GDF15 Is an Inflammation-Induced Central Mediator of Tissue Tolerance

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.

The effect of empagliflozin on growth differentiation factor 15 in patients with heart failure: a randomized controlled trial (Empire HF Biomarker)

Background

Plasma growth differentiation factor-15 (GDF-15) biomarker levels increase in response to inflammation and tissue injury, and increased levels of GDF-15 are associated with increased risk of mortality in patients with heart failure with reduced ejection fraction (HFrEF). Sodium-glucose cotransporter-2 (SGLT2) inhibitors, which improve outcome in HFrEF, have been shown to increase plasma GDF-15 in diabetic patients. We aimed to investigate the effect of empagliflozin on GDF-15 in HFrEF patients.

Methods

This Empire HF Biomarker substudy was from the multicentre, randomized, double-blind, placebo-controlled Empire HF trial that included 190 patients from June 29, 2017, to September 10, 2019. Stable ambulatory HFrEF patients with ejection fraction of ≤ 40% were randomly assigned (1:1) to empagliflozin 10 mg once daily, or matching placebo for 12 weeks. Changes from baseline to 12 weeks in plasma levels of GDF-15, high-sensitive C-reactive protein (hsCRP), and high-sensitive troponin T (hsTNT) were assessed.

Results

A total of 187 patients who were included in this study, mean age was 64 ± 11 years; 85% male, 12% with type 2 diabetes, mean ejection fraction 29 ± 8, with no differences between the groups. Baseline median plasma GDF-15 was 1189 (918–1720) pg/mL with empagliflozin, and 1299 (952–1823) pg/mL for placebo. Empagliflozin increased plasma GDF-15 compared to placebo (adjusted between-groups treatment effect; ratio of change (1·09 [95% confidence interval (CI), 1.03–1.15]: p = 0.0040). The increase in plasma GDF15 was inversely associated with a decrease in left ventricular end-systolic (R = – 0.23, p = 0.031), and end-diastolic volume (R = – 0.29, p = 0.0066). There was no change in plasma hsCRP (1.09 [95%CI, 0.86–1.38]: p = 0.48) or plasma hsTNT (1.07 [95%CI, 0.97–1.19]: p = 0.18) compared to placebo. Patients with diabetes and treated with metformin demonstrated no increase in plasma GDF-15 with empagliflozin, p for interaction = 0·01.

Conclusion

Empagliflozin increased plasma levels of GDF-15 in patients with HFrEF, with no concomitant increase in hsTNT nor hsCRP.

Trial registration: The Empire HF trial is registered with ClinicalTrials.gov, NCT03198585.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01463-2.

Growth differentiation factor 15 (GDF15) is associated with non-alcoholic fatty liver disease (NAFLD) in youth with overweight or obesity

OBJECTIVE

Growth differentiation factor 15 (GDF15) has been associated with food intake and weight regulation in response to metabolic stress. In animal models, it has been noted that it may play a role in the progression of non-alcoholic fatty liver disease (NAFLD), the leading cause of chronic liver disease in children.

DESIGN

In the current study, we explored the association of circulating plasma concentrations of GDF15 with NAFLD in youth with overweight/obesity, and whether changes in plasma concentrations in GDF15 parallel the changes in intrahepatic fat content (HFF%) over time.

METHODS

Plasma GDF15 concentrations were measured by ELISA in 175 youth with overweight/obesity who underwent an oral glucose tolerance test (OGTT) and magnetic resonance imaging (MRI) to assess intrahepatic, visceral, and subcutaneous fat. Baseline fasting GDF15 concentrations were measured in twenty-two overweight/obese youth who progressed (n = 11) or regressed (n = 11) in HFF% by more than 30% of original over a 2-year period.

RESULTS

Youth with NAFLD had significantly higher plasma concentrations of GDF15 than those without NAFLD, independent of age, sex, ethnicity, BMI z-score (BMIz), and visceral fat (P = 0.002). During the OGTT, there was a decline in plasma GDF15 concentrations from 0 to 60 min, but GDF15 concentrations returned to basal levels by the end of the study. There was a statistically significant association between change in HFF% and change in GDF15 (P = 0.008; r2 = 0.288) over ~2 years of follow-up.

CONCLUSIONS

These data suggest that plasma GDF15 concentrations change with change in intrahepatic fat content in youth with overweight/obesity and may serve as a biomarker for NAFLD in children.

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.

Growth differentiation factor-15 prevents glucotoxicity and connexin-36 downregulation in pancreatic beta-cells

Pancreatic beta cell dysfunction is a hallmark of type 2 diabetes. Growth differentiation factor 15 (GDF15), which is an energy homeostasis regulator, has been shown to improve several metabolic parameters in the context of diabetes. However, its effects on pancreatic beta-cell remain to be identified. We, therefore, performed experiments using cell models and histological sectioning of wild-type and knock-out GDF15 mice to determine the effect of GDF15 on insulin secretion and cell viability. A bioinformatics analysis was performed to identify GDF15-correlated genes. GDF15 prevents glucotoxicity-mediated altered glucose-stimulated insulin secretion (GSIS) and connexin-36 downregulation. Inhibition of endogenous GDF15 reduced GSIS in cultured mouse beta-cells under standard conditions while it had no impact on GSIS in cells exposed to glucolipotoxicity, which is a diabetogenic condition. Furthermore, this inhibition exacerbated glucolipotoxicity-reduced cell survival. This suggests that endogenous GDF15 in beta-cell is required for cell survival but not GSIS in the context of glucolipotoxicity.

LPS induces rapid increase in GDF15 levels in mice, rats, and humans but is not required for anorexia in mice

Growth differentiation factor 15 (GDF15), a TGFβ superfamily cytokine, acts through its receptor, cell line-derived neurotrophic factorfamily receptor α-like (GFRAL), to suppress food intake and promote nausea. GDF15 is broadly expressed at low levels but increases in states of disease such as cancer, cachexia, and sepsis. Whether GDF15 is necessary for inducing sepsis-associated anorexia and body weight loss is currently unclear. To test this we used a model of moderate systemic infection in GDF15KO and GFRALKO mice with lipopolysaccharide (LPS) treatment to define the role of GDF15 signaling in infection-mediated physiologic responses. Since physiological responses to LPS depend on housing temperature, we tested the effects of subthermoneutral and thermoneutral conditions on eliciting anorexia and inducing GDF15. Our data demonstrate a conserved LPS-mediated increase in circulating GDF15 levels in mouse, rat, and human. However, we did not detect differences in LPS-induced anorexia between WT and GDF15KO or GFRALKO mice. Furthermore, there were no differences in anorexia or circulating GDF15 levels at either thermoneutral or subthermoneutral housing conditions in LPS-treated mice. These data demonstrate that GDF15 is not necessary to drive food intake suppression in response to moderate doses of LPS.NEW & NOTEWORTHY Although many responses to LPS depend on housing temperature, the anorexic response to LPS does not. LPS results in a potent and rapid increase in circulating levels of GDF15 in mice, rats, and humans. Nevertheless, GDF15 and its receptor (GFRAL) are not required for the anorexic response to systemic LPS administration. The anorexic response to LPS likely involves a myriad of complex physiological alterations.

Camptothecin effectively treats obesity in mice through GDF15 induction

Elevated circulating levels of growth differentiation factor 15 (GDF15) have been shown to reduce food intake and lower body weight through activation of hindbrain receptor glial-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL) in rodents and nonhuman primates, thus endogenous induction of this peptide holds promise for obesity treatment. Here, through in silico drug-screening methods, we found that small molecule Camptothecin (CPT), a previously identified drug with potential antitumor activity, is a GDF15 inducer. Oral CPT administration increases circulating GDF15 levels in diet-induced obese (DIO) mice and genetic ob/ob mice, with elevated Gdf15 expression predominantly in the liver through activation of integrated stress response. In line with GDF15's anorectic effect, CPT suppresses food intake, thereby reducing body weight, blood glucose, and hepatic fat content in obese mice. Conversely, CPT loses these beneficial effects when Gdf15 is inhibited by a neutralizing antibody or AAV8-mediated liver-specific knockdown. Similarly, CPT failed to reduce food intake and body weight in GDF15's specific receptor GFRAL-deficient mice despite high levels of GDF15. Together, these results indicate that CPT is a promising anti-obesity agent through activation of GDF15-GFRAL pathway.

