Biomechanical Contributions to Macrophage Activation in the Tumor Microenvironment

The influence of biophysical niche on tumor-associated macrophages in liver cancer

HCC, the most common type of primary liver cancer, is a leading cause of cancer-related mortality worldwide. Although the advancement of immunotherapies by immune checkpoint inhibitors (ICIs) that target programmed cell death 1 or programmed cell death 1-ligand 1 has revolutionized the treatment for HCC, the majority is still not beneficial. Accumulating evidence has pointed out that the potent immunosuppressive tumor microenvironment in HCC poses a great challenge to ICI therapeutic efficacy. As a key component in tumor microenvironment, tumor-associated macrophages (TAMs) play vital roles in HCC development, progression, and ICI low responsiveness. Mechanistically, TAM can promote cancer invasion and metastasis, angiogenesis, epithelial-mesenchymal transition, maintenance of stemness, and most importantly, immunosuppression. Targeting TAMs, therefore, represents an opportunity to enhance the ICI therapeutic efficacy in patients with HCC. While previous research has primarily focused on biochemical cues influencing macrophages, emerging evidence highlights the critical role of biophysical signals, such as substrate stiffness, topography, and external forces. In this review, we summarize the influence of biophysical characteristics within the tumor microenvironment that regulate the phenotype and function of TAMs in HCC pathogenesis and progression. We also explore the possible mechanisms and discuss the potential of manipulating biophysical cues in regulating TAM for HCC therapy. By gaining a deeper understanding of how macrophages sense and respond to mechanical forces, we may potentially usher in a path toward a curative approach for combinatory cancer immunotherapies.

Profibrotic Subsets of SPP1+ Macrophages and POSTN+ Fibroblasts Contribute to Fibrotic Scarring in Acne Keloidalis

Acne keloidalis is a primary scarring alopecia characterized by longstanding inflammation in the scalp causing keloid-like scar formation and hair loss. Histologically, acne keloidalis is characterized by mixed leukocytic infiltrates in the acute stage followed by a granulomatous reaction and extensive fibrosis in the later stages. To further explore its pathogenesis, bulk RNA sequencing, single-cell RNA sequencing, and spatial transcriptomics were applied to occipital scalp biopsy specimens of lesional and adjacent no-lesional skin in patients with clinically active disease. Unbiased clustering revealed 19 distinct cell populations, including 2 notable populations: POSTN+ fibroblasts with enriched extracellular matrix signatures and SPP1+ myeloid cells with an M2 macrophage phenotype. Cell communication analyses indicated that fibroblasts and myeloid cells communicated by SPP1 signaling networks in lesional skin. A reverse transcriptomics in silico approach identified corticosteroids as possessing the capability to reverse the gene expression signatures of SPP1+ myeloid cells and POSTN+ fibroblasts. Intralesional corticosteroid injection greatly reduced SPP1 and POSTN gene expression as well as acne keloidalis disease activity. Spatial transcriptomics and immunofluorescence staining verified microanatomic specificity of SPP1+ myeloid cells and POSTN+ fibroblasts with disease activity. In summary, the communication between POSTN+ fibroblasts and SPP1+ myeloid cells by SPP1 axis may contribute to the pathogenesis of acne keloidalis.

Laminin-derived peptide, IKVAV, modulates macrophage phenotype through integrin mediation

Macrophages are highly plastic immune cells known to exist on a spectrum of phenotypes including pro-inflammatory (M1) or pro-healing (M2). Macrophages interact with extracellular matrix (ECM) ligands, such as fragments of collagen and laminin. Interaction of macrophages with ECM ligands is mediated through integrin receptors. However, the role of ECM ligands in directing macrophage function through integrins is not yet fully understood. Particularly, α2β1 has been implicated in modulating macrophage function, but complexity in mechanisms employed for integrin-ligation especially with laminin-derived peptides makes it challenging to understand macrophage-ECM interactions. We hypothesize that targeting α2β1 through laminin-derived peptide, IKVAV, will modulate macrophage phenotype. In this work we: i) investigated macrophage response to IKVAV in 2D and in a 3D platform, and ii) identified α2β1's role as it pertains to macrophage modulation via IKVAV. Soluble IKVAV treatment significantly reduced M1 markers and increased M2 markers via immunocytochemistry and gene expression. While the 3D ECM-mimicking PEG-IKVAV hydrogels did not have significant effects in modulating macrophage phenotype, we found that macrophage modulation via IKVAV is dependent on the concentration of peptide used and duration of exposure. To investigate integrin-ligand interactions for macrophages, α2β1 signaling was modulated by antagonists and agonists. We observed that blocking α2β1 reduces M1 activation. To understand integrin-ligand interactions and leveraging the therapeutic ability of macrophages in designing immunomodulatory solutions, it is critical to elucidate IKVAV's role in mediating macrophage phenotype.

Human Fibroblast-Derived Matrix Hydrogel Accelerates Regenerative Wound Remodeling Through the Interactions with Macrophages

Herein, a novel extracellular matrix (ECM) hydrogel is proposed fabricated solely from decellularized, human fibroblast-derived matrix (FDM) toward advanced wound healing. This FDM-gel is physically very stable and viscoelastic, while preserving the natural ECM diversity and various bioactive factors. Subcutaneously transplanted FDM-gel provided a permissive environment for innate immune cells infiltration. Compared to collagen hydrogel, excellent wound healing indications of FDM-gel treated in the full-thickness wounds are noticed, particularly hair follicle formation via highly upregulated β-catenin. Sequential analysis of the regenerated wound tissues disclosed that FDM-gel significantly alleviated pro-inflammatory cytokine and promoted M2-like macrophages, along with significantly elevated vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) level. A mechanistic study demonstrated that macrophages-FDM interactions through cell surface integrins α5β1 and α1β1 resulted in significant production of VEGF and bFGF, increased Akt phosphorylation, and upregulated matrix metalloproteinase-9 activity. Interestingly, blocking such interactions using specific inhibitors (ATN161 for α5β1 and obtustatin for α1β1) negatively affected those pro-healing growth factors secretion. Macrophages depletion animal model significantly attenuated the healing effect of FDM-gel. This study demonstrates that the FDM-gel is an excellent immunomodulatory material that is permissive for host cells infiltration, resorbable with time, and interactive with macrophages, where it thus enables regenerative matrix remodeling toward a complete wound healing.

