The glycoprotein follistatin-like 1 promotes brown adipose thermogenesis

From Beats to Metabolism: the Heart at the Core of Interorgan Metabolic Cross Talk

The heart, once considered a mere blood pump, is now recognized as a multifunctional metabolic and endocrine organ. Its function is tightly regulated by various metabolic processes, at the same time it serves as an endocrine organ, secreting bioactive molecules that impact systemic metabolism. In recent years, research has shed light on the intricate interplay between the heart and other metabolic organs, such as adipose tissue, liver, and skeletal muscle. The metabolic flexibility of the heart and its ability to switch between different energy substrates play a crucial role in maintaining cardiac function and overall metabolic homeostasis. Gaining a comprehensive understanding of how metabolic disorders disrupt cardiac metabolism is crucial, as it plays a pivotal role in the development and progression of cardiac diseases. The emerging understanding of the heart as a metabolic and endocrine organ highlights its essential contribution to whole body metabolic regulation and offers new insights into the pathogenesis of metabolic diseases, such as obesity, diabetes, and cardiovascular disorders. In this review, we provide an in-depth exploration of the heart's metabolic and endocrine functions, emphasizing its role in systemic metabolism and the interplay between the heart and other metabolic organs. Furthermore, emerging evidence suggests a correlation between heart disease and other conditions such as aging and cancer, indicating that the metabolic dysfunction observed in these conditions may share common underlying mechanisms. By unraveling the complex mechanisms underlying cardiac metabolism, we aim to contribute to the development of novel therapeutic strategies for metabolic diseases and improve overall cardiovascular health.

Brown adipose tissue-derived metabolites and their role in regulating metabolism

The discovery and rejuvenation of metabolically active brown adipose tissue (BAT) in adult humans have offered a new approach to treat obesity and metabolic diseases. Beyond its accomplished role in adaptive thermogenesis, BAT secretes signaling molecules known as "batokines", which are instrumental in regulating whole-body metabolism via autocrine, paracrine, and endocrine action. In addition to the intrinsic BAT metabolite-oxidizing activity, the endocrine functions of these molecules may help to explain the association between BAT activity and a healthy systemic metabolic profile. Herein, we review the evidence that underscores the significance of BAT-derived metabolites, especially highlighting their role in controlling physiological and metabolic processes involving thermogenesis, substrate metabolism, and other essential biological processes. The conversation extends to their capacity to enhance energy expenditure and mitigate features of obesity and its related metabolic complications. Thus, metabolites derived from BAT may provide new avenues for the discovery of metabolic health-promoting drugs with far-reaching impacts. This review aims to dissect the complexities of the secretory role of BAT in modulating local and systemic metabolism in metabolic health and disease.

Cardiac-to-adipose axis in metabolic homeostasis and diseases: special instructions from the heart

Adipose tissue is essential for maintaining systemic metabolic homeostasis through traditional metabolic regulation, endocrine crosstalk, and extracellular vesicle production. Adipose dysfunction is a risk factor for cardiovascular diseases. The heart is a traditional pump organ. However, it has recently been recognized to coordinate interorgan cross-talk by providing peripheral signals known as cardiokines. These molecules include specific peptides, proteins, microRNAs and novel extracellular vesicle-carried cargoes. Current studies have shown that generalized cardiokine-mediated adipose regulation affects systemic metabolism. Cardiokines regulate lipolysis, adipogenesis, energy expenditure, thermogenesis during cold exposure and adipokine production. Moreover, cardiokines participate in pathological processes such as obesity, diabetes and ischemic heart injury. The underlying mechanisms of the cardiac-to-adipose axis mediated by cardiokines will be further discussed to provide potential therapeutic targets for metabolic diseases and support a new perspective on the need to correct adipose dysfunction after ischemic heart injury.

Contribution of High-Intensity Interval Exercise in the Fasted State to Fat Browning: Potential Roles of Lactate and β-Hydroxybutyrate

PURPOSE

Fat browning contributes to energy consumption and may have metabolic benefits against obesity; however, the potential roles of lactate and β-hydroxybutyrate (β-HB) in fat browning remain unclear. We investigated the roles of a single bout of aerobic exercise that increases lactate and β-HB levels in the fasted state on the regulation of fat browning in rats and humans.

