Fibroblast growth factor 21 and exercise-induced hepatic mitochondrial adaptations

The Influence of Physical Exercise, Ketogenic Diet, and Time-Restricted Eating on De Novo Lipogenesis: A Narrative Review

De novo lipogenesis (DNL) is a metabolic pathway that converts carbohydrates into fatty acids, primarily occurring in the liver and, to a lesser extent, in adipose tissue. While hepatic DNL is highly responsive to dietary carbohydrate intake and regulated by insulin via transcription factors like SREBP-1c, adipose DNL is more modest and less sensitive to dietary overfeeding. Dysregulated DNL contributes to metabolic disorders, including metabolic dysfunction-associated steatotic liver disease (MASLD). Lifestyle interventions, such as physical exercise, ketogenic diets, and time-restricted eating (TRE) offer promising strategies to regulate DNL and improve metabolic health. Physical exercise enhances glucose uptake in muscles, reduces insulin levels, and promotes lipid oxidation, thereby suppressing hepatic DNL. Endurance and resistance training also improve mitochondrial function, further mitigating hepatic triglyceride accumulation. Ketogenic diets shift energy metabolism toward fatty acid oxidation and ketogenesis, lower insulin, and directly downregulate lipogenic enzyme activity in the liver. TRE aligns feeding with circadian rhythms by optimizing AMP-activated protein kinase (AMPK) activation during fasting periods, which suppresses DNL and enhances lipid metabolism. The combined effects of these interventions demonstrate significant potential for improving lipid profiles, reducing hepatic triglycerides, and preventing lipotoxicity. By addressing the distinct roles of the liver and adipose DNL, these strategies target systemic and localized lipid metabolism dysregulation. Although further research is needed to fully understand their long-term impact, these findings highlight the transformative potential of integrating these approaches into clinical practice to manage metabolic disorders and their associated complications.

The Influence of Hyperglycemia on Liver Triglyceride Deposition in Partially Pancreatectomized Rats

Nonalcoholic fatty liver disease and diabetes always coexist. The relationship of fatty liver and hyperglycemia is not clear. We studied the influence of hyperglycemia on triglyceride (TG) accumulation in the liver and explored its possible mechanisms. SD rats were divided into three groups: Group A (sham operation control), Group B (partially pancreatectomized rats), and Group C (partially pancreatectomized rats treated with insulin). At 4 weeks after surgery, pancreatic weights and liver TG contents were measured. Serum biochemical parameters were determined, and oral glucose tolerance tests (OGTT) were performed. The gene expression of sterol regulatory element-binding protein1c (SREBP-1c), carbohydrate regulatory element-binding protein (ChREBP), fatty acid synthase(FAS), carnitine palmitoyltransferase 1 (CPT-1), and fibroblast growth factor 21 (FGF21) was determined by real-time PCR. Compared with Group A, postprandial glucose increased significantly; the concentrations of insulin and C-peptides, pancreatic weights and serum FGF21 levels were decreased, liver TG was increased significantly in Group B, and insulin treatment improved these changes. Compared with Group A, the gene expressions of FGF21, CPT-1 and FAS in the liver were decreased in Group B (all p<0.05). Compared with Group B, the gene expressions of FGF21, FAS, ChREBP, SREBP-1c and CPT-1 in the liver in Group C were all increased significantly (p<0.05, respectively). Hyperglycemia induced by partial pancreatectomy could lead to increased liver TG. Insulin treatment could decrease glucose levels and improve fatty liver, and genes related to lipid metabolism may play a role in this process.

