A novel mouse model of inflammatory bowel disease links mammalian target of rapamycin-dependent hyperproliferation of colonic epithelium to inflammation-associated tumorigenesis

Temporal dynamics of immune-stromal cell interactions in fracture healing

Bone fracture repair is a complex, multi-step process that involves communication between immune and stromal cells to coordinate the repair and regeneration of damaged tissue. In the US, 10% of all bone fractures do not heal properly without intervention, resulting in non-union. Complications from non-union fractures are physically and financially debilitating. We now appreciate the important role that immune cells play in tissue repair, and the necessity of the inflammatory response in initiating healing after skeletal trauma. The temporal dynamics of immune and stromal cell populations have been well characterized across the stages of fracture healing. Recent studies have begun to untangle the intricate mechanisms driving the immune response during normal or atypical, delayed healing. Various in vivo models of fracture healing, including genetic knockouts, as well as in vitro models of the fracture callus, have been implemented to enable experimental manipulation of the heterogeneous cellular environment. The goals of this review are to (1): summarize our current understanding of immune cell involvement in fracture healing (2); describe state-of-the art approaches to study inflammatory cells in fracture healing, including computational and in vitro models; and (3) identify gaps in our knowledge concerning immune-stromal crosstalk during bone healing.

Mannose attenuates intestinal epithelial tight junction damage in experimental colitis mice by activating the AXIN-AMPK pathway

Mannose is a unique natural sugar that can be found in a variety of fruits and vegetables. During the past decades, mannose has been reported to be effective in promoting immune tolerance and suppressing inflammatory diseases. Metabolic dysfunction and altered inflammation have clear implications for the development and progression of inflammatory diseases. Herein, we intended to reveal the molecular mechanism of mannose in protecting against intestinal epithelial damage in experimental colitis. We showed that mannose treatment significantly attenuated dextran sodium sulfate (DSS)-induced intestinal barrier damage. The AMPK pathway was responsible for the mannose-mediated protective effect in DSS-induced intestinal epithelial damage. Mechanistically, mannose promoted the axis inhibition protein (AXIN)-based AMPK activation, thereby preventing mitochondrial dysfunction and tight junction disruption in response to the DSS challenge. Cumulatively, the results indicate the use of mannose as a novel approach to treat IBD and other diseases involving tight junction dysfunction. The therapeutic effect of mannose is related to its regulatory function in AMPK pathway activation.

Clonal Expansion in Cardiovascular Pathology

Clonal expansion refers to the proliferation and selection of advantageous "clones" that are better suited for survival in a Darwinian manner. In recent years, we have greatly enhanced our understanding of cell clonality in the cardiovascular context. However, our knowledge of the underlying mechanisms behind this clonal selection is still severely limited. There is a transpiring pattern of clonal expansion of smooth muscle cells and endothelial cells-and, in some cases, macrophages-in numerous cardiovascular diseases irrespective of their differing microenvironments. These findings indirectly suggest the possible existence of stem-like vascular cells which are primed to respond during disease. Subsequent clones may undergo further phenotypic changes to adopt either protective or detrimental roles. By investigating these clone-forming vascular cells, we may be able to harness this inherent clonal nature for future therapeutic intervention. This review comprehensively discusses what is currently known about clonal expansion across the cardiovascular field. Comparisons of the clonal nature of vascular cells in atherosclerosis (including clonal hematopoiesis of indeterminate potential), pulmonary hypertension, aneurysm, blood vessel injury, ischemia- and tumor-induced angiogenesis, and cerebral cavernous malformations are evaluated. Finally, we discuss the potential clinical implications of these findings and propose that proper understanding and specific targeting of these clonal cells may provide unique therapeutic options for the treatment of these cardiovascular conditions.

Tackling Tissue Macrophage Heterogeneity by SplitCre Transgenesis

Macrophages represent a broad spectrum of distinct, but closely related tissue-resident immune cells. This presents a major challenge for the study of functional aspects of these cells using classical Cre recombinase-mediated conditional mutagenesis in mice, since single promoter-driven Cre transgenic models often display limited specificity toward their intended target. The advent of CRISPR/Cas9 technology has now provided a time- and cost-effective method to explore the full potential of binary transgenic, intersectional genetics. Specifically, the use of two promoters driving inactive Cre fragments that, when co-expressed, dimerize and only then gain recombinase activity allows the characterization and manipulation of genetically defined tissue macrophage subpopulations. Here, we will elaborate on the use of this protocol to capitalize on these recent technological advances in mouse genetics and discuss their strengths and pitfalls to improve the study of tissue macrophage subpopulations in physiology and pathophysiology.

Distinct hypoxia-induced translational profiles of embryonic and adult-derived macrophages

Tissue resident macrophages are largely of embryonic (fetal liver) origin and long-lived, while bone marrow-derived macrophages (BMDM) are recruited following an acute perturbation, such as hypoxia in the setting of myocardial ischemia. Prior transcriptome analyses identified BMDM and fetal liver-derived macrophage (FLDM) differences at the RNA expression level. Posttranscriptional regulation determining mRNA stability and translation rate may override transcriptional signals in response to hypoxia. We profiled differentially regulated BMDM and FLDM transcripts in response to hypoxia at the level of mRNA translation. Using a translating ribosome affinity purification (TRAP) assay and RNA-seq, we identified non-overlapping transcripts with increased translation rate in BMDM (Ly6e, vimentin, PF4) and FLDM (Ccl7, Ccl2) after hypoxia. We further identified hypoxia-induced transcripts within these subsets that are regulated by the RNA-binding protein HuR. These findings define translational differences in macrophage subset gene expression programs, highlighting potential therapeutic targets in ischemic myocardium.

The Past, Present, and Future of Genetically Engineered Mouse Models for Skeletal Biology

The ability to create genetically engineered mouse models (GEMMs) has exponentially increased our understanding of many areas of biology. Musculoskeletal biology is no exception. In this review, we will first discuss the historical development of GEMMs and how these developments have influenced musculoskeletal disease research. This review will also update our 2008 review that appeared in BONEKey, a journal that is no longer readily available online. We will first review the historical development of GEMMs in general, followed by a particular emphasis on the ability to perform tissue-specific (conditional) knockouts focusing on musculoskeletal tissues. We will then discuss how the development of CRISPR/Cas-based technologies during the last decade has revolutionized the generation of GEMMs.

IL-1β turnover by the UBE2L3 ubiquitin conjugating enzyme and HECT E3 ligases limits inflammation

The cytokine interleukin-1β (IL-1β) has pivotal roles in antimicrobial immunity, but also incites inflammatory disease. Bioactive IL-1β is released following proteolytic maturation of the pro-IL-1β precursor by caspase-1. UBE2L3, a ubiquitin conjugating enzyme, promotes pro-IL-1β ubiquitylation and proteasomal disposal. However, actions of UBE2L3 in vivo and its ubiquitin ligase partners in this process are unknown. Here we report that deletion of Ube2l3 in mice reduces pro-IL-1β turnover in macrophages, leading to excessive mature IL-1β production, neutrophilic inflammation and disease following inflammasome activation. An unbiased RNAi screen identified TRIP12 and AREL1 E3 ligases of the Homologous to E6 C-terminus (HECT) family in adding destabilising K27-, K29- and K33- poly-ubiquitin chains on pro-IL-1β. We show that precursor abundance determines mature IL-1β production, and UBE2L3, TRIP12 and AREL1 limit inflammation by shrinking the cellular pool of pro-IL-1β. Our study uncovers fundamental processes governing IL-1β homeostasis and provides molecular insights that could be exploited to mitigate its adverse actions in disease.

T helper 2 cells control monocyte to tissue-resident macrophage differentiation during nematode infection of the pleural cavity

The recent revolution in tissue-resident macrophage biology has resulted largely from murine studies performed in C57BL/6 mice. Here, using both C57BL/6 and BALB/c mice, we analyze immune cells in the pleural cavity. Unlike C57BL/6 mice, naive tissue-resident large-cavity macrophages (LCMs) of BALB/c mice failed to fully implement the tissue-residency program. Following infection with a pleural-dwelling nematode, these pre-existing differences were accentuated with LCM expansion occurring in C57BL/6, but not in BALB/c mice. While infection drove monocyte recruitment in both strains, only in C57BL/6 mice were monocytes able to efficiently integrate into the resident pool. Monocyte-to-macrophage conversion required both T cells and interleukin-4 receptor alpha (IL-4Rα) signaling. The transition to tissue residency altered macrophage function, and GATA6+ tissue-resident macrophages were required for host resistance to nematode infection. Therefore, during tissue nematode infection, T helper 2 (Th2) cells control the differentiation pathway of resident macrophages, which determines infection outcome.

