Introduction and Objective. Osteochondral allograft (OCA) transplants have been used clinically for more than 40 years as a surgical option for joint restoration, particularly for young and active patients. While immediate graft rejection responses have not been documented, it is believed that the host's immunological responses may directly impact OCA viability, incorporation, integrity, and survival, and therefore, it is of the utmost importance to further optimize OCA transplantation outcomes. The influences of sub-rejection immune responses on OCA transplantation failures have not been fully elucidated therefore aimed to further characterize cellular features of OCA failures using immunohistochemistry (IHC) in our continued hopes for the successful optimization of this valuable surgical procedure. Materials and Methods. With IRB approval, osteochondral tissues that were resected from the knee, hip, and ankle of patients undergoing standard-of-care revision surgeries (N=23) to treat OCA failures and tissues from unused portions of OCAs (N=7) that would otherwise be discarded were recovered. Subjective histologic assessments were performed on hematoxylin and eosin-stained and toluidine blue-stained sections by a pathologist who was blinded to patient demographics, outcomes data, and tissue source. IHC for CD3, CD8, and CD20 were performed to further characterize the and allow for subjective assessment of relevant immune responses. Results. Eleven (48%) of the failed OCAs had aggregates of CD3+, CD8+, and CD20+ lymphocytes around small blood vessels in the bone marrow spaces and adipose/collagenous tissue of the allograft, while the non-implanted healthy control OCA tissues did not show any evidence of inflammation. The remaining failed OCAs (52%) did not show a similar pattern of T- and B-cell infiltrates around blood vessels. Other histologic abnormalities associated with failed OCAs included avascular necrosis, subchondral micro and macro fractures, subchondral collapse, bacterial infection, and/or articular cartilage erosion or delamination. Conclusions. The results from the present study support this possibility in that mixed aggregates of CD3+, CD8+, and CD20+ lymphocytes were observed around small blood vessels in approximately half of the failed OCAs. This potentially cytotoxic immune response may have contributed to the lack of functional survival of the OCA noted in these cases, and warrants further investigation as a possible failure mechanism that may be mitigated using post-transplantation management strategies

Chronic lateral ankle instability (CLAI) is treated operatively, whereas acute ligament injury is usually treated nonoperatively. Such treatments have been widely validated. Apoptosis is known to cause ligament degeneration; however, few reports have focused on the possible role of apoptosis in degeneration of ruptured lateral ankle ligaments. The aim of our study is to elucidate the apoptosis that occurs within anterior talofibular ligament (ATFL) to further validate current CLAI treatments by adducing molecular and cellular evidence. Between March 2019 and February 2021, 50 patients were prospectively enrolled in this study. Ruptured ATFL tissues were collected from 21 CLAI patients (group C) and 17 acute ankle fracture patients (group A). Apoptotic cells were counted using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) assay. Western blotting for caspases 3, 7, 8, and 9 and cytochrome c, was performed to explore intrinsic and extrinsic apoptotic pathways. Immunohistochemistry was used to detect caspases 3, 7, 8, and 9 and cytochrome c, in ligament vessel endothelial cells. More apoptotic cells were observed in group C than group A in TUNEL assay. Western blotting revealed that the apoptotic activities of group C ligaments were significantly higher than those of group A (all p < 0.001). Immunohistochemistry revealed increased expression of caspases 3, 7, 8, and 9, and cytochrome c, in group C compared to group A. The ATFL apoptotic activities of CLAI patients were significantly higher than those of acute ankle fracture patients, as revealed biochemically and histologically. Our data further validate current CLAI treatments from a molecular and cellular perspective. Efforts should be made to reverse or prevent ATFL apoptosis in CLAI patients