Time-restricted feeding combined with resistance exercise prevents obesity and improves lipid metabolism in the liver of mice fed a high-fat diet

Nonalcoholic fatty liver disease (NAFLD), a condition characterized by the accumulation of fat in the liver, is estimated to be the most common liver disease worldwide. Obesity is a major risk factor and contributor, and, accordingly, weight loss can improve NAFLD. Previous studies in preclinical models of diet-induced obesity and fatty liver disease have shown the independent benefits of resistance exercise training (RT) and time-restricted feeding (TRF) in preventing weight gain and hepatic build-up of fat. Here, we tested the combined effect of TRF and RT on obesity and NAFLD in mice fed a high-fat diet. Our results showed that both TRF-8-h food access in the active phase-and RT-consisting of three weekly sessions of ladder climbing-attenuated body weight gain, improved glycemic homeostasis, and decreased the accumulation of lipids in the liver. TRF combined with RT improved the respiratory exchange rate, energy expenditure, and mitochondrial respiration in the liver. Furthermore, gene expression analysis in the liver revealed lower mRNA expression of lipogenesis and inflammation genes along with increased mRNA of fatty acid oxidation genes in the TRF + RT group. Importantly, combined TRF + RT was shown to be more efficient in preventing obesity and metabolic disorders. In conclusion, TRF and RT exert complementary actions compared with isolated interventions, with significant effects on metabolic disorders and NAFLD in mice.NEW & NOTEWORTHY Whether time-restricted feeding (TRF) combined with resistance exercise training (RT) may be more efficient compared with these interventions alone is still unclear. We show that when combined with RT, TRF provided additional benefits, being more effective in increasing energy expenditure, preventing weight gain, and regulating glycemic homeostasis than each intervention alone. Thus, our results demonstrate that TRF and RT have complementary actions on some synergistic pathways that prevented obesity and hepatic liver accumulation.

Exerkines and redox homeostasis

Exercise physiology has gained increasing interest due to its wide effects to promote health. Recent years have seen a growth in this research field also due to the finding of several circulating factors that mediate the effects of exercise. These factors, termed exerkines, are metabolites, growth factors, and cytokines secreted by main metabolic organs during exercise to regulate exercise systemic and tissue-specific effects. The metabolic effects of exerkines have been broadly explored and entail a promising target to modulate beneficial effects of exercise in health and disease. However, exerkines also have broad effects to modulate redox signaling and homeostasis in several cellular processes to improve stress response. Since redox biology is central to exercise physiology, this review summarizes current evidence for the cross-talk between redox biology and exerkines actions. The role of exerkines in redox biology entails a response to oxidative stress-induced pathological cues to improve health outcomes and to modulate exercise adaptations that integrate redox signaling.

Concurrent betaine administration enhances exercise-induced improvements to glucose handling in obese mice

BACKGROUND AND AIMS

Betaine supplementation has been shown to enhance hepatic lipid metabolism in obese mice and improve exercise performance in healthy populations. We examined effects of betaine supplementation, alone or in combination with treadmill exercise, on the metabolic consequences of high fat diet (HFD)-induced obesity in mice.

METHODS AND RESULTS

Male C57BL/6 J mice were fed chow or HFD. After 15 weeks, HFD mice were split into: HFD, HFD with betaine (1.5% w/v), HFD with treadmill exercise, and HFD with both betaine and exercise (15 m/min for 45min, 6 days/week; n = 12/group) for 10 weeks. Compared to HFD mice, body weight was significantly reduced in exercise and exercise-betaine mice, but not in mice given betaine alone. Similarly, adiposity was reduced by exercise but not by betaine alone. HFD-induced glucose intolerance was slightly improved by exercise, but not with betaine alone. Significantly greater benefits were observed in exercise-betaine mice, compared to exercise alone, such that GTT-outcomes were similar to controls. This was associated with reduced insulin levels during ipGTT, suggesting enhanced insulin sensitivity. Modest benefits were observed in fatty acid metabolism genes in skeletal muscle, whilst limited effects were observed in the liver. HFD-induced increases in hepatic Mpc1 (mitochondrial pyruvate carrier 1) were normalized by all treatments, suggesting potential links to altered glucose metabolism.

CONCLUSIONS

Our data show that drinking 1.5% betaine was sufficient to augment metabolic benefits of exercise in obese mice. These processes appear to be facilitated by altered glucose metabolism, with limited effects on hepatic lipid metabolism.

