Effects of Excess Sodium Consumption on Arterial Function in C57BL/6 Mice.

Excess sodium consumption contributes to arterial dysfunction in humans. The C57BL/6 strain of mice have been used to identify mechanisms by which arterial dysfunction occurs after excess sodium consumption. However, there are concerns that C57BL/6 mice have strain-specific resistance to high-sodium (HS) diet-induced hypertension. To address this concern, we performed a meta-analysis to determine if excess sodium consumption in C57BL/6 mice induces arterial dysfunction. Databases were searched for HS vs. standard diet studies that measured arterial function (i.e., systolic blood pressure [BP], endothelium-dependent dilation [EDD], and central arterial stiffness) in C57BL/6 mice. A total of 39 studies were included, demonstrating that HS condition resulted in higher systolic BP than control mice with a mean difference of 9.8 mmHg (95% CI [5.6, 14], P<0.001). Subgroup analysis indicated that the systolic BP was higher in HS compared to the control condition when measured during night compared to daytime with telemetry (P<0.001). We also identified that the difference in systolic BP between HS and control was ~2.5-fold higher when administered through drinking water than through food (P<0.001). A total of 12 studies were included, demonstrating that HS condition resulted in lower EDD than control with a weighted mean difference of -12.0% (95% CI [-20.0, -4.1], P=0.003). It should be noted that there was considerable variability across studies with more than half of the studies showing no effect of HS condition on systolic BP and EDD. In summary, excess sodium consumption elevates systolic BP and impairs EDD in C57BL/6 mice.

High-salt diet augments systolic blood pressure and induces arterial dysfunction in outbred, genetically diverse mice.

Excess salt consumption contributes to hypertension and arterial dysfunction in humans living in industrialized societies. However, this arterial phenotype is not typically observed in inbred, genetically identical mouse strains that consume a high-salt (HS) diet. Therefore, we sought to determine the effects of HS diet consumption on systolic blood pressure (BP) and arterial function in UM-HET3 mice, an outbred, genetically diverse strain of mice. Male and female UM-HET3 mice underwent a low-salt [LS (1% NaCl)] or HS (4% NaCl) diet for 12 wk. Systolic BP and aortic stiffness, determined by pulse wave velocity (PWV), were increased in HS after 2 and 4 wk, respectively, compared with baseline and continued to increase through week 12 (P < 0.05). Systolic BP was higher from weeks 2-12 and PWV was higher from weeks 4-12 in HS compared with LS mice (P < 0.05). Aortic collagen content was ∼81% higher in HS compared with LS (P < 0.05), whereas aortic elastin content was similar between groups (P > 0.05). Carotid artery endothelium-dependent dilation (EDD) was ∼10% lower in HS compared with LS (P < 0.05), endothelium-independent dilation was similar between groups (P > 0.05). Finally, there was a strong relationship between systolic BP and PWV (r2 = 0.40, P < 0.05), as well as inverse relationship between EDD and systolic BP (r2 = 0.21, P < 0.05) or PWV (r2 = 0.20, P < 0.05). In summary, HS diet consumption in UM-HET3 mice increases systolic BP, which is accompanied by aortic stiffening and impaired EDD. These data suggest that outbred, genetically diverse mice may provide unique translational insight into arterial adaptations of humans that consume an HS diet.NEW & NOTEWORTHY Excess salt consumption is a contributor to hypertension and arterial dysfunction in humans living in industrialized societies, but this phenotype is not observed in inbred, genetically identical mice that consume a high-salt (HS) diet. This study reveals that a HS diet in outbred, genetically diverse mice progressively increases systolic blood pressure and induce arterial dysfunction. These data suggest that genetically diverse mice may provide translational insight into arterial adaptations in humans that consume an HS diet.

Therapeutic strategies targeting the endothelial glycocalyx.

