Increase of circulating CD11b(+)Gr1(+) cells and recruitment into the synovium in osteoarthritic mice with hyperlipidemia

OA foundations - experimental models of osteoarthritis

Osteoarthritis (OA) is increasingly recognised as a disease of diverse phenotypes with variable clinical presentation, progression, and response to therapeutic intervention. This same diversity is readily apparent in the many animal models of OA. However, model selection, study design, and interpretation of resultant findings, are not routinely done in the context of the target human (or veterinary) patient OA sub-population or phenotype. This review discusses the selection and use of animal models of OA in discovery and therapeutic-development research. Beyond evaluation of the different animal models on offer, this review suggests focussing the approach to OA-animal model selection on study objective(s), alignment of available models with OA-patient sub-types, and the resources available to achieve valid and translatable results. How this approach impacts model selection is discussed and an experimental design checklist for selecting the optimal model(s) is proposed. This approach should act as a guide to new researchers and a reminder to those already in the field, as to issues that need to be considered before embarking on in vivo pre-clinical research. The ultimate purpose of using an OA animal model is to provide the best possible evidence if, how, when and where a molecule, pathway, cell or process is important in clinical disease. By definition this requires both model and study outcomes to align with and be predictive of outcomes in patients. Keeping this at the forefront of research using pre-clinical OA models, will go a long way to improving the quality of evidence and its translational value.

Mild hypobaric hypoxia influences splenic proliferation during the later phase of stress erythropoiesis

Tissue trauma and hemorrhagic shock are common battlefield injuries that can induce hypoxia, inflammation, and/or anemia. Inflammation and hypoxia can initiate adaptive mechanisms, such as stress erythropoiesis in the spleen, to produce red blood cells and restore the oxygen supply. In a military context, mild hypobaric hypoxia-part of the environmental milieu during aeromedical evacuation or en route care-may influence adaptive mechanisms, such as stress erythropoiesis, and host defense. In the present study, healthy (control), muscle trauma, and polytrauma (muscle trauma and hemorrhagic shock) mice were exposed to normobaric normoxia or hypobaric hypoxia for ∼17.5 h to test the hypothesis that hypobaric hypoxia exposure influences splenic erythropoiesis and splenic inflammation after polytrauma. This hypothesis was partially supported. The polytrauma + hypobaric hypoxia group exhibited more splenic neutrophils, fewer total spleen cells, and fewer splenic proliferating cells than the polytrauma+normobaric normoxia group; however, no splenic erythroid cell differences were detected between the two polytrauma groups. We also compared splenic erythropoiesis and myeloid cell numbers among control, muscle trauma, and polytrauma groups. More reticulocytes at 1.7 days (40 h) post-trauma (dpt) and neutrophils at 4 dpt were produced in the muscle trauma mice than corresponding control mice. In contrast to muscle trauma, polytrauma led to a reduced red blood cell count and elevated serum erythropoietin levels at 1.7 dpt. There were more erythroid subsets and apoptotic reticulocytes in the polytrauma mice than muscle trauma mice at 4 and 8 dpt. At 14 dpt, the red blood cell count of the polytrauma + normobaric normoxia mice was 12% lower than that of the control + normobaric normoxia mice; however, no difference was observed between polytrauma + hypobaric hypoxia and control + hypobaric hypoxia mice. Our findings suggest muscle trauma alone induces stress erythropoiesis; in a polytrauma model, hypobaric hypoxia exposure may result in the dysregulation of splenic cells, requiring a treatment plan to ensure adequate immune functioning.

Regulation of Tumor Necrosis Factor-α by Peptide Lv in Bone Marrow Macrophages and Synovium

Background: Bone marrow-derived monocytes/macrophages are recruited into synovial tissue, where they contribute to synovial inflammation in osteoarthritis through inflammatory cytokine production. Recent studies have suggested that V-Set and transmembrane domain-containing 4 (VSTM4) and its fragment, peptide Lv, exhibit immunosuppressive activity on T cells and vascular endothelial growth factor (VEGF)-like activity, respectively. Given that evidence suggests that VEGF may play a role in macrophage function, we investigated peptide Lv-mediated regulation of inflammatory cytokines in bone marrow macrophages (BMMs) and synovial inflammation. Method: To investigate the effects of peptide Lv, BMMs were stimulated with vehicle, LPS, or LPS + peptide Lv, and Tnfa, Il1b, Il6, and Ifng expression were evaluated using quantitative PCR (qPCR). TNF-α and IFN-γ production was measured using ELISA. To examine the effect of peptide Lv deficiency on macrophages and synovitis, peptide Lv-deficient mice were generated using genome editing. LPS-induced Tnfa and Ifng expression and TNF-α and IFN-γ production were evaluated in BMM isolated from wild-type and peptide Lv-deficient mice. Additionally, Tnfa and Ifng expression levels were compared between wild-type and peptide Lv-deficient mice before and after knee injury. Results: Peptide Lv suppressed the LPS-mediated elevation in TNF-α and IFN-γ. LPS stimulation significantly increased TNF-α and IFN-γ production in BMM derived from peptide Lv-deficient mice compared to wild-type mice. Synovial TNF-α expression in the injured knee was elevated in peptide Lv-deficient compared to wild-type mice. Conclusion: Peptide Lv suppressed TNF-α in macrophages and plays a role in synovial inflammation. Thus, peptide Lv may be a useful therapeutic target for synovitis.

