Substrate viscoelasticity affects human macrophage morphology and phagocytosis

A crosstalk between adhesion and phagocytosis integrates macrophage functions into their microenvironment

Phagocytosis is the process of actin-dependent internalization and degradation of large particles. Macrophages, which are professional phagocytes, are present in all tissues and are, thus, exposed to environments with different mechanical properties. How mechanical cues from macrophages' environment affect their ability to phagocytose and, in turn, how phagocytosis influences how phagocytic cells interact with their environment remain poorly understood. We found that the ability of macrophages to perform phagocytosis varied with the substrate stiffness. Using live traction force microscopy, we showed that phagocytosing macrophages applied more dynamic traction forces to their substrate. In addition, integrin-mediated phagocytosis triggered a transient loss of podosomes that was associated with decreased degradation of the extracellular matrix, concomitantly with RhoA activation and F-actin recruitment at phagocytic cups. Overall, these results highlight a crosstalk between macrophage phagocytosis and cell adhesion. Mechanical properties of the microenvironment influence phagocytosis, which, in turn, impacts how macrophages interact with their surroundings.

Matrix Viscoelasticity Orchestrates Osteogenesis via Mechanotransduction Mediated Metabolic Switch in Macrophages

Understanding the interplay between extracellular matrix (ECM) mechanics and macrophage cellular processes is crucial for bone regeneration. While ECM stiffness has been extensively studied, the role of ECM viscoelasticity (e.g., stress relaxation) in the bone marrow niche and its effects on macrophage function remain unclear. Here, this study reveals how matrix viscoelasticity orchestrates osteogenesis by modulating macrophage metabolism through vasodilator-stimulated phosphoprotein (VASP) / hypoxia-inducible factor 1 alpha (HIF1α) signaling. In the rapid maxillary expansion (RME) model, significant stress relaxation occurs in regenerated bone marrow during the initial 17 days, coinciding with increased transforming growth factor-beta 1 (TGF-β1+) F4/80+ macrophages. Fast stress relaxation enhances macrophage recruitment of mesenchymal stem cells (MSCs) by upregulating TGF-β1. Using a hydrogel-macrophage system mimicking bone marrow viscoelasticity, cranial defect regeneration is significantly improved. Moreover, fast stress relaxation shifts macrophage metabolism from glycolysis to oxidative phosphorylation (OXPHOS) via VASP/HIF1α signaling, facilitating a reparative phenotype. These findings elucidate the relationship between ECM viscoelasticity and macrophage metabolism, suggesting new therapeutic avenues for bone regeneration through mechanomedicine.

CaMKK2 Regulates Macrophage Polarization Induced by Matrix Stiffness: Implications for Shaping the Immune Response in Stiffened Tissues

Macrophages are essential for immune responses and maintaining tissue homeostasis, exhibiting a wide range of phenotypes depending on their microenvironment. The extracellular matrix (ECM) is a vital component that provides structural support and organization to tissues, with matrix stiffness acting as a key regulator of macrophage behavior. Using physiologically relevant 3D stiffening hydrogel models, it is found that increased matrix stiffness alone promoted macrophage polarization toward a pro-regenerative phenotype, mimicking the effect of interleukin-4(IL-4) in softer matrices. Blocking Calcium/calmodulin-dependent kinase kinase 2 (CaMKK2) selectively inhibited stiffness-induced macrophage polarization without affecting IL-4-driven pro-regenerative pathways. In functional studies, CaMKK2 deletion prevented M2-like/pro-tumoral polarization caused by matrix stiffening, which in turn hindered tumor growth. In a murine wound healing model, loss of CaMKK2 impaired matrix stiffness-mediated macrophage accumulation, ultimately disrupting vascularization. These findings highlight the critical role of CaMKK2 in the macrophage mechanosensitive fate determination and gene expression program, positioning this kinase as a promising therapeutic target to selectively modulate macrophage responses in pathologically stiff tissues.

The Molecular Mechanism of Macrophages in Response to Mechanical Stress

Macrophages, a type of functionally diversified immune cell involved in the progression of many physiologies and pathologies, could be mechanically activated. The physical properties of biomaterials including stiffness and topography have been recognized as exerting a considerable influence on macrophage behaviors, such as adhesion, migration, proliferation, and polarization. Recent articles and reviews on the physical and mechanical cues that regulate the macrophage's behavior are available; however, the underlying mechanism still deserves further investigation. Here, we summarized the molecular mechanism of macrophage behavior through three parts, as follows: (1) mechanosensing on the cell membrane, (2) mechanotransmission by the cytoskeleton, (3) mechanotransduction in the nucleus. Finally, the present challenges in understanding the mechanism were also noted. In this review, we clarified the associated mechanism of the macrophage mechanotransduction pathway which could provide mechanistic insights into the development of treatment for diseases like bone-related diseases as molecular targets become possible.

