Evidence for the role of AMPK in regulating PGC-1 alpha expression and mitochondrial proteins in mouse epididymal adipose tissue

New concepts in the roles of AMPK in adipocyte stem cell biology

Obesity is a major risk factor for many life-threatening diseases. Adipose tissue dysfunction is emerging as a driving factor in the transition from excess adiposity to comorbidities such as metabolic-associated fatty liver disease, cardiovascular disease, Type 2 diabetes and cancer. However, the transition from healthy adipose expansion to the development of these conditions is poorly understood. Adipose stem cells, residing in the vasculature and stromal regions of subcutaneous and visceral depots, are responsible for the expansion and maintenance of organ function, and are now recognised as key mediators of pathological transformation. Impaired tissue expansion drives inflammation, dysregulation of endocrine function and the deposition of lipids in the liver, muscle and around vital organs, where it is toxic. Contrary to previous hypotheses, it is the promotion of healthy adipose tissue expansion and function, not inhibition of adipogenesis, that presents the most attractive therapeutic strategy in the treatment of metabolic disease. AMP-activated protein kinase, a master regulator of energy homeostasis, has been regarded as one such target, due to its central role in adipose tissue lipid metabolism, and its apparent inhibition of adipogenesis. However, recent studies utilising AMP-activated protein kinase (AMPK)-specific compounds highlight a more subtle, time-dependent role for AMPK in the process of adipogenesis, and in a previously unexplored repression of leptin, independent of adipocyte maturity. In this article, I discuss historic evidence for AMPK-mediated adipogenesis inhibition and the multi-faceted roles for AMPK in adipose tissue.

Differential expression of ADRB1 causes different responses to norepinephrine in adipocytes of Duroc-Landrace-Yorkshire pigs and min pigs

Research has shown that pigs from different regions exhibit varying responses to cold stimuli. Typically, cold stimuli induce browning of white adipose tissue mediated by adrenaline, promoting non-shivering thermogenesis. However, the molecular mechanisms underlying differential response of pig breeds to norepinephrine are unclear. The aim of this study was to investigate the differences and molecular mechanisms of the effects of norepinephrine (NE) treatment on adipocytes of Min pigs (a cold-resistant pig breed) and Duroc-Landrace-Yorkshire (DLY) pigs. Real time-qPCR, western blot, and immunofluorescence were performed following NE treatment on cell cultures of adipocytes originating from Min pigs (n = 3) and DLY pigs (n = 3) to assess the expressions of adipogenesis markers, beige fat markers, and mitochondrial biogenesis markers. The results showed that NE did not affect browning of adipocytes in DLY pigs, whereas promoted browning of adipocytes in Min pigs. Further, the expression of ADRB1 (Adrenoceptor Beta 1, ADRB1) was higher in subcutaneous adipose tissue and adipocytes of Min pigs than those of DLY pigs. Overexpression of ADRB1 in DLY pig adipocytes enhanced sensitivity to NE, exhibiting decreased adipogenesis markers, upregulated beige fat markers, and increased mitochondrial biogenesis. Conversely, adipocytes treated with ADRB1 antagonist in Min pigs resulted in decreased cellular sensitivity to NE. Further studies revealed differential CpG island methylation in ADRB1 promoter region, with lower methylation levels in Min pigs compared to DLY pigs. In conclusion, differential methylation of the ADRB1 promoter region leads to different ADRB1 expression, resulting in varying responsiveness to NE in adipocytes of two pig breeds. Our results provide new insights for further analysis of the differential cold responsiveness in pig breeds from different regions.

Protective Mechanisms of SGLTi in Ischemic Heart Disease

Ischemic heart disease (IHD) is a common clinical cardiovascular disease with high morbidity and mortality. Sodium glucose cotransporter protein inhibitor (SGLTi) is a novel hypoglycemic drug. To date, both clinical trials and animal experiments have shown that SGLTi play a protective role in IHD, including myocardial infarction (MI) and ischemia/reperfusion (I/R). The protective effects may be involved in mechanisms of energy metabolic conversion, anti-inflammation, anti-fibrosis, ionic homeostasis improvement, immune cell development, angiogenesis and functional regulation, gut microbiota regulation, and epicardial lipids. Thus, this review summarizes the above mechanisms and aims to provide theoretical evidence for therapeutic strategies for IHD.

Clcn3 deficiency ameliorates high-fat diet-induced obesity and improves metabolism in mice

Objective

Obesity is defined as excess body fat and is a current health epidemic associated with increased risk for type 2 diabetes and cardiovascular disease. The ClC-3 chloride channel/antiporter, encoded by the Clcn3, is associated with some diseases, like carcinoma, nervous system diseases, and metabolic diseases. To verify the relationship between the Clcn3 and weight including metabolic changes, searching for a new target for metabolic therapy of obesity, we designed the experiment.

Methods

The mice were divided into 4 different groups: Clcn3+/+ mice + high-fat diet (HFD), Clcn3-/- mice + HFD, Clcn3+/+ mice + normal diet (ND), Clcn3-/- mice + ND, and fed for 16 weeks. After the glucose tolerance test and insulin tolerance test, peripheral blood and adipose tissues were collected. Moreover, we performed transcriptome sequencing for the epididymal white adipose tissue from Clcn3+/+ and Clcn3-/- mice with the high-fat diet. Western blotting verified the changes in protein levels of relevant metabolic genes.

Results

We found that the Clcn3-/- mice had lower body weight and visceral fat, refining glucose and lipid metabolism in HFD-induced mice, but had no effect in normal diet mice. RNA-seq and Western blotting indicated that Clcn3 deficiency may inhibit obesity through the AMPK-UCP1 axis.

Conclusion

Modulation of Clcn3 may provide an appealing therapeutic target for obesity and associated metabolic syndrome.

Anti-Obesity Effect of Jeju Roasted Citrus Peel Extract in High-Fat Diet-Induced Obese Mice and 3T3-L1 Adipocytes Via Lipid Metabolism Regulation

Lipid accumulation in adipocytes occurs through multifactorial effects such as overnutrition due to unbalanced eating habits, reduced physical activity, and genetic factors. In addition, obesity can be intensified by the dis-regulation of various metabolic systems such as differentiation, lipogenesis, lipolysis, and energy metabolism of adipocytes. In this study, the Jeju roasted peel extract from Citrus unshiu S.Markov. (JRC), which is discarded as opposed to the pulp of C. unshiu S.Markov., is commonly consumed to ameliorate obesity. To investigate the anti-obesity effect of JRC, these studies were conducted on differentiated 3T3-L1 cells and in high-fat diet-induced mice, and related methods were used to confirm whether it decreased lipid accumulation in adipocytes. The mechanism of inhibiting obesity by JRC was confirmed through mRNA expression studies. JRC suppressed lipid accumulation in adipocytes and adipose tissue, and significantly improved enzymes such as alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyl transferase and serum lipid profiles. In addition, it effectively modulated the expression of genes related to lipid and energy metabolism in adipose tissue. As a result, these findings suggest that JRC could be a therapeutic regulator of body fat accumulation by significantly alleviating the dis-regulation of intracellular lipid metabolism in adipocytes and by enhancement of energy metabolism (Approval No. CNU IACUC-YB-2023-98).

AMP-activated protein kinase activation suppresses leptin expression independently of adipogenesis in primary murine adipocytes

Adipogenesis, defined as the development of mature adipocytes from stem cell precursors, is vital for the expansion, turnover and health of adipose tissue. Loss of adipogenic potential in adipose stem cells, or impairment of adipogenesis is now recognised as an underlying cause of adipose tissue dysfunction and is associated with metabolic disease. In this study, we sought to determine the role of AMP-activated protein kinase (AMPK), an evolutionarily conserved master regulator of energy homeostasis, in adipogenesis. Primary murine adipose-derived stem cells were treated with a small molecule AMPK activator (BI-9774) during key phases of adipogenesis, to determine the effect of AMPK activation on adipocyte commitment, maturation and function. To determine the contribution of the repression of lipogenesis by AMPK in these processes, we compared the effect of pharmacological inhibition of acetyl-CoA carboxylase (ACC). We show that AMPK activation inhibits adipogenesis in a time- and concentration-dependent manner. Transient AMPK activation during adipogenic commitment leads to a significant, ACC-independent, repression of adipogenic transcription factor expression. Furthermore, we identify a striking, previously unexplored inhibition of leptin gene expression in response to both short-term and chronic AMPK activation irrespective of adipogenesis. These findings reveal that in addition to its effect on adipogenesis, AMPK activation switches off leptin gene expression in primary mouse adipocytes independently of adipogenesis. Our results identify leptin expression as a novel target of AMPK through mechanisms yet to be identified.

