Phytanic acid activates PPARα to promote beige adipogenic differentiation of preadipocytes

Addressing chemically-induced obesogenic metabolic disruption: selection of chemicals for in vitro human PPARα, PPARγ transactivation, and adipogenesis test methods

Whilst western diet and sedentary lifestyles heavily contribute to the global obesity epidemic, it is likely that chemical exposure may also contribute. A substantial body of literature implicates a variety of suspected environmental chemicals in metabolic disruption and obesogenic mechanisms. Chemically induced obesogenic metabolic disruption is not yet considered in regulatory testing paradigms or regulations, but this is an internationally recognised human health regulatory development need. An early step in the development of relevant regulatory test methods is to derive appropriate minimum chemical selection lists for the target endpoint and its key mechanisms, such that the test method can be suitably optimised and validated. Independently collated and reviewed reference and proficiency chemicals relevant for the regulatory chemical universe that they are intended to serve, assist regulatory test method development and validation, particularly in relation to the OECD Test Guidelines Programme. To address obesogenic mechanisms and modes of action for chemical hazard assessment, key initiating mechanisms include molecular-level Peroxisome Proliferator-Activated Receptor (PPAR) α and γ agonism and the tissue/organ-level key event of perturbation of the adipogenesis process that may lead to excess white adipose tissue. Here we present a critical literature review, analysis and evaluation of chemicals suitable for the development, optimisation and validation of human PPARα and PPARγ agonism and human white adipose tissue adipogenesis test methods. The chemical lists have been derived with consideration of essential criteria needed for understanding the strengths and limitations of the test methods. With a weight of evidence approach, this has been combined with practical and applied aspects required for the integration and combination of relevant candidate test methods into test batteries, as part of an Integrated Approach to Testing and Assessment for metabolic disruption. The proposed proficiency and reference chemical list includes a long list of negatives and positives (20 chemicals for PPARα, 21 for PPARγ, and 11 for adipogenesis) from which a (pre-)validation proficiency chemicals list has been derived.

Unveiling the Potential of Natural Compounds: A Comprehensive Review on Adipose Thermogenesis Modulation

The process of adipocyte browning has recently emerged as a novel therapeutic target for combating obesity and obesity-related diseases. Non-shivering thermogenesis is the process of biological heat production in mammals and is primarily mediated via brown adipose tissue (BAT). The recruitment and activation of BAT can be induced through chemical drugs and nutrients, with subsequent beneficial health effects through the utilization of carbohydrates and fats to generate heat to maintain body temperature. However, since potent drugs may show adverse side effects, nutritional or natural substances could be safe and effective as potential adipocyte browning agents. This review aims to provide an extensive overview of the natural food compounds that have been shown to activate brown adipocytes in humans, animals, and in cultured cells. In addition, some key genetic and molecular targets and the mechanisms of action of these natural compounds reported to have therapeutic potential to combat obesity are discussed.

Phytanic acid, an inconclusive phytol metabolite: A review

Phytanic acid (PA: 3,7,11,15-tetramethylhexadecanoic acid) is an important biometabolite of the chlorophyll-derived diterpenoid phytol. Its biological sources (occurrence) and ADME (absorption, distribution, metabolism, and elimination) profile are well-discussed in the literature. Cumulative literature suggests that PA has beneficial as well as harmful biological roles in humans and other animals. This study aimed to sketch a brief summary of PA's beneficial and harmful pharmacological effects in test systems on the basis of existing literature reports. Literature findings propose that PA has anti-inflammatory and immunomodulatory, antidiabetic, anti-obesity, anticancer, and oocyte maturation effects. Although a high plasma PA-level mediated SLS remains controversial, it is evident to link it with Refsum's disease and other peroxisomal enzyme deficiency diseases in humans, including RCDP and LD; ZHDA and Alzheimer's disease; progressive ataxia and dysarthria; and an increased risk of some lymphomas such as LBL, FL, and NHL. PA exerts toxic effects on different kinds of cells, including neuronal, cardiac, and renal cells, through diverse pathways such as oxidative stress, mitochondrial disturbance, apoptosis, disruption of Na+/K+-ATPase activity, Ca2+ homeostasis, alteration of AChE and MAO activities, etc. PA is considered a cardiac biomarker in humans. In conclusion, PA may be one of the most important biometabolites in humans.

