Hemodynamics and Mechanobiology of Aortic Valve Inflammation and Calcification

Cardiac valves function in a mechanically complex environment, opening and closing close to a billion times during the average human lifetime, experiencing transvalvular pressures and pulsatile and oscillatory shear stresses, as well as bending and axial stress. Although valves were originally thought to be passive pieces of tissue, recent evidence points to an intimate interplay between the hemodynamic environment and biological response of the valve. Several decades of study have been devoted to understanding these varied mechanical stimuli and how they might induce valve pathology. Here, we review efforts taken in understanding the valvular response to its mechanical milieu and key insights gained from in vitro and ex vivo whole-tissue studies in the mechanobiology of aortic valve remodeling, inflammation, and calcification

An Ex Vivo Study of the Biological Properties of Porcine Aortic Valves in Response to Circumferential Cyclic Stretch

Normal physiological mechanical forces cause constant tissue renewal in aortic valve leaflets (AVL) while altered mechanical forces incite changes in their structural and biological properties. The current study aims at characterizing the remodeling properties of AVL subjected to cyclic circumferential stretch in a sterile ex vivo bioreactor. The leaflets cultured were stretched at a maximum rate of 300%s(−1) corresponding to a 15% strain for 48 h. Collagen, sulfated glycosaminoglycan (sGAG), and elastin contents of the stretched, fresh, and statically incubated leaflets were measured. Cusp morphology and cell phenotype were also examined. AVLs exposed to cyclic stretch showed a significant increase in collagen content (p < 0.05) when compared to fresh and statically incubated AVLs. sGAG content was significantly reduced in the stretched AVLs (p < 0.05) when compared to the fresh leaflets and was comparable between stretched and statically incubated AVLs. There was no statistically significant change in elastin content in all the three groups of AVLs (p > 0.05). Native aortic valve morphology was well preserved in stretched leaflets. Immunohistochemistry and immunoblotting studies showed an increased expression of α-smooth muscle actin (α-SMA) in stretched leaflets while α-SMA expression was reduced in statically incubated AVLs when compared to the fresh leaflets. To conclude, circumferential cyclic stretch altered the extracellular matrix remodeling activity of valvular cells, and consequently the extracellular matrix composition of the AVLs. Most interestingly, the contractile and fibrotic phenotypic expression of valve interstitial cells was enhanced. These results show that circumferential cyclic stretch is a possible mediator for AVL remodeling activity

Engineered FGF compositions and methods of use thereof

The present invention relates to the development of stable mutants of FGF-1 and FGF-2. In particular, it relates to novel engineered FGF-1 and FGF-2 polypeptides as well as polynucleotides, DNA constructs, and vectors encoding such polypeptides. In another aspect, pharmaceutical compositions and hydrogels including the disclosed polypeptides, polynucleotides, DNA constructs, and vectors are provided. In a still further aspect, methods of treating conditions using the compositions disclosed herein are provided

Engineered FGF1 and FGF2 compositions and methods of use thereof

Engineered FGF1 and FGF2 polypeptides, polynucleotides encoding these polypeptides and DNA constructs, vectors and compositions including these engineered polypeptides are provided herein. The engineered FGF1 and FGF2 polypeptides are more stable than their wild-type counterparts and may be more effective at treating a variety of conditions that FGF1 and FGF2 are useful for treating such as wound healing

Cyclic strain induces dualmode endothelial-mesenchymal transformation of the cardiac valve

