Adipose-specific deletion of TFAM increases mitochondrial oxidation and protects mice against obesity and insulin resistance

Illuminating mitochondrial translation through mouse models

Mitochondria are hubs of metabolic activity with a major role in ATP conversion by oxidative phosphorylation (OXPHOS). The mammalian mitochondrial genome encodes 11 mRNAs encoding 13 OXPHOS proteins along with 2 rRNAs and 22 tRNAs, that facilitate their translation on mitoribosomes. Maintaining the internal production of core OXPHOS subunits requires modulation of the mitochondrial capacity to match the cellular requirements and correct insertion of particularly hydrophobic proteins into the inner mitochondrial membrane. The mitochondrial translation system is essential for energy production and defects result in severe, phenotypically diverse diseases, including mitochondrial diseases that typically affect postmitotic tissues with high metabolic demands. Understanding the complex mechanisms that underlie the pathologies of diseases involving impaired mitochondrial translation is key to tailoring specific treatments and effectively targeting the affected organs. Disease mutations have provided a fundamental, yet limited, understanding of mitochondrial protein synthesis, since effective modification of the mitochondrial genome has proven challenging. However, advances in next generation sequencing, cryoelectron microscopy, and multi-omic technologies have revealed unexpected and unusual features of the mitochondrial protein synthesis machinery in the last decade. Genome editing tools have generated unique models that have accelerated our mechanistic understanding of mitochondrial translation and its physiological importance. Here we review the most recent mouse models of disease pathogenesis caused by defects in mitochondrial protein synthesis and discuss their value for preclinical research and therapeutic development.

Defective mitochondria remodelling in B cells leads to an aged immune response

The B cell response in the germinal centre (GC) reaction requires a unique bioenergetic supply. Although mitochondria are remodelled upon antigen-mediated B cell receptor stimulation, mitochondrial function in B cells is still poorly understood. To gain a better understanding of the role of mitochondria in B cell function, here we generate mice with B cell-specific deficiency in Tfam, a transcription factor necessary for mitochondrial biogenesis. Tfam conditional knock-out (KO) mice display a blockage of the GC reaction and a bias of B cell differentiation towards memory B cells and aged-related B cells, hallmarks of an aged immune response. Unexpectedly, blocked GC reaction in Tfam KO mice is not caused by defects in the bioenergetic supply but is associated with a defect in the remodelling of the lysosomal compartment in B cells. Our results may thus describe a mitochondrial function for lysosome regulation and the downstream antigen presentation in B cells during the GC reaction, the dysruption of which is manifested as an aged immune response.

Race/Ethnicity and Other Predictors of Early-Onset Type 2 Diabetes Mellitus in the US Population

OBJECTIVES

Among US adults aged 20 + years in the USA with previously diagnosed type 2 diabetes mellitus (T2DM), we aimed to estimate the prevalence of early-onset T2DM (onset at age < 50.5 years) and to test associations between early-onset T2DM and race/ethnicity, and other hypothesized predictors.

METHODS

We pooled data from the annual National Health and Nutrition Examination Surveys (NHANES) over the years 2001 through 2018. We tested hypotheses of association and identified predictors using stepwise logistic regression analysis, and 11 supervised machine learning classification algorithms.

RESULTS

After appropriate weighting, we estimated that among adults in the USA aged 20 + years with previously diagnosed T2DM, the prevalence of early-onset was 52.9% (95% confidence intervals, 49.6 to 56.2%). Among Non-Hispanic Whites (NHW) the prevalence was 48.6% (95% CI, 44.6 to 52.6%), among Non-Hispanic Blacks: 56.9% (95% CI, 51.8 to 62.0%), among Hispanics: 62.7% (95% CI, 53.2 to 72.3%). In the final multivariable logistic regression model, the top-3 markers predicting early-onset T2DM in males were NHB ethnicity (OR = 2.97; 95% CI: 2.24-3.95) > tobacco smoking (OR = 2.79; 95% CI: 2.18-3.58) > high education level (OR = 1.65; 95% CI: 1.27-2.14) in males. In females, the ranking was tobacco smoking (OR = 2.59; 95% CI: 1.90-3.53) > Hispanic ethnicity (OR = 1.49; 95% CI: 1.08-2.05) > obesity (OR = 1.30; 95% CI: 0.91-1.86) in females. The acculturation score emerged from the machine learning approach as the dominant marker explaining the race disparity in early-onset T2DM.

CONCLUSIONS

The prevalence of early-onset T2DM was higher among NHB and Hispanic people, than among NHW people. Independently of race/ethnicity, acculturation, tobacco smoking, education level, marital status, obesity, and hypertension were also predictive.

Mitochondria and diabetes: insights and potential therapies

INTRODUCTION

Type 2 diabetes (T2D) presents significant global health and economic challenges, contributing to complications such as stroke, cardiovascular disease, kidney dysfunction, and cancer. The current review explores the crucial role of mitochondria, essential for fuel metabolism, in diabetes-related processes.

AREAS COVERED

Mitochondrial deficits impact insulin-resistant skeletal muscles, adipose tissue, liver, and pancreatic β-cells, affecting glucose and lipid balance. Exercise emerges as a key factor in enhancing mitochondrial function, thereby reducing insulin resistance. Additionally, the therapeutic potential of mitochondrial uncoupling, which generates heat instead of ATP, is discussed. We explore the intricate link between mitochondrial function and diabetes, investigating genetic interventions to mitigate diabetes-related complications. We also cover the impact of insulin deficiency on mitochondrial function, the role of exercise in addressing mitochondrial defects in insulin resistance, and the potential of mitochondrial uncoupling. Furthermore, a comprehensive analysis of Mitochondrial Replacement Therapies (MRT) techniques is presented.

EXPERT OPINION

MRTs hold promise in preventing the transmission of mitochondrial disease. However, addressing ethical, regulatory, and technical considerations is crucial. Integrating mitochondrial-based treatments requires a careful balance between innovation and safety. Ethical dimensions and regulatory aspects of MRT are examined, emphasizing collaborative efforts for the responsible advancement of human health.

Mitochondrial DNA copy number reduction via in vitro TFAM knockout remodels the nuclear epigenome and transcriptome

Mitochondrial DNA copy number (mtDNA-CN) is associated with several age-related chronic diseases and is a predictor of all-cause mortality. Here, we examine site-specific differential nuclear DNA (nDNA) methylation and differential gene expression resulting from in vitro reduction of mtDNA-CN to uncover shared genes and biological pathways mediating the effect of mtDNA-CN on disease. Epigenome and transcriptome profiles were generated for three independent human embryonic kidney (HEK293T) cell lines harbouring a mitochondrial transcription factor A (TFAM) heterozygous knockout generated via CRISPR-Cas9, and matched control lines. We identified 4,242 differentially methylated sites, 228 differentially methylated regions, and 179 differentially expressed genes associated with mtDNA-CN. Integrated analysis uncovered 381 Gene-CpG pairs. GABAA receptor genes and related pathways, the neuroactive ligand receptor interaction pathway, ABCD1/2 gene activity, and cell signalling processes were overrepresented, providing insight into the underlying biological mechanisms facilitating these associations. We also report evidence implicating chromatin state regulatory mechanisms as modulators of mtDNA-CN effect on gene expression. We demonstrate that mitochondrial DNA variation signals to the nuclear DNA epigenome and transcriptome and may lead to nuclear remodelling relevant to development, aging, and complex disease.

