Growth Differentiation Factor 15 Mediates Systemic Glucose Regulatory Action of T-Helper Type 2 Cytokines

Development of a Competitive Nutrient-Based T-Cell Immunotherapy Designed to Block the Adaptive Warburg Effect in Acute Myeloid Leukemia

Background: T-cell-based adoptive cell therapies have emerged at the forefront of cancer immunotherapies; however, failed long-term survival and inevitable exhaustion of transplanted T lymphocytes in vivo limits clinical efficacy. Leukemia blasts possess enhanced glycolysis (Warburg effect), exploiting their microenvironment to deprive nutrients (e.g., glucose) from T cells, leading to T-cell dysfunction and leukemia progression. Methods: Thus, we explored whether genetic reprogramming of T-cell metabolism could improve their survival and empower T cells with a competitive glucose-uptake advantage against blasts and inhibit their uncontrolled proliferation. Results: Here, we discovered that high-glucose concentration reduced the T-cell expression of glucose transporter GLUT1 (SLC2A1) and TFAM (mitochondrion transcription factor A), an essential transcriptional regulator of mitochondrial biogenesis, leading to their impaired expansion ex vivo. To overcome the glucose-induced genetic deficiency in metabolism, we engineered T cells with lentiviral overexpression of SLC2A1 and/or TFAM transgene. Multi-omics analyses revealed that metabolic reprogramming promoted T-cell proliferation by increasing IL-2 release and reducing exhaustion. Moreover, the engineered T cells competitively deprived glucose from allogenic blasts and lessened leukemia burden in vitro. Conclusions: Our findings propose a novel T-cell immunotherapy that utilizes a dual strategy of starving blasts and cytotoxicity for preventing uncontrolled leukemia proliferation.

GDF-15 levels in patients with polycystic ovary syndrome treated with metformin: a combined clinical and in silico pathway analysis

Objective

Polycystic ovary syndrome (PCOS) is an endocrine disease characterized by metabolic, reproductive, and psychological manifestations. Growth and differentiation factor 15 (GDF-15) is a cytokine associated with metabolic and inflammatory disorders. Metformin is commonly used for the treatment of PCOS. We investigated the relationship between GDF-15 levels and PCOS, the effect of metformin on GDF-15 levels, and potential biologic pathways related to GDF-15.

Subjects and methods

The study included 35 women with PCOS and 32 women without PCOS (controls). Both groups were compared in terms of GDF-15 levels. Additional analysis was conducted on samples from 22 women with PCOS who were treated with either metformin (n = 7) or placebo (n = 15), retrieved from a previous randomized, controlled trial. Levels of GDF-15 were measured using MILLIPLEX. The biologic pathways related to GDF-15 were evaluated using the databases STRING, SIGNOR, and Pathway Commons. The statistical analysis was conducted using the software SPSS.

Results

Levels of GDF-15 were higher in the PCOS group compared with the non-PCOS group (p = 0.039). Among women with PCOS, GDF-15 levels were higher in those treated with metformin compared with placebo (p = 0.007). The proteins related to GDF-15 overlapped between the databases, and a significant interaction was found between GDF-15 and proteins related to PCOS and its complications, including those related to estrogen response, oxidative stress, ovarian infertility, interleukin (IL)-18, IL-4, the ratio of advanced glycation end products to their receptor (AGE/RAGE), leptin, transforming growth factor beta (TGF-β), adipogenesis, and insulin.

Conclusion

The findings of the present study suggest a relationship between GDF-15 and PCOS and a potential increase in GDF-15 levels with metformin treatment. An additional finding was that GDF-15 could be involved in biologic pathways related to PCOS complications.

The impact of the expression level of growth differentiation factor 15 in tumor tissue on the response to immunotherapy in non-small cell lung cancer

BACKGROUND

Growth differentiation factor-15 (GDF-15), a member of the TGF-β superfamily, is overexpressed in various cancers and facilitates immune evasion by inhibiting T-cell activation. GDFATHER-TRIAL's phase 2a results demonstrated promising outcomes when combining the GDF-15 neutralizing antibody visugromab (CTL002) with nivolumab, enhancing the response to immunotherapy. This study evaluated the prognostic significance of GDF-15 expression in non-small cell lung cancer (NSCLC) tumor tissues in terms of immunotherapy response.

METHODS

This retrospective study included 50 patients with metastatic NSCLC treated with nivolumab at Gazi University Hospital between January 2021 and July 2023. GDF-15 expression was evaluated using immunochemistry staining and categorized based on the intensity of cytoplasmic or membranous staining. Samples were divided into a low expression group (scores 0 and 1) and a high expression group (scores 2 and 3). The primary outcomes were progression-free survival (PFS) and overall survival (OS), which were analyzed using Kaplan‒Meier and Cox proportional hazards models. Objective response rates were assessed in secondary outcomes.

RESULTS

Of the 50 patients, 43 were men (86%), with a median age of 63.9 years. Half of the patients exhibited low GDF-15 expression. High GDF-15 expression correlated with shorter PFS and OS. The median PFS was 7.8 months for the low-expression group versus 4.4 months for the high-expression group (HR, 0.41; 95% CI, 0.20-0.83; p = 0.013). The median OS was 18.1 months for the low-expression group compared to 11.8 months for the high-expression group (HR, 0.36; 95% CI, 0.16-0.78; p = 0.007). The objective response rate was significantly greater in the low GDF-15 group (52%) than in the high GDF-15 group (24%) (p = 0.040).

CONCLUSION

Elevated GDF-15 expression in NSCLC tumor tissues is associated with poorer response to nivolumab, suggesting that GDF-15 is a potential prognostic biomarker for immunotherapy efficacy. These findings warrant further validation through prospective studies to optimize treatment strategies for NSCLC patients.

Growth differentiation factor 15 is not modified after weight loss induced by liraglutide in South Asians and Europids with type 2 diabetes mellitus

Glucagon-like peptide-1 receptor (GLP-1R) agonists induce weight loss in patients with type 2 diabetes mellitus (T2DM), but the underlying mechanism is unclear. Recently, the mechanism by which metformin induces weight loss could be explained by an increase in growth differentiation factor 15 (GDF15), which suppresses appetite. Therefore, we aimed to investigate whether the GLP-1R agonist liraglutide modifies plasma GDF15 levels in patients with T2DM. GDF15 levels were measured in plasma samples obtained from Dutch Europids and Dutch South Asians with T2DM before and after 26 weeks of treatment with daily liraglutide (n = 44) or placebo (n = 50) added to standard care. At baseline, circulating GDF15 levels did not differ between South Asians and Europids with T2DM. Treatment with liraglutide, compared to placebo, decreased body weight, but did not modify plasma GDF15 levels in all patients, or when data were split by ethnicity. Also, the change in plasma GDF15 levels after treatment with liraglutide did not correlate with changes in body weight or HbA1c levels. In addition, the dose of metformin used did not correlate with baseline plasma GDF15 levels. Compared to placebo, liraglutide treatment for 26 weeks does not modify plasma GDF15 levels in Dutch Europid or South Asian patients with T2DM. Thus, the weight loss induced by liraglutide is likely explained by other mechanisms beyond the GDF15 pathway. HIGHLIGHTS: What is the central question of this study? Growth differentiation factor 15 (GDF15) suppresses appetite and is increased by metformin: does the GLP-1R agonist liraglutide modify plasma GDF15 levels in patients with type 2 diabetes mellitus (T2DM)? What is the main finding and its importance? Plasma GDF15 levels did not differ between South Asians and Europids with T2DM and were not modified by 26 weeks of liraglutide in either ethnicity. Moreover, there was no correlation between the changes in plasma GDF15 levels and dosage of metformin administered, changes in body weight or HbA1c levels. The appetite-suppressing effect of liraglutide is likely exerted via pathways other than GDF15.

