Time course of high-fat diet-induced reductions in adipose tissue mitochondrial proteins: potential mechanisms and the relationship to glucose intolerance

New insights into the role of mitochondrial dynamics in oxidative stress-induced diseases

The accumulation of excess reactive oxygen species (ROS) can lead to oxidative stress (OS), which can induce gene mutations, protein denaturation, and lipid peroxidation directly or indirectly. The expression is reduced ATP level in cells, increased cytoplasmic Ca2+, inflammation, and so on. Consequently, ROS are recognized as significant risk factors for human aging and various diseases, including diabetes, cardiovascular diseases, and neurodegenerative diseases. Mitochondria are involved in the production of ROS through the respiratory chain. Abnormal mitochondrial characteristics, including mitochondrial OS, mitochondrial fission, mitochondrial fusion, and mitophagy, play an important role in various tissues. However, previous excellent reviews focused on OS-induced diseases. In this review, we focus on the latest progress of OS-induced mitochondrial dynamics, discuss OS-induced mitochondrial damage-related diseases, and summarize the OS-induced mitochondrial dynamics-related signaling pathways. Additionally, it elaborates on potential therapeutic methods aimed at preventing oxidative stress from further exacerbating mitochondrial disorders.

Dysfunction of the Brown Adipose Organ in HFD-Obese Rats and Effect of Tart Cherry Supplementation

Obesity has a great impact on adipose tissue biology, based on its function as a master regulator of energy balance. Brown adipose tissue (BAT) undergoes remodeling, and its activity declines in obese subjects due to a whitening process. The anti-obesity properties of fruit extracts have been reported. The effects of tart cherry against oxidative stress, inflammation, and the whitening process in the BAT of obese rats were investigated. Intrascapular BAT (iBAT) alterations and effects of Prunus cerasus L. were debated in rats fed for 17 weeks with a high-fat diet (DIO), in DIO supplemented with seed powder (DS), and with seed powder plus the juice (DJS) of tart cherry compared to CHOW rats fed with a normo-caloric diet. iBAT histologic observations revealed a whitening process in DIO rats that was reduced in the DS and DJS groups. A modulation of uncoupling protein-1 (UCP-1) protein and gene expression specifically were detected in the obese phenotype. An upregulation of UCP-1 and related thermogenic genes after tart cherry intake was detected compared to the DIO group. Metabolic adjustment, endoplasmic reticulum stress, protein carbonylation, and the inflammatory microenvironment in the iBAT were reported in DIO rats. The analysis demonstrated an iBAT modulation that tart cherry promoted. In addition to our previous results, these data confirm the protective impact of tart cherry consumption on obesity.

Pennogenin 3-O-β-Chacotrioside Attenuates Hypertrophied Lipid Accumulation by Enhancing Mitochondrial Oxidative Capacity

Excessive lipid accumulation in adipocytes is a primary contributor to the development of metabolic disorders, including obesity. The consumption of bioactive compounds derived from natural sources has been recognized as being safe and effective in preventing and alleviating obesity. Therefore, we aimed to explore the antilipidemic effects of pennogenin 3-O-β-chacotrioside (P3C), a steroid glycoside, on hypertrophied 3T3-L1 adipocytes. Oil Red O and Nile red staining demonstrated a P3C-induced reduction in lipid droplet accumulation. Additionally, the increased expression of adipogenic and lipogenic factors, including PPARγ and C/EBPα, during the differentiation process was significantly decreased by P3C treatment at both the protein and mRNA levels. Furthermore, P3C treatment upregulated the expression of fatty acid oxidation-related genes such as PGC1α and CPT1a. Moreover, mitochondrial respiration and ATP generation increased following P3C treatment, as determined using the Seahorse XF analyzer. P3C treatment also increased the protein expression of mitochondrial oxidative phosphorylation in hypertrophied adipocytes. Our findings suggest that P3C could serve as a natural lipid-lowering agent, reducing lipogenesis and enhancing mitochondrial oxidative capacity. Therefore, P3C may be a promising candidate as a therapeutic agent for obesity-related diseases.

The Emerging Importance of Mitochondria in White Adipocytes: Neither Last nor Least

The growing recognition of mitochondria's crucial role in the regulation of white adipose tissue remodeling and energy balance underscores its significance. The marked metabolic diversity of mitochondria provides the molecular and cellular foundation for enabling adipose tissue plasticity in response to various metabolic cues. Effective control of mitochondrial function at the cellular level, not only in thermogenic brown and beige adipocytes but also in energy-storing white adipocytes, exerts a profound influence on adipose homeostasis. Furthermore, mitochondria play a pivotal role in intercellular communication within adipose tissue via production of metabolites with signaling properties. A more comprehensive understanding of mitochondrial regulation within white adipocytes will empower the development of targeted and efficacious strategies to enhance adipose function, leading to advancements in overall metabolic health.

Impact of GLP-1 receptor agonist versus omega-3 fatty acids supplement on obesity-induced alterations of mitochondrial respiration

OBJECTIVE

To compare administration of the glucagon-like peptide-1 (GLP-1) analogue, exenatide, versus dietary supplementation with the omega-3 fatty acid-rich Calanus oil on obesity-induced alterations in mitochondrial respiration.

METHODS

Six-week-old female C57BL/6JOlaHSD mice were given high fat diet (HFD, 45% energy from fat) for 12 weeks to induce obesity. Thereafter, they were divided in three groups where one received exenatide (10 μg/kg/day) via subcutaneously implanted mini-osmotic pumps, a second group received 2% Calanus oil as dietary supplement, while the third group received HFD without any treatment. Animals were sacrificed after 8 weeks of treatment and tissues (skeletal muscle, liver, and white adipose tissue) were collected for measurement of mitochondrial respiratory activity by high-resolution respirometry, using an Oroboros Oxygraph-2k (Oroboros instruments, Innsbruck, Austria).

RESULTS

It was found that high-fat feeding led to a marked reduction of mitochondrial respiration in adipose tissue during all three states investigated - LEAK, OXPHOS and ETS. This response was to some extent attenuated by exenatide treatment, but not with Calanus oil treatment. High-fat feeding had no major effect on hepatic mitochondrial respiration, but exenatide treatment resulted in a significant increase in the various respiratory states in liver. Mitochondrial respiration in skeletal muscle was not significantly influenced by high-fat diet or any of the treatments. The precise evaluation of mitochondrial respiration considering absolute oxygen flux and ratios to assess flux control efficiency avoided misinterpretation of the results.

CONCLUSIONS

Exenatide increased hepatic mitochondrial respiration in high-fat fed mice, but no clear beneficial effect was observed in skeletal muscle or fat tissue. Calanus oil did not negatively affect respiratory activity in these tissues, which maintains its potential as a dietary supplement, due to its previously reported benefits on cardiac function.

Bimatoprost promotes satiety and attenuates body weight gain in rats fed standard or obesity-promoting diets

Bimatoprost is a synthetic prostamide F_2α analog that down-regulates adipogenesis in vitro. This effect has been attributed to participation in a negative feedback loop that regulates anandamide-induced adipogenesis. A follow-on investigation has now been conducted into the broader metabolic effects of bimatoprost using rats under both normal state and obesity-inducing conditions. Chronic bimatoprost administration attenuated weight gain in a dose dependent-manner in rats fed either standard [max effect -7%] or obesity-promoting diets [max effect -23%] over a 9-10 week period. Consistent with these findings, bimatoprost promoted satiety as measured by decreased food intake [max effect, -7%], gastric emptying [max effect, -33-50%] and decreased circulating concentrations of the gut hormones, ghrelin and GLP-1 [max effect, -33-50%]. Additionally, subcutaneous, and visceral fat mass were distinctly affected by treatment [-30% diet independent]. Taken together, these results suggest that bimatoprost regulates energy homeostasis through promoting satiety and a decrease in food intake. These newly reported activities of bimatoprost reveal an additional method of metabolic disease intervention for potential therapeutic exploitation.