Mitochondria as a target for exercise-mitigated type 2 diabetes

Type 2 diabetes mellitus (T2DM) is one of most common metabolic diseases and continues to be a leading cause of death worldwide. Although great efforts have been made to elucidate the pathogenesis of diabetes, the underlying mechanism still remains unclear. Notably, overwhelming evidence has demonstrated that mitochondria are tightly correlated with the development of T2DM, and the defects of mitochondrial function in peripheral insulin-responsive tissues, such as skeletal muscle, liver and adipose tissue, are crucial drivers of T2DM. Furthermore, exercise training is considered as an effective stimulus for improving insulin sensitivity and hence is regarded as the best strategy to prevent and treat T2DM. Although the precise mechanisms by which exercise alleviates T2DM are not fully understood, mitochondria may be critical for the beneficial effects of exercise.

Effects of myonectin on porcine intramuscular adipocyte differentiation and exogenous free fatty acid utilization

As an important factor secreted by skeletal muscle, myonectin can regulate lipid metabolism and energy metabolism, but its role in the utilization of peripheral free fatty acids (FFAs) by porcine intramuscular fat cells remains to be further investigated. In this study, porcine intramuscular adipocytes were treated with recombinant myonectin and palmitic acid (PA), either alone or in combination, and then were examined for their uptake of exogenous FFAs, intracellular lipid synthesis and catabolism, and mitochondrial oxidation of fatty acids. The results showed that myonectin decreased the area of lipid droplets in intramuscular adipocytes (p < 0.05) and significantly increased (p < 0.05) the expression levels of hormone-sensitive lipase (HSL) and lipoprotein lipase (LPL). Moreover, myonectin can up-regulate the expression of p38 mitogen-activated protein kinase (p38 MAPK). Myonectin significantly promoted the uptake of peripheral FFAs (p < 0.01), improved (p < 0.05) the expression of fatty transport protein 1 (FATP1) and fatty acid binding protein 4 (FABP4) in intramuscular adipocytes. Myonectin also significantly increased (p < 0.05) the expression levels of fatty acid oxidation markers: transcription factor (TFAM), uncoupling protein-2 (UCP2) and oxidative respiratory chain marker protein complex I (NADH-CoQ) in mitochondria of intramuscular adipocytes. In summary, myonectin promoted the absorption, transport, and oxidative metabolism of exogenous FFAs in mitochondria, thereby inhibiting lipid deposition in porcine intramuscular adipocytes.

SLC35D3 promotes white adipose tissue browning to ameliorate obesity by NOTCH signaling

White adipose tissue browning can promote lipid burning to increase energy expenditure and improve adiposity. Here, we show that Slc35d3 expression is significantly lower in adipose tissues of obese mice. While adipocyte-specific Slc35d3 knockin is protected against diet-induced obesity, adipocyte-specific Slc35d3 knockout inhibits white adipose tissue browning and causes decreased energy expenditure and impaired insulin sensitivity in mice. Mechanistically, we confirm that SLC35D3 interacts with the NOTCH1 extracellular domain, which leads to the accumulation of NOTCH1 in the endoplasmic reticulum and thus inhibits the NOTCH1 signaling pathway. In addition, knockdown of Notch1 in mouse inguinal white adipose tissue mediated by orthotopic injection of AAV8-adiponectin-shNotch1 shows considerable improvement in obesity and glucolipid metabolism, which is more pronounced in adipocyte-specific Slc35d3 knockout mice than in knockin mice. Overall, in this study, we reveal that SLC35D3 is involved in obesity via NOTCH1 signaling, and low adipose SLC35D3 expression in obesity might be a therapeutic target for obesity and associated metabolic disorders.

Mitochondrial disorders as a mechanism for the development of obese Sarcopenia

Obese sarcopenia is a severe and prevalent disease in an aging society. Compared to sarcopenia alone, the development and advanced stage of obesity sarcopenia is faster and more severe. Diagnosis of the cause of adipocyte accumulation is also more complicated; however, no effective pharmacological treatment is available. Chronic inflammation is one of the causes of sarcopenia, and obese patients, who are more likely to develop chronic inflammation, may simultaneously suffer from obesity and sarcopenia. Mitochondrial metabolic disorders have been more easily observed in the tissue cells of patients with obesity and sarcopenia. Mitochondrial metabolic disorders include abnormal mtDNA release, mitochondrial autophagy, and dynamic mitochondrial disorders. Therefore, this review will reveal the mechanism of development of obesity myasthenia gravis from the perspective of mitochondria and discuss the currently existing small-molecule drugs.

TMEM135 links peroxisomes to the regulation of brown fat mitochondrial fission and energy homeostasis

Mitochondrial morphology, which is controlled by mitochondrial fission and fusion, is an important regulator of the thermogenic capacity of brown adipocytes. Adipose-specific peroxisome deficiency impairs thermogenesis by inhibiting cold-induced mitochondrial fission due to decreased mitochondrial membrane content of the peroxisome-derived lipids called plasmalogens. Here, we identify TMEM135 as a critical mediator of the peroxisomal regulation of mitochondrial fission and thermogenesis. Adipose-specific TMEM135 knockout in mice blocks mitochondrial fission, impairs thermogenesis, and increases diet-induced obesity and insulin resistance. Conversely, TMEM135 overexpression promotes mitochondrial division, counteracts obesity and insulin resistance, and rescues thermogenesis in peroxisome-deficient mice. Mechanistically, thermogenic stimuli promote association between peroxisomes and mitochondria and plasmalogen-dependent localization of TMEM135 in mitochondria, where it mediates PKA-dependent phosphorylation and mitochondrial retention of the fission factor Drp1. Together, these results reveal a previously unrecognized inter-organelle communication regulating mitochondrial fission and energy homeostasis and identify TMEM135 as a potential target for therapeutic activation of BAT.

Molecular and cellular regulation of thermogenic fat

Thermogenic fat, consisting of brown and beige adipocytes, dissipates energy in the form of heat, in contrast to the characteristics of white adipocytes that store energy. Increasing energy expenditure by activating brown adipocytes or inducing beige adipocytes is a potential therapeutic strategy for treating obesity and type 2 diabetes. Thus, a better understanding of the underlying mechanisms of thermogenesis provides novel therapeutic interventions for metabolic diseases. In this review, we summarize the recent advances in the molecular regulation of thermogenesis, focusing on transcription factors, epigenetic regulators, metabolites, and non-coding RNAs. We further discuss the intercellular and inter-organ crosstalk that regulate thermogenesis, considering the heterogeneity and complex tissue microenvironment of thermogenic fat.

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.

Impact of adrenomedullin on mitochondrial respiratory capacity in human adipocyte

Mitochondrial function in adipocyte is an important aspect in maintaining metabolic homeostasis. Our previous observation showed that circulating levels of adrenomedullin (ADM) and mRNA and protein for ADM in omental adipose tissue were higher in patients with gestational diabetes mellitus (GDM), and these alterations are accompanied by glucose and lipid metabolic dysregulation, but the impact of ADM on mitochondrial biogenesis and respiration in human adipocyte remain elusive. The present study demonstrated that: (1) Increasing doses of glucose and ADM inhibit human adipocyte mRNA expressions of mitochondrial DNA (mtDNA)-encoded subunits of electron transport chain, including nicotinamide adenine dinucleotide dehydrogenase (ND) 1 and 2, cytochrome (CYT) b, as well as ATPase 6; (2) ADM significantly increases human adipocyte mitochondrial reactive oxygen species generation and this increase is reversed by ADM antagonist, ADM22-52, but treatment with ADM does not significantly affect mitochondrial contents in the adipocytes; (3) Adipocyte basal and maximal oxygen consumption rate are dose-dependently suppressed by ADM, thus results in impaired mitochondrial respiratory capacity. We conclude that elevated ADM observed in diabetic pregnancy may be involved in glucose and lipid dysregulation through compromising adipocyte mitochondrial function, and blockade of ADM action may improve GDM-related glucose and adipose tissue dysfunction.

