The mitochondrial protein Opa1 promotes adipocyte browning that is dependent on urea cycle metabolites

Polyphenols reverse hyperglycemia-induced adipocyte dysfunction: A Metabolomic and Lipidomic study of efficacy

Hyperglycemia leads to metabolic dysfunction in human adipocytes, characterized by decreased AKT phosphorylation, downregulation of glycolysis, TCA cycle, and amino acid metabolism, as well as altered lipid profiles. This study aimed to elucidate these metabolic alterations and evaluate the potential therapeutic effects of selected polyphenols. Comprehensive metabolic profiling revealed profound disruptions, including impaired carbon metabolism, amino acids, and lipids associated with obesity. Importantly, treatment with polyphenols, particularly verbascoside and ferulic acid, effectively mitigated these metabolic disturbances, restoring adipocyte homeostasis. The polyphenols increased metabolites from carbon metabolism and amino acids, improving glycolysis, the TCA cycle, and related pathways. They also modulated lipid profiles that are negatively associated with obesity and related diseases. These findings provide valuable insights into the metabolic pathways underlying adipocyte dysfunction in hyperglycemia and highlight the therapeutic potential of polyphenols in ameliorating metabolic disorders.

Mitochondrial GCN5L1 coordinates with YME1L and MICOS to remodel mitochondrial cristae in white adipocytes and modulate obesity

The relationship between mitochondrial architecture and energy homeostasis in adipose tissues is not well understood. In this study, we utilized GCN5L1-knockout mice in white (AKO) and brown (BKO) adipose tissues to examine mitochondrial homeostasis in adipose tissues. GCN5L1, a regulator of mitochondrial metabolism and dynamics, influences resistance to high-fat-diet-induced obesity in AKO but not BKO mice. This resistance is mediated by an increase in mitochondrial cristae that stabilizes oxidative phosphorylation (OXPHOS) complexes and enhances energy expenditure. Our protein-interactome analysis reveals that GCN5L1 is associated with the mitochondrial crista complex MICOS (MIC13) and the protease YME1L, facilitating the degradation of MICOS and disassembly of cristae during obesity. This interaction results in decreased OXPHOS levels and subsequent adipocyte expansion. Accumulation of GCN5L1 in the mitochondrial intermembrane space is triggered by a high-fat diet. Our findings highlight a regulatory pathway involving YME1L/GCN5L1/MIC13 that remodels mitochondrial cristae in WAT in response to overnutrition-induced obesity.

MOB1 deletion in murine mature adipocytes ameliorates obesity and diabetes

There is currently a global epidemic of obesity and obesity-related diseases such as type 2 diabetes due to decreased physical activity, excessive food intake, and/or genetic predisposition. The Hippo-YAP1 pathway has attracted attention as a potential therapeutic target because YAP1/TAZ activation in murine immature adipocytes in vitro suppresses their differentiation by inhibiting PPARγ activity. However, the role of YAP1 activation in mature adipocytes in vivo remains unclear. MOB1, whose expression is increased in obesity, is the hub of the Hippo core molecule complex and negatively regulates YAP1/TAZ activation. Therefore, we generated aMob1DKO mutant mice, which feature deficiency of Mob1a/b specifically in mature adipocytes. Compared to controls, aMob1DKO mice subjected to a high-fat diet showed beneficial changes consistent with resistance to diet-induced obesity. The mutants exhibited increases in basal lipolysis, "beiging," and energy expenditure, as well as suppression of ROS production and inflammation in white adipose tissue. Insulin sensitivity and glucose tolerance were improved, and ectopic fat accumulation was reduced. Most of these changes were dependent on the YAP1 activation observed in mature white adipose tissue of aMob1DKO mice. FGF21, which improves lipid metabolism, was upregulated directly via YAP1 activation, and many of the phenotypes seen in aMob1DKO mice were also dependent on FGF21. Thus, the aMob1DKO mouse is an interesting model for the study of the metabolic effects of diet-induced obesity and protection against diabetes. Our work suggests that a YAP1-FGF21 axis exists in adipocytes that may be a potential therapeutic target for obesity.

Adipocyte-derived ferroptotic signaling mitigates obesity

Ferroptosis is characterized as an iron-dependent and lipophilic form of cell death. However, it remains unclear what role ferroptosis has in adipose tissue function and activity. Here, we find a lower ferroptotic signature in the adipose tissue of individuals and mice with obesity. We further find that activation of ferroptotic signaling by a non-lethal dose of ferroptosis agonists significantly reduces lipid accumulation in primary adipocytes and high-fat diet (HFD)-fed mice. Notably, adipocyte-specific overexpression of acyl-coenzyme A synthetase long-chain family member 4 (Acsl4) or deletion of ferritin heavy chain (Fth) protects mice from HFD-induced adipose expansion and metabolic disorders via activation of ferroptotic signaling. Mechanistically, we find that 5,15-dihydroxyeicosatetraenoic acid (5,15-DiHETE) activates ferroptotic signaling, resulting in the degradation of hypoxia-inducible factor-1α (HIF1α), thereby derepressing a thermogenic program regulated by the c-Myc-peroxisome proliferator-activated receptor gamma coactivator-1 beta (Pgc1β) pathway. Our findings suggest that activating ferroptosis signaling in adipose tissues might help to prevent and treat obesity and its related metabolic disorders.

Blocking Adipocyte YY1 Decouples Thermogenesis From Beneficial Metabolism by Promoting Spermidine Production

The accumulation of mitochondria in thermogenic adipose tissue (i.e., brown and beige fat) increases energy expenditure, which can aid in alleviating obesity and metabolic disorders. However, recent studies have shown that knocking out key proteins required to maintain mitochondrial function inhibits the energy expenditure in thermogenic fat, and yet the knockout (KO) mice are unexpectedly protected from developing obesity or metabolic disorders when fed a high-fat diet (HFD). In the current study, nonbiased sequencing-based screening revealed the importance of Yin Yang 1 (YY1) in the transcription of electron transport chain genes and the enhancement of mitochondrial function in thermogenic adipose tissue. Specifically, YY1 adipocyte-null (YAKO) mice showed lower energy expenditure and were intolerant to cold stress. Interestingly, YAKO mice showed alleviation of HFD-induced metabolic disorders, which can be attributed to a suppression of adipose tissue inflammation. Metabolomic analysis revealed that blocking YY1 directed glucose metabolism toward lactate, enhanced the uptake of glutamine, and promoted the production of anti-inflammatory spermidine. Conversely, blocking spermidine production in YAKO mice reversed their resistance to HFD-induced disorders. Thus, although blocking adipocyte YY1 impairs the thermogenesis, it promotes spermidine production, alleviates adipose tissue inflammation, and therefore leads to an uncoupling of adipose tissue energy expenditure from HFD-induced metabolic disorders.

ARTICLE HIGHLIGHTS

Chromatin open atlas profiling in white, beige, and brown adipocytes identified Yin Yang 1 (YY1) as a key transcription factor governing electron transport chain gene expression and mitochondrial function in thermogenic adipocytes. Knocking out adipocyte YY1 leads to impaired thermogenesis under cold stress while protecting the mice from diet-induced obesity and metabolic disorders. YY1-null adipocytes undergo metabolic reprogramming, with increased glutamine use and spermidine generation that combat adipose tissue inflammation and insulin resistance, resulting in an uncoupling of thermogenic capacity and metabolic benefits.

Ablation of FAM210A in Brown Adipocytes of Mice Exacerbates High-Fat Diet-Induced Metabolic Dysfunction

Thermogenesis of brown adipose tissue (BAT) provides metabolic benefits against pathologic conditions, such as type 2 diabetes, obesity, cardiovascular disease, and cancer. The thermogenic function of BAT relies on mitochondria, but whether mitochondrial remodeling is required for the beneficial effects of BAT remains unclear. We recently identified FAM210A as a BAT-enriched mitochondrial protein essential for cold-induced thermogenesis through the modulation of OPA1-dependent cristae remodeling. Here, we report a key role of FAM210A in the systemic response to a high-fat diet (HFD). We discovered that an HFD suppressed FAM210A expression, associated with excessive OPA1 cleavage in BAT. Ucp1-Cre-driven BAT-specific Fam210a knockout (Fam210aUKO) similarly elevated OPA1 cleavage, accompanied by whitening of BAT. When subjected to an HFD, Fam210aUKO mice gained similar fat mass as sibling control mice but developed glucose intolerance, insulin resistance, and liver steatosis. The metabolic dysfunction was associated with overall increased lipid content in both the liver and BAT. Additionally, Fam210aUKO leads to inflammation in white adipose tissue. These data demonstrate that FAM210A in BAT is necessary for counteracting HFD-induced metabolic dysfunction but not obesity.

