Alterations in oxidative phosphorylation complex proteins in the hearts of transgenic mice that overexpress the p38 MAP kinase activator, MAP kinase kinase 6

p38α kinase governs muscle strength through PGC1α in mice

AIMS

Skeletal muscle, with its remarkable plasticity and dynamic adaptation, serves as a cornerstone of locomotion and metabolic homeostasis in the human body. Muscle tissue, with its extraordinary capacity for force generation and energy expenditure, plays a fundamental role in the movement, metabolism, and overall health. In this context, we sought to determine the role of p38α in mitochondrial metabolism since mitochondrial dynamics play a crucial role in the development of muscle-related diseases that result in muscle weakness.

METHODS

We conducted our study using male mice (MCK-cre, p38αMCK-KO and PGC1α MCK-KO) and mouse primary myoblasts. We analyzed mitochondrial metabolic, physiological parameters as well as proteomics, western blot, RNA-seq analysis from muscle samples.

RESULTS

Our findings highlight the critical involvement of muscle p38α in the regulation of mitochondrial function, a key determinant of muscle strength. The absence of p38α triggers changes in mitochondrial dynamics through the activation of PGC1α, a central regulator of mitochondrial biogenesis. These results have substantial implications for understanding the complex interplay between p38α kinase, PGC1α activation, and mitochondrial content, thereby enhancing our knowledge in the control of muscle biology.

CONCLUSIONS

This knowledge holds relevance for conditions associated with muscle weakness, where disruptions in these molecular pathways are frequently implicated in diminishing physical strength. Our research underscores the potential importance of targeting the p38α and PGC1α pathways within muscle, offering promising avenues for the advancement of innovative treatments. Such interventions hold the potential to improve the quality of life for individuals affected by muscle-related diseases.

Inhibition of NADPH Oxidases Prevents the Development of Osteoarthritis

Increased oxidative stress in osteoarthritis (OA) cartilage mediates catabolic signal transduction leading to extracellular matrix degradation and chondrocyte apoptosis. This study aimed to explore the contribution of NADPH oxidase (NOX), a major source of cellular reactive oxygen species (ROS), to the catabolic process of chondrocytes and to OA. The inhibition of NOX isoforms with a pan-NOX inhibitor, APX-115, significantly decreased IL-1β-induced ROS production in primary chondrocytes and, most potently, suppressed the expression of oxidative stress marker genes and catabolic proteases compared with the inhibition of other ROS sources. Catabolic stimuli by IL-1β treatment and in post-traumatic OA conditions upregulated the expression of NOX2 and NOX4 in chondrocytes. In the post-traumatic OA model, the pharmacologic inhibition of NOX protected mice against OA by modulating the oxidative stress and the expression of MMP-13 and Adamts5 in chondrocytes. Mechanistically, NOX inhibition suppresses Rac1, p38, and JNK MAPK signaling consistently and restores oxidative phosphorylation in IL-1β-treated chondrocytes. In conclusion, NOX inhibition prevented the development of OA by attenuating the catabolic signaling and restoring the mitochondrial metabolism and can thus be a promising class of drug for OA.

Induced pluripotent stem cell-derived motor neurons of CMT type 2 patients reveal progressive mitochondrial dysfunction

Axonal Charcot-Marie-Tooth neuropathies (CMT type 2) are caused by inherited mutations in various genes functioning in different pathways. The type of genes and multiplicity of mutations reflect the clinical and genetic heterogeneity in CMT2 disease, which complicates the diagnosis and has halted therapy development. Here, we used CMT2 patient-derived pluripotent stem cells (iPSCs) to identify common hallmarks of axonal degeneration shared by different CMT2 subtypes. We compared the cellular phenotypes of neurons differentiated from CMT2 patient iPSCs with those from healthy controls and a CRISPR/Cas9-corrected isogenic line. Our results demonstrate neurite network alterations along with extracellular electrophysiological abnormalities in the differentiated motor neurons. Progressive deficits in mitochondrial and lysosomal trafficking, as well as in mitochondrial morphology, were observed in all CMT2 patient lines. Differentiation of the same CMT2 iPSC-lines into peripheral sensory neurons, only gave rise to cellular phenotypes in subtypes with sensory involvement, supporting the notion that some gene mutations predominantly affect motor neurons. We revealed a common mitochondrial dysfunction in CMT2-derived motor neurons, supported by alterations in the expression pattern and oxidative phosphorylation, which could be recapitulated in the sciatic nerve tissue of a symptomatic mouse model. Inhibition of a dual leucine zipper kinase (DLK) could partially ameliorate the mitochondrial disease phenotypes in CMT2 subtypes. Altogether, our data reveals shared cellular phenotypes across different CMT2 subtypes and suggests that targeting such common pathomechanisms could allow the development of a uniform treatment for CMT2.

