Comparative whole genome analysis of dengue virus serotype-2 strains differing in trans-endothelial cell leakage induction in vitro.

The role of genetic differences among dengue virus (DENV) in causing increased microvascular permeability is less explored. In the present study, we compared two closely related DENV serotype-2 strains of Cosmopolitan genotype for their in vitro infectivity phenotype and ability to induce trans-endothelial leakage. We found that these laboratory strains differed significantly in infecting human microvascular endothelial cells (HMEC-1) and hepatocytes (Huh7), two major target cells of DENV in in vivo infections. There was a reciprocal correlation in infectivity and vascular leakage induced by these strains, with the less infective strain inducing more trans-endothelial cell leakage in HMEC-1 monolayer upon infection. The cells infected with the strain capable of inducing more permeability were found to secrete more Non-Structural protein (sNS1) into the culture supernatant. A whole genome analysis revealed 37 predicted amino acid changes and changes in the secondary structure of 3' non-translated region between the strains. But none of these changes involved the signal sequence coded by the C-terminal of the Envelope protein and the two glycosylation sites within the NS1 protein critical for its secretion, and the N-terminal NS2A sequence important for surface targeting of NS1. The strain that secreted lower levels of NS1 and caused less leakage had two mutations within the NS1 protein coding region, F103S and T146I that significantly changed amino acid properties. A comparison of the sequences of the two strains with published sequences of various DENV strains known to cause clinically severe dengue identified a number of amino acid changes which could be implicated as possible key genetic differences. Our data supports the earlier observations that the vascular leakage induction potential of DENV strains is linked to the sNS1 levels. The results also indicate that viral genetic determinants, especially the mutations within the NS1 coding region, could affect this critical phenotype of DENV strains.