The elastic modulus of conductance coronary arteries from spontaneously hypertensive rats is increased

Impact of knockout of dual-specificity protein phosphatase 5 on structural and mechanical properties of rat middle cerebral arteries: implications for vascular aging

Vascular aging influences hemodynamics, elevating risks for vascular diseases and dementia. We recently demonstrated that knockout (KO) of Dusp5 enhances cerebral and renal hemodynamics and cognitive function. This improvement correlates with elevated pPKC and pERK1/2 levels in the brain and kidneys. Additionally, we observed that Dusp5 KO modulates the passive mechanical properties of cerebral and renal arterioles, associated with increased myogenic tone at low pressure, enhanced distensibility, greater compliance, and reduced stiffness. The present study evaluates the structural and mechanical properties of the middle cerebral artery (MCA) in Dusp5 KO rats. We found that vascular smooth muscle cell layers and the collagen content in the MCA wall are comparable between Dusp5 KO and control rats. The internal elastic lamina in the MCA of Dusp5 KO rats exhibits increased thickness, higher autofluorescence intensity, smaller fenestrae areas, and fewer fenestrations. Despite an enhanced myogenic response and tone of the MCA in Dusp5 KO rats, other passive mechanical properties, such as wall thickness, cross-sectional area, wall-to-lumen ratio, distensibility, incremental elasticity, circumferential wall stress, and elastic modulus, do not significantly differ between strains. These findings suggest that while Dusp5 KO has a limited impact on altering the structural and mechanical properties of MCA, its primary role in ameliorating hemodynamics and cognitive functions is likely attributable to its enzymatic activity on cerebral arterioles. Further research is needed to elucidate the specific enzymatic mechanisms and explore potential clinical applications in the context of vascular aging.

Role of Dusp5 KO on Vascular Properties of Middle Cerebral Artery in Rats

Vascular aging influences hemodynamics, elevating risks for vascular diseases and dementia. We recently demonstrated that knockout (KO) of Dusp5 enhances cerebral and renal hemodynamics and cognitive function. This improvement correlates with elevated pPKC and pERK1/2 levels in the brain and kidneys. Additionally, we observed that Dusp5 KO modulates the passive mechanical properties of cerebral and renal arterioles, associated with increased myogenic tone at low pressure, enhanced distensibility, greater compliance, and reduced stiffness. The present study evaluates the structural and mechanical properties of the middle cerebral artery (MCA) in Dusp5 KO rats. We found that vascular smooth muscle cell layers and the collagen content in the MCA wall are comparable between Dusp5 KO and control rats. The internal elastic lamina in the MCA of Dusp5 KO rats exhibits increased thickness, higher autofluorescence intensity, smaller fenestrae areas, and fewer fenestrations. Despite an enhanced myogenic response and tone of the MCA in Dusp5 KO rats, other passive mechanical properties, such as wall thickness, cross-sectional area, wall-to-lumen ratio, distensibility, incremental elasticity, circumferential wall stress, and elastic modulus, do not significantly differ between strains. These findings suggest that while Dusp5 KO has a limited impact on altering the structural and mechanical properties of MCA, its primary role in ameliorating hemodynamics and cognitive functions is likely attributable to its enzymatic activity on cerebral arterioles. Further research is needed to elucidate the specific enzymatic mechanisms and explore potential clinical applications in the context of vascular aging.

The Impact of Estrogen Receptor in Arterial and Lymphatic Vascular Diseases

The lower incidence of cardiovascular diseases in pre-menopausal women compared to men is well-known documented. This protection has been largely attributed to the protective effect of estrogens, which exert many beneficial effects against arterial diseases, including vasodilatation, acceleration of healing in response to arterial injury, arterial collateral growth and atheroprotection. More recently, with the visualization of the lymphatic vessels, the impact of estrogens on lymphedema and lymphatic diseases started to be elucidated. These estrogenic effects are mediated not only by the classic nuclear/genomic actions via the specific estrogen receptor (ER) α and β, but also by rapid extra-nuclear membrane-initiated steroid signaling (MISS). The ERs are expressed by endothelial, lymphatic and smooth muscle cells in the different vessels. In this review, we will summarize the complex vascular effects of estrogens and selective estrogen receptor modulators (SERMs) that have been described using different transgenic mouse models with selective loss of ERα function and numerous animal models of vascular and lymphatic diseases.

