Inactivating hepatic follistatin alleviates hyperglycemia

Intravascular Follistatin gene delivery improves glycemic control in a mouse model of type 2 diabetes

Type 2 diabetes (T2D) manifests from inadequate glucose control due to insulin resistance, hypoinsulinemia, and deteriorating pancreatic β-cell function. The pro-inflammatory factor Activin has been implicated as a positive correlate of severity in T2D patients, and as a negative regulator of glucose uptake by skeletal muscle, and of pancreatic β-cell phenotype in mice. Accordingly, we sought to determine whether intervention with the Activin antagonist Follistatin can ameliorate the diabetic pathology. Here, we report that an intravenous Follistatin gene delivery intervention with tropism for striated muscle reduced the serum concentrations of Activin B and improved glycemic control in the db/db mouse model of T2D. Treatment reversed the hyperglycemic progression with a corresponding reduction in the percentage of glycated-hemoglobin to levels similar to lean, healthy mice. Follistatin gene delivery promoted insulinemia and abundance of insulin-positive pancreatic β-cells, even when treatment was administered to mice with advanced diabetes, supporting a mechanism for improved glycemic control associated with maintenance of functional β-cells. Our data demonstrate that single-dose intravascular Follistatin gene delivery can ameliorate the diabetic progression and improve prognostic markers of disease. These findings are consistent with other observations of Activin-mediated mechanisms exerting deleterious effects in models of obesity and diabetes, and suggest that interventions that attenuate Activin signaling could help further understanding of T2D and the development of novel T2D therapeutics.

Targeted Analysis of Three Hormonal Systems Identifies Molecules Associated with the Presence and Severity of NAFLD

AIMS

To investigate circulating levels and liver gene expression of 3 hormonal pathways associated with obesity, insulin resistance, and inflammation to identify leads towards potential diagnostic markers and therapeutic targets in patients with nonalcoholic fatty liver disease (NAFLD).

METHODS

We compared circulating levels of (1) proglucagon-derived hormones (glucagon-like peptide [GLP]-1, GLP-2, glicentin, oxyntomodulin, glucagon, major proglucagon fragment [MPGF]), (2) follistatins-activins (follistatin-like [FSTL]3, activin B), (3) IGF axis (insulin-like growth factor [IGF]-1, total and intact IGF binding protein [IGFBP]-3 and IGFBP-4, and pregnancy-associated plasma protein [PAPP]-A) in 2 studies: (1) 18 individuals with early stage NAFLD versus 14 controls (study 1; early NAFLD study) and in (2) 31 individuals with biopsy proven NAFLD (15 with simple steatosis [SS] and 16 with nonalcoholic steatohepatitis [NASH]), vs 50 controls (24 lean and 26 obese) (study 2). Liver gene expression was assessed in 22 subjects (12 controls, 5 NASH, 5 NASH-related cirrhosis).

RESULTS

Patients in early stages of NAFLD demonstrate higher fasting MPGF and lower incremental increase of glicentin during oral glucose tolerance test than controls. In more advanced stages, FSTL3 levels are higher in NASH than simple steatosis and, within NAFLD patients, in those with more severe lobular and portal inflammation. The IGF-1/intact IGFBP-3 ratio is lower in patients with liver fibrosis. Genes encoding follistatin, activin A, activin B, and the IGF-1 receptor are higher in NASH.

CONCLUSION

MPGF and glicentin may be involved in early stages of NAFLD, whereas FSTL3 and IGF-1/intact IGFBP3 in the progression to NASH and liver fibrosis respectively, suggesting potential as diagnostic markers or therapeutic targets.

Mechanisms involved in follistatin-induced hypertrophy and increased insulin action in skeletal muscle

BACKGROUND

Skeletal muscle wasting is often associated with insulin resistance. A major regulator of muscle mass is the transforming growth factor β (TGF-β) superfamily, including activin A, which causes atrophy. TGF-β superfamily ligands also negatively regulate insulin-sensitive proteins, but whether this pathway contributes to insulin action remains to be determined.