Cholesterol accumulation in macrophages drives NETosis in atherosclerotic plaques via IL-1β secretion

AIMS

Neutrophil extracellular trap formation (NETosis) increases atherosclerotic plaque vulnerability and athero-thrombosis. However, mechanisms promoting NETosis during atherogenesis are poorly understood. We have shown that cholesterol accumulation due to myeloid cell deficiency of the cholesterol transporters ATP Binding Cassette A1 and G1 (ABCA1/G1) promotes NLRP3 inflammasome activation in macrophages and neutrophils and induces prominent NETosis in atherosclerotic plaques. We investigated whether NETosis is a cell-intrinsic effect in neutrophils or is mediated indirectly by cellular crosstalk from macrophages to neutrophils involving IL-1β.

METHODS AND RESULTS

We generated mice with neutrophil or macrophage-specific Abca1/g1 deficiency (S100A8CreAbca1fl/flAbcg1fl/fl or CX3CR1CreAbca1fl/flAbcg1fl/fl mice, respectively), and transplanted their bone marrow into low-density lipoprotein receptor knockout mice. We then fed the mice a cholesterol-rich diet. Macrophage, but not neutrophil Abca1/g1 deficiency activated inflammasomes in macrophages and neutrophils, reflected by caspase-1 cleavage, and induced NETosis in plaques. NETosis was suppressed by administering an interleukin (IL)-1β neutralizing antibody. The extent of NETosis in plaques correlated strongly with the degree of neutrophil accumulation, irrespective of blood neutrophil counts, and neutrophil accumulation was decreased by IL-1β antagonism. In vitro, IL-1β or media transferred from Abca1/g1-deficient macrophages increased NETosis in both control and Abca1/Abcg1 deficient neutrophils. This cell-extrinsic effect of IL-1β on NETosis was blocked by an NLRP3 inhibitor.

CONCLUSION

These studies establish a new link between inflammasome-mediated IL-1β production in macrophages and NETosis in atherosclerotic plaques. Macrophage-derived IL-1β appears to increase NETosis both by increasing neutrophil recruitment to plaques and by promoting neutrophil NLRP3 inflammasome activation.

WNK1 enforces macrophage lineage fidelity

The appropriate development of macrophages, the body's professional phagocyte, is essential for organismal development, especially in mammals. This dependence is exemplified by the observation that loss-of-function mutations in colony stimulating factor 1 receptor (CSF1R) results in multiple tissue abnormalities owing to an absence of macrophages. Despite this importance, little is known about the molecular and cell biological regulation of macrophage development. Here, we report the surprising finding that the chloride-sensing kinase With-no-lysine 1 (WNK1) is required for development of tissue-resident macrophages (TRMs). Myeloid-specific deletion of Wnk1 resulted in a dramatic loss of TRMs, disrupted organ development, systemic neutrophilia, and mortality between 3 and 4 weeks of age. Strikingly, we found that myeloid progenitors or precursors lacking WNK1 not only failed to differentiate into macrophages, but instead differentiated into neutrophils. Mechanistically, the cognate CSF1R cytokine macrophage-colony stimulating factor (M-CSF) stimulates macropinocytosis by both mouse and human myeloid progenitors and precursor cells. Macropinocytosis, in turn, induces chloride flux and WNK1 phosphorylation. Importantly, blocking macropinocytosis, perturbing chloride flux during macropinocytosis, and inhibiting WNK1 chloride-sensing activity each skewed myeloid progenitor differentiation from macrophages into neutrophils. Thus, we have elucidated a role for WNK1 during macropinocytosis and discovered a novel function of macropinocytosis in myeloid progenitors and precursor cells to ensure macrophage lineage fidelity.

Highlights

Myeloid-specific WNK1 loss causes failed macrophage development and premature deathM-CSF-stimulated myeloid progenitors and precursors become neutrophils instead of macrophagesM-CSF induces macropinocytosis by myeloid progenitors, which depends on WNK1Macropinocytosis enforces macrophage lineage commitment.

Protein kinase D3 conditional knockout impairs osteoclast formation and increases trabecular bone volume in male mice

Studies using kinase inhibitors have shown that the protein kinase D (PRKD) family of serine/threonine kinases are required for formation and function of osteoclasts in culture. However, the involvement of individual protein kinase D genes and their in vivo significance to skeletal dynamics remains unclear. In the current study we present data indicating that protein kinase D3 is the primary form of PRKD expressed in osteoclasts. We hypothesized that loss of PRKD3 would impair osteoclast formation, thereby decreasing bone resorption and increasing bone mass. Conditional knockout (cKO) of Prkd3 using a murine Cre/Lox system driven by cFms-Cre revealed that its loss in osteoclast-lineage cells reduced osteoclast differentiation and resorptive function in culture. Examination of the Prkd3 cKO mice showed that bone parameters were unaffected in the femur at 4 weeks of age, but consistent with our hypothesis, Prkd3 conditional knockout resulted in 18 % increased trabecular bone mass in male mice at 12 weeks and a similar increase at 6 months. These effects were not observed in female mice. As a further test of our hypothesis, we asked if Prkd3 cKO could protect against bone loss in a ligature-induced periodontal disease model but did not see any reduction in bone destruction in this system. Together, our data indicate that PRKD3 promotes osteoclastogenesis both in vitro and in vivo.

A timeline of tumour-associated macrophage biology

Tumour progression is modulated by the local microenvironment. This environment is populated by many immune cells, of which macrophages are among the most abundant. Clinical correlative data and a plethora of preclinical studies in mouse models of cancers have shown that tumour-associated macrophages (TAMs) play a cancer-promoting role. Within the primary tumour, TAMs promote tumour cell invasion and intravasation and tumour stem cell viability and induce angiogenesis. At the metastatic site, metastasis-associated macrophages promote extravasation, tumour cell survival and persistent growth, as well as maintain tumour cell dormancy in some contexts. In both the primary and metastatic sites, TAMs are suppressive to the activities of cytotoxic T and natural killer cells that have the potential to eradicate tumours. Such activities suggest that TAMs will be a major target for therapeutic intervention. In this Perspective article, we chronologically explore the evolution of our understanding of TAM biology put into the context of major enabling advances in macrophage biology.

Litchi procyanidins inhibit colon cancer proliferation and metastasis by triggering gut-lung axis immunotherapy

Litchi chinensis seed, as a valuable by-product of the subtropical fruit litchi (Litchi chinensis Sonn.), has been confirmed to be rich in procyanidins (LPC). The anticarcinogenic properties of procyanidins has been primarily attributed to their antioxidant and anti-inflammatory activities. However, there is a comparative paucity of information on if and how LPC inhibits colon cancer. Here, LPC significantly inhibited CT26 colon cancer cells proliferation and metastasis in vivo and in vitro. In CT26 lung metastatic mice, the anti-metastatic effect of LPC relied on its regulation of gut microbiota such as increase of Lachnospiraceae UCG-006, Ruminococcus, and their metabolites such as acetic acid, propionic acid and butyric acid. In addition, LPC significantly inhibited CT26 colon cancer cells metastasis through increasing CD8⁺ cytotoxic T lymphocytes infiltration and decreasing the number of macrophages. Antibiotics treatment demonstrated that the therapeutic effect of LPC depended on the gut microbiota, which regulated T cells immune response. Taken together, LPC had strong inhibitory effects on colon cancer pulmonary metastasis by triggering gut-lung axis to influence the T cells immune response. Our research provides a novel finding for the utilization of procyanidins in the future, that is, supplementing more fruits and vegetables rich in procyanidins is beneficial to the treatment of colon cancer, or it can be used as an adjuvant drug in clinical anti-tumor immunotherapy.

Triptolide attenuates LPS-induced activation of RAW 264.7 macrophages by inducing M1-to-M2 repolarization via the mTOR/STAT3 signaling

CONTEXT

Inflammatory bowel disease (IBD) is a chronic inflammatory disease of gastrointestinal tract, which can develop into colorectal cancer. Triptolide (TP) is a predominant bioactive ingredient of Tripterygium wilfordii Hook.F., and has been proven to have the therapeutic potential for various human diseases.