Skeletal Muscle and Bone - Emerging Targets of Fibroblast Growth Factor-21

Fibroblast growth factor 21 (FGF21) is an atypical member of the FGF family, which functions as a powerful endocrine and paracrine regulator of glucose and lipid metabolism. In addition to liver and adipose tissue, recent studies have shown that FGF21 can also be produced in skeletal muscle. As the most abundant tissue in the human body, skeletal muscle has become increasingly recognized as a major site of metabolic activity and an important modulator of systemic metabolic homeostasis. The function and mechanism of action of muscle-derived FGF21 have recently gained attention due to the findings of considerably increased expression and secretion of FGF21 from skeletal muscle under certain pathological conditions. Recent reports regarding the ectopic expression of FGF21 from skeletal muscle and its potential effects on the musculoskeletal system unfolds a new chapter in the story of FGF21. In this review, we summarize the current knowledge base of muscle-derived FGF21 and the possible functions of FGF21 on homeostasis of the musculoskeletal system with a focus on skeletal muscle and bone.

Moderate-Intensity Continuous Training Improves FGF21 and KLB Expression in Obese Mice

Fibroblast growth factor 21 (FGF21) and β-Klotho (KLB) play an important role in preventing and treating overweight and obesity. However, it is unclear what conditions promote FGF21 and KLB expression in different tissues. Therefore, we studied expression of FGF21 and KLB with respect to two exercise regimes: moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) (two popular strategies in weight loss). Mice were randomly divided into three groups (n = 8 per group): MICT, HIIT, and sedentary lifestyle (SED). All mice were fed a high-fat diet (HFD) for 12 weeks to induce obesity. The exercise was performed on a motorized treadmill for another eight weeks and the diet continued in each group. We found that both MICT and HIIT had positive effects on the loss of HFD-induced body weight increase and serum FGF21 levels. HIIT promoted decrease of the body weight and serum triglyceride (TG) levels, while MICT was more effective at enhancing FGF21 and KLB expression in the liver, brown adipose tissue (BAT), and muscle at the mRNA and protein levels.

Hepatokines as a Molecular Transducer of Exercise

Exercise has health benefits and prevents a range of chronic diseases caused by physiological and biological changes in the whole body. Generally, the metabolic regulation of skeletal muscle through exercise is known to have a protective effect on the pathogenesis of metabolic syndrome, non-alcoholic fatty liver disease (NAFLD), type 2 diabetes (T2D), and cardiovascular disease (CVD). Besides this, the importance of the liver as an endocrine organ is a hot research topic. Hepatocytes also secrete many hepatokines in response to nutritional conditions and/or physical activity. In particular, certain hepatokines play a major role in the regulation of whole-body metabolic homeostasis. In this review, we summarize the recent research findings on the exercise-mediated regulation of hepatokines, including fibroblast growth factor 21, fetuin-A, angiopoietin-like protein 4, and follistatin. These hepatokines serve as molecular transducers of the metabolic benefits of physical activity in chronic metabolic diseases, including NAFLD, T2D, and CVDs, in various tissues.

Exercise and dietary intervention ameliorate high-fat diet-induced NAFLD and liver aging by inducing lipophagy

Exercise and dietary intervention are currently available strategies to treat nonalcoholic fatty liver disease (NAFLD), while the underlying mechanism remains controversial. Emerging evidence shows that lipophagy is involved in the inhibition of the lipid droplets accumulation. However, it is still unclear if exercise and dietary intervention improve NAFLD through regulating lipophagy, and how exercise of skeletal muscle can modulate lipid metabolism in liver. Moreover, NAFLD is associated with aging, and little is known about the effect of lipid accumulation on aging process. Here in vivo and in vitro models, we found that exercise and dietary intervention reduced lipid droplets formation, decreased hepatic triglyceride in the liver induced by high-fat diet. Exercise and dietary intervention enhanced the lipophagy by activating AMPK/ULK1 and inhibiting Akt/mTOR/ULK1 pathways respectively. Furthermore, exercise stimulated FGF21 production in the muscle, followed by secretion to the circulation to promote the lipophagy in the liver via an AMPK-dependent pathway. Importantly, for the first time, we demonstrated that lipid accumulation exacerbated liver aging, which was ameliorated by exercise and dietary intervention through inducing lipophagy. Our findings suggested a new mechanism of exercise and dietary intervention to improve NAFLD through promoting lipophagy. The study also provided evidence to support that muscle exercise is beneficial to other metabolic organs such as liver. The FGF21-mediated AMPK dependent lipophagy might be a potential drug target for NAFLD and aging caused by lipid metabolic dysfunction.

