Introduction: Immune cells responsible for the elimination of β-cells in type 1 diabetes (T1D) release pro-inflammatory cytokines, including interferons, into the islet microenvironment. Interferons induce a phosphorylation cascade that results in expression of antigen presentation complexes, chemokines, nitric oxide synthase (iNOS) and pro-apoptotic proteins in β-cells; all key factors in diabetes development. Blockade of interferon signalling in murine studies protects β-cells from autoimmune destruction. Protein tyrosine phosphatases (PTPs) regulate cell signalling through dephosphorylation of tyrosine residues. PTPs are genetically associated with T1D and negatively regulate interferon signalling in murine and human islets. PTPN1 (PTP1B) is expressed in murine pancreata, however its role in interferon signalling regulation remains unknown.
Aim: To determine the role of PTPN1 in regulation of interferon signalling in β-cells in autoimmune diabetes. We hypothesise that inhibition of PTPN1 will alter interferon signalling in β-cells.
Findings: Inhibition of PTPN1 in isolated non-obese diabetic (NOD) mouse islets reduced interferon induced signalling (P<0.001), assessed by immunoblot densitometry. This was reproduced in insulinoma cell lines treated with the PTPN1 inhibitor (P<0.01) and cells depleted in PTPN1 expression using CRISPR/CAS9 technology (P<0.001). Furthermore, flow cytometry revealed that expression of interferon-induced MHC class I was reduced by PTPN1 inhibitor treatment in both isolated mouse islets (P<0.01) and insulinoma cells (P<0.001). Quantitative-PCR demonstrated that PTPN1 inhibition reduced interferon induced expression of iNOS (P<0.001) and the chemokines CXCL9 (P<0.001) and CXCL10 (P<0.05) in isolated mouse islets. DNA labelling fluorescence microscopy and DNA fragmentation analysis by flow cytometry revealed that PTPN1 inhibition was cytoprotective against interferon and tumour necrosis factor induced cell death in both MIN6 (P<0.001) and NIT-1 (P<0.01) insulinoma cell lines.
Conclusion: Inhibition of PTPN1 prevents interferon signalling in β-cells and reduces the upregulation of genes that promote β-cell death, rendering it a novel target to protect against autoimmune diabetes development.