OBJECTIVE

In our study, we examined the function of TP in the progression of IBD.

METHODS

3-(4,5)dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide assay was used to evaluate the viability of RAW264.7 cells. Quantitative reverse transcription polymerase chain reaction assay was performed to detect the relative gene expression. Western blot was used to detect the relative protein expression. Enzyme-linked immunosorbent assay was utilized to examine the levels of prostaglandin E2 (PGE2), tumor necrosis factor (TNF)-α, interleukin (IL)-10, and IL-6.

RESULT

Our research demonstrated that TP restrained lipopolysaccharide (LPS)-caused activation of RAW264.7 cells, as evidenced by the reduction of PGE2, TNF-α, and IL-6, and increase of IL-10. TP treatment also restrained M1-type macrophage polarization and facilitated M2-type macrophage polarization of RAW 264.7 cells in the presence of LPS. Moreover, TP mitigated LPS-induced activation of the mammalian target of rapamycin (mTOR)/signal transducer and activator of transcription 3 (STAT3) signaling in RAW264.7 cells. Further, activation of the mTOR/STAT3 signaling by MHY1485 attenuated the effect of TP in regulation of macrophage polarization in RAW264.7 cells in the presence of LPS.

CONCLUSION

Overall, our results indicated that TP attenuated LPS-induced activation of RAW 264.7 macrophages by inducing M1-to-M2 repolarization via repression of the mTOR/STAT3 signaling. Therefore, TP might be an effective agent for IBD treatment.

Osteopontin promotes infarct repair

Understanding how macrophages promote myocardial repair can help create new therapies for infarct repair. We aimed to determine what mechanisms underlie the reparative properties of macrophages. Cytokine arrays revealed that neonatal cardiac macrophages from the injured neonatal heart secreted high amounts of osteopontin (OPN). In vitro, recombinant OPN stimulated cardiac cell outgrowth, cardiomyocyte (CM) cell-cycle re-entry, and CM migration. In addition, OPN induced nuclear translocation of the cytoplasmatic yes-associated protein 1 (YAP1) and upregulated transcriptional factors and cell-cycle genes. Significantly, by blocking the OPN receptor CD44, we eliminated the effects of OPN on CMs. OPN also activated the proliferation and migration of non-CM cells: endothelial cells and cardiac mesenchymal stromal cells in vitro. Notably, the significant role of OPN in myocardial healing was demonstrated by impaired healing in OPN-deficient neonatal hearts. Finally, in the adult mice, a single injection of OPN into the border of the ischemic zone induced CM cell-cycle re-entry, improved scar formation, local and global cardiac function, and LV remodelling 30 days after MI. In summary, we have shown, for the first time, that recombinant OPN activates cell-cycle re-entry in CMs. In addition, recombinant OPN stimulates multiple cardiac cells and improves scar formation, LV remodelling, and regional and global function after MI. Therefore, we propose OPN as a new cell-free therapy to optimize infarct repair.

Interleukin 4 Controls the Pro-Tumoral Role of Macrophages in Mammary Cancer Pulmonary Metastasis in Mice

Metastasis is the systemic manifestation of cancer and the main cause of death from breast cancer. In mouse models of lung metastases, recruitment of classical monocytes from blood to the lung and their differentiation to metastasis-associated macrophages (MAMs) facilitate cancer cell extravasation, survival and growth. Ablation of MAMs or their monocytic progenitors inhibits metastasis. We hypothesized that factors controlling macrophage polarization modulate tumor cell extravasation in the lung. We evaluated whether signaling by Th1 or Th2 cytokines in macrophages affected transendothelial migration of tumor cells in vitro. Interferon gamma and LPS inhibited macrophage-dependent tumor cell extravasation while the Th2 cytokine interleukin-4 (IL4) enhanced this process. We demonstrated that IL4 receptor (IL4rα)-null mice developed fewer and smaller lung metastasis in E0771-LG mammary cancer models of this disease. Adoptive transfer of wild-type monocytes to IL4rα-deficient mice partially rescued this phenotype. IL4 signaling in macrophages controlled the expression of the chemokine receptor CXCR2, necessary for IL4-mediated tumor cell extravasation in vitro. Furthermore, IL4 signaling in macrophages regulated the transcript abundance of several other genes already causally associated with mammary cancer lung metastasis including Ccl2, Csf1, Ccr1, Hgf and Flt1. The central role of IL4 signaling in MAMs was confirmed by high-resolution intravital imaging of the lung in mice at the time of metastatic seeding, which showed reduced physical interaction between tumor cells and IL4rα-deficient macrophages. This interaction with wild-type MAMs enhanced tumor cell survival and seeding, which was lost in the IL4rα mice. These data indicate that IL4 signaling in monocytes and macrophages is key during seeding and growth of breast metastasis in the lung, as it regulates pro-tumoral paracrine signaling between cancer cells and macrophages.

CD44 expressed by myeloid cells promotes glioma invasion

Glioblastoma multiforme (GBM) is one of the most common and malignant brain tumors in adulthood with a median survival of only 15 months. This poor prognosis is related to GBM’s ability to extensively infiltrate the surrounding brain parenchyma resulting in diffuse spread of neoplastic cells in the brain, responsible for high rate of recurrence. CD44 (Cluster of Differentiation 44) is a transmembrane protein, overexpressed in multiple cancer types, including gliomas, and implicated in cell motility, proliferation and angiogenesis. Multiple studies have investigated the role of CD44 in GBM cells and have highlighted a link between tumor malignancy and CD44 expression. However up to date, little is known of the role of CD44 on cells from the tumor microenvironment (TME). Here, we have investigated a potential role of CD44 in the TME in regards to GBM invasiveness. Using an ex-vivo organotypic brain slice invasion assay, we show that absence of CD44 from the TME impairs the ability of glioma cells to invade the surrounding brain parenchyma. By deleting CD44 in the astrocytic, endothelial and myeloid compartments, we show that it is specifically CD44 expression in myeloid cells that is responsible for the observed phenotype. Combining in vivo studies in cell-specific knock-out mice and in vitro analyses on primary microglia we demonstrate that myeloid CD44 is implicated in Toll Like Receptor 2 signaling and is a major regulator of Matrix metalloproteinase 9 expression.

A Human CD68 Promoter-Driven Inducible Cre-Recombinase Mouse Line Allows Specific Targeting of Tissue Resident Macrophages

Current genetic tools designed to target macrophages in vivo often target cells from all myeloid lineages. Therefore, we sought to generate a novel transgenic mouse which has a tamoxifen inducible Cre-recombinase under the control of the human CD68 promoter (hCD68-CreERT2). To test the efficiency and specificity of the of Cre-recombinase activity we crossed the hCD68-CreERT2 mice with a loxP-flanked STOP cassette red fluorescent protein variant (tdTomato) mouse. We established that orally dosing mice with 2 mg of tamoxifen for 5 consecutive days followed by a 5-day induction period resulted in robust expression of tdTomato in CD11b+ F4/80+ tissue resident macrophages. Using this induction protocol, we demonstrated tdTomato expression within peritoneal, liver and spleen macrophages and blood Ly6Clow monocytes. Importantly there was limited or no inducible tdTomato expression within other myeloid cells (neutrophils, monocytes, dendritic cells and eosinophils), T cells (CD4+ and CD8+) and B cells (CD19+). We also demonstrated that the level of tdTomato expression can be used as a marker to identify different populations of peritoneal and liver macrophages. We next assessed the longevity of tdTomato expression in peritoneal macrophages, liver and splenic macrophages and demonstrated high levels of tdTomato expression as long as 6 weeks after the last tamoxifen dose. Importantly, hCD68-CreERT2 expression is more restricted than that of LysM-Cre which has significant expression in major myeloid cell types (monocytes and neutrophils). To demonstrate the utility of this novel macrophage-specific Cre driver line we demonstrated tdTomato expression in recruited CD11b+CD64+F4/80+ monocyte-derived macrophages within the atherosclerotic lesions of AAV8-mPCSK9 treated mice, with limited expression in recruited neutrophils. In developing this new hCD68-CreERT2 mouse we have a tool that allows us to target tissue resident macrophages, with the advantage of not targeting other myeloid cells namely neutrophils and inflammatory monocytes.

