Doctor of Philosophy (PhD)
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Biomedical Engineering and Bioengineering
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The aortic valve (AoV) controls unidirectional blood distribution from the left ventricle of the heart to the aorta for systemic circulation. During the systolic and diastolic phases, AoV leaflets rely on a precise extracellular matrix (ECM) microarchitecture for appropriate biomechanical performance based on the arrangement of collagen, elastin, and glycosaminoglycans. The ECM structure is generated and maintained by valvular interstitial cells (VICs), which reside within the leaflets. VICs are a heterogeneous population of cells that are derived from a mixture of developmental precursors. Mainly, VICs arise from endocardial and neural crest cells that migrate into the cardiac cushions during development. The contribution of these diverse populations to the formation of the ECM microarchitecture has not been established. Relatively little is known about the regulation of elastic fibers, though elastin abnormalities result in congenital AoV defects and elastin degradation initiates AoV diseases.
The present study showed for the first time the relationship of pigment presence in the mouse AoV with elastic fiber patterning. To establish the timing of elastin (Eln) expression in the mouse AoV, RT-qPCR was performed and found that Elnpeaks at late embryogenesis (E17.5) and early postnatal stages but remains at low levels in adulthood. Confocal microscopy of AoVs from mutant mice revealed that elastic fibers were almost completely missing in Kitwv/wv mice that have no pigment and were more abundant and disoriented in K5-Edn3 transgenic hyperpigmented mice. Additionally, by combining RNAscope with immunofluorescence, I found that VICs that co-express the melanocyte-specific marker Tyrosinaseand alpha-smooth muscle actin (aSMA) express Elnindicating they are responsible for elastin production. Furthermore, by lineage tracing using the Wnt1-Cre system, I found that these cells are not exclusively derived from the neural crest suggesting a contribution of a third lineage other than the known two. Moreover, using atomic force microscopy I found that the pigment affects the mechanical stiffness of the AoV leaflet, where those from K5-Edn3 have higher overall stiffness when compared to those from Kitwv/wv and wild type mice. Despite a striking phenotype, these mice live normally and have no overt cardiac differences.
In conclusion, the present study showed that pigment is necessary for the proper patterning of the mouse AoV leaflets and contribute to its biomechanical properties. The results also indicated that Elnproducing cells have a unique melanocytic and smooth muscle cell phenotype and are not derived from the neural crest.
Nasim, Sana, "Characterization of Aortic Valve Interstitial Cells Responsible for Elastogenesis" (2020). FIU Electronic Theses and Dissertations. 4581.
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