Differential modulation of AMPK/PPARα/UCP2 axis in relation to hypertension and aging in the brain, kidneys and heart of two closely related spontaneously hypertensive rat strains

UCP2, a Member of the Mitochondrial Uncoupling Proteins: An Overview from Physiological to Pathological Roles

UCP2 is an uncoupling protein homolog to UCP1. Unlike UCP1, which participates in non-shivering thermogenesis by uncoupling oxidative phosphorylation (OXPHOS), UCP2 does not perform a canonical H+ leak, consuming the protonmotive force (Δp) through the inner mitochondrial membrane. The UCP2 biological role is elusive. It can counteract oxidative stress, acting with a "mild uncoupling" process to reduce ROS production, and, in fact, UCP2 activities are related to inflammatory processes, triggering pathological conditions. However, the Δp dissipation by UCP2 activity reduces the mitochondrial ATP production and rewires the bioenergetic metabolism of the cells. In all likelihood, UCP2 works as a carrier of metabolites with four carbon atoms (C4), reversing the anaerobic glycolysis-dependent catabolism to OXPHOS. Indeed, UCP2 can perform catalysis in dual mode: mild uncoupling of OXPHOS and metabolite C4 exchange of mitochondria. In vivo, the UCP2 features in the biology of mitochondria promote healthy ageing, increased lifespan, and can assure cerebro- and cardiovascular protection. However, the pathological conditions responsible for insulin secretion suppression are dependent on UCP2 activity. On balance, the uncertain biochemical mechanisms dependent on UCP2 do not allow us to depict the protective role in mitochondrial bioenergetics.

Resveratrol attenuates cyclosporin A-induced upregulation of the thromboxane A2 receptor and hypertension via the AMPK/SIRT1 and MAPK/NF-κB pathways in the rat mesenteric artery

Cyclosporin A, an immunosuppressive agent, is extensively utilized for the prevention of transplant rejection and treat autoimmune disease in the clinic, despite its association with a high risk of hypertension development among patients. Resveratrol is a kind of non-flavonoid phenolic compound that widely exists in many plants. The aim of the present study was to investigate the mechanism by which resveratrol ameliorates cyclosporin A-induced hypertension. The arterial rings of the mesentery were incubated with cyclosporin A and resveratrol in vitro. Rats were administered cyclosporin A and/or resveratrol for 3 weeks in vivo. Blood pressure was measured via the tail arteries. Vasoconstriction curves were recorded using a sensitive myograph. The protein expression was evaluated through Western blotting. This study demonstrated that resveratrol mitigated the cyclosporin A-induced increase in blood pressure in rats. Furthermore, resveratrol markedly inhibited the cyclosporin A-induced upregulation of thromboxane A2 receptor-mediated vasoconstriction in the rat mesenteric artery both in vitro and in vivo. Moreover, resveratrol activated AMPK/SIRT1 and inhibited the MAPK/NF-κB signaling pathway. In conclusion, resveratrol restored the cyclosporin A-induced upregulation of the thromboxane A2 receptor and hypertension via the AMPK/SIRT1 and MAPK/NF-κB pathways in rats.

Molecular mechanisms of naringenin modulation of mitochondrial permeability transition acting on F1FO-ATPase and counteracting saline load-induced injury in SHRSP cerebral endothelial cells

Naringenin (NRG) was characterized for its ability to counteract mitochondrial dysfunction which is linked to cardiovascular diseases. The F1FO-ATPase can act as a molecular target of NRG. The interaction of NRG with this enzyme can avoid the energy transmission mechanism of ATP hydrolysis, especially in the presence of Ca2+ cation used as cofactor. Indeed, NRG was a selective inhibitor of the hydrophilic F1 domain displaying a binding site overlapped with quercetin in the inside surface of an annulus made by the three α and the three β subunits arranged alternatively in a hexamer. The kinetic constant of inhibition suggested that NRG preferred the enzyme activated by Ca2+ rather than the F1FO-ATPase activated by the natural cofactor Mg2+. From the inhibition type mechanism of NRG stemmed the possibility to speculate that NRG can prevent the activation of F1FO-ATPase by Ca2+. The event correlated to the protective role in the mitochondrial permeability transition pore opening by NRG as well as to the reduction of ROS production probably linked to the NRG chemical structure with antioxidant action. Moreover, in primary cerebral endothelial cells (ECs) obtained from stroke prone spontaneously hypertensive rats NRG had a protective effect on salt-induced injury by restoring cell viability and endothelial cell tube formation while also rescuing complex I activity.

