Mitochondrial metabolic remodeling in response to genetic and environmental perturbations

Protein aggregation and biomolecular condensation in hypoxic environments (Review)

Due to molecular forces, biomacromolecules assemble into liquid condensates or solid aggregates, and their corresponding formation and dissolution processes are controlled. Protein homeostasis is disrupted by increasing age or environmental stress, leading to irreversible protein aggregation. Hypoxic pressure is an important factor in this process, and uncontrolled protein aggregation has been widely observed in hypoxia‑related conditions such as neurodegenerative disease, cardiovascular disease, hypoxic brain injury and cancer. Biomolecular condensates are also high‑order complexes assembled from macromolecules. Although they exist in different phase from protein aggregates, they are in dynamic balance under certain conditions, and their activation or assembly are considered as important regulatory processes in cell survival with hypoxic pressure. Therefore, a better understanding of the relationship between hypoxic stress, protein aggregation and biomolecular condensation will bring marked benefits in the clinical treatment of various diseases. The aim of the present review was to summarize the underlying mechanisms of aggregate assembly and dissolution induced by hypoxic conditions, and address recent breakthroughs in understanding the role of aggregates in hypoxic‑related diseases, given the hypotheses that hypoxia induces macromolecular assemblage changes from a liquid to a solid phase, and that adenosine triphosphate depletion and ATP‑driven inactivation of multiple protein chaperones play important roles among the process. Moreover, it is anticipated that an improved understanding of the adaptation in hypoxic environments could extend the overall survival of patients and provide new strategies for hypoxic‑related diseases.

Paraganglioma of the Head and Neck: A Review

OBJECTIVE

To review the epidemiology, presentation, diagnosis, and management of head and neck paragangliomas.

METHODS

A literature review of english language papers with focus on most current literature.

RESULTS

Paragangliomas (PGLs) are a group of neuroendocrine tumors that arise in the parasympathetic or sympathetic ganglia. Head and neck PGLs (HNPGLs) comprise 65% to 70% of all PGLs and account for 0.6% of all head and neck cancers. The majority of HNPGLs are benign, and 6% to 19% of all HNPGLs develop metastasis outside the tumor site and significantly compromise survival. PGLs can have a familial etiology with germline sequence variations in different susceptibility genes, with the gene encoding succinate dehydrogenase being the most common sequence variation, or they can arise from somatic sequence variations or fusion genes. Workup includes biochemical testing to rule out secretory components, although it is rare in HNPGLs. In addition, imaging modalities, such as computed tomography and magnetic resonance imaging, help in monitoring in surgical planning. Functional imaging with DOTATATE-positron emission tomography, 18F-fluorodeoxyglucose, or 18F-fluorohydroxyphenylalanine may be necessary to rule out sites of metastases. The management of HNPGLs is complex depending on pathology, location, and aggressiveness of the tumor. Treatment ranges from observation to resection to systemic treatment. Similarly, the prognosis ranges from a normal life expectancy to a 5-year survival of 11.8% in patients with distant metastasis.

CONCLUSION

Our review is a comprehensive summary of the incidence, mortality, pathogenesis, presentation, workup and management of HNPGLs.

Succinate Dehydrogenase, Succinate, and Superoxides: A Genetic, Epigenetic, Metabolic, Environmental Explosive Crossroad

Research focused on succinate dehydrogenase (SDH) and its substrate, succinate, culminated in the 1950s accompanying the rapid development of research dedicated to bioenergetics and intermediary metabolism. This allowed researchers to uncover the implication of SDH in both the mitochondrial respiratory chain and the Krebs cycle. Nowadays, this theme is experiencing a real revival following the discovery of the role of SDH and succinate in a subset of tumors and cancers in humans. The aim of this review is to enlighten the many questions yet unanswered, ranging from fundamental to clinically oriented aspects, up to the danger of the current use of SDH as a target for a subclass of pesticides.

