Reduced oxidative capacity in macrophages results in systemic insulin resistance

HIIT may ameliorate inter-organ crosstalk between liver and hypothalamus of HFD-induced MAFLD rats; A two-phase study to investigate the effect of exercise intensity as a stressor

Previous studies demonstrate that GDF15 and its related signaling activators may be affected by exercise training, leading to the suppression of inflammatory factors and the promotion of immune-metabolic balance. Therefore, the purpose of the study was to evaluate the effect of high-intensity interval training (HIIT) on amelioration of inter-organ crosstalk between liver and hypothalamus of the high-fat diet (HFD)-induced metabolic dysfunction-associated fatty liver disease (MAFLD) rats in a two-phase study. In this regard, rats were initially divided into two groups, the normal diet-inactive (NS) and the HFD groups. HFD course lasted 12 weeks to induce MAFLD in the latter group. After ensuring the induction of MAFLD, 25 rats were divided into three groups: the HFD-inactive group (HS), the HFD-HIIT group (HH), as well as the HFD-aerobic group (HA). The training interventions were consistently applied over a period of eight weeks, five days a week, with each session lasting 40-60 min, and the duration of the whole research was 21 weeks. The results of this study displayed that HIIT intervention promotes hypothalamic Gdf15 gene expression and there were similar alterations in genes expression of Foxo1 and Akt2. Moreover, our results confirmed that HIIT ameliorated hypothalamic NFKB gene expression and there was a similar trend in genes expression of Tnfa and Il1b following both HIIT as well as aerobic training protocols. Taking these findings together, it is concluded that interventions, particularly exercise training, uniquely contribute to the reduction of hypothalamic-associated inflammatory responses that result in prolonged and chronic increases in GDF15.

GDF15 suppresses abdominal aortic aneurysm by upregulating AREG expression to adjust macrophage polarization

OBJECTIVE

Inflammation plays a key role in abdominal aortic aneurysm (AAA), with macrophages being crucial. Growth differentiation factor 15 (GDF15) is a new anti-inflammatory cytokine potentially useful in AAA diagnosis and treatment, but its role is unclear.

METHODS AND RESULTS

In mice with AAA, GDF15 expression was higher in lesioned tissues. Daily intraperitoneal injection of recombinant GDF15 (rGDF15) reduced aortic dilation, inflammation, degradation of aortic wall elastin and collagen, cellular apoptosis, and increased smooth muscle cells. GDF15 knockdown worsened AAA severity. Immunohistochemistry and immunofluorescence showed rGDF15 treatment reduced M1 macrophage polarization and enhanced M2 polarization, decreasing the M1/M2 ratio. GDF15 knockdown had the opposite effect. Additionally, Amphiregulin (AREG) expression increased with rGDF15 treatment and decreased with GDF15 knockdown. Immunofluorescence colocalization revealed lower AREG expression in M1 macrophages and higher AREG expression in M2 macrophages, suggesting that AREG may be involved in the regulation of macrophage polarization by GDF15 in AAA. Mechanistically, GDF15 upregulates AREG expression by activating the TGF-βR/SMAD2/3 signaling pathway, thereby inhibiting M1 polarization and promoting M2 polarization of macrophages.

CONCLUSION

This study demonstrates that exogenous injection of rGDF15 upregulates AREG expression and regulates macrophage polarization, thereby inhibiting AAA. GDF15 may not only serve as a diagnostic and prognostic marker for AAA but also as a potential molecular target for therapeutic intervention in AAA.

Revisiting the role of GDF15 in atherosclerosis in mouse and human

Growth differentiation factor 15 (GDF15) is a key regulator of food intake and energy metabolism. GDF15 mimetic drugs for the treatment of metabolic syndrome and obesity are under clinical development. While GDF15 presents a promising target for weight management, its potential cardiovascular actions remain elusive. In this study we investigated the role of GDF15 in macrophage function and atherosclerosis pathogenesis and whether GDF15 acts both as a biomarker and mediator of atherosclerosis severity. ApoE-/- mice were fed a high-cholesterol diet (HCD, 1.25% cholesterol) for 6, 12 or 18 weeks to establish atherosclerotic models. We showed that serum levels of GDF15 were elevated in ApoE-/- mice with atheroprogression; increased serum levels of GDF15 were also observed in patients with coronary artery disease. Enlightened by this finding, we established atherosclerotic model in Gdf15-/- mice by injecting with AAV8-PCSK9D377Y virus and feeding HCD for 12 or 16 weeks. We showed that global Gdf15 knockout, whether in male or female mice, did not alter plaque size in en face aorta, lesion in aortic sinus, size of necrotic core or plaque composition. In macrophage-derived foam cells isolated from atherosclerotic mice, neither Gdf15 deletion nor the treatment with recombinant GDF15 protein (1, 10, 100 ng/mL) affected lipid deposition or macrophage polarization. To translate this finding into a clinically relevant scenario, we performed Mendelian randomization (MR) analysis, and found no significant causal association between circulating GDF15 levels and the incidence of cardiovascular diseases. Furthermore, MR studies suggest that genetic associations between GDF15 and factors such as BMI, ApoB, LDL and HDL were not significant in plasma data from the UK Biobank and the deCODE cohort. In summary, this study demonstrates that global Gdf15 deficiency does not affect the development of atherosclerosis in male or female mice despite the positive association between circulating GDF15 levels and disease progression in mice and human. Thus, GDF15 in circulation is a potential biomarker, but not a causal mediator, of atherosclerosis. Long-term cardiovascular safety of GDF15-targeted therapies warrants further investigation.

The association between serum growth differentiation factor 15 and insulin resistance in women diagnosed with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is strongly associated with metabolic abnormalities, with 50-70% of patients exhibiting insulin resistance (IR), which significantly impacts the reproductive health of women in their reproductive years. Growth differentiation factor 15 (GDF15), a hormone responsive to nutritional stress, has been implicated in several diseases. This study sought to clarify the relationship between GDF15 levels and IR condition in PCOS patients. Based on the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), patients were categorized into an IR-PCOS group (n = 124) and a non-insulin-resistant group (non-IR-PCOS group, n = 109). Fasting blood samples were collected to measure GDF15 concentrations. To assess metabolic complications in relation to GDF15 levels, patients were also classified into high and normal GDF15 groups. Serum GDF15 levels were significantly higher in IR-PCOS patients (median 772.94 pg/ml) compared to non-IR-PCOS patients (median 575.80 pg/ml, P < 0.05). The high GDF15 group showed more severe metabolic and lipid abnormalities than the normal GDF15 group. Spearman correlation analysis revealed a correlation between increased GDF15 levels and impaired glucose metabolism. Logistic regression analysis identified GDF15, HDL-C, and prolactin as risk factors for IR in PCOS, and the fully adjusted regression coefficient for GDF15 levels and IR prevalence was 4.490 (95% CI 1.541 to 13.088). Restricted cubic spline analysis confirmed a positive association between GDF15 levels and IR within a specific range. The combined predictive probability of GDF15, prolactin, and HDL-C for IR was 0.763 (95% CI 0.701 to 0.826) according to ROC analysis. Elevated GDF15 levels may be associated with IR in PCOS patients, suggesting a potential role for GDF15 in the pathophysiology of IR in this condition.

