The role of hexokinase in cardioprotection - mechanism and potential for translation

Unveiling the proteome of the fasting heart: Insights into HIF-1 pathway regulation

Fasting is a common dietary intervention known for its protective effects against metabolic and cardiovascular diseases. While its effects are mostly systemic, understanding tissue-specific changes in the heart is crucial for the identification of the mechanisms underlying fasting-induced cardioprotection. In this study, we performed a proteomic analysis of the fasting heart and attempted to clarify the molecular basis of fasting-induced cardioprotection. Our investigation identified a total of 4,652 proteins, with 127 exhibiting downregulation and 118 showing upregulation after fasting. Annotation analysis highlighted significant changes in processes such as lipid metabolism, the peroxisome pathway, and reactive oxygen species metabolism. Notably, the HIF-1 signaling pathway emerged as one of the focal points, with various HIF-1 targets exhibiting differential responses to fasting. Further experiments demonstrated downregulation of HIF-1α at both transcript and protein levels. Intriguingly, while gene expression of Egln3 decreased, its protein product PHD3 remained unaffected by fasting. The unchanged levels of pro-inflammatory cytokines indicated that the observed reduction in Hif1a expression did not stem from a decrease in basal inflammation. These findings underscore the complex regulation of the well-established cardioprotective HIF-1 signaling within the heart during 3-day fasting.

Skeletal muscle mitochondrial dysfunction mediated by Pseudomonas aeruginosa quorum-sensing transcription factor MvfR: reversing effects with anti-MvfR and mitochondrial-targeted compounds

Sepsis and chronic infections with Pseudomonas aeruginosa, a leading "ESKAPE" bacterial pathogen, are associated with increased morbidity and mortality and skeletal muscle atrophy. The actions of this pathogen on skeletal muscle remain poorly understood. In skeletal muscle, mitochondria serve as a crucial energy source, which may be perturbed by infection. Here, using the well-established backburn and infection model of murine P. aeruginosa infection, we deciphered the systemic impact of the quorum-sensing transcription factor MvfR (multiple virulence factor regulator) by interrogating, 5 days post-infection, its effect on mitochondrial-related functions in the gastrocnemius skeletal muscle and the outcome of the pharmacological inhibition of MvfR function and that of the mitochondrial-targeted peptide, Szeto-Schiller 31 (SS-31). Our findings show that the MvfR perturbs adenosine triphosphate generation, oxidative phosphorylation, and antioxidant response, elevates the production of reactive oxygen species, and promotes oxidative damage of mitochondrial DNA in the gastrocnemius muscle of infected mice. These impairments in mitochondrial-related functions were corroborated by the alteration of key mitochondrial proteins involved in electron transport, mitochondrial biogenesis, dynamics and quality control, and mitochondrial uncoupling. Pharmacological inhibition of MvfR using the potent anti-MvfR lead, D88, we developed, or the mitochondrial-targeted peptide SS-31 rescued the MvfR-mediated alterations observed in mice infected with the wild-type strain PA14. Our study provides insights into the actions of MvfR in orchestrating mitochondrial dysfunction in the skeletal murine muscle, and it presents novel therapeutic approaches for optimizing clinical outcomes in affected patients.

IMPORTANCE

Skeletal muscle, pivotal for many functions in the human body, including breathing and protecting internal organs, contains abundant mitochondria essential for maintaining cellular homeostasis during infection. The effect of Pseudomonas aeruginosa (PA) infections on skeletal muscle remains poorly understood. Our study delves into the role of a central quorum-sensing transcription factor, multiple virulence factor regulator (MvfR), that controls the expression of multiple acute and chronic virulence functions that contribute to the pathogenicity of PA. The significance of our study lies in the role of MvfR in the metabolic perturbances linked to mitochondrial functions in skeletal muscle and the effectiveness of the novel MvfR inhibitor and the mitochondrial-targeted peptide SS-31 in alleviating the mitochondrial disturbances caused by PA in skeletal muscle. Inhibiting MvfR or interfering with its effects can be a potential therapeutic strategy to curb PA virulence.

Skeletal Muscle Mitochondrial Dysfunction Mediated by Pseudomonas aeruginosa Quorum Sensing Transcription Factor MvfR: Reversing Effects with Anti-MvfR and Mitochondrial-Targeted Compounds

Sepsis and chronic infections with Pseudomonas aeruginosa, a leading "ESKAPE" bacterial pathogen, are associated with increased morbidity and mortality and skeletal muscle atrophy. The actions of this pathogen on skeletal muscle remain poorly understood. In skeletal muscle, mitochondria serve as a crucial energy source, which may be perturbed by infection. Here, using the well-established backburn and infection model of murine P. aeruginosa infection, we deciphered the systemic impact of the quorum sensing (QS) transcription factor MvfR by interrogating five days post-infection its effect on mitochondrial-related functions in the gastrocnemius skeletal muscle and the outcome of the pharmacological inhibition of MvfR function and that of the mitochondrial-targeted peptide, Szeto-Schiller 31 (SS-31). Our findings show that the MvfR perturbs ATP generation, oxidative phosphorylation (OXPHOS), and antioxidant response, elevates the production of reactive oxygen species, and promotes oxidative damage of mitochondrial DNA in the gastrocnemius muscle of infected mice. These impairments in mitochondrial-related functions were corroborated by the alteration of key mitochondrial proteins involved in electron transport, mitochondrial biogenesis, dynamics and quality control, and mitochondrial uncoupling. Pharmacological inhibition of MvfR using the potent anti-MvfR lead, D88, we developed, or the mitochondrial-targeted peptide SS-31 rescued the MvfR- mediated alterations observed in mice infected with the wild-type strain PA14. Our study provides insights into the actions of MvfR in orchestrating mitochondrial dysfunction in the skeletal murine muscle, and it presents novel therapeutic approaches for optimizing clinical outcomes in affected patients.

Mitochondrial Kinase Signaling for Cardioprotection

Myocardial ischemia/reperfusion injury is reduced by cardioprotective adaptations such as local or remote ischemic conditioning. The cardioprotective stimuli activate signaling cascades, which converge on mitochondria and maintain the function of the organelles, which is critical for cell survival. The signaling cascades include not only extracellular molecules that activate sarcolemmal receptor-dependent or -independent protein kinases that signal at the plasma membrane or in the cytosol, but also involve kinases, which are located to or within mitochondria, phosphorylate mitochondrial target proteins, and thereby modify, e.g., respiration, the generation of reactive oxygen species, calcium handling, mitochondrial dynamics, mitophagy, or apoptosis. In the present review, we give a personal and opinionated overview of selected protein kinases, localized to/within myocardial mitochondria, and summarize the available data on their role in myocardial ischemia/reperfusion injury and protection from it. We highlight the regulation of mitochondrial function by these mitochondrial protein kinases.

The role of glycolytic metabolic pathways in cardiovascular disease and potential therapeutic approaches

Cardiovascular disease (CVD) is a major threat to human health, accounting for 46% of non-communicable disease deaths. Glycolysis is a conserved and rigorous biological process that breaks down glucose into pyruvate, and its primary function is to provide the body with the energy and intermediate products needed for life activities. The non-glycolytic actions of enzymes associated with the glycolytic pathway have long been found to be associated with the development of CVD, typically exemplified by metabolic remodeling in heart failure, which is a condition in which the heart exhibits a rapid adaptive response to hypoxic and hypoxic conditions, occurring early in the course of heart failure. It is mainly characterized by a decrease in oxidative phosphorylation and a rise in the glycolytic pathway, and the rise in glycolysis is considered a hallmark of metabolic remodeling. In addition to this, the glycolytic metabolic pathway is the main source of energy for cardiomyocytes during ischemia-reperfusion. Not only that, the auxiliary pathways of glycolysis, such as the polyol pathway, hexosamine pathway, and pentose phosphate pathway, are also closely related to CVD. Therefore, targeting glycolysis is very attractive for therapeutic intervention in CVD. However, the relationship between glycolytic pathway and CVD is very complex, and some preclinical studies have confirmed that targeting glycolysis does have a certain degree of efficacy, but its specific role in the development of CVD has yet to be explored. This article aims to summarize the current knowledge regarding the glycolytic pathway and its key enzymes (including hexokinase (HK), phosphoglucose isomerase (PGI), phosphofructokinase-1 (PFK1), aldolase (Aldolase), phosphoglycerate metatase (PGAM), enolase (ENO) pyruvate kinase (PKM) lactate dehydrogenase (LDH)) for their role in cardiovascular diseases (e.g., heart failure, myocardial infarction, atherosclerosis) and possible emerging therapeutic targets.

