Targeted GSK3β Ablation in Podocytes Attenuates Glomerular Injury and Albuminuria in Type 2 Diabetic Kidney Disease

Background: Clinical and experimental evidence indicates that overactivation of glycogen synthase kinase 3β (GSK3β)—a key transducer of the insulin signaling cascade that governs glycogenesis and a convergent point for myriad pathways recently implicated in kidney injury, repair, and regeneration—is associated with podocyte injury and progression of diabetic kidney disease (DKD). However, the causative role of GSK3β in diabetic kidney injury remains elusive. Methods: Diabetic db/db mice with doxycycline-inducible podocyte-specific GSK3β knockout were generated to assess the role of GSK3β in diabetic kidney disease. Proteinuria, podocyte injury, and glomerular damage were assessed to evaluate diabetic kidney injury after doxycycline-induced GSK3β ablation. Results: In db/db mice of different ages, GSK3β exhibited progressively increased activity in glomeruli and podocytes, characterized by a sustained decrease in inhibitory phosphorylation at GSK3βS9. Podocyte specific ablation of GSK3β significantly mitigated kidney injury in db/db mice, evidenced by improved glomerular filtration rate and reduced albuminuria, as measured by urinary albumin-to-creatinine ratios. Histologically, signs of diabetic glomerular injury were alleviated, marked by the retention of essential homeostatic marker proteins like podocin and WT-1 on fluorescence immunohistochemistry staining, along with attenuated glomerular ultrastructural changes including podocyte foot process effacement and thickening of glomerular basement membrane, as revealed by transmission electron microscopy. In addition, GSK3β knockout protected against insulin signaling dysfunction in podocytes by averting diabetes-induced inhibitory phosphorylation of IRS-1, thus restoring the sensitivity of insulin pathway. Furthermore, GSK3β ablation enhanced the Nrf2 antioxidant defense and mitigated diabetes-induced premature senescence, as indicated by decreased staining for senescence-associated β-galactosidase and p16INK4A, along with diminished expression of key mediators of senescence signaling like p53 and p21 in podocytes. Conclusion: GSK3β hyperactivity plays a crucial role in podocyte insulin resistance, impaired antioxidant defense, premature senescence, and podocytopathy upon diabetic insults, thereby contributing to type 2 diabetic kidney disease. Funding: NIDDK Support