BNIP3-mediated mitophagy in macrophages regulates obesity-induced adipose tissue metaflammation

Adipose tissue macrophages (ATMs) are key cellular components that respond to nutritional excess, contributing to obesity-induced inflammation and insulin resistance. However, the mechanisms underlying macrophage polarization and recruitment in adipose tissue during obesity remain unclear. In this study, we investigated mitophagy-dependent metabolic reprogramming in ATMs and identified a crucial role of the mitophagy receptor BNIP3 in regulating macrophage polarization in response to obesity. Mitophagic flux in ATMs increased following 12 weeks of high-fat diet (HFD) feeding, with Bnip3 levels upregulated in a HIF1A dependent manner, without affecting other mitophagy receptors. Macrophage-specific bnip3 knockout reduced HFD-induced adipose tissue inflammation and improved glucose tolerance and insulin sensitivity. Mechanistically, hypoxic conditions in vitro induced HIF1A-BNIP3-mediated mitophagy and glycolytic shift in macrophages. Furthermore, HIF1A-BNIP3 signaling-enhanced lipopolysaccharide-induced pro-inflammatory activation in macrophages. These findings demonstrate that BNIP3-mediated mitophagy regulates the glycolytic shift and pro-inflammatory polarization in macrophages and suggest that BNIP3 could be a therapeutical target for obesity-related metabolic diseases.Abbreviation: 2-DG: 2-deoxyglucose; ACADM/MCAD: acyl-CoA dehydrogenase medium chain; ADGRE1/F4/80: adhesion G protein-coupled receptor E1; ATMs: adipose tissue macrophages; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; CLS: crown-like structure; CoCl2: cobalt(II) chloride; COX4/COXIV: cytochrome c oxidase subunit 4; ECAR: extracellular acidification rate; ECM: extraceullular matrix; gWAT: gonadal white adipose tissue; HFD: high-fat diet; HIF1A/HIF-1 α: hypoxia inducible factor 1 subunit alpha; IL1B/IL-1β: interleukin 1 beta; ITGAM/CD11B: integrin subunit alpha M; KO: knockout; LAMs: lipid-associated macrophages; LPS: lipopolysaccharide; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MRC1/CD206: mannose receptor C-type 1; mtDNA: mitochondrial DNA; NCD: normal chow diet; OCR: oxygen consumption rate; OXPHOS: oxidative phosphorylation; PINK1: PTEN induced kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; PTPRC/CD45: protein tyrosine phosphatase receptor type C; SVFs: stromal vascular fractions; TEM: transmission electron microscopy; TMRM: tetramethylrhodamine methyl ester; TOMM20: Translocase of outer mitochondrial membrane 20; TREM2: triggering receptor expressed on myeloid cells 2; WT: wild-type.

Relationship Between Brain Insulin Resistance, Carbohydrate Consumption, and Protein Carbonyls, and the Link Between Peripheral Insulin Resistance, Fat Consumption, and Malondialdehyde

The consumption of a high-fat (HFD) or high-carbohydrate/low-fat (LFD) diet is related to insulin resistance; however, central and peripheral alterations can occur independently. In this study, the timeline of insulin resistance was determined while taking into consideration the role of diet in oxidative damage. Background/Objectives: The aim of this study was to ascertain whether a HFD or LFD induces peripheral insulin resistance (PIR) before brain insulin resistance (BIR), and whether the timing of these alterations correlates with heightened oxidative damage markers in plasma, adipose tissue, and the cerebral cortex. Methodology and Results: Three-month-old C57BL/6 male mice were fed with a HFD, LFD, or standard diet for 1, 2, or 3 months. Glucose and insulin tolerance tests were performed to determine PIR, and the hypothalamic thermogenic response to insulin was used to determine their BIR status. For oxidative damage, the levels of malondialdehyde (MDA) and the protein carbonyl group (PCO) and the enzymatic activity of glutathione peroxidase (GSH-Px) were evaluated in plasma, white adipose tissue, brown adipose tissue, and the cerebral cortex. PIR occurred at 3 months of the HFD, but MDA levels in the white adipose tissue increased at 2 months. BIR occurred at 1 and 2 months of the LFD, but the enzymatic activity of GSH-Px was lower at 1 month and the amount of the PCO increased at 2 months. Conclusions: The intake of a HFD or LFD of different durations can influence the establishment of PIR or BIR, and oxidative damage in the fat tissue and cerebral cortex can play an important role.

Mitochondrial Regulator CRIF1 Plays a Critical Role in the Development and Homeostasis of Alveolar Macrophages via Maintaining Metabolic Fitness

The importance of mitochondrial function in macrophages is well established. Alveolar macrophages (AMs), the tissue-resident macrophages (TRMs) of the lung, are particularly dependent on mitochondria-driven oxidative phosphorylation (OXPHOS) to support their functions and maintain homeostasis. However, the specific genes and pathways that regulate OXPHOS in AMs remain unclear. In this study, we investigated the role of CR6-interacting factor 1 (CRIF1), a mitochondrial regulator, as a key factor that specifically modulates the metabolic fitness and maintenance of AMs. Using single-cell RNA sequencing and transcriptomic analyses, we found CRIF1 to be highly expressed in AMs compared to TRMs from other tissues, correlating with enhanced OXPHOS activity. Genetic ablation of Crif1 in macrophages resulted in a marked reduction in AM populations exclusively in the lung, while other TRM populations were unaffected. CRIF1-deficient AMs exhibited an altered metabolic profile, including impaired mitochondrial function, increased glycolysis, and aberrant lipid accumulation. These findings underscore the essential role of CRIF1 in regulating mitochondrial functions and metabolic fitness in AMs, distinguishing it from broader mitochondrial regulators like mitochondrial transcription factor A, which operates across multiple TRM populations. Our study provides critical insights into the tissue-specific regulation of macrophage metabolism and suggests potential therapeutic avenues for lung diseases associated with AM dysfunction.

Quercetin-Loaded Melanin Nanoparticles Decorated with Collagenase Mediates Synergistic Immunomodulation and Restores Extracellular Matrix Homeostasis in Liver Fibrosis

Liver fibrosis is a chronic disease that lacks effective drug treatment. Chronic damage and inflammation lead to the formation of collagen and fibrous scars. However, the excessive accumulation of collagen I significantly hinders the delivery of drugs into liver tissue. Therefore, this study developed a quercetin-loaded melanin nanoparticle codecorated collagenase (MNP-QUE-COL) for the treatment of liver fibrosis. These results showed that MNP-QUE-COL degraded excessive collagen I, thereby efficiently delivering melanin and quercetin into the liver tissue. MNP-QUE-COL exhibited optimal PA/MRI dual-mode imaging ability. In addition, the synergistic anti-inflammatory and reactive oxygen species scavenging function of quercetin and melanin was achieved by regulation of M1-M2 macrophage polarization and inhibition of pro-inflammatory cytokine release, reshaping the imbalanced extracellular interstitial inflammatory environment. The results of this research suggest that MNP-QUE-COL is a safe and efficient therapeutic nanoplatform for liver fibrosis, showing promise as a potential therapeutic strategy for liver fibrosis and associated diseases.

