Fibroblast Growth Factor 21 and Browning of White Adipose Tissue

The Different Shades of Thermogenic Adipose Tissue

PURPOSE OF REVIEW

By providing a concise overview of adipose tissue types, elucidating the regulation of adipose thermogenic capacity in both physiological contexts and chronic wasting diseases (a protracted hypermetabolic state that precipitates sustained catabolism and consequent progressive corporeal atrophy), and most importantly, delving into the ongoing discourse regarding the role of adipose tissue thermogenic activation in chronic wasting diseases, this review aims to provide researchers with a comprehensive understanding of the field.

RECENT FINDINGS

Adipose tissue, traditionally classified as white, brown, and beige (brite) based on its thermogenic activity and potential, is intricately regulated by complex mechanisms in response to exercise or cold exposure. This regulation is adipose depot-specific and dependent on the duration of exposure. Excessive thermogenic activation of adipose tissue has been observed in chronic wasting diseases and has been considered a pathological factor that accelerates disease progression. However, this conclusion may be confounded by the detrimental effects of excessive lipolysis. Recent research also suggests that such activation may play a beneficial role in the early stages of chronic wasting disease and provide potential therapeutic effects. A more comprehensive understanding of the changes in adipose tissue thermogenesis under physiological and pathological conditions, as well as the underlying regulatory mechanisms, is essential for the development of novel interventions to improve health and prevent disease.

A combination of Citrus aurantifolia fruit rind and Theobroma cacao seed extracts supplementation enhances metabolic rates in overweight subjects: a randomized, placebo-controlled, cross-over study

Background and objective

LN19183 is a proprietary, synergistic combination of Citrus aurantifolia fruit rind and Theobroma cacao seed extracts that increased resting energy expenditure (REE) in high-fat diet (HFD)-fed obese rats. The objective of this study was to validate the thermogenic potential of LN19183 in obese Sprague Dawley (SD) rats and to assess its clinical efficacy in a proof-of-concept, randomized, placebo-controlled, cross-over human trial.

Methods

In the rat study, HFD-fed obese rats were supplemented with either HFD alone or with 45, 90, or 180 mg LN19183 per kg body weight (BW) for 28 days. In the human study, 60 overweight adults (male and female, aged 20-39 years) were randomized. Subjects took LN19183 (450 mg) or a matched placebo capsule on two consecutive days in phases one and two of the study, separated by a 10-day washout period. In each phase, on day 1, REE at pre-dose, 60-, 120-, and 180-min post-dose, and on day 2, metabolic rates at pre-dose and post-dose during and 20 min after exercise were measured using indirect calorimetry.

Results

In rats, LN19183 significantly increased REE, reduced BW gain and fat masses, and increased fat and carbohydrate metabolism marker proteins including beta 3 adrenergic receptor (β3-AR), phospho-AMP-activated protein kinase (AMPK), glucagon-like peptide-1 receptor (GLP-1R) in the liver, and serum adiponectin levels. Furthermore, LN19183-supplemented human volunteers increased (P < 0.05, vs. placebo) the metabolic rates at rest and with exercise; their fat oxidation was increased (P < 0.05, vs. placebo) at rest and 20 min post-exercise. The groups' systolic and diastolic blood pressure (BP), heart rates (HR), and safety parameters were comparable.

Conclusion

These observations suggest that LN19183 is a thermogenic botanical composition with no stimulatory effects on BP and HR.

Gemigliptin mitigates TGF-β-induced renal fibrosis through FGF21-mediated inhibition of the TGF-β/Smad3 signaling pathway

Fibroblast growth factor 21 (FGF21), a well-known regulator of metabolic disorders, exhibits the potential to prevent renal fibrosis by negatively regulating the transforming growth factor β (TGF-β)/Smad3 signaling pathway. Gemigliptin and other dipeptidyl peptidase-4 inhibitors are frequently used for the management of patients with type 2 diabetes. However, the protective effect of gemigliptin against renal fibrosis, particularly its potential to upregulate the expression of FGF21, remains incompletely understood. This study assessed the renoprotective effects of gemigliptin against TGF-β-induced renal fibrosis by enhancing the expression of FGF21 in the cultured human proximal tubular epithelial cell line HK-2. Treatment with FGF21 effectively prevented TGF-β-induced renal fibrosis by attenuating the TGF-β/Smad3 signaling pathway. Similarly, gemigliptin exhibited protective effects against TGF-β-induced renal fibrosis by mitigating TGF-β/Smad3 signaling through the upregulation of FGF21 expression. However, the protective effects of gemigliptin were blocked when FGF21 expression was knocked down in TGF-β-treated HK-2 cells. These results indicate that gemegliptin has the potential to exhibit protective effects against TGF-β-induced renal fibrosis by elevating FGF21 expression levels in cultured human proximal tubular epithelial cells.

Liraglutide induced browning of visceral white adipose through regulation of miRNAs in high-fat-diet-induced obese mice

OBJECTIVE

Obesity is characterized by excessive accumulation of white adipose tissue (WAT). Conversely, brown adipose tissue is protective against obesity. We recently reported liraglutide, a glucagon-like peptide-1 receptor agonist (GLP-1RA), could inhibit high-fat-diet-induced obesity by browning of WAT. However, the molecular mechanism involved is not well defined. Hence, we aimed to explore whether GLP-1RA could promote brown remodeling in WAT by regulating miRNAs.

METHODS

After the obesity model was successfully constructed, C57BL/6J mice were treated with liraglutide (200 μg/kg/d) or equivoluminal saline subcutaneously for 12 weeks. Then, the deposition of abdominal fat was measured by CT scanning. At the end of the treatments, glucose and insulin tolerance in mice were assessed. Serum lipid levels were monitored and epididymal WAT (eWAT) were collected for analysis. Quantitative real-time PCR and western blot analyses were conducted to evaluate the expression of genes and miRNAs associated with white fat browning.

RESULTS

Liraglutide significantly reduced body weight and visceral fat mass. Levels of lipid profile were also improved. Liraglutide upregulated the expression of browning-related genes in eWAT. Meanwhile, the expression level of miRNAs (miR-196a and miR-378a) positively associated with the browning of WAT were increased, while the expression of miR-155, miR-199a, and miR-382 negatively related with browning of WAT were decreased.

CONCLUSION

Our findings suggest that liraglutide could promote brown remodeling of visceral WAT by bi-regulating miRNAs; this might be one of the mechanisms underlying its effect on weight loss.

Cold exposure increases circulating fibroblast growth factor 21 in the evening in males and females

Objectives

Cold exposure is linked to cardiometabolic benefits. Cold activates brown adipose tissue (BAT), increases energy expenditure, and induces secretion of the hormones fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15). The cold-induced increase in energy expenditure exhibits a diurnal rhythm in men. Therefore, we aimed to investigate the effect of cold exposure on serum FGF21 and GDF15 levels in humans and whether cold-induced changes in FGF21 and GDF15 levels differ between morning and evening in males and females.

Method

In this randomized cross-over study, serum FGF21 and GDF15 levels were measured in healthy lean males (n = 12) and females (n = 12) before, during, and after 90 min of stable cold exposure in the morning (07:45 h) and evening (19:45 h) with a 1-day washout period in between.

Results

Cold exposure increased FGF21 levels in the evening compared to the morning both in males (+61% vs -13%; P < 0.001) and in females (+58% vs +8%; P < 0.001). In contrast, cold exposure did not significantly modify serum GDF15 levels, and no diurnal variation was found. Changes in FGF21 and GDF15 levels did not correlate with changes in cold-induced energy expenditure in the morning and evening.

Conclusion

Cold exposure increased serum FGF21 levels in the evening, but not in the morning, in both males and females. GDF15 levels were not affected by cold exposure. Thus, this study suggests that the timing of cold exposure may influence cold-induced changes in FGF21 levels but not GDF15 levels and seems to be independent of changes in energy expenditure.