Sex differences in the structure and function of rat middle cerebral arteries

Epidemiological studies demonstrate that there are sex differences in the incidence, prevalence, and outcomes of cerebrovascular disease (CVD). The present study compared the structure and composition of the middle cerebral artery (MCA), neurovascular coupling, and cerebrovascular function and cognition in young Sprague-Dawley (SD) rats. Wall thickness and the inner diameter of the MCA were smaller in females than males. Female MCA exhibited less vascular smooth muscle cells (VSMCs), diminished contractile capability, and more collagen in the media, and a thicker internal elastic lamina with fewer fenestrae compared with males. Female MCA had elevated myogenic tone, lower distensibility, and higher wall stress. The stress/strain curves shifted to the left in female vessels compared with males. The MCA of females failed to constrict compared with a decrease of 15.5 ± 1.9% in males when perfusion pressure was increased from 40 to 180 mmHg. Cerebral blood flow (CBF) rose by 57.4 ± 4.4 and 30.1 ± 3.1% in females and males, respectively, when perfusion pressure increased from 100 to 180 mmHg. The removal of endothelia did not alter the myogenic response in both sexes. Functional hyperemia responses to whisker-barrel stimulation and cognition examined with an eight-arm water maze were similar in both sexes. These results demonstrate that there are intrinsic structural differences in the MCA between sexes, which are associated with diminished myogenic response and CBF autoregulation in females. The structural differences do not alter neurovascular coupling and cognition at a young age; however, they might play a role in the development of CVD after menopause.

NEW & NOTEWORTHY Using perfusion fixation of the middle cerebral artery (MCA) in calcium-free solution at physiological pressure and systematically randomly sampling the sections prepared from the same M2 segments of MCA, we found that there are structural differences that are associated with altered cerebral blood flow (CBF) autoregulation but not neurovascular coupling and cognition in young, healthy Sprague-Dawley (SD) rats. Understanding the intrinsic differences in cerebrovascular structure and function in males and females is essential to develop new pharmaceutical treatments for cerebrovascular disease (CVD).

Endothelial SIRT1 prevents adverse arterial remodeling by facilitating HERC2-mediated degradation of acetylated LKB1

Aims-SIRT1 exerts potent activity against cellular senescence and vascular ageing. By decreasing LKB1 protein levels, it promotes the survival and regeneration of endothelial cells. The present study aims to investigate the molecular mechanisms underlying SIRT1-mediated LKB1 degradation for the prevention of vascular ageing.

Methods and Results-Co-immunoprecipitation assay demonstrated that SIRT1, via its amino-terminus, binds to the DOC domain of HERC2 [HECT and RLD domain containing E3 ubiquitin protein ligase 2], which then ubiquitinates LKB1 in the nuclear compartment of endothelial cells. Site-directed mutagenesis revealed that acetylation at lysine (K) 64 of LKB1 triggers the formation of SIRT1/HERC2/LKB1 protein complex and subsequent proteasomal degradation. In vitro cellular studies suggested that accumulation of acetylated LKB1 in the nucleus leads to endothelial activation, in turn stimulating the proliferation of vascular smooth muscle cells and the production of extracellular matrix proteins. Chromatin immunoprecipitation quantitative PCR confirmed that acetylated LKB1 interacts with and activates TGFβ1 promoter, which is inhibited by SIRT1. Knocking down either SIRT1 or HERC2 results in an increased association of LKB1 with the positive regulatory elements of TGFβ1 promoter. In mice without endothelial nitric oxide synthase, selective overexpression of human SIRT1 in endothelium prevents hypertension and age-related adverse arterial remodeling. Lentiviral-mediated knockdown of HERC2 abolishes the beneficial effects of endothelial SIRT1 on both arterial remodeling and arterial blood pressure control.