ARTICLE HIGHLIGHTS

FAM210A regulates cold-induced mitochondrial remodeling through control of OPA1 cleavage, but whether it also plays a role in high-fat diet (HFD)-induced cristae remodeling is unknown. We asked if an HFD would alter the FAM210A level and OPA1 cleavage in brown adipose tissue (BAT) and how FAM210A loss of function would affect diet-induced obesity in mice. We found that an HFD diminished FAM210A expression and accelerated OPA1 cleavage in BAT, and Fam210a knockout exacerbated HFD-induced whitening of BAT, cold intolerance, liver steatosis, white adipose tissue inflammation, and metabolic dysfunction. Our work reveals a physiologic role of FAM210A-mediated BAT mitochondrial remodeling in systemic adaptation to an HFD and suggests that BAT mitochondria may be targeted to treat diet-induced metabolic dysfunction.

New insights into the relationship of mitochondrial metabolism and atherosclerosis

Atherosclerotic cardiovascular and cerebrovascular diseases are the number one killer of human health. In view of the important role of mitochondria in the formation and evolution of atherosclerosis, our manuscript aims to comprehensively elaborate the relationship between mitochondria and the formation and evolution of atherosclerosis from the aspects of mitochondrial dynamics, mitochondria-organelle interaction (communication), mitochondria and cell death, mitochondria and vascular smooth muscle cell phenotypic switch, etc., which is combined with genome, transcriptome and proteome, in order to provide new ideas for the pathogenesis of atherosclerosis and the diagnosis and treatment of related diseases.

Brown Adipose Tissue undergoes pathological perturbations and shapes C2C12 myoblast homeostasis in the SOD1-G93A mouse model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the selective loss of motor neurons. The contribution of peripheral organs remains incompletely understood. We focused our attention on brown adipose tissue (BAT) and its secreted extracellular vesicles (EVs) given their role in regulating systemic energy balance. In this study, we employed a multi-omics approach, including RNA sequencing (GEO identifier GSE273052) and proteomics (ProteomeXchange identifier PXD054147), to investigate the alterations in BAT and its EVs in the SOD1-G93A mouse model of ALS. Our results revealed consistent changes in the proteomic and transcriptomic profiles of BAT from SOD1-G93A mice, highlighting alterations such as mitochondrial dysfunction and impaired differentiation capacity. Specifically, primary brown adipocytes (PBAs) from SOD1-G93A mice exhibited differentiation impairment, respiratory defects, and alterations in mitochondrial dynamics. Furthermore, the BAT-derived EVs from SOD1-G93A mice displayed distinct changes in size distribution and cargo content. In parallel, such EVs negatively impacted the differentiation and homeostasis of C2C12 murine myoblasts, as well as induced atrophy in C2C12-derived myotubes. These findings suggest that BAT undergoes pathological perturbations in ALS mouse model and could impact on skeletal muscle homeostasis through the secretion of dysfunctional EVs.

Leptin drives glucose metabolism to promote cardiac protection via OPA1-mediated HDAC5 translocation and Glut4 transcription

Metabolic reprogramming, the shifting from fatty acid oxidation to glucose utilization, improves cardiac function as heart failure (HF) progresses. Leptin plays an essential role in regulating glucose metabolism. However, the crosstalk between leptin and metabolic reprogramming is poorly understood. We tested the hypothesis that leptin improves cardiac function after myocardial infarction via enhancing glucose metabolism. In the isoproterenol (ISO)-induced heart failure model in vitro, H9c2 cell apoptosis was assessed by the TUNEL and Annexin V/PI staining assay. Leptin-mediated mitochondrial fusion was performed via TEM, and glucose oxidation was explored, as well as the ECAR, OCR, and protein expression of the vital metabolic enzymes. By blocking OPA1 expression or HDAC5 inhibition, the mitochondrial dynamic and glucose metabolic were detected to evaluate the role of OPA1 and HDAC5 in leptin-stimulated glucose metabolism. In the mouse model of HF in vivo, intraperitoneal leptin administration appreciably increased glucose oxidation and preserved cardiac function 56 days after coronary artery ligation. In vitro, we identified the OPA1-dependent HDAC5 nucleus export as a crucial process in boosting glucose utilization by activating MEF2 to upregulate Glut4 expression using the RNA interference technique in H9c2 cells. In vivo, leptin promotes glucose utilization and confers heart functional and survival benefits in chronic ischemic HF. The current study provided a novel insight into the role of leptin in metabolic reprogramming and revealed potential therapeutic targets for chronic HF.

Mitochondrial dynamics govern whole-body regeneration through stem cell pluripotency and mitonuclear balance

Tissue regeneration is a complex process involving large changes in cell proliferation, fate determination, and differentiation. Mitochondrial dynamics and metabolism play a crucial role in development and wound repair, but their function in large-scale regeneration remains poorly understood. Planarians offer an excellent model to investigate this process due to their remarkable regenerative abilities. In this study, we examine mitochondrial dynamics during planarian regeneration. We find that knockdown of the mitochondrial fusion gene, opa1, impairs both tissue regeneration and stem cell pluripotency. Interestingly, the regeneration defects caused by opa1 knockdown are rescued by simultaneous knockdown of the mitochondrial fission gene, drp1, which partially restores mitochondrial dynamics. Furthermore, we discover that Mitolow stem cells exhibit an enrichment of pluripotency due to their fate choices at earlier stages. Transcriptomic analysis reveals the delicate mitonuclear balance in metabolism and mitochondrial proteins in regeneration, controlled by mitochondrial dynamics. These findings highlight the importance of maintaining mitochondrial dynamics in large-scale tissue regeneration and suggest the potential for manipulating these dynamics to enhance stem cell functionality and regenerative processes.

Integrated analysis of omics reveals the role of scapular fat in thermogenesis adaptation in sunite sheep

Inhabiting some of the world's most inhospitable climatic regions, the Sunite Mongolian sheep generates average temperatures as low as 4.3 °C and a minimum temperature of -38.8 °C; in these environments, they make essential cold adaptations. In this regard, scapular fat tissues from Mongolian sheep were collected both in winter and summer for transcriptomic and proteomic analyses to identify genes related to adaptive thermogenesis. In the transcriptome analysis, 588 differentially expressed genes were identified to participate in smooth muscle activity and fat metabolism, as well as in nutrient regulation. There were 343 upregulated and 245 downregulated genes. GO and KEGG pathway analyses on these genes revealed their participation in regulating smooth muscle activity, metabolism of fats, and nutrients. Proteomic analysis showed the differential expression of 925 proteins: among them, there are 432 up- and 493 down-expressed proteins. These proteins are mainly involved in oxidative phosphorylation, respiratory chain complex assembly, and ATP production by electron transport. Furthermore, using both sets at a more detailed level of analysis revealed over-representation in gene ontology categories related to hormone signaling, metabolism of lipids, the pentose phosphate pathway, the TCA cycle, and especially the process of oxidative phosphorylation. The identified essential genes and proteins were further validated by quantitative real-time polymerase chain reaction and Western blotting, respectively; key metabolic network constriction was constructed. The present study emphasized the critical role of lipid turnover in scapular fat for thermogenic adaptation in Sunite sheep.