METHODS

Male Sprague-Dawley rats were exposed to 24-h fasting and/or a single bout moderate-intensity aerobic exercise (40 min): sedentary (CON), exercise (ND-EX), fasting (FAST), and exercise + fasting (F-EX). Adult men ( n = 13) were randomly assigned into control with food intake (CON), exercise with intensity at onset of blood lactate accumulation in the fasted state (F-OBLA), and high-intensity interval exercise in the fasted state (F-HIIE) until each participant expended 350 kcal of energy. For evaluating the effects of exercise intensity in rats, we conducted another set of animal experiment, including groups of sedentary fed control, fasting control, and exercise with moderate-intensity or HIIE for 40 min after a 24-h fasting.

RESULTS

Regardless of fasting, single bout of exercise increases the concentration of lactate and β-HB in rats, but the exercise in the fasted state increases the β-HB level more significantly in rats and humans. F-EX-activated fat browning (AMPK-SirT1-PGC1α pathway and PRDM16) and thermogenic factor (UCP1) in white fat of rats. In rats and humans, exercise in the fasted state increased the blood levels of fat browning-related adipomyokines. In particular, compared with F-OBLA, F-HIIE more efficiently increases free fatty acid as well as blood levels of fat browning adipomyokines in humans, which was correlated with blood levels of lactate and β-HB. In rats that performed exercise with different intensity, the higher plasma lactate and β-HB levels, and higher expression of p-AMPK, UCP1, and PRDM16 in white adipose tissue of HIIE group than those of moderate-intensity group, were observed.

CONCLUSIONS

A single bout of aerobic exercise in the fasted state significantly induced fat browning-related pathways, free fatty acid, and adipomyokines, particularly F-HIIE in human. Although further evidence for supporting our results is required in humans, aerobic exercise in the fasted state with high intensity that increase lactate and β-HB may be a modality of fat browning.

The impact of mild hypoxia exposure on myokine secretion in human obesity

BACKGROUND/OBJECTIVE

Compelling evidence indicates that myokines act in an autocrine, paracrine and endocrine manner to alter metabolic homeostasis. The mechanisms underlying exercise-induced changes in myokine secretion remain to be elucidated. Since exercise acutely decreases oxygen partial pressure (pO₂) in skeletal muscle (SM), the present study was designed to test the hypothesis that (1) hypoxia exposure impacts myokine secretion in primary human myotubes and (2) exposure to mild hypoxia in vivo alters fasting and postprandial plasma myokine concentrations in humans.

METHODS

Differentiated primary human myotubes were exposed to different physiological pO₂ levels for 24 h, and cell culture medium was harvested to determine myokine secretion. Furthermore, we performed a randomized single-blind crossover trial to investigate the impact of mild intermittent hypoxia exposure (MIH: 7-day exposure to 15% O₂, 3x2h/day vs. normoxia: 21% O₂) on in vivo SM pO₂ and plasma myokine concentrations in 12 individuals with overweight and obesity (body-mass index ≥ 28 kg/m²).

RESULTS

Hypoxia exposure (1% O₂) increased secreted protein acidic and rich in cysteine (SPARC, p = 0.043) and follistatin like 1 (FSTL1, p = 0.021), and reduced leukemia inhibitory factor (LIF) secretion (p = 0.009) compared to 3% O₂ in primary human myotubes. In addition, 1% O₂ exposure increased interleukin-6 (IL-6, p = 0.004) and SPARC secretion (p = 0.021), whilst reducing fatty acid binding protein 3 (FABP3) secretion (p = 0.021) compared to 21% O₂. MIH exposure in vivo markedly decreased SM pO₂ (≈40%, p = 0.002) but did not alter plasma myokine concentrations.

CONCLUSIONS

Hypoxia exposure altered the secretion of several myokines in primary human myotubes, revealing hypoxia as a novel modulator of myokine secretion. However, both acute and 7-day MIH exposure did not induce alterations in plasma myokine concentrations in individuals with overweight and obesity.

CLINICAL TRIALS IDENTIFIER

This study is registered at the Netherlands Trial Register (NL7120/NTR7325).