Macrophages as a Source and Target of GDF-15

Growth differentiation factor 15 (GDF-15) is a multifunctional cytokine that belongs to the transforming growth factor-beta (TGF-β) superfamily. GDF-15 is involved in immune tolerance and is elevated in several acute and chronic stress conditions, often correlating with disease severity and patient prognosis in cancer172 and metabolic and cardiovascular disorders. Despite these clinical associations, the molecular mechanisms orchestrating its effects remain to be elucidated. The effects of GDF-15 are pleiotropic but cell-specific and dependent on the microenvironment. While GDF-15 expression can be stimulated by inflammatory mediators, its predominant effects were reported as anti-inflammatory and pro-fibrotic. The role of GDF-15 in the macrophage system has been increasingly investigated in recent years. Macrophages produce high levels of GDF-15 during oxidative and lysosomal stress, which can lead to fibrogenesis and angiogenesis at the tissue level. At the same time, macrophages can respond to GDF-15 by switching their phenotype to a tolerogenic one. Several GDF-15-based therapies are under development, including GDF-15 analogs/mimetics and GDF-15-targeting monoclonal antibodies. In this review, we summarize the major physiological and pathological contexts in which GDF-15 interacts with macrophages. We also discuss the major challenges and future perspectives in the therapeutic translation of GDF-15.

Correlations between growth differentiation factor 15 (GDF-15) serum levels and gene polymorphism with type 2 diabetes mellitus

Purpose

To date, the relationship between Growth Differentiation Factor 15 (GDF-15) gene polymorphism and the risk of type 2 diabetes mellitus (T2DM) has not been clarified. Our study aims to explore the association between serum GDF-15 levels and related gene polymorphism with the risk of T2DM in a Chinese rural Yao population.

Methods

This was a 1:1 case-control study with 179 T2DM patients and 179 age- and sex-matched control participants. Serum GDF-15 levels were measured by enzyme-linked immunosorbent assay, and polymorphisms (rs1059519, rs1059369, rs1804826 and rs1054564) were genotyped by MassArray mass spectrometry.

Results

Serum GDF-15 (sGDF-15) levels were higher in patients with T2DM and glycosylated hemoglobin (HbA1c) ≥ 6.5 % compared to that in controls (p < 0.001). The area under the curve (AUC) corresponding to sGDF-15 levels was 0.626. Serum GDF-15 was positively correlated with fasting plasma glucose (FPG) (rs = 0.150, p < 0.001) and HbA1c (rs = 0.160, p < 0.001). The frequency of GDF-15 gene rs1054564 GC + CC genotype was significantly associated with increased risk of T2DM compared to GG genotype (OR = 1.724, 95CI: 1.046-2.841, p = 0.033). Frequencies of rs1804826 T allele (β additive = 113.318, p = 0.026) and rs1054564 C allele (β additive = 247.282, p = 0.001, β dominant = 286.109, p = 0.001) was significantly correlated with higher sGDF-15. The rs1059519 C allele was negatively correlated with FPG (β recessive = -0.607, p = 0.047) and HbA1c (β recessive = -0.456, p = 0.020).

Conclusion

Serum GDF-15 levels were positively correlated with FPG and HbA1c. The GDF-15 rs1054564 GC + CC genotype was associated with a significantly higher T2DM risk. The rs1059519 C allele was negatively correlated with FPG and HbA1c.

IL-4 activates the futile triacylglyceride cycle for glucose utilization in white adipocytes

The development of cardiometabolic complications during obesity is strongly associated with chronic latent inflammation in hypertrophied adipose tissue (AT). IL-4 is an anti-inflammatory cytokine, playing a protective role against insulin resistance, glucose intolerance and weight gain. The positive effects of IL-4 are associated not only with the activation of anti-inflammatory immune cells in AT, but also with the modulation of adipocyte metabolism. IL-4 is known to activate lipolysis and glucose uptake in adipocytes, but the precise regulatory mechanisms and physiological significance of these processes remain unclear. In this study, we detail IL-4 effects on glucose and triacylglycerides (TAGs) metabolism and propose mechanisms of IL-4 metabolic action in adipocytes. We have shown that IL-4 activates glucose oxidation, lipid droplet (LD) fragmentation, lipolysis and thermogenesis in mature 3T3-L1 adipocytes. We found that lipolysis was not accompanied by fatty acids (FAs) release from adipocytes, suggesting FA re-esterification. Moreover, glucose oxidation and thermogenesis stimulation depended on adipocyte triglyceride lipase (ATGL) activity, but not the uncoupling protein (UCP1) expression. Based on these data, IL-4 may activate the futile TAG-FA cycle in adipocytes, which enhances the oxidative activity of cells and heat production. Thus, the positive effect of IL-4 on systemic metabolism can be the result of the activation of non-canonical thermogenic mechanism in AT, increasing TAG turnover and utilization of excessive glucose.

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

Browning of Mesenteric White Adipose Tissue in Crohn's Disease: A New Pathological Change and Therapeutic Target

BACKROUND

Hypertrophic mesenteric adipose tissue [htMAT] is a distinctive hallmark of Crohn's disease [CD], and it affects enteritis via inflammatory adipokine secretion by dysfunctional white adipocytes. White adipocytes can become beige adipocytes, which are characterized by active lipid consumption and favourable endocrine function, via white adipocyte browning. Our study aimed to determine whether white adipocyte browning occurs in htMAT and its role in CD.

METHODS

White adipocyte browning was examined in MAT samples from CD patients and controls. Human MAT explants and primary mesenteric adipocytes were cultured for in vitro experiments. Mice with 2,4,6-trinitrobenzenesulphonic acid solution [TNBS]-induced colitis were used for in vivo studies. A β3-adrenergic receptor agonist [CL316,243] was used to induce white adipocyte browning, and IL-4/STAT6 signalling was analysed to explore the mechanism underlying the anti-inflammatory activity of beige adipocytes.

RESULTS

White adipocyte browning was observed in htMAT from CD patients, as shown by the appearance of uncoupling protein 1 [UCP1]-positive multilocular [beige] adipocytes with lipid-depleting activity and anti-inflammatory endocrine profiles. Both human MAT and primary mesenteric adipocytes from CD patients and controls could be induced to undergo browning, which increased their lipid-depleting and anti-inflammatory activities in vitro. Inducing MAT browning ameliorated mesenteric hypertrophy and inflammation as well as colitis in TNBS-treated mice in vivo. The anti-inflammatory activity of beige adipocytes was at least partially related to STAT6 signalling activation via the autocrine and paracrine effects of IL-4.

CONCLUSION

White adipocyte browning is a newly identified pathological change in htMAT of CD patients and a possible therapeutic target.

Recent progress in understanding mitokines as diagnostic and therapeutic targets in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent tumors worldwide and the leading contributor to cancer-related deaths. The progression and metastasis of HCC are closely associated with altered mitochondrial metabolism, including mitochondrial stress response. Mitokines, soluble proteins produced and secreted in response to mitochondrial stress, play an essential immunomodulatory role. Immunotherapy has emerged as a crucial treatment option for HCC. However, a positive response to therapy is typically dependent on the interaction of tumor cells with immune regulation within the tumor microenvironment. Therefore, exploring the specific immunomodulatory mechanisms of mitokines in HCC is essential for improving the efficacy of immunotherapy. This study provides a comprehensive overview of the association between HCC and the immune microenvironment and highlights recent progress in understanding the involvement of mitochondrial function in preserving liver function. In addition, a systematic review of mitokines-mediated immunomodulation in HCC is presented. Finally, the potential diagnostic and therapeutic roles of mitokines in HCC are prospected and summarized. Recent progress in mitokine research represents a new prospect for mitochondrial therapy. Considering the potential of mitokines to regulate immune function, investigating them as a relevant molecular target holds great promise for the diagnosis and treatment of HCC.

GDF15 Ameliorates Liver Fibrosis by Metabolic Reprogramming of Macrophages to Acquire Anti-Inflammatory Properties

BACKGROUND & AIMS

Liver fibrosis/cirrhosis is significant health burden worldwide, resulting in liver failure or cancer and accounting for many deaths each year. The pathogenesis of liver fibrosis is very complex, which makes treatment challenging. Growth differentiation factor 15 (GDF15), a cysteine knot protein belonging to the transforming growth factor β (TGF-β) superfamily, has been shown to play a protective role after tissue injury and to promote a negative energy balance during obesity and diabetes. However, paucity of literature is available about GDF15 function in liver fibrosis. This study aimed to investigate the immunomodulatory role and therapeutic potential of GDF15 in progression of hepatic fibrosis.

