Mitochondrial remodeling: Rearranging, recycling, and reprogramming

Quantitative proteomics reveals cellular responses to individual mAb expression and tunicamycin in CHO cells

Chinese hamster ovary (CHO) cells are popular in the pharmaceutical industry for their ability to produce high concentrations of antibodies and their resemblance to human cells in terms of protein glycosylation patterns. Current data indicate the relevance of CHO cells in the biopharmaceutical industry, with a high number of product commendations and a significant market share for monoclonal antibodies. To enhance the production capabilities of CHO cells, a deep understanding of their cellular and molecular composition is crucial. Genome sequencing and proteomic analysis have provided valuable insights into the impact of the bioprocessing conditions, productivity, and product quality. In our investigation, we conducted a comparative analysis of proteomic profiles in high and low monoclonal antibody-producing cell lines and studied the impact of tunicamycin (TM)-induced endoplasmic reticulum (ER) stress. We examined the expression levels of different proteins including unfolded protein response (UPR) target genes by using label-free quantification techniques for protein abundance. Our results show the upregulation of proteins associated with protein folding mechanisms in low producer vs. high producer cell line suggesting a form of ER stress related to specific protein production. Further, Hspa9 and Dnaja3 are notable candidates activated by the mitochondria UPR and play important roles in protein folding processes in mitochondria. We identified significant upregulation of Nedd8 and Lgmn proteins in similar levels which may contribute to UPR stress. Interestingly, the downregulation of Hspa5/Bip and Pdia4 in response to tunicamycin treatment suggests a low-level UPR activation. KEY POINTS: • Proteome profiling of recombinant CHO cells under mild TM treatment. • Identified protein clusters are associated with the unfolded protein response (UPR). • The compared cell lines revealed noticeable disparities in protein expression levels.

Mitochondrial calcium uniporter deficiency in dentate granule cells remodels neuronal metabolism and impairs reversal learning

The mitochondrial calcium uniporter (MCU) is the main route of calcium (Ca2+) entry into neuronal mitochondria. This channel has been linked to mitochondrial Ca2+ overload and cell death under neurotoxic conditions, but its physiologic roles for normal brain function remain poorly understood. Despite high expression of MCU in excitatory hippocampal neurons, it is unknown whether this channel is required for learning and memory. Here, we genetically down-regulated the Mcu gene in dentate granule cells (DGCs) of the hippocampus and found that this manipulation increases the overall respiratory activity of mitochondrial complexes I and II, augmenting the generation of reactive oxygen species in the context of impaired electron transport chain. The metabolic remodeling of MCU-deficient neurons also involved changes in the expression of enzymes that participate in glycolysis and the regulation of the tricarboxylic acid cycle, as well as the cellular antioxidant defenses. We found that MCU deficiency in DGCs does not change circadian rhythms, spontaneous exploratory behavior, or cognitive function in middle-aged mice (11-13 months old), when assessed with a food-motivated working memory test with three choices. DGC-targeted down-regulation of MCU significantly impairs reversal learning assessed with an 8-arm radial arm water maze but does not affect their ability to learn the task for the first time. Our results indicate that neuronal MCU plays an important physiologic role in memory formation and may be a potential therapeutic target to develop interventions aimed at improving cognitive function in aging, neurodegenerative diseases, and brain injury.

Sit4 Genetically Interacts with Vps27 to Regulate Mitochondrial Function and Lifespan in Saccharomyces cerevisiae

The Sit4 protein phosphatase plays a key role in orchestrating various cellular processes essential for maintaining cell viability during aging. We have previously shown that SIT4 deletion promotes vacuolar acidification, mitochondrial derepression, and oxidative stress resistance, increasing yeast chronological lifespan. In this study, we performed a proteomic analysis of isolated vacuoles and yeast genetic interaction analysis to unravel how Sit4 influences vacuolar and mitochondrial function. By employing high-resolution mass spectrometry, we show that sit4Δ vacuolar membranes were enriched in Vps27 and Hse1, two proteins that are part of the endosomal sorting complex required for transport-0. In addition, SIT4 exhibited a negative genetic interaction with VPS27, as sit4∆vps27∆ double mutants had a shortened lifespan compared to sit4∆ and vps27∆ single mutants. Our results also show that Vps27 did not increase sit4∆ lifespan by improving protein trafficking or vacuolar sorting pathways. However, Vps27 was critical for iron homeostasis and mitochondrial function in sit4∆ cells, as sit4∆vps27∆ double mutants exhibited high iron levels and impaired mitochondrial respiration. These findings show, for the first time, cross-talk between Sit4 and Vps27, providing new insights into the mechanisms governing chronological lifespan.

Mitochondrial Calcium Uniporter (MCU) is Involved in an Ischemic Postconditioning Effect Against Ischemic Reperfusion Brain Injury in Mice

The phenomenon of ischemic postconditioning (PostC) is known to be neuroprotective against ischemic reperfusion (I/R) injury. One of the key processes in PostC is the opening of the mitochondrial ATP-dependent potassium (mito-KATP) channel and depolarization of the mitochondrial membrane, triggering the release of calcium ions from mitochondria through low-conductance opening of the mitochondrial permeability transition pore. Mitochondrial calcium uniporter (MCU) is known as a highly sensitive transporter for the uptake of Ca2+ present on the inner mitochondrial membrane. The MCU has attracted attention as a new target for treatment in diseases, such as neurodegenerative diseases, cancer, and ischemic stroke. We considered that the MCU may be involved in PostC and trigger its mechanisms. This research used the whole-cell patch-clamp technique on hippocampal CA1 pyramidal cells from C57BL mice and measured changes in spontaneous excitatory post-synaptic currents (sEPSCs), intracellular Ca2+ concentration, mitochondrial membrane potential, and N-methyl-D-aspartate receptor (NMDAR) currents under inhibition of MCU by ruthenium red 265 (Ru265) in PostC. Inhibition of MCU increased the occurrence of sEPSCs (p = 0.014), NMDAR currents (p < 0.001), intracellular Ca2+ concentration (p < 0.001), and dead cells (p < 0.001) significantly after reperfusion, reflecting removal of the neuroprotective effects in PostC. Moreover, mitochondrial depolarization in PostC with Ru265 was weakened, compared to PostC (p = 0.004). These results suggest that MCU affects mitochondrial depolarization in PostC to suppress NMDAR over-activation and prevent elevation of intracellular Ca2+ concentrations against I/R injury.

MCU complex: Exploring emerging targets and mechanisms of mitochondrial physiology and pathology

BACKGROUND

Globally, the onset and progression of multiple human diseases are associated with mitochondrial dysfunction and dysregulation of Ca2+ uptake dynamics mediated by the mitochondrial calcium uniporter (MCU) complex, which plays a key role in mitochondrial dysfunction. Despite relevant studies, the underlying pathophysiological mechanisms have not yet been fully elucidated.

AIM OF REVIEW

This article provides an in-depth analysis of the current research status of the MCU complex, focusing on its molecular composition, regulatory mechanisms, and association with diseases. In addition, we conducted an in-depth analysis of the regulatory effects of agonists, inhibitors, and traditional Chinese medicine (TCM) monomers on the MCU complex and their application prospects in disease treatment. From the perspective of medicinal chemistry, we conducted an in-depth analysis of the structure-activity relationship between these small molecules and MCU and deduced potential pharmacophores and binding pockets. Simultaneously, key structural domains of the MCU complex in Homo sapiens were identified. We also studied the functional expression of the MCU complex in Drosophila, Zebrafish, and Caenorhabditis elegans. These analyses provide a basis for exploring potential treatment strategies targeting the MCU complex and provide strong support for the development of future precision medicine and treatments.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The MCU complex exhibits varying behavior across different tissues and plays various roles in metabolic functions. It consists of six MCU subunits, an essential MCU regulator (EMRE), and solute carrier 25A23 (SLC25A23). They regulate processes, such as mitochondrial Ca2+ (mCa2+) uptake, mitochondrial adenosine triphosphate (ATP) production, calcium dynamics, oxidative stress (OS), and cell death. Regulation makes it a potential target for treating diseases, especially cardiovascular diseases, neurodegenerative diseases, inflammatory diseases, metabolic diseases, and tumors.

