Functional role of HSP90 complexes with endothelial nitric-oxide synthase (eNOS) and calpain on nitric oxide generation in endothelial cells

Expression of CD70 Modulates NO and Redox Status in Endothelial Cells

BACKGROUND

Endothelial dysfunction is a critical component in the pathogenesis of cardiovascular diseases and is closely associated with NO levels and oxidative stress. Here, we report on novel findings linking endothelial expression of CD70 with alterations in NO and reactive oxygen species.

METHODS

CD70 expression was genetically manipulated in human aortic and pulmonary artery endothelial cells. Intracellular NO and hydrogen peroxide (H₂O₂) were measured using genetically encoded biosensors, and cellular phenotypes were assessed.

RESULTS

An unbiased phenome-wide association study demonstrated that polymorphisms in CD70 associate with vascular phenotypes. Endothelial cells treated with CD70-directed short-interfering RNA demonstrated impaired wound closure, decreased agonist-stimulated NO levels, and reduced eNOS (endothelial nitric oxide synthase) protein. This was accompanied by reduced NO bioactivity, increased 3-nitrotyrosine levels, and a decrease in the eNOS binding partner heat shock protein 90. Following treatment with the thioredoxin inhibitor auranofin or with agonist histamine, intracellular H₂O₂ levels increased up to 80% in the cytosol, plasmalemmal caveolae, and mitochondria. There was increased expression of NADPH oxidase 1 complex and gp91phox; expression of copper/zinc and manganese superoxide dismutases was also elevated. CD70 knockdown reduced levels of the H₂O₂ scavenger catalase; by contrast, glutathione peroxidase 1 expression and activity were increased. CD70 overexpression enhanced endothelial wound closure, increased NO levels, and attenuated the reduction in eNOS mRNA induced by TNFα.

CONCLUSIONS

Taken together, these data establish CD70 as a novel regulatory protein in endothelial NO and reactive oxygen species homeostasis, with implications for human vascular disease.

The acute effects of passive heating on endothelial function, muscle microvascular oxygen delivery, and expression of serum HSP90α

Passive heating has been a therapeutic tool used to elevate core temperature and induce increases in cardiac output, blood flow, and shear stress. We aimed to determine the effects of a single bout of passive heating on endothelial function and serum heat shock protein 90α (HSP90α) levels in young, healthy subjects. 8 healthy subjects were recruited to participate in one bout of whole-body passive heating via immersion in a 40 °C hot tub to maintain a 1 °C increase in rectal temperature for 60 min. Twenty-four hours after heating, shear-rate corrected endothelium-dependent dilation increased (pre: 0.004 ± 0.002%SR_AUC; post: 0.006 ± 0.003%SR_AUC; p = 0.034) but serum [HSP90α] was not changed (pre: 36.7 ± 10.3 ng/mL; post: 40.6 ± 15.9 ng/mL; p = 0.39). Neither resting muscle O₂ utilization (pre: 0.17 ± 0.11 ml O₂ min^-1 (100 g)^-1; post: 0.14 ± 0.09 ml O₂ min^-1 (100 g)^-1); p = 0.28) nor mean arterial pressure (pre: 74 ± 11 mmHg; post: 73 ± 11 mmHg; p = 0.79) were influenced by the heating intervention. Finally, time to peak after cuff release was significantly delayed for % O₂ sat (TTP_pre = 39 ± 8.9 s and TTP_post = 43.5 ± 8.2 s; p = 0.007) and deoxy-[heme] (TTP_pre = 41.3 ± 18.1 s and TTP_post = 51.4 ± 16.3 s; p = 0.018), with no effect on oxy-[heme] (p = 0.19) and total-[heme] (p = 0.41). One bout of passive heating improved endothelium-dependent dilation 24 h later in young, healthy subjects. This data suggests that passive heat treatments may provide a simple intervention for improving vascular health.

Targeting mechanosensitive endothelial TXNDC5 to stabilize eNOS and reduce atherosclerosis in vivo

Although atherosclerosis preferentially develops at arterial curvatures and bifurcations where disturbed flow (DF) activates endothelium, therapies targeting flow-dependent mechanosensing pathways in the vasculature are unavailable. Here, we provided experimental evidence demonstrating a previously unidentified causal role of DF-induced endothelial TXNDC5 (thioredoxin domain containing 5) in atherosclerosis. TXNDC5 was increased in human and mouse atherosclerotic lesions and induced in endothelium subjected to DF. Endothelium-specific Txndc5 deletion markedly reduced atherosclerosis in ApoE-/- mice. Mechanistically, DF-induced TXNDC5 increases proteasome-mediated degradation of heat shock factor 1, leading to reduced heat shock protein 90 and accelerated eNOS (endothelial nitric oxide synthase) protein degradation. Moreover, nanoparticles formulated to deliver Txndc5-targeting CRISPR-Cas9 plasmids driven by an endothelium-specific promoter (CDH5) significantly increase eNOS protein and reduce atherosclerosis in ApoE-/- mice. These results delineate a new molecular paradigm that DF-induced endothelial TXNDC5 promotes atherosclerosis and establish a proof of concept of targeting endothelial mechanosensitive pathways in vivo against atherosclerosis.

Endothelial Contribution to Warfarin-Induced Arterial Media Calcification in Mice

Arterial media calcification (AMC) is predominantly regulated by vascular smooth muscle cells (VSMCs), which transdifferentiate into pro-calcifying cells. In contrast, there is little evidence for endothelial cells playing a role in the disease. The current study investigates cellular functioning and molecular pathways underlying AMC, respectively by, an ex vivo isometric organ bath set-up to explore the interaction between VSMCs and ECs and quantitative proteomics followed by functional pathway interpretation. AMC development, which was induced in mice by dietary warfarin administration, was proved by positive Von Kossa staining and a significantly increased calcium content in the aorta compared to that of control mice. The ex vivo organ bath set-up showed calcified aortic segments to be significantly more sensitive to phenylephrine induced contraction, compared to control segments. This, together with the fact that calcified segments as compared to control segments, showed a significantly smaller contraction in the absence of extracellular calcium, argues for a reduced basal NO production in the calcified segments. Moreover, proteomic data revealed a reduced eNOS activation to be part of the vascular calcification process. In summary, this study identifies a poor endothelial function, next to classic pro-calcifying stimuli, as a possible initiator of arterial calcification.