Breast cancer is the most frequent malignancy in women with an estimation of 2.1 million new diagnoses in 2018. Even though primary tumours are usually efficiently removed by surgery, 20–40% of patients will develop metastases in distant organs. Bone is one of the most frequent site of metastases from advanced breast cancer, accounting from 55 to 58% of all metastases. Currently, none of the therapeutic strategies used to manage breast cancer bone metastasis are really curative. Tailoring a suitable model to study and evaluate the disease pathophysiology and novel advanced therapies is one of the major challenges that will predict more effectively and efficiently the clinical response. Preclinical traditional models have been largely used as they can provide standardization and simplicity, moreover, further advancements have been made with 3D cultures, by spheroids and artificial matrices, patient derived xenografts and microfluidics. Despite these models recapitulate numerous aspects of tumour complexity, they do not completely mimic the clinical native microenvironment. Thus, to fulfil this need, in our study we developed a new, advanced and alternative model of human breast cancer bone metastasis as potential biologic assay for cancer research. The study involved breast cancer bone metastasis samples obtained from three female patients undergoing wide spinal decompression and stabilization through a posterior approach. Samples were cultured in a TubeSpin Bioreactor on a rolling apparatus under hypoxic conditions at time 0 and for up to 40 days and evaluated for viability by the Alamar Blue test, gene expression profile, histology and immunohistochemistry. Results showed the maintenance and preservation, at time 0 and after 40 days of culture, of the tissue viability, biological activity, as well as molecular markers, i.e. several key genes involved in the complex interactions between the tumour cells and bone able to drive cancer progression, cancer aggressiveness and metastasis to bone. A good tis sue morphological and microarchitectural preservation with the presence of lacunar osteolysis, fragmented trabeculae locally surrounded by osteoclast cells and malignant cells and an intense infiltration by tumour cells in bone marrow compartment in all examined samples. Histomorphometrical data on the levels of bone resorption and bone apposition parameters remained constant between T0 and T40 for all analysed patients. Additionally, immunohistochemistry showed homogeneous expression and location of CDH1, CDH2, KRT8, KRT18, Ki67, CASP3, ESR1, CD8 and CD68 between T0 and T40, thus further confirming the invasive behaviour of breast cancer cells and indicating the maintaining of the metastatic microenvironment. The novel tissue culture, set-up in this study, has significant advantages in comparison to the pre-existent 3D models: the tumour environment is the same of the clinical scenario, including all cell types as well as the native extracellular matrix; it can be quickly set-up employing only small samples of breast cancer bone metastasis tissue in a simple, ethically correct and cost-effective manner; it bypasses and/or decreases the necessity to use more complex preclinical model, thus reducing the ethical burden following the guiding principles aimed at replacing/reducing/refining (3R) animal use and their suffering for scientific purposes; it can allow the study of the interactions within the breast cancer bone metastasis tissue over a relatively long period of up to 40 days, preserving the tumour morphology and architecture and allowing also the evaluation of different biological factors, parameters and activities. Therefore, the study provides for the first time the feasibility and rationale for the use of a human-derived advanced alternative model for cancer research and testing of drugs and innovative strategies, taking into account patient individual characteristics and specific tumour subtypes so predicting patient specific responses

Tendinopathy is a disease associated with pain and tendon degeneration, leading to a decreased range of motion and an increased risk of tendon rupture. The etiology of this frequent disease is still unknown. In other musculoskeletal tissues like cartilage and intervertebral discs, transient receptor potential channels (TRP- channels) were shown to play a major role in the progression of degeneration. Due to their responsiveness to a wide range of stimuli like temperature, pH, osmolarity and mechanical load, they are potentially relevant factors in tendon degeneration as well. We therefore hypothesize that TRP- channels are expressed in tendon cells and respond to degeneration inducing stimuli. By immunohistochemistry, qRT-PCR and western blot analyses, we found three TRP channel members, belonging to the vanilloid (TRPV), and ankyrin (TRPA) subfamily, respectively, to be expressed in healthy human tendon tissue as well as in rodent tendon, with expression being located to cells within the dense tendon proper, as well as to endotenon resident cells. In vitro-inflammatory and ex vivo-mechanical stimulation led to a significant upregulation of TRPA1 expression in tendon cells, which correlates well with the fact that TRPA1 is considered as mechanosensitive channel being sensitized by inflammatory mediators. This is the first description of TRP- channels in human and rodent tendon. As these channels are pharmacologically targetable by both agonists and antagonists, they may represent a promising target for novel treatments of tendinopathy

Primary bone tumors are rare, complex and highly heterogeneous. Its diagnostic and treatment are a challenge for the multidisciplinary team. Developments on tumor biomarkers, immunohistochemistry, histology, molecular, bioinformatics, and genetics are fundamental for an early diagnosis and identification of prognostic factors. The personalized medicine allows an effective patient tailored treatment. The bone biopsy is essential for diagnosis. Treatment may include systemic therapy and local therapy. Frequently, a limb salvage surgery includes wide resection and reconstruction with endoprosthesis, biological or composites. The risk for local recurrence and distant metastases depends on the primary tumor and treatment response. Cancer patients are living longer and bone metastases are increasing. Bone is the third most frequently location for distant lesions. Bone metastases are associated to pain, pathological fractures, functional impairment, and neurological deficits. It impacts survival and patient quality of life. The treatment of metastatic disease is a challenge due to its complexity and heterogeneity, vascularization, reduced size and limited access. It requires a multidisciplinary treatment and depending on different factors it is palliative or curative-like treatment. For multiple bone metastases it is important to relief pain and increases function in order to provide the best quality of life and expect to prolong survival. Advances in nanotechnology, bioinformatics, and genomics, will increase biomarkers for early detection, prognosis, and targeted treatment effectiveness. We are taking the leap forward in precision medicine and personalized care