The endoplasmic reticulum: Homeostasis and crosstalk in retinal health and disease

The endoplasmic reticulum (ER) is the largest intracellular organelle carrying out a broad range of important cellular functions including protein biosynthesis, folding, and trafficking, lipid and sterol biosynthesis, carbohydrate metabolism, and calcium storage and gated release. In addition, the ER makes close contact with multiple intracellular organelles such as mitochondria and the plasma membrane to actively regulate the biogenesis, remodeling, and function of these organelles. Therefore, maintaining a homeostatic and functional ER is critical for the survival and function of cells. This vital process is implemented through well-orchestrated signaling pathways of the unfolded protein response (UPR). The UPR is activated when misfolded or unfolded proteins accumulate in the ER, a condition known as ER stress, and functions to restore ER homeostasis thus promoting cell survival. However, prolonged activation or dysregulation of the UPR can lead to cell death and other detrimental events such as inflammation and oxidative stress; these processes are implicated in the pathogenesis of many human diseases including retinal disorders. In this review manuscript, we discuss the unique features of the ER and ER stress signaling in the retina and retinal neurons and describe recent advances in the research to uncover the role of ER stress signaling in neurodegenerative retinal diseases including age-related macular degeneration, inherited retinal degeneration, achromatopsia and cone diseases, and diabetic retinopathy. In some chapters, we highlight the complex interactions between the ER and other intracellular organelles focusing on mitochondria and illustrate how ER stress signaling regulates common cellular stress pathways such as autophagy. We also touch upon the integrated stress response in retinal degeneration and diabetic retinopathy. Finally, we provide an update on the current development of pharmacological agents targeting the UPR response and discuss some unresolved questions and knowledge gaps to be addressed by future research.

Reactive nitrogen species as therapeutic targets for autophagy/mitophagy modulation to relieve neurodegeneration in multiple sclerosis: Potential application for drug discovery

Multiple sclerosis (MS) is a neuroinflammatory disease with limited therapeutic effects, eventually developing into handicap. Seeking novel therapeutic strategies for MS is timely important. Active autophagy/mitophagy could mediate neurodegeneration, while its roles in MS remain controversial. To elucidate the exact roles of autophagy/mitophagy and reveal its in-depth regulatory mechanisms, we conduct a systematic literature study and analyze the factors that might be responsible for divergent results obtained. The dynamic change levels of autophagy/mitophagy appear to be a determining factor for final neuron fate during MS pathology. Excessive neuronal autophagy/mitophagy contributes to neurodegeneration after disease onset at the active MS phase. Reactive nitrogen species (RNS) serve as key regulators for redox-related modifications and participate in autophagy/mitophagy modulation in MS. Nitric oxide (•NO) and peroxynitrite (ONOO-), two representative RNS, could nitrate or nitrosate Drp1/parkin/PINK1 pathway, activating excessive mitophagy and aggravating neuronal injury. Targeting RNS-mediated excessive autophagy/mitophagy could be a promising strategy for developing novel anti-MS drugs. In this review, we highlight the important roles of RNS-mediated autophagy/mitophagy in neuronal injury and review the potential therapeutic compounds with the bioactivities of inhibiting RNS-mediated autophagy/mitophagy activation and attenuating MS progression. Overall, we conclude that reactive nitrogen species could be promising therapeutic targets to regulate autophagy/mitophagy for multiple sclerosis treatment.

Identification of the cuproptosis-related hub genes and therapeutic agents for sarcopenia

Background: Along with acceleration of population aging, the increasing prevalence of sarcopenia has posed a heavy burden on families as well as society. In this context, it is of great significance to diagnose and intervene sarcopenia as early as possible. Recent evidence has indicated the role of cuproptosis in the development of sarcopenia. In this study, we aimed to seek the key cuproptosis-related genes that can be used for identification and intervention of sarcopenia.

Methods: The GSE111016 dataset was retrieved from GEO. The 31 cuproptosis-related genes (CRGs) were obtained from previous published studies. The differentially expressed genes (DEGs) and Weighed gene co-expression network analysis (WGCNA) were subsequently analyzed. The core hub genes were acquired by the intersection of DEGs, WGCNA and CRGs. Through logistic regression analysis, we established a diagnostic model of sarcopenia based on the selected biomarkers and was validated in muscle samples from GSE111006 and GSE167186. In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analysis were performed on these genes. Furthermore, the gene set enrichment analysis (GSEA), and immune cell infiltration were also conducted on the identified core genes. Finally, we screened the potential drugs targeting the potential biomarkers of sarcopenia.

Results: A total of 902 DEGs and WGCNA containing 1,281 significant genes were preliminarily selected. Intersection of DEGs, WGCNA and CRGs yielded four core genes (PDHA1, DLAT, PDHB, and NDUFC1) as potential biomarkers for the prediction of sarcopenia. The predictive model was established and validated with high AUC values. KEGG pathway and Gene Ontology biological analysis indicated these core genes may play a crucial role in energy metabolism in mitochondria, oxidation process, and aging-related degenerative diseases. In addition, the immune cells may be involved in the development of sarcopenia through mitochondrial metabolism. Finally, metformin was identified as a promising strategy of sarcopenia treatment via targeting NDUFC1.

Conclusion: The four cuproptosis-related genes PDHA1, DLAT, PDHB and NDUFC1 may be the diagnostic biomarkers for sarcopenia, and metformin holds great potential to be developed as a therapy for sarcopenia. These outcomes provide new insights for better understanding of sarcopenia and innovative therapeutic approaches.

Mitochondrial dysfunction in human hypertrophic cardiomyopathy is linked to cardiomyocyte architecture disruption and corrected by improving NADH-driven mitochondrial respiration

AIMS

Genetic hypertrophic cardiomyopathy (HCM) is caused by mutations in sarcomere protein-encoding genes (i.e. genotype-positive HCM). In an increasing number of patients, HCM occurs in the absence of a mutation (i.e. genotype-negative HCM). Mitochondrial dysfunction is thought to be a key driver of pathological remodelling in HCM. Reports of mitochondrial respiratory function and specific disease-modifying treatment options in patients with HCM are scarce.

METHODS AND RESULTS

Respirometry was performed on septal myectomy tissue from patients with HCM (n = 59) to evaluate oxidative phosphorylation and fatty acid oxidation. Mitochondrial dysfunction was most notably reflected by impaired NADH-linked respiration. In genotype-negative patients, but not genotype-positive patients, NADH-linked respiration was markedly depressed in patients with an indexed septal thickness ≥10 compared with <10. Mitochondrial dysfunction was not explained by reduced abundance or fragmentation of mitochondria, as evaluated by transmission electron microscopy. Rather, improper organization of mitochondria relative to myofibrils (expressed as a percentage of disorganized mitochondria) was strongly associated with mitochondrial dysfunction. Pre-incubation with the cardiolipin-stabilizing drug elamipretide and raising mitochondrial NAD+ levels both boosted NADH-linked respiration.

CONCLUSION

Mitochondrial dysfunction is explained by cardiomyocyte architecture disruption and is linked to septal hypertrophy in genotype-negative HCM. Despite severe myocardial remodelling mitochondria were responsive to treatments aimed at restoring respiratory function, eliciting the mitochondria as a drug target to prevent and ameliorate cardiac disease in HCM. Mitochondria-targeting therapy may particularly benefit genotype-negative patients with HCM, given the tight link between mitochondrial impairment and septal thickening in this subpopulation.

Structural basis of Ca2+ uptake by mitochondrial calcium uniporter in mitochondria: a brief review

Mitochondria are cellular organelles that perform various functions within cells. They are responsible for ATP production, cell-signal regulation, autophagy, and cell apoptosis. Because the mitochondrial proteins that perform these functions need Ca²⁺ ions for their activity, mitochondria have ion channels to selectively uptake Ca²⁺ ions from the cytoplasm. The ion channel known to play the most important role in the Ca²⁺ uptake in mitochondria is the mitochondrial calcium uniporter (MCU) holo-complex located in the inner mitochondrial membrane (IMM). This ion channel complex exists in the form of a complex consisting of the pore-forming protein through which the Ca²⁺ ions are transported into the mitochondrial matrix, and the auxiliary protein involved in regulating the activity of the Ca²⁺ uptake by the MCU holo-complex. Studies of this MCU holocomplex have long been conducted, but we didn't know in detail how mitochondria uptake Ca²⁺ ions through this ion channel complex or how the activity of this ion channel complex is regulated. Recently, the protein structure of the MCU holo-complex was identified, enabling the mechanism of Ca²⁺ uptake and its regulation by the MCU holo-complex to be confirmed. In this review, I will introduce the mechanism of action of the MCU holo-complex at the molecular level based on the Cryo-EM structure of the MCU holo-complex to help understand how mitochondria uptake the necessary Ca²⁺ ions through the MCU holo-complex and how these Ca²⁺ uptake mechanisms are regulated. [BMB Reports 2022; 55(11): 528-534].