Mitochondrial mechanotransduction through MIEF1 coordinates the nuclear response to forces

Tissue-scale architecture and mechanical properties instruct cell behaviour under physiological and diseased conditions, but our understanding of the underlying mechanisms remains fragmentary. Here we show that extracellular matrix stiffness, spatial confinements and applied forces, including stretching of mouse skin, regulate mitochondrial dynamics. Actomyosin tension promotes the phosphorylation of mitochondrial elongation factor 1 (MIEF1), limiting the recruitment of dynamin-related protein 1 (DRP1) at mitochondria, as well as peri-mitochondrial F-actin formation and mitochondrial fission. Strikingly, mitochondrial fission is also a general mechanotransduction mechanism. Indeed, we found that DRP1- and MIEF1/2-dependent fission is required and sufficient to regulate three transcription factors of broad relevance-YAP/TAZ, SREBP1/2 and NRF2-to control cell proliferation, lipogenesis, antioxidant metabolism, chemotherapy resistance and adipocyte differentiation in response to mechanical cues. This extends to the mouse liver, where DRP1 regulates hepatocyte proliferation and identity-hallmark YAP-dependent phenotypes. We propose that mitochondria fulfil a unifying signalling function by which the mechanical tissue microenvironment coordinates complementary cell functions.

Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications

For a long time, white adipocytes were thought to function as lipid storages due to the sizeable unilocular lipid droplet that occupies most of their space. However, recent discoveries have highlighted the critical role of white adipocytes in maintaining energy homeostasis and contributing to obesity and related metabolic diseases. These physiological and pathological functions depend heavily on the mitochondria that reside in white adipocytes. This article aims to provide an up-to-date overview of the recent research on the function and dysfunction of white adipocyte mitochondria. After briefly summarizing the fundamental aspects of mitochondrial biology, the article describes the protective role of functional mitochondria in white adipocyte and white adipose tissue health and various roles of dysfunctional mitochondria in unhealthy white adipocytes and obesity. Finally, the article emphasizes the importance of enhancing mitochondrial quantity and quality as a therapeutic avenue to correct mitochondrial dysfunction, promote white adipocyte browning, and ultimately improve obesity and its associated metabolic diseases. © 2024 American Physiological Society. Compr Physiol 14:5581-5640, 2024.

Nuclear Factor Erythroid 2 Related Factor 2 and Mitochondria Form a Mutually Regulating Circuit in the Prevention and Treatment of Metabolic Syndrome

Significance: Metabolic syndrome (MetS) has become a major global public health problem and there is an urgent need to elucidate its pathogenesis and find more effective targets and modalities for intervention. Recent Advances: Oxidative stress and inflammation are two of the major causes of MetS-related symptoms such as insulin resistance and obesity. Nuclear factor erythroid 2 related factor 2 (Nrf2) is one of the important systems responding to oxidative stress and inflammation. As cells undergo stress, cysteines within Kelch-like ECH-associated protein 1 (Keap1) are oxidized or electrophilically modified, allowing Nrf2 to escape ubiquitination and be translocated from the cytoplasm to the nucleus, facilitating the initiation of the antioxidant transcriptional program. Meanwhile, a growing body of evidence points out a specific modulation of mitochondrial homeostasis by Nrf2. After nuclear translocation, Nrf2 activates downstream genes involved in various aspects of mitochondrial homeostasis, including mitochondrial biogenesis and dynamics, mitophagy, aerobic respiration, and energy metabolism. In turn, mitochondria reciprocally activate Nrf2 by releasing reactive oxygen species and regulating antioxidant enzymes. Critical Issues: In this review, we first summarize the interactions between Nrf2 and mitochondria in the modulation of oxidative stress and inflammation to ameliorate MetS, then propose that Nrf2 and mitochondria form a mutually regulating circuit critical to maintaining homeostasis during MetS. Future Directions: Targeting the Nrf2-mitochondrial circuit may be a promising strategy to ameliorate MetS, such as obesity, diabetes, and cardiovascular diseases.

Ndufa8 promotes white fat Browning by improving mitochondrial respiratory chain complex I function to ameliorate obesity by in vitro and in vivo

Obesity and its complications have become a global health problem that needs to be addressed urgently. White adipose tissue (WAT) browning contributes to consuming excess energy in WAT, which is important for improving obesity and maintaining a healthy energy homeostasis. Mitochondria, as the energy metabolism center of cells, are extensively involved in many metabolic processes, including the browning of WAT. NADH: Ubiquinone oxidoreductase subunit A8 (NDUFA8) is a constituent subunit of respiratory chain complex I (CI), which has been found to participate in a wide range of physiological processes by affecting the activity of respiratory CI. However, the regulatory effect of Ndufa8 on the browning of WAT has not been reported. Here, we used β3-adrenergic agonis CL316, 243 to construct WAT browning models in vivo and in vitro to investigate the role and mechanism of Ndufa8 in the regulation of WAT browning. Briefly, Ndufa8 significantly increased CI activity and suppressed mitochondrial ROS levels in vitro, thereby improving mitochondrial function. Ndufa8 also increased the transcriptional levels and protein levels of UCP1 in vitro and in vivo, which promoted WAT browning. Our findings provide a new molecular approach for the research of browning of WAT in animals, as well as a new target for animal metabolism improvement and obesity treatments.

Mechanistic insights into metabolic function of dynamin-related protein 1

Dynamin-related protein 1 (DRP1) plays crucial roles in mitochondrial and peroxisome fission. However, the mechanisms underlying the functional regulation of DRP1 in adipose tissue during obesity remain unclear. To elucidate the metabolic and pathological significance of diminished DRP1 in obese adipose tissue, we utilized adipose tissue-specific DRP1 KO mice challenged with a high-fat diet. We observed significant metabolic dysregulations in the KO mice. Mechanistically, DRP1 exerts multifaceted functions in mitochondrial dynamics and endoplasmic reticulum (ER)-lipid droplet crosstalk in normal mice. Loss of function of DRP1 resulted in abnormally giant mitochondrial shapes, distorted mitochondrial membrane structure, and disrupted cristae architecture. Meanwhile, DRP1 deficiency induced the retention of nascent lipid droplets in ER, leading to perturbed overall lipid dynamics in the KO mice. Collectively, dysregulation of the dynamics of mitochondria, ER, and lipid droplets contributes to whole-body metabolic disorders, as evidenced by perturbations in energy metabolites. Our findings demonstrate that DRP1 plays diverse and critical roles in regulating energy metabolism within adipose tissue during the progression of obesity.

HIF-1α limits myocardial infarction by promoting mitophagy in mouse hearts adapted to chronic hypoxia

AIM

The transcriptional factor HIF-1α is recognized for its contribution to cardioprotection against acute ischemia/reperfusion injury. Adaptation to chronic hypoxia (CH) is known to stabilize HIF-1α and increase myocardial ischemic tolerance. However, the precise role of HIF-1α in mediating the protective effect remains incompletely understood.

METHODS

Male wild-type (WT) mice and mice with partial Hif1a deficiency (hif1a +/-) were exposed to CH for 4 weeks, while their respective controls were kept under normoxic conditions. Subsequently, their isolated perfused hearts were subjected to ischemia/reperfusion to determine infarct size, while RNA-sequencing of isolated cardiomyocytes was performed. Mitochondrial respiration was measured to evaluate mitochondrial function, and western blots were performed to assess mitophagy.

RESULTS

We demonstrated enhanced ischemic tolerance in WT mice induced by adaptation to CH compared with their normoxic controls and chronically hypoxic hif1a +/- mice. Through cardiomyocyte bulk mRNA sequencing analysis, we unveiled significant reprogramming of cardiomyocytes induced by CH emphasizing mitochondrial processes. CH reduced mitochondrial content and respiration and altered mitochondrial ultrastructure. Notably, the reduced mitochondrial content correlated with enhanced autophagosome formation exclusively in chronically hypoxic WT mice, supported by an increase in the LC3-II/LC3-I ratio, expression of PINK1, and degradation of SQSTM1/p62. Furthermore, pretreatment with the mitochondrial division inhibitor (mdivi-1) abolished the infarct size-limiting effect of CH in WT mice, highlighting the key role of mitophagy in CH-induced cardioprotection.

CONCLUSION

These findings provide new insights into the contribution of HIF-1α to cardiomyocyte survival during acute ischemia/reperfusion injury by activating the selective autophagy pathway.