Continuous short-term acclimation to moderate cold elicits cardioprotection in rats, and alters β-adrenergic signaling and immune status

Moderate cold acclimation (MCA) is a non-invasive intervention mitigating effects of various pathological conditions including myocardial infarction. We aim to determine the shortest cardioprotective regimen of MCA and the response of β1/2/3-adrenoceptors (β-AR), its downstream signaling, and inflammatory status, which play a role in cell-survival during myocardial infarction. Adult male Wistar rats were acclimated (9 °C, 1-3-10 days). Infarct size, echocardiography, western blotting, ELISA, mitochondrial respirometry, receptor binding assay, and quantitative immunofluorescence microscopy were carried out on left ventricular myocardium and brown adipose tissue (BAT). MultiPlex analysis of cytokines and chemokines in serum was accomplished. We found that short-term MCA reduced myocardial infarction, improved resistance of mitochondria to Ca2+-overload, and downregulated β1-ARs. The β2-ARs/protein kinase B/Akt were attenuated while β3-ARs translocated on the T-tubular system suggesting its activation. Protein kinase G (PKG) translocated to sarcoplasmic reticulum and phosphorylation of AMPKThr172 increased after 10 days. Principal component analysis revealed a significant shift in cytokine/chemokine serum levels on day 10 of acclimation, which corresponds to maturation of BAT. In conclusion, short-term MCA increases heart resilience to ischemia without any negative side effects such as hypertension or hypertrophy. Cold-elicited cardioprotection is accompanied by β1/2-AR desensitization, activation of the β3-AR/PKG/AMPK pathways, and an immunomodulatory effect.

Identity, structure, and function of the mitochondrial permeability transition pore: controversies, consensus, recent advances, and future directions

The mitochondrial permeability transition (mPT) describes a Ca2+-dependent and cyclophilin D (CypD)-facilitated increase of inner mitochondrial membrane permeability that allows diffusion of molecules up to 1.5 kDa in size. It is mediated by a non-selective channel, the mitochondrial permeability transition pore (mPTP). Sustained mPTP opening causes mitochondrial swelling, which ruptures the outer mitochondrial membrane leading to subsequent apoptotic and necrotic cell death, and is implicated in a range of pathologies. However, transient mPTP opening at various sub-conductance states may contribute several physiological roles such as alterations in mitochondrial bioenergetics and rapid Ca2+ efflux. Since its discovery decades ago, intensive efforts have been made to identify the exact pore-forming structure of the mPT. Both the adenine nucleotide translocase (ANT) and, more recently, the mitochondrial F1FO (F)-ATP synthase dimers, monomers or c-subunit ring alone have been implicated. Here we share the insights of several key investigators with different perspectives who have pioneered mPT research. We critically assess proposed models for the molecular identity of the mPTP and the mechanisms underlying its opposing roles in the life and death of cells. We provide in-depth insights into current controversies, seeking to achieve a degree of consensus that will stimulate future innovative research into the nature and role of the mPTP.

Regulation of Autophagy via Carbohydrate and Lipid Metabolism in Cancer

Metabolic changes are an important component of tumor cell progression. Tumor cells adapt to environmental stresses via changes to carbohydrate and lipid metabolism. Autophagy, a physiological process in mammalian cells that digests damaged organelles and misfolded proteins via lysosomal degradation, is closely associated with metabolism in mammalian cells, acting as a meter of cellular ATP levels. In this review, we discuss the changes in glycolytic and lipid biosynthetic pathways in mammalian cells and their impact on carcinogenesis via the autophagy pathway. In addition, we discuss the impact of these metabolic pathways on autophagy in lung cancer.

Arsenic exposure elevated ROS promotes energy metabolic reprogramming with enhanced AKT-dependent HK2 expression

Exposure to inorganic or organic arsenic compounds continues to pose substantial public health concerns for hundreds of millions of people around the globe. Highly exposed individuals are susceptible to various illnesses, including impairments and cancers of the lung, liver, skin and bladder. Long-term exposure to low-dose arsenic has been identified to induce aerobic glycolysis, which contributes to cells aberrant proliferation. However, the mechanism underlying arsenic-induced aerobic glycolysis is still unclear. Here, mtDNA copy number is enhanced in arsenic-exposed populations and a positive correlation between serum HK2 and urinary total arsenic was observed in the individuals with high urine arsenic (≥ 0.032 mg/L). In a rat model of trivalent arsenic (iAs³⁺) exposure, the levels of HK2, NDUFA9 and NDUFB8 were increased in the rats treated with iAs³⁺ daily by gavage for 12 weeks than those in the control rats. Subsequently, in a low-dose arsenic exposure cell model we found that 0.2 μmol/L iAs³⁺ induced aerobic glycolysis to promote L-02 cells proliferation and inhibit apoptosis, in which HK2 played an important role. Further studies showed accumulated ROS determined the metabolic reprogramming via activating AKT and then increasing HK2 expression. On the one hand, activated AKT induced aerobic glycolysis by increasing HK2 to promote L-02 cells viability and DNA synthesis; on the other hand, phosphorylated AKT induced HK2 mitochondrial outer-membrane location with VDAC1 to inhibit apoptosis. Taken together, our results indicated that ROS induced by low-dose arsenic exposure determined energy metabolic reprogramming and acted a critical regulator for AKT-dependent HK2 expression and aerobic glycolysis.

Hypothermia Prevents Cardiac Dysfunction during Acute Ischemia Reperfusion by Maintaining Mitochondrial Bioenergetics and by Promoting Hexokinase II Binding to Mitochondria

Background

Hypothermia (H), cardioplegia (CP), and both combined (HCP) are known to be protective against myocardial ischemia reperfusion (IR) injury. Mitochondria have molecular signaling mechanisms that are associated with both cell survival and cell death. In this study, we investigated the dynamic changes in proapoptotic and prosurvival signaling pathways mediating H, CP, or HCP-induced protection of mitochondrial function after acute myocardial IR injury.

Methods

Rats were divided into five groups. Each group consists of 3 subgroups based on a specific reperfusion time (5, 20, or 60 min) after a 25-min global ischemia. The time control (TC) groups were not subjected to IR but were perfused with 37 °C Krebs-Ringer's (KR) buffer, containing 4.5 mM K⁺, in a specific perfusion protocol that corresponded with the duration of each IR protocol. The IR group (control) was perfused for 20 min with KR, followed by 25-min global ischemia, and then KR reperfusion for 5, 20, or 60 min. The treatment groups were exposed to 17 °C H, 37 °C CP (16 mM K⁺), or HCP (17 °C + CP) for 5 min before ischemia and for 2 min on reperfusion before switching to 37 °C KR perfusion for the remainder of each of the reperfusion times. Cardiac function and mitochondrial redox state (NADH/FAD) were monitored online in the ex vivo hearts before, during, and after ischemia. Mitochondria were isolated at the end of each specified reperfusion time, and changes in O₂ consumption, membrane potential (ΔΨ_m), and Ca²⁺ retention capacity (CRC) were assessed using complex I and complex II substrates. In another set of hearts, mitochondrial and cytosolic fractions were isolated after a specified reperfusion time to conduct western blot assays to determine hexokinase II (HKII) and Bax binding/translocation to mitochondria, cytosolic pAkt levels, and cytochrome c (Cyto-c) release into the cytosol.

Results

H and HCP were more protective of mitochondrial integrity and, concomitantly, cardiac function than CP alone; H and HCP improved post-ischemic cardiac function by (1) maintaining mitochondrial bioenergetics, (2) maintaining HKII binding to mitochondria with an increase in pAkt levels, (3) increasing CRC, and (4) decreasing Cyto-c release during reperfusion. Bax translocation/binding to mitochondria was unaffected by any treatment, regardless of cardiac functional recovery.

Conclusions

Hypothermia preserved mitochondrial function and cardiac function, in part, by maintaining mitochondrial bioenergetics, by retaining HKII binding to mitochondria via upstream pAkt, and by reducing Cyto-c release independently of Bax binding to mitochondria.

