The redox-sensitive GSK3ß is a key regulator of glomerular podocyte injury in type 2 diabetic kidney disease.

ABSTRACT

Emerging evidence suggests that GSK3ß, a redox-sensitive transducer downstream of insulin signaling, acts as a convergent point for myriad pathways implicated in kidney injury, repair, and regeneration. However, its role in diabetic kidney disease remains controversial. In cultured glomerular podocytes, exposure to a milieu of type 2 diabetes elicited prominent signs of podocyte injury and degeneration, marked by loss of homeostatic marker proteins like synaptopodin, actin cytoskeleton disruption, oxidative stress, apoptosis, and stress-induced premature senescence, as shown by increased staining for senescence-associated ß-galactosidase activity, amplified formation of γH2AX foci, and elevated expression of mediators of senescence signaling, like p21 and p16INK4A. These degenerative changes coincided with GSK3ß hyperactivity, as evidenced by GSK3ß overexpression and reduced inhibitory phosphorylation of GSK3ß, and were averted by tideglusib, a highly-selective small molecule inhibitor of GSK3ß. In agreement, post-hoc analysis of a publicly-available glomerular transcriptomics dataset from patients with type 2 diabetic nephropathy revealed that the curated diabetic nephropathy-related gene set was enriched in high GSK3ß expression group. Mechanistically, GSK3ß-modulated nuclear factor Nrf2 signaling is involved in diabetic podocytopathy, because GSK3ß knockdown reinforced Nrf2 antioxidant response and suppressed oxidative stress, resulting in an improvement in podocyte injury and senescence. Conversely, ectopic expression of the constitutively active mutant of GSK3ß impaired Nrf2 antioxidant response and augmented oxidative stress, culminating in an exacerbated diabetic podocyte injury and senescence. Moreover, IRS-1 was found to be a cognate substrate of GSK3ß for phosphorylation at IRS-1S332, which negatively regulates IRS-1 activity. GSK3ß hyperactivity promoted IRS-1 phosphorylation, denoting a desensitized insulin signaling. Consistently, in vivo in db/db mice with diabetic nephropathy, GSK3ß was hyperactive in glomerular podocytes, associated with IRS-1 hyperphosphorylation, impaired Nrf2 response and premature senescence. Our finding suggests that GSK3ß is likely a novel therapeutic target for treating type 2 diabetic glomerular injury.