Mitochondrial reprogramming in peripheral blood mononuclear cells of patients with glycogen storage disease type Ia

BACKGROUND

Glycogen storage disease type Ia (GSDIa) is an inborn metabolic disorder caused by the deficiency of glucose-6-phospatase-α (G6Pase-α) leading to mitochondrial dysfunction. It remains unclear whether mitochondrial dysfunction is present in patients' peripheral blood mononuclear cells (PBMC) and whether dietary treatment can play a role. The aim of this study was to investigate mitochondrial function in PBMC of GSDIa patients.

METHODS

Ten GSDIa patients and 10 age-, sex- and fasting-time matched controls were enrolled. Expression of genes involved in mitochondrial function and activity of key fatty acid oxidation (FAO) and Krebs cycle proteins were assessed in PBMC. Targeted metabolomics and assessment of metabolic control markers were also performed.

RESULTS

Adult GSDIa patients showed increased CPT1A, SDHB, TFAM, mTOR expression (p < 0.05) and increased VLCAD, CPT2 and citrate synthase activity in PBMC (p < 0.05). VLCAD activity directly correlated with WC (p < 0.01), BMI (p < 0.05), serum malonycarnitine levels (p < 0.05). CPT2 activity directly correlated with BMI (p < 0.05).

CONCLUSION

Mitochondrial reprogramming is detectable in PBMC of GSDIa patients. This feature may develop as an adaptation to the liver enzyme defect and may be triggered by dietary (over)treatment in the frame of G6Pase-α deficiency. PBMC can represent an adequate mean to assess (diet-induced) metabolic disturbances in GSDIa.

From Obesity-Induced Low-Grade Inflammation to Lipotoxicity and Mitochondrial Dysfunction: Altered Multi-Crosstalk between Adipose Tissue and Metabolically Active Organs

Obesity is a major risk factor for several metabolic diseases, including type 2 diabetes, hyperlipidemia, cardiovascular diseases, and brain disorders. Growing evidence suggests the importance of inter-organ metabolic communication for the progression of obesity and the subsequent onset of related disorders. This review provides a broad overview of the pathophysiological processes that from adipose tissue dysfunction leading to altered multi-tissue crosstalk relevant to regulating energy homeostasis and the etiology of obesity. First, a comprehensive description of the role of adipose tissue was reported. Then, attention was turned toward the unhealthy expansion of adipose tissue, low-grade inflammatory state, metabolic inflexibility, and mitochondrial dysfunction as root causes of systemic metabolic alterations. In addition, a short spot was devoted to iron deficiency in obese conditions and the role of the hepcidin-ferroportin relationship in the management of this issue. Finally, different classes of bioactive food components were described with a perspective to enhance their potential preventive and therapeutic use against obesity-related diseases.

Mitochondrial Methionyl-tRNA Formyltransferase Deficiency Alleviates Metaflammation by Modulating Mitochondrial Activity in Mice

Various studies have revealed the association of metabolic diseases with inflammation. Mitochondria are key organelles involved in metabolic regulation and important drivers of inflammation. However, it is uncertain whether the inhibition of mitochondrial protein translation results in the development of metabolic diseases, such that the metabolic benefits related to the inhibition of mitochondrial activity remain unclear. Mitochondrial methionyl-tRNA formyltransferase (Mtfmt) functions in the early stages of mitochondrial translation. In this study, we reveal that feeding with a high-fat diet led to the upregulation of Mtfmt in the livers of mice and that a negative correlation existed between hepatic Mtfmt gene expression and fasting blood glucose levels. A knockout mouse model of Mtfmt was generated to explore its possible role in metabolic diseases and its underlying molecular mechanisms. Homozygous knockout mice experienced embryonic lethality, but heterozygous knockout mice showed a global reduction in Mtfmt expression and activity. Moreover, heterozygous mice showed increased glucose tolerance and reduced inflammation, which effects were induced by the high-fat diet. The cellular assays showed that Mtfmt deficiency reduced mitochondrial activity and the production of mitochondrial reactive oxygen species and blunted nuclear factor-κB activation, which, in turn, downregulated inflammation in macrophages. The results of this study indicate that targeting Mtfmt-mediated mitochondrial protein translation to regulate inflammation might provide a potential therapeutic strategy for metabolic diseases.

Nanoparticle-Based Artificial Mitochondrial DNA Transcription Regulator: MitoScript

The growing knowledge of the links between aberrant mitochondrial gene transcription and human diseases necessitates both an effective and dynamic approach to control mitochondrial DNA (mtDNA) transcription. To address this challenge, we developed a nanoparticle-based synthetic mitochondrial transcription regulator (MitoScript). MitoScript provides great colloidal stability, excellent biocompatibility, efficient cell uptake, and selective mitochondria targeting and can be monitored in live cells using near-infrared fluorescence. Notably, MitoScript controlled mtDNA transcription in a human cell line in an effective and selective manner. MitoScript targeting the light strand promoter region of mtDNA resulted in the downregulation of ND6 gene silencing, which eventually affected cell redox status, with considerably increased reactive oxygen species (ROS) generation. In summary, we developed MitoScript for the efficient, nonviral modification of mitochondrial DNA transcription. Our platform technology can potentially contribute to understanding the fundamental mechanisms of mitochondrial disorders and developing effective treatments for mitochondrial diseases.

Impact of Adrenomedullin on Mitochondrial Respiratory Capacity in Human Adipocyte

For metabolic homeostasis adequate mitochondrial function in adipocytes is essential. Our previous observation showed that circulating levels of adrenomedullin (ADM) and mRNA and protein for ADM in omental adipose tissue were higher in patients with gestational diabetes mellitus (GDM) compared with normal pregnancy, and these alterations are accompanied by glucose and lipid metabolic dysregulation, but the impact of ADM on mitochondrial biogenesis and respiration in human adipocyte remain elusive. In this study we demonstrated that: (1) Increasing doses of glucose and ADM inhibit human adipocyte mRNA expressions of mitochondrial DNA (mtDNA)-encoded subunits of electron transport chain (ETC), including nicotinamide adenine dinucleotide dehydrogenase (ND) 1 and 2, cytochrome (CYT) b, as well as ATPase 6; (2) ADM significantly increases human adipocyte mitochondrial reactive oxygen species (ROS) generation and this increase is reversed by ADM antagonist, ADM22-52, but does not significantly affect adipocyte mitochondrial contents; (3) Adipocyte basal and maximal oxygen consumption rate (OCR) are dose-dependently suppressed by ADM, and results in impaired mitochondrial respiratory capacity. We conclude that elevatedADM observed in diabetic pregnancy may be involved in glucose and lipid dysregulation through compromising adipocyte mitochondrial function, and blockade of ADM actions in adipocytes may improve GDM-related metabolic complications.

TFAM deficiency in dendritic cells leads to mitochondrial dysfunction and enhanced antitumor immunity through cGAS-STING pathway

BACKGROUND

Mitochondrial transcription factor A (TFAM) is a transcription factor that maintains mitochondrial DNA (mtDNA) stabilization and initiates mtDNA replication. However, little is known about the immune regulation function and TFAM expression in immune cells in the tumors.

METHODS

Mouse tumor models were applied to analyze the effect of TFAM deficiency in myeloid cell lineage on tumor progression and tumor microenvironment (TME) modification. In vitro, primary mouse bone marrow-derived dendritic cells (BMDCs) were used in the investigation of the altered function and the activated pathway. OVA was used as the model antigen to validate the activation of immune responses in vivo. STING inhibitors were used to confirm the STING activation provoked by Tfam deficient in DCs.

RESULTS

The deletion of TFAM in DCs led to mitochondrial dysfunction and mtDNA cytosolic leakage resulting in the cGAS-STING pathway activation in DCs, which contributed to the enhanced antigen presentation. The deletion of TFAM in DCs has interestingly reversed the immune suppressive TME and inhibited tumor growth and metastasis in tumor models.