PURPOSE OF REVIEW: This review will highlight recent studies that have examined the endothelial glycocalyx in a variety of health conditions, as well as potential glycocalyx-targeted therapies. RECENT FINDINGS: A degraded glycocalyx is present in individuals that consume high sodium diet or have kidney disease, diabetes, preeclampsia, coronavirus disease 2019 (COVID-19), or sepsis. Specifically, these conditions are accompanied by elevated glycocalyx components in the blood, such as syndecan-1, syndecans-4, heparin sulfate, and enhanced heparinase activity. Impaired glycocalyx barrier function is accompanied by decreased nitric oxide bioavailability, increased leukocyte adhesion to endothelial cells, and vascular permeability. Glycocalyx degradation appears to play a key role in the progression of cardiovascular complications. However, studies that have used glycocalyx-targeted therapies to treat these conditions are scarce. Various therapeutics can restore the glycocalyx in kidney disease, diabetes, COVID-19, and sepsis. Exposing endothelial cells to glycocalyx components, such as heparin sulfate and hyaluronan protects the glycocalyx. SUMMARY: We conclude that the glycocalyx is degraded in a variety of health conditions, although it remains to be determined whether glycocalyx degradation plays a causal role in disease progression and severity, and whether glycocalyx-targeted therapies improve patient health outcomes. Future studies are warranted to investigate therapeutic strategies that target the endothelial glycocalyx.

Microcirculatory and glycocalyx properties are lowered by high-salt diet but augmented by Western diet in genetically heterogeneous mice.

Many individuals in industrialized societies consume a high-salt, Western diet(WD); however, the effects of this diet on microcirculatory properties and glycocalyx barrier function are unknown. Young genetically heterogeneous male and female mice underwent 12 wk of normal chow (NC) diet, NC diet with 4% salt (NC4%), Western diet (WD), or WD with 4% salt (WD4%). Microcirculatory properties and glycocalyx barrier function were evaluated in the mesenteric microcirculation, using an intravital microscope equipped with an automated capture and analysis system. Total microvascular density summed across 4- to 25-µm microvessel segment diameters was lower in NC4% than in NC and WD (P < 0.05). Perfused boundary region (PBR), a marker of glycocalyx barrier function, averaged across 4- to 25-µm microvessel segment diameters was similar between NC and NC4%, as well as between WD and WD4% (P > 0.05). PBR was lower in WD and WD4% than in NC and NC4% (P < 0.05), indicating augmented glycocalyx barrier function in WD and WD4%. There were strong, inverse relationships between PBR and adiposity and blood glucose (r = -0.44 to -0.61, P < 0.05). In summary, NC4% induces deleterious effects on microvascular density, whereas WD augments glycocalyx barrier function. Interestingly, the combination of high-salt, Western diet in WD4% resulted in lower total microvascular density like NC4% and augmented glycocalyx barrier function like WD. These data suggest distinct microcirculatory adaptations to high-salt and Western diets that coincide when these diets are combined in young genetically heterogeneous male and female mice.NEW & NOTEWORTHY Many individuals in industrialized societies consume a combination of high-salt and Western diet; however, the effects of this diet on microcirculatory and glycocalyx properties are unknown. This study reveals that a high-salt diet lowers microcirculatory and glycocalyx properties, whereas a Western diet augments glycocalyx barrier function and thickness. Taken together, these data indicate that there are distinct microcirculatory adaptations to high-salt and Western diets that coincide when high-salt and Western diets are combined.

T cells mediate cell non-autonomous arterial ageing in mice.

