Rho-kinase inhibition improves vasodilator responsiveness during hyperinsulinemia in the metabolic syndrome

Advanced glycation end-products regulate extracellular matrix-adipocyte metabolic crosstalk in diabetes

The adipose tissue extracellular matrix (ECM) regulates adipocyte cellular metabolism and is altered in obesity and type 2 diabetes, but mechanisms underlying ECM-adipocyte metabolic crosstalk are poorly defined. Advanced glycation end-product (AGE) formation is increased in diabetes. AGE alter tissue function via direct effects on ECM and by binding scavenger receptors on multiple cell types and signaling through Rho GTPases. Our goal was to determine the role and underlying mechanisms of AGE in regulating human ECM-adipocyte metabolic crosstalk. Visceral adipocytes from diabetic and non-diabetic humans with obesity were studied in 2D and 3D-ECM culture systems. AGE is increased in adipose tissue from diabetic compared to non-diabetic subjects. Glycated collagen 1 and AGE-modified ECM regulate adipocyte glucose uptake and expression of AGE scavenger receptors and Rho signaling mediators, including the DIAPH1 gene, which encodes the human Diaphanous 1 protein (hDia1). Notably, inhibition of hDia1, but not scavenger receptors RAGE or CD36, attenuated AGE-ECM inhibition of adipocyte glucose uptake. These data demonstrate that AGE-modification of ECM contributes to adipocyte insulin resistance in human diabetes, and implicate hDia1 as a potential mediator of AGE-ECM-adipocyte metabolic crosstalk.

Therapeutic potentials of the Rho kinase inhibitor Fasudil in experimental autoimmune encephalomyelitis and the related mechanisms

Multiple sclerosis (MS), Parkinson's disease (PD), Alzheimer's disease (AD), and other neurodegenerative diseases of central nervous system (CNS) disorders are serious human health problems. Rho-kinase (ROCK) is emerging as a potentially important therapeutic target relevant to inflammatory neurodegeneration diseases. This is supported by studies showing the beneficial effects of fasudil, a ROCK inhibitor, in inflammatory neurodegeneration diseases. MS is an autoimmune disease resulting from inflammation and demyelination in the white matter of the CNS. It has been postulated that activation of Rho/ROCK causes neuropathological changes accompanied with related clinical symptoms, which are improved by treatment with ROCK inhibitors. Therefore, inhibition of abnormal activation of the Rho/ROCK signaling pathway appears to be a new mechanism for treating CNS diseases. In this review, we extensively discussed the role of ROCK inhibitors, summarized the efficacy of fasudil in the MS conventional animal model of experimental autoimmune encephalomyelitis (EAE), both in vivo and in vitro, and highlighted the mechanism involved. Overall, the findings collected in this review support the role of the ROCK signaling pathway in neurodegenerative diseases. Hence, ROCK inhibitors such as fasudil can be novel, and efficacious treatment for inflammatory neurodegenerative diseases.

Beneficial Effects of Apelin on Vascular Function in Patients With Central Obesity

Patients with central obesity have impaired insulin-stimulated vasodilation and increased ET-1 (endothelin 1) vasoconstriction, which may contribute to insulin resistance and vascular damage. Apelin enhances insulin sensitivity and glucose disposal but also acts as a nitric oxide (NO)–dependent vasodilator and a counter-regulator of AT 1 (angiotensin [Ang] II type 1) receptor–induced vasoconstriction. We, therefore, examined the effects of exogenous (Pyr 1 )apelin on NO-mediated vasodilation and Ang II– or ET-1–dependent vasoconstrictor tone in obese patients. In the absence of hyperinsulinemia, forearm blood flow responses to graded doses of acetylcholine and sodium nitroprusside were not different during saline or apelin administration (both P >0.05). During intra-arterial infusion of regular insulin, however, apelin enhanced the vasodilation induced by both acetylcholine and nitroprusside (both P <0.05). Interestingly, the vasodilator effect of concurrent blockade of AT 1 (telmisartan) and AT 2 (PD 123,319) receptors was blunted by apelin (3±5% versus 32±9%; P <0.05). Similarly, during apelin administration, blockade of ET A receptors (BQ-123) resulted in lower vasodilator response than during saline (23±10% versus 65±12%; P <0.05). NO synthase inhibition by L-NMMA ( l - N -monometylarginine) during the concurrent blockade of either Ang II or ET A receptors resulted in similar vasoconstriction in the absence or presence of apelin ( P >0.05). In conclusion, in patients with central obesity, apelin has favorable effects not only to improve insulin-stimulated endothelium-dependent and endothelium-independent vasodilator responses but also to blunt Ang II– and ET-1–dependent vasoconstriction by a mechanism not involving NO. Taken together, our results suggest that targeting the apelin system might favorably impact some hemodynamic abnormalities of insulin-resistant states like obesity.

