Age-related modifications of aorta and coronaries in the rabbit: a morphological and morphometrical assessment

Identification of cellular heterogeneity and key signaling pathways associated with vascular remodeling and calcification in young and old primate aortas based on single-cell analysis

Aging of the vascular system is the main cause of many cardiovascular diseases. The structure and function of the blood vessel wall change with aging. To prevent age-related cardiovascular diseases, it is essential to understand the cellular heterogeneity of vascular wall and changes of cellular communication among cell subpopulations during aging. Here, using published single-cell RNA sequencing datasets of young and old monkey aortas, we analyzed the heterogeneity of vascular endothelial cells and smooth muscle cells in detail and identified a distinct endothelial cell subpopulation that involved in vascular remodeling and calcification. Moreover, cellular communication that changed with aging was analyzed and we identified a number of signaling pathways that associated with vascular aging. We found that EGF signaling pathway play an essential role in vascular remodeling and calcification of aged aortas. This work provided a better understanding of vascular aging and laid the foundation for prevention of age-related vascular pathologies.

Vascular dysfunction as a potential culprit of sarcopenia

Aging-related changes to biological structures such as cardiovascular and musculoskeletal systems contribute to the development of comorbid conditions including cardiovascular disease and frailty, and ultimately lead to premature death. Although, frail older adults often demonstrate both cardiovascular and musculoskeletal comorbidities, the etiology of sarcopenia, and especially the contribution of cardiovascular aging is unclear. Aging-related vascular calcification is prevalent in older adults and is a known risk factor for cardiovascular disease and death. The effect vascular calcification has on function during aging is not well understood. Emerging findings suggest vascular calcification can impact skeletal muscle perfusion, negatively affecting nutrient and oxygen delivery to skeletal muscle, ultimately accelerating muscle loss and functional decline. The present review summarizes existing evidence on the biological mechanisms linking vascular calcification with sarcopenia during aging.

Biomechanical properties and histomorphometric features of aortic tissue in patients with or without bicuspid aortic valve

Background

We sought to investigate and compare biomechanical properties and histomorphometric findings of thoracic ascending aorta aneurysm (TAA) tissue from patients with bicuspid aortic valve (BAV) and tricuspid aortic valve (TAV) in order to clarify mechanisms underlying differences in the clinical course.

Methods

Circumferential sections of TAA tissue in patients with BAV (BAV-TAA) and TAV (TAV-TAA) were obtained during surgery and used for biomechanical tests and histomorphometrical analysis.

Results

In BAV-TAA, we observed biomechanical higher peak stress and lower Young modulus values compared with TAV-TAA wall. The right lateral longitudinal region seemed to be the most fragile zone of the TAA wall. Mechanical stress-induced rupture of BAV-TAA tissue was sudden and uniform in all aortic wall layers, whereas a gradual and progressive aortic wall breakage was described in TAV-TAA. Histomorphometric analysis revealed higher amount of collagen but not elastin in BAV-TAA tunica media.

Conclusions

The higher deformability of BAV-TAA tissue supports the hypothesis that increased wall shear stress doesn’t explain the increased risk of sudden onset of rupture and dissection; other mechanisms, likely related to alteration of specific genetic pathways and epigenetic signals, could be investigated to explain differences in aortic dissection and rupture in BAV patients.

Arterial ageing: from endothelial dysfunction to vascular calcification

Complex structural and functional changes occur in the arterial system with advancing age. The aged artery is characterized by changes in microRNA expression patterns, autophagy, smooth muscle cell migration and proliferation, and arterial calcification with progressively increased mechanical vessel rigidity and stiffness. With age the vascular smooth muscle cells modify their phenotype from contractile to 'synthetic' determining the development of intimal thickening as early as the second decade of life as an adaptive response to forces acting on the arterial wall. The increased permeability observed in intimal thickening could represent the substrate on which low-level atherosclerotic stimuli can promote the development of advanced atherosclerotic lesions. In elderly patients the atherosclerotic plaques tend to be larger with increased vascular stenosis. In these plaques there is a progressive accumulation of both lipids and collagen and a decrease of inflammation. Similarly the plaques from elderly patients show more calcification as compared with those from younger patients. The coronary artery calcium score is a well-established marker of adverse cardiovascular outcomes. The presence of diffuse calcification in a severely stenotic segment probably induces changes in mechanical properties and shear stress of the arterial wall favouring the rupture of a vulnerable lesion in a less stenotic adjacent segment. Oxidative stress and inflammation appear to be the two primary pathological mechanisms of ageing-related endothelial dysfunction even in the absence of clinical disease. Arterial ageing is no longer considered an inexorable process. Only a better understanding of the link between ageing and vascular dysfunction can lead to significant advances in both preventative and therapeutic treatments with the aim that in the future vascular ageing may be halted or even reversed.