The Efficacy of HGF/VEGF Gene Therapy for Limb Ischemia in Mice with Impaired Glucose Tolerance: Shift from Angiogenesis to Axonal Growth and Oxidative Potential in Skeletal Muscle

BACKGROUND

Combined non-viral gene therapy (GT) of ischemia and cardiovascular disease is a promising tool for potential clinical translation. In previous studies our group has developed combined gene therapy by vascular endothelial growth factor 165 (VEGF165) + hepatocyte growth factor (HGF). Our recent works have demonstrated that a bicistronic pDNA that carries both human HGF and VEGF165 coding sequences has a potential for clinical application in peripheral artery disease (PAD). The present study aimed to test HGF/VEGF combined plasmid efficacy in ischemic skeletal muscle comorbid with predominant complications of PAD-impaired glucose tolerance and type 2 diabetes mellitus (T2DM).

METHODS

Male C57BL mice were housed on low-fat (LFD) or high-fat diet (HFD) for 10 weeks and metabolic parameters including FBG level, ITT, and GTT were evaluated. Hindlimb ischemia induction and plasmid administration were performed at 10 weeks with 3 weeks for post-surgical follow-up. Limb blood flow was assessed by laser Doppler scanning at 7, 14, and 21 days after ischemia induction. The necrotic area of m.tibialis anterior, macrophage infiltration, angio- and neuritogenesis were evaluated in tissue sections. The mitochondrial status of skeletal muscle (total mitochondria content, ETC proteins content) was assessed by Western blotting of muscle lysates.

RESULTS

At 10 weeks, the HFD group demonstrated impaired glucose tolerance in comparison with the LFD group. HGF/VEGF plasmid injection aggravated glucose intolerance in HFD conditions. Blood flow recovery was not changed by HGF/VEGF plasmid injection either in LFD or HFD conditions. GT in LFD, but not in HFD conditions, enlarged the necrotic area and CD68+ cells infiltration. However, HGF/VEGF plasmid enhanced neuritogenesis and enlarged NF200+ area on muscle sections. In HFD conditions, HGF/VEGF plasmid injection significantly increased mitochondria content and ETC proteins content.

CONCLUSIONS

The current study demonstrated a significant role of dietary conditions in pre-clinical testing of non-viral GT drugs. HGF/VEGF combined plasmid demonstrated a novel aspect of potential participation in ischemic skeletal muscle regeneration, through regulation of innervation and bioenergetics of muscle. The obtained results made HGF/VEGF combined plasmid a very promising tool for PAD therapy in impaired glucose tolerance conditions.

Mitochondrial Homeostasis in Obesity-related Hypertriglyceridemia

CONTEXT

The prevalence of obesity and hypertriglyceridemia is an alarming worldwide health issue. Mitochondria play a central role in these disorders as they control cell metabolism.

OBJECTIVE

The aim of the present study was to characterize mitochondrial homeostasis in subcutaneous and visceral adipose tissue (SAT and VAT) in grade III obese patients with and without hypertriglyceridemia. Moreover, this study presents the evaluation of mitochondrial fitness as a marker for hypertriglyceridemia improvement.

PATIENTS

Eight control and 12 hypertriglyceridemic (HTG) grade III obese subjects undergoing bariatric surgery were included.

MAIN OUTCOME MEASURES

Anthropometric and biochemical data were obtained before and 3 months after surgery. Mitochondrial homeostasis was evaluated by mitochondrial DNA (mtDNA), gene expression and protein abundance in SAT and VAT.

RESULTS

Mitophagy-related gene expression was increased in HTG SAT and VAT, while mitochondrial marker gene expression and mtDNA were decreased, indicating an altered mitochondrial homeostasis in HTG. Mitophagy protein abundance was increased in VAT of those subjects that did not improve their levels of triglycerides after bariatric surgery, whereas mitochondrial protein was decreased in the same tissue. Indeed, triglyceride levels positively correlated with mitophagy-related genes and negatively with mitochondrial content markers. Moreover, mitochondria content and mitophagy markers seem to be significant predictors of hypertriglyceridemia and hypertriglyceridemia remission.

CONCLUSIONS

Mitochondrial homeostasis of adipose tissue is altered in hypertriglyceridemic patients. At the protein level, mitochondria content and mitophagy are potential markers of hypertriglyceridemia remission in obese patients after bariatric surgery. These results may contribute to the implementation of a clinical approach for personalized medicine.

MPST sulfurtransferase maintains mitochondrial protein import and cellular bioenergetics to attenuate obesity

Given the clinical, economic, and societal impact of obesity, unraveling the mechanisms of adipose tissue expansion remains of fundamental significance. We previously showed that white adipose tissue (WAT) levels of 3-mercaptopyruvate sulfurtransferase (MPST), a mitochondrial cysteine-catabolizing enzyme that yields pyruvate and sulfide species, are downregulated in obesity. Here, we report that Mpst deletion results in fat accumulation in mice fed a high-fat diet (HFD) through transcriptional and metabolic maladaptation. Mpst-deficient mice on HFD exhibit increased body weight and inguinal WAT mass, reduced metabolic rate, and impaired glucose/insulin tolerance. At the molecular level, Mpst ablation activates HIF1α, downregulates subunits of the translocase of outer/inner membrane (TIM/TOM) complex, and impairs mitochondrial protein import. MPST deficiency suppresses the TCA cycle, oxidative phosphorylation, and fatty acid oxidation, enhancing lipid accumulation. Sulfide donor administration to obese mice reverses the HFD-induced changes. These findings reveal the significance of MPST for white adipose tissue biology and metabolic health and identify a potential new therapeutic target for obesity.

Lipidome Alterations with Exercise Among People With and Without HIV: An Exploratory Study

Age-related comorbidities and physical function impairments in aging people with HIV (PWH) can be improved through exercise interventions. The mechanisms underlying these improvements, including lipidomic changes, are unknown. Sedentary adults (50-75 years old) with or without HIV participated in supervised endurance/resistance exercise for 24 weeks. Plasma lipid concentrations (∼1,200 lipid species from 13 lipid classes) at baseline and week 24 were measured by mass spectrometry. Given multiple comparisons, unadjusted and Benjamini-Hochberg corrected p values are reported. Analyses are considered exploratory. Twenty-five PWH and 24 controls had paired samples at baseline and week 24. The change in total triacylglycerol (TAG) concentrations after exercise intervention differed between groups (unadj-p = 0.006, adj-p = 0.078) with concentrations increasing among controls, but not among PWH. Changes in concentrations of TAG species composed of long-chain fatty acids differed between groups (unadj-p < 0.04) with increases among controls, but not among PWH. Changes in total diacylglycerol (DAG) concentration from baseline to week 24 differed between groups (unadj-p = 0.03, adj-p = 0.2) with an increase in PWH and a nonsignificant decrease in controls. Baseline to week 24 changes in DAGs composed of palmitic acid (16:0), palmitoleic acid (16:1), and stearic acid (18:0) differed by serostatus (unadj-p = 0.009-0.03; adj-p 0.10-0.12), with nonsignificant increases and decreases in concentrations in PWH and controls, respectively. Concentrations of individual lysophosphatidylcholine (LPC) and ceramide (CER) species also differed by HIV serostatus (unadj-p < = 0.05). Although exploratory, the effects of exercise on the lipidome may differ among people with and without HIV, potentially due to underlying alterations in lipid processing and fatty acid oxidation in PWH. Clinical Trials NCT02404792.

