Elastin haploinsufficiency induces alternative aging processes in the aorta

Constitutive Modeling of Mouse Arteries Suggests Changes in Directional Coupling and Extracellular Matrix Remodeling That Depend on Artery Type, Age, Sex, and Elastin Amounts

Arterial stiffening occurs during natural aging, is associated with an increased risk of adverse cardiovascular events, and can follow different timelines in males and females. One mechanism of arterial stiffening includes remodeling of the extracellular matrix (ECM), which alters the wall material properties. We used elastin haploinsufficient (Eln+/-) and wildtype (Eln+/+) mice to investigate how material properties of two different arteries (ascending aorta and carotid artery) change with age, sex, and ECM composition. We used a constitutive model by Dong and Sun that is based on the Holzapfel-Gasser-Ogden (HGO) type, but does not require a discrete number of fibrous ECM families and allows varied deformation coupling. We find that the amount of deformation coupling for the best fit model depends on the artery type. We also find that remodeling to maintain homeostatic (i.e., young, wildtype) values of biomechanical parameters with age, sex, and ECM composition depends on the artery type, with ascending aorta being more adaptable than carotid artery. Fitted material constants indicate sex-dependent remodeling that may be important for determining the time course of arterial stiffening in males and females. We correlated fitted material constants with ECM composition measured by biochemical (ascending aorta) or histological (carotid artery) methods. We show significant correlations between ECM composition and material parameters for the mean values for each group, with biochemical measurements correlating more strongly than histological measurements. Understanding how arterial stiffening depends on age, sex, ECM composition, and artery type may help design effective, personalized clinical treatment strategies.

Compromised homeostasis in aged carotid arteries revealed by microstructural studies of elastic lamellae

Healthy arteries are continuously subjected to diverse mechanical stimuli and adapt in order to maintain a mechanical homeostasis which is characterized by a uniform distribution of wall stresses. However, aging may compromise the homeostatic microenvironment within arteries. Structural heterogeneity has been suggested as a potential microstructural mechanism that could lead to homogeneous stress distribution across the arterial wall. Our previous study on the unfolding and stretching of the elastic lamellae revealed the underlying microstructural mechanism for equalizing the circumferential stresses through wall; inner elastic layers are wavier and unfold more than the outer layers which helps to evenly distribute lamellar stretching (Yu et al., 2018). In this study, we investigated the effect of aging on lamellar deformation and its implications for tissue homeostasis. Common carotid arteries from aged mice were imaged under a multi-photon microscope while subjected to biaxial extension and inflation at five different pressures ranging from 0 up to 120 mmHg. Lamellar unfolding during pressurization was then determined from the reconstructed cross-sectional images of elastic lamellae. Tissue-level circumferential stretch was combined with the lamellar unfolding to calculate lamellar stretching. Our results revealed that the straightness gradient of aged elastic lamellae is similar to the young ones. However, during pressurization, the inner elastic lamella of the aged mice unfolded significantly more than the inner layer in young arteries. An important finding of our study is the uneven increase in inter-lamellar space which contributed to a nonuniform stretching of the elastic lamellae of aged mice arteries, elevated stress gradient, and a shifting of the load-bearing component to adventitia. Our results shed light into the complex microstructural mechanisms that take place in aging and adversely affect arterial mechanical behavior and homeostasis.

Environmental and genetic predictors of human cardiovascular ageing

Cardiovascular ageing is a process that begins early in life and leads to a progressive change in structure and decline in function due to accumulated damage across diverse cell types, tissues and organs contributing to multi-morbidity. Damaging biophysical, metabolic and immunological factors exceed endogenous repair mechanisms resulting in a pro-fibrotic state, cellular senescence and end-organ damage, however the genetic architecture of cardiovascular ageing is not known. Here we use machine learning approaches to quantify cardiovascular age from image-derived traits of vascular function, cardiac motion and myocardial fibrosis, as well as conduction traits from electrocardiograms, in 39,559 participants of UK Biobank. Cardiovascular ageing is found to be significantly associated with common or rare variants in genes regulating sarcomere homeostasis, myocardial immunomodulation, and tissue responses to biophysical stress. Ageing is accelerated by cardiometabolic risk factors and we also identify prescribed medications that are potential modifiers of ageing. Through large-scale modelling of ageing across multiple traits our results reveal insights into the mechanisms driving premature cardiovascular ageing and reveal potential molecular targets to attenuate age-related processes.

Characterization of the Zebrafish Elastin a (elnasa12235) Mutant: A New Model of Elastinopathy Leading to Heart Valve Defects

Elastic fibers are extracellular macromolecules that provide resilience and elastic recoil to elastic tissues and organs in vertebrates. They are composed of an elastin core surrounded by a mantle of fibrillin-rich microfibrils and are essentially produced during a relatively short period around birth in mammals. Thus, elastic fibers have to resist many physical, chemical, and enzymatic constraints occurring throughout their lives, and their high stability can be attributed to the elastin protein. Various pathologies, called elastinopathies, are linked to an elastin deficiency, such as non-syndromic supravalvular aortic stenosis (SVAS), Williams-Beuren syndrome (WBS), and autosomal dominant cutis laxa (ADCL). To understand these diseases, as well as the aging process related to elastic fiber degradation, and to test potential therapeutic molecules in order to compensate for elastin impairments, different animal models have been proposed. Considering the many advantages of using zebrafish, we here characterize a zebrafish mutant for the elastin a paralog (elna^sa12235) with a specific focus on the cardiovascular system and highlight premature heart valve defects at the adult stage.

Elastin haploinsufficiency accelerates age-related structural and functional changes in the renal microvasculature and impairment of renal hemodynamics in female mice

Age-related decline in functional elastin is associated with increased arterial stiffness, a known risk factor for developing cardiovascular disease. While the contribution of elastin insufficiency to the stiffening of conduit arteries is well described, little is known about the impact on the structure and function of the resistance vasculature, which contributes to total peripheral resistance and the regulation of organ perfusion. In this study, we determined how elastin insufficiency impinges on age-related changes in the structure and biomechanical properties of the renal microvasculature, altering renal hemodynamics and the response of the renal vascular bed to changes in renal perfusion pressure (RPP) in female mice. Using Doppler ultrasonography, we found that resistive index and pulsatility index were elevated in young Eln +/- and aged mice. Histological examination showed thinner internal and external elastic laminae, accompanied by increased elastin fragmentation in the medial layer without any calcium deposits in the small intrarenal arteries of kidneys from young Eln +/- and aged mice. Pressure myography of interlobar arteries showed that vessels from young Eln +/- and aged mice had a slight decrease in distensibility during pressure loading but a substantial decline in vascular recoil efficiency upon pressure unloading. To examine whether structural changes in the renal microvasculature influenced renal hemodynamics, we clamped neurohumoral input and increased renal perfusion pressure by simultaneously occluding the superior mesenteric and celiac arteries. Increased renal perfusion pressure caused robust changes in blood pressure in all groups; however, changes in renal vascular resistance and renal blood flow (RBF) were blunted in young Eln +/- and aged mice, accompanied by decreased autoregulatory index, indicating greater impairment of renal autoregulation. Finally, increased pulse pressure in aged Eln +/- mice positively correlated with high renal blood flow. Together, our data show that the loss of elastin negatively affects the structural and functional integrity of the renal microvasculature, ultimately worsening age-related decline in kidney function.

Role of elastic fiber degradation in disease pathogenesis

Elastin is a crucial extracellular matrix protein that provides structural integrity to tissues. Crosslinked elastin and associated microfibrils, named elastic fiber, contribute to biomechanics by providing the elasticity required for proper function. During aging and disease, elastic fiber can be progressively degraded and since there is little elastin synthesis in adults, degraded elastic fiber is not regenerated. There is substantial evidence linking loss or damage of elastic fibers to the clinical manifestation and pathogenesis of a variety of diseases. Disruption of elastic fiber networks by hereditary mutations, aging, or pathogenic stimuli results in systemic ailments associated with the production of elastin degradation products, inflammatory responses, and abnormal physiology. Due to its longevity, unique mechanical properties, and widespread distribution in the body, elastic fiber plays a central role in homeostasis of various physiological systems. While pathogenesis related to elastic fiber degradation has been more thoroughly studied in elastic fiber rich tissues such as the vasculature and the lungs, even tissues containing relatively small quantities of elastic fibers such as the eyes or joints may be severely impacted by elastin degradation. Elastic fiber degradation is a common observation in certain hereditary, age, and specific risk factor exposure induced diseases representing a converging point of pathological clinical phenotypes which may also help explain the appearance of co-morbidities. In this review, we will first cover the role of elastic fiber degradation in the manifestation of hereditary diseases then individually explore the structural role and degradation effects of elastic fibers in various tissues and organ systems. Overall, stabilizing elastic fiber structures and repairing lost elastin may be effective strategies to reverse the effects of these diseases.