Understanding the Role of Yeast Yme1 in Mitochondrial Function Using Biochemical and Proteomics Analyses

Mitochondrial i-AAA proteinase Yme1 is a multifunctional protein that plays important roles in maintaining mitochondrial protein homeostasis and regulating biogenesis and function of mitochondrial proteins. However, due to the complex interplay of mitochondria and the multifunctional nature of Yme1, how Yme1 affects mitochondrial function and protein homeostasis is still poorly understood. In this study, we investigated how YME1 deletion affects yeast Saccharomyces cerevisiae growth, chronological life span, mitochondrial protein homeostasis and function, with a focus on the mitochondrial oxidative phosphorylation (OXPHOS) complexes. Our results show that whilst the YME1 deleted cells grow poorly under respiratory conditions, they grow similar to wild-type yeast under fermentative conditions. However, the chronological life span is impaired, indicating that Yme1 plays a key role in longevity. Using highly enriched mitochondrial extract and proteomic analysis, we show that the abundances of many mitochondrial proteins are altered by YME1 deletion. Several components of the respiratory chain complexes II, III, IV and V were significantly decreased, suggesting that Yme1 plays an important role in maintaining the level and function of complexes II-V. This result was confirmed using blue native-PAGE and in-solution-based enzyme activity assays. Taken together, this study shows that Yme1 plays an important role in the chronological life span and mitochondrial protein homeostasis and has deciphered its function in maintaining the activity of mitochondrial OXPHOS complexes.

Structural basis of Ca2+ uptake by mitochondrial calcium uniporter in mitochondria: a brief review

Mitochondria are cellular organelles that perform various functions within cells. They are responsible for ATP production, cell-signal regulation, autophagy, and cell apoptosis. Because the mitochondrial proteins that perform these functions need Ca2+ ions for their activity, mitochondria have ion channels to selectively uptake Ca2+ ions from the cytoplasm. The ion channel known to play the most important role in the Ca2+ uptake in mitochondria is the mitochondrial calcium uniporter (MCU) holo-complex located in the inner mitochondrial membrane (IMM). This ion channel complex exists in the form of a complex consisting of the pore-forming protein through which the Ca2+ ions are transported into the mitochondrial matrix, and the auxiliary protein involved in regulating the activity of the Ca2+ uptake by the MCU holo-complex. Studies of this MCU holocomplex have long been conducted, but we didn't know in detail how mitochondria uptake Ca2+ ions through this ion channel complex or how the activity of this ion channel complex is regulated. Recently, the protein structure of the MCU holo-complex was identified, enabling the mechanism of Ca2+ uptake and its regulation by the MCU holo-complex to be confirmed. In this review, I will introduce the mechanism of action of the MCU holo-complex at the molecular level based on the Cryo-EM structure of the MCU holo-complex to help understand how mitochondria uptake the necessary Ca2+ ions through the MCU holo-complex and how these Ca2+ uptake mechanisms are regulated. [BMB Reports 2022; 55(11): 528-534].

Bone marrow adipocytes drive the development of tissue invasive Ly6Chigh monocytes during obesity

During obesity and high fat-diet (HFD) feeding in mice, sustained low-grade inflammation includes not only increased pro-inflammatory macrophages in the expanding adipose tissue, but also bone marrow (BM) production of invasive Ly6C^high monocytes. As BM adiposity also accrues with HFD, we explored the relationship between the gains in BM white adipocytes and invasive Ly6C^high monocytes by in vivo and ex vivo paradigms. We find a temporal and causal link between BM adipocyte whitening and the Ly6C^high monocyte surge, preceding the adipose tissue macrophage rise during HFD in mice. Phenocopying this, ex vivo treatment of BM cells with conditioned media from BM adipocytes or bona fide white adipocytes favoured Ly6C^high monocyte preponderance. Notably, Ly6C^high skewing was preceded by monocyte metabolic reprogramming towards glycolysis, reduced oxidative potential and increased mitochondrial fission. In sum, short-term HFD changes BM cellularity, resulting in local adipocyte whitening driving a gradual increase and activation of invasive Ly6C^high monocytes.

Expanding the phenotypic spectrum of non-alcoholic fatty liver disease and hypertriglyceridemia

Background and aims

Hypertriglyceridemia is a common feature of metabolic syndrome (MetS), as well as of non-alcoholic fatty liver disease (NAFLD), which is considered the hepatic manifestation of MetS. Fat accumulation in hepatocytes may alter mitochondrial homeostasis predisposing to advanced liver disease. Here, we report a case of a 40-year-old woman with early aggressive NAFLD due to severe hypertriglyceridemia that ensued from a combination of genetic variants and additional metabolic risk factors.

Methods

Genetic screening was performed by using whole-exome sequencing (WES), and mitochondrial structures were evaluated by TEM.

Results

At presentation, the patient is reported to have hepatomegaly, hypertriglyceridemia, and raised transaminases. Genetic analysis revealed that the patient beard heritable alterations in genes implicated in lipid handling, among which APOB, APOE, CETP, and HSPG2, accompanied by missense mutations in genes involved in mitochondrial function, i.e., AK2, ALG6, ASPA, NDUFAF1, POLG, and TMEM70. Abdominal ultrasound (US) and transient elastography were suggestive of severe hepatic steatosis and fibrosis. A liver biopsy confirmed the diagnosis of non-alcoholic steatohepatitis (NASH)-related fibrosis. Thus, to better outline whether mutations involved in lipid remodeling and mitochondrial function may also affect organelles’ morphology, we exploited TEM. Along with multifaceted abnormalities of mitochondrial architecture that have been already observed in patients with NAFLD, astonishing ultrastructural defects, such as mitochondrial vacuolization, sub-compartmentalization, and onion-like mitochondria, were identified.

Conclusion

The anomalies reported may expand the phenotypic spectrum of mitochondrial abnormalities observed in patients with NAFLD, which may contribute to the switching toward a progressive disease.

Cellular Bioenergetics: Experimental Evidence for Alcohol-induced Adaptations

At-risk alcohol use is associated with multisystemic effects and end-organ injury, and significantly contributes to global health burden. Several alcohol-mediated mechanisms have been identified, with bioenergetic maladaptation gaining credence as an underlying pathophysiological mechanism contributing to cellular injury. This evidence-based review focuses on the current knowledge of alcohol-induced bioenergetic adaptations in metabolically active tissues: liver, cardiac and skeletal muscle, pancreas, and brain. Alcohol metabolism itself significantly interferes with bioenergetic pathways in tissues, particularly the liver. Alcohol decreases states of respiration in the electron transport chain, and activity and expression of respiratory complexes, with a net effect to decrease ATP content. In addition, alcohol dysregulates major metabolic pathways, including glycolysis, the tricarboxylic acid cycle, and fatty acid oxidation. These bioenergetic alterations are influenced by alcohol-mediated changes in mitochondrial morphology, biogenesis, and dynamics. The review highlights similarities and differences in bioenergetic adaptations according to tissue type, pattern of (acute vs. chronic) alcohol use, and energy substrate availability. The compromised bioenergetics synergizes with other critical pathophysiological mechanisms, including increased oxidative stress and accelerates cellular dysfunction, promoting senescence, programmed cell death, and end-organ injury.

Mitochondrial Quality Control in the Heart: The Balance between Physiological and Pathological Stress

Alterations in mitochondrial function and morphology are critical adaptations to cardiovascular stress, working in concert in an attempt to restore organelle-level and cellular-level homeostasis. Processes that alter mitochondrial morphology include fission, fusion, mitophagy, and biogenesis, and these interact to maintain mitochondrial quality control. Not all cardiovascular stress is pathologic (e.g., ischemia, pressure overload, cardiotoxins), despite a wealth of studies to this effect. Physiological stress, such as that induced by aerobic exercise, can induce morphologic adaptations that share many common pathways with pathological stress, but in this case result in improved mitochondrial health. Developing a better understanding of the mechanisms underlying alterations in mitochondrial quality control under diverse cardiovascular stressors will aid in the development of pharmacologic interventions aimed at restoring cellular homeostasis.

