Mitochondrial and sarcoplasmic protein changes in hearts from copper-deficient rats: up-regulation of PGC-1alpha transcript and protein as a cause for mitochondrial biogenesis in copper deficiency

Maternal dietary copper deficiency induces cardiomyopathy and liver injury in mice by activating autophagy

Maternal nutritional deficiencies during pregnancy result in birth defects and elevate the risk of cardiovascular diseases and metabolic diseases. Accumulating evidence suggests that deficiency of copper, a fundamental trace element involved in several pivotal physiological processes, promotes the onset of multiple diseases, notably heart and liver diseases. Yet, exploration into the effects of maternal copper deficiency (CuD) on offspring is still limited. In this study, we hypothesized that maternal CuD induced cardiomyopathy and liver injury in offspring through the activation of autophagy. We established a maternal CuD mouse model by feeding pregnant C57BL/6 mice with a CuD diet until the end of the experiment. Echocardiography, histological analysis, western blotting, and quantitative polymerase chain reaction were performed on offspring at postnatal day 14. We found that maternal CuD caused growth retardation and early postnatal death in the offspring. Furthermore, our results revealed that CuD induced cardiac systolic dysfunction, cardiac hypertrophy, hepatic steatosis, and liver injury. Moreover, higher expression of LC3 and lower expression of p62 were observed in the heart tissues and liver tissues of CuD mice compared with the control group, indicating that CuD induced autophagy activation. In conclusion, maternal CuD caused severely deleterious effects on the heart and liver of the offspring via activating autophagy.

Copper homeostasis and copper-induced cell death in the pathogenesis of cardiovascular disease and therapeutic strategies

Copper is a vital mineral, and an optimal amount of copper is required to support normal physiologic processes in various systems, including the cardiovascular system. Over the past few decades, copper-induced cell death, named cuproptosis, has become increasingly recognized as an important process mediating the pathogenesis and progression of cardiovascular disease (CVD), including atherosclerosis, stroke, ischemia-reperfusion injury, and heart failure. Therefore, an in-depth understanding of the regulatory mechanisms of cuproptosis in CVD may be useful for improving CVD management. Here, we review the relationship between copper homeostasis and cuproptosis-related pathways in CVD, as well as therapeutic strategies addressing copper-induced cell death in CVD.

Morinda officinalis polysaccharide attenuates osteoporosis in rats underwent bilateral ovariectomy by suppressing the PGC-1α/PPARγ pathway

OBJECTIVE

Osteoporosis (OP) is a widespread disease that causes risks of spine and hip fractures. Morinda officinalis polysaccharide (MOP) shows therapeutic potential in OP. This article intended to understand the mechanism by which MOP impacts bone mineral density (BMD) and serum trace elements in OP rats.

METHODS

OP rat models were established by bilateral ovariectomy (OVX). Rats were intragastrically administered with MOP or ZLN005 [the activator of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α)] since the first day after operation for 8 weeks. Microstructural changes in OP rats were analyzed using micro-computed tomography system. Contents of serum Zn, Cu, Fe, and Mg in rats were measured. Levels of serum superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), GSH, and malondialdehyde (MDA) in rats were determined by Enzyme-linked immunosorbent assay. Protein levels of PGC-1α and peroxisome proliferator-activated receptor γ (PPARγ) in cartilage tissues of rats were determined via Western blotting.

RESULTS

MOP enhanced BMD, bone volume per trabecular volume (BV/TV), Tb.N, and Tb.Th and reduced Tb.Sp in the distal femur of OVX rats, elevated levels of serum Cu, Fe, and Mg and contents of SOD, GSH, and GSH-PX and decreased MDA content. Moreover, MOP suppressed the PGC-1α/PPARγ pathway. Activation of PGC-1α partially abolished the action of MOP on ameliorating OP in OVX rats and strengthening anti-oxidation ability.

CONCLUSION

MOP mitigated OP in OVX rats by inhibiting the PGC-1α/PPARγ pathway.