The insulin receptor family in the heart: new light on old insights

Insulin was discovered over 100 years ago. Whilst the first half century defined many of the physiological effects of insulin, the second emphasised the mechanisms by which it elicits these effects, implicating a vast array of G proteins and their regulators, lipid and protein kinases and counteracting phosphatases, and more. Potential growth-promoting and protective effects of insulin on the heart emerged from studies of carbohydrate metabolism in the 1960s, but the insulin receptors (and the related receptor for insulin-like growth factors 1 and 2) were not defined until the 1980s. A related third receptor, the insulin receptor-related receptor remained an orphan receptor for many years until it was identified as an alkali-sensor. The mechanisms by which these receptors and the plethora of downstream signalling molecules confer cardioprotection remain elusive. Here, we review important aspects of the effects of the three insulin receptor family members in the heart. Metabolic studies are set in the context of what is now known of insulin receptor family signalling and the role of protein kinase B (PKB or Akt), and the relationship between this and cardiomyocyte survival versus death is discussed. PKB/Akt phosphorylates numerous substrates with potential for cardioprotection in the contractile cardiomyocytes and cardiac non-myocytes. Our overall conclusion is that the effects of insulin on glucose metabolism that were initially identified remain highly pertinent in managing cardiomyocyte energetics and preservation of function. This alone provides a high level of cardioprotection in the face of pathophysiological stressors such as ischaemia and myocardial infarction.

Hexokinase 1 cellular localization regulates the metabolic fate of glucose

The product of hexokinase (HK) enzymes, glucose-6-phosphate, can be metabolized through glycolysis or directed to alternative metabolic routes, such as the pentose phosphate pathway (PPP) to generate anabolic intermediates. HK1 contains an N-terminal mitochondrial binding domain (MBD), but its physiologic significance remains unclear. To elucidate the effect of HK1 mitochondrial dissociation on cellular metabolism, we generated mice lacking the HK1 MBD (ΔE1HK1). These mice produced a hyper-inflammatory response when challenged with lipopolysaccharide. Additionally, there was decreased glucose flux below the level of GAPDH and increased upstream flux through the PPP. The glycolytic block below GAPDH is mediated by the binding of cytosolic HK1 with S100A8/A9, resulting in GAPDH nitrosylation through iNOS. Additionally, human and mouse macrophages from conditions of low-grade inflammation, such as aging and diabetes, displayed increased cytosolic HK1 and reduced GAPDH activity. Our data indicate that HK1 mitochondrial binding alters glucose metabolism through regulation of GAPDH.

Mitochondrial proteins that connected with calcium: do their pathways changes in PAH?

Calcium can be regulated by mitochondria and also plays a significant role in mitochondrial pathways. Recent study showed mitochondrial protein changes in the right ventricle in pulmonary arterial hypertension, which affects calcium network at the same time. The specific objective of this study is to assess the pathway of calcium transport by permeable pore in mitochondria and investigate the regulation of mitochondrial proteins in order to find the connection between mitochondrial proteins and right ventricular dysfunction in PAH (pulmonary arterial hypertension). This literature-based review came out by searching articles in Pubmed and Science Direct. And the related flow chart is expressed by the form of PRISMA. There is a network between mitochondria and calcium through the transport chain called mitochondria permeability transition pore (MPTP) as well as different kinds of proteins that are located in the mitochondria. MPTP is a kind of mitochondria pore and can have conformational changes after protein phosphorylation or reaction between mitochondrial proteins to activate the apoptosis capase cascade process in cell death. In addition, MPTP can be activated by other mitochondrial protein like signal transducer activator of transcription3 (STAT3) to activate cytochrome c in pro-apoptosis to initiate cell death at the same time. The most obvious finding from this study is the role of calcium regulation in therapeutic treatment in PAH patients, which suggest an imaginable role for calcium transporter like mitochondria calcium uniporter (MCU) promoting bio-markers in cardiovascular disease resulting from mitochondrial dysfunction. In addition, right ventricle is a target of PAH in which mitochondria in RV would play an essential role in pathways such as ATP production via mitochondria metabolism.

Mitochondrial Drp1 recognizes and induces excessive mPTP opening after hypoxia through BAX-PiC and LRRK2-HK2

Mitochondrial mass imbalance is one of the key causes of cardiovascular dysfunction after hypoxia. The activation of dynamin-related protein 1 (Drp1), as well as its mitochondrial translocation, play important roles in the changes of both mitochondrial morphology and mitochondrial functions after hypoxia. However, in addition to mediating mitochondrial fission, whether Drp1 has other regulatory roles in mitochondrial homeostasis after mitochondrial translocation is unknown. In this study, we performed a series of interaction and colocalization assays and found that, after mitochondrial translocation, Drp1 may promote the excessive opening of the mitochondrial permeability transition pore (mPTP) after hypoxia. Firstly, mitochondrial Drp1 maximumly recognizes mPTP channels by binding Bcl-2-associated X protein (BAX) and a phosphate carrier protein (PiC) in the mPTP. Then, leucine-rich repeat serine/threonine-protein kinase 2 (LRRK2) is recruited, whose kinase activity is inhibited by direct binding with mitochondrial Drp1 after hypoxia. Subsequently, the mPTP-related protein hexokinase 2 (HK2) is inactivated at Thr-473 and dissociates from the mitochondrial membrane, ultimately causing structural disruption and overopening of mPTP, which aggravates mitochondrial and cellular dysfunction after hypoxia. Thus, our study interprets the dual direct regulation of mitochondrial Drp1 on mitochondrial morphology and functions after hypoxia and proposes a new mitochondrial fission-independent mechanism for the role of Drp1 after its translocation in hypoxic injury.

Cardiac expression and location of hexokinase changes in a mouse model of pure creatine deficiency

Creatine kinase (CK) is considered the main phosphotransfer system in the heart, important for overcoming diffusion restrictions and regulating mitochondrial respiration. It is substrate limited in creatine-deficient mice lacking l-arginine:glycine amidinotransferase (AGAT) or guanidinoacetate N-methyltranferase (GAMT). Our aim was to determine the expression, activity, and mitochondrial coupling of hexokinase (HK) and adenylate kinase (AK), as these represent alternative energy transfer systems. In permeabilized cardiomyocytes, we assessed how much endogenous ADP generated by HK, AK, or CK stimulated mitochondrial respiration and how much was channeled to mitochondria. In whole heart homogenates, and cytosolic and mitochondrial fractions, we measured the activities of AK, CK, and HK. Lastly, we assessed the expression of the major HK, AK, and CK isoforms. Overall, respiration stimulated by HK, AK, and CK was ∼25, 90, and 80%, respectively, of the maximal respiration rate, and ∼20, 0, and 25%, respectively, was channeled to the mitochondria. The activity, distribution, and expression of HK, AK, and CK did not change in GAMT knockout (KO) mice. In AGAT KO mice, we found no changes in AK, but we found a higher HK activity in the mitochondrial fraction, greater expression of HK I, but a lower stimulation of respiration by HK. Our findings suggest that mouse hearts depend less on phosphotransfer systems to facilitate ADP flux across the mitochondrial membrane. In AGAT KO mice, which are a model of pure creatine deficiency, the changes in HK may reflect changes in metabolism as well as influence mitochondrial regulation and reactive oxygen species production.NEW & NOTEWORTHY In creatine-deficient AGAT-/- and GAMT-/- mice, the myocardial creatine kinase system is substrate limited. It is unknown whether subcellular localization and mitochondrial ADP channeling by hexokinase and adenylate kinase may compensate as alternative phosphotransfer systems. Our results show no changes in adenylate kinase, which is the main alternative to creatine kinase in heart. However, we found increased expression and activity of hexokinase I in AGAT-/- cardiomyocytes. This could affect mitochondrial regulation and reactive oxygen species production.

Knockout of VDAC1 in H9c2 Cells Promotes Oxidative Stress-Induced Cell Apoptosis through Decreased Mitochondrial Hexokinase II Binding and Enhanced Glycolytic Stress

Background/Aims:

The role of VDAC1, the most abundant mitochondrial outer membrane protein, in cell death depends on cell types and stimuli. Both silencing and upregulation of VDAC1 in various type of cancer cell lines can stimulate apoptosis. In contrast, in mouse embryonic stem (MES) cells and mouse embryonic fibroblasts (MEFs), the roles of VDAC1 knockout (VDAC1^−/−) in apoptotic cell death are contradictory. The contribution and underlying mechanism of VDAC1^−/− in oxidative stress-induced cell death in cardiac cells has not been established. We hypothesized that VDAC1 is an essential regulator of oxidative stress-induced cell death in H9c2 cells.

Methods:

We knocked out VDAC1 in this rat cardiomyoblast cell line with CRISPR-Cas9 genome editing technique to produce VDAC1^−/− H9c2 cells, and determined if VDAC1 is critical in promoting cell death via oxidative stress induced by tert-butylhydroper-oxide (tBHP), an organic peroxide, or rotenone (ROT), an inhibitor of mitochondrial complex I by measuring cell viability with MTT assay, cell death with TUNEL stain and LDH release. The mitochondrial and glycolytic stress were examined by measuring O₂ consumption rate (OCR) and extracellular acidification rate (ECAR) with a Seahorse XFp analyzer.

