Human nail bed extracellular matrix facilitates bone regeneration via macrophage polarization mediated by the JAK2/STAT3 pathway

Decellularized diseased tissues: current state-of-the-art and future directions

Decellularized matrices derived from diseased tissues/organs have evolved in the most recent years, providing novel research perspectives for understanding disease occurrence and progression and providing accurate pseudo models for developing new disease treatments. Although decellularized matrix maintaining the native composition, ultrastructure, and biomechanical characteristics of extracellular matrix (ECM), alongside intact and perfusable vascular compartments, facilitates the construction of bioengineered organ explants in vitro and promotes angiogenesis and tissue/organ regeneration in vivo, the availability of healthy tissues and organs for the preparation of decellularized ECM materials is limited. In this paper, we review the research advancements in decellularized diseased matrices. Considering that current research focuses on the matrices derived from cancers and fibrotic organs (mainly fibrotic kidney, lungs, and liver), the pathological characterizations and the applications of these diseased matrices are mainly discussed. Additionally, a contrastive analysis between the decellularized diseased matrices and decellularized healthy matrices, along with the development in vitro 3D models, is discussed in this paper. And last, we have provided the challenges and future directions in this review. Deep and comprehensive research on decellularized diseased tissues and organs will promote in-depth exploration of source materials in tissue engineering field, thus providing new ideas for clinical transformation.

Matrisomal components involved in regenerative wound healing in axolotl and Acomys: implications for biomaterial development

Achieving regeneration in humans has been a long-standing goal of many researchers. Whereas amphibians like the axolotl (Ambystoma mexicanum) are capable of regenerating whole organs and even limbs, most mammals heal their wounds via fibrotic scarring. Recently, the African spiny mouse (Acomys sp.) has been shown to be injury resistant and capable of regenerating several tissue types. A major focal point of research with Acomys has been the identification of drivers of regeneration. In this search, the matrisome components related to the extracellular matrix (ECM) are often overlooked. In this review, we compare Acomys and axolotl skin wound healing and blastema-mediated regeneration by examining their wound healing responses and comparing the expression pattern of matrisome genes, including glycosaminoglycan (GAG) related genes. The goal of this review is to identify matrisome genes that are upregulated during regeneration and could be potential candidates for inclusion in pro-regenerative biomaterials. Research papers describing transcriptomic or proteomic coverage of either skin regeneration or blastema formation in Acomys and axolotl were selected. Matrisome and GAG related genes were extracted from each dataset and the resulting lists of genes were compared. In our analysis, we found several genes that were consistently upregulated, suggesting possible involvement in regenerative processes. Most of the components have been implicated in regulation of cell behavior, extracellular matrix remodeling and wound healing. Incorporation of such pro-regenerative factors into biomaterials may help to shift pro-fibrotic processes to regenerative responses in treated wounds.

Biomimetic hydrogel derived from decellularized dermal matrix facilitates skin wounds healing

Cutaneous wound healing affecting millions of people worldwide represents an unsolvable clinical issue that is frequently challenged by scar formation with dramatical pain, impaired mobility and disfigurement. Herein, we prepared a kind of light-sensitive decellularized dermal extracellular matrix-derived hydrogel with fast gelling performance, biomimetic porous microstructure and abundant bioactive functions. On account of its excellent cell biocompatibility, this ECM-derived hydrogel could induce a marked cellular infiltration and enhance the tube formation of HUVECs. In vivo experiments based upon excisional wound splinting model showed that the hydrogel prominently imparted skin wound healing, as evidenced by notably increased skin appendages and well-organized collagen expression, coupled with significantly enhanced angiogenesis. Moreover, the skin regeneration mediated by this bioactive hydrogel was promoted by an accelerated M1-to-M2 macrophage phenotype transition. Consequently, the decellularized dermal matrix-derived bioactive hydrogel orchestrates the entire skin healing microenvironment to promote wound healing and will be of high value in treatment of cutaneous wound healing. As such, this biomimetic ddECMMA hydrogel provides a promising versatile opinion for the clinical translation.

