Association between Type I interferon and depletion and dysfunction of endothelial progenitor cells in C57BL/6 mice deficient in both apolipoprotein E and Fas ligand

Patients with systemic lupus erythematosus (SLE) have a tremendously increased risk for cardiovascular disease (CVD), which could not be accounted in entirety by traditional Framingham risk factors. To study whether the accelerated atherosclerosis in SLE patients is mediated by type I interferon (IFN-I) through the regulation of endothelial progenitor cells (EPCs), we created a line of C57BL/6 mice with deficiency in both apolipoprotein E (ApoE−/−) and fas ligand (FasL−/−, gld.). As expected, the resultant gld. ApoE−/− mice exhibited both aggravated lupus-like disease and atherosclerosis under normal diet. Increased expression of IFN-I-stimulated genes (ISGs) was closely associated with depletion and dysfunction of EPCs, as well as with accelerated atherosclerotic lesion in gld. ApoE−/− mice. While only IFN-α instead of other interventions, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IRS423 and IRS661, impaired EPC function in vitro. Mechanistically, activation or inhibition of the TLR7/9 signaling could modulate EPC number and function in vivo. Decreased proliferation rate and increased apoptotic rate of EPCs induced by IFN-α might contribute to the results to a certain extent. Thus, our data suggest that excessive expression of IFN-I through the activation of TLR7/9 signaling may induce accelerated atherosclerosis in lupus through the depletion or dysfunction of EPCs, suggesting that targeting IFN-I might have potential therapeutic effects on both lupus disease and premature atherosclerosis in SLE patients.