Elastic Fiber Biology - The Role of Elastin in Tissue Development and Integrity

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Elastic fibers are present in the extracellular matrix of many tissues, but are most prevalent in tissues that undergo repetitive stretch and recoil, such as blood vessels, lung and skin. At maturity, elastin synthesis is negligible and there is little, if any, turnover of the protein. The lack of elastin synthesis in the adult makes it clear that proper formation of elastic fibers during development is critical, as these structures must remain intact and functional for a lifetime. To better understand the function of elastin, an elastin gene (Eln) knockout mouse was made. Since elastin is essential for the function of the aorta and lungs, we predicted that these mice would not be viable due to aortic rupture or respiratory failure. Surprisingly, mice without elastin are born and can breathe, but they die postnatally - not from vascular rupture, but from occlusion of the aorta due to overproliferation of the vascular smooth muscle cells (vSMCs). Over the past funding period, we made a new elastin mouse model that expresses a reduced level of elastin (ElnR). Using this hypomorph mouse model, we propose to determine how the dosage level of elastin affects tissue development and integrity. In our first aim, we will determine the dosage levels of elastin being produced in ElnR/+, ElnR/R and ElnR/- mouse aortas, and characterize the ultrastructure of the aorta and lung in these mice. Based on the ultrastructure of the elastin-null (Eln-/-) mouse lung, which has arrested alveolar development, we hypothesize that Eln-/- mice are systemically hypoxic, and that this contributes to the abnormal proliferation of the vSMCs seen in these mice. Our preliminary data has shown that hypoxia-inducible factor-1 alpha (HIF-1a) is significantly upregulated in the Eln-/- aorta, indicating that the aortic wall is indeed hypoxic. In our second aim, we will test our hypothesis in vivo and in vitro. For our in vivo studies, we will determine the expression and protein levels of HIF-1a and ETS-1, a transcription factor induced by the activity of HIF-1a, in Eln+/+, ElnR/R, ElnR/- and Eln-/- mouse aortas. Additional in vivo and in vitro studies will explore the expression, protein levels and localization of vSMC differentiation markers and TGF-beta-PI3K/Akt signaling molecules, a signaling pathway induced by hypoxia. Ultimately, our results will provide novel data relating hypoxia to elastic fiber assembly, and support our long-term goal of elucidating the role of elastin in tissue development and homeostasis. The dissemination of our research will provide the field with novel insights on elastic fiber function in several tissues, and will be important to Canada as abnormal development and/or destruction of elastic fibers in the aorta and lungs cause many diseases that affect Canadians. Thus, the identification of novel regulators of elastogenic cells has the potential to lead to the development of better disease treatments, especially in collaboration with bioengineers.