Endothelial Dysfunction Driven by Hypoxia-The Influence of Oxygen Deficiency on NO Bioavailability

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. The initial stage of CVDs is characterized by endothelial dysfunction, defined as the limited bioavailability of nitric oxide (NO). Thus, any factors that interfere with the synthesis or metabolism of NO in endothelial cells are involved in CVD pathogenesis. It is well established that hypoxia is both the triggering factor as well as the accompanying factor in cardiovascular disease, and diminished tissue oxygen levels have been reported to influence endothelial NO bioavailability. In endothelial cells, NO is produced by endothelial nitric oxide synthase (eNOS) from L-Arg, with tetrahydrobiopterin (BH₄) as an essential cofactor. Here, we discuss the mechanisms by which hypoxia affects NO bioavailability, including regulation of eNOS expression and activity. What is particularly important is the fact that hypoxia contributes to the depletion of cofactor BH₄ and deficiency of substrate L-Arg, and thus elicits eNOS uncoupling-a state in which the enzyme produces superoxide instead of NO. eNOS uncoupling and the resulting oxidative stress is the major driver of endothelial dysfunction and atherogenesis. Moreover, hypoxia induces impairment in mitochondrial respiration and endothelial cell activation; thus, oxidative stress and inflammation, along with the hypoxic response, contribute to the development of endothelial dysfunction.

Nitric Oxide Synthase Inhibitors into the Clinic at Last

The 1998 Nobel Prize in Medicine and Physiology for the discovery of nitric oxide, a nitrogen containing reactive oxygen species (also termed reactive nitrogen or reactive nitrogen/oxygen species) stirred great hopes. Clinical applications, however, have so far pertained exclusively to the downstream signaling of cGMP enhancing drugs such as phosphodiesterase inhibitors and soluble guanylate cyclase stimulators. All clinical attempts, so far, to inhibit NOS have failed even though preclinical models were strikingly positive and clinical biomarkers correlated perfectly. This rather casts doubt on our current way of target identification in drug discovery in general and our way of patient stratification based on correlating but not causal biomarkers or symptoms. The opposite, NO donors, nitrite and enhancing NO synthesis by eNOS/NOS3 recoupling in situations of NO deficiency, are rapidly declining in clinical relevance or hold promise but need yet to enter formal therapeutic guidelines, respectively. Nevertheless, NOS inhibition in situations of NO overproduction often jointly with enhanced superoxide (or hydrogen peroxide production) still holds promise, but most likely only in acute conditions such as neurotrauma (Stover et al., J Neurotrauma 31(19):1599-1606, 2014) and stroke (Kleinschnitz et al., J Cereb Blood Flow Metab 1508-1512, 2016; Casas et al., Proc Natl Acad Sci U S A 116(14):7129-7136, 2019). Conversely, in chronic conditions, long-term inhibition of NOS might be too risky because of off-target effects on eNOS/NOS3 in particular for patients with cardiovascular risks or metabolic and renal diseases. Nitric oxide synthases (NOS) and their role in health (green) and disease (red). Only neuronal/type 1 NOS (NOS1) has a high degree of clinical validation and is in late stage development for traumatic brain injury, followed by a phase II safety/efficacy trial in ischemic stroke. The pathophysiology of NOS1 (Kleinschnitz et al., J Cereb Blood Flow Metab 1508-1512, 2016) is likely to be related to parallel superoxide or hydrogen peroxide formation (Kleinschnitz et al., J Cereb Blood Flow Metab 1508-1512, 2016; Casas et al., Proc Natl Acad Sci U S A 114(46):12315-12320, 2017; Casas et al., Proc Natl Acad Sci U S A 116(14):7129-7136, 2019) leading to peroxynitrite and protein nitration, etc. Endothelial/type 3 NOS (NOS3) is considered protective only and its inhibition should be avoided. The preclinical evidence for a role of high-output inducible/type 2 NOS (NOS2) isoform in sepsis, asthma, rheumatic arthritis, etc. was high, but all clinical development trials in these indications were neutral despite target engagement being validated. This casts doubt on the role of NOS2 in humans in health and disease (hence the neutral, black coloring).

Extending the Calpain-Cathepsin Hypothesis to the Neurovasculature: Protection of Brain Endothelial Cells and Mice from Neurotrauma

The calpain-cathepsin hypothesis posits a key role for elevated calpain-1 and cathepsin-B activity in the neurodegeneration underlying neurotrauma and multiple disorders including Alzheimer's disease (AD). AD clinical trials were recently halted on alicapistat, a selective calpain-1 inhibitor, because of insufficient exposure of neurons to the drug. In contrast to neuroprotection, the ability of calpain-1 and cathepsin-B inhibitors to protect the blood-brain barrier (BBB), is understudied. Since cerebrovascular dysfunction underlies vascular dementia, is caused by ischemic stroke, and is emerging as an early feature in the progression of AD, we studied protection of brain endothelial cells (BECs) by selective and nonselective calpain-1 and cathepsin-B inhibitors. We show these inhibitors protect both neurons and murine BECs from ischemia-reperfusion injury. Cultures of primary BECs from ALDH2 ^-/- mice that manifest enhanced oxidative stress were sensitive to ischemia, leading to reduced cell viability and loss of tight junction proteins; this damage was rescued by calpain-1 and cathepsin-B inhibitors. In ALDH2 ^-/- mice 24 h after mild traumatic brain injury (mTBI), BBB damage was reflected by significantly increased fluorescein extravasation and perturbation of tight junction proteins, eNOS, MMP-9, and GFAP. Both calpain and cathepsin-B inhibitors alleviated BBB dysfunction caused by mTBI. No clear advantage was shown by selective versus nonselective calpain inhibitors in these studies. The lack of recognition of the ability of calpain inhibitors to protect the BBB may have led to the premature abandonment of this therapeutic approach in AD clinical trials and requires further mechanistic studies of cerebrovascular protection by calpain-1 inhibitors.