METHODS

To elucidate if TGF-β superfamily ligands regulate insulin action, we used an adeno-associated virus gene editing approach to overexpress an activin A inhibitor, follistatin (Fst288), in mouse muscle of lean and diet-induced obese mice. We determined basal and insulin-stimulated 2-deoxy-glucose uptake using isotopic tracers in vivo. Furthermore, to evaluate whether circulating Fst and activin A concentrations are associated with obesity, insulin resistance, and weight loss in humans, we analysed serum from morbidly obese subjects before, 1 week, and 1 year after Roux-en-Y gastric bypass (RYGB).

RESULTS

Fst288 muscle overexpression markedly increased in vivo insulin-stimulated (but not basal) glucose uptake (+75%, P < 0.05) and increased protein expression and intracellular insulin signalling of AKT, TBC1D4, PAK1, pyruvate dehydrogenase-E1α, and p70S6K, while decreasing TBC1D1 signaling (P < 0.05). Fst288 increased both basal and insulin-stimulated protein synthesis, but no correlation was observed between the Fst288-driven hypertrophy and the increase in insulin-stimulated glucose uptake. Importantly, Fst288 completely normalized muscle glucose uptake in insulin-resistant diet-induced obese mice. RYGB surgery doubled circulating Fst and reduced activin A (-24%, P < 0.05) concentration 1 week after surgery before any significant weight loss in morbidly obese normoglycemic patients, while major weight loss after 1 year did not further change the concentrations.

CONCLUSIONS

We here present evidence that Fst is a potent regulator of insulin action in muscle, and in addition to AKT and p70S6K, we identify TBC1D1, TBC1D4, pyruvate dehydrogenase-E1α, and PAK1 as Fst targets. Circulating Fst more than doubled post-RYGB surgery, a treatment that markedly improved insulin sensitivity, suggesting a role for Fst in regulating glycaemic control. These findings demonstrate the therapeutic potential of inhibiting TGF-β superfamily ligands to improve insulin action and Fst's relevance to muscle wasting-associated insulin-resistant conditions in mice and humans.

Short-term treatment with high dose liraglutide improves lipid and lipoprotein profile and changes hormonal mediators of lipid metabolism in obese patients with no overt type 2 diabetes mellitus: a randomized, placebo-controlled, cross-over, double-blind clinical trial

OBJECTIVE

Long-term treatment with up to 1.8 mg liraglutide improves cardiovascular and all-cause mortality in patients with type 2 diabetes at high risk for cardiovascular disease (CVD) and is currently under investigation in subjects without diabetes. Aim of our study was to investigate whether high dose (3 mg) short-term (5 weeks) treatment with liraglutide in obese patients with no overt type 2 diabetes affects metabolites, lipid and lipoprotein profile and components of activin-follistatin axis in cardiovascular beneficial or detrimental way.

RESEARCH DESIGN AND METHODS

Twenty obese patients participated in a randomized, placebo-controlled, cross-over, double-blind study and were administrated liraglutide 3 mg or placebo for 5 weeks. Metabolites, fatty acids, lipid-lipoprotein profile and concentrations of activins and follistatins (250 parameters) were assessed in serum at start and completion of each treatment.

RESULTS

Concentrations of important cardiovascular markers such as total, free and remnant cholesterol were reduced with liraglutide before and after adjusting for weight loss. Similarly, reductions in number of small and medium size LDL particles and in their total lipid concentration were observed with liraglutide and partially weight-loss related. Tyrosine levels were reduced and behenic acid levels were increased whereas only minor changes were observed in HDL, VLDL and IDL. Concentrations of activin AB and follistatin were significantly reduced in liraglutide-treated group.

CONCLUSIONS

Treatment of obese patients without overt type 2 diabetes with high dose of liraglutide for a short period of time induces changes in lipid-lipoprotein and hormonal profile that are suggestive of lower risk of atherosclerosis and CVD. Trial registration ClinicalTrials.gov Identifier: NCT02944500. Study ID Number 2015P000327. Registered November 2016.