Results:

We found that under control conditions, VDAC1^−/− did not affect H9c2 cell proliferation or mitochondrial respiration. However, compared to the wildtype (WT) cells, exposure to either tBHP or ROT enhanced the production of ROS, ECAR, and the proton (H⁺) production rate (PPR) from glycolysis, as well as promoted apoptotic cell death in VDAC1^−/− H9c2 cells. VDAC1^−/− H9c2 cells also exhibited markedly reduced mitochondria-bound hexokinase II (HKII) and Bax. Restoration of VDAC1 in VDAC1^−/− H9c2 cells reinstated mitochondria-bound HKII and concomitantly decreased tBHP and ROT-induced ROS production and cell death. Interestingly, mitochondrial respiration remained the same after tBHP treatment in VDAC1^−/− and WT H9c2 cells.

Conclusion:

Our results suggest that VDAC1^−/− in H9c2 cells enhances oxidative stress-mediated cell apoptosis that is directly linked to the reduction of mitochondria-bound HKII and concomitantly associated with enhanced ROS production, ECAR, and PPR.

The Future of Direct Cardiac Reprogramming: Any GMT Cocktail Variety?

Direct cardiac reprogramming has emerged as a novel therapeutic approach to treat and regenerate injured hearts through the direct conversion of fibroblasts into cardiac cells. Most studies have focused on the reprogramming of fibroblasts into induced cardiomyocytes (iCMs). The first study in which this technology was described, showed that at least a combination of three transcription factors, GATA4, MEF2C and TBX5 (GMT cocktail), was required for the reprogramming into iCMs in vitro using mouse cells. However, this was later demonstrated to be insufficient for the reprogramming of human cells and additional factors were required. Thereafter, most studies have focused on implementing reprogramming efficiency and obtaining fully reprogrammed and functional iCMs, by the incorporation of other transcription factors, microRNAs or small molecules to the original GMT cocktail. In this respect, great advances have been made in recent years. However, there is still no consensus on which of these GMT-based varieties is best, and robust and highly reproducible protocols are still urgently required, especially in the case of human cells. On the other hand, apart from CMs, other cells such as endothelial and smooth muscle cells to form new blood vessels will be fundamental for the correct reconstruction of damaged cardiac tissue. With this aim, several studies have centered on the direct reprogramming of fibroblasts into induced cardiac progenitor cells (iCPCs) able to give rise to all myocardial cell lineages. Especially interesting are reports in which multipotent and highly expandable mouse iCPCs have been obtained, suggesting that clinically relevant amounts of these cells could be created. However, as of yet, this has not been achieved with human iCPCs, and exactly what stage of maturity is appropriate for a cell therapy product remains an open question. Nonetheless, the major concern in regenerative medicine is the poor retention, survival, and engraftment of transplanted cells in the cardiac tissue. To circumvent this issue, several cell pre-conditioning approaches are currently being explored. As an alternative to cell injection, in vivo reprogramming may face fewer barriers for its translation to the clinic. This approach has achieved better results in terms of efficiency and iCMs maturity in mouse models, indicating that the heart environment can favor this process. In this context, in recent years some studies have focused on the development of safer delivery systems such as Sendai virus, Adenovirus, chemical cocktails or nanoparticles. This article provides an in-depth review of the in vitro and in vivo cardiac reprograming technology used in mouse and human cells to obtain iCMs and iCPCs, and discusses what challenges still lie ahead and what hurdles are to be overcome before results from this field can be transferred to the clinical settings.

Melatonin as a protective agent in cardiac ischemia-reperfusion injury: Vision/Illusion?

Melatonin, an emphatic endogenous molecule exerts protective effects either via activation of G-protein coupled receptors (Melatonin receptors, MTR 1-3), tumor necrosis factor receptor (TNFR), toll like receptors (TLRS), nuclear receptors (NRS) or by directly scavenging the free radicals. MTRs are extensively expressed in the heart as well as in the coronary vasculature. Accumulating evidences have indicated the existence of a strong correlation between reduction in the circulating level of melatonin and precipitation of heart attack. Apparently, melatonin exhibits cardioprotective effects via modulating inextricably interlinked pathways including modulation of mitochondrial metabolism, mitochondrial permeability transition pore formation, nitric oxide release, autophagy, generation of inflammatory cytokines, regulation of calcium transporters, reactive oxygen species, glycosaminoglycans, collagen accumulation, and regulation of apoptosis. Convincingly, this review shall describe the various signaling pathways involved in salvaging the heart against ischemia-reperfusion injury.

Hexokinase II dissociation alone cannot account for changes in heart mitochondrial function, morphology and sensitivity to permeability transition pore opening following ischemia

We previously demonstrated that hexokinase II (HK2) dissociation from mitochondria during cardiac ischemia correlates with cytochrome c (cyt-c) loss, oxidative stress and subsequent reperfusion injury. However, whether HK2 release is the primary signal mediating this ischemia-induced mitochondrial dysfunction was not established. To investigate this, we studied the effects of dissociating HK2 from isolated heart mitochondria. Mitochondria isolated from Langendorff-perfused rat hearts before and after 30 min global ischemia ± ischemic preconditioning (IPC) were subject to in vitro dissociation of HK2 by incubation with glucose-6-phosphate at pH 6.3. Prior HK2 dissociation from pre- or end-ischemic heart mitochondria had no effect on their cyt-c release, respiration (± ADP) or mitochondrial permeability transition pore (mPTP) opening. Inner mitochondrial membrane morphology was assessed indirectly by monitoring changes in light scattering (LS) and confirmed by transmission electron microscopy. Although no major ultrastructure differences were detected between pre- and end-ischemia mitochondria, the amplitude of changes in LS was reduced in the latter. This was prevented by IPC but not mimicked in vitro by HK2 dissociation. We also observed more Drp1, a mitochondrial fission protein, in end-ischemia mitochondria. IPC failed to prevent this increase but did decrease mitochondrial-associated dynamin 2. In vitro HK2 dissociation alone cannot replicate ischemia-induced effects on mitochondrial function implying that in vivo dissociation of HK2 modulates end-ischemia mitochondrial function indirectly perhaps involving interaction with mitochondrial fission proteins. The resulting changes in mitochondrial morphology and cristae structure would destabilize outer / inner membrane interactions, increase cyt-c release and enhance mPTP sensitivity to [Ca2+].

Regulation of the mitochondrial permeability transition pore and its effects on aging

Aging is an evolutionarily conserved process and is tightly connected to mitochondria. To uncover the aging molecular mechanisms related to mitochondria, different organisms have been extensively used as model systems. Among these, the budding yeast Saccharomyces cerevisiae has been reported multiple times as a model of choice when studying cellular aging. In particular, yeast provides a quick and trustworthy system to identify shared aging genes and pathway patterns. In this viewpoint on aging and mitochondria, I will focus on the mitochondrial permeability transition pore (mPTP), which has been reported and proposed as a main player in cellular aging. I will make several parallelisms with yeast to highlight how this unicellular organism can be used as a guidance system to understand conserved cellular and molecular events in multicellular organisms such as humans. Overall, a thread connecting the preservation of mitochondrial functionality with the activity of the mPTP emerges in the regulation of cell survival and cell death, which in turn could potentially affect aging and aging-related diseases.

Delayed ischaemic contracture onset by empagliflozin associates with NHE1 inhibition and is dependent on insulin in isolated mouse hearts

AIMS

Sodium glucose cotransporter 2 (SGLT2) inhibitors have sodium-hydrogen exchanger (NHE) inhibition properties in isolated cardiomyocytes, but it is unknown whether these properties extend to the intact heart during ischaemia-reperfusion (IR) conditions. NHE inhibitors as Cariporide delay time to onset of contracture (TOC) during ischaemia and reduce IR injury. We hypothesized that, in the ex vivo heart, Empagliflozin (Empa) mimics Cariporide during IR by delaying TOC and reducing IR injury. To facilitate translation to in vivo conditions with insulin present, effects were examined in the absence and presence of insulin.