Micronutrient deficiencies in heart failure: Mitochondrial dysfunction as a common pathophysiological mechanism?

Heart failure is a devastating clinical syndrome, but current therapies are unable to abolish the disease burden. New strategies to treat or prevent heart failure are urgently needed. Over the past decades, a clear relationship has been established between poor cardiac performance and metabolic perturbations, including deficits in substrate uptake and utilization, reduction in mitochondrial oxidative phosphorylation and excessive reactive oxygen species production. Together, these perturbations result in progressive depletion of cardiac adenosine triphosphate (ATP) and cardiac energy deprivation. Increasing the delivery of energy substrates (e.g., fatty acids, glucose, ketones) to the mitochondria will be worthless if the mitochondria are unable to turn these energy substrates into fuel. Micronutrients (including coenzyme Q10, zinc, copper, selenium and iron) are required to efficiently convert macronutrients to ATP. However, up to 50% of patients with heart failure are deficient in one or more micronutrients in cross-sectional studies. Micronutrient deficiency has a high impact on mitochondrial energy production and should be considered an additional factor in the heart failure equation, moving our view of the failing myocardium away from an "an engine out of fuel" to "a defective engine on a path to self-destruction." This summary of evidence suggests that supplementation with micronutrients-preferably as a package rather than singly-might be a potential therapeutic strategy in the treatment of heart failure patients.

Mitochondrial membrane transporters and metabolic switch in heart failure

Mitochondrial dysfunction is widely recognized as a major factor for the progression of cardiac failure. Mitochondrial uptake of metabolic substrates and their utilization for ATP synthesis, electron transport chain activity, reactive oxygen species levels, ion homeostasis, mitochondrial biogenesis, and dynamics as well as levels of reactive oxygen species in the mitochondria are key factors which regulate mitochondrial function in the normal heart. Alterations in these functions contribute to adverse outcomes in heart failure. Iron imbalance and oxidative stress are also major factors for the evolution of cardiac hypertrophy, heart failure, and aging-associated pathological changes in the heart. Mitochondrial ATP-binding cassette (ABC) transporters have a key role in regulating iron metabolism and maintenance of redox status in cells. Deficiency of mitochondrial ABC transporters is associated with an impaired mitochondrial electron transport chain complex activity, iron overload, and increased levels of reactive oxygen species, all of which can result in mitochondrial dysfunction. In this review, we discuss the role of mitochondrial ABC transporters in mitochondrial metabolism and metabolic switch, alterations in the functioning of ABC transporters in heart failure, and mitochondrial ABC transporters as possible targets for therapeutic intervention in cardiac failure.

Perspectives on the Role and Relevance of Copper in Cardiac Disease

Cardiac hypertrophy as a result of dietary copper deficiency has been studied for 40 plus years and is the subject of this review. While connective tissue anomalies occur, a hallmark pathology is cardiac hypertrophy, increased mitochondrial biogenesis, with disruptive cristae, vacuolization of mitochondria, and deposition of lipid droplets. Electrocardiogram abnormalities have been demonstrated along with biochemical changes especially as it relates to the copper-containing enzyme cytochrome c oxidase. The master controller of mitochondrial biogenesis, PGC1-α expression and protein, along with other proteins and transcriptional factors that play a role are upregulated. Nitric oxide, vascular endothelial growth factor, and cytochrome c oxidase all may enhance the upregulation of mitochondrial biogenesis. Marginal copper intakes reveal similar pathologies in the absence of cardiac hypertrophy. Reversibility of the copper-deficient rat heart with a copper-replete diet has resulted in mixed results, depending on both the animal model used and temporal relationships. New information has revealed that copper supplementation may rescue cardiac hypertrophy induced by pressure overload.

