Mitochondrial function/dysfunction in white adipose tissue

Molecular targets for management of diabetes: Remodelling of white adipose to brown adipose tissue

Diabetes mellitus is a disorder characterised metabolic dysfunction that results in elevated glucose level in the bloodstream. Diabetes is of two types, type1 and type 2 diabetes. Obesity is considered as one of the major reasons intended for incidence of diabetes hence it turns out to be essential to study about the adipose tissue which is responsible for fat storage in body. Adipose tissues play significant role in maintaining the balance between energy stabilization and homeostasis. The three forms of adipose tissue are - White adipose tissue (WAT), Brown adipose tissue (BAT) and Beige adipose tissue (intermediate form). The amount of BAT gets reduced, and WAT starts to increase with the age. WAT when exposed to certain stimuli gets converted to BAT by the help of certain transcriptional regulators. The browning of WAT has been a matter of study to treat the metabolic disorders and to initiate the expenditure of energy. The three main regulators responsible for the browning of WAT are PRDM16, PPARγ and PGC-1α via various cellular and molecular mechanism. Presented review article includes the detailed elaborative aspect of genes and proteins involved in conversion of WAT to BAT.

Endotoxin-induced alterations of adipose tissue function: a pathway to bovine metabolic stress

During the periparturient period, dairy cows exhibit negative energy balance due to limited appetite and increased energy requirements for lactogenesis. The delicate equilibrium between energy availability and expenditure puts cows in a state of metabolic stress characterized by excessive lipolysis in white adipose tissues (AT), increased production of reactive oxygen species, and immune cell dysfunction. Metabolic stress, especially in AT, increases the risk for metabolic and inflammatory diseases. Around parturition, cows are also susceptible to endotoxemia. Bacterial-derived toxins cause endotoxemia by promoting inflammatory processes and immune cell infiltration in different organs and systems while impacting metabolic function by altering lipolysis, mitochondrial activity, and insulin sensitivity. In dairy cows, endotoxins enter the bloodstream after overcoming the defense mechanisms of the epithelial barriers, particularly during common periparturient conditions such as mastitis, metritis, and pneumonia, or after abrupt changes in the gut microbiome. In the bovine AT, endotoxins induce a pro-inflammatory response and stimulate lipolysis in AT, leading to the release of free fatty acids into the bloodstream. When excessive and protracted, endotoxin-induced lipolysis can impair adipocyte's insulin signaling pathways and lipid synthesis. Endotoxin exposure can also induce oxidative stress in AT through the production of reactive oxygen species by inflammatory cells and other cellular components. This review provides insights into endotoxins' impact on AT function, highlighting the gaps in our knowledge of the mechanisms underlying AT dysfunction, its connection with periparturient cows' disease risk, and the need to develop effective interventions to prevent and treat endotoxemia-related inflammatory conditions in dairy cattle.

Diabetes Mellitus, Energy Metabolism, and COVID-19

Obesity, diabetes mellitus (mostly type 2), and COVID-19 show mutual interactions because they are not only risk factors for both acute and chronic COVID-19 manifestations, but also because COVID-19 alters energy metabolism. Such metabolic alterations can lead to dysglycemia and long-lasting effects. Thus, the COVID-19 pandemic has the potential for a further rise of the diabetes pandemic. This review outlines how preexisting metabolic alterations spanning from excess visceral adipose tissue to hyperglycemia and overt diabetes may exacerbate COVID-19 severity. We also summarize the different effects of SARS-CoV-2 infection on the key organs and tissues orchestrating energy metabolism, including adipose tissue, liver, skeletal muscle, and pancreas. Last, we provide an integrative view of the metabolic derangements that occur during COVID-19. Altogether, this review allows for better understanding of the metabolic derangements occurring when a fire starts from a small flame, and thereby help reducing the impact of the COVID-19 pandemic.

Mitochondria isolated from lipid droplets of white adipose tissue reveal functional differences based on lipid droplet size

Recent studies in brown adipose tissue (BAT) described a unique subpopulation of mitochondria bound to lipid droplets (LDs), which were termed PeriDroplet Mitochondria (PDM). PDM can be isolated from BAT by differential centrifugation and salt washes. Contrary to BAT, this approach has so far not led to the successful isolation of PDM from white adipose tissue (WAT). Here, we developed a method to isolate PDM from WAT with high yield and purity by an optimized proteolytic treatment that preserves the respiratory function of mitochondria. Using this approach, we show that, contrary to BAT, WAT PDM have lower respiratory and ATP synthesis capacities compared with WAT cytoplasmic mitochondria (CM). Furthermore, by isolating PDM from LDs of different sizes, we found a negative correlation between LD size and the respiratory capacity of their PDM in WAT. Thus, our new isolation method reveals tissue-specific characteristics of PDM and establishes the existence of heterogeneity in PDM function determined by LD size.

Mitochondrial transfer - a novel promising approach for the treatment of metabolic diseases

Metabolic disorders remain a major global health concern in the 21st century, with increasing incidence and prevalence. Mitochondria play a critical role in cellular energy production, calcium homeostasis, signal transduction, and apoptosis. Under physiological conditions, mitochondrial transfer plays a crucial role in tissue homeostasis and development. Mitochondrial dysfunction has been implicated in the pathogenesis of metabolic disorders. Numerous studies have demonstrated that mitochondria can be transferred from stem cells to pathologically injured cells, leading to mitochondrial functional restoration. Compared to cell therapy, mitochondrial transplantation has lower immunogenicity, making exogenous transplantation of healthy mitochondria a promising therapeutic approach for treating diseases, particularly metabolic disorders. This review summarizes the association between metabolic disorders and mitochondria, the mechanisms of mitochondrial transfer, and the therapeutic potential of mitochondrial transfer for metabolic disorders. We hope this review provides novel insights into targeted mitochondrial therapy for metabolic disorders.

Hepatic Runx1t1 improves body fat index after endurance exercise in obese mice

Endurance exercise could attenuate obesity induced by high fat diet (HFD). Thus, the purpose of this study was to explore the crucial targets that play key roles in the improvement of body fat index (BFI) in obese mice by endurance exercise. Firstly, we constructed murine obesity models: High fat diet control (HFD) group, HFD exercise (HFE) group, normal chow diet control (NC) group, and normal chow diet exercise (NE) group. Next, we identified the BFI improvement related genes using differential gene analysis, and investigated these genes' functional pathways using functional enrichment analysis. The qRT-PCR and western blot assays were used to determine the gene expression and protein expression, respectively. Gene set enrichment analysis was used to explore the potential pathways associated with endurance exercise in obese mice and Mitochondrial respiratory control ratio (RCR) assay was applied to determine the RCR in the liver tissues of mice. We discovered that endurance exercise remarkably reduced the body weights and BFI of HFD-induced obese mice. Runx1t1 was related to the improvement of BFI by endurance exercise in HFD-induced obese mice. Runx1t1 mRNA and protein levels in liver tissues were observably decreased in HFD mice compared to mice in HFE, NC and NE groups. Moreover, Glucagon signaling pathway that was associated with mitochondrial function was significantly activated in HFE mice. The Runx1t1 expression exhibited an observable negative correlation with Acaca in HFD mice. Moreover, the mitochondrial RCR level was significantly increased in HFE mice than that in HFD mice. In HFD-induced obese mice, Runx1t1 was implicated in the improvement of BFI via endurance exercise. Endurance exercise could improve mitochondrial dysfunction in obese mice by activating the Runx1t1.

Butyrate prevents visceral adipose tissue inflammation and metabolic alterations in a Friedreich's ataxia mouse model

Friedreich's ataxia (FA) is a neurodegenerative disease resulting from a mutation in the FXN gene, leading to mitochondrial frataxin deficiency. FA patients exhibit increased visceral adiposity, inflammation, and heightened diabetes risk, negatively affecting prognosis. We investigated visceral white adipose tissue (vWAT) in a murine model (KIKO) to understand its role in FA-related metabolic complications. RNA-seq analysis revealed altered expression of inflammation, angiogenesis, and fibrosis genes. Diabetes-like traits, including larger adipocytes, immune cell infiltration, and increased lactate production, were observed in vWAT. FXN downregulation in cultured adipocytes mirrored vWAT diabetes-like features, showing metabolic shifts toward glycolysis and lactate production. Metagenomic analysis indicated a reduction in fecal butyrate-producing bacteria, known to exert antidiabetic effects. A butyrate-enriched diet restrained vWAT abnormalities and mitigated diabetes features in KIKO mice. Our work emphasizes the role of vWAT in FA-related metabolic issues and suggests butyrate as a safe and promising adjunct for FA management.