METHODS AND RESULTS

Isolated C57Bl/6NCrl mouse hearts were subjected to 25 min I and 120 min R without and with 50 mU/L insulin. Without insulin, Empa and Cari delayed TOC by 100 and 129 s, respectively, yet only Cariporide reduced IR injury [infarct size (mean ± SEM in %) from 51 ± 6 to 34 ± 5]. Empa did not delay TOC in the presence of the NHE1 inhibitor Eniporide. Insulin perfusion increased tissue glycogen content at baseline (from 2 ± 2 µmol to 42 ± 1 µmol glycosyl units/g heart dry weight), amplified G6P and lactate accumulation at end-ischaemia, thereby decreased mtHKII and exacerbated IR injury. Under these conditions, Empa (1 µM) and Cariporide (10 µM) were without effect on TOC and IR injury. Empa and Cariporide both inhibited NHE activity, in isolated cardiomyocytes, independent of insulin.

CONCLUSIONS

In the absence of insulin, Empa and Cariporide strongly delayed the time to onset of contracture during ischaemia. In the presence of insulin, both Empa and Cari were without effect on IR, possibly because of severe ischaemic acidification. Insulin exacerbates IR injury through increased glycogen depletion during ischaemia and consequently mtHKII dissociation. The data suggest that also in the ex vivo intact heart Empa exerts direct cardiac effects by inhibiting NHE during ischaemia, but not during reperfusion.

Cardiac metabolism as a driver and therapeutic target of myocardial infarction

Reducing infarct size during a cardiac ischaemic-reperfusion episode is still of paramount importance, because the extension of myocardial necrosis is an important risk factor for developing heart failure. Cardiac ischaemia-reperfusion injury (IRI) is in principle a metabolic pathology as it is caused by abruptly halted metabolism during the ischaemic episode and exacerbated by sudden restart of specific metabolic pathways at reperfusion. It should therefore not come as a surprise that therapy directed at metabolic pathways can modulate IRI. Here, we summarize the current knowledge of important metabolic pathways as therapeutic targets to combat cardiac IRI. Activating metabolic pathways such as glycolysis (eg AMPK activators), glucose oxidation (activating pyruvate dehydrogenase complex), ketone oxidation (increasing ketone plasma levels), hexosamine biosynthesis pathway (O-GlcNAcylation; administration of glucosamine/glutamine) and deacetylation (activating sirtuins 1 or 3; administration of NAD+ -boosting compounds) all seem to hold promise to reduce acute IRI. In contrast, some metabolic pathways may offer protection through diminished activity. These pathways comprise the malate-aspartate shuttle (in need of novel specific reversible inhibitors), mitochondrial oxygen consumption, fatty acid oxidation (CD36 inhibitors, malonyl-CoA decarboxylase inhibitors) and mitochondrial succinate metabolism (malonate). Additionally, protecting the cristae structure of the mitochondria during IR, by maintaining the association of hexokinase II or creatine kinase with mitochondria, or inhibiting destabilization of FO F1 -ATPase dimers, prevents mitochondrial damage and thereby reduces cardiac IRI. Currently, the most promising and druggable metabolic therapy against cardiac IRI seems to be the singular or combined targeting of glycolysis, O-GlcNAcylation and metabolism of ketones, fatty acids and succinate.

Ageing, sex, and cardioprotection

Translation of cardioprotective interventions aimed at reducing myocardial injury during ischaemia-reperfusion from experimental studies to clinical practice is an important yet unmet need in cardiovascular medicine. One particular challenge facing translation is the existence of demographic and clinical factors that influence the pathophysiology of ischaemia-reperfusion injury of the heart and the effects of treatments aimed at preventing it. Among these factors, age and sex are prominent and have a recognised role in the susceptibility and outcome of ischaemic heart disease. Remarkably, some of the most powerful cardioprotective strategies proven to be effective in young animals become ineffective during ageing. This article reviews the mechanisms and implications of the modulatory effects of ageing and sex on myocardial ischaemia-reperfusion injury and their potential effects on cardioprotective interventions. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Programmed necrosis in cardiomyocytes: mitochondria, death receptors and beyond

Excessive death of cardiac myocytes leads to many cardiac diseases, including myocardial infarction, arrhythmia, heart failure and sudden cardiac death. For the last several decades, most work on cell death has focused on apoptosis, which is generally considered as the only form of regulated cell death, whereas necrosis has been regarded to be an unregulated process. Recent findings reveal that necrosis also occurs in a regulated manner and that it is closely related to the physiology and pathophysiology of many organs, including the heart. The recognition of necrosis as a regulated process mandates a re-examination of cell death in the heart together with the mechanisms and therapy of cardiac diseases. In this study, we summarize the regulatory mechanisms of the programmed necrosis of cardiomyocytes, that is, the intrinsic (mitochondrial) and extrinsic (death receptor) pathways. Furthermore, the role of this programmed necrosis in various heart diseases is also delineated. Finally, we describe the currently known pharmacological inhibitors of several of the key regulatory molecules of regulated cell necrosis and the opportunities for their therapeutic use in cardiac disease. We intend to systemically summarize the recent progresses in the regulation and pathological significance of programmed cardiomyocyte necrosis along with its potential therapeutic applications to cardiac diseases. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Rapid radiochemical filter paper assay for determination of hexokinase activity and affinity for glucose-6-phosphate

Glucose phosphorylation by hexokinase (HK) is a rate-limiting step in glucose metabolism. Regulation of HK includes feedback inhibition by its product glucose-6-phosphate (G6P) and mitochondria binding. HK affinity for G6P is difficult to measure because its natural product (G6P) inhibits enzyme activity. HK phosphorylates several hexoses, and we have taken advantage of the fact that 2-deoxyglucose (2-DG)-6-phosphate does not inhibit HK activity. By this, we have developed a new method for rapid radiochemical analysis of HK activity with 2-DG as a substrate, which allows control of the concentrations of G6P to investigate HK affinity for inhibition by G6P. We verified that 2-DG serves as a substrate for the HK reaction with linear time and concentration dependency as well as expected maximal velocity and KM. This is the first simple assay that evaluates feedback inhibition of HK by its product G6P and provides a unique technique for future research evaluating the regulation of glucose phosphorylation under various physiological conditions.

NEW & NOTEWORTHY Traditionally, hexokinase activity has been analyzed spectrophotometrically in which the product formation of glucose-6-phosphate (G6P) is analyzed by an indirect reaction coupled to NADPH formation during conversion of G6P to 6-P gluconolactone. By nature, this assay prevents measurements of hexokinase (HK) affinity for inhibition by G6P. We have developed a rapid radiochemical filter paper assay to study HK affinity for G6P by use of radiolabeled 2-deoxyglucose as substrate to study physiological regulation of HK affinity for G6P-induced inhibition.

Over-expression of mitochondrial creatine kinase in the murine heart improves functional recovery and protects against injury following ischaemia-reperfusion

Aims

Mitochondrial creatine kinase (MtCK) couples ATP production via oxidative phosphorylation to phosphocreatine in the cytosol, which acts as a mobile energy store available for regeneration of ATP at times of high demand. We hypothesized that elevating MtCK would be beneficial in ischaemia-reperfusion (I/R) injury.

Methods and results

Mice were created over-expressing the sarcomeric MtCK gene with αMHC promoter at the Rosa26 locus (MtCK-OE) and compared with wild-type (WT) littermates. MtCK activity was 27% higher than WT, with no change in other CK isoenzymes or creatine levels. Electron microscopy confirmed normal mitochondrial cell density and mitochondrial localization of transgenic protein. Respiration in isolated mitochondria was unaltered and metabolomic analysis by 1 H-NMR suggests that cellular metabolism was not grossly affected by transgene expression. There were no significant differences in cardiac structure or function under baseline conditions by cine-MRI or LV haemodynamics. In Langendorff-perfused hearts subjected to 20 min ischaemia and 30 min reperfusion, MtCK-OE exhibited less ischaemic contracture, and improved functional recovery (Rate pressure product 58% above WT; P < 0.001). These hearts had reduced myocardial infarct size, which was confirmed in vivo: 55 ± 4% in WT vs. 29 ± 4% in MtCK-OE; P < 0.0001). Isolated cardiomyocytes from MtCK-OE hearts exhibited delayed opening of the mitochondrial permeability transition pore (mPTP) compared to WT, which was confirmed by reduced mitochondrial swelling in response to calcium. There was no detectable change in the structural integrity of the mitochondrial membrane.

Conclusions

Modest elevation of MtCK activity in the heart does not adversely affect cellular metabolism, mitochondrial or in vivo cardiac function, but modifies mPTP opening to protect against I/R injury and improve functional recovery. Our findings support MtCK as a prime therapeutic target in myocardial ischaemia.