METHODS

GDF15 expression was studied in patients with fibrosis/cirrhosis and in 2 murine models of liver fibrosis, including mice treated with CCl4 or DDC diet. GDF15 involvement in the pathogenesis of liver fibrosis was assessed in Gdf15 knockout mouse using both CCl4 and DDC diet experimental models. We used the CCl4 and/or DDC diet-induced liver fibrosis model to examine the antifibrotic and anti-inflammatory effects of AAV8-mediated GDF15 overexpression in hepatocytes or recombinant mouse GDF15.

RESULTS

GDF15 expression is decreased in the liver of animal models and patients with liver fibrosis/cirrhosis compared with those without liver disease. In vivo studies showed that GDF15 deficiency aggravated CCl4 and DDC diet-induced liver fibrosis, while GDF15 overexpression mediated by AAV8 or its recombinant protein alleviated CCl4 and/or DDC diet-induced liver fibrosis. In Gdf15 knockout mice, the intrahepatic microenvironment that developed during fibrosis showed relatively more inflammation, as demonstrated by enhanced infiltration of monocytes and neutrophils and increased expression of proinflammatory factors, which could be diminished by AAV8-mediated GDF15 overexpression in hepatocytes. Intriguingly, GDF15 exerts its effects by reprogramming the metabolic pathways of macrophages to acquire an oxidative phosphorylation-dependent anti-inflammatory functional fate. Furthermore, adoptive transfer of GDF15-preprogrammed macrophages to mouse models of liver fibrosis induced by CCl4 attenuated inflammation and alleviated the progression of liver fibrosis.

CONCLUSION

GDF15 ameliorates liver fibrosis via modulation of liver macrophages. Our data implicate the importance of the liver microenvironment in macrophage programming during liver fibrosis and suggest that GDF15 is a potentially attractive therapeutic target for the treatment of patients with liver fibrosis.

Growth differentiation factor 15 and cardiovascular risk: individual patient meta-analysis

AIMS

Levels of growth differentiation factor 15 (GDF-15), a cytokine secreted in response to cellular stress and inflammation, have been associated with multiple types of cardiovascular (CV) events. However, its comparative prognostic performance across different presentations of atherosclerotic cardiovascular disease (ASCVD) remains unknown.

METHODS AND RESULTS

An individual patient meta-analysis was performed using data pooled from eight trials including 53 486 patients. Baseline GDF-15 concentration was analyzed as a continuous variable and using established cutpoints (<1200 ng/L, 1200-1800 ng/L, > 1800 ng/L) to evaluate its prognostic performance for CV death/hospitalization for heart failure (HHF), major adverse cardiovascular events (MACE), and their components using Cox models adjusted for clinical variables and established CV biomarkers. Analyses were further stratified on ASCVD status: acute coronary syndrome (ACS), stabilized after recent ACS, and stable ASCVD. Overall, higher GDF-15 concentration was significantly and independently associated with an increased rate of CV death/HHF and MACE (P < 0.001 for each). However, while GDF-15 showed a robust and consistent independent association with CV death and HHF across all presentations of ASCVD, its prognostic association with future myocardial infarction (MI) and stroke only remained significant in patients stabilized after recent ACS or with stable ASCVD [hazard ratio (HR): 1.24, 95% confidence interval (CI): 1.17-1.31 and HR: 1.16, 95% CI: 1.05-1.28 for MI and stroke, respectively] and not in ACS (HR: 0.98, 95% CI: 0.90-1.06 and HR: 0.87, 95% CI: 0.39-1.92, respectively).

CONCLUSION

Growth differentiation factor 15 consistently adds prognostic information for CV death and HHF across the spectrum of ASCVD. GDF-15 also adds prognostic information for MI and stroke beyond clinical risk factors and cardiac biomarkers but not in the setting of ACS.

Significant increase of serum extracellular vesicle-packaged growth differentiation factor 15 in type 2 diabetes mellitus: a cross-sectional study

BACKGROUND

Growth differentiation factor 15 (GDF15) is a stress-inducible factor involved in the inflammatory progression of many complications, including type 2 diabetes mellitus (T2DM). Growing evidence suggests that molecules in extracellular vesicles (EVs) are associated with diabetes or diabetes-related complications. However, the correlation between serum extracellular vesicle-derived growth differentiation factor15 (EV-GDF15) and T2DM is unknown. The aim of this cross-sectional study is to investigate whether serum EV-GDF15 is associated with T2DM incidence.

METHODS

116 individuals, including 78 T2DM and 38 non-T2DM, were recruited as participants. The concentrations of serum EV-GDF15 and serum GDF15 were determined by Luminex assay. Serum EVs were obtained by ultracentrifugation. Multivariate stepwise regression analysis was used to determine the association between serum GDF15 levels and fasting plasma glucose (FPG) as well as glycated hemoglobin (HbA1c). The association of serum EV-GDF15 levels with T2DM was determined by multivariate logistic regression analysis.

RESULTS

Our data showed that the levels of serum EV-GDF15 and serum GDF15 were significantly increased in T2DM patients compared with non-T2DM subjects (EV-GDF15 levels, 13.68 (6.61-23.44) pg/mL vs. 5.56 (3.44-12.09) pg/mL, P < 0.001; and serum GDF15 levels, 1025.49 (677.87-1626.36) pg/mL vs. 675.46 (469.53-919.98) pg/mL, P < 0.001). There was a linear correlation between EV-GDF15 levels and fasting plasma glucose (FPG) and Hemoglobin A1C (HbA1c) levels (normalized β = 0.357, P < 0.001; normalized β = 0.409, P < 0.001, respectively). Elevated levels of EV-GDF15 were accompanied by an increase in the proportion of patients with T2DM (from 47.5 to 78.9%) and a progressive independent association with the incidence of T2DM (from OR = 3.06, 95% CI 1.02-9.19, P = 0.047 to OR = 3.75, 95% CI 1.14-12.26, P = 0.029). Notably, high levels of serum GDF15 plus high levels of serum EV-GDF15 were significantly associated with T2DM more than either alone.

CONCLUSION

This study elucidated that increased levels of GDF15 in serum EVs were independently associated with T2DM.

Growth differentiation factor-15 is independently associated with metabolic syndrome and hyperglycemia in non-elderly subjects

Metabolic syndrome (MetS) is a major health issue worldwide accompanied by cardiovascular comorbidities. Growth differentiation factor-15 (GDF-15) is a stress-responsive cytokine expressed in cardiomyocytes, adipocytes, macrophages, and endothelial cells. Previous research in elderly subjects revealed that GDF-15 levels were associated with the MetS. However, the association between GDF-15 levels and MetS or its components in the non-elderly subjects remains unclear. In this study, a total of 279 subjects younger than 65-year-old with (n = 84) or without (n = 195) MetS were recruited. MetS was defined according to modified NCEP/ATP III criteria. The GDF-15 levels were measured by an enzyme-linked immunosorbent assay. A multiple linear regression analysis was conducted to identify factors independently associated with GDF-15 levels. Subjects with MetS had higher GDF-15 levels than those without MetS (median (interquartile range), 1.72 ng/mL (1.38, 2.26) vs. 1.63 ng/mL (1.27, 2.07), P = 0.037). With the number of MetS components increased, the GDF-15 levels increased significantly (P for trend = 0.005). Multiple linear regression analysis revealed that the presence of MetS was positively associated with the GDF-15 levels (β = 0.132, P = 0.037). When substituting MetS with its components, only the presence of hyperglycemia was positively associated with the GDF-15 levels after adjustment for covariates (β = 0.193, P = 0.003). Taken together, the presence of the MetS in non-elderly was associated with higher GDF-15 levels. Among the MetS components, only hyperglycemia was significantly associated with the GDF-15 levels. Future longitudinal studies will be needed to explore whether GDF-15 has the potential to be a biomarker of gluco-metabolic dysfunction in non-elderly subjects.

Knocking on GDF15's door for the treatment of type 2 diabetes mellitus

Although a large number of drugs are available for the treatment of type 2 diabetes mellitus (T2DM), many patients do not achieve adequate disease control despite adhering to medication. Recent findings indicate that the pharmacological modulation of the stress-induced cytokine growth differentiation factor 15 (GDF15) shows promise for the treatment of T2DM. GDF15 suppresses appetite and reduces inflammation, increases thermogenesis and lipid catabolism, sustains AMP-activated protein kinase (AMPK) activity, and ameliorates insulin resistance and hepatic steatosis. In addition, circulating GDF15 levels are elevated in response to several antidiabetic drugs, including metformin, with GDF15 mediating some of their effects. Here, we review the mechanistic insights into the beneficial effects of recently explored therapeutic approaches that target GDF15 for the treatment of T2DM.