KEY POINTS: Increased large artery stiffness and impaired endothelium-dependent dilatation occur with advanced age. We sought to determine whether T cells mechanistically contribute to age-related arterial dysfunction. We found that old mice exhibited greater proinflammatory T cell accumulation around both the aorta and mesenteric arteries. Pharmacologic depletion or genetic deletion of T cells in old mice resulted in ameliorated large artery stiffness and greater endothelium-dependent dilatation compared with mice with T cells intact. ABSTRACT: Ageing of the arteries is characterized by increased large artery stiffness and impaired endothelium-dependent dilatation. T cells contribute to hypertension in acute rodent models but whether they contribute to chronic age-related arterial dysfunction is unknown. To determine whether T cells directly mediate age-related arterial dysfunction, we examined large elastic artery and resistance artery function in young (4-6 months) and old (22-24 months) wild-type mice treated with anti-CD3 F(ab'2) fragments to deplete T cells (150 µg, i.p. every 7 days for 28 days) or isotype control fragments. Old mice exhibited greater numbers of T cells in both aorta and mesenteric vasculature when compared with young mice. Old mice treated with anti-CD3 fragments exhibited depletion of T cells in blood, spleen, aorta and mesenteric vasculature. Old mice also exhibited greater numbers of aortic and mesenteric IFN-γ and TNF-α-producing T cells when compared with young mice. Old control mice exhibited greater large artery stiffness and impaired resistance artery endothelium-dependent dilatation in comparison with young mice. In old mice, large artery stiffness was ameliorated with anti-CD3 treatment. Anti-CD3-treated old mice also exhibited greater endothelium-dependent dilatation than age-matched controls. We also examined arterial function in young and old Rag-1-/- mice, which lack lymphocytes. Rag-1-/- mice exhibited blunted increases in large artery stiffness with age compared with wild-type mice. Old Rag-1-/- mice also exhibited greater endothelium-dependent dilatation compared with old wild-type mice. Collectively, these results demonstrate that T cells play an important role in age-related arterial dysfunction.

Mechanisms of Dysfunction in the Aging Vasculature and Role in Age-Related Disease.

Advancing age promotes cardiovascular disease (CVD), the leading cause of death in the United States and many developed nations. Two major age-related arterial phenotypes, large elastic artery stiffening and endothelial dysfunction, are independent predictors of future CVD diagnosis and likely are responsible for the development of CVD in older adults. Not limited to traditional CVD, these age-related changes in the vasculature also contribute to other age-related diseases that influence mammalian health span and potential life span. This review explores mechanisms that influence age-related large elastic artery stiffening and endothelial dysfunction at the tissue level via inflammation and oxidative stress and at the cellular level via Klotho and energy-sensing pathways (AMPK [AMP-activated protein kinase], SIRT [sirtuins], and mTOR [mammalian target of rapamycin]). We also discuss how long-term calorie restriction-a health span- and life span-extending intervention-can prevent many of these age-related vascular phenotypes through the prevention of deleterious alterations in these mechanisms. Lastly, we discuss emerging novel mechanisms of vascular aging, including senescence and genomic instability within cells of the vasculature. As the population of older adults steadily expands, elucidating the cellular and molecular mechanisms of vascular dysfunction with age is critical to better direct appropriate and measured strategies that use pharmacological and lifestyle interventions to reduce risk of CVD within this population.

Induced Trf2 deletion leads to aging vascular phenotype in mice associated with arterial telomere uncapping, senescence signaling, and oxidative stress.

Age-related vascular dysfunction in large elastic and resistance arteries is associated with reductions in microvascular perfusion and elevations in blood pressure. Recent evidence indicates that telomere uncapping-induced senescence in vascular cells may be an important source of oxidative stress and vascular dysfunction in aging, but the causal relationship between these processes has yet to be elucidated. To test this important unexplored hypothesis, we measured arterial senescence signaling and oxidative stress, carotid and mesenteric artery endothelium-dependent vasodilatory capacity, markers of mesenteric microvascular perfusion and endothelial glycocalyx deterioration, and blood pressure in a novel mouse model of Cre-inducible whole body Trf2 deletion and telomere uncapping. Trf2 deletion led to a 320% increase in arterial senescence signaling (P < .05). There was a concurrent 29% and 22% reduction in peak endothelium-dependent vasodilation in carotid and mesenteric arteries, respectively, as well as a 63% reduction in mesenteric microvascular endothelial glycocalyx thickness (all P ≤ .01). Mesenteric microvascular perfusion was reduced by 8% and systolic blood pressure was increased by 9% following Trf2 deletion (both P < .05). Trf2 deletion also led to a pro-oxidative arterial phenotype characterized by increased in NADPH oxidase gene expression; a 210% increase in superoxide levels that was partly dependent on NADPH oxidase activity; and an oxidative stress mediated reduction in carotid artery vasodilation (all P ≤ .05). Collectively, our findings demonstrate that induced Trf2 deletion leads to telomere uncapping, increased senescence signaling, and oxidative stress mediated functional impairments in the vasculature similar to those seen in human aging.

