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To assess monocyte-based delivery of conjugated polymer nanoparticles (CPNs) for improved photodynamic therapy (PDT) in glioblastoma (GBM). Human monocyte cells (THP-1) and murine monocytes isolated from bone marrow (mBMDMs) were employed as stealth CPN carriers to penetrate into GBM spheroids and an orthotopic model of the tumor. The success of PDT, using this cell-mediated targeting strategy, was determined by its effect on the spheroids. CPNs did not affect monocyte viability in the absence of light and did not show nonspecific release after cell loading. Activated monocytes incorporated CPNs in a higher proportion than monocytes in their naive state, without a loss of cellular functionality. PDT efficacy using cell-mediated delivery was superior to that using non vehiculized CPNs. CPN-loaded monocytes could efficiently deliver CPNs into GBM spheroids and the orthotopic model. Improved PDT in spheroids was confirmed using this delivery strategy.

The distal pathways for differentiation into monocytes and monocyte-derived macrophages are not fully elucidated. Feuerer and colleagues describe a clonogenic, monocyte- and macrophage-restricted progenitor derived from the macrophage–dendritic cell progenitor. Monocytes, macrophages and dendritic cells (DCs) are developmentally related regulators of the immune system that share the monocyte-macrophage DC progenitor (MDP) as a common precursor. Unlike differentiation into DCs, the distal pathways for differentiation into monocytes and monocyte-derived macrophages are not fully elucidated. We have now demonstrated the existence of a clonogenic, monocyte- and macrophage-restricted progenitor cell derived from the MDP. This progenitor was a Ly6C + proliferating cell present in the bone marrow and spleen that generated the major monocyte subsets and macrophages, but not DCs or neutrophils. By in-depth quantitative proteomics, we characterized changes in the proteome during monocyte differentiation, which provided insight into the molecular principles of developing monocytes, such as their functional maturation. Thus, we found that monocytes and macrophages were renewed independently of DCs from a committed progenitor.

Aims This study aimed to investigate the specific mechanism by which angiopoietin‐2 (ANGPT2)/Tie2 signaling in macrophages promotes endothelial cell (EC) proliferation in the chronically ischaemic brain (CIB). Methods We first analyzed the polarization status of primary Tie2‐expressing macrophages (TEMs) and Tie2‐overexpressing THP‐1‐derived macrophages (Tie2‐TDMs) following ANGPT2 treatment and detected the expression of representative proangiogenic factors. Subsequently, lysine lactylation (Kla) levels were measured, and chromatin immunoprecipitation (ChIP) assays were performed to explore the downstream activity of ANGPT2/Tie2 signaling. Additionally, in vitro functional assays using human umbilical vein endothelial cells (HUVECs) and in vivo experiments in a rat model of chronic cerebral ischaemia were conducted to confirm the effect of ANGPT2/Tie2‐regulated macrophages on angiogenesis. Results In response to ANGPT2 treatment, the expression of M2 polarization markers and proangiogenic factors increased in TEMs and Tie2‐TDMs. Concurrently, LDHA and H3K18la were elevated, and ChIP assays confirmed the regulatory role of ANGPT2/Tie2 signaling in H3K18la‐mediated transcriptional regulation. The viability of HUVECs cocultured with Tie2‐TDMs was increased. Finally, ANGPT2 overexpression increased M2‐polarized TEM infiltration in the CIB; additionally, rats injected with ANGPT2‐pretreated TEMs exhibited more prominent EC proliferation. Conclusion ANGPT2/Tie2 induces the H3K18la‐mediated M2 polarization of macrophages to facilitate EC proliferation and angiogenesis in the CIB. ANGPT2/Tie2 signaling upregulates LDHA and increases H3K18la, promoting the polarization of macrophages towards an M2 phenotype. Such M2 macrophages secrete high levels of proangiogenic factors, which facilitate endothelial cell proliferation and angiogenesis in the chronically ischaemic brain.

