Objective Diagnosis of periprosthetic joint infection (PJI) in patients with inflammatory arthritis (IA) is challenging, as features of IA flares can mimic infection. We aimed to cross-sectionally determine if the optimal tests to diagnose PJI in osteoarthritis were present in patients with IA flares. Methods We enrolled patients from October 2020 to July 2022 in 3 groups: (a) PJI—total joint arthroplasty patients undergoing revision for infection, (b) IA Flare—IA patients with a flaring native joint, and (c) IA Aseptic—total joint arthroplasty patients with IA undergoing aseptic arthroplasty revision. We compared blood and synovial fluid markers between the cohorts using Kruskal-Wallis and Fisher exact tests to assess marker sensitivity and specificity. Results Of 52 cases overall, 40% had rheumatoid arthritis, 20% psoriatic arthritis, and 11% osteoarthritis (in PJI group). PJI cases had higher C-reactive protein (CRP) and synovial fluid polymorphonuclear neutrophil percentage (%PMN). Alpha-defensin tested positive in 93% of PJI cases, 20% of IA Flares, and 6% of IA Aseptic (p < 0.01). Synovial white blood cell count >3000/μL and positive alpha-defensin were highly sensitive (100%) in diagnosing infection; however, specificity was 50% for white blood cell counts and 79% for alpha-defensin. PJI diagnosis was nearly 5 times more likely with positive alpha-defensin and almost 6 times more likely with %PMNs >80. Blood markers interleukin-6, procalcitonin, and d-dimer were neither sensitive nor specific, whereas erythrocyte sedimentation rate and CRP showed 80% sensitivity, but 47% and 58% respective specificities. Conclusions Although synovial %PMNs, CRP, and alpha-defensin are sensitive tests for diagnosing PJI, they are less specific and may be positive in IA flares.

Objective: Diagnosis of periprosthetic joint infection (PJI) in patients with inflammatory arthritis (IA) is challenging, as features of IA flares can mimic infection. We aimed to cross-sectionally determine if the optimal tests to diagnose PJI in osteoarthritis were present in patients with IA flares. Methods: We enrolled patients from October 2020 to July 2022 in 3 groups: (a) PJI-total joint arthroplasty patients undergoing revision for infection, (b) IA Flare-IA patients with a flaring native joint, and (c) IA Aseptic-total joint arthroplasty patients with IA undergoing aseptic arthroplasty revision. We compared blood and synovial fluid markers between the cohorts using Kruskal-Wallis and Fisher exact tests to assess marker sensitivity and specificity. Results: Of 52 cases overall, 40% had rheumatoid arthritis, 20% psoriatic arthritis, and 11% osteoarthritis (in PJI group). PJI cases had higher C-reactive protein (CRP) and synovial fluid polymorphonuclear neutrophil percentage (%PMN). Alpha-defensin tested positive in 93% of PJI cases, 20% of IA Flares, and 6% of IA Aseptic (p < 0.01). Synovial white blood cell count >3000/mu L and positive alpha-defensin were highly sensitive (100%) in diagnosing infection; however, specificity was 50% for white blood cell counts and 79% for alpha-defensin. PJI diagnosis was nearly 5 times more likely with positive alpha-defensin and almost 6 times more likely with %PMNs >80. Blood markers interleukin-6, procalcitonin, and d-dimer were neither sensitive nor specific, whereas erythrocyte sedimentation rate and CRP showed 80% sensitivity, but 47% and 58% respective specificities. Conclusions: Although synovial %PMNs, CRP, and alpha-defensin are sensitive tests for diagnosing PJI, they are less specific and may be positive in IA flares.

