Myeloperoxidase-Oxidized LDLs Enhance an Anti-Inflammatory M2 and Antioxidant Phenotype in Murine Macrophages

Inhibition of differentiation of monocyte-derived macrophages toward an M2-Like phenotype May Be a neglected mechanism of β-AR receptor blocker therapy for atherosclerosis

The clinical efficacy of adrenergic β-receptor (β-AR) blockers in significantly stabilizing atherosclerotic plaques has been extensively supported by evidence-based medical research; however, the underlying mechanism remains unclear. Recent findings have highlighted the impact of lipid-induced aberrant polarization of macrophages during normal inflammatory-repair and regenerative processes on atherosclerosis formation and progression. In this review, we explore the relationship between macrophage polarization and atherosclerosis, as well as the influence of β-AR blockers on macrophage polarization. Based on the robust evidence supporting the use of β-AR blockers for treating atherosclerosis, we propose that their main mechanism involves inhibiting monocyte-derived macrophage differentiation towards an M2-like phenotype.

Interplay between Senescence and Macrophages in Diabetic Cardiomyopathy: A Review of the Potential Role of GDF-15 and Klotho

Type 2 diabetes mellitus (T2DM) is a critical health problem, with 700 million diagnoses expected worldwide by 2045. Uncontrolled high blood glucose levels can lead to serious complications, including diabetic cardiomyopathy (DCM). Diabetes induces cardiovascular aging and inflammation, increasing cardiomyopathy risk. DCM is characterized by structural and functional abnormalities in the heart. Growing evidence suggests that cellular senescence and macrophage-mediated inflammation participate in the pathogenesis and progression of DCM. Evidence indicates that growth differentiation factor-15 (GDF-15), a protein that belongs to the transforming growth factor-beta (TGF-β) superfamily, is associated with age-related diseases and exerts an anti-inflammatory role in various disease models. Although further evidence suggests that GDF-15 can preserve Klotho, a transmembrane antiaging protein, emerging research has elucidated the potential involvement of GDF-15 and Klotho in the interplay between macrophages-induced inflammation and cellular senescence in the context of DCM. This review explores the intricate relationship between senescence and macrophages in DCM while highlighting the possible contributions of GDF-15 and Klotho.

Biofilms exacerbate atherogenesis through macrophage-induced inflammatory responses in a fibrous plaque microsystem model

BACKGROUND

Microbes have been implicated in atherosclerosis development and progression, but the impact of bacterial-based biofilms on fibrous plaque rupture remains poorly understood.

RESULTS

Here, we developed a comprehensive atherosclerotic model to reflect the progression of fibrous plaque under biofilm-induced inflammation (FP-I). High expressions of biofilm-specific biomarkers algD, pelA and pslB validated the presence of biofilms. Biofilm promotes the polarization of macrophages towards a pro-inflammatory (M1) phenotype, as demonstrated by an increase in M1 macrophage-specific marker CD80 expression in CD68+ macrophages. The increase in the number of intracellular lipid droplets (LDs) and foam cell percentage highlighted the potential role of biofilms on lipid synthesis or metabolic pathways in macrophage-derived foam cells. In addition, collagen I production by myofibroblasts associated with the fibrous cap was significantly reduced along with the promotion of apoptosis of myofibroblasts, indicating that biofilms affect the structural integrity of the fibrous cap and potentially undermine its strength.

CONCLUSION

We validated the unique role of biofilm-based inflammation in exacerbating fibrous plaque damage in the FP-I model, increasing fibrous plaque instability and risk of thrombosis. Our results lay the foundation for mechanistic studies of the role of biofilms in fibrous plaques, allowing the evaluation of preclinical combination strategies for drug therapy.