PACT establishes a posttranscriptional brake on mitochondrial biogenesis by promoting the maturation of miR-181c

The double-stranded RNA-dependent protein kinase activating protein (PACT), an RNA-binding protein that is part of the RNA-induced silencing complex, plays a key role in miR-mediated translational repression. Previous studies showed that PACT regulates the expression of various miRs, selects the miR strand to be loaded onto RNA-induced silencing complex, and determines proper miR length. Apart from PACT's role in mediating the antiviral response in immune cells, what PACT does in other cell types is unknown. Strikingly, it has also been shown that cold exposure leads to marked downregulation of PACT protein in mouse brown adipose tissue (BAT), where mitochondrial biogenesis and metabolism play a central role. Here, we show that PACT establishes a posttranscriptional brake on mitochondrial biogenesis (mitobiogenesis) by promoting the maturation of miR-181c, a key suppressor of mitobiogenesis that has been shown to target mitochondrial complex IV subunit I (Mtco1) and sirtuin 1 (Sirt1). Consistently, we found that a partial reduction in PACT expression is sufficient to enhance mitobiogenesis in brown adipocytes in culture as well as during BAT activation in mice. In conclusion, we demonstrate an unexpected role for PACT in the regulation of mitochondrial biogenesis and energetics in cells and BAT.

Role of OCT3 and DRP1 in the Transport of Paraquat in Astrocytes: A Mouse Study

BACKGROUND

Paraquat (PQ) is a pesticide, exposure to which has been associated with an increased risk of Parkinson's disease; however, PQ transport mechanisms in the brain are still unclear. Our previous studies indicated that the organic cation transporter 3 (OCT3) expressed on astrocytes could uptake PQ and protect the dopaminergic (DA) neurons from a higher level of extracellular PQ. At present, it is unknown how OCT3 levels are altered during chronic PQ exposure or aging, nor is it clear how the compensatory mechanisms are triggered by OCT3 deficiency. Dynamic related protein 1 (DRP1) was previously reported to ameliorate the loss of neurons during Parkinson's disease. Nowadays, mounting studies have revealed the functions of astrocyte DRP1, prompting us to hypothesize that DRP1 could regulate the PQ transport capacity of astrocytes.

OBJECTIVES

The present study aimed to further explore PQ transport mechanisms in the nigrostriatal system and identify pathways involved in extracellular PQ clearance.

METHODS

Models of PQ-induced neurodegeneration were established by intraperitoneal (i.p.) injection of PQ in wild-type (WT) and organic cation transporter-3-deficient (Oct3-/-) mice. DRP1 knockdown was achieved by viral tools in vivo and small interfering RNA (siRNA) in vitro. Extracellular PQ was detected by in vivo microdialysis. In vitro transport assays were used to directly observe the functions of different transporters. PQ-induced neurotoxicity was evaluated by tyrosine hydroxylase immunohistochemistry, in vivo microdialysis for striatal DA and behavior tests. Western blotting analysis or immunofluorescence was used to evaluate the expression levels and locations of proteins in vitro or in vivo.

RESULTS

Older mice and those chronically exposed to PQ had a lower expression of brain OCT3 and, following exposure to a 10-mg/kg i.p. PQ2+ loading dose, a higher concentration of extracellular PQ. DRP1 levels were higher in astrocytes and neurons of WT and Oct3-/- mice after chronic exposure to PQ; this was supported by finding higher levels of DRP1 after PQ treatment of dopamine transporter-expressing neurons with and without OCT3 inhibition and in primary astrocytes of WT and Oct3-/- mice. Selective astrocyte DRP1 knockdown ameliorated the PQ2+-induced neurotoxicity in Oct3-/- mice but not in WT mice. GL261 astrocytes with siRNA-mediated DRP1 knockdown had a higher expression of alanine-serine-cysteine transporter 2 (ASCT2), and transport studies suggest that extracellular PQ was transported into astrocytes by ASCT2 when OCT3 was absent.

DISCUSSION

The present study mainly focused on the transport mechanisms of PQ between the dopaminergic neurons and astrocytes. Lower OCT3 levels were found in the older or chronically PQ-treated mice. Astrocytes with DRP1 inhibition (by viral tools or mitochondrial division inhibitor-1) had higher levels of ASCT2, which we hypothesize served as an alternative transporter to remove extracellular PQ when OCT3 was deficient. In summary, our data suggest that OCT3, ASCT2 located on astrocytes and the dopamine transporter located on DA terminals may function in a concerted manner to mediate striatal DA terminal damage in PQ-induced neurotoxicity. https://doi.org/10.1289/EHP9505.

Protective effects of natural products against myocardial ischemia/reperfusion: Mitochondria-targeted therapeutics

Patients with ischemic heart disease receiving reperfusion therapy still need to face left ventricular remodeling and heart failure after myocardial infarction. Reperfusion itself paradoxically leads to further cardiomyocyte death and systolic dysfunction. Ischemia/reperfusion (I/R) injury can eliminate the benefits of reperfusion therapy in patients and causes secondary myocardial injury. Mitochondrial dysfunction and structural disorder are the basic driving force of I/R injury. We summarized the basic relationship and potential mechanisms of mitochondrial injury in the development of I/R injury. Subsequently, this review summarized the natural products (NPs) that have been proven to targeting mitochondrial therapeutic effects during I/R injury in recent years and related cellular signal transduction pathways. We found that these NPs mainly protected the structural integrity of mitochondria and improve dysfunction, such as reducing mitochondrial division and fusion abnormalities, improving mitochondrial Ca²⁺ overload and inhibiting reactive oxygen species overproduction, thereby playing a role in protecting cardiomyocytes during I/R injury. This data would deepen the understanding of I/R-induced mitochondrial pathological process and suggested that NPs are expected to be transformed into potential therapies targeting mitochondria.

Mitochondrial dynamics in the neonatal brain - a potential target following injury?

The impact of birth asphyxia and its sequelae, hypoxic–ischaemic (HI) brain injury, is long-lasting and significant, both for the infant and for their family. Treatment options are limited to therapeutic hypothermia, which is not universally successful and is unavailable in low resource settings. The energy deficits that accompany neuronal death following interruption of blood flow to the brain implicate mitochondrial dysfunction. Such HI insults trigger mitochondrial outer membrane permeabilisation leading to release of pro-apoptotic proteins into the cytosol and cell death. More recently, key players in mitochondrial fission and fusion have been identified as targets following HI brain injury. This review aims to provide an introduction to the molecular players and pathways driving mitochondrial dynamics, the regulation of these pathways and how they are altered following HI insult. Finally, we review progress on repurposing or repositioning drugs already approved for other indications, which may target mitochondrial dynamics and provide promising avenues for intervention following brain injury. Such repurposing may provide a mechanism to fast-track, low-cost treatment options to the clinic.

The regulatory mechanism between lysosomes and mitochondria in the aetiology of cardiovascular diseases

Coordinated action among various organelles maintains cellular functions. For instance, mitochondria and lysosomes are the main organelles contributing to cellular metabolism and provide energy for cardiomyocyte contraction. They also provide essential signalling platforms in the cell that regulate many key processes such as autophagy, apoptosis, oxidative stress, inflammation and cell death. Often, abnormalities in mitochondrial or lysosomal structures and functions bring about cardiovascular diseases (CVDs). Although the communication between mitochondria and lysosomes throughout the cardiovascular system is intensely studied, the regulatory mechanisms have not been completely understood. Thus, we summarize the most recent studies related to mitochondria and lysosomes' role in CVDs and their potential connections and communications under cardiac pathophysiological conditions. Further, we discuss limitations and future perspectives regarding diagnosis, therapeutic strategies and drug discovery in CVDs.

Chronic Hypoxia Inhibits Respiratory Complex IV Activity and Disrupts Mitochondrial Dynamics in the Fetal Guinea Pig Forebrain

Mitochondrial dysfunction is an underlying cause of childhood neurological disease secondary to the crucial role of mitochondria in proper neurodevelopment. We hypothesized that chronic intrauterine hypoxia (HPX) induces mitochondrial deficits by altering mitochondrial biogenesis and dynamics in the fetal brain. Pregnant guinea pigs were exposed to either normoxia (NMX, 21%O2) or HPX (10.5%O2) starting at 28-day (early onset, EO-HPX) or 50-day (late onset, LO-HPX) gestation until term (65 days). Near-term male and female fetuses were extracted from anesthetized sows, and mitochondria were isolated from excised fetal forebrains (n = 6/group). Expression of mitochondrial complex subunits I-V (CI-CV), fission (Drp-1), and fusion (Mfn-2) proteins was measured by Western blot. CI and CIV enzyme activities were measured by colorimetric assays. Chronic HPX reduced fetal body wts and increased (P < 0.05) brain/body wt ratios of both sexes. CV subunit levels were increased in EO-HPX males only and CII levels increased in LO-HPX females only compared to NMX. Both EO- and LO-HPX decreased CIV activity in both sexes but had no effect on CI activity. EO-HPX increased Drp1 and decreased Mfn2 levels in males, while LO-HPX had no effect on either protein levels. In females, both EO-HPX and LO-HPX increased Drp1 but had no effect on Mfn2 levels. Chronic HPX alters abundance and activity of select complex subunits and shifts mitochondrial dynamics toward fission in a sex-dependent manner in the fetal guinea pig brain. This may be an underlying mechanism of reduced respiratory efficiency leading to disrupted metabolism and increased vulnerability to a second neurological injury at the time of birth in HPX fetal brains.