Heat shock protein 90α increases superoxide generation from neuronal nitric oxide synthases

Neuronal nitric oxide synthase (nNOS) generates superoxide, particularly at sub-optimal l-arginine (l-Arg) substrate concentrations. Heat shock protein 90 (Hsp90) was reported to inhibit superoxide generation from nNOS protein. However, commercially available Hsp90 product from bovine brain tissues with unspecified Hsp90α and Hsp90β contents and an undefined Hsp90 protein oligomeric state was utilized. These two Hsp90s can have opposite effect on superoxide production by NOS. Importantly, emerging evidence indicates that nNOS splice variants are involved in different biological functions by functioning distinctly in redox signaling. In the present work, purified recombinant human Hsp90α, in its native dimeric state, was used in electron paramagnetic resonance (EPR) spin trapping experiments to study the effects of Hsp90α on superoxide generation from nNOS splice variants nNOSμ and nNOSα. Human Hsp90α was found to significantly increase superoxide generation from nNOSμ and nNOSα proteins under l-Arg-depleted conditions and Hsp90α influenced superoxide production by nNOSμ and nNOSα at varying degrees. Imidazole suppressed the spin adduct signal, indicating that superoxide was produced at the heme site of nNOS in the presence of Hsp90α, whereas l-Arg repletion diminished superoxide production by the nNOS-Hsp90α. Moreover, NADPH consumption rate values exhibited a similar trend/difference as a function of Hsp90α and l-Arg. Together, these EPR spin trapping and NADPH oxidation kinetics results demonstrated noticeable Hsp90α-induced increases in superoxide production by nNOS and a distinguishable effect of Hsp90α on nNOSμ and nNOSα proteins.

Heat therapy: possible benefits for cognitive function and the aging brain

Alzheimer's disease (AD) is the most common neurodegenerative disease, yet there are no disease-modifying treatments available and there is no cure. It is becoming apparent that metabolic and vascular conditions such as type 2 diabetes (T2D) and hypertension promote the development and accumulation of Alzheimer's disease-related dementia pathologies. To this end, aerobic exercise, which is a common lifestyle intervention for both metabolic disease and hypertension, is shown to improve brain health during both healthy aging and dementia. However, noncompliance or other barriers to exercise response are common in exercise treatment paradigms. In addition, reduced intracellular proteostasis and mitochondrial function could contribute to the etiology of AD. Specifically, compromised chaperone systems [i.e., heat shock protein (HSP) systems] can contribute to protein aggregates (i.e., β-amyloid plaques and neurofibrillary tangles) and reduced mitochondrial quality control (i.e., mitophagy). Therefore, novel therapies that target whole body metabolism, the vasculature, and chaperone systems (like HSPs) are needed to effectively treat AD. This review focuses on the role of heat therapy in the treatment and prevention of AD. Heat therapy has been independently shown to reduce whole body insulin resistance, improve vascular function, activate interorgan cross talk via endocytic vesicles, and activate HSPs to improve mitochondrial function and proteostasis in a variety of tissues. Thus, heat therapy could offer immense clinical benefit to patients suffering from AD. Importantly, future studies in patients are needed to determine the safety and efficacy of heat therapy in preventing AD.

Post-translational modifications of Hsp90 and translating the chaperone code

Cells have a remarkable ability to synthesize large amounts of protein in a very short period of time. Under these conditions, many hydrophobic surfaces on proteins may be transiently exposed, and the likelihood of deleterious interactions is quite high. To counter this threat to cell viability, molecular chaperones have evolved to help nascent polypeptides fold correctly and multimeric protein complexes assemble productively, while minimizing the danger of protein aggregation. Heat shock protein 90 (Hsp90) is an evolutionarily conserved molecular chaperone that is involved in the stability and activation of at least 300 proteins, also known as clients, under normal cellular conditions. The Hsp90 clients participate in the full breadth of cellular processes, including cell growth and cell cycle control, signal transduction, DNA repair, transcription, and many others. Hsp90 chaperone function is coupled to its ability to bind and hydrolyze ATP, which is tightly regulated both by co-chaperone proteins and post-translational modifications (PTMs). Many reported PTMs of Hsp90 alter chaperone function and consequently affect myriad cellular processes. Here, we review the contributions of PTMs, such as phosphorylation, acetylation, SUMOylation, methylation, O-GlcNAcylation, ubiquitination, and others, toward regulation of Hsp90 function. We also discuss how the Hsp90 modification state affects cellular sensitivity to Hsp90-targeted therapeutics that specifically bind and inhibit its chaperone activity. The ultimate challenge is to decipher the comprehensive and combinatorial array of PTMs that modulate Hsp90 chaperone function, a phenomenon termed the "chaperone code."

Pharmacological management of vascular endothelial dysfunction in diabetes: TCM and western medicine compared based on biomarkers and biochemical parameters

Diabetes, a worldwide health concern while burdening significant populace of countries with time due to a hefty increase in both incidence and prevalence rates. Hyperglycemia has been buttressed both in clinical and experimental studies to modulate widespread molecular actions that effect macro and microvascular dysfunctions. Endothelial dysfunction, activation, inflammation, and endothelial barrier leakage are key factors contributing to vascular complications in diabetes, plus the development of diabetes-induced cardiovascular diseases. The recent increase in molecular, transcriptional, and clinical studies has brought a new scope to the understanding of molecular mechanisms and the therapeutic targets for endothelial dysfunction in diabetes. In this review, an attempt made to discuss up to date critical and emerging molecular signaling pathways involved in the pathophysiology of endothelial dysfunction and viable pharmacological management targets. Importantly, we exploit some Traditional Chinese Medicines (TCM)/TCM isolated bioactive compounds modulating effects on endothelial dysfunction in diabetes. Finally, clinical studies data on biomarkers and biochemical parameters involved in the assessment of the efficacy of treatment in vascular endothelial dysfunction in diabetes was compared between clinically used western hypoglycemic drugs and TCM formulas.

Could Heat Therapy Be an Effective Treatment for Alzheimer's and Parkinson's Diseases? A Narrative Review

Neurodegenerative diseases involve the progressive deterioration of structures within the central nervous system responsible for motor control, cognition, and autonomic function. Alzheimer's disease and Parkinson's disease are among the most common neurodegenerative disease and have an increasing prevalence over the age of 50. Central in the pathophysiology of these neurodegenerative diseases is the loss of protein homeostasis, resulting in misfolding and aggregation of damaged proteins. An element of the protein homeostasis network that prevents the dysregulation associated with neurodegeneration is the role of molecular chaperones. Heat shock proteins (HSPs) are chaperones that regulate the aggregation and disaggregation of proteins in intracellular and extracellular spaces, and evidence supports their protective effect against protein aggregation common to neurodegenerative diseases. Consequently, upregulation of HSPs, such as HSP70, may be a target for therapeutic intervention for protection against neurodegeneration. A novel therapeutic intervention to increase the expression of HSP may be found in heat therapy and/or heat acclimation. In healthy populations, these interventions have been shown to increase HSP expression. Elevated HSP may have central therapeutic effects, preventing or reducing the toxicity of protein aggregation, and/or peripherally by enhancing neuromuscular function. Broader physiological responses to heat therapy have also been identified and include improvements in muscle function, cerebral blood flow, and markers of metabolic health. These outcomes may also have a significant benefit for people with neurodegenerative disease. While there is limited research into body warming in patient populations, regular passive heating (sauna bathing) has been associated with a reduced risk of developing neurodegenerative disease. Therefore, the emerging evidence is compelling and warrants further investigation of the potential benefits of heat acclimation and passive heat therapy for sufferers of neurodegenerative diseases.

