Mitochondrial sodium/calcium exchanger (NCLX) regulates basal and starvation-induced autophagy through calcium signaling.

Mitochondria shape intracellular Ca2+ signaling through the concerted activity of Ca2+ uptake via mitochondrial calcium uniporters and efflux by Na+ /Ca2+ exchangers (NCLX). Here, we describe a novel relationship among NCLX, intracellular Ca2+ , and autophagic activity. Conditions that stimulate autophagy in vivo and in vitro, such as caloric restriction and nutrient deprivation, upregulate NCLX expression in hepatic tissue and cells. Conversely, knockdown of NCLX impairs basal and starvation-induced autophagy. Similarly, acute inhibition of NCLX activity by CGP 37157 affects bulk and endoplasmic reticulum autophagy (ER-phagy) without significant impacts on mitophagy. Mechanistically, CGP 37157 inhibited the formation of FIP200 puncta and downstream autophagosome biogenesis. Inhibition of NCLX caused decreased cytosolic Ca2+ levels, and intracellular Ca2+ chelation similarly suppressed autophagy. Furthermore, chelation did not exhibit an additive effect on NCLX inhibition of autophagy, demonstrating that mitochondrial Ca2+ efflux regulates autophagy through the modulation of Ca2+ signaling. Collectively, our results show that the mitochondrial Ca2+ extrusion pathway through NCLX is an important regulatory node linking nutrient restriction and autophagy regulation.

Goldilocks calcium concentrations and the regulation of oxidative phosphorylation: Too much, too little, or just right.

Calcium (Ca2+) is a key regulator in diverse intracellular signaling pathways and has long been implicated in metabolic control and mitochondrial function. Mitochondria can actively take up large amounts of Ca2+, thereby acting as important intracellular Ca2+ buffers and affecting cytosolic Ca2+ transients. Excessive mitochondrial matrix Ca2+ is known to be deleterious due to opening of the mitochondrial permeability transition pore (mPTP) and consequent membrane potential dissipation, leading to mitochondrial swelling, rupture, and cell death. Moderate Ca2+ within the organelle, on the other hand, can directly or indirectly activate mitochondrial matrix enzymes, possibly impacting on ATP production. Here, we aimed to determine in a quantitative manner if extra- or intramitochondrial Ca2+ modulates oxidative phosphorylation in mouse liver mitochondria and intact hepatocyte cell lines. To do so, we monitored the effects of more modest versus supraphysiological increases in cytosolic and mitochondrial Ca2+ on oxygen consumption rates. Isolated mitochondria present increased respiratory control ratios (a measure of oxidative phosphorylation efficiency) when incubated with low (2.4 ± 0.6 µM) and medium (22.0 ± 2.4 µM) Ca2+ concentrations in the presence of complex I-linked substrates pyruvate plus malate and α-ketoglutarate, respectively, but not complex II-linked succinate. In intact cells, both low and high cytosolic Ca2+ led to decreased respiratory rates, while ideal rates were present under physiological conditions. High Ca2+ decreased mitochondrial respiration in a substrate-dependent manner, mediated by mPTP. Overall, our results uncover a Goldilocks effect of Ca2+ on liver mitochondria, with specific "just right" concentrations that activate oxidative phosphorylation.

Metabolic dysfunction induced by HFD + L-NAME preferentially affects hippocampal mitochondria, impacting spatial memory in rats.

High-fat diet-induced metabolic changes are not restricted to the onset of cardiovascular diseases, but also include effects on brain functions related to learning and memory. This study aimed to evaluate mitochondrial markers and function, as well as cognitive function, in a rat model of metabolic dysfunction. Eight-week-old male Wistar rats were subjected to either a control diet or a two-hit protocol combining a high fat diet (HFD) with the nitric oxide synthase inhibitor L-NAME in the drinking water. HFD plus L-NAME induced obesity, hypertension, and increased serum cholesterol. These rats exhibited bioenergetic dysfunction in the hippocampus, characterized by decreased oxygen (O2) consumption related to ATP production, with no changes in H2O2 production. Furthermore, OPA1 protein expression was upregulated in the hippocampus of HFD + L-NAME rats, with no alterations in other morphology-related proteins. Consistently, HFD + L-NAME rats showed disruption of performance in the Morris Water Maze Reference Memory test. The neocortex did not exhibit either bioenergetic changes or alterations in H2O2 production. Calcium uptake rate and retention capacity in the neocortex of HFD + L-NAME rats were not altered. Our results indicate that hippocampal mitochondrial bioenergetic function is disturbed in rats exposed to a HFD plus L-NAME, thus disrupting spatial learning, whereas neocortical function remains unaffected.

