Abstract Body: Proinflammatory cytokines significantly contribute to the initiation and propagation of inflammation and to impaired functional recovery in neuroinflammatory diseases. We identified that microglia express and secrete interferon alpha-inducible protein 27 like 2A (Ifi27l2a) in response to inflammatory signals. However, the functional role of Ifi27l2a in inflammation has not been well defined. Through a combination of cell culture and in vivo mouse models, we now demonstrate that Ifi27l2a acts as a novel hub protein that regulates proinflammatory responses in microglia.
Methods: Endotoxemia was induced by LPS administration in aged mice to determine the subsequent circulating Ifi27l2a protein levels in the plasma. Sim-A9 cells and primary microglia were stimulated with recombinant Ifi27l2a (rIfi27l2a) at concentrations of 10 and 100 ng/ml to investigate whether Ifi27l2a promotes mitochondrial dysfunction and conversion of microglial phenotype. RNA-seq was performed on primary microglia to define transcriptional changes induced by Ifi27l2a as well as alterations in cellular signaling associated with proinflammatory microglia.
Results: Systemic injection of LPS increased circulating Ifi27l2a protein levels in the plasma of aged mice (Veh: 38.1, LPS: 122.1 pg/ml, n=4-5, p<0.05). To investigate how exogenous Ifi27l2a modulates microglial phenotypic changes, we treated microglia to rIfi27l2a. Reactive oxygen species (ROS) levels were elevated by rIfi27l2a treatment in both Sim-A9 and primary microglia (n=6-8, p<0.05). Notably, treatment with rIfi27l2a increased the ATP production, which LPS did not, as assessed by Seahorse cell analysis (n=10-21, p<0.05). In addition, inflammation marker genes (Il1b, Tnfa, and Mmp9) were significantly elevated in rIfi27l2a-treated microglia compared to the control. Transcriptional analysis of rIfi27l2a treatment with RNA-seq (n=5) revealed that a set of proinflammatory genes, including Mmps, were highly upregulated. The data also showed that microglial phagocytosis-related genes and disease-associated microglia (DAM)-related genes were suppressed by rIfi27l2a.
Conclusions: These data suggest a novel role for Ifi27l2a in brain inflammation through the shifting of microglia toward a proinflammatory phenotype and away from the reparative DAM phenotype. We propose that selective disruption of Ifi27l2a signaling may provide a new therapeutic strategy to reduce harmful inflammation and improve functional outcome following stroke.