Cellular Carcinogenesis: Role of Polarized Macrophages in Cancer Initiation

Simple Summary

Inflammation is a hallmark of many cancers. Macrophages are key participants in innate immunity and important drivers of inflammation. When chronically polarized beyond normal homeostatic responses to infection, injury, or aging, macrophages can express several pro-carcinogenic phenotypes. In this review, evidence supporting polarized macrophages as endogenous sources of carcinogenesis is discussed. In addition, the depletion or modulation of macrophages by small molecule inhibitors and probiotics are reviewed as emerging strategies in cancer prevention.

Abstract

Inflammation is an essential hallmark of cancer. Macrophages are key innate immune effector cells in chronic inflammation, parainflammation, and inflammaging. Parainflammation is a form of subclinical inflammation associated with a persistent DNA damage response. Inflammaging represents low-grade inflammation due to the dysregulation of innate and adaptive immune responses that occur with aging. Whether induced by infection, injury, or aging, immune dysregulation and chronic macrophage polarization contributes to cancer initiation through the production of proinflammatory chemokines/cytokines and genotoxins and by modulating immune surveillance. This review presents pre-clinical and clinical evidence for polarized macrophages as endogenous cellular carcinogens in the context of chronic inflammation, parainflammation, and inflammaging. Emerging strategies for cancer prevention, including small molecule inhibitors and probiotic approaches, that target macrophage function and phenotype are also discussed.

Histone deacetylase 5 is a phosphorylation substrate of protein kinase D in osteoclasts

Protein kinase D (PRKD) family kinases are required for formation and function of osteoclasts. However, the substrates of PRKD in osteoclasts are unknown. To identify PRKD-dependent protein phosphorylation in osteoclasts, we performed a quantitative LC-MS/MS phosphoproteomics screen for proteins showing differential phosphorylation in osteoclasts after treatment with the PRKD inhibitor CRT0066101. We identified 757 phosphopeptides showing significant changes following PRKD inhibition. Among the changes, we found a group of 13 proteins showing decreased phosphorylation at PRKD consensus phosphorylation motifs. This group includes histone deacetylase 5 (HDAC5), which is a previously validated PRKD target. Considering this known interaction, work suggesting HDACs may be important regulators of osteoclasts, and studies suggesting potential functional redundancy between HDACs, we further investigated the relationship between PRKD and class IIa HDACs in osteoclasts. We confirmed that CRT0066101 inhibits phosphorylation of endogenous HDAC5 and to a lesser extent HDAC4, whereas HDAC7 phosphorylation was not affected. Osteoclast cultures from Hdac5 global knockout mice displayed impaired differentiation and reduced ability to resorb bone, while conditional knockout of Hdac4 in osteoclasts showed no phenotype in vitro or in vivo. The inhibitory effect of CRT0066101 was reduced in Hdac5 KO osteoclasts. Together these data indicate that the PRKD/HDAC5 axis contributes to osteoclast formation in vitro and suggest that this pathway may contribute to regulation of skeletal dynamics in vivo.

Macrophage Fate Mapping

Tissue-resident macrophages are present in all tissues where they perform homeostatic and immune surveillance functions. In many tissues, resident macrophages develop from embryonic progenitors, which mature into a self-maintaining population through local proliferation. However, tissue-resident macrophages can be supported by recruited monocyte-derived macrophages during scenarios such as tissue growth, infection, or sterile inflammation. Circulating blood monocytes arise from hematopoietic stem cell progenitors and possess unique gene profiles that support additional functions within the tissue. Determining cell origins (ontogeny) and cellular turnover within tissues has become important to understanding monocyte and macrophage contributions to tissue homeostasis and disease. Fate mapping, or lineage tracing, is a promising approach to tracking cells based on unique gene expression driving reporter systems, often downstream of a Cre-recombinase-mediated excision event, to express a fluorescent protein. This approach is typically deployed temporally with developmental stage, disease onset, or in association with key stages of inflammation resolution. Importantly, myeloid fate mapping can be combined with many emerging technologies, including single-cell RNA-sequencing and spatial imaging. The application of myeloid cell fate mapping approaches has allowed for impactful discoveries regarding myeloid ontogeny, tissue residency, and monocyte fate within disease models. This protocol outline will discuss a variety of myeloid fate mapping approaches, including constitutive and inducible labeling approaches in adult and embryo tissues. This article outlines basic approaches and models used in mice for fate mapping macrophages. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Adult Fate Mapping Basic Protocol 2: Embryonic Fate Mapping.

VCAM1 confers innate immune tolerance on haematopoietic and leukaemic stem cells

Haematopoietic stem cells (HSCs) home to the bone marrow via, in part, interactions with vascular cell adhesion molecule-1 (VCAM1)^1-3. Once in the bone marrow, HSCs are vetted by perivascular phagocytes to ensure their self-integrity. Here we show that VCAM1 is also expressed on healthy HSCs and upregulated on leukaemic stem cells (LSCs), where it serves as a quality-control checkpoint for entry into bone marrow by providing 'don't-eat-me' stamping in the context of major histocompatibility complex class-I (MHC-I) presentation. Although haplotype-mismatched HSCs can engraft, Vcam1 deletion, in the setting of haplotype mismatch, leads to impaired haematopoietic recovery due to HSC clearance by mononuclear phagocytes. Mechanistically, VCAM1 'don't-eat-me' activity is regulated by β2-microglobulin MHC presentation on HSCs and paired Ig-like receptor-B (PIR-B) on phagocytes. VCAM1 is also used by cancer cells to escape immune detection as its expression is upregulated in multiple cancers, including acute myeloid leukaemia (AML), where high expression associates with poor prognosis. In AML, VCAM1 promotes disease progression, whereas VCAM1 inhibition or deletion reduces leukaemia burden and extends survival. These results suggest that VCAM1 engagement regulates a critical immune-checkpoint gate in the bone marrow, and offers an alternative strategy to eliminate cancer cells via modulation of the innate immune tolerance.

Dendritic cell functions in vivo: a user's guide to current and next generation mutant mouse models

Dendritic cells (DCs) do not just excel in antigen presentation. They orchestrate information transfer from innate to adaptive immunity, by sensing and integrating a variety of danger signals, and translating them to naïve T cells, to mount specifically tailored immune responses. This is accomplished by distinct DC types specialized in different functions and because each DC is functionally plastic, assuming different activation states depending on the input signals received. Mouse models hold the key to untangle this complexity and determine which DC types and activation states contribute to which functions. Here, we aim to provide comprehensive information for selecting the most appropriate mutant mouse strains to address specific research questions on DCs, considering three in vivo experimental approaches: (i) interrogating the roles of DC types through their depletion; (ii) determining the underlying mechanisms by specific genetic manipulations; (iii) deciphering the spatiotemporal dynamics of DC responses. We summarize the advantages, caveats, suggested use and perspectives for a variety of mutant mouse strains, discussing in more detail the most widely used or accurate models. Finally, we discuss innovative strategies to improve targeting specificity, for the next generation mutant mouse models, and briefly address how humanized mouse models can accelerate translation into the clinic. This article is protected by copyright. All rights reserved.

Current Perspectives on the Immunosuppressive Niche and Role of Fibrosis in Hepatocellular Carcinoma and the Development of Antitumor Immunity

Immune checkpoint inhibitors have become the mainstay of treatment for hepatocellular carcinoma (HCC). However, they are ineffective in some cases. Previous studies have reported that genetic alterations in oncogenic pathways such as Wnt/β-catenin are the important triggers in HCC for primary refractoriness. T-cell exhaustion has been reported in various tumors and is likely to play a prominent role in the emergence of HCC due to chronic inflammation and cirrhosis-associated immune dysfunction. Immunosuppressive cells including regulatory T-cells and tumor-associated macrophages infiltrating the tumor are associated with hyperprogressive disease in the early stages of immune checkpoint inhibitor treatment. In addition, stellate cells and tumor-associated fibroblasts create an abundant desmoplastic environment by producing extracellular matrix. This strongly contributes to epithelial to mesenchymal transition via signaling activities including transforming growth factor beta, Wnt/β-catenin, and Hippo pathway. The abundant desmoplastic environment has been demonstrated in pancreatic ductal adenocarcinoma and cholangiocarcinoma to suppress cytotoxic T-cell infiltration, PD-L1 expression, and neoantigen expression, resulting in a highly immunosuppressive niche. It is possible that a similar immunosuppressive environment is created in HCC with advanced fibrosis in the background liver. Although sufficient understanding is required for the establishment of immune therapies of HCC, further investigations are still required in this field.

