Stress-induced FGF21 and GDF15 in obesity and obesity resistance

Molecular mechanisms of UCP1-independent thermogenesis: the role of futile cycles in energy dissipation

Adipose tissue thermogenesis has emerged as a prominent research focus for the treatment of metabolic diseases, particularly through mitochondrial uncoupling, which oxidizes nutrients to produce heat rather than synthesizing ATP. Uncoupling protein 1 (UCP1) has garnered significant attention as a core protein mediating non-shivering thermogenesis(NST). However, recent studies indicate that energy dissipation can also occur via UCP1-independent thermogenesis, partially driven by futile metabolic cycles. These cycles involve ATP depletion coupled with reversible energy reactions, resulting in futile energy expenditure. Unlike classical UCP1-mediated thermogenesis, futile cycling is not confined to brown and beige adipose tissue, suggesting a broader range of therapeutic targets. These findings open new avenues for targeting these pathways to enhance metabolic health. This review explores the characteristics and distinctions of the primary metabolic organs (adipose tissue, liver, and skeletal muscle) involved in the futile cycles of thermogenesis. It further elaborates on the cellular and molecular mechanisms underlying calcium, creatine, and lipid cycling, emphasizing their strengths, limitations, and roles beyond thermogenesis.

Differential effects of bariatric surgery on circulating GDF15 and FGF21 levels: Implications for glycemic status and weight loss outcomes

BACKGROUND

Type 2 diabetes (T2D) is a comorbidity commonly associated with obesity. Elevated concentrations of growth differentiation factor 15 (GDF15) and fibroblast growth factor 21 (FGF21) are associated with these conditions, making both cytokines interesting candidates to combat them. This study aimed to analyse the relationship between changes in plasma GDF15 and FGF21 levels and the resolution of T2D or obesity improvements after bariatric surgery.

METHODS

Plasma samples from 104 patients (52 with obesity and normoglycemia and 52 with obesity and impaired glucose tolerance or T2D) were analysed before and after Roux-en-Y-gastric bypass surgery.

RESULTS

Plasma GDF15 levels increased significantly after bariatric surgery in patients with obesity and normoglycemia (p < 0.01), as well as in those with obesity and impaired glucose tolerance or T2D (p < 0.05). This increase was significant in patients analysed up to 8 months after surgery in both groups (p < 0.01) but not in those analysed between 8 to 15 months after surgery, suggesting that GDF15 concentrations exhibit an early increase after surgery but may return to baseline levels over time. In contrast, plasma FGF21 levels after bariatric surgery decreased significantly in patients with impaired glucose tolerance or T2D (p < 0.05). Pre-surgery FGF21 concentrations were negatively correlated with the percentage of excess weight loss and the percentage of fat loss.

CONCLUSIONS

GDF15 and FGF21 exhibit a different behaviour after Roux-en-Y-gastric bypass surgery, with FGF21 being more closely associated with glycemic status and weight loss. Elevated pre-surgery FGF21 concentrations could predict a higher difficulty in losing the excess weight after surgery.

Dual-responsive nanoparticles targeting ACE-II senescence for therapeutic mitigation of acute lung injury

Acute lung injury (ALI) is a life-threatening condition characterized by severe pulmonary dysfunction, with alveolar type II epithelial cell (ACE-II) senescence playing a pivotal role in its progression. In this study, we developed pH/reactive oxygen species (ROS) dual-responsive nanoparticles (GNPsanti-SP-C) for the targeted delivery of Growth Differentiation Factor 15 (GDF15) to counteract ACE-II senescence. These nanoparticles (NPs) effectively activate the AMP-activated protein kinase (AMPK)/Sirtuin 1 (SIRT1) signaling pathway, inducing the mitochondrial unfolded protein response (UPRmt) and reversing senescence-associated cellular dysfunction. GNPsanti-SP-C were systematically engineered and demonstrated robust pH/ROS sensitivity, efficient GDF15 release, and precise ACE-II targeting. In lipopolysaccharide (LPS)-induced ALI mouse model, GNPsanti-SP-C treatment significantly mitigated lung injury, reduced inflammatory responses, and enhanced pulmonary function, as evidenced by decreased inflammatory markers, lung edema, and improved histopathology. Single-cell transcriptomic and proteomic analyses revealed increased ACE-II cell populations, reduced expression of senescence markers, and upregulation of AMPK/SIRT1 signaling. In vitro studies further demonstrated that UPRmt activation is associated with the NPs' therapeutic effects, suggesting a potential role in their mechanism of action. These findings demonstrate the potential of GDF15-loaded dual-responsive NPs as an innovative strategy to address cellular senescence and alleviate ALI-associated pulmonary damage.

Association of FGF21 with Metabolic and Cardiovascular Diseases: A Mendelian Randomization Analysis

Studies have covered a possible relevance between fibroblast growth factor 21 (FGF21) and obesity-related metabolic complications and cardiovascular disease (CVD). Nevertheless, whether FGF21 is a causative factor in these diseases is not known. Using a bidirectional, two-sample Mendelian randomization (MR) approach, this study sought to establish a causal relationship between FGF21 and seven metabolic diseases and six CVDs. A large-scale meta-analysis dataset of genome-wide association studies (GWAS) was analyzed to generate summary-level statistics for FGF21. The diseases we studied included non-alcoholic fatty liver disease (NAFLD), obesity, type 2 diabetes (T2DM), hypertension, gestational diabetes (GDM), gestational hypertension (GHTN), pre-eclampsia or eclampsia (PE), atherosclerosis, cardiomyopathy (CMP), coronary heart disease (CHD), coronary atherosclerosis, heart failure (HF), myocardial infarction (MI) and the corresponding summary GAWS data were retrieved from the FinnGen Biobank and IEU Open GWAS Project database. The inverse variance-weighted (IVW) algorithm was the primary approach utilized for the MR analysis. The MR-Egger regression and MR-PRESSO tests were implemented to evaluate horizontal pleiotropy. The heterogeneity of instrumental variables was subsequently assessed utilizing Cochran's Q statistics.When diseases are used as exposures, MR analysis results of the IVW method indicated that NAFLD (Beta=- 0.047, 95% CI=- 0.08 to - 0.014; p=0.006), obesity (Beta=0.087, 95% CI=0.021-0.153; p=0.009), T2DM (Beta=0.071, 95% CI=0.037-0.106; p<0.001) correlated causally with FGF21. Nevertheless, FGF21 was not causally related to the remaining metabolic diseases and CVDs, according to the results of the MR analysis (p>0.05). It was demonstrated that the aforementioned results were robust and devoid of pleiotropy.Our study supports a causal association between NAFLD, obesity, and T2DM with FGF21. No substantial evidence exists to establish a causal relationship between FGF21 and other diseases. This study provides opportunities for the early prevention and innovative therapy of NAFLD, obesity, and T2DM.

Circulating GDF15 May Estimate Vasculitis Activity and Predict Poor Outcomes During the Disease Course of ANCA-Associated Vasculitis

Objective: This study investigated whether circulating growth differentiation factor 15 (GDF15) at diagnosis could estimate the Birmingham Vasculitis Activity Score (BVAS) and potentially predict all-cause mortality and end-stage kidney disease (ESKD) during follow-up in patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). Methods: This study included 79 patients selected from a cohort of Korean patients with AAV. Circulating GDF15 was measured from patients' sera collected at diagnosis and stored at -80 °C. Clinical data at diagnosis and during follow-up were reviewed. Results: The median age was 64.0 years (40.5% men, and 59.5% women). Median circulating GDF15 was measured as 995.0 pg/mL. Of the 79 patients, 6 (7.6%) died and 20 (25.3%) progressed to ESKD during the disease course. Circulating GDF15 levels were significantly correlated with BVAS (r = 0.340) at diagnosis. Patients with circulating GDF15 ≥ 3350.5 pg/mL exhibited a significantly higher risk of the highest tertile of BVAS than those without (relative risk [RR], 11.229). Similarly, patients with circulating GDF15 ≥ 2239.5 pg/mL and ≥2208.5 pg/mL showed higher risks of all-cause mortality (RR, 7.733) and progression to ESKD (RR 7.125) than those without. Patients with circulating GDF15 ≥ 2239.5 pg/mL and ≥2208.5 pg/mL also showed significantly lower patient and ESKD-free survival rates than those without. Conclusions: Circulating GDF15 at diagnosis is useful in estimating BVAS and potentially predicts all-cause mortality and ESKD progression in patients with AAV.

The effects of SGLT2 inhibitors on metabolic phenotype and FGF-21 expression from the adipose tissue and the liver are less pronounced in ob/ob mice

BACKGROUND

the metabolic effects of sodium-glucose cotransporter-2 inhibitors (SGLT2i), such as lipolysis and ectopic fat reduction, seem related to the synthesis of fibroblast growth factor-21 (FGF-21), and FGF-21 analogs are now under investigation for the treatment of obesity complications such as metabolic dysfunction-associated steatotic liver disease. However, FGF-21 levels are paradoxically higher in obesity, indicating a hormone-resistant state that may hinder the benefits of SGLT2i.

