Cellular microRNAs Repress Vesicular Stomatitis Virus but Not Theiler's Virus Replication

Modulation of Type 5 Metabotropic Glutamate Receptor-Mediated Intracellular Calcium Mobilization by Regulator of G Protein Signaling 4 (RGS4) in Cultured Astrocytes

Acting as GTPase activating proteins promoting the silencing of activated G-proteins, regulators of G protein signaling (RGSs) are generally considered negative modulators of cell signaling. In the CNS, the expression of RGS4 is altered in diverse pathologies and its upregulation was reported in astrocytes exposed to an inflammatory environment. In a model of cultured cortical astrocytes, we herein investigate the influence of RGS4 on intracellular calcium signaling mediated by type 5 metabotropic glutamate receptor (mGluR5), which is known to support the bidirectional communication between neurons and glial cells. RGS4 activity was manipulated by exposure to the inhibitor CCG 63802 or by infecting the cells with lentiviruses designed to achieve the silencing or overexpression of RGS4. The pharmacological inhibition or silencing of RGS4 resulted in a decrease in the percentage of cells responding to the mGluR5 agonist DHPG and in the proportion of cells showing typical calcium oscillations. Conversely, RGS4-lentivirus infection increased the percentage of cells showing calcium oscillations. While the physiological implication of cytosolic calcium oscillations in astrocytes is still under investigation, the fine-tuning of calcium signaling likely determines the coding of diverse biological events. Indirect signaling modulators such as RGS4 inhibitors, used in combination with receptor ligands, could pave the way for new therapeutic approaches for diverse neurological disorders with improved efficacy and selectivity.

Resilience in Long-Term Viral Infection: Genetic Determinants and Interactions

Virus-induced neurological sequelae resulting from infection by Theiler's murine encephalomyelitis virus (TMEV) are used for studying human conditions ranging from epileptic seizures to demyelinating disease. Mouse strains are typically considered susceptible or resistant to TMEV infection based on viral persistence and extreme phenotypes, such as demyelination. We have identified a broader spectrum of phenotypic outcomes by infecting strains of the genetically diverse Collaborative Cross (CC) mouse resource. We evaluated the chronic-infection gene expression profiles of hippocampi and thoracic spinal cords for 19 CC strains in relation to phenotypic severity and TMEV persistence. Strains were clustered based on similar phenotypic profiles and TMEV levels at 90 days post-infection, and we categorized distinct TMEV response profiles. The three most common profiles included "resistant" and "susceptible," as before, as well as a "resilient" TMEV response group which experienced both TMEV persistence and mild neurological phenotypes even at 90 days post-infection. Each profile had a distinct gene expression signature, allowing the identification of pathways and networks specific to each TMEV response group. CC founder haplotypes for genes involved in these pathways/networks revealed candidate response-specific alleles. These alleles demonstrated pleiotropy and epigenetic (miRNA) regulation in long-term TMEV infection, with particular relevance for resilient mouse strains.

miR-7/EGFR/MEGF9 axis regulates cartilage degradation in osteoarthritis via PI3K/AKT/mTOR signaling pathway

Osteoarthritis (OA) is a common degenerative disease in middle-aged and elderly people. Our previous study has proved that microRNA-7 (miR-7) exacerbated the OA process. This study was aimed to explore the downstream genes and mechanism regulated by miR-7 to affect OA. Multiple EGF-like-domains 9 (MEGF9) was the predicted target of miR-7 by databases. Luciferase report experiment results confirmed that MEGF9 could bind to miR-7. Among the 10 collected pairs of OA and healthy samples, the expression levels of miR-7 and MEGF9 were both up-regulated when compared with healthy subjects by qRT-PCR and immunohistochemistry (IHC). The increased MEGF9 levels were due to the interaction with epidermal growth factor receptor (EGFR) by co-immunoprecipitation. Evaluations found that upregulation of miR-7 or MEGF9 can increase the expression of EGFR, matrix metalloproteinase-13 (MMP-13) and a disintegrin like and metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS-5), so as to aggravate cartilage degradation. In addition, this effect induced by miR-7/EGFR/MEGF9 axis was by activation of PI3K/AKT signaling. The IHC and western blot assay results on OA model mice also demonstrated that miR-7/EGFR/MEGF9 axis regulated cartilage degradation in vivo. In summary, miR-7/EGFR/MEGF9 axis may perform a crucial function in the regulation of OA, providing potential for OA treatment.

Facets of Theiler's Murine Encephalomyelitis Virus-Induced Diseases: An Update

Theiler’s murine encephalomyelitis virus (TMEV), a naturally occurring, enteric pathogen of mice is a Cardiovirus of the Picornaviridae family. Low neurovirulent TMEV strains such as BeAn cause a severe demyelinating disease in susceptible SJL mice following intracerebral infection. Furthermore, TMEV infections of C57BL/6 mice cause acute polioencephalitis initiating a process of epileptogenesis that results in spontaneous recurrent epileptic seizures in approximately 50% of affected mice. Moreover, C3H mice develop cardiac lesions after an intraperitoneal high-dose application of TMEV. Consequently, TMEV-induced diseases are widely used as animal models for multiple sclerosis, epilepsy, and myocarditis. The present review summarizes morphological lesions and pathogenic mechanisms triggered by TMEV with a special focus on the development of hippocampal degeneration and seizures in C57BL/6 mice as well as demyelination in the spinal cord in SJL mice. Furthermore, a detailed description of innate and adaptive immune responses is given. TMEV studies provide novel insights into the complexity of organ- and mouse strain-specific immunopathology and help to identify factors critical for virus persistence.

Homologous recombination is an intrinsic defense against antiviral RNA interference

RNA interference (RNAi) is the major antiviral defense mechanism of plants and invertebrates, rendering the capacity to evade it a defining factor in shaping the viral landscape. Here we sought to determine whether different virus replication strategies provided any inherent capacity to evade RNAi in the absence of an antagonist. Through the exploitation of host microRNAs, we recreated an RNAi-like environment in vertebrates and directly compared the capacity of positive- and negative-stranded RNA viruses to cope with this selective pressure. Applying this defense against four distinct viral families revealed that the capacity to undergo homologous recombination was the defining attribute that enabled evasion of this defense. Independent of gene expression strategy, positive-stranded RNA viruses that could undergo strand switching rapidly excised genomic material, while negative-stranded viruses were effectively targeted and cleared upon RNAi-based selection. These data suggest a dynamic relationship between host antiviral defenses and the biology of virus replication in shaping pathogen prevalence.

Homologous recombination is an intrinsic defense against antiviral RNA interference

RNA interference (RNAi) is the major antiviral defense mechanism of plants and invertebrates, rendering the capacity to evade it a defining factor in shaping the viral landscape. Here we sought to determine whether different virus replication strategies provided any inherent capacity to evade RNAi in the absence of an antagonist. Through the exploitation of host microRNAs, we recreated an RNAi-like environment in vertebrates and directly compared the capacity of positive- and negative-stranded RNA viruses to cope with this selective pressure. Applying this defense against four distinct viral families revealed that the capacity to undergo homologous recombination was the defining attribute that enabled evasion of this defense. Independent of gene expression strategy, positive-stranded RNA viruses that could undergo strand switching rapidly excised genomic material, while negative-stranded viruses were effectively targeted and cleared upon RNAi-based selection. These data suggest a dynamic relationship between host antiviral defenses and the biology of virus replication in shaping pathogen prevalence.