T cell protein tyrosine phosphatase (TCPTP) deficiency in muscle does not alter insulin signalling and glucose homeostasis in mice

Abstract

Aims/hypothesis: Insulin activates insulin receptor protein tyrosine kinase and downstream phosphatidylinositol-3-kinase (PI3K)/Akt signalling in muscle to promote glucose uptake. The insulin receptor can serve as a substrate for the protein tyrosine phosphatase (PTP) 1B and T cell protein tyrosine phosphatase (TCPTP), which share a striking 74% sequence identity in their catalytic domains. PTP1B is a validated therapeutic target for the alleviation of insulin resistance in type 2 diabetes. PTP1B dephosphorylates the insulin receptor in liver and muscle to regulate glucose homeostasis, whereas TCPTP regulates insulin receptor signalling and gluconeogenesis in the liver. In this study we assessed for the first time the role of TCPTP in the regulation of insulin receptor signalling in muscle. Methods: We generated muscle-specific TCPTP-deficient (Mck-Cre;Ptpn2 lox/lox ) mice (Mck, also known as Ckm) and assessed the impact on glucose homeostasis and muscle insulin receptor signalling in chow-fed versus high-fat-fed mice. Results: Blood glucose and insulin levels, insulin and glucose tolerance, and insulin-induced muscle insulin receptor activation and downstream PI3K/Akt signalling remained unaltered in chow-fed Mck-Cre;Ptpn2 lox/lox versus Ptpn2 lox/lox mice. In addition, body weight, adiposity, energy expenditure, insulin sensitivity and glucose homeostasis were not altered in high-fat-fed Mck-Cre;Ptpn2 lox/lox versus Ptpn2 lox/lox mice. Conclusions/interpretation: These results indicate that TCPTP deficiency in muscle has no effect on insulin signalling and glucose homeostasis, and does not prevent high-fat diet-induced insulin resistance. Thus, despite their high degree of sequence identity, PTP1B and TCPTP contribute differentially to insulin receptor regulation in muscle. Our results are consistent with the notion that these two highly related PTPs make distinct contributions to insulin receptor regulation in different tissues. © 2011 Springer-Verlag.