STATEMENT OF SIGNIFICANCE

A microsystem-based model was developed to reveal interactions in fibrous plaque during biofilm-induced inflammation (FP-I). Real-time assessment of biofilm formation and its role in fibrous plaque progression was achieved. The presence of biofilms enhanced the expression of pro-inflammatory (M1) specific marker CD80, lipid droplets, and foam cells and reduced anti-inflammatory (M2) specific marker CD206 expression. Fibrous plaque exposure to biofilm-based inflammation reduced collagen I expression and increased apoptosis marker Caspase-3 expression significantly. Overall, we demonstrate the unique role of biofilm-based inflammation in exacerbating fibrous plaque damage in the FP-I model, promoting fibrous plaque instability and enhanced thrombosis risk. Our findings lay the groundwork for mechanistic studies, facilitating the evaluation of preclinical drug combination strategies.

Impact of Lipid Metabolism on Macrophage Polarization: Implications for Inflammation and Tumor Immunity

Macrophage polarization is influenced by lipids, which also exert significant control over macrophage functions. Lipids and their metabolites are players in intricate signaling pathways that modulate macrophages' responses to pathogens, phagocytosis, ferroptosis, and inflammation. This review focuses on lipid metabolism and macrophage functions and addresses potential molecular targets for the treatment of macrophage-related diseases. While lipogenesis is crucial for lipid accumulation and phagocytosis in M1 macrophages, M2 macrophages likely rely on fatty acid β-oxidation to utilize fatty acids as their primary energy source. Cholesterol metabolism, regulated by factors such as SREBPs, PPARs, and LXRs, is associated with the cholesterol efflux capacity and the formation of foam cells (M2-like macrophages). Foam cells, which are targets for atherosclerosis, are associated with an increase in inflammatory cytokines. Lipolysis and fatty acid uptake markers, such as CD36, also contribute to the production of cytokines. Enhancing the immune system through the inhibition of lipid-metabolism-related factors can potentially serve as a targeted approach against tumor cells. Cyclooxygenase inhibitors, which block the conversion of arachidonic acid into various inflammatory mediators, influence macrophage polarization and have generated attention in cancer research.

Unexpected Role of MPO-Oxidized LDLs in Atherosclerosis: In between Inflammation and Its Resolution

Inflammation and its resolution are the result of the balance between pro-inflammatory and pro-resolving factors, such as specialized pro-resolving mediators (SPMs). This balance is crucial for plaque evolution in atherosclerosis, a chronic inflammatory disease. Myeloperoxidase (MPO) has been related to oxidative stress and atherosclerosis, and MPO-oxidized low-density lipoproteins (Mox-LDLs) have specific characteristics and effects. They participate in foam cell formation and cause specific reactions when interacting with macrophages and endothelial cells. They also increase the production of intracellular reactive oxygen species (ROS) in macrophages and the resulting antioxidant response. Mox-LDLs also drive macrophage polarization. Mox-LDLs are known to be pro-inflammatory particles. However, in the presence of Mox-LDLs, endothelial cells produce resolvin D1 (RvD1), a SPM. SPMs are involved in the resolution of inflammation by stimulating efferocytosis and by reducing the adhesion and recruitment of neutrophils and monocytes. RvD1 also induces the synthesis of other SPMs. In vitro, Mox-LDLs have a dual effect by promoting RvD1 release and inducing a more anti-inflammatory phenotype macrophage, thereby having a mixed effect on inflammation. In this review, we discuss the interrelationship between MPO, Mox-LDLs, and resolvins, highlighting a new perception of the role of Mox-LDLs in atherosclerosis.