Opa1 processing is dispensable in mouse development but is protective in mitochondrial cardiomyopathy

Mitochondrial fusion and fission accompany adaptive responses to stress and altered metabolic demands. Inner membrane fusion and cristae morphogenesis depends on optic atrophy 1 (Opa1), which is expressed in different isoforms and is cleaved from a membrane-bound, long to a soluble, short form. Here, we have analyzed the physiological role of Opa1 isoforms and Opa1 processing by generating mouse lines expressing only one cleavable Opa1 isoform or a non-cleavable variant thereof. Our results show that expression of a single cleavable or non-cleavable Opa1 isoform preserves embryonic development and the health of adult mice. Opa1 processing is dispensable under metabolic and thermal stress but prolongs life span and protects against mitochondrial cardiomyopathy in OXPHOS-deficient Cox10-/- mice. Mechanistically, loss of Opa1 processing disturbs the balance between mitochondrial biogenesis and mitophagy, suppressing cardiac hypertrophic growth in Cox10-/- hearts. Our results highlight the critical regulatory role of Opa1 processing, mitochondrial dynamics, and metabolism for cardiac hypertrophy.

Novel insight into the role of A-kinase anchoring proteins (AKAPs) in ischemic stroke and therapeutic potentials

Ischemic stroke, a devastating disease associated with high mortality and disability worldwide, has emerged as an urgent public health issue. A-kinase anchoring proteins (AKAPs) are a group of signal-organizing molecules that compartmentalize and anchor a wide range of receptors and effector proteins and have a major role in stabilizing mitochondrial function and promoting neurodevelopmental development in the central nervous system (CNS). Growing evidence suggests that dysregulation of AKAPs expression and activity is closely associated with oxidative stress, ion disorder, mitochondrial dysfunction, and blood-brain barrier (BBB) impairment in ischemic stroke. However, the underlying mechanisms remain inadequately understood. This review provides a comprehensive overview of the composition and structure of A-kinase anchoring protein (AKAP) family members, emphasizing their physiological functions in the CNS. We explored in depth the molecular and cellular mechanisms of AKAP complexes in the pathological progression and risk factors of ischemic stroke, including hypertension, hyperglycemia, lipid metabolism disorders, and atrial fibrillation. Herein, we highlight the potential of AKAP complexes as a pharmacological target against ischemic stroke in the hope of inspiring translational research and innovative clinical approaches.

Mitochondrial heterogeneity and adaptations to cellular needs

Although it is well described that mitochondria are at the epicentre of the energy demands of a cell, it is becoming important to consider how each cell tailors its mitochondrial composition and functions to suit its particular needs beyond ATP production. Here we provide insight into mitochondrial heterogeneity throughout development as well as in tissues with specific energy demands and discuss how mitochondrial malleability contributes to cell fate determination and tissue remodelling.

Plasticity of Adipose Tissues: Interconversion among White, Brown, and Beige Fat and Its Role in Energy Homeostasis

Obesity, characterized by the excessive accumulation of adipose tissue, has emerged as a major public health concern worldwide. To develop effective strategies for treating obesity, it is essential to comprehend the biological properties of different adipose tissue types and their respective roles in maintaining energy balance. Adipose tissue serves as a crucial organ for energy storage and metabolism in the human body, with functions extending beyond simple fat storage to encompass the regulation of energy homeostasis and the secretion of endocrine factors. This review provides an overview of the key characteristics, functional differences, and interconversion processes among white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue. Moreover, it delves into the molecular mechanisms and recent research advancements concerning the browning of WAT, activation of BAT, and whitening of BAT. Although targeting adipose tissue metabolism holds promise as a potential approach for obesity treatment, further investigations are necessary to unravel the intricate biological features of various adipose tissue types and elucidate the molecular pathways governing their interconversion. Such research endeavors will pave the way for the development of more efficient and targeted therapeutic interventions in the fight against obesity.

Inhibitory effects of naringenin on estrogen deficiency-induced obesity via regulation of mitochondrial dynamics and AMPK activation associated with white adipose tissue browning

AIMS

Post-ovariectomy (OVX) changes in hormones induce obesity and white adipose tissue (WAT) inflammation. Increased energy expenditure via WAT browning is a novel therapeutic strategy for treating obesity. Naringenin (NAR) reduces inflammation and lipogenesis in obesity and attenuates estrogen deficiency-associated metabolic disorders; however, its role in WAT browning remains unclear.

MATERIALS AND METHODS

We investigated NAR ability to inhibit estrogen deficiency-associated obesity in vivo using a rat model and in vitro using 3T3-L1 adipocytes.

KEY FINDINGS

NAR significantly decreased the body weight and WAT mass of rats. O2 consumption, CO2 production, and energy expenditure were significantly lower in the OVX group than in the sham group, but NAR treatment reversed these effects of OVX. NAR treatment markedly improved glucose intolerance and lipid profiles as well as leptin, adiponectin, and irisin levels. NAR upregulated markers of browning and mitochondrial biogenesis in inguinal WAT. Moreover, it enhanced markers of mitochondrial fusion and inhibited fission via activating the AMP-activated protein kinase pathway. Similar results were observed in 3T3-L1 adipocytes. Moreover, NAR-induced mitochondrial biogenesis and fusion were suppressed by dorsomorphin (an AMP-activated protein kinase inhibitor).

SIGNIFICANCE

NAR alleviates obesity and metabolic dysfunction through the induction of WAT browning achieved via the modulation of AMP-activated protein kinase-regulated mitochondrial dynamics in WATs. NAR supplementation may therefore represent a potential intervention for preventing postmenopausal adipose tissue dysregulation.

The inhibition of inner mitochondrial fusion in hepatocytes reduces non-alcoholic fatty liver and improves metabolic profile during obesity by modulating bile acid conjugation

AIMS

Mitochondria are plastic organelles that continuously undergo biogenesis, fusion, fission, and mitophagy to control cellular energy metabolism, calcium homeostasis, hormones, sterols, and bile acids (BAs) synthesis. Here, we evaluated how the impairment of mitochondrial fusion in hepatocytes affects diet-induced liver steatosis and obesity.

METHODS AND RESULTS

Male mice selectively lacking the key protein involved in inner mitochondrial fusion, optic atrophy 1 (OPA1) (OPA1ΔHep) were fed a high fat diet (HFD) for 20 weeks. OPA1ΔHep mice were protected from the development of hepatic steatosis and obesity because of reduced lipid absorption; a profile which was accompanied by increased respiratory exchange ratio in vivo, suggesting a preference for carbohydrates in OPA1ΔHep compared to controls. At the molecular level, this phenotype emerged as a consequence of poor mitochondria-peroxisome- endoplasmic reticulum (ER) tethering in OPA1 deficient hepatocytes, which impaired BAs conjugation and release in the bile, thus impacting lipid absorption from the diet. Concordantly, the liver of subjects with non-alcoholic fatty liver disease (NAFLD) presented an increased expression of OPA1 and of the network of proteins involved in mitochondrial function when compared with controls.

CONCLUSION

Patients with NAFLD present increased expression of proteins involved in mitochondrial fusion in the liver. The selective deficency of OPA1 in hepatocytes protects mice from HFD-induced metabolic dysfunction by reducing BAs secretion and dietary lipids absorption as a consequence of reduced liver mitochondria-peroxisome-ER tethering.

Mitochondrial Dynamics, Diabetes, and Cardiovascular Disease

Mitochondria undergo repeated cycles of fusion and fission that regulate their size and shape by a process known as mitochondrial dynamics. Numerous studies have revealed the importance of this process in maintaining mitochondrial health and cellular homeostasis, particularly in highly metabolically active tissues such as skeletal muscle and the heart. Here, we review the literature on the relationship between mitochondrial dynamics and the pathophysiology of type 2 diabetes and cardiovascular disease (CVD). Importantly, we emphasize divergent outcomes resulting from downregulating distinct mitochondrial dynamics proteins in various tissues. This review underscores compensatory mechanisms and adaptive pathways that offset potentially detrimental effects, resulting instead in improved metabolic health. Finally, we offer a perspective on potential therapeutic implications of modulating mitochondrial dynamics proteins for treatment of diabetes and CVD.