Sevoflurane Pre-conditioning Ameliorates Diabetic Myocardial Ischemia/Reperfusion Injury Via Differential Regulation of p38 and ERK

Diabetes mellitus (DM) significantly increases myocardial ischemia/reperfusion (MI/R) injury. During DM, cardioprotection induced by conventional pre-conditioning (PreCon) is decreased due to impaired AMP-activated protein kinase (AMPK) signaling. The current study investigated whether PreCon with inhaled anesthetic sevoflurane (SF-PreCon) remains cardioprotective during DM, and identified the involved mechanisms. Normal diet (ND) and high-fat diet (HFD)-induced DM mice were randomized into control and SF-PreCon (3 cycles of 15-minute period exposures to 2% sevoflurane) groups before MI/R. SF-PreCon markedly reduced MI/R injury in DM mice, as evidenced by improved cardiac function (increased LVEF and ±Dp/dt), decreased infarct size, and decreased apoptosis. To determine the relevant role of AMPK, the effect of SF-PreCon was determined in cardiac-specific AMPKα2 dominant negative expressing mice (AMPK-DN). SF-PreCon decreased MI/R injury in AMPK-DN mice. To explore the molecular mechanisms responsible for SF-PreCon mediated cardioprotection in DM mice, cell survival molecules were screened. Interestingly, in ND mice, SF-PreCon significantly reduced MI/R-induced activation of p38, a pro-death MAPK, without altering ERK and JNK. In DM and AMPK-DN mice, the inhibitory effect of SF-PreCon upon p38 activation was significantly blunted. However, SF-PreCon significantly increased phosphorylation of ERK1/2, a pro-survival MAPK in DM and AMPK-DN mice. We demonstrate that SF-PreCon protects the heart via AMPK-dependent inhibition of pro-death MAPK in ND mice. However, SF-PreCon exerts cardioprotective action via AMPK-independent activation of a pro-survival MAPK member in DM mice. SF-PreCon may be beneficial compared to conventional PreCon in diabetes or clinical scenarios in which AMPK signaling is impaired.

Periostin alters transcriptional profile in a rat model of isoproterenol-induced cardiotoxicity

Periostin is an extracellular matrix protein from the fasciclin family that guides cellular trafficking and extracellular matrix organization. Periostin stimulates mature cardiomyocytes to reenter the cell cycle. The molecular mechanism behind such stimulation remains to be explored. A DNA microarray technology constituting 30,429 gene-level probe sets was utilized to investigate effects of recombinant murine periostin peptide on the gene expression pattern in a rat model of isoproterenol (ISO)-induced myocardial injury. The experiment was performed on 84 adult male Sprague-Dawley rats in four groups ( n = 21): (1) control group, (2) only periostin applied group, (3) ISO cardiotoxicity group, and (4) ISO + periostin group. The experiment was continued for 28 days, and rats were killed on days 1, 7, and 28 ( n = 7). Microarray analyses revealed that periostin significantly altered the expression of at least ±2-fold of 2474 genes in the ISO + periostin group compared to the ISO cardiotoxicity group of which 521 genes altered out of 30,429 gene-level probe sets. Ingenuity pathway analysis indicated that multiple pathway networks were affected by periostin, with predominant changes occurring in the expression of genes involved in oxidative phosphorylation, oxidative stress, fatty acid metabolism, and TNF-α NF-κB signaling pathways. These findings indicate that periostin alters gene expression profile in the ISO-induced myocardial injury and modulates local myocardial inflammation, possibly mitigating inflammation through TNF-α NF-κB signaling pathway along with a decreased Casp7 activity and apoptotic cell death.