M2 Monocyte Polarization in Dialyzed Patients Is Associated with Increased Levels of M-CSF and Myeloperoxidase-Associated Oxidative Stress: Preliminary Results

Cardiovascular diseases represent a major issue in terms of morbidity and mortality for dialysis patients. This morbidity is due to the accelerated atherosclerosis observed in these patients. Atherosclerosis is a chronic inflammatory disease characterized by key players such as monocytes, macrophages, or oxidized LDLs. Monocytes-macrophages are classified into subsets of polarized cells, with M1 and M2 macrophages considered, respectively, as pro- and anti-inflammatory. (1) Methods: The monocyte subsets and phenotypes were analyzed by flow cytometry. These data were completed by the quantification of plasma M-CSF, IL-8, CRP, Mox-LDLs, Apo-B, Apo-AI, chloro-tyrosine, and homocitrulline concentrations. The statistical differences and associations between two continuous variables were assessed using the Mann-Whitney U test and Spearman's correlation coefficient, respectively. (2) Results: Hemodialyzed patients showed a significant increase in their concentrations of CRP, M-CSF, and IL-8 (inflammation biomarkers), as well as chloro-tyrosine and homocitrulline (myeloperoxidase-associated oxidative stress biomarkers). Moreover, we observed a higher percentage of M2 monocytes in the plasma of hemodialysis patients as compared to the controls. (3) Conclusions: Our data suggest that oxidative stress and an inflammatory environment, which is amplified in hemodialysis patients, seems to favor an increase in the concentration of circulating M-CSF, therefore leading to an increase in M2 polarization among circulating monocytes.

Cycling hypoxia promotes a pro-inflammatory phenotype in macrophages via JNK/p65 signaling pathway

Cycling hypoxia (cyH), also called intermittent hypoxia, occurs in solid tumors and affects different cell types in the tumor microenvironment and in particular the tumor-associated macrophages (TAMs). As cyH and TAMs both favor tumor progression, we investigated whether cyH could drive the pro-tumoral phenotype of macrophages. Here, the effects of cyH on human THP-1 macrophages and murine bone marrow-derived macrophages (BMDM), either unpolarized M0, or polarized in M1 or M2 phenotype were studied. In M0 macrophages, cyH induced a pro-inflammatory phenotype characterized by an increase in TNFα and IL-8/MIP-2 secretion. CyH amplified the pro-inflammatory phenotype of M1 macrophages evidenced by an increased pro-inflammatory cytokine secretion and pro-inflammatory gene expression. Furthermore, cyH increased c-jun activation in human M0 macrophages and highly increased c-jun and NF-κB activation in M1 macrophages. C-jun and p65 are implicated in the effects of cyH on M0 and M1 macrophages since inhibition of their activation prevented the cyH pro-inflammatory effects. In conclusion, we demonstrated that cyH induces or amplifies a pro-inflammatory phenotype in M0 and M1 macrophages by activating JNK/p65 signaling pathway. These results highlight a specific role of cyH in the amplification of tumor-related inflammation by modulating the inflammatory phenotype of macrophages.

Adipose-derived Mesenchymal Stromal Cells Modulate Lipid Metabolism and Lipid Droplet Biogenesis via AKT/mTOR -PPARγ Signalling in Macrophages

Mesenchymal stromal cells (MSCs) are a potential therapy for many chronic inflammatory diseases due to their regenerative, immunologic and anti-inflammatory properties. The two-way dialogue between MSCs and macrophages is crucial to tissue regeneration and repair. Previous research demonstrated that murine adipose-derived MSC conditioned medium (ASCcm) reprograms macrophages to an M2-like phenotype which protects from experimental colitis and sepsis. Here, our focus was to determine the molecular mechanism of lipid droplet biogenesis in macrophages re-educated using ASCcm. Adipose-derived MSC conditioned medium promotes phosphorylation of AKT/mTOR pathway proteins in macrophages. Furthermore, increased expression of PPARγ, lipid droplet biogenesis and PGE₂ synthesis were observed in M2-like phenotype macrophages (high expression of arginase 1 and elevated IL-10). Treatment with mTOR inhibitor rapamycin or PPARγ inhibitor GW9662 suppressed lipid droplets and PGE₂ secretion. However, these inhibitors had no effect on arginase-1 expression. Rapamycin, but not GW9662, inhibit IL-10 secretion. In conclusion, we demonstrate major effects of ASCcm to reprogram macrophage immunometabolism through mTOR and PPARγ dependent and independent pathways.

