Pathology of Calcific Aortic Valve Disease: The Role of Mechanical and Biochemical Stimuli in Modulating the Phenotype of and Calcification by Valvular Interstitial Cells

Calcific aortic valve disease (CAVD) occurs through multiple mutually non-exclusive mechanisms that are mediated by valvular interstitial cells (VICs). VICs undergo pathological differentiation during the progression of valve calcification; however the factors that regulate cellular differentiation are not well defined. Most commonly recognized are biochemical factors that induce pathological differentiation, but little is known regarding the biochemical factors that may suppress this process. Further, the contribution of matrix mechanics in valve pathology has been overlooked, despite increasing evidence of close relationships between changes in tissue mechanics, disease progression and the regulation of cellular response. In this thesis, the effect of matrix stiffness on the differentiation of and calcification by VICs in response to pro-calcific and anti-calcific biochemical factors was investigated. Matrix stiffness modulated the response of VICs to pro-calcific factors, leading to two distinct calcification processes. VICs cultured on the more compliant matrices underwent calcification via osteoblast differentiation, whereas those cultured on the stiffer matrices were prone to myofibroblast differentiation. The transition of fibroblastic VICs to myofibroblasts increased cellular contractility, which led to contraction-mediated, apoptosis-dependent calcification. In addition, C-type natriuretic peptide (CNP), a putative protective molecule against CAVD, was identified. CNP supressed myofibroblast and osteoblast differentiation of VICs, and thereby inhibited calcification in vitro. Matrix stiffness modulated the expression of CNP-regulated transcripts, with only a small number of CNP-regulated transcripts not being sensitive to matrix mechanics. These data demonstrate the combined effects of mechanical and biochemical cues in defining VIC phenotype and responses, with implications for the interpretation of in vitro models of VIC calcification and possibly disease devleopment. The findings from this thesis emphasize the necessity to consider both biochemical and mechanical factors in order to improve fundamental understanding of VIC biology.Ph

Autoinducer-2-Regulated Genes in Streptococcus mutans UA159 and Global Metabolic Effect of the luxS Mutation▿ †

Autoinducer 2 (AI-2) is the only species-nonspecific autoinducer known in bacteria and is produced by both gram-negative and gram-positive organisms. Consequently, it is proposed to function as a universal quorum-sensing signal for interaction between bacterial species. AI-2 is produced as the by-product of a metabolic transformation carried out by the LuxS enzyme. To separate the metabolic function of the LuxS enzyme from the signaling role of AI-2, we carried out a global transcriptome analysis of a luxS null mutant culture of Streptococcus mutans UA159, an important cariogenic bacterium and a crucial component of the dental plaque biofilm community, in comparison to a luxS null mutant culture supplemented with chemically pure 4,5-dihydroxy-2,3-pentanedione, the precursor of AI-2. The data revealed fundamental changes in gene expression affecting 585 genes (30% of the genome) which could not be restored by the signal molecule AI-2 and are therefore not caused by quorum sensing but by lack of the transformation carried out by the LuxS enzyme in the activated methyl cycle. All functional classes of enzymes were affected, including genes known to be important for biofilm formation, bacteriocin synthesis, competence, and acid tolerance. At the same time, 59 genes were identified whose transcription clearly responded to the addition of AI-2. Some of them were related to protein synthesis, stress, and cell division. Three membrane transport proteins were upregulated which are not related to any of the known AI-2 transporters. Three transcription factors were identified whose transcription was stimulated repeatedly by AI-2 addition during growth. Finally, a global regulatory protein, the δ subunit of the RNA polymerase (rpoE), was induced 147-fold by AI-2, representing the largest differential gene expression observed. The data show that many phenotypes related to the luxS mutation cannot be ascribed to quorum sensing and have identified for the first time regulatory proteins potentially mediating AI-2-based signaling in gram-positive bacteria

Identification and Characterization of Aortic Valve Mesenchymal Progenitor Cells with Robust Osteogenic Calcification Potential

Advanced valvular lesions often contain ectopic mesenchymal tissues, which may be elaborated by an unidentified multipotent progenitor subpopulation within the valve interstitium. The identity, frequency, and differentiation potential of the putative progenitor subpopulation are unknown. The objectives of this study were to determine whether valve interstitial cells (VICs) contain a subpopulation of multipotent mesenchymal progenitor cells, to measure the frequencies of the mesenchymal progenitors and osteoprogenitors, and to characterize the osteoprogenitor subpopulation because of its potential role in calcific aortic valve disease. The multilineage potential of freshly isolated and subcultured porcine aortic VICs was tested in vitro. Progenitor frequencies and self-renewal capacity were determined by limiting dilution and colony-forming unit assays. VICs were inducible to osteogenic, adipogenic, chondrogenic, and myofibrogenic lineages. Osteogenic differentiation was also observed in situ in sclerotic porcine leaflets. Primary VICs had strikingly high frequencies of mesenchymal progenitors (48.0 ± 5.7%) and osteoprogenitors (44.1 ± 12.0%). High frequencies were maintained for up to six population doublings, but decreased after nine population doublings to 28.2 ± 9.9% and 5.8 ± 1.3%, for mesenchymal progenitors and osteoprogenitors, respectively. We further identified the putative osteoprogenitor subpopulation as morphologically distinct cells that occur at high frequency, self-renew, and elaborate bone matrix from single cells. These findings demonstrate that the aortic valve is rich in a mesenchyma l progenitor cell population that has strong potential to contribute to valve calcification

State of the science in women's cardiovascular disease : a Canadian perspective on the influence of sex and gender

Cardiovascular disease (CVD) is the leading cause of premature death for women in Canada.1 Although it has long been recognized that estrogen impacts vascular responses in women, there is emerging evidence that physiologic and pathophysiologic cardiovascular responses are uniquely affected across the spectrum of a woman's life. Despite a global understanding that manifestations and outcomes of CVD are known to differ between men and women, uptake of the recognition of sex and gender influences on the clinical care of women has been slow or absent.2 To highlight the need for better research, diagnosis, treatment, awareness, and support of women with CVD in Canada, the Canadian Women's Heart Health Alliance (CWHHA), supported by the University of Ottawa Heart Institute, and in collaboration with the Heart and Stroke Foundation of Canada (HSFC), undertook a comprehensive review of the evidence on sex‐ and gender‐specific differences in comorbidities, risk factors, disease awareness, presentation, diagnosis, and treatment across the entire spectrum of CVD. The intent of this review was not to directly compare women and men on epidemiological and outcome measures of CVD, but to synthesize the state of the evidence for CVD in women and identify significant knowledge gaps that hinder the transformation to clinical practice and care that is truly tailored for women, a significant health challenge that has only been recognized in Canada relatively recently. This review highlights the scarcity of Canadian data on CVD in women as part of the ongoing struggle to increase awareness of and improve outcomes for women with CVD. Because of a paucity of published Canada‐specific evidence, the purpose of this review is to provide an infrastructure to summarize world‐wide published evidence, including knowledge gaps that must be understood to then make effective recommendations to alleviate the glaring “unders” of CVD for women in Canada: under‐aware, under‐diagnosed and under‐treated, under‐researched, and under‐support