Higher expression of TSR2 aggravating hypertension via the PPAR signaling pathway

Hypertension is a complex disease with unknown causes. Therefore, it's crucial to deeply study its molecular mechanism. The hypertension dataset was obtained from Gene Expression Omnibus data base (GEO), and miRNA regulating central hub genes was screened via weighted gene co-expression network (DEGs) and gene set enrichment (GSEA). Cell experiments validated TSR2's role and the PPAR signaling pathway through western blotting. 500 DEGs were identified for hypertension, mainly enriched in actin cross-linking, insulin signaling, PPAR signaling, and protein localization. Eight hub genes (SEC61G, SRP14, Liy AR, NIP7, SDAD1, POLR1D, DYNLL2, TSR2) were identified. Four hub genes (LYAR, SDAD1, POLR1D, TSR2) exhibited high expression levels in the hypertensive tissue samples, while showing low expression levels in the normal tissue samples. This led us to speculate that they may have relevant regulatory effects on hypertension. When TSR2 was knocked down in the hypertension peripheral blood mononuclear cells (PBMC) model, the critical proteins in the PPAR signaling pathway (FABP, PPAR, PLTP, ME1, SCD1, CYP27, FABP1, OLR1, CPT-1, PGAR, CAP, ADIPO, MMP1, UCP1, ILK, PDK1 UBC AQP7) were downregulated. This also occurred in the hypertension peripheral blood mononuclear cells (PBMC) + TSR2_ OV model. TSR2 is highly expressed in individuals with hypertension and may play a significant role in the development of hypertension through the PPAR signaling pathway. TSR2 could serve as a molecular target for the early diagnosis and precise treatment of hypertension, providing a valuable direction for the mechanism research of this condition.

Renal Epithelial Mitochondria: Implications for Hypertensive Kidney Disease

According to the Centers for Disease Control and Prevention, 1 in 2 U.S. adults have hypertension, and more than 1 in 7 chronic kidney disease. In fact, hypertension is the second leading cause of kidney failure in the United States; it is a complex disease characterized by, leading to, and caused by renal dysfunction. It is well-established that hypertensive renal damage is accompanied by mitochondrial damage and oxidative stress, which are differentially regulated and manifested along the nephron due to the diverse structure and functions of renal cells. This article provides a summary of the relevant knowledge of mitochondrial bioenergetics and metabolism, focuses on renal mitochondrial function, and discusses the evidence that has been accumulated regarding the role of epithelial mitochondrial bioenergetics in the development of renal tissue dysfunction in hypertension. © 2024 American Physiological Society. Compr Physiol 14:5225-5242, 2024.

Uncoupling Protein 2 as a Pathogenic Determinant and Therapeutic Target in Cardiovascular and Metabolic Diseases

Uncoupling protein 2 (UCP2) is a mitochondrial protein that acts as an anion carrier. It is involved in the regulation of several processes, including mitochondrial membrane potential, generation of reactive oxygen species within the inner mitochondrial membrane and calcium homeostasis. UCP2 expression can be regulated at different levels: genetic (gene variants), transcriptional [by peroxisome proliferator-activated receptors (PPARs) and microRNAs], and post-translational. Experimental evidence indicates that activation of UCP2 expression through the AMPK/PPAR-α axis exerts a protective effect toward renal damage and stroke occurrence in an animal model of ischemic stroke (IS) associated with hypertension. UCP2 plays a key role in heart diseases (myocardial infarction and cardiac hypertrophy) and metabolic disorders (obesity and diabetes). In humans, UCP2 genetic variants (-866G/A and Ala55Val) associate with an increased risk of type 2 diabetes mellitus and IS development. Over the last few years, many agents that modulate UCP2 expression have been identified. Some of them are natural compounds of plant origin, such as Brassica oleracea, curcumin, berberine and resveratrol. Other molecules, currently used in clinical practice, include anti-diabetic (gliptin) and chemotherapeutic (doxorubicin and taxol) drugs. This evidence highlights the relevant role of UCP2 for the treatment of a wide range of diseases, which affect the national health systems of Western countries. We will review current knowledge on the physiological and pathological implications of UCP2 with particular regard to cardiovascular and metabolic disorders and will focus on the available therapeutic approaches affecting UCP2 level for the treatment of human diseases.

An interplay between UCP2 and ROS protects cells from high-salt-induced injury through autophagy stimulation

The mitochondrial uncoupling protein 2 (UCP2) plays a protective function in the vascular disease of both animal models and humans. UCP2 downregulation upon high-salt feeding favors vascular dysfunction in knock-out mice, and accelerates cerebrovascular and renal damage in the stroke-prone spontaneously hypertensive rat. Overexpression of UCP2 counteracts the negative effects of high-salt feeding in both animal models. We tested in vitro the ability of UCP2 to stimulate autophagy and mitophagy as a mechanism mediating its protective effects upon high-salt exposure in endothelial and renal tubular cells. UCP2 silencing reduced autophagy and mitophagy, whereas the opposite was true upon UCP2 overexpression. High-salt exposure increased level of reactive oxygen species (ROS), UCP2, autophagy and autophagic flux in both endothelial and renal tubular cells. In contrast, high-salt was unable to induce autophagy and autophagic flux in UCP2-silenced cells, concomitantly with excessive ROS accumulation. The addition of an autophagy inducer, Tat-Beclin 1, rescued the viability of UCP2-silenced cells even when exposed to high-salt. In summary, UCP2 mediated the interaction between high-salt-induced oxidative stress and autophagy to preserve viability of both endothelial and renal tubular cells. In the presence of excessive ROS accumulation (achieved upon UCP2 silencing and high-salt exposure of silenced cells) autophagy was turned off. In this condition, an exogenous autophagy inducer rescued the cellular damage induced by excess ROS level. Our data confirm the protective role of UCP2 toward high-salt-induced vascular and renal injury, and they underscore the role of autophagy/mitophagy as a mechanism counteracting the high-salt-induced oxidative stress damage.