GDF15/MIC-1: a stress-induced immunosuppressive factor which promotes the aging process

The GDF15 protein, a member of the TGF-β superfamily, is a stress-induced multifunctional protein with many of its functions associated with the regulation of the immune system. GDF15 signaling provides a defence against the excessive inflammation induced by diverse stresses and tissue injuries. Given that the aging process is associated with a low-grade inflammatory state, called inflammaging, it is not surprising that the expression of GDF15 gradually increases with aging. In fact, the GDF15 protein is a core factor secreted by senescent cells, a state called senescence-associated secretory phenotype (SASP). Many age-related stresses, e.g., mitochondrial and endoplasmic reticulum stresses as well as inflammatory, metabolic, and oxidative stresses, induce the expression of GDF15. Although GDF15 signaling is an effective anti-inflammatory modulator, there is robust evidence that it is a pro-aging factor promoting the aging process. GDF15 signaling is not only an anti-inflammatory modulator but it is also a potent immunosuppressive enhancer in chronic inflammatory states. The GDF15 protein can stimulate immune responses either non-specifically via receptors of the TGF-β superfamily or specifically through the GFRAL/HPA/glucocorticoid pathway. GDF15 signaling stimulates the immunosuppressive network activating the functions of MDSCs, Tregs, and M2 macrophages and triggering inhibitory immune checkpoint signaling in senescent cells. Immunosuppressive responses not only suppress chronic inflammatory processes but they evoke many detrimental effects in aged tissues, such as cellular senescence, fibrosis, and tissue atrophy/sarcopenia. It seems that the survival functions of GDF15 go awry in persistent inflammation thus promoting the aging process and age-related diseases.

The Downregulation of CRIF1 Exerts Antitumor Effects Partially via TP53-Induced Glycolysis and Apoptosis Regulator Induction in BT549 Breast Cancer Cells

BACKGROUND/OBJECTIVES

Mitochondrial oxidative phosphorylation (OXPHOS) has been exploited as a therapeutic target in cancer treatments because of its crucial role in tumorigenesis. CR6-interacting factor 1 (CRIF1), a mitochondrial ribosomal subunit protein, is essential for the regulation of mitochondrial OXPHOS capacity. However, the mechanism of CRIF1 in triple-negative breast cancer (TNBC) cells remains unclear.

METHODS/RESULTS

We showed that the downregulation of CRIF1 reduced cell proliferation in the TNBC cell lines MDA-MB-468, MDA-MB-231, and, especially, BT549. In addition, wound scratch and Transwell assays showed that CRIF1 deficiency inhibited the migration and invasion of BT549 cells. CRIF1 downregulation resulted in the suppression of mitochondrial bioenergetics in BT549 cells, specifically affecting the inhibition of OXPHOS complexes I and II. This was evidenced by a decrease in the mitochondrial oxygen consumption rate and the depolarization of the mitochondrial membrane potential. Damage to mitochondria resulted in a lower adenosine triphosphate level and an elevated production of mitochondrial reactive oxygen species. In addition, CRIF1 deficiency decreased hypoxia-inducible factor 1α accumulation, NADPH synthesis, and TP53-induced glycolysis and apoptosis regulator (TIGAR) expression in BT549 cells. These events contributed to G0/G1-phase cell cycle inhibition and the upregulation of the cell cycle protein markers p53, p21, and p16. Transfection with a TIGAR overexpression plasmid reversed these effects and prevented CRIF1 downregulation-induced proliferation and migration reduction.

CONCLUSIONS

These results indicate that blocking mitochondrial OXPHOS synthesis via CRIF1 may have a therapeutic antitumor effect in BT549 TNBC cells.

GDF15 associates with, but is not responsible for, exercise-induced increases in corticosterone and indices of lipid utilization in mice

Growth differentiation factor 15 (GDF15) is a stress-induced cytokine that increases with exercise and is thought to increase corticosterone and lipid utilization. How postexercise nutrient availability impacts GDF15 and the physiological role that GDF15 plays during and/or in the recovery from exercise has not been elucidated. The purpose of this investigation was to examine how postexercise nutrient availability impacts GDF15 and to use this as a model to explore associations between GDF15, corticosterone, and indices of lipid and carbohydrate metabolism. In addition, we explored the causality of these relationships using GDF15-deficient mice. Male and female C57BL/6J mice ran for 2 hours on a treadmill and were euthanized immediately or 3 hours after exercise with or without access to a chow diet. In both sexes, circulating concentrations of GDF15, corticosterone, nonesterified fatty acids (NEFA), and beta-hydroxybutyrate (BHB) were higher immediately postexercise and remained elevated when food was withheld during the recovery period. While serum GDF15 was positively associated with corticosterone, BHB, and NEFA, increases in these factors were similar in wild-type and GDF15-/- mice following exercise. The lack of a genotype effect was not explained by differences in insulin, glucagon, or epinephrine after exercise. Our findings provide evidence that while GDF15 is associated with increases in corticosterone and indices of lipid utilization this is not a causal relationship.NEW & NOTEWORTHY Circulating growth differentiation factor 15 (GDF15) increases during exercise, but the physiological role that it plays has not been elucidated. Recent data suggest that GDF15 regulates corticosterone and lipid utilization. Here we demonstrate that postexercise nutrient availability influences GDF15 in the recovery from exercise and GDF15 is associated with corticosterone and indices of lipid utilization. However, the associations were not causal as exercise-induced increases in fatty acids, beta-hydroxybutyrate, and corticosterone were intact in GDF15-/- mice.

ZBTB18 regulates cytokine expression and affects microglia/macrophage recruitment and commitment in glioblastoma

Glioma associated macrophages/microglia (GAMs) play an important role in glioblastoma (GBM) progression, due to their massive recruitment to the tumor site and polarization to a tumor promoting phenotype. GAMs secrete a variety of cytokines, which facilitate tumor cell growth and invasion, and prevent other immune cells from mounting an immune response against the tumor. Here, we demonstrate that zinc finger and BTB containing domain 18 (ZBTB18), a transcriptional repressor with tumor suppressive function in glioblastoma, impairs the production of key cytokines, which function as chemoattractant for GAMs. Consistently, we observe a reduced migration of GAMs when ZBTB18 is expressed by glioblastoma cells, both in cell culture and in vivo experiments. Moreover, RNA sequencing analysis shows that the presence of ZBTB18 in glioblastoma cells alters the commitment of conditioned microglia, suggesting the loss of the immune-suppressive phenotype and the acquisition of pro-inflammatory features. Thus, therapeutic approaches to increase ZBTB18 expression in GBM cells could represent an effective adjuvant to immune therapy in GBM.

The implicated role of GDF15 in gastrointestinal cancer

BACKGROUND

Growth differentiation factor 15 (GDF15), a stress-responsive cytokine from transforming growth factor superfamily, is highly expressed in mammalian tissues, including pancreas, stomach and intestine under pathological conditions. In particular, elevated levels of GDF15 might play an important role in the development and progression of various gastrointestinal cancers (GCs), suggesting its potential as a promising target for disease prediction and treatment.

METHODS

In this review, systematic reviews addressing the role of GDF15 in GCs were updated, along with the latest clinical trials focussing on the GDF15-associated digestive malignancies.

RESULTS

The multiple cellular pathways through which GDF15 is involved in the regulation of physiological and pathological conditions were first summarized. Then, GDF15 was also established as a valuable clinical index, functioning as a predictive marker in diverse GCs. Notably, latest clinical treatments targeting GDF15 were also highlighted, demonstrating its promising potential in mitigating and curing digestive malignancies.

CONCLUSIONS

This review unveils the pivotal roles of GDF15 and its potential as a promising target in the pathogenesis of GCs, which may provide insightful directions for future investigations.