ARTICLE HIGHLIGHTS

A review for the correlation between optic atrophy 1-dependent mitochondrial fusion and cardiovascular disorders

Mitochondrial dynamics homeostasis is sustained by continuous and balanced fission and fusion, which are determinants of morphology, abundance, biogenesis and mitophagy of mitochondria. Optic atrophy 1 (OPA1), as the only inner mitochondrial membrane fusion protein, plays a key role in stabilizing mitochondrial dynamics. The disturbance of mitochondrial dynamics contributes to the pathophysiological progress of cardiovascular disorders, which are the main cause of death worldwide in recent decades and result in tremendous social burden. In this review, we describe the latest findings regarding OPA1 and its role in mitochondrial fusion. We summarize the post-translational modifications (PTMs) for OPA1 and its regulatory role in mitochondrial dynamics. Then the diverse cell fates caused by OPA1 expression during cardiovascular disorders are discussed. Moreover, cardiovascular disorders (such as heart failure, myocardial ischemia/reperfusion injury, cardiomyopathy and cardiac hypertrophy) relevant to OPA1-dependent mitochondrial dynamics imbalance have been detailed. Finally, we highlight the potential that targeting OPA1 to impact mitochondrial fusion may be used as a novel strategy against cardiovascular disorders.

Mitochondrial transplantation reduces lower limb ischemia-reperfusion injury by increasing skeletal muscle energy and adipocyte browning

Recent studies have shown that mitochondrial transplantation can repair lower limb IRI, but the underlying mechanism of the repair effect remains unclear. In this study, we found that in addition to being taken up by skeletal muscle cells, human umbilical cord mesenchymal stem cells (hMSCs)-derived mitochondria were also taken up by adipocytes, which was accompanied by an increase in optic atrophy 1 (OPA1) and uncoupling protein 1. Transplantation of hMSCs-derived mitochondria could not only supplement the original damaged mitochondrial function of skeletal muscle, but also promote adipocyte browning by increasing the expression of OPA1. In this process, mitochondrial transplantation can reduce cell apoptosis and repair muscle tissue, which promotes the recovery of motor function in vivo. To the best of our knowledge, there is no study on the therapeutic mechanism of mitochondrial transplantation from this perspective, which could provide a theoretical basis.

COX6A2 deficiency leads to cardiac remodeling in human pluripotent stem cell-derived cardiomyocytes

BACKGROUND

Cardiac remodeling is the initiating factor for the development of heart failure, which can result from various cardiomyopathies. Cytochrome c oxidase subunit 6A2 (COX6A2) is one of the components of cytochrome c oxidase that drives oxidative phosphorylation. The pathogenesis of myocardial remodeling caused by COX6A2 deficiency in humans remains unclear because there are no suitable research models. In this study, we established a COX6A2-deficient human cardiac myocyte (CM) model that mimics the human COX6A2 homozygous mutation and determined the effects of COX6A2 dysfunction and its underlying mechanism.

METHODS

A human COX6A2 homozygous knockout cardiomyocyte model was established by combining CRISPR/Cas9 gene editing technology and hiPSC-directed differentiation technology. Cell model phenotypic assays were done to characterize the pathological features of the resulting COX6A2-deficient cardiomyocytes.

RESULTS

COX6A2 gene knockout did not affect the pluripotency and differentiation efficiency of hiPSCs. Myocardial cells with a COX6A2 gene knockout showed abnormal energy metabolism, increased oxidative stress levels, abnormal calcium transport activity, and decreased contractility. In addition, L-carnitine and trimetazidine significantly improved energy metabolism in the COX6A2-deficient human myocardial model.

CONCLUSIONS

We have established a COX6A2-deficient human cardiomyocyte model that exhibits abnormal energy metabolism, elevated oxidative stress levels, abnormal calcium transport, and reduced contractility. This model represents an important tool to gain insight into the mechanism of action of energy metabolism disorders resulting in myocardial remodeling, elucidate the gene-phenotype relationship of COX6A2 deficiency, and facilitate drug screening.

Lipopolysaccharide-induced persistent inflammation ameliorates fat accumulation by promoting adipose browning in vitro and in vivo

This work aimed to explore whether the persistent inflammation induced by lipopolysaccharide (LPS) ameliorates fat accumulation by promoting adipose browning in vitro and in vivo. LPS over 1 ng/mL reduced lipid accumulation while increasing the expressions of specific genes involved in inflammation, mitochondrial biogenesis, and adipose browning in 3T3-L1 adipocytes. Moreover, LPS in intraperitoneal injection decreased white adipose tissue weight and elevated interscapular brown adipose tissue weight in mice. According to RT-PCR and western blot analysis results, the expressions of genes and proteins related to inflammation, mitochondrial biogenesis, lipolysis, and brown or beige markers in different tissues were elevated after LPS intervention. Cumulatively, LPS-induced persistent inflammation may potentially ameliorate fat accumulation by facilitating adipose browning in 3T3-L1 adipocytes and mice. These results offer new perspectives into the effect of persistent inflammation induced by LPS on regulating fat metabolism, thereby reducing fat accumulation by boosting adipose browning procedure.

Maternal consumption of l-malic acid enriched diets improves antioxidant capacity and glucose metabolism in offspring by regulating the gut microbiota

Maternal diets during pregnancy and lactation are key determinants that regulate the development of metabolic syndrome (MetS) in offspring. l-malic acid (MA) was previously reported to improve antioxidant capacity and aerobic metabolism. However, the effects of maternal MA consumption on the metabolic features of offspring remain largely unexplored. Herein, through pig models consuming MA-enriched diets during late pregnancy and lactation, we found that maternal MA consumption potentiated the anti-inflammatory and antioxidant capacity of sows, thereby improving their reproductive performance and the growth performance of piglets. Maternal MA consumption also induced a transition of slow-twitch to fast-twitch fibers in the early life of offspring. Along with muscle growth and fiber-type transition, insulin sensitivity and glucose metabolism, including aerobic metabolism and glycolysis, were improved in the skeletal muscle of offspring. An untargeted metabolomic analysis further revealed the contribution of modified amino acid metabolism to the improved aerobic metabolism. Mechanistically, maternal MA consumption remodeled colonic microbiota of their offspring. Briefly, the abundance of Colidextribacter, Romboutsia, and Family_XIII_AD3011_group increased, which were positively associated with the antioxidant capacity and glucose metabolism of skeletal muscles. A decreased abundance of Prevotella, Blautia, Prevotellaceae_NK3B31_group, and Collinsella was also detected, which were involved in less insulin sensitivity. Notably, milk metabolites, such as ascorbic acid (AA) and granisetron (GS), were found as key effectors regulating the gut microbiota composition of piglets. The properties of AA and GS in alleviating insulin resistance, inflammation, and oxidative stress were further verified through mice treated with high-fat diets. Overall, this study revealed that maternal MA consumption could modulate the inflammatory response, antioxidant capacity, and glucose metabolism by regulating the gut microbiota of offspring through the vertical transmission of milk metabolites. These findings suggest the potential of MA in the prevention and treatment of MetS in early life.

Obesity and its comorbidities, current treatment options and future perspectives: Challenging bariatric surgery?

Obesity and its comorbidities, including type 2 diabetes mellitus, cardiovascular disease, heart failure and non-alcoholic liver disease are a major health and economic burden with steadily increasing numbers worldwide. The need for effective pharmacological treatment options is strong, but, until recently, only few drugs have proven sufficient efficacy and safety. This article provides a comprehensive overview of obesity and its comorbidities, with a special focus on organ-specific pathomechanisms. Bariatric surgery as the so far most-effective therapeutic strategy, current pharmacological treatment options and future treatment strategies will be discussed. An increasing knowledge about the gut-brain axis and especially the identification and physiology of incretins unfolds a high number of potential drug candidates with impressive weight-reducing potential. Future multi-modal therapeutic concepts in obesity treatment may surpass the effectivity of bariatric surgery not only with regard to weight loss, but also to associated comorbidities.

Malonate induces the browning of white adipose tissue in high-fat diet induced obesity model

Obesity increases the risk of various diseases, and many studies have examined prevention and treatment strategies. Browning of white adipocytes promotes triglyceride (TG) metabolism and is the new focus for treating obesity. This study investigated the role of malonate-a modulator of mitochondrial function-in adipocyte browning, and its potential as a therapeutic agent in obesity. Our findings revealed that malonate increased oxygen consumption without inhibiting ATP synthesis. Malonate induced expression of PRDM16-an important transcription factor for browning-and uncoupling protein 1 (beige adipocyte marker), suggesting that malonate induces browning in white adipocytes. In an obesity mouse model induced by a high-fat diet, malonate significantly reduced body weight and white adipose tissue weight, as well as improved insulin resistance. Importantly, malonate stimulated browning in white adipose tissue and maintained the mass of brown adipose tissue in the high-fat diet-induced obesity mouse model. We propose that manipulation of mitochondrial function by malonate is a promising therapeutic approach for obesity.