Fibroblast growth factor 21

Fibroblast growth factor 21 (FGF21) belongs to the FGF19 subfamily and acts systemically, playing a key role in inter-organ crosstalk. Ranging from metabolism, reproduction, and immunity, FGF21 is a pleiotropic hormone which contributes to various physiological processes. Although most of its production across species stems from hepatic tissues, expression of FGF21 in mice has also been identified in adipose tissue, thymus, heart, pancreas, and skeletal muscle. Elevated FGF21 levels are affiliated with various diseases and conditions, such as obesity, type 2 diabetes, preeclampsia, as well as cancer. Murine knockout models are viable and show modest weight gain, while overexpression and gain-of-function models display resistance to weight gain, altered bone volume, and enhanced immunity. In addition, FGF21-based therapies are at the forefront of biopharmaceutical strategies aimed at treating metabolic dysfunction-associated steatotic liver disease.

Adipokines and their role in acute pancreatitis

Acute pancreatitis (AP) is characterized by an inflammatory response that leads to edema and haemorrhaging of pancreatic tissue. In severe cases, it can even result in the necrosis of pancreatic tissue following activation within the pancreas. Adipokines are biologically active molecules released by adipose tissue that have a wide-ranging impact on health and disease. Adipokines are cytokines produced not only in white adipose tissue but also in the fat surrounding the pancreas, and they play a role in the body's inflammatory response. The presence of increased adipose tissue, often associated with obesity, has been linked to a heightened systemic inflammatory response in cases of AP. According to the literature, there are many adipokines. This article summarizes the role of adipokines in AP. Adipokines could be promising biomarkers for both diagnostic and new therapeutic treatment strategies in AP. However, a deeper knowledge of the signaling pathways of adipokines and their potential therapeutic role in AP is necessary.

The Role of Exerkines in Obesity-Induced Disruption of Mitochondrial Homeostasis in Thermogenic Fat

There is a notable correlation between mitochondrial homeostasis and metabolic disruption. In this review, we report that obesity-induced disruption of mitochondrial homeostasis adversely affects lipid metabolism, adipocyte differentiation, oxidative capacity, inflammation, insulin sensitivity, and thermogenesis in thermogenic fat. Elevating mitochondrial homeostasis in thermogenic fat emerges as a promising avenue for developing treatments for metabolic diseases, including enhanced mitochondrial function, mitophagy, mitochondrial uncoupling, and mitochondrial biogenesis. The exerkines (e.g., myokines, adipokines, batokines) released during exercise have the potential to ameliorate mitochondrial homeostasis, improve glucose and lipid metabolism, and stimulate fat browning and thermogenesis as a defense against obesity-associated metabolic diseases. This comprehensive review focuses on the manifold benefits of exercise-induced exerkines, particularly emphasizing their influence on mitochondrial homeostasis and fat thermogenesis in the context of metabolic disorders associated with obesity.

SLC25A28 Overexpression Promotes Adipogenesis by Reducing ATGL

Adipose tissue dysfunction is seen among obese and type 2 diabetic individuals. Adipocyte proliferation and hypertrophy are the root causes of adipose tissue expansion. Solute carrier family 25 member 28 (SLC25A28) is an iron transporter in the inner mitochondrial membrane. This study is aimed at validating the involvement of SLC25A28 in adipose accumulation by tail vein injection of adenovirus (Ad)-SLC25A28 and Ad-green fluorescent protein viral particles into C57BL/6J mice. After 16 weeks, the body weight of the mice was measured. Subsequently, morphological analysis was performed to establish a high-fat diet (HFD)-induced model. SLC25A28 overexpression accelerated lipid accumulation in white and brown adipose tissue (BAT), enhanced body weight, reduced serum triglyceride (TG), and impaired serum glucose tolerance. The protein expression level of lipogenesis, lipolysis, and serum adipose secretion hormone was evaluated by western blotting. The results showed that adipose TG lipase (ATGL) protein expression was reduced significantly in white and BAT after overexpression SLC25A28 compared to the control group. Moreover, SLC25A28 overexpression inhibited the BAT formation by downregulating UCP-1 and the mitochondrial biosynthesis marker PGC-1α. Serum adiponectin protein expression was unregulated, which was consistent with the expression in inguinal white adipose tissue (iWAT). Remarkably, serum fibroblast growth factor (FGF21) protein expression was negatively related to the expansion of adipose tissue after administrated by Ad-SLC25A28. Data from the current study indicate that SLC25A28 overexpression promotes diet-induced obesity and accelerates lipid accumulation by regulating hormone secretion and inhibiting lipolysis in adipose tissue.

Fibroblast growth factor 21: An emerging pleiotropic regulator of lipid metabolism and the metabolic network

Fibroblast growth factor 21 (FGF21) was originally identified as an important metabolic regulator which plays a crucial physiological role in regulating a variety of metabolic parameters through the metabolic network. As a novel multifunctional endocrine growth factor, the role of FGF21 in the metabolic network warrants extensive exploration. This insight was obtained from the observation that the FGF21-dependent mechanism that regulates lipid metabolism, glycogen transformation, and biological effectiveness occurs through the coordinated participation of the liver, adipose tissue, central nervous system, and sympathetic nerves. This review focuses on the role of FGF21-uncoupling protein 1 (UCP1) signaling in lipid metabolism and how FGF21 alleviates non-alcoholic fatty liver disease (NAFLD). Additionally, this review reveals the mechanism by which FGF21 governs glucolipid metabolism. Recent research on the role of FGF21 in the metabolic network has mostly focused on the crucial pathway of glucolipid metabolism. FGF21 has been shown to have multiple regulatory roles in the metabolic network. Since an adequate understanding of the concrete regulatory pathways of FGF21 in the metabolic network has not been attained, this review sheds new light on the metabolic mechanisms of FGF21, explores how FGF21 engages different tissues and organs, and lays a theoretical foundation for future in-depth research on FGF21-targeted treatment of metabolic diseases.

Pulling the trigger: Noncoding RNAs in white adipose tissue browning

White adipose tissue (WAT) serves as the primary site for energy storage and endocrine regulation in mammals, while brown adipose tissue (BAT) is specialized for thermogenesis and energy expenditure. The conversion of white adipocytes to brown-like fat cells, known as browning, has emerged as a promising therapeutic strategy for reversing obesity and its associated co-morbidities. Noncoding RNAs (ncRNAs) are a class of transcripts that do not encode proteins but exert regulatory functions on gene expression at various levels. Recent studies have shed light on the involvement of ncRNAs in adipose tissue development, differentiation, and function. In this review, we aim to summarize the current understanding of ncRNAs in adipose biology, with a focus on their role and intricate mechanisms in WAT browning. Also, we discuss the potential applications and challenges of ncRNA-based therapies for overweight and its metabolic disorders, so as to combat the obesity epidemic in the future.

An update on the secretory functions of brown, white, and beige adipose tissue: Towards therapeutic applications

Adipose tissue, including white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, is vital in modulating whole-body energy metabolism. While WAT primarily stores energy, BAT dissipates energy as heat for thermoregulation. Beige adipose tissue is a hybrid form of adipose tissue that shares characteristics with WAT and BAT. Dysregulation of adipose tissue metabolism is linked to various disorders, including obesity, type 2 diabetes, cardiovascular diseases, cancer, and infertility. Both brown and beige adipocytes secrete multiple molecules, such as batokines, packaged in extracellular vesicles or as soluble signaling molecules that play autocrine, paracrine, and endocrine roles. A greater understanding of the adipocyte secretome is essential for identifying novel molecular targets in treating metabolic disorders. Additionally, microRNAs show crucial roles in regulating adipose tissue differentiation and function, highlighting their potential as biomarkers for metabolic disorders. The browning of WAT has emerged as a promising therapeutic approach in treating obesity and associated metabolic disorders. Many browning agents have been identified, and nanotechnology-based drug delivery systems have been developed to enhance their efficacy. This review scrutinizes the characteristics of and differences between white, brown, and beige adipose tissues, the molecular mechanisms involved in the development of the adipocytes, the significant roles of batokines, and regulatory microRNAs active in different adipose tissues. Finally, the potential of WAT browning in treating obesity and atherosclerosis, the relationship of BAT with cancer and fertility disorders, and the crosstalk between adipose tissue with circadian system and circadian disorders are also investigated.