FSTL1 promotes liver fibrosis by reprogramming macrophage function through modulating the intracellular function of PKM2

OBJECTIVE

Follistatin-like protein 1 (FSTL1) is widely recognised as a secreted glycoprotein, but its role in modulating macrophage-related inflammation during liver fibrosis has not been documented. Herein, we aimed to characterise the roles of macrophage FSTL1 in the development of liver fibrosis.

DESIGN

Expression analysis was conducted with human liver samples obtained from 33 patients with liver fibrosis and 18 individuals without fibrosis serving as controls. Myeloid-specific FSTL1-knockout (FSTL1^M-KO) mice were constructed to explore the function and mechanism of macrophage FSTL1 in 3 murine models of liver fibrosis induced by carbon tetrachloride injection, bile duct ligation or a methionine-deficient and choline-deficient diet.

RESULTS

FSTL1 expression was significantly elevated in macrophages from fibrotic livers of both humans and mice. Myeloid-specific FSTL1 deficiency effectively attenuated the progression of liver fibrosis. In FSTL1^M-KO mice, the microenvironment that developed during liver fibrosis showed relatively less inflammation, as demonstrated by attenuated infiltration of monocytes/macrophages and neutrophils and decreased expression of proinflammatory factors. FSTL1^M-KO macrophages exhibited suppressed proinflammatory M1 polarisation and nuclear factor kappa B pathway activation in vivo and in vitro. Furthermore, this study showed that, through its FK domain, FSTL1 bound directly to the pyruvate kinase M2 (PKM2). Interestingly, FSTL1 promoted PKM2 phosphorylation and nuclear translocation, reduced PKM2 ubiquitination to enhance PKM2-dependent glycolysis and increased M1 polarisation. Pharmacological activation of PKM2 (DASA-58) partially countered FSTL1-mediated glycolysis and inflammation.

CONCLUSION

Macrophage FSTL1 promotes the progression of liver fibrosis by inducing M1 polarisation and inflammation based on the intracellular PKM2 reprogramming function of macrophages.

MANF in POMC Neurons Promotes Brown Adipose Tissue Thermogenesis and Protects Against Diet-Induced Obesity

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an emerging regulator in metabolic control. Hypothalamic proopiomelanocortin (POMC) neurons play critical roles in maintaining whole-body energy homeostasis. Whether MANF in POMC neurons is required for the proper regulation of energy balance remains unknown. Here, we showed that mice lacking MANF in POMC neurons were more prone to develop diet-induced obesity. In addition, the ablation of MANF induced endoplasmic reticulum (ER) stress and leptin resistance in the hypothalamus, reduced POMC expression and posttranslational processing, and ultimately decreased sympathetic nerve activity and thermogenesis in brown adipose tissue (BAT). Conversely, MANF overexpression in hypothalamic POMC neurons attenuated ER stress, increased POMC expression and processing, and then stimulated sympathetic innervation and activity in BAT, resulting in increased BAT thermogenesis, thus protecting mice against dietary obesity. Overall, our findings provide evidence that MANF is required for POMC neurons to combat obesity.

The Complex Roles of Adipokines in Polycystic Ovary Syndrome and Endometriosis

Polycystic ovary syndrome (PCOS) and endometriosis are frequent diseases of the female reproductive tract causing high morbidity as they can significantly affect fertility and quality of life. Adipokines are pleiotropic signaling molecules secreted by white or brown adipose tissues with a central role in energy metabolism. More recently, their involvement in PCOS and endometriosis has been demonstrated. In this review article, we provide an update on the role of adipokines in both diseases and summarize previous findings. We also address the results of multi-omics approaches in adipokine research to examine the role of single nucleotide polymorphisms (SNPs) in genes coding for adipokines and their receptors, the secretome of adipocytes and to identify epigenetic alterations of adipokine genes that might be conferred from mother to child. Finally, we address novel data on the role of brown adipose tissue (BAT), which seems to have notable effects on PCOS. For this review, original research articles on adipokine actions in PCOS and endometriosis are considered, which are listed in the PubMed database.