The immunomodulatory effects of RNA-based biomaterials on bone regeneration

The use of RNA as therapeutic agents is a visionary idea in contemporary medicine. Some forms of RNA can modulate the immune response of the host to enhance tissue regeneration events such as osteogenesis. Herein, RNA molecules commercially available for immunomodulatory applications (imRNA) were used to prepare biomaterials for bone regeneration. The polyanionic imRNA stabilized calcium phosphate ionic clusters to produce imRNA-ACP that had the capacity to mineralize the intrafibrillar compartments of collagen fibrils. For the first time, it was shown that incorporating imRNA-ACP into collagen scaffolds resulted in rapid new bone formation in cranial defects of mice. Both in vivo and in vitro results demonstrated that macrophage polarization was highly-sensitive to the imRNA-ACP containing collagen scaffolds. Macrophages were polarized into the anti-inflammatory M2 phenotype that produced anti-inflammation cytokines and growth factors. The favorable osteoimmunological microenvironment created by the scaffolds prevented their immunorejection and facilitated osteogenesis. The potential of RNA in creating immunomodulatory biomaterials has been underestimated in the past. The overall aim of this study was to explore the potential application of imRNA-based biomaterials in bone tissue engineering, with the competitive edge of facile synthesis and excellent biocompatibility. STATEMENT OF SIGNIFICANCE: In this work, commercially available RNA extracted from bovine spleens for immunomodulatory applications (imRNA) were used to stabilize amorphous calcium phosphate (ACP) and induce mineralization within collagen fibrils. Incorporation of imRNA-ACP into collagen scaffolds regenerated new bone in-situ. Because of its immunomodulatory effects, the imRNA-ACP that was incorporated into collagen scaffolds modulated the local immune environment of murine cranial defects by altering the macrophage phenotype through JAK2/STAT3 signaling pathway. The novelty of this work existed in the discovery of RNA's potential in creating immunomodulatory biomaterials. With the competitive edge of facile synthesis and excellent biocompatibility, the imRNA-based biomaterials are potentially useful for future bone tissue engineering applications.

Criteria, Challenges, and Opportunities for Acellularized Allogeneic/Xenogeneic Bone Grafts in Bone Repairing

As bone grafts become more commonly needed by patients and as donors become scarcer, acellularized bone grafts (ABGs) are becoming more popular for restorative purposes. While autogeneic grafts are reliable as a gold standard, allogeneic and xenogeneic ABGs have been shown to be of particular interest due to the limited availability of autogeneic resources and reduced patient well-being in long-term surgeries. Because of the complete similarity of their structures with native bone, excellent mechanical properties, high biocompatibility, and similarities of biological behaviors (osteoinductive and osteoconductive) with local bones, successful outcomes of allogeneic and xenogeneic ABGs in both in vitro and in vivo research have raised hopes of repairing patients' bone injuries in clinical applications. However, clinical trials have been delayed due to a lack of standardized protocols pertaining to acellularization, cell seeding, maintenance, and diversity of ABG evaluation criteria. This study sought to uncover these factors by exploring the bone structures, ossification properties of ABGs, sources, benefits, and challenges of acellularization approaches (physical, chemical, and enzymatic), cell loading, and type of cells used and effects of each of the above items on the regenerative technologies. To gain a perspective on the repair and commercialization of products before implementing new research activities, this study describes the differences between ABGs created by various techniques and methods applied to them. With a comprehensive understanding of ABG behavior, future research focused on treating bone defects could provide a better way to combine the treatment approaches needed to treat bone defects.

Immunomodulatory strategies for bone regeneration: A review from the perspective of disease types

Tissue engineering strategies for treating bone loss to date have largely focused on targeting stem cells or vascularization. Immune cells, including macrophages and T cells, can also indirectly enhance bone healing via cytokine secretion to interact with other bone niche cells. Bone niche cues and local immune environment vary depending on anatomical location, size of defects and disease types. As such, it is critical to evaluate the role of the immune system in the context of specific bone niche and different disease types. This review focuses on immunomodulation research for bone applications using biomaterials and cell-based strategies, with a unique perspective from different disease types. We first reviewed applications for prolonging orthopaedic implant lifetime and enhancing fracture healing, two clinical challenges where immunomodulatory strategies were initially developed for orthopedic applications. We then reviewed recent research progress in harnessing immunomodulatory strategies for regenerating critical-sized, long bone or cranial bone defects, and treating osteolytic bone diseases. Remaining gaps in knowledge, future directions and opportunities were also discussed.

