prosurvival factors, such as Bcl-xL. Moreover, the ADR-elicited podocytopenia and podocyte death was significantly attenuated in GSK3β knockout mice, associated with a protection against podocyte mitochondrial damage and reduced phosphorylation and activation of cyclophilin F, a structural component of mitochondria permeability transition pores. Overall, our findings suggest that the β isoform of GSK3 mediates autonomous podocyte injury in glomerulopathy by integrating multiple podocytopathic signalling pathways.

Podocyte GSK3α is important for autophagy and its loss detrimental for glomerular function

“…However, we found that even this near complete knockdown of GSK3α in cultured podocytes did not elicit any increase in insulin sensitivity, consistent with our in vivo observations. Similarly, we did not observe any beneficial effect of podocyte GSK3α knockdown in in vivo and in vitro Adriamycin injury models contrary to results reported using podocyte‐specific GSK3β knockout mice . Our results suggest that GSK3α does not represent a potential target for augmentation of podocyte insulin signaling and that it is the reduction in GSK3β and not GSK3α activity that is responsible for the beneficial anti‐albuminuric and podocyte protective effects of pharmacological GSK3 inhibitors .…”

“…This is consistent with reports of FSGS and renal failure in patients on long‐term lithium therapy for conditions such as bipolar disorder . In contrast, a number of recent studies suggest that partial pharmacological inhibition of GSK3 as well as specific genetic knockout of the β isoform in podocytes can be beneficial in a number of experimental glomerular disease models including diabetic nephropathy, lupus nephritis and Adriamycin nephropathy . However, the role of podocyte GSK3α has received little consideration and it is not known whether this isoform has a specific role in podocyte homeostasis or if its loss can also have a podocyte protective effect.…”

Lack of serum‐ and glucocorticoid‐inducible kinase 3 leads to podocyte dysfunction

“…Liang et al (49) reported that GSK3 was related to the epithelial‐mesenchymal transition during podocyte damage, which supports the changes to desmin expression in our lentivirus and animal experiments. Moreover, GSK3 participates in podocyte injury and apoptosis (14, 33), and activation of GSK3 (50) could inhibit podocin expression (33, 48), all of which are consistent with the findings in this study, which suggests that inhibiting SGK3 activation could result in decreased mRNA and protein expression levels of podocin. Based on this information, SGK3 could be involved in regulating podocyte injury by affecting the transcriptional levels of podocin.…”

Ecdysone Elicits Chronic Renal Impairment via Mineralocorticoid-Like Pathogenic Activities

“…For immunohistochemistry, the sections were prepared for heat-induced epitope retrieval by using microwave. Peroxidase immunohistochemical staining was performed as described before [28] with primary antibodies against fibronectin (1:100, Abcam, San Francisco, CA, USA) or cleaved caspase-3 (1:100, Cell Signaling Technology, MA, USA). As a negative control, the primary antibody was replaced by nonimmune serum from the same species.…”

“…Samples were processed for immunoblot analysis as previously described [28]. Antibodies against the following molecules were used as primary antibodies to probe blots: cleaved caspase-3 (1:1000, Cell Signaling Technology, MA, USA), fibronectin (1:2000, Abcam, San Francisco, CA, USA), α-SMA (1:1000, Abcam, San Francisco, CA, USA), collagen IV (1:500, Santa Cruz Biotechnology, Santa Cruz, CA), glyceraldehyde 3-phosphate dehydrogenase (GAPDH, 1:5000, Santa Cruz Biotechnology, Santa Cruz, CA).…”