Matrix stiffness affects tumor-associated macrophage functional polarization and its potential in tumor therapy

The extracellular matrix (ECM) plays critical roles in cytoskeletal support, biomechanical transduction and biochemical signal transformation. Tumor-associated macrophage (TAM) function is regulated by matrix stiffness in solid tumors and is often associated with poor prognosis. ECM stiffness-induced mechanical cues can activate cell membrane mechanoreceptors and corresponding mechanotransducers in the cytoplasm, modulating the phenotype of TAMs. Currently, tuning TAM polarization through matrix stiffness-induced mechanical stimulation has received increasing attention, whereas its effect on TAM fate has rarely been summarized. A better understanding of the relationship between matrix stiffness and macrophage function will contribute to the development of new strategies for cancer therapy. In this review, we first introduced the overall relationship between macrophage polarization and matrix stiffness, analyzed the changes in mechanoreceptors and mechanotransducers mediated by matrix stiffness on macrophage function and tumor progression, and finally summarized the effects of targeting ECM stiffness on tumor prognosis to provide insight into this new field.

Macrophages and platelets in liver fibrosis and hepatocellular carcinoma

During fibrosis, (myo)fibroblasts deposit large amounts of extracellular matrix proteins, thereby replacing healthy functional tissue. In liver fibrosis, this leads to the loss of hepatocyte function, portal hypertension, variceal bleeding, and increased susceptibility to infection. At an early stage, liver fibrosis is a dynamic and reversible process, however, from the cirrhotic stage, there is significant progression to hepatocellular carcinoma. Both liver-resident macrophages (Kupffer cells) and monocyte-derived macrophages are important drivers of fibrosis progression, but can also induce its regression once triggers of chronic inflammation are eliminated. In liver cancer, they are attracted to the tumor site to become tumor-associated macrophages (TAMs) polarized towards a M2- anti-inflammatory/tumor-promoting phenotype. Besides their role in thrombosis and hemostasis, platelets can also stimulate fibrosis and tumor development by secreting profibrogenic factors and regulating the innate immune response, e.g., by interacting with monocytes and macrophages. Here, we review recent literature on the role of macrophages and platelets and their interplay in liver fibrosis and hepatocellular carcinoma.

Perfusability and immunogenicity of implantable pre-vascularized tissues recapitulating features of native capillary network

Vascularization is a key pre-requisite to engineered anatomical scale three dimensional (3-D) constructs to ensure their nutrient and oxygen supply upon implantation. Presently, engineered pre-vascularized 3-D tissues are limited to only micro-scale hydrogels, which meet neither the anatomical scale needs nor the complexity of natural extracellular matrix (ECM) environments. Anatomical scale perfusable constructs are critically needed for translational applications. To overcome this challenge, we previously developed pre-vascularized ECM sheets with long and oriented dense microvascular networks. The present study further evaluated the patency, perfusability and innate immune response toward these pre-vascularized constructs. Macrophage-co-cultured pre-vascularized constructs were evaluated in vitro to confirm micro-vessel patency and perturbations in macrophage metabolism. Subcutaneously implanted pre-vascularized constructs remained viable and formed a functional anastomosis with host vasculature within 3 days of implantation. This completely biological pre-vascularized construct holds great potential as a building block to engineer perfusable anatomical scale tissues.

Protective effects of macrophage-specific integrin α5 in myocardial infarction are associated with accentuated angiogenesis

Macrophages sense changes in the extracellular matrix environment through the integrins and play a central role in regulation of the reparative response after myocardial infarction. Here we show that macrophage integrin α5 protects the infarcted heart from adverse remodeling and that the protective actions are associated with acquisition of an angiogenic macrophage phenotype. We demonstrate that myeloid cell- and macrophage-specific integrin α5 knockout mice have accentuated adverse post-infarction remodeling, accompanied by reduced angiogenesis in the infarct and border zone. Single cell RNA-sequencing identifies an angiogenic infarct macrophage population with high Itga5 expression. The angiogenic effects of integrin α5 in macrophages involve upregulation of Vascular Endothelial Growth Factor A. RNA-sequencing of the macrophage transcriptome in vivo and in vitro followed by bioinformatic analysis identifies several intracellular kinases as potential downstream targets of integrin α5. Neutralization assays demonstrate that the angiogenic actions of integrin α5-stimulated macrophages involve activation of Focal Adhesion Kinase and Phosphoinositide 3 Kinase cascades.

The peritumor microenvironment: physics and immunity

Cancer initiation and progression drastically alter the microenvironment at the interface between healthy and malignant tissue. This site, termed the peritumor, bears unique physical and immune attributes that together further promote tumor progression through interconnected mechanical signaling and immune activity. In this review, we describe the distinct physical features of the peritumoral microenvironment and link their relationship to immune responses. The peritumor is a region rich in biomarkers and therapeutic targets and thus is a key focus for future cancer research as well as clinical outlooks, particularly to understand and overcome novel mechanisms of immunotherapy resistance.