The regulatory role of adipocyte mitochondrial homeostasis in metabolism-related diseases

Adipose tissue is the most important energy storage organ in the body, maintaining its normal energy metabolism function and playing a vital role in keeping the energy balance of the body to avoid the harm caused by obesity and a series of related diseases resulting from abnormal energy metabolism. The dysfunction of adipose tissue is closely related to the occurrence of diseases related to obesity metabolism. Among various organelles, mitochondria are the main site of energy metabolism, and mitochondria maintain their quality through autophagy, biogenesis, transfer, and dynamics, which play an important role in maintaining metabolic homeostasis of adipocytes. On the other hand, mitochondria have mitochondrial genomes which are vulnerable to damage due to the lack of protective structures and their proximity to sites of reactive oxygen species generation, thus affecting mitochondrial function. Notably, mitochondria are closely related to other organelles in adipocytes, such as lipid droplets and the endoplasmic reticulum, which enhances the function of mitochondria and other organelles and regulates energy metabolism processes, thus reducing the occurrence of obesity-related diseases. This article introduces the structure and quality control of mitochondria in adipocytes and their interactions with other organelles in adipocytes, aiming to provide a new perspective on the regulation of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases, and to provide theoretical reference for further revealing the molecular mechanism of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases.

Cold-inducible PPA1 is critical for the adipocyte browning in mice

Promoting the thermogenic capacity of brown/beige adipocytes is becoming a promising strategy to counteract obesity and related metabolic diseases. Inorganic pyrophosphatase 1 (PPA1) is an enzyme that catalyzes the hydrolysis of PPi to Pi, and its presence is required for anabolism to take place in cells. Our previous study demonstrated the importance of PPA1 in maintaining adipose tissue function and whole-body metabolic homeostasis. In this study, we found that the expression of PPA1 was positively associated with the thermogenic capacity of brown/beige adipocytes. PPA1+/- mice exhibited less browning capacity in subcutaneous white adipose tissue compared to wild-type mice and also showed apparent cold intolerance. We found that decreased PPA1 abundance may lead to mitochondrial dysfunction and inhibited adipocyte browning both in vivo and in vitro. Furthermore, our study also revealed that PPA1 worked as a new target gene of nuclear respiratory factor 1 (NRF1), a major transcription regulator of mitochondrial biogenesis. Together, our findings indicated an essential role of PPA1 in mitochondrial function and browning in adipocytes and suggested PPA1 as a new therapeutic target for increasing thermogenesis to combat obesity and metabolic diseases.

FAM210A is essential for cold-induced mitochondrial remodeling in brown adipocytes

Cold stimulation dynamically remodels mitochondria in brown adipose tissue (BAT) to facilitate non-shivering thermogenesis in mammals, but what regulates mitochondrial plasticity is poorly understood. Comparing mitochondrial proteomes in response to cold revealed FAM210A as a cold-inducible mitochondrial inner membrane protein. An adipocyte-specific constitutive knockout of Fam210a (Fam210aAKO) disrupts mitochondrial cristae structure and diminishes the thermogenic activity of BAT, rendering the Fam210aAKO mice vulnerable to lethal hypothermia under acute cold exposure. Induced knockout of Fam210a in adult adipocytes (Fam210aiAKO) does not affect steady-state mitochondrial structure under thermoneutrality, but impairs cold-induced mitochondrial remodeling, leading to progressive loss of cristae and reduction of mitochondrial density. Proteomics reveals an association between FAM210A and OPA1, whose cleavage governs cristae dynamics and mitochondrial remodeling. Mechanistically, FAM210A interacts with mitochondrial protease YME1L and modulates its activity toward OMA1 and OPA1 cleavage. These data establish FAM210A as a key regulator of mitochondrial cristae remodeling in BAT and shed light on the mechanism underlying mitochondrial plasticity in response to cold.

Mitochondrial Cristae Morphology Reflecting Metabolism, Superoxide Formation, Redox Homeostasis, and Pathology

Significance: Mitochondrial (mt) reticulum network in the cell possesses amazing ultramorphology of parallel lamellar cristae, formed by the invaginated inner mitochondrial membrane. Its non-invaginated part, the inner boundary membrane (IBM) forms a cylindrical sandwich with the outer mitochondrial membrane (OMM). Crista membranes (CMs) meet IBM at crista junctions (CJs) of mt cristae organizing system (MICOS) complexes connected to OMM sorting and assembly machinery (SAM). Cristae dimensions, shape, and CJs have characteristic patterns for different metabolic regimes, physiological and pathological situations. Recent Advances: Cristae-shaping proteins were characterized, namely rows of ATP-synthase dimers forming the crista lamella edges, MICOS subunits, optic atrophy 1 (OPA1) isoforms and mitochondrial genome maintenance 1 (MGM1) filaments, prohibitins, and others. Detailed cristae ultramorphology changes were imaged by focused-ion beam/scanning electron microscopy. Dynamics of crista lamellae and mobile CJs were demonstrated by nanoscopy in living cells. With tBID-induced apoptosis a single entirely fused cristae reticulum was observed in a mitochondrial spheroid. Critical Issues: The mobility and composition of MICOS, OPA1, and ATP-synthase dimeric rows regulated by post-translational modifications might be exclusively responsible for cristae morphology changes, but ion fluxes across CM and resulting osmotic forces might be also involved. Inevitably, cristae ultramorphology should reflect also mitochondrial redox homeostasis, but details are unknown. Disordered cristae typically reflect higher superoxide formation. Future Directions: To link redox homeostasis to cristae ultramorphology and define markers, recent progress will help in uncovering mechanisms involved in proton-coupled electron transfer via the respiratory chain and in regulation of cristae architecture, leading to structural determination of superoxide formation sites and cristae ultramorphology changes in diseases. Antioxid. Redox Signal. 39, 635-683.

Amino acids contribute to adaptive thermogenesis. New insights into the mechanisms of action of recent drugs for metabolic disorders are emerging

Adaptive thermogenesis is the heat production by muscle contractions (shivering thermogenesis) or brown adipose tissue (BAT) and beige fat (non-shivering thermogenesis) in response to external stimuli, including cold exposure. BAT and beige fat communicate with peripheral organs and the brain through a variegate secretory and absorption processes - controlling adipokines, microRNAs, extracellular vesicles, and metabolites - and have received much attention as potential therapeutic targets for managing obesity-related disorders. The sympathetic nervous system and norepinephrine-releasing adipose tissue macrophages (ATM) activate uncoupling protein 1 (UCP1), expressed explicitly in brown and beige adipocytes, dissolving the electrochemical gradient and uncoupling tricarboxylic acid cycle and the electron transport chain from ATP production. Mounting evidence has attracted attention to the multiple effects of dietary and endogenously synthesised amino acids in BAT thermogenesis and metabolic phenotype in animals and humans. However, the mechanisms implicated in these processes have yet to be conclusively characterized. In the present review article, we aim to define the principal investigation areas in this context, including intestinal microbiota constitution, adipose autophagy modulation, and secretome and metabolic fluxes control, which lead to increased brown/beige thermogenesis. Finally, also based on our recent epicardial adipose tissue results, we summarise the evidence supporting the notion that the new dual and triple agonists of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon (GCG) receptor - with never before seen weight loss and insulin-sensitizing efficacy - promote thermogenic-like amino acid profiles in BAT with robust heat production and likely trigger sympathetic activation and adaptive thermogenesis by controlling amino acid metabolism and ATM expansion in BAT and beige fat.

