IL-6 Contributes To The Defective Osteogenesis Of Bone Marrow Stromal Cells From The Vertebral Body Of The Glucocorticoid-induced Osteoporotic Mouse

Osteoporosis is one of the most prevalent skeletal system diseases. It is characterized by a decrease in bone mass and microarchitectural changes in bone tissue that lead to an attenuation of bone resistance and susceptibility to fracture. Glucocorticoid(GC)are potent immunomodulatory drugs that are commonly used to treat a variety of inflammatory conditions and autoimmune disorders. However, therapeutic use of GC often leads to sever clinical complications, such as bone loss and fracture risk. Glucocorticoid-induced osteoporosis is the most common form of secondary osteoporosis.Osteoporotic vertebral fracture(OVF) is by far the most prevalent osteoporotic fracture. In addition to pain, osteoporotic vertebral fractures result in immobility that can lead to chest infection, muscle loss, the inability to cope with daily activities, and social isolation. In the musculoskeletal system, osteoblasts, originated from bone marrow stromal cells(BMSC), are responsible for osteoid synthesis and mineralization. In osteoporosis, BMSC osteogenic differentiation is defective. However, to date, what leads to the defective BMSC osteogenesis in osteoporosis remains an open question. In the current study, we made attempts to answer this question.Fristly, a mouse model of glucocorticoid-induced osteoporosis(GIO) was established by subcutaneous implantation of slow-release pellets containing prednisolone for 4 weeks. At the time the mice were sacrificed, the thoracic and lumbar vertebrae(L1–L4) were prepared for bone minal density(BMD) measurement and BMSC isolation; L5 was used for histomorphometric analysis. Serum specimens were also taken for the measurement of osteocalcin and C-telopeptide of type I collagen(CTX-I). The BMSCs were induced to undergo osteogenesis by BMP2 in vitro for three weeks. The ALP and Alizarin Red staining were made respectively. Total RNA was extracted and subjected to quantitative RT-PCR to determine the expression of several osteogenic markers including Runx2,OPN, and osteocalcin.Secondly, the expression profiles of thirty-six factors, which play important roles in bone metabolism were compared through antibody array between normal and osteoporotic BMSC. Hence further comprehensive using the above methods and the Wnt/?-catenin signaling pathway related factors(blocker and activtor) treatment, IL-6 neutralizing antibodies, shRNA lentivirus infection to explore the molecular mechanism of GIO BMSC osteogenesis disorder.Lastly, in vivo administration of IL-6 neutralizing antibody was employed to observe the curative effect to the osteoporotic mouse.The experiments verified the phenomenon that GIO vertebral body BMSC proliferated slowly and osteogenic differention was defective. We also obtain the following conclusions:1.IL-6 over-secretion was found in GIO vertebral body BMSC cultivation in vitro, even using BMP2 to induce osteogenesis;2. IL-6 over-secretion was one of the most important reasons of GIO vertebral body BMSC defective osteogenic differentiation;3. IL-6 acts upstream of Wnt/ ?-catenin to negatively modulate ?-catenin of osteoporotic BMSC;4. In vivo administration of IL-6 neutralizing antibody was found to be helpful to rescue the osteoporotic phenotype of mouse vertebral body.Our study provides a deeper insight into the pathophysiology of osteoporosis and identifies IL-6 as a promising target for osteoporosis therapy.