METHODS

To define if a different energy status influences the response to SGLT2i, we evaluated the effects of dapagliflozin administration on nine-week-old C57BL/6J wild-type and B6.V-LEP ob/ob mice as a model of genetic obesity. Blood glucose, body weight and food intake were evaluated, and the FGF-21 expression was determined in subcutaneous adipose tissue (SAT), visceral adipose tissue (VAT), and brown adipose tissue (BAT). In the liver, FGF-21 gene expression, protein concentration and triglyceride content were evaluated.

RESULTS

glucose plasma levels and body weight were higher in ob/ob than in lean mice. After four weeks of treatment, dapagliflozin reduced blood glucose levels and body weight in both animal models, but weight loss was more significant in lean mice. The baseline expression of FGF-21 was higher in both SAT, VAT and the liver of ob/ob mice, whereas it was almost undetectable in BAT in both animal groups. After the treatment period, dapagliflozin was shown to increase FGF-21 expression in VAT only in lean animals, while the expression was unaffected in ob/ob mice. Similar effects were observed in the liver analyses, along with no variation in triglyceride content.

CONCLUSIONS

SGLT2i administration results in less pronounced metabolic effects in ob/ob mice than in lean mice. This data suggests a less sensitive response in obesity, probably due to a chronic stimulation leading to abnormalities of the SGLT2i-FGF-21 axis which should be considered in managing patients affected by genetic obesity.

Mitochondrial and Stress-Related Psychobiological Regulation of FGF21 in Humans

FGF21 is a metabolic hormone induced by fasting, metabolic stress, and mitochondrial oxidative phosphorylation (OxPhos) defects that cause mitochondrial diseases (MitoD). Here we report that acute psychosocial stress alone (without physical exertion) decreases serum FGF21 by an average of 20% (p<0.0001) in healthy controls but increases FGF21 by 32% (p<0.0001) in people with MitoD-pointing to a functional interaction between the stress response and OxPhos capacity in regulating FGF21. We further define co-activation patterns between FGF21 and stress-related neuroendocrine hormones and report novel associations between FGF21 and psychosocial factors related to stress and wellbeing, highlighting a potential role for FGF21 in meeting the energetic needs of acute and chronic psychosocial stress.

Genotype-Phenotype Correlation in Progressive External Ophthalmoplegia: Insights From a Retrospective Analysis

BACKGROUND

Progressive external ophthalmoplegia (PEO) is a classic manifestation of mitochondrial disease. However, the link between its genetic characteristics and clinical presentations remains poorly investigated.

METHODS

We analysed the clinical, pathological and genetic characteristics of a large cohort of patients with PEO, based on the type of their mtDNA variations. Eighty-two PEO patients were enrolled and grouped into three categories: mtDNA single large-scale deletions (SLDs), multiple deletions (MulDs) and the m.3243A > G point variant. Patients in the SLD category were further divided into 'common deletion' and 'noncommon deletion' groups based on the presence or absence of a 4977-bp deletion. The mutational load of deleted mtDNA of these patients was comprehensively detected by real-time polymerase chain reaction (RT-PCR).

RESULTS

SLD Patients showed the highest proportion of cytochrome C oxidase-negative (COX-n) fibres on muscle biopsy. The mutational load of deleted mtDNA exhibited an inverse relationship with deletion length and a direct relationship with the COX-n fibre ratio. Compared with patients having noncommon deletions, those with common deletions tend to have other muscle involvement, lower body mass index (BMI) scores (17 ± 3 vs. 22 ± 4 kg/m2), higher mutational load in muscle (63% ± 22% vs. 46% ± 24%), more COX-n fibres (26% vs. 9%, interquartile range [IQR]: 15%-32% vs. 6%-26%) and higher growth and differentiation factor 15 (GDF15) levels (2583 vs. 1472, IQR: 1746-4081 vs. 924-2155 pg/mL). MulDs patients displayed milder symptoms, especially compared to patients with m.3243A > G variant, as indicated by their later age of onset (31 vs. 13, IQR: 27-49 vs. 6-29 years), higher BMI scores (24.0 ± 4 vs. 16.5 ± 3.4 kg/m2), lower lactate (1.6 ± 1.1 vs. 6.3 ± 6.0 mmol/L) levels and lower proportion of ragged-blue fibres (RBFs) (3 vs. 16, IQR: 1%-9% vs. 7%-27%).

CONCLUSION

The m.3243A > G variant group exhibits more severe symptoms compared to other subgroups, particularly MulDs patients. In the SLD group, those with common deletions experience more severe clinical and pathological manifestations. These findings enhance our understanding of PEO, facilitating its diagnosis, prognosis and genetic counselling.

The mechanism of action of indole-3-propionic acid on bone metabolism

Indole-3-propionic acid (IPA), a metabolite produced by gut microbiota through tryptophan metabolism, has recently been identified as playing a pivotal role in bone metabolism. IPA promotes osteoblast differentiation by upregulating mitochondrial transcription factor A (Tfam), contributing to increased bone density and supporting bone repair. Simultaneously, it inhibits the formation and activity of osteoclasts, reducing bone resorption, possibly through modulation of the nuclear factor-κB (NF-κB) pathway and downregulation of osteoclast-associated factors, thereby maintaining bone structural integrity. Additionally, IPA provides indirect protection to bone health by regulating host immune responses and inflammation via activation of receptors such as the Aryl hydrocarbon Receptor (AhR) and the Pregnane X Receptor (PXR). This review summarizes the roles and signaling pathways of IPA in bone metabolism and its impact on various bone metabolic disorders. Furthermore, we discuss the therapeutic potential and limitations of IPA in treating bone metabolic diseases, aiming to offer novel strategies for clinical management.

Effects of exercise intensity and diet on cardiac tissue structure and FGF21/β-Klotho signaling in type 2 diabetic mice: a comparative study of HFD and HFD + STZ induced type 2 diabetes models in mice

BACKGROUND

Structural heart disease is one of the leading causes of death in people with type 2 diabetes (T2D), which is not known to have an effect on exercise training. The aim of this study was to compare the effects of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on heart tissue structure, the serum level of FGF21 and the heart tissue level of β-Klotho, an FGF21 coreceptor, in HFD and HFD + STZ-induced diabetic mice.

METHODS

Thirty-six male C57BL/6J mice were divided into high-fat diet (HFD) and normal chow diet (ND) groups. After 20 weeks of diet, the HFD mice were divided into HFD and HFD + STZ groups, and the latter group was injected with STZ. Then, the mice in the ND, HFD and HFD + STZ groups were divided into three subgroups of control (C), HIIT and MICT, and mice were placed in one of nine groups ND-C, ND-HIIT, ND-MICT, HFD-C, HFD-HIIT, HFD-MICT, HFD + STZ-C, HFD + STZ-HIIT, and HFD + STZ-MICT. The mice in the exercise training (ET) groups were run on a treadmill for eight weeks. Finally, the tissue and serum samples were collected and analyzed by two-way ANOVA.

RESULTS

Statistical analyses showed that the main effect of diabetes inducing model (DIM) was significant for all variables (p < 0.05), except vascular density (p = 0.055); the main effect of ET type on fasting blood glucose and FGF21 was significant (p < 0.001); and the interaction was significant for fasting blood glucose, heart weight and FGF21 (p < 0.001). Post hoc and subgroup analysis showed a superior effect of MICT over HIIT in decreasing fasting blood glucose and serum level of FGF21 (p < 0.001). Additionally, the results of the myocardial tissue qualitative analyses differed between the diabetic mouse models and the ET groups.

CONCLUSIONS

In a mouse model, type 2 diabetes can negatively affect heart tissue structure and FGF21 signaling in cardiac tissue, and both HIIT and MICT can prevent this effect. However, MICT likely more effective that HIIT in reducing circulating FGF21.

The Role of Mitokines in Diabetic Nephropathy

Diabetic nephropathy (DN) has gradually become one of the main causes of end-stage renal disease (ESRD). However, there is still a lack of effective preventive measures to delay its progression. As the energy factory in the cell, mitochondria play an irreplaceable role in maintaining cell homeostasis. Interestingly, recent studies have shown that in addition to maintaining homeostasis in cells in which mitochondria reside, when mitochondrial perturbations occur in one tissue, distal tissues can also sense and act through mitochondrial stress response pathways through a group of proteins or peptides called "mitokines". Here, we reviewed the mitokines that have been found thus far and summarized their research progress in DN. Finally, we explored the possibility of mitokines as potential therapeutic targets for DN.