Polysaccharides derived from natural edible and medicinal sources as agents targeting exercise-induced fatigue: A review

Exercise-induced fatigue (EF) is a common occurrence during prolonged endurance and excessive exercise and is mainly caused by energy depletion, harmful metabolite accumulation, oxidative stress, and inflammation. EF usually leads to a reduction in initiating or maintaining spontaneous activities and muscle performance and ultimately results in a decrease in the quality of life of people who engage in physical work. Therefore, the interest in investigating EF-targeting agents with minimal side effects and good long-term efficacy has substantially increased. Natural edible and medicinal polysaccharides have shown positive anti-EF effects, but the relevant reviews are rare. This review comprehensively summarizes studies on natural polysaccharides from edible and medicinal sources that can relieve EF and improve physical performance from the past decade, focusing on their sources, monosaccharide compositions, anti-EF effects, and possible molecular mechanisms. Most of these anti-EF polysaccharides are heteropolysaccharides and are mainly composed of glucose, arabinose, galactose, rhamnose, xylose, and mannose. In EF animal models, the polysaccharides exert positive EF-alleviating effects through energy supply, metabolic regulation, antioxidation, anti-inflammation, and gut microbiota remodeling. However, further studies are still needed to clarify the anti-EF effects of these polysaccharides on human beings. In summary, the present review expects to provide scientific data for the future research and development of natural polysaccharide-based anti-EF drugs, dietary supplements, and health-care products for specific fatigue groups.

Extracellular Superoxide Dismutase Attenuates Hepatic Oxidative Stress in Nonalcoholic Fatty Liver Disease through the Adenosine Monophosphate-Activated Protein Kinase Activation

Oxidative stress is key in type 2 diabetes-associated nonalcoholic fatty liver disease (NAFLD). We explored whether extracellular superoxide dismutase (EC-SOD) activates adenosine monophosphate-activated protein kinase (AMPK) to enhance antioxidant synthesis and lipid metabolism in NAFLD. Human recombinant EC-SOD (hEC-SOD) was administered to 8-week-old male C57BLKS/J db/db mice through intraperitoneal injection once a week for 8 weeks. Target molecules involved in oxidative stress and lipid metabolism were investigated. hEC-SOD improved insulin resistance and systemic and hepatic oxidative stress characterized by increases in urinary 8-hydroxy-deoxyguanosine and 8-isoprostane levels in db/db mice and a decrease in DHE expression in the liver, respectively. Hepatic SOD3 expression in db/db mice was reversed by hEC-SOD, which improved hepatic steatosis, inflammation with M2 polarization, apoptosis, autophagy, fibrosis and lipid metabolism in db/db mice, as reflected by the changes in serum and hepatic markers, monocyte chemoattractant protein-1, tumor necrosis factor-α, TUNEL-positive cells, Bcl-2/BAX ratio, beclin1 and LC3-II/LC3-1. At the molecular level, hEC-SOD increased phosphorylated-AMPK related to CaMKKß, activation of peroxisome proliferative-activated receptor-gamma coactivator (PGC)-1α and dephosphorylation of forkhead box O (FoxO)1 and their subsequent downstream signaling. In HepG2Cs cells using AMPKα1 and AMPKα2 siRNA, hEC-SOD demonstrated a protective effect via the direct activation of both AMPK-PGC-1α and AMPK-FoxO1. EC-SOD might be a potential therapeutic agent for NAFLD through the activation of AMPK-PGC-1α and AMPK-FoxO1 signaling in hepatocytes, which modulates lipid metabolism, leading to anti-inflammatory, antioxidative and antiapoptotic effects and improving autophagy in the liver.

AMPK and the Endocrine Control of Metabolism

Complex multicellular organisms require a coordinated response from multiple tissues to maintain whole-body homeostasis in the face of energetic stressors such as fasting, cold, and exercise. It is also essential that energy is stored efficiently with feeding and the chronic nutrient surplus that occurs with obesity. Mammals have adapted several endocrine signals that regulate metabolism in response to changes in nutrient availability and energy demand. These include hormones altered by fasting and refeeding including insulin, glucagon, glucagon-like peptide-1, catecholamines, ghrelin, and fibroblast growth factor 21; adipokines such as leptin and adiponectin; cell stress-induced cytokines like tumor necrosis factor alpha and growth differentiating factor 15, and lastly exerkines such as interleukin-6 and irisin. Over the last 2 decades, it has become apparent that many of these endocrine factors control metabolism by regulating the activity of the AMPK (adenosine monophosphate-activated protein kinase). AMPK is a master regulator of nutrient homeostasis, phosphorylating over 100 distinct substrates that are critical for controlling autophagy, carbohydrate, fatty acid, cholesterol, and protein metabolism. In this review, we discuss how AMPK integrates endocrine signals to maintain energy balance in response to diverse homeostatic challenges. We also present some considerations with respect to experimental design which should enhance reproducibility and the fidelity of the conclusions.

Bmp8a deletion leads to obesity through regulation of lipid metabolism and adipocyte differentiation

The role of bone morphogenetic proteins (BMPs) in regulating adipose has recently become a field of interest. However, the underlying mechanism of this effect has not been elucidated. Here we show that the anti-fat effect of Bmp8a is mediated by promoting fatty acid oxidation and inhibiting adipocyte differentiation. Knocking out the bmp8a gene in zebrafish results in weight gain, fatty liver, and increased fat production. The bmp8a-/- zebrafish exhibits decreased phosphorylation levels of AMPK and ACC in the liver and adipose tissues, indicating reduced fatty acid oxidation. Also, Bmp8a inhibits the differentiation of 3T3-L1 preadipocytes into mature adipocytes by activating the Smad2/3 signaling pathway, in which Smad2/3 binds to the central adipogenic factor PPARγ promoter to inhibit its transcription. In addition, lentivirus-mediated overexpression of Bmp8a in 3T3-L1 cells significantly increases NOD-like receptor, TNF, and NF-κB signaling pathways. Furthermore, NF-κB interacts with PPARγ, blocking PPARγ's activation of its target gene Fabp4, thereby inhibiting adipocyte differentiation. These data bring a signal bridge between immune regulation and adipocyte differentiation. Collectively, our findings indicate that Bmp8a plays a critical role in regulating lipid metabolism and adipogenesis, potentially providing a therapeutic approach for obesity and its comorbidities.

Omentin-1 promotes mitochondrial biogenesis via PGC1α-AMPK pathway in chondrocytes

OBJECTIVE

Omentin-1 is a newly discovered metabolic regulatory adipokine. Studies have shown that omentin-1 possesses pleiotropic effects in different types of cells. This study aims to investigate the regulation by omentin-1 on mitochondrial biogenesis in chondrocytes.

METHODOLOGY

C-28/I2 chondrocytes were treated with omentin-1 (150 and 300 ng/ml) for 24 h. The expression of mitochondrial regulators, markers and the DNA copy was assessed. The mitochondrial morphology was observed by electron microscopy. The mitochondrial respiratory rate and ATP production in chondrocytes were measured by cell lysates.

