Bone Renin-angiotensin System Research Articles

Glucocorticoids activate the local renin–angiotensin system in bone: possible mechanism for glucocorticoid-induced osteoporosis

Bone metabolism disorder has been identified to play a vital role in the pathogenesis of glucocorticoid-induced osteoporosis (GIOP). The local renin-angiotensin system (RAS) in bone is newly defined to be closely related to the bone metabolism. However, it is unknown whether the local RAS is involved in GIOP. Adult male New Zealand white rabbits were treated with saline, dexamethasone (DXM) alone, or DXM combined with perindopril. The expression of main RAS components in trabecular bone was examined at mRNA and/or protein levels. Bone metabolism was analyzed using dual-energy X-ray absorptiometry, histomorphometry, biomechanics, biochemical techniques, and quantitative RT-PCR. The expressions of local bone angiotensin II, angiotensin types 1 and 2 receptors, and angiotensin-converting enzyme at mRNA and/or protein levels increased when DXM-induced osteoporosis was present. Whereas, perindopril significantly blocked the activation of the local RAS and partially reversed GIOP. Mineralizing surface, mineral apposition rate, and bone formation rate were decreased by DXM, along with serum osteocalcin being downregulated. These changes were then reversed by the use of perindopril. Osteoclast number, osteoclast surface, and eroded surface increased after the administration of DXM, and urinary deoxypyridinoline was upregulated. These were also inhibited when perindopril was given. Quantitative RT-PCR using RNA isolated from the lumbar vertebrae revealed an increase in the SOST expression and a decrease in the Runx2 expression, whereas the receptor activator of nuclear factor-κB ligand/osteoprotegerin ratio and the expression of tartrate resistant acid phosphatase were increased, which were all inhibited by perindopril. The results of this study provide evidence for the role of local RAS is involved in GIOP, and GIOP may be ameliorated by blocking the activation of local RAS in the bone.

Inhibition of angiotensin‐converting enzyme stimulates fracture healing and periosteal callus formation – role of a local renin‐angiotensin system

The renin-angiotensin system (RAS) regulates blood pressure and electrolyte homeostasis. In addition, 'local' tissue-specific RAS have been identified, regulating regeneration, cell growth, apoptosis, inflammation and angiogenesis. Although components of the RAS are expressed in osteoblasts and osteoclasts, a local RAS in bone has not yet been described and there is no information on whether the RAS is involved in fracture healing. Therefore, we studied the expression and function of the key RAS component, angiotensin-converting enzyme (ACE), during fracture healing. In a murine femur fracture model, animals were treated with the ACE inhibitor perindopril or vehicle only. Fracture healing was analysed after 2, 5 and 10 weeks using X-ray, micro-CT, histomorphometry, immunohistochemistry, Western blotting and biomechanical testing. ACE was expressed in osteoblasts and hypertrophic chondrocytes in the periosteal callus during fracture healing, accompanied by expression of the angiotensin type-1 and type-2 receptors. Perindopril treatment reduced blood pressure and bone mineral density in unfractured femora. However, it improved periosteal callus formation, bone bridging of the fracture gap and torsional stiffness. ACE inhibition did not affect cell proliferation, but reduced apoptotic cell death. After 10 week treatment, a smaller callus diameter and bone volume after perindopril treatment indicated an advanced stage of bone remodelling. Our study provides evidence for a local RAS in bone that influenced the process of fracture healing. We show for the first time that inhibition of ACE is capable of accelerating bone healing and remodelling.

Genetic Disruption of All NO Synthase Isoforms Enhances BMD and Bone Turnover in Mice In Vivo: Involvement of the Renin-Angiotensin System

NO is synthesized by three different NO synthase (NOS) isoforms, including neuronal (nNOS), inducible (iNOS) and endothelial NOS (eNOS). The roles of NO in bone metabolism have been extensively investigated in pharmacological studies and in studies with NOS isoform-deficient mice. However, because of the nonspecificity of agents and compensation among the NOS isoforms, the ultimate roles of endogenous NO are still poorly understood. To address this point, we successfully generated mice in which all three NOS genes are completely disrupted. In this study, we examined whether bone metabolism is abnormal in those mice. Experiments were performed in 12-wk-old male wildtype, singly nNOS(-/-), iNOS(-/-), and eNOS(-/-) and triply n/i/eNOS(-/-) mice. BMD was assessed by DXA. The kinetics of osteoblastic bone formation and those of osteoclastic bone resorption were evaluated by measurements of morphological and biochemical markers. BMD was significantly higher only in the triply NOS(-/-) mice but not in any singly NOS(-/-) mice compared with the wildtype mice. Markers of osteoblastic bone formation, including bone formation rate, mineral apposition rate, and serum alkaline phosphatase concentration, were also significantly larger only in the triply NOS(-/-) mice compared with wildtype mice. Furthermore, markers of osteoclastic bone resorption, including osteoclast number, osteoclast surface, and urinary deoxypyridinoline excretion, were again significantly greater only in the triply NOS(-/-) mice. Importantly, the renin-angiotensin system in bone was significantly activated in the triply NOS(-/-) mice, and long-term oral treatment with an angiotensin II type 1 (AT(1)) receptor blocker normalized this pathological bone remodeling in those mice. These results provide the first direct evidence that genetic disruption of the whole NOS system enhances BMD and bone turnover in mice in vivo through the AT(1) receptor pathway, showing the critical role of the endogenous NO/NOS system in maintaining bone homeostasis.