Elevated Levels of Growth/Differentiation Factor-15 in the Aqueous Humor and Serum of Glaucoma Patients

Dysregulated levels of growth/differentiation factor-15 (GDF15), a divergent member of the transforming growth factor-beta super family, have been found to be associated with the pathology of various diseases. In this study, we evaluated the levels of GDF15 in aqueous humor (AH) and serum samples derived from primary open-angle glaucoma (POAG) and age- and gender-matched non-glaucoma (cataract) patients to assess the plausible association between GDF15 and POAG. GDF15 levels were determined using an enzyme-linked immunosorbent assay, and data analysis was performed using the Wilcoxon rank sum test, or the Kruskal–Wallis test and linear regression. GDF15 levels in the AH (n = 105) of POAG patients were significantly elevated (by 7.4-fold) compared to cataract patients (n = 117). Serum samples obtained from a subgroup of POAG patients (n = 41) also showed a significant increase in GDF15 levels (by 50%) compared to cataract patients. GDF15 levels were elevated in male, female, African American, and Caucasian POAG patients. This study reveals a significant and marked elevation of GDF15 levels in the AH of POAG patients compared to non-glaucoma cataract control patients. Although serum GDF15 levels were also elevated in POAG patients, the magnitude of difference was much smaller relative to that found in the AH.

Circulating cardiomyocyte-derived extracellular vesicles reflect cardiac injury during systemic inflammatory response syndrome in mice

The release of extracellular vesicles (EVs) is increased under cellular stress and cardiomyocyte damaging conditions. However, whether the cardiomyocyte-derived EVs eventually reach the systemic circulation and whether their number in the bloodstream reflects cardiac injury, remains unknown. Wild type C57B/6 and conditional transgenic mice expressing green fluorescent protein (GFP) by cardiomyocytes were studied in lipopolysaccharide (LPS)-induced systemic inflammatory response syndrome (SIRS). EVs were separated both from platelet-free plasma and from the conditioned medium of isolated cardiomyocytes of the left ventricular wall. Size distribution and concentration of the released particles were determined by Nanoparticle Tracking Analysis. The presence of GFP + cardiomyocyte-derived circulating EVs was monitored by flow cytometry and cardiac function was assessed by echocardiography. In LPS-treated mice, systemic inflammation and the consequent cardiomyopathy were verified by elevated plasma levels of TNFα, GDF-15, and cardiac troponin I, and by a decrease in the ejection fraction. Furthermore, we demonstrated elevated levels of circulating small- and medium-sized EVs in the LPS-injected mice. Importantly, we detected GFP+ cardiomyocyte-derived EVs in the circulation of control mice, and the number of these circulating GFP+ vesicles increased significantly upon intraperitoneal LPS administration (P = 0.029). The cardiomyocyte-derived GFP+ EVs were also positive for intravesicular troponin I (cTnI) and muscle-associated glycogen phosphorylase (PYGM). This is the first direct demonstration that cardiomyocyte-derived EVs are present in the circulation and that the increased number of cardiac-derived EVs in the blood reflects cardiac injury in LPS-induced systemic inflammation (SIRS).

Exploratory Phase II Multicenter, Open-Label, Clinical Trial of ST266, a Novel Secretome for Treatment of Persistent Corneal Epithelial Defects

Objective

An exploratory phase II, multicenter, open-label, clinical trial (NCT03687632) was conducted to evaluate the safety and effectiveness in treating persistent corneal epithelial defects (PEDs) with ST266, a proprietary novel multi-cytokine platform biologic solution secreted by cultured Amnion-derived Multipotent Progenitor (AMP) cells.

Methods

Subjects with a PED were treated with ST266 eye drops 4 times daily for 28 days, then followed for 1 week. Safety was assessed by monitoring of adverse events (AEs) and serious adverse events (SAEs). Efficacy was assessed by measuring the area of the PED by slit lamp biomicroscopy. Tolerability of ST266, percentage of eyes with complete healing, reduction in area of the epithelial defect, and maintenance of a reduction in the area of the epithelial defect 7 days after treatment were recorded.

Results

Thirteen patients were enrolled into the trial at one of eight sites. The first patient withdrew after 5 days. The remaining 12 patients with PEDs with median duration of 39 days (range = 12 to 393 days) completed treatment. Ten of the 12 eyes had been refractory to treatment with various conventional therapies prior to enrollment. After 28 days of treatment, there was a significant decrease in mean PED area compared with baseline (66.4% ± 35.3%, P = 0.001). At follow-up, 1 week after completion of treatment, on day 35, the PED area was further reduced by 78.8% ± 37.5% (P = 0.01) compared with baseline. During 28 days of treatment, 5 eyes (41.7%) had complete wound closure. There were no AEs of concern thought to be related to the drug, and no SAEs were noted.

Conclusions

In this trial, we found ST266 eye drops might promote corneal epithelization, thereby reducing the PED area, including in refractory cases in a wide range of etiologies. ST266 was well-tolerated by most patients.

GDF15 in Appetite and Exercise: Essential Player or Coincidental Bystander?

Growth differentiation factor 15 (GDF15) has recently moved to the forefront of metabolism research. When administered pharmacologically, GDF15 reduces food intake and lowers body weight via the hindbrain-situated receptor GFRAL (glial cell-derived neurotrophic factor family receptor alpha-like). Endogenous GDF15 is a ubiquitous cellular stress signal that can be produced and secreted by a variety of cell types. Circulating levels are elevated in a series of disease states, but also in response to exogenous agents such as metformin, colchicine, AICAR, and cisplatin. Recently, exercise has emerged as a relevant intervention to interrogate GDF15 physiology. Prolonged endurance exercise increases circulating GDF15 to levels otherwise associated with certain pathological states and in response to metformin treatment. The jury is still out on whether GDF15 is a functional "exerkine" mediating organ-to-brain crosstalk or whether it is a coincidental bystander. In this review, we discuss the putative physiological implication of exercise-induced GDF15, focusing on the potential impact on appetite and metabolism.

RET receptor signaling: Function in development, metabolic disease, and cancer

The RET proto-oncogene encodes a receptor tyrosine kinase whose alterations are responsible for various human cancers and developmental disorders, including thyroid cancer, non-small cell lung cancer, multiple endocrine neoplasia type 2, and Hirschsprung's disease. RET receptors are physiologically activated by glial cell line-derived neurotrophic factor (GDNF) family ligands that bind to the coreceptor GDNF family receptor α (GFRα). Signaling via the GDNF/GFRα1/RET ternary complex plays crucial roles in the development of the enteric nervous system, kidneys, and urinary tract, as well as in the self-renewal of spermatogonial stem cells. In addition, another ligand, growth differentiation factor-15 (GDF15), has been shown to bind to GFRα-like and activate RET, regulating body weight. GDF15 is a stress response cytokine, and its elevated serum levels affect metabolism and anorexia-cachexia syndrome. Moreover, recent development of RET-specific kinase inhibitors contributed significantly to progress in the treatment of patients with RET-altered cancer. This review focuses on the broad roles of RET in development, metabolic diseases, and cancer.

GDF-15 as a Therapeutic Target of Diabetic Complications Increases the Risk of Gallstone Disease: Mendelian Randomization and Polygenic Risk Score Analysis

Growth differentiation factor 15 (GDF-15) levels have been revealed as a robust biomarker for metformin use. We conducted Mendelian randomization (MR) analysis to explore the association between GDF-15 and gallstone disease to inform potential therapeutic effects targeting GDF-15. Four genetic variants associated with GDF-15 levels at p < 5 × 10^-8 were selected as instrumental variables from a genome-wide association meta-analysis including 21,758 individuals. Two-sample MR analysis was conducted using summary-level data from UK Biobank (10,520 gallstone cases and 350,674 controls) and FinnGen consortium (19,023 gallstone cases and 195,144 controls). Polygenic risk score analysis using individual-level data in UK biobank was performed to complement the MR findings by examining the non-linearity of the association. Diabetic complications were taken as positive controls to validate the therapeutic effect of targeting GDF-15. Linear and nonlinear associations between genetically predicted GDF-15 levels and gallstones were estimated with stratification by the diabetic status. In the two-sample MR analysis, the odds ratio (OR) of gallstones was 1.09 (95% confidence interval (CI), 1.03-1.15; p = 0.001) for one standard deviation increase in genetically predicted GDF-15 levels in the meta-analysis of two datasets. Polygenic risk score analysis found this association to be U-shaped (p = 0.037). The observed association was predominantly seen in nondiabetic population (OR = 1.11, 95% CI: 1.01-1.21; p = 0.003). An inverse association between genetically predicted GDF-15 levels and diabetic complications (OR = 0.77, 95% CI: 0.62-0.96; p = 0.023) was observed, validating the potential therapeutic effects of targeting GDF-15 levels. This MR study indicates that the increased risk of gallstone disease should be taken into account when considering GDF-15 as a therapeutic target for diabetic complications.