Overexpression of Growth Differentiation Factor 15 Reduces Neuronal Cell Damage Induced by Oxygen-Glucose Deprivation/Reoxygenation via Inhibiting Endoplasmic Reticulum Stress-Mediated Ferroptosis

Growth differentiation factor 15 (GDF15) can be induced under various stress conditions. This study aimed to explore the role of GDF15 in oxygen-glucose deprivation/reoxygenation (OGD/R)-induced HT22 cells. OGD/R was employed to induce the HT22 cell model, and GDF15 expression was upregulated via transfection. Subsequently, the effects on inflammatory factors, oxidative stress markers, apoptosis-related proteins, and ferroptosis markers were detected. Relevant indicators were evaluated using techniques such as ELISA, probes, flow cytometry, and western blotting. Furthermore, changes in these phenotypes under the influence of the endoplasmic reticulum (ER) stress agonist tunicamycin (TM) were evaluated. The result showed that GDF15 was significantly up-regulated in OGD/R-treated HT22 cells. Overexpression of GDF15 significantly reduced the levels of inflammatory factors tumor necrosis factor-α, IL (interleukin)-1β, and IL-6, inhibited the production of reactive oxygen species and MDA, and improved activity of superoxide dismutase and GSH-Px. Flow cytometry and western blotting results showed that GDF15 overexpression significantly reduced cell apoptosis, reduced caspase3 activity, and regulated the expression of Bcl2 and Bax. In addition, overexpression of GDF15 reduces the levels of ferroptosis markers by inhibiting ER stress. ER stress inducer TM can reverse the protective effects of GDF15 overexpression and promote inflammation, oxidative stress, and apoptosis. This study shows that overexpression of GDF15 reduces OGD/R-induced HT22 cell damage, and ER stress-mediated ferroptosis is included in the regulatory mechanisms. This provides a theoretical basis for GDF15 as a new target for the treatment of cerebral ischemia-reperfusion injury.

GDF-15 as a proxy for epigenetic aging: associations with biological age markers, and physical function

Growth differentiation factor 15 (GDF-15) has emerged as a significant biomarker of aging, linked to various physiological and pathological processes. This study investigates circulating GDF-15 levels in a cohort of healthy individuals from the Balearic Islands, exploring its associations with biological age markers, including multiple DNA methylation (DNAm) clocks, physical performance, and other age-related biomarkers. Seventy-two participants were assessed for general health, body composition, and physical function, with GDF-15 levels quantified using ELISA. Our results indicate that GDF-15 levels significantly increase with age, particularly in individuals over 60. Strong positive correlations were observed between GDF-15 levels and DNAm GrimAge, DNAm PhenoAge, Hannum, and Zhang clocks, suggesting that GDF-15 could serve as a proxy for epigenetic aging. Additionally, GDF-15 levels were linked to markers of impaired glycemic control, systemic inflammation, and physical decline, including decreased lung function and grip strength, especially in men. These findings highlight the use of GDF-15 as a biomarker for aging and age-related functional decline. Given that GDF-15 is easier to measure than DNA methylation, it has the potential to be more readily implemented in clinical settings for broader health assessment and management.

A gut microbial metabolite cocktail fights against obesity through modulating the gut microbiota and hepatic leptin signaling

BACKGROUND

Excessive body weight and obesity elevate the risk of chronic non-communicable diseases. The judicious application of the gut microbiome, encompassing both microorganisms and their derived compounds, holds considerable promise in the treatment of obesity.

RESULTS

In this study, we showed that a cocktail of gut microbiota-derived metabolites, comprising indole 3-propionic acid (IPA), sodium butyrate (SB) and valeric acid (VA), alleviated various symptoms of obesity in both male and female mice subjected to a high-fat diet (HFD). The 16S ribosomal RNA (rRNA) sequencing revealed that administering the cocktail via oral gavage retained the gut microbiota composition in obese mice. Fecal microbiota transplantation using cocktail-treated mice as donors mitigated the obesity phenotype of HFD-fed mice. Transcriptomic sequencing analysis showed that the cocktail preserved the gene expression profile of hepatic tissues in obese mice, especially up-regulated the expression level of leptin receptor. Gene delivery via in vivo fluid dynamics further validated that the anti-obesity efficacy of the cocktail was dependent on leptin signaling at least partly. The cocktail also inhibited the expression of appetite stimulators in hypothalamus. Together, the metabolite cocktail combated adiposity by retaining the gut microbiota configuration and activating the hepatic leptin signaling pathway.

CONCLUSIONS

Our findings provide a sophisticated regulatory network between the gut microbiome and host, and highlight a cocktail of gut microbiota-derived metabolites, including IPA, SB, and VA, might be a prospective intervention for anti-obesity in a preclinical setting. © 2024 Society of Chemical Industry.

Spop deficiency impairs adipogenesis and promotes thermogenic capacity in mice

As the adaptor protein that determines substrate specificity of the Cul3-SPOP-Rbx1 E3 ligase complex, SPOP is involved in numerous biological processes. However, its physiological connections with adipogenesis and thermogenesis remain poorly understood. In the current study, we report that the conditional knockout of Spop in mice results in substantial changes in protein expression, including the upregulation of a critical factor associated with thermogenesis, UCP1. Loss of SPOP also led to defects in body weight gain. In addition, conditional knockout mice exhibited resistance to high-fat-diet-induced obesity. Proteomics analysis found that proteins upregulated in the knockout mice are primarily enriched for functions in glycolysis/gluconeogenesis, oxidative phosphorylation, and thermogenesis. Furthermore, Spop knockout mice were more resilient during cold tolerance assay compared with the wild-type controls. Finally, the knockout of SPOP efficiently impaired adipogenesis in primary preadipocytes and the expression of associated genes. Collectively, these findings demonstrate the critical roles of SPOP in regulating adipogenesis and thermogenic capacity in mice.

Depression in childhood to early adulthood and respiratory health in early adulthood

BACKGROUND

Both depression and respiratory disease are common today in young populations. However, little is known about the relationship between them.

AIMS

This study aims to explore the association between depression in childhood to early adulthood and respiratory health outcomes in early adulthood, and the potential underlying mechanisms.

METHOD

A prospective study was conducted based on the Swedish BAMSE (Barn, Allergi, Miljö, Stockholm, Epidemiologi [Children, Allergy, Milieu, Stockholm, Epidemiology]) birth cohort (n = 4089). We identified clinically diagnosed depression through the dispensation of antidepressants, using national register data confirmed by self-reported diagnosis. At the 24-year follow-up, respiratory health was assessed via questionnaires and clinical evaluation. Metabolic and inflammatory profiles were analysed to explore potential mechanisms.

RESULTS

Among the 2994 participants who provided study data, 403 (13.5%) had depression at any time point from around age 10 to 25 years. Depression was associated with higher risks of any chronic bronchitis symptoms (odds ratio = 1.58, 95% CI 1.21-2.06) and respiratory symptoms (odds ratio = 1.41, 95% CI 1.11-1.80) in early adulthood, independent of body mass index (BMI) and smoking status. Compared to individuals without depression, those with depression had a higher fat mass index (FMI (β = 0.48, 95% CI 0.22-0.74)) and increased blood levels of fibroblast growth factor 21 and Interleukin-6 in early adulthood. These markers together with FMI were found to partly mediate the association between depression and respiratory symptoms (total mediation proportion: 19.8 and 15.4%, respectively, P < 0.01).

CONCLUSIONS

Depression in childhood to early adulthood was associated with an increased risk of respiratory ill-health in early adulthood, independently of smoking. Metabolic and inflammatory dysregulations may underlie this link.

LncRNA Snhg3 aggravates hepatic steatosis via PPARγ signaling

LncRNAs are involved in modulating the individual risk and the severity of progression in metabolic dysfunction-associated fatty liver disease (MASLD), but their precise roles remain largely unknown. This study aimed to investigate the role of lncRNA Snhg3 in the development and progression of MASLD, along with the underlying mechanisms. The result showed that Snhg3 was significantly downregulated in the liver of high-fat diet-induced obesity (DIO) mice. Notably, palmitic acid promoted the expression of Snhg3 and overexpression of Snhg3 increased lipid accumulation in primary hepatocytes. Furthermore, hepatocyte-specific Snhg3 deficiency decreased body and liver weight, alleviated hepatic steatosis and promoted hepatic fatty acid metabolism in DIO mice, whereas overexpression induced the opposite effect. Mechanistically, Snhg3 promoted the expression, stability and nuclear localization of SND1 protein via interacting with SND1, thereby inducing K63-linked ubiquitination modification of SND1. Moreover, Snhg3 decreased the H3K27me3 level and induced SND1-mediated chromatin loose remodeling, thus reducing H3K27me3 enrichment at the Pparg promoter and enhancing PPARγ expression. The administration of PPARγ antagonist T0070907 improved Snhg3-aggravated hepatic steatosis. Our study revealed a new signaling pathway, Snhg3/SND1/H3K27me3/PPARγ, responsible for mice MASLD and indicates that lncRNA-mediated epigenetic modification has a crucial role in the pathology of MASLD.