Deciphering adipose development: Function, differentiation and regulation

The overdevelopment of adipose tissues, accompanied by excess lipid accumulation and energy storage, leads to adipose deposition and obesity. With the increasing incidence of obesity in recent years, obesity is becoming a major risk factor for human health, causing various relevant diseases (including hypertension, diabetes, osteoarthritis and cancers). Therefore, it is of significance to antagonize obesity to reduce the risk of obesity-related diseases. Excess lipid accumulation in adipose tissues is mediated by adipocyte hypertrophy (expansion of pre-existing adipocytes) or hyperplasia (increase of newly-formed adipocytes). It is necessary to prevent excessive accumulation of adipose tissues by controlling adipose development. Adipogenesis is exquisitely regulated by many factors in vivo and in vitro, including hormones, cytokines, gender and dietary components. The present review has concluded a comprehensive understanding of adipose development including its origin, classification, distribution, function, differentiation and molecular mechanisms underlying adipogenesis, which may provide potential therapeutic strategies for harnessing obesity without impairing adipose tissue function.

Spermidine activates adipose tissue thermogenesis through autophagy and fibroblast growth factor 21

Spermidine exerts protective roles in obesity, while the mechanism of spermidine in adipose tissue thermogenesis remains unclear. The present study first investigated the effect of spermidine on cold-stimulation and β3-adrenoceptor agonist-induced thermogenesis in lean and high-fat diet-induced obese mice. Next, the role of spermidine on glucose and lipid metabolism in different types of adipose tissue was determined. Here, we found that spermidine supplementation did not affect cold-stimulated thermogenesis in lean mice, while significantly promoting the activation of adipose tissue thermogenesis under cold stimulation and β3-adrenergic receptor agonist treatment in obese mice. Spermidine treatment markedly enhanced glucose and lipid metabolism in adipose tissues, and these results were associated with the activated autophagy pathway. Moreover, spermidine up-regulated fibroblast growth factor 21 (FGF21) signaling and its downstream pathway, including PI3K/AKT and AMPK pathways in vivo and in vitro. Knockdown of Fgf21 or inhibition of PI3K/AKT and AMPK pathways in brown adipocytes abolished the thermogenesis-promoting effect of spermidine, suggesting that the effect of spermidine on adipose tissue thermogenesis might be regulated by FGF21 signaling via the PI3K/AKT and AMPK pathways. The present study provides new insight into the mechanism of spermidine on obesity and its metabolic complications, thereby laying a theoretical basis for the clinical application of spermidine.

The Role of Obesity in Type 2 Diabetes Mellitus-An Overview

Obesity or excessive weight gain is identified as the most important and significant risk factor in the development and progression of type 2 diabetes mellitus (DM) in all age groups. It has reached pandemic dimensions, making the treatment of obesity crucial in the prevention and management of type 2 DM worldwide. Multiple clinical studies have demonstrated that moderate and sustained weight loss can improve blood glucose levels, insulin action and reduce the need for diabetic medications. A combined approach of diet, exercise and lifestyle modifications can successfully reduce obesity and subsequently ameliorate the ill effects and deadly complications of DM. This approach also helps largely in the prevention, control and remission of DM. Obesity and DM are chronic diseases that are increasing globally, requiring new approaches to manage and prevent diabetes in obese individuals. Therefore, it is essential to understand the mechanistic link between the two and design a comprehensive approach to increase life expectancy and improve the quality of life in patients with type 2 DM and obesity. This literature review provides explicit information on the clinical definitions of obesity and type 2 DM, the incidence and prevalence of type 2 DM in obese individuals, the indispensable role of obesity in the pathophysiology of type 2 DM and their mechanistic link. It also discusses clinical studies and outlines the recent management approaches for the treatment of these associated conditions. Additionally, in vivo studies on obesity and type 2 DM are discussed here as they pave the way for more rigorous development of therapeutic approaches.

Parkin depletion prevents the age-related alterations in the FGF21 system and the decline in white adipose tissue thermogenic function in mice

Parkin is an ubiquitin-E3 ligase that is involved in cellular mitophagy and was recently shown to contribute to controlling adipose tissue thermogenic plasticity. We found that Parkin expression is induced in brown (BAT) and white (WAT) adipose tissues of aged mice. We determined the potential role of Parkin in the aging-associated decline in the thermogenic capacity of adipose tissues by analyzing subcutaneous WAT, interscapular BAT, and systemic metabolic and physiological parameters in young (5 month-old) and aged (16 month-old) mice with targeted invalidation of the Parkin (Park2) gene, and their wild-type littermates. Our data indicate that suppression of Parkin prevented adipose accretion, increased energy expenditure and improved the systemic metabolic derangements, such as insulin resistance, seen in aged mice. This was associated with maintenance of browning and reduction of the age-associated induction of inflammation in subcutaneous WAT. BAT in aged mice was much less affected by Parkin gene invalidation. Such protection was associated with a dramatic prevention of the age-associated induction of fibroblast growth factor-21 (FGF21) levels in aged Parkin-invalidated mice. This was associated with a parallel reduction in FGF21 gene expression in adipose tissues and liver in aged Parkin-invalidated mice. Additionally, Parkin invalidation prevented the protein down-regulation of β-Klotho (a key co-receptor mediating FGF21 responsiveness in tissues) in aged adipose tissues. We conclude that Parkin down-regulation leads to improved systemic metabolism in aged mice, in association with maintenance of adipose tissue browning and FGF21 system functionality.

ATF4 expression in thermogenic adipocytes is required for cold-induced thermogenesis in mice via FGF21-independent mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially by increasing FGF21 expression. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis under physiological stress by generating mice selectively lacking either Atf4 (ATF4 BKO) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum-fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue. Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum-fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis under fed conditions likely in a FGF21-independent manner, in part via increased amino acid uptake and metabolism.

Resistance and Aerobic Training Were Effective in Activating Different Markers of the Browning Process in Obesity

Lifestyle changes regarding diet composition and exercise training have been widely used as a non-pharmacological clinical strategy in the treatment of obesity, a complex and difficult-to-control disease. Taking the potential of exercise in the browning process and in increasing thermogenesis into account, the aim of this paper was to evaluate the effect of resistance, aerobic, and combination training on markers of browning of white adipose tissue from rats with obesity who were switched to a balanced diet with normal calorie intake. Different types of training groups promote a reduction in the adipose tissue and delta mass compared to the sedentary high-fat diet group (HS). Interestingly, irisin in adipose tissues was higher in the resistance exercise (RE) and aerobic exercise (AE) groups compared to control groups. Moreover, in adipose tissue, the fibroblast growth factor 21 (FGF21), coactivator 1 α (PGC1α), and peroxisome proliferator-activated receptor gamma (PPARγ) were higher in response to resistance training RE compared with the control groups, respectively. Additionally, uncoupling protein 1 (UCP1) showed higher levels in response to group AE compared to the HS group. In conclusion, the browning process in white adipose tissue responds differently toward different training exercise protocols, with resistance and aerobic training efficient in activating different biomarkers of the browning process, upregulating irisin, FGF21, PGC1α, PPARγ, and UCP1 in WAT, which together may suggest an improvement in the thermogenic process in the adipose tissue. Considering the experimental conditions of the present investigation, we suggest future research to pave new avenues to be applied in clinical practices to combat obesity.

ATF4 Expression in Thermogenic Adipocytes is Required for Cold-Induced Thermogenesis in Mice via FGF21-Independent Mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially via upregulation of FGF21. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis by generating mice selectively lacking either Atf4 ( ATF4 BKO ) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum -fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue (WAT). Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum -fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis by activating amino acid metabolism in BAT in a FGF21-independent manner.