Macrophages and T cells in metabolic disorder-associated cancers

Cancer and metabolic disorders have emerged as major global health challenges, reaching epidemic levels in recent decades. Often viewed as separate issues, metabolic disorders are shown by mounting evidence to heighten cancer risk and incidence. The intricacies underlying this connection are still being unraveled and encompass a complex interplay between metabolites, cancer cells and immune cells within the tumour microenvironment (TME). Here, we outline the interplay between metabolic and immune cell dysfunction in the context of three highly prevalent metabolic disorders, namely obesity; two associated liver diseases, metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH); and type 2 diabetes. We focus primarily on macrophages and T cells, the critical roles of which in dictating inflammatory response and immune surveillance in metabolic disorder-associated cancers are widely reported. Moreover, considering the ever-increasing number of patients prescribed with metabolism disorder-altering drugs and diets in recent years, we discuss how these therapies modulate systemic and local immune phenotypes, consequently impacting cancer malignancy. Collectively, unraveling the determinants of metabolic disorder-associated immune landscape and their role in fuelling cancer malignancy will provide a framework essential to therapeutically address these highly prevalent diseases.

Unraveling the roles and mechanisms of mitochondrial translation in normal and malignant hematopoiesis

Due to spatial and genomic independence, mitochondria possess a translational mechanism distinct from that of cytoplasmic translation. Several regulators participate in the modulation of mitochondrial translation. Mitochondrial translation is coordinated with cytoplasmic translation through stress responses. Importantly, the inhibition of mitochondrial translation leads to the inhibition of cytoplasmic translation and metabolic disruption. Therefore, defects in mitochondrial translation are closely related to the functions of hematopoietic cells and various immune cells. Finally, the inhibition of mitochondrial translation is a potential therapeutic target for treating multiple hematologic malignancies. Collectively, more in-depth insights into mitochondrial translation not only facilitate our understanding of its functions in hematopoiesis, but also provide a basis for the discovery of new treatments for hematological malignancies and the modulation of immune cell function.

Dynamic Roles and Expanding Diversity of Adipose Tissue Macrophages in Obesity

Adipose tissue macrophages (ATMs) are key regulators of adipose tissue (AT) inflammation and insulin resistance in obesity, and the traditional M1/M2 characterization of ATMs is inadequate for capturing their diversity in obese conditions. Single-cell transcriptomic profiling has revealed heterogeneity among ATMs that goes beyond the old paradigm and identified new subsets with unique functions. Furthermore, explorations of their developmental origins suggest that multiple differentiation pathways contribute to ATM variety. These advances raise concerns about how to define ATM functions, how they are regulated, and how they orchestrate changes in AT. This review provides an overview of the current understanding of ATMs and their updated categorization in both mice and humans during obesity. Additionally, diverse ATM functions and contributions in the context of obesity are discussed. Finally, potential strategies for targeting ATM functions as therapeutic interventions for obesity-induced metabolic diseases are addressed.

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

Objective

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

Subjects and methods

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

Results

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

Conclusion

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Macrophage-Capturing Self-Assembly Photosensitizer Nanoparticles Induces Immune Microenvironment Re-Programming and Golgi-Responsive Immunogenic Cell Death in Head and Neck Carcinoma

Head and neck carcinoma treatment is shifted toward the combination of therapy causing immune checkpoint blockade (ICB) and immunogenic cell death. In this study, a CSFRi-chimeric TAMCSFR+-targeting extracellular vesicle (EV@CSFRi) platform is developed and designed an intracellular protoporphyrin conjugated with RVRR peptide sequence for furin-cleavage to perform Golgi-targeting and generating ROS (GT-RG). The graphical abstract illustrates the self-assembly of GT-RG nanoparticles into nanofiber through the hydrophily of RVRR and hydrophobicity of RG, and the red line indicates the site of furin cleavage. As is shown in the Graphical abstract, the Golgi-targeting Protoporphyrin-RVRR platform is composed with CSFRi-chimeric extracellular vesicles and forms the tumor-responsive TAM-reprogramming bilayers (GT-RGEV@CSFRi). The GT-RGEV@CSFRi acted as a multifunctional theranostic platform, which can induce immunogenic cell death and further help modulate TAM, thus suppressing the HNC xenograft model by combination therapy with anti-PD-1.

Interleukin-10: a novel metabolic inducer of macrophage differentiation and subsequently contributing to improved pregnancy outcomes of mice by orchestrating oxidative phosphorylation metabolism†

Metabolism regulates the phenotype and function of macrophages. After recruitment to local tissues, monocytes are influenced by the local microenvironment and differentiate into various macrophages depending on different metabolic pathways. However, the metabolic mechanisms underlying decidual macrophage differentiation remain unknown. Interleukin-10 (IL-10) is an important decidual macrophage inducer and promotes oxidative phosphorylation (OXPHOS) of bone marrow-derived macrophages. In this study, we mainly investigate the metabolic changes involved in IL-10-generated macrophages from monocytes using in vitro models. We demonstrate that exposure of monocytes (either peripheral or THP-1) to IL-10 altered the phenotype and function of resultant macrophages that are linked with OXPHOS changes. Interleukin-10 enhanced the mitochondrial complex I and III activity of THP-1 cell-differentiated macrophages and increased the mitochondrial membrane potential, intracellular adenosine triphosphate, and reactive oxygen species levels. Oxidative phosphorylation blockage with oligomycin changed the cell morphology of IL-10-generated macrophages and the expression levels of cytokines, such as transforming growth factor beta, tumor necrosis factor-alpha, interferon gamma, and IL-10, apart from changes in the expression level of the surface markers CD206, CD209, and CD163. Moreover, in vivo IL-10 administration reduced the lipopolysaccharide (LPS)-induced embryo resorption rate, and this effect was diminished when OXPHOS was inhibited, demonstrating that OXPHOS is important for the improved pregnancy outcomes of IL-10 in LPS-induced abortion-prone mice. Our findings provide deep insights into the roles of IL-10 in macrophage biology and pregnancy maintenance. Nevertheless, the direct evidence that OXPHOS is involved in decidual macrophage differentiation needs further investigations.

Macrophages as a Source and Target of GDF-15

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

Metabolic flux in macrophages in obesity and type-2 diabetes

Recent literature extensively investigates the crucial role of energy metabolism in determining the inflammatory response and polarization status of macrophages. This rapidly expanding area of research highlights the importance of understanding the link between energy metabolism and macrophage function. The metabolic pathways in macrophages are intricate and interdependent, and they can affect the polarization of macrophages. Previous studies suggested that glucose flux through cytosolic glycolysis is necessary to trigger pro-inflammatory phenotypes of macrophages, and fatty acid oxidation is crucial to support anti-inflammatory responses. However, recent studies demonstrated that this understanding is oversimplified and that the metabolic control of macrophage polarization is highly complex and not fully understood yet. How the metabolic flux through different metabolic pathways (glycolysis, glucose oxidation, fatty acid oxidation, ketone oxidation, and amino acid oxidation) is altered by obesity- and type 2 diabetes (T2D)-associated insulin resistance is also not fully defined. This mini-review focuses on the impact of insulin resistance in obesity and T2D on the metabolic flux through the main metabolic pathways in macrophages, which might be linked to changes in their inflammatory responses. We closely evaluated the experimental studies and methodologies used in the published research and highlighted priority research areas for future investigations.

GDF15: Immunomodulatory Role in Hepatocellular Carcinoma Pathogenesis and Therapeutic Implications

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths globally and the sixth most common cancer worldwide. Evidence shows that growth differentiation factor 15 (GDF15) contributes to hepatocarcinogenesis through various mechanisms. This paper reviews the latest insights into the role of GDF15 in the development of HCC, its role in the immune microenvironment of HCC, and its molecular mechanisms in metabolic dysfunction associated steatohepatitis (MASH) and metabolic associated fatty liver disease (MAFLD)-related HCC. Additionally, as a serum biomarker for HCC, diagnostic and prognostic value of GDF15 for HCC is summarized. The article elaborates on the immunological effects of GDF15, elucidating its effects on hepatic stellate cells (HSCs), liver fibrosis, as well as its role in HCC metastasis and tumor angiogenesis, and its interactions with anticancer drugs. Based on the impact of GDF15 on the immune response in HCC, future research should identify its signaling pathways, affected immune cells, and tumor microenvironment interactions. Clinical studies correlating GDF15 levels with patient outcomes can aid personalized treatment. Additionally, exploring GDF15-targeted therapies with immunotherapies could improve anti-tumor responses and patient outcomes.