Promotion Effect of Coexposure to a High-Fat Diet and Nano-Diethylnitrosamine on the Progression of Fatty Liver Malignant Transformation into Liver Cancer

Overconsumption of high-fat foods increases the risk of fatty liver disease (FLD) and liver cancer with long pathogenic cycles. It is also known that the intake of the chemical poison nitrosamine and its nanopreparations can promote the development of liver injuries, such as FLD, and hepatic fibrosis, and significantly shorten the formation time of the liver cancer cycle. The present work confirmed that the coexposure of a high-fat diet (HFD) and nano-diethylnitrosamine (nano-DEN) altered the tumor microenvironment and studied the effect of this coexposure on the progression of fatty liver malignant transformation into liver cancer. Gene transcriptomics and immunostaining were used to evaluate the tumor promotion effect of the coexposure in mice. After coexposure treatment, tumor nodules were obviously increased, and inflammation levels were elevated. The liver transcriptomics analysis showed that the expression levels of inflammatory, fatty, and fibrosis-related factors in the coexposed group were increased in comparison with the nano-DEN- and high-fat-alone groups. The Kyoto Encyclopedia of Genes and Genomes (KEGG) results showed that coexposure aggravated the high expression of genes related to the carcinomatous pathway and accelerated the formation of the tumor microenvironment. The immunohistochemical staining results showed that the coexposure significantly increased the abnormal changes in proteins related to inflammation, proliferation, aging, and hypoxia in mouse liver tissues. The coexposure of high fat and nano-DEN aggravated the process of steatosis and carcinogenesis. In conclusion, the habitual consumption of pickled foods containing nitrosamines in a daily HFD significantly increases the risk of liver pathology lesions progressing from FLD to liver cancer.

Altered H3K4me3 profile at the TFAM promoter causes mitochondrial alterations in preadipocytes from first-degree relatives of type 2 diabetics

BACKGROUND

First-degree relatives of type 2 diabetics (FDR) exhibit a high risk of developing type 2 diabetes (T2D) and feature subcutaneous adipocyte hypertrophy, independent of obesity. In FDR, adipose cell abnormalities contribute to early insulin-resistance and are determined by adipocyte precursor cells (APCs) early senescence and impaired recruitment into the adipogenic pathway. Epigenetic mechanisms signal adipocyte differentiation, leading us to hypothesize that abnormal epigenetic modifications cause adipocyte dysfunction and enhance T2D risk. To test this hypothesis, we examined the genome-wide histone profile in APCs from the subcutaneous adipose tissue of healthy FDR.

RESULTS

Sequencing-data analysis revealed 2644 regions differentially enriched in lysine 4 tri-methylated H3-histone (H3K4me3) in FDR compared to controls (CTRL) with significant enrichment in mitochondrial-related genes. These included TFAM, which regulates mitochondrial DNA (mtDNA) content and stability. In FDR APCs, a significant reduction in H3K4me3 abundance at the TFAM promoter was accompanied by a reduction in TFAM mRNA and protein levels. FDR APCs also exhibited reduced mtDNA content and mitochondrial-genome transcription. In parallel, FDR APCs exhibited impaired differentiation and TFAM induction during adipogenesis. In CTRL APCs, TFAM-siRNA reduced mtDNA content, mitochondrial transcription and adipocyte differentiation in parallel with upregulation of the CDKN1A and ZMAT3 senescence genes. Furthermore, TFAM-siRNA significantly expanded hydrogen peroxide (H2O2)-induced senescence, while H2O2 did not affect TFAM expression.

CONCLUSIONS

Histone modifications regulate APCs ability to differentiate in mature cells, at least in part by modulating TFAM expression and affecting mitochondrial function. Reduced H3K4me3 enrichment at the TFAM promoter renders human APCs senescent and dysfunctional, increasing T2D risk.

Physiological Approaches Targeting Cellular and Mitochondrial Pathways Underlying Adipose Organ Senescence

The adipose organ is involved in many metabolic functions, ranging from the production of endocrine factors to the regulation of thermogenic processes. Aging is a natural process that affects the physiology of the adipose organ, leading to metabolic disorders, thus strongly impacting healthy aging. Cellular senescence modifies many functional aspects of adipose tissue, leading to metabolic alterations through defective adipogenesis, inflammation, and aberrant adipocytokine production, and in turn, it triggers systemic inflammation and senescence, as well as insulin resistance in metabolically active tissues, leading to premature declined physiological features. In the various aging fat depots, senescence involves a multiplicity of cell types, including mature adipocytes and immune, endothelial, and progenitor cells that are aging, highlighting their involvement in the loss of metabolic flexibility, one of the common features of aging-related metabolic disorders. Since mitochondrial stress represents a key trigger of cellular senescence, and senescence leads to the accumulation of abnormal mitochondria with impaired dynamics and hindered homeostasis, this review focuses on the beneficial potential of targeting mitochondria, so that strategies can be developed to manage adipose tissue senescence for the treatment of age-related metabolic disorders.

Depot-specific adaption of adipose tissue for different exercise approaches in high-fat diet/streptozocin-induced diabetic mice

Background: Adipose tissue pathology plays a crucial role in the pathogenesis of type 2 diabetes mellitus. Understanding the impact of exercise training on adipose tissue adaptation is of paramount importance in enhancing metabolic health. In this study, we aimed to investigate the effects of various exercise modalities on three distinct adipose tissue depots, namely, interscapular brown adipose tissue (iBAT), subcutaneous white adipose tissue (sWAT), and epididymal white adipose tissue (eWAT), in a murine model of diabetes. Methods: Male C57BL/6J mice received a 12-week high-fat diet and a single injection of streptozotocin, followed by an 8-week exercise intervention. The exercise intervention included swimming, resistance training, aerobic exercise, and high-intensity interval training (HIIT). Results: We found that exercise training reduced body weight and body fat percentage, diminished adipocyte size and increased the expression of mitochondria-related genes (PGC1, COX4, and COX8B) in three adipose tissue depots. The effects of exercise on inflammatory status include a reduction in crown-like structures and the expression of inflammatory factors, mainly in eWAT. Besides, exercise only induces the browning of sWAT, which may be related to the expression of the sympathetic marker tyrosine hydroxylase. Among the four forms of exercise, HIIT was the most effective in reducing body fat percentage, increasing muscle mass and reducing eWAT adipocyte size. The expression of oxidative phosphorylation and thermogenesis-related genes in sWAT and eWAT was highest in the HIIT group. Conclusion: When targeting adipose tissue to improve diabetes, HIIT may offer superior benefits and thus represents a more advantageous choice.

Engineered allele substitution at PPARGC1A rs8192678 alters human white adipocyte differentiation, lipogenesis, and PGC-1α content and turnover

AIMS/HYPOTHESIS

PPARGC1A encodes peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α), a central regulator of energy metabolism and mitochondrial function. A common polymorphism in PPARGC1A (rs8192678, C/T, Gly482Ser) has been associated with obesity and related metabolic disorders, but no published functional studies have investigated direct allele-specific effects in adipocyte biology. We examined whether rs8192678 is a causal variant and reveal its biological function in human white adipose cells.

METHODS

We used CRISPR-Cas9 genome editing to perform an allelic switch (C-to-T or T-to-C) at rs8192678 in an isogenic human pre-adipocyte white adipose tissue (hWAs) cell line. Allele-edited single-cell clones were expanded and screened to obtain homozygous T/T (Ser482Ser), C/C (Gly482Gly) and heterozygous C/T (Gly482Ser) isogenic cell populations, followed by functional studies of the allele-dependent effects on white adipocyte differentiation and mitochondrial function.

RESULTS

After differentiation, the C/C adipocytes were visibly less BODIPY-positive than T/T and C/T adipocytes, and had significantly lower triacylglycerol content. The C allele presented a dose-dependent lowering effect on lipogenesis, as well as lower expression of genes critical for adipogenesis, lipid catabolism, lipogenesis and lipolysis. Moreover, C/C adipocytes had decreased oxygen consumption rate (OCR) at basal and maximal respiration, and lower ATP-linked OCR. We determined that these effects were a consequence of a C-allele-driven dysregulation of PGC-1α protein content, turnover rate and transcriptional coactivator activity.

