Impaired myogenic tone in mesenteric arteries from overweight rats

Phosphodiesterases Mediate the Augmentation of Myogenic Constriction by Inhibitory G Protein Signaling and is Negatively Modulated by the Dual Action of RGS2 and 5

G protein regulation by regulators of G protein signaling (RGS) proteins play a key role in vascular tone maintenance. The loss of Gi/o and Gq/11 regulation by RGS2 and RGS5 in non-pregnant mice is implicated in augmented vascular tone and decreased uterine blood flow (UBF). RGS2 and 5 are closely related and co-expressed in uterine arteries (UA). However, whether and how RGS2 and 5 coordinate their regulatory activities to finetune G protein signaling and regulate vascular tone are unclear. Here, we determined how the integrated activity of RGS2 and 5 modulates vascular tone to promote UBF. Using ultrasonography and pressure myography, we examined uterine hemodynamics and myogenic tone (MT) of UA of wild type (WT), Rgs2-/-, Rgs5-/-, and Rgs2/5 dbKO mice. We found that MT was reduced in Rgs5-/- relative to WT or Rgs2-/- UA. Activating Gi/o with dopamine increased, whereas exogenous cAMP decreased MT in Rgs5-/- UA to levels in WT UA. Dual deletion of Rgs2 and 5 abolished the reduced MT due to the absence of Rgs5 and enhanced dopamine-induced Gi/o effects in Rgs2/5 dbKO UA. Conversely, and as in WT UA, Gi/o inhibition with pertussis toxin or exogenous cAMP decreased MT in Rgs2/5 dbKO to levels in Rgs5-/- UA. Inhibition of phosphodiesterases (PDE) concentration-dependently decreased and normalized MT in all genotypes, and blocked dopamine-induced MT augmentation in Rgs2-/-, Rgs5-/-, and Rgs2/5 dbKO UA. We conclude that Gi/o augments UA MT in the absence of RGS2 by a novel mechanism involving PDE-mediated inhibition of cAMP-dependent vasodilatation..

Luseogliflozin, a sodium-glucose cotransporter-2 inhibitor, reverses cerebrovascular dysfunction and cognitive impairments in 18-mo-old diabetic animals

Diabetes mellitus (DM) is a leading risk factor for age-related dementia, but the mechanisms involved are not well understood. We previously discovered that hyperglycemia induced impaired myogenic response (MR) and cerebral blood flow (CBF) autoregulation in 18-mo-old DM rats associated with blood-brain barrier (BBB) leakage, impaired neurovascular coupling, and cognitive impairment. In the present study, we examined whether reducing plasma glucose with a sodium-glucose cotransporter-2 inhibitor (SGLT2i) luseogliflozin can ameliorate cerebral vascular and cognitive function in diabetic rats. Plasma glucose and HbA1c levels of 18-mo-old DM rats were reduced, and blood pressure was not altered after treatment with luseogliflozin. SGLT2i treatment restored the impaired MR of middle cerebral arteries (MCAs) and parenchymal arterioles and surface and deep cortical CBF autoregulation in DM rats. Luseogliflozin treatment also rescued neurovascular uncoupling, reduced BBB leakage and cognitive deficits in DM rats. However, SGLT2i did not have direct constrictive effects on vascular smooth muscle cells and MCAs isolated from normal rats, although it decreased reactive oxygen species production in cerebral vessels of DM rats. These results provide evidence that normalization of hyperglycemia with an SGLT2i can reverse cerebrovascular dysfunction and cognitive impairments in rats with long-standing hyperglycemia, possibly by ameliorating oxidative stress-caused vascular damage.NEW & NOTEWORTHY This study demonstrates that luseogliflozin, a sodium-glucose cotransporter-2 inhibitor, improved CBF autoregulation in association with reduced vascular oxidative stress and AGEs production in the cerebrovasculature of 18-mo-old DM rats. SGLT2i also prevented BBB leakage, impaired functional hyperemia, neurodegeneration, and cognitive impairment seen in DM rats. Luseogliflozin did not have direct constrictive effects on VSMCs and MCAs isolated from normal rats. These results provide evidence that normalization of hyperglycemia with an SGLT2i can reverse cerebrovascular dysfunction and cognitive impairments in rats with long-standing hyperglycemia, possibly by ameliorating oxidative stress-caused vascular damage.