Can individual fatty acids be used as functional biomarkers of dairy fat consumption in relation to cardiometabolic health? A narrative review

In epidemiological studies, dairy food consumption has been associated with minimal effect or decreased risk of some cardiometabolic diseases (CMD). However, current methods of dietary assessment do not provide objective and accurate measures of food intakes. Thus, the identification of valid and reliable biomarkers of dairy product intake is an important challenge to best determine the relationship between dairy consumption and health status. This review investigated potential biomarkers of dairy fat consumption, such as odd-chain, trans- and branched-chain fatty acids (FA), which may improve the assessment of full-fat dairy product consumption. Overall, the current use of serum/plasma FA as biomarkers of dairy fat consumption is mostly based on observational evidence, with a lack of well-controlled, dose-response intervention studies to accurately assess the strength of the relationship. Circulating odd-chain SFA and trans-palmitoleic acid are increasingly studied in relation to CMD risk and seem to be consistently associated with a reduced risk of type 2 diabetes in prospective cohort studies. However, associations with CVD are less clear. Overall, adding less studied FA such as vaccenic and phytanic acids to the current available evidence may provide a more complete assessment of dairy fat intake and minimise potential confounding from endogenous synthesis. Finally, the current evidence base on the direct effect of dairy fatty acids on established biomarkers of CMD risk (e.g. fasting lipid profiles and markers of glycaemic control) mostly derives from cross-sectional, animal and in vitro studies and should be strengthened by well-controlled human intervention studies.

Resveratrol improves muscle regeneration in obese mice through enhancing mitochondrial biogenesis

Obesity is increasing rapidly worldwide and is accompanied by many complications, including impaired muscle regeneration. Obesity is known to inhibit AMP-activated protein kinase (AMPK) activity, which impedes mitochondrial biogenesis, myogenic differentiation and muscle regeneration. Resveratrol has an effective anti-obesity effect, but its effect on regeneration of muscle in obese mice remains to be tested. We hypothesized that resveratrol activates AMPK and mitochondrial biogenesis to improve muscle regeneration. Male C57BL/6J mice were fed a control diet or a 60% high-fat diet with or without resveratrol supplementation for 8 weeks and, then, the tibialis anterior muscle was subjected to cardiotoxin-induced muscle injury. Muscle tissue was collected at 3 and 7 d after injury. We found that resveratrol enhanced both proliferation and differentiation of satellite cells following injury in obese mice. Markers of mitochondrial biogenesis were upregulated in resveratrol-treated mice. In C2C12 myogenic cells, resveratrol activated AMPK and stimulated the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha, which were associated with enhanced myogenic differentiation. Such effects of resveratrol were abolished by AMPKα1 ablation, showing the mediatory roles of AMPK. In summary, dietary resveratrol activates AMPK/ proliferator-activated receptor gamma coactivator 1-alpha axis to facilitate mitochondrial biogenesis and muscle regeneration impaired due to obesity.

LCDM medium supports the derivation of bovine extended pluripotent stem cells with embryonic and extraembryonic potency in bovine-mouse chimeras from iPSCs and bovine fetal fibroblasts

Cattle have emerged as one of the most important domestic animals widely used for meat, milk, and fur. Derivation of bovine pluripotent stem cells (PSCs) can be applied in drug selecting and human disease modeling and facilitated agriculture-related applications such as production of genetically excellent cattle by gene editing. Extended PSCs (EPSCs), capable of differentiating into embryonic and extraembryonic parts, have been generated in mouse, human, and pig. Whether bovine EPSCs could be generated, and their chimeric competency remains unclear. This study focused on derivation of bovine EPSCs using LCDM medium and exploring the characteristics of EPSCs among different species, including bovine, mouse, and human EPSCs. Here, using LCDM medium (consisting of hLIF, CHIR99021, (S)-(+)-dimethindene maleate, and minocycline hydrochloride) enables the derivation of bovine EPSCs from induced PSCs (iPSCs) and bovine fetal fibroblasts (BFF) with stable morphology, pluripotent marker expression, and in vitro differentiation ability. Notably, bovine EPSCs exhibited interspecies chimeric contribution to embryonic and extraembryonic tissues in pre-implantation blastocysts and postimplantation bovine-mouse chimeras. Transcriptome analysis revealed the unique molecular characteristics of bovine EPSCs compared with iPSCs. The similarities and differences in molecular features across bovine, human, and mouse EPSCs were also described by transcriptome analysis. Taken together, the LCDM culture system containing chemical cocktails can be used for the establishment and long-term passaging of bovine EPSCs with embryonic and extraembryonic potency in bovine-mouse chimeras. Our findings lay the foundation of generating PSCs in domestic animals and open avenues for basic and applied research in biology, medicine, and agriculture. DATABASE: Gene expression data of bovine EPSCs and bovine iPSCs are available in the GEO databases under the accession number PRJNA693452.