Latest advances in the regulatory genes of adipocyte thermogenesis

An energy imbalance cause obesity: more energy intake or less energy expenditure, or both. Obesity could be the origin of many metabolic disorders, such as type 2 diabetes and cardiovascular disease. UCP1 (uncoupling protein1), which is highly and exclusively expressed in the thermogenic adipocytes, including beige and brown adipocytes, can dissipate proton motive force into heat without producing ATP to increase energy expenditure. It is an attractive strategy to combat obesity and its related metabolic disorders by increasing non-shivering adipocyte thermogenesis. Adipocyte thermogenesis has recently been reported to be regulated by several new genes. This work provided novel and potential targets to activate adipocyte thermogenesis and resist obesity, such as secreted proteins ADISSP and EMC10, enzyme SSU72, etc. In this review, we have summarized the latest research on adipocyte thermogenesis regulation to shed more light on this topic.

Propionic acid induces alterations in mitochondrial morphology and dynamics in SH-SY5Y cells

Propionic acid (PPA) is used to study the role of mitochondrial dysfunction in neurodevelopmental conditions like autism spectrum disorders. PPA is known to disrupt mitochondrial biogenesis, metabolism, and turnover. However, the effect of PPA on mitochondrial dynamics, fission, and fusion remains challenging to study due to the complex temporal nature of these mechanisms. Here, we use complementary quantitative visualization techniques to examine how PPA influences mitochondrial ultrastructure, morphology, and dynamics in neuronal-like SH-SY5Y cells. PPA (5 mM) induced a significant decrease in mitochondrial area (p < 0.01), Feret's diameter and perimeter (p < 0.05), and in area2 (p < 0.01). Mitochondrial event localiser analysis demonstrated a significant increase in fission and fusion events (p < 0.05) that preserved mitochondrial network integrity under stress. Moreover, mRNA expression of cMYC (p < 0.0001), NRF1 (p < 0.01), TFAM (p < 0.05), STOML2 (p < 0.0001), and OPA1 (p < 0.01) was significantly decreased. This illustrates a remodeling of mitochondrial morphology, biogenesis, and dynamics to preserve function under stress. Our data provide new insights into the influence of PPA on mitochondrial dynamics and highlight the utility of visualization techniques to study the complex regulatory mechanisms involved in the mitochondrial stress response.

Mechanisms of Modulation of Mitochondrial Architecture

Mitochondrial network architecture plays a critical role in cellular physiology. Indeed, alterations in the shape of mitochondria upon exposure to cellular stress can cause the dysfunction of these organelles. In this scenario, mitochondrial dynamics proteins and the phospholipid composition of the mitochondrial membrane are key for fine-tuning the modulation of mitochondrial architecture. In addition, several factors including post-translational modifications such as the phosphorylation, acetylation, SUMOylation, and o-GlcNAcylation of mitochondrial dynamics proteins contribute to shaping the plasticity of this architecture. In this regard, several studies have evidenced that, upon metabolic stress, mitochondrial dynamics proteins are post-translationally modified, leading to the alteration of mitochondrial architecture. Interestingly, several proteins that sustain the mitochondrial lipid composition also modulate mitochondrial morphology and organelle communication. In this context, pharmacological studies have revealed that the modulation of mitochondrial shape and function emerges as a potential therapeutic strategy for metabolic diseases. Here, we review the factors that modulate mitochondrial architecture.

Identification of mitochondrial related signature associated with immune microenvironment in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease. Mitochondrial dysfunction and immune responses are important factors in the pathogenesis of AD, but their crosstalk in AD has not been studied. In this study, the independent role and interaction of mitochondria-related genes and immune cell infiltration in AD were investigated using bioinformatics methods.

METHODS

The datasets of AD were obtained from NCBI Gene Expression Omnibus (GEO), and the data of mitochondrial genes was from MitoCarta3.0 database. Subsequently, differential expression genes (DEGs) screening and GSEA functional enrichment analysis were performed. The intersection of DEGs and mitochondrial related genes was used to obtain MitoDEGs. The MitoDEGs most relevant to AD were determined by Least absolute shrinkage and selection operator and multiple support vector machine recursive feature elimination, as well as protein-protein interactions (PPI) network and random forest. The infiltration of 28 kinds of immune cells in AD was analyzed by ssGSEA, and the relationship between hub MitoDEGs and the proportion of immune infiltration was studied. The expression levels of hub MitoDEGs were verified in cell models and AD mice, and the role of OPA1 in mitochondrial damage and neuronal apoptosis was investigated.

RESULTS

The functions and pathways of DEGs were significantly enriched in AD, including immune response activation, IL1R pathway, mitochondrial metabolism, oxidative damage response and electron transport chain-oxphos system in mitochondria. Hub MitoDEGs closely related to AD were obtained based on PPI network, random forest and two machine learning algorithms. Five hub MitoDEGs associated with neurological disorders were identified by biological function examination. The hub MitoDEGs were found to be correlated with memory B cell, effector memory CD8 T cell, activated dendritic cell, natural killer T cell, type 17 T helper cell, Neutrophil, MDSC, plasmacytoid dendritic cell. These genes can also be used to predict the risk of AD and have good diagnostic efficacy. In addition, the mRNA expression levels of BDH1, TRAP1, OPA1, DLD in cell models and AD mice were consistent with the results of bioinformatics analysis, and expression levels of SPG7 showed a downward trend. Meanwhile, OPA1 overexpression alleviated mitochondrial damage and neuronal apoptosis induced by Aβ1-42.

CONCLUSIONS

Five potential hub MitoDEGs most associated with AD were identified. Their interaction with immune microenvironment may play a crucial role in the occurrence and prognosis of AD, which provides a new insight for studying the potential pathogenesis of AD and exploring new targets.

High-fat diet causes mitochondrial damage and downregulation of mitofusin-2 and optic atrophy-1 in multiple organs

High-fat consumption promotes the development of obesity, which is associated with various chronic illnesses. Mitochondria are the energy factories of eukaryotic cells, maintaining self-stability through a fine-tuned quality-control network. In the present study, we evaluated high-fat diet (HFD)-induced changes in mitochondrial ultrastructure and dynamics protein expression in multiple organs. C57BL/6J male mice were fed HFD or normal diet (ND) for 24 weeks. Compared with ND-fed mice, HFD-fed mice exhibited increased body weight, cardiomyocyte enlargement, pulmonary fibrosis, hepatic steatosis, renal and splenic structural abnormalities. The cellular apoptosis of the heart, liver, and kidney increased. Cellular lipid droplet deposition and mitochondrial deformations were observed. The proteins related to mitochondrial biogenesis (TFAM), fission (DRP1), autophagy (LC3 and LC3-II: LC3-I ratio), and mitophagy (PINK1) presented different changes in different organs. The mitochondrial fusion regulators mitofusin-2 (MFN2) and optic atrophy-1 (OPA1) were consistently downregulated in multiple organs, even the spleen. TOMM20 and ATP5A protein were enhanced in the heart, skeletal muscle, and spleen, and attenuated in the kidney. These results indicated that high-fat feeding caused pathological changes in multiple organs, accompanied by mitochondrial ultrastructural damage, and MFN2 and OPA1 downregulation. The mitochondrial fusion proteins may become promising targets and/or markers for treating metabolic disease.

Quantitative analysis of metabolic fluxes in brown fat and skeletal muscle during thermogenesis

Adaptive thermogenesis by brown adipose tissue (BAT) dissipates calories as heat, making it an attractive anti-obesity target. Yet how BAT contributes to circulating metabolite exchange remains unclear. Here, we quantified metabolite exchange in BAT and skeletal muscle by arteriovenous metabolomics during cold exposure in fed male mice. This identified unexpected metabolites consumed, released and shared between organs. Quantitative analysis of tissue fluxes showed that glucose and lactate provide ~85% of carbon for adaptive thermogenesis and that cold and CL316,243 trigger markedly divergent fuel utilization profiles. In cold adaptation, BAT also dramatically increases nitrogen uptake by net consuming amino acids, except glutamine. Isotope tracing and functional studies suggest glutamine catabolism concurrent with synthesis via glutamine synthetase, which avoids ammonia buildup and boosts fuel oxidation. These data underscore the ability of BAT to function as a glucose and amino acid sink and provide a quantitative and comprehensive landscape of BAT fuel utilization to guide translational studies.

