To develop an imaging mass cytometry method for identifying complex cell phenotypes, inter-cellular interactions, and population changes in the synovium and infrapatellar fat pad (IFP) of the mouse knee following a non-invasive compression injury. Fifteen male C57BL/6 mice were fed a high-fat diet for 8 weeks prior to random assignment to sham, 0.88 ​mm, or 1.7 ​mm knee compression displacement at 24 weeks of age. 2-weeks after loading, limbs were prepared for histologic and imaging mass cytometry analysis, focusing on myeloid immune cell populations in the synovium and IFP. 1.7 ​mm compression caused anterior cruciate ligament (ACL) rupture, development of post-traumatic osteoarthritis, and a 2- to 3-fold increase in cellularity of synovium and IFP tissues compared to sham or 0.88 ​mm compression. Imaging mass cytometry identified 11 myeloid cell subpopulations in synovium and 7 in IFP, of which approximately half were elevated 2 weeks after ACL injury in association with the vasculature. Notably, two monocyte/macrophage subpopulations and an MHC II^hi population were elevated 2-weeks post-injury in the synovium but not IFP. Vascular and immune cell interactions were particularly diverse in the synovium, incorporating 8 unique combinations of 5 myeloid cell populations, including a monocyte/macrophage population, an MHC II^hi population, and 3 different undefined F4/80⁺ myeloid populations. Developing an imaging mass cytometry method for the mouse enabled us to identify a diverse array of synovial and IFP vascular-associated myeloid cell subpopulations. These subpopulations were differentially elevated in synovial and IFP tissues 2-weeks post injury, providing new details on tissue-specific immune regulation.

Background/Objectives: Osteoarthritis is a degenerative joint disease that affects people worldwide. It is characterized by joint pain, synovial inflammation, and the degradation of articular cartilage with subchondral bone. Presently, there is no known cure, and pharmacological treatment options are limited. Blueberries contain phytochemicals, which have been linked to positive health benefits and may offer therapeutic benefits. Therefore, the purpose of this study was to examine the dose-dependent effects of whole blueberries on arthritis symptoms in a monosodium iodoacetate (MIA)-induced rat model of osteoarthritis. Methods: Forty female rats were used for this study. Thirty were injected with MIA to induce joint degradation associated with osteoarthritis. Ten served as controls without MIA induction. The MIA-induced rats were randomized into three groups. All groups were fed a casein-based diet, with two of the MIA-induced groups receiving an addition of whole-blueberry powder at 5% and 10%. Fasted blood specimens and tissues of interest were collected post-euthanasia for analysis. Mechanical allodynia and joint widths were assessed throughout this study. Results: MIA induction resulted in changes in pain behaviors and the development of mechanical allodynia. The MIA injection produced inflammation, pain symptoms, and behaviors that are representative of those observed in humans with osteoarthritis. The incorporation of whole blueberries into diets reduced pain behaviors and inflammation. Conclusions: Overall, whole blueberries showed limited, non-dose-dependent effects in the MIA-induced rat model of osteoarthritis. While some outcomes improved in blueberry-treated groups, the overall results were not consistently significant. These preliminary findings suggest potential biological activity and support the further investigation of blueberries’ therapeutic efficacy.