An Overview of the Posttranslational Modifications and Related Molecular Mechanisms in Diabetic Nephropathy

Diabetic nephropathy (DN), a common diabetic microvascular complication, is characterized by its complex pathogenesis, higher risk of mortality, and the lack of effective diagnosis and treatment methods. Many studies focus on the diagnosis and treatment of diabetes mellitus (DM) and have reported that the pathophysiology of DN is very complex, involving many molecules and abnormal cellular activities. Given the respective pivotal roles of NF-κB, Nrf2, and TGF-β in inflammation, oxidative stress, and fibrosis during DN, we first review the effect of posttranslational modifications on these vital molecules in DN. Then, we describe the relationship between these molecules and related abnormal cellular activities in DN. Finally, we discuss some potential directions for DN treatment and diagnosis. The information reviewed here may be significant in the design of further studies to identify valuable therapeutic targets for DN.

The effects of UCP2 on autophagy through the AMPK signaling pathway in septic cardiomyopathy and the underlying mechanism

Background

Mitochondrial dysfunction plays an important role in the development of septic cardiomyopathy. This study aimed to reveal the protective role of uncoupling protein 2 (UCP2) in mitochondria through AMP-activated protein kinase (AMPK) on autophagy during septic cardiomyopathy.

Methods

UCP2 knockout mice via a cecal ligation and puncture (CLP) model and the H9C2 cardiomyocyte cell line in response to lipopolysaccharide (LPS) in vitro were used to study the effect. The myocardial morphological alterations, indicators of mitochondrial injury and levels of autophagy-associated proteins (pAMPK, pmTOR, pULK1, pTSC2, Beclin-1, and LC3-I/II) were assessed. In addition, the mechanism of the interaction between UCP2 and AMPK was further studied through gain- and loss-of-function studies.

Results

Compared with the wild-type mice, the UCP2 knockout mice exhibited more severe cardiomyocyte injury after CLP, and the AMPK agonist AICAR protected against such injury. Consistent with this result, silencing UCP2 augmented the LPS-induced pathological damage and mitochondrial injury in the H9C2 cells, limited the upregulation of autophagy proteins and reduced AMPK phosphorylation. AICAR protected the cells from morphological changes and mitochondrial membrane potential loss and promoted autophagy. The silencing and overexpression of UCP2 led to correlated changes in the AMPK upstream kinases pLKB1 and CAMKK2.

Conclusions

UCP2 exerts cardioprotective effects on mitochondrial dysfunction during sepsis via the action of AMPK on autophagy.

Vasa Vasorum Lumen Narrowing in Brain Vascular Hyalinosis in Systemic Hypertension Patients Who Died of Ischemic Stroke

Ischemic stroke is a major cause of death among patients with systemic hypertension. The narrowing of the lumen of the brain vasculature contributes to the increased incidence of stroke. While hyalinosis represents the major pathological lesions contributing to vascular lumen narrowing and stroke, the pathogenic mechanism of brain vascular hyalinosis has not been well characterized. Thus, the present study examined the postmortem brain vasculature of human patients who died of ischemic stroke due to systemic hypertension. Hematoxylin and eosin staining and immunohistochemistry showed the occurrence of brain vascular hyalinosis with infiltrated plasma proteins along with the narrowing of the vasa vasorum and oxidative stress. Transmission electron microscopy revealed endothelial cell bulge protrusion into the vasa vasorum lumen and the occurrence of endocytosis in the vasa vasorum endothelium. The treatment of cultured microvascular endothelial cells with adrenaline also promoted the formation of the bulge as well as endocytic vesicles. The siRNA knockdown of sortin nexin-9 (a mediator of clathrin-mediated endocytosis) inhibited adrenaline-induced endothelial cell bulge formation. Adrenaline promoted protein-protein interactions between sortin nexin-9 and neural Wiskott–Aldrich syndrome protein (a regulator of actin polymerization). Spontaneously hypertensive stroke-prone rats also exhibited lesions indicative of brain vascular hyalinosis, the endothelial cell protrusion into the lumen of the vasa vasorum, and endocytosis in vasa vasorum endothelial cells. We propose that endocytosis-dependent endothelial cell bulge protrusion narrows the vasa vasorum, resulting in ischemic oxidative damage to cerebral vessels, the formation of hyalinosis, the occurrence of ischemic stroke, and death in systemic hypertension patients.

Soluble epoxide hydrolase inhibition improves cognitive function and parenchymal artery dilation in a hypertensive model of chronic cerebral hypoperfusion

OBJECTIVE

Parenchymal arterioles (PAs) regulate perfusion of the cerebral microcirculation, and impaired PA endothelium-dependent dilation occurs in dementia models mimicking chronic cerebral hypoperfusion (CCH). Epoxyeicosatrienoic acids (EETs) are vasodilators; their actions are potentiated by soluble epoxide hydrolase (sEH) inhibition. We hypothesized that chronic sEH inhibition with trifluoromethoxyphenyl-3 (1-propionylpiperidin-4-yl) urea (TPPU) would prevent cognitive dysfunction and improve PA dilation in a hypertensive CCH model.