Increased mitochondrial ROS generation mediates the loss of the anti-contractile effects of perivascular adipose tissue in high-fat diet obese mice

BACKGROUND AND PURPOSE

Obesity is associated with structural and functional changes in perivascular adipose tissue (PVAT), favouring release of reactive oxygen species (ROS), vasoconstrictor and proinflammatory factors. The cytokine TNF-α induces vascular dysfunction and is produced by PVAT. We tested the hypothesis that obesity-associated PVAT dysfunction was mediated by augmented mitochondrial ROS (mROS) generation due to increased TNF-α production in this tissue.

EXPERIMENTAL APPROACH

C57Bl/6J and TNF-α receptor-deficient mice received control or high fat diet (HFD) for 18 weeks. We used pharmacological tools to determine the participation of mROS in PVAT dysfunction. Superoxide anion (O₂^.- ) and H₂ O₂ were assayed in PVAT and aortic rings were used to assess vascular function.

KEY RESULTS

Aortae from HFD-fed obese mice displayed increased contractions to phenylephrine and loss of PVAT anti-contractile effect. Inactivation of O₂^.- , dismutation of mitochondria-derived H₂ O₂ , uncoupling of oxidative phosphorylation and Rho kinase inhibition, decreased phenylephrine-induced contractions in aortae with PVAT from HFD-fed mice. O₂^.- and H₂ O₂ were increased in PVAT from HFD-fed mice. Mitochondrial respiration analysis revealed decreased O₂ consumption rates in PVAT from HFD-fed mice. TNF-α inhibition reduced H₂ O₂ levels in PVAT from HFD-fed mice. PVAT dysfunction, i.e. increased contraction to phenylephrine in PVAT-intact aortae, was not observed in HFD-obese mice lacking TNF-α receptors. Generation of H₂ O₂ was prevented in PVAT from TNF-α receptor deficient obese mice.

CONCLUSION AND IMPLICATIONS

TNF-α-induced mitochondrial oxidative stress is a key and novel mechanism involved in obesity-associated PVAT dysfunction. These findings elucidate molecular mechanisms whereby oxidative stress in PVAT could affect vascular function.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Multitarget intervention of Fasudil in the neuroprotection of dopaminergic neurons in MPTP-mouse model of Parkinson's disease

Recent studies have demonstrated that activation of the Rho-associated kinase (ROCK) pathway participates in the dopaminergic neuron degeneration and possibly in Parkinson's disease (PD). In the current study, we tried to observe the therapeutic potential of ROCK inhibitor Fasudil against dopaminergic neuron injury in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-mouse model of PD, and explore possible molecular mechanisms by enzyme-linked immunosorbent assay (ELISA), western blot and immunofluorescent assays. The results showed that MPTP-PD mice presented motor deficits, dopaminergic neuron loss, activation of inflammatory response and oxidative stress as well as ROCK and glycogen synthase kinase 3β (GSK-3β) signaling pathways. The administration of Fasudil exhibited neuroprotective effects against the dopaminergic neurons and improved the motor function recovery in the MPTP-PD mice, accompanied by the suppression of inflammatory responses (IL-1β, TNF-α, NF-κB-p65 and TLR-2), and oxidative stress (iNOS and gp91Phox), which might be associated with the inhibition of ROCK and GSK-3β activity. Simultaneously, the administration of Fasudil resulted in the shift from inflammatory M1 to anti-inflammatory/neurorepair M2 microglia. Additionally, Fasudil intervention enhanced the expression of anti-oxidative factors such as NF-E2-related factor 2 (Nrf2), Hmox as well as neurotrophic factor including GDNF. Our observations defined the neuroprotective effects of Fasudil in MPTP-PD mice, and we found a series of novel effector molecules and pathways for explaining the neuroprotective effects against dopaminergic neurons. However, a lot of investigations are warranted to further elucidate the crosstalk among Fasudil, oxidative stress, inflammatory response, GDNF and ROCK/NF-kB/Nrf2 pathways in the therapeutic potential of PD.