Circulating Levels of Apelin, GDF-15 and Sarcopenia: Lack of Association in the MAPT Study

OBJECTIVES

Apelin and GDF-15 have been proposed as biomarkers of age-related sarcopenia but evidence in human models is scarce. This study aimed to explore the associations between blood apelin and GDF-15 with sarcopenia incidence and the evolution of sarcopenia components over two years in older adults >70 years.

DESIGN

Secondary longitudinal analysis of the Multidomain Alzheimer Preventive Trial.

PARTICIPANTS

Older adults (>70 years) attending primary care centers in France and Monaco.

SETTING

Community.

MEASUREMENTS

Serum Apelin (pg/mL) and plasma GDF-15 (pg/mL) were measured. Outcomes included sarcopenia defined by the European Working Group on Sarcopenia in Older People (EWGSOP) and its determinants (appendicular lean mass [ALM] evaluated through a Dual-energy X-ray Absorptiometry (DXA) scan, handgrip strength (HGS) and the 4-meter gait speed) measured over 2 years. Linear mixed models and logistic regression were used to explore the longitudinal associations.

RESULTS

We included 168 subjects from MAPT (median age=76y, IQR=73-79; 78% women). Serum apelin was not significantly associated with sarcopenia incidence (OR=1.001;95%CI=1.000,1.001;p-value>0.05 in full-adjusted models) nor with ALM (β=-5.8E-05;95%CI=-1.0E-04,2.12E-04;p>0.05), HGS (β=-1.1E-04;95%CI=-5.0E-04,2.8E-04;p>0.05), and GS (β=-5.1E-06;95%CI=-1.0E-05,2.0E-05;p>0.05) in fully adjusted models. Similarly, plasma GDF-15 was not associated with both the incidence of sarcopenia (OR=1.001,95%CI=1.000,1.002,p>0.05) and the evolution of its determinants ([ALM, β=2.1E-05;95%CI=-2.6E-04,3.03E-04;p>0.05], HGS [β=-5.9E-04;95%CI=-1.26E-03,8.1E-05; p>0.05] nor GS [β=-2.6E-06;95%CI=-3.0E-05, 2.3E-05;p>0.05]) in fully adjusted models.

CONCLUSIONS

Blood apelin and GDF-15 were not associated with sarcopenia incidence or with the evolution of sarcopenia components over a 2-year follow-up in community-dwelling older adults. Well-powered longitudinal studies are needed to confirm or refute our findings.

Arachidonic Acid in Follicular Fluid of PCOS Induces Oxidative Stress in a Human Ovarian Granulosa Tumor Cell Line (KGN) and Upregulates GDF15 Expression as a Response

Polycystic ovarian ovary syndrome (PCOS) is the main cause of ovulatory infertility and a common reproductive endocrine disease of women in reproductive age. In addition, nearly half of PCOS patients are associated with obesity, and their total free fatty acids tend to increase. Arachidonic acid (AA) is a polyunsaturated fatty acid. Oxidation products of AA reacting with various enzymes[cyclooxygenases (COX), lipoxygenases (LOX), cytochrome P450s (CYP)] can change cellular mitochondrial distribution and calcium ion concentration, and increase reactive oxygen species (ROS) production. In this study, we analyzed the follicular fluid fatty acids and found higher levels of C20:4n6 (AA) in PCOS patients than in normal control subjects. Also, to determine whether AA induces oxidative stress (OS) in the human ovarian granulosa tumor cell line (KGN) and affects its function, we treated KGN cells with or without reduced glutathione (GSH) and then stimulated them with AA. The results showed that AA significantly reduced the total antioxidant capacity (TAC) and activity of antioxidant enzymes and increased the malondialdehyde (MDA), ROS and superoxide anion(O_2-)levels in KGN cells. In addition, AA was also found to impair the secretory and mitochondrial functions of KGN cells and induce their apoptosis. We further investigated the downstream genes affected by AA in KGN cells and its mechanism of action. We found that AA upregulated the expression of growth differentiation factor 15 (GDF15), which had a protective effect on inflammation and tissue damage. Therefore, we investigated whether AA-induced OS in KGN cells upregulates GDF15 expression as an OS response.Through silencing of GDF15 and supplementation with recombinant GDF15 (rGDF15), we found that GDF15, expressed as an OS response, protected KGN cells against AA-induced OS effects, such as impairment of secretory and mitochondrial functions and apoptosis. Therefore, this study suggested that AA might induce OS in KGN cells and upregulate the expression of GDF15 as a response to OS.

Circulating FGF21 and GDF15 as Biomarkers for Screening, Diagnosis, and Severity Assessment of Primary Mitochondrial Disorders in Children

BACKGROUND

Primary mitochondrial disorders (PMDs) are a diagnostic challenge for paediatricians, and identification of reliable and easily measurable biomarkers has become a high priority. This study aimed to investigate the role of serum fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15) in children with PMDs.

METHODS

We analysed serum FGF21 and GDF15 concentrations by enzyme-linked immunosorbent assay (ELISA) in children with PMDs, patients with non-mitochondrial neuromuscular disorders (NMDs), and aged-matched healthy children, and compared them with serum lactate and ratio of lactate and pyruvate (L/P). We also evaluated correlations between these biomarkers and the phenotype, genotype, and severity of PMDs.

RESULTS

The median serum GDF15 and FGF21 concentrations were significantly elevated in fifty-one patients with PMDs (919.46 pg/ml and 281.3 pg/ml) compared with those of thirty patients with NMDs (294.86 pg/ml and 140.51 pg/ml, both P < 0.05) and fifty healthy controls (221.21 pg/ml and 85.02 pg/ml, both P < 0.05). The area under the curve of GDF15 for the diagnosis of PMDs was 0.891, which was higher than that of the other biomarkers, including FGF21 (0.814), lactate (0.863) and L/P ratio (0.671). Calculated by the maximum Youden index, the critical value of GDF15 was 606.369 pg/ml, and corresponding sensitivity and specificity were 74.5and 100%. In the PMD group, FGF21 was significantly correlated with International Paediatric Mitochondrial Disease Scale (IPMDS) score. The levels of GDF15 and FGF21 were positively correlated with age, critical illness condition, and multisystem involvement but were not correlated with syndromic/non-syndromic PMDs, different mitochondrial syndromes, nuclear DNA/mitochondrial DNA pathogenic variants, gene functions, or different organ/system involvement.

CONCLUSION

Regardless of clinical phenotype and genotype, circulating GDF15 and FGF21 are reliable biomarkers for children with PMDs. GDF15 can serve as a screening biomarker for diagnosis, and FGF21 can serve as a severity biomarker for monitoring.

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.

Growth differentiation factor-15 as a modulator of bone and muscle metabolism

This study aims to clarify the potential role of growth differentiation factor-15 (GDF-15) as a myokine in bone metabolism and muscle function in females with osteoporosis. In total, 45 female participants (71.0 ± 8.5 years) with distal radius fractures were recruited. Participants were classified as healthy/osteopenic (n = 28) (CON) or osteoporotic (n = 17) (OP) according to their T-score from the areal bone mineral density (aBMD) of the femoral neck. Body mass index, upper arm and calf circumferences, and handgrip strength were assessed. Total hip, femoral neck, and lumbar spine aBMD was measured via dual-energy x-ray absorptiometry. The focal bone quality of the distal radius was evaluated via 3D reconstructed computed tomographic images. Serum levels of GDF-15, insulin-like growth factor-1, and inflammatory markers such as tumor necrosis factor-α (TNF-α), interleukin-6, and interleukin-1β (IL-1β), as well as the corresponding mRNA levels in the pronator quadratus muscle were determined. Participants in the OP group had higher serum GDF-15 levels than those in the CON group. The mRNA levels of GDF-15, IL-1β, and TNF-α in the pronator quadratus muscle were significantly higher in the OP group than in the CON one. Levels of both serum GDF-15 and GDF-15 mRNA in muscle were positively correlated with age and negatively associated with the aBMD of the total hip and focal bone quality of the distal radius. Handgrip power was not correlated with circulating GDF-15 levels but was correlated with circumferences of the upper arm and calf, and levels of GDF-15 mRNA in muscle specimens. The mRNA levels of GDF-15 were correlated with those of inflammatory cytokines such as TNF-α and IL-1β. The mRNA levels of TNF-α were associated with circumferences of the upper arm and calf and with the aBMD of the total hip. The mRNA levels of GDF-15 in muscle were correlated with serum levels of GDF-15 and TNF-α. GDF-15 may have associations with bone metabolism in humans via paracrinological and endocrinological mechanisms. Maintenance of muscle mass and function would be influenced more by GDF-15 in muscle than by circulating GDF-15. The role of GDF-15 in bone metabolism and muscle homeostasis could be related to inflammatory responses.

