Assessing the advantages of 3D bioprinting and 3D spheroids in deciphering the osteoarthritis healing mechanism using human chondrocytes and polarized macrophages

The molecular niche of an osteoarthritic microenvironment comprises the native chondrocytes, the circulatory immune cells, and their respective inflammatory mediators. Although M2 macrophages infiltrate the joint tissue during osteoarthritis (OA) to initiate cartilage repair, the mechanistic crosstalk that dwells underneath is still unknown. Our study established a co-culture system of human OA chondrocytes and M2 macrophages in 3D spheroids and 3D bioprinted silk-gelatin constructs. It is already well established that Silk fibroin-gelatin bioink supports chondrogenic differentiation due to upregulation of the Wnt/β-catenin pathway. Additionally, the presence of anti-inflammatory M2 macrophages significantly upregulated the expression of chondrogenic biomarkers (COL-II, ACAN) with an attenuated expression of the chondrocyte hypertrophy (COL-X), chondrocyte dedifferentiation (COL-I) and matrix catabolism (MMP-1 and MMP-13) genes even in the absence of the interleukins. Furthermore, the 3D bioprinted co-culture model displayed an upper hand in stimulating cartilage regeneration and OA inhibition than the spheroid model, underlining the role of silk fibroin-gelatin in encouraging chondrogenesis. Additionally, the 3D bioprinted silk-gelatin constructs further supported the maintenance of stable anti-inflammatory phenotype of M2 macrophage. Thus, the direct interaction between the primary OAC and M2 macrophages in the 3D context, along with the release of the soluble anti-inflammatory factors by the M2 cells, significantly contributed to a better understanding of the molecular mechanisms responsible for immune cell-mediated OA healing.

Immune Privileges as a Result of Mutual Regulation of Immune and Stem Systems

Immune privileges of cancer stem cells is a well-known and widely studied problem, as presence of such cells in tumors is associated with refractoriness, recurrence, and metastasis. Accumulating evidence also suggests presence of immune privileges in non-pathological stem cells in addition to their other defense mechanisms against damaging factors. This similarity between pathological and normal stem cells raises the question of why stem cells have such a potentially dangerous property. Regulation of vital processes of autoimmunity control and regeneration realized through interactions between immune cells, stem cells, and their microenvironment are reviewed in this work as causes of formation of the stem cell immune privilege. Deep mutual integration between regulations of stem and immune cells is noted. Considering diversity and complexity of mutual regulation of stem cells, their microenvironment, and immune system, I suggest the term "stem system".

A Fresh Glimpse into Cartilage Immune Privilege

The increasing prevalence of degenerative cartilage disorders in young patients is a growing public concern worldwide. Cartilage's poor innate regenerative capacity has inspired the exploration and development of cartilage replacement treatments such as tissue-engineered cartilages and osteochondral implants as potential solutions to cartilage loss. The clinical application of tissue-engineered implants is hindered by the lack of long-term follow-up demonstrating efficacy, biocompatibility, and bio-integration. The historically reported immunological privilege of cartilage tissue was based on histomorphological observations pointing out the lack of vascularity and the presence of a tight extracellular matrix. However, clinical studies in humans and animals do not unequivocally support the immune-privilege theory. More in-depth studies on cartilage immunology are needed to make clinical advances such as tissue engineering more applicable. This review analyzes the literature that supports and opposes the concept that cartilage is an immune-privileged tissue and provides insight into mechanisms conferring various degrees of immune privilege to other, more in-depth studied tissues such as testis, eyes, brain, and cancer.

