Glycogen Synthase Kinase 3β Is a Novel Regulator of High Glucose- and High Insulin-induced Extracellular Matrix Protein Synthesis in Renal Proximal Tubular Epithelial Cells

High glucose (30 mM) and high insulin (1 nM), pathogenic factors of type 2 diabetes, increased mRNA expression and synthesis of laminin beta 1 and fibronectin after 24 h of incubation in kidney proximal tubular epithelial (MCT) cells. We tested the hypothesis that inactivation of glycogen synthase kinase 3 beta(GSK3 beta) by high glucose and high insulin induces increase in synthesis of laminin beta 1 via activation of eIF2B epsilon. Both high glucose and high insulin induced Ser-9 phosphorylation and inactivation of GSK3 beta at 2 h that lasted for up to 48 h. This was associated with dephosphorylation of eIF2B epsilon and eEF2, and increase in phosphorylation of 4E-BP1 and eIF4E. Expression of the kinase-dead mutant of GSK3 beta or constitutively active kinase led to increased and diminished laminin beta 1 synthesis, respectively. Incubation with selective kinase inhibitors showed that high glucose- and high insulin-induced laminin beta 1 synthesis and phosphorylation of GSK3 beta were dependent on PI 3-kinase, Erk, and mTOR. High glucose and high insulin augmented activation of Akt, Erk, and p70S6 kinase. Dominant negative Akt, but not dominant negative p70S6 kinase, inhibited GSK3 beta phosphorylation induced by high glucose and high insulin, suggesting Akt but not p70S6 kinase was upstream of GSK3 beta. Status of GSK3 beta was examined in vivo in renal cortex of db/db mice with type 2 diabetes at 2 weeks and 2 months of diabetes. Diabetic mice showed increased phosphorylation of renal cortical GSK3 beta and decreased phosphorylation of eIF2B epsilon, which correlated with renal hypertrophy at 2 weeks, and increased laminin beta 1 and fibronectin protein content at 2 months. GSK3 beta and eIF2B epsilon play a role in augmented protein synthesis associated with high glucose- and high insulin-stimulated hypertrophy and matrix accumulation in renal disease in type 2 diabetes.