Molecular Pathways Regulating Macrovascular Pathology and Vascular Smooth Muscle Cells Phenotype in Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a disease reaching a pandemic proportion in developed countries and a major risk factor for almost all cardiovascular diseases and their adverse clinical manifestations. T2DM leads to several macrovascular and microvascular alterations that influence the progression of cardiovascular diseases. Vascular smooth muscle cells (VSMCs) are fundamental players in macrovascular alterations of T2DM patients. VSMCs display phenotypic and functional alterations that reflect an altered intracellular biomolecular scenario of great vessels of T2DM patients. Hyperglycemia itself and through intraparietal accumulation of advanced glycation-end products (AGEs) activate different pathways, in particular nuclear factor-κB and MAPKs, while insulin and insulin growth-factor receptors (IGFR) are implicated in the activation of Akt and extracellular-signal-regulated kinases (ERK) 1/2. Nuclear factor-κB is also responsible of increased susceptibility of VSMCs to pro-apoptotic stimuli. Down-regulation of insulin growth-factor 1 receptors (IGFR-1R) activity in diabetic vessels also influences negatively miR-133a levels, so increasing apoptotic susceptibility of VSMCs. Alterations of those bimolecular pathways and related genes associate to the prevalence of a synthetic phenotype of VSMCs induces extracellular matrix alterations of great vessels. A better knowledge of those biomolecular pathways and related genes in VSMCs will help to understand the mechanisms leading to macrovascular alterations in T2DM patients and to suggest new targeted therapies.

The contribution of resident vascular stem cells to arterial pathology

Intimal accumulation of smooth muscle cells contributes to the development and progression of atherosclerotic lesions and restenosis following endovascular procedures. Arterial smooth muscle cells display heterogeneous phenotypes in both physiological and pathological conditions. In response to injury, dedifferentiated or synthetic smooth muscle cells proliferate and migrate from the tunica media into the intima. As a consequence, smooth muscle cells in vascular lesions show a prevalent dedifferentiated phenotype compared to the contractile appearance of normal media smooth muscle cells. The discovery of abundant stem antigen-expressing cells in vascular lesions also rarely detected in the tunica media of normal adult vessels stimulated a great scientific debate concerning the possibility that proliferating vascular wall-resident stem cells accumulate into the neointima and contribute to the progression of lesions. Although several experimental studies support this hypothesis, others researchers suggest a positive effect of stem cells on plaque stabilization. So, the real contribute of vascular wall-resident stem cells to pathological vascular remodelling needs further investigation. This review will examine the evidence and the contribution of vascular wall-resident stem cells to arterial pathobiology, in order to address future investigations as potential therapeutic target to prevent the progression of vascular diseases.

Aortopathy in Marfan syndrome: an update

Marfan syndrome (MFS) is an inherited autosomal dominant multisystem disease caused by mutations in the FBN1 gene encoding fibrillin-1, an extracellular matrix glycoprotein widely distributed in mesenchymal-derived tissues that provide a scaffold for elastin deposition. MFS is characterized by variable clinical manifestations, including skeletal, ocular, and cardiovascular abnormalities; ascending aortic aneurysm with ensuing dissection and rupture is the main life-threatening cardiovascular manifestation of MFS. Histological aspects of MFS aortopathy include a medial degeneration from disarray and fragmentation of elastic fibers and accumulation of basophilic ground substance areas depleted of smooth muscle cells (SMCs). Transmission electron microscopy well evidences the high number of interruptions and the thick appearance of the elastic lamellae and the accumulation of abundant extracellular glycosaminoglycan-rich material, sometimes SMCs showing a prevalent synthetic phenotype. The aberrant signaling of transforming growth factor-β (TGF-β) as the consequence of the altered structure of fibrillin-1 induces activation and the overexpression of Smad-dependent profibrotic signaling pathway and ERK1/2-mediated increased synthesis of matrix metalloproteinases. In addition, MFS is accompanied by an impaired aortic contractile function and aortic endothelial-dependent relaxation, which is caused by an enhancement of the oxidative stress and increased reactive oxygen species during the progression of the disease. Many studies are currently evaluating the contribution of TGF-β-mediated biomolecular pathways to the progression of MFS aortopathy and aneurysm development, in order to discover new targets for pharmacological strategies aimed to counteract aortic dilation.

