Mechanisms of increased vascular stiffness down the aortic tree in aging, premenopausal female monkeys

Mapping the unicellular transcriptome of the ascending thoracic aorta to changes in mechanosensing and mechanoadaptation during aging

Aortic stiffening is an inevitable manifestation of chronological aging, yet the mechano-molecular programs that orchestrate region- and layer-specific adaptations along the length and through the wall of the aorta are incompletely defined. Here, we show that the decline in passive cyclic distensibility is more pronounced in the ascending thoracic aorta (ATA) compared to distal segments of the aorta and that collagen content increases in both the medial and adventitial compartments of the ATA during aging. The single-cell RNA sequencing of aged ATA tissues reveals altered cellular senescence, remodeling, and inflammatory responses accompanied by enrichment of T-lymphocytes and rarefaction of vascular smooth muscle cells, compared to young samples. T lymphocyte clusters accumulate in the adventitia, while the activation of mechanosensitive Piezo-1 enhances vasoconstriction and contributes to the overall functional decline of ATA tissues. These results portray the immuno-mechanical aging of the ATA as a process that culminates in a stiffer conduit permissive to the accrual of multi-gerogenic signals priming to disease development.

Preventing spontaneous cerebral microhemorrhages in aging mice: a novel approach targeting cellular senescence with ABT263/navitoclax

Emerging evidence from both clinical and preclinical studies underscores the role of aging in potentiating the detrimental effects of hypertension on cerebral microhemorrhages (CMHs, or cerebral microbleeds). CMHs progressively impair neuronal function and contribute to the development of vascular cognitive impairment and dementia. There is growing evidence showing accumulation of senescent cells within the cerebral microvasculature during aging, which detrimentally affects cerebromicrovascular function and overall brain health. We postulated that this build-up of senescent cells renders the aged cerebral microvasculature more vulnerable, and consequently, more susceptible to CMHs. To investigate the role of cellular senescence in CMHs' pathogenesis, we subjected aged mice, both with and without pre-treatment with the senolytic agent ABT263/Navitoclax, and young control mice to hypertension via angiotensin-II and L-NAME administration. The aged cohort exhibited a markedly earlier onset, heightened incidence, and exacerbated neurological consequences of CMHs compared to their younger counterparts. This was evidenced through neurological examinations, gait analysis, and histological assessments of CMHs in brain sections. Notably, the senolytic pre-treatment wielded considerable cerebromicrovascular protection, effectively delaying the onset, mitigating the incidence, and diminishing the severity of CMHs. These findings hint at the potential of senolytic interventions as a viable therapeutic avenue to preempt or alleviate the consequences of CMHs linked to aging, by counteracting the deleterious effects of senescence on brain microvasculature.

Association of NOTCH3 With Elastic Fiber Dispersion in the Infrarenal Abdominal Aorta of Cynomolgus Monkeys

BACKGROUND

The regional heterogeneity of vascular components and transcriptomes is an important determinant of aortic biology. This notion has been explored in multiple mouse studies. In the present study, we examined the regional heterogeneity of aortas in nonhuman primates.

METHODS

Aortic samples were harvested from the ascending, descending thoracic, suprarenal, and infrarenal regions of young control monkeys and adult monkeys with high fructose consumption for 3 years. The regional heterogeneity of aortic structure and transcriptomes was examined by histological and bulk RNA sequencing analyses, respectively.

RESULTS

Immunostaining of CD31 and αSMA (alpha-smooth muscle actin) revealed that endothelial and smooth muscle cells were distributed homogeneously across the aortic regions. In contrast, elastic fibers were less abundant and dispersed in the infrarenal aorta compared with other regions and associated with collagen deposition. Bulk RNA sequencing identified a distinct transcriptome related to the Notch signaling pathway in the infrarenal aorta with significantly increased NOTCH3 mRNA compared with other regions. Immunostaining revealed that NOTCH3 protein was increased in the media of the infrarenal aorta. The abundance of medial NOTCH3 was positively correlated with the dispersion of elastic fibers. Adult cynomolgus monkeys with high fructose consumption displayed vascular wall remodeling, such as smooth muscle cell loss and elastic fiber disruption, predominantly in the infrarenal region. The correlation between NOTCH3 and elastic fiber dispersion was enhanced in these monkeys.