Aberrant Expression of ACO1 in Vasculatures Parallels Progression of Idiopathic Pulmonary Fibrosis

Rationale: Idiopathic pulmonary fibrosis (IPF) is characterized by mitochondrial dysfunction. However, details about the non-mitochondrial enzymes that sustain the proliferative nature of IPF are unclear. Aconitases are a family of enzymes that sustain metabolism inside and outside mitochondria. It is hypothesized that aconitase 1 (ACO1) plays an important role in the pathogenesis of IPF given that ACO1 represents an important metabolic hub in the cytoplasm.

Objectives: To determine if ACO1 expression in IPF lungs shows specific patterns that may be important in the pathogenesis of IPF. To determine the similarities and differences in ACO1 expression in IPF, bleomycin-treated, and aging lungs.

Methods: ACO1 expression in IPF lungs were characterized and compared to non-IPF controls by western blotting, immunostaining, and enzymatic activity assay. ACO1-expressing cell types were identified by multicolor immunostaining. Using similar methods, the expression profiles of ACO1 in IPF lungs versus bleomycin-treated and aged mice were investigated.

Measurements and main results: Lower lobes of IPF lungs, unlike non-IPF controls, exhibit significantly high levels of ACO1. Most of the signals colocalize with von Willebrand factor (vWF), a lineage marker for vascular endothelial cells. Bleomycin-treated lungs also show high ACO1 expressions. However, most of the signals colocalize with E-cadherin and/or prosurfactant protein C, representative epithelial cell markers, in remodeled areas.

Conclusions: A characteristic ACO1 expression profile observed in IPF vasculatures may be a promising diagnostic target. It also may give clues as to how de novo angiogenesis contributes to the irreversible nature of IPF.

Systems approaches to understand oxygen sensing: how multi-omics has driven advances in understanding oxygen-based signalling

Hypoxia is a common denominator in the pathophysiology of a variety of human disease states. Insight into how cells detect, and respond to low oxygen is crucial to understanding the role of hypoxia in disease. Central to the hypoxic response is rapid changes in the expression of genes essential to carry out a wide range of functions to adapt the cell/tissue to decreased oxygen availability. These changes in gene expression are co-ordinated by specialised transcription factors, changes to chromatin architecture and intricate balances between protein synthesis and destruction that together establish changes to the cellular proteome. In this article, we will discuss the advances of our understanding of the cellular oxygen sensing machinery achieved through the application of 'omics-based experimental approaches.

Beyond mitochondria: Alternative energy-producing pathways from all strata of life

It is well-established that mitochondria are the powerhouses of the cell, producing adenosine triphosphate (ATP), the universal energy currency. However, the most significant strengths of the electron transport chain (ETC), its intricacy and efficiency, are also its greatest downfalls. A reliance on metal complexes (FeS clusters, hemes), lipid moities such as cardiolipin, and cofactors including alpha-lipoic acid and quinones render oxidative phosphorylation vulnerable to environmental toxins, intracellular reactive oxygen species (ROS) and fluctuations in diet. To that effect, it is of interest to note that temporal disruptions in ETC activity in most organisms are rarely fatal, and often a redundant number of failsafes are in place to permit continued ATP production when needed. Here, we highlight the metabolic reconfigurations discovered in organisms ranging from parasitic Entamoeba to bacteria such as pseudomonads and then complex eukaryotic systems that allow these species to adapt to and occasionally thrive in harsh environments. The overarching aim of this review is to demonstrate the plasticity of metabolic networks and recognize that in times of duress, life finds a way.

Ca2+ transfer to mitochondria: a spark of life in unexpected conditions

The inositol 1,4,5-triphosphate receptor (InsP3R)-mediated calcium (Ca²⁺) transfer to mitochondria is important to maintain mitochondrial respiration and bioenergetics in normal and cancer cells, even though cancer cells have defective oxidative phosphorylation (OXPHOS). Here, we discuss how tumor mitochondria could become a feasible therapeutic target to treat tumors that depend on reductive carboxylation.

