Evaluating Smooth Muscle Cells from CaCl₂-Induced Rat Aortal Expansions as a Surrogate Culture Model for Study of Elastogenic Induction of Human Aneurysmal Cells

Abstract

Regression of abdominal aortic aneurysms (AAAs) via regeneration of new elastic matrix is constrained by poor elastin synthesis by adult vascular cells and absence of methods to stimulate the same. We recently showed hyaluronan oligomers (HA-o) and TGF-b1 (termed elastogenic factors) to enhance elastin synthesis and matrix formation by healthy rat aortic smooth muscle cells (RASMCs). We also determined that these factors could likewise elastogenically induce aneurysmal RASMCs isolated from periadventitial CaCl 2 -injury induced rat AAAs (aRASMCs). However, the factor doses should be increased for these diseased cell types, as even when induced, elastic matrix amounts are roughly one order of magnitude lower than those produced by healthy RASMCs. We presently investigate the dose-specific elastogenic effects of HA-o (0-20 mg/mL) and TGF-b1 (0-10 ng/mL) factors on aRASMCs and compare their phenotype and elastogenic responses to those of human AAA-derived SMCs (aHASMCs); we seek to determine whether aRASMCs are appropriate surrogate cell types to study in the context of inducing elastic matrix regeneration within human AAAs. The periadventitial CaCl 2 -injury model of AAAs exhibits many of the pathological characteristics of human AAAs, including similarities in terms of decreased SMC contractile activity, enhanced proliferation, and reduced elastogenic capacity of aneurysmal SMCs (relative to healthy SMCs) when isolated and expanded in culture. Both aRASMCs and aHASMCs can be elastogenically stimulated by HA-o and TGF-b1 and show broadly similar trends in their dosespecific responses to these factors. However, compared with aHASMCs, aRASMCs appear to be far less elastogenically inducible. This may be due to differences in maturity of the AAAs studied, with the CaCl 2 -injury induced aortal expansion barely qualifying as an aneurysm and the human AAA representing a more welldeveloped condition. Further study of SMCs from stage-matched CaCl 2 -injury induced rat aortal expansions and human AAAs will be necessary to more rigorously evaluate their basal and induced elastogenic responses.

A Peptide Antagonist of Thrombospondin-1 Promotes Abdominal Aortic Aneurysm Progression in the Angiotensin II–Infused Apolipoprotein-E–Deficient Mouse

“…6,7 Data from animal experiments examining AAA in a range of models, such as rat transplant, rat elastase, mouse calcium chloride, and mouse angiotensin II (AngII), however, suggest that TGF-β1 inhibits AAA development. [8][9][10][11] TGF-β1 activation is a multistep process. The TGF-β1 precursor interacts with a latency-associated peptide and forms a complex called small latent complex.…”

Magnetically Responsive Bone Marrow Mesenchymal Stem Cell-Derived Smooth Muscle Cells Maintain Their Benefits to Augmenting Elastic Matrix Neoassembly

“…Unlike collagen fibers, which undergo natural regenerative repair postdisruption, elastic fibers are poorly restored, due to poor elastogenesis, and impaired elastic fiber assembly by postneonatal and diseased vascular SMCs. 6,7,29,30 Thus, to achieve AAA growth arrest, elastin regeneration must significantly exceed its breakdown. 31 Previously, 10 we showed that BM-SMCs exhibit high elastogenesis and generate paracrine secretions that stimulate elastogenesis by EaRASMCs, findings which support their use for matrix regenerative AAA therapy, provided they can be efficiently delivered to the AAA wall.…”

“…As we previously published, 6,7 21-day cultures within Permanox chamber slides were fixed with 2% w/v cacodylate glutaraldehyde (12 h), postfixed in 1% w/v osmium tetroxide (1 h), dehydrated in a graded ethanol series (50-100% v/v), and embedded in Epon 812 resin. The sections were mounted on copper grids, stained with uranyl acetate and lead citrate, and visualized on a Hitachi TEM (Model H7600T).…”

“…Although inhibiting MMPs may slow AAA growth, 4 AAA growth arrest and restoration of vessel recoil properties are challenged by poor regenerative repair of elastic fibers by adult vascular smooth muscle cells (SMCs). [5][6][7] A proelastogenesis stimulus is thus needed that may be effective in the proteolytic AAA tissue milieu.…”

Impact of Cyclic Stretch on Induced Elastogenesis Within Collagenous Conduits

“…Elastogenic factors (EFs) were also added to stimulate cellular elastic matrix generation in this study, with the doses (i.e., 0.1 ng/mL transforming growth factor-beta 1 [TGF-b1] and 0.2 mg/mL hyaluronan oligomers [HA-o]) based on results obtained previously. 14 In light of results of other studies in our lab that demonstrate that human aortic smooth muscle cells (HASMCs) respond to elastogenic stimulation by EFs, 30 we have focused on study of this cell type to provide greater clinical relevance.…”