Objective Macrophages are believed to play a critical role in the inflammation associated with the development of osteoarthritis (OA) in obesity. The objective of the study was to investigate whether short-term, systemic depletion of macrophages would mitigate OA following injury in obese mice. Methods CSF-1R–GFP+ Macrophage Fas-Induced Apoptosis (MaFIA) transgenic mice that allow conditional depletion of macrophages were placed on a high-fat diet and underwent surgery to induce knee OA. A small molecule (AP20187) was administrated to deplete macrophages in MaFIA mice. The effect of macrophage depletion on acute joint inflammation, OA severity, and arthritic bone changes were evaluated using histology and microCT. Immunohistochemistry was used to identify various immune cells. Serum and synovial fluid cytokines were also measured. Results Macrophage-depleted mice had significantly fewer M1 and M2 macrophages in the surgical operated-joints relative to controls and exhibited decreased osteophyte formation immediately following depletion. Surprisingly, macrophage depletion did not attenuate OA with obesity; instead, it induced systemic inflammation and led to a massive infiltration of CD3+ T cells and particularly neutrophils, but not B cells, into the injured joints. Macrophage-depleted mice also demonstrated markedly increased pro-inflammatory cytokines including granulocyte-colony stimulating factor (G-CSF), IL-1β, IL-6, IL-8, and TNF-α in both serum and joint synovial fluid, although animals showed trends for decreased serum insulin and leptin levels after depletion. Conclusion Our findings indicate that macrophages are vital in modulating the homeostasis of immune cells in obesity and suggest that more targeted approaches of different macrophage subtypes may be necessary to mitigate inflammation and OA with obesity.

Background Soft tissue repair is currently limited by the availability of autologous tissue sources and the absence of an ideal soft tissue replacement comparable to native adipose tissue. Extracellular matrix (ECM)-based biomaterials have demonstrated great potential as instructive scaffolds for regenerative medicine, mechanically and biochemically defined by the tissue of origin. As such, the distinctive high lipid content of adipose tissue requires unique processing conditions to generate a biocompatible scaffold for soft tissue repair. Methods Human adipose tissue was decellularized to obtain a matrix devoid of lipids and cells, while preserving ECM architecture and bioactivity. To control degradation and volume persistence, the scaffold was crosslinked using hexamethylene diisocyanate and 1-Ethyl-3-(-3-dimethylaminopropyl) carbodiimide. In vitro studies with human adipose-derived stem cells were used to assess cell viability and adipogenic differentiation on the biomaterial. In vivo biocompatibility and volume persistence were evaluated by subcutaneous implantation over 12 weeks in a small animal model. Results The scaffold provided a biocompatible matrix supporting the growth and differentiation of adipose-derived stem cells in vitro. Crosslinking the matrix increased its resistance to enzymatic degradation. Subcutaneous implantation of the acellular adipose matrix in Sprague-Dawley rats showed minimal inflammatory reaction. Adipose tissue development and vascularization was observed in the implant, with host cells migrating into the matrix indicating the instructive potential of the matrix for guiding tissue remodeling and regeneration. Conclusions With its unique biological and mechanical properties, decellularized adipose ECM is a promising biomaterial scaffold that can potentially be used allogenically for the correction of soft tissue defects.

Post-traumatic arthritis (PTA) is a rapidly progressive form of arthritis that develops due to joint injury, including articular fracture. Current treatments are limited to surgical restoration and stabilization of the joint; however, evidence suggests that PTA progression is mediated by the upregulation of pro-inflammatory cytokines, such as interleukin-1 (IL-1) or tumor necrosis factor-α (TNF-α). Although these cytokines provide potential therapeutic targets for PTA, intra-articular injections of anti-cytokine therapies have proven difficult due to rapid clearance from the joint space. In this study, we examined the ability of a cross-linked elastin-like polypeptide (xELP) drug depot to provide sustained intra-articular delivery of IL-1 and TNF-α inhibitors as a beneficial therapy. Mice sustained a closed intra-articular tibial plateau fracture; treatment groups received a single intra-articular injection of drug encapsulated in xELP. Arthritic changes were assessed 4 and 8 weeks after fracture. Inhibition of IL-1 significantly reduced the severity of cartilage degeneration and synovitis. Inhibition of TNF-α alone or with IL-1 led to deleterious effects in bone morphology, articular cartilage degeneration, and synovitis. These findings suggest that IL-1 plays a critical role in the pathogenesis of PTA following articular fracture, and sustained intra-articular cytokine inhibition may provide a therapeutic approach for reducing or preventing joint degeneration following trauma.