Complementary action of the PGC-1 coactivators in mitochondrial biogenesis and brown fat differentiation

Aging adipose: Depot location dictates age-associated expansion and dysfunction

Adipose tissue has a variety of diverse functions that maintain energy homeostasis. In conditions of excess energy availability, adipose tissue increases its lipid storage and communicates the nutritional abundance to various organs in the body. In conditions of energy depletion, such as fasting, cold exposure, or prolonged exercise, triglycerides stored in adipose tissue are released as free fatty acids to support the shift to catabolic metabolism. These diverse functions of storage, communication, and energy homeostasis are shared between numerous adipose depots including subcutaneous, visceral, brown, beige, intramuscular, marrow, and dermal adipose tissue. As organisms age, the cellular composition of these depots shifts to facilitate increased inflammatory cell infiltration, decreased vasculature, and increased adipocyte quantity and lipid droplet size. The purpose of this review is to give a comprehensive overview of the molecular and cellular changes that occur in various aged adipose depots and discuss their impact on physiology. The molecular signature of aged adipose leads to higher prevalence of metabolic disease in aged populations including type 2 diabetes, cardiovascular disease, Alzheimer's disease, and certain types of cancer.

Developmental exposure to DDT or DDE alters sympathetic innervation of brown adipose in adult female mice

BACKGROUND

Exposure to the bioaccumulative pesticide dichlorodiphenyltrichloroethane (DDT) and its metabolite dichlorodiphenyldichloroethylene (DDE) has been associated with increased risk of insulin resistance and obesity in humans and experimental animals. These effects appear to be mediated by reduced brown adipose tissue (BAT) thermogenesis, which is regulated by the sympathetic nervous system. Although the neurotoxicity of DDT is well-established, whether DDT alters sympathetic innervation of BAT is unknown. We hypothesized that perinatal exposure to DDT or DDE promotes thermogenic dysfunction by interfering with sympathetic regulation of BAT thermogenesis.

METHODS

Pregnant C57BL/6 J mice were administered environmentally relevant concentrations of DDTs (p,p'-DDT and o,p'-DDT) or DDE (p,p'-DDE), 1.7 mg/kg and 1.31 mg/kg, respectively, from gestational day 11.5 to postnatal day 5 by oral gavage, and longitudinal body temperature was recorded in male and female offspring. At 4 months of age, metabolic parameters were measured in female offspring via indirect calorimetry with or without the β3 adrenergic receptor agonist, CL 316,243. Immunohistochemical and neurochemical analyses of sympathetic neurons innervating BAT were evaluated.

RESULTS

We observed persistent thermogenic impairment in adult female, but not male, mice perinatally exposed to DDTs or p,p'-DDE. Perinatal DDTs exposure significantly impaired metabolism in adult female mice, an effect rescued by treatment with CL 316,243 immediately prior to calorimetry experiments. Neither DDTs nor p,p'-DDE significantly altered BAT morphology or the concentrations of norepinephrine and its metabolite DHPG in the BAT of DDTs-exposed mice. However, quantitative immunohistochemistry revealed a 20% decrease in sympathetic axons innervating BAT in adult female mice perinatally exposed to DDTs, but not p,p'-DDE, and 48 and 43% fewer synapses in stellate ganglia of mice exposed to either DDTs or p,p'-DDE, respectively, compared to control.

CONCLUSIONS

These data demonstrate that perinatal exposure to DDTs or p,p'-DDE impairs thermogenesis by interfering with patterns of connectivity in sympathetic circuits that regulate BAT.

MicroRNA-33 Inhibits Adaptive Thermogenesis and Adipose Tissue Beiging

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Mitochondrial proton leaks and uncoupling proteins

Non-shivering thermogenesis in brown adipose tissue is mediated by uncoupling protein 1 (UCP1), which provides a carefully regulated proton re-entry pathway across the mitochondrial inner membrane operating in parallel to the ATP synthase and allowing respiration, and hence thermogenesis, to be released from the constraints of respiratory control. In the 40 years since UCP1 was first described, an extensive, and frequently contradictory, literature has accumulated, focused on the acute physiological regulation of the protein by fatty acids, purine nucleotides and possible additional factors. The purpose of this review is to examine, in detail, the experimental evidence underlying these proposed mechanisms. Emphasis will be placed on the methodologies employed and their relation to the physiological constraints under which the protein functions in the intact cell. The nature of the endogenous, UCP1-independent, proton leak will also be discussed. Finally, the troubled history of the putative novel uncoupling proteins, UCP2 and UCP3, will be evaluated.

PGC-1s in the Spotlight with Parkinson's Disease

Parkinson's disease is one of the most common neurodegenerative disorders worldwide, characterized by a progressive loss of dopaminergic neurons mainly localized in the substantia nigra pars compacta. In recent years, the detailed analyses of both genetic and idiopathic forms of the disease have led to a better understanding of the molecular and cellular pathways involved in PD, pointing to the centrality of mitochondrial dysfunctions in the pathogenic process. Failure of mitochondrial quality control is now considered a hallmark of the disease. The peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1) family acts as a master regulator of mitochondrial biogenesis. Therefore, keeping PGC-1 level in a proper range is fundamental to guarantee functional neurons. Here we review the major findings that tightly bond PD and PGC-1s, raising important points that might lead to future investigations.

A cold-stress-inducible PERK/OGT axis controls TOM70-assisted mitochondrial protein import and cristae formation

The architecture of cristae provides a spatial mitochondrial organization that contains functional respiratory complexes. Several protein components including OPA1 and MICOS complex subunits organize cristae structure, but upstream regulatory mechanisms are largely unknown. Here, in vivo and in vitro reconstitution experiments show that the endoplasmic reticulum (ER) kinase PERK promotes cristae formation by increasing TOM70-assisted mitochondrial import of MIC19, a critical subunit of the MICOS complex. Cold stress or β-adrenergic stimulation activates PERK that phosphorylates O-linked N-acetylglucosamine transferase (OGT). Phosphorylated OGT glycosylates TOM70 on Ser94, enhancing MIC19 protein import into mitochondria and promoting cristae formation and respiration. In addition, PERK-activated OGT O-GlcNAcylates and attenuates CK2α activity, which mediates TOM70 Ser94 phosphorylation and decreases MIC19 mitochondrial protein import. We have identified a cold-stress inter-organelle PERK-OGT-TOM70 axis that increases cell respiration through mitochondrial protein import and subsequent cristae formation. These studies have significant implications in cellular bioenergetics and adaptations to stress conditions.

Inhibition of the sodium-glucose co-transporter SGLT2 by canagliflozin ameliorates diet-induced obesity by increasing intra-adipose sympathetic innervation

BACKGROUND AND PURPOSE

Inhibition of the sodium-glucose cotransporter 2 (SGLT2) induces hypoglycaemia by increasing urinary glucose excretion and increasing the use of fat. However, the underlying mechanism is poorly understood. This study was aimed to determine the effects of canagliflozin, a selective SGLT2 inhibitor, on diet-induced obesity and the underlying mechanism(s).

EXPERIMENTAL APPROACH

Adult C57BL/6J male mice were fed with a standard chow diet or high-fat diet supplemented with vehicle or canagliflozin. Whole body energy expenditure was monitored by metabolic cages, noradrenaline levels were measured by HPLC, glucose uptake was measured by PET/CT, and mRNA and protein expression were measured by RT-PCR and western blotting analysis.

KEY RESULTS

Mice treated with canagliflozin were resistant to high-fat diet-induced obesity and its metabolic consequences. Canagliflozin treatment decreased fat mass and increased energy expenditure via increasing thermogenesis and lipolysis in adipose tissue. Mechanistically, SGLT2 inhibition by canagliflozin elevated adipose sympathetic innervation and fat mobilization via a β₃ -adrenoceptor-cAMP-PKA signalling pathway. Finally, we showed that canagliflozin improved insulin resistance and hepatic steatosis in mice fed with a high-fat diet.

CONCLUSIONS AND IMPLICATIONS

Chronic inhibition of SGLT2 increased energy consumption by increasing intra-adipose sympathetic innervation to counteract diet-induced obesity. The present study reveals a new therapeutic function for SGLT2 inhibitors in regulating energy homeostasis.

Adipocyte integrin-linked kinase plays a key role in the development of diet-induced adipose insulin resistance in male mice

Objective

Increased deposition of the extracellular matrix (ECM) in adipose tissue (AT) during obesity contributes to insulin resistance. The integrin receptors transmit changes in the extracellular environment causing corresponding intracellular adaptations. Integrin-linked kinase (ILK), an adaptor protein, is a central hub for intracellular signaling of integrins. This study determined the role of ILK in adipose function and insulin resistance.

