Strain transfer through the aortic valve

The complex structural organization of the aortic valve (AV) extracellular matrix (ECM) enables large and highly nonlinear tissue level deformations. The collagen and elastin (elastic) fibers within the ECM form an interconnected fibrous network (FN) and are known to be the main load-bearing elements of the AV matrix. The role of the FN in enabling deformation has been investigated and documented. However, there is little data on the correlation between tissue level and FN-level strains. Investigating this correlation will help establish the mode of strain transfer (affine or nonaffine) through the AV tissue as a key feature in microstructural modeling and will also help characterize the local FN deformation across the AV sample in response to applied tissue level strains. In this study, the correlation between applied strains at tissue level, macrostrains across the tissue surface, and local FN strains were investigated. Results showed that the FN strain distribution across AV samples was inhomogeneous and nonuniform, as well as anisotropic. There was no direct transfer of the deformation applied at tissue level to the fibrous network. Loading modes induced in the FN are different than those applied at the tissue as a result of different local strains in the valve layers. This nonuniformity of local strains induced internal shearing within the FN of the AV, possibly exposing the aortic valve interstitial cells (AVICs) to shear strains and stresses.     

Cathepsin proteases have distinct roles in trophoblast function and vascular remodelling

Trophoblast giant cells are instrumental in promoting blood flow towards the mouse embryo by invading the uterine endometrium and remodelling the maternal vasculature. This process involves the degradation of the perivascular smooth muscle layer and the displacement of vascular endothelial cells to form trophoblast-lined blood sinuses. How this vascular remodelling is achieved at the molecular level remains largely elusive. Here, we show that two placenta-specific cathepsins, Cts7 and Cts8, are expressed in distinct but largely overlapping subsets of giant cells that are in direct contact with maternal arteries. We find that Cts8, but not Cts7, has the capacity to mediate loss of smooth muscle alpha-actin and to disintegrate blood vessels. Consequently, conditional ubiquitous overexpression of Cts8 leads to midgestational embryonic lethality caused by severe vascularization defects. In addition, both cathepsins determine trophoblast cell fate by inhibiting the self-renewing capacity of trophoblast stem cells when overexpressed in vitro. Similarly, transgenic overexpression of Cts7 and Cts8 affects trophoblast proliferation and differentiation by prolonging mitotic cell cycle progression and promoting giant cell differentiation, respectively. We also show that the cell cycle effect is directly caused by some proportion of CTS7 localizing to the nucleus, highlighting the emerging functional diversity of these typically lysosomal proteases in distinct intracellular compartments. Our findings provide evidence for the highly specialized functions of closely related cysteine cathepsin proteases in extra-embryonic development, and reinforce their importance for a successful outcome of pregnancy.     

Cloning, expression, and substrate specificity of a fungal chymotrypsin. Evidence for lateral gene transfer from an actinomycete bacterium

Unlike trypsins, chymotrypsins have not until now been found in fungi. Expressed sequence tag analysis of the deuteromycete Metarhizium anisopliae identified two trypsins (family S1) and a novel chymotrypsin (CHY1). CHY1 resembles actinomycete (bacterial) chymotrypsins (family S2) rather than other eukaryote enzymes (family S1) in being synthesized as a precursor species (374 amino acids, pI/MW: 5.07/38,279) containing a large N-terminal fragment (186 amino acids). Chy1 was expressed in Pichia pastoris yielding an enzyme with a chymotrypsin specificity for branched aliphatic and aromatic C-terminal amino acids. This is predictable as key catalytic residues determining the specificity of Streptomyces griseus chymotrypsins are conserved with CHY1. Mature (secreted) CHY1 (pI/MW: 8.29/18,499) shows closest overall amino acid identity to S. griseus protease C (55%) and clustered with other secreted bacterial S2 chymotrypsins that diverged widely from animal and endocellular bacterial enzymes in phylogenetic trees of the chymotrypsin superfamily. Conversely, actinomycete chymotrypsins are much more closely related to fungal proteases than to other eubacterial sequences. Complete genomes of yeast, gram eubacteria, archaebacteria, and mitochondria do not contain paralogous genes. Expressed sequence tag data bases from other fungi also lack chymotrypsin homologs. In light of this patchy distribution, we conclude that chy1 probably arose by lateral gene transfer from an actinomycete bacterium.