No abstract

Polymyxins are the last line of defense against lethal infections caused by multidrug resistant Gram-negative pathogens. Very recently, the use of polymyxins has been greatly challenged by the emergence of the plasmid-borne mobile colistin resistance gene (mcr-1). However, the mechanistic aspects of the MCR-1 colistin resistance are still poorly understood. Here we report the comparative genomics of two new mcr-1-harbouring plasmids isolated from the human gut microbiota, highlighting the diversity in plasmid transfer of the mcr-1 gene. Further genetic dissection delineated that both the trans-membrane region and a substrate-binding motif are required for the MCR-1-mediated colistin resistance. The soluble form of the membrane protein MCR-1 was successfully prepared and verified. Phylogenetic analyses revealed that MCR-1 is highly homologous to its counterpart PEA lipid A transferase in Paenibacili, a known producer of polymyxins. The fact that the plasmid-borne MCR-1 is placed in a subclade neighboring the chromosome-encoded colistin-resistant Neisseria LptA (EptA) potentially implies parallel evolutionary paths for the two genes. In conclusion, our finding provids a first glimpse of mechanism for the MCR-1-mediated colistin resistance.

The outbreak of 2019-nCoV in the central Chinese city of Wuhan at the end of 2019 poses unprecedent public health challenges to both China and the rest world 1 . The new coronavirus shares high sequence identity to SARS-CoV and a newly identified bat coronavirus 2 . While bats may be the reservoir host for various coronaviruses, whether 2019-nCoV has other hosts is still ambiguous. In this study, one coronavirus isolated from Malayan pangolins showed 100%, 98.2%, 96.7% and 90.4% amino acid identity with 2019-nCoV in the E, M, N and S genes, respectively. In particular, the receptor-binding domain of the S protein of the Pangolin-CoV is virtually identical to that of 2019-nCoV, with one amino acid difference. Comparison of available genomes suggests 2019-nCoV might have originated from the recombination of a Pangolin-CoV-like virus with a Bat-CoV-RaTG13-like virus. Infected pangolins showed clinical signs and histopathological changes, and the circulating antibodies reacted with the S protein of 2019-nCoV.

Cellular senescence is associated with renal disease progression, and accelerated tubular cell senescence promotes the pathogenesis of renal fibrosis. However, the underlying mechanism is unknown. We assessed the potential role of Wnt9a in tubular cell senescence and renal fibrosis. Compared with tubular cells of normal subjects, tubular cells of humans with a variety of nephropathies and those of several mouse models of CKD expressed high levels of Wnt9a that colocalized with the senescence-related protein p16 Wnt9a expression level correlated with the extent of renal fibrosis, decline of eGFR, and expression of p16 Furthermore, ectopic expression of Wnt9a after ischemia-reperfusion injury (IRI) induced activation of -catenin and exacerbated renal fibrosis. Overexpression of Wnt9a exacerbated tubular senescence, evidenced by increased detection of p16 expression and senescence-associated -galactosidase activity. Conversely, shRNA-mediated knockdown of Wnt9a repressed IRI-induced renal fibrosis and impeded the growth of senescent tubular epithelial cells in culture. Notably, Wnt9a-induced renal fibrosis was inhibited by shRNA-mediated silencing of p16 in the IRI mouse model. In a human proximal tubular epithelial cell line and primary renal tubular cells, Wnt9a remarkably upregulated levels of senescence-related p16, p19, p53, and p21 and decreased the phosphorylation of retinoblastoma protein. Wnt9a also induced senescent tubular cells to produce TGF-1, which promoted proliferation and activation in normal rat kidney fibroblasts. Thus, Wnt9a drives tubular senescence and fibroblast activation. Furthermore, the Wnt9a-TGF- pathway appears to create a reciprocal activation loop between senescent tubular cells and activated fibroblasts that promotes and accelerates the pathogenesis of renal fibrosis.