CONCLUSIONS

We have revealed that TFAM knockout in DCs ameliorated immune-suppressive microenvironment in tumors through STING pathway. Our work suggests that specific TFAM knockout in DCs might be a compelling strategy for designing novel immunotherapy methods in the future.

Loss of fatty acid degradation by astrocytic mitochondria triggers neuroinflammation and neurodegeneration

Astrocytes provide key neuronal support, and their phenotypic transformation is implicated in neurodegenerative diseases. Metabolically, astrocytes possess low mitochondrial oxidative phosphorylation (OxPhos) activity, but its pathophysiological role in neurodegeneration remains unclear. Here, we show that the brain critically depends on astrocytic OxPhos to degrade fatty acids (FAs) and maintain lipid homeostasis. Aberrant astrocytic OxPhos induces lipid droplet (LD) accumulation followed by neurodegeneration that recapitulates key features of Alzheimer's disease (AD), including synaptic loss, neuroinflammation, demyelination and cognitive impairment. Mechanistically, when FA load overwhelms astrocytic OxPhos capacity, elevated acetyl-CoA levels induce astrocyte reactivity by enhancing STAT3 acetylation and activation. Intercellularly, lipid-laden reactive astrocytes stimulate neuronal FA oxidation and oxidative stress, activate microglia through IL-3 signalling, and inhibit the biosynthesis of FAs and phospholipids required for myelin replenishment. Along with LD accumulation and impaired FA degradation manifested in an AD mouse model, we reveal a lipid-centric, AD-resembling mechanism by which astrocytic mitochondrial dysfunction progressively induces neuroinflammation and neurodegeneration.

Effects of the second-generation antipsychotic drugs aripiprazole and olanzapine on human adipocyte differentiation

Second-generation antipsychotics (SGAs), used as the cornerstone treatment for schizophrenia and other mental disorders, can cause adverse metabolic effects (e.g. obesity and type 2 diabetes). We investigated the effects of SGAs on adipocyte differentiation and metabolism. The presence of therapeutic concentrations of aripiprazole (ARI) or its active metabolite dehydroaripiprazole (DARI) during human adipocyte differentiation impaired adipocyte glucose uptake while the expression of gene markers of fatty acid oxidation were increased. Additionally, the use of a supra-therapeutic concentration of ARI inhibited adipocyte differentiation. Furthermore, olanzapine (OLA), a highly obesogenic SGA, directly increased leptin gene expression but did not affect adipocyte differentiation and metabolism. These molecular insights are novel, and suggest that ARI, but not OLA, may directly act via alterations in adipocyte differentiation and potentially by causing a switch from glucose to lipid utilization in human adipocytes. Additionally, SGAs may effect crosstalk with other organs, such as the brain, to exert their adverse metabolic effects.

A mouse model of human mitofusin-2-related lipodystrophy exhibits adipose-specific mitochondrial stress and reduced leptin secretion

Mitochondrial dysfunction has been reported in obesity and insulin resistance, but primary genetic mitochondrial dysfunction is generally not associated with these, arguing against a straightforward causal relationship. A rare exception, recently identified in humans, is a syndrome of lower body adipose loss, leptin-deficient severe upper body adipose overgrowth, and insulin resistance caused by the p.Arg707Trp mutation in MFN2, encoding mitofusin 2. How the resulting selective form of mitochondrial dysfunction leads to tissue- and adipose depot-specific growth abnormalities and systemic biochemical perturbation is unknown. To address this, Mfn2R707W/R707W knock-in mice were generated and phenotyped on chow and high fat diets. Electron microscopy revealed adipose-specific mitochondrial morphological abnormalities. Oxidative phosphorylation measured in isolated mitochondria was unperturbed, but the cellular integrated stress response was activated in adipose tissue. Fat mass and distribution, body weight, and systemic glucose and lipid metabolism were unchanged, however serum leptin and adiponectin concentrations, and their secretion from adipose explants were reduced. Pharmacological induction of the integrated stress response in wild-type adipocytes also reduced secretion of leptin and adiponectin, suggesting an explanation for the in vivo findings. These data suggest that the p.Arg707Trp MFN2 mutation selectively perturbs mitochondrial morphology and activates the integrated stress response in adipose tissue. In mice, this does not disrupt most adipocyte functions or systemic metabolism, whereas in humans it is associated with pathological adipose remodelling and metabolic disease. In both species, disproportionate effects on leptin secretion may relate to cell autonomous induction of the integrated stress response.

Dopaminergic and adrenergic receptors synergistically stimulate browning in 3T3-L1 white adipocytes

The browning of white adipose tissue (WAT) has attracted considerable attention in the scientific community as a popular strategy for enhancing energy expenditure to combat obesity. As a part of this strategy, β3-adrenergic receptor (β3-AR) is the most widely studied receptor that mediates thermogenesis. Parenthetically, further studies in search for additional receptors expressed in adipocytes that can mediate thermogenesis has been appearing, and this paper reports that dopaminergic receptor 1 (DRD1) and β3-AR synergistically stimulate browning in 3T3-L1 white adipocytes. qRT-PCR and immunoblot analysis methods were applied to evaluate the effects of DRD1 on the target proteins downstream of β3-AR and other markers involved in lipid metabolism, mitochondrial biogenesis, and browning events. These results show that DRD1 is expressed in epididymal WAT (eWAT), brown adipose tissue (BAT), and inguinal WAT (iWAT) of normal and high-fat-fed mice, and a deficiency of DRD1 downregulates the expression of brown adipocyte-specific proteins. Silencing of DRD1 affected lipid metabolic activity in 3T3-L1 adipocytes by reducing mitochondrial biogenesis as well as levels of lipolytic and fat oxidative marker proteins in a similar pattern to β3-AR. Moreover, mechanistic studies showed that the depletion of DRD1 downregulates β3-AR and its downstream molecules, suggesting both receptors might synergistically stimulate browning. Parallel to the UCP1-dependent thermogenesis, the depletion of DRD1 also downregulates the expression of core proteins responsible for UCP1-independent thermogenesis. Overall, DRD1 mediates β3-AR-dependent 3T3-L1 browning and UCP1-independent thermogenesis.

Identification of biomarkers, pathways, and potential therapeutic targets for heart failure using next-generation sequencing data and bioinformatics analysis

BACKGROUND

Heart failure (HF) is the most common cardiovascular diseases and the leading cause of cardiovascular diseases related deaths. Increasing molecular targets have been discovered for HF prognosis and therapy. However, there is still an urgent need to identify novel biomarkers. Therefore, we evaluated biomarkers that might aid the diagnosis and treatment of HF.

METHODS

We searched next-generation sequencing (NGS) dataset (GSE161472) and identified differentially expressed genes (DEGs) by comparing 47 HF samples and 37 normal control samples using limma in R package. Gene ontology (GO) and pathway enrichment analyses of the DEGs were performed using the g: Profiler database. The protein-protein interaction (PPI) network was plotted with Human Integrated Protein-Protein Interaction rEference (HiPPIE) and visualized using Cytoscape. Module analysis of the PPI network was done using PEWCC1. Then, miRNA-hub gene regulatory network and TF-hub gene regulatory network were constructed by Cytoscape software. Finally, we performed receiver operating characteristic (ROC) curve analysis to predict the diagnostic effectiveness of the hub genes.

RESULTS

A total of 930 DEGs, 464 upregulated genes and 466 downregulated genes, were identified in HF. GO and REACTOME pathway enrichment results showed that DEGs mainly enriched in localization, small molecule metabolic process, SARS-CoV infections, and the citric acid tricarboxylic acid (TCA) cycle and respiratory electron transport. After combining the results of the PPI network miRNA-hub gene regulatory network and TF-hub gene regulatory network, 10 hub genes were selected, including heat shock protein 90 alpha family class A member 1 (HSP90AA1), arrestin beta 2 (ARRB2), myosin heavy chain 9 (MYH9), heat shock protein 90 alpha family class B member 1 (HSP90AB1), filamin A (FLNA), epidermal growth factor receptor (EGFR), phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1), cullin 4A (CUL4A), YEATS domain containing 4 (YEATS4), and lysine acetyltransferase 2B (KAT2B).