Physiological Impact of a Synthetic Elastic Protein in Arterial Diseases Related to Alterations of Elastic Fibers: Effect on the Aorta of Elastin-Haploinsufficient Male and Female Mice

Elastic fibers, made of elastin (90%) and fibrillin-rich microfibrils (10%), are the key extracellular components, which endow the arteries with elasticity. The alteration of elastic fibers leads to cardiovascular dysfunctions, as observed in elastin haploinsufficiency in mice (Eln+/-) or humans (supravalvular aortic stenosis or Williams-Beuren syndrome). In Eln+/+ and Eln+/- mice, we evaluated (arteriography, histology, qPCR, Western blots and cell cultures) the beneficial impact of treatment with a synthetic elastic protein (SEP), mimicking several domains of tropoelastin, the precursor of elastin, including hydrophobic elasticity-related domains and binding sites for elastin receptors. In the aorta or cultured aortic smooth muscle cells from these animals, SEP treatment induced a synthesis of elastin and fibrillin-1, a thickening of the aortic elastic lamellae, a decrease in wall stiffness and/or a strong trend toward a reduction in the elastic lamella disruptions in Eln+/- mice. SEP also modified collagen conformation and transcript expressions, enhanced the aorta constrictive response to phenylephrine in several animal groups, and, in female Eln+/- mice, it restored the normal vasodilatory response to acetylcholine. SEP should now be considered as a biomimetic molecule with an interesting potential for future treatments of elastin-deficient patients with altered arterial structure/function.

Rapid Regeneration of a Neoartery with Elastic Lamellae

Native arteries contain a distinctive intima-media composed of organized elastin and an adventitia containing mature collagen fibrils. In contrast, implanted biodegradable small-diameter vascular grafts do not present spatially regenerated, organized elastin. The elastin-containing structures within the intima-media region encompass the elastic lamellae (EL) and internal elastic lamina (IEL) and are crucial for normal arterial function. Here, the development of a novel electrospun small-diameter vascular graft that facilitates de novo formation of a structurally appropriate elastin-containing intima-media region following implantation is described. The graft comprises a non-porous microstructure characterized by tropoelastin fibers that are embedded in a PGS matrix. After implantation in mouse abdominal aorta, the graft develops distinct cell and extracellular matrix profiles that approximate the native adventitia and intima-media by 8 weeks. Within the newly formed intima-media region there are circumferentially aligned smooth muscle cell layers that alternate with multiple EL similar to that found in the arterial wall. By 8 months, the developed adventitia region contains mature collagen fibrils and the neoartery presents a distinct IEL with thickness comparable to that in mouse abdominal aorta. It is proposed that this new class of material can generate the critically required, organized elastin needed for arterial regeneration.

Elastin, arterial mechanics, and stenosis

Elastin is a long-lived extracellular matrix protein that is organized into elastic fibers that provide elasticity to the arterial wall, allowing stretch and recoil with each cardiac cycle. By forming lamellar units with smooth muscle cells, elastic fibers transduce tissue-level mechanics to cell-level changes through mechanobiological signaling. Altered amounts or assembly of elastic fibers leads to changes in arterial structure and mechanical behavior that compromise cardiovascular function. In particular, genetic mutations in the elastin gene (ELN) that reduce elastin protein levels are associated with focal arterial stenosis, or narrowing of the arterial lumen, such as that seen in supravalvular aortic stenosis and Williams-Beuren syndrome. Global reduction of Eln levels in mice allows investigation of the tissue- and cell-level arterial mechanical changes and associated alterations in smooth muscle cell phenotype that may contribute to stenosis formation. A loxP-floxed Eln allele in mice highlights cell type- and developmental origin-specific mechanobiological effects of reduced elastin amounts. Eln production is required in distinct cell types for elastic layer formation in different parts of the mouse vasculature. Eln deletion in smooth muscle cells from different developmental origins in the ascending aorta leads to characteristic patterns of vascular stenosis and neointima. Dissecting the mechanobiological signaling associated with local Eln depletion and subsequent smooth muscle cell response may help develop new therapeutic interventions for elastin-related diseases.

Mouse aortic biomechanics are affected by short-term defective autophagy in vascular smooth muscle cells

The physiology of vascular smooth muscle (VSMC) cells is affected by autophagy, a catabolic cellular mechanism responsible for nutrient recycling. Autophagy-inducing compounds may reverse arterial stiffening, whereas congenital VSMC-specific autophagy deficiency promotes arterial stiffening. The elevated aortic stiffness in 3.5-month-old C57Bl/6 mice, in which the essential autophagy-related gene Atg7 was specifically deleted in the VSMCs (Atg7F/F SM22α-Cre+ mice) was mainly due to passive aortic wall remodeling. The present study investigated whether aortic stiffness was also modulated by a shorter duration of autophagy deficiency. Therefore, aortic segments of 2-month-old Atg7F/F SM22α-Cre+ mice were studied. Similarly to the older mice, autophagy deficiency in VSMCs promoted aortic stiffening by elastin degradation and elastin breaks, and increased the expression of the calcium binding protein S100A4 (+ 157%), the aortic wall thickness (+ 27%), the sensitivity of the VSMCs to depolarization and the contribution of VGCC mediated Ca2+ influx to α1 adrenergic contractions. Hence, all these phenomena occurred before the age of 2 months. When compared to autophagy deficiency in VSMCs at 3.5 months, shorter term autophagy deficiency led to higher segment diameter at 80 mmHg (+ 7% versus - 2%), normal baseline tonus (versus increased), unchanged IP3-mediated phasic contractions (versus enhanced), and enhanced endothelial cell function (versus normal). Overall, and because in vivo cardiac parameters or aortic pulse wave velocity were not affected, these observations indicate that congenital autophagy deficiency in VSMCs of Atg7F/F SM22α-Cre+ mice initiates compensatory mechanisms to maintain circulatory homeostasis.

Apelin expression deficiency in mice contributes to vascular stiffening by extracellular matrix remodeling of the aortic wall

Numerous recent studies have shown that in the continuum of cardiovascular diseases, the measurement of arterial stiffness has powerful predictive value in cardiovascular risk and mortality and that this value is independent of other conventional risk factors, such as age, cholesterol levels, diabetes, smoking, or average blood pressure. Vascular stiffening is often the main cause of arterial hypertension (AHT), which is common in the presence of obesity. However, the mechanisms leading to vascular stiffening, as well as preventive factors, remain unclear. The aim of the present study was to investigate the consequences of apelin deficiency on the vascular stiffening and wall remodeling of aorta in mice. This factor freed by visceral adipose tissue, is known for its homeostasic role in lipid and vascular metabolisms, or again in inflammation. We compared the level of metabolic markers, inflammation of white adipose tissue (WAT), and aortic wall remodeling from functional and structural approaches in apelin-deficient and wild-type (WT) mice. Apelin-deficient mice were generated by knockout of the apelin gene (APL-KO). From 8 mice by groups, aortic stiffness was analyzed by pulse wave velocity measurements and by characterizations of collagen and elastic fibers. Mann-Whitney statistical test determined the significant data (p < 5%) between groups. The APL-KO mice developed inflammation, which was associated with significant remodeling of visceral WAT, such as neutrophil elastase and cathepsin S expressions. In vitro, cathepsin S activity was detected in conditioned medium prepared from adipose tissue of the APL-KO mice, and cathepsin S activity induced high fragmentations of elastic fiber of wild-type aorta, suggesting that the WAT secretome could play a major role in vascular stiffening. In vivo, remodeling of the extracellular matrix (ECM), such as collagen accumulation and elastolysis, was observed in the aortic walls of the APL-KO mice, with the latter associated with high cathepsin S activity. In addition, pulse wave velocity (PWV) and AHT were increased in the APL-KO mice. The latter could explain aortic wall remodeling in the APL-KO mice. The absence of apelin expression, particularly in WAT, modified the adipocyte secretome and facilitated remodeling of the ECM of the aortic wall. Thus, elastolysis of elastic fibers and collagen accumulation contributed to vascular stiffening and AHT. Therefore, apelin expression could be a major element to preserve vascular homeostasis.

