Objective: Mechanical loading and joint health have a unique relationship in osteoarthritis (OA) onset and progression. Although high load levels adversely affect cartilage health, exercise that involves low to moderate load levels can alleviate OA symptoms. We sought to isolate the beneficial effects of mechanical loading using controlled in vivo cyclic tibial compression. We hypothesized that low-level cyclic compression would attenuate post-traumatic OA symptoms induced by destabilization of the medial meniscus (DMM). Methods: 10-week-old C57Bl/6J male mice underwent DMM surgery (n ¼ 51). After a 5-day postoperative recovery period, we applied daily cyclic tibial compression to the operated limbs at low (1.0N or 2.0N) or moderate (4.5N) magnitudes for 2 or 6 weeks. At the completion of loading, we compared cartilage and peri-articular bone features of mice that underwent DMM and loading to mice that only underwent DMM. Results: Compared to DMM alone, low-level cyclic compression for 6 weeks attenuated DMM-induced cartilage degradation (OARSI score, P ¼ 0.008, 95% confidence interval (CI): 0.093 to 0.949). Low-level loading attenuated DMM-induced osteophyte formation after 2 weeks (osteophyte size, P ¼ 0.033, 95% CI: 3.27e114.45 mm), and moderate loading attenuated subchondral bone sclerosis after 6 weeks (tissue mineral density (TMD), P ¼ 0.011, 95% CI: 6.32e70.60 mg HA/ccm) compared to limbs that only underwent DMM. Finally, loading had subtle beneficial effects on cartilage cellularity and aggrecanase activity after DMM. Conclusion: Low-level cyclic compression is beneficial to joint health after an injury. Therefore, the progression of early OA may be attenuated by applying well controlled, low-level loading shortly following joint trauma.
In mammals, hematopoiesis migrates to the bone marrow during embryogenesis coincident with the appearance of mineralized bone, where hematopoietic stem cells (HSCs) and their progeny are maintained by the surrounding microenvironment or niche, and sustain the entirety of the hematopoietic system. Genetic manipulation of niche factors and advances in cell lineage tracing techniques have implicated cells of both hematopoietic and nonhematopoietic origin as important regulators of hematopoiesis in health and disease. Among them, cells of the osteoblast lineage, from stromal skeletal stem cells to matrix-embedded osteocytes, are vital niche residents with varying capacities for hematopoietic support depending on stage of differentiation. Here, we review populations of osteoblasts at differing stages of differentiation and summarize the current understanding of the role of the osteoblast lineage in supporting hematopoiesis.
Teriparatide, recombinant parathyroid hormone (PTH[1‐34]), and abaloparatide, an analogue of PTH related‐peptide (PTHrP[1‐34]), are both anabolic medications for osteoporosis that target the PTH receptor PTH1R. PTH1R is a G protein–coupled receptor, and the stimulatory Gs protein is an important mediator of the anabolic actions of PTH1R activation in bone. We have published that mice lacking the α subunit of Gs in osteoprogenitors do not increase bone mass in response to PTH(1‐34). Unexpectedly, however, PTH(1‐34) still increases osteoblast numbers and bone formation rate in male mice, suggesting that PTH1R may have both Gs‐dependent and ‐independent actions in bone. Here we examine the role of Gs signaling in the anabolic actions of abaloparatide. We find that abaloparatide increases bone formation in male mice with postnatal deletion of G s α in Osx‐expressing osteoprogenitors (P‐G s α OsxKO mice) but not in female P‐G s α OsxKO mice. Therefore, abaloparatide has anabolic effects on bone in male but not female mice that appear to be independent of Gs‐mediated signaling. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
mine-induced cognitive deficit and that its anti-amnesic effect might be due to the activation of choline acetyltransferase. acetyltransferase. acetyltransferase. acetyltransferase. acetyltransferase.
Osteoarthritis (OA) is a degenerative disease that manifests as joint damage and synovial inflammation. To date, most studies have focused on the decrease in cartilage stiffness, chondrocyte viability, and changes in matrix-degrading enzymes. With the exception of a few inflammatory cytokines and macrophages, the immune response in OA is poorly characterized, and the crosstalk of joint damage with T and B cells in local lymph nodes is unknown. Here, using an in vivo mouse model of mechanical loading of mouse tibia, we demonstrate that CD8+ T cells and subsets of CD4+ T cells, and not B cells, increase in the local lymph nodes and contribute to the progression of load-induced OA pathology. We demonstrate that T cell response is sex-and age-dependent. Mechanical loading of T cell knock-out mice that lack αβ T cell receptor carrying cells resulted in attenuation of both cartilage degradation and osteophyte formation in loaded joints, with a concomitant increase in γδ+ T cells. Restricting the migration of T cells in lymphoid tissues through the systemic treatment using Sphingosine-1-phosphate (S1P) inhibitor, decreased localization of T cells in synovium, and attenuated cartilage degradation. Our results lay the foundation of the role T cells play in the joint damage of load-induced OA and allude to the use of S1P inhibitors and T cell immunotherapies for slowing the progression of OA pathology.
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