HIGD1A links SIRT1 activity to adipose browning by inhibiting the ROS/DNA damage pathway

Energy-dissipating adipocytes have the potential to improve metabolic health. Here, we identify hypoxia-induced gene domain protein-1a (HIGD1A), a mitochondrial inner membrane protein, as a positive regulator of adipose browning. HIGD1A is induced in thermogenic fats by cold exposure. Peroxisome proliferator-activated receptor gamma (PPARγ) transactivates HIGD1A expression synergistically with peroxisome proliferators-activated receptor γ coactivator α (PGC1α). HIGD1A knockdown inhibits adipocyte browning, whereas HIGD1A upregulation promotes the browning process. Mechanistically, HIGD1A deficiency impairs mitochondrial respiration to increase reactive oxygen species (ROS) level. This increases NAD⁺ consumption for DNA damage repair and curtails the NAD⁺/NADH ratio, which inhibits sirtuin1 (SIRT1) activity, thereby compromising adipocyte browning. Conversely, overexpression of HIGD1A blunts the above process to promote adaptive thermogenesis. Furthermore, mice with HIGD1A knockdown in inguinal and brown fat have impaired thermogenesis and are prone to diet-induced obesity (DIO). Overexpression of HIGD1A favors adipose tissue browning, ultimately preventing DIO and metabolic disorders. Thus, the mitochondrial protein HIGD1A links SIRT1 activity to adipocyte browning by inhibiting ROS levels.

Mitochondria-associated regulation in adipose tissues and potential reagents for obesity intervention

Introduction

A systematic review analysis was used to assess the profile of mitochondrial involvement in adipose tissue regulation and potential reagents to intervene in obesity through the mitochondrial pathway.

Methods

Three databases, PubMed, Web of Science, and Embase, were searched online for literature associated with mitochondria, obesity, white adipose tissue, and brown adipose tissue published from the time of their creation until June 22, 2022, and each paper was screened.

Results

568 papers were identified, of which 134 papers met the initial selection criteria, 76 were selected after full-text review, and 6 were identified after additional searches. A full-text review of the included 82 papers was performed.

Conclusion

Mitochondria play a key role in adipose tissue metabolism and energy homeostasis, including as potential therapeutic agents for obesity.

Multifaceted mitochondrial quality control in brown adipose tissue

Brown adipose tissue (BAT) controls mammalian core body temperature by non-shivering thermogenesis. BAT is extraordinarily rich in mitochondria, which have the peculiarity of generating heat by uncoupled respiration. Since the mitochondrial activity of BAT is subject to cycles of activation and deactivation in response to environmental temperature changes, an integrated mitochondrial quality control (MQC) system is of fundamental importance to ensure BAT physiology. Here, we provide an overview of the conventional and alternative mechanisms through which thermogenic adipocytes selectively remove damaged parts of mitochondria and how macrophages participate in the MQC system by removing extracellular mitochondrial waste to maintain the thermogenic function of BAT.

Proteolytic rewiring of mitochondria by LONP1 directs cell identity switching of adipocytes

Mitochondrial proteases are emerging as key regulators of mitochondrial plasticity and acting as both protein quality surveillance and regulatory enzymes by performing highly regulated proteolytic reactions. However, it remains unclear whether the regulated mitochondrial proteolysis is mechanistically linked to cell identity switching. Here we report that cold-responsive mitochondrial proteolysis is a prerequisite for white-to-beige adipocyte cell fate programming during adipocyte thermogenic remodelling. Thermogenic stimulation selectively promotes mitochondrial proteostasis in mature white adipocytes via the mitochondrial protease LONP1. Disruption of LONP1-dependent proteolysis substantially impairs cold- or β3 adrenergic agonist-induced white-to-beige identity switching of mature adipocytes. Mechanistically, LONP1 selectively degrades succinate dehydrogenase complex iron sulfur subunit B and ensures adequate intracellular succinate levels. This alters the histone methylation status on thermogenic genes and thereby enables adipocyte cell fate programming. Finally, augmented LONP1 expression raises succinate levels and corrects ageing-related impairments in white-to-beige adipocyte conversion and adipocyte thermogenic capacity. Together, these findings reveal that LONP1 links proteolytic surveillance to mitochondrial metabolic rewiring and directs cell identity conversion during adipocyte thermogenic remodelling.

Oxidization of optic atrophy 1 cysteines occurs during heart ischemia-reperfusion and amplifies cell death by oxidative stress

During cardiac ischemia-reperfusion, excess reactive oxygen species can damage mitochondrial, cellular and organ function. Here we show that cysteine oxidation of the mitochondrial protein Opa1 contributes to mitochondrial damage and cell death caused by oxidative stress. Oxy-proteomics of ischemic-reperfused hearts reveal oxidation of the C-terminal C786 of Opa1 and treatment of perfused mouse hearts, adult cardiomyocytes, and fibroblasts with H₂O₂ leads to the formation of a reduction-sensitive ∼180 KDa Opa1 complex, distinct from the ∼270 KDa one antagonizing cristae remodeling. This Opa1 oxidation process is curtailed by mutation of C786 and of the other 3 Cys residues of its C-terminal domain (Opa1^TetraCys). When reintroduced in Opa1^-/- cells, Opa1^TetraCys is not efficiently processed into short Opa1^TetraCys and hence fails to fuse mitochondria. Unexpectedly, Opa1^TetraCys restores mitochondrial ultrastructure in Opa1^-/- cells and protects them from H₂O₂-induced mitochondrial depolarization, cristae remodeling, cytochrome c release and cell death. Thus, preventing the Opa1 oxidation occurring during cardiac ischemia-reperfusion reduces mitochondrial damage and cell death induced by oxidative stress independent of mitochondrial fusion.

Loss of APOO (MIC26) aggravates obesity-related whitening of brown adipose tissue via PPARα-mediated functional interplay between mitochondria and peroxisomes

BACKGROUND

Mitochondrial dysfunction and aberrant structure in adipose tissue occur in obesity and obesity-linked brown adipose tissue (BAT) whitening; however, whether this aberrant architecture contributes to or is the result of obesity is unknown. Apolipoprotein O (APOO) is a constitutive protein of the mitochondrial cristae organizing system complex. This study aimed to characterize the physiological consequences of APOO deficiency in vivo.

METHODS

APOO expression was analyzed in different human and murine adipose depots, and mice lacking APOO in adipocytes (Apoo^ACKO) are developed to examine the metabolic consequences of adipocyte-specific APOO ablation in vitro and in vivo.

RESULTS

Results showed that APOO expression is reduced in BAT from both diet-induced and leptin-deficient obese mice. APOO-knockout mice showed increased adiposity, BAT dysfunction and whitening, reduced non-shivering thermogenesis, and blunted responses to cold stimuli. APOO deficiency disrupted mitochondrial structure in brown adipocytes and impaired oxidative phosphorylation, thereby inducing a shift from oxidative to glycolytic metabolism, increasing lipogenic enzyme levels and BAT whitening. APOO inactivation inhibited thermogenesis in BAT by reducing mitochondrial long-chain fatty acid oxidation. It also disturbed peroxisomal biogenesis and very long-chain fatty acid oxidation via peroxisome proliferator-activated receptor α.

CONCLUSIONS

Altogether, APOO deficiency in adipocytes aggravates BAT whitening and diet-induced obesity; thus, APOO could be a therapeutic target for obesity.

Inhibition of the mitochondria-shaping protein Opa1 restores sensitivity to Gefitinib in a lung adenocarcinomaresistant cell line

Drug resistance limits the efficacy of chemotherapy and targeted cancer treatments, calling for the identification of druggable targets to overcome it. Here we show that the mitochondria-shaping protein Opa1 participates in resistance against the tyrosine kinase inhibitor gefitinib in a lung adenocarcinoma cell line. Respiratory profiling revealed that oxidative metabolism was increased in this gefitinib-resistant lung cancer cell line. Accordingly, resistant cells depended on mitochondrial ATP generation, and their mitochondria were elongated with narrower cristae. In the resistant cells, levels of Opa1 were increased and its genetic or pharmacological inhibition reverted the mitochondrial morphology changes and sensitized them to gefitinib-induced cytochrome c release and apoptosis. In vivo, the size of gefitinib-resistant lung orthotopic tumors was reduced when gefitinib was combined with the specific Opa1 inhibitor MYLS22. The combo gefitinib-MYLS22 treatment increased tumor apoptosis and reduced its proliferation. Thus, the mitochondrial protein Opa1 participates in gefitinib resistance and can be targeted to overcome it.