Early Aberrant Angiogenesis Due to Elastic Fiber Fragmentation in Aortic Valve Disease

Elastic fiber fragmentation (EFF) is a hallmark of aortic valve disease (AVD), and neovascularization has been identified as a late finding related to inflammation. We sought to characterize the relationship between early EFF and aberrant angiogenesis. To examine disease progression, regional anatomy and pathology of aortic valve tissue were assessed using histochemistry, immunohistochemistry, and electron microscopy from early-onset (<40 yo) and late-onset (≥40 yo) non-syndromic AVD specimens. To assess the effects of EFF on early AVD processes, valve tissue from Williams and Marfan syndrome patients was also analyzed. Bicuspid aortic valve was more common in early-onset AVD, and cardiovascular comorbidities were more common in late-onset AVD. Early-onset AVD specimens demonstrated angiogenesis without inflammation or atherosclerosis. A distinct pattern of elastic fiber components surrounded early-onset AVD neovessels, including increased emilin-1 and decreased fibulin-5. Different types of EFF were present in Williams syndrome (WS) and Marfan syndrome (MFS) aortic valves; WS but not MFS aortic valves demonstrated angiogenesis. Aberrant angiogenesis occurs in early-onset AVD in the absence of inflammation, implicating EFF. Elucidation of underlying mechanisms may inform the development of new pharmacologic treatments.

Large artery stiffness and brain health: insights from animal models

There are no effective treatments available to halt or reverse the progression of age-related cognitive decline and Alzheimer's disease. Thus, there is an urgent need to understand the underlying mechanisms of disease etiology and progression to identify novel therapeutic targets. Age-related changes to the vasculature, particularly increases in stiffness of the large elastic arteries, are now recognized as important contributors to brain aging. There is a growing body of evidence for an association between greater large artery stiffness and cognitive impairment among both healthy older adults and patients with Alzheimer's disease. However, studies in humans are limited to only correlative evidence, whereas animal models allow researchers to explore the causative mechanisms linking arterial stiffness to neurocognitive dysfunction and disease. Recently, several rodent models of direct modulation of large artery stiffness and the consequent effects on the brain have been reported. Common outcomes among these models have emerged, including evidence that greater large artery stiffness causes cerebrovascular dysfunction associated with increased oxidative stress and inflammatory signaling. The purpose of this mini-review is to highlight the recent findings associating large artery stiffness with deleterious brain outcomes, with a specific focus on causative evidence obtained from animal models. We will also discuss the gaps in knowledge that remain in our understanding of how large artery stiffness affects brain function and disease outcomes.

Elastin haploinsufficiency in mice has divergent effects on arterial remodeling with aging depending on sex

Elastin is a primary structural protein in the arterial wall that contributes to vascular mechanical properties and degrades with aging. Aging is associated with arterial stiffening and an increase in blood pressure. There is evidence that arterial aging follows different timelines with sex. Our objective was to investigate how elastin content affects arterial remodeling in male and female mice with aging. We used male and female wild-type (Eln^+/+) and elastin heterozygous (Eln^+/-) mice at 6, 12, and 24 mo of age and measured their blood pressure and arterial morphology, wall structure, protein content, circumferential stress, stretch ratio, and stiffness. Two arteries were used with varying contents of elastin: the left common carotid and ascending aorta. We show that Eln^+/- arteries start at a different homeostatic set point for circumferential wall stress, stretch, and material stiffness but show similar increases with aging to Eln^+/+ mice. With aging, structural stiffness is greatly increased, while material stiffness and circumferential stress are only slightly increased, highlighting the importance of maintaining these homeostatic values. Circumferential stretch shows the smallest change with age and may be important for controlling cellular phenotype. Independent sex differences are mostly associated with males being larger than females; however, many of the measured factors show age × sex and/or genotype × sex interactions, indicating that males and females follow different cardiovascular remodeling timelines with aging and are differentially affected by reduced elastin content.NEW & NOTEWORTHY A comprehensive study on arterial mechanical behavior as a function of elastin content, aging, and sex in mice. Elastin haploinsufficient arteries start at a different homeostatic set point for mechanical parameters such as circumferential stress, stretch, and material stiffness. Structural stiffness of the arterial wall greatly increases with aging, as expected, but there are interactions between sex and aging for most of the mechanical parameters that are important to consider in future work.

Dill Extract Induces Elastic Fiber Neosynthesis and Functional Improvement in the Ascending Aorta of Aged Mice with Reversal of Age-Dependent Cardiac Hypertrophy and Involvement of Lysyl Oxidase-Like-1

Elastic fibers (90% elastin, 10% fibrillin-rich microfibrils) are synthesized only in early life and adolescence mainly by the vascular smooth muscle cells through the cross-linking of its soluble precursor, tropoelastin. Elastic fibers endow the large elastic arteries with resilience and elasticity. Normal vascular aging is associated with arterial remodeling and stiffening, especially due to the end of production and degradation of elastic fibers, leading to altered cardiovascular function. Several pharmacological treatments stimulate the production of elastin and elastic fibers. In particular, dill extract (DE) has been demonstrated to stimulate elastin production in vitro in dermal equivalent models and in skin fibroblasts to increase lysyl oxidase-like-1 (LOXL-1) gene expression, an enzyme contributing to tropoelastin crosslinking and elastin formation. Here, we have investigated the effects of a chronic treatment (three months) of aged male mice with DE (5% or 10% v/v, in drinking water) on the structure and function of the ascending aorta. DE treatment, especially at 10%, of aged mice protected pre-existing elastic lamellae, reactivated tropoelastin and LOXL-1 expressions, induced elastic fiber neo-synthesis, and decreased the stiffness of the aging aortic wall, probably explaining the reversal of the age-related cardiac hypertrophy also observed following the treatment. DE could thus be considered as an anti-aging product for the cardiovascular system.

Rise and fall of elastic fibers from development to aging. Consequences on arterial structure-function and therapeutical perspectives

In the arteries of vertebrates, evolution has given rise to resilient macromolecular structures, elastin and elastic fibers, capable of sustaining an elevated blood pressure and smoothening the discontinuous blood flow and pressure generated by the heart. Elastic fibers are produced only during development and childhood, before being progressively degraded by mechanical stress and enzymatic activities during adulthood and aging. During this period, arterial elastic fiber calcification and loading of lipids also occur, all of these events conducting to arteriosclerosis. This leads to a progressive dysfunction of the large elastic arteries inducing elevated blood pressure as well as altered hemodynamics and organ perfusion, which induce more global malfunctions of the body during normal aging. Additionally, some arterial conditions occur more frequently with advancing age, such as atherosclerosis or aneurysms, which are called age-related diseases or pathological aging. The physiological or pathological degradation of elastic fibers and function of elastic arteries seemed to be rather inevitable over time. However, during the recent years, different molecules - including several ATP-dependent potassium channel openers, such as minoxidil - have been shown to re-induce elastin production and elastic fiber assembly, leading to improvements in the arterial structure and function or in organ perfusion. This review summarizes the changes in the arterial elastic fibers and structure from development until aging, and presents some of the potential pharmacotherapies leading to elastic fiber neosynthesis and arterial function improvement.