RESULTS

Omentin-1 treatment up-regulated PGC-1α, NRF-1 and mitochondrial transcription factor A (TFAM) in cultured chondrocytes, indicating that omentin-1 could be involved in the regulation of mitochondrial function. Omentin-1 promoted mtDNA/nDNA and four mitochondrial genes (Tomm20, Tomm40, Timm9 and Atp5c1), mRNA transcripts as well as two mitochondrial protein expressions (SDHB and MTCO1). At a cellular level, omentin-1 enhanced the mitochondrial respiratory rate and ATP production. Mechanistically, we proved that omentin-1 increased AMPKα activation, and the blockage of AMPKα by its inhibitor compound C abolished the inductive effect of omentin-1 on PGC1α expression and mtDNA/nDNA ratio, indicating that the effect of omentin-1 is dependent on AMPKα activation.

CONCLUSION

Omentin-1 is a positive regulator of mitochondrial biogenesis in chondrocytes, and its action is dependent on the AMPK-PGC1α pathway. This study, therefore, implies that omentin-1 has the potential to remedy chondrocyte damage in the prevention and treatment of osteoarthritis.

Echinochrome A Prevents Diabetic Nephropathy by Inhibiting the PKC-Iota Pathway and Enhancing Renal Mitochondrial Function in db/db Mice

Echinochrome A (EchA) is a natural bioproduct extracted from sea urchins, and is an active component of the clinical drug, Histochrome®. EchA has antioxidant, anti-inflammatory, and antimicrobial effects. However, its effects on diabetic nephropathy (DN) remain poorly understood. In the present study, seven-week-old diabetic and obese db/db mice were injected with Histochrome (0.3 mL/kg/day; EchA equivalent of 3 mg/kg/day) intraperitoneally for 12 weeks, while db/db control mice and wild-type (WT) mice received an equal amount of sterile 0.9% saline. EchA improved glucose tolerance and reduced blood urea nitrogen (BUN) and serum creatinine levels but did not affect body weight. In addition, EchA decreased renal malondialdehyde (MDA) and lipid hydroperoxide levels, and increased ATP production. Histologically, EchA treatment ameliorated renal fibrosis. Mechanistically, EchA suppressed oxidative stress and fibrosis by inhibiting protein kinase C-iota (PKCι)/p38 mitogen-activated protein kinase (MAPK), downregulating p53 and c-Jun phosphorylation, attenuating NADPH oxidase 4 (NOX4), and transforming growth factor-beta 1 (TGFβ1) signaling. Moreover, EchA enhanced AMPK phosphorylation and nuclear factor erythroid-2-related factor 2 (NRF2)/heme oxygenase 1 (HO-1) signaling, improving mitochondrial function and antioxidant activity. Collectively, these findings demonstrate that EchA prevents DN by inhibiting PKCι/p38 MAPK and upregulating the AMPKα/NRF2/HO-1 signaling pathways in db/db mice, and may provide a therapeutic option for DN.

The regulatory effects of second-generation antipsychotics on lipid metabolism: Potential mechanisms mediated by the gut microbiota and therapeutic implications

Second-generation antipsychotics (SGAs) are the mainstay of treatment for schizophrenia and other neuropsychiatric diseases but cause a high risk of disruption to lipid metabolism, which is an intractable therapeutic challenge worldwide. Although the exact mechanisms underlying this lipid disturbance are complex, an increasing body of evidence has suggested the involvement of the gut microbiota in SGA-induced lipid dysregulation since SGA treatment may alter the abundance and composition of the intestinal microflora. The subsequent effects involve the generation of different categories of signaling molecules by gut microbes such as endogenous cannabinoids, cholesterol, short-chain fatty acids (SCFAs), bile acids (BAs), and gut hormones that regulate lipid metabolism. On the one hand, these signaling molecules can directly activate the vagus nerve or be transported into the brain to influence appetite via the gut-brain axis. On the other hand, these molecules can also regulate related lipid metabolism via peripheral signaling pathways. Interestingly, therapeutic strategies directly targeting the gut microbiota and related metabolites seem to have promising efficacy in the treatment of SGA-induced lipid disturbances. Thus, this review provides a comprehensive understanding of how SGAs can induce disturbances in lipid metabolism by altering the gut microbiota.

Bavachin and Corylifol A Improve Muscle Atrophy by Enhancing Mitochondria Quality Control in Type 2 Diabetic Mice

Type 2 diabetes reduces muscle mass and function. Chronic inflammation and mitochondrial dysfunction play critical roles in muscle atrophy pathogenesis. Here, we investigated the effects of bavachin and corylifol A from Psoralea corylifolia L. seeds on muscle atrophy in dexamethasone-treated mice and in db/db mice. Bavachin and corylifol A enhanced muscle strength and muscle mass in dexamethasone-treated mice. In diabetic mice, they enhanced muscle strength and cross-sectional areas. Bavachin and corylifol A suppressed inflammatory cytokine (interleukin-6 and tumor necrosis factor-α) expression levels by downregulating nuclear factor-κB phosphorylation. They decreased the muscle atrophic factor (myostatin, atrogin-1, and muscle RING finger-1) expression levels. They activated the AKT synthetic signaling pathway and induced a switch from fast-type glycolytic fibers (type 2B) to slow-type oxidative fibers (types I and 2A). They increased mitochondrial biogenesis and dynamic factor (optic atrophy-1, mitofusin-1/2, fission, mitochondrial 1, and dynamin 1-like) expression levels via the AMP-activated protein kinase-peroxisome proliferator-activated receptor gamma coactivator 1-alpha signaling pathway. They also improved mitochondrial quality by upregulating the mitophagy factor (p62, parkin, PTEN-induced kinase-1, and BCL2-interacting protein-3) expression levels. Therefore, bavachin and corylifol A exert potential therapeutic effects on muscle atrophy by suppressing inflammation and improving mitochondrial function.

Discovery of a potent allosteric activator of DGKQ that ameliorates obesity-induced insulin resistance via the sn-1,2-DAG-PKCε signaling axis

sn-1,2-diacylglycerol (sn-1,2-DAG)-mediated activation of protein kinase Cε (PKCε) is a key pathway that is responsible for obesity-related lipid metabolism disorders, which induces hepatic insulin resistance and type 2 diabetes. No small molecules have been previously reported to ameliorate these diseases through this pathway. Here, we screened and identified the phytochemical atractylenolide II (AT II) that reduces the hepatic sn-1,2-DAG levels, deactivates PKCε activity, and improves obesity-induced hyperlipidemia, hepatosteatosis, and insulin resistance. Furthermore, using the ABPP strategy, the diacylglycerol kinase family member DGKQ was identified as a direct target of AT II. AT II may act on a novel drug-binding pocket in the CRD and PH domains of DGKQ to thereby allosterically regulate its kinase activity. Moreover, AT II also increases weight loss by activating DGKQ-AMPK-PGC1α-UCP-1 signaling in adipose tissue. These findings suggest that AT II is a promising lead compound to improve obesity-induced insulin resistance.

The effects of camelina sativa oil and high-intensity interval training on liver function and metabolic outcomes in male type 2 diabetic rats

Objectives

The purpose of this study was to evaluate the independent and combined effects of camelina sativa oil and high-intensity interval training (HIIT) on liver function, and metabolic outcomes in streptozotocin-induced diabetic rats.

Methods

Forty male Wistar rats were randomly assigned to five equal groups (8 per group): Normal control (NC), diabetic control (DC), diabetic + camelina sativa oil (300 mg/kg by oral gavage per day; D + CSO), diabetic + HIIT (running on a treadmill 5 days/week for 8 weeks; D + HIIT), diabetic + camelina sativa oil + HIIT (D + CSO +  HIIT).

Results

In all three intervention groups (D + CSO, D + HIIT, and D + CSO + HIIT) compared to the DC, hepatic TNF-α, MDA, and histopathology markers, decreased and hepatic PGC-1α, and PPAR-γ increased (p < 0.05). However, the effect of D + CSO was greater than D + HIIT alone. Hepatic TG decreased significantly in D + HIIT and D + CSO + HIIT compared to other groups (p < 0.001). Fasting plasma glucose in all three intervention groups (D + CSO, D + HIIT, and D + CSO + HIIT) and HOMA-IR in D + CSO and D + CSO + HIIT were decreased compared to DC (p < 0.001). Only hepatic TAC and fasting plasma insulin remained unaffected in the three diabetic groups (p < 0.001). Overall, D + CSO + HIIT had the largest effect on all outcomes.