Effect of exercise intensity on circulating hepatokine concentrations in healthy men

Fibroblast growth factor 21 (FGF21), follistatin and leukocyte cell-derived chemotaxin 2 (LECT2) are novel hepatokines that are modulated by metabolic stresses. This study investigated whether exercise intensity modulates the hepatokine response to acute exercise. Ten young, healthy men undertook three 8-h experimental trials: moderate-intensity exercise (MOD; 55% peak oxygen uptake), high-intensity exercise (HIGH; 75% peak oxygen uptake), and control (CON; rest), in a randomised, counterbalanced order. Exercise trials commenced with a treadmill run of varied duration to match gross exercise energy expenditure between trials (MOD vs HIGH; 2475 ± 70 vs 2488 ± 58 kJ). Circulating FGF21, follistatin, LECT2, glucagon, insulin, glucose and nonesterified fatty acids (NEFA) were measured before exercise and at 0, 1, 2, 4, and 7 h postexercise. Plasma FGF21 concentrations were increased up to 4 h postexercise compared with CON (P ≤ 0.022) with greater increases observed at 1, 2, and 4 h postexercise during HIGH versus MOD (P ≤ 0.025). Irrespective of intensity (P ≥ 0.606), plasma follistatin concentrations were elevated at 4 and 7 h postexercise (P ≤ 0.053). Plasma LECT2 concentrations were increased immediately postexercise (P ≤ 0.046) but were not significant after correcting for plasma volume shifts. Plasma glucagon (1 h; P = 0.032) and NEFA (4 and 7 h; P ≤ 0.029) responses to exercise were accentuated in HIGH versus MOD. These findings demonstrate that acute exercise augments circulating FGF21 and follistatin. Exercise-induced changes in FGF21 are intensity-dependent and may support the greater metabolic benefit of high-intensity exercise.

The Liver as an Endocrine Organ-Linking NAFLD and Insulin Resistance

The liver is a dynamic organ that plays critical roles in many physiological processes, including the regulation of systemic glucose and lipid metabolism. Dysfunctional hepatic lipid metabolism is a cause of nonalcoholic fatty liver disease (NAFLD), the most common chronic liver disorder worldwide, and is closely associated with insulin resistance and type 2 diabetes. Through the use of advanced mass spectrometry "omics" approaches and detailed experimentation in cells, mice, and humans, we now understand that the liver secretes a wide array of proteins, metabolites, and noncoding RNAs (miRNAs) and that many of these secreted factors exert powerful effects on metabolic processes both in the liver and in peripheral tissues. In this review, we summarize the rapidly evolving field of "hepatokine" biology with a particular focus on delineating previously unappreciated communication between the liver and other tissues in the body. We describe the NAFLD-induced changes in secretion of liver proteins, lipids, other metabolites, and miRNAs, and how these molecules alter metabolism in liver, muscle, adipose tissue, and pancreas to induce insulin resistance. We also synthesize the limited information that indicates that extracellular vesicles, and in particular exosomes, may be an important mechanism for intertissue communication in normal physiology and in promoting metabolic dysregulation in NAFLD.

Regulation of Hepatic Metabolism, Recent Advances, and Future Perspectives

PURPOSE OF REVIEW

The purpose of this review is to provide a brief summary of recent advances in our understanding of liver metabolism. The critical role of the liver in controlling whole-body energy homeostasis makes such understanding crucial to efficiently design new treatments for metabolic syndrome diseases, including type 2 diabetes (T2D).

RECENT FINDINGS

Significant advances have been made regarding our understanding of the direct and indirect effects of insulin on hepatic metabolism and the communication between the liver and other tissues. Moreover, the catabolic functions of glucagon, as well as the importance of hepatic redox status for the regulation of glucose production, are emerging as potential targets to reduce hyperglycemia. A resolution to the long-standing question "insulin suppression of hepatic glucose production, direct or indirect effect?" is starting to emerge. New advances in our understanding of important fasting-induced hepatic metabolic fluxes may help design better therapies for T2D.