Mitochondrial fragmentation affects neither the sensitivity to TNFα-induced apoptosis of Brucella-infected cells nor the intracellular replication of the bacteria

Mitochondria are complex organelles that participate in many cellular functions, ranging from ATP production to immune responses against viruses and bacteria. This integration of a plethora of functions within a single organelle makes mitochondria a very attractive target to manipulate for intracellular pathogens. We characterised the crosstalk that exists between Brucella abortus, the causative agent of brucellosis, and the mitochondria of infected cells. Brucella replicates in a compartment derived from the endoplasmic reticulum (ER) and modulates ER functionality by activating the unfolded protein response. However, the impact of Brucella on the mitochondrial population of infected cells still requires a systematic study. We observed physical contacts between Brucella containing vacuoles and mitochondria. We also found that B. abortus replication is independent of mitochondrial oxidative phosphorylation and that mitochondrial reactive oxygen species do not participate to the control of B. abortus infection in vitro. We demonstrated that B. abortus and B. melitensis induce a drastic mitochondrial fragmentation at 48 hours post-infection in different cell types, including myeloid and non-myeloid cells. This fragmentation is DRP1-independent and might be caused by a deficit of mitochondrial fusion. However, mitochondrial fragmentation does not change neither Brucella replication efficiency, nor the susceptibility of infected cells to TNFα-induced apoptosis.

A pathogenetic role for M1 macrophages in peritoneal dialysis-associated fibrosis

Peritoneal fibrosis (PF) is a frequent complication of peritoneal dialysis (PD) accompanied by the infiltration of inflammatory cells. Recently, the function of macrophages in an inflammatory microenvironment during PD remains unknown. This study aimed to elucidate the role of distinct macrophage phenotypes in the progression of PF through macrophage depletion in a peritoneal dialysis-induced mouse model. After injection of 200 μl liposomal clodronate (LC) at the start of instillation PD fluids (PDFs), mice were injected with 100 μL LC every 4 days after the first time injection for longer macrophage depletion, while control mice were co-treated with PBS liposomes. For macrophages transfusion,primary macrophages (M0) were stimulated into M1 and M2 macrophages and transfuritoneal fibrosis (PF) is a frequent complication of peritoneal dialysis (PD) accompanied by the infiltration of inflammatory cells. Recently, the function of macrophages in an inflammatory microenvironment during PD remains unknown. This study aimed to elucidate the role of distinct macrophage phenotypes in the progression of PF through macrophage depletion in a peritoneal dialysis-induced mouse model. After injection of 200 μl liposomal clodronate (LC) at the start of instillation PD fluids (PDFs), mice were injected with 100 μL LC every 4 days after the first time injection for longer macrophage depletion, while control mice were co-treated with PBS liposomes. For macrophages transfusion,primary macrophages (M0) were stimulated into M1 and M2 macrophages and transfused into the mice the next day after each LC injection. Mice were sacrificed after 6 weeks of PDFs treatment for the assessment of histological changes, ECM deposition and peritoneal ultrafiltration function. Systemic monocyte/macrophage depletion resulted in less severe structural alterations, including thickening and cubic transformation of mesothelial cells, fibrin deposition, fibrous capsule formation, and interstitial fibrosis. A strong reduction of alpha-smooth muscle actin (α-SMA) and fibronectin expression, as well as an increased E-cadherin expression was also observed, indicating an overall inhibition of peritoneal fibrosis in macrophages depletion mice.M1 macrophage reperfusion showed a significant increase in histological damages, ECM deposition and peritoneal ultrafiltration functional decline compared with those of the M2 and control groups. TLR4 expression was enhanced in M1 macrophage-treated group. These results suggest that M1 macrophages are an important mediator of peritoneal fibrosis.