Increased Trypanosoma cruzi Growth during Infection of Macrophages Cultured on Collagen I Matrix

The interactions between cell and cellular matrix confers plasticity to each body tissue, influencing the cellular migratory capacity. Macrophages rely on motility to promote their physiological function. These phagocytes are determinant for the control of invasive infections, and their immunological role largely depends on their ability to migrate and adhere to tissue. Therefore, they interact with the components of the extracellular matrix through their adhesion receptors, conferring morphological modifications that change their shape during migration. Nevertheless, the need to use in vitro cell growth models with the conditioning of three-dimensional synthetic matrices to mimic the dynamics of cell-matrix interaction has been increasingly studied. This becomes more important to effectively understand the changes occurring in phagocyte morphology in the context of infection progression, such as in Chagas disease. This disease is caused by the intracellular pathogen Trypanosoma cruzi, capable of infecting macrophages, determinant cells in the anti-trypanosomatid immunity. In the present study, we sought to understand how an in vitro extracellular matrix model interferes with T. cruzi infection in macrophages. Using different time intervals and parasite ratios, we evaluated the cell morphology and parasite replication rate in the presence of 3D collagen I matrix. Nevertheless, microscopy techniques such as scanning electron microscopy were crucial to trace macrophage-matrix interactions. In the present work, we demonstrated for the first time that the macrophage-matrix interaction favors T. cruzi in vitro replication and the release of anti-inflammatory cytokines during macrophage infection, in addition to drastically altering the morphology of the macrophages and promoting the formation of migratory macrophages.

The Extracellular Matrix: Its Composition, Function, Remodeling, and Role in Tumorigenesis

The extracellular matrix (ECM) is a ubiquitous member of the body and is key to the maintenance of tissue and organ integrity. Initially thought to be a bystander in many cellular processes, the extracellular matrix has been shown to have diverse components that regulate and activate many cellular processes and ultimately influence cell phenotype. Importantly, the ECM's composition, architecture, and stiffness/elasticity influence cellular phenotypes. Under normal conditions and during development, the synthesized ECM constantly undergoes degradation and remodeling processes via the action of matrix proteases that maintain tissue homeostasis. In many pathological conditions including fibrosis and cancer, ECM synthesis, remodeling, and degradation is dysregulated, causing its integrity to be altered. Both physical and chemical cues from the ECM are sensed via receptors including integrins and play key roles in driving cellular proliferation and differentiation and in the progression of various diseases such as cancers. Advances in 'omics' technologies have seen an increase in studies focusing on bidirectional cell-matrix interactions, and here, we highlight the emerging knowledge on the role played by the ECM during normal development and in pathological conditions. This review summarizes current ECM-targeted therapies that can modify ECM tumors to overcome drug resistance and better cancer treatment.

Tumor-associated macrophages: Prognostic and therapeutic targets for cancer in humans and dogs

Macrophages are ancient, phagocytic immune cells thought to have their origins 500 million years ago in metazoan phylogeny. The understanding of macrophages has evolved to encompass their foundational roles in development, homeostasis, tissue repair, inflammation, and immunity. Notably, macrophages display high plasticity in response to environmental cues, capable of a strikingly wide variety of dynamic gene signatures and phenotypes. Macrophages are also involved in many pathological states including neural disease, asthma, liver disease, heart disease, cancer, and others. In cancer, most tumor-associated immune cells are macrophages, coined tumor-associated macrophages (TAMs). While some TAMs can display anti-tumor properties such as phagocytizing tumor cells and orchestrating an immune response, most macrophages in the tumor microenvironment are immunosuppressive and pro-tumorigenic. Macrophages have been implicated in all stages of cancer. Therefore, interest in manipulating macrophages as a therapeutic strategy against cancer developed as early as the 1970s. Companion dogs are a strong comparative immuno-oncology model for people due to documented similarities in the immune system and spontaneous cancers between the species. Data from clinical trials in humans and dogs can be leveraged to further scientific advancements that benefit both species. This review aims to provide a summary of the current state of knowledge on macrophages in general, and an in-depth review of macrophages as a therapeutic strategy against cancer in humans and companion dogs.

A positive feedback loop driven by fibronectin and IL-1β sustains the inflammatory microenvironment in breast cancer

Inflammatory alterations of the extracellular matrix shape the tumor microenvironment and promote all stages of carcinogenesis. This study aims to determine the impact of cellular fibronectin on inflammatory facets of tumor-associated macrophages (TAMs) in breast cancer. Cellular fibronectin (FN) harboring the alternatively spliced extra domain A (FN-EDA) was determined to be a matrix component produced by the triple-negative breast cancer (TNBC) cells. High levels of FN-EDA correlated with poor survival in breast cancer patients. The proinflammatory cytokine IL-1β enhanced the expression of cellular fibronectin including FN-EDA. TAMs were frequently observed in the tumor areas rich in FN-EDA. Conditioned media from TNBC cells induced the differentiation of CD206⁺CD163⁺ macrophages and stimulated the STAT3 pathway, ex vivo. In the macrophages, the STAT3 pathway enhanced FN-EDA-induced IL-1β secretion and NF-κB signaling. In conclusion, our data indicate a self-reinforcing mechanism sustained by FN-EDA and IL-1β through NF-κB and STAT3 signaling in TAMs which fosters an inflammatory environment in TNBC.

Immunometabolic attributes and mitochondria-associated signaling of Tumor-Associated Macrophages in tumor microenvironment modulate cancer progression

Macrophages are specialized immune cells, which have the capacity to phagocytize and destroy the target cells, including tumor cells. Some macrophages, however on their way to devour the cancer cells undergo a change due to a complex set of signaling pathways. They are induced to change into a polarized state known as M2. The M2 macrophages help in metastasis, tumor suppression, and angiogenesis. The macrophage which gets associated with this TME, are referred to as tumor-associated macrophages (TAMs). TAMS undergo a metabolic reprogramming toward oxidative metabolism for bioenergetic purposes (OXPHOS), fatty acid oxidation (FAO), decreased glycolysis, decreased metabolism via the PPP, and upregulation of arginase 1 (ARG1) which triggers immunosuppressive pro-tumor signaling in the tumor microenvironment (TME) in which mitochondria plays an instrumental role. Reports have suggested that a complex series of interactions and exchange of materials, such as cytokines, metabolic intermediates and sometimes even transfer of mitochondria take place between TAMS and other TME components most importantly cancer cells that reprogram their metabolism to encourage cell growth, division, epithelial to mesenchymal transition, that ultimately play an important role in tumor progression. This review will try to focus on the crosstalk between the TAMs with several other components of TME, what instrumental role mitochondria play in that and also try to explore some of the therapeutic options available in cancer patients.