Sex Differences in Cardiac Mitochondria in the New Zealand Obese Mouse

Background: Obesity is a risk factor for diseases including type 2 diabetes mellitus (T2DM) and cardiovascular disorders. Diabetes itself contributes to cardiac damage. Thus, studying cardiovascular events and establishing therapeutic intervention in the period of type T2DM onset and manifestation are of highest importance. Mitochondrial dysfunction is one of the pathophysiological mechanisms leading to impaired cardiac function. Methods: An adequate animal model for studying pathophysiology of T2DM is the New Zealand Obese (NZO) mouse. These mice were maintained on a high-fat diet (HFD) without carbohydrates for 13 weeks followed by 4 week HFD with carbohydrates. NZO mice developed severe obesity and only male mice developed manifest T2DM. We determined cardiac phenotypes and mitochondrial function as well as cardiomyocyte signaling in this model. Results: The development of an obese phenotype and T2DM in male mice was accompanied by an impaired systolic function as judged by echocardiography and MyH6/7 expression. Moreover, the mitochondrial function only in male NZO hearts was significantly reduced and ERK1/2 and AMPK protein levels were altered. Conclusions: This is the first report demonstrating that the cardiac phenotype in male diabetic NZO mice is associated with impaired cardiac energy function and signaling events.

Impairment of Mitochondrial Biogenesis and Dynamics Involved in Isoniazid-Induced Apoptosis of HepG2 Cells Was Alleviated by p38 MAPK Pathway

Isoniazid (INH), a widely used first-line antitubercular drug, has been noted to be associated with hepatotoxicity. In spite of extensive researches over many decades, the mechanism of INH-induced hepatotoxicity still remains poorly understood. Recently, mitochondrial toxicity has been emerging as a new paradigm for INH-induced hepatotoxicity. In this study, we showed that INH impaired mitochondrial biogenesis and dynamics in human hepatocarcinoma HepG2 cells. INH reduced mitochondrial membrane potential (MMP) and induced mitochondria swelling. INH also inhibited the protein expressions of three major mitochondrial biogenesis regulators, SIRT1, PGC1α and NRF1, along with increased acetylation of PGC1α. Meanwhile, INH decreased the number of mitochondria, accompanied by decreased expression of mitochondrial protein COX IV. INH caused mitochondrial fragmentation involving decreased levels of the fusion protein MFN2 as well as the fission protein DRP1. INH-reduced DRP1 expression was associated with the increase of apoptosis, suggesting the existence of pro-survival fission and its involvement in mitochondrial quality control. INH activated p38 MAPK, whereas inhibition of p38 MAPK aggravated INH-induced decreases of SIRT1, PGC1α, NRF1, COX IV and DRP1 expressions. P38 MAPK inhibition also further up-regulated the acetylation of PGC1α and exacerbated INH-induced MMP loss, mitochondrial swelling and apoptosis. Taken together, INH-activated p38 MAPK induced mitochondrial biogenesis to alleviate apoptosis through partly recovering SIRT1-PGC1α pathway activation. In the meantime, p38 MAPK activation by INH promoted protective mitochondrial fission to alleviate apoptosis by partial recovery of DRP1 expression.

Cardioprotective effects of salidroside on myocardial ischemia-reperfusion injury in coronary artery occlusion-induced rats and Langendorff-perfused rat hearts

BACKGROUND/OBJECTIVES

The current study was designed to investigate the protective role of salisroside on rats through the study of energy metabolism homeostasis and inflammation both in ex vivo and in vivo.

METHODS

Energy metabolism homeostasis and inflammation injury were respectively assessed in global ischemia of isolated hearts and coronary artery ligated rats.

RESULTS

Excessive release of cardiac enzymes and pro-inflammatory cytokines was inhibited by salidroside in coronary artery occlusion-induced rats. ST segment was also restored with the treatment of salidroside. Triphenyltetrazolium chloride staining (TTC) staining and pathological analysis showed that salidroside could significantly alleviate myocardial injury in vivo. Accumulated data in ex vivo indicated that salidroside improved heart function recovery, which was reflected by enhanced myocardial contractility and coronary flow in isolated hearts. The contents of ATP and glycogen both in ex vivo and in vivo were restored by salidroside compared with those in the model group. Besides, the expressions of p-AMPK, PPAR-α and PGC-1α in rats and isolated hearts subjected to salidroside were significantly elevated, while the levels of p-NF-κBp65, p-IκBα, p-IKKα and p-IKKβ were dramatically reduced by salidroside.

CONCLUSIONS

The present study comprehensively elaborated the protective effects of salidroside on myocardial injury and demonstrated that AMPK/PGC-1α and AMPK/NF-κB signaling cascades were implicated in the myocardial ischemia-reperfusion injury (I/R) model.