Deletion of Robo4 prevents high-fat diet-induced adipose artery and systemic metabolic dysfunction.

OBJECTIVE: Accumulating evidence suggests the vascular endothelium plays a fundamental role in the pathophysiology of obesity by regulating the functional status of white adipose and systemic metabolism. Robo4 is expressed specifically in endothelial cells and increases vascular stability and inhibits angiogenesis. We sought to determine the role of Robo4 in modulating cardiometabolic function in response to high-fat feeding. METHODS: We examined exercise capacity, glucose tolerance, and white adipose tissue artery gene expression, endothelium-dependent dilation (EDD), and angiogenesis in wild type and Robo4 knockout (KO) mice fed normal chow (NC) or a high-fat diet (HFD). RESULTS: We found Robo4 deletion enhances exercise capacity in NC-fed mice and HFD markedly increased the expression of the Robo4 ligand, Slit2, in white adipose tissue. Deletion of Robo4 increased angiogenesis in white adipose tissue and protected against HFD-induced impairments in white adipose artery vasodilation and glucose intolerance. CONCLUSIONS: We demonstrate a novel functional role for Robo4 in endothelial cell function and metabolic homeostasis in white adipose tissue, with Robo4 deletion protecting against endothelial and metabolic dysfunction associated with a HFD. Our findings suggest that Robo4-dependent signaling pathways may be a novel target in anti-obesity therapy.

Advanced age results in a diminished endothelial glycocalyx.

Age-related microvascular dysfunction is well characterized in rodents and humans, but little is known about the properties of the microvascular endothelial glycocalyx in advanced age. We examined the glycocalyx in microvessels of young and old male C57BL6 mice (young: 6.1 ± 0.1 mo vs. old: 24.6 ± 0.2 mo) using intravital microscopy and transmission electron microscopy and in human participants (young: 29 ± 1 yr vs. old: 60 ± 2 yr) using intravital microscopy. Glycocalyx thickness in mesenteric and skeletal muscle microvessels was 51-54% lower in old compared with young mice. We also observed 33% lower glycocalyx thickness in the sublingual microcirculation of humans in advanced age. The perfused boundary region, a marker of glycocalyx barrier function, was also obtained using an automated capture and analysis system. In advanced age, we observed a 10-22% greater perfused boundary region in mice and humans, indicating a more penetrable glycocalyx. Finally, using this automated analysis system, we examined perfused microvascular density and red blood cell (RBC) fraction. Perfused microvascular density is a marker of microvascular function that reflects the length of perfused microvessel segments in a given area; RBC fraction represents the heterogeneity in RBC presence between microvessel segments. Compared with young, the perfused microvascular density was 16-21% lower and RBC fraction was 5-14% lower in older mice and in older humans. These data provide novel evidence that, across mammalian species, a diminished glycocalyx is present in advanced age and is accompanied by markers of impaired microvascular perfusion. Age-related glycocalyx deterioration may be an important contributor to microvascular dysfunction in older adults and subsequent pathophysiology. NEW & NOTEWORTHY Advanced age is characterized by microvascular dysfunction that contributes to age-related cardiovascular diseases, but little is known about endothelial glycocalyx properties in advanced age. This study reveals, for the first time, lower glycocalyx thickness and barrier function that is accompanied by impaired microvascular perfusion in both mice and humans in advanced age.

Attenuated nitric oxide bioavailability in systemic sclerosis: Evidence from the novel assessment of passive leg movement.