Conclusion-By downregulating acetylated LKB1 protein via HERC2, SIRT1 fine-tunes the crosstalk between endothelial and vascular smooth muscle cells to prevent adverse arterial remodeling and maintain vascular homeostasis.

Coronary microvascular disease as an early culprit in the pathophysiology of diabetes and metabolic syndrome

Metabolic syndrome (MetS) is a group of cardio-metabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia; these are also a combination of independent coronary artery disease (CAD) risk factors. Alarmingly, the prevalence of MetS risk factors are increasing and a leading cause for mortality. In the vasculature, complications from MetS and type 2 diabetes (T2D) can be divided into microvascular (retinopathy and nephropathy) and macrovascular (cardiovascular diseases and erectile dysfunction). In addition to vascular and endothelial dysfunction, vascular remodeling and stiffness are also hallmarks of cardiovascular disease (CVD), and well-characterized vascular changes that are observed in the early stages of hypertension, T2D, and obesity [1-3]. In the heart, the link between obstructive atherosclerosis of coronary macrovessels and myocardial ischemia (MI) is well established. However, recent studies show that abnormalities in the coronary microcirculation are associated with functional and structural changes in coronary microvessels (classically defined as being ≤150-200μm internal diameter), which may cause or contribute to MI even in the absence of obstractive CAD. This suggests a prognostic value of an abnormal coronary microcirculation as an early sub-clinical culprit in the pathogenesis and progression of heart disease in T2D and MetS. The aim of this review is to summarize recent studies investigating the coronary microvascular remodeling in an early pre-atherosclerotic phase of MetS and T2D, and to explore potential mechanisms associated with the timing of coronary microvascular remodeling relative to that of the macrovasculature.

Imaging and modeling of acute pressure-induced changes of collagen and elastin microarchitectures in pig and human resistance arteries

The impact of disease-related changes in the extracellular matrix (ECM) on the mechanical properties of human resistance arteries largely remains to be established. Resistance arteries from both pig and human parietal pericardium (PRA) display a different ECM microarchitecture compared with frequently used rodent mesenteric arteries. We hypothesized that the biaxial mechanics of PRA mirror pressure-induced changes in the ECM microarchitecture. This was tested using isolated pig PRA as a model system, integrating vital imaging, pressure myography, and mathematical modeling. Collagenase and elastase digestions were applied to evaluate the load-bearing roles of collagen and elastin, respectively. The incremental elastic modulus linearly related to the straightness of adventitial collagen fibers circumferentially and longitudinally (both R2 ≥ 0.99), whereas there was a nonlinear relationship to the internal elastic lamina elastin fiber branching angles. Mathematical modeling suggested a collagen recruitment strain (means ± SE) of 1.1 ± 0.2 circumferentially and 0.20 ± 0.01 longitudinally, corresponding to a pressure of ~40 mmHg, a finding supported by the vital imaging. The integrated method was tested on human PRA to confirm its validity. These showed limited circumferential distensibility and elongation and a collagen recruitment strain of 0.8 ± 0.1 circumferentially and 0.06 ± 0.02 longitudinally, reached at a distending pressure below 20 mmHg. This was confirmed by vital imaging showing negligible microarchitectural changes of elastin and collagen upon pressurization. In conclusion, we show here, for the first time in resistance arteries, a quantitative relationship between pressure-induced changes in the extracellular matrix and the arterial wall mechanics. The strength of the integrated methods invites for future detailed studies of microvascular pathologies.

NEW & NOTEWORTHY This is the first study to quantitatively relate pressure-induced microstructural changes in resistance arteries to the mechanics of their wall. Principal findings using a pig model system were confirmed in human arteries. The combined methods provide a strong tool for future hypothesis-driven studies of microvascular pathologies.