Hepatocyte-specific GDF15 overexpression improves high-fat diet-induced obesity and hepatic steatosis in mice via hepatic FGF21 induction

GDF15 and FGF21, stress-responsive cytokines primarily secreted from the liver, are promising therapeutic targets for metabolic dysfunction-associated steatotic liver disease (MASLD). However, the interaction between GDF15 and FGF21 remains unclear. We examined the effects of hepatocyte-specific GDF15 or FGF21 overexpression in high-fat diet (HFD)-fed mice for 8 weeks. Hydrodynamic injection of GDF15 or FGF21 sustained high circulating levels of GDF15 or FGF21, respectively, resulting in marked reductions in body weight, epididymal fat mass, insulin resistance, and hepatic steatosis. In addition, GDF15 treatment led to early reduction in body weight despite no change in food intake, indicating the role of GDF15 other than appetite loss. GDF15 treatment increased liver-derived serum FGF21 levels, whereas FGF21 treatment did not affect GDF15 expression. GDF15 promoted eIF2α phosphorylation and XBP1 splicing, leading to FGF21 induction. In murine AML12 hepatocytes treated with free fatty acids (FFAs), GDF15 overexpression upregulated Fgf21 mRNA levels and promoted eIF2α phosphorylation and XBP1 splicing. Overall, continuous exposure to excess FFAs resulted in a gradual increase of β-oxidation-derived reactive oxygen species and endoplasmic reticulum stress, suggesting that GDF15 enhanced this pathway and induced FGF21 expression. GDF15- and FGF21-related crosstalk is an important pathway for the treatment of MASLD.

The association between fatty acids and atherosclerotic diseases: A mendelian randomization study

BACKGROUND

The current observational studies have disputed the relationship between various fatty acids and atherosclerotic diseases, and the causal relationship between the two is still unclear.

METHODS

In this study, we utilized the available genome-wide association studies (GWAS) summary data on fatty acids and atherosclerotic diseases from the IEU OpenGWAS project. After identifying the appropriate single nucleotide polymorphisms (SNPs) as instrumental variables, we employed the MR-PRESSO outlier test to remove extreme values. Subsequently, we conducted a two-sample mendelian randomization (MR) analysis and performed sensitivity analyses to ensure the reliability of the results.

RESULTS

The results of MR analysis suggest that ratio of saturated fatty acids to total fatty acids is positively correlated with the incidence rate of coronary heart disease (OR = 1.341, 95% CI = 1.016-1.769, P value = 0.038), monounsaturated fatty acid levels is negatively correlated with the incidence of stroke (OR = 0.800, 95% CI = 0.642-0.996, P value = 0.046), and docosahexaenoic acid levels is negatively correlated with the incidence of peripheral artery disease (OR = 0.747, 95% CI = 0.572-0.976, P value = 0.033). All results showed no heterogeneity or pleiotropy, but leave-one-out tests showed that the analysis results of some fatty acids were driven by a single SNP.

CONCLUSIONS

This study highlights the existence of causal relationships between fatty acids and atherosclerotic diseases at the genetic level. These findings provide valuable insights for potential prevention measures and therapeutic targets for the three atherosclerotic diseases.

Bitter-tasting drugs tune GDF15 and GLP-1 expression via bitter taste or motilin receptors in the intestine of patients with obesity

OBJECTIVE

Growth differentiation factor 15 (GDF15), a stress related cytokine, was recently identified as a novel satiety signal acting via the GFRAL receptor located in the hindbrain. Bitter compounds are known to induce satiety via the release of glucagon-like peptide 1 (GLP-1) through activation of bitter taste receptors (TAS2Rs, 25 subtypes) on enteroendocrine cells in the gut. This study aimed to investigate whether and how bitter compounds induce a stress response in intestinal epithelial cells to affect GDF15 expression in patients with obesity, thereby facilitating satiety signaling from the gut.

METHODS

The acute effect of oral intake of the bitter-containing medication Plaquenil (hydroxychloroquine sulfate) on plasma GDF15 levels was evaluated in a placebo-controlled, double-blind, randomized, two-visit crossover study in healthy volunteers. Primary crypts isolated from the jejunal mucosa from patients with obesity were stimulated with vehicle or bitter compounds, and the effect on GDF15 expression was evaluated using RT-qPCR or ELISA. Immunofluorescence colocalization studies were performed between GDF15, epithelial cell type markers and TAS2Rs. The role of TAS2Rs was tested by 1) pretreatment with a TAS2R antagonist, GIV3727; 2) determining TAS2R4/43 polymorphisms that affect taste sensitivity to TAS2R4/43 agonists.

RESULTS

Acute intake of hydroxychloroquine sulfate increased GDF15 plasma levels, which correlated with reduced hunger scores and plasma ghrelin levels in healthy volunteers. This effect was mimicked in primary jejunal cultures from patients with obesity. GDF15 was expressed in enteroendocrine and goblet cells with higher expression levels in patients with obesity. Various bitter-tasting compounds (medicinal, plant extracts, bacterial) either increased or decreased GDF15 expression, with some also affecting GLP-1. The effect was mediated by specific intestinal TAS2R subtypes and the unfolded protein response pathway. The bitter-induced effect on GDF15/GLP-1 expression was influenced by the existence of TAS2R4 amino acid polymorphisms and TAS2R43 deletion polymorphisms that may predict patient's therapeutic responsiveness. However, the effect of the bitter-tasting antibiotic azithromycin on GDF15 release was mediated via the motilin receptor, possibly explaining some of its aversive side effects.

CONCLUSIONS

Bitter chemosensory and pharmacological receptors regulate the release of GDF15 from human gut epithelial cells and represent potential targets for modulating metabolic disorders or cachexia.

ATF4-dependent and independent mitokine secretion from OPA1 deficient skeletal muscle in mice is sexually dimorphic

Introduction

Reducing Optic Atrophy 1 (OPA1) expression in skeletal muscle in male mice induces Activation Transcription Factor 4 (ATF4) and the integrated stress response (ISR). Additionally, skeletal muscle secretion of Fibroblast Growth Factor 21 (FGF21) is increased, which mediates metabolic adaptations including resistance to diet-induced obesity (DIO) and glucose intolerance in these mice. Although FGF21 induction in this model can be reversed with pharmacological attenuation of ER stress, it remains to be determined if ATF4 is responsible for FGF21 induction and its metabolic benefits in this model.

Methods

We generated mice with homozygous floxed Opa1 and Atf4 alleles and a tamoxifen-inducible Cre transgene controlled by the human skeletal actin promoter to enable simultaneous depletion of OPA1 and ATF4 in skeletal muscle (mAO DKO). Mice were fed high fat (HFD) or control diet and evaluated for ISR activation, body mass, fat mass, glucose tolerance, insulin tolerance and circulating concentrations of FGF21 and growth differentiation factor 15 (GDF15).

Results

In mAO DKO mice, ATF4 induction is absent. Other indices of ISR activation, including XBP1s, ATF6, and CHOP were induced in mAO DKO males, but not in mOPA1 or mAO DKO females. Resistance to diet-induced obesity was not reversed in mAO DKO mice of both sexes. Circulating FGF21 and GDF15 illustrated sexually dimorphic patterns. Loss of OPA1 in skeletal muscle increases circulating FGF21 in mOPA1 males, but not in mOPA1 females. Additional loss of ATF4 decreased circulating FGF21 in mAO DKO male mice, but increased circulating FGF21 in female mAO DKO mice. Conversely, circulating GDF15 was increased in mAO DKO males and mOPA1 females, but not in mAO DKO females.

Conclusion

Sex differences exist in the transcriptional outputs of the ISR following OPA deletion in skeletal muscle. Deletion of ATF4 in male and female OPA1 KO mice does not reverse the resistance to DIO. Induction of circulating FGF21 is ATF4 dependent in males, whereas induction of circulating GDF15 is ATF4 dependent in females. Elevated GDF15 in males and FGF21 in females could reflect activation by other transcriptional outputs of the ISR, that maintain mitokine-dependent metabolic protection in an ATF4-independent manner.

Imbalanced Skeletal Muscle Mitochondrial Proteostasis Causes Bone Loss

Although microgravity has been implicated in osteoporosis, the precise molecular mechanism remains elusive. Here, we found that microgravity might induce mitochondrial protein buildup in skeletal muscle, alongside reduced levels of LONP1 protein. We revealed that disruptions in mitochondrial proteolysis, induced by the targeted skeletal muscle-specific deletion of the essential mitochondrial protease LONP1 or by the acute inducible deletion of muscle LONP1 in adult mice, cause reduced bone mass and compromised mechanical function. Moreover, the bone loss and weakness phenotypes were recapitulated in skeletal muscle-specific overexpressing ΔOTC mice, a known protein degraded by LONP1. Mechanistically, mitochondrial proteostasis imbalance triggered the mitochondrial unfolded protein response (UPRmt) in muscle, leading to an up-regulation of multiple myokines, including FGF21, which acts as a pro-osteoclastogenic factor. Surprisingly, this mitochondrial proteostasis stress influenced muscle-bone crosstalk independently of ATF4 in skeletal muscle. Furthermore, we established a marked association between serum FGF21 levels and bone health in humans. These findings emphasize the pivotal role of skeletal muscle mitochondrial proteostasis in responding to alterations in loading conditions and in coordinating UPRmt to modulate bone metabolism.