The interleukin-6/gp130-associated Janus Kinases/STAT3 axis is known to play an important role in mediating inflammatory signals, resulting in production of matrix metalloproteinase-3 (MMP-3). The hip joints with rapidly destructive coxopathy (RDC) demonstrate rapid chondrolysis, probably by increased production of MMP-3 observed in the early stage of RDC. In the recent study, no apparent activation of STAT3 has been shown in the synovial tissues obtained from the osteoarthritic joint at operation. However, no data are currently available on STAT3 activation in the synovial tissues in the early stage of RDC. This study aimed to elucidate STAT3 activation in the synovial tissues in the early stage of RDC. Synovial tissues within 7 months from the disease onset were obtained from four RDC patients with femoral head destruction and high serum levels of MMP-3. RDC synovial tissues showed the synovial lining hyperplasia with an increase of CD68-positive macrophages and CD3-positive T lymphocytes. STAT3 phosphorylation was found in the synovial tissues by immunohistochemistry using anti-phospho-STAT3 antibody. The majority of phospho-STAT3-positive cells were the synovial lining cells and exhibited negative expression of macrophage or T cell marker. Treatment with tofacitinib, a Janus Kinase inhibitor, resulted in a decrease in phospho-STAT3-positive cells, especially with high intensity, indicating effective suppression of STAT3 activation in RDC synovial tissues. Inhibitory effect of tofacitinib could act through the Janus Kinase/STAT3 axis in the synovial tissues in the early stage of RDC. Therefore, STAT3 may be a potential therapeutic target for prevention of joint structural damage in RDC. Acknowledgements: This study was supported by Katakami Foundation for Clinical Research

The effect of high-fat diet and testosterone replacement therapy upon bone remodelling was investigated in orchiectomised male APOE-/- mice. Mice were split in to three groups: sham surgery + placebo treatment (control, n=9), orchiectomy plus placebo treatment (n=8) and orchiectomy plus testosterone treatment (n=10). Treatments were administered via intramuscular injection once a fortnight for 17 weeks before sacrifice at 25 weeks of age. Tibiae were scanned ex-vivo using µCT followed by post-analysis histology and immunohistochemistry. Previously presented µCT data demonstrated orchiectomised, placebo treated mice exhibited significantly reduced trabecular bone volume, number, thickness and BMD compared to control mice despite no significant differences in body weight. Trabecular parameters were rescued back to control levels in orchiectomised mice treated with testosterone. No significant differences were observed in the cortical bone. Assessment of TRAP stained FFPE sections revealed no significant differences in osteoclast or osteoblast number along the endocortical surface. IHC assessment of osteoprotegerin (OPG) expression in osteoblasts is to be quantified alongside markers of osteoclastogenesis including RANK and RANKL. Results support morphological analysis of cortical bone where no change in cortical bone volume or density between groups is in line with no significant change in osteoblast or osteoclast number and percentage across all three groups. Future work will include further IHC assessment of bone remodelling and adiposity, as well as utilisation of mechanical testing to establish the effects of observed morphological differences in bone upon mechanical properties. Additionally, the effects of hormone treatments upon murine-derived bone cells will be investigated to provide mechanistic insights

As peri-prosthetic aseptic loosening is one of the main causes of implant failure, inhibiting wear particles induced macrophages inflammation is considered as a promising therapy for AL to expand the lifespan of implant. Here, we aim at exploring the role of p110δ, a member of class IA PI3K family, and Krüppel-like factor 4 (KLF4) in titanium particles (TiPs) induced macrophages-inflammation and osteolysis. Firstly, IC87114, the inhibitor of p110δ and siRNA targeting p110δ were applied and experiments including ELISA and immunofluorescence assay were conducted to explore the role of p110δ. Sequentially, KLF4 was predicted as the transcription factor of p110δ and the relation was confirmed by dual luciferase reporter assay. Next, assays including RT-PCR, western blotting and flow cytometry were performed to ensure the specific role of KLF4. Finally, TiPs-induced mice cranial osteolysis model was established, and micro-CT scanning and immunohistochemistry assay were performed to reveal the role of p110δ and KLF4 in vivo. Here, we found that p110δ was upregulated in TiPs-stimulated macrophages. The inhibition of p110δ or knockdown of p110δ could significantly dampen the TiPs-induced secretion of TNFα and IL-6. Further mechanistic studies confirmed that p110δ was responsible for TNFα and IL-6 trafficking out of Golgi complex without affecting their expression in TiPs-treated macrophages. Additionally, we explored the upstream regulators and confirmed that Krüppel-like factor 4 (KLF4) was the transcription repressor of p110δ. Apart from that, KLF4, targeted by miR-92a, could also attenuate TiPs-induced inflammation by mediating NF-κB pathway and M1/M2 polarization. By the establishment of TiPs-induced mice cranial osteolysis model, we found that KLF4 knockdown exacerbated TiPs-induced osteolysis which was strikingly ameliorated by knockdown of p110δ. In summary, our study suggests the key role of miR-92a/KLF4/p110δ signal in TiPs-induced macrophages inflammation and osteolysis