Methods

The pathogenic role of ILK in obesity and insulin resistance was studied in human adipose tissue and adipocyte-specific ILK-deficient mice (ILK^lox/loxAdCre). ILK^lox/loxAdCre mice together with wild-type littermates (ILK^lox/lox) were fed a chow diet or 60% high-fat (HF) diet for 16 weeks. In vivo insulin sensitivity was determined by hyperinsulinemic-euglycemic clamps.

Results

AT ILK expression was increased by HF diet feeding in mice and increased in visceral fat of morbidly obese humans. The HF-fed ILK^lox/loxAdCre mice displayed reduced fat mass and improved glucose tolerance relative to the HF-fed ILK^lox/lox mice. During a hyperinsulinemic-euglycemic clamp, the HF-fed ILK^lox/loxAdCre mice exhibited partially improved insulin resistance in AT. Lipolysis was suppressed to a greater extent by insulin and glucose uptake in brown AT (BAT) increased. Increased inhibition of lipolysis may have been attributed to increased vascularization in white AT, while increased glucose uptake in BAT was associated with increased Akt phosphorylation and P38/JNK dephosphorylation. Notably, AT insulin sensitivity in lean mice was not affected by ILK deletion. Moreover, reduced fat mass in the HF-fed ILK^lox/loxAdCre mice may have been attributed to decreased free fatty acid uptake into adipocytes via the downregulation of CD36 gene expression. Consistent with the results in the mice, knockdown and knockout of ILK in 3T3-L1 cells decreased lipid accumulation and CD36 gene expression during adipogenesis.

Conclusions

These data show that adipocyte ILK is important for regulating HF diet-mediated insulin resistance in AT in a manner consistent with AT function.

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ILK protein increased in visceral adipose tissue of obese humans and mice.

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Mice lacking adipocyte ILK had less fat and improved glucose tolerance in obesity.

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Adipocyte ILK deletion improved anti-lipolytic action of insulin in obese mice.

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Adipocyte ILK deletion stimulated brown adipose tissue glucose uptake in obese mice.

Mitophagy receptor FUNDC1 is regulated by PGC-1α/NRF1 to fine tune mitochondrial homeostasis

Mitophagy is an essential cellular autophagic process that selectively removes superfluous and damaged mitochondria, and it is coordinated with mitochondrial biogenesis to fine tune the quantity and quality of mitochondria. Coordination between these two opposing processes to maintain the functional mitochondrial network is of paramount importance for normal cellular and organismal metabolism. However, the underlying mechanism is not completely understood. Here we report that PGC-1α and nuclear respiratory factor 1 (NRF1), master regulators of mitochondrial biogenesis and metabolic adaptation, also transcriptionally upregulate the gene encoding FUNDC1, a previously characterized mitophagy receptor, in response to cold stress in brown fat tissue. NRF1 binds to the classic consensus site in the promoter of Fundc1 to upregulate its expression and to enhance mitophagy through its interaction with LC3. Specific knockout of Fundc1 in BAT results in reduced mitochondrial turnover and accumulation of functionally compromised mitochondria, leading to impaired adaptive thermogenesis. Our results demonstrate that FUNDC1-dependent mitophagy is directly coupled with mitochondrial biogenesis through the PGC-1α/NRF1 pathway, which dictates mitochondrial quantity, quality, and turnover and contributes to adaptive thermogenesis.

Brown/Beige adipose tissues and the emerging role of their secretory factors in improving metabolic health: The batokines

Brown and beige adipose tissues are the primary sites for adaptive non-shivering thermogenesis. Although they have been known principally for their thermogenic effects, in recent years, it has emerged that, just like white adipose tissue (WAT), brown and beige adipose tissues also play an important role in the regulation of metabolic health through secretion of various brown adipokines (batokines) in response to various physiological cues. These secreted batokines target distant organs and tissues such as the liver, heart, skeletal muscles, brain, WAT, and perform various local and systemic functions in an autocrine, paracrine, or endocrine manner. Brown and beige adipose tissues are therefore now receiving increasing levels of attention with respect to their effects on various other organs and tissues. Identification of novel secreted factors by these tissues may help in the discovery of drug candidates for the treatment of various metabolic disorders such as obesity, type-2 diabetes, skeletal deformities, cardiovascular diseases, dyslipidemia. In this review, we comprehensively describe the emerging secretory role of brown/beige adipose tissues and the metabolic effects of various brown/beige adipose tissues secreted factors on other organs and tissues in endocrine/paracrine manners, and as well as on brown/beige adipose tissue itself in an autocrine manner. This will provide insights into understanding the potential secretory role of brown/beige adipose tissues in improving metabolic health.

Withaferin A exerts an anti-obesity effect by increasing energy expenditure through thermogenic gene expression in high-fat diet-fed obese mice

BACKGROUND

The enhancement of energy expenditure has attracted attention as a therapeutic target for the management of body weight. Withaferin A (WFA), a major constituent of Withania somnifera extract, has been reported to possess anti-obesity properties, however the underlying mechanism remains unknown.

PURPOSE

To investigate whether WFA exerts anti-obesity effects via increased energy expenditure, and if so, to characterize the underlying pathway.

METHODS

C57BL/6 J mice were fed a high-fat diet (HFD) for 10 weeks, and WFA was orally administered for 7 days. The oxygen consumption rate of mice was measured at 9 weeks using an OxyletPro™ system. Hematoxylin and eosin (H&E), immunohistochemistry, immunoblotting, and real-time PCR methods were used.

RESULTS

Treatment with WFA ameliorated HFD-induced obesity by increasing energy expenditure by improving of mitochondrial activity in brown adipose tissue (BAT) and promotion of subcutaneous white adipose tissue (scWAT) browning via increasing uncoupling protein 1 levels. WFA administration also significantly increased AMP-activated protein kinase (AMPK) phosphorylation in the BAT of obese mice. Additionally, WFA activated mitogen-activated protein kinase (MAPK) signaling, including p38/extracellular signal-regulated kinase MAPK, in both BAT and scWAT.

CONCLUSION

WFA enhances energy expenditure and ameliorates obesity via the induction of AMPK and activating p38/extracellular signal-regulated kinase MAPK, which triggers mitochondrial biogenesis and browning-related gene expression.

Danshen Extracts Prevents Obesity and Activates Mitochondrial Function in Brown Adipose Tissue

BACKGROUND

Danshen has been widely used in oriental medicine to improve body function. The purpose of this study is to investigate the effect of water-soluble Danshen extract (DE) on weight loss and on activation proteins involved in mitochondrial biogenesis in brown adipose tissue (BAT) in obese mice.

METHODS

BAT was isolated from 7-week-old male Sprague-Dawley rats, and expression of proteins related to mitochondrial biogenesis was confirmed in both brown preadipocytes and mature brown adipocytes treated with DE. For the in vivo study, low-density lipoprotein receptor knock out mice were divided into three groups and treated for 17 weeks with: standard diet; high fat diet (HFD); HFD+DE. Body weight was measured every week, and oral glucose tolerance test was performed after DE treatment in streptozotocin-induced diabetic mice. To observe the changes in markers related to thermogenesis and adipogenesis in the BAT, white adipose tissue (WAT) and liver of experimental animals, tissues were removed and immediately frozen in liquid nitrogen.

RESULTS

DE increased the expression of uncoupling protein 1 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha in brown preadipocytes, and also promoted the brown adipocyte differentiation and mitochondrial function in the mature brown adipocytes. Reactive oxygen species production in brown preadipocytes was increased depending on the concentration of DE. DE activates thermogenesis in BAT and normalizes increased body weight and adipogenesis in the liver due to HFD. Browning of WAT was increased in WAT of DE treatment group.

CONCLUSION

DE protects against obesity and activates mitochondrial function in BAT.

DsbA-L deficiency in T cells promotes diet-induced thermogenesis through suppressing IFN-γ production

Adipose tissue-resident T cells have been recognized as a critical regulator of thermogenesis and energy expenditure, yet the underlying mechanisms remain unclear. Here, we show that high-fat diet (HFD) feeding greatly suppresses the expression of disulfide-bond A oxidoreductase-like protein (DsbA-L), a mitochondria-localized chaperone protein, in adipose-resident T cells, which correlates with reduced T cell mitochondrial function. T cell-specific knockout of DsbA-L enhances diet-induced thermogenesis in brown adipose tissue (BAT) and protects mice from HFD-induced obesity, hepatosteatosis, and insulin resistance. Mechanistically, DsbA-L deficiency in T cells reduces IFN-γ production and activates protein kinase A by reducing phosphodiesterase-4D expression, leading to increased BAT thermogenesis. Taken together, our study uncovers a mechanism by which T cells communicate with brown adipocytes to regulate BAT thermogenesis and whole-body energy homeostasis. Our findings highlight a therapeutic potential of targeting T cells for the treatment of over nutrition-induced obesity and its associated metabolic diseases.