Liver-based inter-organ communication: A disease perspective

Inter-organ communication through hormones, cytokines and extracellular vesicles (EVs) has emerged to contribute to the physiological states and pathological processes of the human body. Notably, the liver coordinates multiple tissues and organs to maintain homeostasis and maximize energy utilization, with the underlying mechanisms being unraveled in recent studies. Particularly, liver-derived EVs have been found to play a key role in regulating health and disease. As an endocrine organ, the liver has also been found to perform functions via the secretion of hepatokines. Investigating the multi-organ communication centered on the liver, especially in the manner of EVs and hepatokines, is of great importance to the diagnosis and treatment of liver-related diseases. This review summarizes the crosstalk between the liver and distant organs, including the brain, the bone, the adipose tissue and the intestine in noticeable situations. The discussion of these contents will add to a new dimension of organismal homeostasis and shed light on novel theranostics of pathologies.

Serum growth differentiation factor 15 is a novel biomarker with high predictive capability for liver cancer occurrence in patients with MASLD regardless of liver fibrosis

BACKGROUND AND AIMS

Although metabolic dysfunction-associated steatotic liver disease (MASLD) patients with a Fib-4 index >1.3 are recommended for fibrosis evaluation via elastography or biopsy, a more convenient method identifying high-risk populations requiring follow-up is needed. We explored the utility of serum levels of growth differentiation factor-15 (GDF15), a cell stress-responsive cytokine related to metabolic syndrome, for stratifying the risk of clinical events in MASLD patients.

METHODS

Serum GDF15 levels were measured in 518 biopsy-performed MASLD patients, 216 MASLD patients for validation, and 361 health checkup recipients with MASLD.

RESULTS

In the biopsy-MASLD cohort, multivariate analysis indicated that the serum GDF15 level was a risk factor for liver cancer, independent of the fibrosis stage or Fib-4 index. Using a GDF15 cutoff of 1.75 ng/mL based on the Youden index, high-GDF15 patients, regardless of fibrosis status, had a higher liver cancer incidence rate. While patients with a Fib-4 index <1.3 or low-GDF15 rarely developed liver cancer, high-GDF15 patients with a Fib-4 index >1.3 developed liver cancer and decompensated liver events at significantly higher rates and had poorer prognoses. In the validation cohort, high-GDF15 patients had significantly higher incidences of liver cancer and decompensated liver events and poorer prognoses than low-GDF15 patients, whether limited to high-Fib-4 patients. Among health checkup recipients with MASLD, 23.0% had a Fib-4 index >1.3, 2.7% had a Fib-4 index >1.3 and >1.75 ng/mL GDF15.

CONCLUSIONS

Serum GDF15 is a biomarker for liver cancer with high predictive capability and is useful for identifying MASLD patients requiring regular surveillance.

BACH1 inhibits senescence, obesity, and short lifespan by ferroptotic FGF21 secretion

Ferroptosis is a type of regulated cell death characterized by iron-dependent lipid peroxidation. A model cell system is constructed to induce ferroptosis by re-expressing the transcription factor BACH1, a potent ferroptosis inducer, in immortalized mouse embryonic fibroblasts (iMEFs). The transfer of the culture supernatant from ferroptotic iMEFs activates the proliferation of hepatoma cells and other fibroblasts and suppresses cellular senescence-like features. The BACH1-dependent secretion of the longevity factor FGF21 is increased in ferroptotic iMEFs. The anti-senescent effects of the culture supernatant from these iMEFs are abrogated by Fgf21 knockout. BACH1 activates the transcription of Fgf21 by promoting ferroptotic stress and increases FGF21 protein expression by suppressing its autophagic degradation through transcriptional Sqstm1 and Lamp2 repression. The BACH1-induced ferroptotic FGF21 secretion suppresses obesity in high-fat diet-fed mice and the short lifespan of progeria mice. The inhibition of these aging-related phenotypes can be physiologically significant regarding ferroptosis.

Overview of growth differentiation factor 15 (GDF15) in metabolic diseases

GDF15 is a stress response cytokine and a distant member of the transforming growth factor beta (TGFβ) superfamily, its levels increase in response to cell stress and certain diseases in the serum. To exert its effects, GDF15 binds to glial-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL), which was firstly identified in 2017 and highly expressed in the brain stem. Many studies have demonstrated that elevated serum GDF15 is associated with anorexia and weight loss. Herein, we focus on the biology of GDF15, specifically how this circulating protein regulates appetite and metabolism in influencing energy homeostasis through its actions on hindbrain neurons to shed light on its impact on diseases such as obesity and anorexia/cachexia syndromes. It works as an endocrine factor and transmits metabolic signals leading to weight reduction effects by directly reducing appetite and indirectly affecting food intake through complex mechanisms, which could be a promising target for the treatment of energy-intake disorders.

Moderate-intensity constant or high-intensity interval training? Metabolic effects on candidates to undergo bariatric surgery

BACKGROUND & AIMS

Bariatric surgery is highly effective against obesity. Pre-surgical exercise programs are recommended to prepare the candidate physically and metabolically for surgery-related rapid weight loss. However, the ideal exercise prescription in this population is unknown. This study aimed to compare the metabolic effects of moderate-intensity constant (MICT) vs. a high-intensity interval training (HIIT) program in candidates to undergo bariatric surgery.

METHODS AND RESULTS

Twenty-five candidates (22 women) to undergo sleeve gastrectomy aged from 18 to 60 years old were recruited. At baseline, we measured body composition, physical activity levels, grip strength, and aerobic capacity. Further, we assessed metabolic function through glycemia and insulinemia (both fasting and after oral glucose tolerance test (OGTT)), homeostatic model assessment for insulin resistance (HOMA-IR), lipid profile, glycated haemoglobin (HbA1c), transaminases, fibroblast growth factor 21 (FGF21), growth differentiation factor 15 (GDF15), apelin, and adiponectin. Afterward, participants were randomized into MICT (n = 14) or HIIT (n = 11). Both training programs consisted of 10 sessions (2-3 times/week, 30 min per session) distributed during 4 weeks before the surgery. After this, all outcomes were measured again at the end of the training programs and 1 month after the surgery (follow-up). A mixed effect with Tukey's post-hoc analysis was performed to compare values at baseline vs. post-training vs. postsurgical follow-up. Both training programs increased aerobic capacity after training (p < 0.05), but only after MICT these changes were kept at follow-up (p < 0.05). However, only MICT decreased fat mass and increased total muscle mass and physical activity levels (p < 0.05). Metabolically, MICT decreased insulinemia after OGTT (p < 0.05), whereas HIIT increased adiponectin after training and GDF15 at follow-up (both p < 0.05).

CONCLUSIONS

Both MICT and HIIT conferred benefits in candidates to undergo bariatric surgery, however, several of those effects were program-specific, suggesting that exercise intensity should be considered when preparing these patients. Future studies should explore the potential benefits of prescribing MICT or HIIT in a customized fashion depending on a pretraining screening, along with possible summatory effects by combining these two exercise programs (MICT + HIIT).

CLINICAL TRIAL REGISTRATION

International Traditional Medicine Clinical Trial Registry, N° ISRCTN42273422.

A study on the early metabolic effects of salt and fructose consumption: the protective role of water

Increasing serum osmolality has recently been linked with acute stress responses, which over time can lead to increased risk for obesity, hypertension, and other chronic diseases. Salt and fructose are two major stimuli that can induce acute changes in serum osmolality. Here we investigate the early metabolic effects of sodium and fructose consumption and determine whether the effects of sodium or fructose loading can be mitigated by blocking the change in osmolality with hydration. Forty-four healthy subjects without disease and medication were recruited into four groups. After overnight fasting, subjects in Group 1 drank 500 mL of salty soup, while those in Group 2 drank 500 mL of soup without salt for 15 min. Subjects in Group 3 drank 500 mL of 100% apple juice in 5 min, while subjects in Group 4 drank 500 mL of 100% apple juice and 500 mL of water in 5 min. Blood pressure (BP), plasma sodium, and glucose levels were measured every 15 min in the first 2 h. Serum and urine osmolarity, serum uric acid, cortisol, fibroblast growth factor 21 (FGF21), aldosterone, adrenocorticotropic hormone (ACTH) level, and plasma renin activity (PRA) were measured at the baseline and 2 h. Both acute intake of salt or fructose increased serum osmolality (maximum ∼4 mOsm/L peaking at 75 min) associated with a rise in systolic and diastolic BP, PRA, aldosterone, ACTH, cortisol, plasma glucose, uric acid, and FGF21. Salt tended to cause greater activation of the renin-angiotensin-system (RAS), while fructose caused a greater rise in glucose and FGF21. In both cases, hydration could prevent the osmolality and largely block the acute stress response. Acute changes in serum osmolality can induce remarkable activation of the ACTH-cortisol, RAS, glucose metabolism, and uric acid axis that is responsive to hydration. In addition to classic dehydration, salt, and fructose-containing sugars can activate these responses. Staying well hydrated may provide benefits despite exposure to sugar and salt. More studies are needed to investigate whether hydration can block the chronic effects of sugar and salt on disease.

