The Arenaviridae is a large family of viruses causing both acute and persistent infections and causing significant public health concerns in afflicted regions. A "trademark" of infection is the quick and efficient immuno-suppression mediated in part by a 3'-5' RNA exonuclease domain (ExoN) of the Nucleoprotein (NP). Mopeia virus, the eastern African counterpart of Lassa virus, carries such ExoN domain, but does not suppress the host innate immunity. We have recently reported the crystal structure of the Mopeia virus ExoN domain, which presents a conserved fold and active site. In the present study, we show that the ExoN activity rules out a direct link between ExoN activity and alteration of the host innate immunity. We found that the Arenavirus ExoN, however, is able to excise mis-incorporated bases present at the 3'-end of double stranded RNA.ExoN(-) arenaviruses cultured in cells dampened in innate immunity still replicated in spite of a significant reduction in the viral charge over several passages. The remaining ExoN(-) virus population showed an increased base substitution rate on a narrow nucleotide spectrum, linking the ExoN activity to genome editing. Since, the Arenavirus ExoN belongs to the same nuclease family as that of the nsp14 coronavirus ExoN ; which has been recently shown to promote viral RNA synthesis proofreading; we propose that Arenavirus ExoN is involved in a "limited RNA editing" mechanism mainly controlled by structural constraints and a low mutational/fitness ratio.

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Experimental and clinical studies reported that type 2 diabetes mellitus (T2DM) is associated with cognitive dysfunction and promotes the onset of dementia. Metformin is an antihyperglycemic drug used for the treatment of T2DM. A growing number of evidence revealed neuroprotective, antioxidant, and anti-inflammation effects exerted by metformin. The present study aimed to investigate the effect of metformin on cognitive function, systemic proinflammatory cytokines and amyloid-beta 1-42 (Aβ1-42) which is a pathological hallmark of Alzheimer’s disease (AD) in diabetic mice. C57BL/6N mice were divided into the following experimental groups: normal control group (NC); diabetes mellitus group (DM) induced by a high-fat diet combined with streptozotocin (STZ) injection; diabetes mellitus treated with metformin 100 mg/kg (DM+Met). Cognitive performance was evaluated by the novel object recognition test (NORT). Systemic proinflammatory cytokines and Aβ1-42 were assessed by the enzyme-linked immunosorbant assay (ELISA) test. We found that diabetic mice exhibited cognitive impairment in NORT whereas the treatment with metformin restored the cognitive function of diabetic mice. Moreover, diabetic mice presented an increase in plasma IL-6 and TNF-α levels while Aβ1-42 was decreased when compared to NC mice. Nevertheless, the administration of metformin allowed the levels of plasma IL-6, TNF-α, and Aβ1-42 to normalize in diabetic mice. Taken together, our findings suggest that metformin improves the cognitive function of diabetic mice possibly via the modulation of plasma pro-inflammatory cytokines and Aβ1-42 levels. Metformin may potentially be used as a therapeutic agent for patients with T2DM who show cognitive deficits. Keywords: Diabetes mellitus, Cognitive impairments, Pro-inflammatory cytokines, Amyloid-beta, Metformin