ABSTRACT
Bone marrow adipocytes (BMAds) affect bone homeostasis, but the mechanism remains unclear. Here, we showed that exercise inhibited PCNA clamp-associated factor (PCLAF) secretion from the bone marrow macrophages to inhibit BMAds senescence and thus alleviated skeletal aging. The genetic deletion of PCLAF in macrophages inhibited BMAds senescence and delayed skeletal aging. In contrast, the transplantation of PCLAF-mediated senescent BMAds into the bone marrow of healthy mice suppressed bone turnover. Mechanistically, PCLAF bound to the ADGRL2 receptor to inhibit AKT/mTOR signaling that triggered BMAds senescence and subsequently spread senescence among osteogenic and osteoclastic cells. Of note, we developed a PCLAF-neutralizing antibody and showed its therapeutic effects on skeletal health in old mice. Together, these findings identify PCLAF as an inducer of BMAds senescence and provide a promising way to treat age-related osteoporosis.
Subject(s)
Adipocytes , Aging , Cellular Senescence , Animals , Adipocytes/metabolism , Cellular Senescence/physiology , Mice , Aging/physiology , Mice, Inbred C57BL , Bone Marrow Cells/metabolism , Bone and Bones/metabolism , Bone and Bones/physiology , Male , Osteogenesis/physiology , Signal Transduction , Macrophages/metabolismABSTRACT
Exercise can prevent osteoporosis and improve immune function, but the mechanism remains unclear. Here, we show that exercise promotes reticulocalbin-2 secretion from the bone marrow macrophages to initiate bone marrow fat lipolysis. Given the crucial role of lipolysis in exercise-stimulated osteogenesis and lymphopoiesis, these findings suggest that reticulocalbin-2 is a pivotal regulator of a local adipose-osteogenic/immune axis. Mechanistically, reticulocalbin-2 binds to a functional receptor complex, which is composed of neuronilin-2 and integrin beta-1, to activate a cAMP-PKA signaling pathway that mobilizes bone marrow fat via lipolysis to fuel the differentiation and function of mesenchymal and hematopoietic stem cells. Notably, the administration of recombinant reticulocalbin-2 in tail-suspended and old mice remarkably decreases bone marrow fat accumulation and promotes osteogenesis and lymphopoiesis. These findings identify reticulocalbin-2 as a novel mechanosensitive lipolytic factor in maintaining energy homeostasis in bone resident cells, and it provides a promising target for skeletal and immune health.
Subject(s)
Mesenchymal Stem Cells , Osteogenesis , Animals , Bone Marrow/metabolism , Bone Marrow Cells/metabolism , Cell Differentiation , Cells, Cultured , Lipolysis , Lymphopoiesis , Mesenchymal Stem Cells/metabolism , MiceABSTRACT
OBJECTIVES: Scavenger receptor class A, member 3 (Scara3) was involved in adipogenesis. However, the effect of Scara3 on the switch between osteogenesis and adipogenesis of bone marrow mesenchymal stem cells (BMSCs) remains elusive. MATERIALS AND METHODS: The correlations between SCARA3 with the osteogenic-related were analysed based on the GTEx database. The effects of Scara3 on osteogenic or adipogenic differentiation of BMSCs were evaluated by qPCR, Western blot (WB) and cell staining. The mechanisms of Scara3 regulating Foxo1 and autophagy were validated by co-expression analysis, WB and immunofluorescence. In vivo, Scara3 adeno-associated virus was injected into intra-bone marrow of the aged mice and ovariectomized (OVX) mice whose phenotypes were confirmed by micro-CT, calcein double labelling and immunochemistry (HE and OCN staining). RESULTS: SCARA3 was positively correlated with osteogenic-related genes. Scara3 expression gradually decreased during adipogenesis but increased during osteogenesis. Moreover, the deletion of Scara3 favoured adipogenesis over osteogenesis, whereas overexpression of Scara3 significantly enhanced the osteogenesis at the expense of adipogenesis. Mechanistically, Scara3 controlled the cell fate by promoting Foxo1 expression and autophagy flux. In vivo, Scara3 promoted bone formation and reduced bone marrow fat accumulation in OVX mice. In the aged mice, Scara3 overexpression alleviated bone loss as well. CONCLUSIONS: This study suggested that Scara3 regulated the switch between adipocyte and osteoblast differentiation, which represented a potential therapeutic target for bone loss and osteoporosis.