Idiopathic pulmonary fibrosis and lung cancer: future directions and challenges

Idiopathic pulmonary fibrosis (IPF) is a progressive disease of pulmonary scarring. New treatments slow disease progression and allow pulmonary fibrosis patients to live longer. Persistent pulmonary fibrosis increases a patient's risk of developing lung cancer. Lung cancer in patients with IPF differs from cancers that develop in the non-fibrotic lung. Peripherally located adenocarcinoma is the most frequent cell type in smokers who develop lung cancer, while squamous cell carcinoma is the most frequent in pulmonary fibrosis. Increased fibroblast foci in IPF are associated with more aggressive cancer behaviour and shorter doubling times. Treatment of lung cancer in fibrosis is challenging because of the risk of inducing an exacerbation of fibrosis. In order to improve patient outcomes, modifications of current lung cancer screening guidelines in patients with pulmonary fibrosis will be necessary to avoid delays in treatment. 2-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET) computed tomography (CT) imaging can help identify cancer earlier and more reliably than CT alone. Increased use of wedge resections, proton therapy and immunotherapy may increase survival by decreasing the risk of exacerbation, but further research will be necessary.

The complex interactions between the cellular and non-cellular components of the brain tumor microenvironmental landscape and their therapeutic implications

Glioblastoma (GBM), an aggressive high-grade glial tumor, is resistant to therapy and has a poor prognosis due to its universal recurrence rate. GBM cells interact with the non-cellular components in the tumor microenvironment (TME), facilitating their rapid growth, evolution, and invasion into the normal brain. Herein we discuss the complexity of the interactions between the cellular and non-cellular components of the TME and advances in the field as a whole. While the stroma of non-central nervous system (CNS) tissues is abundant in fibrillary collagens, laminins, and fibronectin, the normal brain extracellular matrix (ECM) predominantly includes proteoglycans, glycoproteins, and glycosaminoglycans, with fibrillary components typically found only in association with the vasculature. However, recent studies have found that in GBMs, the microenvironment evolves into a more complex array of components, with upregulated collagen gene expression and aligned fibrillary ECM networks. The interactions of glioma cells with the ECM and the degradation of matrix barriers are crucial for both single-cell and collective invasion into neighboring brain tissue. ECM-regulated mechanisms also contribute to immune exclusion, resulting in a major challenge to immunotherapy delivery and efficacy. Glioma cells chemically and physically control the function of their environment, co-opting complex signaling networks for their own benefit, resulting in radio- and chemo-resistance, tumor recurrence, and cancer progression. Targeting these interactions is an attractive strategy for overcoming therapy resistance, and we will discuss recent advances in preclinical studies, current clinical trials, and potential future clinical applications. In this review, we also provide a comprehensive discussion of the complexities of the interconnected cellular and non-cellular components of the microenvironmental landscape of brain tumors to guide the development of safe and effective therapeutic strategies against brain cancer.

The Roles of Tumor-Associated Macrophages in Prostate Cancer

The morbidity of prostate cancer (PCa) is rising year by year, and it has become the primary cause of tumor-related mortality in males. It is widely accepted that macrophages account for 50% of the tumor mass in solid tumors and have emerged as a crucial participator in multiple stages of PCa, with the huge potential for further treatment. Oftentimes, tumor-associated macrophages (TAMs) in the tumor microenvironment (TME) behave like M2-like phenotypes that modulate malignant hallmarks of tumor lesions, ranging from tumorigenesis to metastasis. Several clinical studies indicated that mean TAM density was higher in human PCa cores versus benign prostatic hyperplasia (BPH), and increased biopsy TAM density potentially predicts worse clinicopathological characteristics as well. Therefore, TAM represents a promising target for therapeutic intervention either alone or in combination with other strategies to halt the “vicious cycle,” thus improving oncological outcomes. Herein, we mainly focus on the fundamental aspects of TAMs in prostate adenocarcinoma, while reviewing the mechanisms responsible for macrophage recruitment and polarization, which has clinical translational implications for the exploitation of potentially effective therapies against TAMs.

Tetraspanin CD82 restrains phagocyte migration but supports macrophage activation

Phagocytes migrate into tissues to combat infection and maintain tissue homeostasis. As dysregulated phagocyte migration and function can lead to inflammation or susceptibility to infection, identifying molecules that control these processes is critical. Here, we show that the tetraspanin CD82 restrains the migration of neutrophils and macrophages into tissues. Cd82^−/− phagocytes exhibited excessive migration during in vivo models of peritoneal inflammation, superfusion of CXCL1, retinopathy of prematurity, and infection with the protozoan parasite L. mexicana. However, with the latter, while Cd82^−/− macrophages infiltrated infection sites at higher proportions, cutaneous L. mexicana lesions were larger and persisted, indicating a failure to control infection. Analyses of in vitro bone-marrow-derived macrophages showed CD82 deficiency altered cellular morphology, and impaired gene expression and metabolism in response to anti-inflammatory activation. Altogether, this work reveals an important role for CD82 in restraining phagocyte infiltration and mediating their differentiation in response to stimulatory cues.