Microbiota and body weight control: Weight watchers within?

Background

Despite several decades of research, managing body weight remains an unsolved clinical problem. Health problems associated with dysregulated body weight, such as obesity and cachexia, exhibit several gut microbiota alterations. There is an increased interest in utilising the gut microbiota for body weight control, as it responds to intervention and plays an important role in energy extraction from food, as well as biotransformation of nutrients.

Scope of the review

This review provides an overview of the role of the gut microbiota in the physiological and metabolic alterations observed in two body weight dysregulation-related disorders, namely obesity and cachexia. Second, we assess the available evidence for different strategies, including caloric restriction, intermittent fasting, ketogenic diet, bariatric surgery, probiotics, prebiotics, synbiotics, high-fibre diet, and fermented foods – effects on body weight and gut microbiota composition. This approach was used to give insights into the possible link between body weight control and gut microbiota configuration.

Major conclusions

Despite extensive associations between body weight and gut microbiota composition, limited success could be achieved in the translation of microbiota-related interventions for body weight control in humans. Manipulation of the gut microbiota alone is insufficient to alter body weight and future research is needed with a combination of strategies to enhance the effects of lifestyle interventions.

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The gut microbiota is involved in the control of nutrient availability, appetite, and body weight.

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Both obesity and cachexia are associated with altered gut microbiota.

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Specific dietary and surgical approaches positively impact body weight and gut microbiota.

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Manipulation of the gut microbiota alone is insufficient to alter body weight in humans.

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.

GDF15 Supports the Inflammatory Response of PdL Fibroblasts Stimulated by P. gingivalis LPS and Concurrent Compression

Periodontitis is characterized by bacterially induced inflammatory destruction of periodontal tissue. This also affects fibroblasts of the human periodontal ligaments (HPdLF), which play a coordinating role in force-induced tissue and alveolar bone remodeling. Excessive inflammation in the oral tissues has been observed with simultaneous stimulation by pathogens and mechanical forces. Recently, elevated levels of growth differentiation factor 15 (GDF15), an immuno-modulatory member of the transforming growth factor (TGFB) superfamily, were detected under periodontitis-like conditions and in force-stressed PdL cells. In view of the pleiotropic effects of GDF15 in various tissues, this study aims to investigate the role of GDF15 in P. gingivalis-related inflammation of HPdLF and its effect on the excessive inflammatory response to concurrent compressive stress. To this end, the expression and secretion of cytokines (IL6, IL8, COX2/PGE2, TNFα) and the activation of THP1 monocytic cells were analyzed in GDF15 siRNA-treated HPdLF stimulated with P. gingivalis lipopolysaccharides alone and in combination with compressive force. GDF15 knockdown significantly reduced cytokine levels and THP1 activation in LPS-stimulated HPdLF, which was less pronounced with additional compressive stress. Overall, our data suggest a pro-inflammatory role for GDF15 in periodontal disease and demonstrate that GDF15 partially modulates the force-induced excessive inflammatory response of PdLF under these conditions.

Titanium Nanoparticles Enhance Production and Suppress Stabilin-1-Mediated Clearance of GDF-15 in Human Primary Macrophages

Macrophages are key innate immune cells that mediate implant acceptance or rejection. Titanium implants degrade over time inside the body, which results in the release of implant wear-off particles. Titanium nanoparticles (TiNPs) favor pro-inflammatory macrophage polarization (M1) and lower tolerogenic activation (M2). GDF-15 regulates immune tolerance and fibrosis and is endocytosed by stabilin-1. How TiNPs affect the healing activities of macrophages and their release of circulating cytokines is an open question in regenerative medicine. In this study for the first time, we identified the transcriptional program induced and suppressed by TiNPs in human pro-inflammatory and healing macrophages. Microarray analysis revealed that TiNPs altered the expression of 5098 genes in M1 (IFN-γ-stimulated) and 4380 genes in M2 (IL-4–stimulated) macrophages. 1980 genes were differentially regulated in both M1 and M2. Affymetrix analysis, confirmed by RT-PCR, demonstrated that TiNPs upregulate expression of GDF-15 and suppress stabilin-1, scavenger receptor of GDF-15. TiNPs also significantly stimulated GDF-15 protein secretion in inflammatory and healing macrophages. Flow cytometry demonstrated, that scavenging activity of stabilin-1 was significantly suppressed by TiNPs. Confocal microscopy analysis showed that TiNPs impair internalization of stabilin-1 ligand acLDL and its transport to the endocytic pathway. Our data demonstrate that TiNPs have a dual effect on the GDF-15/stabilin-1 interaction in macrophage system, by increasing the production of GDF-15 and suppressing stabilin-1-mediated clearance function. In summary, this process can result in a significant increase of GDF-15 in the extracellular space and in circulation leading to unbalanced pro-fibrotic reactions and implant complications.

The spectrum of inflammatory responses

[Figure: see text].

Dysregulated Inflammation During Obesity: Driving Disease Severity in Influenza Virus and SARS-CoV-2 Infections

Acute inflammation is a critical host defense response during viral infection. When dysregulated, inflammation drives immunopathology and tissue damage. Excessive, damaging inflammation is a hallmark of both pandemic influenza A virus (IAV) infections and Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) infections. Chronic, low-grade inflammation is also a feature of obesity. In recent years, obesity has been recognized as a growing pandemic with significant mortality and associated costs. Obesity is also an independent risk factor for increased disease severity and death during both IAV and SARS-CoV-2 infection. This review focuses on the effect of obesity on the inflammatory response in the context of viral respiratory infections and how this leads to increased viral pathology. Here, we will review the fundamentals of inflammation, how it is initiated in IAV and SARS-CoV-2 infection and its link to disease severity. We will examine how obesity drives chronic inflammation and trained immunity and how these impact the immune response to IAV and SARS-CoV-2. Finally, we review both medical and non-medical interventions for obesity, how they impact on the inflammatory response and how they could be used to prevent disease severity in obese patients. As projections of global obesity numbers show no sign of slowing down, future pandemic preparedness will require us to consider the metabolic health of the population. Furthermore, if weight-loss alone is insufficient to reduce the risk of increased respiratory virus-related mortality, closer attention must be paid to a patient’s history of health, and new therapeutic options identified.

GDF15: an emerging modulator of immunity and a strategy in COVID-19 in association with iron metabolism

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a pandemic of respiratory and cardiovascular diseases, known as coronavirus disease 2019 (COVID-19). SARS-CoV-2 encodes the structural proteins spike (S), envelope (E), membrane (M), and nucleocapsid (N). The receptor-binding domain on the surface subunit S1 is responsible for attachment of the virus to angiotensin (Ang)-converting enzyme 2 (ACE2), which is highly expressed in host cells. The cytokine storm observed in patients with COVID-19 contributes to the endothelial vascular dysfunction, which can lead to acute respiratory distress syndrome, multiorgan failure, alteration in iron homeostasis, and death. Growth and differentiation factor 15 (GDF15), which belongs to the transforming growth factor-β (TGF-β) superfamily of proteins, has a pivotal role in the development and progression of diseases because of its role as a metabolic regulator. In COVID-19, GDF15 activity increases in response to tissue damage. GDF15 appears to be a strong predictor of poor outcomes in patients critically ill with COVID-19 and acts as an 'inflammation-induced central mediator of tissue tolerance' via its metabolic properties. In this review, we examine the potential properties of GDF15 as an emerging modulator of immunity in COVID-19 in association with iron metabolism. The virus life cycle in host cell provides potential targets for drug therapy.