Anatomically distinct fibroblast subsets determine skin autoimmune patterns

The skin serves as a physical barrier and an immunological interface that protects the body from the external environment^1-3. Aberrant activation of immune cells can induce common skin autoimmune diseases such as vitiligo, which are often characterized by bilateral symmetric lesions in certain anatomic regions of the body^4-6. Understanding what orchestrates the activities of cutaneous immune cells at an organ level is necessary for the treatment of autoimmune diseases. Here we identify subsets of dermal fibroblasts that are responsible for driving patterned autoimmune activity, by using a robust mouse model of vitiligo that is based on the activation of endogenous auto-reactive CD8⁺ T cells that target epidermal melanocytes. Using a combination of single-cell analysis of skin samples from patients with vitiligo, cell-type-specific genetic knockouts and engraftment experiments, we find that among multiple interferon-γ (IFNγ)-responsive cell types in vitiligo-affected skin, dermal fibroblasts are uniquely required to recruit and activate CD8⁺ cytotoxic T cells through secreted chemokines. Anatomically distinct human dermal fibroblasts exhibit intrinsic differences in the expression of chemokines in response to IFNγ. In mouse models of vitiligo, regional IFNγ-resistant fibroblasts determine the autoimmune pattern of depigmentation in the skin. Our study identifies anatomically distinct fibroblasts with permissive or repressive IFNγ responses as the key determinant of body-level patterns of lesions in vitiligo, and highlights mesenchymal subpopulations as therapeutic targets for treating autoimmune diseases.

Exploring the Early Phase of Crohn's Disease

The development of Crohn's disease (CD) is characterized by a breakdown of homeostatic immune-bacterial communication, which takes place at the intestinal mucosa when environmental triggers impact genetically predisposed individuals. Converging lines of evidence support the hypothesis that this pathogenetic model develops through sequential, although inter-related, steps that indicate failure of mucosal defense mechanisms at various stages. In this context, immunologic phenomena that mediate the initial appearance of inflammatory lesions across the intestinal tissue may differ substantially from those that mediate and perpetuate chronic inflammatory responses. A compromise in the integrity of the epithelial barrier is among the earliest events and leads to accelerated influx of intraluminal antigens and intact microorganisms within the immunologically rich lamina propria. Inadequate clearance of invading microorganisms also may occur as a result of defects in innate immunity, preventing the timely and complete resolution of acute inflammatory responses. The final step is the development of persistent adaptive responses, which also differ between early and late Crohn's disease. Current progress in our ability to delineate single-cell transcriptomics and proteomics has allowed the discovery of cellular and molecular mechanisms that participate in each sequential step of CD development. This not only will advance our understanding of CD pathogenesis, but also facilitate the design of targeted therapeutic approaches.

An Insight into GPCR and G-Proteins as Cancer Drivers

G-protein-coupled receptors (GPCRs) are the largest family of cell surface signaling receptors known to play a crucial role in various physiological functions, including tumor growth and metastasis. Various molecules such as hormones, lipids, peptides, and neurotransmitters activate GPCRs that enable the coupling of these receptors to highly specialized transducer proteins, called G-proteins, and initiate multiple signaling pathways. Integration of these intricate networks of signaling cascades leads to numerous biochemical responses involved in diverse pathophysiological activities, including cancer development. While several studies indicate the role of GPCRs in controlling various aspects of cancer progression such as tumor growth, invasion, migration, survival, and metastasis through its aberrant overexpression, mutations, or increased release of agonists, the explicit mechanisms of the involvement of GPCRs in cancer progression is still puzzling. This review provides an insight into the various responses mediated by GPCRs in the development of cancers, the molecular mechanisms involved and the novel pharmacological approaches currently preferred for the treatment of cancer. Thus, these findings extend the knowledge of GPCRs in cancer cells and help in the identification of therapeutics for cancer patients.

Divergent regulation of inflammatory cytokines by mTORC1 in THP-1-derived macrophages and intestinal epithelial Caco-2 cells

AIMS

The sustained activation of intestinal mechanistic target of rapamycin complex 1 (mTORC1) brought about by repeated mucosal insult or injury has been linked to escalation of gut inflammatory response, which may progress to damage the epithelium if not controlled. This study investigated the role of mTORC1 in the response of macrophage and enterocyte to inflammatory stimuli.

MATERIALS AND METHODS

We genetically manipulated human THP-1 monocytes and epithelial intestinal Caco-2 cells to generate stable cell lines with baseline, low or high mTORC1 kinase activity. The effects of THP-1 macrophage secretions onto Caco-2 cells were investigated by means of conditioned media transfer experiments.

KEY FINDINGS

The priming of mTORC1 for activation promoted lipopolysaccharide (LPS)-mediated THP-1 macrophage immune response as evidenced by the stimulation of inflammatory mediators (TNFα, IL-6, IL-8, IL-1β and IL-10). The treatment of THP-1 macrophages with LPS more than the manipulated level of mTORC1 activity of macrophages determined whether cytokine gene expression was induced in Caco-2 cells. LPS carry over was not responsible for the stimulation of Caco-2 cells' cytokine response. Knocking down Raptor in Caco-2 cells or treating Caco-2 cells with rapamycin enhanced Caco-2 TNFα gene expression revealing the anti-inflammatory role of a functional mTORC1 in intestinal epithelial cells exposed to macrophage-derived pro-inflammatory stimuli.

SIGNIFICANCE

Taken together, mTORC1 differentially impacts the immune responses of THP-1-derived macrophages and Caco-2 epithelial cells when placed in a pro-inflammatory microenvironment.

Beyond Immunity: Underappreciated Functions of Intestinal Macrophages

The gastrointestinal tract hosts the largest compartment of macrophages in the body, where they serve as mediators of host defense and immunity. Seeded in the complex tissue-environment of the gut, an array of both hematopoietic and non-hematopoietic cells forms their immediate neighborhood. Emerging data demonstrate that the functional diversity of intestinal macrophages reaches beyond classical immunity and includes underappreciated non-immune functions. In this review, we discuss recent advances in research on intestinal macrophage heterogeneity, with a particular focus on how non-immune functions of macrophages impact tissue homeostasis and function. We delve into the strategic localization of distinct gut macrophage populations, describe the potential factors that regulate their identity and functional heterogeneity within these locations, and provide open questions that we hope will inspire research dedicated to elucidating a holistic view on macrophage-tissue cell interactions in the body's largest mucosal organ.

Macrophage-Related SPP1 as a Potential Biomarker for Early Lymph Node Metastasis in Lung Adenocarcinoma

Lymph node metastasis is a major factor that affects prognosis in patients with lung adenocarcinoma (LUAD). In some cases, lymph node metastasis has already occurred when the primary tumors are still small (i.e., early T stages), however, relevant studies on early lymph node metastasis are limited, and effective biomarkers remain lacking. This study aimed to explore new molecular biomarker for early lymph node metastasis in LUAD using transcriptome sequencing and experimental validation. Here, we performed transcriptome sequencing on tissues from 16 matched patients with Stage-T1 LUAD (eight cases of lymph node metastasis and eight cases of non-metastasis), and verified the transcriptome profiles in TCGA, GSE68465, and GSE43580 cohorts. With the bioinformatics analysis, we identified a higher abundance of M0 macrophages in the metastatic group using the CIBERSORT algorithm and immunohistochemistry (IHC) analysis and the enrichment of the epithelial–mesenchymal transition (EMT) pathway was identified in patients with higher M0 infiltration levels. Subsequently, the EMT hallmark gene SPP1, encoding secreted phosphoprotein 1 (SPP1), was identified to be significantly correlated with macrophage infiltration and M2 polarization, and was determined to be a key risk indicator for early lymph node metastasis. Notably, SPP1 in the blood, as detected by enzyme-linked immunosorbent assay (ELISA) showed a superior predictive capability for early lymph node metastasis [area under the curve (AUC) = 0.74]. Furthermore, a long non-coding RNA (lncRNA, AC037441), negatively correlated with SPP1 and macrophage infiltration, had also been identified and validated to be involved in the regulation of early lymph node metastasis. In conclusion, we revealed the potential role of macrophages in lymph node metastasis and identified the macrophage-related gene SPP1 as a potential biomarker for early lymph node metastasis in LUAD.

