Dermal fibroblast phagocytosis of apoptotic cells: A novel pathway for wound resolution

Application of Tendon-Derived Matrix and Carbodiimide Crosslinking Matures the Engineered Tendon-Like Proteome on Meltblown Scaffolds

Background: Tendon injuries are increasingly common and heal by fibrosis rather than scar-less regeneration. Tissue engineering seeks to improve repair using synthetic polymer scaffolds with biomimetic factors to enhance the regenerative potential. Methods: In this study, we compared three groups, namely, poly(lactic acid) (PLA) meltblown scaffolds, PLA meltblown scaffolds coated with tendon-derived matrix (TDM), and PLA meltblown scaffolds with carbodiimide crosslinked TDM (2.5:1:1 EDC:NHS:COOH ratio) (EDC-TDM) and determined their potential for engineered tendon development. We cultured human adipose stem cells (hASCs) for 28 days on meltblown scaffolds (n = 4-6/group) and measured tensile mechanical function, matrix synthesis, and matrix composition using biochemical assays and proteomics. Results: Coating PLA meltblown scaffolds with TDM improved yield stretch and stress at 28 days compared with PLA. Matrix synthesis rates for TDM or EDC-TDM were similar to PLA. Proteomic analysis revealed that hASCs produced a collagen-rich extracellular matrix, with many tendon-related matrix proteins. Coating scaffolds with TDM led to an increase in collagen type I whereas EDC-TDM scaffolds had an increase in glycoproteins and ECM regulators compared with other groups, consistent with increased maturity of the newly deposited matrix. Conclusions: TDM coating and crosslinking of meltblown scaffolds demonstrated matricellular benefits for the proteome of engineered tendon development but provided fewer clear benefits toward mechanical, biochemical, and rate of matrix accumulation than expected, and that previous work with electrospun scaffolds would suggest. However, electrospun scaffolds have different fiber structure and microarchitecture than meltblown, suggesting that further consideration of these differences and refinement of TDM application methods to meltblown scaffolds is required.

Antigen-presenting fibroblasts: emerging players in immune modulation and therapeutic targets

Antigen-presenting fibroblasts are a newly recognized subset that challenges the traditional view of these cells as mere structural components. Under pathological or environmental stimuli, fibroblasts acquire antigen-presenting capabilities through the expression of MHC-II molecules and co-stimulatory factors, enabling them to interact with T cells and modulate immune responses. These specialized fibroblasts have been identified across various tissues and diseases, where they play context-dependent roles, either amplifying immune dysregulation or contributing to immune homeostasis. This review synthesizes recent advances in understanding the origins, activation, and functions of antigen-presenting fibroblasts. It highlights their role in promoting pathogenic immune responses and offering therapeutic opportunities through targeted modulation. Advancing our understanding of antigen-presenting fibroblasts holds great promise for developing innovative approaches to immune modulation and therapy across a range of diseases.

Modulation of IFN-γ induced macrophage inflammatory responses via indomethacin-loaded NLCs for OA management

Macrophages are the main cells present in the synovial membrane. They play an important role in the development and progression of osteoarthritis (OA). After the establishment of the disease macrophages mostly adopt a pro-inflammatory secretory phenotype (OA phenotype) further inducing cartilage degradation. Indomethacin (IND) is a non-steroidal anti-inflammatory drug (NSAID) able to inhibit the synthesis of prostaglandins mediated by both cyclooxygenase isoforms depicting a potent anti-inflammatory capacity. However, the lack of specificity and short half-like of free drugs within the joint cavity limits its utility in controlling inflammation after intra-articular administration. This study aims at developing IND loaded glycosylated nanostructured lipid carriers (NLCs) to selectively target macrophages and promote their reprogramming to an anti-inflammatory phenotype. This approach focused on the local administration of the NLCs, offers a promising therapeutic strategy for treating OA by modulating the inflammatory environment within the joint. NLCs will be designed by combining experimental and in silico docking analyses, and thoroughly characterized to obtain drug delivery systems with high stability and suitable physicochemical properties. The proposed mannose-functionalized systems exhibited adequate particle sizes (≈ 70 nm) and positive surface charges (> 20 mV) to be efficiently retained in the joint cavity. Moreover, the developed NLCs demonstrated effective and specific uptake by OA-like macrophages leading to a significant decrease in the secretion of the pro-inflammatory cytokines IL-6, IL-8 and TNF-α similarly to the free drug. Therefore, these systems effectively reprogrammed OA-associated macrophages to adopt a more regenerative phenotype, offering a promising strategy for managing inflammation in OA.