Chronic administration of minoxidil protects elastic fibers and stimulates their neosynthesis with improvement of the aorta mechanics in mice

Arterial wall elastic fibers, made of 90% elastin, are arranged into elastic lamellae which are responsible for the resilience and elastic properties of the large arteries (aorta and its proximal branches). Elastin is synthesized only in early life and adolescence mainly by the vascular smooth muscles cells (VSMC) through the cross-linking of its soluble precursor, tropoelastin. In normal aging, the elastic fibers become fragmented and the mechanical load is transferred to collagen fibers, which are 100-1000 times stiffer than elastic fibers. Minoxidil, an ATP-dependent K⁺ channel opener, has been shown to stimulate elastin expression in vitro, and in vivo in the aorta of male aged mice and young adult hypertensive rats. Here, we have studied the effect of a 3-month chronic oral treatment with minoxidil (120 mg/L in drinking water) on the abdominal aorta structure and function in adult (6-month-old) and aged (24-month-old) male and female mice. Our results show that minoxidil treatment preserves elastic lamellae integrity at both ages, which is accompanied by the formation of newly synthesized elastic fibers in aged mice. This leads to a generally decreased pulse pressure and a significant improvement of the arterial biomechanical properties in female mice, which present an increased distensibility and a decreased rigidity of the aorta. Our studies show that minoxidil treatment reversed some of the major adverse effects of arterial aging in mice and could be an interesting anti-arterial aging agent, also potentially usable for female-targeted therapies.

Minoxidil versus placebo in the treatment of arterial wall hypertrophy in children with Williams Beuren Syndrome: a randomized controlled trial

Background

Insufficient elastin synthesis leads to vascular complications and arterial hypertension in children with Williams-Beuren syndrome. Restoring sufficient quantity of elastin should then result in prevention or inhibition of vascular malformations and improvement in arterial blood pressure.

Methods

The aim of this study was to assess the efficacy and safety of minoxidil on Intima Media Thickness (IMT) on the right common carotid artery after twelve-month treatment in patient with Williams-Beuren syndrome. We performed a randomized placebo controlled double blind trial. All participants were treated for 12 months and followed for 18 months. The principal outcome was assessed by an independent adjudication committee blinded to the allocated treatment groups.

Results

The principal outcome was available for 9 patients in the placebo group and 8 patients in the minoxidil group. After 12-month treatment, the IMT in the minoxidil group increased by 0.03 mm (95% CI -0.002, 0.06) compared with 0.01 mm (95%CI - 0.02, 0.04 mm) in the placebo group (p = 0.4). Two serious adverse events unrelated to the treatment occurred, one in the minoxidil and 1 in the placebo group. After 18 months, the IMT increased by 0.07 mm (95% CI 0.04, 0.10 mm) in the minoxidil compared with 0.01 mm (95% CI -0.02, 0.04 mm) in the placebo group (p = 0.008).

Conclusion

Our results suggest a slight increase after 12 and 18-month follow-up in IMT. More understanding of the biological changes induced by minoxidil should better explain its potential role on elastogenesis in Williams-Beuren syndrome.

Trials registration

US National Institutes of Health Clinical Trial Register (NCT00876200). Registered 3 April 2009 (retrospectively registered).

Electronic supplementary material

The online version of this article (10.1186/s12887-019-1544-1) contains supplementary material, which is available to authorized users.

Cerebral and skeletal muscle feed artery vasoconstrictor responses in a mouse model with greater large elastic artery stiffness

NEW FINDINGS

What is the central question of this study? Greater large artery stiffness is associated with dysfunctional resistance artery vasodilatory responses, impaired memory and greater risk of Alzheimer's disease. However, it is unknown whether stiffer large arteries affect cerebral and skeletal muscle feed artery responses to vasoconstrictors. What is the main finding and its importance? In a mouse model with greater large artery stiffness (Eln^+/- ), we find an exacerbated vasoconstrictor response to angiotensin II in cerebral arteries, but not skeletal muscle feed arteries, thus implicating altered cerebral artery angiotensin II responsiveness in the poor brain outcomes associated with greater large artery stiffness.

ABSTRACT

Greater stiffness of the large elastic arteries is associated with end-organ damage and dysfunction. At the same time, resistance artery vasoconstrictor responsiveness influences vascular tone and organ blood flow. However, it is unknown whether large elastic artery stiffness modulates the responsiveness to vasoconstrictors in resistance arteries of the cerebral or skeletal muscle circulations. We previously described the elastin haploinsufficient (Eln^+/- ) mouse as a model with greater aortic stiffness, but with similar cerebral and skeletal muscle feed artery stiffness to wild-type (Eln^+/+ ) mice. Here, we used this model to examine the relationship between large elastic artery stiffness and resistance artery vasoconstrictor responses. In middle cerebral arteries (MCAs), vasoconstriction in response to angiotensin II (Ang II) was ∼40% greater in Eln^+/- compared with Eln^+/+ mice (P = 0.02), and this group difference was ameliorated by losartan, indicating a role for Ang II type 1 receptors (AT1Rs). In gastrocnemius feed arteries, Eln^+/- and Eln^+/+ mice did not differ in the response to Ang II. In addition, the vasoconstrictor responses to noradrenaline, endothelin-1 and potassium chloride were not different between Eln^+/- and Eln^+/+ mice for either MCAs or gastrocnemius feed arteries. The MCA AT1R gene expression did not differ between groups, whereas Ang II type 2 receptor gene expression was ∼50% lower in MCAs from Eln^+/- versus Eln^+/+ mice (P = 0.01). In conclusion, greater large elastic artery stiffness is associated with an exacerbated vasoconstriction response to Ang II in cerebral arteries, but is not associated with the responses to other vasoconstrictors in either cerebral or skeletal muscle feed arteries.

Compromised mechanical homeostasis in arterial aging and associated cardiovascular consequences

Aging leads to central artery stiffening and associated hemodynamic sequelae. Because healthy arteries exhibit differential geometry, composition, and mechanical behaviors along the central vasculature, we sought to determine whether wall structure and mechanical function differ across five vascular regions-the ascending and descending thoracic aorta, suprarenal and infrarenal abdominal aorta, and common carotid artery-in 20 versus 100-week-old male wild-type mice. Notwithstanding generally consistent changes across these regions, including a marked thickening of the arterial wall, diminished in vivo axial stretch, and loss of elastic energy storage capacity, the degree of changes tended to be slightly greater in abdominal than in thoracic or carotid vessels. Likely due to the long half-life of vascular elastin, most mechanical changes in the arterial wall resulted largely from a distributed increase in collagen, including thicker fibers in the media, and localized increases in glycosaminoglycans. Changes within the central arteries associated with significant increases in central pulse pressure and adverse changes in the left ventricle, including increased cardiac mass and decreased diastolic function. Given the similar half-life of vascular elastin in mice and humans but very different life-spans, there are important differences in the aging of central vessels across these species. Nevertheless, the common finding of aberrant matrix remodeling contributing to a compromised mechanical homeostasis suggests that studies of central artery aging in the mouse can provide insight into mechanisms and treatment strategies for the many adverse effects of vascular aging in humans.

Early growth response factor-1 DNA enzyme 1 inhibits the formation of abdominal aortic aneurysm in rats

The aim of the present study was to characterize the effects of early growth response factor-1 DNA enzyme (EDRz) in a rat abdominal aortic aneurysm (AAA) model to determine the mechanism by which EDRz inhibits AAA and affects the formation of AAA by regulating the activity of matrix metalloproteinase (MMP)-2 and MMP-9. EDRz was transfected into the abdominal aorta of rats using the jetPRIME transfection reagent following infusion with elastase. Fluorescent microscopy, hematoxylin and eosin staining, ultrastructural analysis, reverse transcription-quantitative polymerase chain reaction, western blotting and immunohistochemical analysis were performed to characterize the response to EDRz. The EDRz group showed minimal aneurysm formation when compared with the control group, with significantly lower aortic diameter expansion (2.5±0.1 vs. 3.5±0.1 mm; P<0.05). Early growth response factor 1 (Egr-1) mRNA and protein levels were significantly decreased in the EDRz group, as expected. The decrease in Egr-1 was accompanied by decreases in the mRNA and protein levels of MMP-2 and MMP-9 (P<0.05). Transfection of the Egr-1 specific synthetic DNA enzyme EDRz significantly reduced AAA following elastase infusion in rats, at least in part due to the decreased expression of downstream MMP-2 and MMP-9.