HIF-1α Preconditioning Potentiates Antioxidant Activity in Ischemic Injury: The Role of Sequential Administration of Dihydrotanshinone I and Protocatechuic Aldehyde in Cardioprotection

Aims: The management of myocardial ischemia has been challenged by reperfusion injury. Reactive oxygen species (ROS) production is the critical cause of reperfusion injury, but antioxidant treatment failed to gain satisfactory effects. We hypothesized that improvement of redox homeostasis by preconditioning regulation should potentiate the ability of antioxidants to protect the heart from reperfusion injury. Results: By phenotype-based screening, we identified that dihydrotanshinone I (DT) and protocatechuic aldehyde (PCA) potently protected cardiomyocytes through preconditioning regulation and antioxidant activity, respectively. DT induced transient ROS generation via reversible inhibition of mitochondrial respiratory complex I and thereby stabilizing HIF-1α, while PCA elevated the levels of reduced glutathione (GSH) by providing reducing equivalents to scavenge ROS. HIF-1α, stabilized by DT, transcriptionally upregulated Nrf2 and thereby activated antioxidant enzymes, potentiating PCA to protect cardiomyocytes from reperfusion injury by strengthening intrinsic ROS scavenging capacity. In rat ischemia/reperfusion (I/R) model, sequential administration of DT and PCA, but not in reverse, additively protected the heart from I/R injury, manifested by reduced infarct size and improved cardiac function. These results were further supported by sequential administration of metformin and vitamin E in the rat and porcine I/R models. Innovation and Conclusion: Our work demonstrates that preconditioning regulation of redox state is essential for antioxidants to protect the heart from I/R injury, providing a new direction for the treatment of myocardial injury.

Metabolic mechanisms of Fuzheng-Huayu formula against liver fibrosis in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Fuzheng-Huayu formula (FZHY) is traditionally used to treat liver fibrosis in clinic. The study was conducted to investigate the metabolic mechanisms of FZHY against liver fibrosis in rats.

MATERIALS AND METHODS

Rats with CCl₄ -induced liver fibrosis were treated with FZHY and its components, including amygdalin, cordyceps polysaccharide and gypenoside, respecitively. Liver fibrosis and function were assesed by histopathological examination, Western blot and serum biochemical detection. Metabolic profiling of liver tissue, serum and urine in each group were detected by gas chromatography-mass spectrometry (GC-MS) and transcriptomic changes were tested by gene chip. RT-qPCR was used to validate levels of different expressed genes (DEGs) with statistical significance. Metabolic network together with DEGs was constructed based on KEGG database.

RESULTS

FZHY effectively improved liver fibrosis better than the mixture or single use of gypenoside, cordyceps sinensis mycelia and amygdalin. FZHY treatment widely modulated the metabolic profiles perturbed by liver fibrosis, involving several important metabolic pathways, including glycolysis/gluconeogenesis, glucose-alanine cycle, citrate cycle, galactose metabolism, tryptophan metabolism, urea cycle, etc. It also increased alanine and decreased glucose levels in liver tissue and decreased both of them in serum and urine, which were dysregulated by CCl₄ treatment. Additionally, FZHY also upregulated expression of metabolic enzymes including Hk2, Adh1 and Gpt increased, and downregulated Gs and Acss2.

CONCLUSION

FZHY improved liver fibrosis in rats via altering the metabolic pathways and regulating gene expression of involved metabolic enzymes.

Regulation of permeability transition pore opening in mitochondria by external NAD(H)

BACKGROUND

The opening of the permeability transition pore (PTP) in mitochondria plays a critical role in the pathogenesis of numerous diseases. Mitochondrial matrix pyridine nucleotides are potent regulators of the PTP, but the role of extramitochondrial nucleotides is unclear.

METHODS

The PTP opening was explored in isolated mitochondria and mitochondria in permeabilized differentiated and undifferentiated cells in the presence of added NAD(P)(H) in combination with Mg²⁺, adenine nucleotides (AN), and the inhibitors of AN translocase (ANT), voltage-dependent anion channel (VDAC), and cyclophilin D.

RESULTS

Added NAD(H) and AN, but not NADP(H), inhibited the PTP opening with comparable potency. PTP suppression required neither NAD(H) oxidation nor reduction. The protective effects of NAD(H) and cyclosporin A were synergistic, and the effects of NAD(H) and millimolar AN were additive. The conformation-specific ANT inhibitors were unable to cancel the protective effect of NADH even under total ANT inhibition. Besides, NAD(H) activated the efflux of mitochondrial AN via ANT. VDAC ligand (Mg²⁺) and blockers (G3139 and 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid) potentiated and attenuated the protective effect of NAD(H), respectively. However, in embryonic and cancer (undifferentiated) cells, in contrast to isolated differentiated hepatocytes and cardiocytes, the suppression of PTP opening by NADH was negligible though all cells tested possessed a full set of VDAC isoforms.

CONCLUSIONS

The study revealed a novel mechanism of PTP regulation by external (cytosolic) NAD(H) through the allosteric site in the OM or the intermembrane space.

GENERAL SIGNIFICANCE

The mechanism might contribute to the resistance of differentiated cells under different pathological conditions including ischemia/reperfusion.

Mitochondrial genome modulates myocardial Akt/Glut/HK salvage pathway in spontaneously hypertensive rats adapted to chronic hypoxia

Recently we have shown that adaptation to continuous normobaric hypoxia (CNH) decreases myocardial ischemia/reperfusion injury in spontaneously hypertensive rats (SHR) and in a conplastic strain (SHR-mt^BN). The protective effect was stronger in the latter group characterized by a selective replacement of the SHR mitochondrial genome with that of a more ischemia-resistant Brown Norway strain. The aim of the present study was to examine the possible involvement of the hypoxia inducible factor (HIF)-dependent pathway of the protein kinase B/glucose transporters/hexokinase (Akt/GLUT/HK) in this mitochondrial genome-related difference of the cardioprotective phenotype. Adult male rats were exposed for 3 wk to CNH ([Formula: see text] 0.1). The expression of dominant isoforms of Akt, GLUT, and HK in left ventricular myocardium was determined by real-time RT-PCR and Western blotting. Subcellular localization of GLUTs was assessed by quantitative immunofluorescence. Whereas adaptation to hypoxia markedly upregulated protein expression of HK2, GLUT1, and GLUT4 in both rat strains, Akt2 protein level was significantly increased in SHR-mt^BN only. Interestingly, a higher content of HK2 was revealed in the sarcoplasmic reticulum-enriched fraction in SHR-mt^BN after CNH. The increased activity of HK determined in the mitochondrial fraction after CNH in both strains suggested an increase of HK association with mitochondria. Interestingly, HIF1a mRNA increased and HIF2a mRNA decreased after CNH, the former effect being more pronounced in SHR-mt^BN than in SHR. Pleiotropic effects of upregulated Akt2 along with HK translocation to mitochondria and mitochondria-associated membranes can potentially contribute to a stronger CNH-afforded cardioprotection in SHR-mt^BN compared with progenitor SHR.

Cardioprotective signalling: Past, present and future

A few decades ago, cardiac muscle was discovered to possess signalling pathways that, when activated, protect the myocardium against the damage induced by ischaemia-reperfusion. The ability of cardiac muscle to protect itself against injury has been termed 'cardioprotection'. Many compounds and procedures can trigger cardioprotection including conditionings (exposure to brief episodes of ischaemia-reperfusion to protect against sustained ischaemia-reperfusion), hypoxia, adenosine, acetylcholine, adrenomedullin, angiotensin, bradykinin, catecholamines, endothelin, estrogens, phenylephrine, opioids, testosterone, and many more. These triggers activate many intracellular signalling factors including protein kinases, different enzymes, transcription factors and defined signalling pathways to target structures in mitochondria, sarcoplasmic reticulum, nucleus and sarcolemma to mediate cardioprotection. Although a lot of information about cardioprotection has been acquired, there are still two major outstanding issues to be addressed in the future 1) better understanding of spatio-temporal relationships between signalling elements, and; 2) devising therapeutic strategies against myocardial diseases based on cardioprotective signalling. Further research is required to paint integral picture of cardioprotective signalling and more clinical studies are required to properly test clinical efficacy and safety of potential cardioprotective strategies. Therapies against cardiac diseases based on cardioprotective strategies would be a perfect adjunct to current therapeutic strategies based on restitution of coronary blood flow and regulation of myocardial metabolic demands.