FGF19 and FGF21 for the Treatment of NASH-Two Sides of the Same Coin? Differential and Overlapping Effects of FGF19 and FGF21 From Mice to Human

FGF19 and FGF21 analogues are currently in clinical development for the potential treatment of NASH. In Phase 2 clinical trials analogues of FGF19 and FGF21 decrease hepatic steatosis with up to 70% (MRI-PDFF) after 12 weeks and as early as 12-16 weeks of treatment an improvement in NASH resolution and fibrosis has been observed. Therefore, this class of compounds is currently of great interest in the field of NASH. FGF19 and FGF21 belong to the endocrine FGF19 subfamily and both require the co-receptor beta-klotho for binding and signalling through the FGF receptors. FGF19 is expressed in the ileal enterocytes and is released into the enterohepatic circulation in response to bile acids stimuli and in the liver FGF19 inhibits hepatic bile acids synthesis by transcriptional regulation of Cyp7A1, which is the rate limiting enzyme. FGF21 is, on the other hand, highly expressed in the liver and is released in response to high glucose, high free-fatty acids and low amino-acid supply and regulates energy, glucose and lipid homeostasis by actions in the CNS and in the adipose tissue. FGF19 and FGF21 are differentially expressed, have distinct target tissues and separate physiological functions. It is therefore of peculiar interest to understand why treatment with both FGF19 and FGF21 analogues have strong beneficial effects on NASH parameters in mice and human and whether the mode of action is overlapping This review will highlight the physiological and pharmacological effects of FGF19 and FGF21. The potential mode of action behind the anti-steatotic, anti-inflammatory and anti-fibrotic effects of FGF19 and FGF21 will be discussed. Finally, development of drugs is always a risk benefit analysis and the human relevance of adverse effects observed in pre-clinical species as well as findings in humans will be discussed. The aim is to provide a comprehensive overview of the current understanding of this drug class for the potential treatment of NASH.

Physical exercise and liver "fitness": Role of mitochondrial function and epigenetics-related mechanisms in non-alcoholic fatty liver disease

BACKGROUND

Modern lifestyles, especially high-caloric intake and physical inactivity, contribute to the increased prevalence of non-alcoholic fatty liver disease (NAFLD), which becomes a significant health problem worldwide. Lifestyle changes, however, affect not only parental generation, but also their offspring, reinforcing the need for efficient preventive approaches to deal with this disease. This transgenerational influence of phenotypes dependent on parents (particularly maternal) behaviours may open additional research avenues. Despite persistent attempts to design an effective pharmacological therapy against NAFLD, physical activity, as a non-pharmacological approach, emerges as an exciting strategy.

SCOPE OF REVIEW

Here we briefly review the effect of physical exercise on liver mitochondria adaptations in NAFLD, highlighting the importance of mitochondrial metabolism and transgenerational and epigenetic mechanisms in liver diseases.

MAJOR CONCLUSIONS

A deeper look into cellular mechanisms sheds a light on possible effects of physical activity in the prevention and treatment of NAFLD through modulation of function and structure of particular organelles, namely mitochondria. Additionally, despite of increasing evidence regarding the contribution of epigenetic mechanisms in the pathogenesis of different diseases, the role of microRNAs, DNA methylation, and histone modification in NAFLD pathogenesis still needs to be elucidated.

Role of exercise-induced hepatokines in metabolic disorders

The health-promoting effects of physical activity to prevent and treat metabolic disorders are numerous. However, the underlying molecular mechanisms are not yet completely deciphered. In recent years, studies have referred to the liver as an endocrine organ, since it releases specific proteins called hepatokines. Some of these hepatokines are involved in whole body metabolic homeostasis and are theorized to participate in the development of metabolic disease. In this regard, the present review describes the role of Fibroblast Growth Factor 21, Fetuin-A, Angiopoietin-like protein 4, and Follistatin in metabolic disease and their production in response to acute exercise. Also, we discuss the potential role of hepatokines in mediating the beneficial effects of regular exercise and the future challenges to the discovery of new exercise-induced hepatokines.