Madecassoside Inhibits Body Weight Gain via Modulating SIRT1-AMPK Signaling Pathway and Activating Genes Related to Thermogenesis

BACKGROUND

Pre-clinical research studies have shown that Madecassoside (MA) has favorable therapeutic effects on arthritis, acne, vitiligo and other diseases. However, the effects of MA on obesity have not yet been studied. This study mainly aimed to investigate the effects of MA in protecting against obesity and its underlying mechanism in reducing obesity.

METHODS

Obese diabetic KKay/TaJcl mice model was adopted to the study. The body weight of all animals was recorded daily, and the blood glucose, blood lipid, and serum aminotransferase levels were examined, respectively. The expression of P-AMPK, SIRT1, P-LKB1, P-ACC, and P-HSL in abdominal fat, mesenteric fat, and epididymal fat was measured by western blotting, and the levels of PPARα, CPT1a, PGC-1α, UCP-1, Cidea, Cox7a1, and Cox8b were examined by real-time quantitative PCR (RT-qPCR).

RESULTS

The results revealed that the body weight of the mice in MA group was significantly reduced, and the body mass index (BMI) showed significant difference between the two groups after 8 weeks of MA treatment. Further research revealed that it affected the mesenteric fat and epididymis fat by activating SIRT1/AMPK signaling pathway, and then promoted fatty acid oxidation of epididymal fat (PPARα ↑, CPT1a↑, and PGC-1α↑). Last but not the least, it also promoted the expression of UCP-1 and stimulated thermoregulatory genes (Cidea, Cox7a1, and Cox8b) in brown fat and mesenteric fat.

CONCLUSIONS

Taken together, these findings suggest that MA can inhibit the weight gain in obese diabetic mice, and reduce triglyceride levels, inhibit lipogenesis of mesenteric fat, promote epididymal fat lipolysis and fatty acid oxidation. Furthermore, MA treatment might promote mesenteric fat browning and activate mitochondrial function in brown fat as well as mesenteric fat.

Beige Adipose Tissue Identification and Marker Specificity-Overview

Adipose tissue (AT) is classified based on its location, physiological and functional characteristics. Although there is a clear demarcation of anatomical and molecular features specific to white (WAT) and brown adipose tissue (BAT), the factors that uniquely differentiate beige AT (BeAT) remain to be fully elaborated. The ubiquitous presence of different types of AT and the inability to differentiate brown and beige adipocytes because of similar appearance present a challenge when classifying them one way or another. Here we will provide an overview of the latest advances in BeAT, BAT, and WAT identification based on transcript markers described in the literature. The review paper will highlight some of the difficulties these markers pose and will offer new perspectives on possible transcript-specific identification of BeAT. We hope that this will advance the understanding of the biology of different ATs. In addition, concrete strategies to distinguish different types of AT may be relevant to track the efficacy and mechanisms around interventions aimed to improve metabolic health and thwart excessive weight gain.

Adipose Tissue SIRT1 Regulates Insulin Sensitizing and Anti-Inflammatory Effects of Berberine

Berberine (BBR), which is an active component of Coptis chinensis Franch, has been reported to improve glucose metabolism and insulin resistance in animal and human studies, predominantly via activation of the 5′-adenosine monophosphate kinase (AMPK) pathway and suppression of the inflammation response. However, the mechanisms underlying the effects of BBR on AMPK and inflammation remain unclear. In this present study, we found that BBR upregulated SIRT1 expression in 3T3L-1 adipocytes and adipose tissue. Inhibition of SIRT1 blunted the BBR-induced increase in glucose consumption and uptake in adipocytes. The BBR-induced activation of the AMPK pathway and AKT phosphorylation in adipocytes and adipose tissue were also attenuated by inhibition or knockout of Sirt1. The BBR-induced improvement of systemic insulin sensitivity was impaired by Sirt1 knockout in HFD-induced obese mice. The suppressing effects of BBR on systemic and local inflammatory responses, such as serum concentrations and expression of inflammatory cytokines, phosphorylation of c-Jun N-terminal kinase (JNK) and IKKβ, and the accumulation of F4/80-positive macrophages in adipose tissue were also attenuated in Sirt1 knockout mice. The BBR-induced decrease in PGC-1α acetylation was reversed by inhibition or knockout of Sirt1 in adipocytes and adipose tissue. Together, these results indicate that adipose tissue SIRT1 is a key regulator of the insulin sensitizing and anti-inflammatory effects of BBR, which contributes to the improvement of metabolic dysregulation.

Zinc Finger Transcription Factor Zbtb16 Coordinates the Response to Energy Deficit in the Mouse Hypothalamus

The central nervous system controls feeding behavior and energy expenditure in response to various internal and external stimuli to maintain energy balance. Here we report that the newly identified transcription factor zinc finger and BTB domain containing 16 (Zbtb16) is induced by energy deficit in the paraventricular (PVH) and arcuate (ARC) nuclei of the hypothalamus via glucocorticoid (GC) signaling. In the PVH, Zbtb16 is expressed in the anterior half of the PVH and co-expressed with many neuronal markers such as corticotropin-releasing hormone (Crh), thyrotropin-releasing hormone (Trh), oxytocin (Oxt), arginine vasopressin (Avp), and nitric oxide synthase 1 (Nos1). Knockdown (KD) of Zbtb16 in the PVH results in attenuated cold-induced thermogenesis and improved glucose tolerance without affecting food intake. In the meantime, Zbtb16 is predominantly expressed in agouti-related neuropeptide/neuropeptide Y (Agrp/Npy) neurons in the ARC and its KD in the ARC leads to reduced food intake. We further reveal that chemogenetic stimulation of PVH Zbtb16 neurons increases energy expenditure while that of ARC Zbtb16 neurons increases food intake. Taken together, we conclude that Zbtb16 is an important mediator that coordinates responses to energy deficit downstream of GCs by contributing to glycemic control through the PVH and feeding behavior regulation through the ARC, and additionally reveal its function in controlling energy expenditure during cold-evoked thermogenesis via the PVH. As a result, we hypothesize that Zbtb16 may be involved in promoting weight regain after weight loss.

The Critical Role of SIRT1 in Parkinson's Disease: Mechanism and Therapeutic Considerations

Silence information regulator 1 (SIRT1), a member of the sirtuin family, targets histones and many non-histone proteins and participates in various physiological functions. The enzymatic activity of SIRT1 is decreased in patients with Parkinson’s disease (PD), which may reduce their ability to resist neuronal damage caused by various neurotoxins. As far as we know, SIRT1 can induce autophagy by regulating autophagy related proteins such as AMP-activated protein kinase, light chain 3, mammalian target of rapamycin, and forkhead transcription factor 1. Furthermore, SIRT1 can regulate mitochondrial function and inhibit oxidative stress mainly by maintaining peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) in a deacetylated state and thus maintaining a constant level of PGC-1α. Other studies have demonstrated that SIRT1 may play a role in the pathophysiology of PD by regulating neuroinflammation. SIRT1 deacetylases nuclear factor-kappa B and thus reduces its transcriptional activity, inhibits inducible nitric oxide synthase expression, and decreases tumor necrosis factor-alpha and interleukin-6 levels. SIRT1 can also upregulate heat shock protein 70 by deacetylating heat shock factor 1 to increase the degradation of α-synuclein oligomers. Few studies have focused on the relationship between SIRT1 single nucleotide polymorphisms and PD risk, so this topic requires further research. Based on the neuroprotective effects of SIRT1 on PD, many in vitro and in vivo experiments have demonstrated that some SIRT1 activators, notably resveratrol, have potential neuroprotective effects against dopaminergic neuronal damage caused by various neurotoxins. Thus, SIRT1 plays a critical role in PD development and might be a potential target for PD therapy.

Cold-Inducible Klf9 Regulates Thermogenesis of Brown and Beige Fat

Promoting development and function of brown and beige fat may represent an attractive treatment of obesity. In the current study, we show that fat Klf9 expression is markedly induced by cold exposure and a β-adrenergic agonist. Moreover, Klf9 expression levels in human white adipose tissue (WAT) are inversely correlated with adiposity, and Klf9 overexpression in primary fat cells stimulates cellular thermogenesis, which is Ucp1 dependent. Fat-specific Klf9 transgenic mice gain less weight and have smaller fat pads due to increased thermogenesis of brown and beige fat. Moreover, Klf9 transgenic mice displayed lower fasting blood glucose levels and improved glucose tolerance and insulin sensitivity under the high-fat diet condition. Conversely, Klf9 mutation in brown adipocytes reduces the expression of thermogenic genes, causing a reduction in cellular respiration. Klf9-mutant mice exhibited obesity and cold sensitivity due to impairments in the thermogenic function of fat. Finally, fat Klf9 deletion inhibits the β3 agonist-mediated induction of WAT browning and brown adipose tissue thermogenesis. Mechanistically, cold-inducible Klf9 stimulates expression of Pgc1α, a master regulator of fat thermogenesis, by a direct binding to its gene promoter region, subsequently promoting energy expenditure. The current study reveals a critical role for KLF9 in mediating thermogenesis of brown and beige fat.