The Cytokine Growth Differentiation Factor-15 and Skeletal Muscle Health: Portrait of an Emerging Widely Applicable Disease Biomarker

Growth differentiation factor 15 (GDF-15) is a stress-induced transforming growth factor-β superfamily cytokine with versatile functions in human health. Elevated GDF-15 blood levels associate with multiple pathological conditions, and are currently extensively explored for diagnosis, and as a means to monitor disease progression and evaluate therapeutic responses. This review analyzes GDF-15 in human conditions specifically focusing on its association with muscle manifestations of sarcopenia, mitochondrial myopathy, and autoimmune and viral myositis. The use of GDF-15 as a widely applicable health biomarker to monitor muscle disease is discussed, and its potential as a therapeutic target is explored.

GDF-15: A Potential Biomarker and Therapeutic Target in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a rheumatic disease. Growth differentiation factor 15 (GDF-15) is a member of transforming growth factor-β superfamily. To date, association of GDF-15 with SLE pathogenesis is not clarified. This study discussed GDF-15 serum levels and gene polymorphisms in SLE patients and lupus mouse model further demonstrated the role of GDF-15 in lupus development. We conducted two independent case-control studies for SLE patients. One is to evaluate serum levels of GDF-15 in 54 SLE patients and 90 healthy controls, and the other one is to analyze gene polymorphisms of GDF-15 in 289 SLE patients and 525 healthy controls. Serum levels of GDF-15 were detected by ELISA. GDF-15 gene polymorphisms (rs1055150, rs1058587, rs1059519, rs1059369, rs1227731, rs4808793, and rs16982345) were genotyped by the Kompetitive Allele-Specific PCR (KASP) method. Addition of recombinant GDF-15 into pristane-induced lupus mice evaluated histological and serological changes. Results showed that serum levels of GDF-15 were overexpressed in SLE patients and associated with disease activity. Polymorphisms rs1055150, rs1059369, rs1059519, and rs4808793 of GDF-15 gene were related to SLE risk. Lupus mice showed splenomegaly, severe histological scores, and high levels of autoantibodies [antinuclear antibodies (ANA) and total immunoglobulin G (IgG)], whereas administration of GDF-15 into lupus mice reduced the histological changes. Percentages of CD8⁺, CD11b⁺, CD19⁺, CD11C⁺ cells, T_H2 cells, and pro-inflammatory cytokines (IL-1β, IL-2, IL-4, IL-21, and IL-22) were reduced after GDF-15 treatment in lupus mice. In conclusion, GDF-15 was related to lupus pathogenesis and inhibited lupus development.

Obesity-Mediated Immune Modulation: One Step Forward, (Th)2 Steps Back

Over the past decades, the relationship between the immune system and metabolism has become a major research focus. In this arena of immunometabolism the capacity of adipose tissue to secrete immunomodulatory molecules, including adipokines, within the underlying low-grade inflammation during obesity brought attention to the impact obesity has on the immune system. Adipokines, such as leptin and adiponectin, influence T cell differentiation into different T helper subsets and their activation during immune responses. Furthermore, within the cellular milieu of adipose tissue nutrient availability regulates differentiation and activation of T cells and changes in cellular metabolic pathways. Upon activation, T cells shift from oxidative phosphorylation to oxidative glycolysis, while the differential signaling of the kinase mammalian target of rapamycin (mTOR) and the nuclear receptor PPARγ, amongst others, drive the subsequent T cell differentiation. While the mechanisms leading to a shift from the typical type 2-dominated milieu in lean people to a Th1-biased pro-inflammatory environment during obesity are the subject of extensive research, insights on its impact on peripheral Th2-dominated immune responses become more evident. In this review, we will summarize recent findings of how Th2 cells are metabolically regulated during obesity and malnutrition, and how these states affect local and systemic Th2-biased immune responses.

Deletion of Gdf15 Reduces ER Stress-induced Beta-cell Apoptosis and Diabetes

Endoplasmic reticulum (ER) stress contributes to pancreatic beta-cell apoptosis in diabetes, but the factors involved are still not fully elucidated. Growth differentiation factor 15 (GDF15) is a stress response gene and has been reported to be increased and play an important role in various diseases. However, the role of GDF15 in beta cells in the context of ER stress and diabetes is still unclear. In this study, we have discovered that GDF15 promotes ER stress-induced beta-cell apoptosis and that downregulation of GDF15 has beneficial effects on beta-cell survival in diabetes. Specifically, we found that GDF15 is induced by ER stress in beta cells and human islets, and that the transcription factor C/EBPβ is involved in this process. Interestingly, ER stress-induced apoptosis was significantly reduced in INS-1 cells with Gdf15 knockdown and in isolated Gdf15 knockout mouse islets. In vivo, we found that Gdf15 deletion attenuates streptozotocin-induced diabetes by preserving beta cells and insulin levels. Moreover, deletion of Gdf15 significantly delayed diabetes development in spontaneous ER stress-prone Akita mice. Thus, our findings suggest that GDF15 contributes to ER stress-induced beta-cell apoptosis and that inhibition of GDF15 may represent a novel strategy to promote beta-cell survival and treat diabetes.

Regulation of Glucose Transport in Adipocytes by Interleukin-4

Metabolic abnormalities such as obesity, insulin resistance, and type 2 diabetes mellitus are known to be associated with adipose tissue inflammation and impaired secretion of cytokines. Anti-inflammatory cytokine interleukin-4 (IL-4) was found to promote insulin sensitivity, glucose tolerance, and reduce lipid accumulation in vivo through multiple mechanisms, including direct regulation of lipolysis in adipocytes. However, little is known about its role in adipocyte glucose metabolism. This study reveals that IL-4 upregulates glucose uptake in adipocytes without additional activation of the insulin-dependent IRS1 (insulin receptor substrate 1)-Akt (protein kinase B) pathway. Moreover, the main transcription factor STAT6 (signal transducer and activator of transcription 6), regulated by IL-4, was not involved in adipocyte glucose uptake. The proteomic results showed that IL-4 upregulates expression of proteins involved in mitochondrial biogenesis, renewal, and glucose oxidation. Our study provides a new hypothesis, explaining protective effects of IL-4 against metabolic abnormalities through activation of adipocytes glucose utilization and maintenance of mitochondrial function under metabolic overload conditions.

GDF15, an emerging key player in human aging

Growth differentiation factor 15 (GDF15) is recently emerging not only as a stress-related mitokine, but also as a key player in the aging process, being one of the most up-regulated protein with age and associated with a variety of age-related diseases (ARDs). Many data indicate that GDF15 has protective roles in several tissues during different stress and aging, thus playing a beneficial role in apparent contrast with the observed association with many ARDs. A possible detrimental role for this protein is then hypothesized to emerge with age. Therefore, GDF15 can be considered as a pleiotropic factor with beneficial activities that can turn detrimental in old age possibly when it is chronically elevated. In this review, we summarize the current knowledge on the biology of GDF15 during aging. We also propose GDF15 as a part of a dormancy program, where it may play a role as a mediator of defense processes aimed to protect from inflammatory damage and other stresses, according to the life history theory.

Growth Differentiation Factor-15 in Immunity and Aging

Aging increases susceptibility to and severity of a variety of chronic and infectious diseases. Underlying this is dysfunction of the immune system, including chronic increases in low-grade inflammation (inflammaging) and age-related immunosuppression (immunosenescence). Growth differentiation factor-15 (GDF-15) is a stress-, infection-, and inflammation-induced cytokine which is increased in aging and suppresses immune responses. This mini review briefly covers existing knowledge on the immunoregulatory and anti-inflammatory roles of GDF-15, as well as its potential importance in aging and immune function.

Association of Growth and Differentiation Factor 15 in Rheumatoid Arthritis

Purpose

Rheumatoid arthritis (RA) is an inflammatory rheumatic disease, which has been demonstrated to correlate with mutated genetics. Growth and differentiation factor 15 (GDF-15) is a member of the transforming growth factor-β superfamily and is expressed in different organs, tissues and immune cells. To date, limited studies have evaluated plasma levels of GDF-15 in RA patients, and whether GDF-15 gene polymorphisms correlate with RA risk in the Chinese Han population has not been clarified.

