GPCR in Adipose Tissue Function-Focus on Lipolysis

Inverse agonism of the FFA4 free fatty acid receptor controls both adipogenesis and mature adipocyte function

Adipocyte disfunction is an important component of many metabolic disorders and there is a need for pharmacological approaches that can restore normal adipocyte function. The FFA4 receptor is a G protein coupled receptor (GPCR), activated by long chain free fatty acids (FFAs), that controls adipocyte function. Importantly, adipocytes produce FFAs, which may directly activate FFA4 and there is a need to better understand how FFAs produced by adipocytes interact with FFA4 signalling. In this study we have employed human and mouse adipocyte cell models to determine how pharmacological agonism or antagonism of FFA4 affects adipogenesis, lipolysis and glucose uptake. We show that a commonly used FFA4 antagonist, AH7614, is an inverse agonist and that treating adipocytes with this compound suppressed adipogenesis, inhibits glucose uptake and enhances isoprenaline stimulated lipolysis. In contrast, treatment with a synthetic FFA4 agonist, TUG-891, has only modest effects on adipogenesis and lipolysis, while showing no effect on glucose uptake. To explore the mechanism for why AH7614 but not TUG-891 affects adipocyte function, we demonstrate that during adipogenic differentiation sufficient FFAs are released into the culture medium to activate FFA4, suggesting AH7614 inhibits an autocrine feedback loop to suppress adipogenesis. In contrast, during lipolysis experiments, insufficient FFAs were released to activate the receptor, suggesting that AH7614 must enhance lipolysis by either inhibiting ligand independent FFA4 signalling, or FFA signalling that does not require the FFAs to be released from the cell. This study will help establish how FFA4 targeting therapeutics could be used to treat adipocyte dysfunction.

Obesity, White Adipose Tissue, and Adipokines Signaling in Male Reproduction

Currently, obesity is a global pandemic characterized by systemic metabolic complications that negatively impact several organs, including white adipose tissue (WAT) and the tissues of the male reproductive system. Since the discovery of leptin in 1994, WAT has been recognized as a dynamic endocrine organ for secreting a series of molecules with hormonal functions, collectively called adipokines. The link between obesity, WAT, adipokines, and the male reproductive system is direct and little explored. With changes in nutritional status, WAT undergoes morphofunctional changes, and the secretion of adipokines is altered, negatively impacting reproductive mechanisms, including steroidogenesis and spermatogenesis. In this review, we address in an updated way the structural and functional characteristics of WAT as well as the link between obesity and changes in the signaling pathways of the adipokines leptin, adiponectin, resistin, visfatin, apelin, chemerin, omentin-1, vaspin, and asprosin in male reproduction. Understanding the relationship between obesity, these adipokines, and reproductive dysfunction can contribute to new strategies for the treatment of subfertility and male infertility.

GPCR-mediated regulation of beige adipocyte formation: Implications for obesity and metabolic health

Obesity and its associated complications pose a significant burden on health. The non-shivering thermogenesis (NST) and metabolic capacity properties of brown adipose tissue (BAT), which are distinct from those of white adipose tissue (WAT), in combating obesity and its related metabolic diseases has been well documented. However, beige adipose tissue, the third and relatively novel type of adipose tissue, which emerges in extensive presence of WAT and shares similar favorable metabolic properties with BAT, has garnered considerable attention in recent years. In this review, we focused on the role of G protein-coupled receptors (GPCRs), the largest receptor family and the most successful class of drug targets in humans, in the induction of beige adipocytes. More importantly, we highlight researchers' clinical treatment attempts to ameliorate obesity and other related metabolic diseases through the formation and activation of beige adipose tissue. In summary, this review provides valuable insights into the formation of beige adipose tissue and the involvement of GPCRs, based on the latest advancements in scientific research.

PM2.5, component cause of severe metabolically abnormal obesity: An in silico, observational and analytical study