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Tetraspanin CD82 restrains phagocyte migration in murine models of inflammation

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Excessive migration of Cd82^−/− myeloid cells exacerbates retinal inflammation

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Cd82^−/− macrophages have a reduced ability to clear Leishmania mexicana parasites

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CD82 is required for the normal morphology and activation of M2 macrophages

A Label-Free Segmentation Approach for Intravital Imaging of Mammary Tumor Microenvironment

The ability to visualize complex and dynamic physiological interactions between numerous cell types and the extracellular matrix (ECM) within a live tumor microenvironment is an important step toward understanding mechanisms that regulate tumor progression. While this can be accomplished through current intravital imaging techniques, it remains challenging due to the heterogeneous nature of tissues and the need for spatial context within the experimental observation. To this end, we have developed an intravital imaging workflow that pairs collagen second harmonic generation imaging, endogenous fluorescence from the metabolic co-factor NAD(P)H, and fluorescence lifetime imaging microscopy (FLIM) as a means to non-invasively compartmentalize the tumor microenvironment into basic domains of the tumor nest, the surrounding stroma or ECM, and the vasculature. This non-invasive protocol details the step-by-step process ranging from the acquisition of time-lapse images of mammary tumor models to post-processing analysis and image segmentation. The primary advantage of this workflow is that it exploits metabolic signatures to contextualize the dynamically changing live tumor microenvironment without the use of exogenous fluorescent labels, making it advantageous for human patient-derived xenograft (PDX) models and future clinical use where extrinsic fluorophores are not readily applicable.

Recent research advances of the biomimetic tumor microenvironment and regulatory factors on microfluidic devices: A systematic review

Tumor microenvironment is a multicomponent system consisting of tumor cells, noncancer cells, extracellular matrix, and signaling molecules, which hosts tumor cells with integrated biophysical and biochemical elements. Because of its critical involvement in tumor genesis, invasion, metastasis, and resistance, the tumor microenvironment is emerging as a hot topic of tumor biology and a prospective therapeutic target. Unfortunately, the complex of microenvironment modeling in vitro is technically challenging and does not effectively generalize the local tumor tissue milieu. Recently, significant advances in microfluidic technologies have provided us with an approach to imitate physiological systems that can be utilized to mimic the characterization of tumor responses with pathophysiological relevance in vitro. In this review, we highlight the recent progress and innovations in microfluidic technology that facilitates the tumor microenvironment study. We also discuss the progress and future perspective of microfluidic bionic approaches with high efficiency for the study of tumor microenvironment and the challenges encountered in cancer research, drug discovery, and personalized therapy.

In vivo fluorescence lifetime imaging of macrophage intracellular metabolism during wound responses in zebrafish

The function of macrophages in vitro is linked to their metabolic rewiring. However, macrophage metabolism remains poorly characterized in situ. Here, we used two-photon intensity and lifetime imaging of autofluorescent metabolic coenzymes, nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD), to assess the metabolism of macrophages in the wound microenvironment. Inhibiting glycolysis reduced NAD(P)H mean lifetime and made the intracellular redox state of macrophages more oxidized, as indicated by reduced optical redox ratio. We found that TNFα+ macrophages had lower NAD(P)H mean lifetime and were more oxidized compared to TNFα- macrophages. Both infection and thermal injury induced a macrophage population with a more oxidized redox state in wounded tissues. Kinetic analysis detected temporal changes in the optical redox ratio during tissue repair, revealing a shift toward a more reduced redox state over time. Metformin reduced TNFα+ wound macrophages, made intracellular redox state more reduced and improved tissue repair. By contrast, depletion of STAT6 increased TNFα+ wound macrophages, made redox state more oxidized and impaired regeneration. Our findings suggest that autofluorescence of NAD(P)H and FAD is sensitive to dynamic changes in intracellular metabolism in tissues and can be used to probe the temporal and spatial regulation of macrophage metabolism during tissue damage and repair.

Production of NOS2 and inflammatory cytokines is reduced by selected protein kinase inhibitors with partial repolarization of HL-60 derived and human blood macrophages

JAK/STAT pathway plays a well-known role in macrophage polarization, but other signaling routes may also be involved. The aim of this study was to identify new signaling pathways and repolarize macrophages by selected protein kinase inhibitors. HL-60 derived macrophages were chosen as model cells and human blood macrophages were used for comparison. M1 and M2 polarization of HL60 derived and human blood macrophages was promoted by LPS + IFNγ (LIF) and IL-4 treatments, respectively. In HL-60 derived macrophages, M1 polarization was mediated by Erk1/2 and p38 phosphorylation, while HSP27 phosphorylation was involved in M2 polarization. The inhibition of both MAPK and JAK/STAT pathways reduced the expression of NOS2, IP-10 and TNFα, IL-8 production was decreased by the inhibition of AMPK and PKD, the upstream kinase of HSP27. HSP27 phosphorylation was inhibited by NB 142, a PKD inhibitor. The expression of CD80 (M1 marker) was reduced by MAPK and JAK/STAT inhibitors, without increasing CD206 (M2 marker). On the other hand, CD206 was reduced by PKD and AMPK inhibitors, without increasing CD80 marker. Phagocytic capacity of HL-60 derived macrophages was higher in M1 macrophages and decreased by trametinib and a p38 inhibitor, while in human blood macrophages, where AT 9283, a JAK/STAT inhibitor also caused a significant decrease in M1 polarized macrophages, no difference was observed between M1 and M2 macrophages. Our results suggest that the repolarization of macrophages cannot be achieved by inhibiting their signaling pathways; nevertheless, the expression of certain polarization markers was decreased, therefore a "depolarization" could be observed both in M1 and M2 polarized cells. Selected protein kinase inhibitors of M1 polarization, decreasing NOS 2 and inflammatory cytokines may be potential candidates for therapeutical trials against inflammatory diseases.