Conclusions

At the doses and treatment duration used in the current study, combination of CSO and HIIT was beneficial for reducing liver function and metabolic outcomes other than CSO and HIIT alone.

Environmental toxicants, brown adipose tissue, and potential links to obesity and metabolic disease

Rates of human obesity, type 2 diabetes, and non-alcoholic fatty liver disease (NAFLD) have risen faster than anticipated and cannot solely be explained by excessive caloric intake or physical inactivity. Importantly, this effect is also observed in many other domesticated and non-domesticated mammals, which has led to the hypothesis that synthetic environmental pollutants may be contributing to disease development. While the impact of these chemicals on appetite and adipogenesis has been extensively studied, their potential role in reducing energy expenditure is less studied. An important component of whole-body energy expenditure is adaptive and diet-induced thermogenesis in human brown adipose tissue (BAT). This review summarizes recent evidence that environmental pollutants such as the pesticide chlorpyrifos inhibit BAT function, diet-induced thermogenesis and the potential signaling pathways mediating these effects. Lastly, we discuss the importance of housing experimental mice at thermoneutrality, rather than room temperature, to maximize the translation of findings to humans.

Sodium butyrate attenuated diet-induced obesity, insulin resistance and inflammation partly by promoting fat thermogenesis via intro-adipose sympathetic innervation

Emerging evidence suggests that butyrate, a short-chain fatty acid, may have beneficial effects on obesity and its associated metabolic comorbidities, but the related molecular mechanism is largely unknown. This study aims to investigate the role of butyrate in diet-induced obesity and metabolic disorders and the relevant regulatory mechanisms. Here, dietary supplementation with Sodium butyrate (NaB) was carried out in mice fed with a high-fat diet (HFD) or chow diet. At week 14, mice on HFD displayed an obese phenotype and down-regulated expression of thermogenic regulators including Ucp-1 and Pgc-1α in adipose tissue. Excitingly, NaB add-on treatment abolished these detrimental effects. Moreover, the obesity-induced insulin resistance, inflammation, fatty liver, and intestinal dysfunction were also attenuated by NaB administration. Mechanistically, NaB can promote fat thermogenesis via the increased local sympathetic innervation of adipose tissue, and blocking the β3-adrenergic signaling pathway by 6-hydroxydopamine abolished NaB-induced thermogenesis. Our study reveals a potential pharmacological target for NaB to combat obesity and metabolic disorders.

Short-term moderate caloric restriction in a high-fat diet alleviates obesity via AMPK/SIRT1 signaling in white adipocytes and liver

Background

Obesity is a growing problem for public health worldwide. Calorie restriction (CR) is a safety and effective life intervention to defend against obesity. Short-term moderate CR may be a more favorable strategy against this pathology. However, the mechanisms behind the effects of CR remain to be clarified. Increased energy expenditure in the liver and brown adipose tissue could potentially be manipulated to modulate and improve metabolism in obesity. Moreover, nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin-1 (SIRT1) and AMP-activated protein kinase (AMPK) are well-characterized metabolic modulators. We aim to explore the anti-obesity effects of short-term moderate CR by improving energy metabolism via the SIRT1/AMPK pathway in white adipocytes and liver in a mouse model of obesity.

Methods

Male C57BL/6 mice were randomized into two groups receiving either a standard or a high-fat diet (HFD) for 8 weeks to induce obesity. The HFD-induced obese mice were further randomized into two groups: HFD group or CR group (received 75% of the food eaten by HFD group). Their energy metabolism, white adipose tissue (WAT) contents, hepatic fat deposition, the expression of AMPK, SIRT1, peroxisome proliferators γ-activated receptor coactivator-1α (PGC-1α), nuclear factor kappa B (NF-κB), endothelial nitric oxide synthase (eNOS) in WAT, and hepatic tissues were determined.

Results

After 4 weeks, body weight, total serum cholesterol, fasting blood glucose, and insulin levels were significantly lower in the CR group. Moreover, CR ameliorated hepatocyte steatosis, attenuated white adipogenesis, and increased energy expenditure and expressions of SIRT1, PGC-1α, and phosphorylated AMPK in subcutaneous WAT and the hepatic tissues. In addition, CR reduced the protein levels of NF-κB and increased the eNOS expression.

Conclusion

Short-term moderate CR decreases obesity, increases the thermogenesis, and inhibits inflammation in a mouse model of obesity, probably via the activation of the AMPK/SIRT1 pathway in WAT and liver.

Tissue Transglutaminase Knock-Out Preadipocytes and Beige Cells of Epididymal Fat Origin Possess Decreased Mitochondrial Functions Required for Thermogenesis

Beige adipocytes with thermogenic function are activated during cold exposure in white adipose tissue through the process of browning. These cells, similar to brown adipocytes, dissipate stored chemical energy in the form of heat with the help of uncoupling protein 1 (UCP1). Recently, we have shown that tissue transglutaminase (TG2) knock-out mice have decreased cold tolerance in parallel with lower utilization of their epididymal adipose tissue and reduced browning. To learn more about the thermogenic function of this fat depot, we isolated preadipocytes from the epididymal adipose tissue of wild-type and TG2 knock-out mice and differentiated them in the beige direction. Although differentiation of TG2 knock-out preadipocytes is phenotypically similar to the wild-type cells, the mitochondria of the knock-out beige cells have multiple impairments including an altered electron transport system generating lower electrochemical potential difference, reduced oxygen consumption, lower UCP1 protein content, and a higher portion of fragmented mitochondria. Most of these differences are present in preadipocytes as well, and the differentiation process cannot overcome the functional disadvantages completely. TG2 knock-out beige adipocytes produce more iodothyronine deiodinase 3 (DIO3) which may inactivate thyroid hormones required for the establishment of optimal mitochondrial function. The TG2 knock-out preadipocytes and beige cells are both hypometabolic as compared with the wild-type controls which may also be explained by the lower expression of solute carrier proteins SLC25A45, SLC25A47, and SLC25A42 which transport acylcarnitine, Co-A, and amino acids into the mitochondrial matrix. As a consequence, the mitochondria in TG2 knock-out beige adipocytes probably cannot reach the energy-producing threshold required for normal thermogenic functions, which may contribute to the decreased cold tolerance of TG2 knock-out mice.

Stimulation of Alpha-1-Adrenergic Receptor Ameliorates Obesity-Induced Cataracts by Activating Glycolysis and Inhibiting Cataract-Inducing Factors

BACKGROUND

Obesity, the prevalence of which is increasing due to the lack of exercise and increased consumption of Westernized diets, induces various complications, including ophthalmic diseases. For example, obesity is involved in the onset of cataracts.

METHODS

To clarify the effects and mechanisms of midodrine, an α1-adrenergic receptor agonist, in cataracts induced by obesity, we conducted various analytic experiments in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a rat model of obesity.

RESULTS

Midodrine prevented cataract occurrence and improved lens clearance in OLETF rats. In the lenses of OLETF rats treated with midodrine, we observed lower levels of aldose reductase, tumor necrosis factor-α, and sorbitol, but higher levels of hexokinase, 5'-adenosine monophosphate-activated protein kinase-alpha, adenosine 5´-triphosphate, peroxisome proliferator-activated receptordelta, peroxisome proliferator-activated receptor gamma coactivator 1-alpha, superoxide dismutase, and catalase.

CONCLUSION

The ameliorating effects of midodrine on cataracts in the OLETF obesity rat model are exerted via the following three mechanisms: direct inhibition of the biosynthesis of sorbitol, which causes cataracts; reduction of reactive oxygen species and inflammation; and (3) stimulation of normal aerobic glycolysis.