Nonmuscle Myosin Light Chain Kinase: A Key Player in Intermittent Hypoxia-Induced Vascular Alterations

Background

Obstructive sleep apnea is characterized by repetitive pharyngeal collapses during sleep, leading to intermittent hypoxia (IH), the main contributor of obstructive sleep apnea–related cardiovascular morbidity. In patients and rodents with obstructive sleep apnea exposed to IH, vascular inflammation and remodeling, endothelial dysfunction, and circulating inflammatory markers are linked with IH severity. The nonmuscle myosin light chain kinase (nmMLCK) isoform contributes to vascular inflammation and oxidative stress in different cardiovascular and inflammatory diseases. Thus, in the present study, we hypothesized that nmMLCK plays a key role in the IH‐induced vascular dysfunctions and inflammatory remodeling.

Methods and Results

Twelve‐week‐old nmMLCK^+/+ or nmMLCK^−/− mice were exposed to 14‐day IH or normoxia. IH was associated with functional alterations characterized by an elevation of arterial blood pressure and stiffness and perturbations of NO signaling. IH caused endothelial barrier dysfunction (ie, reduced transendothelial resistance in vitro) and induced vascular oxidative stress associated with an inflammatory remodeling, characterized by an increased intima‐media thickness and an increased expression and activity of inflammatory markers, such as interferon‐γ and nuclear factor‐κB, in the vascular wall. Interestingly, nmMLCK deletion prevented all IH‐induced functional and structural alterations, including the restoration of NO signaling, correction of endothelial barrier integrity, and reduction of both oxidative stress and associated inflammatory response.

Conclusions

nmMLCK is a key mechanism in IH‐induced vascular oxidative stress and inflammation and both functional and structural remodeling.

Proteomic Alterations Associated with Biomechanical Dysfunction are Early Processes in the Emilin1 Deficient Mouse Model of Aortic Valve Disease

Aortic valve (AV) disease involves stiffening of the AV cusp with progression characterized by inflammation, fibrosis, and calcification. Here, we examine the relationship between biomechanical valve function and proteomic changes before and after the development of AV pathology in the Emilin1-/- mouse model of latent AV disease. Biomechanical studies were performed to quantify tissue stiffness at the macro (micropipette) and micro (atomic force microscopy (AFM)) levels. Micropipette studies showed that the Emilin1-/- AV annulus and cusp regions demonstrated increased stiffness only after the onset of AV disease. AFM studies showed that the Emilin1-/- cusp stiffens before the onset of AV disease and worsens with the onset of disease. Proteomes from AV cusps were investigated to identify protein functions, pathways, and interaction network alterations that occur with age- and genotype-related valve stiffening. Protein alterations due to Emilin1 deficiency, including changes in pathways and functions, preceded biomechanical aberrations, resulting in marked depletion of extracellular matrix (ECM) proteins interacting with TGFB1, including latent transforming growth factor beta 3 (LTBP3), fibulin 5 (FBLN5), and cartilage intermediate layer protein 1 (CILP1). This study identifies proteomic dysregulation is associated with biomechanical dysfunction as early pathogenic processes in the Emilin1-/- model of AV disease.

Stiff Substrates Increase Inflammation-Induced Endothelial Monolayer Tension and Permeability

Arterial stiffness and inflammation are associated with atherosclerosis, and each have individually been shown to increase endothelial monolayer tension and permeability. The objective of this study was to determine if substrate stiffness enhanced endothelial monolayer tension and permeability in response to inflammatory cytokines. Porcine aortic endothelial cells were cultured at confluence on polyacrylamide gels of varying stiffness and treated with either tumor necrosis factor-α (TNFα) or thrombin. Monolayer tension was measured through vinculin localization at the cell membrane, traction force microscopy, and phosphorylated myosin light chain quantity and actin fiber colocalization. Cell permeability was measured by cell-cell junction confocal microscopy and a dextran permeability assay. When treated with TNFα or thrombin, endothelial monolayers on stiffer substrates showed increased traction forces, vinculin at the cell membrane, and vinculin phosphorylation, suggesting elevated monolayer tension. Interestingly, VE-cadherin shifted toward a smaller molecular weight in endothelial monolayers on softer substrates, which may relate to increased VE-cadherin endocytosis and degradation. Phosphorylated myosin light chain colocalization with actin stress fibers increased in endothelial monolayers treated with TNFα or thrombin on stiffer substrates, indicating elevated cell monolayer contractility. Endothelial monolayers also developed focal adherens intercellular junctions and became more permeable when cultured on stiffer substrates in the presence of the inflammatory cytokines. Whereas each of these effects was likely mitigated by Rho/ROCK, Rho/ROCK pathway inhibition via Y27632 disrupted cell-cell junction morphology, showing that cell contractility is required to maintain adherens junction integrity. These data suggest that stiff substrates change intercellular junction protein localization and degradation, which may counteract the inflammation-induced increase in endothelial monolayer tension and thereby moderate inflammation-induced junction loss and associated endothelial monolayer permeability on stiffer substrates.

Morphometric changes in the aortic arch with advancing age in fetal to mature thoroughbred horses

Aortic rupture is a well recognized cause of sudden death in thoroughbred horses. Some microscopic lesions, such as those caused by cystic medial necrosis and medionecrosis, can lead to aortic rupture. However, these microscopic lesions are also observed in normal horses. On the other hand, a previous study of aortic rupture suggested that underlying elastin and collagen deposition disorders might be associated with aortic rupture. Therefore, the purpose of this study was to compare the structural components of the tunica media of the aortic arch, which is composed of elastin, collagen, smooth muscle cells and mucopolysaccharides (MPS), in fetal to mature thoroughbred horses. The percentage area of elastin was greatest in the young horses and subsequently decreased with aging. The percentage area of collagen increased with aging, and the elderly horses (aged ≥20) exhibited significantly higher percentage areas of collagen than the young horses. The percentage area of smooth muscle cells did not change with age. The percentage area of MPS was inversely proportional to the percentage area of elastin. The fetuses exhibited a markedly larger percentage area of MPS than the mature horses. We concluded that the medial changes seen in the aortic arch, which included a reduction in the amount of elastin and increases in the amounts of collagen and MPS, were age-related variations.

Hypoxia-Inducible Factor-1α in Smooth Muscle Cells Protects Against Aortic Aneurysms-Brief Report

OBJECTIVE

The purpose of this study was to determine the role of smooth muscle cell-derived hypoxia-inducible factor-1α (Hif-1α) in the pathogenesis of aortic aneurysms.

APPROACH AND RESULTS

Control mice and smooth muscle cell-specific hypoxia-inducible factor-1α-deficient mice were infused with β-aminopropionitrile for 2 weeks and angiotensin II for 6 weeks to induce aortic aneurysm formation. Mutant mice experienced increased levels of aneurysm formation of the thoracic or abdominal aorta with more severe elastin disruption, compared with control mice. Smooth muscle cell-specific hypoxia-inducible factor-1α deficiency did not affect matrix metalloproteinase-2 activity; however, the activity of lysyl oxidase and the levels of tropoelastin mRNA in the angiotensin II- and β-aminopropionitrile-treated aortae, associated with elastin fiber formation, were suppressed. Furthermore, we observed reduced volumes of mature cross-linked elastin in the thoracoabdominal aorta after treatment with angiotensin II and β-aminopropionitrile.

CONCLUSIONS

Deficiency of smooth muscle cell-derived hypoxia-inducible factor-1α augments aortic aneurysms, accompanied by disruption of elastin fiber formation, but not changes of elastin fiber degradation.

Loss of Elastic Fiber Integrity Compromises Common Carotid Artery Function: Implications for Vascular Aging

Competent elastic fibers endow central arteries with the compliance and resilience that are fundamental to their primary mechanical function in vertebrates. That is, by enabling elastic energy to be stored in the arterial wall during systole and then to be used to work on the blood during diastole, elastic fibers decrease ventricular workload and augment blood flow in pulsatile systems. Indeed, because elastic fibers are formed during development and stretched during somatic growth, their continual tendency to recoil contributes to the undulation of the stiffer collagen fibers, which facilitates further the overall compliance of the wall under physiologic pressures while allowing the collagen to limit over-distension during acute increases in blood pressure. In this paper, we use consistent methods of measurement and quantification to compare the biaxial material stiffness, structural stiffness, and energy storage capacity of murine common carotid arteries having graded degrees of elastic fiber integrity - normal, elastin-deficient, fibrillin-1 deficient, fibulin-5 null, and elastase-treated. The finding that the intrinsic material stiffness tends to be maintained nearly constant suggests that intramural cells seek to maintain a favorable micromechanical environment in which to function. Nevertheless, a loss of elastic energy storage capability due to the loss of elastic fiber integrity severely compromises the primary function of these central arteries.