Pravastatin induces NO synthesis by enhancing microsomal arginine uptake in healthy and preeclamptic placentas

BACKGROUND

Pravastatin, a known inducer of endothelial nitric-oxide synthase (eNOS) was demonstrated in human placenta, however the exact mechanism of it's action is not fully understood. Since placental NO (nitric oxide) synthesis is of primary importance in the regulation of placental blood flow, we aimed to clarify the effects of pravastatin on healthy (n = 6) and preeclamptic (n = 6) placentas (Caucasian participants).

METHODS

The eNOS activity of human placental microsomes was determined by the conversion rate of C14 L-arginine into C14 L-citrulline with or without pravastatin and Geldanamycin. Phosphorylation of eNOS (Ser1177) was investigated by Western blot. Microsomal arginine uptake was measured by a rapid filtration method.

RESULTS

Pravastatin significantly increased total eNOS activity in healthy (28%, p<0.05) and preeclamptic placentas (32%, p<0.05) using 1 mM Ca²⁺ promoting the dissociation of a eNOS from it's inhibitor caveolin. Pravastatin and Geldanamycin (Hsp90 inhibitor) cotreatment increased microsomal eNOS activity. Pravastatin treatment had no significant effects on Ser1177 phosphorylation of eNOS in either healthy or preeclamptic placentas. Pravastatin induced arginine uptake of placental microsomes in both healthy (38%, p < 0.05) and preeclamptic pregnancies (34%, p < 0.05).

CONCLUSIONS

This study provides a novel mechanism of pravastatin action on placental NO metabolism. Pravastatin induces the placental microsomal arginine uptake leading to the rapid activation of eNOS independently of Ser1177 phosphorylation. These new findings may contribute to better understanding of preeclampsia and may also have a clinical relevance.

Calpain inhibition improves erectile function in diabetic mice via upregulating endothelial nitric oxide synthase expression and reducing apoptosis

Calpain activation contributes to hyperglycemia-induced endothelial dysfunction and apoptosis. This study was designed to investigate the role of calpain inhibition in improving diabetic erectile dysfunction (ED) in mice. Thirty-eight-week-old male C57BL/6J mice were divided into three groups: (1) nondiabetic control group, (2) diabetic mice + vehicle group, and (3) diabetic mice + MDL28170 (an inhibitor of calpain) group. Type 1 diabetes was induced by intraperitoneal injection of streptozotocin at 60 mg kg⁻¹ body weight for 5 consecutive days. Thirteen weeks later, diabetic mice were treated with MDL28170 or vehicle for 4 weeks. The erectile function was assessed by electrical stimulation of the cavernous nerve. Penile tissues were collected for measurement of calpain activity and the endothelial nitric oxide synthase (eNOS)-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway. Terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeling (TUNEL) staining was used to evaluate apoptosis. Caspase-3 expression and activity were also measured to determine apoptosis. Our results showed that erectile function was enhanced by MDL28170 treatment in diabetic mice compared with the vehicle diabetic group. No differences in calpain-1 and calpain-2 expressions were observed among the three groups. However, calpain activity was increased in the diabetic group and reduced by MDL28170. The eNOS-NO-cGMP pathway was upregulated by MDL28170 treatment in diabetic mice. Additionally, MDL28170 could attenuate apoptosis and increase the endothelium and smooth muscle levels in corpus cavernosum. Inhibition of calpain could improve erectile function, probably by upregulating the eNOS-NO-cGMP pathway and reducing apoptosis.

Mechanistic Role of the Calcium-Dependent Protease Calpain in the Endothelial Dysfunction Induced by MPO (Myeloperoxidase)

MPO (myeloperoxidase) is a peroxidase enzyme secreted by activated leukocytes that plays a pathogenic role in cardiovascular disease, mainly by initiating endothelial dysfunction. The molecular mechanisms of the endothelial damaging action of MPO remain though largely elusive. Calpain is a calcium-dependent protease expressed in the vascular wall. Activation of calpains has been implicated in inflammatory disorders of the vasculature. Using endothelial cells and genetically modified mice, this study identifies the µ-calpain isoform as novel downstream signaling target of MPO in endothelial dysfunction. Mouse lung microvascular endothelial cells were stimulated with 10 nmol/L MPO for 180 minutes. MPO denitrosylated µ-calpain C-terminus domain, and time dependently activated µ-calpain, but not the m-calpain isoform. MPO also reduced Thr¹⁷² AMPK (AMP-activated protein kinase) and Ser¹¹⁷⁷ eNOS (endothelial nitric oxide synthase) phosphorylation via upregulation of PP2A (protein phosphatase 2) expression. At the functional level, MPO increased endothelial VCAM-1 (vascular cell adhesion molecule 1) abundance and the adhesion of leukocytes to the mouse aorta. In MPO-treated endothelial cells, pharmacological inhibition of calpain activity attenuated expression of VCAM-1 and PP2A, and restored Thr¹⁷² AMPK and Ser¹¹⁷⁷ eNOS phosphorylation. Compared with wild-type mice, µ-calpain deficient mice experienced reduced leukocyte adhesion to the aortic endothelium in response to MPO. Our data first establish a role for calpain in the endothelial dysfunction and vascular inflammation of MPO. The MPO/calpain/PP2A signaling pathway may provide novel pharmacological targets for the treatment of inflammatory vascular disorders.