NEW FINDINGS: What is the central question of this study? Do systemic sclerosis patients exhibit impaired nitric oxide-mediated vascular function of the lower limb and are these decrements correlated with plasma biomarkers for inflammation and oxidative stress? What is the main finding and its importance? Findings indicate impaired nitric oxide-mediated vascular function, linked to the incidence of digital ulcers and a milieu of inflammation and oxidative stress. However, the absence of significant correlations between individual biomarkers and blood flow responses suggests that the vasculopathy observed in systemic sclerosis may not be solely the result of derangements in the redox balance or inflammatory signalling. ABSTRACT: Systemic sclerosis (SSc) is an autoimmune disease characterized by vasculopathy, which may be the consequence of inflammation and oxidative stress that ultimately leads to a reduced nitric oxide (NO) bioavailability. Passive leg movement (PLM) is a novel methodology for assessing lower limb vascular function that is predominantly NO dependent. We combined this vascular assessment with a comprehensive panel of plasma biomarkers to assess the axis of inflammation, oxidative stress and NO in SSc patients (n = 12; 62 ± 11 years of age) compared with healthy control subjects (n = 17; 60 ± 16 years of age). The PLM-induced changes in leg blood flow (LBF; 191 ± 104 versus 327 ± 217 ml min-1 ) and LBF area under the curve (39 ± 104 versus 125 ± 131 ml) were reduced in SSc compared with control subjects. Stratification of patients according to history of digital ulcer (DU) formation revealed a further reduction in LBF area under the curve in DU (-13 ± 83 ml) versus non-DU (91 ± 102 ml) patients. Biomarkers of inflammation (C-reactive protein) and oxidative stress (malondialdehyde and protein carbonyl) were all elevated in SSc (C-reactive protein, 3299 ± 2372 versus 984 ± 565 ng ml-1 ; malondialdehyde, 3.2 ± 1.1 versus 1.1 ± 0.7 µm; and protein carbonyl, 0.15 ± 0.05 versus 0.12 ± 0.03 nmol mg-1 ), and C-reactive protein was further elevated in patients with a history of DU (4551 ± 2752 versus 2047 ± 1019 ng ml-1 ) compared with non-DU, although these were not individually correlated with changes in LBF. These findings of impaired NO-mediated vascular function, linked to DU and a milieu of inflammation and oxidative stress, suggest that redox balance plays an important, but not necessarily deterministic, role in the vascular pathophysiology of SSc.

Implications of endothelial shear stress on systemic sclerosis vasculopathy and treatment.

There are no Federal Drug Administration approved drugs for the treatment of systemic sclerosis vascular digital ulcers (DU) in the United States, which are thought to be an end-stage result of prolonged ischaemia due to severe, prolonged Raynaud's phenomenon. Most therapeutics for vasodilation used in SSc work different pathways to target the smooth muscle to induce vessel relaxation. Longitudinal studies of vascular function allow insight into the effects of medications used for Raynaud's phenomenon in the SSc patient population. In this review, we discuss vascular tone, the function of the endothelium in SSc, and provide the rationale for longitudinal studies of vascular function and therapeutics that target the endothelial shear stress in addition to vasodilation for treatment and prevention of DU. This review provides the rationale for vasodilatory medication use for treatment of SSc-related DU and justifies access to non-FDA approved medications for this indication.

Acute oral tetrahydrobiopterin administration ameliorates endothelial dysfunction in systemic sclerosis.

OBJECTIVES: Systemic sclerosis (SSc) is a rare, autoimmune disease characterised by endothelial dysfunction, which is associated with peripheral vasculopathy, such as digital ulcers (DU). We sought to determine if acute oral administration of tetrahydrobiopterin (BH4), an essential cofactor for endothelial nitric oxide synthase, would augment endothelial function in patients with SSc. METHODS: Twelve SSc patients, of whom a majority had a history of DU, were studied 5 hours after oral BH4 administration (10 mg/kg body mass) or placebo on separate days using controlled, counterbalanced, double-blind, crossover experimental design. RESULTS: There were no differences in blood markers of oxidative stress and brachial artery blood pressure, diameter, blood velocity, shear rate, or blood flow at rest between placebo and BH4 (p>0.05). Whereas, after a 5 minute suprasystolic forearm cuff occlusion, brachial artery peak reactive hyperemia (placebo: 313±30 vs. BH4: 347±37 ml/min, p<0.05) and flow-mediated dilation (FMD) (placebo: 3.0±0.8 vs. BH4: 4.8±0.8%, p<0.05) were significantly higher after acute BH4 administration, indicating an improvement in endothelial function. To determine if the vasodilatory effects of BH4 were specific to the vascular endothelium, brachial artery blood flow and vasodilation in response to sublingual nitroglycerin were assessed, and were found to be unaffected by BH4 (p>0.05). CONCLUSIONS: These findings indicate that acute BH4 administration ameliorates endothelial dysfunction in patients with SSc. Given that endothelial dysfunction is known to be associated with DU in SSc patients, this study provides a proof-of-concept for the potential therapeutic benefits of BH4 in the prevention or treatment of DU in this population.