The Role of Organokines in Obesity and Type 2 Diabetes and Their Functions as Molecular Transducers of Nutrition and Exercise

Maintaining systemic homeostasis requires the coordination of different organs and tissues in the body. Our bodies rely on complex inter-organ communications to adapt to perturbations or changes in metabolic homeostasis. Consequently, the liver, muscle, and adipose tissues produce and secrete specific organokines such as hepatokines, myokines, and adipokines in response to nutritional and environmental stimuli. Emerging evidence suggests that dysregulation of the interplay of organokines between organs is associated with the pathophysiology of obesity and type 2 diabetes (T2D). Strategies aimed at remodeling organokines may be effective therapeutic interventions. Diet modification and exercise have been established as the first-line therapeutic intervention to prevent or treat metabolic diseases. This review summarizes the current knowledge on organokines secreted by the liver, muscle, and adipose tissues in obesity and T2D. Additionally, we highlighted the effects of diet/nutrition and exercise on the remodeling of organokines in obesity and T2D. Specifically, we investigated the ameliorative effects of caloric restriction, selective nutrients including ω3 PUFAs, selenium, vitamins, and metabolites of vitamins, and acute/chronic exercise on the dysregulation of organokines in obesity and T2D. Finally, this study dissected the underlying molecular mechanisms by which nutrition and exercise regulate the expression and secretion of organokines in specific tissues.

The FGF21 analog pegozafermin in severe hypertriglyceridemia: a randomized phase 2 trial

Pegozafermin, a long-acting glycopegylated analog of human fibroblast growth factor 21, is in development for the treatment of severe hypertriglyceridemia (SHTG) and nonalcoholic steatohepatitis. Here we report the results of a phase 2, double-blind, randomized, five-arm trial testing pegozafermin at four different doses (n = 67; 52 male) versus placebo (n = 18; 12 male) for 8 weeks in patients with SHTG (triglycerides (TGs), ≥500 mg dl-1 and ≤2,000 mg dl-1). Treated patients showed a significant reduction in median TGs for the pooled pegozafermin group versus placebo (57.3% versus 11.9%, difference versus placebo -43.7%, 95% confidence interval (CI): -57.1%, -30.3%; P < 0.001), meeting the primary endpoint of the trial. Reductions in median TGs ranged from 36.4% to 63.4% across all treatment arms and were consistent regardless of background lipid-lowering therapy. Results for secondary endpoints included significant decreases in mean apolipoprotein B and non-high-density lipoprotein cholesterol concentrations (-10.5% and -18.3% for pooled doses compared to 1.1% and -0.6% for placebo (95% CI: -21.5%, -2.0%; P = 0.019 and 95% CI: -30.7%, -5.1%; P = 0.007, respectively), as well as a significant decrease in liver fat fraction for pooled treatment (n = 17) versus placebo (n = 6; -42.2% pooled pegozafermin, -8.3% placebo; 95% CI: -60.9%, -8.7%; P = 0.012), as assessed in a magnetic resonance imaging sub-study. No serious adverse events were observed to be related to the study drug. If these results are confirmed in a phase 3 trial, pegozafermin could be a promising treatment for SHTG (ClinicalTrials.gov registration: NCT0441186).

Molecular Mechanisms of Obesity-Induced Development of Insulin Resistance and Promotion of Amyloid-β Accumulation: Dietary Therapy Using Weak Organic Acids via Improvement of Lowered Interstitial Fluid pH

Insulin resistance is one of the etiologies of type 2 diabetes mellitus (T2DM) and has been suggested to contribute to the development of Alzheimer's disease by promoting amyloid-β accumulation. Various causes of insulin resistance have been suggested; however, mechanisms of insulin resistance development remain to be elucidated in many respects. Elucidating the mechanisms underlying the development of insulin resistance is one of the key factors in developing methods to prevent the onset of T2DM and Alzheimer's disease. It has been suggested that the body pH environment plays an important role in the control of cellular functions by regulating the action of hormones including insulin and the activity of enzymes and neurons, thereby maintaining homeostatic conditions of the body. This review introduces: (1) Mitochondrial dysfunction through oxidative stress caused by obesity-induced inflammation. (2) Decreased pH of interstitial fluid due to mitochondrial dysfunction. (3) Development of insulin resistance due to diminution of insulin affinity to its receptor caused by the lowered interstitial fluid pH. (4) Accelerated accumulation of amyloid-β due to elevated activities of β- and γ-secretases caused by the lowered interstitial fluid pH. (5) Diet therapies for improving insulin resistance with weak organic acids that act as bases in the body to raise the pH of lowered interstitial fluid and food factors that promote absorption of weak organic acids in the gut.

Glucagon and energy expenditure; Revisiting amino acid metabolism and implications for weight loss therapy

Glucagon receptor (GCGR)-targeted multi-agonists are being developed for the treatment of obesity and metabolic disease. GCGR activity is utilised for its favourable weight loss and metabolic properties, including increased energy expenditure (EE) and hepatic lipid metabolism. GLP1R and GIPR activities are increasingly present in a multi-agonist strategy. Due to the compound effect of increased satiety, reduced food intake and increased energy expenditure, the striking weight loss effects of these multi-agonists has been demonstrated in pre-clinical models of obesity. The precise contribution and mechanism of GCGR activity to enhanced energy expenditure and weight loss in both rodents and humans is not fully understood. In this review, our understanding of glucagon-mediated EE is explored, and an amino acid-centric paradigm contributing to this phenomenon is presented. The current progress of GCGR-targeted multi-agonists in development is also highlighted with a focus on the implications of glucagon-stimulated hypoaminoacidemia.

Effect of a collagen-enriched beverage with or without omega-3 fatty acids on wound healing, metabolic biomarkers, and adipokines in patients with major burns

BACKGROUND & AIMS

This study investigated the effects of collagen hydrolysate and omega-3 fatty acids (FAs) on the rate and quality of wound healing, metabolic disorders, and adipose-derived peptides in patients with major burns.

METHODS

In this randomized clinical trial, 66 patients with 20-45% deep partial or full-thickness burns were randomly assigned to three groups to receive either a beverage containing collagen (40 gr/d), collagen (40 gr/d) plus 3 gr/d omega-3 (ω-3) FAs, or placebo for four weeks. Wound healing rate, Vancouver scar scale (VSS), as well as baseline, weeks two and three serum concentrations of adiponectin, fibroblast growth factor 21 (FGF21), neuregulin 4 (NRG4), transforming growth factor (TGF)-β1, and pre-albumin/hs-CRP ratio were assessed.

RESULTS

The wound healing rate during the weeks post-burn (p = 0.006 and p = 0.01), and days of 95% (21.3 ± 6.8 and 22.9 ± 8.7 vs. 34.3 ± 14.8 days, p = 0.003 and p = 0.03) and complete (26 ± 7.7 and 27.4 ± 9.4 vs. 41.1 ± 16.6 days, p = 0.003 and p = 0.01) wound healing were significantly better with Collagen and Collagen. ω-3 compared to the placebo group. The VSS was significantly lower, indicated better scar status, in the both intervention groups compared to the placebo (p = 0.02 and p = 0.01). Wound healing outcomes were not statistically different between the Collagen and Collagen. ω-3 groups. Hs-CRP/pre-albumin ratio was significantly lower in the Collagen. ω-3 than the placebo group at week three (1.2 ± 1.9 vs. 4.8 ± 7.7 dl/l, p = 0.03). The significant decrease in serum adiponectin seen during the trial course within the placebo (10 ± 8.8 to 5.8 ± 4.9 mg/l, p = 0.03) and Collagen (11.8 ± 14 to 8.6 ± 11.7 mg/l, p = 0.03) groups was prevented in the Collagen. ω-3 group (p = 0.4). Circulating FGF21 decreased significantly within the Collagen (p = 0.005) and Collagen. ω-3 (p = 0.02) groups at the end of week three compared to the baseline.

CONCLUSIONS

Adding collagen hydrolysate as part of adjunctive therapy improved wound healing rate and quality. These findings as well as the efficacy of omega-3 FAs need to be further confirmed in larger populations. This study was registered with the Iranian Registry of Clinical Trials (IRCT20090901002394N42).

