Abdominal aortic aneurysms (AAAs), characterized by degrading aortic elastin matrix and resultant vessel weakening and rupture, causes 15,000 deaths in the United States anually, primarily amongst seniors, and those suffering from inherited matrix disorders. Regression of existing aneurysms by restoring healthy elastin architecture is difficult since adult cells poorly synthesize elastin and no tools are available to induce faithful elastin regeneration. Thus, our long-term goal is to investigate strategies to enable elastin regeneration within AAAs, so as to delay or eliminate surgical intervention. We determined that elastogenic cues based on tetramers of hyaluronan (HA), a matrix glycosaminoglycan, and TGF-2 synergestically upregulate elastin matrix synthesis and assembly by healthy adult vascular smooth muscle cells, and to a lesser extent by aneurysmal cells. The outcomes portend tremendous utility of these cues to similar elastin regeneration within AAs. However, recruitment and crosslinking of soluble elastin precursors into a stable matrix is inefficient and must be up-regulated, an insufficiency we propose to address. Our objective is thus to investigate impact of such cues (LOX, an elastin crosslinking enzyme, and Cu2+ ions), provided concurrent to or independent of elastogenic cues, on elastin synthesis, matrix assembly, and cell phenotype (e.g., elastase and MMP release) by cultured healthy and aneurysmal adult rat aortic SMCs (RASMCs). We also seek to investigate the efficacy of the optimized cues for elastin matrix regeneration in induced rat AAAs. In each of three proposed aims, we will in parallel investigate an `endogenous model'of elastin matrix regeneration, wherein RASMCs (healthy and aneurysmal) will be provided cues to both synthesize, and assemble and crosslink tropoelastin precursors. In the exogenous model, SMCs (healthy and aneurysmal) will be provided LOX and Cu2+ cues only to upregulate cellular assembly and maturation of exogenous tropoelastin.
Aim 1 will investigate dose-specific benefits of exogenous, LOX to elastin synthesis, matrix assembly, and cell phenotype, within RASMC cultures.
Aim 2 will evaluate dose-specific effects of copper ion delivery from copper nanoparticles (CuNP), concurrent with optimized LOX cues, to LOX activity and to elastin synthesis and matrix assembly and cell phenotype within RASMC cultures. Finally, aim 3 will test utility of optimized crosslinking cues (LOX, Cu2+) for in situ cellular assembly of elastin matrices, to stabilize induced rat aortic aneurysms (AAs) in various stages of development, when tropoelastin is (A) endogenously prompted by elastogenic cues, or (B) exogenously supplied. We expect the project outcomes to offer more effective treatment options for AAAs, based on both in situ regeneration and stabilization of elastin matrices that may be employed as a stand-alone option or in consort with existing surgical or future pharmacological approaches. Other applications of the project outcomes, specifically those pertaining to studies of healthy vascular cells, include augumenting elastin synthesis, assembly, and matrix quality within tissue engineered constructs, restoring elastin homeostasis in de-elasticized vascular allografts and xenografts, and possibly even serving as in vitro models to investigate elastogenesis during early morphogenesis, and wound healing in adult vessels.

Public Health Relevance

Abdominal aortic aneurysms (AAAs) are potentially fatal conditions afflicting major blood vessels, which are characterized by a loss of blood vessel wall flexibility, and their ultimate structural weakening and rupture. This occurs due to breakdown and loss of rubber-like protein fibers (elastin) that normally help vessels restore their shape and form after deformation. Since cells within blood vessels cannot themselves produce new elastin, this study proposes to provide cells in culture, or within living blood vessels, a combination of biological molecules that will either induce cells to (a) synthesize new soluble elastin building blocks (precursors) and further assemble them into fiber structures, or (b) only assemble elastin precursors that are also simultaneously provided to them. The project outcomes can significantly benefit the development of new, non-surgical treatment strategies that can halt progress of or even regress existing AAAs by coaxing cells within to regenerate new elastin structures or repair and stabilize existing ones.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Special Emphasis Panel (ZRG1-SBIB-E (03))
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Tolunay, Eser
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Clemson University
Biomedical Engineering
Schools of Engineering
United States
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Swaminathan, Ganesh; Gadepalli, Venkat S; Stoilov, Ivan et al. (2017) Pro-elastogenic effects of bone marrow mesenchymal stem cell-derived smooth muscle cells on cultured aneurysmal smooth muscle cells. J Tissue Eng Regen Med 11:679-693
Deb, Partha Pratim; Ramamurthi, Anand (2017) Spatiotemporal mapping of matrix remodelling and evidence of in situ elastogenesis in experimental abdominal aortic aneurysms. J Tissue Eng Regen Med 11:231-245
Swaminathan, Ganesh; Sivaraman, Balakrishnan; Moore, Lee et al. (2016) Magnetically Responsive Bone Marrow Mesenchymal Stem Cell-Derived Smooth Muscle Cells Maintain Their Benefits to Augmenting Elastic Matrix Neoassembly. Tissue Eng Part C Methods 22:301-11
Sivaraman, Balakrishnan; Sylvester, Andrew; Ramamurthi, Anand (2016) Fibrinolytic PLGA nanoparticles for slow clot lysis within abdominal aortic aneurysms attenuate proteolytic loss of vascular elastic matrix. Mater Sci Eng C Mater Biol Appl 59:145-156
Venkataraman, Lavanya; Sivaraman, Balakrishnan; Vaidya, Pratik et al. (2016) Nanoparticulate delivery of agents for induced elastogenesis in three-dimensional collagenous matrices. J Tissue Eng Regen Med 10:1041-1056
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Venkataraman, Lavanya; Bashur, Chris A; Ramamurthi, Anand (2014) Impact of cyclic stretch on induced elastogenesis within collagenous conduits. Tissue Eng Part A 20:1403-15
Sivaraman, Balakrishnan; Ramamurthi, Anand (2013) Multifunctional nanoparticles for doxycycline delivery towards localized elastic matrix stabilization and regenerative repair. Acta Biomater 9:6511-25
Bashur, Chris A; Eagleton, Matthew J; Ramamurthi, Anand (2013) Impact of electrospun conduit fiber diameter and enclosing pouch pore size on vascular constructs grown within rat peritoneal cavities. Tissue Eng Part A 19:809-23
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