Calpain inhibitor I attenuates atherosclerosis and inflammation in atherosclerotic rats through eNOS/NO/NF-κB pathway

We previously reported that calpain, the Ca2+-sensitive cysteine protease, gets involved in atherogenesis. This study aimed to investigate the effects of calpain inhibitor I (CAI, 5 mg/kg per day) with or without NG-nitro-l-arginine-methyl ester (l-NAME) (100 mg/kg per day), the inhibitor of nitric oxide synthase (NOS), on atherosclerosis and inflammation in a rat model induced by high-cholesterol diet (HCD). The results demonstrated HCD increased protein expression of calpain-1 but not calpain-2 in aortic tissue. In addition, CAI reduced the thickness of atherosclerotic intima compared with HCD group, which was weakened by the l-NAME combination. CAI with or without l-NAME decreased the activity of calpain in the aorta. Also, CAI decreased the expressions of vascular cell adhesion molecule-1 (VCAM-1), intracellular cell adhesion molecule-1 (ICAM-1), and monocyte chemoattractant protein-1 (MCP-1) in the aorta at the levels of both mRNA and protein. Furthermore, CAI increased the activity and the protein expression of endothelial NOS (eNOS) accompanied by increased content of NO and downregulated the protein expression of nuclear factor κB (NF-κB) of the nucleus in the aorta. However, the abovementioned effects were at least partly cancelled by l-NAME except for the protein expression of eNOS. The results suggested that CAI attenuated atherosclerosis and inflammation through eNOS/NO/NF-κB pathway.

Endothelial Cell Metabolism

Endothelial cells (ECs) are more than inert blood vessel lining material. Instead, they are active players in the formation of new blood vessels (angiogenesis) both in health and (life-threatening) diseases. Recently, a new concept arose by which EC metabolism drives angiogenesis in parallel to well-established angiogenic growth factors (e.g., vascular endothelial growth factor). 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3-driven glycolysis generates energy to sustain competitive behavior of the ECs at the tip of a growing vessel sprout, whereas carnitine palmitoyltransferase 1a-controlled fatty acid oxidation regulates nucleotide synthesis and proliferation of ECs in the stalk of the sprout. To maintain vascular homeostasis, ECs rely on an intricate metabolic wiring characterized by intracellular compartmentalization, use metabolites for epigenetic regulation of EC subtype differentiation, crosstalk through metabolite release with other cell types, and exhibit EC subtype-specific metabolic traits. Importantly, maladaptation of EC metabolism contributes to vascular disorders, through EC dysfunction or excess angiogenesis, and presents new opportunities for anti-angiogenic strategies. Here we provide a comprehensive overview of established as well as newly uncovered aspects of EC metabolism.

Nox4 regulates the eNOS uncoupling process in aging endothelial cells

ROS and its associated signaling contribute to vascular aging-associated endothelial disturbance. Since the non-effective endothelial nitric oxide synthase (eNOS) coupling status is related to vascular aging-related phenotypes, eNOS coupled/uncoupled system signaling was studied in human umbilical vein endothelial cells (HUVEC). Nitric oxide (NO) and eNOS Ser1177 were significantly decreased, whereas O₂^- (superoxide anion radical) increased with passage number. In aging cells, NADPH oxidase 4 (Nox4), one of the main superoxide generating enzymes, and its associated protein disulfide isomerase (PDI) chaperone were highly activated, and the resultant ER redox imbalance leads to disturbance of protein folding capability, namely endoplasmic reticulum (ER) stress, ultimately inducing dissociation between HSP90 and IRE-1α or PERK, decreasing HSP90 stability and dissociating the binding of eNOS from the HSP90 and leading to eNOS uncoupling. Through chemical and Nox4 siRNA approaches, Nox4 and its linked ER stress were shown to mainly contribute to eNOS uncoupling and its associated signaling, suggesting that Nox4 and its related ER stress signaling are key signals of the aging process in endothelial cells.

Meta-inflammation and cardiometabolic disease in obesity: Can heat therapy help?

Obesity and associated metabolic dysfunction have reached epidemic proportions worldwide. The current theory linking metabolic disease and obesity involves ischemic adipose tissue initiating an inflammatory cascade that results in systemic insulin resistance and may eventually lead to type II diabetes mellitus. Diabetes and associated metabolic dysfunction increase the risk of developing cardiovascular disease and fatal cardiovascular events. By targeting key steps in this process, ischemia and inflammation, this cascade may be prevented or reversed and thus metabolic and cardiovascular health may be preserved in obesity. Regular heat exposure (termed ‘heat therapy’) offers potential to improve cardiometabolic health in obese individuals through a variety of mechanisms that include but are not limited to heat shock proteins, hypoxia-inducible factor 1α, and hemodynamic effects. The purpose of this review is to highlight the cardiometabolic decline in obese individuals stemming from adipose tissue dysfunction, and examine the ways in which heat therapy and associated cellular and systemic adaptations can intersect with this decline in function to improve or restore cardiovascular and metabolic health.

25-Hydroxycholesterol impairs endothelial function and vasodilation by uncoupling and inhibiting endothelial nitric oxide synthase

Endothelial dysfunction is a key early step in atherosclerosis. 25-Hydroxycholesterol (25-OHC) is found in atherosclerotic lesions. However, whether 25-OHC promotes atherosclerosis is unclear. Here, we hypothesized that 25-OHC, a proinflammatory lipid, can impair endothelial function, which may play an important role in atherosclerosis. Bovine aortic endothelial cells were incubated with 25-OHC. Endothelial cell proliferation, migration, and tube formation were measured. Nitric oxide (NO) production and superoxide anion generation were determined. The expression and phosphorylation of endothelial NO synthase (eNOS) and Akt as well as the association of eNOS and heat shock protein (HSP)90 were detected by immunoblot analysis and immunoprecipitation. Endothelial cell apoptosis was monitored by TUNEL staining and caspase-3 activity, and expression of Bcl-2, Bax, cleaved caspase-9, and cleaved caspase-3 were detected by immunoblot analysis. Finally, aortic rings from Sprague-Dawley rats were isolated and treated with 25-OHC, and endothelium-dependent vasodilation was evaluated. 25-OHC significantly inhibited endothelial cell proliferation, migration, and tube formation. 25-OHC markedly decreased NO production and increased superoxide anion generation. 25-OHC reduced the phosphorylation of Akt and eNOS and the association of eNOS and HSP90. 25-OHC also enhanced endothelial cell apoptosis by decreasing Bcl-2 expression and increasing cleaved caspase-9 and cleaved caspase-3 expressions as well as caspase-3 activity. 25-OHC impaired endothelium-dependent vasodilation. These data demonstrated that 25-OHC could impair endothelial function by uncoupling and inhibiting eNOS activity as well as by inducing endothelial cell apoptosis. Our findings indicate that 25-OHC may play an important role in regulating atherosclerosis.