CONCLUSIONS

This discovery-driven study might be useful to provide a novel insight into the diagnosis and treatment of HF. However, more experiments are needed in the future to investigate the functional roles of these genes in HF.

Pancreastatin inhibitor PSTi8 balances energy homeostasis by attenuating adipose tissue inflammation in high fat diet fed mice

Pancreastatin (PST) is an endogenous bioactive peptide. PST is generated from chromogranin A (Chga) protein which is released by chromaffin and neuroendocrine cells. PST exhibits diabetogenic effect by antagonizing the action of insulin in adipocytes. The level of PST rises during obesity, resulting in persistent low-grade inflammation in adipocytes. Pancreastatin inhibitor 8 (PSTi8), which is developed by modification of PST sequence which antagonizes the action of PST. In this study, we investigated the immunometabolic effect of PSTi8 in the diet-induced obesity (DIO) model in C57BL/6 mice. Here we found PSTi8 decreased the body weight gain, fat mass and increased the lean mass in (DIO) mice. It also showed reduction of adipocyte hypertrophy in eWAT and lipid accumulation in liver of DIO mice. Immunoprofiling of stromal vascular fraction isolated from eWAT of PTSi8 treated mice showed increased anti-inflammatory M2 macrophages, Eosinophil, T-regulatory cells and reduced pro-inflammatory M1 macrophages, CD4 and CD8 T cell population. Apart from this, PSTi8 also improved the mitochondrial function by decreasing reactive oxygen species and increasing mitochondrial membrane potential, NADPH/NADP ratio and citrate synthase activity in eWAT of DIO mice. It also increased the protein expression of pAMPK, pAKT, Arginase -1 and decreased the expression of MHC-II and iNOS in eWAT of DIO mice. In conclusion, PSTi8 exerted its beneficial effect on restoring energy expenditure by reducing adipose tissue inflammation.

GCN5L1-mediated TFAM acetylation at K76 participates in mitochondrial biogenesis in acute kidney injury

BACKGROUND

Mitochondrial dysfunction is an important pathogenic event in acute kidney injury (AKI). GCN5L1 is a specific acetyltransferase in mitochondria, which regulates glucose and fatty acid metabolism. However, the role of GCN5L1 in mitochondrial dysfunction and the pathogenesis of ischemic AKI are not fully understood.

METHODS

The protein level of GCN5L1 was detected by western blot assay. Acetylated proteomics was used to explore the level of acetylated TFAM. Duolink proximity ligation assay and co-immunoprecipitation were used to detect the interaction of TFAM and translocase of outer membrane 70 (TOM70). mtDNA copy number, the expression of mitochondrial electron transport chain complexes, the number and morphology of mitochondria were measured. The renal injury of AKI mice was reflected by the levels of creatinine and urea nitrogen and the pathological changes of renal tissue.

RESULTS

We showed that GCN5L1 was highly expressed in vivo and in vitro and renal tubules specific knockdown of GCN5L1 could effectively attenuate AKI-induced mitochondrial impairment. Besides, acetylated proteomics revealed that acetylated TFAM was significantly upregulated in AKI mice kidney, which reminded us that TFAM might be an acetylating substrate of GCN5L1. Mechanistically, we evidenced that GCN5L1 could acetylate TFAM at its K76 site and subsequently inhibited its binding to TOM70, thereby reducing TFAM import into mitochondria and mitochondrial biogenesis. Clinically, GCN5L1 and acetylated TFAM were positively correlated with disease severity (all p < 0.05).

CONCLUSIONS

In sum, these data demonstrated an unrecognized regulating mechanism of GCN5L1 on TFAM acetylation and its intracellular trafficking, and a potential intervening target for AKI associated mitochondrial disorders as well.

Mitochondrial Stress in Metabolic Inflammation: Modest Benefits and Full Losses

Energy intake and metabolic balance are the pillars of health preservation. Overnutrition causes nonspecific, persistently low inflammatory state known as metabolic inflammation. This condition contributes to the pathophysiology of various metabolic disorders, such as atherosclerosis, obesity, diabetes mellitus, and metabolic syndrome. The mitochondria maintain the balance of energy metabolism. Excessive energy stress can lead to mitochondrial dysfunction, which promotes metabolic inflammation. The inflammatory environment further impairs mitochondrial function. Accordingly, excellent organism design keeps the body metabolically healthy in the context of mitochondrial dysfunction, and moderate mitochondrial stress can have a beneficial effect. This review summarises the research progress on the multifaceted characterisation of mitochondrial dysfunction and its role in metabolic inflammation.

A hypomorphic variant in the translocase of the outer mitochondrial membrane complex subunit TOMM7 causes short stature and developmental delay

Mitochondrial diseases are a heterogeneous group of genetic disorders caused by pathogenic variants in genes encoding gene products that regulate mitochondrial function. These genes are located either in the mitochondrial or in the nuclear genome. The TOMM7 gene encodes a regulatory subunit of the translocase of outer mitochondrial membrane (TOM) complex that plays an essential role in translocation of nuclear-encoded mitochondrial proteins into mitochondria. We report an individual with a homozygous variant in TOMM7 (c.73T>C, p.Trp25Arg) that presented with a syndromic short stature, skeletal abnormalities, muscle hypotonia, microvesicular liver steatosis, and developmental delay. Analysis of mouse models strongly suggested that the identified variant is hypomorphic because mice homozygous for this variant showed a milder phenotype than those with homozygous Tomm7 deletion. These Tomm7 mutant mice show pathological changes consistent with mitochondrial dysfunction, including growth defects, severe lipoatrophy, and lipid accumulation in the liver. These mice die prematurely following a rapidly progressive weight loss during the last week of their lives. Tomm7 deficiency causes a unique alteration in mitochondrial function; despite the bioenergetic deficiency, mutant cells show increased oxygen consumption with normal responses to electron transport chain (ETC) inhibitors, suggesting that Tomm7 deficiency leads to an uncoupling between oxidation and ATP synthesis without impairing the function of the tricarboxylic cycle metabolism or ETC. This study presents evidence that a hypomorphic variant in one of the genes encoding a subunit of the TOM complex causes mitochondrial disease.

Hepatic ER stress suppresses adipose browning through ATF4-CIRP-ANGPTL3 cascade

Hepatic endoplasmic reticulum (ER) stress is a hallmark of obesity-induced liver steatosis and contributes to the progress of steatosis and insulin resistance in liver. However, its influence on adipose function is still unclear. Here, we identify a hepatic ER stress-induced activating transcription factor 4 (ATF4)-cold-inducible RNA-binding protein (CIRP)-angiopoietin-related protein3 (ANGPTL3) cascade critical for the regulation of adipose browning. We find that obesity increases CIRP expression in liver through ER stress-induced ATF4. CIRP in turn binds to the 3' UTR and increases mRNA stability of ANGPTL3. ANGPTL3 secreted from liver suppresses uncoupling protein 1 expression through integrin α_vβ₃ and c-Jun N-terminal kinase in adipose tissue. While hepatic expression of either ATF4, CIRP, or ANGPTL3 suppresses adipose browning, knockdown of CIRP and ANGPTL3 in liver or administration of integrin α_vβ₃ inhibitor cilengitide increases adipose browning process. Taken together, we identify a communication mechanism to link hepatic ER stress and adipose browning that may imply a reciprocal regulation of obesity and liver steatosis.

