Alzheimer’s Disease (AD) and cardiovascular diseases (CVDs) are a major cause ofdisability and death among the older population. Familial Alzheimer’s Disease (FAD) islinked with an early onset AD (EOAD) pathology (<65years) that manifests throughpathogenic mutations in the presenilin (PSEN)1 and PSEN2 genes, leading to theincreased production of central amyloid β (Aβ) peptides. There is increasing evidencethat elevated blood pressure and peripheral arterial stiffness contribute to thedevelopment and increase the risk of β-amyloid deposition in the brain leading to cognitivedecline later in life. We hypothesized that peripheral vascular remodeling and vasculardysfunction in the aorta and mesenteric resistance arteries (MRA) would be observedprior to the development of EOAD. The MRA of male and female C57Bl/6J (control) andAD mice (B6. CApptm1DboTg(APPswe,PSEN1dE9)85Dbo) at 9-weeks-old were isolatedprior to the onset of AD. Acetylcholine-induced relaxation (1pM-30μM) andphenylephrine-induced contraction (0.1nM-30μM) were evaluated using wire myography.Pulse wave velocity (PWV) and H&E staining were used to measure vascular stiffnessand morphology, respectively. Data were analyzed as non-linear curve regression andmaximum response (Rmax) using the Student t test ( p <0.05*). MRA from AD miceshowed impaired relaxation in both males (Rmax: control 90±0.9 vs. AD 59±6.4* %, n=3-4) and females (Rmax: control 90±2.8 vs. AD 70±8.3*%, n=4-6). Interestingly,phenylephrine-induced contraction was reduced in arteries from males (Rmax: control11.7±0.9 vs . AD 7.7±0.8* mN, n=3-4), but not in arteries from females (Rmax: control9.3±1.3 vs. AD 8.1±0.6 mN, n=6-7). However, no differences were observed in the aortawall thickness in the male (control 51.8±2.9 vs. AD 72±9.2 μm, n=3-4), or female (control63.7±9.8 vs. AD 54±4.8μm, n=2-3) AD mice, as well as the PWV analysis from male ADmice (control 2.41±0.44 vs. AD 4.05±1.4 mm/ms, n=6). These data suggest that thechanges observed in the peripheral microvasculature prior to the onset of AD could laterhave direct effects on cerebral blood flow leading to areas of altered blood perfusion andmicrovascular damage, thus contributing to the genesis and maintenance of AD.
Low-grade systemic inflammation is a common manifestation of hypertension; however, the exact mechanisms that initiate this pathophysiological response, thereby contributing to further increases in blood pressure, are not well understood. Aberrant vascular inflammation and reactivity via activation of the innate immune system may be the first step in the pathogenesis of hypertension. One of the functions of the innate immune system is to recognize and respond to danger. Danger signals can arise from not only pathogenic stimuli but also endogenous molecules released following cell injury and/or death [damage-associated molecular patterns (DAMPs)]. In the short-term, activation of the innate immune system is beneficial in the vasculature by providing cytoprotective mechanisms and facilitating tissue repair following injury or infection. However, sustained or excessive immune system activation, such as in autoimmune diseases, may be deleterious and can lead to maladaptive, irreversible changes to vascular structure and function. An initial source of DAMPs that enter the circulation to activate the innate immune system could arise from modest elevations in peripheral vascular resistance. These stimuli could subsequently lead to ischemic- or pressure-induced events aggravating further cell injury and/or death, providing more DAMPs for innate immune system activation. This review will address and critically evaluate the current literature on the role of the innate immune system in hypertension pathogenesis. The role of Toll-like receptor activation on somatic cells of the vasculature in response to the release of DAMPs and the consequences of this activation on inflammation, vasoreactivity, and vascular remodeling will be specifically discussed.