CONCLUSIONS/INTERPRETATION

Our data show allele-specific causal effects of the rs8192678 variant on adipogenic differentiation. The C allele confers lower levels of PPARGC1A mRNA and PGC-1α protein, as well as disrupted dynamics of PGC-1α turnover and activity, with downstream effects on cellular differentiation and mitochondrial function. Our study provides the first experimentally deduced insights on the effects of rs8192678 on adipocyte phenotype.

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.

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.

Sarcopenic Obesity: Involvement of Oxidative Stress and Beneficial Role of Antioxidant Flavonoids

Sarcopenic obesity, which refers to concurrent sarcopenia and obesity, is characterized by decreased muscle mass, strength, and performance along with abnormally excessive fat mass. Sarcopenic obesity has received considerable attention as a major health threat in older people. However, it has recently become a health problem in the general population. Sarcopenic obesity is a major risk factor for metabolic syndrome and other complications such as osteoarthritis, osteoporosis, liver disease, lung disease, renal disease, mental disease and functional disability. The pathogenesis of sarcopenic obesity is multifactorial and complicated, and it is caused by insulin resistance, inflammation, hormonal changes, decreased physical activity, poor diet and aging. Oxidative stress is a core mechanism underlying sarcopenic obesity. Some evidence indicates a protective role of antioxidant flavonoids in sarcopenic obesity, although the precise mechanisms remain unclear. This review summarizes the general characteristics and pathophysiology of sarcopenic obesity and focuses on the role of oxidative stress in sarcopenic obesity. The potential benefits of flavonoids in sarcopenic obesity have also been discussed.

Pleiotropic and multi-systemic actions of physical exercise on PGC-1α signaling during the aging process

Physical training is a potent therapeutic approach for improving mitochondrial health through peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) signaling pathways. However, comprehensive information regarding the physical training impact on PGC-1α in the different physiological systems with advancing age is not fully understood. This review sheds light on the frontier-of-knowledge data regarding the chronic effects of exercise on the PGC-1α signaling pathways in rodents and humans. We address the molecular mechanisms involved in the different tissues, clarifying the precise biological action of PGC-1α, restricted to the aged cell type. Distinct exercise protocols (short and long-term) and modalities (aerobic and resistance exercise) increase the transcriptional and translational PGC-1α levels in adipose tissue, brain, heart, liver, and skeletal muscle in animal models, suggesting that this versatile molecule induces pleiotropic responses. However, PGC-1α function in some human tissues (adipose tissue, heart, and brain) remains challenging for further investigations. PGC-1α is not a simple transcriptional coactivator but supports a biochemical environment of mitochondrial dynamics, controlling physiological processes (primary metabolism, tissue remodeling, autophagy, inflammation, and redox balance). Acting as an adaptive mechanism, the long-term effects of PGC-1α following exercise may reflect the energy demand to coordinate multiple organs and contribute to cellular longevity.

Mitochondrial Dysfunction: A Cellular and Molecular Hub in Pathology of Metabolic Diseases and Infection

Mitochondria are semiautonomous doubly membraned intracellular components of cells. The organelle comprises of an external membrane, followed by coiled structures within the membrane called cristae, which are further surrounded by the matrix spaces followed by the space between the external and internal membrane of the organelle. A typical eukaryotic cell contains thousands of mitochondria within it, which make up 25% of the cytoplasm present in the cell. The organelle acts as a common point for the metabolism of glucose, lipids, and glutamine. Mitochondria chiefly regulate oxidative phosphorylation-mediated aerobic respiration and the TCA cycle and generate energy in the form of ATP to fulfil the cellular energy needs. The organelle possesses a unique supercoiled doubly stranded mitochondrial DNA (mtDNA) which encodes several proteins, including rRNA and tRNA crucial for the transport of electrons, oxidative phosphorylation, and initiating genetic repair processors. Defects in the components of mitochondria act as the principal factor for several chronic cellular diseases. The dysfunction of mitochondria can cause a malfunction in the TCA cycle and cause the leakage of the electron respiratory chain, leading to an increase in reactive oxygen species and the signaling of aberrant oncogenic and tumor suppressor proteins, which further alter the pathways involved in metabolism, disrupt redox balance, and induce endurance towards apoptosis and several treatments which play a major role in developing several chronic metabolic conditions. The current review presents the knowledge on the aspects of mitochondrial dysfunction and its role in cancer, diabetes mellitus, infections, and obesity.

Identification of a weight loss-associated causal eQTL in MTIF3 and the effects of MTIF3 deficiency on human adipocyte function

Genetic variation at the MTIF3 (Mitochondrial Translational Initiation Factor 3) locus has been robustly associated with obesity in humans, but the functional basis behind this association is not known. Here, we applied luciferase reporter assay to map potential functional variants in the haplotype block tagged by rs1885988 and used CRISPR-Cas9 to edit the potential functional variants to confirm the regulatory effects on MTIF3 expression. We further conducted functional studies on MTIF3-deficient differentiated human white adipocyte cell line (hWAs-iCas9), generated through inducible expression of CRISPR-Cas9 combined with delivery of synthetic MTIF3-targeting guide RNA. We demonstrate that rs67785913-centered DNA fragment (in LD with rs1885988, r² > 0.8) enhances transcription in a luciferase reporter assay, and CRISPR-Cas9-edited rs67785913 CTCT cells show significantly higher MTIF3 expression than rs67785913 CT cells. Perturbed MTIF3 expression led to reduced mitochondrial respiration and endogenous fatty acid oxidation, as well as altered expression of mitochondrial DNA-encoded genes and proteins, and disturbed mitochondrial OXPHOS complex assembly. Furthermore, after glucose restriction, the MTIF3 knockout cells retained more triglycerides than control cells. This study demonstrates an adipocyte function-specific role of MTIF3, which originates in the maintenance of mitochondrial function, providing potential explanations for why MTIF3 genetic variation at rs67785913 is associated with body corpulence and response to weight loss interventions.

Bioactivity-based molecular networking-guided identification of guttiferone J from Garcinia cambogia as an anti-obesity candidate

BACKGROUND AND PURPOSE

Pharmacological intervention to induce browning of white adipose tissue provides a promising anti-obesity therapy. The fruits of Garcinia cambogia (Clusiaceae) have been widely applied to manage body weight; however, the chemical principles remain unclear. The current study aims to discover browning inducers from the fruits of G. cambogia and investigate the underlying mechanisms.

EXPERIMENTAL APPROACH

The bioactivity-based molecular networking and Oil Red O staining on 3T3-L1 and C3H10T1/2 adipocytes were applied for guided isolation. High-fat diet-induced obese mice were recruited to evaluate the anti-obesity activity.

KEY RESULTS

The bioactivity-based molecular networking-guided isolation yielded several polycyclic polyprenylated acylphloroglucinols from the fruits of G. cambogia with lipid-lowering effect in adipocytes, including guttiferone J (GOJ), garcinol and 14-deoxygarcinol. As the most potent one, GOJ (10 μM) reduced lipid accumulation by 70% and 76% in 3T3-L1 and C3H10T1/2 adipocytes, respectively. Furthermore, GOJ (2.5-10 μM) increased the expression of the deacetylase sirtuin 3 (SIRT3) and activated it, which, in turn, reduced the acetylation level of PPARγ coactivator-1α to boost mitochondrial biogenesis and promoted uncoupling protein 1 expression to enhance thermogenesis, resulting in browning of adipocytes. In high-fat diet-induced-obese mice, GOJ (10 and 20 mg·kg^-1 ·day^-1 for 12 weeks) protected against adiposity, hyperlipidaemia, insulin resistance and liver lipotoxicity, through boosting SIRT3-mediated browning of inguinal adipose tissue.

CONCLUSION AND IMPLICATIONS

GOJ represents a new scaffold of thermogenic inducer, which is responsible for the anti-obesity property of G. cambogia and can be further developed as a candidate for treating obesity and its related disorders.