Crosstalk between mitogen-activated protein kinases and mitochondria in cardiac diseases: therapeutic perspectives

Cardiovascular diseases cause more mortality and morbidity worldwide than any other diseases. Although many intracellular signaling pathways influence cardiac physiology and pathology, the mitogen-activated protein kinase (MAPK) family has garnered significant attention because of its vast implications in signaling and crosstalk with other signaling networks. The extensively studied MAPKs ERK1/2, p38, JNK, and ERK5, demonstrate unique intracellular signaling mechanisms, responding to a myriad of mitogens and stressors and influencing the signaling of cardiac development, metabolism, performance, and pathogenesis. Definitive relationships between MAPK signaling and cardiac dysfunction remain elusive, despite 30 years of extensive clinical studies and basic research of various animal/cell models, severities of stress, and types of stimuli. Still, several studies have proven the importance of MAPK crosstalk with mitochondria, powerhouses of the cell that provide over 80% of ATP for normal cardiomyocyte function and play a crucial role in cell death. Although many questions remain unanswered, there exists enough evidence to consider the possibility of targeting MAPK-mitochondria interactions in the prevention and treatment of heart disease. The goal of this review is to integrate previous studies into a discussion of MAPKs and MAPK-mitochondria signaling in cardiac diseases, such as myocardial infarction (ischemia), hypertrophy and heart failure. A comprehensive understanding of relevant molecular mechanisms, as well as challenges for studies in this area, will facilitate the development of new pharmacological agents and genetic manipulations for therapy of cardiovascular diseases.

Comparison of detergent-based sample preparation workflows for LTQ-Orbitrap analysis of the Escherichia coli proteome

This work presents a comparative evaluation of several detergent-based sample preparation workflows for the MS-based analysis of bacterial proteomes, performed using the model organism Escherichia coli. Initially, RapiGest- and SDS-based buffers were compared for their protein extraction efficiency and quality of the MS data generated. As a result, SDS performed best in terms of total protein yields and overall number of MS identifications, mainly due to a higher efficiency in extracting high molecular weight (MW) and membrane proteins, while RapiGest led to an enrichment in periplasmic and fimbrial proteins. Then, SDS extracts underwent five different MS sample preparation workflows, including: detergent removal by spin columns followed by in-solution digestion (SC), protein precipitation followed by in-solution digestion in ammonium bicarbonate or urea buffer, filter-aided sample preparation (FASP), and 1DE separation followed by in-gel digestion. On the whole, about 1000 proteins were identified upon LC-MS/MS analysis of all preparations (>1100 with the SC workflow), with FASP producing more identified peptides and a higher mean sequence coverage. Each protocol exhibited specific behaviors in terms of MW, hydrophobicity, and subcellular localization distribution of the identified proteins; a comparative assessment of the different outputs is presented.

Decreased cytochrome c oxidase subunit VIIa in aged rat heart mitochondria: immunocytochemistry

Aging decreases oxidative phosphorylation through cytochrome oxidase (COX) in cardiac interfibrillar mitochondria (IFM) in 24-month old (aged) rats compared to 6-month old adult Fischer 344 rats, whereas subsarcolemmal mitochondria (SSM) located beneath the plasma membrane remain unaffected. Immunoelectron microscopy (IEM) reveals in aged rats a 25% reduction in cardiac COX subunit VIIa in cardiac IFM, but not in SSM. In contrast, the content of subunit IV remains unchanged in both SSM and IFM, irrespective of age. These subunits are localized mainly on cristae membranes. In contrast, semi-quantitative immunoblotting, which detects denatured protein, indicates that the content of COX VIIa is similar in IFM and SSM from both aged and adult hearts. IEM provides a sensitive method for precise localizing and quantifying specific mitochondrial proteins. The lack of immunoreaction of COX VIIa subunit by IEM in aged IFM is not explained by a reduction in protein, but rather by a masking phenomenon or by an in situ change in protein structure affecting COX activity.

Reciprocal transcriptional regulation of metabolic and signaling pathways correlates with disease severity in heart failure

BACKGROUND

Systolic heart failure (HF) is a complex systemic syndrome that can result from a wide variety of clinical conditions and gene mutations. Despite phenotypic similarities, characterized by ventricular dilatation and reduced contractility, the extent of common and divergent gene expression between different forms of HF remains a matter of intense debate.