Patients and Methods

This case-control study recruited 910 age- and sex-matched RA patients and healthy controls. Plasma levels of GDF-15 were examined by enzyme linked immunosorbent assay, and polymorphisms (rs1055150, rs1058587, rs3787023, and rs4808793) were genotyped by KASP method.

Results

RA patients had higher levels of GDF-15 as compared to that in healthy controls. Patients with positive CRP also showed higher levels of GDF-15 when compared to that in patients with negative CRP. Levels of GDF-15 correlated with disease activity score. Frequencies of GG, GC, GG+GC genotypes and G allele in GDF-15 gene rs1058587 were significantly elevated in RA patients compared to controls. Frequencies of CC genotype and C allele in GDF-15 gene rs3787023 were higher in RA patients compared to controls. Other polymorphisms did not correlate with RA susceptibility. Moreover, the four polymorphisms were not correlated with levels of GDF-15.

Conclusion

Plasma levels of GDF-15 were elevated in RA patients and GDF-15 gene polymorphisms were related to RA risk in the Chinese Han population.

GDF15: a potential therapeutic target for type 1 diabetes

INTRODUCTION

Current treatment for type 1 diabetes (T1D) is centered around insulin supplementation to manage the effects of pancreatic β cell loss. GDF15 is a potential preventative therapy against T1D progression that could work to curb increasing disease incidence.

AREAS COVERED

This paper discusses the known actions of GDF15, a pleiotropic protein with metabolic, feeding, and immunomodulatory effects, connecting them to highlight the open opportunities for future research. The role of GDF15 in the prevention of insulitis and protection of pancreatic β cells against pro-inflammatory cytokine-mediated cellular stress are examined and the pharmacological promise of GDF15 and critical areas of future research are discussed.

EXPERT OPINION

GDF15 shows promise as a potential intervention but requires further development. Preclinical studies have shown poor efficacy, but this result may be confounded by the measurement of gross GDF15 instead of the active form. Additionally, the effect of GDF15 in the induction of anorexia and nausea-like behavior and short-half-life present significant challenges to its deployment, but a systems pharmacology approach paired with chronotherapy may provide a possible solution to therapy for this currently unpreventable disease.

GDF-15, a future therapeutic target of glucolipid metabolic disorders and cardiovascular disease

Growth and differentiation factor 15 (GDF-15) was discovered as a member of the transforming growth factor β (TGF-β) superfamily and the serum level of GDF-15 was significantly correlated with glucolipid metabolic disorders (GLMD) and cardiovascular diseases. In 2017, a novel identified receptor of GDF-15-glial-derived neurotrophic factor receptor alpha-like (GFRAL) was found to regulate energy homeostasis (such as obesity, diabetes and non-alcoholic fatty liver disease (NAFLD)). The function of GDF-15/GFRAL in suppressing appetite, enhancing glucose/lipid metabolism and vascular remodeling has been gradually revealed. These effects make it a potential therapeutic target for GLMD and vascular diseases. In this narrative review, we included and reviewed 121 articles by screening 524 articles from literature database. We primarily focused on the function of GDF-15 and its role in GLMD/cardiovascular diseases and discuss its potential clinical application.

Novel Biomolecules in the Pathogenesis of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is one of the most common metabolic diseases in pregnant women. Its early diagnosis seems to have a significant impact on the developing fetus, the course of delivery, and the neonatal period. It may also affect the later stages of child development and subsequent complications in the mother. Therefore, the crux of the matter is to find a biopredictor capable of singling out women at risk of developing GDM as early as the very start of pregnancy. Apart from the well-known molecules with a proven and clear-cut role in the pathogenesis of GDM, e.g., adiponectin and leptin, a potential role of newer biomolecules is also emphasized. Less popular and less known factors with different mechanisms of action include: galectins, growth differentiation factor-15, chemerin, omentin-1, osteocalcin, resistin, visfatin, vaspin, irisin, apelin, fatty acid-binding protein 4 (FABP4), fibroblast growth factor 21, and lipocalin-2. The aim of this review is to present the potential and significance of these 13 less known biomolecules in the pathogenesis of GDM. It seems that high levels of FABP4, low levels of irisin, and high levels of under-carboxylated osteocalcin in the serum of pregnant women can be used as predictive markers in the diagnosis of GDM. Hopefully, future clinical trials will be able to determine which biomolecules have the most potential to predict GDM.

GDF15: emerging biology and therapeutic applications for obesity and cardiometabolic disease

Growth differentiation factor 15 (GDF15) is a member of the TGFβ superfamily whose expression is increased in response to cellular stress and disease as well as by metformin. Elevations in GDF15 reduce food intake and body mass in animal models through binding to glial cell-derived neurotrophic factor family receptor alpha-like (GFRAL) and the recruitment of the receptor tyrosine kinase RET in the hindbrain. This effect is largely independent of other appetite-regulating hormones (for example, leptin, ghrelin or glucagon-like peptide 1). Consistent with an important role for the GDF15-GFRAL signalling axis, some human genetic studies support an interrelationship with human obesity. Furthermore, findings in both mice and humans have shown that metformin and exercise increase circulating levels of GDF15. GDF15 might also exert anti-inflammatory effects through mechanisms that are not fully understood. These unique and distinct mechanisms for suppressing food intake and inflammation makes GDF15 an appealing candidate to treat many metabolic diseases, including obesity, type 2 diabetes mellitus, non-alcoholic fatty liver disease, cardiovascular disease and cancer cachexia. Here, we review the mechanisms regulating GDF15 production and secretion, GDF15 signalling in different cell types, and how GDF15-targeted pharmaceutical approaches might be effective in the treatment of metabolic diseases.

Mitochondrial Metabolic Signatures in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer death worldwide. HCC progression and metastasis are closely related to altered mitochondrial metabolism, including mitochondrial stress responses, metabolic reprogramming, and mitoribosomal defects. Mitochondrial oxidative phosphorylation (OXPHOS) defects and reactive oxygen species (ROS) production are attributed to mitochondrial dysfunction. In response to oxidative stress caused by increased ROS production, misfolded or unfolded proteins can accumulate in the mitochondrial matrix, leading to initiation of the mitochondrial unfolded protein response (UPR^mt). The mitokines FGF21 and GDF15 are upregulated during UPR^mt and their levels are positively correlated with liver cancer development, progression, and metastasis. In addition, mitoribosome biogenesis is important for the regulation of mitochondrial respiration, cell viability, and differentiation. Mitoribosomal defects cause OXPHOS impairment, mitochondrial dysfunction, and increased production of ROS, which are associated with HCC progression in mouse models and human HCC patients. In this paper, we focus on the role of mitochondrial metabolic signatures in the development and progression of HCC. Furthermore, we provide a comprehensive review of cell autonomous and cell non-autonomous mitochondrial stress responses during HCC progression and metastasis.

Th2 Cytokines Increase the Expression of Fibroblast Growth Factor 21 in the Liver

Interleukin-4 (IL-4) and IL-13 are the major T helper 2 (Th2) cytokines, and they are involved in the regulation of metabolism in the adipose tissue. The liver contains diverse innate and adaptive immune cells, but it remains to be determined whether Th2 cytokines modulate energy metabolism in the liver. Here, using gene expression data from the Gene Expression Omnibus (GEO) and the BXD mouse reference population, we determined that the Th2 cytokines IL-4 and IL-13 increase the secretion of fibroblast growth factor 21 (FGF21) in the liver. In vitro experiments confirmed that FGF21 was highly expressed in response to IL-4 and IL-13, and this response was abolished by the Janus kinase (JAK)-signal transducer and activator of transcription 6 (STAT6) blockade. Moreover, FGF21 expression in response to Th2 cytokines was augmented by selective peroxisome proliferator-activated receptor α (PPARα) inhibition. In vivo administration of IL-4 increased FGF21 protein levels in the liver in a STAT6-dependent manner, but FGF21 secretion in response to IL-4 was not observed in the epididymal white adipose tissue (eWAT) despite the activation of STAT6. Intraperitoneal administration of IL-33, an activator of type 2 immune responses, significantly increased the level of FGF21 in the serum and liver after 24 h, but repeated administration of IL-33 attenuated this effect. Taken together, these data demonstrate that the IL-4/IL-13–STAT6 axis regulates metabolic homeostasis through the induction of FGF21 in the liver.