Mitochondrial Energy Metabolism in the Regulation of Thermogenic Brown Fats and Human Metabolic Diseases

Brown fats specialize in thermogenesis by increasing the utilization of circulating blood glucose and fatty acids. Emerging evidence suggests that brown adipose tissue (BAT) prevents the incidence of obesity-associated metabolic diseases and several types of cancers in humans. Mitochondrial energy metabolism in brown/beige adipocytes regulates both uncoupling protein 1 (UCP1)-dependent and -independent thermogenesis for cold adaptation and the utilization of excess nutrients and energy. Many studies on the quantification of human BAT indicate that mass and activity are inversely correlated with the body mass index (BMI) and visceral adiposity. Repression is caused by obesity-associated positive and negative factors that control adipocyte browning, de novo adipogenesis, mitochondrial energy metabolism, UCP1 expression and activity, and noradrenergic response. Systemic and local factors whose levels vary between lean and obese conditions include growth factors, inflammatory cytokines, neurotransmitters, and metal ions such as selenium and iron. Modulation of obesity-associated repression in human brown fats is a promising strategy to counteract obesity and related metabolic diseases through the activation of thermogenic capacity. In this review, we highlight recent advances in mitochondrial metabolism, thermogenic regulation of brown fats, and human metabolic diseases.

Resting and exercise metabolic characteristics in obese children with insulin resistance

Purpose: This study aimed to explore the characteristics of resting energy expenditure (REE) and lipid metabolism during incremental load exercise in obese children and adolescents with insulin resistance (IR) to provide evidence for exercise intervention in obese children and adolescents with IR.

Method: From July 2019 to August 2021, 195 obese children and adolescents aged 13–17 were recruited through a summer camp. The participants were divided into IR (n = 67) and no-IR (without insulin resistance, n = 128) groups and underwent morphology, blood indicators, body composition, and resting energy consumption gas metabolism tests. Thirty participants each were randomly selected from the IR and no-IR groups to carry out the incremental treadmill test.

Results: Significant metabolic differences in resting and exercise duration were found between the IR and no-IR groups. In the resting state, the resting metabolic equivalents (4.33 ± 0.94 ml/min/kg vs. 3.91 ± 0.73 ml/min/kg, p = 0.001) and REE (2464.03 ± 462.29 kcal/d vs. 2143.88 ± 380.07 kcal/d, p < 0.001) in the IR group were significantly higher than in the no-IR group. During exercise, the absolute maximal fat oxidation (0.33 ± 0.07 g/min vs. 0.36 ± 0.09 g/min, p = 0.002) in the IR group was significantly lower than in the no-IR group; maximal fat oxidation intensity (130.9 ± 8.9 bpm vs. 139.9 ± 7.4 bpm, p = 0.040) was significantly lower in the IR group.

Conclusion: Significant resting and exercise metabolic differences were found between obese IR and no-IR children and adolescents. Obese IR children and adolescents have higher REE and lower maximal fat oxidation intensity than obese no-IR children and adolescents.

Mitochondrial RNA stimulates beige adipocyte development in young mice

Childhood obesity is a serious public health crisis and a critical factor that determines future obesity prevalence. Signals affecting adipocyte development in early postnatal life have a strong potential to trigger childhood obesity; however, these signals are still poorly understood. We show here that mitochondrial (mt)RNA efflux stimulates transcription of nuclear-encoded genes for mitobiogenesis and thermogenesis in adipocytes of young mice and human infants. While cytosolic mtRNA is a potential trigger of the interferon (IFN) response, young adipocytes lack such a response to cytosolic mtRNA due to the suppression of IFN regulatory factor (IRF)7 expression by vitamin D receptor signalling. Adult and obese adipocytes, however, strongly express IRF7 and mount an IFN response to cytosolic mtRNA. In turn, suppressing IRF7 expression in adult adipocytes restores mtRNA-induced mitobiogenesis and thermogenesis and eventually mitigates obesity. Retrograde mitochondrion-to-nucleus signalling by mtRNA is thus a mechanism to evoke thermogenic potential during early adipocyte development and to protect against obesity.

OPA1 Regulates Lipid Metabolism and Cold-Induced Browning of White Adipose Tissue in Mice

Mitochondria play a vital role in white adipose tissue (WAT) homeostasis including adipogenesis, fatty acid synthesis, and lipolysis. We recently reported that the mitochondrial fusion protein optic atrophy 1 (OPA1) is required for induction of fatty acid oxidation and thermogenic activation in brown adipocytes. In the current study we investigated the role of OPA1 in WAT function in vivo. We generated mice with constitutive or inducible knockout of OPA1 selectively in adipocytes. Studies were conducted under baseline conditions, at thermoneutrality, following high-fat feeding or during cold exposure. OPA1 deficiency reduced mitochondrial respiratory capacity in white adipocytes, impaired lipolytic signaling, repressed expression of de novo lipogenesis and triglyceride synthesis pathways, and promoted adipose tissue senescence and inflammation. Reduced WAT mass was associated with hepatic triglycerides accumulation and glucose intolerance. Moreover, mice deficient for OPA1 in adipocytes had impaired adaptive thermogenesis and reduced cold-induced browning of subcutaneous WAT and were completely resistant to diet-induced obesity. In conclusion, OPA1 expression and function in adipocytes are essential for adipose tissue expansion, lipid biosynthesis, and fatty acid mobilization of WAT and brown adipocytes and for thermogenic activation of brown and beige adipocytes.

TG/HDL Ratio Is an Independent Predictor for Estimating Resting Energy Expenditure in Adults with Normal Weight, Overweight, and Obesity

Factors that determine resting energy expenditure (REE) remain under investigation, particularly in persons with a high body mass index (BMI). The accurate estimation of energy expenditure is essential for conducting comprehensive nutrition assessments, planning menus and meals, prescribing weight and chronic disease interventions, and the prevention of malnutrition. This study aimed to: (a) determine the contribution of cardiometabolic biomarkers to the inter-individual variation in REE in persons categorized by BMI; and (b) assess the contribution of these biomarkers in the prediction of REE when persons of varying BMI status were categorized by their glycemic and metabolic syndrome status. Baseline data from 645 adults enrolled in diet intervention trials included REE measured by indirect calorimetry, body composition by dual energy X-ray absorptiometry, anthropometrics, and cardiometabolic biomarkers. Multivariate linear regression modeling was conducted to determine the most parsimonious model that significantly predicted REE by BMI category, metabolic syndrome status, and glycemic status. Modeling with the traditional predictors (age, sex, height, weight) accounted for 58-63% of the inter-individual variance in REE. When including age, sex, height, weight and fat-free mass as covariates, adding TG/HDL to regression modeling accounted for 71-87% of the variance in REE. The finding that TG/HDL is an independent predictor in estimating REE was further confirmed when participants were categorized by metabolic syndrome status and by glycemic status. The clinical utility of calculating the TG/HDL ratio not only aids health care providers in identifying patients with impaired lipid metabolism but can optimize the estimation of REE to better meet therapeutic goals for weight and disease management.

Hypoxia as a Double-Edged Sword to Combat Obesity and Comorbidities

The global epidemic of obesity is tightly associated with numerous comorbidities, such as type II diabetes, cardiovascular diseases and the metabolic syndrome. Among the key features of obesity, some studies have suggested the abnormal expansion of adipose-tissue-induced local endogenous hypoxic, while other studies indicated endogenous hyperoxia as the opposite trend. Endogenous hypoxic aggravates dysfunction in adipose tissue and stimulates secretion of inflammatory molecules, which contribute to obesity. In contrast, hypoxic exposure combined with training effectively generate exogenous hypoxic to reduce body weight and downregulate metabolic risks. The (patho)physiological effects in adipose tissue are distinct from those of endogenous hypoxic. We critically assess the latest advances on the molecular mediators of endogenous hypoxic that regulate the dysfunction in adipose tissue. Subsequently we propose potential therapeutic targets in adipose tissues and the small molecules that may reverse the detrimental effect of local endogenous hypoxic. More importantly, we discuss alterations of metabolic pathways in adipose tissue and the metabolic benefits brought by hypoxic exercise. In terms of therapeutic intervention, numerous approaches have been developed to treat obesity, nevertheless durability and safety remain the major concern. Thus, a combination of the therapies that suppress endogenous hypoxic with exercise plans that augment exogenous hypoxic may accelerate the development of more effective and durable medications to treat obesity and comorbidities.