GDF-15 Suppresses Puromycin Aminonucleoside-Induced Podocyte Injury by Reducing Endoplasmic Reticulum Stress and Glomerular Inflammation

GDF15, also known as MIC1, is a member of the TGF-beta superfamily. Previous studies reported elevated serum levels of GDF15 in patients with kidney disorder, and its association with kidney disease progression, while other studies identified GDF15 to have protective effects. To investigate the potential protective role of GDF15 on podocytes, we first performed in vitro studies using a Gdf15-deficient podocyte cell line. The lack of GDF15 intensified puromycin aminonucleoside (PAN)-triggered endoplasmic reticulum stress and induced cell death in cultivated podocytes. This was evidenced by elevated expressions of Xbp1 and ER-associated chaperones, alongside AnnexinV/PI staining and LDH release. Additionally, we subjected mice to nephrotoxic PAN treatment. Our observations revealed a noteworthy increase in both GDF15 expression and secretion subsequent to PAN administration. Gdf15 knockout mice displayed a moderate loss of WT1+ cells (podocytes) in the glomeruli compared to wild-type controls. However, this finding could not be substantiated through digital evaluation. The parameters of kidney function, including serum BUN, creatinine, and albumin-creatinine ratio (ACR), were increased in Gdf15 knockout mice as compared to wild-type mice upon PAN treatment. This was associated with an increase in the number of glomerular macrophages, neutrophils, inflammatory cytokines, and chemokines in Gdf15-deficient mice. In summary, our findings unveil a novel renoprotective effect of GDF15 during kidney injury and inflammation by promoting podocyte survival and regulating endoplasmic reticulum stress in podocytes, and, subsequently, the infiltration of inflammatory cells via paracrine effects on surrounding glomerular cells.

Unraveling the complex roles of macrophages in obese adipose tissue: an overview

Macrophages, a heterogeneous population of innate immune cells, exhibit remarkable plasticity and play pivotal roles in coordinating immune responses and maintaining tissue homeostasis within the context of metabolic diseases. The activation of inflammatory macrophages in obese adipose tissue leads to detrimental effects, inducing insulin resistance through increased inflammation, impaired thermogenesis, and adipose tissue fibrosis. Meanwhile, adipose tissue macrophages also play a beneficial role in maintaining adipose tissue homeostasis by regulating angiogenesis, facilitating the clearance of dead adipocytes, and promoting mitochondrial transfer. Exploring the heterogeneity of macrophages in obese adipose tissue is crucial for unraveling the pathogenesis of obesity and holds significant potential for targeted therapeutic interventions. Recently, the dual effects and some potential regulatory mechanisms of macrophages in adipose tissue have been elucidated using single-cell technology. In this review, we present a comprehensive overview of the intricate activation mechanisms and diverse functions of macrophages in adipose tissue during obesity, as well as explore the potential of drug delivery systems targeting macrophages, aiming to enhance the understanding of current regulatory mechanisms that may be potentially targeted for treating obesity or metabolic diseases.

Emerging Roles of Macrophage Polarization in Osteoarthritis: Mechanisms and Therapeutic Strategies

Osteoarthritis (OA) is the most common chronic degenerative joint disease in middle-aged and elderly people, characterized by joint pain and dysfunction. Macrophages are key players in OA pathology, and their activation state has been studied extensively. Various studies have suggested that macrophages might respond to stimuli in their microenvironment by changing their phenotypes to pro-inflammatory or anti-inflammatory phenotypes, which is called macrophage polarization. Macrophages accumulate and become polarized (M1 or M2) in many tissues, such as synovium, adipose tissue, bone marrow, and bone mesenchymal tissues in joints, while resident macrophages as well as other stromal cells, including fibroblasts, chondrocytes, and osteoblasts, form the joint and function as an integrated unit. In this study, we focus exclusively on synovial macrophages, adipose tissue macrophages, and osteoclasts, to investigate their roles in the development of OA. We review recent key findings related to macrophage polarization and OA, including pathogenesis, molecular pathways, and therapeutics. We summarize several signaling pathways in macrophage reprogramming related to OA, including NF-κB, MAPK, TGF-β, JAK/STAT, PI3K/Akt/mTOR, and NLRP3. Of note, despite the increasing availability of treatments for osteoarthritis, like intra-articular injections, surgery, and cellular therapy, the demand for more effective clinical therapies has remained steady. Therefore, we also describe the current prospective therapeutic methods that deem macrophage polarization to be a therapeutic target, including physical stimulus, chemical compounds, and biological molecules, to enhance cartilage repair and alleviate the progression of OA.

Mitochondria and diabetes: insights and potential therapies

INTRODUCTION

Type 2 diabetes (T2D) presents significant global health and economic challenges, contributing to complications such as stroke, cardiovascular disease, kidney dysfunction, and cancer. The current review explores the crucial role of mitochondria, essential for fuel metabolism, in diabetes-related processes.

AREAS COVERED

Mitochondrial deficits impact insulin-resistant skeletal muscles, adipose tissue, liver, and pancreatic β-cells, affecting glucose and lipid balance. Exercise emerges as a key factor in enhancing mitochondrial function, thereby reducing insulin resistance. Additionally, the therapeutic potential of mitochondrial uncoupling, which generates heat instead of ATP, is discussed. We explore the intricate link between mitochondrial function and diabetes, investigating genetic interventions to mitigate diabetes-related complications. We also cover the impact of insulin deficiency on mitochondrial function, the role of exercise in addressing mitochondrial defects in insulin resistance, and the potential of mitochondrial uncoupling. Furthermore, a comprehensive analysis of Mitochondrial Replacement Therapies (MRT) techniques is presented.

EXPERT OPINION

MRTs hold promise in preventing the transmission of mitochondrial disease. However, addressing ethical, regulatory, and technical considerations is crucial. Integrating mitochondrial-based treatments requires a careful balance between innovation and safety. Ethical dimensions and regulatory aspects of MRT are examined, emphasizing collaborative efforts for the responsible advancement of human health.

Sulforaphane reduces adipose tissue fibrosis via promoting M2 macrophages polarization in HFD fed-mice

Adipose tissue fibrosis has been identified as a novel contributor to the pathomechanism of obesity associated metabolic disorders. Sulforaphane (SFN) has been shown to have an anti-obesity effect. However, the impact of SFN on adipose tissue fibrosis is still not well understood. In this study, obese mice induced by high-fat diets (HFD) were used to examine the effects of SFN on adipose tissue fibrosis. According to the current findings, SFN dramatically enhanced glucose tolerance and decreased body weight in diet-induced-obesity (DIO) mice. Additionally, SFN therapy significantly reduced extracellular matrix (ECM) deposition and altered the expression of genes related to fibrosis. Furthermore, SFN also reduced inflammation and promoted macrophages polarization towards to M2 phenotype in adipose tissue, which protected adipose tissue from fibrosis. Notably, SFN-mediated nuclear factor E2-related factor 2 (Nrf2) activation was crucial in decreasing adipose tissue fibrosis. These results implied that SFN had favorable benefits in adipose tissue fibrosis, which consequently ameliorates obesity-related metabolic problems. Our research provides new treatment strategies for obesity and associated metabolic disorders.

