Increased levels of type I interferon (IFN) and type I IFN-regulated genes are found in patients with systemic lupus erythematosus (SLE) and may be central to its pathogenesis. Mitochondrial antiviral signaling protein (MAVS) is a key regulator of type I IFN that undergoes a dramatic prion-like aggregation and self propagates the activation signal from viral RNA to amplify downstream IFN production. We undertook this study to determine whether such MAVS aggregates might play a role in the sustained increased production of type I IFN in SLE.
Peripheral blood mononuclear cells were isolated and mitochondrial extracts were prepared. MAVS aggregation was detected by semidenatured agarose gel electrophoresis and confirmed by immunofluorescence staining. MAVS-associated signaling proteins were analyzed by Western blotting. MAVS aggregation-associated gene expression signature was analyzed by microarray.
In blood cells from 22 of 67 SLE patients, essentially all MAVS was in a high molecular weight aggregated form. None of 6 rheumatoid arthritis patients and only 3 of 33 healthy controls had abnormal MAVS. Compared to MAVS aggregate-negative patients, MAVS aggregate-positive SLE patients had significantly higher serum levels of IFNβ and significantly increased levels of autoantibodies against Sm and U1 RNP. Gene array data revealed a characteristic gene expression pattern in these patients, with altered expression of genes involved in IFN signaling and membrane trafficking.
Persistent MAVS aggregates may lead to increased type I IFN production and result in unmitigated signals leading to autoimmunity.