Insulin Mimetic Action of Synthetic Phosphorylated Peptide Inhibitors of Glycogen Synthase Kinase-3

Abstract

Glycogen synthase kinase-3 (GSK-3) was shown to be a key factor in attenuation of the cellular action of insulin. We speculated that inhibition of GSK-3 might have a potential therapeutic value in treatment of insulin resistance and type 2 diabetes. Here, we present a novel class of specific phosphorylated peptides inhibitors of GSK-3, which in sharp contrast to other protein kinase inhibitors that are ATP analogs, are substrate-competitive. We show that the GSK-3 peptide inhibitor activated glycogen synthase activity 2.5-fold in human embryonic kidney 293 cells, and increased glucose uptake in primary mouse adipocytes in the absence or presence of insulin compared with cells treated with two respective peptide controls. In addition, an i.p. administration of GSK-3 peptide inhibitor to normal or insulin-resistant obese C57BL/6J mice, improved their performance on glucose tolerance tests compared with control-treated animals. We present here a novel rational strategy for developing specific GSK-3 inhibitors and point toward GSK-3 as a promising therapeutic target in insulin resistance and type-2 diabetes.

Glycogen synthase kinase 3 inhibition improves insulin-stimulated glucose metabolism but not hypertension in high-fat-fed C57BL/6J mice

“…L803-mts is a synthetic phosphorylated peptide derived from the unconventional recognition motif of GSK3, which can act as its substrate competitive inhibitor. As most protein kinases do not require a pre-phosphorylated site on their substrate as part of their recognition motif, this inhibitor is highly specific for GSK3 [2]. Short-term L803-mts treatment has been shown to mimic insulin action in isolated tissue in vitro by increasing glycogen synthase activity and 2-DG uptake and also improve glucose tolerance in vivo [2].…”

“…As most protein kinases do not require a pre-phosphorylated site on their substrate as part of their recognition motif, this inhibitor is highly specific for GSK3 [2]. Short-term L803-mts treatment has been shown to mimic insulin action in isolated tissue in vitro by increasing glycogen synthase activity and 2-DG uptake and also improve glucose tolerance in vivo [2]. Here we show using euglycaemic-hyperinsulinaemic clamps that specific inhibition of GSK3 using L803-mts markedly increased wholebody Rd by improving insulin action in liver and muscle.…”

“…GSK3 peptide inhibitor A substrate competitive peptide inhibitor of GSK3, L803-mts (N-myristol-GKEAPPAPPQS (p)P) was synthesised by Genemed Synthesis, Inc. (San Francisco, CA, USA) as previously described [2]. Mice were injected i.p.…”

“…Glycogen synthase kinase 3 (GSK3) is a constitutively active serine/threonine protein kinase. GSK3 plays an important role in the development of type 2 diabetes, although its precise role remains unclear [1][2][3]. Studies so far have indicated that GSK3 phosphorylates and inhibits glycogen synthase activity [4,5] and also insulin receptor substrate 1 (IRS-1), thereby impairing insulin signalling.…”

“…L803-mts treatment also resulted in decreased phosphoenolpyruvate carboxykinase mRNA levels and higher liver glycogen. In an earlier study, Plotkin et al [2] had reported that shortterm (1 h) treatment with the same inhibitor in a diabetic HF-fed C57BL/6J mouse model improved performance on a glucose tolerance test compared with controls. Based on these promising results, we examined if specific inhibition of GSK3 in an insulin-resistant obese C57BL/6J mouse model of type 2 diabetes would improve insulin action and enhance whole-body glucose uptake and metabolism.…”