Combined stimulation with cyclic stretching and hypoxia increases production of matrix metalloproteinase-9 and cytokines by macrophages

Modulation of macrophages by biophysical cues in health and beyond

Macrophages play a key role in tissue development and homeostasis, innate immune defence against microbes or tumours, and restoring homeostasis through tissue regeneration following infection or injury. The ability to adopt such diverse functions is due to their heterogeneous nature, which is driven largely by their developmental origin and their response to signals they encounter from the microenvironment. The most well-characterized signals driving macrophage phenotype and function are biochemical and metabolic. However, the way macrophages sense and respond to their extracellular biophysical environment is becoming increasingly recognized in the field of mechano-immunology. These biophysical cues can be signals from tissue components, such as the composition and charge of extracellular matrix or topography, elasticity, and stiffness of the tissue surrounding cells; and mechanical forces such as shear stress or stretch. Macrophages are important in determining whether a disease resolves or becomes chronic. Ageing and diseases such as cancer or fibrotic disorders are associated with significant changes in the tissue biophysical environment, and this provides signals that integrate with those from biochemical and metabolic stimuli to ultimately dictate the overall function of macrophages. This review provides a brief overview of macrophage polarization, followed by a selection of commonly recognized physiological and applied biophysical stimuli impacting macrophage activity, and the potential signalling mechanisms driving downstream responses. The effects of biophysical cues on macrophages' function in homeostasis and disease and the associated clinical implications are also highlighted.

Decellularized scaffold and its elicited immune response towards the host: the underlying mechanism and means of immunomodulatory modification

The immune response of the host towards a decellularized scaffold is complex. Not only can a number of immune cells influence this process, but also the characteristics, preparation and modification of the decellularized scaffold can significantly impact this reaction. Such factors can, together or alone, trigger immune cells to polarize towards either a pro-healing or pro-inflammatory direction. In this article, we have comprehensively reviewed factors which may influence the immune response of the host towards a decellularized scaffold, including the source of the biomaterial, biophysical properties or modifications of the scaffolds with bioactive peptides, drugs and cytokines. Furthermore, the underlying mechanism has also been recapitulated.

Macrophage-stroma interactions in fibrosis: biochemical, biophysical, and cellular perspectives

Fibrosis results from aberrant wound healing and is characterized by an accumulation of extracellular matrix, impairing the function of an affected organ. Increased deposition of extracellular matrix proteins, disruption of matrix degradation, but also abnormal post-translational modifications alter the biochemical composition and biophysical properties of the tissue microenvironment - the stroma. Macrophages are known to play an important role in wound healing and tissue repair, but the direct influence of fibrotic stroma on macrophage behaviour is still an under-investigated element in the pathogenesis of fibrosis. In this review, the current knowledge on interactions between macrophages and (fibrotic) stroma will be discussed from biochemical, biophysical, and cellular perspectives. Furthermore, we provide future perspectives with regard to how macrophage-stroma interactions can be examined further to ultimately facilitate more specific targeting of these interactions in the treatment of fibrosis. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Biophysical regulation of macrophages in health and disease

Macrophages perform critical functions for homeostasis and immune defense in tissues throughout the body. These innate immune cells are capable of recognizing and clearing dead cells and pathogens, and orchestrating inflammatory and healing processes that occur in response to injury. In addition, macrophages are involved in the progression of many inflammatory diseases including cardiovascular disease, fibrosis, and cancer. Although it has long been known that macrophages respond dynamically to biochemical signals in their microenvironment, the role of biophysical cues has only recently emerged. Furthermore, many diseases that involve macrophages are also characterized by changes to the tissue biophysical environment. This review will discuss current knowledge about the effects of biophysical cues including matrix stiffness, material topography, and applied mechanical forces, on macrophage behavior. We will also describe the role of molecules that are known to be important for mechanotransduction, including adhesion molecules, ion channels, as well as nuclear mediators such as transcription factors, scaffolding proteins, and epigenetic regulators. Together, this review will illustrate a developing role of biophysical cues in macrophage biology, and also speculate upon molecular targets that may potentially be exploited therapeutically to treat disease.

Mechanical Role of Nesprin-1-Mediated Nucleus-Actin Filament Binding in Cyclic Stretch-Induced Fibroblast Elongation

The intracellular mechanical link tethering the nucleus to the cytoskeleton has been suggested to be the linker of the nucleoskeleton and cytoskeleton (LINC) complex. Previous studies have reported that knockdown of nesprin-1, a component of the LINC complex that directly binds to actin filaments, suppresses cellular morphological response to mechanical stimuli. The relation between nesprin-1 knockdown and cellular morphological changes, however, remains unclear. In this study, we examined the mechanical role of nucleus-actin filament binding in morphological changes of fibroblasts exposed to cyclic stretching. After exposure to 10% cyclic stretching for 6 h, fibroblasts transfected with nesprin-1-specific small interfering RNA showed fewer elongated shapes compared with non-transfected cells. To further examine the mechanical role of the nucleus and nucleus-bound actin filaments, we applied cyclic stretching to fibroblasts treated with Trichostatin A (TSA), which decreases nuclear stiffness and thereby reduces nucleus-binding actin filament tension. TSA-treatment was found to induce more rounded cellular shapes than those of non-treated cells under both static and cyclic stretching conditions. These results suggest that the tension of nucleus-bound actin filaments plays an important role in the formation of elongated fibroblasts under cyclic stretching and that nesprin-1 knockdown causes a decrease of tension in nucleus-associated actin filaments.

Combined effects of interleukin-1β and cyclic stretching on metalloproteinase expression in corneal fibroblasts in vitro

Background

Corneal tensile strain increases if the cornea becomes thin or if intraocular pressure increases. However, the effects of mechanical stress on extracellular matrix (ECM) remodelling in the corneal repair process and the corneal anomalies are unknown.