Obesity is currently one of the most alarming pathological conditions due to the progressive increase in its prevalence. In the last decade, it has been associated with fine particulate matter suspended in the air (PM2.5). The purpose of this study was to explore the mechanistic interaction of PM2.5 with a high-fat diet (HFD) through the differential regulation of transcriptional signatures, aiming to identify the association of these particles with metabolically abnormal obesity. The research design was observational, using bioinformatic methods and an explanatory approach based on Rothman's causal model. We propose three new transcriptional signatures in murine adipose tissue. The sum of transcriptional differences between the group exposed to an HFD and PM2.5, compared to the control group, were 0.851, 0.265, and -0.047 (p > 0.05). The HFD group increased body mass by 20% with two positive biomarkers of metabolic impact. The group exposed to PM2.5 maintained a similar weight to the control group but exhibited three positive biomarkers. Enriched biological pathways (p < 0.05) included PPAR signaling, small molecule transport, adipogenesis genes, cytokine-cytokine receptor interaction, and HIF-1 signaling. Transcriptional regulation predictions revealed CpG islands and common transcription factors. We propose three new transcriptional signatures: FAT-PM2.5-CEJUS, FAT-PM2.5-UP, and FAT-PM2.5-DN, whose transcriptional regulation profile in adipocytes was statistically similar by dietary intake and HFD and exposure to PM2.5 in mice; suggesting a mechanistic interaction between both factors. However, HFD-exposed murines developed moderate metabolically abnormal obesity, and PM2.5-exposed murines developed severe abnormal metabolism without obesity. Therefore, in Rothman's terms, it is concluded that HFD is a sufficient cause of the development of obesity, and PM2.5 is a component cause of severe abnormal metabolism of obesity. These signatures would be integrated into a systemic biological process that would induce transcriptional regulation in trans, activating obesogenic biological pathways, restricting lipid mobilization pathways, decreasing adaptive thermogenesis and angiogenesis, and altering vascular tone thus inducing a severe metabolically abnormal obesity.

The effect of quercetin on adipogenesis, lipolysis, and apoptosis in 3T3-L1 adipocytes: The role of SIRT1 pathways

Background

Lipotoxicity, caused by adipocyte triglyceride over-accumulation, contributes to obesity-related comorbidities such as hypertension, type 2 diabetes, coronary heart disease, respiratory dysfunction, and osteoarthritis. This study focuses on determining how sirtuin-1 (SIRT-1) mediates quercetin's (QCT) effect on 3T3-L1 adipocytes. Key aspects of this study include preventing adipogenesis, inducing lipolysis, and stimulating adipocyte apoptosis.

Methods

3T3-L1 adipocytes underwent treatment with varying QCT doses, lipopolysaccharide (LPS), and the SIRT-1 inhibitor EX-527, followed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide [MTT] assay for cell viability assessment. Furthermore, quantitative real-time polymerase chain reaction measured mRNA expression levels of adipogenesis markers (fatty acid synthase [FASN] and peroxisome proliferator-activated receptor gamma [PPARγ]), lipolysis markers (adipose triglyceride lipase [ATGL] and hormone-sensitive lipase [HSL]), and apoptosis markers (B-cell lymphoma2 [Bcl-2], Bcl-2 Associated -X-protein [BAX] and Caspase-3).

Results

The data showed that LPS + QCT significantly reduced cell viability in a dose- and time-dependent manner, unaffected by LPS + QCT + EX-527. Treatment with LPS + QCT did not affect FASN and PPARγ expression but significantly increased ATGL and HSL mRNA expression compared with LPS alone. Interestingly, EX-527 reversed the effects of LPS + QCT on lipogenesis and lipolysis markers completely. QCT enhanced apoptosis in a SIRT-1 independent pattern.

Conclusion

The data suggest that QCT suppresses adipogenesis while increasing lipolysis via SIRT-1. However, QCT's effects on apoptosis appear to be independent of SIRT-1. These findings provide further evidence for QCT's effects on adipocytes, particularly its interaction with SIRT-1.

Quercetin declines LPS induced inflammation and augments adiponectin expression in 3T3-L1 differentiated adipocytes SIRT-1 dependently

BACKGROUND

Inflammation is an important factor contributing to obesity-induced metabolic disorders. Different investigations confirm that local inflammation in adipose issues is the primary reason for such disorder, resulting in low-grade systemic inflammation. Anti-inflammatory, antioxidant, and epigenetic modification are among the varied properties of Quercetin (QCT) as a natural flavonoid.

OBJECTIVE

The precise molecular mechanism followed by QCT to alleviate inflammation has been unclear. This study explores whether the anti-inflammatory effects of QCT in 3T3-L1 differentiated adipocytes may rely on SIRT-1.