METHODS

Bilateral carotid artery stenosis (BCAS) was used to induce CCH in twenty-week-old male stroke-prone spontaneously hypertensive rats (SHSRP) that were treated with vehicle or TPPU for 8 weeks. Cognitive function was assessed by novel object recognition. PA dilation and structure were assessed by pressure myography, and mRNA expression in brain tissue was assessed by qRT-PCR.

RESULTS

TPPU did not enhance resting cerebral perfusion, but prevented CCH-induced memory deficits. TPPU improved PA endothelium-dependent dilation but reduced the sensitivity of PAs to a nitric oxide donor. TPPU treatment had no effect on PA structure or biomechanical properties. TPPU treatment increased brain mRNA expression of brain derived neurotrophic factor, doublecortin, tumor necrosis factor-alpha, sEH, and superoxide dismutase 3, CONCLUSIONS: These data suggest that sEH inhibitors may be viable treatments for cognitive impairments associated with hypertension and CCH.

Brain Overexpression of Uncoupling Protein-2 (UCP2) Delays Renal Damage and Stroke Occurrence in Stroke-Prone Spontaneously Hypertensive Rats

The downregulation of uncoupling protein-2 (UCP2) is associated with increased brain and kidney injury in stroke-prone spontaneously hypertensive rats (SHRSP) fed with a Japanese style hypersodic diet (JD). Systemic overexpression of UCP2 reduces organ damage in JD-fed SHRSP. We examined the effect of brain-specific UCP2 overexpression on blood pressure (BP), stroke occurrence and kidney damage in JD-fed SHRSP. Rats received a single i.c.v. injection of a lentiviral vector encoding UCP2 (LV-UCP2), or an empty vector. The brain delivery of LV-UCP2 significantly delayed the occurrence of stroke and kidney damage. The large reduction of proteinuria observed after LV-UCP2 injection was unexpected, because BP levels were unchanged. At the time of stroke, rats treated with LV-UCP2 still showed a large UCP2 upregulation in the striatum, associated with increases in OPA1 and FIS1 protein levels, and reductions in PGC1-α, SOD2, TNFα mRNA levels and NRF2 protein levels. This suggested UCP2 overexpression enhanced mitochondrial fusion and fission and reduced oxidative damage and inflammation in the striatum of JD-fed SHRSP rats. Our data suggest the existence of central mechanisms that may protect against hypertension-induced organ damage independently of BP, and strengthen the suitability of strategies aimed at enhancing UCP2 expression for the treatment of hypertensive damage.

Fenofibrate attenuates cardiac and renal alterations in young salt-loaded spontaneously hypertensive stroke-prone rats through mitochondrial protection

OBJECTIVES

The simultaneous presence of cardiac and renal diseases is a pathological condition that leads to increased morbidity and mortality. Several lines of evidence have suggested that lipid dysmetabolism and mitochondrial dysfunction are pathways involved in the pathological processes affecting the heart and kidney. In the salt-loaded spontaneously hypertensive stroke-prone rat (SHRSP), a model of cardiac hypertrophy and nephropathy that shows mitochondrial alterations in the myocardium, we evaluated the cardiorenal effects of fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARα) agonist that acts by modulating mitochondrial and peroxisomal fatty acid oxidation.

METHODS

Male SHRSPs aged 6-7 weeks were divided in three groups: standard diet (n = 6), Japanese diet with vehicle (n = 6), and Japanese diet with fenofibrate 150 mg/kg/day (n = 6) for 5 weeks. Cardiac and renal functions were assessed in vivo by MRI, ultrasonography, and biochemical assays. Mitochondria were investigated by transmission electron microscopy, succinate dehydrogenase (SDH) activity, and gene expression analysis.

RESULTS

Fenofibrate attenuated cardiac hypertrophy, as evidenced by histological and MRI analyses, and protected the kidneys, preventing morphological alterations, changes in arterial blood flow velocity, and increases in 24-h proteinuria. Cardiorenal inflammation, oxidative stress, and cellular senescence were also inhibited by fenofibrate. In salt-loaded SHRSPs, we observed severe morphological mitochondrial alterations, reduced SDH activity, and down-regulation of genes regulating mitochondrial fatty-acid oxidation (i.e. PPARα, SIRT3, and Acadm). These changes were counteracted by fenofibrate. In vitro, a direct protective effect of fenofibrate on mitochondrial membrane potential was observed in albumin-stimulated NRK-52E renal tubular epithelial cells.

CONCLUSION

The results suggest that the cardiorenal protective effects of fenofibrate in young male salt-loaded SHRSPs are explained by its capacity to preserve mitochondrial function.