TFAM expression in brown adipocytes confers obesity resistance by secreting extracellular vesicles that promote self-activation

The occurrence of diet-induced obesity has been increasing worldwide and has become a major health concern. Mitochondria are densely distributed in brown adipose tissue and are involved in lipid consumption. Therefore, increasing energy expenditure through the activation of brown adipocytes may be a potential therapy for obesity. Our findings showed that mitochondrial transcription factor A (TFAM) homozygous transgenic (TgTg) mice had highly activated brown adipocytes and increased expression of oxidative phosphorylation, leading to resistance to obesity. Transplantation models of TFAM-expressing brown adipocytes could mimic the phenotype of TFAM TgTg mice, and proving their anti-obesity effect. We found that brown adipocytes secrete exosomes which enable self-activation in an autocrine and paracrine manner. The secretion was enhanced in TFAM TgTg brown adipocytes, resulting in a higher activation. These findings may lead to a promising treatment strategy for obesity through selective stimulation of exosome secretion.

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Human TFAM overexpression in BAT promotes strong anti-obesity effects

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Increasing mitochondrial function in hTFAM TgTg mice facilitates EVs secretion

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Enhanced EV released in TgTg brown adipocytes induce self-differentiation/activation

Combination of Caloric Restriction and a Mixed Training Protocol as an Effective Strategy to Counteract the Deleterious Effects in Trabecular Bone Microarchitecture Caused by a Diet-Induced Obesity in Sprague Dawley Rats

The association of obesity with changes in bone mass is not clear. Obese individuals tend to have an increased bone mineral density, but other studies have shown that obesity is a major risk factor for fractures. The mechanisms of bone response during a weight loss therapy as well as the possible osteoprotective effect of exercise should be analyzed. The aim of this study was to test the effects of a weight-loss program based on the combination of caloric restriction and/or a mixed training protocol on different parameters of bone morphology and functionality in a DIO rat model. Three stages were established over a 21-week period (obesity induction 0–12 w, weight loss intervention 12–15 w, weight maintenance intervention 15–21 w) in 88 male Sprague Dawley rats. Bone microarchitecture, total mineral and elemental composition, and bone metabolism parameters were assessed. Weight loss interventions were associated to healthy changes in body composition, decreasing body fat and increasing lean body mass. On the other hand, obesity was related to a higher content of bone resorption and inflammatory markers, which was decreased by the weight control interventions. Caloric restriction led to marked changes in trabecular microarchitecture, with a significant decrease in total volume but no changes in bone volume (BV). In addition, the intervention diet caused an increase in trabeculae number and a decrease in trabecular spacing. The training protocol increased the pore diameter and reversed the changes in cortical porosity and density of BV induced by the high protein diet at diaphysis level. Regarding the weight-maintenance stage, diminished SMI values indicate the presence of more plate-like spongiosa in sedentary and exercise groups. In conclusion, the lifestyle interventions of caloric restriction and mixed training protocol implemented as weight loss strategies have been effective to counteract some of the deleterious effects caused by a dietary induction of obesity, specifically in trabecular bone morphometric parameters as well as bone mineral content.

Hepatocyte Mitochondrial Dynamics and Bioenergetics in Obesity-Related Non-Alcoholic Fatty Liver Disease

PURPOSE OF THE REVIEW

Mitochondrial dysfunction has long been proposed to play a crucial role in the pathogenesis of a considerable number of disorders, such as neurodegeneration, cancer, cardiovascular, and metabolic disorders, including obesity-related insulin resistance and non-alcoholic fatty liver disease (NAFLD). Mitochondria are highly dynamic organelles that undergo functional and structural adaptations to meet the metabolic requirements of the cell. Alterations in nutrient availability or cellular energy needs can modify their formation through biogenesis and the opposite processes of fission and fusion, the fragmentation, and connection of mitochondrial network areas respectively. Herein, we review and discuss the current literature on the significance of mitochondrial adaptations in obesity and metabolic dysregulation, emphasizing on the role of hepatocyte mitochondrial flexibility in obesity and NAFLD.

RECENT FINDINGS

Accumulating evidence suggests the involvement of mitochondrial morphology and bioenergetics dysregulations to the emergence of NAFLD and its progress to non-alcoholic steatohepatitis (NASH). Most relevant data suggests that changes in liver mitochondrial dynamics and bioenergetics hold a key role in the pathogenesis of NAFLD. During obesity and NAFLD, oxidative stress occurs due to the excessive production of ROS, leading to mitochondrial dysfunction. As a result, mitochondria become incompetent and uncoupled from respiratory chain activities, further promoting hepatic fat accumulation, while leading to liver inflammation, insulin resistance, and disease's deterioration. Elucidation of the mechanisms leading to dysfunctional mitochondrial activity of the hepatocytes during NAFLD is of predominant importance for the development of novel therapeutic approaches towards the treatment of this metabolic disorder.

Mitochondrial quality control in cardiac ischemia/reperfusion injury: new insights into mechanisms and implications

The current effective method for the treatment of myocardial infarction is timely restoration of the blood supply to the ischemic area of the heart. Although reperfusion is essential for reestablishing oxygen and nutrient supplies, it often leads to additional myocardial damage, creating an important clinical dilemma. Reports from long-term studies have confirmed that mitochondrial damage is the critical mechanism in cardiac ischemia/reperfusion (I/R) injury. Mitochondria are dynamic and possess a quality control system that targets mitochondrial quantity and quality by modifying mitochondrial fusion, fission, mitophagy, and biogenesis and protein homeostasis to maintain a healthy mitochondrial network. The system of mitochondrial quality control involves complex molecular machinery that is highly interconnected and associated with pathological changes such as oxidative stress, calcium overload, and endoplasmic reticulum (ER) stress. Because of the critical role of the mitochondrial quality control systems, many reports have suggested that defects in this system are among the molecular mechanisms underlying myocardial reperfusion injury. In this review, we briefly summarize the important role of the mitochondrial quality control in cardiomyocyte function and focus on the current understanding of the regulatory mechanisms and molecular pathways involved in mitochondrial quality control in cardiac I/R damage.

The Deficiency of SCARB2/LIMP-2 Impairs Metabolism via Disrupted mTORC1-Dependent Mitochondrial OXPHOS

Deficiency in scavenger receptor class B, member 2 (SCARB2) is related to both Gaucher disease (GD) and Parkinson’s disease (PD), which are both neurodegenerative-related diseases without cure. Although both diseases lead to weight loss, which affects the quality of life and the progress of diseases, the underlying molecular mechanism is still unclear. In this study, we found that Scarb2^−/− mice showed significantly reduced lipid storage in white fat tissues (WAT) compared to WT mice on a regular chow diet. However, the phenotype is independent of heat production, activity, food intake or energy absorption. Furthermore, adipocyte differentiation and cholesterol homeostasis were unaffected. We found that the impaired lipid accumulation of Adiponectin-cre; Scarb2^fl/fl mice was due to the imbalance between glycolysis and oxidative phosphorylation (OXPHOS). Mechanistically, the mechanistic target of rapamycin complex 1 (mTORC1)/ eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1) pathway was down-regulated in Scarb2 deficient adipocytes, leading to impaired mitochondrial respiration and enhanced glycolysis. Altogether, we reveal the role of SCARB2 in metabolism regulation besides the nervous system, which provides a theoretical basis for weight loss treatment of patients with neurodegenerative diseases.