Modulating tumor-associated macrophages to enhance the efficacy of immune checkpoint inhibitors: A TAM-pting approach

Tumor-associated macrophages (TAM) plasticity and diversity are both essential hallmarks of the monocyte-macrophage lineage and the tumor-derived inflammation. TAM exemplify the perfect adaptable cell with dynamic phenotypic modifications that reflect changes in their functional polarization status. Under several tumor microenvironment (TME)-related cues, TAM shift their polarization, hence promoting or halting cancer progression. Immune checkpoint inhibitors (ICI) displayed unprecedented clinical responses in various refractory cancers; but only approximately a third of patients experienced durable responses. It is, therefore, crucial to enhance the response rate of immunotherapy. Several mechanisms of resistance to ICI have been elucidated including TAM role with its essential immunosuppressive functions that reduce both anti-tumor immunity and the subsequent ICI efficacy. In the past few years, thorough research has led to a better understanding of TAM biology and innovative approaches can now be adapted through targeting macrophages' recruitment axis as well as TAM activation and polarization status within the TME. Some of these therapeutic strategies are currently being evaluated in several clinical trials in association with ICI agents. This combination between TAM modulation and ICI allows targeting TAM intrinsic immunosuppressive functions and tumor-promoting factors as well as overcoming ICI resistance. Hence, such strategies, with a better understanding of the mechanisms driving TAM modulation, may have the potential to optimize ICI efficacy.

Sites of Cre-recombinase activity in mouse lines targeting skeletal cells

The Cre/Lox system is a powerful tool in the biologist's toolbox, allowing loss-of-function and gain-of-function studies, as well as lineage tracing, through gene recombination in a tissue-specific and inducible manner. Evidence indicates, however, that Cre transgenic lines have a far more nuanced and broader pattern of Cre activity than initially thought, exhibiting "off-target" activity in tissues/cells other than the ones they were originally designed to target. With the goal of facilitating the comparison and selection of optimal Cre lines to be used for the study of gene function, we have summarized in a single manuscript the major sites and timing of Cre activity of the main Cre lines available to target bone mesenchymal stem cells, chondrocytes, osteoblasts, osteocytes, tenocytes, and osteoclasts, along with their reported sites of "off-target" Cre activity. We also discuss characteristics, advantages, and limitations of these Cre lines for users to avoid common risks related to overinterpretation or misinterpretation based on the assumption of strict cell-type specificity or unaccounted effect of the Cre transgene or Cre inducers. © 2021 American Society for Bone and Mineral Research (ASBMR).

Evolving Models and Tools for Microglial Studies in the Central Nervous System

Microglia play multiple roles in such processes as brain development, homeostasis, and pathology. Due to their diverse mechanisms of functions, the complex sub-classifications, and the large differences between different species, especially compared with humans, very different or even opposite conclusions can be drawn from studies with different research models. The choice of appropriate research models and the associated tools are thus key ingredients of studies on microglia. Mice are the most commonly used animal models. In this review, we summarize in vitro and in vivo models of mouse and human-derived microglial research models, including microglial cell lines, primary microglia, induced microglia-like cells, transgenic mice, human-mouse chimeric models, and microglial replacement models. We also summarize recent developments in novel single-cell and in vivo imaging technologies. We hope our review can serve as an efficient reference for the future study of microglia.

Loss of interleukin-10 receptor disrupts intestinal epithelial cell proliferation and skews differentiation towards the goblet cell fate

Intestinal epithelial cells (IEC) are crucial for maintaining proper digestion and overall homeostasis of the gut mucosa. IEC proliferation and differentiation are tightly regulated by well described pathways, however, relatively little is known about how cytokines shape these processes. Given that the anti-inflammatory cytokine interleukin (IL)-10 promotes intestinal barrier function, and insufficient IL-10 signaling increases susceptibility to intestinal diseases like inflammatory bowel disease, we hypothesized that IL-10 signaling modulates processes underlying IEC proliferation and differentiation. This was tested using in vivo and in vitro IEC-specific IL-10 receptor 1 (IL-10R1) depletion under homeostatic conditions. Our findings revealed that loss of IL-10R1 drove lineage commitment toward a dominant goblet cell phenotype while decreasing absorptive cell-related features. Diminished IL-10 signaling also significantly elevated IEC proliferation with relatively minor changes to apoptosis. Characterization of signaling pathways upstream of proliferation demonstrated a significant reduction in the Wnt inhibitor, DKK1, increased nuclear localization of β-catenin, and increased transcripts of the proliferation marker, OLFM4, with IL-10R1 depletion. Phosphorylated STAT3 was nearly completely absent in IL-10R1 knockdown cells and may provide a mechanistic link between our observations and the regulation of these cellular processes. Our results demonstrate a novel role for IL-10 signaling in intestinal mucosal homeostasis by regulating proper balance of proliferation and IEC lineage fate.

Stromal fibroblasts shape the myeloid phenotype in normal colon and colorectal cancer and induce CD163 and CCL2 expression in macrophages

Colorectal cancer (CRC) accounts for about 10% of cancer deaths worldwide. Colon carcinogenesis is critically influenced by the tumor microenvironment. Cancer associated fibroblasts (CAFs) and tumor associated macrophages (TAMs) represent the major components of the tumor microenvironment. TAMs promote tumor progression, angiogenesis and tissue remodeling. However, the impact of the molecular crosstalk of tumor cells (TCs) with CAFs and macrophages on monocyte recruitment and their phenotypic conversion is not known in detail so far. In a 3D human organotypic CRC model, we show that CAFs and normal colonic fibroblasts are critically involved in monocyte recruitment and for the establishment of a macrophage phenotype, characterized by high CD163 expression. This is in line with the steady recruitment and differentiation of monocytes to immunosuppressive macrophages in the normal colon. Cytokine profiling revealed that CAFs produce M-CSF, and IL6, IL8, HGF and CCL2 secretion was specifically induced by CAFs in co-cultures with macrophages. Moreover, macrophage/CAF/TCs co-cultures increased TC invasion. We demonstrate that CAFs and macrophages are the major producers of CCL2 and, upon co-culture, increase their CCL2 production twofold and 40-fold, respectively. CAFs and macrophages expressing high CCL2 were also found in vivo in CRC, strongly supporting our findings. CCL2, CCR2, CSF1R and CD163 expression in macrophages was dependent on active MCSFR signaling as shown by M-CSFR inhibition. These results indicate that colon fibroblasts and not TCs are the major cellular component, recruiting and dictating the fate of infiltrated monocytes towards a specific macrophage population, characterized by high CD163 expression and CCL2 production.

TDP43 Exacerbates Atherosclerosis Progression by Promoting Inflammation and Lipid Uptake of Macrophages

Objective

Atherosclerosis (AS), characterized by cholesterol overloaded-macrophages accumulation and plaque formation in blood vessels, is the major cause of cardiovascular disease. Transactive response DNA-binding protein∼43 kDa (TDP43) has recently been identified as an independent driver of neurodegenerative diseases through triggering inflammatory response. This study investigated whether TDP43 is involved in AS development, especially in macrophages-mediated-foam cell formation and inflammatory responses.

Methods

Transactive response DNA-binding protein∼43 kDa expressions in oxidized low-density lipoprotein (oxLDL)-treated macrophages and peripheral blood mononuclear cells (PBMCs) from patients with coronary artery disease (CAD) were detected by real time-polymerase chain reaction (RT-PCR), Western blot, and immunofluorescence. Gene gain or loss of function was used to investigate the effects of TDP43 on macrophages-mediated lipid untake and inflammation with ELISA, protein immunoprecipitation, RT-PCR, Western blot, and immunofluorescence. Macrophage TDP43 specific knockout mice with ApoE^-/- background were fed with western diet for 12 weeks to establish AS model, and used to explore the role of TDP43 on AS progression.

Results

Transactive response DNA-binding protein∼43 kDa expression increases in oxLDL-treated macrophages and PBMCs from patients with CAD. Furthermore, we find that TDP43 promotes activation of NF-κB to increase inflammatory factor expression in macrophages through triggering mitochondrial DNA release to activate cGAS-STING signaling. Moreover, TDP43 strengthens lipid uptake of macrophages through regulating β-catenin and PPAR-γ complex to promote scavenger receptor gene CD36 transcription. Finally, using macrophage TDP43 specific knockout mice with ApoE^-/- background fed with western diet for 12 weeks to establish AS model, we find that specific knockout of TDP43 in macrophages obviously alleviates western diet-induced AS progression in mice.