Immune Modulatory Properties of Collagen in Cancer

During tumor growth the extracellular matrix (ECM) undergoes dramatic remodeling. The normal ECM is degraded and substituted with a tumor-specific ECM, which is often of higher collagen density and increased stiffness. The structure and collagen density of the tumor-specific ECM has been associated with poor prognosis in several types of cancer. However, the reason for this association is still largely unknown. Collagen can promote cancer cell growth and migration, but recent studies have shown that collagens can also affect the function and phenotype of various types of tumor-infiltrating immune cells such as tumor-associated macrophages (TAMs) and T cells. This suggests that tumor-associated collagen could have important immune modulatory functions within the tumor microenvironment, affecting cancer progression as well as the efficacy of cancer immunotherapy. The effects of tumor-associated collagen on immune cells could help explain why a high collagen density in tumors is often correlated with a poor prognosis. Knowledge about immune modulatory functions of collagen could potentially identify targets for improving current cancer therapies or for development of new treatments. In this review, the current knowledge about the ability of collagen to influence T cell activity will be summarized. This includes direct interactions with T cells as well as induction of immune suppressive activity in other immune cells such as macrophages. Additionally, the potential effects of collagen on the efficacy of cancer immunotherapy will be discussed.

M2 Macrophage-Derived Concentrated Conditioned Media Significantly Improves Skin Wound Healing

BACKGROUND

Macrophages, with many different phenotypes play a major role during wound healing process, secreting the cytokines crucial to angiogenesis, cell recruitment and ECM remodeling. Therefore, macrophage-derived cytokines may be attractive therapeutic resource for wound healing.

METHODS

To obtain a conditioned media (CM) from macrophages, human monocyte THP-1 cells were seeded on TCP or human fibroblast-derived matrix (hFDM) and they were differentiated into M1 or M2 phenotype using distinct protocols. A combination of different substrates and macrophage phenotypes produced M1- and M2-CM or M1-hFDM- and M2-hFDM-CM, respectively. Proteome microarray determines the cytokine contents in those CMs. CMs-treated human dermal fibroblast (hDFB) was analyzed using collagen synthesis and wound scratch assay. Concentrated form of the CM (CCM), obtained by high-speed centrifugation, was administered to a murine full-thickness wound model using alginate patch, where alginate patch was incubated in the M2-CCM overnight at 4 °C before transplantation. On 14 day post-treatment, examination was carried out through H&E and Herovici staining. Keratinocyte and M2 macrophages were also evaluated via immunofluorescence staining.

RESULTS

Cytokine analysis of CMs found CCL1, CCL5, and G-CSF, where CCL5 is more dominant. We found increased collagen synthesis and faster wound closure in hDFB treated with M2-CM. Full-thickness wounds treated by M2-hFDM-CCM containing alginate patch showed early wound closure, larger blood vessels, increased mature collagen deposition, enhanced keratinocyte maturation and more M2-macrophage population.

CONCLUSION

Our study demonstrated therapeutic potential of the CM derived from M2 macrophages, where the cytokines in the CM may have played an active role for enhanced wound healing.

Transglutaminase 2 mediates lung inflammation and remodeling by transforming growth factor beta 1 via alveolar macrophage modulation

Transforming growth factor beta 1 (TGF-β1) induces pulmonary fibrosis by enhancing epithelial apoptosis and affects the enzymatic activity of transglutaminase 2 (TG2). The aim of this study was to determine the role of TG2 in TGF-β1-induced lung remodeling and alveolar macrophage modulation. We characterized the in vivo effects of TGF-β1 and TG2 on lung inflammation, fibrosis, and macrophage activity using transgenic C57BL/6 mice with wild and null TG2 loci. The effect of TG2 inhibition on in vitro TGF-β1-stimulated alveolar macrophages was assessed through mRNA analysis. TG2 was remarkably upregulated in the lungs of TGF-β1 transgenic (TGF-β1 Tg) mice, especially in alveolar macrophages and epithelial cells. In the absence of TG2, TGF-β1-induced inflammation was suppressed, decreasing the number of macrophages in the bronchoalveolar lavage fluid. In addition, the alveolar destruction and peribronchial fibrosis induced by TGF-β1 overexpression were significantly reduced, which correlated with decreases in the expression of fibroblast growth factor and matrix metallopeptidase 12, respectively. However, TG2 deficiency did not compromise the phagocytic activity of alveolar macrophages in TGF-β1 Tg mice. At the same time, TG2 contributed to the regulation of TGF-β1-induced macrophage activation. Inhibition of TG2 did not affect the TGF-β1-induced expression of CD86, an M1 marker, in macrophages, but it did reverse the TGF-β1-induced expression of CD206. This result suggests that TG2 mediates TGF-β1-induced M2-like polarization but does not contribute to TGF-β1-induced M1 polarization. In conclusion, TG2 regulates macrophage modulation and plays an important role in TGF-β1-induced lung inflammation, destruction, and fibrosis.

An emergent Wnt5a/YAP/TAZ regulatory circuit and its possible role in cancer

Wnt5a is a ligand that plays several roles in development, homeostasis, and disease. A growing body of evidence indicates that Wnt5a is involved in cancer progression. Despite extensive research in this field, our knowledge about how Wnt5a is precisely involved in cancer is still incomplete. It is usually thought that certain combinations of Frizzled receptors and co-receptors might explain the observed effects of Wnt5a either as a tumor suppressor or by promoting migration and invasion. While accepting this 'receptor context' model, this review proposes that Wnt5a is integrated within a larger regulatory circuit involving β-catenin, YAP/TAZ, and LATS1/2. Remarkably, WNT5A and YAP1 are transcriptionally regulated by the Hippo and Wnt pathways, respectively, and might form a regulatory circuit acting through LATS kinases and secreted Wnt/β-catenin inhibitors, including Wnt5a itself. Therefore, understanding the precise role of Wnt5a and YAP in cancer requires a systems biology perspective.

3D Model of the Early Melanoma Microenvironment Captures Macrophage Transition into a Tumor-Promoting Phenotype

Simple Summary

We developed a “tumor-in-a-dish” experimental system to study the early events favoring tumor growth and suppression of the immune response in metastatic melanoma. We combined murine melanoma tumor cells with fibroblasts and macrophages in a 3D collagen matrix and characterized how interactions between these three cell types, which are present in the early stages of tumorigenesis, drive immune suppression and the tumor-promoting transition in macrophages that is observed in vivo. Over the course of 7 days in the co-cultures, we quantified the dynamics of cues transmitted by direct cell–cell interactions, through the extracellular matrix and through secretion of immune mediators. We found that macrophages acquired features and a functional profile consistent with those present in in vivo murine melanoma tumors. This system will enable future studies of macrophage–stromal cross-talk in the melanoma microenvironment and provide a platform to test potential therapeutic approaches aimed at stimulating immune activity in macrophages.