Beneficial Effects of Low-Grade Mitochondrial Stress on Metabolic Diseases and Aging

Mitochondria function as platforms for bioenergetics, nutrient metabolism, intracellular signaling, innate immunity regulators, and modulators of stem cell activity. Thus, the decline in mitochondrial functions causes or correlates with diabetes mellitus and many aging-related diseases. Upon stress or damage, the mitochondria elicit a series of adaptive responses to overcome stress and restore their structural integrity and functional homeostasis. These adaptive responses to low-level or transient mitochondrial stress promote health and resilience to upcoming stress. Beneficial effects of low-grade mitochondrial stress, termed mitohormesis, have been observed in various organisms, including mammals. Accumulated evidence indicates that treatments boosting mitohormesis have therapeutic potential in various human diseases accompanied by mitochondrial stress. Here, we review multiple cellular signaling pathways and interorgan communication mechanisms through which mitochondrial stress leads to advantageous outcomes. We also discuss the relevance of mitohormesis in obesity, diabetes, metabolic liver disease, aging, and exercise.

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.

CTRP6 promotes the macrophage inflammatory response, and its deficiency attenuates LPS-induced inflammation

Macrophages play critical roles in inflammation and tissue homeostasis, and their functions are regulated by various autocrine, paracrine, and endocrine factors. We have previously shown that CTRP6, a secreted protein of the C1q family, targets both adipocytes and macrophages to promote obesity-linked inflammation. However, the gene programs and signaling pathways directly regulated by CTRP6 in macrophages remain unknown. Here, we combine transcriptomic and phosphoproteomic analyses to show that CTRP6 activates inflammatory gene programs and signaling pathways in mouse bone marrow-derived macrophages (BMDMs). Treatment of BMDMs with CTRP6 upregulated proinflammatory, and suppressed the antiinflammatory, gene expression. We also showed that CTRP6 activates p44/42-MAPK, p38-MAPK, and NF-κB signaling pathways to promote inflammatory cytokine secretion from BMDMs, and that pharmacologic inhibition of these signaling pathways markedly attenuated the effects of CTRP6. Pretreatment of BMDMs with CTRP6 also sensitized and potentiated the BMDMs response to lipopolysaccharide (LPS)-induced inflammatory signaling and cytokine secretion. Consistent with the metabolic phenotype of proinflammatory macrophages, CTRP6 treatment induced a shift toward aerobic glycolysis and lactate production, reduced oxidative metabolism, and elevated mitochondrial reactive oxygen species production in BMDMs. Importantly, in accordance with our in vitro findings, BMDMs from CTRP6-deficient mice were less inflammatory at baseline and showed a marked suppression of LPS-induced inflammatory gene expression and cytokine secretion. Finally, loss of CTRP6 in mice also dampened LPS-induced inflammation and hypothermia. Collectively, our findings suggest that CTRP6 regulates and primes the macrophage response to inflammatory stimuli and thus may have a role in modulating tissue inflammatory tone in different physiological and disease contexts.

White adipose tissue mitochondrial bioenergetics in metabolic diseases

White adipose tissue (WAT) is an important endocrine organ that regulates systemic energy metabolism. In metabolically unhealthy obesity, adipocytes become dysfunctional through hypertrophic mechanisms associated with a reduced endocrine function, reduced mitochondrial function, but increased inflammation, fibrosis, and extracellular remodelling. A pathologic WAT remodelling promotes systemic lipotoxicity characterized by fat accumulation in tissues such as muscle and liver, leading to systemic insulin resistance and type 2 diabetes. Several lines of evidence from human and animal studies suggest a link between unhealthy obesity and adipocyte mitochondrial dysfunction, and interventions that improve mitochondrial function may reduce the risk of obesity-associated diseases. This review discusses the importance of mitochondrial function and metabolism in human adipocyte biology and intercellular communication mechanisms within WAT. Moreover, a selected interventional approach for better adipocyte mitochondrial metabolism in humans is reviewed. A greater understanding of mitochondrial bioenergetics in WAT might provide novel therapeutic opportunities to prevent or restore dysfunctional adipose tissue in obesity-associated diseases.

Research Progress on the Role and Mechanism of GDF15 in Body Weight Regulation

BACKGROUND

Growth differentiation factor-15 (GDF15) is a member of the growth differentiation factor subfamily in the transforming growth factor beta superfamily. GDF15 has multiple functions and can regulate biological processes. High levels of GDF15 in the circulation can affect metabolic processes. Studies have shown that GDF15 is associated with changes in body weight.

SUMMARY

This review reviews the current knowledge on the relationship between GDF15 and body weight change, focusing on the role and mechanism of GDF15 in body weight regulation. GDF15 plays an important role in reducing food intake, improving insulin resistance, and breaking down fat, suggesting that GDF15 has an important regulatory effect on body weight. The mechanism by which GDF15 causes reduced food intake may be related to changes in food preference, delayed gastric emptying, and conditioned taste aversion. GDF15 can combat insulin resistance induced by inflammation or protect β cell from apoptosis. GDF15 probably promotes lipolysis through a brain-somatic tissue circuit. Several factors and related signaling pathways are also mentioned that can contribute to the effects of GDF15 on reducing weight.

KEY MESSAGE

GDF15 plays an important role in weight regulation and provides a new direction for the treatment of obesity. Its effects on resisting obesity are of great significance to inhibiting the progression of metabolic diseases. It is expected to become a new target for regulating body weight, improving obesity, and treating metabolic diseases such as diabetes.

CR6-Interacting Factor-1 Promotes Osteoclastogenesis Through the NF-κB Signaling Pathway after Irradiation

Radiation exposure arising from radiotherapy may induce rapid bone loss and an increase in the extent of bone resorption. Reactive oxygen species (ROS) caused by radiation exposure play a crucial role during the process of osteoclastogenesis. However, the pathological mechanisms underlying radiation-induced osteoclastogenesis have yet to be fully elucidated. CR6-interacting factor-1 (Crif1) as a multifunctional protein is involved in regulating multiple biological functions in cells. Here, we investigated the role of Crif1 in radiation-induced osteoclastogenesis and found that radiation exposure induced an increase in the expression level of Crif1 and enhanced osteoclastogenesis in osteoclast progenitors. Crif1 and NF-κB p65 co-localized in the cytoplasm after radiation exposure. Crif1 knockdown did not affect the phosphorylation and total protein levels of extracellular signal-regulated kinases (ERK), c-Jun amino (N)-terminal kinases (JNK), p38, and IκB-α before and after irradiation. However, Crif1 knockdown did lead to the reduced phosphorylation and nuclear translocation of NF-κB p65 after irradiation and resulted in a reduced level of osteoclastogenesis in RAW264.7 cells after irradiation. In vivo studies involving Lyz2Cre;Crif1fl/fl mice possessing the myeloid-specific deletion of Crif1 demonstrated the alleviation of bone loss after irradiation when compared with Crif1fl/fl mice. Our findings demonstrate that Crif1 mediated the phosphorylation and nuclear translocation of NF-κB p65 and promoted osteoclastogenesis via the NF-κB signaling pathway after radiation exposure. Thus, our analysis revealed a specific role for Crif1 in the mediation of radiation-induced bone loss and may provide new insight into potential therapeutic strategies for radiation-induced bone loss.