Conclusions

Transactive response DNA-binding protein∼43 kDa exacerbates atherosclerosis progression by promoting inflammation and lipid uptake of macrophages, suggesting TDP43 as a potential target for developing atherosclerotic drug.

Tumor-Associated Macrophages: A Potential Target for Cancer Therapy

Macrophages, an important class of innate immune cells that maintain body homeostasis and ward off foreign pathogens, exhibit a high degree of plasticity and play a supportive role in different tissues and organs. Thus, dysfunction of macrophages may contribute to advancement of several diseases, including cancer. Macrophages within the tumor microenvironment are known as tumor-associated macrophages (TAMs), which typically promote cancer cell initiation and proliferation, accelerate angiogenesis, and tame anti-tumor immunity to promote tumor progression and metastasis. Massive infiltration of TAMs or enrichment of TAM-related markers usually indicates cancer progression and a poor prognosis, and consequently tumor immunotherapies targeting TAMs have gained significant attention. Here, we review the interaction between TAMs and cancer cells, discuss the origin, differentiation and phenotype of TAMs, and highlight the role of TAMs in pro-cancer functions such as tumor initiation and development, invasive metastasis, and immunosuppression. Finally, we review therapies targeting TAMs, which are very promising therapeutic strategies for malignant tumors.

Megakaryocyte production is sustained by direct differentiation from erythromyeloid progenitors in the yolk sac until midgestation

The extra-embryonic yolk sac contains the first definitive multipotent hematopoietic cells, denominated erythromyeloid progenitors. They originate in situ prior to the emergence of hematopoietic stem cells and give rise to erythroid, monocytes, granulocytes, mast cells and macrophages, the latter in a Myb transcription factor-independent manner. We uncovered here the heterogeneity of yolk sac erythromyeloid progenitors, at the single cell level, and discriminated multipotent from committed progenitors, prior to fetal liver colonization. We identified two temporally distinct megakaryocyte differentiation pathways. The first occurs in the yolk sac, bypasses intermediate bipotent megakaryocyte-erythroid progenitors and, similar to the differentiation of macrophages, is Myb-independent. By contrast, the second originates later, from Myb-dependent bipotent progenitors expressing Csf2rb and colonize the fetal liver, where they give rise to megakaryocytes and to large numbers of erythrocytes. Understanding megakaryocyte development is crucial as they play key functions during vascular development, in particular in separating blood and lymphatic networks.

NFAT5 Amplifies Antipathogen Responses by Enhancing Chromatin Accessibility, H3K27 Demethylation, and Transcription Factor Recruitment

The ability of innate immune cells to respond to pathogen-associated molecular patterns across a wide range of intensities is fundamental to limit the spreading of infections. Studies on transcription responses to pathogen-activated TLRs have often used relatively high TLR ligand concentrations, and less is known about their regulation under mild stimulatory conditions. We had shown that the transcription factor NFAT5 facilitates expression of antipathogen genes under TLR stimulation conditions corresponding to low pathogen loads. In this study, we analyze how NFAT5 optimizes TLR-activated responses in mouse macrophages. We show that NFAT5 was required for effective recruitment of central effectors p65/NF-κB and c-Fos to specific proinflammatory target genes, such as Nos2, Il6, and Tnf in primary macrophages responding to low doses of the TLR4 ligand LPS. By contrast, NFAT5 was not required for p65/NF-κB recruitment in response to high LPS doses. Using the transposase-accessible chromatin with high-throughput sequencing assay, we show that NFAT5 facilitated chromatin accessibility mainly at promoter regions of multiple TLR4-responsive genes. Analysis of various histone marks that regulate gene expression in response to pathogens identified H3K27me3 demethylation as an early NFAT5-dependent mechanism that facilitates p65 recruitment to promoters of various TLR4-induced genes. Altogether, these results advance our understanding about specific mechanisms that optimize antipathogen responses to limit infections.

Loss of Mafb and Maf distorts myeloid cell ratios and disrupts fetal mouse testis vascularization and organogenesis†

Testis differentiation is initiated when Sry in pre-Sertoli cells directs the gonad toward a male-specific fate. Sertoli cells are essential for testis development, but cell types within the interstitial compartment, such as immune and endothelial cells, are also critical for organ formation. Our previous work implicated macrophages in fetal testis morphogenesis, but little is known about genes underlying immune cell development during organogenesis. Here we examine the role of the immune-associated genes Mafb and Maf in mouse fetal gonad development, and we demonstrate that deletion of these genes leads to aberrant hematopoiesis manifested by supernumerary gonadal monocytes. Mafb; Maf double knockout embryos underwent initial gonadal sex determination normally, but exhibited testicular hypervascularization, testis cord formation defects, Leydig cell deficit, and a reduced number of germ cells. In general, Mafb and Maf alone were dispensable for gonad development; however, when both genes were deleted, we observed significant defects in testicular morphogenesis, indicating that Mafb and Maf work redundantly during testis differentiation. These results demonstrate previously unappreciated roles for Mafb and Maf in immune and vascular development and highlight the importance of interstitial cells in gonadal differentiation.

Targeting Mammalian Target of Rapamycin: Prospects for the Treatment of Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD) is a general term for a group of chronic and progressive disorders. Several cellular and biomolecular pathways are implicated in the pathogenesis of IBD, yet the etiology is unclear. Activation of the mammalian target of rapamycin (mTOR) pathway in the intestinal epithelial cells was also shown to induce inflammation. This review focuses on the inhibition of the mTOR signaling pathway and its potential application in treating IBD. We also provide an overview of plant-derived compounds that are beneficial for the IBD management through modulation of the mTOR pathway. Data were extracted from clinical, in vitro and in vivo studies published in English between 1995 and May 2019, which were collected from PubMed, Google Scholar, Scopus and Cochrane library databases. Results of various studies implied that inhibition of the mTOR signaling pathway downregulates the inflammatory processes and cytokines involved in IBD. In this context, a number of natural products might reverse the pathological features of the disease. Furthermore, mTOR provides a novel drug target for IBD. Comprehensive clinical studies are required to confirm the efficacy of mTOR inhibitors in treating IBD.

mTORC1 silencing during intestinal epithelial Caco-2 cell differentiation is mediated by the activation of the AMPK/TSC2 pathway

The mechanistic target of rapamycin complex 1 (mTORC1) signaling is the prototypical pathway regulating protein synthesis and cell proliferation. The level of mTORC1 activity is high in intestinal stem cells located at the base of the crypts and thought to gradually decrease as transit-amplifying cells migrate out of the crypts and differentiate into enterocytes, goblet cells or enteroendocrine cells along the epithelium. The unknown mechanism responsible for the silencing of intestinal epithelium mTORC1 during cell differentiation was investigated in Caco-2 cells, which spontaneously differentiate into enterocytes in standard growth medium. The results show that TSC2, an upstream negative regulator of mTORC1 was central to mTORC1 silencing in differentiated Caco-2 cells. AMPK-mediated activation of TSC2 (Ser1387) and repression of Raptor (Ser792), an essential component of mTORC1, were stimulated in differentiated Caco-2 cells. ERK1/2-mediated repression of TSC2 (Ser664) seen in undifferentiated Caco-2 cells was lifted in differentiated cells. IRS-1-mediated activation of AKT (Thr308) phosphorylation was stimulated in differentiated Caco-2 cells and may be involved in cross-pathway repression of ERK1/2. Additionally, PRAS40 (Thr246) phosphorylation was decreased in differentiated Caco-2 cells compared to undifferentiated cells allowing dephosphorylated PRAS40 to displace Raptor thereby repressing mTORC1 kinase activity.

Monocyte Subsets With High Osteoclastogenic Potential and Their Epigenetic Regulation Orchestrated by IRF8

Osteoclasts (OCs) are bone-resorbing cells formed by the serial fusion of monocytes. In mice and humans, three distinct subsets of monocytes exist; however, it is unclear if all of them exhibit osteoclastogenic potential. Here we show that in wild-type (WT) mice, Ly6C^hi and Ly6C^int monocytes are the primary source of OC formation when compared to Ly6C^- monocytes. Their osteoclastogenic potential is dictated by increased expression of signaling receptors and activation of preestablished transcripts, as well as de novo gain in enhancer activity and promoter changes. In the absence of interferon regulatory factor 8 (IRF8), a transcription factor important for myelopoiesis and osteoclastogenesis, all three monocyte subsets are programmed to display higher osteoclastogenic potential. Enhanced NFATc1 nuclear translocation and amplified transcriptomic and epigenetic changes initiated at early developmental stages direct the increased osteoclastogenesis in Irf8-deficient mice. Collectively, our study provides novel insights into the transcription factors and active cis-regulatory elements that regulate OC differentiation. © 2020 American Society for Bone and Mineral Research (ASBMR).

