Fibrillar biopolymer-based scaffolds to study macrophage-fibroblast crosstalk in wound repair

Beyond Encapsulation: Exploring Macrophage-Fibroblast Cross Talk in Implant-Induced Fibrosis

The foreign body response (FBR) and organ fibrosis are complex biological processes involving the interaction between macrophages and fibroblasts. Understanding the molecular mechanisms underlying macrophage-fibroblast cross talk is crucial for developing strategies to mitigate implant encapsulation, a major cause of implant failure. This article reviews the current knowledge on the role of macrophages and fibroblasts in the FBR and organ fibrosis, highlighting the similarities between these processes. The FBR is characterized by the formation of a fibrotic tissue capsule around the implant, leading to functional impairment. Various factors, including material properties such as surface chemistry, stiffness, and topography, influence the degree of encapsulation. Cross talk between macrophages and fibroblasts plays a critical role in both the FBR and organ fibrosis. However, the precise molecular mechanisms remain poorly understood. Macrophages secrete a wide range of cytokines that modulate fibroblast behavior such as abundant collagen deposition and myofibroblast differentiation. However, the heterogeneity of macrophages and fibroblasts and their dynamic behavior in different tissue environments add complexity to this cross talk. Experimental evidence from in vitro studies demonstrates the impact of material properties on macrophage cytokine secretion and fibroblast physiology. However, the correlation between in vitro response and in vivo encapsulation outcomes is not robust. Adverse outcome pathways (AOPs) offer a potential framework to understand and predict process complexity. AOPs describe causal relationships between measurable events leading to adverse outcomes, providing mechanistic insights for in vitro testing and predictive modeling. However, the development of an AOP for the FBR does require a comprehensive understanding of the molecular initiating events and key event relationships to identify which events are essential. In this article, we describe the current knowledge on macrophage-fibroblast cross talk in the FBR and discuss how targeted research can help build an AOP for implant-related fibrosis. Impact statement Biomaterials are widely used to manufacture medical devices, but implantation is associated with a foreign body response (FBR), which may lead to failure of the implants. Surface properties are related to FBR severity. In this review, we zoom in on the cross talk between the two key players, macrophages and fibroblasts, and propose the use of Adverse Outcome Pathways to decipher the causal link between material properties and the severity of the FBR. This approach will help increase a mechanistic understanding of the FBR and, thus, aid in the design of immunomodulatory implant surfaces.

The Influence of Sulfation Degree of Glycosaminoglycan-Functionalized 3D Collagen I Networks on Cytokine Profiles of In Vitro Macrophage-Fibroblast Cocultures

Cell-cell interactions between fibroblasts and immune cells, like macrophages, are influenced by interaction with the surrounding extracellular matrix during wound healing. In vitro hydrogel models that mimic and modulate these interactions, especially of soluble mediators like cytokines, may allow for a more detailed investigation of immunomodulatory processes. In the present study, a biomimetic extracellular matrix model based on fibrillar 3D collagen I networks with a functionalization with heparin or 6-ON-desulfated heparin, as mimics of naturally occurring heparan sulfate, was developed to modulate cytokine binding effects with the hydrogel matrix. The constitution and microstructure of the collagen I network were found to be stable throughout the 7-day culture period. A coculture study of primary human fibroblasts/myofibroblasts and M-CSF-stimulated macrophages was used to show its applicability to simulate processes of progressed wound healing. The quantification of secreted cytokines (IL-8, IL-10, IL-6, FGF-2) in the cell culture supernatant demonstrated the differential impact of glycosaminoglycan functionalization of the collagen I network. Most prominently, IL-6 and FGF-2 were shown to be regulated by the cell culture condition and network constitution, indicating changes in paracrine and autocrine cell-cell communication of the fibroblast-macrophage coculture. From this perspective, we consider our newly established in vitro hydrogel model suitable for mechanistic coculture analyses of primary human cells to unravel the role of extracellular matrix factors in key events of tissue regeneration and beyond.

