Painter, Meghan M.

Abstract Our laboratory generated a transgenic mouse that ubiquitously expresses 3D, a picorno viral RNA-dependent RNA polymerase. 3D transgenic mice display an extreme antiviral phenotype when challenged with viruses from distinct families. To probe this protective molecular mechanism, we assayed differential gene expression in tissues of uninfected 3D transgenic mice. Microarray analysis revealed increased levels of 78 genes >4-fold, including a distinct upregulation of critical innate antiviral effectors across tissues. RT-PCR analysis of liver, lung, kidney, CNS and heart tissue from uninfected 3D mice showed a significant upregulation of antiviral genes (up to 300-fold). Following infection with EMCV, 3D transgenic mice exhibited significantly decreased viral tissue titers and survived lethal viral infection. This effect is specific to the 3D transgene since other mice expressing the picorno viral transgenes VP1 or VP2 did not display an antiviral phenotype. Studies of 3D-Ifnar1-/- or 3D-Ifngr1-/- mice, supported the conclusion that type I IFN signaling is necessary for the antiviral state in 3D mice, whereas IFNg signaling is dispensable. Maintenance of a viral-resistant state in uninfected 3D mice is independent of adaptive immunity since uninfected 3D-Rag1-/- mice are able to highly upregulate antiviral factors. Collectively, our data indicate that intrinsic upregulation of critical innate immune effectors confers broad-spectrum viral resistance in 3D mice.

Triggering receptor expressed on myeloid cells 2 (TREM2) is an innate immune receptor expressed in microglia in the brain. A soluble form of TREM2 (sTREM2) derived from proteolytic cleavage of the cell surface receptor is increased in the preclinical stages of AD and positively correlates with the amounts of total and phosphorylated tau in the cerebrospinal fluid. However, the physiological and pathological functions of sTREM2 remain unknown. Here, we show that sTREM2 promotes microglial survival in a PI3K/Akt-dependent manner and stimulates the production of inflammatory cytokines depending on NF-κB. Variants of sTREM2 carrying AD risk-associated mutations were less potent in both suppressing apoptosis and triggering inflammatory responses. Importantly, sTREM2 delivered to the hippocampi of both wild-type and Trem2-knockout mice elevated the expression of inflammatory cytokines and induced morphological changes of microglia. Collectively, these data indicate that sTREM2 triggers microglial activation inducing inflammatory responses and promoting survival. This study has implications for the pathogenesis of AD and provides insights into targeting sTREM2 pathway for AD therapy.

AbstractCNSregeneration is a desirable goal for diseases of brain and spinal cord. Current therapeutic strategies for the treatment of multiple sclerosis (MS) aim to eliminate detrimental effects of the immune system, so far without reversing disability or affecting long‐term prognosis in patients. Approachable molecular targets that stimulateCNSrepair are not part of the clinical praxis or have not been identified yet. The purpose of this study was to identify the molecular target of the human monoclonal antibodyHIgM12.HIgM12 reverses motor deficits in chronically demyelinated mice, a model ofMS. Here, we identified polysialic acid (PSA) attached to the neural cell adhesion molecule (NCAM) as the antigen forHIgM12 by using differentNCAMknockout strains and throughPSAremoval from theNCAMprotein core. Antibody binding toCNStissue and primary cells, antibody‐mediated cell adhesion, and neurite outgrowth onHIgM12‐coated nitrocellulose was detected only in the presence ofPSAas assessed by western blotting, immunoprecipitation, immunocytochemistry, and histochemistry. We conclude thatHIgM12 mediates it'sin vivoandin vitroeffects through binding toPSAand has the potential to be an effective therapy forMSand neurodegenerative diseases.imageThe human antibody HIgM12 stimulates neurite outgrowthin vitroand promotes function in chronically demyelinated mice, a model of multiple sclerosis. The cellular antigen for HIgM12 was undetermined. Here, we identified polysialic acid attached to NCAM (neural cell adhesion molecule) as the cellular target for HIgM12. This includes glial fibrillary acidic protein (GFAP)‐positive mouse astrocytes (GFAP, red; HIgM12, green; DAPI, blue) among other cell types of the central nervous system. These findings indicate a new strategy for the treatment of neuro‐motor disorders including multiple sclerosis.