Metabolic Effects of Ketogenic Diets: Exploring Whole-Body Metabolism in Connection with Adipose Tissue and Other Metabolic Organs

The ketogenic diet (KD) is characterized by minimal carbohydrate, moderate protein, and high fat intake, leading to ketosis. It is recognized for its efficiency in weight loss, metabolic health improvement, and various therapeutic interventions. The KD enhances glucose and lipid metabolism, reducing triglycerides and total cholesterol while increasing high-density lipoprotein levels and alleviating dyslipidemia. It significantly influences adipose tissue hormones, key contributors to systemic metabolism. Brown adipose tissue, essential for thermogenesis and lipid combustion, encounters modified UCP1 levels due to dietary factors, including the KD. UCP1 generates heat by uncoupling electron transport during ATP synthesis. Browning of the white adipose tissue elevates UCP1 levels in both white and brown adipose tissues, a phenomenon encouraged by the KD. Ketone oxidation depletes intermediates in the Krebs cycle, requiring anaplerotic substances, including glucose, glycogen, or amino acids, for metabolic efficiency. Methylation is essential in adipogenesis and the body's dietary responses, with DNA methylation of several genes linked to weight loss and ketosis. The KD stimulates FGF21, influencing metabolic stability via the UCP1 pathways. The KD induces a reduction in muscle mass, potentially involving anti-lipolytic effects and attenuating proteolysis in skeletal muscles. Additionally, the KD contributes to neuroprotection, possesses anti-inflammatory properties, and alters epigenetics. This review encapsulates the metabolic effects and signaling induced by the KD in adipose tissue and major metabolic organs.

The natural compounds, Magnolol or Honokiol, promote adipose tissue browning and resist obesity through modulating PPARα/γ activity

Non-alcoholic fatty liver disease (NAFLD) is closely associated with the body's energy metabolism. A potential strategy to regulate energy metabolism, combat obesity, and reduce NAFLD is by enhancing adipocyte thermogenesis and increasing energy expenditure. In this study, our objective was to examine the effects of phenolic extracts derived from Magnolia officinalis on the regulation of NAFLD. Specifically, we investigated the impact of Magnolol or Honokiol treatment on high-fat diet (HFD)-induced obese C57BL6/J male mice. Firstly, we monitored energy metabolism, dissected tissues, and analyzed tissue sections. Additionally, we conducted experiments on HepG2 and primary adipocytes to gain insights into the roles of Magnolol or Honokiol. To further understand the effects of these compounds on related signaling pathways and marker genes, we performed molecular docking, dual-luciferase assays, and interfered with target genes. Our findings revealed that Magnolol or Honokiol activate the peroxisome proliferator activated receptor alpha (PPARα) signaling pathway, leading to the alleviation of NAFLD. This activation promotes fatty acid oxidation, reduces lipogenesis, and enhances the expression and secretion of FGF21. Notably, Fibroblast growth factor 21 (FGF21), secreted by the liver, plays a crucial role in improving communication between the liver and adipocytes while also promoting the browning of adipose tissue. Additionally, Magnolol or Honokiol activate the peroxisome proliferator activated receptor gamma (PPARγ) signaling pathway, resulting in increased uncoupling protein 1 (UCP1) expression, heightened heat production in adipose tissue, and anti-obesity. Therefore, Magnolol or Honokiol alleviate NAFLD, promote adipose tissue browning and resist obesity through dual activation of PPARα/γ.

A Narrative Review on Adipose Tissue and Overtraining: Shedding Light on the Interplay among Adipokines, Exercise and Overtraining

Lifestyle factors, particularly physical inactivity, are closely linked to the onset of numerous metabolic diseases. Adipose tissue (AT) has been extensively studied for various metabolic diseases such as obesity, type 2 diabetes, and immune system dysregulation due to its role in energy metabolism and regulation of inflammation. Physical activity is increasingly recognized as a powerful non-pharmacological tool for the treatment of various disorders, as it helps to improve metabolic, immune, and inflammatory functions. However, chronic excessive training has been associated with increased inflammatory markers and oxidative stress, so much so that excessive training overload, combined with inadequate recovery, can lead to the development of overtraining syndrome (OTS). OTS negatively impacts an athlete's performance capabilities and significantly affects both physical health and mental well-being. However, diagnosing OTS remains challenging as the contributing factors, signs/symptoms, and underlying maladaptive mechanisms are individualized, sport-specific, and unclear. Therefore, identifying potential biomarkers that could assist in preventing and/or diagnosing OTS is an important objective. In this review, we focus on the possibility that the endocrine functions of AT may have significant implications in the etiopathogenesis of OTS. During physical exercise, AT responds dynamically, undergoing remodeling of endocrine functions that influence the production of adipokines involved in regulating major energy and inflammatory processes. In this scenario, we will discuss exercise about its effects on AT activity and metabolism and its relevance to the prevention and/or development of OTS. Furthermore, we will highlight adipokines as potential markers for diagnosing OTS.

Adipose Tissue Dysfunction and Energy Balance Paradigms in People Living With HIV

Over the past 4 decades, the clinical care of people living with HIV (PLWH) evolved from treatment of acute opportunistic infections to the management of chronic, noncommunicable comorbidities. Concurrently, our understanding of adipose tissue function matured to acknowledge its important endocrine contributions to energy balance. PLWH experience changes in the mass and composition of adipose tissue depots before and after initiating antiretroviral therapy, including regional loss (lipoatrophy), gain (lipohypertrophy), or mixed lipodystrophy. These conditions may coexist with generalized obesity in PLWH and reflect disturbances of energy balance regulation caused by HIV persistence and antiretroviral therapy drugs. Adipocyte hypertrophy characterizes visceral and subcutaneous adipose tissue depot expansion, as well as ectopic lipid deposition that occurs diffusely in the liver, skeletal muscle, and heart. PLWH with excess visceral adipose tissue exhibit adipokine dysregulation coupled with increased insulin resistance, heightening their risk for cardiovascular disease above that of the HIV-negative population. However, conventional therapies are ineffective for the management of cardiometabolic risk in this patient population. Although the knowledge of complex cardiometabolic comorbidities in PLWH continues to expand, significant knowledge gaps remain. Ongoing studies aimed at understanding interorgan communication and energy balance provide insights into metabolic observations in PLWH and reveal potential therapeutic targets. Our review focuses on current knowledge and recent advances in HIV-associated adipose tissue dysfunction, highlights emerging adipokine paradigms, and describes critical mechanistic and clinical insights.

A novel bystander effect in tamoxifen treatment: PPIB derived from ER+ cells attenuates ER- cells via endoplasmic reticulum stress-induced apoptosis

Tamoxifen (TAM) is the frontline therapy for estrogen receptor-positive (ER+) breast cancer in premenopausal women that interrupts ER signaling. As tumors with elevated heterogeneity, amounts of ER-negative (ER-) cells are present in ER+ breast cancer that cannot be directly killed by TAM. Despite complete remissions have been achieved in clinical practice, the mechanism underlying the elimination of ER- cells during TAM treatment remains an open issue. Herein, we deciphered the elimination of ER- cells in TAM treatment from the perspective of the bystander effect. Markable reductions were observed in tumorigenesis of ER- breast cancer cells by applying both supernatants from TAM-treated ER+ cells and a transwell co-culture system, validating the presence of a TAM-induced bystander effect. The major antitumor protein derived from ER+ cells, peptidyl-prolyl cis-trans isomerase B (PPIB), is the mediator of the TAM-induced bystander effect identified by quantitative proteomics. The attenuation of ER- cells was attributed to activated BiP/eIF2α/CHOP axis and promoted endoplasmic reticulum stress (ERS)-induced apoptosis, which can also be triggered by PPIB independently. Altogether, our study revealed a novel TAM-induced bystander effect in TAM treatment of ER+ breast cancer, raising the possibility of developing PPIB as a synergistic antitumor agent or even substitute endocrine therapy.

Critical role of FGF21 in diabetic kidney disease: from energy metabolism to innate immunity

Diabetic kidney disease (DKD) stands as the predominant cause of chronic kidney disease (CKD) on a global scale, with its incidence witnessing a consistent annual rise, thereby imposing a substantial burden on public health. The pathogenesis of DKD is primarily rooted in metabolic disorders and inflammation. Recent years have seen a surge in studies highlighting the regulatory impact of energy metabolism on innate immunity, forging a significant area of research interest. Within this context, fibroblast growth factor 21 (FGF21), recognized as an energy metabolism regulator, assumes a pivotal role. Beyond its role in maintaining glucose and lipid metabolism homeostasis, FGF21 exerts regulatory influence on innate immunity, concurrently inhibiting inflammation and fibrosis. Serving as a nexus between energy metabolism and innate immunity, FGF21 has evolved into a therapeutic target for diabetes, nonalcoholic steatohepatitis, and cardiovascular diseases. While the relationship between FGF21 and DKD has garnered increased attention in recent studies, a comprehensive exploration of this association has yet to be systematically addressed. This paper seeks to fill this gap by summarizing the mechanisms through which FGF21 operates in DKD, encompassing facets of energy metabolism and innate immunity. Additionally, we aim to assess the diagnostic and prognostic value of FGF21 in DKD and explore its potential role as a treatment modality for the condition.