Central arterial aging and the epidemic of systolic hypertension and atherosclerosis

The structure and function of central arteries change throughout the lifetime of humans and animals. Since atherosclerosis and hypertension are prevalent in epidemic proportion among older persons, it is reasonable to hypothesize that specific mechanisms that underlie the arterial substrate that has been altered by an "aging process" are intimately linked to arterial diseases. Indeed, recent studies reveal a profile of arterial cell and matrix properties that emerges with advancing age within the grossly normal appearing aortic wall of both animals and humans. This profile is proinflammatory, and is manifested by intimal infiltration of fetal cells, increased production of angiotensin II (Ang II)-signaling pathway molecules, eg, matrix metalloproteases (MMPs), and monocyte chemoattractant protein (MCP-1), transforming growth factor B1 (TGF-beta1), enhanced activation of MMPs, TGF-beta, and NADPH oxidase, and reduced nitric oxide (NO) bioavailability. This profile is similar to that induced at younger ages in experimental animal models of hypertension or atherosclerosis. In humans, this proinflammatory state, which occurs in the absence of lipid deposition, appears to be attributable to aging, per se. Other well known human risk factors, eg, altered lipid metabolism, smoking, and lack of exercise, interact with this arterial substrate that is altered by aging and render the aging human artery fertile soil for facilitation of the initiation and progression of arterial diseases. Therapies to reduce or retard this age-associated proinflammatory state within the grossly appearing arterial wall central arteries, in addition to slowing arterial aging, per se, may have a substantial impact on the quintessential age-associated arterial diseases of our society.

Comparative endocrinology of aging and longevity regulation

Hormones regulate growth, development, metabolism, and other complex processes in multicellular animals. For many years it has been suggested that hormones may also influence the rate of the aging process. Aging is a multifactorial process that causes biological systems to break down and cease to function in adult organisms as time passes, eventually leading to death. The exact underlying causes of the aging process remain a topic for debate, and clues that may shed light on these causes are eagerly sought after. In the last two decades, gene mutations that result in delayed aging and extended longevity have been discovered, and many of the affected genes have been components of endocrine signaling pathways. In this review we summarize the current knowledge on the roles of endocrine signaling in the regulation of aging and longevity in various animals. We begin by discussing the notion that conserved systems, including endocrine signaling pathways, "regulate" the aging process. Findings from the major model organisms: worms, flies, and rodents, are then outlined. Unique lessons from studies of non-traditional models: bees, salmon, and naked mole rats, are also discussed. Finally, we summarize the endocrinology of aging in humans, including changes in hormone levels with age, and the involvement of hormones in aging-related diseases. The most well studied and widely conserved endocrine pathway that affects aging is the insulin/insulin-like growth factor system. Mutations in genes of this pathway increase the lifespan of worms, flies, and mice. Population genetic evidence also suggests this pathway's involvement in human aging. Other hormones including steroids have been linked to aging only in a subset of the models studied. Because of the value of comparative studies, it is suggested that the aging field could benefit from adoption of additional model organisms.

Mechanisms Underlying Hypertrophic Remodeling and Increased Stiffness of Mesenteric Resistance Arteries From Aged Rats

The mechanisms associated with structural and mechanical alterations of mesenteric resistance arteries from aged rats were investigated by using pressure myography, confocal microscopy, immunofluorescence, and picrosirius red staining. Arteries from old rats showed: (i) increased wall and media thickness, greater number of smooth muscle cell (SMC) layers but decreased density of SMC; (ii) increased number of adventitial cells; (iii) hypertrophy of nuclei of SMC and endothelial cells; (iv) increased stiffness associated with increased total collagen content and collagen I/III deposition in the media; and (v) similar content but changes in elastin structure in the internal elastic lamina. Hypertrophic outward remodeling in aged rat resistance arteries involve adventitial cells hyperplasia, reorganization of the same number of hypertrophied SMC in more SMC layers leading to thickened media and endothelial cell hypertrophy. Fibrosis associated with collagen deposition and changes in elastin structure might be responsible for the increased stiffness of resistance arteries from aged rats.

Aging, smooth muscle cells and vascular pathobiology: Implications for atherosclerosis

Epidemiological and autopsy studies suggest a close link between aging and the clinical manifestation of atherosclerosis. Several experiments show increased arterial susceptibility to atherogenetic stimuli in aged subjects. All together, these findings support the concept that aging represents an independent atherogenetic risk factor, intimately associated to other parietal, microenvironmental and systemic noxae. Smooth muscle cells (SMCs) represent the major arterial cell population. As aging occurs, SMCs progressively migrate from the tunica media and accumulate into the tunica intima. Myointimal thickening may represent the site where low-grade atherogenic stimuli cause early development and more severe lesion progression. Intimal SMC accumulation is characterized from a switch, from a differentiated to a synthetic phenotype, with reduced myocytic cytoskeletal markers and the expression of new proteins. Aging also associates to changes of SMC proliferative and apoptotic behavior and response to growth factors, such as transforming growth factor-beta1. The alteration of SMC properties represents a crucial event in the pathobiology of arterial wall, since it contributes to the vascular remodeling and decline of function with aging and favors the progression of atherosclerosis. Increased knowledge of biomolecular mechanisms regulating these events helps to develop new strategies aimed at contrasting the adverse effect of vascular aging.