Rho kinase inhibition in diabetic kidney disease

Small GTPases of the Rho family and their down-stream effectors Rho associated kinases (ROCKs) are the molecules that converge a spectrum of pathophysiological signals triggered by the diabetic milieu and represent promising molecular targets for nephroprotective treatment in diabetes. The review discusses recent studies exploring the consequences of diabetes-induced Rho-ROCK activation in the kidney and the effects of ROCK inhibition (ROCKi) in experimental diabetic kidney disease (DKD). Studies in models of type 1 and type 2 diabetes have indicated blood pressure-independent nephroprotective actions of ROCKi in DKD. The underlying mechanisms include attenuation of diabetes-induced increases in renal expression of prosclerotic cytokines and extracellular matrix, anti-oxidant effects and protection of mitochondrial function, resulting in slower development of glomerulosclerosis and interstitial fibrosis. The studies have also shown antiproteinuric effects of ROCKi that could be related to reductions in permeability of the glomerular barrier and beneficial effects on podocytes. Glomerular haemodynamic mechanisms might also be involved. Despite remaining questions in this field, such as the effects in podocytes later in the course of DKD, specificity of currently available ROCKi, or the roles of individual ROCK isoforms, recent evidence in experimental diabetes suggests that ROCKi might in future broaden the spectrum of treatments available for patients with DKD. This is supported by the evidence generated in models of non-diabetic kidney disease and in clinical studies in patients with various cardiovascular disorders.

Oxidative stress in diabetes: implications for vascular and other complications

In recent decades, oxidative stress has become a focus of interest in most biomedical disciplines and many types of clinical research. Increasing evidence shows that oxidative stress is associated with the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure. Based on these studies, an emerging concept is that oxidative stress is the “final common pathway” through which the risk factors for several diseases exert their deleterious effects. Oxidative stress causes a complex dysregulation of cell metabolism and cell–cell homeostasis; in particular, oxidative stress plays a key role in the pathogenesis of insulin resistance and β-cell dysfunction. These are the two most relevant mechanisms in the pathophysiology of type 2 diabetes and its vascular complications, the leading cause of death in diabetic patients.

Activation of ErbB2 and Downstream Signalling via Rho Kinases and ERK1/2 Contributes to Diabetes-Induced Vascular Dysfunction

Diabetes mellitus leads to vascular complications but the underlying signalling mechanisms are not fully understood. Here, we examined the role of ErbB2 (HER2/Neu), a transmembrane receptor tyrosine kinase of the ErbB/EGFR (epidermal growth factor receptor) family, in mediating diabetes-induced vascular dysfunction in an experimental model of type 1 diabetes. Chronic treatment of streptozotocin-induced diabetic rats (1 mg/kg/alt diem) or acute, ex-vivo (10(-6), 10(-5) M) administration of AG825, a specific inhibitor of ErbB2, significantly corrected the diabetes-induced hyper-reactivity of the perfused mesenteric vascular bed (MVB) to the vasoconstrictor, norephinephrine (NE) and the attenuated responsiveness to the vasodilator, carbachol. Diabetes led to enhanced phosphorylation of ErbB2 at multiple tyrosine (Y) residues (Y1221/1222, Y1248 and Y877) in the MVB that could be attenuated by chronic AG825 treatment. Diabetes- or high glucose-mediated upregulation of ErbB2 phosphorylation was coupled with activation of Rho kinases (ROCKs) and ERK1/2 in MVB and in cultured vascular smooth muscle cells (VSMC) that were attenuated upon treatment with either chronic or acute AG825 or with anti-ErbB2 siRNA. ErbB2 likley heterodimerizes with EGFR, as evidenced by increased co-association in diabetic MVB, and further supported by our finding that ERK1/2 and ROCKs are common downstream effectors since their activation could also be blocked by AG1478. Our results show for the first time that ErbB2 is an upstream effector of ROCKs and ERK1/2 in mediating diabetes-induced vascular dysfunction. Thus, potential strategies aimed at modifying actions of signal transduction pathways involving ErbB2 pathway may prove to be beneficial in treatment of diabetes-induced vascular complications.

Obesity-related metabolic syndrome: mechanisms of sympathetic overactivity

The prevalence of the metabolic syndrome has increased worldwide over the past few years. Sympathetic nervous system overactivity is a key mechanism leading to hypertension in patients with the metabolic syndrome. Sympathetic activation can be triggered by reflex mechanisms as arterial baroreceptor impairment, by metabolic factors as insulin resistance, and by dysregulated adipokine production and secretion from visceral fat with a mainly permissive role of leptin and antagonist role of adiponectin. Chronic sympathetic nervous system overactivity contributes to a further decline of insulin sensitivity and creates a vicious circle that may contribute to the development of hypertension and of the metabolic syndrome and favor cardiovascular and kidney disease. Selective renal denervation is an emerging area of interest in the clinical management of obesity-related hypertension. This review focuses on current understanding of some mechanisms through which sympathetic overactivity may be interlaced to the metabolic syndrome, with particular regard to the role of insulin resistance and of some adipokines.