Hypertension has been described as a condition of premature vascular aging, relative to actual chronological age. In fact, many factors that contribute to the deterioration of vascular function as we age are accelerated and exacerbated in hypertension. Nonetheless, the precise mechanisms that underlie the aged phenotype of arteries from hypertensive patients and animals remain elusive. Classically, the aged phenotype is the buildup of cellular debris and dysfunctional organelles. One means by which this can occur is insufficient degradation and cellular recycling. Mitophagy is the selective catabolism of damaged mitochondria. Mitochondria are organelles that contribute importantly to the determination of cellular age via their production of reactive oxygen species (ROS; Harman's free radical theory of aging). Therefore, the accumulation of dysfunctional and ROS-producing mitochondria could contribute to the acceleration of vascular age in hypertension. This review will address and critically evaluate the current literature on mitophagy in vascular physiology and hypertension.
Toll‐like receptor 9 (TLR 9) is a pattern recognition receptor of the innate immune system. Activation of TLR 9 in immune cells leads to the release of pro‐inflammatory cytokines. TLR 9 is also expressed in the vasculature; however, its role in vascular function remains to be clarified. We hypothesized that chronic administration (three i.p. injections within five days) of TLR 9 agonist [synthetic oligonucleotide (ODN 2395); 0.1 μg/i.p.], would augment aortic contractility in female, 13–15 weeks old, Sprague Dawley rats. Concentration response curves were performed ex vivo using the myograph to norepinephrine (NE; 10 −9 –3×10 −5 M), in the presence of either nitric oxide synthase (NOS) inhibitor L‐NNA (10 −4 M; 30 min), or cyclooxygenase inhibitor indomethacin (10 −5 M; 30 min). ODN 2395 amplified the contractile response to NE [E max (% max KCl), ODN 2395: 108±4 vs. Veh: 94±5]. This difference was normalized in the presence of L‐NNA [E max (% max KCl), ODN 2395: 141±6 vs. Veh: 134±10], but not indomethacin [E max (% max KCl), ODN 2395: 105±8 vs. Veh: 89±8]. These data illustrate that NOS activity was decreased in the ODN 2395 treated animals, as NOS inhibition normalized the potentiated contractile response to ODN 2395. Therefore, attenuation of NOS activity by TLR 9 activation could subsequently contribute to the development and progression of vascular diseases such as hypertension. Research Support: Society for Women's Health Research (SWHR)
The aged phenotype is classically viewed as the accumulation of cellular debris and dysfunctional organelles. Although waste products are an inevitable consequence of normal cellular metabolism, multiple systems are devoted to its repair, clearance, or recycling. Autophagy is the constitutively active catabolic process responsible for cellular degradation. Autophagic activity has also been implicated as a modulator of longevity, as well as inversely related with chronological vascular aging and premature vascular aging associated with hypertension. However, the mechanisms by which autophagy exerts anti‐vascular aging effects are still unknown. Evolutionarily, autophagy functions to mobilize nutrients in times of starvation. Specifically, hepatic autophagy releases free fatty acids from triglycerides, which are oxidized to generate ketone bodies. Therefore, we hypothesized that fasting would increase the systemic expression of ketone body β‐hydroxybutyrate (βOHB) in Dahl salt‐sensitive rats fed a low salt‐diet, and this would be prevented by inhibition of autophagy with chloroquine (CQ). As hypothesized, fasting increased serum βOHB, and treatment with CQ blocked this increase (mmol/L, non‐fasting: 0.38±0.01 vs. fasting: 1.01±0.06* vs. fasting+CQ: 0.45±0.04, *p<0.05) (Figure ). Next we questioned whether βOHB could potentially contribute to the anti‐vascular aging effect of autophagy. Previously, we have observed that βOHB is a potent vasodilator via endothelial potassium channels. However, it is not known if βOHB acts as an agonist or antagonist to any specific receptor to mediate endothelium‐dependent relaxation. To help answer this question we needed to switch to a genetic knockout model, as pharmacological antagonists for the βOHB receptors, Gpr109a and Gpr41, do not exist. βOHB activates Gpr109a, whereas it is generally recognized as an antagonist of Gpr41. Therefore, we hypothesized that vascular relaxation to βOHB would be