Podocyte Bioenergetics in the Development of Diabetic Nephropathy: The Role of Mitochondria

Diabetic nephropathy (DN) is the leading cause of kidney failure, with an increasing incidence worldwide. Mitochondrial dysfunction is known to occur in DN and has been implicated in the underlying pathogenesis of disease. These complex organelles have an array of important cellular functions and involvement in signaling pathways, and understanding the intricacies of these responses in health, as well as how they are damaged in disease, is likely to highlight novel therapeutic avenues. A key cell type damaged early in DN is the podocyte, and increasing studies have focused on investigating the role of mitochondria in podocyte injury. This review will summarize what is known about podocyte mitochondrial dynamics in DN, with a particular focus on bioenergetic pathways, highlighting key studies in this field and potential opportunities to target, enhance or protect podocyte mitochondrial function in the treatment of DN.

Inflammation causes remodeling of mitochondrial cytochrome c oxidase mediated by the bifunctional gene C15orf48

Dysregulated mitochondrial function is a hallmark of immune-mediated inflammatory diseases. Cytochrome c oxidase (CcO), which mediates the rate-limiting step in mitochondrial respiration, is remodeled during development and in response to changes of oxygen availability, but there has been little study of CcO remodeling during inflammation. Here, we describe an elegant molecular switch mediated by the bifunctional transcript C15orf48, which orchestrates the substitution of the CcO subunit NDUFA4 by its paralog C15ORF48 in primary macrophages. Expression of C15orf48 is a conserved response to inflammatory signals and occurs in many immune-related pathologies. In rheumatoid arthritis, C15orf48 mRNA is elevated in peripheral monocytes and proinflammatory synovial tissue macrophages, and its expression positively correlates with disease severity and declines in remission. C15orf48 is also expressed by pathogenic macrophages in severe coronavirus disease 2019 (COVID-19). Study of a rare metabolic disease syndrome provides evidence that loss of the NDUFA4 subunit supports proinflammatory macrophage functions.

Acetoacetate protects macrophages from lactic acidosis-induced mitochondrial dysfunction by metabolic reprograming

Lactic acidosis, the extracellular accumulation of lactate and protons, is a consequence of increased glycolysis triggered by insufficient oxygen supply to tissues. Macrophages are able to differentiate from monocytes under such acidotic conditions, and remain active in order to resolve the underlying injury. Here we show that, in lactic acidosis, human monocytes differentiating into macrophages are characterized by depolarized mitochondria, transient reduction of mitochondrial mass due to mitophagy, and a significant decrease in nutrient absorption. These metabolic changes, resembling pseudostarvation, result from the low extracellular pH rather than from the lactosis component, and render these cells dependent on autophagy for survival. Meanwhile, acetoacetate, a natural metabolite produced by the liver, is utilized by monocytes/macrophages as an alternative fuel to mitigate lactic acidosis-induced pseudostarvation, as evidenced by retained mitochondrial integrity and function, retained nutrient uptake, and survival without the need of autophagy. Our results thus show that acetoacetate may increase tissue tolerance to sustained lactic acidosis.

Lactic acidosis is a metabolic state that occurs in injured tissues. Here the authors show that macrophages, in order to remain functional in acidosis, reduce their mitochondrial mass by mitophagy and rely on autophagy for survival, with mitochondrial integrity retained using acetoacetate as alternative fuel.

Mitochondrial quality control in acute ischemic stroke

Mitochondria play a central role in the pathophysiological processes of acute ischemic stroke. Disruption of the cerebral blood flow during acute ischemic stroke interrupts oxygen and glucose delivery, leading to the dysfunction of mitochondrial oxidative phosphorylation and cellular bioenergetic stress. Cells can respond to such stress by activating mitochondrial quality control mechanisms, including the mitochondrial unfolded protein response, mitochondrial fission and fusion, mitophagy, mitochondrial biogenesis, and intercellular mitochondrial transfer. Collectively, these adaptive response strategies contribute to retaining the integrity and function of the mitochondrial network, thereby helping to recover the homeostasis of the neurovascular unit. In this review, we focus on mitochondrial quality control mechanisms occurring in acute ischemic stroke. A better understanding of how these regulatory pathways work in maintaining mitochondrial homeostasis will provide a rationale for developing innovative neuroprotectants when these mechanisms fail in acute ischemic stroke.

Mitochondrial Dynamics in Drug-Induced Liver Injury

Mitochondria have been studied for decades from the standpoint of metabolism and ATP generation. However, in recent years mitochondrial dynamics and its influence on bioenergetics and cellular homeostasis is also being appreciated. Mitochondria undergo regular cycles of fusion and fission regulated by various cues including cellular energy requirements and pathophysiological stimuli, and the network of critical proteins and membrane lipids involved in mitochondrial dynamics is being revealed. Hepatocytes are highly metabolic cells which have abundant mitochondria suggesting a biologically relevant role for mitochondrial dynamics in hepatocyte injury and recovery. Here we review information on molecular mediators of mitochondrial dynamics and their alteration in drug-induced liver injury. Based on current information, it is evident that changes in mitochondrial fusion and fission are hallmarks of liver pathophysiology ranging from acetaminophen-induced or cholestatic liver injury to chronic liver diseases. These alterations in mitochondrial dynamics influence multiple related mitochondrial responses such as mitophagy and mitochondrial biogenesis, which are important adaptive responses facilitating liver recovery in several contexts, including drug-induced liver injury. The current focus on characterization of molecular mechanisms of mitochondrial dynamics is of immense relevance to liver pathophysiology and have the potential to provide significant insight into mechanisms of liver recovery and regeneration after injury.

MicroRNA-214 contributes to Ang II-induced cardiac hypertrophy by targeting SIRT3 to provoke mitochondrial malfunction

Reduction of expression and activity of sirtuin 3 (SIRT3) contributes to the pathogenesis of cardiomyopathy via inducing mitochondrial injury and energy metabolism disorder. However, development of effective ways and agents to modulate SIRT3 remains a big challenge. In this study we explored the upstream suppressor of SIRT3 in angiotensin II (Ang II)-induced cardiac hypertrophy in mice. We first found that SIRT3 deficiency exacerbated Ang II-induced cardiac hypertrophy, and resulted in the development of spontaneous heart failure. Since miRNAs play crucial roles in the pathogenesis of cardiac hypertrophy, we performed miRNA sequencing on myocardium tissues from Ang II-infused Sirt3-/- and wild type mice, and identified microRNA-214 (miR-214) was significantly up-regulated in Ang II-infused mice. Similar results were also obtained in Ang II-treated neonatal mouse cardiomyocytes (NMCMs). Using dual-luciferase reporter assay we demonstrated that SIRT3 was a direct target of miR-214. Overexpression of miR-214 in vitro and in vivo decreased the expression of SIRT3, which resulted in extensive mitochondrial damages, thereby facilitating the onset of hypertrophy. In contrast, knockdown of miR-214 counteracted Ang II-induced detrimental effects via restoring SIRT3, and ameliorated mitochondrial morphology and respiratory activity. Collectively, these results demonstrate that miR-214 participates in Ang II-induced cardiac hypertrophy by directly suppressing SIRT3, and subsequently leading to mitochondrial malfunction, suggesting the potential of miR-214 as a promising intervention target for antihypertrophic therapy.

Adaptation of mitochondrial network dynamics and velocity of mitochondrial movement to chronic stress present in fibroblasts derived from patients with sporadic form of Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Only 10% of all cases are familial form, the remaining 90% are sporadic form with unknown genetic background. The etiology of sporadic AD is still not fully understood. Pathogenesis and pathobiology of this disease are limited due to the limited number of experimental models. We used primary culture of fibroblasts derived from patients diagnosed with sporadic form of AD for investigation of dynamic properties of mitochondria, including fission-fusion process and localization of mitochondria within the cell. We observed differences in mitochondrial network organization with decreased mitochondrial transport velocity, and a drop in the frequency of fusion-fission events. These studies show how mitochondrial dynamics adapt to the conditions of long-term mitochondrial stress that prevails in cells of sporadic form of AD.