Muscle Stem Cell-Derived Extracellular Vesicles Reverse Hydrogen Peroxide-Induced Mitochondrial Dysfunction in Mouse Myotubes

Muscle stem cells (MuSCs) hold great potential as a regenerative therapeutic but have met numerous challenges in treating systemic muscle diseases. Muscle stem cell-derived extracellular vesicles (MuSC-EVs) may overcome these limitations. We assessed the number and size distribution of extracellular vesicles (EVs) released by MuSCs ex vivo, determined the extent to which MuSC-EVs deliver molecular cargo to myotubes in vitro, and quantified MuSC-EV-mediated restoration of mitochondrial function following oxidative injury. MuSCs released an abundance of EVs in culture. MuSC-EVs delivered protein cargo into myotubes within 2 h of incubation. Fluorescent labeling of intracellular mitochondria showed co-localization of delivered protein and mitochondria. Oxidatively injured myotubes demonstrated a significant decline in maximal oxygen consumption rate and spare respiratory capacity relative to untreated myotubes. Remarkably, subsequent treatment with MuSC-EVs significantly improved maximal oxygen consumption rate and spare respiratory capacity relative to the myotubes that were damaged but received no subsequent treatment. Surprisingly, MuSC-EVs did not affect mitochondrial function in undamaged myotubes, suggesting the cargo delivered is able to repair but does not expand the existing mitochondrial network. These data demonstrate that MuSC-EVs rapidly deliver proteins into myotubes, a portion of which co-localizes with mitochondria, and reverses mitochondria dysfunction in oxidatively-damaged myotubes.

Urinary expression of long non-coding RNA TUG1 in non-diabetic patients with glomerulonephritides

Metabolic alterations serve a significant role in the pathogenesis of kidney disease. Long non-coding RNA (lncRNA) taurine upregulated gene 1 (TUG1) is a known regulator of podocyte health and mitochondrial biogenesis. Although TUG1 protects against podocyte loss in models of diabetic nephropathy, it is unknown if urinary TUG1 expression is associated with clinical and histopathological findings in non-diabetic patients diagnosed with glomerulonephritides. In the present study, the expression of TUG1, podocyte-specific markers (nephrin and podocin) and mitochondrial biogenesis-associated mRNAs (transcription factor A mitochondrial, cytochrome C oxidase subunit 5A and peroxisome proliferator-activated receptor γ coactivator 1α) were examined in urinary sediment of non-diabetic patients with biopsy-confirmed glomerulonephritides and healthy controls. Urinary expression of TUG1 was significantly lower in patients with glomerulonephritides, particularly those diagnosed with Focal Segmental Glomerulosclerosis (FSGS). Furthermore, TUG1 levels were associated with urinary expression of podocyte-specific markers and mRNAs associated with mitochondrial biogenesis. Loss of TUG1 expression in urinary sediment was strongly associated with FSGS, highlighting the potential of this lncRNA and its mitochondrial biogenesis-associated targets as non-invasive biomarkers of assessing podocytopathy.

Control of Adipose Cell Browning and Its Therapeutic Potential

Adipose tissue is the largest endocrine organ in humans and has an important influence on many physiological processes throughout life. An increasing number of studies have described the different phenotypic characteristics of fat cells in adults. Perhaps one of the most important properties of fat cells is their ability to adapt to different environmental and nutritional conditions. Hypothalamic neural circuits receive peripheral signals from temperature, physical activity or nutrients and stimulate the metabolism of white fat cells. During this process, changes in lipid inclusion occur, and the number of mitochondria increases, giving these cells functional properties similar to those of brown fat cells. Recently, beige fat cells have been studied for their potential role in the regulation of obesity and insulin resistance. In this context, it is important to understand the embryonic origin of beige adipocytes, the response of adipocyte to environmental changes or modifications within the body and their ability to transdifferentiate to elucidate the roles of these cells for their potential use in therapeutic strategies for obesity and metabolic diseases. In this review, we discuss the origins of the different fat cells and the possible therapeutic properties of beige fat cells.

Sinapic acid induces the expression of thermogenic signature genes and lipolysis through activation of PKA/CREB signaling in brown adipocytes

Lipid accumulation in white adipose tissue is the key contributor to the obesity and orchestrates numerous metabolic health problems such as type 2 diabetes, hypertension, atherosclerosis, and cancer. Nonetheless, the prevention and treatment of obesity are still inadequate. Recently, scientists found that brown adipose tissue (BAT) in adult humans has functions that are diametrically opposite to those of white adipose tissue and that BAT holds promise for a new strategy to counteract obesity. In this study, we evaluated the potential of sinapic acid (SA) to promote the thermogenic program and lipolysis in BAT. SA treatment of brown adipocytes induced the expression of brown-adipocyte activation–related genes such as Ucp1, Pgc-1α, and Prdm16. Furthermore, structural analysis and western blot revealed that SA upregulates protein kinase A (PKA) phosphorylation with competitive inhibition by a pan-PKA inhibitor, H89. SA binds to the adenosine triphosphate (ATP) site on the PKA catalytic subunit where H89 binds specifically. PKA-cat-α1 gene–silencing experiments confirmed that SA activates the thermogenic program via a mechanism involving PKA and cyclic AMP response element–binding protein (CREB) signaling. Moreover, SA treatment promoted lipolysis via a PKA/p38-mediated pathway. Our findings may allow us to open a new avenue of strategies against obesity and need further investigation.

UCHL1 regulates oxidative activity in skeletal muscle

Ubiquitin C-terminal Hydrolase L1 (UCHL1) is a deubiquitinating enzyme that was originally identified in neurons. Our recent study showed that UCHL1 was expressed in C2C12 myoblast cells and mouse skeletal muscle. Here we report that in mouse skeletal muscle, UCHL1 is primarily expressed in oxidative muscle fibers. Skeletal muscle specific gene knockout (smKO) of UCHL1 in mice reduced oxidative activity in skeletal muscle measured by SDH staining. The in situ muscle contraction test revealed that gastrocnemius muscle from UCHL1 smKO mice was more prone to fatigue in response to the repetitive stimulation. This data suggests that UCHL1 plays a role in maintenance of muscle oxidative metabolism. Moreover, UCHL1 smKO caused a significant reduction in key proteins that are involved in mitochondrial oxidative phosphorylation in soleus muscles, suggesting that UCHL1 may be involved in regulation of mitochondrial content and function. Immunostaining showed the co-localization of UCHL1 and mitochondrial marker VDAC in skeletal muscle. Mitochondrial fractionation assay revealed that, although UCHL1 was primarily present in the cytosolic fraction, a low level of UCHL1 protein was present in mitochondrial fraction. The level of phosphorylation of AMPKα, a master regulator of mitochondrial biogenesis, were unchanged in UCHL1 smKO muscle. On the other hand, immunoprecipitation from soleus muscle sample indicated the interaction between UCHL1 and HSP60, a chaperon protein that is involved in mitochondrial protein transport. There was a trend of downregulation of HSP60 in UCHL1 smKO muscle. Overall, our data suggests UCHL1 is a novel regulator of mitochondrial function and oxidative activity in skeletal muscle.

A MicroRNA Linking Human Positive Selection and Metabolic Disorders

Positive selection in Europeans at the 2q21.3 locus harboring the lactase gene has been attributed to selection for the ability of adults to digest milk to survive famine in ancient times. However, the 2q21.3 locus is also associated with obesity and type 2 diabetes in humans, raising the possibility that additional genetic elements in the locus may have contributed to evolutionary adaptation to famine by promoting energy storage, but which now confer susceptibility to metabolic diseases. We show here that the miR-128-1 microRNA, located at the center of the positively selected locus, represents a crucial metabolic regulator in mammals. Antisense targeting and genetic ablation of miR-128-1 in mouse metabolic disease models result in increased energy expenditure and amelioration of high-fat-diet-induced obesity and markedly improved glucose tolerance. A thrifty phenotype connected to miR-128-1-dependent energy storage may link ancient adaptation to famine and modern metabolic maladaptation associated with nutritional overabundance.