Morphometric Properties of the Thoracic Aorta of Warmblood and Friesian Horses with and without Aortic Rupture

Rupture of the aorta is much more common in Friesians compared with other breeds of horse. Rupture always occurs adjacent to the scar of the ligamentum arteriosum. Previous histological examination of ruptured aortic walls suggested the presence of an underlying connective tissue disorder. Therefore, the aim of the present study was to compare the structural characteristics of the tunica media of the mid-thoracic aorta, distant to the lesion, in warmblood and Friesian horses with and without thoracic aortic rupture. In unaffected Friesian horses, the thickness of the tunica media, as well as the percentage area comprised of collagen type I, were significantly higher compared with the warmblood horses, supporting the hypothesis of a primary collagen disorder in the Friesian horse breed. However, in the tunica media of the affected Friesian horses there was no significant wall thickening. Moreover, the percentage area comprised of elastin was significantly lower, while the percentage area comprised of smooth muscle was higher, compared with unaffected Friesian and warmblood horses. These lesions are suggestive of an additional mild elastin deficiency with compensatory smooth muscle cell hypertrophy in affected Friesians.

Background differences in baseline and stimulated MMP levels influence abdominal aortic aneurysm susceptibility

OBJECTIVE

Evidence has demonstrated profound influence of genetic background on cardiovascular phenotypes. Murine models in Marfan syndrome (MFS) have shown that genetic background-related variations affect thoracic aortic aneurysm formation, rupture, and lifespan of mice. MFS mice with C57Bl/6 genetic background are less susceptible to aneurysm formation compared to the 129/SvEv genetic background. In this study, we hypothesize that susceptibility to abdominal aortic aneurysm (AAA) will be increased in 129/SvEv mice versus C57Bl/6 mice. We tested this hypothesis by assessing differences in aneurysm size, tissue properties, immune response, and MMP expression.

METHODS

Mice of C57Bl/6 or 129/SvEv background underwent AAA induction by periaortic application of CaCl2. Baseline aortic diameters, tissue properties and MMP levels were measured. After aneurysm induction, diameters, MMP expression, and immune response (macrophage infiltration and bone marrow transplantation) were measured.

RESULTS

Aneurysms were larger in 129/SvEv mice than C57Bl/6 mice (83.0% ± 13.6 increase compared to 57.8% ± 6.4). The aorta was stiffer in the 129/SvEv mice compared to C57Bl/6 mice (952.5 kPa ± 93.6 versus 621.4 kPa ± 84.2). Baseline MMP-2 and post-aneurysm MMP-2 and -9 levels were higher in 129/SvEv aortas compared to C57Bl/6 aortas. Elastic lamella disruption/fragmentation and macrophage infiltration were increased in 129/SvEv mice. Myelogenous cell reversal by bone marrow transplantation did not affect aneurysm size.

CONCLUSIONS

These data demonstrate that 129/SvEv mice are more susceptible to AAA compared to C57Bl/6 mice. Intrinsic properties of the aorta between the two strains of mice, including baseline expression of MMP-2, influence susceptibility to AAA.

Greater impairments in cerebral artery compared with skeletal muscle feed artery endothelial function in a mouse model of increased large artery stiffness

KEY POINTS

Increased large artery stiffness is a hallmark of arterial dysfunction with advancing age and is also present in other disease conditions such as diabetes. Increased large artery stiffness is correlated with resistance artery dysfunction in humans. Using a mouse model of altered arterial elastin content, this is the first study to examine the cause-and-effect relationship between large artery stiffness and peripheral resistance artery function. Our results indicate that mice with genetically greater large artery stiffness have impaired cerebral artery endothelial function, but generally preserved skeletal muscle feed artery endothelial function. The mechanisms for impaired cerebral artery endothelial function are reduced nitric oxide bioavailability and increased oxidative stress. These findings suggest that interventions that target large artery stiffness may be important to reduce disease risk associated with cerebral artery dysfunction in conditions such as advancing age.

ABSTRACT

Advancing age as well as diseases such as diabetes are characterized by both increased large artery stiffness and impaired peripheral artery function. It has been hypothesized that greater large artery stiffness causes peripheral artery dysfunction; however, a cause-and-effect relationship has not previously been established. We used elastin heterozygote mice (Eln(+/-) ) as a model of increased large artery stiffness without co-morbidities unrelated to the large artery properties. Aortic stiffness, measured by pulse wave velocity, was ∼35% greater in Eln(+/-) mice than in wild-type (Eln(+/+) ) mice (P = 0.04). Endothelium-dependent dilatation (EDD), assessed by the maximal dilatation to acetylcholine, was ∼40% lower in Eln(+/-) than Eln(+/+) mice in the middle cerebral artery (MCA, P < 0.001), but was similar between groups in the gastrocnemius feed arteries (GFA, P = 0.79). In the MCA, EDD did not differ between groups after incubation with the nitric oxide (NO) synthase inhibitor N(ω) -nitro-l-arginine methyl ester (P > 0.05), indicating that lower NO bioavailability contributed to the impaired EDD in Eln(+/-) mice. Superoxide production and content of the oxidative stress marker nitrotyrosine was higher in MCAs from Eln(+/-) compared with Eln(+/+) mice (P < 0.05). In the MCA, after incubation with the superoxide scavenger TEMPOL, maximal EDD improved by ∼65% in Eln(+/-) (P = 0.002), but was unchanged in Eln(+/+) mice (P = 0.17). These results indicate that greater large artery stiffness has a more profound effect on endothelial function in cerebral arteries compared with skeletal muscle feed arteries. Greater large artery stiffness can cause cerebral artery endothelial dysfunction by reducing NO bioavailability and increasing oxidative stress.

Adipose stem cells promote smooth muscle cells to secrete elastin in rat abdominal aortic aneurysm

Background

Abdominal aortic aneurysm (AAA) is a life-threatening disease and its prevalence rate increases with social aging. The degradation of elastic is an important factor in the formation of AAA.

Methods

Adipose derived stem cells (ADSCs) and bone marrow mesenchymal stem cells (BMSCs) were isolated from rats, and identified by Oil red O and alizarin red staining after adipogenesis and osteogenesis induction. In addition, ADSCs were also identified by flow cytometry with CD markers. AAA model in rats was established, and smooth muscle cells (SMCs) were isolated from AAA aortic wall and identified by immunohistochemistry. ADSCs or BMSCs were co-cultured with AAA aortic wall for in vitro experiment, and ADSCs were injected into AAA model for in vivo test. Then orcein staining was used for observing the morphology of elastic fiber, Western blot and real-time PCR were used respectively to detect the protein and gene expression of elastin, gelatinases spectrum analysis was used to detect the activity of matrix metalloproteinase-2 (MMP-2) and MMP-9.

Results

Lots of red lipid droplets were visible by Oil red O staining after adipogenesis induction, and black calcium nodules appeared by alizarin red staining after osteogenesis induction. The results of flow cytometry showed that ADSCs expressed CD44 and CD105, but exhibited negligible expression of CD31 and CD45. SMCs exhibited spindle-like morphology and α-actin protein was positive in cytoplasm. After co-cultured with ADSCs or BMSCs, the elastic fiber recovered normal winding shape, both the gene and protein expression of elastin increased, and the activity of MMP-2 decreased. The in vivo result was similar to that of in vitro.

Conclusions

ADSCs promote the expression of elastin in SMCs and contribute to the reconstruction of elastic fiber, which may provide new ideas for treating AAA.

Aging impairs smooth muscle-mediated regulation of aortic stiffness: a defect in shock absorption function?