Effects of caloric overload before caloric restriction in the murine heart

The beneficial effects of caloric restriction (CR) against cardiac aging and for prevention of cardiovascular diseases are numerous. However, to our knowledge, there is no scientific evidence about how a high-calorie diet (HCD) background influences the mechanisms underlying CR in whole heart tissue (WHT) in experimental murine models. In the current study, CR-treated mice with different alimentary backgrounds were subjected to transthoracic echocardiographic measurements. WHT was then analyzed to determine cardiac energetics, telomerase activity, the expression of energy-sensing networks, tissue-specific adiponectin, and cardiac precursor/cardiac stem cell markers. Animals with a balanced diet consumption before CR presented marked cardiac remodeling with improved ejection fraction (EF) and fractional shortening (FS), enhanced OXPHOS complex I, III, and IV, and CKMT2 enzymatic activity. Mice fed an HCD before CR presented moderate changes in cardiac geometry with diminished EF and FS values, but improved OXPHOS complex IV and CKMT2 activity. Differences in cardiac remodeling, left ventricular systolic/diastolic performance, and mitochondrial energetics, found in the CR-treated mice with contrasting alimentary backgrounds, were corroborated by inconsistencies in the expression of mitochondrial-biogenesis-related markers and associated regulatory networks. In particular, disruption of eNOS and AMPK -PGC-1α-mTOR-related axes. The impact of a past habit of caloric overload on the effects of CR in the WHT is a scarcely explored subject that requires deeper study in combination with analyses of other tissues and organs at higher levels of organization within the organ system. Such research will eventually lead to the development of preventative and therapeutic strategies to promote health and longevity.

Intertwined Relationship of Mitochondrial Metabolism, Gut Microbiome and Exercise Potential

The microbiome has emerged as a key player contributing significantly to the human physiology over the past decades. The potential microbial niche is largely unexplored in the context of exercise enhancing capacity and the related mitochondrial functions. Physical exercise can influence the gut microbiota composition and diversity, whereas a sedentary lifestyle in association with dysbiosis can lead to reduced well-being and diseases. Here, we have elucidated the importance of diverse microbiota, which is associated with an individual's fitness, and moreover, its connection with the organelle, the mitochondria, which is the hub of energy production, signaling, and cellular homeostasis. Microbial by-products, such as short-chain fatty acids, are produced during regular exercise that can enhance the mitochondrial capacity. Therefore, exercise can be employed as a therapeutic intervention to circumvent or subside various metabolic and mitochondria-related diseases. Alternatively, the microbiome-mitochondria axis can be targeted to enhance exercise performance. This review furthers our understanding about the influence of microbiome on the functional capacity of the mitochondria and exercise performance, and the interplay between them.

AMPK and the Adaptation to Exercise

Noncommunicable diseases are chronic diseases that contribute to death worldwide, but these diseases can be prevented and mitigated with regular exercise. Exercise activates signaling molecules and the transcriptional network to promote physiological adaptations, such as fiber type transformation, angiogenesis, and mitochondrial biogenesis. AMP-activated protein kinase (AMPK) is a master regulator that senses the energy state, promotes metabolism for glucose and fatty acid utilization, and mediates beneficial cellular adaptations in many vital tissues and organs. This review focuses on the current, integrative understanding of the role of exercise-induced activation of AMPK in the regulation of system metabolism and promotion of health benefits.

AMPK Activity: A Primary Target for Diabetes Prevention with Therapeutic Phytochemicals

Diabetes is a metabolic syndrome characterized by inadequate blood glucose control and is associated with reduced quality of life and various complications, significantly shortening life expectancy. Natural phytochemicals found in plants have been traditionally used as medicines for the prevention of chronic diseases including diabetes in East Asia since ancient times. Many of these phytochemicals have been characterized as having few side effects, and scientific research into the mechanisms of action responsible has accumulated mounting evidence for their efficacy. These compounds, which may help to prevent metabolic syndrome disorders including diabetes, act through relevant intracellular signaling pathways. In this review, we examine the anti-diabetic efficacy of several compounds and extracts derived from medicinal plants, with a focus on AMP-activated protein kinase (AMPK) activity.

Pharmacological Approaches to Attenuate Inflammation and Obesity with Natural Products Formulations by Regulating the Associated Promoting Molecular Signaling Pathways

Obesity is a public health problem characterized by increased body weight due to abnormal adipose tissue expansion. Bioactive compound consumption from the diet or intake of dietary supplements is one of the possible ways to control obesity. Natural products with adipogenesis-regulating potential act as obesity treatments. We evaluated the synergistic antiangiogenesis, antiadipogenic and antilipogenic efficacy of standardized rebaudioside A, sativoside, and theasaponin E1 formulations (RASE1) in vitro in human umbilical vein endothelial cells (HUVECs), 3T3-L1 preadipocytes respectively, and in vivo using a high-fat and carbohydrate diet-induced obesity mouse model. Orlistat was used as a positive control, while untreated cells and animals were normal controls (NCs). Adipose tissue, liver, and blood were analyzed after dissection. Extracted stevia compounds and green tea seed saponin E1 exhibited pronounced antiobesity effects when combined. RASE1 inhibited HUVEC proliferation and tube formation by suppressing VEGFR2, NF-κB, PIK3, and-catenin beta-1 expression levels. RASE1 inhibited 3T3-L1 adipocyte differentiation and lipid accumulation by downregulating adipogenesis- and lipogenesis-promoting genes. RASE1 oral administration reduced mouse body and body fat pad weight and blood cholesterol, TG, ALT, AST, glucose, insulin, and adipokine levels. RASE1 suppressed adipogenic and lipid metabolism gene expression in mouse adipose and liver tissues and enhanced AMP-activated protein kinase levels in liver and adipose tissues and in serum adiponectin. RASE1 suppressed the NF-κB pathway and proinflammatory cytokines IL-10, IL-6, and TNF-α levels in mice which involve inflammation and progression of obesity. The overall results indicate RASE1 is a potential therapeutic formulation and functional food for treating or preventing obesity and inflammation.

A Novel Multi-Ingredient Supplement Activates a Browning Program in White Adipose Tissue and Mitigates Weight Gain in High-Fat Diet-Fed Mice

We investigated the effects of a novel multi-ingredient supplement comprised of polyphenol antioxidants and compounds known to facilitate mitochondrial function and metabolic enhancement (ME) in a mouse model of obesity. In this study, 6-week-old male C57/BL6J mice were placed on a high-fat diet (HFD; ~60% fat) for 6 weeks, with subsequent allocation into experimentalgroups for 4 weeks: HFD control, HFD + ME10 (10 components), HFD + ME7 (7 components), HFD + ME10 + EX, HFD + EX (where '+EX' animals exercised 3 days/week), and chow-fed control. After the intervention, HFD control animals had significantly greater body weight and fat mass. Despite the continuation of HFD, animals supplemented with multi-ingredient ME or who performed exercise training showed an attenuation of fat mass and preservation of lean body mass, which was further enhanced when combined (ME+EX). ME supplementation stimulated the upregulation of white and brown adipose tissue mRNA transcripts associated with mitochondrial biogenesis, browning, fatty acid transport, and fat metabolism. In WAT depots, this was mirrored by mitochodrial oxidative phosphorylation (OXPHOS) protein expression, and increased in vivo fat oxidation measured via CLAMS. ME supplementation also decreased systemic and local inflammation markers. Herein, we demonstrated that novel multi-ingredient nutritional supplements induced significant fat loss independent of physical activity while preserving muscle mass in obese mice. Mechanistically, these MEs appear to act by inducing a browning program in white adipose tissue and decreasing other pathophysiological impairments associated with obesity, including mitochondrial respiration alterations induced by HFD.