Protective Effects of Coumestrol on Metabolic Dysfunction and Its Estrogen Receptor-Mediated Action in Ovariectomized Mice

Coumestrol, a phytoestrogen compound found in various plants, has been shown to act as a potent estrogen receptor (ER) agonist, with a higher binding affinity for ERβ than for ERα. However, there is currently limited information regarding its beneficial effects in postmenopausal disorders and its ER-mediated mechanisms. Herein, we investigated the effects of coumestrol (subcutaneous or oral treatment) on metabolic dysfunction in ovariectomized (OVX) mice fed a high-fat diet, in comparison with the effects of 17β-estradiol (E2) replacement. Coumestrol was administered daily at a dose of 5 mg/kg for 10 weeks. Coumestrol treatment through the subcutaneous route stimulated uterine growth in OVX mice at a level lower than that of E2. E2 and coumestrol prevented body fat accumulation, adipocyte hypertrophy, and hepatic steatosis, and enhanced voluntary physical activity. Coumestrol showed estrogen-mimetic effects in the regulation of the protein expressions involved in browning of white fat and insulin signaling, including increased hepatic expression of fibroblast growth factor 21. Importantly, the metabolic effects of coumestrol (oral administration at 10 mg/kg for 7 weeks) were mostly abolished following co-treatment with an ERβ-selective antagonist but not with an ERα-selective antagonist, indicating that the metabolic actions of coumestrol in OVX mice are primarily mediated by ERβ. These findings provide important insights into the beneficial effects of coumestrol as a phytoestrogen supplement for the prevention and treatment of postmenopausal symptoms.

Sesamol promotes browning of white adipocytes through liver-adipose crosstalk signal of hepatic fibroblast growth factor 21

Sesamol (SEM), a lignan from sesame oil, exhibited potential benefits on obesity treatment by promoting browning of adipocytes, and the current study is aimed to explore the molecular mechanisms of SEM from the aspect of systemic liver-adipose crosstalk that mediated by hepatic fibroblast growth factor 21 (FGF21). Our in vivo data showed that SEM induced energy expenditure and white adipose tissue (WAT) browning by increasing the expression level of uncoupling protein-1 in high fat diet induced obese C57BL/6J mice. Elevated levels of circulating FGF21 associated with the increased expression of hepatic FGF21 were observed after SEM intervention. Simultaneously, the increased adipose fibroblast growth factor tyrosine kinase receptor 1/beta-klotho indicated that FGF21 sensitivity was enhanced by SEM in WAT. Furthermore, our in vitro results from HepG2 and 3T3-L1 cell lines confirmed the effects and revealed the mechanism of SEM on the white adipocytes browning. We found that with the specific inhibitors of PPARα, the SEM-mediated hepatic FGF21 expression was decreased, and with the specific inhibitors of PPARγ, the browning effect of adipocytes by SEM combining with FGF21 was significantly suppressed. Taken together, the mechanism of SEM for inducing the WAT browning might be the modulation of SEM on liver-adipose crosstalk mediated by FGF21, and the PPARs family might be the targets of SEM. The novel findings from the present study provided evidence that SEM could be a potent obesity-treating compound.

Exercise-induced intertissue communication: adipose tissue and the heart

Exercise leads to numerous beneficial whole-body effects and can protect against the development of obesity, cardiometabolic, and neurodegenerative diseases. Recent studies have highlighted the importance of inter-organ crosstalk with a focus on secretory factors that mediate communication among organs, including adipose tissue and the heart. Studies investigating the effects of exercise on brown adipose tissue (BAT) and white adipose tissue (WAT) demonstrated that adipokines are released in response to exercise and act on the heart to decrease inflammation, alter gene expression, increase angiogenesis, and improve cardiac function. This review discusses the exercise-induced adaptations to BAT and WAT and how these adaptations affect heart health and function, while highlighting the importance of tissue crosstalk.

Adipokines: Deciphering the cardiovascular signature of adipose tissue

Obesity and hypertension are intimately linked due to the various ways that the important cell types such as vascular smooth muscle cells (VSMC), endothelial cells (EC), immune cells, and adipocytes, communicate with one another to contribute to these two pathologies. Adipose tissue is a very dynamic organ comprised primarily of adipocytes, which are well known for their role in energy storage. More recently adipose tissue has been recognized as the largest endocrine organ because of its ability to produce a vast number of signaling molecules called adipokines. These signaling molecules stimulate specific types of cells or tissues with many adipokines acting as indicators of adipocyte healthy function, such as adiponectin, omentin, and FGF21, which show anti-inflammatory or cardioprotective effects, acting as regulators of healthy physiological function. Others, like visfatin, chemerin, resistin, and leptin are often altered during pathophysiological circumstances like obesity and lipodystrophy, demonstrating negative cardiovascular outcomes when produced in excess. This review aims to explore the role of adipocytes and their derived products as well as the impacts of these adipokines on blood pressure regulation and cardiovascular homeostasis.

Cooling down with Entresto. Can sacubitril/valsartan combination enhance browning more than coldness?

BACKGROUND

It is a growing importance to induce a new treatment approach to encourage weight loss but also to improve maintenance of lost weight. It has been shown that promotion of brown adipose tissue (BAT) function or acquisition of BAT characteristics in white adipose tissue (terms referred as "browning") can be protective against obesity.

MAIN TEXT

Amongst numerous established environmental influences on BAT activity, cold exposure is the best interested technique due to its not only effects on of BAT depots in proliferation process but also de novo differentiation of precursor cells via β-adrenergic receptor activation. A novel combination drug, sacubitril/valsartan, has been shown to be more efficient in reducing cardiovascular events and heart failure readmission compared to conventional therapy. Also, this combination of drugs increases the postprandial lipid oxidation contributing to energy expenditure, promotes lipolysis in adipocytes and reduces body weight. To date, there is no research examining potential of combined sacubitril/valsartan use to promote browning or mechanisms in the basis of this thermogenic process.

CONCLUSION

Due to the pronounced effects of cold and sacubitril/valsartan treatment on function and metabolism of BAT, the primary goal of further research should focused on investigation of the synergistic effects of the sacubitril/valsartan treatment at low temperature environmental conditions.

Exercise-Induced Adipose Tissue Thermogenesis and Browning: How to Explain the Conflicting Findings?

Brown adipose tissue (BAT) has been widely studied in targeting against metabolic diseases such as obesity, type 2 diabetes and insulin resistance due to its role in nutrient metabolism and energy regulation. Whether exercise promotes adipose tissue thermogenesis and browning remains controversial. The results from human and rodent studies contradict each other. In our opinion, fat thermogenesis or browning promoted by exercise should not be a biomarker of health benefits, but an adaptation under the stress between body temperature regulation and energy supply and expenditure of multiple organs. In this review, we discuss some factors that may contribute to conflicting experimental results, such as different thermoneutral zones, gender, training experience and the heterogeneity of fat depots. In addition, we explain that a redox state in cells potentially causes thermogenesis heterogeneity and different oxidation states of UCP1, which has led to the discrepancies noted in previous studies. We describe a network by which exercise orchestrates the browning and thermogenesis of adipose tissue with total energy expenditure through multiple organs (muscle, brain, liver and adipose tissue) and multiple pathways (nerve, endocrine and metabolic products), providing a possible interpretation for the conflicting findings.

Suppression of obesity by melatonin through increasing energy expenditure and accelerating lipolysis in mice fed a high-fat diet

Backgrounds/objectives

Melatonin promotes brown adipose tissue (BAT) activity, leading to body mass reduction and energy expenditure. However, the mechanisms governing these beneficial effects are not well-established. This study aimed to assess the effects of (1) melatonin on BAT and energy metabolism, and (2) fibroblast growth factor 21 (FGF21) in BAT-mediated thermogenesis.

Methods

Male C57BL/6 J mice received a high-fat diet (HFD) or normal chow, accompanied by intraperitoneal injection of 20 mg/kg melatonin for 12 weeks. FGF21^−/− mice consumed an HFD with or without melatonin for 8 weeks.

Results

Melatonin attenuated weight gain, insulin resistance, adipocyte hypertrophy, inflammation, and hepatic steatosis induced by the HFD and increased energy expenditure. Furthermore, melatonin improved cold tolerance by increasing BAT uncoupling protein 1 (UCP1) expression and producing heat. Notably, melatonin resulted in a shift in energy metabolism favouring the utilization of fat, and it increased FGF21 in circulating and metabolic tissues and skeletal muscle phosphorylation of AMP-activated protein kinase. However, melatonin did not protect against obesity, insulin resistance, and energy expenditure in HFD-fed FGF21^−/− mice.