Estrogen and voluntary exercise attenuate cardiometabolic syndrome and hepatic steatosis in ovariectomized rats fed a high-fat high-fructose diet

The prevalence of cardiometabolic syndrome (CMS) is increased in women after menopause. While hormone replacement therapy has been prescribed to relieve several components of CMS in postmenopausal women, some aspects of cardiometabolic dysfunction cannot be completely restored. The present study examined the effectiveness of estrogen replacement alone and in combination with exercise by voluntary wheel running (VWR) for alleviating the risks of CMS, insulin-mediated skeletal muscle glucose transport, and hepatic fat accumulation in ovariectomized Sprague-Dawley rats fed a high-fat high-fructose diet (OHFFD). We compared a sham-operated group with OHFFD rats that were subdivided into a sedentary, estradiol replacement (E₂), and E₂ plus VWR for 12 wk. E₂ prevented the development of insulin resistance in skeletal muscle glucose transport and decreased hepatic fat accumulation in OHFFD rats. Furthermore, E₂ treatment decreased visceral fat mass and low-density lipoprotein (LDL)-cholesterol in OHFFD rats, while VWR further decreased LDL-cholesterol and increased the ratio of high-density lipoprotein-cholesterol to total cholesterol to a greater extent. Although E₂ treatment alone did not reduce serum triglyceride levels in OHFFD rats, the combined intervention of E₂ and VWR lowered serum triglycerides in E₂-treated OHFFD rats. The addition of VWR to E₂-treated OHFFD rats led to AMPK activation and upregulation of peroxisome proliferator-activated receptor-γ (PPARγ) coactivator-1α and PPARδ in skeletal muscle along with increased fatty acid oxidation and suppressed fatty acid synthesis in the liver. Collectively, our findings indicate that, to achieve greater health benefits, physical exercise is required for E₂-treated individuals under ovarian hormone deprivation with high-energy consumption.

Fibroblast Growth Factor 21 and Browning of White Adipose Tissue

Interest has been focused on differentiating anatomical, molecular, and physiological characteristics of the types of mammalian adipose tissues. White adipose tissue (WAT) and brown adipose tissue (BAT) are the two main forms of adipose tissue in humans. WAT functions as an endocrine organ and serves as a reservoir of energy in the form of triglycerides. The hormones released by WAT are called adipokines. BAT consists of a group of specialized cells with abundant uncoupling protein 1 (UCP1) in the inner mitochondrial membrane and also fulfills endocrine functions. Following the identification of functional (BAT) in human adults, there has been a great deal of interest in finding out how it is induced, its localization, and the mechanisms by which it regulates thermogenesis. Fibroblast growth factor 21 (FGF21) is a key regulator of the differentiation to brown adipocytes. The main mechanisms occur through enhancing UCP1 expression. In addition, following exposure to cold or exercise, FGF21 induces upregulation of local peroxisome proliferator-activated receptor gamma co-activator (PGC)-1-alfa and thus promotes thermogenesis in adipose tissue and skeletal muscle. FGF21 integrates several pathways allowing the regulation of human energy balance, glucose levels, and lipid metabolism. Such mechanisms and their clinical relevance are summarized in this review.

Pros and cons of insulin administration on liver glucose metabolism in strength-trained healthy mice