Effects of dual angiotensin type 1 receptor/neprilysin inhibition vs. angiotensin type 1 receptor inhibition on target organ injury in the stroke-prone spontaneously hypertensive rat

OBJECTIVES

The combination of AT1 blocker/neutroendopeptidase neprilysin inhibition (ARNi) represents an interesting approach to reduce cardiovascular risk in hypertension. We assessed the efficacy of ARNi, compared with angiotensin II type 1 receptor blockade alone, on blood pressure (BP) and on protection from target organ damage development in the stroke-prone spontaneously hypertensive rat (SHRSP).

METHODS

In high-salt fed SHRSP, we assessed plasma and tissue natriuretic peptides, urinary volume, BP and body weight over a short-term treatment (6 weeks) with either ARNi (sacubitril/valsartan 68 mg/kg per day) or valsartan (30 mg/kg per day), protection from stroke and renal damage (as documented by proteinuria) over 4 months of treatment with either sacubitril/valsartan or valsartan; the ability of either treatment to reduce progression of cerebrovascular and renal damage after 2 weeks of high-salt diet.

RESULTS

Higher levels of plasma and tissue atrial natriuretic peptide, of urinary cyclic guanosine 3'5'monophosphate and urine volumes, along with lower BP levels, were found upon sacubitril/valsartan as compared with valsartan over the short-term treatment. Sacubitril/valsartan caused a significant reduction of both BP and proteinuria levels and complete prevention of stroke over the long-term treatment. Once organ damage was established, a significant delay of its progression was observed with sacubitril/valsartan.

CONCLUSION

The dual angiotensin II type 1 receptor/neutroendopeptidase inhibition significantly increased atrial natriuretic peptide level and reduced BP. Complete prevention of stroke was achieved in this model. The ability of sacubitril/valsartan to reduce organ damage progression was superior to that of valsartan alone. ARNi may represent a highly effective therapeutic agent to protect from target organ damage development in hypertension.

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

Protection Before Impact: the Potential Neuroprotective Role of Nutritional Supplementation in Sports-Related Head Trauma

Even in the presence of underreporting, sports-related concussions/mild traumatic brain injuries (mTBI) are on the rise. In the absence of proper diagnosis, an athlete may return to play prior to full recovery, increasing the risk of second-impact syndrome or protracted symptoms. Recent evidence has demonstrated that sub-concussive impacts, those sustained routinely in practice and competition, result in a quantifiable pathophysiological response and the accumulation of both concussive and sub-concussive impacts sustained over a lifetime of sports participation may lead to long-term neurological impairments and an increased risk of developing neurodegenerative diseases. The pathophysiological, neurometabolic, and neurochemical cascade that initiates subsequent to the injury is complex and involves multiple mechanisms. While pharmaceutical treatments may target one mechanism, specific nutrients and nutraceuticals have been discovered to impact several pathways, presenting a broader approach. Several studies have demonstrated the neuroprotective effect of nutritional supplementation in the treatment of mTBI. However, given that many concussions go unreported and sub-concussive impacts result in a pathophysiological response that, too, may contribute to long-term brain health, protection prior to impact is warranted. This review discusses the current literature regarding the role of nutritional supplements that, when provided before mTBI and traumatic brain injury, may provide neurological protection.

Mitochondrial Uncoupling Proteins: Subtle Regulators of Cellular Redox Signaling

SIGNIFICANCE

Mitochondria are the energetic, metabolic, redox, and information signaling centers of the cell. Substrate pressure, mitochondrial network dynamics, and cristae morphology state are integrated by the protonmotive force Δp or its potential component, ΔΨ, which are attenuated by proton backflux into the matrix, termed uncoupling. The mitochondrial uncoupling proteins (UCP1-5) play an eminent role in the regulation of each of the mentioned aspects, being involved in numerous physiological events including redox signaling. Recent Advances: UCP2 structure, including purine nucleotide and fatty acid (FA) binding sites, strongly support the FA cycling mechanism: UCP2 expels FA anions, whereas uncoupling is achieved by the membrane backflux of protonated FA. Nascent FAs, cleaved by phospholipases, are preferential. The resulting Δp dissipation decreases superoxide formation dependent on Δp. UCP-mediated antioxidant protection and its impairment are expected to play a major role in cell physiology and pathology. Moreover, UCP2-mediated aspartate, oxaloacetate, and malate antiport with phosphate is expected to alter metabolism of cancer cells.

CRITICAL ISSUES

A wide range of UCP antioxidant effects and participations in redox signaling have been reported; however, mechanisms of UCP activation are still debated. Switching off/on the UCP2 protonophoretic function might serve as redox signaling either by employing/releasing the extra capacity of cell antioxidant systems or by directly increasing/decreasing mitochondrial superoxide sources. Rapid UCP2 degradation, FA levels, elevation of purine nucleotides, decreased Mg²⁺, or increased pyruvate accumulation may initiate UCP-mediated redox signaling.

FUTURE DIRECTIONS

Issues such as UCP2 participation in glucose sensing, neuronal (synaptic) function, and immune cell activation should be elucidated. Antioxid. Redox Signal. 29, 667-714.