Non-alcoholic fatty liver disease promotes breast cancer progression through upregulated hepatic fibroblast growth factor 21

Non-alcoholic fatty liver disease (NAFLD) has been shown to influence breast cancer progression, but the underlying mechanisms remain unclear. In this study, we investigated the impact of NAFLD on breast cancer tumor growth and cell viability through the potential mediator, hepatic fibroblast growth factor 21 (FGF21). Both peritumoral and systemic administration of FGF21 promoted breast cancer tumor growth, while FGF21 knockout attenuated the tumor-promoting effects of the high-fat diet. Mechanistically, exogenous FGF21 treatment enhanced the anti-apoptotic ability of breast cancer cells through STAT3 and Akt/FoXO1 signaling pathways, and mitigated doxorubicin-induced cell death. Furthermore, we observed overexpression of FGF21 in tumor tissues from breast cancer patients, which was associated with poor prognosis. These findings suggest a novel role for FGF21 as an upregulated mediator in the context of NAFLD, promoting breast cancer development and highlighting its potential as a therapeutic target for cancer treatment.

Comprehensive Role of GDF15 in Inhibiting Adipogenesis and Hyperlipidemia, Enhancing Cardiovascular Health and Alleviating Inflammation in Metabolic Disorders

Growth Differentiation Factor 15 (GDF15) has emerged as a pivotal signaling molecule implicated in diverse physiological processes, spanning metabolic regulation, inflammation, and cardiovascular health. This study provides a comprehensive exploration of GDF15's multifaceted role, primarily focusing on its association with obesity-related complications and therapeutic potential. GDF15's involvement in energy homeostasis, specifically its regulation of body weight and appetite through hindbrain neuron activation and the GFRAL-RET signaling pathway, underscores its significance as an appetite-regulating hormone. GDF15's intricate modulation within adipose tissue dynamics in response to dietary changes and obesity, coupled with its influence on insulin sensitivity, highlights its critical role in metabolic health. The manuscript delves into the intricate crosstalk between GDF15 and pathways related to insulin sensitivity, macrophage polarization, and adipose tissue function, elucidating its potential as a therapeutic target for metabolic disorders associated with obesity. GDF15's association with chronic low-grade inflammation and its impact on cardiovascular health, particularly during hyperlipidemia and ischemic events, are explored. The intricate relationship between GDF15 and cardiovascular diseases, including its effects on endothelial function, cardiac hypertrophy, and heart failure, emphasizes its multifaceted nature in maintaining overall cardiovascular well-being. Challenges regarding the therapeutic application of GDF15, such as long-term safety concerns and ongoing clinical investigations, are discussed. Lastly, future research directions exploring GDF15's potential in addressing obesity-related complications and cardiovascular risks are proposed, highlighting its promising role as a therapeutic target in reshaping treatment strategies for obesity and associated health conditions.

ROS-induced ribosome impairment underlies ZAKα-mediated metabolic decline in obesity and aging

The ribotoxic stress response (RSR) is a signaling pathway in which the p38- and c-Jun N-terminal kinase (JNK)-activating mitogen-activated protein kinase kinase kinase (MAP3K) ZAKα senses stalling and/or collision of ribosomes. Here, we show that reactive oxygen species (ROS)-generating agents trigger ribosomal impairment and ZAKα activation. Conversely, zebrafish larvae deficient for ZAKα are protected from ROS-induced pathology. Livers of mice fed a ROS-generating diet exhibit ZAKα-activating changes in ribosomal elongation dynamics. Highlighting a role for the RSR in metabolic regulation, ZAK-knockout mice are protected from developing high-fat high-sugar (HFHS) diet-induced blood glucose intolerance and liver steatosis. Finally, ZAK ablation slows animals from developing the hallmarks of metabolic aging. Our work highlights ROS-induced ribosomal impairment as a physiological activation signal for ZAKα that underlies metabolic adaptation in obesity and aging.

GDF15 is a major determinant of ketogenic diet-induced weight loss

A ketogenic diet (KD) has been promoted as an obesity management diet, yet its underlying mechanism remains elusive. Here we show that KD reduces energy intake and body weight in humans, pigs, and mice, accompanied by elevated circulating growth differentiation factor 15 (GDF15). In GDF15- or its receptor GFRAL-deficient mice, these effects of KD disappeared, demonstrating an essential role of GDF15-GFRAL signaling in KD-mediated weight loss. Gdf15 mRNA level increases in hepatocytes upon KD feeding, and knockdown of Gdf15 by AAV8 abrogated the obesity management effect of KD in mice, corroborating a hepatic origin of GDF15 production. We show that KD activates hepatic PPARγ, which directly binds to the regulatory region of Gdf15, increasing its transcription and production. Hepatic Pparγ-knockout mice show low levels of plasma GDF15 and significantly diminished obesity management effects of KD, which could be restored by either hepatic Gdf15 overexpression or recombinant GDF15 administration. Collectively, our study reveals a previously unexplored GDF15-dependent mechanism underlying KD-mediated obesity management.

Endoplasmic reticulum stress inhibitor may substitute for sleeve gastrectomy to alleviate metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is becoming the most common form of chronic liver disease worldwide. We explored the potential mechanisms responsible for the protective role of sleeve gastrectomy (SG) on MASLD in a high-fat diet (HFD) rat model.

METHODS

Rats were fed with HFD for 12 weeks to generate MASLD model that were subjected to SG or sham surgery. The endoplasmic reticulum stress (ERS) inhibitor 4-phenylbutyric acid (4-PBA) was injected intraperitoneally every day for 4 weeks after surgery to identify the impact of ERS.

RESULTS

The MASLD rat model was generated successfully, as indicated by significant upregulation of metabolic parameters. Fibroblast growth factor 21 (FGF21) and ERS-related proteins were increased in HFD rats, while expression of fibroblast growth factor receptor 1 was decreased as expected. An HFD also induced swelling and blurring of the endoplasmic reticulum and mitochondria in hepatocytes, and the above transformation could be relieved by SG and 4-PBA. SG and an ERS inhibitor both inhibited MASLD, but their combined treatment had no additional benefit.

CONCLUSIONS

Dysfunction of the FGF21 signaling pathway and hepatic steatosis and inflammation could be induced by an HFD, potentially causing MASLD. Bariatric surgery and ERS inhibition could alleviate MASLD by relieving ERS-mediated impairment of FGF21 signal transduction. These findings provide a new insight into the use of ERS inhibitors to treat MASLD, especially in patients who prefer to avoid surgery.

Temporal dynamics of muscle mitochondrial uncoupling-induced integrated stress response and ferroptosis defense

Mitochondria play multifaceted roles in cellular function, and impairments across domains of mitochondrial biology are known to promote cellular integrated stress response (ISR) pathways as well as systemic metabolic adaptations. However, the temporal dynamics of specific mitochondrial ISR related to physiological variations in tissue-specific energy demands remains unknown. Here, we conducted a comprehensive 24-hour muscle and plasma profiling of male and female mice with ectopic mitochondrial respiratory uncoupling in skeletal muscle (mUcp1-transgenic, TG). TG mice are characterized by increased muscle ISR, elevated oxidative stress defense, and increased secretion of FGF21 and GDF15 as ISR-induced myokines. We observed a temporal signature of both cell-autonomous and systemic ISR in the context of endocrine myokine signaling and cellular redox balance, but not of ferroptotic signature which was also increased in TG muscle. We show a progressive increase of muscle ISR on transcriptional level during the active phase (night time), with a subsequent peak in circulating FGF21 and GDF15 in the early resting phase. Moreover, we found highest levels of muscle oxidative defense (GPX and NQO1 activity) between the late active to early resting phase, which could aim to counteract excessive iron-dependent lipid peroxidation and ferroptosis in muscle of TG mice. These findings highlight the temporal dynamics of cell-autonomous and endocrine ISR signaling under skeletal muscle mitochondrial uncoupling, emphasizing the importance of considering such dissociation in translational strategies and sample collection for diagnostic biomarker analysis.