Plant extracts in prevention of obesity

Obesity has become a worldwide issue and is accompanied by serious complications. Western high energy diet has been identified to be a major factor contributing to the current obesity pandemic. Thus, it is important to optimize dietary composition, bioactive substances, and agents to prevent and treat obesity. To date, extracts from plants, such as vegetables, tea, fruits, and Chinese herbal medicine, have been showed to have the abilities of regulating adipogenesis and attenuating obesity. These plant extracts mainly contain polyphenols, alkaloids, and terpenoids, which could play a significant role in anti-obesity through various signaling pathways and gut microbiota. Those reported anti-obesity mechanisms mainly include inhibiting white adipose tissue growth and lipogenesis, promoting lipolysis, brown/beige adipose tissue development, and muscle thermogenesis. In this review, we summarize the plant extracts and their possible mechanisms responsible for their anti-obesity effects. Based on the current findings, dietary plant extracts and foods containing these bioactive compounds can be potential preventive or therapeutic agents for obesity and its related metabolic diseases.

Characterization of brown adipose tissue thermogenesis in the naked mole-rat (Heterocephalus glaber), a heterothermic mammal

The naked mole-rat (NMR) is a heterothermic mammal that forms eusocial colonies consisting of one reproductive female (queen), several reproductive males, and subordinates. Despite their heterothermy, NMRs possess brown adipose tissue (BAT), which generally induces thermogenesis in cold and some non-cold environments. Previous studies suggest that NMR-BAT induces thermogenesis by cold exposure. However, detailed NMR-BAT characteristics and whether NMR-BAT thermogenesis occurs in non-cold environments are unknown. Here, we show beta-3 adrenergic receptor (ADRB3)-dependent thermogenic potential of NMR-BAT, which contributes to thermogenesis in the isolated queen in non-cold environments (30 °C). NMR-BAT expressed several brown adipocyte marker genes and showed noradrenaline-dependent thermogenic activity in vitro and in vivo. Although our ADRB3 inhibition experiments revealed that NMR-BAT thermogenesis slightly delays the decrease in body temperature in a cold environment (20 °C), it was insufficient to prevent the decrease in the body temperatures. Even at 30 °C, NMRs are known to prevent the decrease of and maintain their body temperature by heat-sharing behaviors within the colony. However, isolated NMRs maintained their body temperature at the same level as when they are in the colony. Interestingly, we found that queens, but not subordinates, induce BAT thermogenesis in this condition. Our research provides novel insights into NMR thermoregulation.

Branched-Chain Fatty Acids-An Underexplored Class of Dairy-Derived Fatty Acids

Dairy fat and its fatty acids (FAs) have been shown to possess pro-health properties that can support health maintenance and disease prevention. In particular, branched-chain FAs (BCFAs), comprising approximately 2% of dairy fat, have recently been proposed as bioactive molecules contributing to the positive health effects associated with the consumption of full-fat dairy products. This narrative review evaluates human trials assessing the relationship between BCFAs and metabolic risk factors, while potential underlying biological mechanisms of BCFAs are explored through discussion of studies in animals and cell lines. In addition, this review details the biosynthetic pathway of BCFAs as well as the content and composition of BCFAs in common retail dairy products. Research performed with in vitro models demonstrates the potent, structure-specific properties of BCFAs to protect against inflammation, cancers, and metabolic disorders. Yet, human trials assessing the effect of BCFAs on disease risk are surprisingly scarce, and to our knowledge, no research has investigated the specific role of dietary BCFAs. Thus, our review highlights the critical need for scientific inquiry regarding dairy-derived BCFAs, and the influence of this overlooked FA class on human health.