Mitochondrial complex II in intestinal epithelial cells regulates T cell-mediated immunopathology

Intestinal epithelial cell (IEC) damage by T cells contributes to graft-versus-host disease, inflammatory bowel disease and immune checkpoint blockade-mediated colitis. But little is known about the target cell-intrinsic features that affect disease severity. Here we identified disruption of oxidative phosphorylation and an increase in succinate levels in the IECs from several distinct in vivo models of T cell-mediated colitis. Metabolic flux studies, complemented by imaging and protein analyses, identified disruption of IEC-intrinsic succinate dehydrogenase A (SDHA), a component of mitochondrial complex II, in causing these metabolic alterations. The relevance of IEC-intrinsic SDHA in mediating disease severity was confirmed by complementary chemical and genetic experimental approaches and validated in human clinical samples. These data identify a critical role for the alteration of the IEC-specific mitochondrial complex II component SDHA in the regulation of the severity of T cell-mediated intestinal diseases.

Metabolomic Analysis of Diverse Mice Reveals Hepatic Arginase-1 as Source of Plasma Arginase in Plasmodium chabaudi Infection

Infections disrupt host metabolism, but the factors that dictate the nature and magnitude of metabolic change are incompletely characterized. To determine how host metabolism changes in relation to disease severity in murine malaria, we performed plasma metabolomics on eight Plasmodium chabaudi-infected mouse strains with diverse disease phenotypes. We identified plasma metabolic biomarkers for both the nature and severity of different malarial pathologies. A subset of metabolic changes, including plasma arginine depletion, match the plasma metabolomes of human malaria patients, suggesting new connections between pathology and metabolism in human malaria. In our malarial mice, liver damage, which releases hepatic arginase-1 (Arg1) into circulation, correlated with plasma arginine depletion. We confirmed that hepatic Arg1 was the primary source of increased plasma arginase activity in our model, which motivates further investigation of liver damage in human malaria patients. More broadly, our approach shows how leveraging phenotypic diversity can identify and validate relationships between metabolism and the pathophysiology of infectious disease. IMPORTANCE Malaria is a severe and sometimes fatal infectious disease endemic to tropical and subtropical regions. Effective vaccines against malaria-causing Plasmodium parasites remain elusive, and malaria treatments often fail to prevent severe disease. Small molecules that target host metabolism have recently emerged as candidates for therapeutics in malaria and other diseases. However, our limited understanding of how metabolites affect pathophysiology limits our ability to develop new metabolite therapies. By providing a rich data set of metabolite-pathology correlations and by validating one of those correlations, our work is an important step toward harnessing metabolism to mitigate disease. Specifically, we showed that liver damage in P. chabaudi-infected mice releases hepatic arginase-1 into circulation, where it may deplete plasma arginine, a candidate malaria therapeutic that mitigates vascular stress. Our data suggest that liver damage may confound efforts to increase levels of arginine in human malaria patients.

Biomarkers Utility: At the Borderline between Cardiology and Neurology

Biomarkers are important diagnostic and prognostic tools as they provide results in a short time while still being an inexpensive, reproducible and accessible method. Their well-known benefits have placed them at the forefront of research in recent years, with new and innovative discoveries being implemented. Cardiovascular and neurological diseases often share common risk factors and pathological pathways which may play an important role in the use and interpretation of biomarkers' values. Among the biomarkers used extensively in clinical practice in cardiology, hs-TroponinT, CK-MB and NTproBNP have been shown to be strongly influenced by multiple neurological conditions. Newer ones such as galectin-3, lysophosphatidylcholine, copeptin, sST2, S100B, myeloperoxidase and GDF-15 have been extensively studied in recent years as alternatives with an increased sensitivity for cardiovascular diseases, but also with significant results in the field of neurology. Thus, given their low specificity, the values interpretation must be correlated with the clinical judgment and other available investigations.

GDF15 expression in glioma is associated with malignant progression, immune microenvironment, and serves as a prognostic factor

Aims

Growth differentiation factor 15 (GDF15) is involved in lots of crucial inflammatory and immune response. The clinical and immune features for GDF15 in glioma have not been specifically investigated so far.

Methods

Gene expression profiles obtained from public glioma datasets were used to explore the biological function of GDF15 and its impact on immune microenvironment. Interference with GDF15 in several glioma cell lines to verify its functions in vitro. Survival data were used for the survival analysis and establishment of a nomogram predictive model.

Results

GDF15 was up‐regulated in various malignant phenotypes of glioma. Function analysis and in vitro experiments revealed that GDF15 was associated with malignant progression and NF‐κB pathway. GDF15 was closely correlated to inflammatory response, infiltrating immune cells, and immune checkpoint molecules, especially in lower grade glioma (LGG). High expression level of GDF15 predicted poor survival in LGG, while the effect on glioblastoma (GBM) was not significant. A nomogram predictive model combining GDF15 and other prognostic factors was constructed and showed ideal predictive performance.

Conclusions

GDF15 could serve as an interesting prognostic biomarker for LGG. Regulating the expression of GDF15 may help solve the dilemma of immunotherapy in glioma.

Indomethacin: an exploratory study of antiviral mechanism and host-pathogen interaction in COVID-19

Introduction

COVID-19, a dreadful pandemic that has impacted human life like no other pathogenic invasion, has claimed the lives of over 100 million people. The need for effective treatment strategies is still a subject of intense research considering the rapidly evolving genome and continental diversity. Indomethacin is administered mostly as co-treatment for affected patients as a non-steroidal anti-inflammatory drug (NSAID). However, the underlying mechanism of action is unresolved. This study explores the basal mechanism of indomethacin and potency in alleviating the damage caused by SARS-CoV-2 and discusses the experimental and clinical efficacy in recent studies.

Areas covered

The literature search and system biology-based network formation were employed to describe the potent effects and risks associated with indomethacin in in-vitro, in-vivo, and clinical studies. This study also highlights the plausible mechanism of antiviral action of indomethacin with its apparent viral protein targets. The SARS-CoV-2 protein, the interacting host proteins, and the effect of indomethacin on this interactome as a standalone treatment or as part of a co-therapy strategy are particularly emphasized using network modeling.

Expert opinion

Indomethacin has demonstrated excellent clinical endpoint characteristics in several studies, and we recommend that it be utilized in the treatment of mild-to-moderate COVID patients.

Emerging roles of growth differentiation factor-15 in brain disorders (Review)

Brain disorders, such as Alzheimer's and Parkinson's disease and cerebral stroke, are an important contributor to mortality and disability worldwide, where their pathogenesis is currently a topic of intense research. The mechanisms underlying the development of brain disorders are complex and vary widely, including aberrant protein aggregation, ischemic cell necrosis and neuronal dysfunction. Previous studies have found that the expression and function of growth differentiation factor-15 (GDF15) is closely associated with the incidence of brain disorders. GDF15 is a member of the TGFβ superfamily, which is a dimer-structured stress-response protein. The expression of GDF15 is regulated by a number of proteins upstream, including p53, early growth response-1, non-coding RNAs and hormones. In particular, GDF15 has been reported to serve an important role in regulating angiogenesis, apoptosis, lipid metabolism and inflammation. For example, GDF15 can promote angiogenesis by promoting the proliferation of human umbilical vein endothelial cells, apoptosis of prostate cancer cells and fat metabolism in fasted mice, and GDF15 can decrease the inflammatory response of lipopolysaccharide-treated mice. The present article reviews the structure and biosynthesis of GDF15, in addition to the possible roles of GDF15 in Alzheimer's disease, cerebral stroke and Parkinson's disease. The purpose of the present review is to summarize the mechanism underlying the role of GDF15 in various brain disorders, which hopes to provide evidence and guide the prevention and treatment of these debilitating conditions.