Non-diabetic individuals use hormones like insulin to improve muscle strength and performance. However, as insulin also leads the liver and the adipose tissue to an anabolic state, the purpose of this study was to investigate the effects of insulin on liver metabolism in trained non-diabetic Swiss mice. The mice were divided into four groups: sedentary treated with saline (SS) or insulin (SI) and trained treated with saline (TS) or insulin (TI). Training was made in a vertical stair, at 90% of the maximum load, three times per week. Insulin (0.3 U/kg body weight) or saline were given intraperitoneally five times per week. After eight weeks, tissue and blood were collected and in situ liver perfusion with glycerol+lactate or alanine+glutamine (4 mM each) was carried out. The trained animals increased their muscle strength (+100%) and decreased body weight gain (–11%), subcutaneous fat (–42%), mesenteric fat (–45%), and peritoneal adipocyte size (–33%) compared with the sedentary groups. Insulin prevented the adipose effects of training (TI). The gastrocnemius muscle had greater density of muscle fibers (+60%) and less connective tissue in the trained groups. Liver glycogen was increased by insulin (SI +40% and TI +117%), as well as liver basal glucose release (TI +40%). Lactate and pyruvate release were reduced to a half by training. The greater gluconeogenesis from alanine+glutamine induced by training (TS +50%) was reversed by insulin (TI). Insulin administration had no additional effect on muscle strength and reversed some of the lipolytic and gluconeogenic effects of the resistance training. Therefore, insulin administration does not complement training in improving liver glucose metabolism.

Chip-based high resolution tandem mass spectrometric determination of fibroblast growth factor-chondroitin sulfate disaccharides noncovalent interaction

Fibroblast growth factor-2 (FGF-2) is involved in wound healing and embryonic development. Glycosaminoglycans (GAGs), the major components of the extracellular matrix (ECM), play fundamental roles at this level. FGF-GAG noncovalent interactions are in the focus of research, due to their influence upon cell proliferation and tissue regeneration. Lately, high resolution mass spectrometry (MS) coupled with chip-nanoelectrospray (nanoESI) contributed a significant progress in glycosaminoglycomics by discoveries related to novel species and their characterization. We have employed a fully automated chip-nanoESI coupled to a quadrupole time-of-flight (QTOF) MS for assessing FGF-GAG noncovalent complexes. For the first time, a CS disaccharide was involved in a binding assay with FGF-2. The experiments were conducted in 10 mM ammonium acetate/formic acid, pH 6.8, by incubating FGF-2 and CS in buffer. The detected complexes were characterized by top-down in tandem MS (MS/MS) using collision induced-dissociation (CID). CID MS/MS provided data showing for the first time that the binding process occurs via the sulfate group located at C4 in GalNAc. This study has demonstrated that chip-MS may generate reliable data upon the formation of GAG-protein complexes and their structure. Biologically, the findings are relevant for studies focused on the identification of the active domains in longer GAG chains.

Fibroblast growth factor 21 increases hepatic oxidative capacity but not physical activity or energy expenditure in hepatic peroxisome proliferator-activated receptor γ coactivator-1α-deficient mice

NEW FINDINGS

What is the central question of this study? Does a reduction in hepatic peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), which has been observed in an insulin-resistant obese state, impair the ability of fibroblast growth factor 21 (FGF21) to modulate metabolism? What is the main finding and its importance? A deficit in hepatic PGC-1α does not compromise the ability of FGF21 to increase hepatic fatty acid oxidation; however, the effects of FGF21 to regulate whole-body metabolism (i.e. total and resting energy expenditure), as well as ambulatory activity, were altered when hepatic PGC-1α was reduced.

ABSTRACT

Fibroblast growth factor 21 (FGF21) treatment drives metabolic improvements, including increased metabolic flux and reduced hepatic steatosis, but the mechanisms responsible for these effects remain to be elucidated fully. We tested whether a targeted reduction in hepatic peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), which has been shown to occur with obesity, had a negative impact on the metabolic effects of FGF21. We infused FGF21 (1 mg kg^-1  day^-1 ) or saline in chow-fed wild-type (WT) and liver-specific PGC-1α heterozygous (LPGC-1α) mice for 4 weeks. Administration of FGF21 lowered serum insulin and cholesterol (P ≤ 0.05) and tended to lower free fatty acids (P = 0.057). The LPGC-1α mice exhibited reduced complete hepatic fatty acid oxidation (FAO; LPGC-1α, 1788 ± 165 nmol g^-1  h^-1 compared with WT, 2572 ± 437 nmol g^-1  h^-1 ; P < 0.001), which was normalized by FGF21 treatment (2788 ± 519 nmol g^-1  h^-1 ; P < 0.001). FGF21 also increased hepatic incomplete FAO by 12% in both groups and extramitochondrial FAO by 89 and 56% in WT and LPGC-1α mice, respectfully (P = 0.001), and lowered hepatic triacylglycerol by 30-40% (P < 0.001). Chronic treatment with FGF21 lowered body weight and fat mass (P < 0.05), while increasing food consumption (P < 0.05), total energy expenditure [7.3 ± 0.60 versus 6.6 ± 0.39 kcal (12 h)^-1 in WT mice; P = 0.009] and resting energy expenditure [5.4 ± 0.89 versus 4.6 ± 0.21 kcal (12 h)^-1 in WT mice; P = 0.005]. Interestingly, FGF21 only increased ambulatory activity in the WT mice (P = 0.03), without a concomitant increase in non-resting energy expenditure. In conclusion, although reduced hepatic PGC-1α expression was not necessary for FGF21 to increase FAO, it does appear to mediate FGF21-induced changes in total and resting energy expenditure and ambulatory activity in lean mice.