Temporal metabolic and transcriptomic characteristics crossing islets and liver reveal dynamic pathophysiology in diet-induced diabetes

To investigate the molecular mechanisms underlying islet dysfunction and insulin resistance in diet-induced diabetes, we conducted temporal RNA sequencing of tissues responsible for insulin secretion (islets) and action (liver) every 4 weeks in mice on high-fat (HFD) or chow diet for 24 weeks, linking to longitudinal profile of metabolic characteristics. The diverse responses of α, β, and δ cells to glucose and palmitate indicated HFD-induced dynamic deterioration of islet function from dysregulation to failure. Insulin resistance developed with variable time course in different tissues. Weighted gene co-expression network analysis and Ingenuity Pathway Analysis implicated islets and liver jointly programmed β-cell compensatory adaption via cell proliferation at early phase and irreversible islet dysfunction by inappropriate immune response at later stage, and identified interconnected molecules including growth differentiation factor 15. Frequencies of T cell subpopulation showed an early decrement in Tregs followed by increases in Th1 and Th17 cells during progression to diabetes.

Cellular and Intercellular Homeostasis in Adipose Tissue with Mitochondria-Specific Stress

Paracrine interactions are imperative for the maintenance of adipose tissue intercellular homeostasis, and intracellular organelle dysfunction results in local and systemic alterations in metabolic homeostasis. It is currently accepted that mitochondrial proteotoxic stress activates the mitochondrial unfolded protein response (UPRmt) in vitro and in vivo. The induction of mitochondrial chaperones and proteases during the UPRmt is a key cell-autonomous mechanism of mitochondrial quality control. The UPRmt also affects systemic metabolism through the secretion of cell non-autonomous peptides and cytokines (hereafter, metabokines). Mitochondrial function in adipose tissue plays a pivotal role in whole-body metabolism and human diseases. Despite continuing interest in the role of the UPRmt and quality control pathways of mitochondria in energy metabolism, studies on the roles of the UPRmt and metabokines in white adipose tissue are relatively sparse. Here, we describe the role of the UPRmt in adipose tissue, including adipocytes and resident macrophages, and the interactive roles of cell non-autonomous metabokines, particularly growth differentiation factor 15, in local adipose cellular homeostasis and systemic energy metabolism.

GDF15 as a central mediator for integrated stress response and a promising therapeutic molecule for metabolic disorders and NASH

BACKGROUND

Mitochondria is a key organelle for energy production and cellular adaptive response to intracellular and extracellular stresses. Mitochondrial stress can be evoked by various stimuli such as metabolic stressors or pathogen infection, which may lead to expression of 'mitokines' such as growth differentiation factor 15 (GDF15).

SCOPE OF REVIEW

This review summarizes the mechanism of GDF15 expression in response to organelle stress such as mitochondrial stress, and covers pathophysiological conditions or diseases that are associated with elevated GDF15 level. This review also illustrates the in vivo role of GDF15 expression in those stress conditions or diseases, and a potential of GDF15 as a therapeutic agent against metabolic disorders such as NASH.

MAJOR CONCLUSIONS

Mitochondrial unfolded protein response (UPRmt) is a critical process to recover from mitochondrial stress. UPRmt can induce expression of secretory proteins that can exert systemic effects (mitokines) as well as mitochondrial chaperons. GDF15 can have either protective or detrimental systemic effects in response to mitochondrial stresses, suggesting its role as a mitokine. Mounting evidence shows that GDF15 is also induced by stresses of organelles other than mitochondria such as endoplasmic reticulum (ER). GDF15 level is increased in serum or tissue of mice and human subjects with metabolic diseases such as obesity or NASH. GDF15 can modulate metabolic features of those diseases.

GENERAL SIGNIFICANCE

GDF15 play a role as an integrated stress response (ISR) beyond mitochondrial stress response. GDF15 is involved in the pathogenesis of metabolic diseases such as NASH, and also could be a candidate for therapeutic agent against those diseases.

Growth differentiation factor-15 and its role in diabetes and cardiovascular disease

Growth differentiation factor-15 (GDF-15) is cytokine involved in the regulation of multiple systems. Because it has regularly been shown to be increased in cardiovascular disease (CVD) and diabetes, it has been suggested that GDF-15 could be used as a biomarker for these diseases and their severity. However, several studies have demonstrated that GDF-15 has a protective role in regulation of inflammation, endothelial cell function, insulin sensitivity, weight gain, and is cardioprotective in myocardial infarction (MI). While GDF-15 has been implicated in the pathophysiology of many conditions including cancer, this review focuses on the potential functions of GDF-15 and signaling pathways implicated in its role regulating metabolism, insulin sensitivity, and the cardiovascular system.

Growth differentiation factor 15 protects against the aging-mediated systemic inflammatory response in humans and mice

Mitochondrial dysfunction is associated with aging-mediated inflammatory responses, leading to metabolic deterioration, development of insulin resistance, and type 2 diabetes. Growth differentiation factor 15 (GDF15) is an important mitokine generated in response to mitochondrial stress and dysfunction; however, the implications of GDF15 to the aging process are poorly understood in mammals. In this study, we identified a link between mitochondrial stress-induced GDF15 production and protection from tissue inflammation on aging in humans and mice. We observed an increase in serum levels and hepatic expression of GDF15 as well as pro-inflammatory cytokines in elderly subjects. Circulating levels of cell-free mitochondrial DNA were significantly higher in elderly subjects with elevated serum levels of GDF15. In the BXD mouse reference population, mice with metabolic impairments and shorter survival were found to exhibit higher hepatic Gdf15 expression. Mendelian randomization links reduced GDF15 expression in human blood to increased body weight and inflammation. GDF15 deficiency promotes tissue inflammation by increasing the activation of resident immune cells in metabolic organs, such as in the liver and adipose tissues of 20-month-old mice. Aging also results in more severe liver injury and hepatic fat deposition in Gdf15-deficient mice. Although GDF15 is not required for Th17 cell differentiation and IL-17 production in Th17 cells, GDF15 contributes to regulatory T-cell-mediated suppression of conventional T-cell activation and inflammatory cytokines. Taken together, these data reveal that GDF15 is indispensable for attenuating aging-mediated local and systemic inflammation, thereby maintaining glucose homeostasis and insulin sensitivity in humans and mice.

Conserved function of zebrafish (Danio rerio) Gdf15 as a sepsis tolerance mediator

GDF15 is frequently detected in patients suffering from various diseases, especially those associated with pro-inflammatory processes and/or metabolic disorders. Accordingly, sepsis, whose major complications are related to metabolic alterations and systemic inflammation, significantly increases the secretion of GDF15. Indeed, this cytokine could be considered a marker of sepsis severity. However, until the last several years, the involvement of GDF15 in these disorders had not been widely characterized. In mice, GDF15 was recently described as a pivotal inducer of sepsis tolerance by mediating metabolic alterations that reduce tissue damage. In this work we describe a zebrafish gdf15 gene. We found that gdf15 follows an expression pattern similar to that observed in mammals, being highly expressed in the liver and kidney and induced after pro-inflammatory stimuli. Moreover, larvae overexpressing gdf15 were more resistant to bacterial and viral challenges without affecting the pathogen load. Consequently, Gdf15 also protected zebrafish larvae against LPS-induced mortality. As in mice, zebrafish Gdf15 seems to induce sepsis tolerance by altering the metabolic parameters of the individuals.

