Atherosclerosis-related cardiovascular diseases are a leading cause of mortality worldwide. Vascular smooth muscle cells (VSMCs) comprise the medial layer of the arterial wall and undergo phenotypic switching during atherosclerosis to a synthetic phenotype capable of proliferation and migration. The surrounding environment undergoes alterations in extracellular matrix (ECM) stiffness and composition in addition to an increase in addition to an increase in cholesterol content. Using an atherosclerotic murine model, we analyzed how the mechanics of VSMCs isolated from western diet fed apolipoprotein-E knockout (ApoE -/- ) and wild type (WT) mice were altered during atherosclerosis. Increased stiffness of ApoE -/- VSMCs correlated with a greater degree of stress fiber alignment as evidenced by atomic force microscopy (AFM)-generated force maps and stress fiber topography images. On type-1 collagen (COL1)-coated polyacrylamide (PA) gels of varying stiffness, WT VSMCs had higher adhesion forces to N-Cadherin (N-Cad) and COL1. ApoE -/- VSMC stiffness was significantly greater than WT cells with increased cell stiffness with increasing substrate stiffness for both ApoE -/- and WT VSMCs . In addition, ApoE -/- VSMCs showed an enhanced migration capability on COL1-coated substrates and a general decreasing trend in migration capacity with increasing substrate stiffness, correlating with the lower adhesion forces as compared to WT VSMCs. Altogether, these results demonstrate the potential contribution of the alteration in VSMC mechanics in the development of atherosclerosis.
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Diet alters age-related remodeling of aortic collagen in mice susceptible to atherosclerosis
Vascular cells restructure extracellular matrix in response to aging or changes in mechanical loading. Here, we characterized collagen architecture during age-related aortic remodeling in atherosclerosis-prone mice. We hypothesized that changes in collagen fiber orientation reflect an altered balance between passive and active forces acting on the arterial wall. We examined two factors that can alter this balance, endothelial dysfunction and reduced smooth muscle cell (SMC) contractility. Collagen fiber organization was visualized by second-harmonic generation microscopy in aortic adventitia of apolipoprotein E (apoE) knockout (KO) mice at 6 wk and 6 mo of age on a chow diet and at 7.5 mo of age on a Western diet (WD), using image analysis to yield mean fiber orientation. Adventitial collagen fibers became significantly more longitudinally oriented with aging in apoE knockout mice on chow diet. Conversely, fibers became more circumferentially oriented with aging in mice on WD. Total collagen content increased significantly with age in mice fed WD. We compared expression of endothelial nitric oxide synthase and acetylcholine-mediated nitric oxide release but found no evidence of endothelial dysfunction in older mice. Time-averaged volumetric blood flow in all groups showed no significant changes. Wire myography of aortic rings revealed decreases in active stress generation with age that were significantly exacerbated in WD mice. We conclude that the aorta displays a distinct remodeling response to atherogenic stimuli, indicated by altered collagen organization. Collagen reorganization can occur in the absence of altered hemodynamics and may represent an adaptive response to reduced active stress generation by vascular SMCs. NEW & NOTEWORTHY The following major observations were made in this study: 1) aortic adventitial collagen fibers become more longitudinally oriented with aging in apolipoprotein E knockout mice fed a chow diet; 2) conversely, adventitial collagen fibers become more circumferentially oriented with aging in apoE knockout mice fed a high-fat diet; 3) adventitial collagen content increases significantly with age in mice on a high-fat diet; 4) these alterations in collagen organization occur largely in the absence of hemodynamic changes; and 5) circumferential reorientation of collagen is associated with decreased active force generation (contractility) in aged mice on a high-fat diet.
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- Award ID(s):
- 1760906
- NSF-PAR ID:
- 10285467
- Date Published:
- Journal Name:
- American Journal of Physiology-Heart and Circulatory Physiology
- Volume:
- 320
- Issue:
- 1
- ISSN:
- 0363-6135
- Page Range / eLocation ID:
- H52 to H65
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Introduction: Vascular diseases like abdominal aortic aneurysms (AAA) are characterized by a drastic remodeling of the vessel wall, accompanied with changes in the elastin and collagen content. At the macromolecular level, the elastin fibers in AAA have been reported to undergo significant structural alterations. While the undulations (waviness) of the collagen fibers is also reduced in AAA, very little is understood about changes in the collagen fibril at the sub-fiber level in AAA as well as in other vascular pathologies. Materials and Methods: In this study we investigated structural changes in collagen fibrils in human AAA tissue extracted at the time of vascular surgery and in aorta extracted from angiotensin II (AngII) infused ApoE−/− mouse model of AAA. Collagen fibril structure was examined using transmission electron microscopy and atomic force microscopy. Images were analyzed to ascertain length and depth of D-periodicity, fibril diameter and fibril curvature. Tissues were also stained using collagen hybridizing peptide (CHP) and analyzed using fluorescent microscopy and second harmonic generation (SHG) microscopy to locate regions of healthy and degraded collagen. Results: Abnormal collagen fibrils with compromised D-periodic banding were observed in the excised human tissue and in remodeled regions of AAA in AngII infused mice (Figure 1). These abnormal fibrils were characterized by statistically significant reduction in depths of D-periods and an increased curvature of collagen fibrils. These features were more pronounced in human AAA as compared to murine samples. Additionally, regions of abnormal collagen were located within the remodeled areas of AAA tissue and were distinct from healthy collagen regions as ascertained using CHP staining and SHG (Figure 1). Thoracic aorta from Ang II-infused mice, abdominal aorta from saline-infused mice, and abdominal aorta from non-AAA human controls did not contain abnormal collagen fibrils. Conclusions: The structural alterations in abnormal collagen fibrils appear similar to those reported for collagen fibrils subjected to mechanical overload or chronic inflammation in other tissues. Detection of abnormal collagen could be utilized to better understand the functional properties of the underlying extracellular matrix in vascular as well as other pathologies.more » « less
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Methods and results Human retinal punches from donors are collected from an eye bank; lipids are extracted and analyzed to study the alterations in VLC‐PUFAs and their omega‐3/omega‐6 (n‐3/n‐6) ratios. Nile rats are fed a high‐fat diet to induce hyperglycemia, and then an n‐3 PUFA‐rich diet is fed to the experimental group for 2 months. Diabetic male Akita mice and WT mice are fed with 5% fish‐oil mixed in with their chow for 2 months to observe the effect of n‐3 PUFAs. Results indicate that VLC‐PUFA levels are lower in human diabetic and retinopathic retinal punches compared to age‐matched controls. With supplementation of n‐3 PUFAs, there is a significant increase in n‐3/n‐6 VLC‐PUFA ratios in both animal models compared to diabetic controls.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1152/ajpheart.00420.2020