Mitochondrial sodium/calcium exchanger NCLX regulates glycolysis in astrocytes, impacting on cognitive performance.

Intracellular Ca2+ concentrations are strictly controlled by plasma membrane transporters, the endoplasmic reticulum, and mitochondria, in which Ca2+ uptake is mediated by the mitochondrial calcium uniporter complex (MCUc), while efflux occurs mainly through the mitochondrial Na+ /Ca2+ exchanger (NCLX). RNAseq database repository searches led us to identify the Nclx transcript as highly enriched in astrocytes when compared with neurons. To assess the role of NCLX in mouse primary culture astrocytes, we inhibited its function both pharmacologically or genetically. This resulted in re-shaping of cytosolic Ca2+ signaling and a metabolic shift that increased glycolytic flux and lactate secretion in a Ca2+ -dependent manner. Interestingly, in vivo genetic deletion of NCLX in hippocampal astrocytes improved cognitive performance in behavioral tasks, whereas hippocampal neuron-specific deletion of NCLX impaired cognitive performance. These results unveil a role for NCLX as a novel modulator of astrocytic glucose metabolism, impacting on cognition.

Changes in mitochondrial morphology modulate LPS-induced loss of calcium homeostasis in BV-2 microglial cells.

Microglial activation involves both fragmentation of the mitochondrial network and changes in cellular Ca2+ homeostasis, but possible modifications in mitochondrial calcium uptake have never been described in this context. Here we report that activated microglial BV-2 cells have impaired mitochondrial calcium uptake, including lower calcium retention capacity and calcium uptake rates. These changes were not dependent on altered expression of the mitochondrial calcium uniporter. Respiratory capacity and the inner membrane potential, key determinants of mitochondrial calcium uptake, are both decreased in activated microglial BV-2 cells. Modified mitochondrial calcium uptake correlates with impaired cellular calcium signaling, including reduced ER calcium stores, and decreased replenishment by store operated calcium entry (SOCE). Induction of mitochondrial fragmentation through Mfn2 knockdown in control cells mimicked this effect, while inhibiting LPS-induced mitochondrial fragmentation by a dominant negative form of Drp1 prevented it. Overall, our results show that mitochondrial fragmentation induced by LPS promotes altered Ca2+ homeostasis in microglial cells, a new aspect of microglial activation that could be a key feature in the inflammatory role of these cells.

Mitochondrial morphology regulates organellar Ca2+ uptake and changes cellular Ca2+ homeostasis.

Changes in mitochondrial size and shape have been implicated in several physiologic processes, but their role in mitochondrial Ca2+ uptake regulation and overall cellular Ca2+ homeostasis is largely unknown. Here we show that modulating mitochondrial dynamics toward increased fusion through expression of a dominant negative (DN) form of the fission protein [dynamin-related protein 1 (DRP1)] markedly increased both mitochondrial Ca2+ retention capacity and Ca2+ uptake rates in permeabilized C2C12 cells. Similar results were seen using the pharmacological fusion-promoting M1 molecule. Conversely, promoting a fission phenotype through the knockdown of the fusion protein mitofusin (MFN)-2 strongly reduced the mitochondrial Ca2+ uptake speed and capacity in these cells. These changes were not dependent on modifications in mitochondrial calcium uniporter expression, inner membrane potentials, or the mitochondrial permeability transition. Implications of mitochondrial morphology modulation on cellular calcium homeostasis were measured in intact cells; mitochondrial fission promoted lower basal cellular calcium levels and lower endoplasmic reticulum (ER) calcium stores, as indicated by depletion with thapsigargin. Indeed, mitochondrial fission was associated with ER stress. Additionally, the calcium-replenishing process of store-operated calcium entry was impaired in MFN2 knockdown cells, whereas DRP1-DN-promoted fusion resulted in faster cytosolic Ca2+ increase rates. Overall, our results show a novel role for mitochondrial morphology in the regulation of mitochondrial Ca2+ uptake, which impacts cellular Ca2+ homeostasis.-Kowaltowski, A. J., Menezes-Filho, S. L., Assali, E. A., Gonçalves, I. G., Cabral-Costa, J. V., Abreu, P., Miller, N., Nolasco, P., Laurindo, F. R. M., Bruni-Cardoso, A., Shirihai, O. Mitochondrial morphology regulates organellar Ca2+ uptake and changes cellular Ca2+ homeostasis.

