Bisphosphonates improve trabecular bone mass and normalize cortical thickness in ovariectomized, osteoblast connexin43 deficient mice

Authors

Marcus P. Watkins, Jin Yi Norris, Susan K. Grimston, Xiaown Zhang, Roger J. Phipps, Frank H. Ebetino, Roberto Civitelli

Abstract

The gap junction protein, connexin43 (Cx43) controls both bone formation and osteoclastogenesis via osteoblasts and/or osteocytes. Cx43 has also been proposed to mediate an anti-apoptotic effect of bisphosphonates, potent inhibitors of bone resorption. We studied whether bisphosphonates are effective in protecting mice with a conditional Cx43 gene deletion in osteoblasts and osteocytes (cKO) from the consequences of ovariectomy on bone mass and strength. Ovariectomy resulted in rapid loss of trabecular bone followed by a slight recovery in wild type (WT) mice, and a similar degree of trabecular bone loss, albeit slightly delayed, occurred in cKO mice. Treatment with either risedronate (20 μg/kg) or alendronate (40 μg/kg) prevented ovariectomy-induced bone loss in both genotypes. In basal conditions, bones of cKO mice have larger marrow area, higher endocortical osteoclast number, and lower cortical thickness and strength relative to WT. Ovariectomy increased endocortical osteoclast number in WT but not in cKO mice. Both bisphosphonates prevented these increases in WT mice, and normalized endocortical osteoclast number, cortical thickness and bone strength in cKO mice. Thus, lack of osteoblast/osteocyte Cx43 does not alter bisphosphonate action on bone mass and strength in estrogen deficiency. These results support the notion that one of the main functions of Cx43 in cortical bone is to restrain osteoblast and/or osteocytes from inducing osteoclastogenesis at the endocortical surface.

Link to Article

http://dx.doi.org/10.1016/j.bone.2012.06.018

An Age-Dependent Interaction with Leptin Unmasks Ghrelin's Bone-Protective Effects

Authors

Martijn van der Velde, Bram C.J. van der Eerden, Yuxiang Sun, Julia M.M. Almering, Aart-Jan van der Lely, Patric J.D. Delhanty, Roy G. Smith and Johannes P.T.M. van Leeuwen

Abstract

The mutual interplay between energy homeostasis and bone metabolism is an important emerging concept. Ghrelin and leptin antagonize each other in regulating energy balance, but the role of this interaction in bone metabolism is unknown. Using ghrelin receptor and leptin-deficient mice, we show that ghrelin has dual effects on osteoclastogenesis, inhibiting osteoclast progenitors directly and stimulating osteoclastogenesis via a more potent systemic/central pathway. Using mice with combined ghrelin receptor and leptin deficiency, we find that this systemic osteoclastogenic activity is suppressed by leptin, thus balancing the two counterregulatory ghrelin pathways and leading to an unchanged bone structure. With aging, this osteoclastogenic ghrelin pathway is lost, unmasking the direct protective effect of ghrelin on bone structure. In conclusion, we identify a novel regulatory network linking orexigenic and anorectic metabolic factors with bone metabolism that is age dependent.

Link to Article

http://dx.doi.org/10.1210/en.2012-1277

Early Response of Bone Marrow Osteoprogenitors to Skeletal Unloading and Sclerostin Antibody

Authors

Mohammad Shahnazari, Thomas Wronski, Vivian Chu, Alyssa Williams, Alicia Leeper, Marina Stolina, Hua Zhu Ke and Bernard Halloran

Abstract

Sclerostin functions as an antagonist to Wnt signaling and inhibits bone-forming activity. We studied the effects of skeletal unloading and treatment with sclerostin antibody (Scl-Ab) on mesenchymal stem cell, osteoprogenitor and osteoclast precursor pools, and their relationship to bone formation and resorption. Male C57BL/6 mice (5-months-old) were hind limb unloaded for 1 week or allowed normal ambulation and treated with Scl-Ab (25 mg/kg, s.c. injections on days 1 and 4) or placebo. Unloading decreased the serum concentration of bone formation marker P1NP (−35 %), number of colony-forming units (CFU) (−38 %), alkaline phosphatase–positive CFUs (CFU-AP+) (−51 %), and calcified nodules (−35 %); and resulted in a fourfold increase in the number of osteoclast precursors. The effects of Scl-Ab treatment on unloaded and normally loaded mice were nearly identical; Scl-Ab increased serum P1NP and the number of CFU, CFU-AP+, and calcified nodules in ex vivo cultures; and increased osteoblast and bone mineralizing surfaces in vivo. Although the marrow-derived osteoclast precursor population increased with Scl-Ab, the bone osteoclast surface did not change, and the serum concentration of osteoclast activity marker TRACP5b decreased. Our data suggest that short-term Scl-Ab treatment can prevent the decrease in osteoprogenitor population associated with skeletal unloading and increase osteoblast surface and bone mineralizing surface in unloaded animals. The anabolic effects of Scl-Ab treatment on bone are preserved during skeletal unloading. These findings suggest that Scl-Ab treatment can both increase bone formation and decrease bone resorption, and provide a new means for prevention and treatment of disuse osteoporosis.