METHODS AND RESULTS

Using a meta-analysis of 28 experimental (mouse, rat, dog) and human HF microarray studies, we demonstrate that gene expression changes are characterized by a coordinated and reciprocal regulation of major metabolic and signaling pathways. In response to a wide variety of stressors in animal models of HF, including ischemia, pressure overload, tachypacing, chronic isoproterenol infusion, Chagas disease, and transgenic mouse models, major metabolic pathways are invariably downregulated, whereas cell signaling pathways are upregulated. In contrast to this uniform transcriptional pattern that recapitulates a fetal gene expression program in experimental animal models of HF, human HF microarray studies displayed a greater heterogeneity, with some studies even showing upregulation of metabolic and downregulation of signaling pathways in end-stage human hearts. These discrepant results between animal and human studies are due to a number of factors, prominently cardiac disease and variable exposure to cold cardioplegic solution in nonfailing human samples, which can downregulate transcripts involved in oxidative phosphorylation (OXPHOS), thus mimicking gene expression patterns observed in failing samples. Additionally, β-blockers and ACE inhibitor use in end-stage human HF was associated with higher levels of myocardial OXPHOS transcripts, thus partially reversing the fetal gene expression pattern. In human failing samples, downregulation of metabolism was associated with hemodynamic markers of disease severity.

CONCLUSIONS

Irrespective of the etiology, gene expression in failing myocardium is characterized by downregulation of metabolic transcripts and concomitant upregulation of cell signaling pathways. Gene expression changes along this metabolic-signaling axis in mammalian myocardium are a consistent feature in the heterogeneous transcriptional response observed in phenotypically similar models of HF.

Potential therapeutic benefits of strategies directed to mitochondria

The mitochondrion is the most important organelle in determining continued cell survival and cell death. Mitochondrial dysfunction leads to many human maladies, including cardiovascular diseases, neurodegenerative disease, and cancer. These mitochondria-related pathologies range from early infancy to senescence. The central premise of this review is that if mitochondrial abnormalities contribute to the pathological state, alleviating the mitochondrial dysfunction would contribute to attenuating the severity or progression of the disease. Therefore, this review will examine the role of mitochondria in the etiology and progression of several diseases and explore potential therapeutic benefits of targeting mitochondria in mitigating the disease processes. Indeed, recent advances in mitochondrial biology have led to selective targeting of drugs designed to modulate and manipulate mitochondrial function and genomics for therapeutic benefit. These approaches to treat mitochondrial dysfunction rationally could lead to selective protection of cells in different tissues and various disease states. However, most of these approaches are in their infancy.

Therapeutic targeting of mitochondrial superoxide in hypertension

RATIONALE

Superoxide (O2(-) ) has been implicated in the pathogenesis of many human diseases including hypertension; however, commonly used antioxidants have proven ineffective in clinical trials. It is possible that these agents are not adequately delivered to the subcellular sites of superoxide production.

OBJECTIVE

Because the mitochondria are important sources of reactive oxygen species, we postulated that mitochondrial targeting of superoxide scavenging would have therapeutic benefit.

METHODS AND RESULTS

In this study, we found that the hormone angiotensin (Ang II) increased endothelial mitochondrial superoxide production. Treatment with the mitochondria-targeted antioxidant mitoTEMPO decreased mitochondrial O2(-), inhibited the total cellular O2(-), reduced cellular NADPH oxidase activity, and restored the level of bioavailable NO. These effects were mimicked by overexpressing the mitochondrial MnSOD (SOD2), whereas SOD2 depletion with small interfering RNA increased both basal and Ang II-stimulated cellular O2(-). Treatment of mice in vivo with mitoTEMPO attenuated hypertension when given at the onset of Ang II infusion and decreased blood pressure by 30 mm Hg following establishment of both Ang II-induced and DOCA salt hypertension, whereas a similar dose of nontargeted TEMPOL was not effective. In vivo, mitoTEMPO decreased vascular O2(-), increased vascular NO production and improved endothelial-dependent relaxation. Interestingly, transgenic mice overexpressing mitochondrial SOD2 demonstrated attenuated Ang II-induced hypertension and vascular oxidative stress similar to mice treated with mitoTEMPO.

CONCLUSIONS

These studies show that mitochondrial O2(-) is important for the development of hypertension and that antioxidant strategies specifically targeting this organelle could have therapeutic benefit in this and possibly other diseases.