The hepatokine Tsukushi is released in response to NAFLD and impacts cholesterol homeostasis

Nonalcoholic fatty liver disease (NAFLD) prevails in obesity and is linked to several health complications including dyslipidemia and atherosclerosis. How exactly NAFLD induces atherogenic dyslipidemia to promote cardiovascular diseases is still elusive. Here, we identify Tsukushi (TSK) as a hepatokine induced in response to NAFLD. We show that both endoplasmic reticulum stress and inflammation promote the expression and release of TSK in mice. In humans, hepatic TSK expression is also associated with steatosis, and its circulating levels are markedly increased in patients suffering from acetaminophen-induced acute liver failure (ALF), a condition linked to severe hepatic inflammation. In these patients, elevated blood TSK levels were associated with decreased transplant-free survival at hospital discharge, suggesting that TSK could have a prognostic significance. Gain- and loss-of-function studies in mice revealed that TSK impacts systemic cholesterol homeostasis. TSK reduces circulating HDL cholesterol, lowers cholesterol efflux capacity, and decreases cholesterol-to-bile acid conversion in the liver. Our data identify the hepatokine TSK as a blood biomarker of liver stress that could link NAFLD to the development of atherogenic dyslipidemia and atherosclerosis.

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.

A round trip from nonalcoholic fatty liver disease to diabetes: molecular targets to the rescue?

Evidence suggests a close relationship between nonalcoholic fatty liver disease (NAFLD) and type two diabetes (T2D). On the grounds of prevalence of disease, both conditions account for a significant financial cost for health care systems and individuals. Aim of this review article is to explore the epidemiological basis and the putative molecular mechanisms underlying the association of NAFLD with T2D. Epidemiological studies have shown that NAFLD is associated to the development of incident T2D and either reversal or improvement of NAFLD will result into decreased risk of developing incident T2D. On the other side of the coin data have shown that T2D will worsen the course of NAFLD doubling the risk of disease progression (i.e. evolution from simple steatosis to advanced fibrosis, cirrhosis, hepatocellular carcinoma, liver transplant and death). Conversely, NAFLD will contribute to metabolic decompensation of T2D. The pathogenesis of T2D in NAFLD patients may be mediated by several hepatokines impairing metabolic control. Among these, Fetuin-B, which causes glucose intolerance and is increased in patients with T2D and NAFLD with fibrosis is one of the most promising. T2D may affect the progression of NAFLD by acting at different levels of the pathogenic cascade involving gut microbiota and expanded, inflamed, dysfunctional adipose tissue. In conclusion, T2D and NAFLD are mutually, closely and bi-directionally associated. An improved understanding of molecular pathogenesis underlying this bi-directional association may allow us to be able to prevent the development of T2D by halting the progression of NAFLD.

Emerging awareness on the importance of skeletal muscle in liver diseases: time to dig deeper into mechanisms!

Skeletal muscle is a tissue that represents 30–40% of total body mass in healthy humans and contains up to 75% of total body proteins. It is thus the largest organ in non-obese subjects. The past few years have seen increasing awareness of the prognostic value of appreciating changes in skeletal muscle compartment in various chronic diseases. Hence, a low muscle mass, a low muscle function and muscle fatty infiltration are linked with poor outcomes in many pathological conditions. In particular, an affluent body of evidence links the severity, the complications and mortality of chronic liver disease (CLD) with skeletal muscle depletion. Yet it is still not clear whether low muscle mass is a cause, an aggravating factor, a consequence of the ongoing disease, or an epiphenomenon reflecting general alteration in the critically ill patient. The mechanisms by which the muscle compartment influences disease prognosis are still largely unknown. In addition, whether muscle alterations contribute to liver disease progression is an unanswered question. Here, we first review basic knowledge about muscle compartment to draw a conceptual framework for interpreting skeletal muscle alteration in CLD. We next describe recent literature on muscle wasting in cirrhosis and liver transplantation. We then discuss the implication of skeletal muscle compartment in non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH), focusing on plausible metabolic disruption in muscle compartment that might participate in NAFLD progression. Finally, we discuss shortcomings and challenges we need to address in the near future prior to designate the muscle compartment as a therapeutic target in CLD.