The evolving view of thermogenic fat and its implications in cancer and metabolic diseases

The incidence of metabolism-related diseases like obesity and type 2 diabetes mellitus has reached pandemic levels worldwide and increased gradually. Most of them are listed on the table of high-risk factors for malignancy, and metabolic disorders systematically or locally contribute to cancer progression and poor prognosis of patients. Importantly, adipose tissue is fundamental to the occurrence and development of these metabolic disorders. White adipose tissue stores excessive energy, while thermogenic fat including brown and beige adipose tissue dissipates energy to generate heat. In addition to thermogenesis, beige and brown adipocytes also function as dynamic secretory cells and a metabolic sink of nutrients, like glucose, fatty acids, and amino acids. Accordingly, strategies that activate and expand thermogenic adipose tissue offer therapeutic promise to combat overweight, diabetes, and other metabolic disorders through increasing energy expenditure and enhancing glucose tolerance. With a better understanding of its origins and biological functions and the advances in imaging techniques detecting thermogenesis, the roles of thermogenic adipose tissue in tumors have been revealed gradually. On the one hand, enhanced browning of subcutaneous fatty tissue results in weight loss and cancer-associated cachexia. On the other hand, locally activated thermogenic adipocytes in the tumor microenvironment accelerate cancer progression by offering fuel sources and is likely to develop resistance to chemotherapy. Here, we enumerate current knowledge about the significant advances made in the origin and physiological functions of thermogenic fat. In addition, we discuss the multiple roles of thermogenic adipocytes in different tumors. Ultimately, we summarize imaging technologies for identifying thermogenic adipose tissue and pharmacologic agents via modulating thermogenesis in preclinical experiments and clinical trials.

Follistatin-like 1 promotes proliferation of matured human hypoxic iPSC-cardiomyocytes and is secreted by cardiac fibroblasts

The human heart has limited regenerative capacity. Therefore, patients often progress to heart failure after ischemic injury, despite advances in reperfusion therapies generally decreasing mortality. Depending on its glycosylation state, Follistatin-like 1 (FSTL1) has been shown to increase cardiomyocyte (CM) proliferation, decrease CM apoptosis, and prevent cardiac rupture in animal models of ischemic heart disease. To explore its therapeutic potential, we used a human in vitro model of cardiac ischemic injury with human induced pluripotent stem cell-derived CMs (iPSC-CMs) and assessed regenerative effects of two differently glycosylated variants of human FSTL1. Furthermore, we investigated the FSTL1-mediated interplay between human cardiac fibroblasts (cFBs) and iPSC-CMs in hypoxia. Both FSTL1 variants increased viability, while only hypo-glycosylated FSTL1 increased CM proliferation post-hypoxia. Human fetal cardiac fibroblasts (fcFBs) expressed and secreted FSTL1 under normoxic conditions, while FSTL1 secretion increased by iPSC-cFBs upon hypoxia but decreased in iPSC-CMs. Co-culture of iPSC-CMs and cFBs increased FSTL1 secretion compared with cFB mono-culture. Taken together, we confirm that FSTL1 induces iPSC-CM proliferation in a human cardiac in vitro hypoxia damage model. Furthermore, we show hypoxia-related FSTL1 secretion by human cFBs and indications for FSTL1-mediated intercellular communication between cardiac cell types in response to hypoxic conditions.

Follistatin-like 1 and family with sequence similarity to 19 member A5 levels are decreased in obese children and associated with glucose metabolism

INTRODUCTION

Childhood obesity is a significant and growing problem worldwide. Recent evidence suggests Follistatin-like 1 (FSTL1) and family with sequence similarity to 19 member A5 (FAM19A5) to be novel adipokines. However, very few studies have examined the plasma levels of FSTL1 and FAM19A5 in children. Therefore, this cross-sectional study evaluated the association between serum FSTL1 and FAM19A5 levels with obesity in children and investigated the relationship between FSTL1 and FAM19A5 and glucose metabolism or endothelial injury.

METHODS

Fifty-five obese children and 48 healthy controls were recruited. Plasma FSTL1 and FAM19A5 levels were detected using ELISA. In addition, the association between the clinical data and anthropometric parameters was analyzed.