A suggested role for mitochondria in Noonan syndrome

Noonan syndrome (NS) is an autosomal dominant disorder, and a main feature is congenital heart malformation. About 50% of cases are caused by gain-of-function mutations in the tyrosine phosphatase SHP2/PTPN11, a downstream regulator of ERK/MAPK. Recently it was reported that SHP2 also localizes to the mitochondrial intercristae/intermembrane space (IMS), but the role of SHP2 in mitochondria is unclear. The mitochondrial oxidative phosphorylation (OxPhos) system provides the vast majority of cellular energy and produces reactive oxygen species (ROS). Changes in ROS may interfere with organ development such as that observed in NS patients. Several phosphorylation sites have been found in OxPhos components including cytochrome c oxidase (CcO) and cytochrome c (Cytc), and we hypothesized that OxPhos complexes may be direct or indirect targets of SHP2. We analyzed mitochondrial function using mouse fibroblasts from wild-types, SHP2 knockdowns, and D61G SHP2 mutants leading to constitutively active SHP2, as found in NS patients. Levels of OxPhos complexes were similar except for CcO and Cytc, which were 37% and 28% reduced in the D61G cells. However, CcO activity was significantly increased, as we also found for two lymphoblast cell lines from NS patients with two independent mutations in PTPN11. D61G cells showed lower mitochondrial membrane potential and 30% lower ATP content compared to controls. ROS were significantly increased; aconitase activity, a marker for ROS-induced damage, was decreased; and catalase activity was increased in D61G cells. We propose that decreased energy levels and/or increased ROS may explain, at least in part, some of the clinical features in NS that overlap with children with mitochondrial disorders.

Multidimensional protein identification technology for clinical proteomic analysis

Proteomics technologies demonstrate enormous data-gathering capabilities to discover disease-specific biomarkers in serum, plasma, urine, tissue and other biological samples. The traditional way to achieve this consists of protein separation performed using two-dimensional polyacrylamide gel electrophoresis (2DE). However, the 2DE approach has its drawbacks with respect to automation, sensitivity, and throughput. Considerable efforts have been devoted to the development of non-gel-based proteome separation technologies able to resolve complex protein and peptide mixtures prior to mass spectrometric (MS) analysis. This review discusses some of the most recent advances in multidimensional peptide separation techniques compatible with MS analysis, including gel electrophoresis, isoelectric focusing, capillary electrophoresis and liquid chromatography techniques. Based on future perspectives and our experiences, special attention is given to the application of two-dimensional chromatographic separation coupled to MS, the so-called multidimensional protein identification technology approach.

Heterogeneity of mitochondria and mitochondrial function within cells as another level of mitochondrial complexity

Beyond their fundamental role in energy metabolism, mitochondria perform a great variety of other important cellular functions. However, the interplay among these various roles of mitochondria is still poorly understood, and the underlying mechanisms can be related to system level properties. Importantly, mitochondria localized in different regions of a cell may display different morphology, dissimilar biochemical properties, or may differently interact with other intracellular structures. Recent advances in live imaging techniques have also revealed a functional heterogeneity of mitochondria with respect to mitochondrial redox state, membrane potential, respiratory activity, uncoupling proteins, mitochondrial ROS and calcium. An important and still unresolved question is how the heterogeneity of mitochondrial function and the regional specializations of mitochondria are mechanistically realized in the cell and to what extent this could be dependent on environmental aspects. Distinct mitochondrial subsets may also exhibit different responses to substrates and inhibitors and may vary in their sensitivity to pathology, resistance to apoptosis, oxidative stress, thus also demonstrating heterogeneous behavior. All these observations strongly suggest that the intracellular position, organization and the specific surroundings of mitochondria within the cell define their functional features, while also implying that different mitochondrial subpopulations, clusters or even single mitochondrion may execute diverse processes in a cell. The heterogeneity of mitochondrial function demonstrates an additional level of mitochondrial complexity and is a new, challenging area in mitochondrial research that potentially leads to the integration of mitochondrial bioenergetics and cell physiology with various physiological and pathophysiological implications.

Cardiac-specific overexpression of caveolin-3 induces endogenous cardiac protection by mimicking ischemic preconditioning

BACKGROUND

Caveolae, lipid-rich microdomains of the sarcolemma, localize and enrich cardiac-protective signaling molecules. Caveolin-3 (Cav-3), the dominant isoform in cardiac myocytes, is a determinant of caveolar formation. We hypothesized that cardiac myocyte-specific overexpression of Cav-3 would enhance the formation of caveolae and augment cardiac protection in vivo.