Polyphenol hydroxytyrosol present olive oil improves skin wound healing of diabetic mice

The imbalance in oxidant production and chronic inflammation are the main mechanisms that lead to the detrimental effects of diabetes on skin wound healing. Thus, administration of antioxidants could improve diabetic wound healing. This study aimed to understand the effects of extra virgin olive oil (EVOO) or hydroxytyrosol (HT) in skin wound healing under diabetic conditions. Skin wounds in streptozotocin-induced diabetic mice were topically treated with HT. Some diabetic animals were fed with a diet rich in EVOO. Wounds were harvested 7 days later. In in vitro assays, fibroblasts and macrophages were treated with high levels of glucose and HT. The EVOO or HT promoted wound closure and collagen deposition in diabetic mouse wounds. The EVOO or HT reduced the number of infiltrated neutrophils, tumour necrosis factor-α, lipid peroxidation, and nuclear factor erythroid 2-related factor 2 in diabetic mouse wounds. The EVOO or HT also increased the number of macrophages with anti-inflammatory phenotype and interleukin-10 in diabetic mouse wounds. In the in vitro assays, HT promoted the fibroblast migration, collagen gel contraction, and switched macrophages to an anti-inflammatory phenotype under high glucose conditions. In conclusion, the diet supplementation with EVOO or topical application of HT promotes skin wound healing under diabetic conditions and can be a possible therapeutic tool for the treatment of those lesions.

Inflammation and Macrophage Loss Mark Increased Susceptibility in a Genetic Model of Acute Viral Infection-Induced Tissue Damage

M.R2k/b mice are identical to the MA/My parent strain aside from a 5.58-Mb C57L-derived region on chromosome 17 (Cmv5s) that causes increased susceptibility to acute murine CMV (MCMV) infection and the development of significant spleen tissue damage. Spleen pathology begins at the marginal zone (MZ), apparent by 2 d postinfection (dpi), and progresses throughout the red pulp by 4 dpi. To better understand how M.R2k/b mice respond to infection and how Cmv5s contributes to tissue damage in the spleen, we assessed the regulation of myeloid cells and inflammation during acute MCMV infection in MA/My and M.R2k/b mice. We found that Cmv5s drove increased neutrophil accumulation and cell death at the MZ, which corresponded with evidence of localized oxidative stress and increased overall spleen IL-6 and TGF-β1 early during infection. Further assessment of MCMV infection dynamics at the early MZ revealed infected SIGNR1+ MZ macrophages as the first apparent cell type lost during infection in these mice and the likely target of early neutrophil recruitment. Spleen macrophages were also identified as the mediators of differential spleen IL-6 and TGF-β1 between MA/My and M.R2k/b mice. Interrogation of MCMV progression past 2 dpi revealed substantial M.R2k/b F480+ red pulp macrophage loss along with buildup of oxidative stress and MZ macrophage debris that was not neutrophil dependent. Together we identify Cmv5s-driven macrophage loss and inflammation during acute MCMV infection corresponding with the spatial and temporal development of spleen tissue damage.

Apoptosis recognition receptors regulate skin tissue repair in mice

Apoptosis and clearance of apoptotic cells via efferocytosis are evolutionarily conserved processes that drive tissue repair. However, the mechanisms by which recognition and clearance of apoptotic cells regulate repair are not fully understood. Here, we use single-cell RNA sequencing to provide a map of the cellular dynamics during early inflammation in mouse skin wounds. We find that apoptotic pathways and efferocytosis receptors are elevated in fibroblasts and immune cells, including resident Lyve1+ macrophages, during inflammation. Interestingly, human diabetic foot wounds upregulate mRNAs for efferocytosis pathway genes and display altered efferocytosis signaling via the receptor Axl and its ligand Gas6. During early inflammation in mouse wounds, we detect upregulation of Axl in dendritic cells and fibroblasts via TLR3-independent mechanisms. Inhibition studies in vivo in mice reveal that Axl signaling is required for wound repair but is dispensable for efferocytosis. By contrast, inhibition of another efferocytosis receptor, Timd4, in mouse wounds decreases efferocytosis and abrogates wound repair. These data highlight the distinct mechanisms by which apoptotic cell detection coordinates tissue repair and provides potential therapeutic targets for chronic wounds in diabetic patients.