Follistatin-288-Fc Fusion Protein Promotes Localized Growth of Skeletal Muscle

Follistatin is an endogenous glycoprotein that promotes growth and repair of skeletal muscle by sequestering inhibitory ligands of the transforming growth factor-β superfamily and may therefore have therapeutic potential for neuromuscular diseases. Here, we sought to determine the suitability of a newly engineered follistatin fusion protein (FST288-Fc) to promote localized, rather than systemic, growth of skeletal muscle by capitalizing on the intrinsic heparin-binding ability of the follistatin-288 isoform. As determined by surface plasmon resonance and cell-based assays, FST288-Fc binds to activin A, activin B, myostatin (growth differentiation factor GDF8), and GDF11 with high affinity and neutralizes their activity in vitro. Intramuscular administration of FST288-Fc in mice induced robust, dose-dependent growth of the targeted muscle but not of surrounding or contralateral muscles, in contrast to the systemic effects of a locally administered fusion protein incorporating activin receptor type IIB (ActRIIB-Fc). Furthermore, systemic administration of FST288-Fc in mice did not alter muscle mass or body composition as determined by NMR, which again contrasts with the pronounced systemic activity of ActRIIB-Fc when administered by the same route. Subsequent analysis revealed that FST288-Fc in the circulation undergoes rapid proteolysis, thereby restricting its activity to individual muscles targeted by intramuscular administration. These results indicate that FST288-Fc can produce localized growth of skeletal muscle in a targeted manner with reduced potential for undesirable systemic effects. Thus, FST288-Fc and similar agents may be beneficial in the treatment of disorders with muscle atrophy that is focal, asymmetric, or otherwise heterogeneous.

Association of serum follistatin levels with histological types and progression of tumor in human lung cancer

Background

Follistatin (FST), an activin-binding protein, inhibits activin action by interfering with activin binding to its receptor. The prognostic value of FST has been studied in various cancers. However, these studies rarely focus on lung cancer. In our study, we investigated the relationship between serum FST levels and lung cancer with histologic types, TNM staging, and recurrence.

Methods

A total of 150 serum samples were collected, including 91 from patients with SCLC or NSCLC, 22 from patients with benign lung diseases, and 37 from healthy subjects. Enzyme-linked immunosorbent assay was used to determine serum FST levels in healthy subjects, patients with benign lung diseases and patients with lung cancers.

Results

Serum FST levels in patients with LADC, SCC, LASC, LCLC, and SCLC were much higher than those in healthy subjects and in patients with lung benign disease. A ROC curve was constructed for differentiating the lung cancer from the healthy subjects and benign lung diseases. The results indicated that the area under the ROC curve (AUC) was 0.971 and 0.728 respectively. According to TNM staging, serum FST level increased significantly in patients with stage III and IV of LADC. Moreover, serum FST expression were increased in LADC patients with different TNM category. Furthermore, we found that a higher expression of serum FST was correlated with recurrence in LADC patients.

Conclusions

The serum FST levels gradually increased with the rise of TNM staging and category in lung cancer patients. These data suggest that serum FST levels not only can be used in auxiliary diagnosis for lung cancer but also might be associated with the disease progression and metastasis of lung cancers.

Hepatokines-a novel group of exercise factors

Regular physical activity not only improves the exercise capacity of the skeletal muscle performing the contractions, but it is beneficial for the whole body. An extensive search for "exercise factors" mediating these beneficial effects has been going on for decades. Particularly skeletal muscle tissue has been investigated as a source of circulating exercise factors, and several myokines have been identified. However, exercise also has an impact on other tissues. The liver is interposed between energy storing and energy utilising tissues and is highly active during exercise, maintaining energy homeostasis. Recently, a novel group of exercise factors-termed hepatokines-has emerged. These proteins (fibroblast growth factor 21, follistatin, angiopoietin-like protein 4, heat shock protein 72, insulin-like growth factor binding protein 1) are released from the liver and increased in the bloodstream during or in the recovery after an exercise bout. In this narrative review, we evaluate this new group of exercise factors focusing on the regulation and potential function in exercise metabolism and adaptations. These hepatokines may convey some of the beneficial whole-body effects of exercise that could ameliorate metabolic diseases, such as obesity or type 2 diabetes.