Inhibition of autophagy with chloroquine dysregulates mitochondrial quality control and energetics in adipocytes

Autophagy is a complex degradation pathway through which damaged or dysfunctional proteins and organelles are removed. Its pharmacological modulators have been extensively used in a wide range of basic research and preclinical studies. However, the effects of these inhibitors on metabolism, in addition to autophagy inhibition, are not fully elucidated. Chloroquine is a clinically relevant compound that inhibits autophagy by preventing the fusion of autophagosomes with lysosomes. In this study, we aimed to examine the effect of chloroquine on mitochondrial quality control and respiratory function by utilizing 3T3-L1 mouse adipocytes treated with chloroquine at various time points. We found that chloroquine could disturb genes related to mitochondrial fission, biogenesis, and mitophagy, leading to mitochondrial DNA damage. Although the inhibition of autophagy by chloroquine resulted in an increased prohibitin expression, respiratory function was downregulated in a time-dependent manner. Moreover, chloroquine treatment induced oxidative stress, apoptosis, and metabolic dysregulation. These data demonstrated that chloroquine significantly affected mitochondrial respiratory function and metabolism, which was consistent with impaired mitochondrial quality associated with autophagy inhibition.

The Anti-Obesity Potential of Superparamagnetic Iron Oxide Nanoparticles against High-Fat Diet-Induced Obesity in Rats: Possible Involvement of Mitochondrial Biogenesis in the Adipose Tissues

BACKGROUND

Obesity is a pandemic disease that is rapidly growing into a serious health problem and has economic impact on healthcare systems. This bleak image has elicited creative responses, and nanotechnology is a promising approach in obesity treatment. This study aimed to investigate the anti-obesity effect of superparamagnetic iron oxide nanoparticles (SPIONs) on a high-fat-diet rat model of obesity and compared their effect to a traditional anti-obesity drug (orlistat).

METHODS

The obese rats were treated daily with orlistat and/or SPIONs once per week for 8 weeks. At the end of the experiment, blood samples were collected for biochemical assays. Then, the animals were sacrificed to obtain white adipose tissues (WAT) and brown adipose tissues (BAT) for assessment of the expression of thermogenic genes and mitochondrial DNA copy number (mtDNA-CN).

RESULTS

For the first time, we reported promising ameliorating effects of SPIONs treatments against weight gain, hyperglycemia, adiponectin, leptin, and dyslipidemia in obese rats. At the molecular level, surprisingly, SPIONs treatments markedly corrected the disturbed expression and protein content of inflammatory markers and parameters controlling mitochondrial biogenesis and functions in BAT and WAT.

CONCLUSIONS

SPIONs have a powerful anti-obesity effect by acting as an inducer of WAT browning and activator of BAT functions.

Expression of Functional Cannabinoid Type-1 (CB1) Receptor in Mitochondria of White Adipocytes

Via activation of the cannabinoid type-1 (CB₁) receptor, endogenous and exogenous cannabinoids modulate important biochemical and cellular processes in adipocytes. Several pieces of evidence suggest that alterations of mitochondrial physiology might be a possible mechanism underlying cannabinoids' effects on adipocyte biology. Many reports suggest the presence of CB₁ receptor mRNA in both white and brown adipose tissue, but the detailed subcellular localization of CB₁ protein in adipose cells has so far been scarcely addressed. In this study, we show the presence of the functional CB₁ receptor at different subcellular locations of adipocytes from epididymal white adipose tissue (eWAT) depots. We observed that CB₁ is located at different subcellular levels, including the plasma membrane and in close association with mitochondria (mtCB₁). Functional analysis in tissue homogenates and isolated mitochondria allowed us to reveal that cannabinoids negatively regulate complex-I-dependent oxygen consumption in eWAT. This effect requires mtCB₁ activation and consequent regulation of the intramitochondrial cAMP-PKA pathway. Thus, CB₁ receptors are functionally present at the mitochondrial level in eWAT adipocytes, adding another possible mechanism for peripheral regulation of energy metabolism.

Induction of beige-like adipocyte markers and functions in 3T3-L1 cells by Clk1 and PKCβII inhibitory molecules

Excessive dietary intake of fat results in its storage in white adipose tissue (WAT). Energy expenditure through lipid oxidation occurs in brown adipose tissue (BAT). Certain WAT depots can undergo a change termed beiging where markers that BAT express are induced. Little is known about signalling pathways inducing beiging. Here, inhibition of a signalling pathway regulating alternative pre‐mRNA splicing is involved in adipocyte beiging. Clk1/2/4 kinases regulate splicing by phosphorylating factors that process pre‐mRNA. Clk1 inhibition by TG003 results in beige‐like adipocytes highly expressing PGC1α and UCP1. SiRNA for Clk1, 2 and 4, demonstrated that Clk1 depletion increased UCP1 and PGC1α expression, whereas Clk2/4 siRNA did not. TG003‐treated adipocytes contained fewer lipid droplets, are smaller, and contain more mitochondria, resulting in proton leak increases. Additionally, inhibition of PKCβII activity, a splice variant regulated by Clk1, increased beiging. PGC1α is a substrate for both Clk1 and PKCβII kinases, and we surmised that inhibition of PGC1α phosphorylation resulted in beiging of adipocytes. We show that TG003 binds Clk1 more than Clk2/4 through direct binding, and PGC1α binds to Clk1 at a site close to TG003. Furthermore, we show that TG003 is highly specific for Clk1 across hundreds of kinases in our activity screen. Hence, Clk1 inhibition becomes a target for induction of beige adipocytes.

Rutaecarpine Promotes Adipose Thermogenesis and Protects against HFD-Induced Obesity via AMPK/PGC-1α Pathway

Pharmacological activation of adaptive thermogenesis to increase energy expenditure is considered to be a novel strategy for obesity. Peroxisome-proliferator-activated receptor γ co-activator-1α (PGC-1α), which serves as an inducible co-activator in energy expenditure, is highly expressed in brown adipose tissues (BAT). In this study, we found a PGC-1α transcriptional activator, natural compound rutaecarpine (Rut), which promoted brown adipocytes mitochondrial biogenesis and thermogenesis in vitro. Chronic Rut treatment reduced the body weight gain and mitigated insulin sensitivity through brown and beige adipocyte thermogenesis. Mechanistic study showed that Rut activated the energy metabolic pathway AMP-activated protein kinase (AMPK)/PGC-1α axis, and deficiency of AMPK abolished the beneficial metabolic phenotype of the Rut treatment in vitro and in vivo. In summary, a PGC-1α transcriptional activator Rut was found to activate brown and beige adipose thermogenesis to resist diet-induced obesity through AMPK pathway. Our findings serve as a further understanding of the natural compound in adipose tissue and provides a possible strategy to combat obesity and related metabolic disorders.

Preventing White Adipocyte Browning during Differentiation In Vitro: The Effect of Differentiation Protocols on Metabolic and Mitochondrial Phenotypes

Mitochondrial dysfunction in white adipose tissue is strongly associated with obesity and its metabolic complications, which are important health challenges worldwide. Human adipose-derived stromal/stem cells (hASCs) are a promising tool to investigate the underlying mechanisms of such mitochondrial dysfunction and to subsequently provide knowledge for the development of treatments for obesity-related pathologies. A substantial obstacle in using hASCs is that the key compounds for adipogenic differentiation in vitro increase mitochondrial uncoupling, biogenesis, and activity, which are the signature features of brown adipocytes, thus altering the white adipocyte phenotype towards brown-like cells. Additionally, commonly used protocols for hASC adipogenic differentiation exhibit high variation in their composition of media, and a systematic comparison of their effect on mitochondria is missing. Here, we compared the five widely used adipogenic differentiation protocols for their effect on metabolic and mitochondrial phenotypes to identify a protocol that enables in vitro differentiation of white adipocytes and can more faithfully recapitulate the white adipocyte phenotype observed in human adipose tissue. We developed a workflow that included functional assays and morphological analysis of mitochondria and lipid droplets. We observed that triiodothyronine- or indomethacin-containing media and commercially available adipogenic media induced browning during in vitro differentiation of white adipocytes. However, the differentiation protocol containing 1 μM of the peroxisome proliferator-activated receptor gamma (PPARγ) agonist rosiglitazone prevented the browning effect and would be proposed for adipogenic differentiation protocol for hASCs to induce a white adipocyte phenotype. Preserving the white adipocyte phenotype in vitro is a crucial step for the study of obesity and associated metabolic diseases, adipose tissue pathologies, such as lipodystrophies, possible therapeutic compounds, and basic adipose tissue physiology.