Crosstalk between immune cells and bone cells or chondrocytes

The term "osteoimmunology" was coined to denote the bridge between the immune system and the skeletal system. Osteoimmunology is interdisciplinary, and a full understanding and development of this "bridge" will provide an in-depth understanding of the switch between body health and disease development. B lymphocytes can promote the maturation and differentiation of osteoclasts, and osteoclasts have a negative feedback effect on B lymphocytes. Different subtypes of T lymphocytes regulate osteoclasts in different directions. T lymphocytes have a two-way regulatory effect on osteoblasts, while B lymphocytes have minimal regulatory effects on osteoblasts. In contrast, osteoblasts can promote the differentiation and maturation of T lymphocytes and B lymphocytes. Different immune cells have different effects on chondrocytes; some cooperate with each other, while some antagonize each other. In a healthy adult body, bone resorption and bone formation are in a dynamic balance under the action of multiple mechanisms. In this review, we summarize the interactions and key signaling molecular mechanisms between each type of cell in the immune system and the skeletal system.

Repopulation of decellularised articular cartilage by laser-based matrix engraving

BACKGROUND

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

METHODS

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

FINDINGS

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

INTERPRETATION

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

FUNDING

Austrian Research Promotion Agency FFG ("CartiScaff" #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08).

Repopulation of decellularised articular cartilage by laser-based matrix engraving

Background

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

Methods

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

Findings

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

Interpretation

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

Funding

Austrian Research Promotion Agency FFG (“CartiScaff” #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08)

Controlling the Phenotype of Macrophages Promotes Maturation of Tissue-Engineered Cartilage

Tissue reactions after transplantation can affect the maturation and prognosis of the transplanted engineered tissue in regenerative medicine. Since macrophages are broadly subdivided into two major phenotypes, inflammatory (M1) and anti-inflammatory/wound healing (M2), in this study, we examined the properties of macrophages in transplantation of tissue-engineered cartilage, to clarify their effects on cartilage maturation. Human chondrocytes were embedded in a poly-L-lactic acid scaffold, which was transplanted subcutaneously on the back in athymic mice. When the constructs were analyzed by real-time polymerase chain reaction, interleukin 1 expression was detectable at 4 days, and it reached a peak at 7 days. Interleukin 6 expression was increased at 7 to 11 days, suggesting that M1 macrophages were abundant around this time. On the other hand, expression of markers for M2 macrophages occurred rather later, with Fizz and Ym1 expression peaking at around 11 to 14 days, possibly indicating that polarization of macrophages in tissue-engineered cartilage could shift from M1 to M2 around 11 days after transplantation. When cultured by using the conditioned medium of M2 macrophages, chondrocytes showed significantly increased expression of type 2 collagen, suggesting that M2 macrophages could enhance the maturation of tissue-engineered cartilage. Also, by partially depleting macrophages with clodronate liposomes in the initial period, during which M1 macrophages were dominant, more cartilage matrix accumulated in transplanted constructs at 2 weeks. It was suggested that polarization of macrophages shifted from M1 to M2 in the transplantation of tissue-engineered cartilage, and controlling the polarization could be advantageous for the maturation of transplanted engineered tissues. Impact statement In transplantation of engineered tissues, it is imperative for immune reactions to proceed in a proper and timely manner. In this study, we transplanted tissue-engineered cartilage consisting of a biodegradable polymer scaffold and chondrocytes, and examined the properties of macrophages. It was shown that the polarization of macrophages shifted from inflammatory (M1) to anti-inflammatory/wound healing (M2) around 11 days after transplantation. Partial suppression of macrophages at the early stage of transplantation, which were mainly M1 macrophages, promoted more accumulation of cartilage matrix. This study indicates a possible approach to facilitate cartilage maturation by intervening in the polarity of macrophages.

Influence of Damage-Associated Molecular Patterns from Chondrocytes in Tissue-Engineered Cartilage