Inflammation of non-barrier immunologically quiescent tissues is associated with a massive influx of blood-borne innate and adaptive immune cells. Cues from the latter are likely to alter and expand activated states of the resident cells. However, local communications between immigrant and resident cell types in human inflammatory disease remain poorly understood. Here, we explored drivers of fibroblast-like synoviocyte (FLS) heterogeneity in inflamed joints of patients with rheumatoid arthritis using paired single-cell RNA and ATAC sequencing, multiplexed imaging and spatial transcriptomics along with in vitro modeling of cell-extrinsic factor signaling. These analyses suggest that local exposures to myeloid and T cell-derived cytokines, TNF, IFN-γ, IL-1β or lack thereof, drive four distinct FLS states some of which closely resemble fibroblast states in other disease-affected tissues including skin and colon. Our results highlight a role for concurrent, spatially distributed cytokine signaling within the inflamed synovium.

Aging is accompanied by osteopenia, characterized by reduced bone formation and increased bone resorption. Osteocytes, the terminally differentiated osteoblasts, are regulators of bone homeostasis, and parathyroid hormone (PTH) receptor (PPR) signaling in mature osteoblasts/osteocytes is essential for PTH-driven anabolic and catabolic skeletal responses. However, the role of PPR signaling in those cells during aging has not been investigated. The aim of this study was to analyze the role of PTH signaling in mature osteoblasts/osteocytes during aging. Mice lacking PPR in osteocyte (Dmp1-PPRKO) display an age-dependent osteopenia characterized by a significant decrease in osteoblast activity and increase in osteoclast number and activity. At the molecular level, the absence of PPR signaling in mature osteoblasts/osteocytes is associated with an increase in serum sclerostin and a significant increase in osteocytes expressing 4-hydroxy-2-nonenals, a marker of oxidative stress. In Dmp1-PPRKO mice there was an age-dependent increase in p16Ink4a/Cdkn2a expression, whereas it was unchanged in controls. In vitro studies demonstrated that PTH protects osteocytes from oxidative stress-induced cell death. In summary, we reported that PPR signaling in osteocytes is important for protecting the skeleton from age-induced bone loss by restraining osteoclast’s activity and protecting osteocytes from oxidative stresses.

Abstract Age-induced osteoporosis is characterized by a progressive decline in bone formation and increase in bone resorption with uncoupled activities of osteoblasts and osteoclasts. Parathyroid hormone (PTH) is used in the clinic to treat osteoporosis due to its anabolic actions on bone via binding to the PTH receptor (PPR). The receptor is highly expressed in cells of the osteoblastic lineage, including osteocytes. Osteocytes are the most abundant cells in bone and serve as a key regulator of bone remodeling. Despite the significant role of PPR signaling in skeletal homeostasis, its function in osteocytes during aging remains unclear. We have gathered preliminary data demonstrating that mice lacking PPR predominantly in osteocytes (Dmp1-PPRKO) have marked age-induced bone loss due to increased bone resorption and suppressed bone formation. These mice, with aging, develop characteristics of skeletal senescence: a decrease in osteoprogenitors and an increase in bone marrow adiposity and p16Ink4a/Cdkn2a expression in bone. Since senescence of cells in the bone microenvironment has been reported as a cause of age-induced bone loss, we hypothesized that PPR signaling protects osteocytes from senescence. To test this hypothesis, we generated osteocytes (Ocy454-12H), in which the PPR expression was ablated using CRISPR/Cas9 technique. Ocy454-12H-PPRKO and Ocy454-12H-PPRCtrl cells were treated with PTH followed by an exposure to hydrogen peroxide (H2O2). High levels of intracellular reactive oxygen species (ROS), including H2O2, promote protein and DNA oxidation, resulting in cell death and senescence. PTH treatment significantly suppressed the increase in H2O2-induced cell death, measured by resazurin-based assays, in PPRCtrl but not in PPRKO cells. We analyzed intracellular ROS levels using a fluorescent probe and found that PTH treatment significantly suppressed the increase in ROS upon H2O2 exposure, suggesting an antioxidant function of PTH in osteocytes. To further investigate if PTH prevents osteocytes from oxidative stress-induced senescence, we examined senescence-associated β-galactosidase (SA β-gal) activity in cells that were treated with PTH followed by an exposure to low doses of H2O2. Compared to untreated and PPRKO groups, treatment with PTH significantly decreased the number of SA β-gal positive cells, demonstrating that PPR signaling protects osteocytes, and possibly other osteoblastic cells, from H2O2-induced cellular senescence. PTH treatment reduced mRNA expression of p21/Cdkn1a. Taken together these results demonstrate that PPR signaling is important to protect osteocytes from cellular senescence.