Modulation of p66Shc impairs cerebrovascular myogenic tone in low renin but not low nitric oxide models of systemic hypertension

Cerebral blood flow and perfusion are tightly maintained through autoregulation despite changes in transmural pressure. Oxidative stress impairs cerebral blood flow, precipitating cerebrovascular events. Phosphorylation of the adaptor protein p66Shc increases mitochondrial-derived oxidative stress. The effect of p66Shc gain or loss of function in nonhypertensive rats is unclear. We hypothesized that p66Shc gain of function would impair autoregulation of cerebral microcirculation under physiological and pathological conditions. Three previously established transgenic [salt-sensitive (SS) background] p66Shc rats were used, p66-Del/SS (express p66Shc with a nine-amino acid deletion), p66Shc-knockout (KO)/SS (frameshift premature termination codon), and p66Shc signaling and knock-in substitution of Ser36Ala (p66Shc-S36A)/SS (substitution of Ser36Ala). The p66Shc-Del were also bred on Sprague-Dawley (SD) backgrounds (p66-Del/SD), and a subset was exposed to a hypertensive stimulus [NG-nitro-l-arginine methyl ester (l-NAME)] for 4 wk. Active and passive diameters to increasing transmural pressure were measured and myogenic tone was calculated in all groups (SS and SD). Myogenic responses to increasing pressure were impaired in p66Shc-Del/SS rats relative to wild-type (WT)/SS and knock-in substitution of Ser36Ala (S36A; P < 0.05). p66-Del/SD rats did not demonstrate changes in active/passive diameters or myogenic tone relative to WT/SD but did demonstrate attenuated passive diameter responses to higher transmural pressure relative to p66-Del/SS. Four weeks of a hypertensive stimulus (l-NAME) did not alter active or passive diameter responses to increasing transmural pressure (P = 0.86-0.99), but increased myogenic responses relative to p66-Del/SD (P < 0.05). Collectively, we demonstrate the functional impact of p66Shc within the cerebral circulation and demonstrate that the genetic background of p66Shc rats largely drives changes in cerebrovascular function.NEW & NOTEWORTHY We demonstrate that the modulation of p66Shc signaling impairs cerebral artery myogenic tone in a low renin model of hypertension. This impairment is dependent upon the genetic background, as modulated p66Shc signaling in Sprague-Dawley rats does not impair cerebral artery myogenic tone.

Short-term high fat diet alters genes associated with metabolic and vascular dysfunction during adolescence in rats: a pilot study

Background

Diet-induced metabolic dysfunction precedes multiple disease states including diabetes, heart disease, and vascular dysfunction. The critical role of the vasculature in disease progression is established, yet the details of how gene expression changes in early cardiovascular disease remain an enigma. The objective of the current pilot project was to evaluate whether a quantitative assessment of gene expression within the aorta of six-week old healthy male Sprague-Dawley rats compared to those exhibiting symptoms of metabolic dysfunction could reveal potential mediators of vascular dysfunction.

Methods

RNA was extracted from the aorta of eight rats from a larger experiment; four animals fed a high-fat diet (HFD) known to induce symptoms of metabolic dysfunction (hypertension, increased adiposity, fasting hyperglycemia) and four age-matched healthy animals fed a standard chow diet (CHOW). The bioinformatic workflow included Gene Ontology (GO) biological process enrichment and network analyses.