Treatment for delayed wound healing resulting from peripheral vascular diseases and diabetic foot ulcers remain a challenge. A novel surgical technique named Tibial Cortex Transverse Transport has been developed for treating peripheral ischaemia, with encouraging clinical effects. However, its underlying mechanisms remain unclear. In present study, we aimed to explore the wound healing effects after undergoing this novel technique via multiple ways. A novel rat model of Tibial Cortex Transverse Transport was established with a designed external fixator and effects on wound healing were investigated. All rats were randomized into 3 groups, with 12 rats per group: sham group (negative control), fixator group (positive control) and Tibial Cortex Transverse Transport group. Laser speckle perfusion imaging, vessel perfusion, histology and immunohistochemistry were used to evaluate the wound healing processes. Gross and histological examinations showed that Tibial Cortex Transverse Transport technique accelerated wound closure and enhanced the quality of the newly formed skin tissues. In Tibial Cortex Transverse Transport group, HE staining demonstrated a better epidermis and dermis recovery, while immune-histochemical staining showed that Tibial Cortex Transverse Transport technique promoted local collagen deposition. Tibial Cortex Transverse Transport technique also benefited to angiogenesis and immunomodulation. In Tibial Cortex Transverse Transport group, blood flow in the wound area was higher than that ofother groups according to laser speckle imaging with more blood vessels observed. Enhanced neovascularization was seen in the Tibial Cortex Transverse Transport group with double immune-labelling of CD31 and α-SMA. The M2 macrophages at the wound site in the Tibial Cortex Transverse Transport group was also increased. Tibial cortex transverse transport technique accelerated wound healing through enhanced angiogenesis and immunomodulation

Tendon injuries occur frequently in athletes and the general population, with inferior healing leading to deposition of fibrotic scar tissue. New treatments are essential to limit fibrosis and enable tendon regeneration post-injury. In this study, we tested the hypothesis that rapamycin improves tendon repair and limits fibrosis by inhibiting the mTOR pathway. The left hindlimb of female adult Wistar rats was injured by needle puncture and animals were either given daily injections of rapamycin (2mg/kg) or vehicle. Animals were euthanized 1 week or 3 weeks post-injury (n=6/group). Left and right Achilles tendons were harvested, with the right limbs acting as controls. Tendon sections were stained with haematoxylin & eosin, and scored by 2 blinded scorers, assessing alterations in cellularity, cell morphology, vascularity, extracellular matrix (ECM) organization and peritendinous fibrosis. Immunohistochemistry was performed for the tendon pan-vascular marker CD146 and the autophagy marker LC3. Injury resulted in significantly altered ECM organization, cell morphology and cellularity in both rapamycin and vehicle-treated groups, but no alterations in vascularity compared to uninjured tendons. Rapamycin had a limited effect on tendon repair, with a significant reduction in peritendinous fibrosis 3 weeks after injury (p=0.028) but no change in cell morphology, cellularity or ECM organization compared to vehicle treated tendons at either 1 week or 3 weeks post injury. CD146 labelling was increased at the site of injury, but there was no apparent difference in CD146 or LC3 labelling in rapamycin and vehicle treated tendons. The decrease in peritendinous fibrosis post-injury observed in rapamycin treated tendons indicates rapamycin as a potential therapy for tendon adhesions. However, the lack of improvement of other morphological parameters in response to rapamycin treatment indicates that rapamycin is not an effective therapy for injuries to the tendon core. Acknowledgements: This study was funded by Versus Arthritis (22607)

Osteoporotic fracture has become a major problem in ageing population and often requires prolonged healing time. Low Intensity Pulsed Ultrasound (LIPUS) can significantly enhance fracture healing through alteration of osteocyte lacuno-canalicular network (LCN). DMP1 in osteocytes is responsible for maintaining LCN and mineralisation. This study aims to investigate osteocyte-specific DMP1's role in enhanced osteoporotic fracture healing in response to mechanical stimulation. Bilateral ovariectomy was performed in 6-month-old female SD rats to induce osteoporosis. Metaphyseal fracture was created at left distal femur using oscillating micro-saw. Rats were randomised to groups: (1) DMP1 KD, (2) DMP1 KD + LIPUS, (3) Control, or (4) Control + LIPUS, where KD stands for knockdown by injection of shRNA into marrow cavity 2 weeks before surgery. Assessments included weekly radiography, microCT and immunohistochemistry on DMP1, E11, FGF23 and sclerostin. DMP1 KD significantly impaired LIPUS-accelerated fracture healing when comparing KD + LIPUS group to Control + LIPUS group. The X-ray relative opacity showed less tissue growth at all timepoints (Week 1, 3 & 6; p=0.000, 0.001 and 0.003 respectively) and the bone volume fraction was decreased after DMP1 KD at Week 3 (p=0.006). DMP1 KD also significantly altered the expression levels of osteocyte-specific DMP1, E11, FGF23 and sclerostin during healing process. The lower relative opacity and bone volume fraction in DMP1 KD groups indicated that knockdown of DMP1 was associated with poorer fracture healing process compared to non-knockdown groups. The similar results between knockdown group with and without LIPUS showed that blockage of DMP1 would negate LIPUS-induced enhancement on fracture healing. Acknowledgment: General Research Fund (Ref: 14113018)