To obtain stable outcomes in regenerative medicine, the quality of cells for transplantation is of great importance. Cellular stress potentially results in the release of damage-associated molecular patterns (DAMPs) and activates immunological responses, affecting the outcome of transplanted tissue. In this study, we intentionally prepared necrotic chondrocytes that would gradually die and release DAMPs and investigated how the maturation of tissue-engineered cartilage was affected. Necrotic chondrocytes were prepared by a conventional heat-treatment method, by which their viability started to decrease after 24 h. When tissue-engineered cartilage containing necrotic chondrocytes was subcutaneously transplanted into C57BL/6J mice, accumulation of cartilage matrix was decreased compared to the control. Meanwhile, immunohistochemical staining demonstrated that localization of macrophages and neutrophils was more apparent in the constructs of necrotic chondrocytes, suggesting that DAMPs from necrotic chondrocytes could prompt migration of more immune cells. Two-dimensional electrophoresis and mass spectrometry identified prelamin as a significant biomolecule released from necrotic chondrocytes. Also, when prelamin was added to a culture of RAW264, Inos and Il1b were increased in accordance with the content of added prelamin. It was suggested that DAMPs from dying chondrocytes could induce inflammatory properties in surrounding macrophages, impairing the maturation of tissue-engineered cartilage. In conclusion, maturation of tissue-engineered cartilage was hampered when less viable chondrocytes releasing DAMPs were included. Impact statement In regenerative medicine, the quality of cells is of great importance to secure clinical safety. During culture, damage of cells could occur, if not critical enough to cause immediate cell death, but still inducing a less viable status. Damage-associated molecular patterns (DAMPs) are released from necrotic cells, but their influence in regenerative medicine has yet to be clarified. In this study, we elucidated how DAMPs from chondrocytes could affect the maturation of tissue-engineered cartilage. Also, possible DAMPs from necrotic chondrocytes were comprehensively analyzed, and prelamin was identified as a significant molecule, which may serve for detecting the existence of necrotic chondrocytes.

Scaffold strategies for modulating immune microenvironment during bone regeneration

Implanted bone scaffolds often fail to successfully integrate with the host tissue because they do not elicit a favorable immune reaction. Properties of bone scaffold not only provide mechanical and chemical signals to support cell adhesion, migration, proliferation and differentiation, but also play a pivotal role in determining the extent of immune response during bone regeneration. Appropriate design parameters of bone scaffold are of great significance in the process of developing a new generation of bone implants. Herein, this article addresses the recent advances in the field of bone scaffolds for immune response, particularly focusing on the physical and chemical properties of bone scaffold in manipulating the host response. Furthermore, incorporation of bioactive molecules and cells with immunoregulatory function in bone scaffolds are also presented. Finally, continuing challenges and future directions of scaffold-based strategies for modulating immune microenvironment are discussed.

Trophic Effects of Mesenchymal Stem Cells in Tissue Regeneration

Mesenchymal stem cells (MSCs) are considered to hold great therapeutic value for cell-based therapy and for tissue regeneration in particular. Recent evidence indicates that the main underlying mechanism for MSCs' beneficial effects in tissue regeneration is based on their capability to produce a large variety of bioactive trophic factors that stimulate neighboring parenchymal cells to start repairing damaged tissues. These new findings could potentially replace the classical paradigm of MSC differentiation and cell replacement. These bioactive factors have diverse actions like modulating the local immune system, enhancing angiogenesis, preventing cell apoptosis, and stimulating survival, proliferation, and differentiation of resident tissue specific cells. Therefore, MSCs are referred to as conductors of tissue repair and regeneration by secreting trophic mediators. In this review article, we have summarized the studies that focused on the trophic effects of MSC within the context of tissue regeneration. We will also highlight the various underlying mechanisms used by MSCs to act as trophic mediators. Besides the secretion of growth factors, we discuss two additional mechanisms that are likely to mediate MSC's beneficial effects in tissue regeneration, namely the production of extracellular vesicles and the formation of membrane nanotubes, which can both connect different cells and transfer a variety of trophic factors varying from proteins to mRNAs and miRNAs. Furthermore, we postulate that apoptosis of the MSCs is an integral part of the trophic effect during tissue repair.

