Lung fibrosis is induced in ADAR2 overexpressing mice via HuR-induced CTGF signaling.

Adenosine deaminase acting on RNA 2 (ADAR2), an RNA editing enzyme is involved in a site-selective modification of adenosine (A) to inosine (I) in double-stranded RNA (dsRNA). Its role in the lungs is unknown. The phenotypic characterization of Adarb1 mice that lacked ADAR2 auto-regulation due to the deletion of editing complementary sequence (ΔECS mice) determined the functional role of ADAR2 in the lungs. ADAR2 protein expression increased in the ΔECS mice. These mice display immune cell infiltration and alveolar disorganization. The lung wet by dry ratio indicates there is no lung edema in ΔECS mice. Bronchoalveolar lavage (BAL) analysis of ΔECS mice reveals a significant increase in neutrophils. Interestingly, ΔECS mice spontaneously develop lung fibrosis as indicated by Sirius red staining of collagen fibers in the lung sections and a significant increase in hydroxyproline level in their lungs. ADAR2 expression increased significantly in a bleomycin mouse model, implicating a role of ADAR2 in lung fibrosis. Furthermore, there is a likely possibility that the genetically modified ΔECS mice does not model the physiological or pathophysiological process of lung fibrosis. Nevertheless, this model is useful in interrogating the role of ADAR2 in the lungs. The Ctgf mRNA and connective tissue growth factor (CTGF) protein significantly increased in ΔECS lungs and occurs in bronchial epithelial cells. There is a significant increase in Human antigen R (ELAVL1; HuR) protein levels in ΔECS lungs and suggests a role in stabilizing Ctgf mRNA. Lung mechanics such as total respiratory resistance, Newtonian resistance and tissue damping were increased, whereas inspiratory capacity was decreased in the ΔECS mice. Taken together, these data indicate that overexpression of ADAR2 causes spontaneous lung fibrosis via HuR-mediated CTGF signaling and implicate a role for ADAR2 auto-regulation in lung homeostasis. The identification of ADAR2 target genes in ΔECS mice would facilitate a mechanistic understanding of the role of ADAR2 in the lungs and provide a therapeutic strategy for lung fibrosis.

Neuronal CXCL10/CXCR3 Axis Mediates the Induction of Cerebral Hyperexcitability by Peripheral Viral Challenge.

Peripheral infections can potently exacerbate neuropathological conditions, though the underlying mechanisms are poorly understood. We have previously demonstrated that intraperitoneal (i.p.) injection of a viral mimetic, polyinosinic-polycytidylic acid (PIC) induces a robust generation of CXCL10 chemokine in the hippocampus. The hippocampus also features hyperexcitability of neuronal circuits following PIC challenge. The present study was undertaken to determine the role of CXCL10 in mediating the development of hyperexcitability in response to PIC challenge. Briefly, young female C57BL/6 mice were i.p. injected with PIC, and after 24 h, the brains were analyzed by confocal microscopy. CXCL10 staining of neuronal perikarya and a less intense staining of the neuropil was observed in the hippocampus and cortex. CXCL10 staining was also evident in a subpopulation of astrocytes, whereas microglia were CXCL10 negative. CXCR3, the cognate receptor of CXCL10 was present exclusively on neurons, indicating that the CXCL10/CXCR3 axis operates through an autocrine/paracrine neuronal signaling. Blocking cerebral CXCR3 through intracerebroventricular injection of a specific inhibitor, AMG487, abrogated PIC challenge-induced increase in basal synaptic transmission and long-term potentiation (LTP), as well as the reduction of paired-pulse facilitation (PPF), in the hippocampus. The PIC-mediated abolishment of hippocampal long-term depression (LTD) was also restored after administration of AMG487. Moreover, CXCR3 inhibition attenuated seizure hypersensitivity induced by PIC challenge. The efficacy of AMG487 strongly strengthens the notion that CXCL10/CXCR3 axis mediates the induction of cerebral hyperexcitability by PIC challenge.