Healthy versus Unhealthy Adipose Tissue Expansion: the Role of Exercise

Although the hallmark of obesity is the expansion of adipose tissue, not all adipose tissue expansion is the same. Expansion of healthy adipose tissue is accompanied by adequate capillary angiogenesis and mitochondria-centered metabolic integrity, whereas expansion of unhealthy adipose tissue is associated with capillary and mitochondrial derangement, resulting in deposition of immune cells (M1-stage macrophages) and excess production of pro-inflammatory cytokines. Accumulation of these dysfunctional adipose tissues has been linked to the development of obesity comorbidities, such as type 2 diabetes, hypertension, dyslipidemia, and cardiovascular disease, which are leading causes of human mortality and morbidity in modern society. Mechanistically, vascular rarefaction and mitochondrial incompetency (for example, low mitochondrial content, fragmented mitochondria, defective mitochondrial respiratory function, and excess production of mitochondrial reactive oxygen species) are frequently observed in adipose tissue of obese patients. Recent studies have demonstrated that exercise is a potent behavioral intervention for preventing and reducing obesity and other metabolic diseases. However, our understanding of potential cellular mechanisms of exercise, which promote healthy adipose tissue expansion, is at the beginning stage. In this review, we hypothesize that exercise can induce unique physiological stimuli that can alter angiogenesis and mitochondrial remodeling in adipose tissues and ultimately promote the development and progression of healthy adipogenesis. We summarize recent reports on how regular exercise can impose differential processes that lead to the formation of either healthy or unhealthy adipose tissue and discuss key knowledge gaps that warrant future research.

The Influence of Obesity and Weight Loss on the Bioregulation of Innate/Inflammatory Responses: Macrophages and Immunometabolism

Obesity is characterized by low-grade inflammation and more susceptibility to infection, particularly viral infections, as clearly demonstrated in COVID-19. In this context, immunometabolism and metabolic flexibility of macrophages play an important role. Since inflammation is an inherent part of the innate response, strategies for decreasing the inflammatory response must avoid immunocompromise the innate defenses against pathogen challenges. The concept “bioregulation of inflammatory/innate responses” was coined in the context of the effects of exercise on these responses, implying a reduction in excessive inflammatory response, together with the preservation or stimulation of the innate response, with good transitions between pro- and anti-inflammatory macrophages adapted to each individual’s inflammatory set-point in inflammatory diseases, particularly in obesity. The question now is whether these responses can be obtained in the context of weight loss by dietary interventions (low-fat diet or abandonment of the high-fat diet) in the absence of exercise, which can be especially relevant for obese individuals with difficulties exercising such as those suffering from persistent COVID-19. Results from recent studies are controversial and do not point to a clear anti-inflammatory effect of these dietary interventions, particularly in the adipose tissue. Further research focusing on the innate response is also necessary.

Correlation between body mass index and efficacy of anti-PD-1 inhibitor in patients with non-small cell lung cancer

BACKGROUND

High body mass index (BMI) has been reported to be associated with the efficacy of immune checkpoint inhibitors in patients with advanced non-small cell lung cancer (NSCLC), but the association between BMI and efficacy of anti-PD-1 inhibitors remains controversial. The present study investigated this association in patients with advanced NSCLC.

METHODS

We retrospectively reviewed patients with advanced NSCLC who received PD-1 inhibitors at the National Cancer Center Hospital between January 2016 and December 2018. The efficacy of PD-1 inhibitors (progression-free survival [PFS], overall survival [OS], and response rate) was compared between overweight (BMI ≥25 kg/m²) and non-overweight (BMI <25 kg/m²) groups. Cohort 1 included patients with high PD-L1 expression who were treated with pembrolizumab as first-line therapy; Cohort 2 included patients treated with nivolumab/pembrolizumab as second- or later-line treatment.

RESULTS

A total of 324 patients were included in this study and the median BMI (IQR) was 21.4 (19.5-23.6) kg/m2. Of the 324 patients, 279 (86.1%) and 45 (13.9%) were in the non-overweight and overweight groups, respectively. No significant differences in objective response rate (ORR), PFS, or OS were found between overweight and non-overweight patients overall (n = 324; overweight vs. non-overweight: ORR, 28.9% vs. 31.9%, respectively [p = 0.68]; PFS, 7.6 vs. 5.8 months, respectively [p = 0.43]; and OS, 17.6 vs. 15.3 months, respectively [p = 0.90]), or between overweight and non-overweight patients in Cohorts 1 and 2.

CONCLUSIONS

No significant differences in the efficacy of PD-1 inhibitors were observed between overweight and non-overweight patients.

Clinically relevant prognostic and predictive markers for immune-checkpoint-inhibitor (ICI) therapy in non-small cell lung cancer (NSCLC)

BACKGROUND

Immune checkpoint inhibitors (ICI) either alone or in combination with chemotherapy have expanded our choice of agents for the palliative treatment of non-small cell lung cancer (NSCLC) patients. Unfortunately, not all patients will experience favorable response to treatment with ICI and may even suffer from severe side effects. Therefore, prognostic and predictive markers, beyond programmed death ligand 1 (PD-L1) expression status, are of utmost importance for decision making in the palliative treatment. This review focuses on clinical, laboratory and genetic markers, most of them easily to obtain in the daily clinical practice.

RESULTS

Recently, a number of prognostic and predictive factors in association to palliative ICI therapy have been described in NSCLC. Besides biometric parameters and clinical characteristics of the tumor, there are useful markers from routine blood sampling as well as innovative soluble genetic markers which can be determined before and during ICI treatment. Additionally, the level of evidence is noted.

CONCLUSIONS

These factors can be helpful to predict patients' outcome and tumor response to ICI. They should be implemented prospectively in ICI based clinical trials to develop reliable algorithms for palliative NSCLC treatment.

Microbiota-Mitochondria Inter-Talk: A Potential Therapeutic Strategy in Obesity and Type 2 Diabetes

The rising prevalence of obesity and type 2 diabetes (T2D) is a growing concern worldwide. New discoveries in the field of metagenomics and clinical research have revealed that the gut microbiota plays a key role in these metabolic disorders. The mechanisms regulating microbiota composition are multifactorial and include resistance to stress, presence of pathogens, diet, cultural habits and general health conditions. Recent evidence has shed light on the influence of microbiota quality and diversity on mitochondrial functions. Of note, the gut microbiota has been shown to regulate crucial transcription factors, coactivators, as well as enzymes implicated in mitochondrial biogenesis and metabolism. Moreover, microbiota metabolites seem to interfere with mitochondrial oxidative/nitrosative stress and autophagosome formation, thus regulating the activation of the inflammasome and the production of inflammatory cytokines, key players in chronic metabolic disorders. This review focuses on the association between intestinal microbiota and mitochondrial function and examines the mechanisms that may be the key to their use as potential therapeutic strategies in obesity and T2D management.