Substrate curvature influences cytoskeletal rearrangement and modulates macrophage phenotype

Introduction

Inflammation is a vital immune response, tightly orchestrated through both biochemical and biophysical cues. Dysregulated inflammation contributes to chronic diseases, highlighting the need for novel therapies that modulate immune responses with minimal side effects. While several biochemical pathways of inflammation are well understood, the influence of physical properties such as substrate curvature on immune cell behavior remains underexplored. This study investigates how substrate curvature impacts macrophage cytoskeletal dynamics, gene expression, and immunophenotype through mechanosensitive pathways.

Methods

Gelatin-based microgels with tunable surface curvatures were fabricated via water-in-oil emulsification and crosslinked with genipin. Microgels were sorted into three size ranges, yielding high (40-50 µm), intermediate (150-250 µm), and low (350-400 µm) curvature profiles. Macrophages were seeded onto these microgels, and cytoskeletal dynamics were examined using confocal microscopy, SEM, and actin-specific staining. Gene expression of pro- and anti-inflammatory markers was quantified using qPCR. The role of actin polymerization was assessed using Latrunculin-A (Lat-A) treatment.

Results

Macrophages adhered effectively to both high- and low-curvature microgels, displaying curvature-dependent morphological changes. Confocal imaging revealed that macrophages on low-curvature microgels exhibited significantly higher F-actin density than those on high-curvature microgels. Correspondingly, qPCR analysis showed upregulation of pro-inflammatory markers (e.g., Tnf, Nos2) in high-curvature conditions, while anti-inflammatory markers (e.g., Arg1) were elevated in low-curvature conditions. Lat-A treatment reduced F-actin density and modulated gene expression patterns, confirming the cytoskeletal regulation of macrophage phenotype.

Discussion

These findings demonstrate that substrate curvature influences macrophage behavior by modulating cytoskeletal dynamics and associated immunophenotypic markers through actin-mediated transcriptional pathways. By controlling curvature, therapeutic biomaterials may direct immune responses, offering a new avenue for treating inflammatory diseases. This mechanobiological approach presents a promising strategy for precision immunomodulation in regenerative medicine.

Tailoring surface stiffness to modulate senescent macrophage immunomodulation: Implications for osteo-/angio-genesis in aged bone regeneration

The application of biomaterials in bone regeneration is a prevalent clinical practice. However, its efficacy in elderly patients remains suboptimal, necessitating further advancements. While biomaterial properties are known to orchestrate macrophage (MΦ) polarization and local immune responses, the role of biomaterial cues, specifically stiffness, in directing the senescent macrophage (S-MΦ) is still poorly understood. This study aimed to elucidate the role of substrate stiffness in modulating the immunomodulatory properties of S-MΦ and their role in osteo-immunomodulation. Our results demonstrated that employing collagen-coated polyacrylamide hydrogels with varying stiffness values (18, 76, and 295 kPa) as model materials, the high-stiffness hydrogel (295 kPa) steered S-MΦs towards a pro-inflammatory M1 phenotype, while hydrogels with lower stiffness (18 and 76 kPa) promoted an anti-inflammatory M2 phenotype. The immune microenvironment created by S-MΦs promoted the bioactivities of senescent endothelial cells (S-ECs) and senescent bone marrow mesenchymal stem cells BMSCs (S-BMSCs). Furthermore, the M2 S-MΦs, particularly incubated on the 76 kPa hydrogel matrices, significantly enhanced the ability of angiogenesis of S-ECs and osteogenic differentiation of S-BMSCs, which are crucial and interrelated processes in bone healing. This modulation aided in reducing the accumulation of reactive oxygen species in S-ECs and S-BMSCs, thereby significantly contributing to the repair and regeneration of aged bone tissue.

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.