Diameter-dependent axial prestretch of porcine coronary arteries and veins

The pressure-diameter relation (PDR) and the wall strain of coronary blood vessels have important implications for coronary blood flow and arthrosclerosis, respectively. Previous studies have shown that these mechanical quantities are significantly affected by the axial stretch of the vessels. The objective of this study was to measure the physiological axial stretch in the coronary vasculature; i.e., from left anterior descending (LAD) artery tree to coronary sinus vein and to determine its effect on the PDR and hence wall stiffness. Silicone elastomer was perfused through the LAD artery and coronary sinus trees to cast the vessels at the physiologic pressure. The results show that the physiological axial stretch exists for orders 4 to 11 (> 24 μm in diameter) arteries and orders -4 to -12 (>38 μm in diameter) veins but vanishes for the smaller vessels. Statistically, the axial stretch is higher for larger vessels and is higher for arteries than veins. The axial stretch λ(z) shows a linear variation with the order number (n) as: λ(z) = 0.062n + 0.75 (R(2) = 0.99) for artery and λ(z) = -0.029n + 0.89 (R(2) = 0.99) for vein. The mechanical analysis shows that the axial stretch significantly affects the PDR of the larger vessels. The circumferential stretch/strain was found to be significantly higher for the epicardial arteries (orders 9-11), which are free of myocardium constraint, than the intramyocardial arteries (orders 4-8). These findings have fundamental implications for coronary blood vessel mechanics.

Effects of chronic exposure to air pollution from Sao Paulo city on coronary of Swiss mice, from birth to adulthood

To explore the hypothesis that air pollution promotes cardiovascular changes, Swiss mice were continuously exposed, since birth, in two open-top chambers (filtered and nonfiltered for airborne particles <or= 0.3 microm) placed 20 m from a street with heavy traffic in downtown Sao Paulo, twenty-four hours per day for four months. Fine particle (PM(2.5)) concentration was determined gravimetrically; hearts were analyzed by morphometry. There was a reduction of the PM(2.5) inside the filtered chamber (filtered = 8.61+/-0.79 microg/m(3), nonfiltered = 18.05+/-1.25 microg/m(3), p < .001). Coronary arteries showed no evidence of luminal narrowing in the exposed group but presented higher collagen content in the adventitia of LV large-sized and RV midsized vessels (p = .001) and elastic fibers in both tunicae adventitia and intima-media of almost all sized arterioles from both ventricles (p = .03 and p = .001, respectively). We concluded that chronic exposure to urban air since birth induces mild but significant vascular structural alterations in normal individuals, presented as coronary arteriolar fibrosis and elastosis. These results might contribute to altered vascular response and ischemic events in the adulthood.

Passive mechanical properties of porcine left circumflex artery and its mathematical description

The aim of this study was to analyze the pseudoelastic behavior of the coronary wall in vitro and to describe this behavior with three alternative strain energy functions frequently used in arterial mechanics. Six tubular segments of artery were subjected to various levels of simultaneous transmural pressure and axial force encompassing the physiological range of loading. Measured data on force, pressure, stress-free geometry and vessel deformation were used to compute components of the Green strain tensor and to determine by least squares fit the values of constants appearing in the following strain energy functions: Fung's exponential function, a combined polynomial-exponential form and a neo-Hookean plus exponential expression. The results obtained showed large biological variability. A comparison of the relative magnitude of the strain components did not reveal significant deviations from orthotropy under the given experimental conditions, hence shear terms were not included in the present constitutive formulations. The deformational behavior of the coronary artery displayed the high non-linearity typical for arteries of the muscular type. For states of equibiaxial stress the corresponding strains in the axial direction were larger than those in the circumferential direction, at least for loads in the upper and physiological range. All these aspects of coronary elasticity were mimicked fairly well by all three functions, although with slightly different degrees of accuracy.