Long-term, high-fat feeding exacerbates short-term increases in adipose mitochondrial reactive oxygen species, without impairing mitochondrial respiration

White adipose tissue (WAT) dysfunction in obesity is implicated in the onset of whole body insulin resistance. Alterations in mitochondrial bioenergetics, namely impaired mitochondrial respiration and increased mitochondrial reactive oxygen species (mtROS) production, have been suggested to contribute to this metabolic dysregulation. However, techniques investigating mitochondrial function are classically normalized to tissue weight, which may be confounding when considering obesity-related adipocyte hypertrophy. Furthermore, the effect of long-term high-fat diet (HFD) on mtROS in WAT has yet to be elucidated. Therefore, we sought to determine the HFD-mediated temporal changes in mitochondrial respiration and mtROS emission in WAT. C57BL/6N mice received low-fat diet or HFD for 1 or 8 wk and changes in inguinal WAT (iWAT) and epididymal WAT (eWAT) were assessed. While tissue weight-normalized mitochondrial respiration was reduced in iWAT following 8-wk HFD-feeding, this effect was mitigated when adipocyte cell size and/or number were considered. These data suggest HFD does not impair mitochondrial respiratory capacity per adipocyte within WAT. In support of this assertion, within eWAT compensatory increases in lipid-supported and maximal succinate-supported respiration occurred at 8 wk despite cell hypertrophy and increases in WAT inflammation. Although these data suggest impairments in mitochondrial respiration do not contribute to HFD-mediated WAT phenotype, lipid-supported mtROS emission increased following 1-wk HFD in eWAT, while both lipid and carbohydrate-supported mtROS were increased at 8 wk in both depots. Combined, these data establish that while HFD does not impair adipocyte mitochondrial respiratory capacity, increased mtROS is an enduring physiological occurrence within WAT in HFD-induced obesity.

Heat shock protein 60 (HSP60) modulates adiponectin signaling by stabilizing adiponectin receptor

Adiponectin, an adipokine produced and secreted by adipocytes, is involved in regulating the development and progression of insulin resistance, diabetes, and diabetic complications. Heat shock protein 60 (HSP60) is a molecular chaperone, most commonly presenting in mitochondria and participating in the maintenance of protein homeostasis. Accumulating studies have demonstrated that the elevated circulating HSP60 and the decreased intracellular HSP60 are closely associated with diabetic complications such as diabetic cardiomyopathy. However, the underlying mechanism remains poorly understood. In the present study, we reported that HSP60 interacted directly with adiponectin receptors. Its abundance was positively associated with adiponectin action. Furthermore, HSP60 depletion markedly mitigated the protective impacts of adiponectin on high glucose-induced oxidative stress and cell apoptosis in rat cardiac H9c2 cells. In addition, HSP60 knockdown significantly enhanced proteasome activity leading to the degradation of adiponectin receptor 1. Taken together, we showed for the first time that HSP60 interacted with adiponectin receptors and mediated adiponectin signaling through stabilizing adiponectin receptor. This in vitro study also provides an alternative explanation for mechanism by which adiponectin exerts its action.

Proteomic and Metabolite Profiling Reveals Profound Structural and Metabolic Reorganization of Adipocyte Mitochondria in Obesity

OBJECTIVE

Previous studies have revealed decreased mitochondrial respiration in adipocytes of obese mice. This study aimed to identify the molecular underpinnings of altered mitochondrial metabolism in adipocytes.

METHODS

Untargeted proteomics of mitochondria isolated from adipocytes and metabolite profiling of adipose tissues were conducted in diet-induced obese (DIO) and lean mice. Subcutaneous and intra-abdominal adipose tissues were studied to depict depot-specific alterations.

RESULTS

In subcutaneous adipocytes of DIO mice, changes in proteins related to mitochondrial structure and function were observed. Mitochondrial proteins of the inner and outer membrane were strongly reduced, whereas proteins of key matrix metabolic pathways were increased in the obese versus lean state, as further substantiated by metabolite profiling. A pronounced decrease in the oxidative phosphorylation (OXPHOS) enzymatic equipment and cristae density of the inner membrane was identified. In intra-abdominal adipocytes, similar systematic downregulation of the OXPHOS machinery in obesity occurred, but there was no regulation of outer membrane or matrix proteins.

CONCLUSIONS

Protein components of the OXPHOS machinery are systematically downregulated in adipose tissues of DIO mice compared with lean mice. Loss of the mitochondrial OXPHOS capacity in adipocytes may aggravate the development of metabolic disease.

Canagliflozin ameliorates obesity by improving mitochondrial function and fatty acid oxidation via PPARα in vivo and in vitro

AIMS

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have been reported to significantly reduce body weight. This study investigated whether SGLT2 inhibitors directly affect adipose tissues and the underlying mechanisms in vivo and in vitro.

MAIN METHODS

Male C57BL/6 mice were fed a normal diet, high-fat diet (HFD), or HFD with canagliflozin for 14 weeks. 3T3-L1 adipocytes were treated with canagliflozin. Metabolic parameters were measured.

KEY FINDINGS

Canagliflozin reduced body weight, fat mass, and white adipose tissue (WAT) weight and inhibited adipocyte hypertrophy. Canagliflozin improved glucose and lipid metabolic disorders induced by HFD. Furthermore, canagliflozin treatment reversed the suppressed mRNA and protein expression of PGC-1α, NRF1, tfam and CPT1b, which are markers of mitochondrial biogenesis, function and fatty acid oxidation in mice with obesity. In vitro, canagliflozin increased mitochondrial DNA to nuclear DNA and upregulated the expression of PGC-1α, NRF1, tfam, COX5b, COX8b, Atp5o, and CPT1b mRNA and PGC-1α, NRF1, tfam, COX5b, CPT1b protein in 3T3-L1 adipocytes in a dose-dependent manner, while these increases were inhibited by GW6471, a PPARα antagonist.

SIGNIFICANCE

Our study showed that canagliflozin protected against HFD-induced obesity and obesity-related metabolic disorders by improving mitochondrial function and fatty acid oxidation in adipose tissue and adipocytes. Such energy-dissipating effects of canagliflozin may be mediated by PPARα.

White adipose tissue mitochondrial metabolism in health and in obesity

White adipose tissue is one of the largest organs of the body. It plays a key role in whole-body energy status and metabolism; it not only stores excess energy but also secretes various hormones and metabolites to regulate body energy balance. Healthy adipose tissue capable of expanding is needed for metabolic well-being and to prevent accumulation of triglycerides to other organs. Mitochondria govern several important functions in the adipose tissue. We review the derangements of mitochondrial function in white adipose tissue in the obese state. Downregulation of mitochondrial function or biogenesis in the white adipose tissue is a central driver for obesity-associated metabolic diseases. Mitochondrial functions compromised in obesity include oxidative functions and renewal and enlargement of the adipose tissue through recruitment and differentiation of adipocyte progenitor cells. These changes adversely affect whole-body metabolic health. Dysfunction of the white adipose tissue mitochondria in obesity has long-term consequences for the metabolism of adipose tissue and the whole body. Understanding the pathways behind mitochondrial dysfunction may help reveal targets for pharmacological or nutritional interventions that enhance mitochondrial biogenesis or function in adipose tissue.

Electroacupuncture Regulates Inguinal White Adipose Tissue Browning by Promoting Sirtuin-1-Dependent PPARγ Deacetylation and Mitochondrial Biogenesis

BACKGROUND

Previous studies had suggested that electroacupuncture (EA) can promote white adipose tissue (WAT) browning to counter obesity. But the mechanism was still not very clear.

AIM

In this study, we aim to study the effect of EA on promoting inguinal WAT (iWAT) browning and its possible mechanism.

METHOD

Three-week-old rats were randomly divided into a normal diet (ND) group and a high-fat diet (HFD) group. After 10 weeks, the HFD rats were grouped into HFD + EA group and HFD control group. Rats in the EA group were electro-acupunctured for 4 weeks on Tianshu (ST25) acupoint under gas anesthesia with isoflurane, while the rats in HFD group were under gas anesthesia only. Body weight and cumulative food intake were monitored, and H&E staining was performed to assess adipocyte area. The effect of EA on WAT was assessed by qPCR, immunoblotting, immunoprecipitation and Co-immunoprecipitation. Mitochondria were isolated from IWAT to observe the expression of mitochondrial transcription factor A (TFAM).