Increased aortic stiffness is an early and independent biomarker of cardiovascular disease. Here we tested the hypothesis that vascular smooth muscle cells (VSMCs) contribute significantly to aortic stiffness and investigated the mechanisms involved. The relative contributions of VSMCs, focal adhesions (FAs), and matrix to stiffness in mouse aorta preparations at optimal length and with confirmed VSMC viability were separated by the use of small-molecule inhibitors and activators. Using biomechanical methods designed for minimal perturbation of cellular function, we directly quantified changes with aging in aortic material stiffness. An alpha adrenoceptor agonist, in the presence of N(G)-nitro-l-arginine methyl ester (l-NAME) to remove interference of endothelial nitric oxide, increases stiffness by 90-200% from baseline in both young and old mice. Interestingly, increases are robustly suppressed by the Src kinase inhibitor PP2 in young but not old mice. Phosphotyrosine screening revealed, with aging, a biochemical signature of markedly impaired agonist-induced FA remodeling previously associated with Src signaling. Protein expression measurement confirmed a decrease in Src expression with aging. Thus we report here an additive model for the in vitro biomechanical components of the mouse aortic wall in which 1) VSMCs are a surprisingly large component of aortic stiffness at physiological lengths and 2) regulation of the VSMC component through FA signaling and hence plasticity is impaired with aging, diminishing the aorta's normal shock absorption function in response to stressors.

Asymmetric cell-matrix and biomechanical abnormalities in elastin insufficiency induced aortopathy

Aortopathy is characterized by vascular smooth muscle cell (VSMC) abnormalities and elastic fiber fragmentation. Elastin insufficient (Eln (+/-)) mice demonstrate latent aortopathy similar to human disease. We hypothesized that aortopathy manifests primarily in the aorto-pulmonary septal (APS) side of the thoracic aorta due to asymmetric cardiac neural crest (CNC) distribution. Anatomic (aortic root vs. ascending aorta) and molecular (APS vs. non-APS) regions of proximal aorta tissue were examined in adult and aged wild type (WT) and mutant (Eln (+/-)) mice. CNC, VSMCs, elastic fiber architecture, proteoglycan expression, morphometrics and biomechanical properties were examined using histology, 3D reconstruction, micropipette aspiration and in vivo magnetic resonance imaging (MRI). In the APS side of Eln (+/-) aorta, Sonic Hedgehog (SHH) is decreased while SM22 is increased. Elastic fiber architecture abnormalities are present in the Eln (+/-) aortic root and APS ascending aorta, and biglycan is increased in the aortic root while aggrecan is increased in the APS aorta. The Eln (+/-) ascending aorta is stiffer than the aortic root, the APS side is thicker and stiffer than the non-APS side, and significant differences in the individual aortic root sinuses are observed. Asymmetric structure-function abnormalities implicate regional CNC dysregulation in the development and progression of aortopathy.

The function of elastic fibers in the arteries: beyond elasticity

The main components of elastic fibers, elastin and fibrillin-containing microfibrils play a structural and mechanical role in the arteries and their essential function is to provide elasticity and resilience to the tissues. However, through control of the quiescent contractile phenotype of arterial smooth muscle cells, elastin also acts as an autocrine factor and, via the binding of 'latent transforming growth factor (TGF)-β binding protein (LTBP) - latency-associated peptide (LAP) - TGF-β' complexes, fibrillins regulate the activation and availability of TGF-βs. These recent discoveries are detailed in this review.

Williams syndrome predisposes to vascular stiffness modified by antihypertensive use and copy number changes in NCF1

Williams syndrome is caused by the deletion of 26 to 28 genes, including elastin, on human chromosome 7. Elastin insufficiency leads to the cardiovascular hallmarks of this condition, namely focal stenosis and hypertension. Extrapolation from the Eln(+/-) mouse suggests that affected people may also have stiff vasculature, a risk factor for stroke, myocardial infarction, and cardiac death. NCF1, one of the variably deleted Williams genes, is a component of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex and is involved in the generation of oxidative stress, making it an interesting candidate modifier for vascular stiffness. Using a case-control design, vascular stiffness was evaluated by pulse wave velocity in 77 Williams cases and matched controls. Cases had stiffer conducting vessels than controls (P<0.001), with increased stiffness observed in even the youngest children with Williams syndrome. Pulse wave velocity increased with age at comparable rates in cases and controls, and although the degree of vascular stiffness varied, it was seen in both hypertensive and normotensive Williams participants. Use of antihypertensive medication and extension of the Williams deletion to include NCF1 were associated with protection from vascular stiffness. These findings demonstrate that vascular stiffness is a primary vascular phenotype in Williams syndrome and that treatment with antihypertensives or agents inhibiting oxidative stress may be important in managing patients with this condition, potentially even those who are not overtly hypertensive.

Biomechanical phenotyping of central arteries in health and disease: advantages of and methods for murine models

The stiffness and structural integrity of the arterial wall depends primarily on the organization of the extracellular matrix and the cells that fashion and maintain this matrix. Fundamental to the latter is a delicate balance in the continuous production and removal of structural constituents and the mechanical state in which such turnover occurs. Perturbations in this balance due to genetic mutations, altered hemodynamics, or pathological processes result in diverse vascular phenotypes, many of which have yet to be well characterized biomechanically. In this paper, we emphasize the particular need to understand regional variations in the biaxial biomechanical properties of central arteries in health and disease and, in addition, the need for standardization in the associated biaxial testing and quantification. As an example of possible experimental methods, we summarize testing protocols that have evolved in our laboratory over the past 8 years. Moreover, we note advantages of a four fiber family stress-stretch relation for quantifying passive biaxial behaviors, the use of stored energy as a convenient scalar metric of the associated material stiffness, and the utility of appropriate linearizations of the nonlinear, anisotropic relations both for purposes of comparison across laboratories and to inform computational fluid-solid-interaction models. We conclude that, notwithstanding prior advances, there remain many opportunities to advance our understanding of arterial mechanics and mechanobiology, particularly via the diverse genetic, pharmacological, and surgical models that are, or soon will be, available in the mouse.

Reduced elastogenesis: a clue to the arteriosclerosis and emphysematous changes in Schimke immuno-osseous dysplasia?

BACKGROUND

Arteriosclerosis and emphysema develop in individuals with Schimke immuno-osseous dysplasia (SIOD), a multisystem disorder caused by biallelic mutations in SMARCAL1 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1). However, the mechanism by which the vascular and pulmonary disease arises in SIOD remains unknown.

METHODS

We reviewed the records of 65 patients with SMARCAL1 mutations. Molecular and immunohistochemical analyses were conducted on autopsy tissue from 4 SIOD patients.

RESULTS

Thirty-two of 63 patients had signs of arteriosclerosis and 3 of 51 had signs of emphysema. The arteriosclerosis was characterized by intimal and medial hyperplasia, smooth muscle cell hyperplasia and fragmented and disorganized elastin fibers, and the pulmonary disease was characterized by panlobular enlargement of air spaces. Consistent with a cell autonomous disorder, SMARCAL1 was expressed in arterial and lung tissue, and both the aorta and lung of SIOD patients had reduced expression of elastin and alterations in the expression of regulators of elastin gene expression.

CONCLUSIONS

This first comprehensive study of the vascular and pulmonary complications of SIOD shows that these commonly cause morbidity and mortality and might arise from impaired elastogenesis. Additionally, the effect of SMARCAL1 deficiency on elastin expression provides a model for understanding other features of SIOD.

Echocardiographic Characterization of Postnatal Development in Mice with Reduced Arterial Elasticity

PURPOSE

Decreased expression of elastin results in smaller, less compliant arteries and high blood pressure. In mice, these differences become more significant with postnatal development. It is known that arterial size and compliance directly affect cardiac function, but the temporal changes in cardiac function have not been investigated in elastin insufficient mice. The aim of this study is to correlate changes in arterial size and compliance with cardiac function in wildtype (WT) and elastin haploinsufficient (Eln^+/- ) mice from birth to adulthood.

METHODS

Ultrasound scans were performed at the ages of 3, 7, 14, 21, 30, 60, and 90 days on male and female WT and Eln^+/- mice. 2-D ultrasound and pulse wave Doppler images were used to measure the dimensions and function of the left ventricle (LV), ascending aorta and carotid arteries.

RESULTS

Eln^+/- arteries are smaller and less compliant at most ages, with significant differences from WT as early as 3 days old. Surprisingly, there are no correlations (R² < 0.2) between arterial size and compliance with measures of LV hypertrophy or systolic function. There are weak correlations (0.2 < R² < 0.5) between arterial size and compliance with measures of LV diastolic function.

