Human Molecular Genetics Advance Access [Accepted Manuscript] published online on October 13, 2009
Human Molecular Genetics, doi:10.1093/hmg/ddp474
MDA5 and PTPN2, two candidate genes for type 1 diabetes, modify pancreatic β-cell responses to the viral by-product double stranded RNA
From the Laboratory of Experimental Medicine, Université Libre de Bruxelles, B-1070 Brussels, Belgium
Address correspondence and reprint requests to: Dr. Decio L. Eizirik, Laboratory of Experimental Medicine, Université Libre de Bruxelles, Route de Lennik, 808 – CP618, B-1070 – Brussels – Belgium, phone: +32 2 555 6080, fax: +32 2 555 6239, email: deizirik{at}ulb.ac.be
Received July 20, 2009; Revised October 9, 2009; Accepted October 9, 2009
β-cell destruction in type 1 diabetes (T1D) is at least in part consequence of a "dialog" between β-cells and immune system. This dialog may be affected by the individual's genetic background. We presently evaluated whether modulation of MDA5 and PTPN2, two candidate genes for T1D, affects β-cell responses to double-stranded RNA (dsRNA), a by-product of viral replication. These genes were selected following comparison between known candidate genes for T1D and genes expressed in pancreatic β-cells, as identified in previous array analysis. INS-1E cells and primary FACS-purified rat β-cells were transfected with siRNAs targeting MDA5 or PTPN2, and subsequently exposed to intracellular synthetic dsRNA (PIC). Real time RT-PCR, Western blot and viability assays were performed to characterize gene/protein expression and viability. PIC increased MDA5 and PTPN2 mRNA expression, which was inhibited by the specific siRNAs. PIC triggered apoptosis in INS-1E and primary β-cells and this was augmented by PTPN2 knockdown, while inhibition of MDA5 did not modify PIC-induced apoptosis. In contrast, MDA5 silencing decreased PIC-induced cytokine and chemokine expression, while inhibition of PTPN2 induced minor or no changes in these inflammatory mediators. These findings indicate that changes in MDA5 and PTPN2 expression modify β-cell responses to dsRNA. While MDA5 regulates inflammatory signals, PTPN2 may function as a defence mechanism against pro-apoptotic signals generated by dsRNA. These two candidate genes for T1D may thus modulate β-cell apoptosis and/or local release of inflammatory mediators in the course of a viral infection by acting, at least in part, at the pancreatic β-cell level.