Abstract

Tumor immune response is shaped by the tumor microenvironment (TME), which often evolves to be immunosuppressive, promoting disease progression and metastasis. An important example is melanoma tumors, which display high numbers of tumor-associated macrophages (TAMs) that are immunosuppressive but also have the potential to restore anti-tumor activity. However, to therapeutically target TAMs, there is a need to understand the early events that shape their tumor-promoting profile. To address this, we built and optimized 3D in vitro co-culture systems, composed of a collagen-I matrix scaffolding murine bone-marrow-derived macrophages (BMDMs), YUMM1.7 melanoma cells, and fibroblasts to recreate the early melanoma TME and study how interactions with fibroblasts and tumor cells modulate macrophage immune activity. We monitored BMDM behavior and interactions through time-lapse imaging and characterized their activation and secretion. We found that stromal cells induced a rapid functional activation, with increased motility and response from BMDMs. Over the course of seven days, BMDMs acquired a phenotype and secretion profile that resembled melanoma TAMs in established tumors. Overall, the direct cell–cell interactions with the stromal components in a 3D environment shape BMDM transition to a TAM-like immunosuppressive state. Our systems will enable future studies of changes in macrophage–stromal cross-talk in the melanoma TME.

Endogenous and Therapeutic Estrogens: Maestro Conductors of the Microenvironment of ER+ Breast Cancers

Estrogen receptor alpha (ERα) marks heterogeneous breast cancers which display a repertoire of somatic genomic mutations and an immune environment that differs from other breast cancer subtypes. These cancers also exhibit distinct biological behaviors; despite an overall better prognosis than HER2+ or triple negative breast cancers, disseminated dormant cells can lead to disease recurrence decades after the initial diagnosis and treatment. Estrogen is the best studied driver of these cancers, and antagonism or reduction of estrogen activity is the cornerstone of therapeutic approaches. In addition to reducing proliferation of ERα+ cancer cells, these treatments also alter signals to multiple other target cells in the environment, including immune cell subpopulations, cancer-associated fibroblasts, and endothelial cells via several distinct estrogen receptors. In this review, we update progress in our understanding of the stromal cells populating the microenvironments of primary and metastatic ER+ tumors, the effects of estrogen on tumor and stromal cells to modulate immune activity and the extracellular matrix, and net outcomes in experimental and clinical studies. We highlight new approaches that will illuminate the unique biology of these cancers, provide the foundation for developing new treatment and prevention strategies, and reduce mortality of this disease.

Prognostic signature of ovarian cancer based on 14 tumor microenvironment-related genes

BACKGROUND

Ovarian cancer is one of the lethal gynecological diseases in women. However, using tumor microenvironment related genes to identify prognostic signature of ovarian cancer has not been discussed in detail.

METHODS

The mRNA profiles of 386 ovarian cancer patients were retrieved from The Cancer Genome Atlas. Univariate Cox regression and LASSO Cox regression analyses were performed and 14 optimized prognostic genes related to tumor microenvironment were identified.

RESULTS

The multivariate Cox hazards regression showed risk score was an independent prognostic signature for ovarian cancer. Nomogram model could reliably predict the patients' survival. Furthermore, M1 macrophages, M2 macrophages, and follicular helper T cells, differentially expressed between the high- and low-risk groups, were found to be associated with the risk score.

CONCLUSION

CTL-associated antigen 4 (CTLA4) and indoleamine 2,3-Dioxygenase 1 (IDO1), which were previously shown to be important immune checkpoints, probably contribute to the immunosuppressive microenvironment aberration. This study may shed light on the prognosis of ovarian cancer.

Identification of collagen genes related to immune infiltration and epithelial-mesenchymal transition in glioma

Background

Gliomas account for the majority of fatal primary brain tumors, and there is much room for research in the underlying pathogenesis, the multistep progression of glioma, and how to improve survival. In our study, we aimed to identify potential biomarkers or therapeutic targets of glioma and study the mechanism underlying the tumor progression.

Methods

We downloaded the microarray datasets (GSE43378 and GSE7696) from the Gene Expression Omnibus (GEO) database. Then, we used weighted gene co-expression network analysis (WGCNA) to screen potential biomarkers or therapeutic targets related to the tumor progression. ESTIMATE (Estimation of STromal and Immune cells in MAlignant Tumors using Expression data) algorithm and TIMER (Tumor Immune Estimation Resource) database were used to analyze the correlation between the selected genes and the tumor microenvironment. Real-time reverse transcription polymerase chain reaction was used to measure the selected gene. Transwell and wound healing assays were used to measure the cell migration and invasion capacity. Western blotting was used to test the expression of epithelial-mesenchymal transition (EMT) related markers.

Results

We identified specific module genes that were positively correlated with the WHO grade but negatively correlated with OS of glioma. Importantly, we identified that 6 collagen genes (COL1A1, COL1A2, COL3A1, COL4A1, COL4A2, and COL5A2) could regulate the immunosuppressive microenvironment of glioma. Moreover, we found that these collagen genes were significantly involved in the EMT process of glioma. Finally, taking COL3A1 as a further research object, the results showed that knockdown of COL3A1 significantly inhibited the migration, invasion, and EMT process of SHG44 and A172 cells.

Conclusions

In summary, our study demonstrated that collagen genes play an important role in regulating the immunosuppressive microenvironment and EMT process of glioma and could serve as potential therapeutic targets for glioma management.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-01982-0.