Hepatic-Specific FGF21 Knockout Abrogates Ovariectomy-Induced Obesity by Reversing Corticosterone Production

Increased glucocorticoid (GC) levels act as a master contributor to central obesity in estrogen-depleted females; however, what factors cause their increased GC production is unclear. Given (1) liver fibroblast growth factor 21 (FGF21) and GCs regulate each other's production in a feed-forward loop, and (2) circulating FGF21 and GCs are parallelly increased in menopausal women and ovariectomized mice, we thus hypothesized that elevation of hepatic FGF21 secretion causes increased GGs production in estrogen-depleted females. Using the ovariectomized mice as a model for menopausal women, we found that ovariectomy (OVX) increased circulating corticosterone levels, which in turn increased visceral adipose Hsd11b1 expression, thus causing visceral obesity in females. In contrast, liver-specific FGF21 knockout (FGF21 LKO) completely reversed OVX-induced high GCs and high visceral adipose Hsd11b1 expression, thus abrogating OVX-induced obesity in females. Even though FGF21 LKO failed to rescue OVX-induced dyslipidemia, hepatic steatosis, and insulin resistance. What's worse, FGF21 LKO even further exacerbated whole-body glucose metabolic dysfunction as evidenced by more impaired glucose and pyruvate tolerance and worsened insulin resistance. Mechanically, we found that FGF21 LKO reduced circulating insulin levels, thus causing the dissociation between decreased central obesity and the improvement of obesity-related metabolic syndromes in OVX mice. Collectively, our results suggest that liver FGF21 plays an essential role in mediating OVX-induced central obesity by promoting GC production. However, lack of liver FGF21 signaling reduces insulin production and in turn causes the dissociation between decreased central obesity and the improvement of obesity-related metabolic syndromes, highlighting a detrimental role for hepatic FGF21 signals in mediating the development of central obesity but a beneficial role in preventing metabolic abnormality from further exacerbation in estrogen-depleted females.

The roles of FGF21 and GDF15 in mediating the mitochondrial integrated stress response

Various models of mitochondrial stress result in induction of the stress-responsive cytokines fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15). This is an adaptive mechanism downstream of the mitochondrial integrated stress response frequently associated with improvements in systemic metabolic health. Both FGF21 and GDF15 have been shown to modulate energy balance and glucose homeostasis, and their pharmacological administration leads to promising beneficial effects against obesity and associated metabolic diseases in pre-clinical models. Furthermore, endogenous upregulation of FGF21 and GDF15 is associated with resistance to diet-induced obesity (DIO), improved glucose homeostasis and increased insulin sensitivity. In this review, we highlight several studies on transgenic mouse models of mitochondrial stress and will compare the specific roles played by FGF21 and GDF15 on the systemic metabolic adaptations reported in these models.

The Role of Organokines in Obesity and Type 2 Diabetes and Their Functions as Molecular Transducers of Nutrition and Exercise

Maintaining systemic homeostasis requires the coordination of different organs and tissues in the body. Our bodies rely on complex inter-organ communications to adapt to perturbations or changes in metabolic homeostasis. Consequently, the liver, muscle, and adipose tissues produce and secrete specific organokines such as hepatokines, myokines, and adipokines in response to nutritional and environmental stimuli. Emerging evidence suggests that dysregulation of the interplay of organokines between organs is associated with the pathophysiology of obesity and type 2 diabetes (T2D). Strategies aimed at remodeling organokines may be effective therapeutic interventions. Diet modification and exercise have been established as the first-line therapeutic intervention to prevent or treat metabolic diseases. This review summarizes the current knowledge on organokines secreted by the liver, muscle, and adipose tissues in obesity and T2D. Additionally, we highlighted the effects of diet/nutrition and exercise on the remodeling of organokines in obesity and T2D. Specifically, we investigated the ameliorative effects of caloric restriction, selective nutrients including ω3 PUFAs, selenium, vitamins, and metabolites of vitamins, and acute/chronic exercise on the dysregulation of organokines in obesity and T2D. Finally, this study dissected the underlying molecular mechanisms by which nutrition and exercise regulate the expression and secretion of organokines in specific tissues.

GDF15 promotes weight loss by enhancing energy expenditure in muscle

Caloric restriction that promotes weight loss is an effective strategy for treating non-alcoholic fatty liver disease and improving insulin sensitivity in people with type 2 diabetes1. Despite its effectiveness, in most individuals, weight loss is usually not maintained partly due to physiological adaptations that suppress energy expenditure, a process known as adaptive thermogenesis, the mechanistic underpinnings of which are unclear2,3. Treatment of rodents fed a high-fat diet with recombinant growth differentiating factor 15 (GDF15) reduces obesity and improves glycaemic control through glial-cell-derived neurotrophic factor family receptor α-like (GFRAL)-dependent suppression of food intake4-7. Here we find that, in addition to suppressing appetite, GDF15 counteracts compensatory reductions in energy expenditure, eliciting greater weight loss and reductions in non-alcoholic fatty liver disease (NAFLD) compared to caloric restriction alone. This effect of GDF15 to maintain energy expenditure during calorie restriction requires a GFRAL-β-adrenergic-dependent signalling axis that increases fatty acid oxidation and calcium futile cycling in the skeletal muscle of mice. These data indicate that therapeutic targeting of the GDF15-GFRAL pathway may be useful for maintaining energy expenditure in skeletal muscle during caloric restriction.

Social confrontation stress decreases hepatic fibroblast growth factor-21 expression in aged mice

We previously showed that social stress exposure in mature adult mice increased blood corticosterone concentrations at 2 days, disrupted hepatic lipid metabolism-related pathway at 30 days, and increased the risk of overweight with hepatic hypertrophy at 90 days. To further investigate the effects of aging on the physiological responses to social stress, we conducted a study using male BALB/c mice at the ages of 2 months (mature age), 14 months (middle age) and 26 months (old age), and exposed them to confrontation stress for 2 or 7 days. Blood corticosterone concentrations were increased at 2 days of stress, and then returned to baseline concentrations. This change was observed only at 2 months of age. We further examined the effect of aging on hepatic gene expression of fibroblast growth factor-21 (Fgf21) and found that its expression was significantly decreased after 7 days of stress at 14 months of age and after 2 days of stress at 26 months of age, indicating these decreasing effects became more pronounced with age. In conclusion, our study suggests that hepatic Fgf21 expression decrease under exposure to confrontation stress at middle or more age, indicating that stress response on Fgf21 related pathway might be more pronounced with age when exposed to stress.

Hyperphagia of female UCP1-deficient mice blunts anti-obesity effects of FGF21

Increasing energy expenditure through uncoupling protein 1 (UCP1) activity in thermogenic adipose tissue is widely investigated to correct diet-induced obesity (DIO). Paradoxically, UCP1-deficient male mice are resistant to DIO at room temperature. Recently, we uncovered a key role for fibroblast growth factor 21 (FGF21), a promising drug target for treatment of metabolic disease, in this phenomenon. As the metabolic action of FGF21 is so far understudied in females, we aim to investigate potential sexual dimorphisms. Here, we confirm that male UCP1 KO mice display resistance to DIO in mild cold, without significant changes in metabolic parameters. Surprisingly, females gained the same amount of body fat as WT controls. Molecular regulation was similar between UCP1 KO males and females, with an upregulation of serum FGF21, coinciding with beiging of inguinal white adipose tissue and induced lipid metabolism. While energy expenditure did not display significant differences, UCP1 KO females significantly increased their food intake. Altogether, our results indicate that hyperphagia is likely counteracting the beneficial effects of FGF21 in female mice. This underlines the importance of sex-specific studies in (pre)clinical research for personalized drug development.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Serum Concentration of Growth Differentiation Factor 15 and Atherosclerosis among General Older Japanese Individuals with Normal Weight

Growth differentiation factor 15 (GDF-15), which modulates cellular energy balance, is reported to be positively associated with cardiovascular disease. However, there have been no reports about the association between serum GDF-15 concentration and atherosclerosis as evaluated by carotid intima-media thickness (CIMT) among the general population. A cross-sectional study of 536 Japanese individuals aged 60 to 69 years was conducted. To avoid the influence of abnormal cellular energy balance, this study only included participants who had a normal body mass index (BMI) and normal thyroid hormone (free thyroxine and free triiodothyronine) levels. A significant positive association between serum GDF-15 concentration and atherosclerosis was observed. In the sex- and age-adjusted model (Model 1), the odds ratio (OR) (95% confidence interval (CI)) for the logarithmic value of GDF-15 and atherosclerosis was 2.62 (1.67, 5.87). This association remained after adjusting for thyroid function and renal function (Model 2) and further adjusting for known cardiovascular risk factors (Model 3). The corresponding values were 2.61 (1.15, 5.93) for Model 2 and 2.49 (1.08, 5.71) for Model 3, respectively. Serum GDF-15 concentrations could help us to estimate the risk of atherosclerosis by indicating the status of cellular energy balance, which is related to mitochondrial activity among comparative healthy older individuals.

Regulatory mechanisms of macrophage polarization in adipose tissue

In adipose tissue, macrophages are the most abundant immune cells with high heterogeneity and plasticity. Depending on environmental cues and molecular mediators, adipose tissue macrophages (ATMs) can be polarized into pro- or anti-inflammatory cells. In the state of obesity, ATMs switch from the M2 polarized state to the M1 state, which contributes to chronic inflammation, thereby promoting the pathogenic progression of obesity and other metabolic diseases. Recent studies show that multiple ATM subpopulations cluster separately from the M1 or M2 polarized state. Various factors are related to ATM polarization, including cytokines, hormones, metabolites and transcription factors. Here, we discuss our current understanding of the potential regulatory mechanisms underlying ATM polarization induced by autocrine and paracrine factors. A better understanding of how ATMs polarize may provide new therapeutic strategies for obesity-related diseases.