RESULTS

The body weight, WAT/body weight ratio and cumulative food consumption obviously decreased (P < 0.05) in the EA group. The expressions of brown adipose tissue (BAT) markers were increased in the iWAT of EA rats. Nevertheless, the mRNA expressions of WAT genes were suppressed by 4-week EA treatment. Moreover, EA increased the protein expressions of SIRT-1, PPARγ, PGC-1α, UCP1 and PRDM16 which trigger the molecular conversion of iWAT browning. The decrease of PPARγ acetylation was also found in EA group, indicating EA could advance WAT-browning through SIRT-1 dependent PPARγ deacetylation pathway. Besides, we found that EA could activate AMPK to further regulate PGC-1α-TFAM-UCP1 pathway to induce mitochondrial biogenesis.

CONCLUSION

In conclusion, EA can remodel WAT to BAT through inducing SIRT-1 dependent PPARγ deacetylation, and regulating PGC-1α-TFAM-UCP1 pathway to induce mitochondrial biogenesis. This may be one of the mechanisms by which EA affects weight loss.

The Role of Adipose Tissue Mitochondria: Regulation of Mitochondrial Function for the Treatment of Metabolic Diseases

: Mitochondria play a key role in maintaining energy homeostasis in metabolic tissues, including adipose tissues. The two main types of adipose tissues are the white adipose tissue (WAT) and the brown adipose tissue (BAT). WAT primarily stores excess energy, whereas BAT is predominantly responsible for energy expenditure by non-shivering thermogenesis through the mitochondria. WAT in response to appropriate stimuli such as cold exposure and β-adrenergic agonist undergoes browning wherein it acts as BAT, which is characterized by the presence of a higher number of mitochondria. Mitochondrial dysfunction in adipocytes has been reported to have strong correlation with metabolic diseases, including obesity and type 2 diabetes. Dysfunction of mitochondria results in detrimental effects on adipocyte differentiation, lipid metabolism, insulin sensitivity, oxidative capacity, and thermogenesis, which consequently lead to metabolic diseases. Recent studies have shown that mitochondrial function can be improved by using thiazolidinedione, mitochondria-targeted antioxidants, and dietary natural compounds; by performing exercise; and by controlling caloric restriction, thereby maintaining the metabolic homeostasis by inducing adaptive thermogenesis of BAT and browning of WAT. In this review, we focus on and summarize the molecular regulation involved in the improvement of mitochondrial function in adipose tissues so that strategies can be developed to treat metabolic diseases.

Effects of obesity and weight loss on mitochondrial structure and function and implications for colorectal cancer risk

Colorectal cancer (CRC) is the third most common cancer globally. CRC risk is increased by obesity, and by its lifestyle determinants notably physical inactivity and poor nutrition. Obesity results in increased inflammation and oxidative stress which cause genomic damage and contribute to mitochondrial dysregulation and CRC risk. The mitochondrial dysfunction associated with obesity includes abnormal mitochondrial size, morphology and reduced autophagy, mitochondrial biogenesis and expression of key mitochondrial regulators. Although there is strong evidence that increased adiposity increases CRC risk, evidence for the effects of intentional weight loss on CRC risk is much more limited. In model systems, energy depletion leads to enhanced mitochondrial integrity, capacity, function and biogenesis but the effects of obesity and weight loss on mitochondria in the human colon are not known. We are using weight loss following bariatric surgery to investigate the effects of altered adiposity on mitochondrial structure and function in human colonocytes. In summary, there is strong and consistent evidence in model systems and more limited evidence in human subjects that over-feeding and/or obesity result in mitochondrial dysfunction and that weight loss might mitigate or reverse some of these effects.

Maturation of White Adipose Tissue Function in C57BL/6j Mice From Weaning to Young Adulthood

White adipose tissue (WAT) distribution and WAT mitochondrial function contribute to total body metabolic health throughout life. Nutritional interventions starting in the postweaning period may impact later life WAT health and function. We therefore assessed changes in mitochondrial density and function markers in WAT depots of young mice. Inguinal (ING), epididymal (EPI) and retroperitoneal (RP) WAT of 21, 42 and 98 days old C57BL/6j mice was collected. Mitochondrial density [citrate synthase (CS), mtDNA] and function [subunits of oxidative phosphorylation complexes (OXPHOS)] markers were analyzed, together with gene expression of browning markers (Ucp1, Cidea). mRNA of ING WAT of 21 and 98 old mice was sequenced to further investigate functional changes of the mitochondria and alterations in cell populations. CS levels decreased significantly over time in all depots. ING showed most pronounced changes, including significantly decreased levels of OXPHOS complex I, II, and III subunits and gene expression of Ucp1 (PN21-42 and PN42-98) and Cidea (PN42-98). White adipocyte markers were higher at PN98 in ING WAT. Analyses of RNA sequence data showed that the mitochondrial functional profile changed over time from “growth-supporting” mitochondria focused on ATP production (and dissipation), to more steady-state mitochondria with more diverse functions and higher biosynthesis. Mitochondrial density and energy metabolism markers declined in all three depots over time after weaning. This was most pronounced in ING WAT and associated with reduced browning markers, increased whitening and an altered metabolism. In particular the PN21-42 period may provide a time window to study mitochondrial adaptation and effects of nutritional exposures relevant for later life metabolic health.

Inflammation and Metabolic Complications in HIV

PURPOSE OF REVIEW

We aim to provide an in-depth review of recent literature highlighting the role of inflammation involving the adipose tissue, liver, skeletal muscles, and gastrointestinal tract in the development of metabolic complications among persons living with HIV (PLWH).

RECENT FINDINGS

Recent studies in PLWH have demonstrated a significant association between circulating inflammatory markers and development of insulin resistance and metabolic complications. In adipose tissue, pro-inflammatory cytokine expression inhibits adipocyte insulin signaling, which alters lipid and glucose homeostasis. Increased lipolysis and lipogenesis elevate levels of circulating free fatty acids and promote ectopic fat deposition in liver and skeletal muscles. This leads to lipotoxicity characterized by a pro-inflammatory response with worsening insulin resistance. Finally, HIV is associated with gastrointestinal tract inflammation and changes in the gut microbiome resulting in reduced diversity, which is an additional risk factor for diabetes. Metabolic complications in PLWH are in part due to chronic, multisite tissue inflammation resulting in dysregulation of glucose and lipid trafficking, utilization, and storage.

Ectopic lipid deposition mediates insulin resistance in adipose specific 11β-hydroxysteroid dehydrogenase type 1 transgenic mice

CONTEXT

Excessive adipose glucocorticoid action is associated with insulin resistance, but the mechanisms linking adipose glucocorticoid action to insulin resistance are still debated. We hypothesized that insulin resistance from excess glucocorticoid action may be attributed in part to increased ectopic lipid deposition in liver.

METHODS

We tested this hypothesis in the adipose specific 11β-hydroxysteroid dehydrogenase-1 (HSD11B1) transgenic mouse, an established model of adipose glucocorticoid excess. Tissue specific insulin action was assessed by hyperinsulinemic-euglycemic clamps, hepatic lipid content was measured, hepatic insulin signaling was assessed by immunoblotting. The role of hepatic lipid content was further probed by administration of the functionally liver-targeted mitochondrial uncoupler, Controlled Release Mitochondrial Protonophore (CRMP).

