Recently, the SARS-CoV-2 induced disease COVID-19 has spread all over the world. Nearly 20% of the patients have severe or critical conditions. SARS-CoV-2 exploits ACE2 for host cell entry. ACE2 plays an essential role in the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance. ACE2 also protects organs from inflammatory injuries and regulates intestinal functions. ACE2 can be shed by two proteases, ADAM17 and TMPRSS2. TMPRSS2-cleaved ACE2 allows SARS-CoV-2 cell entry, whereas ADAM17-cleaved ACE2 offers protection to organs. SARS-CoV-2 infection-caused ACE2 dysfunction worsens COVID-19 and could initiate multi-organ failure. Here, we will explain the role of ACE2 in the pathogenesis of severe and critical conditions of COVID-19 and discuss auspicious strategies for controlling the disease.Viruses 2020, 12, 491 2 of 10 Profile of ACE2Human angiotensin-converting enzyme-related carboxypeptidase ACE2 is encoded by the ACE2 gene which maps to chromosome Xp22 [6]. ACE2 is a type I transmembrane protein, comprised of an extracellular heavily N-glycosylated N-terminal domain containing the carboxypeptidase site and a short intracellular C-terminal cytoplasmic tail [7]. The N-terminal peptidase domain is also the SARS-CoV binding site [8]. There are two forms of ACE2 protein: cellular (membrane-bound) form and circulating (soluble) form. Cellular ACE2 protein is the full-length protein which is expressed abundantly in pneumocytes and enterocytes of the small intestine [9]. ACE2 is also expressed in vascular endothelial cells of the heart, the kidneys, and other organs, such as the brain. However, ACE2 is absent in the spleen, thymus, lymph nodes, bone marrow, and cells of the immune system (including B and T lymphocytes, and macrophages) [10,11].Circulating ACE2 (with the N-terminal peptidase domain) is cleaved from the full-length ACE2 on the cell membrane by the metalloprotease ADAM17 and then released into the extracellular environment [7]. The type II transmembrane serine protease, TMPRSS2 was found to compete with ADAM17 for ACE2 shedding but cleaves ACE2 differently. Both ADAM17 and TMPRSS2 remove a short C-terminal fragment from ACE2. Arginine and lysine residues within amino acids 652 to 659 are critical for ADAM17 shedding, whereas arginine and lysine residues within amino acids 697 to 716 are essential for TMPRSS2 shedding. Only cleavage by TMPRSS2 results in augmented SARS-CoV cell entry [12][13][14][15]. There are two ways for SARS-CoV to enter the target cell: endocytosis, and fusion of the viral membrane with a membrane of the target cell, which is 100 times more efficient than endocytosis for viral replication [16]. With the help of TMPRSS2, ADAM17-regulated ectodomain shedding of ACE2 could induce SARS-CoV cell entry through endocytosis [7,12]; however, ADAM17 activity is not required for SARS-CoV cell entry through fusion [12]. As the N-terminal domain is the coronavirus binding site, circulating ACE2 also binds to the virus. Iwata-Yoshikawa et al. infected both ...

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Background: Respiratory syncytial virus (RSV) frequently causes acute lower respiratory infection in children under 5, representing a high burden in Gavi-eligible countries (mostly low-income and lower-middle-income). Since multiple RSV interventions, including vaccines and monoclonal antibody (mAb) candidates, are under development, we aim to evaluate the key drivers of the cost-effectiveness of maternal vaccination and infant mAb for 72 Gavi countries. Methods: A static Multi-Country Model Application for RSV Cost-Effectiveness poLicy (MCMARCEL) was developed to follow RSV-related events monthly from birth until 5 years of age. MCMARCEL was parameterised using countryand age-specific demographic, epidemiological, and cost data. The interventions' level and duration of effectiveness were guided by the World Health Organization's preferred product characteristics and other literature. Maternal vaccination and mAb were assumed to require single-dose administration at prices assumed to align with other Gavi-subsidised technologies. The effectiveness and the prices of the interventions were simultaneously varied in extensive scenario analyses. Disability-adjusted life years (DALYs) were the primary health outcomes for cost-effectiveness, integrated with probabilistic sensitivity analyses and Expected Value of Partially Perfect Information analysis.

The gut-liver axis is associated with the progression of non-alcoholic fatty liver disease (NAFLD). Targeting the gut-liver axis and bile acid-based pharmaceuticals are potential therapies for NAFLD. The effect of tauroursodeoxycholic acid (TUDCA), a candidate drug for NAFLD, on intestinal barrier function, intestinal inflammation, gut lipid transport and microbiota composition was analysed in a murine model of NAFLD. EXPERIMENTAL APPROACHThe NAFLD mouse model was established by feeding mice a high-fat diet (HFD) for 16 weeks. TUDCA was administered p.o. during the last 4 weeks. The expression levels of intestinal tight junction genes, lipid metabolic and inflammatory genes were determined by quantitative PCR. Tissue inflammation was evaluated by haematoxylin and eosin staining. The gut microbiota was analysed by 16S rRNA gene sequencing. KEY RESULTSTUDCA administration attenuated HFD-induced hepatic steatosis, inflammatory responses, obesity and insulin resistance in mice. Moreover, TUDCA attenuated gut inflammatory responses as manifested by decreased intestinal histopathology scores and inflammatory cytokine levels. In addition, TUDCA improved intestinal barrier function by increasing levels of tight junction molecules and the solid chemical barrier. The components involved in ileum lipid transport were also reduced by TUDCA administration in HFD-fed mice. Finally, the TUDCA-treated mice showed a different gut microbiota composition compared with that in HFD-fed mice but similar to that in normal chow diet-fed mice. CONCLUSIONS AND IMPLICATIONSTUDCA attenuates the progression of HFD-induced NAFLD in mice by ameliorating gut inflammation, improving intestinal barrier function, decreasing intestinal fat transport and modulating intestinal microbiota composition. Abbreviations ACOX1, peroxisomal acyl-CoA oxidase 1; ANOSIM, analysis of similarities; C3GNT, core 3β1,3-N-acetyl glucosaminyltransferase; CYP7a, cholesterol 7α-hydroxylase; ER, endoplasmic reticulum; FABP, fatty acid-binding protein; FATP4, fatty acid transport protein 4; FAR3, fatty acid receptor 3; H&E, haematoxylin and eosin; HFD, high-fat diet; HOMA-IR, homeostasis model assessment of the insulin resistance index; Iap, intestinal alkaline phosphatase; ICAM1, intercellular cell adhesion molecule-1; IPGTT, i.p. glucose tolerance test; IPITT, i.p. insulin tolerance test; Irak4, IL-1 receptor-associated kinase 4; JAM, junctional adhesion molecule; Lcad, long-chain acyl-CoA dehydrogenase; NAFLD, non-alcoholic fatty liver disease; NAS, non-alcoholic fatty liver disease activity score; NASH, non-alcoholic steatohepatitis; NCD, normal chow diet; OTU, operational taxonomic unit; PCoA, principal coordinates analysis; Tab1, TGF-β activated kinase 1 mitogen-activated protein kinase kinase kinase 7-binding protein 1; TC, total cholesterol; TEERs, transepithelial electrical resistances; TGs, triglycerides; TLR, toll-like receptor; Tram, toll or IL-1 receptor domain-containing adaptor inducing IFN-β-related adaptor molecule; TUDCA, tauroursodeoxycholic acid; UDCA...