Roles of fibrinolytic factors in the alterations in bone marrow hematopoietic stem/progenitor cells during bone repair
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(2020) 40:22
REVIEW
Inflammation and Regeneration
Open Access
Roles of fibrinolytic factors in the alterations in bone marrow hematopoietic stem/progenitor cells during bone repair Kiyotaka Okada1,2*, Minoru Nishioka2 and Hiroshi Kaji2
Abstract In bone tissues, metabolic turnover through bone resorption by osteoclasts and bone formation by osteoblasts, termed bone remodeling, is strictly controlled and maintains homeostasis. Fibrinolytic factors are expressed in osteoclasts and osteoblasts, and are involved in bone remodeling through bone resorption and formation. The repair/regeneration process after bone injury is divided into the acute inflammatory, repair, and remodeling stages. Osteoblasts, osteoclasts, chondrocytes, and macrophages involved in the bone repair process originate from hematopoietic stem/progenitor cells (HSPCs) and mesenchymal stem cells (MSCs) in the bone marrow. Therefore, stem cells in the bone marrow may be strongly influenced by bone injury. The urokinase-type PA (u-PA)/ plasminogen (Plg) system functions in macrophage accumulation/phagocytosis through chemokines in the acute inflammatory stage, and Plg increases blood vessel-related growth factor expression, being involved in vascularization in mice. Plasminogen activator inhivitor-1 (PAI-1) causes bone loss and delayed bone repair through the inhibition of osteoblast differentiation in a drug-induced diabetes model in mice. Plg is considered to induce transforming growth factor-β (TGF-β) production in macrophages in the bone repair process, TGF-β release from the extracellular matrix through the activation of matrix metalloproteinase-9 (MMP-9), and stromal cell-derived factor-1 (SDF-1) expression in endosteal preosteoblasts, leading to the induction of bone marrow HSPCs in mice. Based on the above, establishment of a fibrinolytic factor-targeting method efficiently promoting bone repair/ regeneration and fracture healing, and development of a new osteoporosis treatment method and diagnostic marker are awaited. Keywords: Bone regeneration, Fibrinolytic factor, Hematopoietic stem/progenitor cells, Stromal cell-derived factor-1, Transforming growth factor-β
Background In bone tissues, metabolic turnover, termed bone remodeling, takes place actively. By this mechanism, bone resorption by osteoclasts and bone formation by osteoblasts are strictly controlled and maintain homeostasis [1]. When the balance of bone remodeling is broken and bone resorption relatively surpasses bone formation, the bone mineral density decreases, resulting * Correspondence: [email protected] 1 Department of Arts and Science, Kindai University Faculty of Medicine, Osaka-Sayama, Osaka 589-8511, Japan 2 Department of Physiology and Regenerative Medicine, Kindai University Faculty of Medicine, Osaka-Sayama, Osaka 589-8511, Japan
in osteoporosis. In the regulation of bone metabolism, endocrine factors, such as parathyroid hormone, play a central role [2]. Regulation by the nervous system and regulatory mechanisms by humoral factors secreted from other tissu
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