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

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

Loss of growth differentiation factor 15 exacerbates lung injury in neonatal mice

Growth differentiation factor 15 (GDF15) is a divergent member of the transforming growth factor-β (TGF-β) superfamily, and its expression increases under various stress conditions, including inflammation, hyperoxia, and senescence. GDF15 expression is increased in neonatal murine bronchopulmonary dysplasia (BPD) models, and GDF15 loss exacerbates oxidative stress and decreases cellular viability in vitro. Our overall hypothesis is that the loss of GDF15 will exacerbate hyperoxic lung injury in the neonatal lung in vivo. We exposed neonatal Gdf15-/- mice and wild-type (WT) controls on a similar background to room air or hyperoxia (95% [Formula: see text]) for 5 days after birth. The mice were euthanized on postnatal day 21 (PND 21). Gdf15-/- mice had higher mortality and lower body weight than WT mice after exposure to hyperoxia. Hyperoxia exposure adversely impacted alveolarization and lung vascular development, with a greater impact in Gdf15-/- mice. Interestingly, Gdf15-/- mice showed lower macrophage count in the lungs compared with WT mice both under room air and after exposure to hyperoxia. Analysis of the lung transcriptome revealed marked divergence in gene expression and enriched biological pathways in WT and Gdf15-/- mice and differed markedly by biological sex. Notably, pathways related to macrophage activation and myeloid cell homeostasis were negatively enriched in Gdf15-/- mice. Loss of Gdf15 exacerbates mortality, lung injury, and the phenotype of the arrest of alveolarization in the developing lung with loss of female-sex advantage in Gdf15-/- mice.NEW & NOTEWORTHY We show for the first time that loss of Gdf15 exacerbates mortality, lung injury, and the phenotype of the arrest of alveolarization in the developing lung with loss of female-sex advantage in Gdf15-/- mice. We also highlight the distinct pulmonary transcriptomic response in the Gdf15-/- lung including pathways related to macrophage recruitment and activation.

STING-IRG1 inhibits liver metastasis of colorectal cancer by regulating the polarization of tumor-associated macrophages

The liver is the main site of colorectal cancer (CRC) metastasis. Tumor-associated macrophages (TAMs) play a key role in tumor metastasis. Therefore, modulating the function of tumor-associated macrophages is a potential therapeutic strategy to control tumor metastasis. We found in vivo experiments that the activation of STING inhibited CRC liver metastasis in model mice and affected the macrophage phenotype in the tumor microenvironment. Mechanistically, STING affects TAM polarization and regulates macrophage function through IRG1. And STING activates IRG1 to promote the nuclear translocation of TFEB, affecting the ability of macrophages to suppress tumor metastasis.Therefore, this study highlights the critical role of the STING-IRG1 axis on TAM reprogramming and its role in the process of tumor liver metastasis, which may provide a promising therapeutic strategy for CRC liver metastasis.

Macrophage-mediated PDGF Activation Correlates With Regenerative Outcomes Following Musculoskeletal Trauma

OBJECTIVE

Our objective was to identify macrophage subpopulations and gene signatures associated with regenerative or fibrotic healing across different musculoskeletal injury types.

BACKGROUND

Subpopulations of macrophages are hypothesized to fine tune the immune response after damage, promoting either normal regenerative, or aberrant fibrotic healing.

METHODS

Mouse single-cell RNA sequencing data before and after injury were assembled from models of musculoskeletal injury, including regenerative and fibrotic mouse volumetric muscle loss (VML), regenerative digit tip amputation, and fibrotic heterotopic ossification. R packages Harmony , MacSpectrum , and Seurat were used for data integration, analysis, and visualizations.

RESULTS

There was a substantial overlap between macrophages from the regenerative VML (2 mm injury) and regenerative bone models, as well as a separate overlap between the fibrotic VML (3 mm injury) and fibrotic bone (heterotopic ossification) models. We identified 2 fibrotic-like (FL 1 and FL 2) along with 3 regenerative-like (RL 1, RL 2, and RL 3) subpopulations of macrophages, each of which was transcriptionally distinct. We found that regenerative and fibrotic conditions had similar compositions of proinflammatory and anti-inflammatory macrophages, suggesting that macrophage polarization state did not correlate with healing outcomes. Receptor/ligand analysis of macrophage-to-mesenchymal progenitor cell crosstalk showed enhanced transforming growth factor β in fibrotic conditions and enhanced platelet-derived growth factor signaling in regenerative conditions.

CONCLUSION

Characterization of macrophage subtypes could be used to predict fibrotic responses following injury and provide a therapeutic target to tune the healing microenvironment towards more regenerative conditions.

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

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

YKL-40 derived from infiltrating macrophages cooperates with GDF15 to establish an immune suppressive microenvironment in gallbladder cancer

Despite of the high lethality of gallbladder cancer (GBC), little is known regarding molecular regulation of the tumor immunosuppressive microenvironment. Here, we determined tumor expression levels of YKL-40 and the molecular mechanisms by which YKL-40 regulates escape of anti-tumor immune surveillance. We found that elevated expression levels of YKL-40 in plasma and tissue were correlated with tumor size, stage IV and lymph node metastasis. Single cell transcriptome analysis revealed that YKL-40 was predominantly derived from M2-like subtype of infiltrating macrophages. Blockade of M2-like macrophage differentiation of THP-1 cells with YKL-40 shRNA resulted in reprogramming to M1-like macrophages and restricting tumor development. YKL-40 induced tumor cell expression and secretion of growth differentiation factor 15 (GDF15), thus coordinating to promote PD-L1 expression mediated by PI3K, AKT and/or Erk activation. Interestingly, extracellular GDF15 inhibited intracellular expression of GDF15 that suppressed PD-L1 expression. Thus, YKL-40 disrupted the balance of pro- and anti-PD-L1 regulation to enhance expression of PD-L1 and inhibition of T cell cytotoxicity, leading to tumor immune evasion. The data suggest that YKL-40 and GDF15 could serve as diagnostic biomarkers and immunotherapeutic targets for GBC.

CX3CR1hi macrophages sustain metabolic adaptation by relieving adipose-derived stem cell senescence in visceral adipose tissue

Adipose-derived stem cells (ASCs) drive healthy visceral adipose tissue (VAT) expansion via adipocyte hyperplasia. Obesity induces ASC senescence that causes VAT dysfunction and metabolic disorders. It is challenging to restrain this process by biological intervention, as mechanisms of controlling VAT ASC senescence remain unclear. We demonstrate that a population of CX3CR1hi macrophages is maintained in mouse VAT during short-term energy surplus, which sustains ASCs by restraining their senescence, driving adaptive VAT expansion and metabolic health. Long-term overnutrition induces diminishment of CX3CR1hi macrophages in mouse VAT accompanied by ASC senescence and exhaustion, while transferring CX3CR1hi macrophages restores ASC reservoir and triggers VAT beiging to alleviate the metabolic maladaptation. Mechanistically, visceral ASCs attract macrophages via MCP-1 and shape their CX3CR1hi phenotype via exosomes; these macrophages relieve ASC senescence by promoting the arginase1-eIF5A hypusination axis. These findings identify VAT CX3CR1hi macrophages as ASC supporters and unravel their therapeutic potential for metabolic maladaptation to obesity.

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.