Endothelial-mesenchymal transformation (EMT) is a critical event for the embryonic morphogenesis of cardiac valves. Inducers of EMT during valvulogenesis include VEGF, TGF-β1, and wnt/β-catenin (where wnt refers to the wingless-type mammary tumor virus integration site family of proteins), that are regulated in a spatiotemporal manner. EMT has also been observed in diseased, strain-overloaded valve leaflets, suggesting a regulatory role for mechanical strain. Although the preponderance of studies have focused on the role of soluble mitogens, we asked if the valve tissue microenvironment contributed to EMT. To recapitulate these microenvironments in a controlled, in vitro environment, we engineered 2D valve endothelium from sheep valve endothelial cells, using microcontact printing to mimic the regions of isotropy and anisotropy of the leaflet, and applied cyclic mechanical strain in an attempt to induce EMT. We measured EMT in response to both low (10%) and high strain (20%), where low-strain EMT occurred via increased TGF-β1 signaling and high strain via increased wnt/β-catenin signaling, suggesting dual strain-dependent routes to distinguish EMT in healthy versus diseased valve tissue. The effect was also directionally dependent, where cyclic strain applied orthogonal to axis of the engineered valve endothelium alignment resulted in severe disruption of cell microarchitecture and greater EMT. Once transformed, these tissues exhibited increased contractility in the presence of endothelin-1 and larger basal mechanical tone in a unique assay developed to measure the contractile tone of the engineered valve tissues. This finding is important, because it implies that the functional properties of the valve are sensitive to EMT. Our results suggest that cyclic mechanical strain regulates EMT in a strain magnitude and directionally dependent manner. tight junctions | cytokines | activated myofibroblast C ardiac valves are sophisticated structures that function in a complex mechanical environment, opening and closing more than 3 billion times during the average human lifetime (1). Initially considered passive flaps of tissue, it is now acknowledged that valves contain a highly heterogeneous population of endothelial (VEC) and interstitial (VIC) cells. The VICs exist as synthetic, myofibroblast, or smooth muscle-like phenotypes (2, 3) and alter their tone in response to vasoactive mediators (4-7). The VECs line the surface of the valve leaflet and are unique in their ability to undergo endothelial-mesenchymal transformation (EMT), a process that is crucial for valvulogenesis (8, 9). Recent clinical evidence of EMT has been observed in pathologies such as ischemic cardiomyopathy and concomitant mitral regurgitation and is correlated with increased leaflet mechanical strains (10, 11). These pathological strains can be oriented obliquely to cell and tissue orientation (12, 13), suggesting the possible interaction between mechanical forces and tissue architecture in regulating EMT. Prior work has focused on the regulation of EMT via soluble factors. Modulation of VEGF and increases in wnt/β-catenin and TGF-β1 expression, among other factors, direct EMT during valvulogenesis (8, 14) and in the mature valve (15, 16). Additionally, mechanical forces are known to modulate valve remodeling and disease progression (17, 18). However, the influence of mechanical forces and its synergy with tissue architecture in influencing cardiac valve EMT is unknown. During embryonic development, valve morphogenesis has been correlated with an increase in fluid shear stresses, mechanical strains, and altered geometry of the developing heart (19-22). These observations potentially suggests interaction between mechanical forces and the factors that regulate EMT. Additionally, it is also unknown if EMT results in a functional change of the VEC to a contractile myofibroblast-like VIC. We hypothesized that cyclic strain may potentiate valve EMT in a manner dependent on cell orientation and the direction of applied strain. We developed an in vitro model that combines cyclic stretching of engineered valve endothelium reconstituted from primary sheep VECs for biochemical and expression studies. In addition, we present a functional assay for EMT using valve thin films (vTFs), a biohybrid construct of the engineered valve endothelium on an elastomer thin film that is deformed during tissue contraction. We report strain-dependent dual-mode EMT, with TGF-β1 signaling triggering EMT under low strain (10%) and wnt/β-catenin signaling under high strain (20%). We also report strain-dependent increased contractility of transformed VEC tissues when treated with endothelin-1, suggesting transformation of the normally noncontractile VEC to a contractile VIC-like cell

Aortic valve mechanobiology - the effect of cyclic stretch

Aortic valve disease is among the third most common cardiovascular disease worldwide, and is also a strong predictor for other cardiac related deaths. Altered mechanical forces are believed to cause changes in aortic valve biosynthetic activity, eventually leading to valve disease, however little is known about the cellular and molecular events involved in these processes. To gain a fundamental understanding into aortic valve disease mechanobiology, an ex vivo experimental model was used to study the effects of normal and elevated cyclic stretch on aortic valve remodeling and degenerative disease. The hypothesis of this proposal was that elevated cyclic stretch will result in increased expression of markers related to degenerative valve disease. Three aspects of aortic valve disease were studied: (i) Altered extracellular matrix remodeling; (ii) Aortic Valve Calcification; and (iii) Serotonin-induced valvulopathy. Results showed that elevated stretch resulted in increased matrix remodeling and calcification via a bone morphogenic protein-dependent pathway. In addition, elevated stretch and serotonin resulted in increased collagen biosynthesis and tissue stiffness via a serotonin-2A receptor-mediated pathway. This work adds to current knowledge on aortic valve disease mechanisms, and could pave the way for the development of novel treatments for valve disease and for the design of tissue engineered valve constructs.Ph.D.Committee Chair: Ajit P. Yoganathan; Committee Member: Adrian H. Chester; Committee Member: Hanjoong Jo; Committee Member: Michael S. Sacks; Committee Member: Robert M. Nerem; Committee Member: Stephen L. Hilber

Using Dimensionless Numbers to Predict Centrifugal Jet-Spun Nanofiber Morphology

In this study, we report a method for predictive, controlled, and highly aligned nanofiber production via Centrifugal Jet Spinning (CJS) using polycaprolactone (PCL) as a model polymer. We investigated the effects of fabrication conditions and their resulting dimensionless parameters, namely the Weber, Reynolds, and Capillary numbers, by correlating with fiber morphologies (fiber diameter, fiber alignment, bead frequency, bead aspect ratio, and scaffold porosity) and mechanical properties (linear modulus and ultimate tensile strength). We report a fabrication parameter lookup table based on the aforementioned dimensionless numbers, for the production of nanofiber scaffolds using the CJS. We built a scaled-up version of the CJS that uses a larger reservoir and successfully validated the reported lookup table for PCL as well as other polymers including polyethylene oxide, polylactic acid, and polyvinylpyrrolidone dissolved either in hexafluoroisopropanol or chloroform. We show that by carefully tailoring the polymer intrinsic properties and the Reynolds number, we can fabricate bead-free, continuous fibers. This method will allow other researchers to design and build their own CJS for the production of desired fiber scaffold networks by utilizing the appropriate dimensionless numbers for their system