Electron microscopic observation of human auricular chondrocytes transplanted into peritoneal cavity of nude mice for cartilage regeneration

Restoration of damaged cartilage tissue has been deemed futile with current treatments. Although there have been many studies on cartilage regeneration thus far, there is no report that chondrocytes were completely re-differentiated in vitro. The clarification of cellular composition and matrix production during cartilage regeneration must be elucidated to fabricate viable mature cartilage in vitro. In order to achieve this aim, the chondrocytes cultured on coverslips were transplanted into the peritoneal cavities of mice. At different time points post-transplantation, the cartilage maturation progression and cells composing the regeneration were examined. Cartilage regeneration was confirmed by hematoxylin & eosin (HE) and toluidine blue staining. The maturation progression was carefully examined further by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At the first and second week time points, various cell shapes were observed using SEM. Chronologically, by the third week, the number of fibers increased, suggesting the progression of extracellular matrix (ECM) maturation. Observation through TEM revealed the chondrocytes located in close proximity to various cells including macrophage-like cells. On the second week, infiltration of lymphocytes and capillary vessels were observed, and after the third week, the chondrocytes had matured and were abundantly releasing extracellular matrix. Chronological observation of transplanted chondrocytes by electron microscopy revealed maturation of chondrocytes and accumulation of matrix during the re-differentiation process. Emerging patterns of host-derived cells such as macrophage-like cells and subsequent appearance of lymphocytes-like cells and angiogenesis were documented, providing crucial context for the identification of the cells responsible for in vivo cartilage regeneration.

Biological aspects of tissue-engineered cartilage

Cartilage regenerative medicine has been progressed well, and it reaches the stage of clinical application. Among various techniques, tissue engineering, which incorporates elements of materials science, is investigated earnestly, driven by high clinical needs. The cartilage tissue engineering using a poly lactide scaffold has been exploratorily used in the treatment of cleft lip-nose patients, disclosing good clinical results during 3-year observation. However, to increase the reliability of this treatment, not only accumulation of clinical evidence on safety and usefulness of the tissue-engineered products, but also establishment of scientific background on biological mechanisms, are regarded essential. In this paper, we reviewed recent trends of cartilage tissue engineering in clinical practice, summarized experimental findings on cellular and matrix changes during the cartilage regeneration, and discussed the importance of further studies on biological aspects of tissue-engineered cartilage, especially by the histological and the morphological methods.

Roles of macrophage migration inhibitory factor in cartilage tissue engineering

To obtain stable outcomes in regenerative medicine, understanding and controlling immunological responses in transplanted tissues are of great importance. In our previous study, auricular chondrocytes in tissue-engineered cartilage transplanted in mice were shown to express immunological factors, including macrophage migration inhibitory factor (MIF). Since MIF exerts pleiotropic functions, in this study, we examined the roles of MIF in cartilage regenerative medicine. We made tissue-engineered cartilage consisting of auricular chondrocytes of C57BL/6J mouse, atellocollagen gel and a PLLA scaffold, and transplanted the construct subcutaneously in a syngeneic manner. Localization of MIF was prominent in cartilage areas of tissue-engineered cartilage at 2 weeks after transplantation, though it became less apparent by 8 weeks. Co-culture with RAW264 significantly increased the expression of MIF in chondrocytes, suggesting that the transplanted chondrocytes in tissue-engineered cartilage could enhance the expression of MIF by stimulation of surrounding macrophages. When MIF was added in the culture of chondrocytes, the expression of type II collagen was increased, indicating that MIF could promote the maturation of chondrocytes. Meanwhile, toluidine blue staining of constructs containing wild type (Mif+/+) chondrocytes showed increased metachromasia compared to MIF-knockout (Mif-/-) constructs at 2 weeks. However, this tendency was reversed by 8 weeks, suggesting that the initial increase in cartilage maturation in Mif+/+ constructs deteriorated by 8 weeks. Since the Mif+/+ constructs included more iNOS-positive inflammatory macrophages at 2 weeks, MIF might induce an M1 macrophage-polarized environment, which may eventually worsen the maturation of tissue-engineered cartilage in the long term.