Higher Lactate Level and Lactate-to-Pyruvate Ratio in Autism Spectrum Disorder

Mitochondrial dysfunction is considered one of the pathophysiological mechanisms of autism spectrum disorder (ASD). However, previous studies of biomarkers associated with mitochondrial dysfunction in ASD have revealed inconsistent results. The objective of this study was to evaluate biochemical markers associated with mitochondrial dysfunction in subjects with ASD and their unaffected family members. Lactate and pyruvate levels, as well as the lactate-to-pyruvate ratio, were examined in the peripheral blood of probands with ASD (Affected Group, AG) and their unaffected family members (biological parents and unaffected siblings, Unaffected Group, UG). Lactate ≥22 mg/dl, pyruvate ≥1.4 mg/dl, and lactate-to-pyruvate ratio >25 were defined as abnormal. The clinical variables were compared between subjects with higher (>25) and lower (≤25) lactate-to-pyruvate ratios within the AG. The AG (n=59) had a significantly higher lactate and lactate-to-pyruvate ratio than the UG (n=136). The frequency of subjects with abnormally high lactate levels and lactate-to-pyruvate ratio was significantly higher in the AG (lactate 31.0% vs. 9.5%, ratio 25.9% vs. 7.3%, p<0.01). The relationship between lactate level and the repetitive behavior domain of the Autism Diagnostic Interview-Revised was statistically significant. These results suggest that biochemical markers related to mitochondrial dysfunction, especially higher lactate levels and lactate-to-pyruvate ratio, might be associated with the pathophysiology of ASD. Further larger studies using unrelated individuals are needed to control for the possible effects of age and sex on chemical biomarker levels.

Using complex II as an emerging therapeutic target for the treatment of muscle lesions

After patients has been trapped into skeletal muscle injury, hypoxic and dysfunctional mitochondria brings about a crisis in energy supply that severely disrupts the repair of skeletal muscle. This study aims to elucidate injury-induced adaptations in the mitochondria and provide statistics for the role of complex II in instilling cells with energy under hypoxic conditions. Fifty-six male Wistar rats were divided into control, 12 h, 2 d, 5 d, 7 d, 10 d, 15 d, and 30 d postinjury groups. Contusion injury was made via an instrumented drop-mass technique delivering single impact to the posterior surface of the gastrocnemius of one limb of the rats. ROS levels, loss of mitochondrial membrane potential (MMP), activities of marker enzymes (miCK, LDH, and ALP), and activities of complexes I–III were determined. Our findings reveal that the first 2 d postinjury, especially at 12 h, is the period with most severe oxidative stress. After injury, the activities of mitochondrial complexes I–III display different behaviors based on time and various energy production mechanisms. Our results highlight that complex II participates in electron transport in the acute phase of blunt trauma. We proposed that CII could be a therapeutic target in muscle lesions.

Glutathione deficiency-elicited reprogramming of hepatic metabolism protects against alcohol-induced steatosis

Depletion of glutathione (GSH) is considered a critical pathogenic event promoting alcohol-induced lipotoxicity. We recently show that systemic GSH deficiency in mice harboring a global disruption of the glutamate-cysteine ligase modifier subunit (Gclm) gene confers protection against alcohol-induced steatosis. While several molecular pathways have been linked to the observed hepatic protection, including nuclear factor erythroid 2-related factor 2 and AMP-activated protein kinase pathways, the precise mechanisms are yet to be defined. In this study, to gain insights into the molecular mechanisms underpinning the protective effects of loss of GCLM, global profiling of hepatic polar metabolites combined with liver microarray analysis was carried out. These inter-omics analyses revealed both low GSH- and alcohol-driven changes in multiple cellular pathways involving the metabolism of amino acids, fatty acid, glucose and nucleic acids. Notably, several metabolic changes were uniquely present in alcohol-treated Gclm-null mouse livers, including acetyl-CoA enrichment and diversion of acetyl-CoA flux from lipogenesis to alterative metabolic pathways, elevation in glutamate concentration, and induction of the glucuronate pathway and nucleotide biosynthesis. These metabolic features reflect low GSH-elicited cellular response to chronic alcohol exposure, which is beneficial for the maintenance of hepatic redox and metabolic homeostasis. The current study indicates that fine-tuning of hepatic GSH pool may evoke metabolic reprogramming to cope with alcohol-induced cellular stress.