Could very low-calorie ketogenic diets turn off low grade inflammation in obesity? Emerging evidence

Obesity is an emerging non-communicable disease associated with chronic low-grade inflammation and oxidative stress, compounded by the development of many obesity-related diseases, such as cardiovascular disease, type 2 diabetes mellitus, and a range of cancers. Originally developed for the treatment of epilepsy in drug non-responder children, the ketogenic diet (KD) is being increasingly used in the treatment of many diseases, including obesity and obesity-related conditions. The KD is a dietary pattern characterized by high fat intake, moderate to low protein consumption, and very low carbohydrate intake (<50 g) that has proved to be an effective and weight-loss tool. In addition, it also appears to be a dietary intervention capable of improving the inflammatory state and oxidative stress in individuals with obesity by means of several mechanisms. The main activity of the KD has been linked to improving mitochondrial function and decreasing oxidative stress. β-hydroxybutyrate, the most studied ketone body, has been shown to reduce the production of reactive oxygen species, improving mitochondrial respiration. In addition, KDs exert anti-inflammatory activity through several mechanisms, e.g., by inhibiting activation of the nuclear factor kappa-light-chain-enhancer of activated B cells, and the inflammatory nucleotide-binding, leucine-rich-containing family, pyrin domain-containing-3, and inhibiting histone deacetylases. Given the rising interest in the topic, this review looks at the underlying anti-inflammatory and antioxidant mechanisms of KDs and their possible recruitment in the treatment of obesity and obesity-related disorders.

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.

Diabetes Mellitus: A Path to Amnesia, Personality, and Behavior Change

Simple Summary

Diabetes Mellitus (DM) is a metabolic disorder resulting from a disturbance of insulin secretion, action, or both. Hyperglycemia and overproduction of superoxide induce the development and progression of chronic complications of DM. The impact of DM and its complication on the central nervous system (CNS) such as dementia and Alzheimer’s Disease (AD) still remain obscure. In dementia, there is a gradual decline in cognitive function. The incidence of dementia increases with age, and patient become socially, physically, and mentally more vulnerable and dependent. The symptoms often emerge decades after the onset of pathophysiology, thus impairing early therapeutic intervention. Most diabetic subjects who develop dementia are above the age of 65, but diabetes may also cause an increased risk of developing dementia before 65 years. Vascular dementia is the second most common form of dementia after AD. Type 2 DM (T2DM) increases the incidence of vascular dementia (since its covers the vascular system) and AD. The functional and structural integrity of the CNS is altered in T2DM due to increased synthesis of Aβ. Additionally, hyperphosphorylation of Tau protein also results from dysregulation of various signaling cascades in T2DM, thereby causing neuronal damage and AD. There is the prospect for development of a therapy that may help prevent or halt the progress of dementia resulting from T2DM.

Abstract

Type 2 diabetes mellitus is increasingly being associated with cognition dysfunction. Dementia, including vascular dementia and Alzheimer’s Disease, is being recognized as comorbidities of this metabolic disorder. The progressive hallmarks of this cognitive dysfunction include mild impairment of cognition and cognitive decline. Dementia and mild impairment of cognition appear primarily in older patients. Studies on risk factors, neuropathology, and brain imaging have provided important suggestions for mechanisms that lie behind the development of dementia. It is a significant challenge to understand the disease processes related to diabetes that affect the brain and lead to dementia development. The connection between diabetes mellitus and dysfunction of cognition has been observed in many human and animal studies that have noted that mechanisms related to diabetes mellitus are possibly responsible for aggravating cognitive dysfunction. This article attempts to narrate the possible association between Type 2 diabetes and dementia, reviewing studies that have noted this association in vascular dementia and Alzheimer’s Disease and helping to explain the potential mechanisms behind the disease process. A Google search for “Diabetes Mellitus and Dementia” was carried out. Search was also done for “Diabetes Mellitus”, “Vascular Dementia”, and “Alzheimer’s Disease”. The literature search was done using Google Scholar, Pubmed, Embase, ScienceDirect, and MEDLINE. Keeping in mind the increasing rate of Diabetes Mellitus, it is important to establish the Type 2 diabetes’ effect on the brain and diseases of neurodegeneration. This narrative review aims to build awareness regarding the different types of dementia and their relationship with diabetes.

Impaired phosphocreatine metabolism in white adipocytes promotes inflammation

The mechanisms promoting disturbed white adipocyte function in obesity remain largely unclear. Herein, we integrate white adipose tissue (WAT) metabolomic and transcriptomic data from clinical cohorts and find that the WAT phosphocreatine/creatine ratio is increased and creatine kinase-B expression and activity is decreased in the obese state. In human in vitro and murine in vivo models, we demonstrate that decreased phosphocreatine metabolism in white adipocytes alters adenosine monophosphate-activated protein kinase activity via effects on adenosine triphosphate/adenosine diphosphate levels, independently of WAT beigeing. This disturbance promotes a pro-inflammatory profile characterized, in part, by increased chemokine (C-C motif) ligand 2 (CCL2) production. These data suggest that the phosphocreatine/creatine system links cellular energy shuttling with pro-inflammatory responses in human and murine white adipocytes. Our findings provide unexpected perspectives on the mechanisms driving WAT inflammation in obesity and may present avenues to target adipocyte dysfunction.

Ameliorating effects of lifelong physical activity on healthy aging and mitochondrial function in human white adipose tissue

Growing old is patently among the most prominent risk factors for lifestyle related diseases and deterioration in physical performance. Aging in particular affects mitochondrial homeostasis and maintaining a well-functioning mitochondrial pool is imperative in order to avoid age-associated metabolic decline. White adipose tissue (WAT) is a key organ in energy balance and impaired mitochondrial function in adipocytes has been associated with increased low-grade inflammation, altered metabolism, excessive ROS production and an accelerated aging phenotype. Exercise training improves mitochondrial health but whether lifelong exercise training can sufficiently maintain WAT mitochondrial function is currently unknown. Therefore, to dissect the role and dose-dependence of lifelong exercise training on aging WAT metabolic parameters and mitochondrial function, young and older untrained, as well as moderately and highly exercise trained older male subjects were recruited and abdominal subcutaneous (s)WAT biopsies and venous blood samples were obtained to measure mitochondrial function and key metabolic factors in WAT and plasma. Mitochondrial intrinsic respiratory capacity was lower in sWAT from older than in young subjects. In spite of this, maximal mitochondrial respiration per wet weight, markers of oxidative capacity, and mitophagic capacity were increased in sWAT from lifelong highly exercise trained than all other groups. Furthermore, ROS emission was generally lower in sWAT from lifelong highly exercise trained than older untrained subjects. Taken together, aging reduces intrinsic mitochondrial respiration in human sWAT, but lifelong high volume exercise training increases oxidative capacity by increasing mitochondrial volume likely contributing to healthy aging.

Reliability and variation in mitochondrial respiration in human adipose tissue

Adipose tissue mitochondrial function is gaining increasing interest since it is a good marker of overall health. Methodological challenges and variability in assessing mitochondrial respiration in fresh adipose tissue with high-resolution respirometry are unknown and should be explored. Mitochondrial respiratory capacity (MRC) in human adipose tissue declines in a gradual manner when analyses are postponed 3 h and 24 h, with a statistically significant decline 24 h after obtaining the biopsy. This decline in MRC is associated with a reduced integrity of the outer mitochondrial membrane at both time points. This study suggests that the optimal amount of tissue to be used is 20 mg and that different technicians handling the biopsy do not affect MRC.

Sex-specific genetic regulation of adipose mitochondria and metabolic syndrome by Ndufv2

We have previously suggested a central role for mitochondria in the observed sex differences in metabolic traits. However, the mechanisms by which sex differences affect adipose mitochondrial function and metabolic syndrome are unclear. Here we show that in both mice and humans, adipose mitochondrial functions are elevated in females and are strongly associated with adiposity, insulin resistance and plasma lipids. Using a panel of diverse inbred strains of mice, we identify a genetic locus on mouse chromosome 17 that controls mitochondrial mass and function in adipose tissue in a sex- and tissue-specific manner. This locus contains Ndufv2 and regulates the expression of at least 89 mitochondrial genes in females, including oxidative phosphorylation genes and those related to mitochondrial DNA content. Overexpression studies indicate that Ndufv2 mediates these effects by regulating supercomplex assembly and elevating mitochondrial reactive oxygen species production, which generates a signal that increases mitochondrial biogenesis.