RESULTS

Serum FAM19A5 levels were significantly decreased in the obese children, at 189.39 ± 19.10 pg/mL, compared with those without obesity, at 211.08 ± 38.09 pg/mL. Serum concentrations of FSTL1 were also significantly lower in the obese children, at 0.64 (0.37-0.64) ng/mL, compared with those without obesity, at 1.35 (1.05-2.12) ng/mL. In addition, FAM19A5 (OR = 0.943; P = 0.003) was a predictor of insulin resistance in obese children compared with healthy controls. Lastly, serum FAM19A5 and FSTL1 played mediating roles in insulin resistance in children.

CONCLUSION

The serum levels of FAM19A5 and FSTL1 were decreased in obese children; therefore, FAM19A5 and FSTL1 likely play important roles in glucose metabolism in obese children.

Brown adipose tissue involution associated with progressive restriction in progenitor competence

Human brown adipose tissue (BAT) undergoes progressive involution. This involution process is not recapitulated in rodents, and the underlying mechanisms are poorly understood. Here we show that the interscapular BAT (iBAT) of rabbits whitens rapidly during early adulthood. The transcriptomic remodeling and identity switch of mature adipocytes are accompanied by loss of brown adipogenic competence of progenitors. Single-cell RNA sequencing reveals that rabbit and human iBAT progenitors highly express the FSTL1 gene. When iBAT involutes in rabbits, adipocyte progenitors reduce FSTL1 expression and are refractory to brown adipogenic recruitment. Conversely, FSTL1 is constitutively expressed in mouse iBAT to sustain WNT signaling and prevent involution. Progenitor incompetence and iBAT paucity can be induced in mice by genetic deletion of the Fstl1 gene or ablation of Fstl1⁺ progenitors. Our results highlight the hierarchy and dynamics of the BAT progenitor compartment and implicate the functional incompetence of FSTL1-expressing progenitors in BAT involution.

Adipokines, Hepatokines and Myokines: Focus on Their Role and Molecular Mechanisms in Adipose Tissue Inflammation

Chronic low-grade inflammation in adipose tissue (AT) is a hallmark of obesity and contributes to various metabolic disorders, such as type 2 diabetes and cardiovascular diseases. Inflammation in ATs is characterized by macrophage infiltration and the activation of inflammatory pathways mediated by NF-κB, JNK, and NLRP3 inflammasomes. Adipokines, hepatokines and myokines - proteins secreted from AT, the liver and skeletal muscle play regulatory roles in AT inflammation via endocrine, paracrine, and autocrine pathways. For example, obesity is associated with elevated levels of pro-inflammatory adipokines (e.g., leptin, resistin, chemerin, progranulin, RBP4, WISP1, FABP4, PAI-1, Follistatin-like1, MCP-1, SPARC, SPARCL1, and SAA) and reduced levels of anti-inflammatory adipokines such as adiponectin, omentin, ZAG, SFRP5, CTRP3, vaspin, and IL-10. Moreover, some hepatokines (Fetuin A, DPP4, FGF21, GDF15, and MANF) and myokines (irisin, IL-6, and DEL-1) also play pro- or anti-inflammatory roles in AT inflammation. This review aims to provide an updated understanding of these organokines and their role in AT inflammation and related metabolic abnormalities. It serves to highlight the molecular mechanisms underlying the effects of these organokines and their clinical significance. Insights into the roles and mechanisms of these organokines could provide novel and potential therapeutic targets for obesity-induced inflammation.

Ups and downs: The PPARγ/p-PPARγ seesaw of follistatin-like 1 and integrin receptor signaling in adipogenesis

OBJECTIVE

Although Follistatin-like protein 1 (FSTL1), as an "adipokine", is highly expressed in preadipocytes, the detail role of FSTL1 in adipogenesis and obesity remains not fully understood.

METHODS

In vitro differentiation of both Fstl1^-/- murine embryonic fibroblasts (MEFs) and stromal vascular fraction (SVF) were measured to assess the specific role of FSTL1 in adipose differentiation. Fstl1 adipocyte-specific knockout mice were generated to evaluate its role in obesity development. Gene expression analysis and phosphorylation patterns were performed to check out the molecular mechanism of the biological function of FSTL1.