Link to Article

http://dx.doi.org/10.1007/s00223-012-9610-9

Type 1 IFNs Suppress Accelerated Osteoclastogenesis and Prevent Loss of Bone Mass During Systemic Inflammatory Responses to Pneumocystis Lung Infection

Authors

Michelle Wilkison, Katherine Gauss, Yanchao Ran, Steve Searles, David Taylor, Nicole Meissner

Abstract

HIV infection causes loss of CD4+ T cells and type 1 interferon (IFN)–producing and IFN-responsive dendritic cells, resulting in immunodeficiencies and susceptibility to opportunistic infections, such as Pneumocystis. Osteoporosis and bone marrow failure are additional unexplained complications in HIV-positive patients and patients with AIDS, respectively. We recently demonstrated that mice that lack lymphocytes and type 1 IFN receptor (IFrag−/−) develop bone marrow failure after Pneumocystis lung infection, whereas lymphocyte-deficient, IFN α/β receptor–competent mice (RAG−/−) had normal hematopoiesis. Interestingly, infected IFrag−/− mice also exhibited bone fragility, suggesting loss of bone mass. We quantified bone changes and evaluated the potential connection between progressing bone fragility and bone marrow failure after Pneumocystis lung infection in IFrag−/− mice. We found that Pneumocystis infection accelerated osteoclastogenesis as bone marrow failure progressed. This finding was consistent with induction of osteoclastogenic factors, including receptor-activated nuclear factor-κB ligand and the proapoptotic factor tumor necrosis factor–related apoptosis-inducing ligand, in conjunction with their shared decoy receptor osteoprotegerin, in the bone marrow of infected IFrag−/− mice. Deregulation of this axis has also been observed in HIV-positive individuals. Biphosphonate treatment of IFrag−/− mice prevented bone loss and protected loss of hematopoietic precursor cells that maintained activity in vitro but did not prevent loss of mature neutrophils. Together, these data show that bone loss and bone marrow failure are partially linked, which suggests that the deregulation of the receptor-activated nuclear factor-κB ligand/osteoprotegerin/tumor necrosis factor–related apoptosis-inducing ligand axis may connect the two phenotypes in our model.

Link to Article

http://dx.doi.org/10.1016/j.ajpath.2012.03.023

Black bear parathyroid hormone has greater anabolic effects on trabecular bone in dystrophin-deficient mice than in wild type mice

Authors

Sarah K. Gray, Meghan E. McGee-Lawrence, Jennifer L. Sanders, Keith W. Condon, Chung-Jui Tsai, Seth W. Donahue

Abstract

Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular disease that has deleterious consequences in muscle and bone, leading to decreased mobility, progressive osteoporosis, and premature death. Patients with DMD experience a higher-than-average fracture rate, particularly in the proximal and distal femur and proximal tibia. The dystrophin-deficient mdx mouse is a model of DMD that demonstrates muscle degeneration and fibrosis and osteoporosis. Parathyroid hormone, an effective anabolic agent for post-menopausal and glucocorticoid-induced osteoporosis, has not been explored for DMD. Black bear parathyroid hormone (bbPTH) has been implicated in the maintenance of bone properties during extended periods of disuse (hibernation). We cloned bbPTH and found 9 amino acid residue differences from human PTH. Apoptosis was mitigated and cAMP was activated by bbPTH in osteoblast cultures. We administered 24 nmol/kg of bbPTH 1–84 to 4-week old male mdx and wild type mice via daily (5×/week) subcutaneous injection for 6 weeks. Vehicle-treated mdx mice had 44% lower trabecular bone volume fraction than wild type mice. No changes were found in femoral cortical bone geometry or mechanical properties with bbPTH treatment in wild type mice, and only medio-lateral moment of inertia changed with bbPTH treatment in mdx femurs. However, μCT analyses of the trabecular regions of the distal femur and proximal tibia showed marked increases in bone volume fraction with bbPTH treatment, with a greater anabolic response (7-fold increase) in mdx mice than wild type mice (2-fold increase). Trabecular number increased in mdx long bone, but not wild type bone. Additionally, greater osteoblast area and decreased osteoclast area were observed with bbPTH treatment in mdx mice. The heightened response to PTH in mdx bone compared to wild type suggests a link between dystrophin deficiency, altered calcium signaling, and bone. These findings support further investigation of PTH as an anabolic treatment for DMD-induced osteoporosis.

Link to Article

http://dx.doi.org/10.1016/j.bone.2012.05.003

The use of autologous enriched bone marrow MSCs to enhance osteoporotic bone defect repair in long-term estrogen deficient goats

Authors

Lei Cao, Guangwang Liu, Yaokai Gan, Qiming Fan, Fei Yang, Xiaoling Zhang, Tingting Tang, Kerong Dai

Abstract

Bone defects are common in elderly patients suffering from osteoporosis. Current methods of bone defect treatment for osteoporosis are not always satisfactory. In this study, we demonstrated that bone marrow mesenchymal stem cells (MSCs) harvested from goats with long-term estrogen deficiencies exhibited a lower proliferation rate and decreased osteogenic capacity, which are critical obstacles for bone defect repair in the elderly. However, by combining autologous enriched bone marrow mesenchymal stem cells with porous β-TCP, we successfully repaired critical-sized bone defects in the medial femoral condyle of the osteoporotic goats. Both micro-CT images and histomorphometry analysis illustrated improved bone formation following the enriched MSC therapy. Thus, we proposed autologous enriched bone marrow mesenchymal stem cells as a quick, safe therapeutic strategy to treat osteoporotic bone defects.

Link to Article

http://dx.doi.org/10.1016/j.biomaterials.2012.03.069