Exercise-induced brachial artery blood flow and vascular function is impaired in systemic sclerosis.

Systemic sclerosis (SSc) is a rare autoimmune disease characterized by debilitating fibrosis and vascular dysfunction; however, little is known about the circulatory response to exercise in this population. Therefore, we examined the peripheral hemodynamic and vasodilatory responses to handgrip exercise in 10 patients with SSc (61 ± 4 yr) and 15 age-matched healthy controls (56 ± 5 yr). Brachial artery diameter, blood flow, and mean arterial pressure (MAP) were determined at rest and during progressive static-intermittent handgrip exercise. Patients with SSc and controls were similar in body stature, handgrip strength, and MAP; however, brachial artery blood flow at rest was nearly twofold lower in patients with SSc compared with controls (22 ± 4 vs. 42 ± 5 ml/min, respectively; P < 0.05). Additionally, SSc patients had an ∼18% smaller brachial artery lumen diameter with an ∼28% thicker arterial wall at rest (P < 0.05). Although, during handgrip exercise, there were no differences in MAP between the groups, exercise-induced hyperemia and therefore vascular conductance were ∼35% lower at all exercise workloads in patients with SSc (P < 0.05). Brachial artery vasodilation, as assessed by the relationship between Δbrachial artery diameter and Δshear rate, was significantly attenuated in the patients with SSc (P < 0.05). Finally, vascular dysfunction in the patients with SSc was accompanied by elevated blood markers of oxidative stress and attenuated endogenous antioxidant activity (P < 0.05). Together, these findings reveal attenuated exercise-induced brachial artery blood flow and conduit arterial vasodilatory dysfunction during handgrip exercise in SSc and suggest that elevated oxidative stress may play a role.

Impact of blood pressure perturbations on arterial stiffness.

Although the associations between chronic levels of arterial stiffness and blood pressure (BP) have been fairly well studied, it is not clear whether and how much arterial stiffness is influenced by acute perturbations in BP. The primary aim of this study was to determine magnitudes of BP dependence of various measures of arterial stiffness during acute BP perturbation maneuvers. Fifty apparently healthy subjects, including 25 young (20-40 yr) and 25 older adults (60-80 yr), were studied. A variety of BP perturbations, including head-up tilt, head-down tilt, mental stress, isometric handgrip exercise, and cold pressor test, were used to encompass BP changes induced by physical, mental, and/or mechanical stimuli. When each index of arterial stiffness was plotted with mean BP, all arterial stiffness indices, including cardio-ankle vascular index or CAVI (r = 0.50), carotid-femoral pulse wave velocity or cfPWV (r = 0.51), brachial-ankle pulse wave velocity or baPWV (r = 0.61), arterial compliance (r = -0.42), elastic modulus (r = 0.52), arterial distensibility (r = -0.32), ß-stiffness index (r = 0.19), and Young's modulus (r = 0.35) were related to mean BP (all P < 0.01). Changes in CAVI, cfPWV, baPWV, and elastic modulus were significantly associated with changes in mean BP in the pooled conditions, while changes in arterial compliance, arterial distensibility, ß-stiffness index, and Young's modulus were not. In conclusion, this study demonstrated that BP changes in response to various forms of pressor stimuli were associated with the corresponding changes in arterial stiffness indices and that the strengths of associations with BP varied widely depending on what arterial stiffness indices were examined.

Endothelial cell-specific reduction in mTOR ameliorates age-related arterial and metabolic dysfunction.