New and revisited approaches to preserving the reperfused myocardium

Early coronary artery reperfusion improves outcomes for patients with ST-segment elevation myocardial infarction (STEMI), but morbidity and mortality after STEMI remain unacceptably high. The primary deficits seen in these patients include inadequate pump function, owing to rapid infarction of muscle in the first few hours of treatment, and adverse remodelling of the heart in the months that follow. Given that attempts to further reduce myocardial infarct size beyond early reperfusion in clinical trials have so far been disappointing, effective therapies are still needed to protect the reperfused myocardium. In this Review, we discuss several approaches to preserving the reperfused heart, such as therapies that target the mechanisms involved in mitochondrial bioenergetics, pyroptosis, and autophagy, as well as treatments that harness the cardioprotective properties of inhaled anaesthetic agents. We also discuss potential therapies focused on correcting the no-reflow phenomenon and its effect on healing and adverse left ventricular remodelling.

Effects of ethanol extract of Bombax ceiba leaves and its main constituent mangiferin on diabetic nephropathy in mice

The present study was designed to explore the mechanism by which ethanol extract of Bombax ceiba leaves (BCE) and its main constituent mangiferin (MGF) affect diabetic nephropathy by combating oxidative stress. Oral administration of BCE and MGF to normal and streptozotocin (STZ)-induced diabetic mice were carried out. Fasting blood glucose, 24-h urinary albumin, serum creatinine, and blood urea nitrogen were tested, histopathology, and immunohistochemical analysis of kidney tissues were performed. Moreover, mesangial cells were treated with BCE and MGF for 48 h with or without 25 mmol·L^-1 of glucose. Immunofluorescence, Western blot and apoptosis analyses were used to investigate their regulation of oxidative stress and mitochondrial function. BCE and MGF ameliorated biochemical parameters and restored STZ-induced renal injury in the model mice. In vitro study showed that high glucose stimulation increased oxidative stress and cell apoptosis in mesangial cells. BCE and MGF limited mitochondrial membrane potential (Δψm) collapse by inhibiting Nox4, mitochondrially bound hexokinase II dissociation, and subsequent ROS production, which effectively reduced oxidative stress, cleaved caspase-3 expression and cell apoptosis. Our work indicated that BCE and MGF had protective effects on diabetic caused kidney injury and prevented oxidative stress in mesangial cells by regulation of hexokinase II binding and Nox4 oxidase signaling.

The role of succinate and ROS in reperfusion injury - A critical appraisal

We critically assess the proposal that succinate-fuelled reverse electron flow (REF) drives mitochondrial matrix superoxide production from Complex I early in reperfusion, thus acting as a key mediator of ischemia/reperfusion (IR) injury. Real-time surface fluorescence measurements of NAD(P)H and flavoprotein redox state suggest that conditions are unfavourable for REF during early reperfusion. Furthermore, rapid loss of succinate accumulated during ischemia can be explained by its efflux rather than oxidation. Moreover, succinate accumulation during ischemia is not attenuated by ischemic preconditioning (IP) despite powerful cardioprotection. In addition, measurement of intracellular reactive oxygen species (ROS) during reperfusion using surface fluorescence and mitochondrial aconitase activity detected major increases in ROS only after mitochondrial permeability transition pore (mPTP) opening was first detected. We conclude that mPTP opening is probably triggered initially by factors other than ROS, including increased mitochondrial [Ca2+]. However, IP only attenuates [Ca2+] increases later in reperfusion, again after initial mPTP opening, implying that IP regulates mPTP opening through additional mechanisms. One such is mitochondria-bound hexokinase 2 (HK2) which dissociates from mitochondria during ischemia in control hearts but not those subject to IP. Indeed, there is a strong correlation between the extent of HK2 loss from mitochondria during ischemia and infarct size on subsequent reperfusion. Mechanisms linking HK2 dissociation to mPTP sensitisation remain to be fully established but several related processes have been implicated including VDAC1 oligomerisation, the stability of contact sites between the inner and outer membranes, cristae morphology, Bcl-2 family members and mitochondrial fission proteins such as Drp1.

Acute detachment of hexokinase II from mitochondria modestly increases oxygen consumption of the intact mouse heart

OBJECTIVE

Cardiac hexokinase II (HKII) can translocate between cytosol and mitochondria and change its cellular expression with pathologies such as ischemia-reperfusion, diabetes and heart failure. The cardiac metabolic consequences of these changes are unknown. Here we measured energy substrate utilization in cytosol and mitochondria using stabile isotopes and oxygen consumption of the intact perfused heart for 1) an acute decrease in mitochondrial HKII (mtHKII), and 2) a chronic decrease in total cellular HKII.

METHODS/RESULTS

We first examined effects of 200nM TAT (Trans-Activator of Transcription)-HKII peptide treatment, which was previously shown to acutely decrease mtHKII by ~30%. In Langendorff-perfused hearts TAT-HKII resulted in a modest, but significant, increased oxygen consumption, while cardiac performance was unchanged. At the metabolic level, there was a nonsignificant (p=0.076) ~40% decrease in glucose contribution to pyruvate and lactate formation through glycolysis and to mitochondrial citrate synthase flux (6.6±1.1 vs. 11.2±2.2%), and an 35% increase in tissue pyruvate (27±2 vs. 20±2pmol/mg; p=0.033). Secondly, we compared WT and HKII^+/- hearts (50% chronic decrease in total HKII). RNA sequencing revealed no differential gene expression between WT and HKII^+/- hearts indicating an absence of metabolic reprogramming at the transcriptional level. Langendorff-perfused hearts showed no significant differences in glycolysis (0.34±0.03μmol/min), glucose contribution to citrate synthase flux (35±2.3%), palmitate contribution to citrate synthase flux (20±1.1%), oxygen consumption or mechanical performance between WT and HKII^+/- hearts.

CONCLUSIONS

These results indicate that acute albeit not chronic changes in mitochondrial HKII modestly affect cardiac oxygen consumption and energy substrate metabolism.

Mitochondrial Metabolism in Aging Heart

Altered mitochondrial metabolism is the underlying basis for the increased sensitivity in the aged heart to stress. The aged heart exhibits impaired metabolic flexibility, with a decreased capacity to oxidize fatty acids and enhanced dependence on glucose metabolism. Aging impairs mitochondrial oxidative phosphorylation, with a greater role played by the mitochondria located between the myofibrils, the interfibrillar mitochondria. With aging, there is a decrease in activity of complexes III and IV, which account for the decrease in respiration. Furthermore, aging decreases mitochondrial content among the myofibrils. The end result is that in the interfibrillar area, there is ≈50% decrease in mitochondrial function, affecting all substrates. The defective mitochondria persist in the aged heart, leading to enhanced oxidant production and oxidative injury and the activation of oxidant signaling for cell death. Aging defects in mitochondria represent new therapeutic targets, whether by manipulation of the mitochondrial proteome, modulation of electron transport, activation of biogenesis or mitophagy, or the regulation of mitochondrial fission and fusion. These mechanisms provide new ways to attenuate cardiac disease in elders by preemptive treatment of age-related defects, in contrast to the treatment of disease-induced dysfunction.

Ginsenoside Rg5 increases cardiomyocyte resistance to ischemic injury through regulation of mitochondrial hexokinase-II and dynamin-related protein 1

Hexokinase-II (HK-II) and dynamin-related protein 1 (Drp1) regulate mitochondrial function differently. This study was designed to investigate the cardioprotective effect of ginsenoside Rg5 (Rg5) with emphasis on the regulation of mitochondrial HK-II and Drp1. Saturated acid palmitate (PA) stimulation increased lactate accumulation and induced cellular acidification by impairing the activity of pyruvate dehydrogenase (PDH) in cardiomyocytes, leading to HK-II dissociation from mitochondria. Rg5 improved PDH activity and prevented cellular acidification by combating fatty-acid oxidation, contributing to protecting mitochondrial HK-II. HK-II binding to mitochondria prevented mitochondrial Drp1 recruitment, whereas Drp1 activation decreased the content of mitochondrial HK-II, demonstrating the reciprocal control for binding to mitochondria. Rg5 promoted Akt translocation to mitochondria and increased HK-II binding to mitochondria while coordinately suppressing Drp1 recruitment and mitochondrial fission. Akt inhibitor triciribine or knockdown of Akt with small interfering RNA diminished the effects of Rg5, indicating that Rg5 inhibited Drp1 activation and promoted HK-II mitochondrial binding through Akt activation. Rg5 prevented the opening of mitochondrial permeability transition pore and increased ATP production, resultantly increasing cardiomyocyte resistance to hypoxia/reoxygenation injury. Meanwhile, Rg5 prevented cell apoptosis with increased HK-II binding and reduced Drp1 recruitment to mitochondria in isoproterenol-induced ischemic heart of mice. Taken together, these findings not only established a previously unrecognized role of ginsenosides in cardioprotection but also suggest that mitochondrial HK-II binding and Drp1 recruitment could be targeted therapeutically to prevent ischemic injury in the heart.