AMPK Localization: A Key to Differential Energy Regulation

As the central node between nutrition signaling input and the metabolic pathway, AMP-activated protein kinase (AMPK) is tightly regulated to maintain energy homeostasis. Subcellular compartmentalization of AMPK is one of the critical regulations that enables AMPK to access proper targets and generate appropriate responses to specific perturbations and different levels of stress. One of the characterized localization mechanisms is RanGTPase-driven CRM1 that recognizes the nuclear export sequence (NES) on the α subunit to translocate AMPK into the cytoplasm. Nuclear localization putatively employs RanGTPase-driven importin that might recognize the nuclear localization signal (NLS) present on the AMPKα2 kinase domain. Nucleo-cytoplasmic shuttling of AMPK is influenced by multiple factors, such as starvation, exercise, heat shock, oxidant, cell density, and circadian rhythm. Tissue-specific localization, which distributes AMPK trimers with different combinations, has also been shown to be vital in maintaining tissue-specific metabolism. Tissue-specific and subcellular distribution of AMPK might be attributed to differences in the expression of the subunit, the stabilization by protein regulators, tissue activity, and the localization of AMPK activators. Considering the importance of AMPK localization in coordinating signaling and metabolism, further research is due to fully elucidate the largely unknown complex mechanism underlying this regulation.

HIF-1-Independent Mechanisms Regulating Metabolic Adaptation in Hypoxic Cancer Cells

In solid tumours, cancer cells exist within hypoxic microenvironments, and their metabolic adaptation to this hypoxia is driven by HIF-1 transcription factor, which is overexpressed in a broad range of human cancers. HIF inhibitors are under pre-clinical investigation and clinical trials, but there is evidence that hypoxic cancer cells can adapt metabolically to HIF-1 inhibition, which would provide a potential route for drug resistance. Here, we review accumulating evidence of such adaptions in carbohydrate and creatine metabolism and other HIF-1-independent mechanisms that might allow cancers to survive hypoxia despite anti-HIF-1 therapy. These include pathways in glucose, glutamine, and lipid metabolism; epigenetic mechanisms; post-translational protein modifications; spatial reorganization of enzymes; signalling pathways such as Myc, PI3K-Akt, 2-hyxdroxyglutarate and AMP-activated protein kinase (AMPK); and activation of the HIF-2 pathway. All of these should be investigated in future work on hypoxia bypass mechanisms in anti-HIF-1 cancer therapy. In principle, agents targeted toward HIF-1β rather than HIF-1α might be advantageous, as both HIF-1 and HIF-2 require HIF-1β for activation. However, HIF-1β is also the aryl hydrocarbon nuclear transporter (ARNT), which has functions in many tissues, so off-target effects should be expected. In general, cancer therapy by HIF inhibition will need careful attention to potential resistance mechanisms.

Neurological Implications of COVID-19: Role of Redox Imbalance and Mitochondrial Dysfunction

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 or COVID-19 has been declared as a pandemic disease by the World Health Organization (WHO). Globally, this disease affected 159 million of the population and reported ~ 3.3 million deaths to the current date (May 2021). There is no definitive treatment strategy that has been identified, although this disease has prevailed in its current form for the past 18 months. The main challenges in the (SARS-CoV)-2 infections are in identifying the heterogeneity in viral strains and the plausible mechanisms of viral infection to human tissues. In parallel to the investigations into the patho-mechanism of SARS-CoV-2 infection, understanding the fundamental processes underlying the clinical manifestations of COVID-19 is very crucial for designing effective therapies. Since neurological symptoms are very apparent in COVID-19 infected patients, here, we tried to emphasize the involvement of redox imbalance and subsequent mitochondrial dysfunction in the progression of the COVID-19 infection. It has been articulated that mitochondrial dysfunction is very apparent and also interlinked to neurological symptoms in COVID-19 infection. Overall, this article provides an in-depth overview of redox imbalance and mitochondrial dysfunction involvement in aggravating COVID-19 infection and its probable contribution to the neurological manifestation of the disease.

Non-shivering Thermogenesis Signalling Regulation and Potential Therapeutic Applications of Brown Adipose Tissue

In mammals, thermogenic organs exist in the body that increase heat production and enhance energy regulation. Because brown adipose tissue (BAT) consumes energy and generates heat, increasing energy expenditure via BAT might be a potential strategy for new treatments for obesity and obesity-related diseases. Thermogenic differentiation affects normal adipose tissue generation, emphasizing the critical role that common transcriptional regulation factors might play in common characteristics and sources. An understanding of thermogenic differentiation and related factors could help in developing ways to improve obesity indirectly or directly through targeting of specific signalling pathways. Many studies have shown that the active components of various natural products promote thermogenesis through various signalling pathways. This article reviews recent major advances in this field, including those in the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA), cyclic guanosine monophosphate-GMP-dependent protein kinase G (cGMP-AKT), AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), transforming growth factor-β/bone morphogenic protein (TGF-β/BMP), transient receptor potential (TRP), Wnt, nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κΒ), Notch and Hedgehog (Hh) signalling pathways in brown and brown-like adipose tissue. To provide effective information for future research on weight-loss nutraceuticals or drugs, this review also highlights the natural products and their active ingredients that have been reported in recent years to affect thermogenesis and thus contribute to weight loss via the above signalling pathways.

FGF, Mechanism of Action, Role in Parkinson's Disease, and Therapeutics

Parkinson's disease (PD) is a neurodegenerative disease associated with severe disability and adverse effects on life quality. In PD, motor dysfunction can occur, such as quiescence, muscle stiffness, and postural instability. PD is also associated with autonomic nervous dysfunction, sleep disorders, psychiatric symptoms, and other non-motor symptoms. Degeneration of dopaminergic neurons in the substantia nigra compact (SNPC), Lewy body, and neuroinflammation are the main pathological features of PD. The death or dysfunction of dopaminergic neurons in the dense part of the substantia nigra leads to dopamine deficiency in the basal ganglia and motor dysfunction. The formation of the Lewy body is associated with the misfolding of α-synuclein, which becomes insoluble and abnormally aggregated. Astrocytes and microglia mainly cause neuroinflammation, and the activation of a variety of pro-inflammatory transcription factors and regulatory proteins leads to the degeneration of dopaminergic neurons. At present, PD is mainly treated with drugs that increase dopamine concentration or directly stimulate dopamine receptors. Fibroblast growth factor (FGF) is a family of cellular signaling proteins strongly associated with neurodegenerative diseases such as PD. FGF and its receptor (FGFR) play an essential role in the development and maintenance of the nervous system as well as in neuroinflammation and have been shown to improve the survival rate of dopaminergic neurons. This paper summarized the mechanism of FGF and its receptors in the pathological process of PD and related signaling pathways, involving the development and protection of dopaminergic neurons in SNPC, α-synuclein aggregation, mitochondrial dysfunction, and neuroinflammation. It provides a reference for developing drugs to slow down or prevent the potential of PD.

AMPK mediates energetic stress-induced liver GDF15

Growth differentiating factor-15 (GDF15) is an emerging target for the treatment of obesity and metabolic disease partly due to its ability to suppress food intake. GDF15 expression and secretion are thought to be regulated by a cellular integrated stress response, which involves endoplasmic reticulum (ER) stress. AMPK is another cellular stress sensor, but the relationship between AMPK, ER stress, and GDF15 has not been assessed in vivo. Wildtype (WT), AMPK β1 deficient (AMPKβ1^-/- ), and CHOP^-/- mice were treated with three distinct AMPK activators; AICAR, which is converted to ZMP mimicking the effects of AMP on the AMPKγ isoform, R419, which indirectly activates AMPK through inhibition of mitochondrial respiration, or A769662, a direct AMPK activator which binds the AMPKβ1 isoform ADaM site causing allosteric activation. Following treatments, liver Gdf15, markers of ER-stress, AMPK activity, adenine nucleotides, circulating GDF15, and food intake were assessed. AICAR and R419 caused ER and energetic stress, increased GDF15 expression and secretion, and suppressed food intake. Direct activation of AMPK β1 containing complexes by A769662 increased hepatic Gdf15 expression, circulating GDF15, and suppressed food intake, independent of ER stress. The effects of AICAR, R419, and A769662 on GDF15 were attenuated in AMPKβ1^-/- mice. AICAR and A769662 increased GDF15 to a similar extent in WT and CHOP^-/- mice. Herein, we provide evidence that AMPK plays a role in mediating the induction of GDF15 under conditions of energetic stress in mouse liver in vivo.

