Mutations during the adaptation of H7N9 avian influenza virus to mice lungs enhance human-like sialic acid binding activity and virulence in mice.

The first avian H7N9 influenza outbreak in spring of 2013 emerged in an unprecedented transmission from infected poultry to humans in the Yangtze delta area, eastern China, posing a dual challenge to public health and poultry industry. However, the mechanism for how avian H7N9 influenza virus adapts to mammalian hosts has not been clearly understood. Here, to identify adaptive changes that confer enhanced virulence of H7N9 virus in mammals, we generated a mouse-adapted H7N9 variant virus (S8) by serial lung-to-lung passages of the wild-type SDL124 virus in mice and compared their phenotype in vivo and in vitro. Sequence analysis showed that the two viruses differed by 27 amino acids distributed among six genes, containing changes in PB2 (E627K, D701N) and HA (Q226L) genes. The 50% mouse lethal dose (MLD50) of S8 reduced about 500 folds, to be moderately pathogenic to mice when compared to that of low pathogenic wild-type SDL124. Moreover, S8 replicated efficiently in mouse lungs and displayed expanded tissue tropism, and induced a greater degree of pulmonary edema and higher level of inflammatory cell infiltration in bronchoalveolar lavage fluids than SDL124 did. Interestingly, the mouse adapted S8 virus obtained strong affinity for human-like (SAα-2,6 Gal) receptor during the adaptation in mice. Correspondingly, compared with SDL124 virus, S8 virus showed higher replication efficiency in mammalian cells, whereas lower replication ability in avian cells. Taken together, these findings suggest that these mutations synergistically elevate the ability of H7N9 virus to disseminate to multiple organs and subsequently enhance the virulence of H7N9 virus in mammalian hosts.

Transcriptional regulation of the human, porcine and bovine OCTN2 gene by PPARα via a conserved PPRE located in intron 1.

BACKGROUND: The novel organic cation transporter 2 (OCTN2) is the physiologically most important carnitine transporter in tissues and is responsible for carnitine absorption in the intestine, carnitine reabsorption in the kidney and distribution of carnitine between tissues. Genetic studies clearly demonstrated that the mouse OCTN2 gene is directly regulated by peroxisome proliferator-activated receptor α (PPARα). Despite its well conserved role as an important regulator of lipid catabolism in general, the specific genes under control of PPARα within each lipid metabolic pathway were shown to differ between species and it is currently unknown whether the OCTN2 gene is also a PPARα target gene in pig, cattle, and human. In the present study we examined the hypothesis that the porcine, bovine, and human OCTN2 gene are also PPARα target genes. RESULTS: Using positional cloning and reporter gene assays we identified a functional PPRE, each in the intron 1 of the porcine, bovine, and human OCTN2 gene. Gel shift assay confirmed binding of PPARα to this PPRE in the porcine, bovine, and the human OCTN2 gene. CONCLUSIONS: The results of the present study show that the porcine, bovine, and human OCTN2 gene, like the mouse OCTN2 gene, is directly regulated by PPARα. This suggests that regulation of genes involved in carnitine uptake by PPARα is highly conserved across species.