RESUME EN ANGLAIS
Valvular interstitial cell and aortic stenosis: impact of tissue factor pathway
Defined as the narrowing of the aortic valve, aortic stenosis (AS) is the third cardiovascular
pathology in industrialized countries. Affecting mainly people aged over 65 years, AS
represents a major public health problem because of the aging of the population. After
initially been considered as a passive degenerative process, it is now established that AS is an
"atherosclerosis-like" disease characterized by the processes of inflammation, fibrosis,
neo-angiogenesis and calcification. Some proteins of the coagulation pathway such as tissue
factor (TF) are known to have a pro-fibrotic role and actively participate in the development
of atherosclerotic lesions. Their implication in AS seems, therefore, probable and remain to be
identified.
Prevalent cellular component of the aortic valve, VICs have five distinct subpopulations:
embryonic progenitor cells (EPCs), progenitor cells (pVICs) quiescent (qVICs), activated
(aVICs) and osteoblastic (obVICs). During the valvulogenesis, EPCs allow the cellularization
of the valve, differentiating into qVICs. These cells maintain the valvular homeostasis and, in
case of damage, are activated (aVICs) to effectively repair the valve tissue. The valvular
inflammation and VICs activation initiate the secretion of pro-calcifying proteins inducing the
differentiation of aVICs into obVICs. Finally, pVICs, naturally present within the valve
(called resident) or from the blood circulation (called hematopoietic), seem to promote cell
renewal and may be involved in the angiogenic and osteoblastic processes.
Although described, these subpopulations have never been studied longitudinally, in respect
to their behavior in vitro. Our first objective was to perform this investigation. Our second
objective was to study the potential role of TF pathway in the deleterious mechanisms of AS.
As part of the longitudinal follow-up of VICs from control and pathological human aortic
valves to the in vitro culture performed on plastic and collagen, we first showed that different
subpopulations were present in these valves with different locations and proportions
according to the pathophysiological state of the tissue. After enzymatic digestion, all
subpopulations are found but, in culture, hematopoietic pVICs disappeared, whichever the
support. Thus, we validated the primary culture model of VICs while highlighting its
limitations: lack of hematopoietic pVICs, spontaneous osteoblastic differentiation and
activation of VICs in culture.