Estrogen modulates the mechanical homeostasis of mouse arterial vessels through nitric oxide

We have recently shown that estrogen causes vessel dilation through receptor-mediated stimulation of nitric oxide (NO) production. Here, we hypothesize that estrogen modulates the mechanical homeostasis in the blood vessel wall through NO production. The mechanical properties of female ovariectomized (ovx) mice, female mice lacking the gene for endothelial NO synthase (eNOS(-/-)), and control female and male mice were studied to test the hypothesis. The femoral and carotid arteries and aorta were cannulated in situ and mechanically distended. The stress, strain, elastic modulus, and wall thickness of vessels in ovx and eNOS(-/-) mice, as well as intact female and male mice, were determined. Western blot and immunohistochemistry were used to assess eNOS protein expression in the aorta. Moreover, NO by-products of the femoral and carotid artery were determined by measuring the levels of nitrite and nitrate. Our results show that ovariectomy and eNOS(-/-) significantly decrease the strain in all arteries. Furthermore, the eNOS protein was significantly reduced in ovx mice. Finally, the NO metabolites were significantly decreased both in ovx and eNOS(-/-) mice. We found statistically significant correlations between the structural (wall thickness), mechanical (stress, strain, and elastic modulus), and biochemical parameters (NO by-products). These novel results connect NO to the structural and mechanical properties of the vessel wall. Hence, the effect of endogenous estrogen on the arterial mechanical properties is mediated by the regulation of NO derived from eNOS.

Renal advances in ultrasound elasticity imaging: measuring the compliance of arteries and kidneys in end-stage renal disease

BACKGROUND/AIMS

Ultrasound elasticity imaging visually represents tissue hardness measurements using high-resolution ultrasound speckle-tracking algorithms. This method has recently been applied in the renal setting to measure arterial compliance in end-stage renal disease (ESRD) and the mechanical properties of transplant kidneys in vivo.

METHODS

Ultrasound radio-frequency signal measurements were made of the brachial artery in 5 ESRD subjects and 5 healthy controls and renal transplant measurements in 2 subjects, 1 with chronic allograft nephropathy (CAN) and 1 with normal graft function.

RESULTS

Maximal brachial artery percent strain measurements for healthy controls were 32.9 +/- 10.2% (mean +/- SD) and for ESRD subjects maximal percent strains were 4.9 +/- 1.8%. Transplant renal cortical strain for the subject with CAN was approximately one third that of the healthy transplant recipient.

CONCLUSION

Ultrasound elasticity imaging offers the potential to noninvasively measure the mechanical properties of structures within the body.

Impaired coronary endothelial function in a rat model of spontaneous albuminuria

BACKGROUND

Albuminuria is an independent risk factor of coronary artery disease and has been proposed to reflect a general endothelial disorder. The Munich Wistar Frömter (MWF) rat strain develops spontaneous albuminuria and, therefore, may be an interesting experimental model to study alterations of endothelial function under conditions of increased albuminuria. Our aim was to investigate if the MWF strain shows generalized endothelial dysfunction or endothelial dysfunction localized to the coronary vascular bed, and if so, determine which endothelial dilative mediators are involved.

METHODS

Coronary and mesenteric arteries were investigated for endothelium-dependent relaxation and the contribution of prostacyclin, nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) in MWF rats compared to normal Wistar rats. In addition, as MWF rats show increased blood pressure, spontaneously hypertensive rats (SHR) with similar hypertension but without increased albuminuria also were studied.

RESULTS

Maximal total endothelium-dependent relaxation of coronary arteries was strongly impaired in MWF rats (55 +/- 3%) compared to Wistar (89 +/- 5%) and SHR (89 +/- 2%) P < 0.05, respectively. The NO-mediated relaxation as well as the relaxation mediated by EDH were significantly lower in coronary arteries from MWF compared to Wistar. In mesenteric arteries of MWF the endothelium-dependent relaxation was intact.

CONCLUSIONS

The strong impairment of coronary endothelium-dependent relaxation in the MWF model of spontaneous albuminuria may be due to defects in production or activity of NO and EDH. The intact mesenteric endothelium-dependent relaxation suggests that increased albuminuria may not be related to generalized endothelial vasodilator dysfunction in this model. Selective impairment of coronary endothelial function in a setting of spontaneous albuminuria may be a feature of the MWF that may be employed to further study cause-effect relations between albuminuria and coronary artery disease.