FINDINGS

High fat diet fed HSD11B1 transgenic mice developed more severe hepatic insulin resistance than littermate controls (endogenous suppression of hepatic glucose production was reduced by 3.8-fold, P < 0.05); this was reflected by decreased insulin-stimulated hepatic insulin receptor kinase tyrosine phosphorylation and AKT serine phosphorylation. Hepatic insulin resistance was associated with a 53% increase (P < 0.05) in hepatic triglyceride content, a 73% increase in diacylglycerol content (P < 0.01), and a 66% increase in PKCε translocation (P < 0.05). Hepatic insulin resistance was prevented with administration of CRMP by reversal of hepatic steatosis and prevention of hepatic diacylglycerol accumulation and PKCε activation.

CONCLUSIONS

These findings are consistent with excess adipose glucocorticoid activity being a predisposing factor for the development of lipid (diacylglycerol-PKCε)-induced hepatic insulin resistance.

Obesity, DNA Damage, and Development of Obesity-Related Diseases

Obesity has been recognized to increase the risk of such diseases as cardiovascular diseases, diabetes, and cancer. It indicates that obesity can impact genome stability. Oxidative stress and inflammation, commonly occurring in obesity, can induce DNA damage and inhibit DNA repair mechanisms. Accumulation of DNA damage can lead to an enhanced mutation rate and can alter gene expression resulting in disturbances in cell metabolism. Obesity-associated DNA damage can promote cancer growth by favoring cancer cell proliferation and migration, and resistance to apoptosis. Estimation of the DNA damage and/or disturbances in DNA repair could be potentially useful in the risk assessment and prevention of obesity-associated metabolic disorders as well as cancers. DNA damage in people with obesity appears to be reversible and both weight loss and improvement of dietary habits and diet composition can affect genome stability.

A multicenter study of body mass index in cancer patients treated with anti-PD-1/PD-L1 immune checkpoint inhibitors: when overweight becomes favorable

Background

Recent evidence suggested a potential correlation between overweight and the efficacy of immune checkpoint inhibitors (ICIs) in cancer patients.

Patients and methods

We conducted a retrospective study of advanced cancer patients consecutively treated with anti-PD-1/PD-L1 inhibitors, in order to compare clinical outcomes according to baseline BMI levels as primary analysis. Based on their BMI, patients were categorized into overweight/obese (≥ 25) and non-overweight (< 25). A gender analysis was also performed, using the same binomial cut-off. Further subgroup analyses were performed categorizing patients into underweight, normal weight, overweight and obese.

Results

Between September 2013 and May 2018, 976 patients were evaluated. The median age was 68 years, male/female ratio was 663/313. Primary tumors were: NSCLC (65.1%), melanoma (18.7%), renal cell carcinoma (13.8%) and others (2.4%). ECOG-PS was ≥2 in 145 patients (14.9%). PD-1/PD-L1 inhibitors were administered as first-line treatment in 26.6% of cases. Median BMI was 24.9: 492 patients (50.6%) were non-overweight, 480 patients (50.4%) were overweight/obese. 25.2% of non-overweight patients experienced irAEs of any grade, while 55.6% of overweight/obese patients (p < 0.0001). ORR was significantly higher in overweight/obese patients compared to non-overweight (p < 0.0001). Median follow-up was 17.2 months. Median TTF, PFS and OS were significantly longer for overweight/obese patients in univariate (p < 0.0001, for all the survival intervals) and multivariate models (p = 0.0009, p < 0.0001 and p < 0.0001 respectively). The significance was confirmed in both sex, except for PFS in male patients (p = 0.0668).

Conclusions

Overweight could be considered a tumorigenic immune-dysfunction that could be effectively reversed by ICIs. BMI could be a useful predictive tool in clinical practice and a stratification factor in prospective clinical trials with ICIs.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0527-y) contains supplementary material, which is available to authorized users.

Heat shock protein 72 regulates hepatic lipid accumulation

Induction of the chaperone heat shock protein 72 (HSP72) through heat treatment (HT), exercise, or overexpression improves glucose tolerance and mitochondrial function in skeletal muscle. Less is known about HSP72 function in the liver where lipid accumulation can result in insulin resistance and nonalcoholic fatty liver disease (NAFLD). The purpose of this study was 1) to determine whether weekly in vivo HT induces hepatic HSP72 and improves glucose tolerance in rats fed a high-fat diet (HFD) and 2) to determine the ability of HSP72 to protect against lipid accumulation and mitochondrial dysfunction in primary hepatocytes. Male Wistar rats were fed an HFD for 15 wk and were given weekly HT (41°C, 20 min) or sham treatments (37°C, 20 min) for the final 7 wk. Glucose tolerance and insulin sensitivity were assessed, along with HSP72 induction and triglyceride storage, in the skeletal muscle and liver. The effect of an acute loss of HSP72 in primary hepatocytes was examined via siRNA. Weekly in vivo HT improved glucose tolerance, elevated muscle and hepatic HSP72 protein content, and reduced muscle triglyceride storage. In primary hepatocytes, mitochondrial morphology was changed, and fatty acid oxidation was reduced in small interfering HSP72 (siHSP72)-treated hepatocytes. Lipid accumulation following palmitate treatment was increased in siHSP72-treated hepatocytes. These data suggest that HT may improve systemic metabolism via induction of hepatic HSP72. Additionally, acute loss of HSP72 in primary hepatocytes impacts mitochondrial health as well as fat oxidation and storage. These findings suggest therapies targeting HSP72 in the liver may prevent NAFLD.

Understanding mitochondrial biogenesis through energy sensing pathways and its translation in cardio-metabolic health

Mitochondria play a pivotal role in physiological energy governance. Mitochondrial biogenesis comprises growth and division of pre-existing mitochondria, triggered by environmental stressors such as endurance exercise, caloric restriction, cold exposure and oxidative stress. For normal physiology, balance between energy intake, storage and expenditure is of utmost important for the coordinated regulation of energy homeostasis. In contrast, abnormalities in these regulations render the individual susceptible to cardiometabolic disorders. This review provides a comprehensive coverage and understanding on mitochondrial biogenesis achieved through energy-sensing pathways. This includes the complex coordination of nuclear, cytosolic and mitochondrial events involving energy sensors, transcription factors, coactivators and regulators. It focuses on the importance of mitochondrial biogenesis in cardiometabolic health. Lastly, converging on the benefits of caloric restriction and endurance exercise in achieving cardiometabolic health.

Mitochondrial Chaperones in the Brain: Safeguarding Brain Health and Metabolism?

The brain orchestrates organ function and regulates whole body metabolism by the concerted action of neurons and glia cells in the central nervous system. To do so, the brain has tremendously high energy consumption and relies mainly on glucose utilization and mitochondrial function in order to exert its function. As a consequence of high rate metabolism, mitochondria in the brain accumulate errors over time, such as mitochondrial DNA (mtDNA) mutations, reactive oxygen species, and misfolded and aggregated proteins. Thus, mitochondria need to employ specific mechanisms to avoid or ameliorate the rise of damaged proteins that contribute to aberrant mitochondrial function and oxidative stress. To maintain mitochondria homeostasis (mitostasis), cells evolved molecular chaperones that shuttle, refold, or in coordination with proteolytic systems, help to maintain a low steady-state level of misfolded/aggregated proteins. Their importance is exemplified by the occurrence of various brain diseases which exhibit reduced action of chaperones. Chaperone loss (expression and/or function) has been observed during aging, metabolic diseases such as type 2 diabetes and in neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD) or even Huntington's (HD) diseases, where the accumulation of damage proteins is evidenced. Within this perspective, we propose that proper brain function is maintained by the joint action of mitochondrial chaperones to ensure and maintain mitostasis contributing to brain health, and that upon failure, alter brain function which can cause metabolic diseases.