A new direction in periodontitis treatment: biomaterial-mediated macrophage immunotherapy

Periodontitis is a chronic inflammation caused by a bacterial infection and is intimately associated with an overactive immune response. Biomaterials are being utilized more frequently in periodontal therapy due to their designability and unique drug delivery system. However, local and systemic immune response reactions driven by the implantation of biomaterials could result in inflammation, tissue damage, and fibrosis, which could end up with the failure of the implantation. Therefore, immunological adjustment of biomaterials through precise design can reduce the host reaction while eliminating the periodontal tissue's long-term chronic inflammation response. It is important to note that macrophages are an active immune system component that can participate in the progression of periodontal disease through intricate polarization mechanisms. And modulating macrophage polarization by designing biomaterials has emerged as a new periodontal therapy technique. In this review, we discuss the role of macrophages in periodontitis and typical strategies for polarizing macrophages with biomaterials. Subsequently, we discuss the challenges and potential opportunities of using biomaterials to manipulate periodontal macrophages to facilitate periodontal regeneration.

3D microenvironment attenuates simulated microgravity-mediated changes in T cell transcriptome

Human space travel and exploration are of interest to both the industrial and scientific community. However, there are many adverse effects of spaceflight on human physiology. In particular, there is a lack of understanding of the extent to which microgravity affects the immune system. T cells, key players of the adaptive immune system and long-term immunity, are present not only in blood circulation but also reside within the tissue. As of yet, studies investigating the effects of microgravity on T cells are limited to peripheral blood or traditional 2D cell culture that recapitulates circulating blood. To better mimic interstitial tissue, 3D cell culture has been well established for physiologically and pathologically relevant models. In this work, we utilize 2D cell culture and 3D collagen matrices to gain an understanding of how simulated microgravity, using a random positioning machine, affects both circulating and tissue-resident T cells. T cells were studied in both resting and activated stages. We found that 3D cell culture attenuates the effects of simulated microgravity on the T cells transcriptome and nuclear irregularities compared to 2D cell culture. Interestingly, simulated microgravity appears to have less effect on activated T cells compared to those in the resting stage. Overall, our work provides novel insights into the effects of simulated microgravity on circulating and tissue-resident T cells which could provide benefits for the health of space travellers.

Exosomes from human adipose-derived mesenchymal stromal/stem cells accelerate angiogenesis in wound healing: implication of the EGR-1/lncRNA-SENCR/DKC1/VEGF-A axis

Exosomes (Exos) extracted from human adipose mesenchymal stromal/stem cells (hAD-MSCs) have been reported as therapeutic tools for tissue repair, but how they regulate angiogenesis of endothelial cells remains unknown. In this study, hAD-MSCs were isolated, and early growth response factor-1, Smooth muscle and endothelial cell enriched migration/differentiation-associated long-noncoding RNA (lncRNA-SENCR), and vascular endothelial growth factor-A (VEGF-A) overexpression or knockdown was achieved. Exos extracted from hAD-MSCs (hADSC-Exos) were co-cultured with human umbilical vein endothelial cells (HUVECs) to detect the effects of EGR-1, lncRNA-SENCR, and VEGF-A on angiogenesis and the relationships between EGR-1, lncRNA-SENCR, Dyskerin pseudouridine synthase 1 (DKC1), and VEGF-A. An in vivo experiment verified the effect of hADSC-Exos on the wound healing process. hADSC-Exos substantially promoted the proliferation, migration, and angiogenesis of HUVECs, which could be reversed by short-hairpin RNA SENCR (shSENCR) transfection. hADSC-Exos had elevated expression of EGR-1, which bound to the lncRNA-SENCR promoter. The suppressive effect of Exo-shEGR1 on HUVECs was counteracted by SENCR overexpression. LncRNA-SENCR was shown to interact with DKC1. Overexpression of DKC1 or lncRNA-SENCR maintained stable VEGF-A expression. Overexpression of VEGF-A reversed the suppressive effect of shSENCR on HUVECs. Consistent results were obtained in mice in vivo. Overall, hADSC-Exo EGR-1 upregulates lncRNA-SENCR expression to activate the DKC1/VEGF-A axis, facilitating the wound-healing process by increasing angiogenesis.