METHODS AND RESULTS

Ischemic preconditioning in vivo increased the formation of caveolae. Adenovirus for Cav-3 increased caveolar formation and phosphorylation of survival kinases in cardiac myocytes. A transgenic mouse with cardiac myocyte-specific overexpression of Cav-3 (Cav-3 OE) showed enhanced formation of caveolae on the sarcolemma. Cav-3 OE mice subjected to ischemia/reperfusion injury had a significantly reduced infarct size relative to transgene-negative mice. Endogenous cardiac protection in Cav-3 OE mice was similar to wild-type mice undergoing ischemic preconditioning; no increased protection was observed in preconditioned Cav-3 OE mice. Cav-3 knockout mice did not show endogenous protection and showed no protection in response to ischemic preconditioning. Cav-3 OE mouse hearts had increased basal Akt and glycogen synthase kinase-3beta phosphorylation comparable to wild-type mice exposed to ischemic preconditioning. Wortmannin, a phosphoinositide 3-kinase inhibitor, attenuated basal phosphorylation of Akt and glycogen synthase kinase-3beta and blocked cardiac protection in Cav-3 OE mice. Cav-3 OE mice had improved functional recovery and reduced apoptosis at 24 hours of reperfusion.

CONCLUSIONS

Expression of caveolin-3 is both necessary and sufficient for cardiac protection, a conclusion that unites long-standing ultrastructural and molecular observations in the ischemic heart. The present results indicate that increased expression of caveolins, apparently via actions that depend on phosphoinositide 3-kinase, has the potential to protect hearts exposed to ischemia/reperfusion injury.

Cytoplasmic signaling in the control of mitochondrial uproar?

The concept of a pre-emptive strike as a good means to prevent greater harm may be frequently over-stressed in daily life. However, biological systems in a homeostatic balance are prepared to withstand a certain degree of hostile fire by rather passive means. This also applies to the maintenance of cell survival, where a plethora of protective proteins provide safeguard against erroneous activation of death pathways. Apart from these mechanisms active processes are also essential for the maintenance of cellular homeostasis, commonly referred to as survival signaling. Frequently their targets may be mitochondrial, assuring organelle integrity, which is essential for continued energy production and survival. Transient or permanent failures in these cellular defense strategies result in pathophysiological conditions, which manifest themselves e.g. as cancer or ischemia/reperfusion-associated organ damage.

Transcriptional control of mitochondrial biogenesis: the central role of PGC-1alpha

Although the concept of energy starvation in the failing heart was proposed decades ago, still very little is known about the origin of energetic failure. Recent advances in molecular biology have started to elucidate the transcriptional events governing mitochondrial biogenesis. In particular, a great step was taken with the discovery that peroxisome proliferator-activated receptor gamma co-activator (PGC-1alpha) is the master regulator of mitochondrial biogenesis. The molecular mechanisms underlying the downregulation of PGC-1alpha and the consequent decrease in mitochondrial function in heart failure are, however, still poorly understood. Indeed, the main pathways involved in mitochondrial biogenesis are thought to be up- rather than down-regulated in pathological hypertrophy and heart failure. The current review summarizes recent advances in this field and is restricted to the heart when cardiac data are available.

Molecular mechanisms of angiotensin II-mediated mitochondrial dysfunction: linking mitochondrial oxidative damage and vascular endothelial dysfunction