The development of cytoplasmic processes from in situ chondrocytes is a characteristic feature of early osteoarthritis in human cartilage. The processes involve cytoskeletal elements and are distinct from the short primary cilia described in human chondrocytes. Vimentin is an intermediate filament playing an essential structural and signal-transduction role. We determined cellular levels and distribution of vimentin in chondrocytes of different morphologies in non-degenerate and mildly osteoarthritic cartilage. Femoral heads were obtained after consent from patients undergoing hip arthroplasty following femoral neck fracture. Cartilage explants were graded as non-degenerate (grade 0;G0) or mildly osteoarthritic (grade 1;G1) and labelled with the cytoplasmic dye CMFDA (5-chloromethylfluorescein-diacetate) for cell shape. Explants were cryosectioned and labelled for vimentin by fluorescence immunohistochemistry. In situ chondrocyte morphology was identified by confocal microscopy as either normal (rounded/elliptical) or abnormal (with one or more cytoplasmic process of ≥2µm) and vimentin levels and distribution determined semi-quantitatively and related to chondrocyte morphology. When all cells in G0 and G1 cartilage were compared, there was no difference between average levels of vimentin per cell (P=0.144)[6(261)];femoral heads:cells). When cells were separated on the basis of morphology, there was no difference between vimentin levels in cells with one or more cytoplasmic process compared to those of normal morphology (P>0.05;[6(261)]). However vimentin levels were much greater at the base of cytoplasmic processes compared to distant areas of the same cells (P=0.021)[5(29)]). Although overall levels of chondrocyte vimentin do not change in these early stages of osteoarthritis, the formation and structure of these substantial chondrocyte cytoplasmic processes involves changes to its distribution. These morphological changes are similar to those occurring during chondrocyte de-differentiation to fibroblasts reported in osteoarthritis which results in the formation of mechanically-inferior fibro-cartilage. Alterations to chondrocyte vimentin distribution either directly or indirectly may play a role in cartilage degeneration

The purpose of this study is to enhance massive bone allografts osseointegration used to reconstruct large bone defects. These allografts show >50% complication rate requiring surgical revision in 20% cases. A new protocol for total bone decellularisation exploiting the vasculature can offer a reduction of postoperative complication by annihilating immune response and improving cellular colonization/ osseointegration. The nutrient artery of 18 porcine bones - humerus/femur/radius/ulna - was cannulated. The decellularization process involved immersion and sequential perfusion with specific solvents over a course of one week. Perfusion was realized by a peristaltic pump (mean flow rate: 6ml/min). The benefit of arterial perfusion was compared to a control group kept in immersion baths without perfusion. Bone samples were processed for histology (HE, Masson's trichrome and DAPI for cell detection), immunohistochemistry (IHC : Collagen IV/elastin for intraosseous vascular system evaluation, Swine Leukocyte Antigen – SLA for immunogenicity in addition to cellular clearance) and DNA quantification. Sterility and solvent residues in the graft were also evaluated with thioglycolate test and pH test respectively. Compared to native bones, no cells could be detected and residual DNA was <50ng/mg dry weight. Intramedullary spaces were completely cleaned. IHC showed the preservation of intracortical vasculature with channels bounded by Collagen IV and elastin within Haversian systems. IHC also showed a significant decrease in SLA signaling. All grafts were sterile at the last decellularization step and showed no solvent residue. The control group kept in immersion baths, paired with 6 perfused radii/ulnae, showed that the perfusion is mandatory to ensure complete decellularisation. Our results prove the effectiveness of a new concept of total bone decellularisation by perfusion. These promising results could lead to a new technique of Vascularized Composite Allograft transposable to pre-clinical and clinical models

