Pancreatic T cell protein-tyrosine phosphatase deficiency affects beta cell function in mice

T cell protein tyrosine phosphatase (TCPTP, encoded by PTPN2) regulates cytokine-induced pancreatic beta cell apoptosis and may contribute to the pathogenesis of type 1 diabetes. However, the role of TCPTP in pancreatic endocrine function and insulin secretion remains largely unknown.

To investigate the endocrine role of pancreatic TCPTP we generated mice with pancreas Ptpn2/TCPTP deletion (panc-TCPTP KO).

When fed regular chow, panc-TCPTP KO and control mice exhibited comparable glucose tolerance. However, when challenged with prolonged high fat feeding panc-TCPTP KO mice exhibited impaired glucose tolerance and attenuated glucose-stimulated insulin secretion (GSIS). The defect in GSIS was recapitulated in primary islets ex vivo and after TCPTP pharmacological inhibition or lentiviral-mediated TCPTP knockdown in the glucose-responsive MIN6 beta cells, consistent with this being cell autonomous. Reconstitution of TCPTP in knockdown cells reversed the defect in GSIS demonstrating that the defect was a direct consequence of TCPTP deficiency. The reduced insulin secretion in TCPTP knockdown MIN6 beta cells was associated with decreased insulin content and glucose sensing. Furthermore, TCPTP deficiency led to enhanced tyrosyl phosphorylation of signal transducer and activator of transcription 1 and 3 (STAT 1/3), and substrate trapping studies in MIN6 beta cells identified STAT 1/3 as TCPTP substrates. STAT3 pharmacological inhibition and small interfering RNA-mediated STAT3 knockdown in TCPTP deficient cells restored GSIS to control levels, indicating that the effects of TCPTP deficiency were mediated, at least in part, through enhanced STAT3 phosphorylation and signalling.

These studies identify a novel role for TCPTP in insulin secretion and uncover STAT3 as a physiologically relevant target for TCPTP in the endocrine pancreas.