CONCLUSIONS

Aortas of young cynomolgus monkeys display regional heterogeneity of their transcriptome and the structure of elastin and collagens. Elastic fibers in the infrarenal aorta are dispersed along with upregulation of medial NOTCH3.

Association of NOTCH3 with Elastic Fiber Dispersion in the Infrarenal Abdominal Aorta of Cynomolgus Monkeys

Background

The regional heterogeneity of vascular components and transcriptomes is an important determinant of aortic biology. This notion has been explored in multiple mouse studies. In the present study, we examined the regional heterogeneity of aortas in non-human primates.

Methods

Aortic samples were harvested from the ascending, descending, suprarenal, and infrarenal regions of young control monkeys and adult monkeys provided with high fructose for 3 years. The regional heterogeneity of aortic structure and transcriptomes was examined by histological and bulk RNA sequencing analyses.

Results

Immunostaining of CD31 and αSMA revealed that endothelial and smooth muscle cells were distributed homogeneously across the aortic regions. In contrast, elastic fibers were less abundant and dispersed in the infrarenal aorta compared to other regions and associated with collagen deposition. Bulk RNA sequencing identified a distinct transcriptome related to the Notch signaling pathway in the infrarenal aorta with significantly increased NOTCH3 mRNA compared to other regions. Immunostaining revealed that NOTCH3 protein was increased in the media of the infrarenal aorta. The abundance of medial NOTCH3 was positively correlated with the dispersion of elastic fibers. Adult cynomolgus monkeys provided with high fructose displayed vascular wall remodeling, such as smooth muscle cell loss and elastic fiber disruption, predominantly in the infrarenal region. The correlation between NOTCH3 and elastic fiber dispersion was enhanced in these monkeys.

Conclusions

Aortas of young cynomolgus monkeys display regional heterogeneity of their transcriptome and the structure of elastin and collagens. Elastic fibers in the infrarenal aorta are dispersed along with upregulation of medial NOTCH3.

HIGHLIGHTS

- The present study determined the regional heterogeneity of aortas from cynomolgus monkeys.- Aortas of young cynomolgus monkeys displayed region-specific aortic structure and transcriptomes.- Elastic fibers were dispersed in the infrarenal aorta along with increased NOTCH3 abundance in the media.

GRAPHIC ABSTRACT

Aging of the Arterial System

Aging of the vascular system is associated with deep changes of the structural proprieties of the arterial wall. Arterial hypertension, diabetes mellitus, and chronic kidney disease are the major determinants for the loss of elasticity and reduced compliance of vascular wall. Arterial stiffness is a key parameter for assessing the elasticity of the arterial wall and can be easily evaluated with non-invasive methods, such as pulse wave velocity. Early assessment of vessel stiffness is critical because its alteration can precede clinical manifestation of cardiovascular disease. Although there is no specific pharmacological target for arterial stiffness, the treatment of its risk factors helps to improve the elasticity of the arterial wall.

Region-dependent mechanical characterization of porcine thoracic aorta with a one-to-many correspondence method to create virtual datasets using uniaxial tensile tests

The simulation of the cardiovascular system and in silico clinical trials have garnered attention in the biomedical engineering field. Physics-based modeling is essential to associate with physical and clinical features. In physics-based constitutive modeling, the identification of the parameters and estimation of their ranges based on appropriate experiments are required. Uniaxial tests are commonly used in the field of vascular mechanics, but they have limitations in fully characterizing the regional mechanical behavior of the aorta. Therefore, this study is aimed at identifying a method to integrate constitutive models with experimental data to elucidate regional aortic behavior. To create a virtual two-dimensional dataset, a pair of uniaxial experimental datasets in the longitudinal and circumferential directions was combined using a one-to-many correspondence method such as bootstrap aggregation. The proposed approach is subsequently applied to three constitutive models, i.e., the Fung model, Holzapfel model, and constrained mixture model, to estimate the material parameters based on the four test regions of the porcine thoracic aorta. Finally, the regional difference in the mechanical behavior of the aorta, the correlation between the experimental characteristics and model parameters, and the inter-correlation of the material parameters are confirmed. This integrative approach will enhance the prediction capability of the model with respect to the regions of the aorta.