Mitochondrial Dynamics as a Therapeutic Target for Treating Cardiac Diseases

Mitochondria are dynamic in nature and are able to shift their morphology between elongated interconnected mitochondrial networks and a fragmented disconnected arrangement by the processes of mitochondrial fusion and fission, respectively. Changes in mitochondrial morphology are regulated by the mitochondrial fusion proteins - mitofusins 1 and 2 (Mfn1 and 2), and optic atrophy 1 (Opa1) as well as the mitochondrial fission proteins - dynamin-related peptide 1 (Drp1) and fission protein 1 (Fis1). Despite having a unique spatial arrangement, cardiac mitochondria have been implicated in a variety of disorders including ischemia-reperfusion injury (IRI), heart failure, diabetes, and pulmonary hypertension. In this chapter, we review the influence of mitochondrial dynamics in these cardiac disorders as well as their potential as therapeutic targets in tackling cardiovascular disease.

Mitochondrial involvement in myocyte death and heart failure

As the heart is an energy-demanding organ, impaired cardiac energy metabolism and mitochondrial function have been inexorably linked to cardiac dysfunction. There is a growing recognition that mitochondrial dysfunction contributes to impaired myocardial energetics and increased oxidative stress in cardiomyopathies, cardiac ischemic damage and heart failure (HF), and mitochondrial permeability transition pore opening has been reported a critical trigger of myocyte death and myocardial remodeling. It is well established that mitochondria play pivotal roles in intracellular signaling in both cell death as well as in cardioprotective pathways. Moreover, recent studies have shown that defects in mitochondrial dynamics affecting biogenesis and turnover are linked to cardiac senescence and HF. Accordingly, there has been an increasing interest in targeting mitochondria for HF therapy. This article reviews the background and recent evidence of mitochondrial involvement in several types of cell death (apoptosis, necrosis and autophagy) occurring in HF. In addition, potential strategies for targeting mitochondria are examined, and their utility in HF therapy considered.

Real-Time Fluorescence Measurements of ROS and [Ca2+] in Ischemic / Reperfused Rat Hearts: Detectable Increases Occur only after Mitochondrial Pore Opening and Are Attenuated by Ischemic Preconditioning

Mitochondrial permeability transition pore (mPTP) opening is critical for ischemia / reperfusion (I/R) injury and is associated with increased [Ca²⁺] and reactive oxygen species (ROS). Here we employ surface fluorescence to establish the temporal sequence of these events in beating perfused hearts subject to global I/R. A bespoke fluorimeter was used to synchronously monitor surface fluorescence and reflectance of Langendorff-perfused rat hearts at multiple wavelengths, with simultaneous measurements of hemodynamic function. Potential interference by motion artefacts and internal filtering was assessed and minimised. Re-oxidation of NAD(P)H and flavoproteins on reperfusion (detected using autofluorescence) was rapid (t_0.5 < 15 s) and significantly slower following ischemic preconditioning (IP). This argues against superoxide production from reduced Complex 1 being a critical mediator of initial mPTP opening during early reperfusion. Furthermore, MitoPY1 (a mitochondria-targeted H₂O₂-sensitive fluorescent probe) and aconitase activity measurements failed to detect matrix ROS increases during early reperfusion. However, two different fluorescent cytosolic ROS probes did detect ROS increases after 2–3 min of reperfusion, which was shown to be after initiation of mPTP opening. Cyclosporin A (CsA) and IP attenuated these responses and reduced infarct size. [Ca²⁺]_i (monitored with Indo-1) increased progressively during ischemia, but dropped rapidly within 90 s of reperfusion when total mitochondrial [Ca²⁺] was shown to be increased. These early changes in [Ca²⁺] were not attenuated by IP, but substantial [Ca²⁺] increases were observed after 2–3 min reperfusion and these were prevented by both IP and CsA. Our data suggest that the major increases in ROS and [Ca²⁺] detected later in reperfusion are secondary to mPTP opening. If earlier IP-sensitive changes occur that might trigger initial mPTP opening they are below our limit of detection. Rather, we suggest that IP may inhibit initial mPTP opening by alternative mechanisms such as prevention of hexokinase 2 dissociation from mitochondria during ischemia.

The mechanism of kaempferol induced apoptosis and inhibited proliferation in human cervical cancer SiHa cell: From macro to nano

Kaempferol has been identified as a potential cancer therapeutic agent by an increasing amount of evidences. However, the changes in the topography of cell membrane induced by kaempferol at subcellular- or nanometer-level were still unclear. In this work, the topographical changes of cytomembrane in human cervical cancer cell (SiHa) induced by kaempferol, as well as the role of kaempferol in apoptosis induction and its possible mechanisms, were investigated. At the macro level, MTT assays showed that kaempferol inhibited the proliferation of SiHa cells in a time- and dose-dependent manner. Flow cytometry analysis demonstrated that kaempferol could induce SiHa cell apoptosis, mitochondrial membrane potential disruption, and intracellular free calcium elevation. At the micro level, fluorescence imaging by laser scanning confocal microscopy (LSCM) indicated that kaempferol could also destroy the networks of microtubules. Using high resolution atomic force microscopy (AFM), we determined the precise changes of cellular membrane induced by kaempferol at subcellular or nanometer level. The spindle-shaped SiHa cells shrank after kaempferol treatment, with significantly increased cell surface roughness. These data showed structural characterizations of cellular topography in kaempferol-induced SiHa cell apoptosis and might provide novel integrated information from macro to nano level to assess the impact of kaempferol on cancer cells, which might be important for the understanding of the anti-cancer mechanisms of drugs. SCANNING 38:644-653, 2016. © 2016 Wiley Periodicals, Inc.

'Conditioning the heart' - lessons we have learned from the past and future perspectives for new and old conditioning 'drugs'

LINKED ARTICLES

This article is part of a themed section on Conditioning the Heart - Pathways to Translation. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-8.

Mitochondrial translocator protein (TSPO): From physiology to cardioprotection

The mitochondrial translocator protein (TSPO) is a high affinity cholesterol binding protein which is primarily located in the outer mitochondrial membrane where it has been shown to interact with proteins implicated in mitochondrial permeability transition pore (mPTP) formation. TSPO is found in different species and is expressed at high levels in tissues that synthesize steroids but is also present in other peripheral tissues especially in the heart. TSPO has been involved in the import of cholesterol into mitochondria, a key step in steroidogenesis. This constitutes the main established function of the protein which was recently challenged by genetic studies. TSPO has also been associated directly or indirectly with a wide range of cellular functions such as apoptosis, cell proliferation, differentiation, regulation of mitochondrial function or porphyrin transport. In the heart the role of TSPO remains undefined but a growing body of evidence suggests that TSPO plays a critical role in regulating physiological cardiac function and that TSPO ligands may represent interesting drugs to protect the heart under pathological conditions. This article briefly reviews current knowledge regarding TSPO and discusses its role in the cardiovascular system under physiological and pathologic conditions. More particularly, it provides evidence that TSPO can represent an alternative strategy to develop new pharmacological agents to protect the myocardium against ischemia-reperfusion injury.

Mitochondrial fusion and fission proteins as novel therapeutic targets for treating cardiovascular disease

The past decade has witnessed a number of exciting developments in the field of mitochondrial dynamics - a phenomenon in which changes in mitochondrial shape and movement impact on cellular physiology and pathology. By undergoing fusion and fission, mitochondria are able to change their morphology between elongated interconnected networks and discrete fragmented structures, respectively. The cardiac mitochondria, in particular, have garnered much interest due to their unique spatial arrangement in the adult cardiomyocyte, and the multiple roles they play in cell death and survival. In this article, we review the role of the mitochondrial fusion and fission proteins as novel therapeutic targets for treating cardiovascular disease.

Physiological and pathological roles of the mitochondrial permeability transition pore in the heart

Prolonged mitochondrial permeability transition pore (MPTP) opening results in mitochondrial energetic dysfunction, organelle swelling, rupture, and typically a type of necrotic cell death. However, acute opening of the MPTP has a critical physiologic role in regulating mitochondrial Ca(2+) handling and metabolism. Despite the physiological and pathological roles that the MPTP orchestrates, the proteins that comprise the pore itself remain an area of ongoing investigation. Here, we will discuss the molecular composition of the MPTP and its role in regulating cardiac physiology and disease. A better understanding of MPTP structure and function will likely suggest novel cardioprotective therapeutic approaches.