Microfibril-associated protein 5 and the regulation of skin scar formation

Many factors regulate scar formation, which yields a modified extracellular matrix (ECM). Among ECM components, microfibril-associated proteins have been minimally explored in the context of skin wound repair. Microfibril-associated protein 5 (MFAP5), a small 25 kD serine and threonine rich microfibril-associated protein, influences microfibril function and modulates major extracellular signaling pathways. Though known to be associated with fibrosis and angiogenesis in certain pathologies, MFAP5's role in wound healing is unknown. Using a murine model of skin wound repair, we found that MFAP5 is significantly expressed during the proliferative and remodeling phases of healing. Analysis of existing single-cell RNA-sequencing data from mouse skin wounds identified two fibroblast subpopulations as the main expressors of MFAP5 during wound healing. Furthermore, neutralization of MFAP5 in healing mouse wounds decreased collagen deposition and refined angiogenesis without altering wound closure. In vitro, recombinant MFAP5 significantly enhanced dermal fibroblast migration, collagen contractility, and expression of pro-fibrotic genes. Additionally, TGF-ß1 increased MFAP5 expression and production in dermal fibroblasts. Our findings suggest that MFAP5 regulates fibroblast function and influences scar formation in healing wounds. Our work demonstrates a previously undescribed role for MFAP5 and suggests that microfibril-associated proteins may be significant modulators of wound healing outcomes and scarring.

The critical role of apoptosis in mesenchymal stromal cell therapeutics and implications in homeostasis and normal tissue repair

Mesenchymal stromal cells (MSCs) have been extensively tested for the treatment of numerous clinical conditions and have demonstrated good safety but mixed efficacy. Although this outcome can be attributed in part to the heterogeneity of cell preparations, the lack of mechanistic understanding and tools to establish cell pharmacokinetics and pharmacodynamics, as well as the poorly defined criteria for patient stratification, have hampered the design of informative clinical trials. We and others have demonstrated that MSCs can rapidly undergo apoptosis after their infusion. Apoptotic MSCs are phagocytosed by monocytes/macrophages that are then reprogrammed to become anti-inflammatory cells. MSC apoptosis occurs when the cells are injected into patients who harbor activated cytotoxic T or NK cells. Therefore, the activation state of cytotoxic T or NK cells can be used as a biomarker to predict clinical responses to MSC treatment. Building on a large body of preexisting data, an alternative view on the mechanism of MSCs is that an inflammation-dependent MSC secretome is largely responsible for their immunomodulatory activity. We will discuss how these different mechanisms can coexist and are instructed by two different types of MSC "licensing": one that is cell-contact dependent and the second that is mediated by inflammatory cytokines. The varied and complex mechanisms by which MSCs can orchestrate inflammatory responses and how this function is specifically driven by inflammation support a physiological role for tissue stroma in tissue homeostasis, and it acts as a sensor of damage and initiator of tissue repair by reprogramming the inflammatory environment.

Fibroblast clearance of damaged tissue following laser ablation in engineered microtissues

Although the mechanisms underlying wound healing are largely preserved across wound types, the method of injury can affect the healing process. For example, burn wounds are more likely to undergo hypertrophic scarring than are lacerations, perhaps due to the increased underlying damage that needs to be cleared. This tissue clearance is thought to be mainly managed by immune cells, but it is unclear if fibroblasts contribute to this process. Herein, we utilize a 3D in vitro model of stromal wound healing to investigate the differences between two modes of injury: laceration and laser ablation. We demonstrate that laser ablation creates a ring of damaged tissue around the wound that is cleared by fibroblasts prior to wound closure. This process is dependent on ROCK and dynamin activity, suggesting a phagocytic or endocytic process. Transmission electron microscopy of fibroblasts that have entered the wound area reveals large intracellular vacuoles containing fibrillar extracellular matrix. These results demonstrate a new model to study matrix clearance by fibroblasts in a 3D soft tissue. Because aberrant wound healing is thought to be caused by an imbalance between matrix degradation and production, this model, which captures both aspects, will be a valuable addition to the study of wound healing.