Adaptive responses of mitochondria to mild copper deprivation involve changes in morphology, OXPHOS remodeling and bioenergetics

Copper is an essential cofactor of complex IV of the electron transfer chain, and it is directly involved in the generation of mitochondrial membrane potential. Its deficiency induces the formation of ROS, large mitochondria and anemia. Thus, there is a connection between copper metabolism and bioenergetics, mitochondrial dynamics and erythropoiesis. Copper depletion might end in cellular apoptosis or necrosis. However, before entering into those irreversible processes, mitochondria may execute a series of adaptive responses. Mitochondrial adaptive responses (MAR) may involve multiple and diverse mechanisms for preserving cell life, such as mitochondrial dynamics, OXPHOS remodeling and bioenergetics output. In this study, a mild copper deficiency was produced in an animal model through intraperitoneal injections of bathocuproine disulfonate in order to study the MAR. Under these conditions, a new type of mitochondrial morphology was discovered in the liver. Termed the "butternut squash" mitochondria, it coexisted with normal and swollen mitochondria. Western blot analyses of mitochondrial dynamics proteins showed an up-regulation of MFN-2 and OPA1 fusion proteins. Furthermore, isolated liver mitochondria displayed OXPHOS remodeling through a decrease in supercomplex activity with a concomitant increase at an individual level of complexes I and IV, higher respiratory rates at complex I and II levels, higher oligomycin-insensitive respiration, and lower respiratory control ratio values when compared to the control group. As expected, total ATP and ATP/ADP values were not significantly different, since animal's health was not compromised. As a whole, these results describe a compensatory and adaptive response of metabolism and bioenergetics under copper deprivation.

Can we optimise the exercise training prescription to maximise improvements in mitochondria function and content?

BACKGROUND

While there is agreement that exercise is a powerful stimulus to increase both mitochondrial function and content, we do not know the optimal training stimulus to maximise improvements in mitochondrial biogenesis.

SCOPE OF REVIEW

This review will focus predominantly on the effects of exercise on mitochondrial function and content, as there is a greater volume of published research on these adaptations and stronger conclusions can be made.

MAJOR CONCLUSIONS

The results of cross-sectional studies, as well as training studies involving rats and humans, suggest that training intensity may be an important determinant of improvements in mitochondrial function (as determined by mitochondrial respiration), but not mitochondrial content (as assessed by citrate synthase activity). In contrast, it appears that training volume, rather than training intensity, may be an important determinant of exercise-induced improvements in mitochondrial content. Exercise-induced mitochondrial adaptations are quickly reversed following a reduction or cessation of physical activity, highlighting that skeletal muscle is a remarkably plastic tissue. Due to the small number of studies, more research is required to verify the trends highlighted in this review, and further studies are required to investigate the effects of different types of training on the mitochondrial sub-populations and also mitochondrial adaptations in different fibre types. Further research is also required to better understand how genetic variants influence the large individual variability for exercise-induced changes in mitochondrial biogenesis.

GENERAL SIGNIFICANCE

The importance of mitochondria for both athletic performance and health underlines the importance of better understanding the factors that regulate exercise-induced changes in mitochondrial biogenesis. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.

Elevated circulating levels of copper and nickel are found in elderly subjects with left ventricular hypertrophy

Identified risk factors for left ventricular hypertrophy (LVH) are hypertension, diabetes and obesity. However, since these risk factors only explain a part of the variation in left ventricular mass, we investigated if trace and heavy metals might also play a role in LVH. In the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study, left ventricular mass index (LVMI) and relative wall thickness (RWT) were determined by echocardiography together with eleven different trace and heavy metals in 993 subjects aged 70 years. Only copper levels were significantly related to LVMI following adjustment for sex, blood pressure, antihypertensive treatment, diabetes and body mass index (BMI) (p<0.0001). However, both copper (Cu) and nickel (Ni) were related to RWT following adjustment (p<0.0001). When divided into four geometric groups, both Cu and Ni were elevated in subjects with concentric remodelling and concentric LVH, but not in those with eccentric hypertrophy, when compared to subjects with a normal left ventricle. No relationships were found for zinc, aluminium, manganese, molybdenum, mercury, lead, cadmium, cobalt or chromium. Elevated levels of copper and nickel are found in elderly subjects with LVH, especially of the concentric type, following adjustment for known risk factors for LVH.