Human auricular chondrocytes with high proliferation rate show high production of cartilage matrix

Cartilage has a poor capacity for healing due to its avascular nature. Therefore, cartilage regenerative medicine including autologous chondrocyte implantation (ACI) could be a promising approach. Previous research has proposed various methods to enrich the cultured chondrocytes for ACI, yet it has been difficult to regenerate homogeneous native-like cartilage in vivo. The cell populations with an increased ability to produce cartilage matrix can show somatic stem cells-like characteristics. Stem cells, especially somatic stem cells are able to grow rapidly in vitro yet the growth rate is drastically reduced when placed in in vivo conditions [14]. Thus, in this study we investigated whether proliferation rate has an impact on in vivo regeneration of cartilage constructs by sorting human chondrocytes. The human chondrocytes were fluorescently labeled with CFSE and then cultured in vitro; once analyzed, the histogram showed a widening of fluorescence level, indicating that the cells with various division rates were included in the cell population. To compare the characteristics of the cell groups with different division rates, the chondrocytes were sorted into groups according to the fluorescence intensity (30 or 45 percent of cells plotted in the left and right sides of histogram). Then the cells of the rapid cell group and slow cell group were seeded into PLLA scaffolds respectively, and were transplanted into nude mice. Metachromatic regions stained with toluidine blue were larger in the rapid cell group compared to the slow cell group, indicating that the former had higher chondrogenic ability. We proposed a new method to enrich cell population with high matrix production, using proliferation rate alone.

Avoidance of Total Knee Arthroplasty in Early Osteoarthritis of the Knee with Intra-Articular Implantation of Autologous Activated Peripheral Blood Stem Cells versus Hyaluronic Acid: A Randomized Controlled Trial with Differential Effects of Growth Factor Addition

In this randomized controlled trial, in early osteoarthritis (OA) that failed conservative intervention, the need for total knee arthroplasty (TKA) and WOMAC scores were evaluated, following a combination of arthroscopic microdrilling mesenchymal cell stimulation (MCS) and repeated intra-articular (IA) autologous activated peripheral blood stem cells (AAPBSCs) with growth factor addition (GFA) and hyaluronic acid (HA) versus IA-HA alone. Leukapheresis-harvested AAPBSCs were administered as three weekly IA injections combined with HA and GFA (platelet-rich plasma [PRP] and granulocyte colony-stimulating factor [hG-CSF]) and MCS in group 1 and in group 2 but without hG-CSF while group 3 received IA-HA alone. Each group of 20 patients was evaluated at baseline and at 1, 6, and, 12 months. At 12 months, all patients in the AAPBSC groups were surgical intervention free compared to three patients needing TKA in group 3 (p < 0.033). Total WOMAC scores showed statistically significant improvements at 6 and 12 months for the AAPBSC groups versus controls. There were no notable adverse events. We have shown avoidance of TKA in the AAPBSC groups at 12 months and potent, early, and sustained symptom alleviation through GFA versus HA alone. Differential effects of hG-CSF were noted with an earlier onset of symptom alleviation throughout.

Biodistribution and Immunogenicity of Allogeneic Mesenchymal Stem Cells in a Rat Model of Intraarticular Chondrocyte Xenotransplantation