Uncoupling Protein 2 in Cardiovascular Health and Disease

Uncoupling protein 2 (UCP2) belongs to the family of mitochondrial anion carrier proteins. It uncouples oxygen consumption from ATP synthesis. UCP2 is ubiquitously expressed in most cell types to reduce oxidative stress. It is tightly regulated at the transcriptional, translational, and post-translational levels. UCP2 in the cardiovascular system is being increasingly recognized as an important molecule to defend against various stress signals such as oxidative stress in the pathology of vascular dysfunction, atherosclerosis, hypertension, and cardiac injuries. UCP2 protects against cellular dysfunction through reducing mitochondrial oxidative stress and modulation of mitochondrial function. In view of the different functions of UCP2 in various cell types that contribute to whole body homeostasis, cell type-specific modification of UCP2 expression may offer a better approach to help understanding how UCP2 governs mitochondrial function, reactive oxygen species production and transmembrane proton leak and how dysfunction of UCP2 participates in the development of cardiovascular diseases. This review article provided an update on the physiological regulation of UCP2 in the cardiovascular system, and also discussed the involvement of UCP2 deficiency and associated oxidative stress in the pathogenesis of several common cardiovascular diseases. Drugs targeting UCP2 expression and activity might serve another effective strategy to ameliorate cardiovascular dysfunction. However, more detailed mechanistic study will be needed to dissect the role of UCP2, the regulation of UCP2 expression, and the cellular responses to the changes of UCP2 expression in normal and stressed situations at different stages of cardiovascular diseases.

Dietary cholesterol intake and stroke risk: a meta-analysis

Background/Objectives

The association between dietary cholesterol and stroke risk has remained controversial over the past two decades. The aim of this meta-analysis was to assess the relationship between dietary cholesterol and stroke risk.

Results

Seven prospective studies including 269,777 non-overlapping individuals (4,604 strokes) were included. The combined RR of stroke for higher cholesterol intake (> 300 mg/day) was 0.98 (95% CI, 0.90–1.07), and the combined RR of stroke for higher cholesterol intake (> 300 mg/day) in females (age of ≥ 60 years or body mass index of ≥ 24 kg/m²) was 1.18 (95% CI, 1.02–1.36).

Materials and Methods

The PubMed, Medline, Embase, Web of Knowledge, and Google Scholar databases were searched. Relevant studies were identified by searching these online databases through September 2017. The relative risk (RR) and 95% confidence interval (CI) were used to investigate the strength of the association.

Conclusions

Higher cholesterol intake has no association with the overall stroke risk. Age and body mass index affect the relationship between dietary cholesterol intake and stroke risk. However, the association between higher dietary cholesterol and stroke risk in males remains unclear.

A differential expression of uncoupling protein-2 associates with renal damage in stroke-resistant spontaneously hypertensive rat/stroke-prone spontaneously hypertensive rat-derived stroke congenic lines

OBJECTIVES

Uncoupling protein-2 (UCP2), a mitochondrial anion transporter involved in mitochondrial uncoupling, limiting reactive oxygen species formation, is significantly downregulated in kidneys of high-salt-fed stroke-prone spontaneously hypertensive rat (SHRSP), where it associates with increased renal damage occurrence.

METHODS

We aimed at establishing whether UCP2 differential expression associates with renal damage in two stroke-resistant spontaneously hypertensive rat (SHRSR)/SHRSP-derived stroke congenic lines. For this purpose, SHRSR, SHRSP, and two reciprocal stroke congenic lines carrying the (D1Rat134-Mt1pa) segment of chromosome 1 were fed with Japanese style diet for 8 weeks. At 4, 6, and 8 weeks of Japanese diet, kidneys were removed and analyzed for UCP2 gene and protein expression [UCP2 maps within (D1Rat134-Mt1pa)]; nuclear factor kappa-light-chain-enhancer of activated B cells protein expression; oxidized total protein levels; mitochondrial function; gene expression of cubulin, megalin, and nephrin. At 6 and 8 weeks of Japanese diet, histological damage and percentage of high molecular weight urinary proteins excretion were assessed.

RESULTS

Introgression of UCP2 in the SHRSP configuration within the SHRSR genome led to UCP2 downregulation upon Japanese diet, as compared with the SHRSR, with significantly reduced ATP levels, increased rate of inflammation, oxidative stress, renal damage, and excretion of high molecular weight proteins. The opposite phenomena were observed in the reciprocal congenic line, compared with the SHRSP. In vitro, high-NaCl medium led to UCP2 downregulation, increased apoptosis/necrosis, and reduced viability in primary renal proximal tubular epithelial cells isolated from SHRSP. Exposure of the SHRSP/proximal tubular epithelial cells to recombinant UCP2 rescued the high-salt-dependent deleterious effects.

CONCLUSION

A differential UCP2 expression associates with different degree of renal damage upon Japanese diet in two SHRSR/SHRSP-derived stroke congenic lines through modulation of mitochondrial function, inflammation, and oxidative stress.