Results

The resulting network contained genes relevant to physiological processes including fat and protein metabolism, oxygen transport, hormone regulation, vascular regulation, thermoregulation, and circadian rhythm. The majority of differentially regulated genes were downregulated, including several associated with circadian clock function. In contrast, leptin and 3-hydroxy-3-methylglutaryl-CoA synthase 2 (Hmgcs2) were notably upregulated. Leptin is involved in several major energy balance signaling pathways and Hmgcs2 is a mitochondrial enzyme that catalyzes the first reaction of ketogenesis.

Conclusion

Together, these data describe changes in gene expression within the aortic wall of HFD rats with early metabolic dysfunction and highlight potential pathways and signaling intermediates that may impact the development of early vascular dysfunction.

Regulator of G Protein Signaling 2 Facilitates Uterine Artery Adaptation During Pregnancy in Mice

Background Decreased uterine blood flow is known to contribute to pregnancy complications such as gestational hypertension and preeclampsia. Previously, we showed that the loss of regulator of G protein signaling 2 ( RGS 2), a GTP ase activating protein for G_q/11 and G_i/o class G proteins, decreases uterine blood flow in the nonpregnant state in mice. Here, we examined the effects of the absence of RGS 2 and 5 on uterine blood flow and uterine vascular structure and function at early, mid, and late gestation, as well as peripartum period in mice. Methods and Results Abdominal Doppler ultrasonography was performed on adult female wild-type, Rgs2^-/-, and Rgs5^-/- mice at pre-pregnancy, gestational days 10, 15, and 18, and postpartum day 3. Uterine artery structure and function were also assessed by vessel myograph studies. At mid-pregnancy, uterine blood flow decreased in both Rgs2^-/- and Rgs5^-/- mice, whereas resistive index increased only in Rgs2^-/- mice. In uterine arteries from wild-type mice, mRNA expression of RGS 2 and 4 increased, whereas RGS 5 expression remained elevated at mid-pregnancy. These changes in gene expression were unique to uterine arteries because they were absent in mesenteric arteries and the aorta of wild-type mice. In Rgs2^-/- mice, uterine artery medial cross-sectional area and G protein-coupled receptor-mediated vasoconstriction increased in mid-pregnancy, implicating a role for RGS 2 in structural and functional remodeling of uterine arteries during pregnancy. In contrast, RGS 5 absence increased vasoconstriction only in the peripartum period. Conclusions These data together indicate that RGS 2 plays a critical role in the structural and functional remodeling of uterine arteries to impact uterine blood flow during pregnancy. Targeting the signaling pathway regulated by RGS 2 may therefore be a therapeutic strategy for ameliorating utero-placental perfusion disorders during pregnancy.

Loss of Endothelial FTO Antagonizes Obesity-Induced Metabolic and Vascular Dysfunction

RATIONALE

Increasing prevalence of obesity and its associated risk with cardiovascular diseases demands a better understanding of the contribution of different cell types within this complex disease for developing new treatment options. Previous studies could prove a fundamental role of FTO (fat mass and obesity-associated protein) within obesity; however, its functional role within different cell types is less understood.

OBJECTIVES

We identify endothelial FTO as a previously unknown central regulator of both obesity-induced metabolic and vascular alterations.

METHODS AND RESULTS

We generated endothelial Fto-deficient mice and analyzed the impact of obesity on those mice. While the loss of endothelial FTO did not influence the development of obesity and dyslipidemia, it protected mice from high-fat diet-induced glucose intolerance and insulin resistance by increasing AKT (protein kinase B) phosphorylation in endothelial cells and skeletal muscle. Furthermore, loss of endothelial FTO prevented the development of obesity-induced hypertension by preserving myogenic tone in resistance arteries. In Fto-deficient arteries, microarray analysis identified upregulation of L-Pgds with significant increases in prostaglandin D₂ levels. Blockade of prostaglandin D₂ synthesis inhibited the myogenic tone protection in resistance arteries of endothelial Fto-deficient mice on high-fat diet; conversely, direct addition of prostaglandin D₂ rescued myogenic tone in high-fat diet-fed control mice. Myogenic tone was increased in obese human arteries with FTO inhibitors or prostaglandin D₂ application.