Therapeutic Approaches to Nonalcoholic Fatty Liver Disease: Exercise Intervention and Related Mechanisms

Exercise training ameliorates nonalcoholic fatty liver disease (NAFLD) as well as obesity and metabolic syndrome. Although it is difficult to eliminate the effects of body weight reduction and increased energy expenditure-some pleiotropic effects of exercise training-a number of studies involving either aerobic exercise training or resistance training programs showed ameliorations in NAFLD that are independent of the improvements in obesity and insulin resistance. In vivo studies have identified effects of exercise training on the liver, which may help to explain the "direct" or "independent" effect of exercise training on NAFLD. Exercise training increases peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) expression, improves mitochondrial function and leads to reduced hepatic steatosis, inflammation, fibrosis, and tumor genesis. Crosstalk between the liver and adipose tissue, skeletal muscle and the microbiome is also a possible mechanism for the effect of exercise training on NAFLD. Although numerous studies have reported benefits of exercise training on NAFLD, the optimal duration and intensity of exercise for the prevention or treatment of NAFLD have not been established. Maintaining adherence of patients with NAFLD to exercise training regimes is another issue to be resolved. The use of comprehensive analytical approaches to identify biomarkers such as hepatokines that specifically reflect the effect of exercise training on liver functions might help to monitor the effect of exercise on NAFLD, and thereby improve adherence of these patients to exercise training. Exercise training is a robust approach for alleviating the pathogenesis of NAFLD, although further clinical and experimental studies are required.

Anti-inflammatory effects of exercise training in adipose tissue do not require FGF21

Exercise enhances insulin sensitivity; it also improves adipocyte metabolism and reduces adipose tissue inflammation through poorly defined mechanisms. Fibroblast growth factor 21 (FGF21) is a pleiotropic hormone-like protein whose insulin-sensitizing properties are predominantly mediated via receptor signaling in adipose tissue (AT). Recently, FGF21 has also been demonstrated to have anti-inflammatory properties. Meanwhile, an association between exercise and increased circulating FGF21 levels has been reported in some, but not all studies. Thus, the role that FGF21 plays in mediating the positive metabolic effects of exercise in AT are unclear. In this study, FGF21-knockout (KO) mice were used to directly assess the role of FGF21 in mediating the metabolic and anti-inflammatory effects of exercise on white AT (WAT) and brown AT (BAT). Male FGF21KO and wild-type mice were provided running wheels or remained sedentary for 8 weeks (n = 9-15/group) and compared for adiposity, insulin sensitivity (i.e., HOMA-IR, Adipo-IR) and AT inflammation and metabolic function (e.g., mitochondrial enzyme activity, subunit content). Adiposity and Adipo-IR were increased in FGF21KO mice and decreased by EX. The BAT of FGF21KO animals had reduced mitochondrial content and decreased relative mass, both normalized by EX. WAT and BAT inflammation was elevated in FGF21KO mice, reduced in both genotypes by EX. EX increased WAT Pgc1alpha gene expression, citrate synthase activity, COX I content and total AMPK content in WT but not FGF21KO mice. Collectively, these findings reveal a previously unappreciated anti-inflammatory role for FGF21 in WAT and BAT, but do not support that FGF21 is necessary for EX-mediated anti-inflammatory effects.