The mitochondrial carrier Citrin plays a role in regulating cellular energy during carcinogenesis

Citrin, encoded by SLC25A13 gene, is an inner mitochondrial transporter that is part of the malate-aspartate shuttle, which regulates the NAD+/NADH ratio between the cytosol and mitochondria. Citrullinemia type II (CTLN-II) is an inherited disorder caused by germline mutations in SLC25A13, manifesting clinically in growth failure that can be alleviated by dietary restriction of carbohydrates. The association of citrin with glycolysis and NAD+/NADH ratio led us to hypothesize that it may play a role in carcinogenesis. Indeed, we find that citrin is upregulated in multiple cancer types and is essential for supplementing NAD+ for glycolysis and NADH for oxidative phosphorylation. Consequently, citrin deficiency associates with autophagy, whereas its overexpression in cancer cells increases energy production and cancer invasion. Furthermore, based on the human deleterious mutations in citrin, we found a potential inhibitor of citrin that restricts cancerous phenotypes in cells. Collectively, our findings suggest that targeting citrin may be of benefit for cancer therapy.

Correlation between pri-miR-124 (rs531564) polymorphism and congenital heart disease susceptibility in Chinese population at two different altitudes: a case-control and in silico study

The development of congenital heart disease (CHD) is a complicated process and affected by multiple environmental factors, as genetic factors, and the interactions among those factors. Previous studies have shown that intrauterine hypoxic environment exposure is a risk factor of CHD, but the genetic factors involved in the process are not clear. In this study, given that tetralogy of Fallot (TOF) is a CHD with hypoxemia as its primary pathophysiological manifestation, an in silico analysis was performed to reveal the relationship between potential target genes (miR-124) with the energy metabolism in non-syndromic TOF patients' cardiomyocyte. Furthermore, the study investigated the correlation between the primary miR-124 (rs531564) polymorphism and CHD susceptibility in 432 sporadic patients and 450 controls from two different altitude provinces (city) in China. Our study indicated that the minor C allele of rs531564 correlated with reduced risk of CHD in the low altitude city. Besides, the C allele has elevated frequency in the high-altitude group. Therefore, our findings suggest that the minor C allele of rs531564 SNP may be involved in the reduction of the risk of CHD in a way that interacts with the intrauterine hypoxic environmental factors.

Effects of intermittent hypoxia training on leukocyte pyruvate dehydrogenase kinase 1 (PDK-1) mRNA expression and blood insulin level in prediabetes patients

PURPOSE

Intermittent hypoxia training/treatment (IHT) is an emerging therapeutic approach to alleviate chronic diseases, such as diabetes. The present study investigated the effects of IHT on blood leucocyte pyruvate dehydrogenase kinase 1 (PDK-1) mRNA expression and its relationship with the changes in blood insulin level.

METHODS

Seven adult healthy volunteers and 11 prediabetic patients participated in this study. A 3-week course of IHT consisted of a 40-min session of 4 cycles of 5-min 12% O₂ and 5-min room air breathing per day, 3 sessions per week for 3 weeks (i.e., total 9 sessions of IHT). Plasma insulin levels and leukocyte PDK-1 mRNA expression were determined at various time points either under fasting condition or following oral glucose tolerance test (OGTT). Correlation between the IHT-induced changes in PDK-1 mRNA and insulin or glucose levels in the same serological samples was analyzed.

RESULTS

At pre-IHT baseline, PDK-1 mRNA expression was two times higher in prediabetes than control subjects. IHT resulted in significant augmentation in PDK-1 mRNA expression (> twofold) in prediabetes at the end of 3-week IHT and remained elevated 1 month after IHT, which was correlated with a significantly reduced insulin release and lower blood glucose after glucose loading with OGTT.

CONCLUSION

IHT can trigger beneficial effects in normalizing blood insulin levels in prediabetic patients under oral glucose load, which were closely correlated with an enhanced mRNA expression of PDK-1 in leukocytes. Further clinical trials are warranted to validate the utility of IHT as a non-invasive complementary therapy against diabetes-associated pathologies.