Embryonic exposure to hyper glucocorticoids suppresses brown fat development and thermogenesis via REDD1

Maternal stress during pregnancy is prevailing worldwide, which exposes fetuses to intrauterine hyper glucocorticoids (GC), programming offspring to obesity and metabolic diseases. Despite the importance of brown adipose tissue (BAT) in maintaining long-term metabolic health, impacts of prenatal hyper GC on postnatal BAT thermogenesis and underlying regulations remain poorly defined. Pregnant mice were administrated with synthetic GC dexamethasone (DEX) at levels comparable to fetal GC exposure of stressed mothers. Prenatal GC exposure dose-dependently reduced BAT thermogenic activity, contributing to lower body temperature and higher mortality of neonates; such difference was abolished under thermoneutrality, underscoring BAT deficiency was the major contributor to adverse changes in postnatal thermogenesis due to excessive GC. Prenatal GC exposure highly activated Redd1 expression and reduced Ppargc1a transcription from the alternative promoter (Ppargc1a-AP) in neonatal BAT. During brown adipocyte differentiation, ectopic Redd1 expression reduced Ppargc1a-AP expression and mitochondrial biogenesis; and the inhibitory effects of GC on mitochondrial biogenesis and Ppargc1a-AP expression were blocked by Redd1 ablation. Redd1 reduced protein kinase A phosphorylation and suppressed cyclic adenosine monophosphate (cAMP) -responsive element-binding protein (CREB) binding to the cAMP regulatory element (CRE) in Ppargc1a-AP promoter, leading to Ppargc1a-AP inactivation. In summary, excessive maternal GC exposure during pregnancy dysregulates Redd1-Ppargc1a-AP axis, which impairs fetal BAT development, hampering postnatal thermogenic adaptation and metabolic health of offspring.

Mild-cold water swimming does not exacerbate white adipose tissue browning and brown adipose tissue activation in mice

The present study investigated the effects of swimming physical training either thermoneutral or below thermoneutral water temperature on white (WAT) and brown (BAT) adipose tissue metabolism, morphology, and function. C57BL/6J male mice (n = 40; weight 25.3 ± 0.1 g) were divided into control (CT30), cold control (CT20), trained (TR30), and cold trained (TR20) groups. Swimming training consisted of 30-min exercise at 30°C (control) or 20°C (cold) water temperature. After 8-week training, adipose tissues were excised and inguinal (ingWAT) and BAT were processed for histology, lipolysis, and protein contents of total OXPHOS, PGC1α, and UCP1 by western blotting analysis. Swimming training reduced body weight gain independently of water temperature (P < 0.05). ingWAT mass was decreased for TR30 in comparison to other groups (P < 0.05), while for BAT, there was a significant increase in CT20 in relation to CT30, and both trained groups were significantly increased in relation to control groups (P < 0.05). ingWAT mean adipocyte area was smaller for trained groups, and seemed to present multilocular adipocytes. Lipolytic activity and protein content of UCP1, PGC1α, and mitochondrial markers were increased in trained groups for ingWAT (P < 0.05), independent of water temperature (P > 0.05), and these patterns were not observed for BAT (P > 0.05). Our findings suggest that mild-cold water exposure and swimming physical exercise seem to, independently, promote browning in ingWAT with no effects on BAT; however, the association of exercise and mild-cold water did not exacerbate these effects.

Cold-induced beigeing of stem cell-derived adipocytes is not fully reversible after return to normothermia

Beige adipocytes possess the morphological and biochemical characteristics of brown adipocytes, including the mitochondrial uncoupling protein (UCP)1. Mesenchymal stem cells (MSCs) are somatic multipotent progenitors which differentiate into lipid-laden adipocytes. Induction of MSC adipogenesis under hypothermic culture conditions (ie 32°C) promotes the appearance of a beige adipogenic phenotype, but the stability of this phenotypic switch after cells are returned to normothermic conditions of 37°C has not been fully examined. Here, cells transferred from 32°C to 37°C retained their multilocular beige-like morphology and exhibited an intermediate gene expression profile, with both beige-like and white adipocyte characteristics while maintaining UCP1 protein expression. Metabolic profile analysis indicated that the bioenergetic status of cells initially differentiated at 32°C adapted post-transfer to 37°C, showing an increase in mitochondrial respiration and glycolysis. The ability of the transferred cells to respond under stress conditions (eg carbonyl cyanide-4-phenylhydrazone (FCCP) treatment) demonstrated higher functional capacity of enzymes involved in the electron transport chain and capability to supply substrate to the mitochondria. Overall, MSC-derived adipocytes incubated at 32°C were able to remain metabolically active and retain brown-like features after 3 weeks of acclimatization at 37°C, indicating these phenotypic characteristics acquired in response to environmental conditions are not fully reversible.

Absence of AGPAT2 impairs brown adipogenesis, increases IFN stimulated gene expression and alters mitochondrial morphology

BACKGROUND

Biallelic loss of function variants in AGPAT2, encoding 1-acylglycerol-3-phosphate O-acyltransferase 2, cause congenital generalized lipodystrophy type 1, a disease characterized by near total loss of white adipose tissue and metabolic complications. Agpat2 deficient (Agpat2^-/-) mice completely lacks both white and interscapular brown adipose tissue (iBAT). The objective of the present study was to characterize the effects of AGPAT2 deficiency in brown adipocyte differentiation.

METHODS

Preadipocytes obtained from newborn (P0.5) Agpat2^-/- and wild type mice iBAT were differentiated into brown adipocytes, compared by RNA microarray, RT-qPCR, High-Content Screening (HCS), western blotting and electron microscopy.

RESULTS

1) Differentiated Agpat2^-/- brown adipocytes have fewer lipid-laden cells and lower abundance of Pparγ, Pparα, C/ebpα and Pgc1α, both at the mRNA and protein levels, compared those to wild type cells. Prmd16 levels were equivalent in both, Agpat2^-/- and wild type, while Ucp1 was only induced in wild type cells, 2) These differences were not due to lower abundance of preadipocytes, 3) Differentiated Agpat2^-/- brown adipocytes are enriched in the mRNA abundance of genes participating in interferon (IFN) type I response, whereas genes involved in mitochondrial homeostasis were decreased, 4) Mitochondria in differentiated Agpat2^-/- brown adipocytes had altered morphology and lower mass and contacting sites with lipid droplets concomitant with lower levels of Mitofusin 2 and Perlipin 5.

CONCLUSION

AGPAT2 is necessary for normal brown adipose differentiation. Its absence results in a lower proportion of lipid-laden cells, increased expression of interferon-stimulated genes (ISGs) and alterations in mitochondrial morphology, mass and fewer mitochondria to lipid droplets contacting sites in differentiated brown adipocytes.

An indispensable role for dynamin-related protein 1 in beige and brown adipogenesis

Emerging evidence indicates that proper mitochondrial dynamics are critical for adipocyte differentiation and functional thermogenic capacity. We found that the mitochondrial fission protein dynamin-related protein 1 (DRP1, also known as DNML1) is highly expressed in brown adipose tissue compared to expression in white adipose tissue, and these expression levels increase during brown adipocyte differentiation. Our results reveal that the inhibition of DRP1 using mdivi-1 mitigates beige adipocyte differentiation and differentiation-associated mitochondrial biogenesis. We found that DRP1 is essential for the induction of the early-phase beige adipogenic transcriptional program. Intriguingly, inhibition of DRP1 is dispensable following the induction of beige adipogenesis and adipogenesis-associated mitochondrial biogenesis. Altogether, we demonstrate that DRP1 in preadipocytes plays an essential role in beige and brown adipogenesis.This article has an associated First Person interview with the first author of the paper.

Functional Inactivation of Mast Cells Enhances Subcutaneous Adipose Tissue Browning in Mice

Adipose tissue browning and systemic energy expenditure provide a defense mechanism against obesity and associated metabolic diseases. In high-cholesterol Western diet-fed mice, mast cell (MC) inactivation ameliorates obesity and insulin resistance and improves the metabolic rate, but a direct role of adipose tissue MCs in thermogenesis and browning remains unproven. Here, we report that adrenoceptor agonist norepinephrine-stimulated metabolic rate and subcutaneous adipose tissue (SAT) browning are enhanced in MC-deficient Kit^w-sh/w-sh mice and MC-stabilized wild-type mice on a chow diet. MC reconstitution to SAT in Kit^w-sh/w-sh mice blocks these changes. Mechanistic studies demonstrate that MC inactivation elevates SAT platelet-derived growth factor receptor A (PDGFRα⁺) adipocyte precursor proliferation and accelerates beige adipocyte differentiation. Using the tryptophan hydroxylase 1 (TPH1) inhibitor and TPH1-deficient MCs, we show that MC-derived serotonin inhibits SAT browning and systemic energy expenditure. Functional inactivation of MCs or inhibition of MC serotonin synthesis in SAT promotes adipocyte browning and systemic energy metabolism in mice.