DNA methylation-based biomarkers of aging were slowed down in a two-year diet and physical activity intervention trial: the DAMA study

Several biomarkers of healthy aging have been proposed in recent years, including the epigenetic clocks, based on DNA methylation (DNAm) measures, which are getting increasingly accurate in predicting the individual biological age. The recently developed "next-generation clock" DNAmGrimAge outperforms "first-generation clocks" in predicting longevity and the onset of many age-related pathological conditions and diseases. Additionally, the total number of stochastic epigenetic mutations (SEMs), also known as the epigenetic mutation load (EML), has been proposed as a complementary DNAm-based biomarker of healthy aging. A fundamental biological property of epigenetic, and in particular DNAm modifications, is the potential reversibility of the effect, raising questions about the possible slowdown of epigenetic aging by modifying one's lifestyle. Here, we investigated whether improved dietary habits and increased physical activity have favorable effects on aging biomarkers in healthy postmenopausal women. The study sample consists of 219 women from the "Diet, Physical Activity, and Mammography" (DAMA) study: a 24-month randomized factorial intervention trial with DNAm measured twice, at baseline and the end of the trial. Women who participated in the dietary intervention had a significant slowing of the DNAmGrimAge clock, whereas increasing physical activity led to a significant reduction of SEMs in crucial cancer-related pathways. Our study provides strong evidence of a causal association between lifestyle modification and slowing down of DNAm aging biomarkers. This randomized trial elucidates the causal relationship between lifestyle and healthy aging-related epigenetic mechanisms.

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.

Plasma GDF15 levels are similar between subjects after bariatric surgery and matched controls and are unaffected by meals

Growth differentiating factor 15 (GDF15) is expressed in the intestine and is one of the most recently identified satiety peptides. The mechanisms controlling its secretion are unclear. The present study investigated whether plasma GDF15 concentrations are meal-related and if potential responses depend on macronutrient type or are affected by previous bariatric surgery. The study included 1) volunteers ingesting rapidly vs. slowly digested carbohydrates (sucrose vs. isomaltose; n = 10), 2) volunteers who had undergone Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) surgery and unoperated matched controls ingesting a liquid mixed meal (n = 9-10 in each group), and 3) individuals with previous RYGB compared with unoperated controls ingesting isocaloric glucose, fat, or protein (n = 6 in each group). Plasma was collected after an overnight fast and up to 6 h after ingestion (≥12 time points). In cohort 1, fasting GDF15 concentrations were ∼480 pg/mL. Concentrations after sucrose or isomaltose intake did not differ from baseline (P = 0.26 to P > 0.99) and total area under the curves (tAUCs were similar between groups (P = 0.77). In cohort 2, fasting GDF15 concentrations were as follows (pg/mL): RYGB = 540 ± 41.4, SG = 477 ± 36.4, and controls = 590 ± 41.8, with no between-group differences (P = 0.73). Concentrations did not increase at any postprandial time point (over all time factor: P = 0.10) and tAUCs were similar between groups (P = 0.73). In cohort 3, fasting plasma GDF15 was similar among the groups (P > 0.99) and neither glucose, fat, nor protein intake consistently increased the concentrations. In conclusion, we find that plasma GDF15 was not stimulated by meal intake and that fasting concentrations did not differ between RYGB-, SG-, and body mass index (BMI)-matched controls when investigated during the weight stable phase after RYGB and SG.NEW & NOTEWORTHY Our combined data show that GDF15 does not increase in response to a liquid meal. Moreover, we show for the first time that ingestion of sucrose, isomaltose, glucose, fat, or protein also does not increase plasma GDF15 concentrations, questioning the role of GDF15 in regulation of food source preference. Finally, we find that neither fasting nor postprandial plasma GDF15 concentrations are increased in individuals with previous bariatric surgery compared with unoperated body mass index (BMI)-matched controls.

Metformin strengthens uroepithelial immunity against E. coli infection

Urinary tract infection frequently caused by E. coli is one of the most common bacterial infections. Increasing antibiotic resistance jeopardizes successful treatment and alternative treatment strategies are therefore mandatory. Metformin, an oral antidiabetic drug, has been shown to activate macrophages in the protection against certain infecting microorganisms. Since epithelial cells often form the first line of defense, we here investigated the effect on uroepithelial cells during E. coli infection. Metformin upregulated the human antimicrobial peptides cathelicidin LL-37 and RNase7 via modulation of the TRPA1 channel and AMPK pathway. Interestingly, metformin stimulation enriched both LL-37 and TRPA1 in lysosomes. In addition, metformin specifically increased nitric oxide and mitochondrial, but not cytosolic ROS. Moreover, metformin also triggered mRNA expression of the proinflammatory cytokines IL1B, CXCL8 and growth factor GDF15 in human uroepithelial cells. The GDF15 peptide stimulated macrophages increased LL-37 expression, with increased bacterial killing. In conclusion, metformin stimulation strengthened the innate immunity of uroepithelial cells inducing enhanced extracellular and intracellular bacterial killing suggesting a favorable role of metformin in the host defense.

The Clinical Value of GDF15 and Its Prospective Mechanism in Sepsis

Growth differentiation factor 15 (GDF15) is involved in the occurrence and development of many diseases, and there are few studies on its relationship with sepsis. This article aims to explore the clinical value of GDF15 in sepsis and to preliminarily explore its prospective regulatory effect on macrophage inflammation and its functions. We recruited 320 subjects (132 cases in sepsis group, 93 cases in nonsepsis group, and 95 cases in control group), then detected the serum GDF15 levels and laboratory indicators, and further investigated the correlation between GDF15 and laboratory indicators, and also analyzed the clinical value of GDF15 in sepsis diagnosis, severity assessment, and prognosis. In vitro, we used LPS to stimulate THP-1 and RAW264.7 cells to establish the inflammatory model, and detected the expression of GDF15 in the culture medium and cells under the inflammatory state. After that, we added GDF15 recombinant protein (rGDF15) pretreatment to explore its prospective regulatory effect on macrophage inflammation and its functions. The results showed that the serum GDF15 levels were significantly increased in the sepsis group, which was correlated with laboratory indexes of organ damage, coagulation indexes, inflammatory factors, and SOFA score. GDF15 also has a high AUC in the diagnosis of sepsis, which can be further improved by combining with other indicators. The dynamic monitoring of GDF15 levels can play an important role in the judgment and prognosis of sepsis. In the inflammatory state, the expression of intracellular and extracellular GDF15 increased. GDF15 can reduce the levels of cytokines, inhibit M1 polarization induced by LPS, and promote M2 polarization. Moreover, GDF15 also enhances the phagocytosis and bactericidal function of macrophages. Finally, we observed a decreased level of the phosphorylation of JAK1/STAT3 signaling pathway and the nuclear translocation of NF-κB p65 with the pretreatment of rGDF15. In summary, our study found that GDF15 has good clinical application value in sepsis and plays a protective role in the development of sepsis by regulating the functions of macrophages and inhibiting the activation of JAK1/STAT3 pathway and nuclear translocation of NF-κB p65.

Proteins as Mediators of the Association Between Diet Quality and Incident Cardiovascular Disease and All-Cause Mortality: The Framingham Heart Study

Background

Biological mechanisms underlying the association of a healthy diet with chronic diseases remain unclear. Targeted proteomics may facilitate the understanding of mechanisms linking diet to chronic diseases.

Methods and Results

We examined 6360 participants (mean age 50 years; 54% women) in the Framingham Heart Study. The associations between diet and 71 cardiovascular disease (CVD)‐related proteins were examined using 3 diet quality scores: the Alternate Healthy Eating Index, the modified Mediterranean‐style Diet Score, and the modified Dietary Approaches to Stop Hypertension diet score. A mediation analysis was conducted to examine which proteins mediated the associations of diet with incident CVD and all‐cause mortality. Thirty of the 71 proteins were associated with at least 1 diet quality score (P<0.0007) after adjustment for multiple covariates in all study participants and confirmed by an internal validation analysis. Gene ontology analysis identified inflammation‐related pathways such as regulation of cell killing and neuroinflammatory response (Bonferroni corrected P<0.05). During a median follow‐up of 13 years, we documented 512 deaths and 488 incident CVD events. Higher diet quality scores were associated with lower risk of CVD (P≤0.03) and mortality (P≤0.004). After adjusting for multiple potential confounders, 4 proteins (B2M [beta‐2‐microglobulin], GDF15 [growth differentiation factor 15], sICAM1 [soluble intercellular adhesion molecule 1], and UCMGP [uncarboxylated matrix Gla‐protein]) mediated the association between at least 1 diet quality score and all‐cause mortality (median proportion of mediation ranged from 8.6% to 25.9%). We also observed that GDF15 mediated the association of the Alternate Healthy Eating Index with CVD (median proportion of mediation: 8.6%).