RESULTS

FSTL1 deficiency inhibited preadipocytes differentiation in vitro and obesity development in vivo. Glycosylation at N142 site was pivotal for the biological effect of FSTL1 during adipogenesis; the conversion between PPARγ and p-PPARγ was the key factor for the function of FSTL1. Molecular mechanism studies showed that FSTL1 functions through the integrin/FAK/ERK signaling pathway.

CONCLUSIONS

Our results suggest that FSTL1 promotes adipogenesis by inhibiting the conversion of PPARγ to p-PPARγ through the integrin/FAK/ERK signaling pathway. Glycosylated modification at N142 of FSTL1 is the key site to exert its biological effect.

Follistatin-Like Proteins: Structure, Functions and Biomedical Importance

Main forms of cellular signal transmission are known to be autocrine and paracrine signaling. Several cells secrete messengers called autocrine or paracrine agents that can bind the corresponding receptors on the surface of the cells themselves or their microenvironment. Follistatin and follistatin-like proteins can be called one of the most important bifunctional messengers capable of displaying both autocrine and paracrine activity. Whilst they are not as diverse as protein hormones or protein kinases, there are only five types of proteins. However, unlike protein kinases, there are no minor proteins among them; each follistatin-like protein performs an important physiological function. These proteins are involved in a variety of signaling pathways and biological processes, having the ability to bind to receptors such as DIP2A, TLR4, BMP and some others. The activation or experimentally induced knockout of the protein-coding genes often leads to fatal consequences for individual cells and the whole body as follistatin-like proteins indirectly regulate the cell cycle, tissue differentiation, metabolic pathways, and participate in the transmission chains of the pro-inflammatory intracellular signal. Abnormal course of these processes can cause the development of oncology or apoptosis, programmed cell death. There is still no comprehensive understanding of the spectrum of mechanisms of action of follistatin-like proteins, so the systematization and study of their cellular functions and regulation is an important direction of modern molecular and cell biology. Therefore, this review focuses on follistatin-related proteins that affect multiple targets and have direct or indirect effects on cellular signaling pathways, as well as to characterize the directions of their practical application in the field of biomedicine.

Thermogenic Fat: Development, Physiological Function, and Therapeutic Potential

The concerning worldwide increase of obesity and chronic metabolic diseases, such as T2D, dyslipidemia, and cardiovascular disease, motivates further investigations into preventive and alternative therapeutic approaches. Over the past decade, there has been growing evidence that the formation and activation of thermogenic adipocytes (brown and beige) may serve as therapy to treat obesity and its associated diseases owing to its capacity to increase energy expenditure and to modulate circulating lipids and glucose levels. Thus, understanding the molecular mechanism of brown and beige adipocytes formation and activation will facilitate the development of strategies to combat metabolic disorders. Here, we provide a comprehensive overview of pathways and players involved in the development of brown and beige fat, as well as the role of thermogenic adipocytes in energy homeostasis and metabolism. Furthermore, we discuss the alterations in brown and beige adipose tissue function during obesity and explore the therapeutic potential of thermogenic activation to treat metabolic syndrome.

Inducible beige adipocytes improve impaired glucose metabolism in interscapular BAT-removal mice

Inducible beige adipocytes are emerging as an interesting issue in obesity and metabolism research. There is a neglected possibility that brown adipocytes are equally activated when external stimuli induce the formation of beige adipocytes. Thus, the question is whether beige adipocytes have the same functions as brown adipocytes when brown adipose tissue (BAT) is lacking. This question has not been well studied. Therefore we determine the beneficial effects of beige adipocytes upon cold challenge or CL316243 treatments in animal models of interscapular BAT (iBAT) ablation by surgical denervation. We found that denervated iBAT were activated by cold exposure and CL316243 treatments. The data show that beige adipocytes partly contribute to the improvement of impaired glucose metabolism resulting from denervated iBAT. Thus, we further used iBAT-removal animal models to abolish iBAT functions completely. We found that beige adipocytes upon cold exposure or CL316243 treatments improved impaired glucose metabolism and enhanced glucose uptake in iBAT-removal mice. The insulin signaling was activated in iBAT-removal mice upon cold exposure. Both the activation of insulin signaling and up-regulation of glucose transporter expression were observed in iBAT-removal mice with CL316243 treatments. The data show that inducible beige adipocytes may have different mechanisms to improve impaired glucose metabolism. Inducible beige adipocytes can also enhance energy expenditure and lipolytic activity of white adipose tissues when iBAT is lacking. We provide direct evidences for the beneficial effect of inducible beige adipocytes in glucose metabolism and energy expenditure in the absence of iBAT in vivo.