Genetic Analysis Reveals a Longevity-Associated Protein Modulating Endothelial Function and Angiogenesis

RATIONALE

Long living individuals show delay of aging, which is characterized by the progressive loss of cardiovascular homeostasis, along with reduced endothelial nitric oxide synthase activity, endothelial dysfunction, and impairment of tissue repair after ischemic injury.

OBJECTIVE

Exploit genetic analysis of long living individuals to reveal master molecular regulators of physiological aging and new targets for treatment of cardiovascular disease.

METHODS AND RESULTS

We show that the polymorphic variant rs2070325 (Ile229Val) in bactericidal/permeability-increasing fold-containing-family-B-member-4 (BPIFB4) associates with exceptional longevity, under a recessive genetic model, in 3 independent populations. Moreover, the expression of BPIFB4 is instrumental to maintenance of cellular and vascular homeostasis through regulation of protein synthesis. BPIFB4 phosphorylation/activation by protein-kinase-R-like endoplasmic reticulum kinase induces its complexing with 14-3-3 and heat shock protein 90, which is facilitated by the longevity-associated variant. In isolated vessels, BPIFB4 is upregulated by mechanical stress, and its knock-down inhibits endothelium-dependent vasorelaxation. In hypertensive rats and old mice, gene transfer of longevity-associated variant-BPIFB4 restores endothelial nitric oxide synthase signaling, rescues endothelial dysfunction, and reduces blood pressure levels. Furthermore, BPIFB4 is implicated in vascular repair. BPIFB4 is abundantly expressed in circulating CD34(+) cells of long living individuals, and its knock-down in endothelial progenitor cells precludes their capacity to migrate toward the chemoattractant SDF-1. In a murine model of peripheral ischemia, systemic gene therapy with longevity-associated variant-BPIFB4 promotes the recruitment of hematopoietic stem cells, reparative vascularization, and reperfusion of the ischemic muscle.

CONCLUSIONS

Longevity-associated variant-BPIFB4 may represent a novel therapeutic tool to fight endothelial dysfunction and promote vascular reparative processes.

Interaction between calpain-1 and HSP90: new insights into the regulation of localization and activity of the protease

Here we demonstrate that heat shock protein 90 (HSP90) interacts with calpain-1, but not with calpain-2, and forms a discrete complex in which the protease maintains its catalytic activity, although with a lower affinity for Ca²⁺. Equilibrium gel distribution experiments show that this complex is composed by an equal number of molecules of each protein partner. Moreover, in resting cells, cytosolic calpain-1 is completely associated with HSP90. Since calpain-1, in association with HSP90, retains its proteolytic activity, and the chaperone is displaced by calpastatin also in the absence of Ca²⁺, the catalytic cleft of the protease is not involved in this association. Thus, calpain-1 can form two distinct complexes depending on the availability of calpastatin in the cytosol. The occurrence of a complex between HSP90 and calpain-1, in which the protease is still activable, can prevent the complete inhibition of the protease even in the presence of high calpastatin levels. We also demonstrate that in basal cell conditions HSP90 and calpain-1, but not calpain-2, are inserted in the multi-protein N-Methyl-D-Aspartate receptor (NMDAR) complex. The amount of calpain-1 at the NMDAR cluster is not modified in conditions of increased [Ca²⁺]_i, and this resident protease is involved in the processing of NMDAR components. Finally, the amount of calpain-1 associated with NMDAR cluster is independent from Ca²⁺-mediated translocation. Our findings show that HSP90 plays an important role in maintaining a given and proper amount of calpain-1 at the functional sites.

Novel mechanisms of endothelial mechanotransduction

Atherosclerosis is a focal disease that develops preferentially where nonlaminar, disturbed blood flow occurs, such as branches, bifurcations, and curvatures of large arteries. Endothelial cells sense and respond differently to disturbed flow compared with steady laminar flow. Disturbed flow that occurs in so-called atheroprone areas activates proinflammatory and apoptotic signaling, and this results in endothelial dysfunction and leads to subsequent development of atherosclerosis. In contrast, steady laminar flow as atheroprotective flow promotes expression of many anti-inflammatory genes, such as Kruppel-like factor 2 and endothelial nitric oxide synthase and inhibits endothelial inflammation and athrogenesis. Here we will discuss that disturbed flow and steady laminar flow induce pro- and antiatherogenic events via flow type-specific mechanotransduction pathways. We will focus on 5 mechanosensitive pathways: mitogen-activated protein kinases/extracellular signal-regulated kinase 5/Kruppel-like factor 2 signaling, extracellular signal-regulated kinase/peroxisome proliferator-activated receptor signaling, and mechanosignaling pathways involving SUMOylation, protein kinase C-ζ, and p90 ribosomal S6 kinase. We think that clarifying regulation mechanisms between these 2 flow types will provide new insights into therapeutic approaches for the prevention and treatment of atherosclerosis.

Calpain 1 and -2 play opposite roles in cord formation of lymphatic endothelial cells via eNOS regulation

Calpains are a family of calcium-dependent proteases. Two isoforms, calpain 1 and 2, have been implicated in angiogenesis and endothelial cell adhesion and migration. Calpains regulate the function of eNOS;however, the relation of calpains and eNOS to lymphangiogenesisis still unclear. In the present study, we evaluated the role of calpain and eNOS in the formation of cords by lymphatic endothelial cells on Matrigel. Human lymphatic microvascular dermal-derived endothelial cells were transfected with siRNA against calpain 1 or 2. Calpain 2 knockdown, but not calpain 1 knockdown, significantly reduced cord formation, adhesion, and migration on Matrigel. These decreases correlated with a reduction in eNOS, and phosphorylated eNOS and Hsp90 levels, as assayed by immunoprecipitation and western blotting. In contrast, the knockdown of calpain 1, but not calpain 2,increased cell adhesion, enhanced migration, and stabilized late-stage cord formation by increasing cord length compared to the control. These differences correlated with an increase in the level of phosphorylated eNOS. The results indicated that the functions of calpains and eNOS are important for cord formation by lymphatic endothelial cells. For the first time, we have found different functions of calpain 1 and 2. Calpain 1 is involved in the degradation of eNOS and Hsp90 and the phosphorylation of eNOS,while calpain 2 regulates eNOS phosphorylation during cord formation by lymphatic endothelial cells on Matrigel.