Silencing of Poly(ADP-Ribose) Polymerase-2 Induces Mitochondrial Reactive Species Production and Mitochondrial Fragmentation

PARP2 is a DNA repair protein. The deletion of PARP2 induces mitochondrial biogenesis and mitochondrial activity by increasing NAD⁺ levels and inducing SIRT1 activity. We show that the silencing of PARP2 causes mitochondrial fragmentation in myoblasts. We assessed multiple pathways that can lead to mitochondrial fragmentation and ruled out the involvement of mitophagy, the fusion-fission machinery, SIRT1, and mitochondrial unfolded protein response. Nevertheless, mitochondrial fragmentation was reversed by treatment with strong reductants, such as reduced glutathione (GSH), N-acetyl-cysteine (NAC), and a mitochondria-specific antioxidant MitoTEMPO. The effect of MitoTEMPO on mitochondrial morphology indicates the production of reactive oxygen species of mitochondrial origin. Elimination of reactive oxygen species reversed mitochondrial fragmentation in PARP2-silenced cells.

Structural and Functional Remodeling of Mitochondria in Cardiac Diseases

Mitochondria undergo structural and functional remodeling to meet the cell demand in response to the intracellular and extracellular stimulations, playing an essential role in maintaining normal cellular function. Merging evidence demonstrated that dysregulation of mitochondrial remodeling is a fundamental driving force of complex human diseases, highlighting its crucial pathophysiological roles and therapeutic potential. In this review, we outlined the progress of the molecular basis of mitochondrial structural and functional remodeling and their regulatory network. In particular, we summarized the latest evidence of the fundamental association of impaired mitochondrial remodeling in developing diverse cardiac diseases and the underlying mechanisms. We also explored the therapeutic potential related to mitochondrial remodeling and future research direction. This updated information would improve our knowledge of mitochondrial biology and cardiac diseases’ pathogenesis, which would inspire new potential strategies for treating these diseases by targeting mitochondria remodeling.

Molecular nature and physiological role of the mitochondrial calcium uniporter channel

Calcium (Ca2+) signaling is critical for cell function and cell survival. Mitochondria play a major role in regulating the intracellular Ca2+ concentration ([Ca2+]i). Mitochondrial Ca2+ uptake is an important determinant of cell fate and governs respiration, mitophagy/autophagy, and the mitochondrial pathway of apoptosis. Mitochondrial Ca2+ uptake occurs via the mitochondrial Ca2+ uniporter (MCU) complex. This review summarizes the present knowledge on the function of MCU complex, regulation of MCU channel, and the role of MCU in Ca2+ homeostasis and human disease pathogenesis. The channel core consists of four MCU subunits and essential MCU regulators (EMRE). Regulatory proteins that interact with them include mitochondrial Ca2+ uptake 1/2 (MICU1/2), MCU dominant-negative β-subunit (MCUb), MCU regulator 1 (MCUR1), and solute carrier 25A23 (SLC25A23). In addition to these proteins, cardiolipin, a mitochondrial membrane-specific phospholipid, has been shown to interact with the channel core. The dynamic interplay between the core and regulatory proteins modulates MCU channel activity after sensing local changes in [Ca2+]i, reactive oxygen species, and other environmental factors. Here, we highlight the structural details of the human MCU heteromeric assemblies and their known roles in regulating mitochondrial Ca2+ homeostasis. MCU dysfunction has been shown to alter mitochondrial Ca2+ dynamics, in turn eliciting cell apoptosis. Changes in mitochondrial Ca2+ uptake have been implicated in pathological conditions affecting multiple organs, including the heart, skeletal muscle, and brain. However, our structural and functional knowledge of this vital protein complex remains incomplete, and understanding the precise role for MCU-mediated mitochondrial Ca2+ signaling in disease requires further research efforts.

KRT8 (keratin 8) attenuates necrotic cell death by facilitating mitochondrial fission-mediated mitophagy through interaction with PLEC (plectin)

Dysregulation of mitochondrial homeostasis and accumulation of damaged mitochondria cause degenerative diseases such as age-related macular degeneration (AMD). We studied the effects of the intermediate cytofilament KRT8 (keratin 8) on mitochondrial homeostasis in relation to the morphology and function of mitochondria in retinal pigment epithelial cells under oxidative stress. When the mitochondria were damaged owing to oxidative stress, the damaged mitochondria were readily disposed of via mitophagy following mitochondrial fission. During this process, KRT8 was found to physically interact with the mitochondria through PLEC (plectin) and facilitate the mitochondrial fission-mediated mitophagy. However, the association between PLEC-anchoring mitochondria and KRT8 was dwindled by KRT8 phosphorylation under oxidative stress. The efficient KRT8-facilitated mitophagy flux suppressed the accumulation of damaged mitochondria and consequently diminished necrotic cell death under oxidative stress. Thus, by facilitating mitophagy, KRT8 protects RPE cells against necrotic cell death due to oxidative stress.

Mitochondrial integration and ovarian cancer chemotherapy resistance

Ovarian cancer has been nicknamed the "silent killer". Most patients with ovarian cancer are diagnosed at an advanced stage of the disease for the first time because of its insignificant early clinical symptoms. In addition to the difficulty of early screening and delay in diagnosis, the high recurrence rate and relapsed refractory status of patients with ovarian cancer are also important factors for their high mortality. Patients with recurrent ovarian cancer often use neoadjuvant chemotherapy followed by surgery as the first choice. However, this is often accompanied by chemotherapy resistance, leading to treatment failure and a mortality rate of more than 90%. In the past, it was believed that the anti-tumor effect of chemotherapeutics represented by cisplatin was entirely attributable to its irreversible damage to DNA, but current research has found that it can inhibit cell growth and cytotoxicity via nuclear and cytoplasmic coordinated integration. As an important hub and integration platform for intracellular signal communication, mitochondria are responsible for multiple key factors during tumor occurrence and development, such as metabolic reprogramming, acquisition of metastatic ability, and chemotherapy drug response. The role of mitochondria in ovarian cancer chemotherapy resistance is becoming increasingly recognized. In this review, we discuss the cellular interactive regulatory network surrounding mitochondria, elucidate the mechanisms of tumor cell survival under chemotherapy, and discuss potential means of interfering with mitochondrial function as a novel anti-cancer therapy.

Energy Metabolism During Osteogenic Differentiation: The Role of Akt

Osteogenic differentiation, the process by which bone marrow mesenchymal stem/stromal (a.k.a. skeletal stem) cells and osteoprogenitors form osteoblasts, is a critical event for bone formation during development, fracture repair, and tissue maintenance. Extra cellular and intracellular signaling pathways triggering osteogenic differentiation are relatively well known; however, the ensuing change in cell energy metabolism is less clearly defined. We and others have previously reported activation of mitochondria during osteogenic differentiation. To further elucidate the involved bioenergetic mechanisms and triggers, we tested the effect of osteogenic media containing ascorbate and β-glycerol phosphate, or various osteogenic hormones and growth factors on energy metabolism in long bone (ST2)- and calvarial bone (MC3T3-E1)-derived osteoprogenitors. We show that osteogenic media and differentiation factors, Wnt3a and BMP2, stimulate mitochondrial oxidative phosphorylation (OxPhos) with little effect on glycolysis. The activation of OxPhos occurs acutely, suggesting a metabolic signaling change rather than protein expression change. To this end, we found that the observed mitochondrial activation is Akt dependent. Akt is activated by osteogenic media, Wnt3a, and BMP2, leading to increased phosphorylation of various mitochondrial Akt targets, a phenomenon known to stimulate OxPhos. In sum, our data provide comprehensive analysis of cellular bioenergetics during osteoinduction in cells of two different origins (mesenchyme vs neural crest) and identify Wnt3a and BMP2 as physiological stimulators of mitochondrial respiration through Akt activation.