Follistatin-like 1 as a Novel Adipomyokine Related to Insulin Resistance and Physical Activity

BACKGROUND AND AIMS

Follistatin-like protein-1 (FSTL-1) is considered to be an adipokine or myokine that could be a potential regulator of metabolism. Our purpose is to investigate the relationship between circulating FSTL-1 levels and insulin resistance (IR) in type 2 diabetes mellitus (T2DM) and to identify the regulatory factors.

METHODS

FSTL-1 expression in C57BL/6J and db/db mice was examined by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and Western blots. Serum FSTL-1 levels were measured by enzyme-linked immunosorbent assay in 298 T2DM patients and 202 healthy controls. Changes in the circulating FSTL-1 level were observed during the oral glucose tolerance test, EHC (euglycemic-hyperinsulinemic clamp), lipid infusion, acute exercise, and cold-exposure test.

RESULTS

We found that FSTL-1 protein expression in the adipose tissue of db/db mice was significantly higher than that of wild-type mice. Importantly, circulating FSTL-1 levels in T2DM and overweight/obese participants were higher than those in healthy and lean individuals, and was related to HOMA-IR, adiponectin, and obesity- and metabolism-related parameters. In the intervention study, 45 minutes of physical activity was found to significantly increase the circulating FSTL-1 concentration in young, healthy participants. Further, FSTL-1 protein expression in adipose tissue rose dramatically in response to physical activity in mice. Hyperinsulinemia during EHC and acute elevated FFA induced by lipid infusion resulted in a significant decrease in the circulating FSTL-1 levels. However, no change was found in the circulating FSTL-1 levels in response to the oral glucose challenge or cold-exposure test.

CONCLUSIONS

FSTL-1 may be an adipomyokine associated with insulin resistance and physical activity, and circulating FSTL-1 levels are increased in patients with T2DM.

Adipokines, Myokines, and Cardiokines: The Role of Nutritional Interventions

It is now established that adipose tissue, skeletal muscle, and heart are endocrine organs and secrete in normal and in pathological conditions several molecules, called, respectively, adipokines, myokines, and cardiokines. These secretory proteins constitute a closed network that plays a crucial role in obesity and above all in cardiac diseases associated with obesity. In particular, the interaction between adipokines, myokines, and cardiokines is mainly involved in inflammatory and oxidative damage characterized obesity condition. Identifying new therapeutic agents or treatment having a positive action on the expression of these molecules could have a key positive effect on the management of obesity and its cardiac complications. Results from recent studies indicate that several nutritional interventions, including nutraceutical supplements, could represent new therapeutic agents on the adipo-myo-cardiokines network. This review focuses the biological action on the main adipokines, myokines and cardiokines involved in obesity and cardiovascular diseases and describe the principal nutraceutical approaches able to regulate leptin, adiponectin, apelin, irisin, natriuretic peptides, and follistatin-like 1 expression.

Endocrine Mechanisms Connecting Exercise to Brown Adipose Tissue Metabolism: a Human Perspective

PURPOSE OF REVIEW

To summarize the state-of-the-art regarding the exercise-regulated endocrine signals that might modulate brown adipose tissue (BAT) activity and/or white adipose tissue (WAT) browning, or through which BAT communicates with other tissues, in humans.