Transition metals and mitochondrial metabolism in the heart

Transition metals are essential to many biological processes in almost all organisms from bacteria to humans. Their versatility, which arises from an ability to undergo reduction-oxidation chemistry, enables them to act as critical cofactors of enzymes throughout the cell. Accumulation of metals, however, can also lead to oxidative stress and cellular damage. The importance of metals to both enzymatic reactions and oxidative stress makes them key players in mitochondria. Mitochondria are the primary energy-generating organelles of the cell that produce ATP through a chain of enzymatic complexes that require transition metals, and are highly sensitive to oxidative damage. Moreover, the heart is one of the most mitochondrially-rich tissues in the body, making metals of particular importance to cardiac function. In this review, we focus on the current knowledge about the role of transition metals (specifically iron, copper, and manganese) in mitochondrial metabolism in the heart. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

The cardiac copper chaperone proteins Sco1 and CCS are up-regulated, but Cox 1 and Cox4 are down-regulated, by copper deficiency

Copper is ferried in a cell complexed to chaperone proteins, and in the heart much copper is required for cytochrome c oxidase (Cox). It is not completely understood how copper status affects the levels of these proteins. Here we determined if dietary copper deficiency could up- or down-regulate select copper chaperone proteins and Cox subunits 1 and 4 in cardiac tissue of rats. Sixteen weanling male Long-Evans rats were randomized into treatment groups, one group receiving a copper-deficient diet (<1 mg Cu/kg diet) and one group receiving a diet containing adequate copper (6 mg Cu/kg diet) for 5 weeks. Hearts were removed, weighed, and non-myofibrillar proteins separated to analyze for levels of CCS, Sco1, Ctr1, Cox17, Cox1, and Cox4 by SDS-PAGE and Western blotting. No changes were observed in the concentrations of CTR1 and Cox17 between copper-adequate and copper-deficient rats. CCS and Sco1 were up-regulated and Cox1 and Cox4 were both down-regulated as a result of copper deficiency. These data suggest that select chaperone proteins and may be up-regulated, and Cox1 and 4 down-regulated, by a dietary copper deficiency, whereas others appear not to be affected by copper status.

Influence of copper on early development: prenatal and postnatal considerations

Copper (Cu) is an essential nutrient whose requirement is increased during pregnancy and lactation. These represent times of critical growth and development, and the fetus and neonate are particularly vulnerable to deficiencies of this nutrient. Genetic mutations that predispose the offspring to inadequate stores of Cu can be life threatening as is observed in children with Menkes disease. During the last decade, severe Cu deficiency, once thought to be a rare condition, has been reported in the literature at an increasing frequency. Secondary Cu deficiencies can be induced by a variety of ways such as excessive zinc or iron intake, certain drugs, and bariatric surgery. Premature and low birth weight infants can be born with low Cu stores. A number of mechanisms can contribute to the teratogenicity of Cu including decreased activity of select cuproenzymes, increased oxidative stress, decreased nitric oxide availability, altered iron metabolism, abnormal extracellular matrix protein crosslinking, decreased angiogenesis and altered cell signaling among others. The brain, heart, and vessels as well as tissues such as lung, skin and hair, and systems including the skeletal, immune, and blood systems, are negatively affected by suboptimal Cu during development. Additionally, persistent structural, biochemical, and functional adverse effects in the offspring are noted even when Cu supplementation is initiated after birth, supporting the concept that adequate Cu nutriture during pregnancy and lactation is critical for normal development. Although Cu-containing IUDs are an effective method for increasing intrauterine Cu concentrations and for reducing the risk of pregnancy, high amounts of dietary Cu are not thought to represent a direct developmental risk.