Loss of estrogens at menopause is a major cause of osteoporosis and increased fracture risk. Estrogens protect against bone loss by decreasing osteoclast number through direct actions on cells of the myeloid lineage. Here, we investigated the molecular mechanism of this effect. We report that 17β-estradiol (E 2 ) decreased osteoclast number by promoting the apoptosis of early osteoclast progenitors, but not mature osteoclasts. This effect was abrogated in cells lacking Bak/Bax—two pro-apoptotic members of the Bcl-2 family of proteins required for mitochondrial apoptotic death. FasL has been previously implicated in the pro-apoptotic actions of E 2 . However, we show herein that FasL-deficient mice lose bone mass following ovariectomy indistinguishably from FasL-intact controls, indicating that FasL is not a major contributor to the anti-osteoclastogenic actions of estrogens. Instead, using microarray analysis we have elucidated that ERα-mediated estrogen signaling in osteoclast progenitors decreases “oxidative phosphorylation” and the expression of mitochondria complex I genes. Additionally, E 2 decreased the activity of complex I and oxygen consumption rate. Similar to E 2 , the complex I inhibitor Rotenone decreased osteoclastogenesis by promoting osteoclast progenitor apoptosis via Bak/Bax. These findings demonstrate that estrogens decrease osteoclast number by attenuating respiration, and thereby, promoting mitochondrial apoptotic death of early osteoclast progenitors.

Emerging studies from SARS-CoV-2-infected patients indicate a preponderant role of monocytes/macrophages in the pathogenesis of this viral infection, in a similar way to that previously observed in other coronavirus outbreaks (SARS and MERS). The clinical presentation of severe patients resembles viral-associated hemophagocytic syndrome, a rare condition previously seen during lethal influenza pandemics and during previous SARS and MERS coronavirus outbreaks. SARS-CoV-2 infection triggers an over-exuberant inflammatory response due to the development of a cytokine storm and the depletion of the adaptative immune compartment, which may prelude sepsis in many cases. The present review summarizes past evidence on the role of monocytes/macrophages in previous coronavirus outbreaks and the emerging knowledge on their role in COVID-19 pathogenesis. Treatment strategies incorporating the blockade of migration and differentiation of monocyte-macrophage, such as granulocyte macrophage-colony stimulating factor inhibitors, might enhance the promising results seen so far with selective cytokine blockade.

Gliomas are the most common malignant brain tumors, with complicated etiology and poor prognosis. However, there is still a lack of specific biomarkers for the diagnosis, treatment and prognosis assessment for glioma patients. Hence, the purpose of this study was to screen biomarkers for prognostic assessment and therapeutic interventions in gliomas. We utilized The Cancer Genome Atlas (TCGA) and Chinese Glioma Genome Atlas (CGGA) databases to investigate the role of colony-stimulating factor 3 receptor (CSF3R) in glioma. Data analysis was conducted using R, GEPIA 2, TISCH and DepMap. CSF3R was up-regulated in glioma and associated with the clinical pathological features of the patients. Kaplan-Meier survival analysis indicated a significant association between the expression of CSF3R and prognosis in patients. Univariate and multivariate Cox analyses revealed that patients with high expression of CSF3R have a worse prognosis, and the expression of CSF3R was an independent prognostic factor in gliomas. The nomogram constructed based on the expression of CSF3R demonstrated lower 1-, 3-, and 5-year overall survival (OS) in patients with high CSF3R expression. The biological functional analysis of CSF3R demonstrated its association with various immune regulatory signals. Furthermore, CSF3R was linked to the expression of immune checkpoints and resistance to immunotherapy. Notably, CSF3R was predominantly detected in monocytes/macrophages. Our study suggested that CSF3R might potentially function as an independent prognostic factor for glioma and hold promise as a biomarker and target for immunotherapy in glioma.

Macrophages are innate immune cells that play key roles during both homeostasis and disease. Depending on the microenvironmental cues sensed in different tissues, macrophages are known to acquire specific phenotypes and exhibit unique features that, ultimately, orchestrate tissue homeostasis, defense, and repair. Within the tumor microenvironment, macrophages are referred to as tumor‐associated macrophages (TAMs) and constitute a heterogeneous population. Like their tissue resident counterpart, TAMs are plastic and can switch function and phenotype according to the niche‐derived stimuli sensed. While changes in TAM phenotype are known to be accompanied by adaptive alterations in their cell metabolism, it is reported that metabolic reprogramming of macrophages can dictate their activation state and function. In line with these observations, recent research efforts have been focused on defining the metabolic traits of TAM subsets in different tumor malignancies and understanding their role in cancer progression and metastasis formation. This knowledge will pave the way to novel therapeutic strategies tailored to cancer subtype‐specific metabolic landscapes. This review outlines the metabolic characteristics of distinct TAM subsets and their implications in tumorigenesis across multiple cancer types. Tumor‐associated macrophages (TAMs) constitute up to 50% of the tumor mass, representing a heterogeneous population of tissue‐resident and monocyte‐derived macrophages. TAM phenotype not only involves alterations in cell metabolism but also metabolic reprogramming that can dictate their activation state and function. This review elucidates the diverse roles and metabolic traits of distinct TAM subsets in pancreatic, breast, lung and ovarian malignancies.