RECENT FINDINGS

Exercise induces WAT browning in rodents by means of a variety of physiological mechanism. However, whether exercise induces WAT browning in humans is still unknown. Nonetheless, a number of protein hormones and metabolites, whose signaling can influence thermogenic adipocyte's metabolism, are secreted during and/or after exercise in humans from a variety of tissues and organs, such as the skeletal muscle, the adipose tissue, the liver, the adrenal glands, or the cardiac muscle. Overall, it seems plausible to hypothesize that, in humans, exercise secretes an endocrine cocktail that is likely to induce WAT browning, as it does in rodents. However, even if exercise elicits a pro-browning endocrine response, this might result in a negligible effect if blood flow is restricted in thermogenic adipocyte-rich areas during exercise, which is still to be determined. Future studies are needed to fully characterize the exercise-induced secretion (i.e., to determine the effect of the different exercise frequency, intensity, type, time, and volume) of endocrine signaling molecules that might modulate BAT activity and/or WAT browning or through which BAT communicates with other tissues, during exercise. The exercise effect on BAT metabolism and/or WAT browning could be one of the still unknown mechanisms by which exercise exerts beneficial health effects, and it might be pharmacologically mimicked.

New Insights into Apolipoprotein A5 and the Modulation of Human Adipose-derived Mesenchymal Stem Cells Adipogenesis

Background:

The hallmark of obesity is the excessive accumulation of triglyceride (TG) in adipose tissue. Apolipoprotein A5 (ApoA5) has been shown to influence the prevalence and pathogenesis of obesity. However, the underlying mechanisms remain to be clarified.

Methods:

Human adipose-derived mesenchymal stem cells (AMSCs) were treated with 600 ng/ml human recombinant ApoA5 protein. The effect of ApoA5 on intracellular TG content and adipogenic related factors expression were determined. Furthermore, the effect of ApoA5 on CIDE-C expression was also observed.

Results:

During the process of adipogenesis, ApoA5 treatment reduced the intracellular accumulation of lipid droplets and the TG levels; meanwhile, ApoA5 down-regulated the expression levels of adipogenic related factors, including CCAAT enhancer-binding proteins α/β (C/EBPα/β), fatty acid synthetase (FAS), and fatty acid-binding protein 4 (FABP4). Furthermore, the suppression of adipogenesis by ApoA5 was mediated through the inhibition of CIDE-C expression, an important factor which promotes the process of adipogenesis. However, over-expressing intracellular CIDE-C could lead to the loss-of-function of ApoA5 in inhibiting AMSCs adipogenesis.

Conclusions:

In conclusion, ApoA5 inhibits the adipogenic process of AMSCs through, at least partly, down-regulating CIDE-C expression. The present study provides novel mechanisms whereby ApoA5 prevents obesity via AMSCs in humans.

Preadipocyte factor 1 regulates adipose tissue browning via TNF-α-converting enzyme-mediated cleavage

BACKGROUND

Increasing adaptive thermogenesis in adipose tissue may be a potential therapeutic target for overcoming obesity and obesity-related disorders. Preadipocyte factor 1 (Pref-1), a preadipocyte secreted protein, plays an inhibitory role in adipogenic differentiation. However, the role of Pref-1 in adipose tissue browning remains unknown. We investigated whether Pref-1 regulates thermogenic program and beige fat biogenesis.

METHODS

Pref-1 expression levels were examined in inguinal white adipose tissue (iWAT) and differentiated 3T3-L1 adipocytes in thermogenic conditions induced by cold exposure or a beta-adrenergic stimulus (CL316,243). Overexpression and knockdown studies were performed both in vivo and in vitro to clarify the role of Pref-1 in iWAT browning.

RESULTS

Cold exposure or CL316,243 induced a thermogenic program in adipose tissue of C57BL/6N mice and in 3T3-L1 adipocytes. Notably, Pref-1 levels were down-regulated in iWAT and adipocytes under these conditions. Overexpressing Pref-1 showed reduced thermogenic gene expressions in response to CL316,243 treatment, whereas depletion of Pref-1 augmented thermogenic program in 3T3-L1 adipocytes. Correspondingly, treating C57BL/6N mice with Pref-1 resulted in reduced expression of thermogenic and beige fat markers, a reduced rate of oxygen consumption, blunting of UCP1 expression and beige fat formation in iWAT in response to cold exposure or CL316,243 injection compared to the untreated mice. The opposite phenotype was observed in mice with inducible fat-specific knock-out of Pref-1. Mechanistically, these effects were regulated by modulation of TNF-α-converting enzyme activity and Pref-1 cleavage.

CONCLUSION

Our findings establish a novel role of Pref-1 that regulates adaptive thermogenesis. This offers a unique target for improving energy homeostasis and treating obesity.