Conclusions

Diet quality is associated with new‐onset CVD and mortality and with circulating CVD‐related proteins. Several proteins appear to mediate the association of diet with these outcomes.

GDF15 induces immunosuppression via CD48 on regulatory T cells in hepatocellular carcinoma

BACKGROUND

A better understanding of the molecular mechanisms that manifest in the immunosuppressive tumor microenvironment (TME) is crucial for developing more efficacious immunotherapies for hepatocellular carcinoma (HCC), which has a poor response to current immunotherapies. Regulatory T (Treg) cells are key mediators of HCC-associated immunosuppression. We investigated the selective mechanism exploited by HCC that lead to Treg cells expansion and to find more efficacious immunotherapies.

METHODS

We used matched tumor tissues and blood samples from 150 patients with HCC to identify key factors of Treg cells expansion. We used mass cytometry (CyTOF) and orthotopic cancer mouse models to analyze overall immunological changes after growth differentiation factor 15 (GDF15) gene ablation in HCC. We used flow cytometry, coimmunoprecipitation, RNA sequencing, mass spectrum, chromatin immunoprecipitation and Gdf15 ^-/-, OT-I and GFP transgenic mice to demonstrate the effects of GDF15 on Treg cells and related molecular mechanism. We used hybridoma technology to generate monoclonal antibody to block GDF15 and evaluate its effects on HCC-associated immunosuppression.

RESULTS

GDF15 is positively associated with the elevation of Treg cell frequencies in patients wih HCC. Gene ablation of GDF15 in HCC can convert an immunosuppressive TME to an inflammatory state. GDF15 promotes the generation of peripherally derived inducible Treg (iTreg) cells and enhances the suppressive function of natural Treg (nTreg) cells by interacting with a previously unrecognized receptor CD48 on T cells and thus downregulates STUB1, an E3 ligase that mediates forkhead box P3 (FOXP3) protein degradation. GDF15 neutralizing antibody effectively eradicates HCC and augments the antitumor immunity in mouse.

CONCLUSIONS

Our results reveal the generation and function enhancement of Treg cells induced by GDF15 is a new mechanism for HCC-related immunosuppression. CD48 is the first discovered receptor of GDF15 in the immune system which provide the possibility to solve the molecular mechanism of the immunomodulatory function of GDF15. The therapeutic GDF15 blockade achieves HCC clearance without obvious adverse events.

Targeting Bacteria within Us to Diminish Infection and Autoimmunity

Antibiotics improve clinical outcomes independent of their antibacterial effects. In this issue of Immunity, Almeida et al. and Colaço et al. demonstrate that antibiotic impairment of mitochondrial ribosomes modulates both T-cell-dependent inflammation and host tolerance to infection.

GDF15 and Cardiac Cells: Current Concepts and New Insights

Growth and differentiation factor 15 (GDF15) belongs to the transforming growth factor-β (TGF-β) superfamily of proteins. Glial-derived neurotrophic factor (GDNF) family receptor α-like (GFRAL) is an endogenous receptor for GDF15 detected selectively in the brain. GDF15 is not normally expressed in the tissue but is prominently induced by “injury”. Serum levels of GDF15 are also increased by aging and in response to cellular stress and mitochondrial dysfunction. It acts as an inflammatory marker and plays a role in the pathogenesis of cardiovascular diseases, metabolic disorders, and neurodegenerative processes. Identified as a new heart-derived endocrine hormone that regulates body growth, GDF15 has a local cardioprotective role, presumably due to its autocrine/paracrine properties: antioxidative, anti-inflammatory, antiapoptotic. GDF15 expression is highly induced in cardiomyocytes after ischemia/reperfusion and in the heart within hours after myocardial infarction (MI). Recent studies show associations between GDF15, inflammation, and cardiac fibrosis during heart failure and MI. However, the reason for this increase in GDF15 production has not been clearly identified. Experimental and clinical studies support the potential use of GDF15 as a novel therapeutic target (1) by modulating metabolic activity and (2) promoting an adaptive angiogenesis and cardiac regenerative process during cardiovascular diseases. In this review, we comment on new aspects of the biology of GDF15 as a cardiac hormone and show that GDF15 may be a predictive biomarker of adverse cardiac events.

Neural Mechanisms of Cancer Cachexia

Simple Summary

Cancer cachexia is a devastating wasting syndrome that occurs in many illnesses, with signs and symptoms including anorexia, weight loss, cognitive impairment and fatigue. The brain is capable of exerting overarching homeostatic control of whole-body metabolism and is increasingly being recognized as an important mediator of cancer cachexia. Given the increased recognition and discovery of neural mechanisms of cancer cachexia, we sought to provide an in-depth review and update of mechanisms by which the brain initiates and propagates cancer cachexia programs. Furthermore, recent work has identified new molecular mediators of cachexia that exert their effects through their direct interaction with the brain. Therefore, this review will summarize neural mechanisms of cachexia and discuss recently identified neural mediators of cancer cachexia.

Abstract

Nearly half of cancer patients suffer from cachexia, a metabolic syndrome characterized by progressive atrophy of fat and lean body mass. This state of excess catabolism decreases quality of life, ability to tolerate treatment and eventual survival, yet no effective therapies exist. Although the central nervous system (CNS) orchestrates several manifestations of cachexia, the precise mechanisms of neural dysfunction during cachexia are still being unveiled. Herein, we summarize the cellular and molecular mechanisms of CNS dysfunction during cancer cachexia with a focus on inflammatory, autonomic and neuroendocrine processes and end with a discussion of recently identified CNS mediators of cachexia, including GDF15, LCN2 and INSL3.

Associations between elevated growth differentiation factor-15 and sarcopenia among community-dwelling older adults

BACKGROUND

Growth differentiation factor 15 (GDF-15) is associated with disease progression, mitochondrial dysfunction, and mortality. Elevated GDF-15 level was recently reported to be associated with poorer physical performance in healthy adults. However, the association between serum GDF-15 level and sarcopenia in community-dwelling older adults has not been well characterized.

METHODS

We conducted cross-sectional (n = 929) and two-year prospective analyses (n = 788) among participants aged 70-84 years enrolled in the Korean Frailty and Aging Cohort Study. Participants with an estimated glomerular filtration rate of <60 mL/min/1.73 m 2 were excluded. Appendicular lean mass was measured using dual-energy X-ray absorptiometry. Sarcopenia status was determined according to the Asian Working Group for Sarcopenia-2019 algorithm.

RESULTS

At baseline, 16.6% of the participants had sarcopenia. Median GDF-15 concentration was higher in the sarcopenic group than in the non-sarcopenic group (1221 pg/mL vs. 1019 pg/mL, p<0.001). In the multivariate analysis adjusted for cardiometabolic risk and biological factors, the highest GDF-15 tertile (≥1245 pg/mL) had an increased likelihood of sarcopenia (odds ratio, 1.96; 95% confidence interval, 1.16-3.33) than the lowest tertile (<885 pg/mL). During the two-year follow-up period, 67 (10.1%) individuals without sarcopenia at baseline developed sarcopenia. There were no significant associations between baseline serum GDF-15 levels and incident sarcopenia or its components (all p>0.05).

CONCLUSIONS

Elevated GDF-15 was associated with prevalent sarcopenia but not able to predict incident sarcopenia in the 2-year follow-up. Further studies are needed to explore the pathophysiological roles of GDF-15 in the development of sarcopenia.

Sensing, signaling and surviving mitochondrial stress

Mitochondrial fidelity is a key determinant of longevity and was found to be perturbed in a multitude of disease contexts ranging from neurodegeneration to heart failure. Tight homeostatic control of the mitochondrial proteome is a crucial aspect of mitochondrial function, which is severely complicated by the evolutionary origin and resulting peculiarities of the organelle. This is, on one hand, reflected by a range of basal quality control factors such as mitochondria-resident chaperones and proteases, that assist in import and folding of precursors as well as removal of aggregated proteins. On the other hand, stress causes the activation of several additional mechanisms that counteract any damage that may threaten mitochondrial function. Countermeasures depend on the location and intensity of the stress and on a range of factors that are equipped to sense and signal the nature of the encountered perturbation. Defective mitochondrial import activates mechanisms that combat the accumulation of precursors in the cytosol and the import pore. To resolve proteotoxic stress in the organelle interior, mitochondria depend on nuclear transcriptional programs, such as the mitochondrial unfolded protein response and the integrated stress response. If organelle damage is too severe, mitochondria signal for their own destruction in a process termed mitophagy, thereby preventing further harm to the mitochondrial network and allowing the cell to salvage their biological building blocks. Here, we provide an overview of how different types and intensities of stress activate distinct pathways aimed at preserving mitochondrial fidelity.