Mitochondrial Ca2+ handling as a cell signaling hub: lessons from astrocyte function.

Astrocytes are a heterogenous population of macroglial cells spread throughout the central nervous system with diverse functions, expression signatures, and intricate morphologies. Their subcellular compartments contain a distinct range of mitochondria, with functional microdomains exhibiting widespread activities, such as controlling local metabolism and Ca2+ signaling. Ca2+ is an ion of utmost importance, both physiologically and pathologically, and participates in critical central nervous system processes, including synaptic plasticity, neuron-astrocyte integration, excitotoxicity, and mitochondrial physiology and metabolism. The mitochondrial Ca2+ handling system is formed by the mitochondrial Ca2+ uniporter complex (MCUc), which mediates Ca2+ influx, and the mitochondrial Na+/Ca2+ exchanger (NCLX), responsible for most mitochondrial Ca2+ efflux, as well as additional components, including the mitochondrial permeability transition pore (mtPTP). Over the last decades, mitochondrial Ca2+ handling has been shown to be key for brain homeostasis, acting centrally in physiopathological processes such as astrogliosis, astrocyte-neuron activity integration, energy metabolism control, and neurodegeneration. In this review, we discuss the current state of knowledge regarding the mitochondrial Ca2+ handling system molecular composition, highlighting its impact on astrocytic homeostasis.

Longitudinal left ventricular strain in hypertrophic cardiomyopathy: correlation with nonsustained ventricular tachycardia.

AIMS: Stratifying risk of sudden death is a major issue in the management of hypertrophic cardiomyopathy (HCM). Existing risk factors have low positive predictive value and new parameters are needed. Determination of myocardial deformation (strain) by 2D Speckle tracking is a new methodology for determining LV regional function and could correlate with myocite disarray and fibrosis. The aim of this study was to assess the relationship between strain analysis and nonsustained ventricular tachycardia (NSVT) in patients with HCM. METHODS: Thirty-two consecutive patients with HCM (mean age 55, 17-78) were studied. All underwent standard echocardiographic and two-dimensional strain examination. Twenty-four-hour Holter monitoring was performed and echocardiographic parameters were correlated with NSVT. RESULTS: Nine patients (28%) had one or more episodes of NSVT. Patients with NSVT had a higher value of maximal LV thickness (23.6 mm vs. 19.4 mm, P = 0.027). There were no significant associations between NSVT on Holter monitoring and LV outflow gradient left atrial diameter, E/Em or left ventricle ejection fraction. Patients with HCM and NSVT had significant reductions in mid septal, apical-septal, apical-lateral strain, and in mean longitudinal strain. Midseptal strain >-10.5% had a sensitivity of 89% and a specificity of 74% (area under the curve, 0.787; P < 0.0013) for predicting NSVT independently of age or maximum wall thickness. CONCLUSION: Lower end-systolic peak longitudinal strain obtained by 2D speckle tracking was a predictor of NSVT in HCM patients. This parameter could become a useful tool in stratifying SCD risk in this population.

Noncompaction of the ventricular myocardium: characterization and follow-up of an affected population.

