Metformin is the most commonly prescribed medication for type 2 diabetes, owing to its glucose-lowering effects, which are mediated through the suppression of hepatic glucose production (reviewed in refs. 1-3). However, in addition to its effects on the liver, metformin reduces appetite and in preclinical models exerts beneficial effects on ageing and a number of diverse diseases (for example, cognitive disorders, cancer, cardiovascular disease) through mechanisms that are not fully understood 1-3. Given the high concentration of metformin in the liver and its many beneficial effects beyond glycemic control, we reasoned that metformin may increase the secretion of a hepatocyte-derived endocrine factor that communicates with the central nervous system 4. Here we show, using unbiased transcriptomics of mouse hepatocytes and analysis of proteins in human serum, that metformin induces expression and secretion of growth differentiating factor 15 (GDF15). In primary mouse hepatocytes, metformin stimulates the secretion of GDF15 by increasing the expression of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP; also known as DDIT3). In wild-type mice fed a high-fat diet, oral administration of metformin increases serum GDF15 and reduces food intake, body mass, fasting insulin and glucose intolerance; these effects are eliminated in GDF15 null mice. An increase in serum GDF15 is also associated with weight loss in patients with type 2 diabetes who take metformin. Although further studies will be required to determine the tissue source(s) of GDF15 produced in response to metformin in vivo, our data indicate that the therapeutic benefits of metformin on appetite, body mass and serum insulin depend on GDF15. Metformin is one of the most widely used medications in the world. It is a strong base that exists in its protonated form at physiological pH and therefore does not pass through cellular membranes easily. In rodents, oral administration of metformin (250-300 mg kg-1 body weight) results in clinically relevant plasma concentrations of approximately 10-15 μM; however, concentrations in the

S evere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in December 2019 in Wuhan, China (1). SARS-CoV-2 has since spread to ≈185 countries and infected ≈6 million persons, among whom ≈380,000 have died (2). On January 23, 2020, a case of coronavirus disease (COVID-19) was detected in Toronto, Canada (3); since then, multiple cases have been identified across Canada. As SARS-CoV-2 spreads globally, the virus is likely to adapt and evolve. It is critical to isolate SARS-CoV-2 viruses to characterize their ability to infect and replicate in multiple human cell types and to determine if the virus is evolving in its ability to infect human cells and cause severe disease. Isolating the virus also provides the opportunity to share the virus with other researchers for development and testing of diagnostics, drugs, and vaccines. We isolated SARS-CoV-2 from 2 patients with COVID-19 and determined the genomic sequence of each isolate (SARS-CoV-2/SB2 and SARS-CoV-2/ SB3-TYAGNC). In addition, we studied the replication kinetics of SARS-CoV-2/SB3-TYAGNC in human fibroblast, epithelial, and immune cells. Methods Cells We maintained Vero E6 cells (African green monkey cells; American Type Culture Collection [ATCC], https://www.atcc.org) in Dulbecco's modified Eagle medium (DMEM) supplemented with 10% fetal bovine serum (FBS) (Sigma-Aldrich, https://www.sigmaaldrich.com) and 1× l-glutamine and penicillin/ streptomycin (Pen/Strep; Corning, https://ca.vwr. com). Calu-3 cells (human lung adenocarcinoma derived; ATCC) were cultured as previously mentioned (4), as were THF cells (human telomerase lifeextended cells) (5). THP-1 cells (monocytes; ATCC) were cultured in RPMI medium (Gibco Laboratories, https://www.thermofisher.com) supplemented with 10% FBS, 2mM l-glutamine, 1× penicillin/

The emergence of a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and more recently, the independent evolution of multiple SARS-CoV-2 variants has generated renewed interest in virus evolution and cross-species transmission. While all known human coronaviruses (HCoVs) are speculated to have originated in animals, very little is known about their evolutionary history and factors that enable some CoVs to co-exist with humans as low pathogenic and endemic infections (HCoV-229E, HCoV-NL63, HCoV-OC43, HCoV-HKU1), while others, such as SARS-CoV, MERS-CoV and SARS-CoV-2 have evolved to cause severe disease. In this review, we highlight the origins of all known HCoVs and map positively selected for mutations within HCoV proteins to discuss the evolutionary trajectory of SARS-CoV-2. Furthermore, we discuss emerging mutations within SARS-CoV-2 and variants of concern (VOC), along with highlighting the demonstrated or speculated impact of these mutations on virus transmission, pathogenicity, and neutralization by natural or vaccine-mediated immunity.

Type VI secretion systems (T6SSs) deliver antibacterial effector proteins between neighboring bacteria. Many effectors harbor N-terminal transmembrane domains (TMDs) implicated in effector translocation across target cell membranes. However, the distribution of these TMD-containing effectors remains unknown. Here, we discover prePAAR, a conserved motif found in over 6000 putative TMD-containing effectors encoded predominantly by 15 genera of Proteobacteria. Based on differing numbers of TMDs, effectors group into two distinct classes that both require a member of the Eag family of T6SS chaperones for export. Co-crystal structures of class I and class II effector TMD-chaperone complexes from Salmonella Typhimurium and Pseudomonas aeruginosa, respectively, reveals that Eag chaperones mimic transmembrane helical packing to stabilize effector TMDs. In addition to participating in the chaperone-TMD interface, we find that prePAAR residues mediate effector-VgrG spike interactions. Taken together, our findings reveal mechanisms of chaperone-mediated stabilization and secretion of two distinct families of T6SS membrane protein effectors.

Highlights SARS-CoV-2 induces the expression of type I IFNs in human lung cells Moderate cases of COVID-19 have higher serum levels of IL-10 and IFNa Severe cases of COVID-19 have higher serum levels of IL-6, TNFa and IL-8 Physiological levels of IFNa reduces SARS-CoV-2 replication in human airway cells