Murine in vitro cellular models to better understand adipogenesis and its potential applications

Adipogenesis has been extensively studied using in vitro models of cellular differentiation, enabling long-term regulation of fat cell metabolism in human adipose tissue (AT) material. Many studies promote the idea that manipulation of this process could potentially reduce the prevalence of obesity and its related diseases. It has now become essential to understand the molecular basis of fat cell development to tackle this pandemic disease, by identifying therapeutic targets and new biomarkers. This review explores murine cell models and their applications for study of the adipogenic differentiation process in vitro. We focus on the benefits and limitations of different cell line models to aid in interpreting data and selecting a good cell line model for successful understanding of adipose biology.

PINK1-PRKN mitophagy suppression by mangiferin promotes a brown-fat-phenotype via PKA-p38 MAPK signalling in murine C3H10T1/2 mesenchymal stem cells

OBJECTIVE

Mangiferin (MF), a xanthonoid derived from Mangifera indica, has shown therapeutic effects on various human diseases including cancer, diabetes, and obesity. Nonetheless, the influence of MF on non-shivering thermogenesis and its underlying mechanism in browning remains unclear. Here, our aim was to investigate the effects of MF on browning and its molecular mechanisms in murine C3H10T1/2 mesenchymal stem cells (MSCs).

MATERIALS/METHODS

To determine the function of MF on browning, murine C3H10T1/2 MSCs were treated with MF in an adipogenic differentiation cocktail and the thermogenic and correlated metabolic responses were assessed using MF-mediated signalling. Human adipose-derived MSCs were differentiated and treated with MF to confirm its role in thermogenic induction.

RESULTS

MF treatment induced the expression of a brown-fat signature, UCP1, and reduced triglyceride (TG) in C3H10T1/2 MSCs. MF also induced the expression of major thermogenesis regulators: PGC1α, PRDM16, and PPARγ and up-regulated the expression of beiging markers CD137, HSPB7, TBX1, and COX2 in both murine C3H10T1/2 MSCs and human adipose-derived mesenchymal stem cells (hADMSC). We also observed that MF treatment increased the mitochondrial DNA and improved mitochondrial homeostasis by regulating mitofission-fusion plasticity via suppressing PINK1-PRKN-mediated mitophagy. Furthermore, MF treatment improved mitochondrial respiratory function by increasing mitochondrial oxygen consumption and expression of oxidative-phosphorylation (OXPHOS)-related proteins. Chemical-inhibition and gene knockdown experiments revealed that β3-AR-dependent PKA-p38 MAPK-CREB signalling is crucial for MF-mediated brown-fat formation via suppression of mitophagy in C3H10T1/2 MSCs.

CONCLUSIONS

MF promotes the brown adipocyte phenotype by suppressing mitophagy, which is regulated by PKA-p38MAPK-CREB signalling in C3H10T1/2 MSCs. Thus, we propose that MF may be a good browning inducer that can ameliorate obesity.

Maternal obesity impairs fetal mitochondriogenesis and brown adipose tissue development partially via upregulation of miR-204-5p

Maternal obesity (MO) predisposes offspring to metabolic disorders, but the mechanisms remain poorly defined. Recent studies emphasize the importance of brown adipose tissue (BAT) in maintaining metabolic health, and MO was recently demonstrated to impair BAT thermogenic function in offspring. The current study aimed to investigate the mechanisms leading to the impairment in fetal BAT development due to MO. Female C57BL/6J mice were fed a control diet or a 60% high-fat diet for 10 weeks, mated and maintained on their respective diets during pregnancy. Fetal tissue was collected at E18.5, the late stage of pregnancy. Fetal BAT contained more triglycerides compared to the control, which was correlated with higher expression of white adipogenic markers. On the other hand, the expression of BAT markers was down-regulated in the MO fetal BAT. Based on RNA-sequencing analyses, genes related to mitochondriogenesis and myogenesis were found to be down-regulated, while those related to white adipocyte differentiation were up-regulated in MO fetal BAT. Because brown adipocytes are derived from myogenic progenitors, the down-regulation of myogenic genes might partially explain hampered brown adipogenesis in MO fetal BAT. Consistently, mitochondrial DNA and mitochondrial biogenesis markers were also down-regulated in MO fetal BAT. MicroRNA-sequencing identified that miR-204-5p expression was elevated in MO fetal BAT. This microRNA targeted the 3'-untranslated regions of PGC1α and Sirt1 mRNA to suppress their expression and impair mitochondriogenesis. In summary, MO impaired fetal BAT development through suppressing myogenesis and brown adipogenesis while enhancing white adipogenic commitment, and inhibited mitochondriogenesis partially through enhancing miR-204-5p expression.