Xenogeneic chondrocytes and allogeneic mesenchymal stem cells (MSC) are considered a potential source of cells for articular cartilage repair. We here assessed the immune response triggered by xenogeneic chondrocytes when injected intraarticularly, as well as the immunoregulatory effect of allogeneic bone marrow-derived MSC after systemic administration. To this end, a discordant xenotransplantation model was established by injecting three million porcine articular chondrocytes (PAC) into the femorotibial joint of Lewis rats and monitoring the immune response. First, the fate of MSC injected using various routes was monitored in an in vivo imaging system. The biodistribution revealed a dependency on the injection route with MSC injected intravenously (i.v.) succumbing early after 24 h and MSC injected intraperitoneally (i.p.) lasting locally for at least 5 days. Importantly, no migration of MSC to the joint was detected in rats previously injected with PAC. MSC were then administered either i.v. 1 week before PAC injection or i.p. 3 weeks after to assess their immunomodulatory function on humoral and adaptive immune parameters. Anti-PAC IgM and IgG responses were detected in all PAC-injected rats with a peak at week 2 postinjection and reactivity remaining above baseline levels by week 18. IgG2a and IgG2b were the predominant and long-lasting IgG subtypes. By contrast, no anti-MSC antibody response was detected in the cohort injected with MSC only, but infusion of MSC before PAC injection temporarily augmented the anti-PAC antibody response. Consistent with a cellular immune response to PAC in PAC-injected rats, cytokine/chemokine profiling in serum by antibody array revealed a distinct pattern relative to controls characterized by elevation of multiple markers at week 2, as well as increases in proliferation in draining lymph nodes. Notably, systemic administration of allogeneic MSC under the described conditions did not diminish the immune response. IL-2 measurements in cocultures of rat peripheral blood lymphocytes with PAC indicated that PAC injection induced some T-cell hyporesponsiveness that was not enhanced in the cohorts additionally receiving MSC. Thus, PAC injected intraarticularly in Lewis rats induced a cellular and humoral immune response that was not counteracted by the systemic administration of allogeneic MSC under the described conditions.

Developing a Clinically Representative Model of Periprosthetic Joint Infection

➤The poor treatment outcomes for periprosthetic joint infection (PJI) reflect the limited understanding that currently exists regarding the pathogenesis of this devastating clinical problem.➤Current animal models of PJI are limited in their translational nature primarily because of their inability to recreate the periprosthetic environment.➤A greater mechanistic understanding of the musculoskeletal and immune systems of small animals, such as mice and rats, provides a more robust platform for modeling and examining the pathogenesis of PJI.➤A clinically representative PJI model must involve an implant that recreates the periprosthetic space and be amenable to methodologies that identify implant biofilm as well as quantify the peri-implant bacterial load.

Human chondroprogenitors in alginate-collagen hybrid scaffolds produce stable cartilage in vivo

The goal of this study was to evaluate human epiphyseal chondroprogenitor cells (ECPs) as a potential new cell source for cartilage regeneration. ECPs were compared to human bone marrow stromal cells (MSCs) and human adult articular chondrocytes (ACs) for their chondrogenic potential and phenotypic stability in vitro and in vivo. The cells were seeded in Optimaix-3D scaffolds at 5 × 10⁴ cells/mm³ and gene expression, matrix production and mechanical properties were analysed up to 6 weeks. In vitro, ECPs synthesized consistently high collagen 2 and low collagen 10. AC-seeded constructs exhibited high donor variability in GAG/DNA values as well as in collagen 2 staining, but showed low collagen 10 production. MSCs, on the other hand, expressed high levels of collagen 2 but also of collagens 1 and 10, and were therefore not considered further. In vivo, there was considerable loss of matrix proteins in ECPs compared to in vitro cultured samples. To overcome this, a second implantation study investigated the effect of mixing cells with alginate prior to seeding in the scaffold. ECPs in alginate maintained their cartilage matrix and resisted mineralization and vessel infiltration better 6 weeks after subcutaneous implantation, whereas ACs lost their chondrogenic matrix completely. This study shows the great potential of ECPs as an off-the-shelf, highly chondrogenic cell type that produces stable cartilage in vivo. Copyright © 2016 John Wiley & Sons, Ltd.

Bone Marrow Mesenchymal Stem Cell-Based Engineered Cartilage Ameliorates Polyglycolic Acid/Polylactic Acid Scaffold-Induced Inflammation Through M2 Polarization of Macrophages in a Pig Model