Systemic inhibition of the mammalian target of rapamycin (mTOR) delays aging and many age-related conditions including arterial and metabolic dysfunction. However, the mechanisms and tissues involved in these beneficial effects remain largely unknown. Here, we demonstrate that activation of S6K, a downstream target of mTOR, is increased in arteries with advancing age, and that this occurs preferentially in the endothelium compared with the vascular smooth muscle. Induced endothelial cell-specific deletion of mTOR reduced protein expression by 60-70%. Although this did not significantly alter arterial and metabolic function in young mice, endothelial mTOR reduction reversed arterial stiffening and improved endothelium-dependent dilation (EDD) in old mice, indicating an improvement in age-related arterial dysfunction. Improvement in arterial function in old mice was concomitant with reductions in arterial cellular senescence, inflammation, and oxidative stress. The reduction in endothelial mTOR also improved glucose tolerance in old mice, and this was associated with attenuated hepatic gluconeogenesis and improved lipid tolerance, but was independent of alterations in peripheral insulin sensitivity, pancreatic beta cell function, or fasted plasma lipids in old mice. Lastly, we found that endothelial mTOR reduction suppressed gene expression of senescence and inflammatory markers in endothelial-rich (i.e., lung) and metabolically active organs (i.e., liver and adipose tissue), which may have contributed to the improvement in metabolic function in old mice. This is the first evidence demonstrating that reducing endothelial mTOR in old age improves arterial and metabolic function. These findings have implications for future drug development.

Glycocalyx-targeted therapy ameliorates age-related arterial dysfunction.

Advanced age is accompanied by arterial dysfunction, as well as a diminished glycocalyx, which may be linked to reduced high molecular weight-hyaluronan (HMW-HA) synthesis. However, the impact of glycocalyx deterioration in age-related arterial dysfunction is unknown. We sought to determine if manipulations in glycocalyx properties would alter arterial function. Tamoxifen-induced hyaluronan synthase 2 (Has2) reduction was used to decrease glycocalyx properties. Three weeks post-tamoxifen treatment, glycocalyx thickness was lower in Has2 knockout compared to wild-type mice (P<0.05). Has2 reduction induced arterial dysfunction, demonstrated by impaired endothelium-dependent dilation (EDD) and elevated aortic stiffness (P<0.05). To augment glycocalyx properties, old mice received 10 weeks of a glycocalyx-targeted therapy via Endocalyx™ (old+ECX), which contains HMW-HA and other glycocalyx components. Compared to old control mice, glycocalyx properties and EDD were augmented, and aortic stiffness decreased in old+ECX mice (P<0.05). Old+ECX mice had a more youthful aortic phenotype, demonstrated by lower collagen content and higher elastin content than old control mice (P<0.05). Functional outcomes were repeated in old mice that underwent a diet supplemented solely with HMW-HA (old+HA). Compared to old controls, glycocalyx properties and EDD were augmented, and aortic stiffness was lower in old+HA mice (P<0.05). We did not observe any differences between old+HA and old+ECX mice (P>0.05). Has2 reduction phenocopies age-related arterial dysfunction, while 10 weeks of glycocalyx-targeted therapy that restores the glycocalyx also ameliorates age-related arterial dysfunction. These findings suggest that the glycocalyx may be a viable therapeutic target to ameliorate age-related arterial dysfunction.

Ovariectomy aggravates the pathophysiological response to exertional heat stroke in mice.

