Exploring molecular profiles of calcification in aortic vascular smooth muscle cells and aortic valvular interstitial cells

Cardiovascular calcification can occur in vascular and valvular structures and is commonly associated with calcium deposition and tissue mineralization leading to stiffness and dysfunction. Patients with chronic kidney disease and associated hyperphosphatemia have an elevated risk for coronary artery calcification (CAC) and calcific aortic valve disease (CAVD). However, there is mounting evidence to suggest that the susceptibility and pathobiology of calcification in these two cardiovascular structures may be different, yet clinically they are similarly treated. To better understand diversity in molecular and cellular processes that underlie hyperphosphatemia-induced calcification in vascular and valvular structures, we exposed aortic vascular smooth muscle cells (AVSMCs) and aortic valve interstitial cells (AVICs) to high (2.5 mM) phosphate (Ph) conditions in vitro, and examined cell-specific responses. To further identify hyperphosphatemic-specific responses, parallel studies were performed using osteogenic media (OM) as an alternative calcific stimulus. Consistent with clinical observations made by others, we show that AVSMCs are more susceptible to calcification than AVICs. In addition, bulk RNA-sequencing reveals that AVSMCs and AVICs activate robust ossification-programs in response to high phosphate or OM treatments, however, the signaling pathways, cellular processes and osteogenic-associated markers involved are cell- and treatment-specific. For example, compared to VSMCs, VIC-mediated calcification involves biological processes related to osteo-chondro differentiation and down regulation of 'actin cytoskeleton'-related genes, that are not observed in VSMCs. Furthermore, hyperphosphatemic-induced calcification in AVICs and AVSMCs is independent of P13K signaling, which plays a role in OM-treated cells. Together, this study provides a wealth of information suggesting that the pathogenesis of cardiovascular calcifications is significantly more diverse than previously appreciated.

Abstract P3095: Correlating Spatial Wall Shear Stress With Transcriptomics In Pre-calcific Stages Of Bicuspid Aortic Valve Disease

Bicuspid aortic valve (BAV) is the most common congenital cardiovascular defect and characterized by formation of two, rather than three cusps. Approximately 50% of young adults with BAV prematurely develop calcification and significant stenosis, which is typically more severe in right/non-coronary (R/NC) fusion. Mechanisms underlying this process are unknown. However, based on BAV-induced narrowing of the valve orifice and obstruction of blood flow, it has been speculated that abnormal biomechanical stimuli play a major role. Despite this, validation studies correlating these stimuli to molecular changes that promote calcification in BAV are lacking. Our objective is to define biomechanical stimuli in young patients and mice with R/NC BAV prior to calcification onset, and further use the murine model to correlate biomechanical indices with transcriptomic changes indicative of mechanosensitive regulators of calcification.Fluid-structure interaction (FSI) models and quantified biomechanical indices (wall shear stress (WSS), von Mises stress) are being generated from echocardiography and MRI from young adults and NfatC1 cre(+) ;Exoc5 fl/+ mice with R/NC BAV, and age-matched tricuspid aortic valve controls. In parallel, tissue sections collected from diseased mice are being subject to spatial transcriptomics (10x Visium) to determine the localization of differentially expressed genes relative to abnormal biomechanical stimuli. FSI results from a 23 y/o BAV patient indicate that cusp fusion leads to higher WSS on the fibrosa surface compared to the control, and high von Mises stress at the fusion site, both of which are regions prone to calcification in humans. To date, we have identified aortic valve stenosis in 25% NfatC1 cre(+) ;Exoc5 fl/+ mice, and spatial transcriptomics in these mice is currently underway. To our knowledge these are the first FSI models to characterize biomechanical stimuli for a young adult with R/NC BAV prior to calcification. Our FSI studies in mice will validate the use of a mouse model to study human disease by comparison of biomechanical indices. Furthermore, parallel transcriptomic studies in BAV mice will allow us to correlate biomechanical stimuli with transcriptomic changes underlying premature calcification.

Molecular and Mechanical Mechanisms of Calcification Pathology Induced by Bicuspid Aortic Valve Abnormalities

Bicuspid aortic valve (BAV) is a congenital defect affecting 1-2% of the general population that is distinguished from the normal tricuspid aortic valve (TAV) by the existence of two, rather than three, functional leaflets (or cusps). BAV presents in different morphologic phenotypes based on the configuration of cusp fusion. The most common phenotypes are Type 1 (containing one raphe), where fusion between right coronary and left coronary cusps (BAV R/L) is the most common configuration followed by fusion between right coronary and non-coronary cusps (BAV R/NC). While anatomically different, BAV R/L and BAV R/NC configurations are both associated with abnormal hemodynamic and biomechanical environments. The natural history of BAV has shown that it is not necessarily the primary structural malformation that enforces the need for treatment in young adults, but the secondary onset of premature calcification in ~50% of BAV patients, that can lead to aortic stenosis. While an underlying genetic basis is a major pathogenic contributor of the structural malformation, recent studies have implemented computational models, cardiac imaging studies, and bench-top methods to reveal BAV-associated hemodynamic and biomechanical alterations that likely contribute to secondary complications. Contributions to the field, however, lack support for a direct link between the external valvular environment and calcific aortic valve disease in the setting of BAV R/L and R/NC BAV. Here we review the literature of BAV hemodynamics and biomechanics and discuss its previously proposed contribution to calcification. We also offer means to improve upon previous studies in order to further characterize BAV and its secondary complications.