Exploring the contribution of mitochondrial dynamics to multiple acyl-CoA dehydrogenase deficiency-related phenotype

Mitochondrial fatty acid β-oxidation disorders (FAOD) are among the diseases detected by newborn screening in most developed countries. Alterations of mitochondrial functionality are characteristic of these metabolic disorders. However, many questions remain to be clarified, namely how the interplay between the signaling pathways harbored in mitochondria contributes to the disease-related phenotype. Herein, we overview the role of mitochondria on the regulation of cell homeostasis through the production of ROS, mitophagy, apoptosis, and mitochondrial biogenesis. Emphasis is given to the signaling pathways involving MnSOD, sirtuins and PGC-1α, which seem to contribute to FAOD phenotype, namely to multiple acyl-CoA dehydrogenase deficiency (MADD). The association between phenotype and genotype is not straightforward, suggesting that specific molecular mechanisms may contribute to MADD pathogenesis, making MADD an interesting model to better understand this interplay. However, more work needs to be done envisioning the development of novel therapeutic strategies.

"Janus-Faced" α-Synuclein: Role in Parkinson's Disease

Parkinson's disease (PD) is a pathological condition characterized by the aggregation and the resultant presence of intraneuronal inclusions termed Lewy bodies (LBs) and Lewy neurites which are mainly composed of fibrillar α-synuclein (α-syn) protein. Pathogenic aggregation of α-syn is identified as the major cause of LBs deposition. Several mutations in α-syn showing varied aggregation kinetics in comparison to the wild type (WT) α-syn are reported in PD (A30P, E46K, H 50Q, G51D, A53E, and A53T). Also, the cell-to-cell spread of pathological α-syn plays a significant role in PD development. Interestingly, it has also been suggested that the pathology of PD may begin in the gastrointestinal tract and spread via the vagus nerve (VN) to brain proposing the gut-brain axis of α-syn pathology in PD. Despite multiple efforts, the behavior and functions of this protein in normal and pathological states (specifically in PD) is far from understood. Furthermore, the etiological factors responsible for triggering aggregation of this protein remain elusive. This review is an attempt to collate and present latest information on α-syn in relation to its structure, biochemistry and biophysics of aggregation in PD. Current advances in therapeutic efforts toward clearing the pathogenic α-syn via autophagy/lysosomal flux are also reviewed and reported.

Role of PGC-1α in the Mitochondrial NAD+ Pool in Metabolic Diseases

Mitochondria play vital roles, including ATP generation, regulation of cellular metabolism, and cell survival. Mitochondria contain the majority of cellular nicotinamide adenine dinucleotide (NAD⁺), which an essential cofactor that regulates metabolic function. A decrease in both mitochondria biogenesis and NAD⁺ is a characteristic of metabolic diseases, and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) orchestrates mitochondrial biogenesis and is involved in mitochondrial NAD⁺ pool. Here we discuss how PGC-1α is involved in the NAD⁺ synthesis pathway and metabolism, as well as the strategy for increasing the NAD⁺ pool in the metabolic disease state.

The phytochemical hyperforin triggers thermogenesis in adipose tissue via a Dlat-AMPK signaling axis to curb obesity

Stimulation of adipose tissue thermogenesis is regarded as a promising avenue in the treatment of obesity. However, pharmacologic engagement of this process has proven difficult. Using the Connectivity Map (CMap) approach, we identified the phytochemical hyperforin (HPF) as an anti-obesity agent. We found that HPF efficiently promoted thermogenesis by stimulating AMPK and PGC-1α via a Ucp1-dependent pathway. Using LiP-SMap (limited proteolysis-mass spectrometry) combined with a microscale thermophoresis assay and molecular docking analysis, we confirmed dihydrolipoamide S-acetyltransferase (Dlat) as a direct molecular target of HPF. Ablation of Dlat significantly attenuated HPF-mediated adipose tissue browning both in vitro and in vivo. Furthermore, genome-wide association study analysis indicated that a variation in DLAT is significantly associated with obesity in humans. These findings suggest that HPF is a promising lead compound in the pursuit of a pharmacological approach to promote energy expenditure in the treatment of obesity.

Lipid Inhibitory Effect of (-)-loliolide Isolated from Sargassum horneri in 3T3-L1 Adipocytes: Inhibitory Mechanism of Adipose-Specific Proteins

Sargassum horneri (S. horneri) is a well-known brown seaweed widely distributed worldwide. Several biological activities of S. horneri have been reported. However, its effects on lipid metabolism and the underlying mechanisms remain elusive. In the present study, we examined the inhibitory effect of the active compound "(-)-loliolide ((6S,7aR)-6-hydroxy-4,4,7a-trimethyl-5,6,7,7a-tetrahydro-1-benzofuran-2(4H)-one (HTT))" from S. horneri extract on lipid accumulation in differentiated adipocytes. MTT assays demonstrated that (-)-loliolide is not toxic to 3T3-L1 adipocytes in a range of concentrations. (-)-loliolide significantly reduced intracellular lipid accumulation in the differentiated phase of 3T3-L1 adipocytes as shown by Oil Red O staining. Western blot analysis revealed that (-)-loliolide increased the expression of lipolytic protein phospho-hormone-sensitive lipase (p-HSL) and thermogenic protein peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1). Additionally, (-)-loliolide decreased expression of adipogenic and lipogenic proteins, including sterol regulatory element-binding protein-1 (SREBP-1), peroxisome proliferator-activated receptor-γ (PPAR-γ), CCAAT/enhancer-binding protein-α (C/EBP-α), and fatty acid-binding protein 4 (FABP4) in 3T3-L1 adipocytes. These results indicate that (-)-loliolide from S. horneri could suppress lipid accumulation via regulation of antiadipogenic and prolipolytic mechanisms in 3T3-L1 cells. Considering the multifunctional effect of (-)-loliolide, it can be useful as a lipid-lowering agent in the management of patients who suffer from obesity.

Intricate role of mitochondrial calcium signalling in mitochondrial quality control for regulation of cancer cell fate

Mitochondrial quality control is crucial for sustaining cellular maintenance. Mitochondrial Ca²⁺ plays an important role in the maintenance of mitochondrial quality control through regulation of mitochondrial dynamics, mitophagy and mitochondrial biogenesis for preserving cellular homeostasis. The regulation of this dynamic interlink between these mitochondrial networks and mitochondrial Ca²⁺ appears indispensable for the adaptation of cells under external stimuli. Moreover, dysregulation of mitochondrial Ca²⁺ divulges impaired mitochondrial control that results in several pathological conditions such as cancer. Hence this review untangles the interplay between mitochondrial Ca²⁺ and quality control that govern mitochondrial health and mitochondrial coordinates in the development of cancer.

Loss of FEZ1, a gene deleted in Jacobsen syndrome, causes locomotion defects and early mortality by impairing motor neuron development

FEZ1-mediated axonal transport plays important roles in central nervous system development but its involvement in the peripheral nervous system is not well-characterized. FEZ1 is deleted in Jacobsen syndrome (JS), an 11q terminal deletion developmental disorder. JS patients display impaired psychomotor skills, including gross and fine motor delay, suggesting that FEZ1 deletion may be responsible for these phenotypes, given its association with the development of motor-related circuits. Supporting this hypothesis, our data show that FEZ1 is selectively expressed in the rat brain and spinal cord. Its levels progressively increase over the developmental course of human motor neurons (MN) derived from embryonic stem cells. Deletion of FEZ1 strongly impaired axon and dendrite development, and significantly delayed the transport of synaptic proteins into developing neurites. Concurring with these observations, Drosophila unc-76 mutants showed severe locomotion impairments, accompanied by a strong reduction of synaptic boutons at neuromuscular junctions. These abnormalities were ameliorated by pharmacological activation of UNC-51/ATG1, a FEZ1-activating kinase, with rapamycin and metformin. Collectively, the results highlight a role for FEZ1 in MN development and implicate its deletion as an underlying cause of motor impairments in JS patients.