Introduction and Objective. Alveolar bone resorption following tooth extraction or periodontal disease compromises the bone volume required to ensure the stability of an implant. Guided bone regeneration (GBR) is one of the most attractive technique for restoring oral bone defects, where an occlusive membrane is positioned over the bone graft material, providing space maintenance required to seclude soft tissue infiltration and to promote bone regeneration. However, bone regeneration is in many cases impeded by a lack of an adequate tissue vascularization and/or by bacterial contamination. Using simultaneous spray coating of interacting species (SSCIS) process, a bone inspired coating made of calcium phosphate-chitosan-hyaluronic acid was built on one side of a nanofibrous GBR collagen membrane in order to improve its biological properties. Materials and Methods. First, the physicochemical characterizations of the resulting hybrid coating were performed by scanning electron microscopy, X-ray photoelectron, infrared spectroscopies and high-resolution transmission electron microscopy. Then human mesenchymal stem cells (MSCs) and human monocytes were cultured on those membranes. Biocompatibility and bioactivity of the hybrid coated membrane were respectively evaluated through MSCs proliferation (WST-1 and DNA quantification) and visualization; and cytokine release by MSCs and monocytes (ELISA and endothelial cells recruitment). Antibacterial properties of the hybrid coating were then tested against S. aureus and P. aeruginosa, and through MSCs/bacteria interactions. Finally, a preclinical in vivo study was conducted on rat calvaria bone defect. The newly formed bone was characterized 8 weeks post implantation through μCT reconstructions, histological characterizations (Masson's Trichrome and Von Kossa stain), immunohistochemistry analysis and second harmonic generation. Biomechanical features of newly formed bone were determined. Results. The resulting hybrid coating of about 1 μm in thickness is composed of amorphous calcium phosphate and carbonated poorly crystalline hydroxyapatite, wrapped within chitosan/hyaluronic acid polysaccharide complex. Hybrid coated membrane possesses excellent bioactivity and capability of inducing an overwhelmingly positive response of MSCs and monocytes in favor of bone regeneration. Furthermore, the antibacterial experiments showed that the hybrid coating provides contact-killing properties by disturbing the cell wall integrity of Gram-positive and Gram-negative bacteria. Its combination with MSCs, able to release antibacterial agents and mediators of the innate immune response, constitutes an excellent strategy for fighting bacteria. A preclinical in vivo study was therefore conducted in rat calvaria bone defect. μCT reconstructions showed that hybrid coated membrane favored bone regeneration, as we observed a two-fold increase in bone volume / total volume ratios vs. uncoated membrane. The histological characterizations revealed the presence of mineralized collagen (Masson's Trichrome and Von Kossa stain), and immunohistochemistry analysis highlighted a bone vascularization at 8 weeks post-implantation. However, second harmonic generation analysis showed that the newly formed collagen was not fully organized. Despite a significant increase in the elastic modulus of the newly formed bone with hybrid coated membrane (vs. uncoated membrane), the obtained values were lower than those for native bone (approximately 3 times less). Conclusions. These significant data shed light on the regenerative potential of such bioinspired hybrid coating, providing a suitable environment for bone regeneration and vascularization, as well as an ideal strategy to prevent bone implant-associated infections

Energy storing tendons such as the human Achilles and equine superficial digital flexor tendon (SDFT) are prone to age-related injury. Tendons have poor healing capacity and a lack of effective treatments can lead to ongoing pain, reduced function and re-injury. It is therefore important to identify the mechanisms underpinning age-related tendinous changes in order to develop more effective treatments. Our recent single cell sequencing data has shown that tendon cell populations have extensive heterogeneity and cells housed in the tendon interfascicular matrix (IFM) are preferentially affected by ageing. There is, however, a lack of established surface markers for cell populations in tendon, limiting the capacity to isolate distinct cell populations and study their contribution to age-related tendon degeneration. Here, we investigate the presence of the cell surface proteins MET proto-oncogene (MET), integrin subunit alpha 10 (ITGA10), fibroblast activation protein alpha (FAP) and platelet derived growth factor receptor alpha (PDGFRA) in the equine SDFT cell populations and their co-localisation with known markers. Using Western blot we validated the specificity of selected antibodies in equine tissue before performing immunohistochemistry to establish the location of the respective proteins in the SDFT. We subsequently used double labelling immunofluorescence with the established mural cell marker desmin (DES) to distinguish between tenocyte and mural cell populations. In situ, MET, ITGA10, and FAP presence was found in cells throughout the tendon whereas PDGFRA was present in cells within the IFM. Double labelling immunofluorescence with the mural cell marker DES showed lack of co-localisation between PDGFRA and DES suggesting PDGFRA is labelling an IFM cell population distinct from those associated with blood vessels. PDGFRA is a promising target for the specific cell sorting of IFM-localised tenocytes, enabling their isolation and subsequent characterisation. Acknowledgments: The authors acknowledge the Biotechnology and Biological Sciences Research Council (BB/W007282/1) for funding this work