Methods

In this study, the combined effects of interleukin-1β (IL-1β) on matrix metalloproteinases (MMPs) in corneal fibroblasts under cyclic stretching were investigated in vitro. Cultured rabbit corneal fibroblasts were subjected to 5, 10 or 15 % cyclic equibiaxial stretching at 0.1 Hz for 36 h in the presence of IL-1β. Conditioned medium was harvested for the analysis of MMP2 and MMP9 protein production using the gelatin zymography and western blot techniques.

Results and conclusions

Cyclic equibiaxial stretching changed the cell morphology by increasing the contractility of F-actin fibres. IL-1β alone induced the expression of MMP9 and increased the production of MMP2, and 5 % stretching alone decreased the production of MMP2, which indicates that a low stretching magnitude can reduce ECM degradation. In the presence of IL-1β, 5 and 10 % stretching increased the production of MMP2, whereas 15 % stretching increased the production of MMP9. These results indicate that MMP expression is enhanced by cyclic mechanical stimulation in the presence of IL-1β, which is expected to contribute to corneal ECM degradation, leading to the development of post-refractive surgery keratectasia.

Low oxygen tension increased fibronectin fragment induced catabolic activities--response prevented with biomechanical signals

Introduction

The inherent low oxygen tension in normal cartilage has implications on inflammatory conditions associated with osteoarthritis (OA). Biomechanical signals will additionally contribute to changes in tissue remodelling and influence the inflammatory response. In this study, we investigated the combined effects of oxygen tension and fibronectin fragment (FN-f) on the inflammatory response of chondrocytes subjected to biomechanical signals.

Methods

Chondrocytes were cultured under free-swelling conditions at 1%, 5% and 21% oxygen tension or subjected to dynamic compression in an ex vivo 3D/bioreactor model with 29 kDa FN-f, interleukin-1beta (IL-1β) and/or the nitric oxide synthase (NOS) inhibitor for 6 and 48 hours. Markers for catabolic activity (NO, PGE₂), tissue remodelling (GAG, MMPs) and cytokines (IL-1β, IL-6 and TNFα) were quantified by biochemical assay. Aggrecan, collagen type II, iNOS and COX-2 gene expression were examined by real-time quantitative PCR. Two-way ANOVA and a post hoc Bonferroni-corrected t-test were used to analyse data.

Results

Both FN-fs and IL-1β increased NO, PGE₂ and MMP production (all P < 0.001). FN-f was more active than IL-1β with greater levels of NO observed at 5% than 1% or 21% oxygen tension (P < 0.001). Whilst FN-f reduced GAG synthesis at all oxygen tension, the effect of IL-1β was significant at 1% oxygen tension. In unstrained constructs, treatment with FN-f or IL-1β increased iNOS and COX-2 expression and reduced aggrecan and collagen type II (all P < 0.001). In unstrained constructs, FN-f was more effective than IL-1β at 5% oxygen tension and increased production of NO, PGE₂, MMP, IL-1β, IL-6 and TNFα. At 5% and 21% oxygen tension, co-stimulation with compression and the NOS inhibitor abolished fragment or cytokine-induced catabolic activities and restored anabolic response.

Conclusions

The present findings revealed that FN-fs are more potent than IL-1β in exerting catabolic effects dependent on oxygen tension via iNOS and COX-2 upregulation. Stimulation with biomechanical signals abolished catabolic activities in an oxygen-independent manner and NOS inhibitors supported loading-induced recovery resulting in reparative activities. Future investigations will utilize the ex vivo model as a tool to identify key targets and therapeutics for OA treatments.

Interleukin-6-signal transducer and activator of transcription-3 signaling mediates aortic dissections induced by angiotensin II via the T-helper lymphocyte 17-interleukin 17 axis in C57BL/6 mice

OBJECTIVE

Dysregulated angiotensin II (Ang II) signaling induces local vascular interleukin-6 (IL-6) secretion, producing leukocyte infiltration and life-threatening aortic dissections. Precise mechanisms by which IL-6 signaling induces leukocyte recruitment remain unknown. T-helper 17 lymphocytes (Th17) have been implicated in vascular pathology, but their role in the development of aortic dissections is poorly understood. Here, we tested the relationship of IL-6-signal transducer and activator of transcription-3 signaling with Th17-induced inflammation in the formation of Ang II-induced dissections in C57BL/6 mice.

APPROACH AND RESULTS

Ang II infusion induced aortic dissections and CD4(+)-interleukin 17A (IL-17A)-expressing Th17 cell accumulation in C57BL/6 mice. A blunted local Th17 activation, macrophage recruitment, and reduced incidence of aortic dissections were seen in IL-6(-/-) mice. To determine the pathological roles of Th17 lymphocytes, we treated Ang II-infused mice with IL-17A-neutralizing antibody or infused Ang II in genetically deficient IL-17A mice and found decreased aortic chemokine monocytic chemotactic protein-1 production and macrophage recruitment, leading to a reduction in aortic dissections. This effect was independent of blood pressure in IL-17A-neutralizing antibody experiment. Application of a cell-permeable signal transducer and activator of transcription-3 inhibitor to downregulate the IL-6 pathway decreased aortic dilation and Th17 cell recruitment. We also observed increased aortic Th17 infiltration and IL-17 mRNA expression in patients with thoracic aortic dissections. Finally, we found that Ang II-mediated aortic dissections occurred independent of blood pressure changes.

CONCLUSIONS

Our results indicate that the IL-6-signal transducer and activator of transcription-3 signaling pathway converges on Th17 recruitment and IL-17A signaling upstream of macrophage recruitment, mediating aortic dissections.