CONCLUSIONS

These data identify endothelial FTO as a previously unknown regulator in the development of obesity-induced metabolic and vascular changes, which is independent of its known function in regulation of obesity.

Soluble TNFα Signaling within the Spinal Cord Contributes to the Development of Autonomic Dysreflexia and Ensuing Vascular and Immune Dysfunction after Spinal Cord Injury

Cardiovascular disease and susceptibility to infection are leading causes of morbidity and mortality for individuals with spinal cord injury (SCI). A major contributor to these is autonomic dysreflexia (AD), an amplified reaction of the autonomic nervous system (hallmarked by severe hypertension) in response to sensory stimuli below the injury. Maladaptive plasticity of the spinal sympathetic reflex circuit below the SCI results in AD intensification over time. Mechanisms underlying this maladaptive plasticity are poorly understood, restricting the identification of treatments. Thus, no preventative treatments are currently available. Neuroinflammation has been implicated in other pathologies associated with hyperexcitable neural circuits. Specifically, the soluble form of TNFα (sTNFα) is known to play a role in neuroplasticity. We hypothesize that persistent expression of sTNFα in spinal cord underlies AD exacerbation. To test this, we intrathecally administered XPro1595, a biologic that renders sTNFα nonfunctional, after complete, high-level SCI in female rats. This dramatically attenuated the intensification of colorectal distension-induced and naturally occurring AD events. This improvement is mediated via decreased sprouting of nociceptive primary afferents and activation of the spinal sympathetic reflex circuit. We also examined peripheral vascular function using ex vivo pressurized arterial preparations and immune function via flow cytometric analysis of splenocytes. Diminishing AD via pharmacological inhibition of sTNFα mitigated ensuing vascular hypersensitivity and immune dysfunction. This is the first demonstration that neuroinflammation-induced sTNFα is critical for altering the spinal sympathetic reflex circuit, elucidating a novel mechanism for AD. Importantly, we identify the first potential pharmacological, prophylactic treatment for this life-threatening syndrome.SIGNIFICANCE STATEMENT Autonomic dysreflexia (AD), a disorder that develops after spinal cord injury (SCI) and is hallmarked by sudden, extreme hypertension, contributes to cardiovascular disease and susceptibility to infection, respectively, two leading causes of mortality and morbidity in SCI patients. We demonstrate that neuroinflammation-induced expression of soluble TNFα plays a critical role in AD, elucidating a novel underlying mechanism. We found that intrathecal administration after SCI of a biologic that inhibits soluble TNFα signaling dramatically attenuates AD and significantly reduces AD-associated peripheral vascular and immune dysfunction. We identified mechanisms behind diminished plasticity of neuronal populations within the spinal sympathetic reflex circuit. This study is the first to pinpoint a potential pharmacological, prophylactic strategy to attenuate AD and ensuing cardiovascular and immune dysfunction.

Genetic Deletion of NADPH Oxidase 1 Rescues Microvascular Function in Mice With Metabolic Disease

RATIONALE

Early vascular changes in metabolic disease that precipitate the development of cardiovascular complications are largely driven by reactive oxygen species accumulation, yet the extent to which excess reactive oxygen species derive from specific NADPH oxidase isoforms remains ill defined.

OBJECTIVE

Identify the role of Nox1 in the development of microvascular dysfunction in metabolic disease.