CONCLUSIONS

Eln^+/- mice have similar cardiac function to WT throughout postnatal development, demonstrating the remarkable ability of the developing cardiovascular system to adapt to mechanical and hemodynamic changes. Correlations between arterial size and compliance with diastolic function show that these measures may be useful indicators of early diastolic dysfunction.

[Elastin and microfibrils in vascular development and ageing: complementary or opposite roles?]

Large arteries allow the vascular system to be more than a simple route in which the blood circulates within the organism. The elastic fibers present in the wall endow these vessels with elasticity and are responsible for the smoothing of the blood pressure and flow, which are delivered discontinuously by the heart. This function is very important to ensure appropriate hemodynamics. Elastic fibers are composed of elastin (90%) and fibrillin-rich microfibrils (10%) which provide the vessels with elasticity and are also signals able to bind to relatively specific cell membrane receptors. Stimulation of the high affinity elastin receptor by elastin peptides or tropoelastin--the elastin precursor--triggers an increase in intracellular free calcium in vascular cells, especially endothelial cells, associated with attachment, migration or proliferation. Similar effects of the stimulation of endothelial cells by microfibrils or fibrillin-1 fragments, which bind to integrins, have been demonstrated. This dual function--mechanical and in signaling--makes the elastic fibers an important actor of the development and ageing processes taking place in blood vessels. An alteration of the elastin (Eln) or fibrillin (Fbn) gene products leads to severe genetic pathologies of the cardiovascular system, such as supravalvular aortic stenosis, or Williams Beuren syndrome--in which elastin deficiency induces aortic stenoses--or Marfan syndrome, in which on the contrary fibrillin-1 deficiency promotes the appearance of aortic aneurysms. Genetically-engineered mouse models of these pathologies (such as Eln+/- mice and Fbn-1+/mgΔ mice, Eln+/-Fbn-1+/- mice) have permitted a better understanding of the pathogenesis of these syndromes. In particular, it has been shown that elastin and fibrillin-1 roles can be complementary in some aspects, while they can be opposed in some other situations. For instance, the double heterozygosity in elastin and fibrillin-1 leads to increased arterial wall stress--compared to the level induced by one of these two deficiencies alone--while the decrease in diameter induced by Eln deficiency is partly compensated by an additional deficiency in Fbn-1. Also, it is now clear that early modifications of elastin or fibrillin-1 availability can alter the normal signaling action of these proteins and lead to long term modifications of the vascular physiology and ageing processes.

Mechanical testing of mouse carotid arteries: from newborn to adult

The large conducting arteries in vertebrates are composed of a specialized extracellular matrix designed to provide pulse dampening and reduce the work performed by the heart. The mix of matrix proteins determines the passive mechanical properties of the arterial wall(1). When the matrix proteins are altered in development, aging, disease or injury, the arterial wall remodels, changing the mechanical properties and leading to subsequent cardiac adaptation(2). In normal development, the remodeling leads to a functional cardiac and cardiovascular system optimized for the needs of the adult organism. In disease, the remodeling often leads to a negative feedback cycle that can cause cardiac failure and death. By quantifying passive arterial mechanical properties in development and disease, we can begin to understand the normal remodeling process to recreate it in tissue engineering and the pathological remodeling process to test disease treatments. Mice are useful models for studying passive arterial mechanics in development and disease. They have a relatively short lifespan (mature adults by 3 months and aged adults by 2 years), so developmental(3) and aging studies(4) can be carried out over a limited time course. The advances in mouse genetics provide numerous genotypes and phenotypes to study changes in arterial mechanics with disease progression(5) and disease treatment(6). Mice can also be manipulated experimentally to study the effects of changes in hemodynamic parameters on the arterial remodeling process(7). One drawback of the mouse model, especially for examining young ages, is the size of the arteries. We describe a method for passive mechanical testing of carotid arteries from mice aged 3 days to adult (approximately 90 days). We adapt a commercial myograph system to mount the arteries and perform multiple pressure or axial stretch protocols on each specimen. We discuss suitable protocols for each age, the necessary measurements and provide example data. We also include data analysis strategies for rigorous mechanical characterization of the arteries.

Protocadherin-12 deficiency leads to modifications in the structure and function of arteries in mice

We studied the role of protocadherin-12 on arterial function. This protein belongs to the cadherin superfamily and is located at the intercellular junctions of endothelial cells where it promotes homotypic cellular adhesion. We previously showed that mice deficient for PCDH12 exhibited developmental growth retardation owing to placenta defects without altering neither survival nor fertility. Here, we investigated the effects of PCDH12 deficiency on the structural, mechanical properties and functionality of arteries from adult mice. Histological studies of the PCDH12(-/-) mouse arteries have shown age-independent modifications such as ramifications of medial elastic lamellae, accompanied by the appearance of radial fibers linking together two successive concentric elastic lamellae. Mechanical studies also revealed some age-independent modifications in the PCDH12(-/-) mice arteries such as an increase in inner-diameter and circumferential mid-wall stress. Moreover, the PCDH12(-/-) mice exhibited a mild reduction of blood pressure, thus maintaining the inner-diameter close to its normal value and a normal circumferential wall stress for vascular cells. This is likely a compensation mechanism enabling normal blood flow in the arteries. The vascular phenotypic differences observed between PCDH12(-/-) and wild type mice arteries did not seem to be age-dependent, except for some results regarding the carotid artery: the reactivity to acetylcholine and the circumferential mid-wall stress decreased with ageing in the PCDH12(-/-) mice, as opposed to the increase observed in the wild types. In conclusion, deficiency in one specific interendothelial junction component leads to significant changes in the structure and function of the vascular wall. Possible explanations for the observed modifications are discussed.

Analysis of the molecular mobility of collagen and elastin in safe, atheromatous and aneurysmal aortas

AIM OF THE STUDY

In this study, we propose to use a thermal technique, Differential Scanning Calorimetry (DSC) to follow the evolution of elastin and collagen in safe and pathological cardiovascular tissues.

PATIENTS AND METHODS

The first part of this study deals with the analysis of the elastin network and associated proteins during ageing (from children to old persons) in aortic walls. The second part is devoted to the characterization of the collagenic phase in aneurysms. In both cases, physical data are correlated with biochemical analyses.

RESULTS AND CONCLUSION

For old persons aortas with atheromatous stades, elastin and associated proteins are found to interpenetrate to form a homogenous phase. Abdominal aortic aneurysms (AAA) are characterized by structural alterations of the aortic wall resulting from the degradation of elastic fibers and an increase of collagen/elastin ratio. Notable modifications are evidenced between collagen from control tissue and collagen from AAA, particularly concerning the thermal denaturation. Biochemical and thermal results are compatible with the increase of new collagen deposition and/or impairment of the collagen phase stability in the extracellular matrix of AAAs.

Coacervation of tropoelastin

The coacervation of tropoelastin represents the first major stage of elastic fiber assembly. The process has been modeled in vitro by numerous studies, initially with mixtures of solubilized elastin, and subsequently with synthetic elastin peptides that represent hydrophobic repeat units, isolated hydrophobic domains, segments of alternating hydrophobic and cross-linking domains, or the full-length monomer. Tropoelastin coacervation in vitro is characterized by two stages: an initial phase separation, which involves a reversible inverse temperature transition of monomer to n-mer; and maturation, which is defined by the irreversible coalescence of coacervates into large species with fibrillar structures. Coacervation is an intrinsic ability of tropoelastin. It is primarily influenced by the number, sequence, and contextual arrangement of hydrophobic domains, although hydrophilic sequences can also affect the behavior of the hydrophobic domains and thus affect coacervation. External conditions including ionic strength, pH, and temperature also directly influence the propensity of tropoelastin to self-associate. Coacervation is an endothermic, entropically-driven process driven by the cooperative interactions of hydrophobic domains following destabilization of the clathrate-like water shielding these regions. The formation of such assemblies is believed to follow a helical nucleation model of polymerization. Coacervation is closely associated with conformational transitions of the monomer, such as increased β-structures in hydrophobic domains and α-helices in cross-linking domains. Tropoelastin coacervation in vivo is thought to mainly involve the central hydrophobic domains. In addition, cell-surface glycosaminoglycans and microfibrillar proteins may regulate the process. Coacervation is essential for progression to downstream elastogenic stages, and impairment of the process can result in elastin haploinsufficiency disorders such as supravalvular aortic stenosis.