A combined proteomic and transcriptomic approach shows diverging molecular mechanisms in thoracic aortic aneurysm development in patients with tricuspid- and bicuspid aortic valve

Thoracic aortic aneurysm is a pathological local dilatation of the aorta, potentially leading to aortic rupture or dissection. The disease is a common complication of patients with bicuspid aortic valve, a congenital disorder present in 1-2% of the population. Using two dimensional fluorescence difference gel electrophoresis proteomics followed by mRNA expression, and alternative splicing analysis of the identified proteins, differences in dilated and nondilated aorta tissues between 44 patients with bicuspid and tricuspid valves was examined. The pattern of protein expression was successfully validated with LC-MS/MS. A multivariate analysis of protein expression data revealed diverging protein expression fingerprints in patients with tricuspid compared with the patients with bicuspid aortic valves. From 302 protein spots included in the analysis, 69 and 38 spots were differentially expressed between dilated and nondilated aorta specifically in patients with tricuspid and bicuspid aortic valve, respectively. 92 protein spots were differentially expressed between dilated and nondilated aorta in both phenotypes. Similarly, mRNA expression together with alternative splicing analysis of the identified proteins also showed diverging fingerprints in the two patient groups. Differential splicing was abundant but the expression levels of differentially spliced mRNA transcripts were low compared with the wild type transcript and there was no correlation between splicing and the number of spots. Therefore, the different spots are likely to represent post-translational modifications. The identification of differentially expressed proteins suggests that dilatation in patients with a tricuspid aortic valve involves inflammatory processes whereas aortic aneurysm in patients with BAV may be the consequence of impaired repair capacity. The results imply that aortic aneurysm formation in patients with bicuspid and tricuspid aortic valves involve different biological pathways leading to the same phenotype.

Nitric oxide in the regulation of the sleep-wake states

Nitric oxide (NO) production involves four different NO-synthases (NOSs) that are either constitutive (neuronal, nNOS; endothelial, eNOS; mitochondrial, mNOS) or inducible (iNOS) in nature. Three main processes regulate NO/NOSs output, i.e., the L-arginine/arginase substrate-competing system, the L-citrulline/arginosuccinate-recycling system and the asymmetric dimethyl-/monomethyl-L-arginine-inhibiting system. In adult animals, nNOS exhibits a dense innervation intermingled with pontine sleep structures. It is well established that the NO/nNOS production makes a key contribution to daily homeostatic sleep (slow-wave sleep, SWS; rapid eye movement sleep, REM sleep). In the basal hypothalamus, the NO/nNOS production further contributes to the REM sleep rebound that takes place after a sleep deprivation (SD). This production may also contribute to the sleep rebound that is associated with an immobilization stress (IS). In adult animals, throughout the SD time-course, an additional NO/iNOS production takes place in neurons. Such production mediates a transitory SD-related SWS rebound. A transitory NO/iNOS production is also part of the immune system. Such a production contributes to the SWS increase that accompanies inflammatory events and is ensured by microglial cells and astrocytes. Finally, with aging, the iNOS expression becomes permanent and the corresponding NO/iNOS production is important to ensure an adequate maintenance of REM sleep and, to a lesser extent, SWS. Despite such maintenance, aged animals, however, are not able to elicit a sleep rebound to deal with the challenge of SD or IS. Sleep regulatory processes in adult animals thus become impaired with age. Reduced iNOS expression during aging may contribute to accelerated senescence, as observed in senescence-accelerated mice (SAMP-8 mice).

N-terminal domain of soluble epoxide hydrolase negatively regulates the VEGF-mediated activation of endothelial nitric oxide synthase

AIMS

The mammalian soluble epoxide hydrolase (sEH) has both an epoxide hydrolase and a phosphatase domain. The role of sEH hydrolase activity in the metabolism of epoxyeicosatrienoic acids (EETs) and the activation of endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs) has been well defined. However, far less is known about the role of sEH phosphatase activity in eNOS activation. In the present study, we investigated whether the phosphatase domain of sEH was involved in the eNOS activation in ECs.

METHODS AND RESULTS

The level of eNOS phosphorylation in aortas is higher in the sEH knockout (sEH(-/-)) mice than in wild-type mice. In ECs, pharmacological inhibition of sEH phosphatase or overexpressing sEH with an inactive phosphatase domain enhanced vascular endothelial growth factor (VEGF)-induced NO production and eNOS phosphorylation. In contrast, overexpressing the phosphatase domain of sEH prevented the VEGF-mediated NO production and eNOS phosphorylation at Ser617, Ser635, and Ser1179. Additionally, treatment with VEGF induced a c-Src kinase-dependent increase in transient tyrosine phosphorylation of sEH and the formation of a sEH-eNOS complex, which was abolished by treatment with a c-Src kinase inhibitor, PP1, or the c-Src dominant-negative mutant K298M. We also demonstrated that the phosphatase domain of sEH played a key role in VEGF-induced angiogenesis by detecting the tube formation in ECs and neovascularization in Matrigel plugs in mice.

CONCLUSION

In addition to epoxide hydrolase activity, phosphatase activity of sEH plays a pivotal role in the regulation of eNOS activity and NO-mediated EC functions.

Tear me down: role of calpain in the development of cardiac ventricular hypertrophy

Cardiac hypertrophy develops most commonly in response to hypertension and is an independent risk factor for the development of heart failure. The mechanisms by which cardiac hypertrophy may be reversed to reduce this risk have not been fully determined to the point where mechanism-specific therapies have been developed. Recently, proteases in the calpain family have been implicated in the regulation of the development of cardiac hypertrophy in preclinical animal models. In this review, we summarize the molecular mechanisms by which calpain inhibition has been shown to modulate the development of cardiac (specifically ventricular) hypertrophy. The context within which calpain inhibition might be developed for therapeutic intervention of cardiac hypertrophy is then discussed.