Conclusions

Melatonin suppressed obesity and insulin resistance resulting from the HFD by enhancing BAT activity and energy expenditure, and these effects were dependent on FGF21.

Do Sugar-Sweetened Beverages Increase Fasting FGF21 Irrespective of the Type of Added Sugar? A Secondary Exploratory Analysis of a Randomized Controlled Trial

Human fibroblast growth factor 21 (FGF21) is a multifaceted metabolic regulator considered to control sugar intake and to exert beneficial effects on glucose and lipid metabolism. Elevated serum FGF21 levels are associated with metabolic syndrome, suggesting a state of FGF21 resistance. Further, given the evidence of a hepatic ChREBP and FGF21 signaling axis, it can be assumed that SSBs containing fructose would possibly increase FGF21 concentrations. We investigated the effects of sugar-sweetened beverage (SSB) consumption on fasting FGF21 levels in healthy, lean men, discriminating the effects of glucose, fructose, and their disaccharide sucrose by secondary data analysis from a randomized controlled trial. Seven weeks of daily SSB consumption resulted in increased fasting FGF21 in healthy, lean men, irrespective of the sugar type. Medians of ΔFGF21 between post-SSB intervention values (week 7) and no-intervention period values (IQR) in pg/mL were: glucose 17.4 (0.4–45.8), fructose 22.9 (−8.6–35.1), and sucrose 13.7 (2.2–46.1). In contrast, this change in FGF21 concentration was only 6.3 (−20.1–26.9) pg/mL in the control group. The lack of a fructose-specific effect on FGF21 concentrations is contrary to our assumption. It is concluded that SSB intake may impact FGF21 concentrations and could contribute to the increased FGF21 concentrations observed in subjects suffering from metabolic syndrome that is possibly associated with decreased FGF21 responsiveness.

Browning of the white adipose tissue regulation: new insights into nutritional and metabolic relevance in health and diseases

Adipose tissues are dynamic tissues that play crucial physiological roles in maintaining health and homeostasis. Although white adipose tissue and brown adipose tissue are currently considered key endocrine organs, they differ functionally and morphologically. The existence of the beige or brite adipocytes, cells displaying intermediary characteristics between white and brown adipocytes, illustrates the plastic nature of the adipose tissue. These cells are generated through white adipose tissue browning, a process associated with augmented non-shivering thermogenesis and metabolic capacity. This process involves the upregulation of the uncoupling protein 1, a molecule that uncouples the respiratory chain from Adenosine triphosphate synthesis, producing heat. β-3 adrenergic receptor system is one important mediator of white adipose tissue browning, during cold exposure. Surprisingly, hyperthermia may also induce beige activation and white adipose tissue beiging. Physical exercising copes with increased levels of specific molecules, including Beta-Aminoisobutyric acid, irisin, and Fibroblast growth factor 21 (FGF21), which induce adipose tissue browning. FGF21 is a stress-responsive hormone that interacts with beta-klotho. The central roles played by hormones in the browning process highlight the relevance of the individual lifestyle, including circadian rhythm and diet. Circadian rhythm involves the sleep-wake cycle and is regulated by melatonin, a hormone associated with UCP1 level upregulation. In contrast to the pro-inflammatory and adipose tissue disrupting effects of the western diet, specific food items, including capsaicin and n-3 polyunsaturated fatty acids, and dietary interventions such as calorie restriction and intermittent fasting, favor white adipose tissue browning and metabolic efficiency. The intestinal microbiome has also been pictured as a key factor in regulating white tissue browning, as it modulates bile acid levels, important molecules for the thermogenic program activation. During embryogenesis, in which adipose tissue formation is affected by Bone morphogenetic proteins that regulate gene expression, the stimuli herein discussed influence an orchestra of gene expression regulators, including a plethora of transcription factors, and chromatin remodeling enzymes, and non-coding RNAs. Considering the detrimental effects of adipose tissue browning and the disparities between adipose tissue characteristics in mice and humans, further efforts will benefit a better understanding of adipose tissue plasticity biology and its applicability to managing the overwhelming burden of several chronic diseases.

Multi-organ FGF21-FGFR1 signaling in metabolic health and disease

Metabolic syndrome is a chronic systemic disease that is particularly manifested by obesity, diabetes, and hypertension, affecting multiple organs. The increasing prevalence of metabolic syndrome poses a threat to public health due to its complications, such as liver dysfunction and cardiovascular disease. Impaired adipose tissue plasticity is another factor contributing to metabolic syndrome. Emerging evidence demonstrates that fibroblast growth factors (FGFs) are critical players in organ crosstalk via binding to specific FGF receptors (FGFRs) and their co-receptors. FGFRs activation modulates intracellular responses in various cell types under metabolic stress. FGF21, in particular is considered as the key regulator for mediating systemic metabolic effects by binding to receptors FGFR1, FGFR3, and FGFR4. The complex of FGFR1 and beta Klotho (β-KL) facilitates endocrine and paracrine communication networks that physiologically regulate global metabolism. This review will discuss FGF21-mediated FGFR1/β-KL signaling pathways in the liver, adipose, and cardiovascular systems, as well as how this signaling is involved in the interplay of these organs during the metabolic syndrome. Furthermore, the clinical implications and therapeutic strategies for preventing metabolic syndrome and its complications by targeting FGFR1/β-KL are also discussed.

Thermogenic adipose tissue aging: Mechanisms and implications

Adipose tissue undergoes significant anatomical and functional changes with aging, leading to an increased risk of metabolic diseases. Age-related changes in adipose tissue include overall defective adipogenesis, dysfunctional adipokine secretion, inflammation, and impaired ability to produce heat by nonshivering thermogenesis. Thermogenesis in adipose tissue is accomplished by brown and beige adipocytes, which also play a role in regulating energy homeostasis. Brown adipocytes develop prenatally, are found in dedicated depots, and involute in early infancy in humans. In contrast, beige adipocytes arise postnatally in white adipose tissue and persist throughout life, despite being lost with aging. In recent years, there have been significant advances in the understanding of age-related reduction in thermogenic adipocyte mass and function. Mechanisms underlying such changes are beginning to be delineated. They comprise diminished adipose precursor cell pool size and adipogenic potential, mitochondrial dysfunction, decreased sympathetic signaling, and altered paracrine and endocrine signals. This review presents current evidence from animal models and human studies for the mechanisms underlying thermogenic adipocyte loss and discusses potential strategies targeting brown and beige adipocytes to increase health span and longevity.

Sexual Dimorphism in Adipose-Hypothalamic Crosstalk and the Contribution of Aryl Hydrocarbon Receptor to Regulate Energy Homeostasis

There are fundamental sex differences in the regulation of energy homeostasis. Better understanding of the underlying mechanisms of energy balance that account for this asymmetry will assist in developing sex-specific therapies for sexually dimorphic diseases such as obesity. Multiple organs, including the hypothalamus and adipose tissue, play vital roles in the regulation of energy homeostasis, which are regulated differently in males and females. Various neuronal populations, particularly within the hypothalamus, such as arcuate nucleus (ARC), can sense nutrient content of the body by the help of peripheral hormones such leptin, derived from adipocytes, to regulate energy homeostasis. This review summarizes how adipose tissue crosstalk with homeostatic network control systems in the brain, which includes energy regulatory regions and the hypothalamic–pituitary axis, contribute to energy regulation in a sex-specific manner. Moreover, development of obesity is contingent upon diet and environmental factors. Substances from diet and environmental contaminants can exert insidious effects on energy metabolism, acting peripherally through the aryl hydrocarbon receptor (AhR). Developmental AhR activation can impart permanent alterations of neuronal development that can manifest a number of sex-specific physiological changes, which sometimes become evident only in adulthood. AhR is currently being investigated as a potential target for treating obesity. The consensus is that impaired function of the receptor protects from obesity in mice. AhR also modulates sex steroid receptors, and hence, one of the objectives of this review is to explain why investigating sex differences while examining this receptor is crucial. Overall, this review summarizes sex differences in the regulation of energy homeostasis imparted by the adipose–hypothalamic axis and examines how this axis can be affected by xenobiotics that signal through AhR.