Maturation of Cardiac Energy Metabolism During Perinatal Development

As one of the highest energy consumer organ in mammals, the heart has to be provided with a high amount of energy as soon as its first beats in utero. During the development of this organ, energy is produced within the cardiac muscle cell depending on substrate availability, oxygen pressure and cardiac workload that drastically change at birth. Thus, energy metabolism relying essentially on carbohydrates in fetal heart is very different from the adult one and birth is the trigger of a profound maturation which ensures the transition to a highly oxidative metabolism depending on lipid utilization. To face the substantial increase in cardiac workload resulting from the growth of the organism during the postnatal period, the heart not only develops its capacity for energy production but also undergoes a hypertrophic growth to adapt its contractile capacity to its new function. This leads to a profound cytoarchitectural remodeling of the cardiomyocyte which becomes a highly compartmentalized structure. As a consequence, within the mature cardiac muscle, energy transfer between energy producing and consuming compartments requires organized energy transfer systems that are established in the early postnatal life. This review aims at describing the major rearrangements of energy metabolism during the perinatal development.

Preconditioning of primary human renal proximal tubular epithelial cells without tryptophan increases survival under hypoxia by inducing autophagy

PURPOSE

Hypoxia plays a significant role in the pathogenesis of acute kidney injury (AKI). Autophagy protects from AKI. Amino acid deprivation induces autophagy. The effect of L-tryptophan depletion on survival and autophagy in cultures of renal proximal tubular epithelial cells (RPTECs) under hypoxia was evaluated.

METHODS

RPTECs were preconditioned in a medium containing or not tryptophan, following culture under hypoxia and treatment with or without the autophagy inhibitor chloroquine. Cell survival was assessed by cell imaging, the level of certain proteins by western blotting and cellular ATP fluorometrically.

RESULTS

Preconditioning of RPTECs in a medium without tryptophan activated general control nonderepressible 2 kinase and induced changes that favored autophagy and cell survival under hypoxic conditions. Additionally, it increased cellular ATP, while it inhibited apoptosis. Inhibition of autophagy nullified the induced increase in cellular ATP and cell survival by the absence of tryptophan. The absence of tryptophan increased p53, although its effect on p53's transcriptional targets was heterogeneous. In accordance with the decreased apoptosis, expression of p21 increased, while expression of Bax decreased. The expression of BNIP3L, which may be pro-apoptotic or pro-autophagic, increased. Considering the decreased apoptosis, it is likely that tryptophan depletion enhances autophagy through a p53-mediated increase of BNIP3L.

CONCLUSION

Preconditioning of primary human RPTECs in a medium without tryptophan increases their survival under hypoxia by inducing autophagy. Identifying new molecular mechanisms that protect renal tissue from hypoxia could be proved clinically important in the prevention of AKI.

Developmental plasticity of mitochondrial function in American alligators, Alligator mississippiensis

The effect of hypoxia on cellular metabolism is well documented in adult vertebrates, but information is entirely lacking for embryonic organisms. The effect of hypoxia on embryonic physiology is particularly interesting, as metabolic responses during development may have life-long consequences, due to developmental plasticity. To this end, we investigated the effects of chronic developmental hypoxia on cardiac mitochondrial function in embryonic and juvenile American alligators (Alligator mississippiensis). Alligator eggs were incubated in 21% or 10% oxygen from 20 to 90% of embryonic development. Embryos were either harvested at 90% development or allowed to hatch and then reared in 21% oxygen for 3 yr. Ventricular mitochondria were isolated from embryonic/juvenile alligator hearts. Mitochondrial respiration and enzymatic activities of electron transport chain complexes were measured with a microrespirometer and spectrophotometer, respectively. Developmental hypoxia induced growth restriction and increased relative heart mass, and this phenotype persisted into juvenile life. Embryonic mitochondrial function was not affected by developmental hypoxia, but at the juvenile life stage, animals from hypoxic incubations had lower levels of Leak respiration and higher respiratory control ratios, which is indicative of enhanced mitochondrial efficiency. Our results suggest developmental hypoxia can have life-long consequences for alligator morphology and metabolic function. Further investigations are necessary to reveal the adaptive significance of the enhanced mitochondrial efficiency in the hypoxic phenotype.