Cystamine reduces vascular stiffness in Western diet-fed female mice

Consumption of diets high in fat, sugar, and salt (Western diet, WD) is associated with accelerated arterial stiffening, a major independent risk factor for cardiovascular disease (CVD). Women with obesity are more prone to develop arterial stiffening leading to more frequent and severe CVD compared with men. As tissue transglutaminase (TG2) has been implicated in vascular stiffening, our goal herein was to determine the efficacy of cystamine, a nonspecific TG2 inhibitor, at reducing vascular stiffness in female mice chronically fed a WD. Three experimental groups of female mice were created. One was fed regular chow diet (CD) for 43 wk starting at 4 wk of age. The second was fed a WD for the same 43 wk, whereas a third cohort was fed WD, but also received cystamine (216 mg/kg/day) in the drinking water during the last 8 wk on the diet (WD + C). All vascular stiffness parameters assessed, including aortic pulse wave velocity and the incremental modulus of elasticity of isolated femoral and mesenteric arteries, were significantly increased in WD- versus CD-fed mice, and reduced in WD + C versus WD-fed mice. These changes coincided with respectively augmented and diminished vascular wall collagen and F-actin content, with no associated effect in blood pressure. In cultured human vascular smooth muscle cells, cystamine reduced TG2 activity, F-actin:G-actin ratio, collagen compaction capacity, and cellular stiffness. We conclude that cystamine treatment represents an effective approach to reduce vascular stiffness in female mice in the setting of WD consumption, likely because of its TG2 inhibitory capacity.NEW & NOTEWORTHY This study evaluates the novel role of transglutaminase 2 (TG2) inhibition to directly treat vascular stiffness. Our data demonstrate that cystamine, a nonspecific TG2 inhibitor, improves vascular stiffness induced by a diet rich in fat, fructose, and salt. This research suggests that TG2 inhibition might bear therapeutic potential to reduce the disproportionate burden of cardiovascular disease in females in conditions of chronic overnutrition.

Vascular Stiffness in Aging and Disease

The goal of this review is to provide further understanding of increased vascular stiffness with aging, and how it contributes to the adverse effects of major human diseases. Differences in stiffness down the aortic tree are discussed, a topic requiring further research, because most prior work only examined one location in the aorta. It is also important to understand the divergent effects of increased aortic stiffness between males and females, principally due to the protective role of female sex hormones prior to menopause. Another goal is to review human and non-human primate data and contrast them with data in rodents. This is particularly important for understanding sex differences in vascular stiffness with aging as well as the changes in vascular stiffness before and after menopause in females, as this is controversial. This area of research necessitates studies in humans and non-human primates, since rodents do not go through menopause. The most important mechanism studied as a cause of age-related increases in vascular stiffness is an alteration in the vascular extracellular matrix resulting from an increase in collagen and decrease in elastin. However, there are other mechanisms mediating increased vascular stiffness, such as collagen and elastin disarray, calcium deposition, endothelial dysfunction, and the number of vascular smooth muscle cells (VSMCs). Populations with increased longevity, who live in areas called “Blue Zones,” are also discussed as they provide additional insights into mechanisms that protect against age-related increases in vascular stiffness. Such increases in vascular stiffness are important in mediating the adverse effects of major cardiovascular diseases, including atherosclerosis, hypertension and diabetes, but require further research into their mechanisms and treatment.

Changes in aortic collagen in β-aminopropionitrile-induced acute aortic dissection

Background

The precise role collagen plays in acute aortic dissection (AAD) was investigated in an animal model of β-aminopropinitrile (BAPN)-induced AAD.

