Mononuclear cell infiltration and type I interferon (IFN) system activation play an important role in primary Sjögren's syndrome (SS). We undertook this study to investigate the mechanism of poly(ADP-ribose) polymerase family member 9 (PARP-9) on mononuclear cell infiltration triggered by type I IFN.
A proteomic study was conducted in peripheral blood mononuclear cells from patients with primary SS (n = 30) and healthy controls (n = 30) to determine differentially expressed proteins (DEPs) (P < 0.05; fold change >1.20). Labial salivary glands (LSGs) were isolated for hematoxylin and eosin staining and immunohistochemical analysis. CD19+ B cells were purified by magnetic cell sorting for immunofluorescence staining, lentivirus-PARP-9 transfection, and IFNα treatment experiments. PARP-9 small interfering RNA (siRNA) and DTX3L siRNA were delivered into female NOD/LtJ female mice to determine their effect.
The overexpression of PARP-9 and CXCL10 as well as their colocalization was confirmed in primary SS. PARP-9 levels in LSGs rose with increased Chisholm scores in patients with primary SS. PARP-9 and DTX3L were present in the infiltrating mononuclear cells from salivary glands in female NOD/LtJ mouse models. Additionally, Ingenuity Pathway Analysis networks of DEPs demonstrated that PARP-9, STAT1, and IFN-induced protein with tetratricopeptide repeats 1 (IFIT-1) participated in the IFN-related pathway. Furthermore, PARP-9 could up-regulate the expression of IFIT1 and CXCL10 in B cells. Moreover, PARP-9 and CXCL10 could be induced by IFNα in B cells.
This study is the first to implicate PARP-9 as a regulator of infiltration of mononuclear cells in primary SS progression and to reveal that PARP-9 increases CXCL10 expression through up-regulating IFIT-1, which is mediated by the phosphorylation of STAT1. PARP-9 might therefore be a novel therapeutic target for primary SS.