Diverse origins and activation of fibroblasts in cardiac fibrosis

Cardiac fibroblasts (cFBs) have emerged as a heterogenous cell population. Fibroblasts are considered the main cell source for synthesis of the extracellular matrix (ECM) and as such a dysregulation in cFB function, activity, or viability can lead to disrupted ECM structure or fibrosis. Fibrosis can be initiated in response to different injuries and stimuli, and can be reparative (beneficial) or reactive (damaging). FBs need to be activated to myofibroblasts (MyoFBs) which have augmented capacity in synthesizing ECM proteins, causing fibrosis. In addition to the resident FBs in the myocardium, a number of other cells (pericytes, fibrocytes, mesenchymal, and hematopoietic cells) can transform into MyoFBs, further driving the fibrotic response. Multiple molecules including hormones, cytokines, and growth factors stimulate this process leading to generation of activated MyoFBs. Contribution of different cell types to cFBs and MyoFBs can result in an exponential increase in the number of MyoFBs and an accelerated pro-fibrotic response. Given the diversity of the cell sources, and the array of interconnected signalling pathways that lead to formation of MyoFBs and subsequently fibrosis, identifying a single target to limit the fibrotic response in the myocardium has been challenging. This review article will delineate the importance and relevance of fibroblast heterogeneity in mediating fibrosis in different models of heart failure and will highlight important signalling pathways implicated in myofibroblast activation.

Tumor-Associated Neutrophils and Macrophages-Heterogenous but Not Chaotic

Tumor-associated macrophages (TAMs) and tumor-associated neutrophils (TANs) have been extensively studied. Their pleotropic roles were observed in multiple steps of tumor progression and metastasis, and sometimes appeared to be inconsistent across different studies. In this review, we collectively discussed many lines of evidence supporting the mutual influence between cancer cells and TAMs/TANs. We focused on how direct interactions among these cells dictate co-evolution involving not only clonal competition of cancer cells, but also landscape shift of the entire tumor microenvironment (TME). This co-evolution may take distinct paths and contribute to the heterogeneity of cancer cells and immune cells across different tumors. A more in-depth understanding of the cancer-TAM/TAN co-evolution will shed light on the development of TME that mediates metastasis and therapeutic resistance.

Nanomedicine enables spatiotemporally regulating macrophage-based cancer immunotherapy

Cancer immunotherapy, leveraging the host's coordinated immune system to fight against tumor has been clinically validated. However, the modest response owing to the multiple ways of tumor immune evasion is one of the challenges in cancer immunotherapy. Tumor associated macrophages (TAMs), as a major component of the leukocytes infiltrating in all tumors, play crucial roles in driving cancer initiation, progress and metastasis via multiple mechanisms such as mediating chronic inflammation, promoting angiogenesis, taming protective immune responses, and supporting migration and intravasation. TAMs targeted therapeutics have achieved remarkable successes in clinical trials mostly through the use of small-molecule agents and antibodies. However, efforts for further application have met with challenges of limited efficacy and safety. Nanomaterials can provide versatile approaches to realize the superior spatiotemporal control over immunomodulation to amplify immune responses, ultimately enhancing the therapeutic benefits and reducing toxicity. Here, the potential drugs used in TAM-centered cancer treatment in clinic are summarized and the recent advances of TAMs targeted nanomedicines in this filed are highlighted. More importantly, we focus on how nanomedicine can exert their advantages in spatial and temporal control of immunomodulation.

Curcumin steers THP-1 cells under LPS and mTORC1 challenges toward phenotypically resting, low cytokine-producing macrophages

The persistent activation of intestinal mechanistic target of rapamycin complex 1 (mTORC1) triggered by mucosal stress has been linked to deregulation of the gut immune response resulting in intestinal inflammation and cell death. The present study investigated the regulatory properties of food-derived mTORC1 modulators, curcumin, and piperine, toward the polarization of stimulated macrophages and the differentiation of monocytes at two mTORC1 activity levels (baseline and elevated). To that end, we created stable human THP-1 monocytes exhibiting normal or constitutively active mTORC1. Curcumin or its combination with piperine, but not piperine alone, suppressed mTORC1 kinase activity, curtailed lipopolysaccharide-mediated inflammatory response of THP-1 macrophages, and repressed macrophage activation by inhibiting signaling pathways involved in M1 (mTORC1) and M2 (mTORC2 and cAMP response element binding protein) polarization. The effects of piperine in the curcumin/piperine combination were modest overall, indicating it was curcumin that modulated differentiating monocytes into acquiring a M0 macrophage phenotype characterized by low inflammatory cytokine output.

Curcumin represses mTORC1 signaling in Caco-2 cells by a two-sided mechanism involving the loss of IRS-1 and activation of AMPK

The mechanistic target of rapamycin complex 1 (mTORC1) is a central modulator of inflammation and tumorigenesis in the gastrointestinal tract. Growth factors upregulate mTORC1 via the PI3K/AKT and/or Ras/MAPK signal pathways. Curcumin (CUR), a polyphenol found in turmeric roots (Curcuma longa) can repress mTORC1 kinase activity in colon cancer cell lines; however, key aspects of CUR mechanism of action remain to be elucidated including its primary cellular target. We investigated the molecular effects of physiologically attainable concentration of CUR (20 μM) in the intestinal lumen on mTORC1 signaling in Caco-2 cells. CUR markedly inhibited mTORC1 kinase activity as determined by the decreased phosphorylation of p70S6K (Thr389, -99%, P < 0.0001) and S6 (Ser235/236, -92%, P < 0.0001). Mechanistically, CUR decreased IRS-1 protein abundance (-80%, P < 0.0001) thereby downregulating AKT phosphorylation (Ser473, -94%, P < 0.0001) and in turn PRAS40 phosphorylation (Thr246, -99%, P < 0.0001) while total PRAS40 abundance was unchanged. The use of proteasome inhibitor MG132 showed that CUR-mediated loss of IRS-1 involved proteasomal degradation. CUR lowered Raptor protein abundance, which combined with PRAS40 hypophosphorylation, suggests CUR repressed mTORC1 activity by inducing compositional changes that hinder the complex assembly. In addition, CUR activated AMPK (Thr172 phosphorylation, P < 0.0001), a recognized repressor of mTORC1, and AMPK upstream regulator LKB1. Although cargo adapter protein p62 was decreased by CUR (-49%, P < 0.004), CUR did not significantly induce autophagy. Inhibition of AKT/mTORC1 signaling by CUR may have lifted the cross-inhibition onto MAPK signaling, which became induced; p-ERK1/2 (+670%, P < 0.0001), p-p38 (+1433%, P < 0.0001). By concomitantly targeting IRS-1 and AMPK, CUR's mechanism of mTORC1 inhibition is distinct from that of rapamycin.

Activation of mTORC1 by LSECtin in macrophages directs intestinal repair in inflammatory bowel disease

Damage to intestinal epithelial cells and the induction of cellular apoptosis are characteristics of inflammatory bowel disease. The C-type lectin receptor family member LSECtin promotes apoptotic cell clearance by macrophages and induces the production of anti-inflammatory/tissue growth factors, which direct intestinal repair in experimental colitis. However, the mechanisms by which the phagocytosis of apoptotic cells triggers the pro-repair function of macrophages remain largely undefined. Here, using immunoprecipitation in combination with mass spectrometry to identify LSECtin-interacting proteins, we found that LSECtin interacted with mTOR, exhibiting a role in activating mTORC1. Mechanistically, apoptotic cells enhance the interaction between LSECtin and mTOR, and increase the activation of mTORC1 induced by LSECtin in macrophages. Elevated mTORC1 signaling triggers macrophages to produce anti-inflammatory/tissue growth factors that contribute to the proliferation of epithelial cells and promote the reestablishment of tissue homeostasis. Collectively, our findings suggest that LSECtin-dependent apoptotic cell clearance by macrophages activates mTORC1, and thus contributes to intestinal regeneration and the remission of colitis.