Hyperthermia-induced Hsp90·eNOS preserves mitochondrial respiration in hyperglycemic endothelial cells by down-regulating Glut-1 and up-regulating G6PD activity

Uncoupling of NO production from NADPH oxidation by endothelial nitric-oxide synthase (eNOS) is enhanced in hyperglycemic endothelium, potentially due to dissociation of heat shock proteins 90 (Hsp90), and cellular glucose homeostasis is enhanced by a ROS-induced positive feed back mechanism. In this study we investigated how such an uncoupling impacts oxygen metabolism and how the oxidative phosphorylation can be preserved by heat shock (42 °C for 2 h, hyperthermia) in bovine aortic endothelial cells. Normal and heat-shocked bovine aortic endothelial cells were exposed to normoglycemia (NG, 5.0 mM) or hyperglycemia (30 mM). With hyperglycemia treatment, O(2) consumption rate was reduced (from V(O(2)max) = 7.51 ± 0.54 to 2.35 ± 0.27 mm Hg/min/10(6) cells), whereas in heat-shocked cells, O(2) consumption rate remained unaltered (8.19 ± 1.01 mm Hg/min/10 × 10(6) cells). Heat shock was found to enhance Hsp90/endothelial NOS interactions and produce higher NO. Moreover, ROS generation in the hyperglycemic condition was also reduced in heat-shocked cells. Interestingly, glucose uptake was reduced in heat-shocked cells as a result of decrease in Glut-1 protein level. Glucose phosphate dehydrogenase activity that gives rise to NADPH generation was increased by hyperthermia, and mitochondrial oxidative metabolism was preserved. In conclusion, the present study provides a novel mechanism wherein the reduced oxidative stress in heat-shocked hyperglycemic cells down-regulates Glut-1 and glucose uptake, and fine-tuning of this pathway may be a potential approach to use for therapeutic benefit of diabetes mellitus.

Protein complex formation with heat shock protein 90 in chronic hypoxia-induced pulmonary hypertension in newborn piglets

Aberrant interactions between heat shock protein (Hsp)90 and its client proteins could contribute to pulmonary hypertension. We tested the hypotheses that 1) the interaction between Hsp90 and its known client protein, endothelial nitric oxide synthase (eNOS), is impaired in pulmonary resistance arteries (PRAs) from piglets with pulmonary hypertension caused by exposure to 3 or 10 days of hypoxia and 2) Hsp90 interacts with the prostanoid pathway proteins prostacyclin synthase (PGIS) and/or thromboxane synthase (TXAS). We also determined whether Hsp90 antagonism with geldanamycin alters the agonist-induced synthesis of prostacyclin and thromboxane or alters PRA responses to these prostaglandin metabolites. Compared with normoxic piglets, less eNOS coimmunoprecipitated with Hsp90 in PRAs from hypoxic piglets. Despite reduced Hsp90-eNOS interactions, dilation to ACh was enhanced in geldanamycin-treated PRAs from hypoxic, but not normoxic, piglets. In PRAs from all groups of piglets, PGIS and TXAS coimmunoprecipitated with Hsp90. Geldanamycin reduced the ACh-induced synthesis of prostacyclin and thromboxane and altered responses to the thromboxane mimetic U-46619 in PRAs from all groups. Although geldanamycin enhanced responses to prostacyclin in PRAs from both groups of hypoxic piglets, geldanamycin had no effect on prostacyclin responses in PRAs from either group of normoxic piglets. Our findings indicate that Hsp90 influences both prostanoid and eNOS signaling in the pulmonary circulation of newborn piglets and that the impact of pharmacological inhibition of Hsp90 on these signaling pathways is altered during exposure to chronic hypoxia.

PKCzeta decreases eNOS protein stability via inhibitory phosphorylation of ERK5

PKCζ has emerged as a pathologic mediator of endothelial cell dysfunction, based on its essential role in tumor necrosis factor α (TNFα)-mediated inflammation. In contrast, extracellular signal-regulated kinase 5 (ERK5) function is required for endothelial cell homeostasis as shown by activation of Krüppel-like factor 2 (KLF2), increased endothelial nitric-oxide synthase (eNOS) expression, and inhibition of apoptosis. We hypothesized that protein kinase C ζ (PKCζ) activation by TNFα would inhibit the ERK5/KLF2/eNOS pathway. TNFα inhibited the steady laminar flow-induced eNOS expression, and this effect was reversed by the dominant-negative form of PKCζ (Ad.DN-PKCζ). In addition, ERK5 function was inhibited by either TNFα or the transfection of the catalytic domain of PKCζ. This inhibition was reversed by PKCζ small interfering RNA. PKCζ was found to bind to ERK5 under basal conditions with coimmunoprecipitation and the mammalian 2-hybrid assay. Furthermore, PKCζ phosphorylates ERK5, and mutation analysis showed that the preferred site is S486. Most importantly, we found that the predominant effect of TNFα stimulation of PKCζ was to decrease eNOS protein stability that was recapitulated by transfecting Ad.ERK5S486A mutant. Finally, aortic en face analysis of ERK5/PKCζ activity showed high PKCζ and ERK5 staining in the athero-prone region. Taken together our results show that PKCζ binds and phosphorylates ERK5, thereby decreasing eNOS protein stability and contributing to early events of atherosclerosis.

Activation of Hsp90/NOS and increased NO generation does not impair mitochondrial respiratory chain by competitive binding at cytochrome c oxidase in low oxygen concentrations

Nitric oxide (NO) is known to regulate mitochondrial respiration, especially during metabolic stress and disease, by nitrosation of the mitochondrial electron transport chain (ETC) complexes (irreversible) and by a competitive binding at O2 binding site of cytochrome c oxidase (CcO) in complex IV (reversible). In this study, by using bovine aortic endothelial cells, we demonstrate that the inhibitory effect of endogenously generated NO by nitric oxide synthase (NOS) activation, by either NOS stimulators or association with heat shock protein 90 (Hsp90), is significant only at high prevailing pO2 through nitrosation of mitochondrial ETC complexes, but it does not inhibit the respiration by competitive binding at CcO at very low pO2. ETC complexes activity measurements confirmed that significant reduction in complex IV activity was noticed at higher pO2, but it was unaffected at low pO2 in these cells. This was further extended to heat-shocked cells, where NOS was activated by the induction/activation of (Hsp90) through heat shock at an elevated temperature of 42 degrees C. From these results, we conclude that the entire attenuation of respiration by endogenous NO is due to irreversible inhibition by nitrosation of ETC complexes but not through reversible inhibition by competing with O2 binding at CcO at complex IV.

Membrane rafts and caveolae in cardiovascular signaling

PURPOSE OF REVIEW

Substantial evidence documents the key role of lipid (membrane) rafts and caveolae as microdomains that concentrate a wide variety of receptors and postreceptor components regulated by hormones, neurotransmitters and growth factors.

RECENT FINDINGS

Recent data document that these microdomains are important in regulating vascular endothelial and smooth muscle cells and renal epithelial cells, and particularly in signal transduction across the plasma membrane.

SUMMARY

Raft/caveolae domains are cellular regions, including in cardiovascular and renal epithelial cells, which organize a large number of signal transduction components, thereby providing spatially and temporally efficient regulation of cell function.