Proto-oncogene FAM83A contributes to casein kinase 1-mediated mitochondrial maintenance and white adipocyte differentiation

Family with sequence similarity 83 A (FAM83A) is a newly discovered proto-oncogene that has been shown to play key roles in various cancers. However, the function of FAM83A in other physiological processes is not well known. Here, we report a novel function of FAM83A in adipocyte differentiation. We used an adipocyte-targeting fusion oligopeptide (FITC-ATS-9R) to deliver a FAM83A-sgRNA/Cas9 plasmid to knockdown Fam83a (ATS/sg-FAM83A) in white adipose tissue in mice, which resulted in reduced white adipose tissue mass, smaller adipocytes, and mitochondrial damage that was aggravated by a high-fat diet. In cultured 3T3-L1 adipocytes, we found loss or knockdown of Fam83a significantly repressed lipid droplet formation and downregulated the expression of lipogenic genes and proteins. Furthermore, inhibition of Fam83a decreased mitochondrial ATP production through blockage of the electron transport chain, associated with enhanced apoptosis. Mechanistically, we demonstrate FAM83A interacts with casein kinase 1 (CK1) and promotes the permeability of the mitochondrial outer membrane. Furthermore, loss of Fam83a in adipocytes hampered the formation of the TOM40 complex and impeded CK1-driven lipogenesis. Taken together, these results establish FAM83A as a critical regulator of mitochondria maintenance during adipogenesis.

Role of adipocyte browning in prostate and breast tumor microenvironment

Prostate cancer (PC) and breast cancer (BC) are the most common cancers in men and women, respectively, in developed countries. The increased incidence of PC and BC largely reflects an increase in the prevalence of obesity and metabolic syndrome. In pathological conditions involving the development and progression of PC and BC, adipose tissue plays an important role via paracrine and endocrine signaling. The increase in the amount of local adipose tissue, specifically periprostatic adipose tissue, may be a key contributor to the PC pathobiology. Similarly, breast adipose tissue secretion affects various aspects of BC by influencing tumor progression, angiogenesis, metastasis, and microenvironment. In this context, the role of white adipose tissue (WAT) has been extensively studied. However, the influence of browning of the WAT on the development and progression of PC and BC is unclear and has received less attention. In this review, we highlight that adipose tissue plays a vital role in the regulation of the tumor microenvironment in PC or BC and highlight the probable underlying mechanisms linking adipose tissue with PC or BC. We further discuss whether the browning of WAT could be a therapeutic strategy for the treatment of PC and BC.

Mitochondrial calcium uniporter stabilization preserves energetic homeostasis during Complex I impairment

Calcium entering mitochondria potently stimulates ATP synthesis. Increases in calcium preserve energy synthesis in cardiomyopathies caused by mitochondrial dysfunction, and occur due to enhanced activity of the mitochondrial calcium uniporter channel. The signaling mechanism that mediates this compensatory increase remains unknown. Here, we find that increases in the uniporter are due to impairment in Complex I of the electron transport chain. In normal physiology, Complex I promotes uniporter degradation via an interaction with the uniporter pore-forming subunit, a process we term Complex I-induced protein turnover. When Complex I dysfunction ensues, contact with the uniporter is inhibited, preventing degradation, and leading to a build-up in functional channels. Preventing uniporter activity leads to early demise in Complex I-deficient animals. Conversely, enhancing uniporter stability rescues survival and function in Complex I deficiency. Taken together, our data identify a fundamental pathway producing compensatory increases in calcium influx during Complex I impairment.

Adipose mitochondrial metabolism controls body growth by modulating systemic cytokine and insulin signaling

Animals must adapt their growth to fluctuations in nutrient availability to ensure proper development. These adaptations often rely on specific nutrient-sensing tissues that control whole-body physiology through inter-organ communication. While the signaling mechanisms that underlie this communication are well studied, the contributions of metabolic alterations in nutrient-sensing tissues are less clear. Here, we show how the reprogramming of adipose mitochondria controls whole-body growth in Drosophila larvae. We find that dietary nutrients alter fat-body mitochondrial morphology to lower their bioenergetic activity, leading to rewiring of fat-body glucose metabolism. Strikingly, we find that genetic reduction of mitochondrial bioenergetics just in the fat body is sufficient to accelerate body growth and development. These growth effects are caused by inhibition of the fat-derived secreted peptides ImpL2 and tumor necrosis factor alpha (TNF-α)/Eiger, leading to enhanced systemic insulin signaling. Our work reveals how reprogramming of mitochondrial metabolism in one nutrient-sensing tissue can couple nutrient availability to whole-body growth.

Mitochondrially targeted tamoxifen alleviates markers of obesity and type 2 diabetes mellitus in mice

Type 2 diabetes mellitus represents a major health problem with increasing prevalence worldwide. Limited efficacy of current therapies has prompted a search for novel therapeutic options. Here we show that treatment of pre-diabetic mice with mitochondrially targeted tamoxifen, a potential anti-cancer agent with senolytic activity, improves glucose tolerance and reduces body weight with most pronounced reduction of visceral adipose tissue due to reduced food intake, suppressed adipogenesis and elimination of senescent cells. Glucose-lowering effect of mitochondrially targeted tamoxifen is linked to improvement of type 2 diabetes mellitus-related hormones profile and is accompanied by reduced lipid accumulation in liver. Lower senescent cell burden in various tissues, as well as its inhibitory effect on pre-adipocyte differentiation, results in lower level of circulating inflammatory mediators that typically enhance metabolic dysfunction. Targeting senescence with mitochodrially targeted tamoxifen thus represents an approach to the treatment of type 2 diabetes mellitus and its related comorbidities, promising a complex impact on senescence-related pathologies in aging population of patients with type 2 diabetes mellitus with potential translation into the clinic.

Senescent cells play a role in pathogenesis of diabetes, and senolytic agents can improve obesity- and diabetes-related pathologies. Here the authors report that mitochondrially targeted tamoxifen, a potential anti-cancer agent with senolytic activity, alleviates symptoms of obesity and prediabetes in mice, potentially via reduction of food intake and elimination of senescent cells.

Adipose Mitochondrial Complex I Deficiency Modulates Inflammation and Glucose Homeostasis in a Sex-Dependent Manner

Mitochondrial dysfunction in adipose tissue has been associated with type 2 diabetes, but it is unclear whether it is a cause or the consequence. Mitochondrial complex I is a major site of reactive oxygen species generation and a therapeutic target. Here we report that genetic deletion of the complex I subunit Ndufs4 specifically in adipose tissue results in an increased propensity to develop diet-induced weight gain, glucose intolerance, and elevated levels of fat inflammatory genes. This outcome is apparent in young males but not in young females, suggesting that females are relatively protected from the adverse consequences of adipose mitochondrial dysfunction for metabolic health. Mutant mice of both sexes exhibit defects in brown adipose tissue thermogenesis. Fibroblast growth factor 21 (FGF21) signaling in adipose tissue is selectively blunted in male mutant mice relative to wild-type littermates, consistent with sex-dependent regulation of its autocrine/paracrine action in adipocytes. Together, these findings support that adipocyte-specific mitochondrial dysfunction is sufficient to induce tissue inflammation and can cause systemic glucose abnormalities in male mice.

Mitochondrial dysfunction by TFAM depletion disrupts self-renewal and lineage differentiation of human PSCs by affecting cell proliferation and YAP response

Genetic mitochondrial dysfunction is frequently associated with various embryonic developmental defects. However, how mitochondria contribute to early development and cell fate determination is poorly studied, especially in humans. Using human pluripotent stem cells (hPSCs), we established a Dox-induced knockout model with mitochondrial dysfunction and evaluated the effect of mitochondrial dysfunction on human pluripotency maintenance and lineage differentiation. The nucleus-encoded gene TFAM (transcription factor A, mitochondrial), essential for mitochondrial gene transcription and mitochondrial DNA replication, is targeted to construct the mitochondrial dysfunction model. The hPSCs with TFAM depletion exhibit the decrease of mtDNA level and oxidative respiration efficiency, representing a typical mitochondrial dysfunction phenotype. Mitochondrial dysfunction leads to impaired self-renewal in hPSCs due to proliferation arrest. Although the mitochondrial dysfunction does not affect pluripotent gene expression, it results in a severe defect in lineage differentiation. Further study in mesoderm differentiation reveals that mitochondrial dysfunction causes proliferation disability and YAP nuclear translocalization and thus together blocks mesoderm lineage differentiation. These findings provide new insights into understanding the mitochondrial function in human pluripotency maintenance and mesoderm differentiation.