METHODS AND RESULTS

Four genotypes were generated by breeding Nox1 knockout mice with db/db mice: lean (H_dbW_nox1), lean Nox1 knockout (H_dbK_nox1), obese (K_dbW_nox1), and obese KK (K_dbK_nox1). The degree of adiposity, insulin resistance, and dyslipidemia in KW mice was not influenced by Nox1 deletion as determined by nuclear magnetic resonance spectroscopy, glucose tolerance tests, and plasma analyses. Endothelium-dependent responses to acetylcholine in pressurized mesenteric arteries were reduced in KW versus HW (P<0.01), whereas deletion of Nox1 in KW mice normalized dilation. Vasodilator responses after inhibition of NO synthase blunted acetylcholine responses in KK and lean controls, but had no impact in KW, attributing recovered dilatory capacity in KK to normalization of NO. Acetylcholine responses were improved (P<0.05) with Tempol, and histochemistry revealed oxidative stress in KW animals, whereas Tempol had no impact and reactive oxygen species staining was negligible in KK. Blunted dilatory responses to an NO donor and loss of myogenic tone in KW animals were also rescued with Nox1 deletion.

CONCLUSIONS

Nox1 deletion reduces oxidant load and restores microvascular health in db/db mice without influencing the degree of metabolic dysfunction. Therefore, targeted Nox1 inhibition may be effective in the prevention of vascular complications.

Obesity Induces Artery-Specific Alterations: Evaluation of Vascular Function and Inflammatory and Smooth Muscle Phenotypic Markers

Vascular alterations are expected to occur in obese individuals but the impact of obesity could be different depending on the artery type. We aimed to evaluate the obesity effects on the relaxing and contractile responses and inflammatory and smooth muscle (SM) phenotypic markers in two vascular beds. Obesity was induced in C57Bl/6 mice by 16-week high-fat diet and vascular reactivity, mRNA expression of inflammatory and SM phenotypic markers, and collagen deposition were evaluated in small mesenteric arteries (SMA) and thoracic aorta (TA). Endothelium-dependent relaxation in SMA and TA was not modified by obesity. In contrast, contraction induced by depolarization and contractile agonists was reduced in SMA, whereas only contraction induced by adrenergic agonist was reduced in TA of obese mice. Obesity increased the mRNA expression of pro- and anti-inflammatory cytokines in SMA and TA. The expression of genes necessary for maintaining contractile ability was increased by obesity, but the increase was more pronounced in TA. Collagen deposition was increased in SMA, but not in TA, of obese mice. Although the endothelial function was still preserved, the SM of the two artery types was impaired by obesity, but the impairment was higher in SMA, which could be associated with SM phenotypic changes.

RGS2 squelches vascular Gi/o and Gq signaling to modulate myogenic tone and promote uterine blood flow

Uterine artery blood flow (UABF) is critical to maintaining uterine perfusion in nonpregnant states and for uteroplacental delivery of nutrients and oxygen to the fetus during pregnancy. Impaired UABF is implicated in infertility and several pregnancy complications including fetal growth restriction, small for gestational age, and preeclampsia. The etiology of abnormal UABF is not known. Here, we determined whether deficiency or loss of RGS2, a GTPase-activating protein for Gq/11 and Gi/o class G proteins, affects UABF in nonpregnant mice. We used Doppler ultrasonography to assess UABF in wild type (WT), Rgs2 heterozygous (Rgs2+/-), and homozygous knockout (Rgs2-/-) mice. Video microscopy was used for ex vivo examination of uterine artery myogenic tone and fura-2 imaging for in vitro assessment of internal stores Ca(2+) release. We found that baseline UABF velocity was markedly decreased while impedance measured as resistive index (WT = 0.58 ± 0.04 vs. Rgs2-/- = 0.71 ± 0.03, P < 0.01) and pulsatile index (WT = 0.90 ± 0.06 vs. Rgs2-/- = 1.25 ± 0.11, P < 0.01) was increased in Rgs2-/- mice. Uterine artery tone was augmented in Rgs2+/- and Rgs2-/- mice, which was normalized to WT levels following Gi/o and Gq inactivation. Conversely, blockade of ryanodine receptors increased WT myogenic tone to RGS2 mutant levels. The data together indicate that RGS2 deficiency decreases UABF by increasing myogenic tone at least partly through prolonged G protein activation. Mutations that decrease vascular RGS2 expression may be a predisposition to decreased uterine blood flow. Targeting G protein signaling therefore might improve uterine and uteroplacental underperfusion disorders.