Intravital Metabolic Autofluorescence Imaging Captures Macrophage Heterogeneity Across Normal and Cancerous Tissue

Macrophages are dynamic immune cells that govern both normal tissue function and disease progression. However, standard methods to measure heterogeneity in macrophage function within tissues require tissue excision and fixation, which limits our understanding of diverse macrophage function in vivo. Two-photon microscopy of the endogenous metabolic co-enzymes NAD(P)H and flavin adenine dinucleotide (FAD) (metabolic autofluorescence imaging) enables dynamic imaging of mouse models in vivo. Here, we demonstrate metabolic autofluorescence imaging to assess cell-level macrophage heterogeneity in response to normal and cancerous tissue microenvironments in vivo. NAD(P)H and FAD fluorescence intensities and lifetimes were measured for both tissue-resident macrophages in mouse ear dermis and tumor-associated macrophages in pancreatic flank tumors. Metabolic and spatial organization of macrophages were determined by performing metabolic autofluorescence imaging and single macrophage segmentation in mice engineered for macrophage-specific fluorescent protein expression. Tumor-associated macrophages exhibited decreased optical redox ratio [NAD(P)H divided by FAD intensity] compared to dermal macrophages, indicating that tumor-associated macrophages are more oxidized than dermal macrophages. The mean fluorescence lifetimes of NAD(P)H and FAD were longer in dermal macrophages than in tumor-associated macrophages, which reflects changes in NAD(P)H and FAD protein-binding activities. Dermal macrophages had greater heterogeneity in optical redox ratio, NAD(P)H mean lifetime, and FAD mean lifetime compared to tumor-associated macrophages. Similarly, standard markers of macrophage phenotype (CD206 and CD86) assessed by immunofluorescence revealed greater heterogeneity in dermal macrophages compared to tumor-associated macrophages. Ultimately, metabolic autofluorescence imaging provides a novel tool to assess tissue-specific macrophage behavior and cell-level heterogeneity in vivo in animal models.

The matrix in cancer

The extracellular matrix is a fundamental, core component of all tissues and organs, and is essential for the existence of multicellular organisms. From the earliest stages of organism development until death, it regulates and fine-tunes every cellular process in the body. In cancer, the extracellular matrix is altered at the biochemical, biomechanical, architectural and topographical levels, and recent years have seen an exponential increase in the study and recognition of the importance of the matrix in solid tumours. Coupled with the advancement of new technologies to study various elements of the matrix and cell-matrix interactions, we are also beginning to see the deployment of matrix-centric, stromal targeting cancer therapies. This Review touches on many of the facets of matrix biology in solid cancers, including breast, pancreatic and lung cancer, with the aim of highlighting some of the emerging interactions of the matrix and influences that the matrix has on tumour onset, progression and metastatic dissemination, before summarizing the ongoing work in the field aimed at developing therapies to co-target the matrix in cancer and cancer metastasis.

CCR7 Has Potential to Be a Prognosis Marker for Cervical Squamous Cell Carcinoma and an Index for Tumor Microenvironment Change

The tumor microenvironment (TME) has an essential role in the development of cervical squamous cell carcinoma (CSCC); however, the dynamic role of the stromal and immune cells is still unclear in TME. We downloaded data from The Cancer Genome Atlas (TCGA) database and applied ESTIMATE and CIBERSORT algorithms to measure the quantity of stromal and immune cells and the composition of tumor-infiltrating immune cell (TIC) in 253 CSCC cases. The protein-protein interaction (PPI) network and Cox regression analysis presented the differentially expressed genes (DEGs). Then, C-C chemokine receptor type 7 (CCR7) was screened out as a prognostic marker by the univariate Cox and intersection analysis of PPI. Further analysis showed a positive correlation between the expression of CCR7 and the survival of CSCC patients. The result of the Gene Set Enrichment Analysis (GSEA) of genes in the high CCR7 expression group displayed a predominant enrichment in immune-related pathways. An enrichment in metabolic activities was observed in the low CCR7 expression group. CIBERSORT analysis showed a positive correlation between Plasma cells, CD8⁺ T cells, and regulatory T cells and the CCR7 expression, suggesting that CCR7 might play a crucial role in maintaining the immunological dominance status for TME. Therefore, the expression level of CCR7 might help predict the survival of CSCC cases and be an index that the status of TME transitioned from immunological dominance to metabolic activation, which presented a new insight into the treatment of CSCC.

Macrophages and Extracellular Matrix in Breast Cancer: Partners in Crime or Protective Allies?

Solid cancers such as breast tumors comprise a collection of tumor, stromal and immune cells, embedded within a network of tumor-specific extracellular matrix. This matrix is associated with tumor aggression, treatment failure, chemo- and radio-resistance, poor survival and metastasis. Recent data report an immunomodulatory role for the matrix in cancer, via the creation of niches that control the migration, localization, phenotype and function of tumor-infiltrating immune cells, ultimately contributing to escape of immune surveillance. Macrophages are crucial components of the immune infiltrate in tumors; they are associated with a poor prognosis in breast cancer and contribute to shaping the anti-tumor immune response. We and others have described how matrix molecules commonly upregulated within the tumor stroma, such as tenascin-C, fibronectin and collagen, exert a complex influence over macrophage behavior, for example restricting or enhancing their infiltration into the tumor, and driving their polarization towards or away from a pro-tumoral phenotype, and how in turn macrophages can modify matrix production in the tumor to favor tumor growth and metastasis. Targeting specific domains of matrix molecules to reinstate an efficient anti-tumor immune response, and effectively control tumor growth and spread, is emerging as a promising field offering a new angle for cancer therapy. Here, we review current knowledge on the interactions between tumor-associated macrophages and matrix molecules that occur within the tumor microenvironment of breast cancer, and discuss how these pathways can be targeted for new immunotherapies for hard to treat, desmoplastic tumors.

Hydrogels to engineer tumor microenvironments in vitro

Illustration of engineered hydrogel to recapitulate aspects of the tumor microenvironment.