Investigation of resident and recruited macrophages following disc injury in mice

Macrophages, particularly M1 macrophages, produce proinflammatory cytokines and contribute to the degenerative process in injured intervertebral discs (IVDs). We previously showed that macrophages in both intact and injured IVDs increased following IVD injury. Resident macrophages and macrophages recruited from the peripheral blood have distinct roles in tissue. However, it remains to be determined whether increased macrophages derive from resident or recruited macrophages. We investigated the origin of M1 macrophages in injured IVDs using green fluorescent protein (GFP) transgenic bone marrow chimeric mice. The M1 macrophage marker, CD86, increased in both disc-derived resident macrophages and bone marrow-derived macrophages (BMMs) after lipopolysaccharide/interferon γ stimulation in vitro. Following IVD injury, the proportion of cells positive for the CD86 ligand, the F4/80 antigen, and the surface glycoprotein CD11b (CD86+ CD11b+ F4/80+) significantly increased in GFP+ populations at days 3, 7, and 14. In contrast, CD86+ CD11b+ F4/80+ cells in GFP- populations significantly increased on day 3, and thereafter decreased on days 7 and 14. The proportion of CD86+ CD11b+ F4/80+ cells in the GFP+ populations was significantly higher than that in the GFP- populations at days 1, 3, 7, and 14. Monocyte chemoattractant protein-1 expression in disc-derived macrophages, but not in BMMs, increased following interleukin-1β stimulation. Our results suggest M1 macrophages following IVD injury originate from recruited macrophages. Resident macrophages may behave differently in IVD injury. The role of resident macrophages needs to be clarified. Further investigation is needed.

Allogeneic yet major histocompatibility complex-matched bone marrow transplantation in mice results in an impairment of osteoblasts and a significantly reduced trabecular bone

Secondary osteopenia following allogeneic bone marrow or stem cell transplantation (BMT or HSCT) is a significant source of morbidity in patients. It is believed to be caused by a number of factors related to the myeloablative conditioning and subsequent therapy regimen. We here aimed to investigate whether the allogeneic bone marrow by itself directly impacts on the bone mass of the patient. We thus performed syn- and allogeneic BMT between two inbred mouse strains, which share an identical major histocompatibility complex background yet differ in their bone phenotypes. BMT was well tolerated, yielded survival rates of 97% and allowed for a regular physiological development. However, allogeneic BMT led to a significant reduction of trabecular bone mass that was independent of strain, sex, immunosuppressive medication, complications resulting from graft versus host disease, underlying bone phenotype and numbers of osteoclasts. Instead, reduced trabecular bone mass correlated with reduced plasma levels of amino-terminal propeptide of type I collagen. Our results suggest that osteopenia following allogeneic BMT is significantly influenced by an impaired osteoblast activity that may stem from a lack of communication between the resident osteoblasts and an allogeneic bone marrow-derived cell type. Elucidating this incompatibility will open new approaches for the therapy of secondary osteopenia.

Nerve Growth Factor Regulation by TNF-α and IL-1β in Synovial Macrophages and Fibroblasts in Osteoarthritic Mice

To investigate the role of macrophages as a regulator and producer of nerve growth factor (NGF) in the synovial tissue (ST) of osteoarthritis (OA) joints, the gene expression profiles of several inflammatory cytokines in the ST, including synovial macrophages and fibroblasts, of OA mice (STR/Ort) were characterized. Specifically, real-time polymerase chain reaction analysis was used to evaluate the expression of tumor necrosis factor- (TNF-) α, interleukin- (IL-) 1β, IL-6, and NGF in CD11b+ and CD11b- cells isolated from the ST of a murine OA model. The effects of TNF-α, IL-1β, and IL-6 on the expression of NGF in cultured synovial cells were also examined. The expression of TNF-α, IL-1β, IL-6, and NGF in the ST of STR/Ort was higher than that in C57/BL6J mice. Compared to the CD11b- cell fraction, higher expression levels of TNF-α, IL-1β, and IL-6 were detected in the CD11b+ cell fraction, whereas no differences in the expression of NGF were detected between the two cell fractions. Notably, TNF-α upregulated NGF expression in synovial fibroblasts and macrophages and IL-1β upregulated NGF expression in synovial fibroblasts. IL-1β and TNF-α may regulate NGF signaling in OA joints and be suitable therapeutic targets for treating OA pain.

