Effect of severe bioprosthetic valve tissue ingrowth and inflow calcification on valve-in-valve performance
JOURNAL OF BIOMECHANICS
Authors: Hatoum, Hoda; Dollery, Jennifer; Lilly, Scott M.; Crestanello, Juan A.; Dasi, Lakshmi Prasad
Abstract
While in vivo studies clearly demonstrate that supra-annular Valve-in-Valve (ViV) implantation provides the highest probability for optimal post-ViV pressure gradients (PG), there is still no physical insight into explaining anomalies where some supra-annular ViV implantations yield high pressure gradients while some sub-annular implantations yield low pressure gradients. The aim of this study is to explain how severe tissue ingrowth and calcification (TIC) in a surgical aortic valve (SAV) can be one physical mechanism leading to anomalous ViV performance characteristic. The ViV hemodynamic performance was evaluated as a function of axial positioning -9.8, -6.2, 0, and +6 mm in SAVs with and without TIC. Effective orifice area (EOA) and PG were compared. Leaflet high-speed imaging and particle image velocimetry were performed to elucidate flutter and forward jet characteristics. ViV without TIC showed significantly lower PG and greater EOA (p < 0.01). EOA and PG improve with supra-annular deployment (p < 0.01) while for ViV with TIC, EOA and PG worsen as the deployment varies from -9.8 mm to 0 mm (p < 0.01) only to recover at + 6 mm (p < 0.01). Separated jet flow at the TIC site, and consequently induced stronger TAV leaflet fluttering highlight the dynamic compromising nature of TIC on jet width and performance reduction. We conclude that the inflow TIC greatly influence ViV performance due to dynamic effects that results in a real anomalous performance characteristic different than that seen in most ViV in vivo. Further in vivo studies are needed to evaluate ViV outcomes in the presence of severe TIC in SAVs. (C) 2018 Elsevier Ltd. All rights reserved.
Cauliflower mosaic virus transactivator protein (TAV) can suppress nonsense-mediated decay by targeting VARICOSE, a scaffold protein of the decapping complex
SCIENTIFIC REPORTS
Authors: Lukhovitskaya, Nina; Ryabova, Lyubov A.
Abstract
During pathogenesis, viruses hijack the host cellular machinery to access molecules and subcellular structures needed for infection. We have evidence that the multifunctional viral translation transactivator/viroplasmin (TAV) protein from Cauliflower mosaic virus (CaMV) can function as a suppressor of nonsense-mediated mRNA decay (NMD). TAV interacts specifically with a scaffold protein of the decapping complex VARICOSE (VCS) in the yeast two-hybrid system, and co-localizes with components of the decapping complex in planta. Notably, plants transgenic for TAV accumulate endogenous NMD-elicited mRNAs, while decay of AU-rich instability element (ARE)-signal containing mRNAs are not affected. Using an agroinfiltration-based transient assay we confirmed that TAV specifically stabilizes mRNA containing a premature termination codon (PTC) in a VCS-dependent manner. We have identified a TAV motif consisting of 12 of the 520 amino acids in the full-length sequence that is critical for both VCS binding and the NMD suppression effect. Our data suggest that TAV can intercept NMD by targeting the decapping machinery through the scaffold protein VARICOSE, indicating that 5'-3' mRNA decapping is a late step in NMD-related mRNA degradation in plants.