: The regeneration of tissue-engineered cartilage in an immunocompetent environment usually fails due to severe inflammation induced by the scaffold and their degradation products. In the present study, we compared the tissue remodeling and the inflammatory responses of engineered cartilage constructed with bone marrow mesenchymal stem cells (BMSCs), chondrocytes, or both and scaffold group in pigs. The cartilage-forming capacity of the constructs in vitro and in vivo was evaluated by histological, biochemical, and biomechanical analyses, and the inflammatory response was investigated by quantitative analysis of foreign body giant cells and macrophages. Our data revealed that BMSC-based engineered cartilage suppressed in vivo inflammation through the alteration of macrophage phenotype, resulting in better tissue survival compared with those regenerated with chondrocytes alone or in combination with BMSCs. To further confirm the macrophage phenotype, an in vitro coculture system established by engineered cartilage and macrophages was studied using immunofluorescence, enzyme-linked immunosorbent assay, and gene expression analysis. The results demonstrated that BMSC-based engineered cartilage promoted M2 polarization of macrophages with anti-inflammatory phenotypes including the upregulation of CD206, increased IL-10 synthesis, decreased IL-1β secretion, and alterations in gene expression indicative of M1 to M2 transition. It was suggested that BMSC-seeded constructs have the potential to ameliorate scaffold-induced inflammation and improve cartilaginous tissue regeneration through M2 polarization of macrophages.

SIGNIFICANCE

Finding a strategy that can prevent scaffold-induced inflammation is of utmost importance for the regeneration of tissue-engineered cartilage in an immunocompetent environment. This study demonstrated that bone marrow mesenchymal stem cell (BMSC)-based engineered cartilage could suppress inflammation by increasing M2 polarization of macrophages, resulting in better tissue survival in a pig model. Additionally, the effect of BMSC-based cartilage on the phenotype conversion of macrophages was further studied through an in vitro coculture system. This study could provide further support for the regeneration of cartilage engineering in immunocompetent animal models and provide new insight into the interaction of tissue-engineered cartilage and macrophages.

Repositioning Bevacizumab: A Promising Therapeutic Strategy for Cartilage Regeneration

Drug discovery and development has been garnering an increasing trend of research due to the growing incidence of the diverse types of diseases. Recently, drug repositioning, also known as drug repurposing, has been emerging parallel to cancer and tissue engineering studies. Drug repositioning involves the application of currently approved or even abandoned drugs as alternative treatments to other diseases or as biomaterials in other fields including cell therapy and tissue engineering. In this review, the advancement of the antiangiogenesis drugs that were used as treatment for cancer and other diseases, with particular focus on bevacizumab, will be described. This will include an overview of the nature and progression of osteoarthritis (OA), one of the leading global degenerative diseases that cause morbidity, and the development of its therapeutic strategies. In addition, this will also feature the nonsteroidal anti-inflammatory drugs that are commonly prescribed for OA and the benefits of repositioning bevacizumab as alternative treatments for other diseases and as biomaterials for cartilage regeneration. To date, a few number of studies, employing different modes of administration and varying dosages in diverse animal models, have shown that bevacizumab can be used as a signal and can promote both in vitro and in vivo cartilage regeneration. However, other antiangiogenesis drugs and their effects in chondrogenesis and cartilage regeneration are also worth investigating.

Cartilage Repair in the Inflamed Joint: Considerations for Biological Augmentation Toward Tissue Regeneration

Cartilage repair/regeneration procedures (e.g., microfracture, autologous chondrocyte implantation [ACI]) typically result in a satisfactory outcome in selected patients. However, the vast majority of patients with chronic symptoms and, in general, a more diseased joint, do not benefit from these surgical techniques. The aims of this work were to (1) review factors negatively influencing the joint environment; (2) review current adjuvant therapies that can be used to improve results of cartilage repair/regeneration procedures in patients with more diseased joints, (3) outline future lines of research and promising experimental approaches. Chronicity of symptoms and advancing patient age appear to be the most relevant factors negatively affecting clinical outcome of cartilage repair/regeneration. Preliminary experience with hyaluronic acid, platelet-rich plasma, and mesenchymal stem cell has been positive but there is no strong evidence supporting the use of these products and this requires further assessment with high-quality, prospective clinical trials. The use of a Tissue Therapy strategy, based on more mature engineered tissues, holds promise to tackle limitations of standard ACI procedures. Current research has highlighted the need for more targeted therapies, and (1) induction of tolerance with granulocyte colony-stimulating factor (G-CSF) or by preventing IL-6 downregulation; (2) combined IL-4 and IL-10 local release; and (3) selective activation of the prostaglandin E2 (PGE2) signaling appear to be the most promising innovative strategies. For older patients and for those with chronic symptoms, adjuvant therapies are needed in combination with microfracture and ACI.