Cell-penetrating TLR inhibitor peptide alleviates ulcerative colitis by the functional modulation of macrophages

Toll-like receptors (TLRs) have a crucial role not only in triggering innate responses against microbes but in orchestrating an appropriate adaptive immunity. However, deregulated activation of TLR signaling leads to chronic inflammatory conditions such as inflammatory bowel disease (IBD). In this study, we evaluated the immunomodulatory potential of a TLR inhibitor in the form of a cell-penetrating peptide using an ulcerative colitis animal model. A peptide derived from the TIR domain of the TLR adaptor molecule TIRAP that was conjugated with a cell-penetrating sequence (cpTLR-i) suppressed the induction of pro-inflammatory cytokines such as TNF-α and IL-1β in macrophages. In DSS-induced colitis mice, cpTLR-i treatment ameliorated colitis symptoms, colonic tissue damage, and mucosal inflammation. Intriguingly, cpTLR-i attenuated the induction of TNF-α-expressing proinflammatory macrophages while promoting that of regulatory macrophages expressing arginase-1 and reduced type 17 helper T cell (Th17) responses in the inflamed colonic lamina propria. An in vitro study validated that cpTLR-i enhanced the differentiation of monocyte-driven macrophages into mature macrophages with a regulatory phenotype in a microbial TLR ligand-independent manner. Furthermore, the cocultivation of CD4 T cells with macrophages revealed that cpTLR-i suppressed the activation of Th17 cells through the functional modulation of macrophages. Taken together, our data show the immunomodulatory potential of the TLR inhibitor peptide and suggest cpTLR-i as a novel therapeutic candidate for the treatment of IBD.

Metformin-chlorogenic acid combination reduces skeletal muscle inflammation in c57BL/6 mice on high-fat diets

BACKGROUND

Inflammation at the low-grade level has been found to contribute to obesity-induced insulin resistance in the skeletal muscle (SM). This study investigated the anti-inflammatory potential of metformin (MET) combined with chlorogenic acid (CGA) in SM of mice fed a high-fat diet (HFD).

MATERIALS AND METHODS

The C57BL/6 mice were divided into five groups of ten each, normal diet, HFD, HFD + MET, HFD + CGA and HFD + MET + CGA.

RESULTS

The results revealed that MET and CGA, alone or in combination, have a reducing effect on weight gain, plasma triglyceride, glucose and insulin levels. MET in combination with CGA led to attenuation of SM inflammation, an effect that was associated with decreasing macrophages infiltration rate. Combined treatment of MET and CGA also resulted in switching macrophages from M1 to M2 phenotype, presented by the higher expression levels of arginase and CD206 (M2 markers) and lower expression levels of iNOS and cd11c markers (M1). In addition, combination treatment was more effective in increasing the anti-inflammatory cytokines expression (IL-10) and decreasing the expression of pro-inflammatory mediators (TNF-α, IL-1β, MCP-1 and IL-6).

CONCLUSION

These findings suggest that the combination treatment of MET and CGA is likely to be a promising approach to control SM inflammation in the HFD-fed model.

The Role of Macrophages in the Pathogenesis of Atherosclerosis

A wide variety of cell populations, including both immune and endothelial cells, participate in the pathogenesis of atherosclerosis. Among these groups, macrophages deserve special attention because different populations of them can have completely different effects on atherogenesis and inflammation in atherosclerosis. In the current review, the significance of different phenotypes of macrophages in the progression or regression of atherosclerosis will be considered, including their ability to become the foam cells and the consequences of this event, as well as their ability to create a pro-inflammatory or anti-inflammatory medium at the site of atherosclerotic lesions as a result of cytokine production. In addition, several therapeutic strategies directed to the modulation of macrophage activity, which can serve as useful ideas for future drug developments, will be considered.

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

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

Acetylation of PPARγ in macrophages promotes visceral fat degeneration in obesity

Obesity is characterized by chronic, low-grade inflammation, which is driven by macrophage infiltration of adipose tissue. PPARγ is well established to have an anti-inflammatory function in macrophages, but the mechanism that regulates its function in these cells remains to be fully elucidated. PPARγ undergoes post-translational modifications (PTMs), including acetylation, to mediate ligand responses, including on metabolic functions. Here, we report that PPARγ acetylation in macrophages promotes their infiltration into adipose tissue, exacerbating metabolic dysregulation. We generated a mouse line that expresses a macrophage-specific, constitutive acetylation-mimetic form of PPARγ (K293Qflox/flox:LysM-cre, mK293Q) to dissect the role of PPARγ acetylation in macrophages. Upon high-fat diet feeding to stimulate macrophage infiltration into adipose tissue, we assessed the overall metabolic profile and tissue-specific phenotype of the mutant mice, including responses to the PPARγ agonist Rosiglitazone. Macrophage-specific PPARγ K293Q expression promotes proinflammatory macrophage infiltration and fibrosis in epididymal white adipose tissue, but not in subcutaneous or brown adipose tissue, leading to decreased energy expenditure, insulin sensitivity, glucose tolerance, and adipose tissue function. Furthermore, mK293Q mice are resistant to Rosiglitazone-induced improvements in adipose tissue remodeling. Our study reveals that acetylation is a new layer of PPARγ regulation in macrophage activation, and highlights the importance and potential therapeutic implications of such PTMs in regulating metabolism.

Lipedema: Insights into Morphology, Pathophysiology, and Challenges

Lipedema is an adipofascial disorder that almost exclusively affects women. Lipedema leads to chronic pain, swelling, and other discomforts due to the bilateral and asymmetrical expansion of subcutaneous adipose tissue. Although various distinctive morphological characteristics, such as the hyperproliferation of fat cells, fibrosis, and inflammation, have been characterized in the progression of lipedema, the mechanisms underlying these changes have not yet been fully investigated. In addition, it is challenging to reduce the excessive fat in lipedema patients using conventional weight-loss techniques, such as lifestyle (diet and exercise) changes, bariatric surgery, and pharmacological interventions. Therefore, lipedema patients also go through additional psychosocial distress in the absence of permanent treatment. Research to understand the pathology of lipedema is still in its infancy, but promising markers derived from exosome, cytokine, lipidomic, and metabolomic profiling studies suggest a condition distinct from obesity and lymphedema. Although genetics seems to be a substantial cause of lipedema, due to the small number of patients involved in such studies, the extrapolation of data at a broader scale is challenging. With the current lack of etiology-guided treatments for lipedema, the discovery of new promising biomarkers could provide potential solutions to combat this complex disease. This review aims to address the morphological phenotype of lipedema fat, as well as its unclear pathophysiology, with a primary emphasis on excessive interstitial fluid, extracellular matrix remodeling, and lymphatic and vasculature dysfunction. The potential mechanisms, genetic implications, and proposed biomarkers for lipedema are further discussed in detail. Finally, we mention the challenges related to lipedema and emphasize the prospects of technological interventions to benefit the lipedema community in the future.

Adipose tissue macrophages: Regulators of adipose tissue immunometabolism during obesity

BACKGROUND

Adipose tissue macrophages (ATMs) are a well characterized regulator of adipose tissue inflammatory tone. Previously defined by the M1 vs M2 classification, we now have a better understanding of ATM diversity that departs from the old paradigm and reports a spectrum of ATM function and phenotypes in both brown and white adipose tissue.

SCOPE OF REVIEW

This review provides an updated overview of ATM activation and function, ATM diversity in humans and rodents, and novel ATM functions that contribute to metabolic homeostasis and disease.

MAJOR CONCLUSIONS

While the paradigm that resident ATMs predominate in the lean state and obesity leads to the accumulation of lipid-associated and inflammatory ATMs still broadly remains rigorously supported, the details of this model continue to be refined and single cell data provide new insight into ATM subtypes and states.