Early changes within articular cartilage during human idiopathic osteoarthritis are poorly understood. However alterations to chondrocyte morphology occur with the development of fine cytoplasmic processes and cell clusters, potentially playing a role in cartilage degeneration. The aggrecanase ADAMTS-4 (A disintegrin and metalloproteinase with thrombospondin motifs-4) has been implicated as an important factor in cartilage degradation, so we investigated the relationship between chondrocyte morphology and levels of ADAMTS-4 in both non-degenerate and mildly osteoarthritic human cartilage. Human femoral heads were obtained following consent from patients undergoing hip arthroplasty following femoral neck fracture. Cartilage explants of normal (grade 0; G0) and mildly osteoarthritic (grade 1; G1) cartilage were labelled with the cytoplasmic dye CMFDA (5-chloromethylfluorescein-diacetate). Explants were cryosectioned (30μm sections), and labelled for ADAMTS-4 by fluorescence immunohistochemistry. Sections were imaged with confocal microscopy, allowing the semi-quantitative analysis of ADAMTS-4 and 3D visualisation of in situ cell morphology. With cartilage degeneration from G0 to G1, there was a decrease in the proportion of chondrocytes with normal rounded morphology (P<0.001) but an increase in the proportion of cells with processes (P<0.01) and those in clusters (P<0.001;[4(1653)]; femoral heads:cells). Although average levels of ADAMTS-4 for all cells was the same between G0 and G1 (P>0.05), a change was evident in the distribution curves for cell-specific ADAMTS-4 labelling. Cell-by-cell analysis showed that ADAMTS-4 levels were higher in chondrocytes with cytoplasmic processes compared to normal cells (P=0.044) however cells in clusters had lower levels than normal cells (P=0.003;[3(436)]). Preliminary data suggested that ADAMTS-4 levels increased with larger chondrocyte clusters. These results suggest complex heterogeneous changes to levels of cell-associated ADAMTS-4 with early cartilage degeneration – increasing in cells with processes and initially decreasing in clusters. Increased levels of ADAMTS-4 are likely to produce focal areas of matrix weakness potentially leading to early cartilage degeneration

The purpose of this study was to evaluate the beneficial effects of r-Irisin (IR) on human primary tenocytes (hTCs) in vitro. Indeed, Irisin is secreted from muscles in response to exercise and mediates many beneficial effects on tissues and organs. Tissue samples (n=3) were analyzed by histology and immunohistochemistry for αVβ5 receptor. hTCs isolated, culture expanded were treated with: 1) RPMI medium as control; 2) IR at different concentrations; 3) IL-1β; 4) pre-treated with IL-1β for 24 h and then co-treated with IR; 5) pre-treated with IR for 24 h and then co-treated with IL-1β. We evaluated: cell metabolic activity (MTT); cell proliferation (trypan blue staining and PicoGreen); nitrite concentration (Griess). The analysis were performed in triplicate for each donor and each experiment was repeated at least three times. Data were expressed as mean ± S.D. One-way ANOVA analysis was used to compare the groups under exam. We found the presence of the αVβ5 receptor on hTCs plasma membrane supporting the potential interaction with irisin. Cell proliferation was significantly increased with IR at 5, 10 and 25 ng/mL. IR 25 ng/mL after IL1β pre-treatment was able to counteract the increase of nitrite production (p < 0.001) compared to the inflamed hTCs (p < 0.01; p < 0.0001), as well as IR at 10 and 25 ng/ml showed a protective role from oxidative damage. We observed a significant increase in cell metabolic viability in culture under IR at 5 and 25 ng/mL (p < 0.001; p < 0.05) in the pre-treated IR groups, whereas IR showed anti-inflammatory effects at the highest concentration of r-Irisin (p < 0.05). This is the first study reporting the capability of irisin to attenuate tendinopathy in vitro by acting on acute inflamed tenocytes. Our results confirmed and highlighted the potential cross-talk mechanism between muscle and tendon

In this work, we combined tissue engineering and gene therapy technologies to develop a therapeutic platform for bone regeneration. We have developed photothermal fibrin-based hydrogels that incorporate degradable CuS nanoparticles (CuSNP) which transduce incident near-infrared (NIR) light into heat. A heat-activated and rapamycin-dependent transgene expression system was incorporated into mesenchymal stem cells to conditionally control the production of bone morphogenetic protein 2 (BMP-2). Genetically engineered cells were entrapped in the photothermal hydrogels. In the presence of rapamycin, photoinduced mild hyperthermia induced the release of BMP-2 from the NIR responsive cell constructs. Transcriptome analysis of BMP-2 expressing cells showed a signature of induced genes related to stem cell proliferation and angiogenesis. We next generated 4 mm diameter calvarial defects in the left parietal bone of immunocompetent mice. The defects were filled with NIR-responsive hydrogels entrapping cells that expressed BMP-2 under the control of the gene circuit. After one and eight days, rapamycin was administered intraperitoneally followed by irradiation with an NIR laser. Ten weeks after implantation, the animals were euthanized and samples from the bone defect zone were processed for histological analysis using Masson's trichrome staining and for immunohistochemistry analyses using specific CD31 and CD105 antibodies. Samples from mice that were only administered rapamycin or vehicle or that were only NIR-irradiated showed the persistence of fibrous tissue bridging the defect. In animals that were treated with rapamycin, NIR irradiation of implants resulted in the formation of new mineralized tissue with a high degree of vascularization, thus indicating the therapeutic potential of the approach. Acknowledgements: This research was supported by grants RTI2018-095159-B-I00 and PID2021-126325OB-I00 (MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”), by grant P2022/BMD- 7406 (Regional Government of Madrid). M.A.L-J. is the recipient of predoctoral fellowship PRE2019-090430 (MCIN/AEI/10.13039/501100011033)