Effect of a COL1A1 Sp1 binding site polymorphism on arterial pulse wave velocity: an index of compliance

-Reduced arterial compliance precedes changes in blood pressure, which may be mediated through alterations in vessel wall matrix composition. We investigated the effect of the collagen type I-alpha1 gene (COL1A1) +2046G>T polymorphism on arterial compliance in healthy individuals. We recruited 489 subjects (251 men and 238 women; mean age, 22.6+/-1.6 years). COL1A1 genotypes were determined using polymerase chain reaction and digestion by restriction enzyme Bal1. Arterial pulse wave velocities were measured in 3 segments, aortoiliac (PWVA), aortoradial (PWVB), and aorto-dorsalis-pedis (PWVF), as an index of compliance using a noninvasive optical method. Data were available for 455 subjects. The sample was in Hardy-Weinberg equilibrium with genotype distributions and allele frequencies that were not significantly different from those reported previously. The T allele frequency was 0.22 (95% confidence interval, 0.19 to 0.24). Two hundred eighty-three (62.2%) subjects were genotype GG, 148 (35.5%) subjects were genotype GT, and 24 (5.3%) subjects were genotype TT. A comparison of GG homozygotes with GT and TT individuals demonstrated a statistically significant association with arterial compliance: PWVF 4.92+/-0.03 versus 5.06+/-0.05 m/s (ANOVA, P=0.009), PWVB 4.20+/-0.03 versus 4.32+/-0.04 m/s (ANOVA, P=0.036), and PWVA 3.07+/-0.03 versus 3.15+/-0.03 m/s (ANOVA, P=0.045). The effects of genotype were independent of age, gender, smoking, mean arterial pressure, body mass index, family history of hypertension, and activity scores. We report an association between the COL1A1 gene polymorphism and arterial compliance. Alterations in arterial collagen type 1A deposition may play a role in the regulation of arterial compliance.

Trandolapril treatment at low dose improves mechanical and functional properties in perfused coronary arteries of spontaneously hypertensive rat

The ex-vivo effects of a 1-month treatment period with trandolapril at a low dose (0.3 mg/kg/day) were assessed on the mechanical and functional alterations observed in SHR coronary arteries. The in-vitro intrinsic elastic properties of the wall in treated SHR coronary arteries were determined in comparison to those of SHR rats. In preconstricted preparations, agonist- and flow-induced dilatations were investigated in arteries of both groups. Arterial segments were cannulated at both ends using an arteriograph system. Internal diameter and wall thickness were continuously monitored while intraluminal pressure and flow were controlled. Wall thickness was reduced in arteries of treated rats compared to those in control SHR (mm): 52 +/- 2 vs. 41 +/- 2, P < 0.001, respectively. Arterial stiffness, expressed by the incremental elastic modulus-stress relationship, was significantly lower in arteries of treated compared to control SHRs. In preconstricted preparations, dilatations induced by bradykinin were significantly greater in treated SHR compared to control SHR arteries whereas dilatations induced by acetylcholine were slightly but not significantly increased. On the other hand, starting flow at the plateau of 5-HT-induced constriction led to dilatations which were not significantly different in the treated compared to the control group. The maximal dilatation induced by flow in arteries of treated rats was obtained for the same value of shear stress compared to that determined in preparations of control SHRs: (dyn/cm2) 63 +/- 3 vs. 61 +/- 2, respectively, NS. These results show that together with hypertrophy, the abnormal mechanical properties observed in the coronary arterial wall of SHR were improved by a low dose of trandolapril treatment. However, differential effects of trandolapril treatment were observed on agonist and flow-induced dilatations. Although flow-induced dilatation seemed to remain unaffected, acetylcholine-induced dilatation was slightly improved and bradykinin-induced dilatation was markedly increased by trandolapril treatment.