Aging influences development and progression of early aortic atherosclerotic lesions in cholesterol-fed rabbits

The arterial wall in aged animals shows an increased susceptibility to develop atherosclerotic lesions, although the mechanisms by which aging acts are still unclear. We investigated early aortic lesions in aged rabbits (5 to 6 years old, AH group) and young rabbits (2 months old, YH group) after 2 months of 0.2% cholesterol feeding. Fatty streaks or spots mainly in the proximal segments occupied a relative surface area that was greater in AH than in YH rabbits, although plasma cholesterol and lipoprotein levels did not differ. YH lesions showed an irregular endothelial profile mainly from accumulations of large, rounded, RAM 11-positive macrophagic foam cells. There was a higher percentage of myocytic, CD-5-positive, proliferating, and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells and larger accumulation of glycosaminoglycans in AH fatty streaks than in YH lesions. Ligation-mediated polymerase chain reaction confirmed differences in apoptosis. Early fibromuscular coats and subendothelial plasma-like insudate were also observed in AH lesions. Aged-matched normocholesterolemic rabbits showed a diffuse aortic intimal thickening composed of myocytic cells with a synthetic phenotype and extracellular matrix rich in glycosaminoglycans. In addition, in aged rabbits, we observed a spontaneous increase of monocytes adhering to the endothelial surface and a reduced expression of endothelial nitric oxide synthase in areas distant from the branches. These plasma cholesterol-independent spontaneous changes in the aortic wall of aged rabbits seem to act as a multiple atherogenic risk factor. Moreover, age-related differences in the distribution, composition, and proliferative and apoptotic rates represent crucial events during the progression of early fatty streaks to advanced plaques.

Age-related changes affecting atherosclerotic risk. Potential for pharmacological intervention

The incidence of cardiovascular diseases that are related to the atherosclerotic process increases exponentially with age. Organ lesions, the clinical manifestation of atherosclerotic disease, are late events due to complications in the plaque (ulceration, thrombosis, calcification) which are the result of an increased vulnerability to disruption of a previously stable plaque. The higher incidence of age-related clinical events could be explained by a rising sensitivity of plaques to destabilising factors, both parietal and humoral. The increased probability that a plaque in an elderly patient will became vulnerable could be related to those destabilising factors that significantly increase with aging, such as advanced glycation end-products. For these reasons, it seems most important that the analysis of these age-related destabilising factors, rather than those factors that promote the development of early atherosclerotic plaques, should be undertaken. Taking the point of view of a pharmacological intervention, this should eventually lead to a more complete understanding of this process.

Propionyl-L-carnitine prevents the progression of atherosclerotic lesions in aged hyperlipemic rabbits

We have characterized the extent and the phenotype of total and proliferating cell population of aortic plaques in aged rabbits receiving a long-term low-dose cholesterol hyperlipemic diet, which represents an experimental model of atherosclerosis. For nine months, rabbits received the hypercholesterolemic diet alone or in addition to a treatment with propionyl-L-carnitine (PLC), a derivative of carnitine, an intramitochondrial carrier of fatty acids present in most cell types. We observed that, in both PLC-treated and control hyperlipemic rabbits, the ratio between proliferating macrophage-derived and smooth muscle cells was 2:1. PLC in addition to the hypercholesterolemic diet induced a marked lowering of plasma triglycerides, very low density lipoprotein (VLDL) and intermediate density lipoprotein (IDL) triglycerides, while plasma cholesterol was slightly and transiently reduced. Moreover, PLC-treated hyperlipemic rabbits exhibited a reduction of plaque thickness and extent, a slight but significant reduction of the percentage of macrophage-derived cells as compared to control hyperlipemic animals and a reduction of the number of both proliferating macrophage- and smooth muscle cell-derived foam cells. Finally, both proliferating and non-proliferating plaque cells expressed large amounts of macrophage colony-stimulating factor protein, in particular macrophage-derived foam cells. These results indicate that a modification of plasma lipemic pattern obtained by a long-term oral administration of PLC was associated with a decrease of plaque cell proliferation and severity of aortic atherosclerotic lesions.