Induction of UCP1 and thermogenesis by a small molecule via AKAP1/PKA modulation

Strategies to increase energy expenditure are an attractive approach to reduce excess fat storage and body weight to improve metabolic health. In mammals, uncoupling protein-1 (UCP1) in brown and beige adipocytes uncouples fatty acid oxidation from ATP generation in mitochondria and promotes energy dissipation as heat. We set out to identify small molecules that enhance UCP1 levels and activity using a high-throughput screen of nearly 12,000 compounds in mouse brown adipocytes. We identified a family of compounds that increase Ucp1 expression and mitochondrial activity (including un-coupled respiration) in mouse brown adipocytes and human brown and white adipocytes. The mechanism of action may be through compound binding to A kinase anchoring protein (AKAP) 1, modulating its localization to mitochondria and its interaction with protein kinase A (PKA), a known node in the β-adrenergic signaling pathway. In mice, the hit compound increased body temperature, UCP1 protein levels, and thermogenic gene expression. Some of the compound effects on mitochondrial function were UCP1- or AKAP1-independent, suggesting compound effects on multiple nodes of energy regulation. Overall, our results highlight a role for AKAP1 in thermogenesis, uncoupled respiration, and regulation energy balance.

Biochanin A induces a brown-fat phenotype via improvement of mitochondrial biogenesis and activation of AMPK signaling in murine C3H10T1/2 mesenchymal stem cells

In this study, we investigated the effect of Biochanin A (BioA), an O-methylated isoflavone on the brown-fat phenotype formation and on the associated thermogenic program including mitochondrial biogenesis and lipolysis in C3H10T1/2 MSCs. Our data demonstrates that Treatment with BioA in an adipogenic differentiation cocktail induced formation of brown-fat-like adipocytes from C3H10T1/2 MSCs without treatment with a known browning inducer (rosiglitazone or T3) at an early stage of differentiation. The formation of brown-fat-like adipocytes by BioA treatment was evidenced by upregulation of key thermogenic markers: Ucp1, Pgc1α, Prdm16, and Pparγ. BioA also increased the expression of beige (Cd137 and Fgf21) and brown (Elovl3 and Zic1)-specific markers. Additionally, BioA treatment promoted mitochondrial biogenesis, judging by the upregulation of genes; Cox8b, Cidea, Dio2, Sirt1, Opa1, and Fis1. BioA treatment increased the amount of mitochondrial DNA and its encoded proteins: oxidative phosphorylation complexes (I-V); this change was associated with high oxygen consumption by C3H10T1/2 MSCs. A small-interfering-RNA-induced gene knockdown and experiments with dorsomorphin-driven competitive inhibition revealed that BioA exerts the thermogenic action via activation of AMPK signaling. Our study shows the mechanism of BioA-induced promotion of a brown-fat phenotype. Nonetheless, clinical research is necessary to validate BioA as a brown-fat-like signature inducer.

Excessive Glucocorticoids During Pregnancy Impair Fetal Brown Fat Development and Predispose Offspring to Metabolic Dysfunctions

Maternal stress during pregnancy exposes fetuses to hyperglucocorticoids, which increases the risk of metabolic dysfunctions in offspring. Despite being a key tissue for maintaining metabolic health, the impacts of maternal excessive glucocorticoids (GC) on fetal brown adipose tissue (BAT) development and its long-term thermogenesis and energy expenditure remain unexamined. For testing, pregnant mice were administered dexamethasone (DEX), a synthetic GC, in the last trimester of gestation, when BAT development is the most active. DEX offspring had glucose, insulin resistance, and adiposity and also displayed cold sensitivity following cold exposure. In BAT of DEX offspring, Ppargc1a expression was suppressed, together with reduced mitochondrial density, and the brown progenitor cells sorted from offspring BAT demonstrated attenuated brown adipogenic capacity. Increased DNA methylation in Ppargc1a promoter had a fetal origin; elevated DNA methylation was also detected in neonatal BAT and brown progenitors. Mechanistically, fetal GC exposure increased GC receptor/DNMT3b complex in binding to the Ppargc1a promoter, potentially driving its de novo DNA methylation and transcriptional silencing, which impaired fetal BAT development. In summary, maternal GC exposure during pregnancy increases DNA methylation in the Ppargc1a promoter, which epigenetically impairs BAT thermogenesis and energy expenditure, predisposing offspring to metabolic dysfunctions.

Disabling MNK protein kinases promotes oxidative metabolism and protects against diet-induced obesity

Objectives

Diet-driven obesity is increasingly widespread. Its consequences pose major challenges to human health and health care systems. There are MAP kinase-interacting kinases (MNKs) in mice, MNK1 and MNK2. Studies have demonstrated that mice lacking either MNK1 or MNK2 were partially protected against high-fat diet (HFD)-induced weight gain and insulin resistance. The aims of this study were to evaluate the phenotype of mice lacking both MNKs when given an HFD, to assess whether pharmacological inhibition of MNK function also protects against diet-induced obesity (DIO) and its consequences and to probe the mechanisms underlying such protection.

Methods

Male wild-type (WT) C57Bl6 mice or mice lacking both MNK1 and MNK2 (double knockout, DKO) were fed an HFD or control diet (CD) for up to 16 weeks.

In a separate study, WT mice were also given an HFD for 6 weeks, after which half were treated with the recently-developed MNK inhibitor ETC-206 daily for 10 more weeks while continuing an HFD. Metabolites and other parameters were measured, and the expression of selected mRNAs and proteins was assessed.

Results

MNK-DKO mice were almost completely protected from HFD-induced obesity. Higher energy expenditure (EE) in MNK-DKO mice was observed, which probably reflects the changes in a number of genes or proteins linked to lipolysis, mitochondrial function/biogenesis, oxidative metabolism, and/or ATP consumption. The MNK inhibitor ETC-206 also prevented HFD-induced weight gain, confirming that the activity of the MNKs facilitates weight gain due to excessive caloric consumption.

Conclusions

Disabling MNKs in mice, either genetically or pharmacologically, strongly prevents weight gain on a calorie-rich diet. This finding likely results from increased energy utilisation, involving greater ATP consumption, mitochondrial oxidative metabolism, and other processes.

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Knockout of MNK1/MNK2 protects mice against diet-induced obesity.

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MNK1/2 DKO mice have higher energy expenditure.

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MNK1/2 DKO increases the expression of genes of lipid and mitochondrial metabolism.

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Pharmacological inhibition of MNKs has similar effects.

The colorful versatility of adipocytes: white-to-brown transdifferentiation and its therapeutic potential in humans

Brown and brite adipocytes contribute to energy expenditure through nonshivering thermogenesis. Though these cell types are thought to arise primarily from the de novo differentiation of precursor cells, their abundance is also controlled through the transdifferentiation of mature white adipocytes. Here, we review recent advances in our understanding of the regulation of white-to-brown transdifferentiation, as well as the conversion of brown and brite adipocytes to dormant, white-like fat cells. Converting mature white adipocytes into brite cells or reactivating dormant brown and brite adipocytes has emerged as a strategy to ameliorate human metabolic disorders. We analyze the evidence of learning from mice and how they translate to humans to ultimately scrutinize the relevance of this concept. Moreover, we estimate that converting a small percentage of existing white fat mass in obese subjects into active brite adipocytes could be sufficient to achieve meaningful benefits in metabolism. In conclusion, novel browning agents have to be identified before adipocyte transdifferentiation can be realized as a safe and efficacious therapy.

Brown adipocyte-derived exosomal miR-132-3p suppress hepatic Srebf1 expression and thereby attenuate expression of lipogenic genes

Recent evidence has revealed a novel signaling mechanism through which brown adipose tissue (BAT)-derived exosomal microRNAs (miRNAs) influence hepatic gene expression. Here, we uncover neuronal control of these miRNAs and identify exosomal miR-132-3p as a regulator of hepatic lipogenesis under cold stress conditions. Norepinephrine, a sympathetic nervous system neurotransmitter mediating cold-induced BAT activation, altered the composition of brown adipocyte (BAC)-derived exosomal miRNAs; among them, miR-132-3p was significantly induced. The isolated BAC-derived exosomes suppressed expression of hepatic Srebf1, a predicted target of miR-132-3p. In an indirect co-culture system, BACs suppressed expression of hepatic Srebf1 and its target lipogenic genes; this effect was not seen with miR-132-3p-inhibited BACs. Srebf1 was experimentally validated as an miR-132-3p target. Cold stimuli consistently induced miR-132-3p expression in BAT and attenuated Srebf1 expression in the liver. Our results suggest that BAT-derived exosomal miR-132-3p acts as an endocrine factor that regulates hepatic lipogenesis for cold adaptation.