The Role of Epicardial Adipose Tissue in the Development of Atrial Fibrillation, Coronary Artery Disease and Chronic Heart Failure in the Context of Obesity and Type 2 Diabetes Mellitus: A Narrative Review

Cardiovascular diseases (CVDs) are a significant burden globally and are especially prevalent in obese and/or diabetic populations. Epicardial adipose tissue (EAT) surrounding the heart has been implicated in the development of CVDs as EAT can shift from a protective to a maladaptive phenotype in diseased states. In diabetic and obese patients, an elevated EAT mass both secretes pro-fibrotic/pro-inflammatory adipokines and forms intramyocardial fibrofatty infiltrates. This narrative review considers the proposed pathophysiological roles of EAT in CVDs. Diabetes is associated with a disordered energy utilization in the heart, which promotes intramyocardial fat and structural remodeling. Fibrofatty infiltrates are associated with abnormal cardiomyocyte calcium handling and repolarization, increasing the probability of afterdepolarizations. The inflammatory phenotype also promotes lateralization of connexin (Cx) proteins, undermining unidirectional conduction. These changes are associated with conduction heterogeneity, together creating a substrate for atrial fibrillation (AF). EAT is also strongly implicated in coronary artery disease (CAD); inflammatory adipokines from peri-vascular fat can modulate intra-luminal homeostasis through an “outside-to-inside” mechanism. EAT is also a significant source of sympathetic neurotransmitters, which promote progressive diastolic dysfunction with eventual cardiac failure. Further investigations on the behavior of EAT in diabetic/obese patients with CVD could help elucidate the pathogenesis and uncover potential therapeutic targets.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

miR-375 is cold exposure sensitive and drives thermogenesis in visceral adipose tissue derived stem cells

Activation of brown adipose tissue may increase energy expenditure by non-shivering thermogenesis. Cold exposure is one of the options to activate brown adipocytes. To link changes in energy metabolism with microRNA expression (miRNAs), we analyzed 158 miRNAs in serum of 169 healthy individuals before and after cold exposure. Validating the results of a miRNA array, a significant down-regulation of miR-375 after cold exposure (P < 0.0001) was detected. These changes went along with a significant negative correlation between miR-375 and visceral adipose tissue (VAT) mass (P < 0.0001), implicating a specific function of miR-375 in this depot. Significantly higher expression levels of miR-375 were found in VAT in comparison to subcutaneous fat (SAT). Using in silico prediction, we identified putative miR-375 target genes involved in the thermogenesis pathway. Cold-stimulation of subcutaneous and visceral pre-adipocytes (PACs) led to significantly higher expression levels of FABP4, FGF21, PPARGC1A and PRDM16 in VC-PACs. Analyzing miR-375 knock down and cold stimulated VC-PACs revealed a significant up-regulation of thermogenesis associated genes PPARGC1A, ELOVL3 and PRDM16. In summary, our findings identified miR-375 as a potential adipogenic and thermogenesis-associated miRNA exclusively acting in visceral adipose tissue.

Physiological and pathophysiological role of endocrine fibroblast growth factors

The endocrine subfamily of fibroblast growth factors (FGF) includes three factors: FGF19, FGF21, FGF23. They act on distal tissues through FGF receptors (FGFRs). The FGFR activation requires two cofactors: α- and β-Klotho, which are structurally related single-pass transmembrane proteins. The endocrine FGFs regulate various metabolic processes involved in the regulation of glucose and lipid metabolism as well as bile acid circulation, vitamin D modulation, and phosphate homeostasis. The FGF-FGFR dysregulation is widely implicated in the pathogenesis of various disorders. Significant alterations in plasma FGF concentration are associated with the most prevalent chronic diseases, including dyslipidemia, type 2 diabetes, cardiovascular diseases, obesity, non-alcoholic fatty liver disease, diseases of the biliary tract, chronic kidney disease, inflammatory bowel disease, osteomalacia, various malignancies, and depression. Therefore, the endocrine FGFs may serve as disease predictors or biomarkers, as well as potential therapeutic targets. Currently, numerous analogues and inhibitors of endocrine FGFs are under development for treatment of various disorders, and recently, a human monoclonal antibody against FGF23 has been approved for treatment of X-linked hypophosphatemia. The aim of this review is to summarize the current data on physiological and pathophysiological actions of the endocrine FGF subfamily and recent research concerning the therapeutic potential of the endocrine FGF pathways.

Effects of aerobic exercise on fibroblast growth factor 21 in overweight and obesity. A systematic review

Fibroblast growth factor 21 (FGF21) has been suggested to improve metabolism during aerobic exercise in obesity. However, the variability of exercise interventions gives rise to discrepancies in the field. Therefore, we aimed to systematically review the available literature regarding the effects of aerobic exercise on FGF21 in the context of overweight and obesity. Our search included original articles published between 2009 and November 2021 found in PubMed, Science Direct, and Medline. Clinical and preclinical studies were included. Studies, where subjects or animals presented with other conditions (e.g., cancer, stroke), were excluded. From an initial 43 studies, 19 (clinical studies = 9; preclinical studies = 10) were eligible for inclusion in this review. The main findings were that acute exercise tended to increase circulatory levels of FGF21. In contrast, chronic exercise programs (≥4 weeks) had the opposite effect along with inducing mRNA and protein increases of FGF receptors and β-klotho in adipose tissue, liver, and skeletal muscle. In conclusion, both clinical and preclinical studies showed that aerobic exercise exerts changes in circulatory and tissue FGF21, along with its receptors and co-receptor. Future research is needed to elucidate the mechanisms, along with the physiological and clinical implications of these changes.

Beyond appetite regulation: Targeting energy expenditure, fat oxidation, and lean mass preservation for sustainable weight loss

New appetite-regulating antiobesity treatments such as semaglutide and agents under investigation such as tirzepatide show promise in achieving weight loss of 15% or more. Energy expenditure, fat oxidation, and lean mass preservation are important determinants of weight loss and weight-loss maintenance beyond appetite regulation. This review discusses prior failures in clinical development of weight-loss drugs targeting energy expenditure and explores novel strategies for targeting energy expenditure: mitochondrial proton leak, uncoupling, dynamics, and biogenesis; futile calcium and substrate cycling; leptin for weight maintenance; increased sympathetic nervous system activity; and browning of white fat. Relevant targets for preserving lean mass are also reviewed: growth hormone, activin type II receptor inhibition, and urocortin 2 and 3. We endorse moderate modulation of energy expenditure and preservation of lean mass in combination with efficient appetite reduction as a means of obtaining a significant, safe, and long-lasting weight loss. Furthermore, we suggest that the regulatory guidelines should be revisited to focus more on the quality of weight loss and its maintenance rather than the absolute weight loss. Commitment to this research focus both from a scientific and from a regulatory point of view could signal the beginning of the next era in obesity therapies.

Histone Deacetylases as Modulators of the Crosstalk Between Skeletal Muscle and Other Organs

Skeletal muscle plays a major role in controlling body mass and metabolism: it is the most abundant tissue of the body and a major source of humoral factors; in addition, it is primarily responsible for glucose uptake and storage, as well as for protein metabolism. Muscle acts as a metabolic hub, in a crosstalk with other organs and tissues, such as the liver, the brain, and fat tissue. Cytokines, adipokines, and myokines are pivotal mediators of such crosstalk. Many of these circulating factors modulate histone deacetylase (HDAC) expression and/or activity. HDACs form a numerous family of enzymes, divided into four classes based on their homology to their orthologs in yeast. Eleven family members are considered classic HDACs, with a highly conserved deacetylase domain, and fall into Classes I, II, and IV, while class III members are named Sirtuins and are structurally and mechanistically distinct from the members of the other classes. HDACs are key regulators of skeletal muscle metabolism, both in physiological conditions and following metabolic stress, participating in the highly dynamic adaptative responses of the muscle to external stimuli. In turn, HDAC expression and activity are closely regulated by the metabolic demands of the skeletal muscle. For instance, NAD+ levels link Class III (Sirtuin) enzymatic activity to the energy status of the cell, and starvation or exercise affect Class II HDAC stability and intracellular localization. SUMOylation or phosphorylation of Class II HDACs are modulated by circulating factors, thus establishing a bidirectional link between HDAC activity and endocrine, paracrine, and autocrine factors. Indeed, besides being targets of adipo-myokines, HDACs affect the synthesis of myokines by skeletal muscle, altering the composition of the humoral milieu and ultimately contributing to the muscle functioning as an endocrine organ. In this review, we discuss recent findings on the interplay between HDACs and circulating factors, in relation to skeletal muscle metabolism and its adaptative response to energy demand. We believe that enhancing knowledge on the specific functions of HDACs may have clinical implications leading to the use of improved HDAC inhibitors for the treatment of metabolic syndromes or aging.