On the predictive utility of animal models of osteoarthritis

Animal models of osteoarthritis are extensively used for investigating disease pathways and for preclinical testing of novel therapies. Their predictive utility, however, has often been questioned, mainly because preclinical efficacy of novel therapeutics is poorly translated in clinical trials. In the current narrative review, we consider the preclinical models that were used to support undertaking clinical trials for disease-modifying osteoarthritis drugs, and compare outcomes between clinical and preclinical studies. We discuss this in light of the 1999 Food and Drug Administration draft guidelines for industry for use in the development of drugs, devices, and biological products intended for the treatment of osteoarthritis, which raised five considerations on the usefulness of osteoarthritis models. We systematically discuss what has been learnt regarding these five points since 1999, with emphasis on replicating distinct risk factors and subtypes of human osteoarthritis, and on comprehensive evaluation of the disease in animals, including pathology of all joint tissues, biomarker analysis, and assessment of pain and joint function. Finally, we discuss lessons learnt and propose some recommendations for how the evidence from preclinical research might be strengthened with a view to improving success in clinical translation.

CD11c(+) macrophages and levels of TNF-α and MMP-3 are increased in synovial and adipose tissues of osteoarthritic mice with hyperlipidaemia

To understand more clearly the link between osteoarthritis and hyperlipidaemia, we investigated the inflammatory macrophage subsets and macrophage-regulated matrix metalloprotease-3 (MMP-3) and A disintegrin and metalloprotease with thrombospondin motifs-4 (ADAMTS4) in synovial (ST) and adipose tissues (AT) of osteoarthritic mice with hyperlipidaemia (STR/Ort). CD11c(+) F4/80(+) CD11b(+) macrophage populations in the ST and AT of 9-month-old STR/Ort and C57BL/6J mice were characterized and compared by flow cytometry and real-time polymerase chain reaction (PCR) analyses. Expression of tumour necrosis factor (TNF)-α, MMP-3 and ADAMTS4, and the response of these factors to anionic liposomal clodronate induced-macrophage depletion were also evaluated by real-time PCR. Expression of TNF-α in CD11c(+) cells, which were isolated by magnetic beads, was compared to CD11c(-) cells. In addition, the effect of TNF-α on cultured synovial fibroblasts and adipocytes was investigated. CD11c(+) F4/80(+) CD11b(+) macrophages were increased in ST and AT of STR/Ort mice. The CD11c(+) cell fraction highly expressed TNF-α. Expression of TNF-α and MMP3 was increased in ST and AT, and was decreased upon macrophage depletion. TNF-α treatment of cultured synovial fibroblasts and adipocytes markedly up-regulated MMP-3. CD11c(+) F4/80(+) CD11b(+) macrophages were identified as a common inflammatory subset in the AT and ST of STR/Ort mice with hyperlipidaemia. The induction of inflammation in AT and ST may be part of a common mechanism that regulates MMP3 expression through TNF-α. Our findings suggest that increased numbers of CD11c(+) macrophages and elevated levels of TNF-α and MMP-3 in AT and ST may explain the relationship between hyperlipidaemia and OA.

Platelet rich plasma enhances the immunohistochemical expression of platelet derived growth factor and vascular endothelial growth factor in the synovium of the meniscectomized rat models of osteoarthritis

This study was carried out on a rat model of surgically-induced osteoarthritis (OA) to assess the histological and immunohistochemical changes in the synovial membrane and to evaluate the effects of intra-articular injection of platelet rich plasma (PRP) in such cases. Forty five male albino rats were divided into 3 equal groups; control, surgically-induced OA and surgically-induced OA followed by intra-articular injection of PRP. Knee joints were processed for histological and immunohistochemical staining with anti-platelet derived growth factor (PDGF-A) and anti-vascular endothelial growth factor (VEGF) and the area percentages of immunostaining were measured by digital image analysis. Serum levels of PDGF-A and VEGF were analyzed by ELISA. The osteoarthritis research society international (OARSI) score was significantly higher in OA (2433.8±254) than in control (230.4±37.8; p<0.001) and in PRP-treated tissues (759.7±45.8; p<0.001). The immunostained area percentages for PDGF-A was significantly higher in PRP-treated tissues (20.6±2.4) than in OA (11.06±1.3; p=0.007) and in control tissues (4.1±0.78; p<0.001). Likewise, the immunostained area percentage for VEGF was significantly higher in PRP-treated tissues (22.5±1.6) than in OA (14.9±1; p=0. 002) and in control tissues (6.5±0.7; p<0.001). ELISA analysis revealed a significant increase in serum levels of the PDGF-A and VEGF after intraarticular PRP injection when compared to the other groups (p<0.000). The present study concluded that intra-articular injection of PRP could produce optimizing effects in surgically induced OA in the form of; decreasing the OARSI score, improving the inflammatory events in synovium and modulating the PDGF-A and VEGF serum levels and synovial tissue immunoexpression. These effects could be reflected positively on the associated chondral defect.