METHODS

The authors isolated 3T3-L1 pre-adipocyte cells and exposed them to varying concentrations of QCT, lipopolysaccharide (LPS), and a selective inhibitor of silent mating type information regulation 2 homolog 1 (SIRT-1) called EX-527. After determining the optimal dosages of QCT, LPS, and EX-527, they assessed the mRNA expression levels of IL-18, IL-1, IL-6, TNF-α, SIRT-1, and adiponectin using quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

RESULTS

The study showed considerable cytotoxic effects of LPS (200 ng/mL) + QCT (100 µM) + EX-527 (10 µM) on 3T3-L1 differentiated adipocytes after 48 h of incubation. QCT significantly upregulated the expression levels of adiponectin and SIRT-1 (p < 0.0001). However, introducing SIRT-1 inhibitor (p < 0.0001) reversed the impact of QCT on adiponectin expression. Additionally, QCT reduced SIRT-1-dependent pro-inflammatory cytokines in 3T3-L1 differentiated adipocytes (p < 0.0001).

CONCLUSION

This study revealed that QCT treatment reduced crucial pro-inflammatory cytokines levels and increased adiponectin levels following LPS treatment. This finding implies that SIRT-1 may be a crucial factor for the anti-inflammatory activity of QCT.

Clinically Effective Molecules of Natural Origin for Obesity Prevention or Treatment

The prevalence and incidence of obesity and the comorbidities linked to it are increasing worldwide. Current therapies for obesity and associated pathologies have proven to cause a broad number of adverse effects, and often, they are overpriced or not affordable for all patients. Among the alternatives currently available, natural bioactive compounds stand out. These are frequently contained in pharmaceutical presentations, nutraceutical products, supplements, or functional foods. The clinical evidence for these molecules is increasingly solid, among which epigallocatechin-3-gallate, ellagic acid, resveratrol, berberine, anthocyanins, probiotics, carotenoids, curcumin, silymarin, hydroxy citric acid, and α-lipoic acid stand out. The molecular mechanisms and signaling pathways of these molecules have been shown to interact with the endocrine, nervous, and gastroenteric systems. They can regulate the expression of multiple genes and proteins involved in starvation-satiety processes, activate the brown adipose tissue, decrease lipogenesis and inflammation, increase lipolysis, and improve insulin sensitivity. This review provides a comprehensive view of nature-based therapeutic options to address the increasing prevalence of obesity. It offers a valuable perspective for future research and subsequent clinical practice, addressing everything from the molecular, genetic, and physiological bases to the clinical study of bioactive compounds.

Challenges in Pharmacological Intervention in Perilipins (PLINs) to Modulate Lipid Droplet Dynamics in Obesity and Cancer

Perilipins (PLINs) are the most abundant proteins in lipid droplets (LD). These LD-associated proteins are responsible for upgrading LD from inert lipid storage structures to fully functional organelles, fundamentally integrated in the lipid metabolism. There are five distinct perilipins (PLIN1-5), each with specific expression patterns and metabolic activation, but all capable of regulating the activity of lipases on LD. This plurality creates a complex orchestrated mechanism that is directly related to the healthy balance between lipogenesis and lipolysis. Given the essential role of PLINs in the modulation of the lipid metabolism, these proteins can become interesting targets for the treatment of lipid-associated diseases. Since reprogrammed lipid metabolism is a recognized cancer hallmark, and obesity is a known risk factor for cancer and other comorbidities, the modulation of PLINs could either improve existing treatments or create new opportunities for the treatment of these diseases. Even though PLINs have not been, so far, directly considered for pharmacological interventions, there are many established drugs that can modulate PLINs activity. Therefore, the aim of this study is to assess the involvement of PLINs in diseases related to lipid metabolism dysregulation and whether PLINs can be viewed as potential therapeutic targets for cancer and obesity.

Adipocyte G Protein-Coupled Receptors as Potential Targets for Novel Antidiabetic Drugs

The functional state of adipocytes plays a central role in regulating numerous important metabolic functions, including energy and glucose homeostasis. While white adipocytes store excess calories as fat (triglycerides) and release free fatty acids as a fuel source in times of need, brown and beige adipocytes (so-called thermogenic adipocytes) convert chemical energy stored in substrates (e.g., fatty acids or glucose) into heat, thus promoting energy expenditure. Like all other cell types, adipocytes express many G protein-coupled receptors (GPCRs) that are linked to four major functional classes of heterotrimeric G proteins (Gs, Gi/o, Gq/11, and G12/13). During the past few years, novel experimental approaches, including the use of chemogenetic strategies, have led to a series of important new findings regarding the metabolic consequences of activating or inhibiting distinct GPCR/G protein signaling pathways in white, brown, and beige adipocytes. This novel information should guide the development of novel drugs capable of modulating the activity of specific adipocyte GPCR signaling pathways for the treatment of obesity, type 2 diabetes, and related metabolic disorders.