In cartilage tissue engineering (TE),new solutions are needed to effectively drive chondrogenic differentiation of mesenchymal stromal cells in both normal and inflammatory milieu. Ultrasound waves represent an interesting tool to facilitate chondrogenesis. In particular, low intensity pulsed ultrasound (LIPUS)has been shown to regulate the differentiation of adipose mesenchymal stromal cells. Hydrogels are promising biomaterials capable of encapsulating MSCs by providing an instructive biomimetic environment, graphene oxide (GO) has emerged as a promising nanomaterial for cartilage TE due to its chondroinductive properties when embedded in polymeric formulations, and piezoelectric nanomaterials, such as barium titanate nanoparticles (BTNPs),can be exploited as nanoscale transducers capable of inducing cell growth/differentiation. The aim of this study was to investigate the effect of dose-controlled LIPUS in counteracting inflammation and positively committing chondrogenesis of ASCs embedded in a 3D piezoelectric hydrogel. ASCs at 2*10. 6. cells/mL were embedded in a 3D VitroGel RGD. ®. hydrogel without nanoparticles (Control) or doped with 25 µg/ml of GO nanoflakes and 50 µg/ml BTNPs.The hydrogels were exposed to basal or inflammatory milieu (+IL1β 10ng/ml)and then to LIPUS stimulation every 2 days for 10 days of culture. Hydrogels were chondrogenic differentiated and analyzed after 2,10 and 28 days. At each time point cell viability, cytotoxicity, gene expression and immunohistochemistry (COL2, aggrecan, SOX9, COL1)and inflammatory cytokines were evaluated. Ultrasound stimulation significantly induced chondrogenic differentiation of ASCs loaded into 3D piezoelectric hydrogels under basal conditions: COL2, aggrecan and SOX9 were significantly overexpressed, while the fibrotic marker COL1 decreased compared to control samples. LIPUS also has potent anti-inflammatory effects by reducing IL6 and IL8 and maintaining its ability to boost chondrogenesis. These results suggest that the combination of LIPUS and piezoelectric hydrogels promotes the differentiation of ASCs encapsulated in a 3D hydrogel by reducing the inflammatory milieu, thus representing a promising tool in the field of cartilage TE. Acknowledgements: This work received funding from the European Union's Horizon 2020 research and innovation program, grant agreement No 814413, project ADMAIORA (AdvanceD nanocomposite MAterIals for in situ treatment and ultRAsound-mediated management of osteoarthritis)

Abstract. Cranial cruciate ligament (CrCL) disease/rupture causes pain and osteoarthritis (OA) in dogs. α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-2 and kainate (KA)-1 glutamate receptors (GluR) and the excitatory amino acid transporter-1 (EAAT-1) and EAAT-3 are expressed in joint tissues from OA patients and rodent arthritis models and represent potential therapeutic targets. Objectives. To evaluate glutamate signalling in canine diseased and normal CrCL and meniscus by immunohistochemistry (IHC). Methods. Surgical waste (CrCL, n=5 and medial meniscus, n=3) were obtained from canines with CrCL disease (RCVS ethics approval:2017/14/Alves) and normal analogous tissues (n=2). IHC optimization was performed for rabbit polyclonal (AMPA-2:ab52176, KA-1:ab67402, EAAT-1:ab416) and monoclonal (EAAT-3:ab124802) antibodies from Abcam. IHC was optimised over antibody dilutions from 1:100 to 1:5000 alongside equivalent IgG isotype controls (ab37415 and ab172730) and negative controls (TBS/Tween buffer without primary antibodies). IHC staining was compared in diseased and normal tissues and disclosed with 3,3’-Diaminobenzidine (DAB). Results. Specific immunostaining was observed for all primary antibodies, at concentrations between 2.0×10. −4. mg/mL to 1.0×10. −2. mg/mL, depending on the tissue and primary antibody. All GluR and transporters were expressed in the cellular membrane, in the normal and diseased CrCL and meniscus. Healthy CrCL showed a well-organized microstructure, with normal positively labelled ligamentocytes, whereas diseased CrCL microstructure was disrupted, with many positively stained fibroblastic cells in the epiligamentous region and evident neovascularization, indicative of ongoing repair. The normal and diseased meniscal tissues showed similar chondrocytes-like cells labelling and microstructure. Negative controls demonstrated no labelling. Conclusions. GluR and transporters expression is altered in canine diseased CrCLs, implicating glutamate signalling in this pathology. Since AMPA/KA GluR antagonists alleviate joint degeneration in post-traumatic OA in rodent models, they may be useful for the treatment of CrCL disease in dogs, as well as translated to other veterinary and human orthopaedic diseases