The cyclin dependent kinase inhibitor Roscovitine prevents diet-induced metabolic disruption in obese mice

Most strategies to treat obesity-related disorders have involved prevention of diet-induced weight gain in lean mice. Treatment of obese individuals will require therapies that reverse the detrimental effects of excess body weight. Cyclin-dependent kinases have been shown to contribute to obesity and its adverse complications. Here, we show that roscovitine; a an orally available cyclin-dependent kinase inhibitor; given to male mice during the last six weeks of a 19-week high fat diet, reduced weight gain and prevented accompanying insulin resistance, hepatic steatosis, visceral adipose tissue (eWAT) inflammation/fibrosis as well as restored insulin secretion and enhanced whole body energy expenditure. Proteomics and phosphoproteomics analysis of eWAT demonstrated that roscovitine suppressed expression of peptides and phosphopeptides linked to inflammation and extracellular matrix proteins. It also identified 17 putative protein kinases perturbed by roscovitine, including CMGC kinases, AGC kinases and CAMK kinases. Pathway enrichment analysis showed that lipid metabolism, TCA cycle, fatty acid beta oxidation and creatine biosynthesis are enriched following roscovitine treatment. For brown adipose tissue (BAT), analysis of upstream kinases controlling the phosphoproteome revealed two major kinase groups, AGC and CMGC kinases. Among the top enriched pathways were insulin signaling, regulation of lipolysis in adipocytes, thyroid hormone signaling, thermogenesis and cAMP-PKG signaling. We conclude that roscovitine is effective at preventing prolonged diet-induced metabolic disruption and restoring mitochondrial activity in BAT and eWAT.

Developmental programming and ageing of male reproductive function

Developmental programming predisposes offspring to metabolic, behavioural and reproductive dysfunction in adult life. Evidence is accumulating that ageing phenotype and longevity are in part developmentally programmed in each individual. Unfortunately, there are few studies addressing the effects of developmental programming by maternal nutrition on the rate of ageing of the male reproductive system. This review will discuss effects of foetal exposure to maternal environmental challenges on male offspring fertility and normal ageing of the male reproductive system. We focus on several key factors involved in reproductive ageing such as decreased hormone production, DNA fragmentation, oxidative stress, telomere shortening, epigenetics, maternal lifestyle and nutrition. There is compelling evidence that ageing of the male reproductive system is developmentally programmed. Both maternal over- or undernutrition accelerate ageing of male offspring reproductive function through similar mechanisms such as decreased serum testosterone levels, increase in oxidative stress biomarkers in both the testes and sperm and changes in sperm quality. Importantly, even in adult life, exercise in male offspring of obese mothers improves adverse effects of programming on reproductive function. Maternal consumption of a low-protein diet causes transgenerational effects in progeny via the paternal line. The seminal fluid has effects on the intrauterine environment. Programming by male factors may involve more than just the sperm. Improving knowledge on developmental programming ageing interactions will improve not only male health and life span but also the health of future generations by reducing programming via the paternal line.

Hydrogen Sulfide Prevents Mesenteric Adipose Tissue Damage, Endothelial Dysfunction, and Redox Imbalance From High Fructose Diet-Induced Injury in Aged Rats

A high fructose diet (HFD) and advanced age are key factors for the gradual loss of physiological integrity of adipose tissue. Endogenous hydrogen sulfide (H₂S) has beneficial effects on cytoprotection and redox balance. But its interactive effects on age-related damage of mesenteric vessels and connective and adipose tissues (MA) during HFD which could be the base of the development of effective physiological-based therapeutic strategy are unknown. The aim of study was to investigate age- and HFD-induced mesenteric cellular changes and activities of enzymes in H₂S synthesis and to test the effects of sodium hydrosulfide (NaHS) which is considered an H₂S donor on them. Adult and aged male rats on a standard diet (SD) or 4-week HFD were exposed to acute water-immersion restraint stress (WIRS) for evaluation of mesenteric subcellular and cellular adaptive responses by electron microscopy. The effects of exogenous NaHS (5.6 mg/kg/day for 9 days) versus vehicle on mesentery changes were investigated. Serum glucose level, thiobarbituric acid reactive substances (TBARS), and activities of cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), thiosulfate-dithiol sulfurtransferase (TST), and sulfite oxidase (SO) were examined by spectrophotometry. In both adult and aged SD groups, treatment with NaHS protected mesenteric cells after WIRS. In both groups, the treatment with NaHS also protected MA mitochondria, microvascular endothelial and sub-endothelial structures, and fibroblasts versus the vehicle-treated group that had signs of damage. HFD increased MA injury and mitochondrial changes in both aged and adult rats. HFD-associated malfunction is characterized by low activities of CSE, CBS, TST, SO, and increased TBARS. Finally, we demonstrated that pretreatment with NaHS inhibited MA and mitochondria alterations in aged rats exposed to HFD and WIRS, lowered TBARS, and enhanced H₂S enzyme activities in contrast to the vehicle-treated group. Mitochondrial integrity alterations, endothelial damage, and redox imbalance are key factors for rat mesenteric adipose tissue damage during advanced age. These alterations and MA hypertrophic changes retain the central for HFD-induced damage. Moreover, H₂S signaling contributes to MA and mitochondria redox balance that is crucial for advanced age and HFD injury. The future study of H₂S donors’ effects on mesenteric cells is fundamental to define novel therapeutic strategies against metabolic changes.

The Interplay Between Mitochondrial Reactive Oxygen Species, Endoplasmic Reticulum Stress, and Nrf2 Signaling in Cardiometabolic Health

Significance: Mitochondria-derived reactive oxygen species (mtROS) are by-products of normal physiology that may disrupt cellular redox homeostasis on a regular basis. Nonetheless, failure to resolve sustained mitochondrial stress to mitigate high levels of mtROS might contribute to the etiology of numerous pathological conditions, such as obesity, insulin resistance, and cardiovascular disease (CVD). Recent Advances: Notably, recent studies have demonstrated that moderate mitochondrial stress might result in the induction of different stress response pathways that ultimately improve the organism's ability to deal with subsequent stress, a process termed mitohormesis. mtROS have been shown to play a key role in regulating this adaptation. Critical Issue: mtROS regulate the convergence of different signaling pathways that, when disturbed, might impair cardiometabolic health. Conversely, mtROS seem to be required to mediate activation of prosurvival pathways, contributing to improved cardiometabolic fitness. In the present review, we will primarily focus on the role of mtROS in the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant pathway and examine the role of endoplasmic reticulum (ER) stress in coordinating the convergence of ER stress and oxidative stress signaling through activation of Nrf2 and activating transcription factor 4 (ATF4). Future Directions: The mechanisms underlying cardiometabolic protection in response to mitochondrial stress have only started to be investigated. Integrated understanding of how mtROS and ER stress cooperatively promote activation of prosurvival pathways might shed mechanistic insight into the role of mitohormesis in mediating cardiometabolic protection and might inform future therapeutic avenues for the treatment of metabolic diseases contributing to CVD. Antioxid. Redox Signal. 35, 252-269.

Strength training improves insulin resistance and differently affects mitochondria in skeletal muscle and visceral adipose tissue in high-fat fed mice

AIMS

Strength training (ST) improves insulin resistance and glucose tolerance by yet unknown mechanisms. The aims of this study were to investigate the effects of ST on mitochondrial adaptation in skeletal muscle and adipose tissue, on heat shock protein 72 (Hsp72) in skeletal muscle, and on visceral adipocyte size in mice with high-fat diet (HFD)-induced insulin resistance.

MATERIALS AND METHODS

Male Balb/c mice were divided into sedentary control-chow (C-chow), strength trained-chow (ST-chow), sedentary control-HFD (C-HFD) and strength trained-HFD (ST-HFD). Diet was provided for 12 weeks, while ladder climbing ST was performed for the final six weeks of the study at a frequency of three days per week.

KEY FINDINGS

Strength training led to increased strength, muscular endurance, and skeletal muscle hypertrophy. Compared to the C-HFD group, mice in the ST-HFD group decreased their whole-body insulin resistance, improved their glucose tolerance, and had higher activation of the insulin pathway in skeletal muscle. ST increased citrate synthase (CS) activity in skeletal muscle, but this increase was blunted in ST-HFD. Conversely, HFD reduced adipose tissue CS activity regardless of training status. Hsp72 content was reduced in C-HFD, but returned to control levels in ST-HFD. Finally, reduced epididymal adipocyte size was observed in ST-HFD.

SIGNIFICANCE

These results suggest that the improvement in insulin resistance induced by ST is related to mitochondrial adaptation in skeletal muscle, but not in adipose tissue. Moreover, this improvement might be related to increased skeletal muscle Hsp72 and reduced epididymal adipocyte size.