Zika Virus-Induced Neuronal Apoptosis via Increased Mitochondrial Fragmentation

The 2015 to 2016 outbreak of Zika virus (ZIKV) infections in the Americas coincided with a dramatic increase in neurodevelopmental abnormalities, including fetal microcephaly, in newborns born to infected women. In this study, we observed mitochondrial fragmentation and disrupted mitochondrial membrane potential after 24 h of ZIKV infection in human neural stem cells and the SNB-19 glioblastoma cell line. The severity of these changes correlated with the amount of ZIKV proteins expressed in infected cells. ZIKV infection also decreased the levels of mitofusin 2, which modulates mitochondria fusion. Mitochondrial division inhibitor 1 (Mdivi-1), a small molecule inhibiting mitochondria fission, ameliorated mitochondria disruptions and reduced cell death in ZIKV-infected cells. Collectively, this study suggests that abnormal mitochondrial fragmentation contributes to ZIKV-induced neuronal cell death; rebalancing mitochondrial dynamics of fission-fusion could be a therapeutic strategy for drug development to treat ZIKV-mediated neuronal apoptosis.

Calcium, Bioenergetics, and Parkinson's Disease

Degeneration of substantia nigra (SN) dopaminergic (DAergic) neurons is responsible for the core motor deficits of Parkinson’s disease (PD). These neurons are autonomous pacemakers that have large cytosolic Ca²⁺ oscillations that have been linked to basal mitochondrial oxidant stress and turnover. This review explores the origin of Ca²⁺ oscillations and their role in the control of mitochondrial respiration, bioenergetics, and mitochondrial oxidant stress.

Cellular Reprogramming Approaches to Engineer Cardiac Pacemakers

PURPOSE OF REVIEW

The goal of this paper is to review present knowledge regarding biological pacemakers created by somatic reprogramming as a platform for mechanistic and metabolic understanding of the rare subpopulation of pacemaker cells, with the ultimate goal of creating biological alternatives to electronic pacing devices.

RECENT FINDINGS

Somatic reprogramming of cardiomyocytes by reexpression of embryonic transcription factor T-box 18 (TBX18) converts them into pacemaker-like. Recent studies take advantage of this model to gain insight into the electromechanical, metabolic, and architectural intricacies of the cardiac pacemaker cell across various models, including a surgical model of complete atrioventricular block (CAVB) in adult rats. The studies reviewed here reinforce the potential utility of TBX18-induced pacemaker myocytes (iPMS) as a minimally invasive treatment for heart block. Several challenges which must be overcome to develop a viable therapeutic intervention based on these observations are discussed.

Targeting the Mitochondria in Heart Failure: A Translational Perspective

The burden of heart failure (HF) in terms of health care expenditures, hospitalizations, and mortality is substantial and growing. The failing heart has been described as "energy-deprived" and mitochondrial dysfunction is a driving force associated with this energy supply-demand imbalance. Existing HF therapies provide symptomatic and longevity benefit by reducing cardiac workload through heart rate reduction and reduction of preload and afterload but do not address the underlying causes of abnormal myocardial energetic nor directly target mitochondrial abnormalities. Numerous studies in animal models of HF as well as myocardial tissue from explanted failed human hearts have shown that the failing heart manifests abnormalities of mitochondrial structure, dynamics, and function that lead to a marked increase in the formation of damaging reactive oxygen species and a marked reduction in on demand adenosine triphosphate synthesis. Correcting mitochondrial dysfunction therefore offers considerable potential as a new therapeutic approach to improve overall cardiac function, quality of life, and survival for patients with HF.

Mitochondrial Trafficking and Processing of Telomerase RNA TERC

Mitochondrial dysfunctions play major roles in many diseases. However, how mitochondrial stresses are relayed to downstream responses remains unclear. Here we show that the RNA component of mammalian telomerase TERC is imported into mitochondria, processed to a shorter form TERC-53, and then exported back to the cytosol. We found that the import is regulated by PNPASE, and the processing is controlled by mitochondrion-localized RNASET2. Cytosolic TERC-53 levels respond to changes in mitochondrial functions but have no direct effect on these functions. These findings uncover a mitochondrial RNA trafficking pathway and provide a potential mechanism for mitochondria to relay their functional states to other cellular compartments.

Proteome Oxidative Modifications and Impairment of Specific Metabolic Pathways During Cellular Senescence and Aging

Accumulation of oxidatively modified proteins is a hallmark of organismal aging in vivo and of cellular replicative senescence in vitro. Failure of protein maintenance is a major contributor to the age-associated accumulation of damaged proteins that is believed to participate to the age-related decline in cellular function. In this context, quantitative proteomics approaches, including 2-D gel electrophoresis (2-DE)-based methods, represent powerful tools for monitoring the extent of protein oxidative modifications at the proteome level and for identifying the targeted proteins, also referred as to the "oxi-proteome." Previous studies have identified proteins targeted by oxidative modifications during replicative senescence of human WI-38 fibroblasts and myoblasts and have been shown to represent a restricted set within the total cellular proteome that fall in key functional categories, such as energy metabolism, protein quality control, and cellular morphology. To provide mechanistic support into the role of oxidized proteins in the development of the senescent phenotype, untargeted metabolomic profiling is also performed for young and senescent myoblasts and fibroblasts. Metabolomic profiling is indicative of energy metabolism impairment in both senescent myoblasts and fibroblasts, suggesting a link between oxidative protein modifications and the altered cellular metabolism associated with the senescent phenotype of human myoblasts and fibroblasts.

Matrix-guided control of mitochondrial function in cardiac myocytes

In ventricular myocardium, extracellular matrix (ECM) remodeling is a hallmark of physiological and pathological growth, coincident with metabolic rewiring of cardiac myocytes. However, the direct impact of the biochemical and mechanical properties of the ECM on the metabolic function of cardiac myocytes is mostly unknown. Furthermore, understanding the impact of distinct biomaterials on cardiac myocyte metabolism is critical for engineering physiologically-relevant models of healthy and diseased myocardium. For these reasons, we systematically measured morphological and metabolic responses of neonatal rat ventricular myocytes cultured on fibronectin- or gelatin-coated polydimethylsiloxane (PDMS) of three elastic moduli and gelatin hydrogels with four elastic moduli. On all substrates, total protein content, cell morphology, and the ratio of mitochondrial DNA to nuclear DNA were preserved. Cytotoxicity was low on all substrates, although slightly higher on PDMS compared to gelatin hydrogels. We also quantified oxygen consumption rates and extracellular acidification rates using a Seahorse extracellular flux analyzer. Our data indicate that several metrics associated with baseline glycolysis and baseline and maximum mitochondrial function are enhanced when cardiac myocytes are cultured on gelatin hydrogels compared to all PDMS substrates, irrespective of substrate rigidity. These results yield new insights into how mechanical and biochemical cues provided by the ECM impact mitochondrial function in cardiac myocytes. STATEMENT OF SIGNIFICANCE: Cardiac development and disease are associated with remodeling of the extracellular matrix coincident with metabolic rewiring of cardiac myocytes. However, little is known about the direct impact of the biochemical and mechanical properties of the extracellular matrix on the metabolic function of cardiac myocytes. In this study, oxygen consumption rates were measured in neonatal rat ventricular myocytes maintained on several commonly-used biomaterial substrates to reveal new relationships between the extracellular matrix and cardiac myocyte metabolism. Several mitochondrial parameters were enhanced on gelatin hydrogels compared to synthetic PDMS substrates. These data are important for comprehensively understanding matrix-regulation of cardiac myocyte physiology. Additionally, these data should be considered when selecting scaffolds for engineering in vitro cardiac tissue models.

Induced cardiac pacemaker cells survive metabolic stress owing to their low metabolic demand

Cardiac pacemaker cells of the sinoatrial node initiate each and every heartbeat. Compared with our understanding of the constituents of their electrical excitation, little is known about the metabolic underpinnings that drive the automaticity of pacemaker myocytes. This lack is largely owing to the scarcity of native cardiac pacemaker myocytes. Here, we take advantage of induced pacemaker myocytes generated by TBX18-mediated reprogramming (TBX18-iPMs) to investigate comparative differences in the metabolic program between pacemaker myocytes and working cardiomyocytes. TBX18-iPMs were more resistant to metabolic stresses, exhibiting higher cell viability upon oxidative stress. TBX18-induced pacemaker myocytes (iPMs) expensed a lower degree of oxidative phosphorylation and displayed a smaller capacity for glycolysis compared with control ventricular myocytes. Furthermore, the mitochondria were smaller in TBX18-iPMs than in the control. We reasoned that a shift in the balance between mitochondrial fusion and fission was responsible for the smaller mitochondria observed in TBX18-iPMs. We identified a mitochondrial inner membrane fusion protein, Opa1, as one of the key mediators of this process and demonstrated that the suppression of Opa1 expression increases the rate of synchronous automaticity in TBX18-iPMs. Taken together, our data demonstrate that TBX18-iPMs exhibit a low metabolic demand that matches their mitochondrial morphology and ability to withstand metabolic insult.