Activation of the hypothalamic-pituitary-adrenal axis by exogenous and endogenous GDF15

An acute increase in the circulating concentration of glucocorticoid hormones is essential for the survival of severe somatic stresses. Circulating concentrations of GDF15, a hormone that acts in the brain to reduce food intake, are frequently elevated in stressful states. We now report that GDF15 potently activates the hypothalamic-pituitary-adrenal (HPA) axis in mice and rats. A blocking antibody to the GDNF-family receptor α-like receptor completely prevented the corticosterone response to GDF15 administration. In wild-type mice exposed to a range of stressful stimuli, circulating levels of both corticosterone and GDF15 rose acutely. In the case of Escherichia coli or lipopolysaccharide injections, the vigorous proinflammatory cytokine response elicited was sufficient to produce a near-maximal HPA response, regardless of the presence or absence of GDF15. In contrast, the activation of the HPA axis seen in wild-type mice in response to the administration of genotoxic or endoplasmic reticulum toxins, which do not provoke a marked rise in cytokines, was absent in Gdf15 ^-/- mice. In conclusion, consistent with its proposed role as a sentinel hormone, endogenous GDF15 is required for the activation of the protective HPA response to toxins that do not induce a substantial cytokine response. In the context of efforts to develop GDF15 as an antiobesity therapeutic, these findings identify a biomarker of target engagement and a previously unrecognized pharmacodynamic effect, which will require monitoring in human studies.

Expression of the Body-Weight Signaling Players: GDF15, GFRAL and RET and their clinical relevance in Gastric Cancer

The existence, the functional role and clinical relevance of GDF15 and its signaling through a GFRAL/RET-dependent complex in gastric cancer (GC) and other human tumors remain to be elucidated, despite the widespread recognition of obesity as an important cancer-predisposing factor. Therefore, we aimed to analyze the expression levels of GDF15, GFRAL and RET in GC tissues in relation to each other and clinicopathological features, including patient survival, in order to establish a potential implication of the body-weight signaling pathway in the pathology and clinical outcome of GC. Protein expression was examined by immunohistochemistry on tissue microarrays containing 104 and 30 consecutive GC and normal gastric mucosa samples, whereas gene expression data for The Cancer Genome Atlas cohort of 413 GC patients were obtained from public sources. We found that the protein expression of GDF15, GFRAL and RET was significantly elevated and positively correlated in our set of GC tissues, which was reflected in their tendency to be overexpressed in low-grade and intermediate-grade tumors rather than high-grade ones. No other relationships between the expression status of the examined proteins and clinicopathological characteristics of GC patients were found. Through in silico data analysis, we showed that high GDF15 expression was associated with better overall survival (OS) of GC patients, whereas the opposite was true for high levels of GFRAL or RET. Specifically, GFRAL and RET emerged as independent prognostic factors associated with poor OS. Furthermore, high combined expression of the three markers: GDF15+GFRAL+RET was significantly associated with reduced OS, and it was an independent prognostic factor of borderline significance in terms of OS, when adjusted for covariates. If validated in large-scale studies, the individual and combined expression of GDF15, GFRAL and RET may provide significant clinical implications for the prognosis prediction of GC patients.

Growth Differentiation Factor-15 Produces Analgesia by Inhibiting Tetrodotoxin-Resistant Nav1.8 Sodium Channel Activity in Rat Primary Sensory Neurons

Growth differentiation factor 15 (GDF-15) is a member of the transforming growth factor-β superfamily. It is widely distributed in the central and peripheral nervous systems. Whether and how GDF-15 modulates nociceptive signaling remains unclear. Behaviorally, we found that peripheral GDF-15 significantly elevated nociceptive response thresholds to mechanical and thermal stimuli in naïve and arthritic rats. Electrophysiologically, we demonstrated that GDF-15 decreased the excitability of small-diameter dorsal root ganglia (DRG) neurons. Furthermore, GDF-15 concentration-dependently suppressed tetrodotoxin-resistant sodium channel Nav1.8 currents, and shifted the steady-state inactivation curves of Nav1.8 in a hyperpolarizing direction. GDF-15 also reduced window currents and slowed down the recovery rate of Nav1.8 channels, suggesting that GDF-15 accelerated inactivation and slowed recovery of the channel. Immunohistochemistry results showed that activin receptor-like kinase-2 (ALK2) was widely expressed in DRG medium- and small-diameter neurons, and some of them were Nav1.8-positive. Blockade of ALK2 prevented the GDF-15-induced inhibition of Nav1.8 currents and nociceptive behaviors. Inhibition of PKA and ERK, but not PKC, blocked the inhibitory effect of GDF-15 on Nav1.8 currents. These results suggest a functional link between GDF-15 and Nav1.8 in DRG neurons via ALK2 receptors and PKA associated with MEK/ERK, which mediate the peripheral analgesia of GDF-15.

Role of microbiota-gut-brain axis dysfunctions induced by infections in the onset of anorexia nervosa

Anorexia nervosa (AN) is an eating disorder characterized by low food intake, severe body weight loss, intense fear of gaining weight, and dysmorphophobia. This chronic disease is associated with both psychiatric and somatic comorbidities. Over the years, clinical studies have accumulated evidence that viral or bacterial infections may promote the onset of eating disorders such as AN. This review aims to describe how infections and the subsequent immune responses affect food intake regulation in the short term and also how these processes may lead to long-term intestinal disorders, including gut barrier disruption and gut microbiota dysbiosis, even after the clearance of the pathogens. We discuss in particular how infection-mediated intestinal dysbiosis may promote the onset of several AN symptoms and comorbidities, including appetite dysregulation, functional gastrointestinal disorders, and mood disorders.

Growth differentiation factor 15 neutralization does not impact anorexia or survival in lipopolysaccharide-induced inflammation

Growth differentiation factor 15 (GDF15) causes anorexia and weight loss in animal models, and higher circulating levels are associated with cachexia and reduced survival in cancer and other chronic diseases such as sepsis. To investigate the role of sepsis-induced GDF15, we examined whether GDF15 neutralization via a validated and highly potent monoclonal antibody, mAB2, modulates lipopolysaccharide (LPS)-induced anorexia, weight loss, and mortality in rodents. LPS injection transiently increased circulating GDF15 in wild-type mice, decreased food intake and body weight, and increased illness behavior and mortality at a high dose. GDF15 neutralization with mAB2 did not prevent or exacerbate any of the effects of LPS. Similarly, in GDF15 knockout mice, the LPS effect on appetite and survival was comparable with that observed in wild-type controls. Therefore, effective inhibition of circulating active GDF15 via an antibody or via gene knockout demonstrated that survival in the LPS acute inflammation model was independent of GDF15.

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A novel highly potent anti-GDF15 antibody, mAB2, was characterized

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LPS transiently increased GDF15 production in mice

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mAB2 did not prevent or exacerbate the effects of LPS on anorexia or survival

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GDF15 knockout mice showed comparable effects of LPS with wild-type controls

Hallmarks of T cell aging

The aged adaptive immune system is characterized by progressive dysfunction as well as increased autoimmunity. This decline is responsible for elevated susceptibility to infection and cancer, as well as decreased vaccination efficacy. Recent evidence indicates that CD4⁺ T cell-intrinsic alteratins contribute to chronic inflammation and are sufficient to accelerate an organism-wide aging phenotype, supporting the idea that T cell aging plays a major role in body-wide deterioration. In this Review, we propose ten molecular hallmarks to represent common denominators of T cell aging. These hallmarks are grouped into four primary hallmarks (thymic involution, mitochondrial dysfunction, genetic and epigenetic alterations, and loss of proteostasis) and four secondary hallmarks (reduction of the TCR repertoire, naive-memory imbalance, T cell senescence, and lack of effector plasticity), and together they explain the manifestation of the two integrative hallmarks (immunodeficiency and inflammaging). A major challenge now is weighing the relative impact of these hallmarks on T cell aging and understanding their interconnections, with the final goal of defining molecular targets for interventions in the aging process.