Methods

The 30 3-week-old male specific-pathogen free (SPF)-grade Sprague-Dawley (SD) rats were randomly divided into two groups: 10 in the Control group and 20 in the Model group. The Model group was treated with 0.1% BAPN for 4 weeks, while the Control group received untreated water. Histopathological staining and western blot were used to detect changes of the extracellular matrix (ECM) and collagen content in the aorta.

Results

At the end of the experiment, the incidence of AAD was 25%, the aortic ECM of surviving rats was severely damaged, and the arrangement was disordered. Fibroblast cells are unevenly distributed, with wide gaps, collagen fibers were also distributed unevenly in a disordered arrangement and their thickness was uneven. The elastic membrane disappeared over a large area. Compare to Control group, the Collagen types I, III and their subunits were upregulated (P<0.05), while matrix metalloproteinase (MMP) 2 and MMP9 were downregulated in the aorta of Model group (P<0.05).

Conclusions

In the animal model of BAPN-induced AAD, collagen types I, III and subunits were increased, while MMP2 and MMP9 were decreased in thoracic aorta, which may lead to stiffness of the aorta and be the cause of dissection.

Effect of genetic depletion of MMP-9 on neurological manifestations of hypertension-induced intracerebral hemorrhages in aged mice

Clinical and experimental studies show that hypertension induces intracerebral hemorrhages (ICH), including cerebral microhemorrhages in the aged brain, which contribute to the pathogenesis of vascular cognitive impairment (VCI). Previous studies showed that aging increased oxidative stress-mediated activation of matrix metalloproteinases (MMPs) that importantly contributes to the pathogenesis of ICHs. In particular, oxidative stress has been implicated in activation of MMP-9, which is known to be involved in the degradation of the extracellular matrix and cleavage of collagen IV, a key constituent of the basal membrane of cerebral vessels. To determine the role of MMP-9 activation in the genesis of ICHs, we induced hypertension in 20-month-old MMP-9 null and age-matched control mice by angiotensin II and L-NAME treatment. Contrary to our hypothesis, MMP-9 deficiency did not delay the onset or incidence of neurological consequences of hypertension-induced ICHs. Our results indicate that MMP-9 activation does not play a role in the age-related exacerbation of hypertension-induced ICH.

Mutation of the 5'-untranslated region stem-loop mRNA structure reduces type I collagen deposition and arterial stiffness in male obese mice

Arterial stiffening, a characteristic feature of obesity and type 2 diabetes, contributes to the development and progression of cardiovascular diseases (CVD). Currently, no effective prophylaxis or therapeutics is available to prevent or treat arterial stiffening. A better understanding of the molecular mechanisms underlying arterial stiffening is vital to identify newer targets and strategies to reduce CVD burden. A major contributor to arterial stiffening is increased collagen deposition. In the 5'-untranslated regions of mRNAs encoding for type I collagen, an evolutionally conserved stem-loop (SL) structure plays an essential role in its stability and post-transcriptional regulation. Here, we show that feeding a high-fat/high-sucrose (HFHS) diet for 28 wk increases adiposity, insulin resistance, and blood pressure in male wild-type littermates. Moreover, arterial stiffness, assessed in vivo via aortic pulse wave velocity, and ex vivo using atomic force microscopy in aortic explants or pressure myography in isolated femoral and mesenteric arteries, was also increased in those mice. Notably, all these indices of arterial stiffness, along with collagen type I levels in the vasculature, were reduced in HFHS-fed mice harboring a mutation in the 5'SL structure, relative to wild-type littermates. This protective vascular phenotype in 5'SL-mutant mice did not associate with a reduction in insulin resistance or blood pressure. These findings implicate the 5'SL structure as a putative therapeutic target to prevent or reverse arterial stiffening and CVD associated with obesity and type 2 diabetes.NEW & NOTEWORTHY In the 5'-untranslated (UTR) regions of mRNAs encoding for type I collagen, an evolutionally conserved SL structure plays an essential role in its stability and posttranscriptional regulation. We demonstrate that a mutation of the SL mRNA structure in the 5'-UTR decreases collagen type I deposition and arterial stiffness in obese mice. Targeting this evolutionarily conserved SL structure may hold promise in the management of arterial stiffening and CVD associated with obesity and type 2 diabetes.