Clinical Trial and In Vitro Study for the Role of Cartilage and Synovia in Acute Articular Infection

OBJECTIVE

Osteoarthritis is a long-term complication of acute articular infections. However, the roles of cartilage and synovia in this process are not yet fully understood.

METHODS

Patients with acute joint infections were enrolled in a prospective clinical trial and the cytokine composition of effusions compared in patients with arthroplasty (n = 8) or with intact joints (n = 67). Cytokines and cell function were also analyzed using a human in vitro model of joint infection.

RESULTS

Synovial IL-1β levels were significantly higher in patients with arthroplasty (p = 0.004). Higher IL-1β concentrations were also found in the in vitro model without chondrocytes (p < 0.05). The anti-inflammatory cytokines IL-4 and IL-10 were consistently expressed in vivo and in vitro, showing no association with the presence of cartilage or chondrocytes. In contrast, FasL levels increased steadily in vitro, reaching higher levels without chondrocytes (p < 0.05). Likewise, the viability of synovial fibroblasts (SFB) during infection was higher in the presence of chondrocytes. The cartilage-metabolism markers aggrecan and bFGF were at higher concentrations in intact joints, but also synthesized by SFB.

CONCLUSIONS

Our data suggest an anti-inflammatory effect of cartilage associated with the SFBs' increased resistance to infections, which displayed the ability to effectively synthesize cartilage metabolites.The trial is registered with DRKS 00003536, MISSinG.

Bone marrow derived cells facilitate urinary bladder regeneration by attenuating tissue inflammatory responses

Introduction

Inflammatory responses following tissue injury are essential for proper tissue regeneration. However, dysfunctional or repetitive inflammatory tissue assaults can lead to poor tissue regeneration and ultimate tissue failure via fibrosis. Previous attempts at urinary bladder tissue regeneration utilizing polymeric and biologic scaffolding materials tended to elicit these responses leading to poor tissue regeneration. Recent advances in bladder regeneration utilizing bone marrow derived mesenchymal stem cells (MSCs) and CD34⁺ hematopoietic stem/progenitor cells (HSPCs) with biocompatible citric acid based scaffolds have provided an environment that not only promotes the growth of architecturally germane and physiologically functional tissue, but also modulates aspects of the innate immune response.

Material and methods

Within this study MSCs, CD34⁺ HSPCs, or MSC/CD34⁺ HSPC seeded POC [poly (1,8-octanediol-co-citrate)] scaffolds were utilized in an established rodent bladder augmentation model to evaluate inflammation as it pertains to bladder tissue regeneration.

Results

Quantified data from post-augmentation regenerated tissue samples at the 4 week time-point demonstrated that POC/MSC and POC/MSC + CD34⁺ HSPC grafts markedly reduced the presence of pro-inflammatory CD68⁺ macrophages and MPO⁺ neutrophils compared to unseeded POC or POC/CD34⁺ HSPC-only seeded grafts. Pro-inflammatory cytokines TNFα and IL-1b were also significantly down-regulated with a concomitant increase in the anti-inflammatory cytokines IL-10 and IL-13 in the aforementioned POC/MSC and POC/MSC + CD34⁺ HSPC composites. Furthermore, this led to fewer instances of bladder tissue granuloma formation combined with greater muscle content and tissue angiogenic events as previous data has demonstrated.

Conclusions

Data indicates that POC/MSC and POC/MSC + CD34⁺ HSPC grafts attenuate the innate inflammatory response and promote bladder tissue regeneration.