Mitochondrial dysfunction is a prominent feature of most cardiovascular diseases. Angiotensin (Ang) II is an important stimulus for atherogenesis and hypertension; however, its effects on mitochondrial function remain unknown. We hypothesized that Ang II could induce mitochondrial oxidative damage that in turn might decrease endothelial nitric oxide (NO.) bioavailability and promote vascular oxidative stress. The effect of Ang II on mitochondrial ROS, mitochondrial respiration, membrane potential, glutathione, and endothelial NO. was studied in isolated mitochondria and intact bovine aortic endothelial cells using electron spin resonance, dihydroethidium high-performance liquid chromatography -based assay, Amplex Red and cationic dye fluorescence. Ang II significantly increased mitochondrial H2O2 production. This increase was blocked by preincubation of intact cells with apocynin (NADPH oxidase inhibitor), uric acid (scavenger of peroxynitrite), chelerythrine (protein kinase C inhibitor), N(G)-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor), 5-hydroxydecanoate (mitochondrial ATP-sensitive potassium channels inhibitor), or glibenclamide. Depletion of p22(phox) subunit of NADPH oxidase with small interfering RNA also inhibited Ang II-mediated mitochondrial ROS production. Ang II depleted mitochondrial glutathione, increased state 4 and decreased state 3 respirations, and diminished mitochondrial respiratory control ratio. These responses were attenuated by apocynin, 5-hydroxydecanoate, and glibenclamide. In addition, 5-hydroxydecanoate prevented the Ang II-induced decrease in endothelial NO. and mitochondrial membrane potential. Therefore, Ang II induces mitochondrial dysfunction via a protein kinase C-dependent pathway by activating the endothelial cell NADPH oxidase and formation of peroxynitrite. Furthermore, mitochondrial dysfunction in response to Ang II modulates endothelial NO. and generation, which in turn has ramifications for development of endothelial dysfunction.

Localization of phosphorylated alphaB-crystallin to heart mitochondria during ischemia-reperfusion

The cytosolic small heat shock protein alphaB-crystallin (alphaBC) is a molecular chaperone expressed in large quantities in the heart, where it protects from stresses such as ischemia-reperfusion (I/R). Upon I/R, p38 MAP kinase activation leads to phosphorylation of alphaBC on Ser(59) (P-alphaBC-S59), which increases its protective ability. alphaBC confers protection, in part, by interacting with and affecting the functions of key components in stressed cells. We investigated the hypothesis that protection from I/R damage in the heart by P-alphaBC-S59 can be mediated by localization to mitochondria. We found that P-alphaBC-S59 localized to mitochondria isolated from untreated mouse hearts and that this localization increased more than threefold when the hearts were subjected to ex vivo I/R. Mitochondrial P-alphaBC-S59 decreased when hearts were treated with the p38 inhibitor SB-202190. Moreover, SB-202190-treated hearts exhibited more tissue damage and less functional recovery upon reperfusion than controls. I/R activates mitochondrial permeability transition (MPT) pore opening, which increases cell damage. We found that mitochondria incubated with a recombinant mutant form of alphaBC that mimics P-alphaBC-S59 exhibited decreased calcium-induced MPT pore opening. These results indicate that mitochondria may be among the key components in stressed cells with which P-alphaBC-S59 interacts and that this localization may protect the myocardium, in part, by modulating MPT pore opening and, thus, reducing I/R injury.

Mitochondrial and energetic cardiac phenotype in hypothyroid rat. Relevance to heart failure

Changes in thyroid status are associated with profound alterations in biochemical and physiological functioning of cardiac muscle, although its impact on cardiac energy metabolism is still debated. Similarities between the changes in cardiac gene expression in pathological hypertrophy leading to heart failure and hypothyroidism prompted scientists to suggest a role for thyroid hormone status in the development of metabolic and functional alterations in this disease. We thus investigated the effects of hypothyroidism on cardiac energy metabolism. Hypothyroid state (HYPO) was induced by thyroidectomy and propyl-thio-uracyl in male rats for 3 weeks. We examined the effects of hypothyroid state on oxidative capacity and mitochondrial substrate utilization by measuring oxygen consumption of saponin permeabilized cardiac fibers, mitochondrial biogenesis by reverse transcription polymerase chain reaction and energy metabolism, and energy transfer enzymes by spectrophotometry. The results show that maximal oxidative capacity of the myocardium was decreased from 24.9 +/- 0.9 in control (CT) to 19.3 +/- 0.7 micromol O(2) min(-1) g dry weight(-1) in HYPO. However, protein content and messenger RNA (mRNA) of PGC-1alpha and mRNA of its transcription cascade that is thought to control mitochondrial content in normal myocardium and heart failure, were unchanged in HYPO. Mitochondrial utilization of glycerol-3P (-70%), malate (-45%), and octanoate (-24%) but not pyruvate was decreased in HYPO. Moreover, the creatine kinase system and energy transfer were hardly affected in HYPO. Besides, hypothyroidism decreased the activation of other signaling pathways like p38 mitogen-activated protein kinases, AMP-activated protein kinase, and calcineurin. These results show that cellular hypothyroidism can hardly account for the specific energetic alterations of heart failure.