The reactivation of latent human cytomegalovirus (HCMV) infection after transplantation is associated with high morbidity and mortality. In vivo, myeloid cells and their progenitors are an important site of HCMV latency, whose establishment and/or maintenance require expression of the viral transcript UL138. Using stable isotope labeling by amino acids in cell culture-based mass spectrometry, we found a dramatic UL138-mediated loss of cell surface multidrug resistance-associated protein-1 (MRP1) and the reduction of substrate export by this transporter. Latency-associated loss of MRP1 and accumulation of the cytotoxic drug vincristine, an MRP1 substrate, depleted virus from naturally latent CD14⁺ and CD34⁺ progenitors, all of which are in vivo sites of latency. The UL138-mediated loss of MRP1 provides a marker for detecting latent HCMV infection and a therapeutic target for eliminating latently infected cells before transplantation.

We studied HLA class II molecules on blood monocyte subsets, blood dendritic cells, sputum macrophages, and monocyte-derived macrophages at the protein (flow cytometry) and mRNA level (RT-PCR) in adult patients with cystic fibrosis (CF) and healthy control subjects as putative contributors to the CF phenotype. In healthy donors, we found a high average HLA-DQ expression of 4.35 mean specific fluorescence intensity units (ΔMnI) on classical blood monocytes. In F508del homozygous CF patients, the average ΔMnI was low (1.80). Patients were divided into two groups, in which 14 of these patients had HLA-DQ expression above 2 ΔMnI (average 3.25 ΔMnI, CF-DQ group1 ) and 36 below (average 1.24 ΔMnI, CF-DQ group2 ). Also, the CD16-positive monocyte subset and blood dendritic cells showed much lower levels of HLA-DQ for the CF-DQ group2 patients compared with healthy controls. In macrophages from sputum and derived from monocytes, in vitro HLA-DQ expression was dramatically decreased to background levels in CF-DQ group2 . MHC class II transcripts were reduced in CF with a sevenfold decrease in HLA-DQβ1 for CF-DQ group2 patients. Higher levels of the inflammation marker CRP were associated with low HLA-DQ protein expression, and in vitro treatment with the inflammatory molecule lipopolysaccharide reduced HLA-DQ expression. Interferon γ (IFNγ) could overcome this effect in healthy donor cells while, in CF, the IFNγ-induced activation was impaired. Our data demonstrate a pronounced reduction of HLA-DQ expression in CF, which is associated with inflammation and a reduced response to IFNγ. Key message • CF patients show a reduced expression of MHCII molecules in monocytes and macrophages. • HLA-DQ and HLA-DR transcript levels are also reduced in CF patients. • CF patient C-reactive protein levels correlate with low HLA-DQ expression. • Reduced expression of MHC class II molecules appears to be linked to inflammation. • CF patients exhibit an impaired response to IFNgamma.

Epitranscriptomics refers to posttranscriptional alterations on an mRNA sequence that are dynamic and reproducible, and affect gene expression in a similar way to epigenetic modifications. However, the functional relevance of those modifications for the transcript, the cell, and the organism remain poorly understood. Here, we focus on RNA editing and show that Apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-1 (APOBEC1), together with its cofactor RBM47, mediates robust editing in different tissues. The majority of editing events alter the sequence of the 3′UTR of targeted transcripts, and we focus on one cell type (monocytes) and on a small set of highly edited transcripts within it to show that editing alters gene expression by modulating translation (but not RNA stability or localization). We further show that specific cellular processes (phagocytosis and transendothelial migration) are enriched for transcripts that are targets of editing and that editing alters their function. Finally, we survey bone marrow progenitors and demonstrate that common monocyte progenitor cells express high levels of APOBEC1 and are susceptible to loss of the editing enzyme. Overall, APOBEC1-mediated transcriptome diversification is required for the fine-tuning of protein expression in monocytes, suggesting an epitranscriptomic mechanism for the proper maintenance of homeostasis in innate immune cells.