Protective effects of estrogen against cardiovascular disease mediated via oxidative stress in the brain

During their reproductive years women produce significant levels of estrogens, predominantly in the form of estradiol, that are thought to play an important role in cardioprotection. Mechanisms underlying this action include both estrogen-mediated changes in gene expression, and post-transcriptional activation of protein signaling cascades in the heart and in neural centers controlling cardiovascular function, in particular, in the brainstem. There, specific neurons, especially those of the bulbar region play an important role in the neuronal control of the cardiovascular system because they control the outflow of sympathetic activity and parasympathetic activity as well as the reception of chemical and mechanical signals. In the present review, we discuss how estrogens exert their cardioprotective effect in part by modulating the actions of internally generated products of cellular oxidation such as reactive oxygen species (ROS) in brain stem neurons. The significance of this review is in integrating the literature of oxidative damage in the brain with the literature of neuroprotection by estrogen in order to better understand both the benefits and limitations of using this hormone to prevent cardiovascular disease.

Uncoupling Protein 2: A Key Player and a Potential Therapeutic Target in Vascular Diseases

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane protein that belongs to the uncoupling protein family and plays an important role in lowering mitochondrial membrane potential and dissipating metabolic energy with prevention of oxidative stress accumulation. In the present article, we will review the evidence that UCP2, as a consequence of its roles within the mitochondria, represents a critical player in the predisposition to vascular disease development in both animal models and in humans, particularly in relation to obesity, diabetes, and hypertension. The deletion of the UCP2 gene contributes to atherosclerosis lesion development in the knockout mice, also showing significantly shorter lifespan. The UCP2 gene downregulation is a key determinant of higher predisposition to renal and cerebrovascular damage in an animal model of spontaneous hypertension and stroke. In contrast, UCP2 overexpression improves both hyperglycemia- and high-salt diet-induced endothelial dysfunction and ameliorates hypertensive target organ damage in SHRSP. Moreover, drugs (fenofibrate and sitagliptin) and several vegetable compounds (extracts from Brassicaceae, berberine, curcumin, and capsaicin) are able to induce UCP2 expression level and to exert beneficial effects on the occurrence of vascular damage. As a consequence, UCP2 becomes an interesting therapeutic target for the treatment of common human vascular diseases.

Endogenous Nampt upregulation is associated with diabetic nephropathy inflammatory-fibrosis through the NF-κB p65 and Sirt1 pathway; NMN alleviates diabetic nephropathy inflammatory-fibrosis by inhibiting endogenous Nampt

Nicotinamide phosphoribosyltransferase (Nampt) is a key enzyme in the nicotinamide adenine dinucleotide (NAD⁺) biosynthetic pathway. Exogenous extra cellular Nampt has been reported to increase the synthesis of pro-fibrotic molecules in various types of renal cells. However, the role of endogenous Namptenzymatic activity in diabetic renal cells, particularly those associated with inflammation and fibrosis through the nuclear factor (NF)-κB p65 and sirtuin 1 (Sirt1) pathway is still unknown. In the present study, a possible mechanism by which endogenous Nampt upregulation affects the expression of pro-inflammatory and pro-fibrotic cytokines in vivo and in vitro, is reported. The present results demonstrate that the expression of vimentin and fibronectin was directly implicated in endogenous Nampt upregulation. The expression levels of Poly(ADP-ribose) polymerase-1, NF-κB p65, forkhead box protein O1 and B-cell lymphoma 2-like protein 4 were also significantly increased at 96 h compared with control group (P<0.01) respectively in response to endogenous Nampt upregulation. Furthermore, the expression level of Sirt1 was significantly reduced (P<0.05), and the NAD and NADH levels, and the NAD/NADH ratio are significantly altered in STZ-induced diabetic rats (P<0.01). Treatment with FK866 and nicotinamide mononucleotide (NMN) led to downregulation of vimentin and fibronectin, respectively. These results suggest a novel role of Nampt as a pro-inflammatory cytokine of mesangial fibrotic signaling. The Nampt-NF-κB p65 and Sirt1 signaling pathway serves a pivotal role in affecting the expression of fibrosis factors in diabetic nephropathy (DN) glomerular fibrosis processing. It is also suggested that prevention of endogenous Nampt upregulation may be critical in the treatment of DN pro-inflammatory fibrosis and NMN is likely to be a potential pharmacological agent for the treatment of resistant DN nephritic fibrosis.

Reduced brain UCP2 expression mediated by microRNA-503 contributes to increased stroke susceptibility in the high-salt fed stroke-prone spontaneously hypertensive rat