Tracing the evolutionary history of blood cells to the unicellular ancestor of animals

Blood cells are thought to have emerged as phagocytes in the common ancestor of animals followed by the appearance of novel blood cell lineages such as thrombocytes, erythrocytes, and lymphocytes, during evolution. However, this speculation is not based on genetic evidence and it is still possible to argue that phagocytes in different species have different origins. It also remains to be clarified how the initial blood cells evolved; whether ancient animals have solely developed de novo programs for phagocytes or they have inherited a key program from ancestral unicellular organisms. Here, we traced the evolutionary history of blood cells, and cross-species comparison of gene expression profiles revealed that phagocytes in various animal species and Capsaspora (C.) owczarzaki, a unicellular organism, are transcriptionally similar to each other. We also found that both phagocytes and C. owczarzaki share a common phagocytic program, and that CEBPα is the sole transcription factor highly expressed in both phagocytes and C. owczarzaki. We further showed that the function of CEBPα to drive phagocyte program in nonphagocytic blood cells has been conserved in tunicate, sponge, and C. owczarzaki. We finally showed that, in murine hematopoiesis, repression of CEBPα to maintain nonphagocytic lineages is commonly achieved by polycomb complexes. These findings indicate that the initial blood cells emerged inheriting a unicellular organism program driven by CEBPα and that the program has also been seamlessly inherited in phagocytes of various animal species throughout evolution.

Angiogenesis in Wound Repair: Too Much of a Good Thing?

Angiogenesis, or the growth of new blood vessels from the preexisting vasculature, is a visible and important component of wound repair. When tissue damage occurs, disruption of the vasculature structure leads to hypoxia. The restoration of normoxia is essential for appropriate and durable tissue repair. Angiogenesis in wounds is regulated by endogenous proangiogenic mediators, which cause rapid growth of a new vascular bed that is much denser than that of normal tissue. Such rapid growth of the capillary bed results in capillaries that are abnormal, and the newly formed vessels are tortuous, dilated, and immature. During wound resolution, this substantial neocapillary bed is pruned back to normal density with attendant maturation. Many poorly healing wounds, including nonhealing ulcers and scars, exhibit an aberrant angiogenic response. The fine-tuning of capillary regrowth in wounds is an area of significant therapeutic potential.

Understanding the Phagocytosis of Particles: the Key for Rational Design of Vaccines and Therapeutics

A robust comprehension of phagocytosis is crucial for understanding its importance in innate immunity. A detailed description of the molecular mechanisms that lead to the uptake and clearance of endogenous and exogenous particles has helped elucidate the role of phagocytosis in health and infectious or autoimmune diseases. Furthermore, knowledge about this cellular process is important for the rational design and development of particulate systems for the administration of vaccines or therapeutics. Depending on these specific applications and the required biological responses, particles must be designed to encourage or avoid their phagocytosis and prolong their circulation time. Functionalization with specific polymers or ligands and changes in the size, shape, or surface of particles have important effects on their recognition and internalization by professional and nonprofessional phagocytes and have a major influence on their fate and safety. Here, we review the phagocytosis of particles intended to be used as carrier or delivery systems for vaccines or therapeutics, the cells involved in this process depending on the route of administration, and the strategies employed to obtain the most desirable particles for each application through the manipulation of their physicochemical characteristics. We also offer a view of the challenges and potential opportunities in the field and give some recommendations that we expect will enable the development of improved approaches for the rational design of these systems.

Modulation of Cell Behavior by 3D Biocompatible Hydrogel Microscaffolds with Precise Configuration

Three-dimensional (3D) micronano structures have attracted much attention in tissue engineering since they can better simulate the microenvironment in vivo. Two-photon polymerization (TPP) technique provides a powerful tool for printing arbitrary 3D structures with high precision. Here, the desired 3D biocompatible hydrogel microscaffolds (3D microscaffold) with structure design referring to fibroblasts L929 have been fabricated by TPP technology, particularly considering the relative size of cell seed (cell suspension), spread cell, strut and strut spacing of scaffold. Modulation of the cell behavior has been studied by adjusting the porosity from 69.7% to 89.3%. The cell culture experiment results reveal that the obvious modulation of F-actin can be achieved by using the 3D microscaffold. Moreover, cells on 3D microscaffolds exhibit more lamellipodia than those on 2D substrates, and thus resulting in a more complicated 3D shape of single cell and increased cell surface. 3D distribution can be also achieved by employing the designed 3D microscaffold, which would effectively improve the efficiency of information exchange and material transfer. The proposed protocol enables us to better understand the cell behavior in vivo, which would provide high prospects for the further application in tissue engineering.