New Role for Growth/Differentiation Factor 15 in the Survival of Transplanted Brown Adipose Tissues in Cooperation with Interleukin-6

To identify factors involved in the earliest phase of the differentiation of human embryonic stem cells (hESCs) into brown adipocytes (BAs), we performed multi-time point microarray analyses. We found that growth/differentiation factor 15 (GDF15) expressions were specifically upregulated within three days of differentiation, when expressions of immature hESC markers were sustained. Although GDF15 expressions continued to increase in the subsequent differentiation phases, GDF15-deficient hESCs differentiated into mature BAs (Day 10) without apparent abnormalities. In addition, GDF15-deficient mice had normal brown adipose tissue (BAT) and were metabolically healthy. Unexpectedly, we found that interleukin-6 (IL6) expression was significantly lowered in the BAT of GDF15^-/- mice. In addition, GDF15^-/- hESCs showed abortive IL6 expressions in the later phase (>Day 6) of the differentiation. Interestingly, GDF15 expression was markedly repressed throughout the whole course of the differentiation of IL6^-/- hESCs into BAs, indicating IL6 is essential for the induction of GDF15 in the differentiation of hESCs. Finally, intraperitoneally transplanted BAT grafts of GDF15^-/- donor mice, but not those of wild-type (WT) mice, failed in the long-term survival (12 weeks) in GDF15^-/- recipient mice. Collectively, GDF15 is required for long-term survival of BAT grafts by creating a mutual gene induction loop with IL6.

Gene Expression Profiling of Human Adipose Tissue Stem Cells during 2D versus 3D Adipogenesis

Much of the current understanding on molecular and cellular events of adipose developmental biology comes from monolayer cell culture models using preadipocyte cell lines, although in vivo adipose tissue consists of a much more complex three-dimensional microenvironment of diverse cell types, extracellular network, and tissue-specific morphological and functional features. Added to this fact, the preadipocytes, on which the adipogenesis mechanisms are mostly explored, possess some serious limitations (e.g., time of initial subculture and adipogenic differentiation time), which, perhaps, can efficiently be replaced with progenitor cells such as adipose tissue-derived stem cells (ASCs). With the objective of developing a better in vitro model for adipose developmental biology, this project involves gene expression profiling of human ASCs (hASCs) during their differentiation to adipocytes in a 2D versus 3D culture model. This transcriptional-level analysis revealed that gene expression patterns of adipogenesis-induced hASCs in a 3D self-assembled polypeptide hydrogel are relatively different from the 2D monolayered cells on plastic hard substrate. Moreover, analysis of adipogenic lineage progression 9 days after adipogenic induction shows earlier differentiation of hASCs in 2D over their 3D counterparts. However, differentiation in 2D shows some unexpected behavior in terms of gene expression, which does not seem to be related to adipogenic lineage specification. Since hASCs are already being used in clinical trials due to their therapeutic potential, it is important to have a clear understanding of the molecular mechanisms in an in vivo model microenvironment like the one presented here.

Growth/Differentiation Factor-15 (GDF-15): From Biomarker to Novel Targetable Immune Checkpoint

Growth/differentiation factor-15 (GDF-15), also named macrophage inhibitory cytokine-1, is a divergent member of the transforming growth factor β superfamily. While physiological expression is barely detectable in most somatic tissues in humans, GDF-15 is abundant in placenta. Elsewhere, GDF-15 is often induced under stress conditions, seemingly to maintain cell and tissue homeostasis; however, a moderate increase in GDF-15 blood levels is observed with age. Highly elevated GDF-15 levels are mostly linked to pathological conditions including inflammation, myocardial ischemia, and notably cancer. GDF-15 has thus been widely explored as a biomarker for disease prognosis. Mechanistically, induction of anorexia via the brainstem-restricted GDF-15 receptor GFRAL (glial cell-derived neurotrophic factor [GDNF] family receptor α-like) is well-documented. GDF-15 and GFRAL have thus become attractive targets for metabolic intervention. Still, several GDF-15 mediated effects (including its physiological role in pregnancy) are difficult to explain via the described pathway. Hence, there is a clear need to better understand non-metabolic effects of GDF-15. With particular emphasis on its immunomodulatory potential this review discusses the roles of GDF-15 in pregnancy and in pathological conditions including myocardial infarction, autoimmune disease, and specifically cancer. Importantly, the strong predictive value of GDF-15 as biomarker may plausibly be linked to its immune-regulatory function. The described associations and mechanistic data support the hypothesis that GDF-15 acts as immune checkpoint and is thus an emerging target for cancer immunotherapy.

Comprehensive Proteomics Analysis of Stressed Human Islets Identifies GDF15 as a Target for Type 1 Diabetes Intervention

Type 1 diabetes (T1D) results from the progressive loss of β cells, a process propagated by pro-inflammatory cytokine signaling that disrupts the balance between pro- and anti-apoptotic proteins. To identify proteins involved in this process, we performed comprehensive proteomics of human pancreatic islets treated with interleukin-1β and interferon-γ, leading to the identification of 11,324 proteins, of which 387 were significantly regulated by treatment. We then tested the function of growth/differentiation factor 15 (GDF15), which was repressed by the treatment. We found that GDF15 translation was blocked during inflammation, and it was depleted in islets from individuals with T1D. The addition of exogenous GDF15 inhibited interleukin-1β+interferon-γ-induced apoptosis of human islets. Administration of GDF15 reduced by 53% the incidence of diabetes in NOD mice. Our approach provides a unique resource for the identification of the human islet proteins regulated by cytokines and was effective in discovering a potential target for T1D therapy.

Inflammatory Signaling and Brown Fat Activity

Obesity is characterized by a state of chronic inflammation in adipose tissue mediated by the secretion of a range of inflammatory cytokines. In comparison to WAT, relatively little is known about the inflammatory status of brown adipose tissue (BAT) in physiology and pathophysiology. Because BAT and brown/beige adipocytes are specialized in energy expenditure they have protective roles against obesity and associated metabolic diseases. BAT appears to be is less susceptible to developing inflammation than WAT. However, there is increasing evidence that inflammation directly alters the thermogenic activity of brown fat by impairing its capacity for energy expenditure and glucose uptake. The inflammatory microenvironment can be affected by cytokines secreted by immune cells as well as by the brown adipocytes themselves. Therefore, pro-inflammatory signals represent an important component of the thermogenic potential of brown and beige adipocytes and may contribute their dysfunction in obesity.

Sequential Transcriptome Changes in the Penumbra after Ischemic Stroke

To investigate the changes in the expression of specific genes that occur during the acute-to-chronic post-stroke phase, we identified differentially expressed genes (DEGs) between naive cortical tissues and peri-infarct tissues at 1, 4, and 8 weeks after photothrombotic stroke. The profiles of DEGs were subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and gene ontology analyses, followed by string analysis of the protein-protein interactions (PPI) of the products of these genes. We found 3771, 536, and 533 DEGs at 1, 4, and 8 weeks after stroke, respectively. A marked decrease in biological-process categories, such as brain development and memory, and a decrease in neurotransmitter synaptic and signaling pathways were observed 1 week after stroke. The PPI analysis showed the downregulation of Dlg4, Bdnf, Gria1, Rhoa, Mapk8, and glutamatergic receptors. An increase in biological-process categories, including cell population proliferation, cell adhesion, and inflammatory responses, was detected at 4 and 8 weeks post-stroke. The KEGG pathways of complement and coagulation cascades, phagosomes, antigen processing, and antigen presentation were also altered. CD44, C1, Fcgr2b, Spp1, and Cd74 occupied a prominent position in network analyses. These time-dependent changes in gene profiles reveal the unique pathophysiological characteristics of stroke and suggest new therapeutic targets for this disease.

Association between MIC-1 and Type 2 Diabetes: A Combined Analysis

BACKGROUND AND OBJECTIVES

Type 2 diabetes mellitus (T2DM) is an epidemic disease that endangers human health seriously. Recently, a large number of reports have revealed that macrophage-inhibiting cytokine-1 (MIC-1) is linked with T2DM, but the results were inconclusive. The aim of this study was to perform bioinformatics analysis of the association between MIC-1 and T2DM.

MATERIAL AND METHODS

Datasets and relevant literatures were searched in Gene Expression Omnibus (GEO), PubMed, Google Scholar, and Web of Science till September 20, 2019. Expression levels of MIC-1 were extracted, pooled, and compared between T2DM cases and controls.

RESULTS

In summary, 11 GEO datasets and 3 articles with 421 T2DM cases and 711 controls were finally included. The expression level of MIC-1 was significantly higher in T2DM patients compared with controls, with a standard mean difference (SMD) of 0.54 and a 95% confidence interval (95% CI) of 0.24-0.83; in blood samples, the difference was still significant (SMD = 0.65; 95%CI = 0.24-1.06). Meanwhile, the expression level of MIC-1 plays a significant role in differentiating T2DM cases from controls; the combined sensitivity, specificity, and odds ratio were 0.83 (95%CI = 0.72-0.90), 0.59 (95%CI = 0.45-0.72), and 1.64 (95%CI = 1.35-1.99), respectively. The summary receiver operating characteristic (SROC) curve demonstrated that the area under the curve (AUC) was 0.81 (95%CI = 0.77-0.84).