Association of uncoupling protein (Ucp) gene polymorphisms with cardiometabolic diseases

The hereditary aspect of obesity is a major focus of modern medical genetics. The genetic background is known to determine a higher-than-average prevalence of obesity in certain regions, like Oceania. There is evidence that dysfunction of brown adipose tissue (BAT) may be a risk factor for obesity and type 2 diabetes (T2D). A significant number of studies in the field focus on the UCP family. The Ucp genes code for electron transport carriers. UCP1 (thermogenin) is the most abundant protein of the UCP superfamily and is expressed in BAT, contributing to its capability of generating heat. Single nucleotide polymorphisms (SNPs) of Ucp1-Ucp3 were recently associated with risk of cardiometabolic diseases. This review covers the main Ucp SNPs A-3826G, A-1766G, A-112C, Met229Leu, Ala64Thr (Ucp1), Ala55Val, G-866A (Ucp2), and C-55 T (Ucp3), which may be associated with the development of obesity, disturbance in lipid metabolism, T2D, and cardiovascular diseases.

Natural products, PGC-1 , and Duchenne muscular dystrophy

Peroxisome proliferator-activated receptor γ (PPARγ) is a transcriptional coactivator that binds to a diverse range of transcription factors. PPARγ coactivator 1 (PGC-1) coactivators possess an extensive range of biological effects in different tissues, and play a key part in the regulation of the oxidative metabolism, consequently modulating the production of reactive oxygen species, autophagy, and mitochondrial biogenesis. Owing to these findings, a large body of studies, aiming to establish the role of PGC-1 in the neuromuscular system, has shown that PGC-1 could be a promising target for therapies targeting neuromuscular diseases. Among these, some evidence has shown that various signaling pathways linked to PGC-1α are deregulated in muscular dystrophy, leading to a reduced capacity for mitochondrial oxidative phosphorylation and increased reactive oxygen species (ROS) production. In the light of these results, any intervention aimed at activating PGC-1 could contribute towards ameliorating the progression of muscular dystrophies. PGC-1α is influenced by different patho-physiological/pharmacological stimuli. Natural products have been reported to display modulatory effects on PPARγ activation with fewer side effects in comparison to synthetic drugs. Taken together, this review summarizes the current knowledge on Duchenne muscular dystrophy, focusing on the potential effects of natural compounds, acting as regulators of PGC-1α.

Regulation of adipocyte thermogenesis: mechanisms controlling obesity

Adipocyte biology has been intensely researched in recent years due to the emergence of obesity as a serious global health concern and because of the realization that adipose tissue is more than simply a cell type that stores and releases lipids. The plasticity of adipose tissues, to rapidly adapt to altered physiological states of energy demand, is under neuronal and endocrine control. The capacity for white adipocytes to store chemical energy in lipid droplets is key for protecting other organs from the toxic effects of ectopic lipid deposition. In contrast, thermogenic (brown and beige) adipocytes combust macronutrients to generate heat. The thermogenic activity of adipocytes allows them to protect themselves and other tissues from lipid overaccumulation. Advances in brown fat biology have uncovered key molecular players involved in adipocyte determination, differentiation, and thermogenic activation. It is now, well appreciated that three distinct adipocyte types exist: white, beige, and brown. Moreover, functional differences are present within adipocyte subtypes located in anatomically distinct locations. Adding to this complexity is the recent realization from single-cell sequencing studies that adipocyte progenitors are also heterogeneous. Understanding the molecular details of how to increase the number of thermogenic fat cells and their activation may delineate some of the pathophysiological basis of obesity and obesity-related diseases. Here, we review recent advances that have extended our understanding of the central role that adipose tissue plays in energy balance and the mechanisms that control their amount and function.

MiR-337-3p Promotes Adipocyte Browning by Inhibiting TWIST1

The prevalence of metabolic syndrome (MetS) and obesity is an alarming health issue worldwide. Obesity is characterized by an excessive accumulation of white adipose tissue (WAT), and it is associated with diminished brown adipose tissue (BAT) activity. Twist1 acts as a negative feedback regulator of BAT metabolism. Therefore, targeting Twist1 could become a strategy for obesity and metabolic disease. Here, we have identified miR-337-3p as an upstream regulator of Twist1. Increased miR-337-3p expression paralleled decreased expression of TWIST1 in BAT compared to WAT. Overexpression of miR-337-3p in brown pre-adipocytes provoked a reduction in Twist1 expression that was accompanied by increased expression of brown/mitochondrial markers. Luciferase assays confirmed an interaction between the miR-337 seed sequence and Twist1 3′UTR. The inverse relationship between the expression of TWIST1 and miR-337 was finally validated in adipose tissue samples from non-MetS and MetS subjects that demonstrated a dysregulation of the miR-337-Twist1 molecular axis in MetS. The present study demonstrates that adipocyte miR-337-3p suppresses Twist1 repression and enhances the browning of adipocytes.

Meat Protein in High-Fat Diet Induces Adipogensis and Dyslipidemia by Altering Gut Microbiota and Endocannabinoid Dysregulation in the Adipose Tissue of Mice

Endocannabinoids modulate insulin and adipokine expression in adipocytes through cannabinoid receptors and their levels are elevated during hyperglycemia and obesity, but little is known about how diets affect them. We assessed the effects of dietary casein, chicken, beef, and pork proteins in a high-fat diet mode, on endocannabinoids, adipogenesis, and biomarkers associated with dyslipemdia. A high-fat beef or chicken diet upregulated cannabinoid 1 receptor, N-acyl phosphatidylethanolamine-selective phospholipase-D and diacylglycerol lipase α in adipose tissue and reduced the immunoreactivity of mitochondrial uncoupling protein 1 in brown adipose tissue. In addition, the high-fat diets with beef and chicken protein had a significant impact on adipocyte differentiation and mitochondrial biogenesis in obese mice. A 16S rRNA gene sequencing indicated that high-fat diets, regardless of the protein source, significantly enhanced the ratio of Firmicutes to Bacteroidetes in colon. Meat proteins in a high-fat diet significantly decreased the relative abundances of Akkermansia and Bifidobacteria but enhanced the lipopolysaccharides level in the serum, which promoted the adipogenesis process by causing dysregulation in the endocannabinoid receptors. Consumption of meat protein with high-fat-induced adiposity, visceral obesity, and dyslipidemia reduced the thermogenesis and had a distinctive effect on the mitochondrial biogenesis compared with casein protein.

The Impact of Moderate-Intensity Continuous or High-Intensity Interval Training on Adipogenesis and Browning of Subcutaneous Adipose Tissue in Obese Male Rats

This study compares the effect of two types of exercise training, i.e., moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT) on the browning of subcutaneous white adipose tissue (scWAT) in obese male rats. Effects on fat composition, metabolites, and molecular markers of differentiation and energy expenditure were examined. Forty male Wistar rats were assigned to lean (n = 8) or obese (n = 32) groups and fed either a standard chow or high-fat obesogenic diet for 10 weeks. Eight lean and obese rats were then blood and tissue sampled, and the remaining obese animals were randomly allocated into sedentary, MICT, or HIIT (running on a treadmill 5 days/week) groups that were maintained for 12 weeks. Obesity increased plasma glucose and insulin and decreased irisin and FGF-21. In scWAT, this was accompanied with raised protein abundance of markers of adipocyte differentiation, i.e., C/EBP-α, C/EBP-β, and PPAR-γ, whereas brown fat-related genes, i.e., PRDM-16, AMPK/SIRT1/PGC-1α, were reduced as was UCP1 and markers of fatty acid transport, i.e., CD36 and CPT1. Exercise training increased protein expression of brown fat-related markers, i.e., PRDM-16, AMPK/SIRT1/PGC-1α, and UCP1, together with gene expression of fatty acid transport, i.e., CD36 and CPT1, but decreased markers of adipocyte differentiation, i.e., C/EBP-α, C/EBP-β, and plasma glucose. The majority of these adaptations were greater with HIIT compared to MICT. Our findings indicate that prolonged exercise training promotes the browning of white adipocytes, possibly through suppression of adipogenesis together with white to beige trans-differentiation and is dependent on the intensity of exercise.