Role of Mitochondrial Complex IV in Age-Dependent Obesity

Aging is associated with progressive white adipose tissue (WAT) enlargement initiated early in life, but the molecular mechanisms involved remain unknown. Here we show that mitochondrial complex IV (CIV) activity and assembly are already repressed in white adipocytes of middle-aged mice and involve a HIF1A-dependent decline of essential CIV components such as COX5B. At the molecular level, HIF1A binds to the Cox5b proximal promoter and represses its expression. Silencing of Cox5b decreased fatty acid oxidation and promoted intracellular lipid accumulation. Moreover, local in vivo Cox5b silencing in WAT of young mice increased the size of adipocytes, whereas restoration of COX5B expression in aging mice counteracted adipocyte enlargement. An age-dependent reduction in COX5B gene expression was also found in human visceral adipose tissue. Collectively, our findings establish a pivotal role for CIV dysfunction in progressive white adipocyte enlargement during aging, which can be restored to alleviate age-dependent WAT expansion.

Physical exercise remodels visceral adipose tissue and mitochondrial lipid metabolism in rats fed a high-fat diet

We aimed to investigate the effects of two physical exercise models, voluntary physical activity (VPA) and endurance training (ET) as preventive and therapeutic strategies, respectively, on lipid accumulation regulators and mitochondrial content in VAT of rats fed a high-fat diet (HFD). Sprague-Dawley rats (6 weeks old, n=60) were assigned into sedentary and VPA groups fed isoenergetic diets: standard (S, 35 kcal% fat) or HFD (71 kcal% fat). The VPA groups had free access to wheel running during the entire protocol. After 9 weeks, half of the sedentary animals were exercised on a treadmill while maintaining the dietary treatments. The HFD induced no changes in plasma non-esterified fatty acids (NEFA) and glycerol levels and decreased oxidative phosphorylation (OXPHOS) subunit IV and increased truncated/full-length sterol regulatory element-binding transcription factor 1c (SREBP1c) ratio in epididymal white adipose tissue (eWAT). VPA decreased plasma glycerol levels, aquaglyceroporin 7 (AQP7) and increased subunit I of cytochrome c oxidase (COX) protein, in standard diet fed animals. Eight weeks of ET decreased body weight, visceral adiposity and adipocyte size and plasma NEFA and glycerol levels, as well as AQP7 protein expression in eWAT. ET increased fatty acid translocase (FAT/CD36), mitochondrial content of complexes IV and V subunits, mitochondrial biogenesis and dynamic (mitofusins and optic atrophy 1)-related proteins. Moreover, lipogenesis-related markers (SREBP1c and acetyl CoA carboxylase) were reduced after 8 weeks of ET. In conclusion, ET-induced alterations reflect a positive effect on mitochondrial function and the overall VAT metabolism of HFD-induced obese rats.

Adipose Tissue in HIV Infection

HIV infection and antiretroviral therapy (ART) treatment exert diverse effects on adipocytes and stromal-vascular fraction cells, leading to changes in adipose tissue quantity, distribution, and energy storage. A HIV-associated lipodystrophic condition was recognized early in the epidemic, characterized by clinically apparent changes in subcutaneous, visceral, and dorsocervical adipose depots. Underlying these changes is altered adipose tissue morphology and expression of genes central to adipocyte maturation, regulation, metabolism, and cytokine signaling. HIV viral proteins persist in circulation and locally within adipose tissue despite suppression of plasma viremia on ART, and exposure to these proteins impairs preadipocyte maturation and reduces adipocyte expression of peroxisome proliferator-activated receptor gamma (PPAR-γ) and other genes involved in cell regulation. Several early nucleoside reverse transcriptase inhibitor and protease inhibitor antiretroviral drugs demonstrated substantial adipocyte toxicity, including reduced mitochondrial DNA content and respiratory chain enzymes, reduced PPAR-γ and other regulatory gene expression, and increased proinflammatory cytokine production. Newer-generation agents, such as integrase inhibitors, appear to have fewer adverse effects. HIV infection also alters the balance of CD4+ and CD8+ T cells in adipose tissue, with effects on macrophage activation and local inflammation, while the presence of latently infected CD4+ T cells in adipose tissue may constitute a protected viral reservoir. This review provides a synthesis of the literature on how HIV virus, ART treatment, and host characteristics interact to affect adipose tissue distribution, immunology, and contribution to metabolic health, and adipocyte maturation, cellular regulation, and energy storage. © 2017 American Physiological Society. Compr Physiol 7:1339-1357, 2017.

A fish oil diet induces mitochondrial uncoupling and mitochondrial unfolded protein response in epididymal white adipose tissue of mice

White adipose tissue (WAT) mitochondrial dysfunction is linked to the pathogenesis of obesity driven insulin resistance. Dietary conditions that alter fat mass are known to affect white adipocyte mitochondrial function, however, the impact of high calorie diets on white adipocyte mitochondria is not fully understood. The aim of this study is to assess the effect of a diet rich in saturated or polyunsaturated fat on mitochondrial unfolded protein response (UPR^mt), a retrograde signaling response that maintains mitochondrial homeostasis, in epididymal WAT (eWAT). Mice were fed a low fat diet (LFD), saturated fat diet (SFD) or fish oil (unsaturated fat diet, UFD) and assessed changes in eWAT mitochondria. Compared to mice fed a LFD, SFD-fed mice have reduced mitochondrial biogenesis markers, mitochondrial fatty acid oxidation enzymes and TCA cycle enzymes, suggesting an impaired mitochondrial function that could contribute to increased fat mass. In contrast, isocaloric UFD-fed mice have increased expression of mitochondrial uncoupling protein 1 (UCP1) and peroxisomal fatty acid oxidation enzymes suggesting that elevated mitochondrial uncoupling and peroxisomal fatty acid oxidation could contribute to the reduction in fat mass. Interestingly, expression of UPR^mt-associated proteins caseinolytic peptidase (ClpP) and heat shock protein 60 (Hsp60) are induced by UFD, whereas SFD reduced the expression of ClpP. Based on our data, we propose that induction of UPR^mt helps to preserve a functional mitochondria and efficient utilization of fat by UFD whereas a dampened UPR^mt response might impair mitochondrial function and promote fat accumulation by SFD. Thus, our findings suggest a potential role of UPR^mt in mediating the beneficial effects of fish oil.

Browning effects of (-)-epicatechin on adipocytes and white adipose tissue

In this study, we demonstrate that (-)-epicatechin (Epi), a cacao flavanol, induces the browning of fat by promoting mitochondrial biogenesis, enhancing indicators of mitochondrial structure and function, increasing fatty acid metabolism and upregulating the expression of brown adipose tissue-specific proteins in a high-fat diet mouse model of obesity and in cultured human adipocytes. Epi treatment significantly improved mitochondrial function, as measured by citrate synthase activity, and also reduced protein acetylation of total and specific regulators in both adipose tissue and human adipocytes. Browning of fat via Epi was evidenced by the increased expression of key thermogenic genes, phosphorylation of upstream regulators of fatty acid oxidation, and reduced triglyceride levels. Properly designed clinical trials are needed to explore the potential of Epi as an agent that promotes the browning of fat.