Genistein supplementation prevents weight gain but promotes oxidative stress and inflammation in the vasculature of female obese ob/ob mice

Obesity, a state of chronic low-grade inflammation, is strongly associated with the development of hypertension and diabetes. Superoxide, a free radical elevated in obese individuals, promotes hypertension through scavenging the endogenous vasodilator nitric oxide. The hypothesis was a genistein-enriched diet would promote weight loss and reduce oxidative stress and inflammation in the vasculature of intact female ob/ob mice. Aortas and mesenteric arteries were isolated from female ob/ob mice fed genistein-free (0mg genistein/kg diet; n=6), standard chow (200-300mg genistein/kg diet; n=11) or genistein-enriched (600mg genistein/kg diet; n=9) diets for 4weeks. Sections of isolated vessels were labeled with the superoxide indicator dihydroethidium and fluorescence was measured by confocal microscopy. Protein expression of the inflammatory marker inducible nitric oxide synthase (iNOS) was measured in the perivascular adipose tissue (PVAT) surrounding each vessel and plasma concentrations of superoxide dismutase (SOD) were quantified. Genistein-enriched diet promoted less weight gain compared to animals fed standard chow (P=.008). Standard chow promoted increased superoxide in the aorta (P=.030) and mesenteric arteries (P=.024) compared to a diet devoid of genistein. At all tested concentrations, genistein significantly increased iNOS expression in mesenteric artery PVAT (vs. standard chow, P<.001; vs. genistein-enriched, P=.002) and tended to increase iNOS within the aortic PVAT (standard chow, P=.075) compared to the genistein-free group. Plasma SOD activity was significantly downregulated in genistein-enriched animals as compared to those fed a genistein-free diet (P=.028). In summary, although genistein prevents weight gain, it promotes vascular oxidative stress and inflammation in obese ovarian-intact female mice.

Ageing alters perivascular nerve function of mouse mesenteric arteries in vivo

Abstract  Mesenteric arteries (MAs) are studied widely in vitro but little is known of their reactivity in vivo. Transgenic animals have enabled Ca(2+) signalling to be studied in isolated MAs but the reactivity of these vessels in vivo is undefined. We tested the hypothesis that ageing alters MA reactivity to perivascular nerve stimulation (PNS) and adrenoreceptor (AR) activation during blood flow control. First- (1A), second- (2A) and third-order (3A) MAs of pentobarbital-anaesthetized Young (3-6 months) and Old (24-26 months) male and female Cx40(BAC)-GCaMP2 transgenic mice (C57BL/6 background; positive or negative for the GCaMP2 transgene) were studied with intravital microscopy. A segment of jejunum was exteriorized and an MA network was superfused with physiological salt solution (pH 7.4, 37°C). Resting tone was 10% in MAs of Young and Old mice; diameters were ∼5% (1A), 20% (2A) and 40% (3A) smaller (P 0.05) in Old mice. Throughout MA networks, vasoconstriction increased with PNS frequency (1-16 Hz) but was ∼20% less in Young vs. Old mice (P 0.05) and was inhibited by tetrodotoxin (1 μm). Capsaicin (10 μm; to inhibit sensory nerves) enhanced MA constriction to PNS (P 0.05) by ∼20% in Young but not Old mice. Phenylephrine (an α1AR agonist) potency was greater in Young mice (P 0.05) with similar efficacy (∼60% constriction) across ages and MA branches. Constrictions to UK14304 (an α2AR agonist) were less (∼20%; P 0.05) and were unaffected by ageing. Irrespective of sex or transgene expression, ageing consistently reduced the sensitivity of MAs to α1AR vasoconstriction while blunting the attenuation of sympathetic vasoconstriction by sensory nerves. These findings imply substantive alterations in splanchnic blood flow control with ageing.