Molecular Characterization of PGC-1β (PPAR Gamma Coactivator 1β) and its Roles in Mitochondrial Biogenesis in Blunt Snout Bream (Megalobrama amblycephala)

This study aimed at achieving the molecular characterization of peroxisome proliferator-activated receptor-gamma coactivator 1β (PGC-1β) and exploring its modulatory roles in mitochondria biogenesis in blunt snout bream (Megalobrama amblycephala). A full-length cDNA of PGC-1β was cloned from liver which covered 3110 bp encoding 859 amino acids. The conserved motifs of PGC-1β family proteins were gained by MEME software, and the phylogenetic analyses showed motif loss and rearrangement of PGC-1β in fish. The function of PGC-1β was evaluated through overexpression and knockdown of PGC-1β in primary hepatocytes of blunt snout bream. We observed overexpression of PGC-1β along with enhanced mitochondrial transcription factor A (TFAM) expression and mtDNA copies in hepatocytes, and its knockdown led to slightly reduced NRF1 expression. However, knockdown of PGC-1β did not significantly influence TFAM expression or mtDNA copies. The alterations in mitochondria biogenesis were assessed following high-fat intake, and the results showed that it induces downregulation of PGC-1β. Furthermore, significant decreases in mitochondrial respiratory chain activities and mitochondria biogenesis were observed by high-fat intake. Our findings demonstrated that overexpression of PGC-1β induces the enhancement of TFAM expression and mtDNA amount but not NRF-1. Therefore, it could be concluded that PGC-1β is involved in mitochondrial biogenesis in blunt snout bream but not through PGC-1β/NRF-1 pathway.

Sinapic acid induces the expression of thermogenic signature genes and lipolysis through activation of PKA/CREB signaling in brown adipocytes

Lipid accumulation in white adipose tissue is the key contributor to the obesity and orchestrates numerous metabolic health problems such as type 2 diabetes, hypertension, atherosclerosis, and cancer. Nonetheless, the prevention and treatment of obesity are still inadequate. Recently, scientists found that brown adipose tissue (BAT) in adult humans has functions that are diametrically opposite to those of white adipose tissue and that BAT holds promise for a new strategy to counteract obesity. In this study, we evaluated the potential of sinapic acid (SA) to promote the thermogenic program and lipolysis in BAT. SA treatment of brown adipocytes induced the expression of brown-adipocyte activation-related genes such as Ucp1, Pgc-1α, and Prdm16. Furthermore, structural analysis and western blot revealed that SA upregulates protein kinase A (PKA) phosphorylation with competitive inhibition by a pan-PKA inhibitor, H89. SA binds to the adenosine triphosphate (ATP) site on the PKA catalytic subunit where H89 binds specifically. PKA-cat-α1 gene-silencing experiments confirmed that SA activates the thermogenic program via a mechanism involving PKA and cyclic AMP response element-binding protein (CREB) signaling. Moreover, SA treatment promoted lipolysis via a PKA/p38-mediated pathway. Our findings may allow us to open a new avenue of strategies against obesity and need further investigation. [BMB Reports 2020; 53(3): 142-147].

Peroxisome proliferator-activated receptor-coactivator 1-beta (PGC-1β) modulates the expression of genes involved in adipogenesis during preadipocyte differentiation in chicken

To study the influence of the PGC-1β gene on chicken adipocyte proliferation and differentiation, we constructed RNA interference (RNAi) vectors that target the PGC-1β gene and transfected these vectors into adipocytes. Oil Red O staining and a CCK-8 cell kit were used to determine cell triglyceride accumulation status and cell proliferation after transfection, respectively. The mRNA abundances of PGC-1β and adipocyte-differentiation-related genes (PPARγ, C/EBPα, SREBP-1c, FAS, and A-FABP) were detected by real-time PCR. The results showed that the mRNA and protein abundances of PGC-1β in PGC-1β-shRNA transfected adipocytes were significantly lower than those in the control. Interference decreased cell differentiation, but did not depress the cell proliferation. PGC-1β interference impeded the triglyceride accumulation, the mRNA expression levels of nuclear receptors PPARγ and SREBP-1c, and fatty acid synthetase (FAS), and both proteins PPARγ and SREBP-1c, and the fatty acids transporting protein A-FABP. Generally, PGC-1β modulated the cell differentiation and triglyceride accumulation in chicken adipocytes.

Characterization of different adipose depots in fattened buffalo: histological features and expression profiling of adipocyte markers

Adipose tissue (AT) is a multi-depot organ in mammals. AT from various depots differs in composition and function. Revealing the composition feature of AT depots will provide valuable information for further research on the development and fat deposition patterns in buffalo. This study explored the cellular morphology and gene expression profiles of brown and beige markers in seven AT depots of fattened buffalo: three subcutaneous depots (back, sternum, and inguinal) and four visceral depots (perirenal, mesenteric, pericardial, and omental). Histological results showed unilocular adipocytes in all seven AT depots. Uncoupling protein 1 (UCP1) mRNA, a brown and beige adipocyte gene, was detected in all depots with the highest level in VAT depots, and a limited number of UCP1-positive unilocular adipocytes were observed in the three VAT depots. The mRNAs of PPARG coactivator 1 alpha (PGC1 α ) and transmembrane protein 26 (TMEM26), brown or beige adipocyte markers, were identified in all seven depots and were mainly expressed in VAT depots. However, the mRNA of zinc finger protein of the cerebellum 1 (ZIC1), a brown adipocyte-specific marker, was almost undetectable. Our results demonstrated that all seven AT depots are white adipose tissue (WAT), with potential function of non-shivering thermogenesis in fattened buffalo. Beige adipocytes are more active in VAT depots than in WAT depots. These results improve our knowledge on the feature of different adipose tissue depots in buffalo, which will be useful for the research of fat deposition.

Isocitrate dehydrogenase 2 protects mice from high-fat diet-induced metabolic stress by limiting oxidative damage to the mitochondria from brown adipose tissue

Isocitrate dehydrogenase 2 (IDH2) is an NADP+-dependent enzyme that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate in the mitochondrial matrix, and is critical for the production of NADPH to limit the accumulation of mitochondrial reactive oxygen species (ROS). Here, we showed that high-fat diet (HFD) feeding resulted in accelerated weight gain in the IDH2KO mice due to a reduction in whole-body energy expenditure. Moreover, the levels of NADP+, NADPH, NAD+, and NADH were significantly decreased in the brown adipose tissue (BAT) of the HFD-fed IDH2KO animals, accompanied by decreased mitochondrial function and reduced expression of key genes involved in mitochondrial biogenesis, energy expenditure, and ROS resolution. Interestingly, these changes were partially reversed when the antioxidant butylated hydroxyanisole was added to the HFD. These observations reveal a crucial role for IDH2 in limiting ROS-dependent mitochondrial damage when BAT metabolism is normally enhanced to limit weight gain in response to dietary caloric overload.

Multiple Levels of PGC-1α Dysregulation in Heart Failure

Metabolic adaption is crucial for the heart to sustain its contractile activity under various physiological and pathological conditions. At the molecular level, the changes in energy demand impinge on the expression of genes encoding for metabolic enzymes. Among the major components of an intricate transcriptional circuitry, peroxisome proliferator-activated receptor γ coactivator 1 alpha (PGC-1α) plays a critical role as a metabolic sensor, which is responsible for the fine-tuning of transcriptional responses to a plethora of stimuli. Cumulative evidence suggests that energetic impairment in heart failure is largely attributed to the dysregulation of PGC-1α. In this review, we summarize recent studies revealing how PGC-1α is regulated by a multitude of mechanisms, operating at different regulatory levels, which include epigenetic regulation, the expression of variants, post-transcriptional inhibition, and post-translational modifications. We further discuss how the PGC-1α regulatory cascade can be impaired in the failing heart.

Phenylbutyrate Ameliorates High-Fat Diet-Induced Obesity via Brown Adipose Tissue Activation

Obesity, which is characterized by an excessive accumulation of body fat, is one of the critical factors causing metabolic syndrome. Many studies have been performed to identify appropriate agents to control obesity, but toxicity remains a problem. Herein, we identified that phenylbutyrate (PBA), which has been used to treat urea cycle disorder with very low toxicity for a long time, efficiently inhibited high fat-induced body weight gain in a diet-induced obesity mouse model (DIO model). PBA treatment decreased body fat mass and increased lean composition. Moreover, PBA increased brown adipose tissue (BAT) activity by increasing glucose uptake, thereby improving glucose tolerance and insulin tolerance. Interestingly, PBA could induce the expression of liver type phosphofructokinase (PFKL), a key enzyme in the glycolytic pathway, and knocking down PFKL dramatically repressed the expression level of Ucp1 as well as those of Prdm16, Cidea, Pgc1α, and Pparγ, which are marker genes for BAT activation. These results strongly suggested that PBA could increase energy expenditure by increasing BAT activity via the induction of PFKL. Taken together, PBA could be used as a therapeutic agent for people with obesity to prevent the development of metabolic syndrome.