The heart’s pacemaker cells contain mitochondria that are smaller than average and require less energy than other heart cells, properties that help make them naturally resilient to stress. Cardiac pacemaker cells constitute a tiny proportion of the heart’s cells, yet play a critical role in maintaining a steady heartbeat. However, quite how pacemaker cells maintain their automatic rhythm is unclear because their scarcity makes them difficult to study. To examine the cells’ metabolic state further, Hee Cheol Cho at Emory University, Atlanta, and Brian Foster at Johns Hopkins University School of Medicine, Baltimore, and co-workers therefore induced pacemaker cells by adding an embryonic protein to heart muscle cells. The induced pacemaker cells survived well under oxidative stress. The team identified a protein in the pacemakers’ mitochondrial membranes, the expression of which directly influences rhythm responses.

Mitochondrial AAA proteases: A stairway to degradation

Mitochondrial protein quality control requires the action of proteases to remove damaged or unnecessary proteins and perform key regulatory cleavage events. Important components of the quality control network are the mitochondrial AAA proteases, which capture energy from ATP hydrolysis to destabilize and degrade protein substrates on both sides of the inner membrane. Dysfunction of these proteases leads to the breakdown of mitochondrial proteostasis and is linked to the development of severe human diseases. In this review, we will describe recent insights into the structure and motions of the mitochondrial AAA proteases and related enzymes. Together, these studies have revealed the mechanics of ATP-driven protein destruction and significantly advanced our understanding of how these proteases maintain mitochondrial health.

Mitochondrion-processed TERC regulates senescence without affecting telomerase activities

Mitochondrial dysfunctions play major roles in ageing. How mitochondrial stresses invoke downstream responses and how specificity of the signaling is achieved, however, remains unclear. We have previously discovered that the RNA component of Telomerase TERC is imported into mitochondria, processed to a shorter form TERC-53, and then exported back to the cytosol. Cytosolic TERC-53 levels respond to mitochondrial functions, but have no direct effect on these functions, suggesting that cytosolic TERC-53 functions downstream of mitochondria as a signal of mitochondrial functions. Here, we show that cytosolic TERC-53 plays a regulatory role on cellular senescence and is involved in cognition decline in 10 months old mice, independent of its telomerase function. Manipulation of cytosolic TERC-53 levels affects cellular senescence and cognition decline in 10 months old mouse hippocampi without affecting telomerase activity, and most importantly, affects cellular senescence in terc^−/− cells. These findings uncover a senescence-related regulatory pathway with a non-coding RNA as the signal in mammals.

Huangqi-Danshen Decoction Ameliorates Adenine-Induced Chronic Kidney Disease by Modulating Mitochondrial Dynamics

Chronic kidney disease (CKD) is a leading public health problem with high morbidity and mortality. However, the therapies remain limited. Traditional Chinese medicine (TCM) has been used for treating kidney disease for thousands of years and is an effective alternative treatment for CKD patients in China and other Asian countries. In the present study, we aimed to investigate the effect and mechanism of Huangqi-Danshen decoction (HDD), a TCM herbal decoction, on treating CKD. CKD rat model was induced by adding 0.75% adenine to the diet for 4 weeks. HDD extract was administrated orally to CKD rats at the dose of 4.7 g/kg/d for consecutive 4 weeks in adenine-induced CKD rats. Kidney function was evaluated by the levels of serum creatinine (Scr) and blood urea nitrogen (BUN). The pathological changes of kidney tissues were observed by periodic acid-Schiff (PAS) and Masson's trichrome staining. The proteins expression of renal fibrosis and mitochondrial dynamics were determined and quantified by Western blot analysis. CKD rats showed obvious decline in renal function as evidenced by increased levels of Scr and BUN, which were blunted by HDD treatment. HDD could also improve tubular atrophy and interstitial fibrosis of CKD rats. Moreover, HDD downregulated fibronectin, type IV collagen, and α-smooth muscle actin expression in CKD rats. Furthermore, mitochondrial dynamics was disturbed in CKD rats, which manifested as increased mitochondrial fission and decreased mitochondrial fusion. HDD treatment restored mitochondrial dynamics in CKD rats by repressing dynamin-related protein 1 and Mid 49/51 expression, promoting mitofusin 2 expression, and suppressing optic atrophy 1 proteolysis. In conclusion, HDD could significantly retard CKD progression through modulating mitochondrial dynamics.

Crosstalk between mitochondrial dysfunction, oxidative stress, and age related neurodegenerative disease: Etiologies and therapeutic strategies

Mitochondrial function is vital for normal cellular processes. Mitochondrial damage and oxidative stress have been greatly implicated in the progression of aging, along with the pathogenesis of age-related neurodegenerative diseases (NDs), such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Although antioxidant therapy has been proposed for the prevention and treatment of age-related NDs, unraveling the molecular mechanisms of mitochondrial dysfunction can lead to significant progress in the development of effective treatments against such diseases. Aging is associated with the generation and accumulation of reactive oxygen species (ROS) that are the major contributors to oxidative stress. Oxidative stress is caused because of the imbalance between the production of ROS and their oxidation, which can affect the mitochondrial respiratory chain function, thereby altering the membrane permeability and calcium homeostasis, along with increasing the heteroplasmic mtDNA and weakening the mitochondrial defense systems. Mitochondrial dysfunction mainly affects mitochondrial biogenesis and dynamics that are prominent in several age-related NDs. Mitochondrial dysfunction has a crucial role in the pathophysiology of age-related NDs. Several mitochondria targeted strategies, such as enhancing the antioxidant bioavailability via novel delivery systems, identifying unique mitochondrial proteins as specific drug targets, investigating the signaling pathways of mitochondrial biogenesis and dynamics, and identifying effective natural products are potentially effective to counteract mitochondrial dysfunction-related NDs.

Mitochondrial Membrane Potential Regulates Nuclear Gene Expression in Macrophages Exposed to Prostaglandin E2

Metabolic engagement is intrinsic to immune cell function. Prostaglandin E2 (PGE2) has been shown to modulate macrophage activation, yet how PGE2 might affect metabolism is unclear. Here, we show that PGE2 caused mitochondrial membrane potential (Δψm) to dissipate in interleukin-4-activated (M(IL-4)) macrophages. Effects on Δψm were a consequence of PGE2-initiated transcriptional regulation of genes, particularly Got1, in the malate-aspartate shuttle (MAS). Reduced Δψm caused alterations in the expression of 126 voltage-regulated genes (VRGs), including those encoding resistin-like molecule α (RELMα), a key marker of M(IL-4) cells, and genes that regulate the cell cycle. The transcription factor ETS variant 1 (ETV1) played a role in the regulation of 38% of the VRGs. These results reveal ETV1 as a Δψm-sensitive transcription factor and Δψm as a mediator of mitochondrial-directed nuclear gene expression.

Ultrastructural Remodeling of the Neurovascular Unit in the Female Diabetic db/db Model–Part II: Microglia and Mitochondria

Obesity, insulin resistance, and type 2 diabetes mellitus are associated with diabetic cognopathy. This study tested the hypothesis that neurovascular unit(s) (NVU) within cerebral cortical gray matter regions may depict abnormal cellular remodeling. The monogenic (Leprdb) female diabetic db/db [BKS.CgDock7m +/+Leprdb/J] (DBC) mouse model was utilized for this ultrastructural study. Upon sacrifice (20 weeks), left-brain hemispheres of the DBC and age-matched nondiabetic control C57BL/KsJ (CKC) mice were immediately immersion-fixed. We observed an attenuation/loss of endothelial blood–brain barrier tight/adherens junctions and pericytes, thickened basement membranes, adherent red and white blood cells, neurovascular unit microbleeds and pathologic remodeling of protoplasmic astrocytes. In this second of a three-part series, we focus on the observational ultrastructural remodeling of microglia and mitochondria in relation to the NVU in leptin receptor deficient DBC models. This study identified novel ultrastructural core signature remodeling changes, which consisted of invasive activated microglia, microglial aberrant mitochondria with nuclear chromatin condensation and adhesion of white blood cells to an activated endothelium of the NVU. In conclusion, the results implicate activated microglia in NVU uncoupling and the resulting ischemic neuronal and synaptic damage, which may be related to impaired cognition and diabetic cognopathy.