Ganoderma atrum polysaccharide modulates the M1/M2 polarization of macrophages linked to the Notch signaling pathway

Macrophages could be polarized into two major sub-populations including classically activated (M1) and alternatively activated (M2) macrophages. The present study aimed to investigate the effects of Ganoderma atrum polysaccharide (PSG-1) on the regulation of macrophage polarization and further explored the associated molecular mechanisms. In this work, a lipopolysaccharide (LPS) plus IFN-γ and IL-4 were used to establish an in vitro model of two extreme states, namely pro-inflammatory M1 and anti-inflammatory M2. The results showed that PSG-1 had effects on the behavior modification of macrophage polarization by reducing CD80 expression in LPS plus IFN-γ-induced M1 macrophages, and attenuating CD23 expression in IL-4-induced M2 macrophages. Further study revealed that PSG-1-modulated M1 and M2 macrophage polarization was associated with controlling phagocytosis, reactive oxygen species generation, NO and cytokines (IL-1β, IL-6 and IL-10). Subsequently, the treatment of M1 macrophages with a combination of PSG-1 and a Notch-response inhibitor (DAPT) did not alter CD80 expression compared with DAPT alone, while several pro-inflammatory parameters were considerably decreased, suggesting that the Notch signaling pathway partly mediated the effects of PSG-1 on modulating macrophage polarization. Together, our findings suggested that PSG-1 could repair the chaos in the polarization of M1/M2 macrophages and the molecular mechanism linked to the Notch signaling pathway.

To regenerate or not to regenerate: Vertebrate model organisms of regeneration-competency and -incompetency

Why only certain species can regenerate their appendages (e.g. tails and limbs) remains one of the biggest mysteries of nature. Unlike anuran tadpoles and salamanders, humans and other mammals cannot regenerate their limbs, but can only regrow lost digit tips under specific circumstances. Numerous hypotheses have been postulated to explain regeneration-incompetency in mammals. By studying model organisms that show varying regenerative abilities, we now have more opportunities to uncover what contributes to regeneration-incompetency and functionally test which perturbations restore appendage regrowth. Particularly, Xenopus laevis tail and limb, and mouse digit tip model systems exhibit naturally occurring variations in regenerative capacities. Here, we discuss major hypotheses that are suggested to contribute to regeneration-incompetency, and how species with varying regenerative abilities reflect on these hypotheses.

Decellularised Human Umbilical Artery as a Vascular Graft Elicits Minimal Pro-Inflammatory Host Response Ex Vivo and In Vivo

Small diameter (<6 mm) vessel grafts still pose a challenge for scientists worldwide. Decellularised umbilical artery (dUA) remains promising as small diameter tissue engineered vascular graft (TEVG), yet their immunogenicity remains unknown. Herein, we evaluated the host immune responses, with a focus on the innate part, towards human dUA implantation in mice, and confirmed our findings in an ex vivo allogeneic human setup. Overall, we did not observe any differences in the number of circulating white blood cells nor the number of monocytes among three groups of mice (1) dUA patch; (2) Sham; and (3) Mock throughout the study (day -7 to 28). Likewise, we found no difference in systemic inflammatory and anti-inflammatory cytokine levels between groups. However, a massive local remodelling response with M2 macrophages were observed in the dUA at day 28, whereas M1 macrophages were less frequent. Moreover, human monocytes from allogeneic individuals were differentiated into macrophages and exposed to lyophilised dUA to maximize an eventual M1 response. Yet, dUA did not elicit any immediate M1 response as determined by the absence of CCR7 and CXCL10. Together this suggests that human dUA elicits a minimal pro-inflammatory response further supporting its use as a TEVG in an allogeneic setup.

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.

A finger on the pulse of regeneration: insights into the cellular mechanisms of adult digit tip regeneration

In mammals, multi-tissue regeneration is largely restricted to the distal portion of the digit tip and involves the formation of a blastema, a transient, proliferating cell mass that reforms the diverse tissues of the digit. Historically little was known about the mammalian blastema but with recent advances in single cell transcriptomic approaches and genetic lineage tracing, a more precise understanding of this critical structure has begun to emerge. In this review we summarise the cellular mechanisms underlying adult mammalian digit tip regeneration. We posit that understanding how some mammals naturally regenerate complex tissues will lead to strategies for enhancing regenerative abilities in humans.