Mitochondrial protein import determines lifespan through metabolic reprogramming and de novo serine biosynthesis

Sustained mitochondrial fitness relies on coordinated biogenesis and clearance. Both processes are regulated by constant targeting of proteins into the organelle. Thus, mitochondrial protein import sets the pace for mitochondrial abundance and function. However, our understanding of mitochondrial protein translocation as a regulator of longevity remains enigmatic. Here, we targeted the main protein import translocases and assessed their contribution to mitochondrial abundance and organismal physiology. We find that reduction in cellular mitochondrial load through mitochondrial protein import system suppression, referred to as MitoMISS, elicits a distinct longevity paradigm. We show that MitoMISS triggers the mitochondrial unfolded protein response, orchestrating an adaptive reprogramming of metabolism. Glycolysis and de novo serine biosynthesis are causatively linked to longevity, whilst mitochondrial chaperone induction is dispensable for lifespan extension. Our findings extent the pro-longevity role of UPR^mt and provide insight, relevant to the metabolic alterations that promote or undermine survival and longevity.

Mitochondrial function is linked to lifespan. Here the authors show that inhibition of mitochondrial protein import leads to a reduction in mitochondrial abundance and extends lifespan in Caenorhabditis elegans via activation of glycolysis and de novo serine biosynthesis.

Thyroid hormone-dependent regulation of metabolism and heart regeneration

While adult zebrafish and newborn mice possess a robust capacity to regenerate their hearts, this ability is generally lost in adult mammals. The logic behind the diversity of cardiac regenerative capacity across the animal kingdom is not well understood. We have recently reported that animal metabolism is inversely correlated to the abundance of mononucleated diploid cardiomyocytes in the heart, which retain proliferative and regenerative potential. Thyroid hormones are classical regulators of animal metabolism, mitochondrial function, and thermogenesis, and a growing body of scientific evidence demonstrates that these hormonal regulators also have direct effects on cardiomyocyte proliferation and maturation. We propose that thyroid hormones dually control animal metabolism and cardiac regenerative potential through distinct mechanisms, which may represent an evolutionary tradeoff for the acquisition of endothermy and loss of heart regenerative capacity. In this review, we describe the effects of thyroid hormones on animal metabolism and cardiomyocyte regeneration and highlight recent reports linking the loss of mammalian cardiac regenerative capacity to metabolic shifts occurring after birth.

HEK293T Cells with TFAM Disruption by CRISPR-Cas9 as a Model for Mitochondrial Regulation

The mitochondrial transcription factor A (TFAM) is considered a key factor in mitochondrial DNA (mtDNA) copy number. Given that the regulation of active copies of mtDNA is still not fully understood, we investigated the effects of CRISPR-Cas9 gene editing of TFAM in human embryonic kidney (HEK) 293T cells on mtDNA copy number. The aim of this study was to generate a new in vitro model by CRISPR-Cas9 system by editing the TFAM locus in HEK293T cells. Among the resulting single-cell clones, seven had high mutation rates (67-96%) and showed a decrease in mtDNA copy number compared to control. Cell staining with Mitotracker Red showed a reduction in fluorescence in the edited cells compared to the non-edited cells. Our findings suggest that the mtDNA copy number is directly related to TFAM control and its disruption results in interference with mitochondrial stability and maintenance.

Inhibition of protein tyrosine phosphatase improves mitochondrial bioenergetics and dynamics, reduces oxidative stress, and enhances adipogenic differentiation potential in metabolically impaired progenitor stem cells

BACKGROUND

Protein tyrosine phosphatase 1B (PTP1B) and low molecular weight protein tyrosine phosphatase (LMPTP) are implicated in the development of metabolic disorders. Yet, their role in progenitor stem cell adipogenic differentiation and modulation of mitochondrial dynamics remains elusive.

METHODS

In this study, we decided to investigate whether inhibition of PTP1B and LMPTP enhance adipogenic differentiation of metabolically impaired progenitor stem cells via modulation of mitochondrial bioenergetics and dynamics. Cells were cultured under adipogenic conditions in the presence of PTP1B and LMPTP inhibitors, and were subjected to the analysis of the main adipogenic-related and mitochondrial-related genes using RT-qPCR. Protein levels were established with western blot while mitochondrial morphology with MicroP software.

RESULTS

Selective inhibitors of both PTP1B and MPTP enhanced adipogenic differentiation of metabolically impaired progenitor stem cells. We have observed enhanced expression of PPARy and adiponectin in treated cells. What is more, increased antioxidative defence and alternations in mitochondrial bioenergetics were observed. We have found that inhibition of PTP1B as well as C23 activates oxidative phosphorylation and enhances mitochondrial fusion contributing to enhanced adipogenesis.

CONCLUSIONS

The presented data provides evidence that the application of PTP1B and LMPTP inhibitors enhances adipogenesis through the modulation of mitochondrial dynamics. Video abstract.

Stress-induced FGF21 and GDF15 in obesity and obesity resistance

Fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) are established as stress-responsive cytokines that can modulate energy balance by increasing energy expenditure or suppressing food intake, respectively. Despite their pharmacologically induced beneficial effects on obesity and comorbidities, circulating levels of both cytokines are elevated during obesity and related metabolic complications. On the other hand, endocrine crosstalk via FGF21 and GDF15 was also reported to play a crucial role in genetically modified mouse models of mitochondrial perturbations leading to diet-induced obesity (DIO) resistance. This review aims to dissect the complexities of endogenous FGF21 and GDF15 action in obesity versus DIO resistance for the regulation of energy balance in metabolic health and disease.

ATF4 activation promotes hepatic mitochondrial dysfunction by repressing NRF1-TFAM signalling in alcoholic steatohepatitis

OBJECTIVE

Mitochondrial dysfunction plays a dominant role in the pathogenesis of alcoholic liver disease (ALD); however, the underlying mechanisms remain to be fully understood. We previously found that hepatic activating transcription factor 4 (ATF4) activation was associated with mitochondrial dysfunction in ALD. This study aimed to investigate the function and mechanism of ATF4 in alcohol-induced hepatic mitochondrial dysfunction.

DESIGN

ATF4 activation was detected in the livers of patients with severe alcoholic hepatitis (AH). The role of ATF4 and mitochondrial transcription factor A (TFAM) in alcohol-induced liver damage was determined in hepatocyte-specific ATF4 knockout mice and liver-specific TFAM overexpression mice, respectively.

RESULTS

Hepatic PERK-eIF2α-ATF4 ER stress signalling was upregulated in patients with AH. Hepatocyte-specific ablation of ATF4 in mice ameliorated alcohol-induced steatohepatitis. ATF4 ablation also attenuated alcohol-impaired mitochondrial biogenesis and respiratory function along with the restoration of TFAM. Cell studies confirmed that TFAM expression was negatively regulated by ATF4. TFAM silencing in hepatoma cells abrogated the protective effects of ATF4 knockdown on ethanol-mediated mitochondrial dysfunction and cell death. Moreover, hepatocyte-specific TFAM overexpression in mice attenuated alcohol-induced mitochondrial dysfunction and liver damage. Mechanistic studies revealed that ATF4 repressed the transcription activity of nuclear respiratory factor 1 (NRF1), a key regulator of TFAM, through binding to its promoter region. Clinical relevance among ATF4 activation, NRF1-TFAM pathway disruption and mitochondrial dysfunction was validated in the livers of patients with AH.

CONCLUSION

This study demonstrates that hepatic ATF4 plays a pathological role in alcohol-induced mitochondrial dysfunction and liver injury by disrupting the NRF1-TFAM pathway.