significantly attenuated in isolated mesenteric resistance arteries from Gpr109a −/− mice, but not Gpr41 −/− mice. As hypothesized, vasodilatory effect of βOHB was significantly blunted in Gpr109a −/− mice, but not Gpr41 −/− mice [E max (%relaxation), WT: 75±2 vs. Gpr109a−/−: 53±3* vs. Gpr41 −/− : 73±1, *p<0.05] (Figure ). Overall, these data reveal that ketone body βOHB is stimulated by autophagy and that activation of Gpr109a by βOHB can cause vasodilation of isolated resistance arteries. Significantly, our data define a novel mechanism that underlies the anti‐vascular aging effect of autophagy. Support or Funding Information American Heart Association (18POST34060003) and National Institutes of Health (R00GM118885 and R01HL143082). Fasting (24 h) stimulates serum βOHB expression and this is prevented by autophagy inhibition (chloroquine 50 mg/kg i.p. ; CQ). n=6–10. One way ANOVA: *p<0.05. Figure 1 βOHB mediates vasodilation partially via Gpr109a, and not Gpr41. Concentration response curves to βOHB. n=2–4. Two‐way ANOVA: *p<0.05. vs. wild type (WT). Figure 2
Endogenous ouabain is elevated in patients and experimental models of hypertension and is associated with elevated mortality. In this context, it is reasonable to assume that a new antihypertensive drug that inhibits the deleterious effects of endogenous ouabain may be a specific pharmacological tool for hypertension treatment. Here, we investigated the effects of rostafuroxin (ROSTA), an ouabain inhibitor, on SBP, endothelial dysfunction and oxidative stress in deoxycorticosterone acetate (DOCA)-salt rats.A hypertensive model was established in uninephrectomized Wistar rats using DOCA-salt. After SBP stabilization, DOCA-salt rats were divided into two groups: DOCA-salt (control) and DOCA-salt treatment with ROSTA (1 mg/kg per day gavage, 3 weeks). The SBP was measured using the tail-cuff method, and vascular function was assessed in mesenteric-resistance arteries (MRAs) using a wire myograph. Nitric oxide and reactive oxygen species production were investigated. Western blot was performed to quantify protein expression. Our results indicated that ROSTA treatment decreased SBP, improved acetylcholine-induced relaxation via enhanced nitric oxide synthesis and bioavailability, decreased superoxide anion generation from NAD(P)H oxidase and cyclooxygenase-2 and reduced cytoplasmic tyrosine kinase Src phosphorylation without changes in NaKATPase activity in MRA from DOCA-salt rats.This study reports the critical role of endogenous ouabain in volume-dependent hypertension. In MRA from DOCA-salt rats, the binding of endogenous ouabain to NaK-ATPase results in downstream c-SRC activation, oxidative stress and endothelial dysfunction. Endogenous ouabain is a putative target for the treatment of hypertension, and ROSTA may represent a novel therapeutic approach.
Ketone bodies are essential energy substrates in the absence of exogenous nutrients, and more recently, they have been suggested to prevent disease and improve longevity. β-hydroxybutyrate (βHB) is the most abundant ketone body. The secondary alcohol, 1,3-butanediol (1,3-BD), is commonly administered to raise βHB bioavailability in vivo and in the absence of nutrient deprivation. However, the concentration of 1,3-BD that yields a systemic concentration of βHB similar to that observed after a 24-hour fast has yet to be determined. To evaluate this knowledge gap, we administered 5%, 10%, or 20% 1,3-BD via the drinking water to adult, male Wistar-Kyoto rats for four weeks. In addition to systemic and excreted βHB concentration, physiologic, metabolic, and toxicologic parameters were measured. We report that only 20% 1,3-BD significantly elevates the systemic and urinary concentrations of βHB. Rats treated with 20% 1,3-BD had a rapid and sustained reduction in body mass. All concentrations of 1,3-BD decreased food consumption, but only the 20% concentration decreased fluid consumption. Urine volume, red blood cell count, and hematocrit suggested dehydration in the 10% and 20% 1,3-BD–treated rats. Finally, 20% 1,3-BD–treated rats presented with indicators of metabolic acidosis and sinusoidal dilation, but no evidence of fatty liver or hepatotoxicity. In summary, we report that 20% 1,3-BD, but not 5% or 10%, produces a systemic concentration of βHB similar to that observed after a 24-hour fast. However, this concentration is associated with deleterious side effects such as body mass loss, dehydration, metabolic acidosis, and sinusoidal dilation.