Associations between RNA-Binding Motif Protein 3, Fibroblast Growth Factor 21, and Clinical Outcome in Patients with Stroke

Background: RNA-binding motif protein 3 (RBM3) is a cold-induced marker of good functional outcome of ischemic stroke that is promising as a protective target. Fibroblast growth factor 21 (FGF21) is an obesity- and temperature-related hormone that upregulates the expression of RBM3, which is beneficial as a recombinant treatment and has been tested under different experimental pathological conditions, including stroke. However, the interaction between RBM3 and FGF21 has not yet been tested for clinical stroke conditions. Methods: In a sample of 66 stroke patients, we analyzed the associations between the FGF21 and RBM3 serum concentrations on admission and at 72 h, body weight, maximum temperature during the first 24 h, and the outcome of patients at 3 months. We also analyzed their association with biomarkers of obesity (adiponectin and leptin) and inflammation (interleukin-6 (IL-6) and interleukin (IL-10)). Results: Higher concentrations of FGF21 on admission and RBM3 at 72 h were associated with good outcomes. Serum FGF21 and RBM3 were directly related to body mass index and inversely related to the maximum temperature during the first 24 h. We found a positive association between the FGF21 concentrations in obese patients with leptin and a negative correlation with adiponectin in non-obese participants. Conclusions: This clinical study demonstrates the association between RBM3 and FGF21 levels and the outcome of stroke patients. Although further investigations are required, these data support the pharmacological induction of RBM3 as a promising protective therapy.

Serum Fibroblast Growth Factor 21 Level Is Associated with Aortic Stiffness in Patients on Maintenance Hemodialysis

Background. Fibroblast growth factor 21 (FGF-21) is a hormone that regulates glucose and lipid metabolism. High serum FGF-21 levels are associated with carotid atherosclerosis and coronary artery disease. This cross-sectional study aimed to assess the relationship between serum FGF-21 levels and carotid-femoral pulse wave velocity (cfPWV) in patients on maintenance hemodialysis (HD). Methods. Blood samples and baseline characteristics were collected from 130 HD patients. Serum FGF-21 concentrations were measured with an enzyme-linked immunosorbent assay kit. Aortic stiffness was defined as a carotid-femoral pulse wave velocity (cfPWV) of more than 10 m/s. Results. Of the 130 HD patients, aortic stiffness was diagnosed in 54 (41.5%). Serum FGF-21 levels were significantly higher in those with aortic stiffness than those without $\left(P<0.001\right)$ . The FGF-21 level was independently associated with aortic stiffness (odds ratio (OR): 1.008; 95% CI: 1.003–1.012; $P=0.001$ ) after adjusting for diabetes mellitus, age, hypertension, C-reactive protein, and body weight in multivariable logistic regression analysis. Multivariable forward stepwise linear regression analysis also confirmed that the logarithmically transformed FGF-21 level (β = 3.245, 95% CI: 1.593–4.987, $P<0.001$ ) was an independent predictor of cfPWV values. The area under the receiver operating characteristic (ROC) curve predicting aortic stiffness by the serum FGF-21 level was 0.693 (95% CI: 0.606–0.771, $P<0.001$ ). Conclusions. Serum FGF-21 level positively correlates with cfPWV and is also an independent predictor of aortic stiffness in maintenance HD patients.

Brite Adipocyte FGF21 Attenuates Cardiac Ischemia/Reperfusion Injury in Rat Hearts by Modulating NRF2

Although the optimal therapy for myocardial infarction includes reperfusion to restore blood flow to the ischemic area, myocardial injury after ischemia/reperfusion usually leads to an inflammatory response, oxidative stress, and cardiomyocyte apoptosis. In this study, rat adipose-derived stem cells were differentiated into low-thermogenic beige adipocytes (LBACs) and high-thermogenic beige adipocytes (HBACs) to study the different cardioprotective effects of heterogeneous expression of brown adipocytes. We found that antioxidant and antiapoptotic factors in H9c2 cardiomyocytes were upregulated by high levels of secreted FGF21 in HBAC conditioned medium (HBAC-CM), whereas FGF21 in HBAC-CM did not affect antioxidative or antiapoptotic cell death in H9c2 cardiomyocytes with Nrf2 knockdown. These results show that NRF2 mediates antioxidative and antiapoptotic effects through the HBAC-secreted factor FGF21. Consistent with this finding, the expression of antioxidant and antiapoptotic genes was upregulated by highly secreted FGF21 after HBAC-CM treatment compared to LBAC-CM treatment in H9c2 cardiomyocytes via NRF2 activation. Furthermore, HBAC-CM significantly attenuated ischemic rat heart tissue injury via NRF2 activation. Based on these findings, we propose that HBAC-CM exerts beneficial effects in rat cardiac ischemia/reperfusion injury by modulating NRF2 and has potential as a promising therapeutic agent for myocardial infarction.

SNAP25 mutation disrupts metabolic homeostasis, steroid hormone production and central neurobehavior

OBJECTIVE

SNAP-25 is one of the key proteins involved in formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes that are at the core of hormonal secretion and synaptic transmission. Altered expression or function of SNAP-25 can contribute to the development of neuropsychiatric and metabolic disease. A dominant negative (DN) I67T missense mutation in the b-isoform of SNAP-25 (DN-SNAP25mut) mice leads to abnormal interactions within the SNARE complex and impaired exocytotic vesicle recycling, yet the significance of this mutation to any association between the central nervous system and metabolic homeostasis is unknown.

METHODS

Here we explored aspects of metabolism, steroid hormone production and neurobehavior of DN-SNAP25mut mice.

RESULTS

DN-SNAP25mut mice displayed enhanced insulin function through increased Akt phosphorylation, alongside increased adrenal and gonadal hormone production. In addition, increased anxiety behavior and beigeing of white adipose tissue with increased energy expenditure were observed in mutants.

CONCLUSIONS

Our results show that SNAP25 plays an important role in bridging central neurological systems with peripheral metabolic homeostasis, and provide potential insights between metabolic disease and neuropsychiatric disorders in humans.

Multifactorial Mechanism of Sarcopenia and Sarcopenic Obesity. Role of Physical Exercise, Microbiota and Myokines

Obesity and ageing place a tremendous strain on the global healthcare system. Age-related sarcopenia is characterized by decreased muscular strength, decreased muscle quantity, quality, and decreased functional performance. Sarcopenic obesity (SO) is a condition that combines sarcopenia and obesity and has a substantial influence on the older adults’ health. Because of the complicated pathophysiology, there are disagreements and challenges in identifying and diagnosing SO. Recently, it has become clear that dysbiosis may play a role in the onset and progression of sarcopenia and SO. Skeletal muscle secretes myokines during contraction, which play an important role in controlling muscle growth, function, and metabolic balance. Myokine dysfunction can cause and aggravate obesity, sarcopenia, and SO. The only ways to prevent and slow the progression of sarcopenia, particularly sarcopenic obesity, are physical activity and correct nutritional support. While exercise cannot completely prevent sarcopenia and age-related loss in muscular function, it can certainly delay development and slow down the rate of sarcopenia. The purpose of this review was to discuss potential pathways to muscle deterioration in obese individuals. We also want to present the current understanding of the role of various factors, including microbiota and myokines, in the process of sarcopenia and SO.