The SGLT2 inhibitor canagliflozin suppresses lipid synthesis and interleukin-1 beta in ApoE deficient mice

Sodium-glucose cotransporter 2 inhibitors such as canagliflozin lower blood glucose and reduce cardiovascular events in people with type 2 diabetes through mechanisms that are not fully understood. Canagliflozin has been shown to increase the activity of the AMP-activated protein kinase (AMPK), a metabolic energy sensor important for increasing fatty acid oxidation and energy expenditure and suppressing lipogenesis and inflammation, but whether AMPK activation is important for mediating some of the beneficial metabolic effects of canagliflozin has not been determined. We, therefore, evaluated the effects of canagliflozin in female ApoE-/- and ApoE-/-AMPK β1-/- mice fed a western diet. Canagliflozin increased fatty acid oxidation and energy expenditure and lowered adiposity, blood glucose and the respiratory exchange ratio independently of AMPK β1. Canagliflozin also suppressed liver lipid synthesis and the expression of ATP-citrate lyase, acetyl-CoA carboxylase and sterol response element-binding protein 1c independently of AMPK β1. Canagliflozin lowered circulating IL-1β and studies in bone marrow-derived macrophages indicated that in contrast with the metabolic adaptations, this effect required AMPK β1. Canagliflozin had no effect on the size of atherosclerotic plaques in either ApoE-/- and ApoE-/-AMPK β1-/- mice. Future studies investigating whether reductions in liver lipid synthesis and macrophage IL-1β are important for the cardioprotective effects of canagliflozin warrant further investigation.

Methionine sulfoxide reductase B3 deficiency inhibits the development of diet-induced insulin resistance in mice

Oxidative and endoplasmic reticulum (ER) stress are involved in mediating high-fat diet (HFD)-induced insulin resistance. As the ER-localized methionine sulfoxide reductase B3 (MsrB3) protects cells against oxidative and ER stress, we hypothesized that MsrB3 might be associated with HFD-induced insulin resistance. To test this hypothesis, we examined the effect of MsrB3 deficiency on HFD-induced insulin resistance using MsrB3 knockout (KO) mice. Mice were fed a control diet or HFD for 12 weeks and insulin sensitivity was measured using a hyperinsulinemic-euglycemic clamp. HFD consumption increased the body weight of both wild-type and MsrB3 KO mice, and no significant difference was observed between the genotypes. The HFD increased oxidative stress and induced insulin resistance in the skeletal muscle of wild-type mice, but did not affect either in MsrB3 KO mice. The unfolded protein response (UPR) was increased in MsrB3 KO mice upon consumption of HFD, but not in wild-type mice. Mitochondrial oxidative phosphorylation proteins and the levels of superoxide dismutase 2 and glutathione peroxidase 1 were increased in MsrB3 KO mice upon HFD consumption. The respiratory control ratio was reduced in wild-type mice consuming HFD but not in MsrB3 KO mice. The levels of calcium/calmodulin-dependent protein kinase kinase β, phosphorylated AMP-activated protein kinase, and peroxisome proliferator-activated receptor gamma coactivator 1α were increased in MsrB3 KO mice following HFD consumption. These results suggest that MsrB3 deficiency inhibits HFD-induced insulin resistance, and the increased mitochondrial biogenesis and antioxidant induction might be the mechanisms underlying this phenomenon.

The diabetes medication canagliflozin promotes mitochondrial remodelling of adipocyte via the AMPK-Sirt1-Pgc-1α signalling pathway

The diabetes medication canagliflozin (Cana) is a sodium glucose cotransporter 2 (SGLT2) inhibitor acting by increasing urinary glucose excretion and thus reducing hyperglycaemia. Cana treatment also reduces body weight. However, it remains unclear whether Cana could directly work on adipose tissue. In the present study, the pharmacological effects of Cana and the associated mechanism were investigated in adipocytes and mice. Stromal-vascular fractions (SVFs) were isolated from subcutaneous adipose tissue and differentiated into mature adipocytes. Our results show that Cana treatment directly increased cellular energy expenditure of adipocytes by inducing mitochondrial biogenesis independently of SGLT2 inhibition. Along with mitochondrial biogenesis, Cana also increased mitochondrial oxidative phosphorylation, fatty acid oxidation and thermogenesis. Mechanistically, Cana promoted mitochondrial biogenesis and function via an Adenosine monophosphate-activated protein kinase (AMPK) - silent information regulator 1 (Sirt1) - peroxisome proliferator-activated receptor γ coactivator-1α (Pgc-1α) signalling pathway. Consistently, in vivo study demonstrated that Cana increased AMPK phosphorylation and the expression of Sirt1 and Pgc-1α. The present study reveals a new therapeutic function for Cana in regulating energy homoeostasis.

ABBREVIATIONS

Ucp-1, uncoupling protein 1; cAMP, cyclic adenosine monophosphate; PKA, cAMP-dependent protein kinase A; SGLT, sodium glucose cotransporter; Cana, canagliflozin; T2DM: type 2 diabetes; Veh, vehicle; Pgc-1α, peroxisome proliferator-activated receptor γ coactivator-1α; SVFs, stromal-vascular fractions; FBS, bovine serum; Ad, adenovirus; mtDNA, mitochondrial DNA; COX2, cytochrome oxidase subunit 2; RT-PCR, real-time PCR; SDS-PAGE, sodium dodecyl sulphate-polyacrylamide gel electrophoresis; Prdm16, PR domain zinc finger protein 16; Cidea, cell death inducing DFFA-like effector A; Pgc-1β, peroxisome proliferator-activated receptor γ coactivator-1β; NRF1, nuclear respiratory factor 1; Tfam, mitochondrial transcription factor A; OXPHOS, oxidative phosphorylation; FAO, fatty acid oxidation; AMPK, Adenosine monophosphate-activated protein kinase; p-AMPK, phosphorylated AMPK; Sirt1, silent information regulator 1; mTOR, mammalian target of rapamycin; WAT, white adipose tissue; Fabp4, fatty acid binding protein 4; Lpl, lipoprotein lipase; Slc5a2, solute carrier family 5 member 2; ERRα, oestrogen related receptor α; Uqcrc2, ubiquinol-cytochrome c reductase core protein 2; Uqcrfs1, ubiquinol-cytochrome c reductase, Rieske iron-sulphur polypeptide 1; Cox4, cytochrome c oxidase subunit 4; Pparα, peroxisome proliferator activated receptor α; NAD⁺, nicotinamide adenine dinucleotide; Dio2, iodothyronine deiodinase 2; Tmem26, transmembrane protein 26; Hoxa9, homeobox A9; FCCP, carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone; Rot/AA, rotenone/antimycin A; OCR, oxygen consumption rate; Pparγ, peroxisome proliferator activated receptor γ; C/ebp, CCAAT/enhancer binding protein; LKB1, liver kinase B1; AUC, area under the cure; Vd, apparent volume of distribution.

The Relationship Between Reactive Oxygen Species and Endothelial Cell Metabolism

Cardiovascular disease (CVD) has been the leading cause of death for many decades, highlighting the importance of new research and treatments in the field. The role of hypoxia and subsequent free radical production [reactive oxygen species (ROS)] have become an area of particular interest in CVD. Interestingly, our laboratory and other laboratories have recently reported positive roles of subcellular ROS in modulating endothelial cell (EC) metabolism, proliferation, and angiogenesis. This bidirectional relationship between ROS and EC metabolism, as well as functional changes, continues to be an area of active research. Interestingly, ECs have been shown to rely on anaerobic processes for ATP generation, despite their direct access to oxygen. This paradox has proven to be beneficial as the major reliance on glycolysis produces ATP faster, preserves oxygen, and results in reduced ROS levels in contrast to oxidative phosphorylation. This review will address the relationship between ROS and carbohydrate, lipid, and nitrogen metabolism in ECs, and their effects on EC phenotype such as sprouting angiogenesis.