SIGNIFICANCE STATEMENT
1,3-Butanediol (1,3-BD) is often administered to stimulate the biosynthesis of the most abundant ketone body, β-hydroxybutyrate (βHB), and its purported salubrious effects. This article reports that suprapharmacological concentrations of 1,3-BD are necessary to yield a systemic concentration of βHB similar to that observed after a 24-hour fast, and this is associated with undesirable side effects. On the other hand, low concentrations of 1,3-BD were better tolerated and may improve health independent of its conversion into βHB.
Vascular hyporeactivity to adrenergic stimulation is a significant independent prognostic factor of mortality in sepsis. Loss of vascular tone occurs through complex, multifactorial mechanisms that have not been fully elucidated. Formyl peptide receptor (FPR) is an innate immune system receptor that is activated by bacterial and mitochondrial fragments called N‐formyl peptides. Previously, we have observed that FPR stimulation with both mitochondrial and bacterial N‐formyl peptides leads to reduced noradrenaline‐induced contraction in resistance arteries and hypotension. Therefore, we first hypothesized that the absence of FPR would increase vascular noradrenaline contraction. To test this hypothesis we used male, 8–10 week old wild‐type (WT; C57BL/6) or FPR‐1 knockout (KO) mice to measure vascular function in mesenteric resistance arteries (MRA, diameter ~180 μm) and aorta. Surprisingly our hypothesis was refuted, since the absence of global FPR induced similar hyporesponsiveness to noradrenaline‐induced contraction (10 −10 –10 −4 M) in all arterial beds (E max : MRA: WT: 10.6 ± 0.4 vs. FPR‐1 KO: 8.3 ± 0.5 mN, p<0.05; Aorta: WT: 5.4 ± 1.2 vs. FPR‐1 KO: 0.6 ± 0.2 mN, p<0.05). This result suggested that the absence of FPR mimics its desensitization which leads to vascular unresponsiveness to noradrenaline. Loss of vascular tone and desensitization to adrenergic agents could be a result of cytoskeleton disruption. In fact, it is known that FPR activation by N‐formyl peptides leads to changes in cytoskeleton‐regulating proteins in leukocytes. Consequently, we hypothesized that the mechanistic pathway that leads to vascular unresponsiveness following FPR desensitization and/or absence is due to a disruption in actin polymerization. To assess if FPR‐1 interferes with actin polymerization, some arteries from WT or FPR‐KO mice were incubated with cytochalasin B (CYTO B, 10 −6 M) (inhibits both the rate of actin polymerization and the interaction of actin filaments in solution) or jasplakinolide (JASP, 10 −7 M) (promotes actin‐stabilizing and polymerization). JASP increased noradrenaline‐induced contraction only in arteries from FPR‐1 KO. On the other hand, CYTO abolished noradrenaline‐induced‐contraction in arteries from both strains of mice, suggesting that actin polymerization is crucial for noradrenaline‐induced contraction. Overall, these data suggest that FPR hyperstimulation, which leads to desensitization, and absence induces vascular unresponsiveness in conductance and resistance arteries via disruption of actin polymerization. Given that patients with sepsis have high levels of N‐formyl peptides (bacterial and mitochondrial), FPR desensitization can occur in these patients due to its hyperstimulation. Since noradrenaline administration is known to be ineffective at reversing vascular collapse and hypotension in septic patients, perhaps reconstituting FPR sensitization and/or actin polymerization could be putative treatment targets. Support or Funding Information Research Support: National Institutes of Health (NIH: 1K99GM118885‐01)
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