The osteoinductive property of strontium was repeatedly proven in the last decades. Compellingin vitrodata demonstrated that strontium hydroxyapatite nanoparticles exert a dual action, by promoting osteoblasts-driven matrix secretion and inhibiting osteoclasts-driven matrix resorption. Recombinant human bone morphogenetic protein 2 (rhBMP2) is a powerful osteoinductive biologic, used for the treatment of vertebral fractures and critically-sized bone defects. Although effective, the use of rhBMP2 has limitations due its recombinant morphogen nature. In this study, we examined the comparison between two osteoinductive agents: rhBMP2 and the innovative strontium-substituted hydroxyapatite nanoparticles. To test their effectiveness, we independently loaded Gelfoam sponges with the two osteoinductive agents and used the sponges as agent-carriers. Gelfoam are FDA-approved biodegradable medical devices used as delivery system for musculoskeletal defects. Their porous structure and spongy morphology make them attractive in orthopedic field. The abiotic characterization of the loaded sponges, involving ion release pattern and structure investigation, was followed byin vivoimplantation onto the periosteum of healthy mice and comparison of the effects induced by each implant was performed. Abiotic analysis demonstrated that strontium was continuously released from the sponges over 28 days with a pattern similar to rhBMP2. Histological observations and gene expression analysis showed stronger endochondral ossification elicited by strontium compared to rhBMP2. Osteoclast activity was more inhibited by strontium than by rhBMP2. These results demonstrated the use of sponges loaded with strontium nanoparticles as potential bone grafts might provide better outcomes for complex fractures. Strontium nanoparticles are a novel and effective non-biologic treatment for bone injuries and can be used as novel powerful therapeutics for bone regeneration.

Bone is a highly metabolic organ that undergoes continuous remodeling to maintain its structural integrity. During development, bones, in particular osteoblasts, rely on glucose uptake. However, the role of glucose metabolism in osteocytes is unknown. Osteocytes are terminally differentiated osteoblasts orchestrating bone modeling and remodeling. In these cells, parathyroid hormone (PTH) suppresses Sost/sclerostin expression (a potent inhibitor of bone formation) by promoting nuclear translocation of class IIa histone deacetylase (HDAC) 4 and 5 and the repression of myocyte enhancer factor 2 (MEF2) type C. Recently, Scriptaid, an HDAC complex co-repressor inhibitor, has been shown to induce MEF2 activation and exercise-like adaptation in mice. In muscles, Scriptaid disrupts the HDAC4/5 co-repressor complex, increases MEF2C function, and promotes cell respiration. We hypothesized that Scriptaid, by affecting HDAC4/5 localization and MEF2C activation, might affect osteocyte functions. Treatment of the osteocytic Ocy454-12H cells with Scriptaid increased metabolic gene expression, cell respiration, and glucose uptake. Similar effects were also seen upon treatment with PTH, suggesting that both Scriptaid and PTH can promote osteocyte metabolism. Similar to PTH, Scriptaid potently suppressed Sost expression. Silencing of HDAC5 in Ocy454-12H cells abolished Sost suppression but not glucose transporter type 4 (Glut4) up-regulation induced by Scriptaid. These results demonstrate that Scriptaid increases osteocyte respiration and glucose uptake by mechanisms independent of HDAC complex inhibition. In osteocytes, Scriptaid, similar to PTH, increases binding of HDAC5 to Mef2c with suppression of Sost but only partially increases receptor activator of NF-B ligand (Rankl) expression, suggesting a potential bone anabolic effect.