Understanding Macrophage-Tumor Interactions: Insights from Single-Cell Behavior Monitoring in a Sessile Microdroplet System

Interaction between tumor-associated macrophages and tumor cells is crucial for tumor development, metastasis, and the related immune process. However, the macrophages are highly heterogeneous spanning from anti-tumorigenic to pro-tumorigenic, which needs to be understood at the single-cell level. Herein, a sessile microdroplet system designed for monitoring cellular behavior and analyzing intercellular interaction, demonstrated with macrophage-tumor cell pairs is presented. An automatic procedure based on the inkjet printing method is utilized for the precise pairing and co-encapsulation of heterotypic cells within picoliter droplets. The sessile nature of microdroplets ensures controlled fusion and provides stable environments conducive to adherent cell culture. The nitric oxide generation and morphological changes over incubation are explored to reveal the complicated interactions from a single-cell perspective. The immune response of macrophages under distinct cellular microenvironments is recorded. The results demonstrate that the tumor microenvironment displays a modulating role in polarizing macrophages from anti-tumorigenic into pro-tumorigenic phenotype. The approach provides a versatile and compatible platform to investigate intercellular interaction at the single-cell level, showing promising potential for advancing single-cell behavior studies.

Substrate Curvature Influences Cytoskeletal Rearrangement and Modulates Macrophage Phenotype

Inflammation serves as a critical defense mechanism against pathogens and tissue damage but can lead to chronic diseases, such as cardiovascular disease and diabetes, when dysregulated. Macrophages play a pivotal role in orchestrating inflammatory responses, transitioning from pro-inflammatory M1 to anti-inflammatory M2 phenotypes to resolve inflammation and promote tissue repair. Current approaches to modulate macrophage phenotype predominantly rely on biochemical cues, which may induce systemic side effects. Given the mechanosensitivity of macrophages, this study investigates biophysical cues, specifically substrate curvature, as a localized strategy to regulate macrophage phenotype and minimize systemic repercussions. We hypothesized that substrate curvature influences macrophage immunophenotype by modulating F-actin polymerization. To test this hypothesis, we fabricated spherical microgels with tunable curvatures and characterized their biophysical properties. Our findings indicate that macrophages adhere to microgel surfaces irrespective of curvature, but the curvature significantly alters F-actin dynamics. Furthermore, manipulating cytoskeletal dynamics via selective actin inhibition partially reversed curvature-induced changes in macrophage phenotype. These results underscore the pivotal role of substrate curvature in modulating macrophage behavior and immunophenotype. Overall, our study demonstrates that substrate curvature significantly influences macrophage cytoskeletal dynamics and resulting immunophenotype. This simple approach can be utilized as a localized immunomodulatory treatment for inflammatory diseases.

Dental-derived stem cells in tissue engineering: the role of biomaterials and host response

Dental-derived stem cells (DSCs) are attractive cell sources due to their easy access, superior growth capacity and low immunogenicity. They can respond to multiple extracellular matrix signals, which provide biophysical and biochemical cues to regulate the fate of residing cells. However, the direct transplantation of DSCs suffers from poor proliferation and differentiation toward functional cells and low survival rates due to local inflammation. Recently, elegant advances in the design of novel biomaterials have been made to give promise to the use of biomimetic biomaterials to regulate various cell behaviors, including proliferation, differentiation and migration. Biomaterials could be tailored with multiple functionalities, e.g., stimuli-responsiveness. There is an emerging need to summarize recent advances in engineered biomaterials-mediated delivery and therapy of DSCs and their potential applications. Herein, we outlined the design of biomaterials for supporting DSCs and the host response to the transplantation.

Potential effects of biomaterials on macrophage function and their signalling pathways

The use of biomaterials in biomedicine and healthcare has increased in recent years. Macrophages are the primary immune cells that induce inflammation and tissue repair after implantation of biomaterials. Given that macrophages exhibit high heterogeneity and plasticity, the influence of biomaterials on macrophage phenotype should be considered a crucial evaluation criterion during the development of novel biomaterials. This review provides a comprehensive summary of the physicochemical, biological, and dynamic characteristics of biomaterials that drive the regulation of immune responses in macrophages. The mechanisms involved in the interaction between macrophages and biomaterials, including endocytosis, receptors, signalling pathways, integrins, inflammasomes and long non-coding RNAs, are summarised in this review. In addition, research prospects of the interaction between macrophages and biomaterials are discussed. An in-depth understanding of mechanisms underlying the spatiotemporal changes in macrophage phenotype induced by biomaterials and their impact on macrophage polarization can facilitate the identification and development of novel biomaterials with superior performance. These biomaterials may be used for tissue repair and regeneration, vaccine or drug delivery and immunotherapy.