Female mice have a greater capacity for exercising in the heat than male mice, reaching greater power output and longer times of heat exposure before succumbing to exertional heat stroke (EHS). Differences in body mass, size, or testosterone do not explain these distinct sex responses. Whether the ovaries could account for the superior exercise capacity in the heat in females remains unknown. Here, we determined the influence of ovariectomy (OVX) on exercise capacity in the heat, thermoregulation, intestinal damage, and heat shock response in a mouse EHS model. We performed bilateral OVX (n = 10) or sham (n = 8) surgeries in young adult (4 mo) female C57/BL6J mice. Upon recovery from surgeries, mice exercised on a forced wheel placed inside an environmental chamber set at 37.5 °C and 40% relative humidity until experiencing loss of consciousness (LOC). Terminal experiments were performed 3 h after LOC. OVX increased body mass by the time of EHS (sham = 3.8 ± 1.1, OVX = 8.3 ± 3.2 g, P < 0.05), resulted in shorter running distance (sham = 753 ± 189, OVX = 490 ± 87 m, P < 0.05), and shorter time to LOC (sham = 126.3 ± 21, OVX = 99.1 ± 19.8 min, P < 0.05). Histopathological assessment of the intestines revealed damage in the jejunum (sham = 0.2 ± 0.7, OVX = 2.1 ± 1.7 AU, P < 0.05) and ileum (sham = 0.3 ± 0.5, OVX = 1.8 ± 1.4 AU, P < 0.05). OVX increased mesenteric microvascular density (sham = 101 ± 25, OVX = 156 ± 66 10-2 mm/mm2, P < 0.05) and decreased concentration of circulatory heat shock protein 72 (HSP72) (sham = 26.7 ± 15.8, OVX = 10.3 ± 4.6 ng/mL, P < 0.05). No differences were observed in cytokines or chemokines between groups. Our findings indicate that OVX aggravates the pathophysiological response to EHS in mice.NEW & NOTEWORTHY Females outperform males in a mouse model of exertional heat stroke (EHS). Here, we show for the first time the impact of ovariectomy (OVX) on EHS pathophysiology. OVX resulted in a shorter exercise capacity in the heat, greater intestinal damage, and lower heat shock response following EHS.

Pyridoxamine treatment ameliorates large artery stiffening and cerebral artery endothelial dysfunction in old mice.

Age-related increases in large artery stiffness are associated with cerebrovascular dysfunction and cognitive impairment. Pyridoxamine treatment prevents large artery stiffening with advancing age, but the effects of pyridoxamine treatment on the cerebral vasculature or cognition is unknown. The purpose of this study was to investigate the effects of pyridoxamine on blood pressure, large artery stiffness, cerebral artery function, and cognitive function in old mice. Old male C57BL/6 mice consumed either pyridoxamine (2 g/L) or vehicle control in drinking water for ∼7.5 months and were compared with young male C57BL/6 mice. From pre- to post-treatment, systolic blood pressure increased in old control mice, but was maintained in pyridoxamine treated mice. Large artery stiffness decreased in pyridoxamine-treated mice but was unaffected in control mice. Pyridoxamine-treated mice had greater cerebral artery endothelium-dependent dilation compared with old control mice, and not different from young mice. Old control mice had impaired cognitive function; however, pyridoxamine only partially preserved cognitive function in old mice. In summary, pyridoxamine treatment in old mice prevented age-related increases in blood pressure, reduced large artery stiffness, preserved cerebral artery endothelial function, and partially preserved cognitive function. Taken together, these results suggest that pyridoxamine treatment may limit vascular aging.

Endothelial cell telomere dysfunction induces senescence and results in vascular and metabolic impairments.

In advanced age, increases in oxidative stress and inflammation impair endothelial function, which contributes to the development of cardiovascular disease (CVD). One plausible source of this oxidative stress and inflammation is an increase in the abundance of senescent endothelial cells. Cellular senescence is a cell cycle arrest that occurs in response to various damaging stimuli. In the present study, we tested the hypothesis that advanced age results in endothelial cell telomere dysfunction that induces senescence. In both human and mouse endothelial cells, advanced age resulted in an increased abundance of dysfunctional telomeres, characterized by activation of DNA damage signaling at telomeric DNA. To test whether this results in senescence, we selectively reduced the telomere shelterin protein telomere repeat binding factor 2 (Trf2) from endothelial cells of young mice. Trf2 reduction increased endothelial cell telomere dysfunction and resulted in cellular senescence. Furthermore, induction of endothelial cell telomere dysfunction increased inflammatory signaling and oxidative stress, resulting in impairments in endothelial function. Finally, we demonstrate that endothelial cell telomere dysfunction-induced senescence impairs glucose tolerance. This likely occurs through increases in inflammatory signaling in the liver and adipose tissue, as well as reductions in microvascular density and vasodilation to metabolic stimuli. Cumulatively, the findings of the present study identify age-related telomere dysfunction as a mechanism that leads to endothelial cell senescence. Furthermore, these data provide compelling evidence that senescent endothelial cells contribute to age-related increases in oxidative stress and inflammation that impair arterial and metabolic function.