Noncompaction of the ventricular myocardium (NVM) is a rare congenital disease caused by an arrest in normal myocardial embryogenesis, leading to persistence of numerous prominent trabeculations which communicate with the left ventricle. It was first described as a congenital condition affecting children, but several cases have been reported of late presentation, and recent studies suggest it may be underdiagnosed. The main clinical manifestations are congestive heart failure, arrhythmias (supraventricular or ventricular) and systemic embolism. We describe a series of twenty patients, focusing on clinical history, echocardiography and follow-up.

[Severe left ventricular outflow tract obstruction as a complication of mitral valve repair: case report]. / Obstrução grave do tracto de saída do ventrículo esquerdo como complicação de valvuloplastia mitral: a propósito de um caso clínico.

Systolic anterior motion (SAM) is a postoperative complication of mitral valve repair, with an incidence of 5 to 10%. Early recognition of the signs and symptoms of SAM is essential for the management of these patients. This article focuses on the pathophysiology and dynamics of SAM and the treatment strategies described in the literature. The authors present a case study and echocardiographic images illustrating the clinical relevance of the mechanism involved, in order to clarify whether surgical reintervention is necessary.

[Description of a new mutation in a female patient with Fabry disease]. / Mutação de novo causadora de doença de Fabry em paciente do sexo feminino.

Fabry disease is caused by intracellular accumulation of glycosphingolipids in various tissues, secondary to mutations in the GLA gene (Xq22). Classically described as affecting hemizygous males with no residual alpha-galactosidase A activity, it is now known to affect both sexes, with later and less severe manifestations in females. The manifestations of this disease are systemic: neurological, cutaneous (angiokeratomas), renal, cardiovascular (left ventricular hypertrophy, valve thickening or rhythm disturbances), cochlear-vestibular, and cerebrovascular. In the absence of treatment there is progressive damage to vital organs with renal failure, stroke, heart failure or rhythm perturbations, leading to severe impairment of quality of life as well as reduced life expectancy. We describe the case of a female patient with a history of cryptogenic ischemic stroke at the age of 38 years and chronic renal failure with proteinuria, who presented to the emergency room with atrial fibrillation. The echocardiogram revealed concentric left ventricular hypertrophy, diastolic dysfunction and decreased longitudinal strain in the basal septum. In the context of a screening protocol, she was diagnosed with Fabry disease and a previously undescribed mutation was identified.

Delayed lead perforation: a rare cause of pacemaker dysfunction.

A 65-year-old woman with a dual-chamber pacemaker implanted in 2006 for symptomatic carotid sinus hypersensitivity was incidentally found to have loss of ventricular capture on routine pacemaker interrogation. A chest X-ray raised the suspicion of perforation and migration of the right ventricular lead, confirmed by three-dimensional echocardiogram and CT scan. On the basis of this case, we review myocardial lead perforation, including predisposing factors, pathophysiological mechanisms, diagnostic approach and therapeutic options.

Effects of a high fat diet on liver mitochondria: increased ATP-sensitive K+ channel activity and reactive oxygen species generation.

High fat diets are extensively associated with health complications within the spectrum of the metabolic syndrome. Some of the most prevalent of these pathologies, often observed early in the development of high-fat dietary complications, are non-alcoholic fatty liver diseases. Mitochondrial bioenergetics and redox state changes are also widely associated with alterations within the metabolic syndrome. We investigated the mitochondrial effects of a high fat diet leading to non-alcoholic fatty liver disease in mice. We found that the diet does not substantially alter respiratory rates, ADP/O ratios or membrane potentials of isolated liver mitochondria. However, H(2)O(2) release using different substrates and ATP-sensitive K(+) transport activities are increased in mitochondria from animals on high fat diets. The increase in H(2)O(2) release rates was observed with different respiratory substrates and was not altered by modulators of mitochondrial ATP-sensitive K(+) channels, indicating it was not related to an observed increase in K(+) transport. Altogether, we demonstrate that mitochondria from animals with diet-induced steatosis do not present significant bioenergetic changes, but display altered ion transport and increased oxidant generation. This is the first evidence, to our knowledge, that ATP-sensitive K(+) transport in mitochondria can be modulated by diet.