The Roles of Dietary, Nutritional and Lifestyle Interventions in Adipose Tissue Adaptation and Obesity

The obesity and the associated non-communicable diseases (NCDs) are globally increasing in their prevalence. While the modern-day lifestyle required less ventilation of metabolic energy through muscular activities, this lifestyle transition also provided the unlimited accession to foods around the clock, which prolong the daily eating period of foods that contained high calorie and high glycemic load. These situations promote the high continuous flux of carbon substrate availability in mitochondria and induce the indecisive bioenergetic switches. The disrupted bioenergetic milieu increases the uncoupling respiration due to the excess flow of the substrate-derived reducing equivalents and reduces ubiquinones into the respiratory chain. The diversion of the uncoupling proton gradient through adipocyte thermogenesis will then alleviate the damaging effects of free radicals to mitochondria and other organelles. The adaptive induction of white adipose tissues (WAT) to beige adipose tissues (beAT) has shown beneficial effects on glucose oxidation, ROS protection and mitochondrial function preservation through the uncoupling protein 1 (UCP1)-independent thermogenesis of beAT. However, the maladaptive stage can eventually initiate with the persistent unhealthy lifestyles. Under this metabolic gridlock, the low oxygen and pro-inflammatory environments promote the adipose breakdown with sequential metabolic dysregulation, including insulin resistance, systemic inflammation and clinical NCDs progression. It is unlikely that a single intervention can reverse all these complex interactions. A comprehensive protocol that includes dietary, nutritional and all modifiable lifestyle interventions, can be the preferable choice to decelerate, stop, or reverse the NCDs pathophysiologic processes.

The transcriptional regulator Zfat is essential for maintenance and differentiation of the adipocytes

Adipocytes play crucial roles in the control of whole‐body energy homeostasis. Differentiation and functions of the adipocytes are regulated by various transcription factors. Zfat (zinc‐finger protein with AT‐hook) is a transcriptional regulator that controls messenger RNA expression of specific genes through binding to their transcription start sites. Here we report important roles of Zfat in the adipocytes. We establish inducible Zfat‐knockout (Zfat iKO) mice where treatment with tamoxifen causes a marked reduction in Zfat expression in various tissues. Tamoxifen treatment of Zfat iKO mice reduces the white adipose tissues (WATs) mass, accompanied by the decreased triglyceride levels. Zfat is expressed in both the adipose‐derived stem cells (ADSCs) and mature adipocytes in the WATs. In ex vivo assays of the mature adipocytes differentiated from the Zfat iKO ADSCs, loss of Zfat in the mature adipocytes reduces the triglyceride levels, suggesting cell autonomous roles of Zfat in the maintenance of the mature adipocytes. Furthermore, we identify the Atg13, Brf1, Psmc3, and Timm22 genes as Zfat‐target genes in the mature adipocytes. In contrast, loss of Zfat in the ADSCs impairs adipocyte differentiation with the decreased expression of C/EBPα and adiponectin. Thus, we propose that Zfat plays crucial roles in maintenance and differentiation of the adipocytes.

Salvia hispanica L. (chia) seed promotes body fat depletion and modulates adipocyte lipid handling in sucrose-rich diet-fed rats

The aim of this study was to analyze the effects of Salvia hispanica L. (chia) seed upon metabolic pathways that play a key role in adipose tissue lipid handling which could be involved in visceral adiposity reduction developed in rats fed a sucrose-rich diet (SRD). Male Wistar rats were fed with a reference diet (RD) -6 months- or SRD-3 months. Then, the last group was randomly divided into two subgroups. One subgroup continued receiving the SRD up to 6 months and the other was fed with a SRD where whole chia seed was incorporated as the source of dietary fat for the next 3 months (SRD + CHIA). Results showed that chia seed in the SRD-fed rat reduced the abdominal and thoracic circumferences, carcass fat content, adipose tissue weights, and visceral adiposity index. This was accompanied by an improvement in insulin sensitivity and plasma lipid profile. In epididymal adipose tissue, the decreased fat cell triglyceride content was associated with a reduction in both, FAT/CD 36 plasma membrane levels and the fat synthesis enzyme activities. There were not changes in oxidative CPT enzyme activities. PKCβ and the precursor and mature forms of SREBP-1 protein levels were decreased, while pAMPK was increased. Our findings suggest that chia seed supplementation can modulate essential pathways of lipid metabolism in adipose tissue, contributing to reduced visceral fat accumulation in SRD-fed rats.

New Insights Into Mitochondrial Dysfunction at Disease Susceptibility Loci in the Development of Type 2 Diabetes

This study investigated the potential genetic mechanisms which underlie adipose tissue mitochondrial dysfunction in Type 2 diabetes (T2D), by systematically identifying nuclear-encoded mitochondrial genes (NEMGs) among the genes regulated by T2D-associated genetic loci. The target genes of these 'disease loci' were identified by mapping genetic loci associated with both disease and gene expression levels (expression quantitative trait loci, eQTL) using high resolution genetic maps, with independent estimates co-locating to within a small genetic distance. These co-locating signals were defined as T2D-eQTL and the target genes as T2D cis-genes. In total, 763 cis-genes were associated with T2D-eQTL, of which 50 were NEMGs. Independent gene expression datasets for T2D and insulin resistant cases and controls confirmed that the cis-genes and cis-NEMGs were enriched for differential expression in cases, providing independent validation that genetic maps can identify informative functional genes. Two additional results were consistent with a potential role of T2D-eQTL in regulating the 50 identified cis-NEMGs in the context of T2D risk: (1) the 50 cis-NEMGs showed greater differential expression compared to other NEMGs and (2) other NEMGs showed a trend towards significantly decreased expression if their expression levels correlated more highly with the subset of 50 cis-NEMGs. These 50 cis-NEMGs, which are differentially expressed and associated with mapped T2D disease loci, encode proteins acting within key mitochondrial pathways, including some of current therapeutic interest such as the metabolism of branched-chain amino acids, GABA and biotin.

SPOCK1 induces adipose tissue maturation: New insights into the function of SPOCK1 in metabolism

SPOCK1 is a calcium-binding matricellular proteoglycan that has been extensively studied in several cancer cells. Previously, we generated a mouse line overexpressing SPOCK1 (Spock1-Tg mouse) and showed that SPOCK1 might play an important role in drug-induced gingival overgrowth, indicating that it possesses physiological functions in non-cancer diseases as well. Although SPOCK1 was reported to be secreted from human adipocytes, its role in adipocyte physiology has not been addressed yet. In this study, SPOCK1 protein expression was confirmed in pancreas, adipose tissues, spleen, and liver of normal diet (ND)-fed mice. Interestingly, SPOCK1 was up-regulated in the pancreas and adipose tissues of the high-fat diet (HFD)-fed mice. Spock1-Tg mice fed with ND showed increased maturation in epididymal and inguinal adipose tissues. In addition, Spock1 overexpression strongly decreased expression of UCP-1 in adipose tissues, suggesting that SPOCK1 might regulate thermogenic function through suppression of UCP-1 expression. Finally, exogenous SPOCK1 treatment directly accelerated the differentiation of 3T3-L1 adipocytes, accompanied by the up-regulation of adipocyte differentiation-related gene expression. In conclusion, we demonstrated for the first time that SPOCK1 induced adipocyte differentiation via the up-regulation of adipogenesis-related genes.

Sea buckthorn (Hippophae rhamnoides L.) oil enhances proliferation, adipocytes differentiation and insulin sensitivity in 3T3-L1 cells

The objective of this study is to investigate the effects of sea buckthorn oil (SBO) on proliferation, adipogenic differentiation and insulin sensitivity of 3T3-L1 cells. Results showed that SBO increased cell proliferation ability, accompanied by up-regulated proliferating cell nuclear antigen content (p < 0.05) and p38 activity (p < 0.05). SBO also promoted adipogenesis and enhanced adipogenic transcriptional factors expression. Mitochondrial biogenesis related gene expressions were elevated in SBO treated cells (p < 0.05). Of note, SBO also increased glucose uptake and glucose transporter 4 abundance (p < 0.05). Cells treated with SBO exhibited greater phosphorylated insulin receptor substrate 1 (p < 0.05), phosphorylated-Akt (p < 0.05) and phosphorylated AMP-activated protein kinase (p < 0.01) contents. When taken together, these results suggest that SBO promotes 3T3-L1 cells proliferation, adipogenesis and insulin sensitivity.