UCP2 maps nearby the lod score peak of STR1-stroke QTL in the SHRSP rat strain. We explored the potential contribution of UCP2 to the high-salt diet (JD)-dependent increased stroke susceptibility of SHRSP. Male SHRSP, SHRSR, two reciprocal SHRSR/SHRSP-STR1/QTL stroke congenic lines received JD for 4 weeks to detect brain UCP2 gene/protein modulation as compared with regular diet (RD). Brains were also analyzed for NF-κB protein expression, oxidative stress level and UCP2-targeted microRNAs expression level. Next, based on knowledge that fenofibrate and Brassica Oleracea (BO) stimulate UCP2 expression through PPARα activation, we monitored stroke occurrence in SHRSP receiving JD plus fenofibrate versus vehicle, JD plus BO juice versus BO juice plus PPARα inhibitor. Brain UCP2 expression was markedly reduced by JD in SHRSP and in the (SHRsr.SHRsp-(D1Rat134-Mt1pa)) congenic line, whereas NF-κB expression and oxidative stress level increased. The opposite phenomenon was observed in the SHRSR and in the (SHRsp.SHRsr-(D1Rat134-Mt1pa)) reciprocal congenic line. Interestingly, the UCP2-targeted rno-microRNA-503 was significantly upregulated in SHRSP and decreased in SHRSR upon JD, with consistent changes in the two reciprocal congenic lines. Both fenofibrate and BO significantly decreased brain microRNA-503 level, upregulated UCP2 expression and protected SHRSP from stroke occurrence. In vitro overexpression of microRNA-503 in endothelial cells suppressed UCP2 expression and led to a significant increase of cell mortality with decreased cell viability. Brain UCP2 downregulation is a determinant of increased stroke predisposition in high-salt-fed SHRSP. In this context, UCP2 can be modulated by both pharmacological and nutraceutical agents. The microRNA-503 significantly contributes to mediate brain UCP2 downregulation in JD-fed SHRSP.

A Decrease of Brain MicroRNA-122 Level Is an Early Marker of Cerebrovascular Disease in the Stroke-Prone Spontaneously Hypertensive Rat

Based on preliminary evidence that highlights microRNA-122 as a contributing factor to stroke pathogenesis, we aimed at assessing its expression level, along with the presence of early signs of cerebrovascular disease, in the brain of stroke-prone spontaneously hypertensive rat (SHRSP), a suitable model of human disease that accelerates stroke occurrence under a high sodium/low potassium (Japanese-style) diet (JD). After one month of JD, before stroke occurrence, brain microRNA-122 level was significantly decreased in SHRSP as compared to the stroke-resistant SHR (SHRSR). At this time, levels of markers of oxidative stress and inflammation, as well as of endothelial integrity and function, apoptosis and necrosis were differently modulated in the brains of JD-fed SHRSP as compared to SHRSR, pointing to a significant activation of all deleterious mechanisms underlying subsequent stroke development in SHRSP. We also showed that miR-122 improved survival of rat endothelial cerebral cells upon stress stimuli (excess NaCl, hydrogen peroxide). Our data suggest that a decrease of brain microRNA-122 level is deleterious and can be considered as an early marker of stroke in the SHRSP. Understanding the mechanisms by which microRNA-122 protects vascular cells from stress stimuli may provide a useful approach to improve preventive and treatment strategies against stroke.

Developmental Sex Differences in the Metabolism of Cardiolipin in Mouse Cerebral Cortex Mitochondria

Cardiolipin (CL) is a mitochondrial-specific phospholipid. CL content and acyl chain composition are crucial for energy production. Given that estradiol induces CL synthesis in neurons, we aimed to assess CL metabolism in the cerebral cortex (CC) of male and female mice during early postnatal life, when sex steroids induce sex-dimorphic maturation of the brain. Despite the fact that total amount of CL was similar, its fatty acid composition differed between males and females at birth. In males, CL was more mature (lower saturation ratio) and the expression of the enzymes involved in synthetic and remodeling pathways was higher, compared to females. Importantly, the sex differences found in CL metabolism were due to the testosterone peak that male mice experience perinatally. These changes were associated with a higher expression of UCP-2 and its activators in the CC of males. Overall, our results suggest that the perinatal testosterone surge in male mice regulates CL biosynthesis and remodeling in the CC, inducing a sex-dimorphic fatty acid composition. In male's CC, CL is more susceptible to peroxidation, likely explaining the testosterone-dependent induction of neuroprotective molecules such as UCP-2. These differences may account for the sex-dependent mitochondrial susceptibility after perinatal hypoxia/ischemia.

Mitochondrial Dysfunction Contributes to Hypertensive Target Organ Damage: Lessons from an Animal Model of Human Disease

Mechanisms underlying hypertensive target organ damage (TOD) are not completely understood. The pathophysiological role of mitochondrial oxidative stress, resulting from mitochondrial dysfunction, in development of TOD is unclear. The stroke-prone spontaneously hypertensive rat (SHRSP) is a suitable model of human hypertension and of its vascular consequences. Pathogenesis of TOD in SHRSP is multifactorial, being determined by high blood pressure levels, high salt/low potassium diet, and genetic factors. Accumulating evidence points to a key role of mitochondrial dysfunction in increased susceptibility to TOD development of SHRSP. Mitochondrial abnormalities were described in both heart and brain of SHRSP. Pharmacological compounds able to protect mitochondrial function exerted a significant protective effect on TOD development, independently of blood pressure levels. Through our research efforts, we discovered that two genes encoding mitochondrial proteins, one (Ndufc2) involved in OXPHOS complex I assembly and activity and the second one (UCP2) involved in clearance of mitochondrial ROS, are responsible, when dysregulated, for vascular damage in SHRSP. The suitability of SHRSP as a model of human disease represents a promising background for future translation of the experimental findings to human hypertension. Novel therapeutic strategies toward mitochondrial molecular targets may become a valuable tool for prevention and treatment of TOD in human hypertension.