Cycling our way to fit fat

Adipose tissue is increasingly being recognized as a key regulator of whole body carbohydrate and lipid metabolism. In conditions of obesity and insulin resistance mitochondrial content in this tissue is reduced, while treatment with insulin sensitizing drugs such as thiazolidinediones (TZDs) increase mitochondrial content. It has been known for decades that exercise increases mitochondrial content in skeletal muscle and now several laboratories have shown similar effects in adipose tissue. To date the specific mechanisms mediating this effect have not been fully identified. In this review we highlight recent work suggesting that increases in lipolysis and subsequently fatty acid re‐esterification trigger the activation of 5' AMP‐activated protein kinase (AMP) activated protein kinase and ultimately the induction of mitochondrial biogenesis. It is our current view that this pathway could be a unifying mechanism linking numerous systemic factors (catecholamines, interleukin‐6, meteorin‐like) to induction of mitochondrial biogenesis following exercise.

Mitochondria-related transcriptional signature is downregulated in adipocytes in obesity: a study of young healthy MZ twins

AIMS/HYPOTHESIS

Low mitochondrial activity in adipose tissue is suggested to be an underlying factor in obesity and its metabolic complications. We aimed to find out whether mitochondrial measures are downregulated in obesity also in isolated adipocytes.

METHODS

We studied young adult monozygotic (MZ) twin pairs discordant (n = 14, intrapair difference ΔBMI ≥ 3 kg/m²) and concordant (n = 5, ΔBMI < 3 kg/m²) for BMI, identified from ten birth cohorts of 22- to 36-year-old Finnish twins. Abdominal body fat distribution (MRI), liver fat content (magnetic resonance spectroscopy), insulin sensitivity (OGTT), high-sensitivity C-reactive protein, serum lipids and adipokines were measured. Subcutaneous abdominal adipose tissue biopsies were obtained to analyse the transcriptomics patterns of the isolated adipocytes as well as of the whole adipose tissue. Mitochondrial DNA transcript levels in adipocytes were measured by quantitative real-time PCR. Western blots of oxidative phosphorylation (OXPHOS) protein levels in adipocytes were performed in obese and lean unrelated individuals.

RESULTS

The heavier (BMI 29.9 ± 1.0 kg/m²) co-twins of the discordant twin pairs had more subcutaneous, intra-abdominal and liver fat and were more insulin resistant (p < 0.01 for all measures) than the lighter (24.1 ± 0.9 kg/m²) co-twins. Altogether, 2538 genes in adipocytes and 2135 in adipose tissue were significantly differentially expressed (nominal p < 0.05) between the co-twins. Pathway analysis of these transcripts in both isolated adipocytes and adipose tissue revealed that the heavier co-twins displayed reduced expression of genes relating to mitochondrial pathways, a result that was replicated when analysing the pathways behind the most consistently downregulated genes in the heavier co-twins (in at least 12 out of 14 pairs). Consistently upregulated genes in adipocytes were related to inflammation. We confirmed that mitochondrial DNA transcript levels (12S RNA, 16S RNA, COX1, ND5, CYTB), expression of mitochondrial ribosomal protein transcripts and a major mitochondrial regulator PGC-1α (also known as PPARGC1A) were reduced in the heavier co-twins' adipocytes (p < 0.05). OXPHOS protein levels of complexes I and III in adipocytes were lower in obese than in lean individuals.

CONCLUSIONS/INTERPRETATION

Subcutaneous abdominal adipocytes in obesity show global expressional downregulation of oxidative pathways, mitochondrial transcripts and OXPHOS protein levels and upregulation of inflammatory pathways.

DATA AVAILABILITY

The datasets analysed and generated during the current study are available in the figshare repository, https://dx.doi.org/10.6084/m9.figshare.3806286.v1.

Obesity, Oxidative Stress, Adipose Tissue Dysfunction, and the Associated Health Risks: Causes and Therapeutic Strategies

Obesity is gaining acceptance as a serious primary health burden that impairs the quality of life because of its associated complications, including diabetes, cardiovascular diseases, cancer, asthma, sleep disorders, hepatic dysfunction, renal dysfunction, and infertility. It is a complex metabolic disorder with a multifactorial origin. Growing evidence suggests that oxidative stress plays a role as the critical factor linking obesity with its associated complications. Obesity per se can induce systemic oxidative stress through various biochemical mechanisms, such as superoxide generation from NADPH oxidases, oxidative phosphorylation, glyceraldehyde auto-oxidation, protein kinase C activation, and polyol and hexosamine pathways. Other factors that also contribute to oxidative stress in obesity include hyperleptinemia, low antioxidant defense, chronic inflammation, and postprandial reactive oxygen species generation. In addition, recent studies suggest that adipose tissue plays a critical role in regulating the pathophysiological mechanisms of obesity and its related co-morbidities. To establish an adequate platform for the prevention of obesity and its associated health risks, understanding the factors that contribute to the cause of obesity is necessary. The most current list of obesity determinants includes genetic factors, dietary intake, physical activity, environmental and socioeconomic factors, eating disorders, and societal influences. On the basis of the currently identified predominant determinants of obesity, a broad range of strategies have been recommended to reduce the prevalence of obesity, such as regular physical activity, ad libitum food intake limiting to certain micronutrients, increased dietary intake of fruits and vegetables, and meal replacements. This review aims to highlight recent findings regarding the role of oxidative stress in the pathogenesis of obesity and its associated risk factors, the role of dysfunctional adipose tissue in development of these risk factors, and potential strategies to regulate body weight loss/gain for better health benefits.

Reduced ATGL-mediated lipolysis attenuates β-adrenergic-induced AMPK signaling, but not the induction of PKA-targeted genes, in adipocytes and adipose tissue

5'-AMP-activated protein kinase (AMPK) is activated as a consequence of lipolysis and has been shown to play a role in regulation of adipose tissue mitochondrial content. Conversely, the inhibition of lipolysis has been reported to potentiate the induction of protein kinase A (PKA)-targeted genes involved in the regulation of oxidative metabolism. The purpose of the current study was to address these apparent discrepancies and to more fully examine the relationship between lipolysis, AMPK, and the β-adrenergic-mediated regulation of gene expression. In 3T3-L1 adipocytes, the adipose tissue triglyceride lipase (ATGL) inhibitor ATGListatin attenuated the Thr(172) phosphorylation of AMPK by a β3-adrenergic agonist (CL 316,243) independent of changes in PKA signaling. Similarly, CL 316,243-induced increases in the Thr(172) phosphorylation of AMPK were reduced in adipose tissue from whole body ATGL-deficient mice. Despite reductions in the activation of AMPK, the induction of PKA-targeted genes was intact or, in some cases, increased. Similarly, markers of mitochondrial content and respiration were increased in adipose tissue from ATGL knockout mice independent of changes in the Thr(172) phosphorylation of AMPK. Taken together, our data provide evidence that AMPK is not required for the regulation of adipose tissue oxidative capacity in conditions of reduced fatty acid release.

Mitochondria in White, Brown, and Beige Adipocytes

Mitochondria play a key role in energy metabolism in many tissues, including cardiac and skeletal muscle, brain, liver, and adipose tissue. Three types of adipose depots can be identified in mammals, commonly classified according to their colour appearance: the white (WAT), the brown (BAT), and the beige/brite/brown-like (bAT) adipose tissues. WAT is mainly involved in the storage and mobilization of energy and BAT is predominantly responsible for nonshivering thermogenesis. Recent data suggest that adipocyte mitochondria might play an important role in the development of obesity through defects in mitochondrial lipogenesis and lipolysis, regulation of adipocyte differentiation, apoptosis, production of oxygen radicals, efficiency of oxidative phosphorylation, and regulation of conversion of white adipocytes into brown-like adipocytes. This review summarizes the main characteristics of each adipose tissue subtype and describes morphological and functional modifications focusing on mitochondria and their activity in healthy and unhealthy adipocytes.