Neurological disorders and mitochondria.

The brain is highly dependent on mitochondrial energy metabolism. As a result, mitochondrial dysfunction is a central aspect of many adult-onset neurological diseases, including stroke, ALS, Alzheimer's, Huntington's, and Parkinson's diseases. We review here how different mitochondrial functions, including oxidative phosphorylation, mitochondrial dynamics, oxidant generation, cell death regulation, Ca2+ homeostasis, and proteostasis are involved in these disorders.

Double coronary thrombosis in a patient with Behçet's disease.

Behçet's disease is a chronic relapsing multisystem autoinflammatory condition, in which cardiac involvement is rare, but among the most life-threatening complications. Treatment is largely empirical, and is aimed at suppressing vasculitis. In this role glucocorticoids and colchicine are frequently used. We present the case of a 42-year-old male with previously diagnosed Behçet's disease presenting to our emergency department with an anterior-inferior STEMI. He presented combined thrombosis of the distal anterior descending coronary artery and proximal right coronary artery, and was treated with sequential primary percutaneous coronary interventions and implantation of drug-eluting stents, but required two interventions due to high thrombotic load. His clinical course during hospitalization was good, with no systolic dysfunction at discharge. During follow-up, he has so far had no new cardiovascular events.

Left ventricular noncompaction: diagnosis by three-dimensional echocardiography.

Left ventricular noncompaction (LVNC) is a rare congenital disease caused by an arrest in normal myocardial embryogenesis, leading to persistence of numerous prominent trabeculations that communicate with the left ventricle. It was first described as a congenital condition affecting children, but several cases have been reported of late presentation. The main clinical manifestations are congestive heart failure, arrhythmias (supraventricular or ventricular) and systemic embolism. We present the case of a 51-year-old patient brought to our emergency department after an episode of symptomatic ventricular flutter requiring electrical cardioversion. Two-dimensional echocardiography with color Doppler suggested the diagnosis and the three-dimensional echocardiogram revealed the deep trabeculations typical of LVNC.

Intermittent fasting uncovers and rescues cognitive phenotypes in PTEN neuronal haploinsufficient mice.

Phosphatase and tensin homolog (PTEN) is an important protein with key modulatory functions in cell growth and survival. PTEN is crucial during embryogenesis and plays a key role in the central nervous system (CNS), where it directly modulates neuronal development and synaptic plasticity. Loss of PTEN signaling function is associated with cognitive deficits and synaptic plasticity impairment. Accordingly, Pten mutations have a strong link with autism spectrum disorder. In this study, neuronal Pten haploinsufficient male mice were subjected to a long-term environmental intervention - intermittent fasting (IF) - and then evaluated for alterations in exploratory, anxiety and learning and memory behaviors. Although no significant effects on spatial memory were observed, mutant mice showed impaired contextual fear memory in the passive avoidance test - an outcome that was effectively rescued by IF. In this study, we demonstrated that IF modulation, in addition to its rescue of the memory deficit, was also required to uncover behavioral phenotypes otherwise hidden in this neuronal Pten haploinsufficiency model.

skn-1 is required for interneuron sensory integration and foraging behavior in Caenorhabditis elegans.

Nrf2/skn-1, a transcription factor known to mediate adaptive responses of cells to stress, also regulates energy metabolism in response to changes in nutrient availability. The ability to locate food sources depends upon chemosensation. Here we show that Nrf2/skn-1 is expressed in olfactory interneurons, and is required for proper integration of multiple food-related sensory cues in Caenorhabditis elegans. Compared to wild type worms, skn-1 mutants fail to perceive that food density is limiting, and display altered chemo- and thermotactic responses. These behavioral deficits are associated with aberrant AIY interneuron morphology and migration in skn-1 mutants. Both skn-1-dependent AIY autonomous and non-autonomous mechanisms regulate the neural circuitry underlying multisensory integration of environmental cues related to energy acquisition.