CONCLUSION

Our results suggested that the expression levels of MIC-1 were significantly higher in T2DM patients in multiple tissues including blood samples.

Regulation of Systemic Glucose Homeostasis by T Helper Type 2 Cytokines

Obesity results in an inflammatory microenvironment in adipose tissue, leading to the deterioration of tissue protective mechanisms. Although recent studies suggested the importance of type 2 immunity in an anti-inflammatory microenvironment in adipose tissue, the regulatory effects of T helper 2 (Th2) cytokines on systemic metabolic regulation are not fully understood. Recently, we identified the roles of the Th2 cytokine (interleukin 4 [IL-4] and IL-13)-induced adipokine, growth differentiation factor 15 (GDF15), in adipose tissue in regulating systemic glucose metabolism via signal transducer and activator of transcription 6 (STAT6) activation. Moreover, we showed that mitochondrial oxidative phosphorylation is required to maintain these macrophage-regulating autocrine and paracrine signaling pathways via Th2 cytokine-induced secretion of GDF15. In this review, we discuss how the type 2 immune response and Th2 cytokines regulate metabolism in adipose tissue. Specifically, we review the systemic regulatory roles of Th2 cytokines in metabolic disease and the role of mitochondria in maintenance of type 2 responses in adipose tissue homeostasis.

The endocrine function of adipose tissues in health and cardiometabolic disease

In addition to their role in glucose and lipid metabolism, adipocytes respond differentially to physiological cues or metabolic stress by releasing endocrine factors that regulate diverse processes, such as energy expenditure, appetite control, glucose homeostasis, insulin sensitivity, inflammation and tissue repair. Both energy-storing white adipocytes and thermogenic brown and beige adipocytes secrete hormones, which can be peptides (adipokines), lipids (lipokines) and exosomal microRNAs. Some of these factors have defined targets; for example, adiponectin and leptin signal through their respective receptors that are expressed in multiple organs. For other adipocyte hormones, receptors are more promiscuous or remain to be identified. Furthermore, many of these hormones are also produced by other organs and tissues, which makes defining the endocrine contribution of adipose tissues a challenge. In this Review, we discuss the functional role of adipose tissue-derived endocrine hormones for metabolic adaptations to the environment and we highlight how these factors contribute to the development of cardiometabolic diseases. We also cover how this knowledge can be translated into human therapies. In addition, we discuss recent findings that emphasize the endocrine role of white versus thermogenic adipocytes in conditions of health and disease.

Exercise training promotes a GDF15-associated reduction in fat mass in older adults with obesity

Obesity is a major risk factor for metabolic disease. Growth differentiation factor 15 (GDF15) has shown promise as a weight loss agent for obesity in animal studies. In healthy lean humans, fasting plasma GDF15 increases after acute exercise. However, the role of GDF15 in human obesity and the response of plasma GDF15 to exercise training in patients with obesity is unknown. Here, 24 sedentary volunteers with obesity [age: 65 ± 1 yr; body mass index (BMI): 35.3 ± 0.9 kg/m²] participated in a supervised 12-wk aerobic exercise intervention: 1 h/day, 5 days/wk at ~85% maximum heart rate with controlled isocaloric diet. As a result, plasma GDF15 was significantly increased (PRE: 644.1 ± 42.6 pg/ml, POST: 704.4 ± 47.2 pg/ml, P < 0.01) after the exercise intervention. Inconsistent with animal models, ΔGDF15 was not correlated with change in weight, BMI, or resting energy expenditure. However, ΔGDF15 was correlated with a reduction in total fat mass (P < 0.05), abdominal fat mass (P < 0.05), and android fat mass (P ≤ 0.05). Participants with a positive GDF15 response to exercise had increased total fat oxidation (PRE: 0.25 ± 0.05 mg·kg^-1·min^-1, POST: 0.43 ± 0.07 mg·kg^-1·min^-1, P ≤ 0.05), metabolic flexibility [PRE: -0.01 ± 0.01 delta respiratory quotient (RQ), POST: 0.06 ± 0.01 delta RQ, P < 0.001], and insulin sensitivity (PRE: 0.33 ± 0.01 QUICKI index, POST: 0.34 ± 0.01 QUICKI index, P < 0.01), suggesting a link between GDF15 and fat mass loss as well as exercise-induced metabolic improvement in humans with obesity. We conclude that the exercise-induced increase in plasma GDF15 and the association with reduced fat mass may indicate a role for GDF15 as a therapeutic target for human obesity.

Prognostication of clinical outcomes in diabetes mellitus: Emerging role of cardiac biomarkers

Type 2 diabetes mellitus (T2DM) remains substantial health problem and one of the most prevalent metabolic diseases worldwide. The impact of T2DM on CV mortality and morbidity is embedded through a nature evolution of the disease and is modulated by numerous risk factors, such as hypertension, obesity, dyslipidemia. There is large body of evidence regarding use of the cardiac biomarkers to risk stratification at higher CV risk individuals who belongs to general population and cohort with established CV disease. Although T2DM patients have higher incidence of cardiac and vascular complications than the general population, whether cardiac biomarkers would be effective to risk stratification of the T2DM is not fully understood. The aim of the review is to summarize our knowledge regarding clinical implementation of cardiac biomarkers in risk assessment for T2DM patients. The role of natriuretic peptides, soluble ST2, galectin-3, growth differentiation factor-15, and cardiac troponins are widely discussed.

Biomarkers and clinical rating scales for sodium pyruvate therapy in patients with mitochondrial disease

Biomarkers and two clinical rating scales-the Japanese mitochondrial disease-rating scale (JMDRS) and Newcastle mitochondrial disease adult scale (NMDAS)-are clinically used when treating patients with mitochondrial disease. We explored the biomarker(s) and clinical rating scale(s) that are appropriate in preparing the protocol for a future clinical trial of sodium pyruvate (SP) therapy. A 48-week, prospective, single-centre, exploratory, clinical study enrolled 11 Japanese adult patients with genetically, biochemically, and clinically confirmed mitochondrial disease; they had intractable lactic acidosis and received SP (0.5 g/kg t.i.d. PO). Plasma concentrations of lactate and pyruvate, lateral ventricular levels of lactate, and serum concentrations of growth differentiation factor 15 (GDF15) and fibroblast growth factor 21 were measured at baseline and at weeks 12 and 48 of SP therapy. At week 48, plasma lactate (P = .004), the lactate/pyruvate ratio (P = .012), serum GDF15 (P = .020), and lateral ventricular lactate (P = .038) decreased significantly from the baseline values; the JMDRS and NMDAS scores did not decrease significantly, although the NMDAS overall score showed a strong tendency (P = .059). Two patients with end-stage MELAS at baseline died during SP therapy. The present study showed significant decreases in plasma and lateral ventricular lactate, the L/P ratio, and serum GDF15. Therefore, the protocol for a future clinical study of SP therapy in this patient population needs to include plasma and lateral ventricular lactate, the L/P ratio, and serum GDF15 as diagnostic indicators, and exclude patients with end-stage mitochondrial disease.

EZH2-Mediated Epigenetic Suppression of GDF15 Predicts a Poor Prognosis and Regulates Cell Proliferation in Non-Small-Cell Lung Cancer

Growth differentiation factor 15 (GDF15), a member of the TGF-β superfamily of cytokines, has been reported to exert very heterogeneous functions in various tumors. However, its expression and roles in mediating non-small-cell lung cancer (NSCLC) progression remain unknown. In this study, we found that GDF15 is downregulated in paired NSCLC tissues and correlated with poor clinical outcomes in NSCLC. A functional experiment demonstrated that overexpression of GDF15 significantly repressed NSCLC proliferation both in vitro and in vivo. Mechanistic studies reveal that inhibition of EZH2 expression prevented its binding to the GDF15 promoter region and reduced the trimethylation modification pattern of H3K27. Together, our data uncover that GDF15 is a direct target of EZH2 and, as a regulator of proliferation, might serve as a candidate prognostic biomarker and target for new therapies in human NSCLC.