Sex and age modify biochemical and skeletal manifestations of chronic hyperparathyroidism by altering target organ responses to Ca2+ and PTH in mice

Authors

Zhiqiang Cheng, Nathan Liang, Tsui-Hua Chen, Alfred Li, Christian Santa Maria, Michael You, Hanson Ho, Fuqing Song, Daniel Bikle, Chialing Tu, Dolores Shoback, Wenhan Chang

Abstract

We studied mice with or without heterozygous deletion of the Casr in the parathyroid gland (PTG) [PTGCaSR(+/-)] to delineate effects of age and sex on manifestations of hyperparathyroidism (HPT). In control mice, aging induced a left-shift in the Ca2+/parathyroid hormone (PTH) set-point accompanied by increased PTG CaSR expression along with lowered serum Ca2+ and mildly increased PTH levels, suggesting adaptive responses of PTGs to aging-induced changes in mineral homeostasis. The aging effects on Ca2+/PTH set-point and CaSR expression were significantly blunted in PTGCaSR(+/-) mice who showed instead progressively elevated PTH levels with age, especially in 12-month-old females. These 12-month-old knockout mice demonstrated resistance to their high PTH levels in that serum 1,25-dihydroxyvitamin D (1,25-D) levels and RNA expression of renal Cyp27b1 and expression of genes involved in Ca2+ transport in kidney and intestine were unresponsive to the rising PTH levels. Such changes may promote negative Ca2+ balance, which further exacerbate the HPT. Skeletal responses to HPT were age-, sex-, and site-dependent. In control mice of either sex, trabecular bone in the distal femur decreased while cortical bone in the tibiofibular junction increased with age. In male PTGCaSR(+/-) mice, anabolic actions of the elevated PTH levels seemed to protect against trabecular bone loss at ≥3 months of age at the expense of cortical bone loss. In contrast, HPT produced catabolic effects on trabecular bone and anabolic effects on cortical bone in 3-month-old females; but these effects reversed by 12 months, preserving trabecular bone in aging mice. We demonstrate that the CaSR plays a central role in the adaptive responses of parathyroid function to age-induced changes in mineral metabolism and in target organ responses to calciotropic hormones. Restraining the ability of the PTG to upregulate CaSRs by heterozygous gene deletion contributes to biochemical and skeletal manifestations of HPT, especially in aging females.

Link to Article

http://dx.doi.org/10.1002/jbmr.1846

Transplantation of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells or Their Conditioned Medium Prevents Bone Loss in Ovariectomized Nude Mice

Authors

Jee Hyun An, Hyojung Park, Jung Ah Song, Kyung Ho Ki, Jae-Yeon Yang, Hyung Jin Choi, Sun Wook Cho, Sang Wan Kim, Seong Yeon Kim, Jeong Joon Yoo, Wook-Young Baek, Jung-Eun Kim, Soo Jin Choi, Wonil Oh, and Chan Soo Shin

Abstract

Umbilical cord blood (UCB) has recently been recognized as a new source of mesenchymal stem cells (MSCs) for use in stem cell therapy. We studied the effects of systemic injection of human UCB-MSCs and their conditioned medium (CM) on ovariectomy (OVX)-induced bone loss in nude mice. Ten-week-old female nude mice were divided into six groups: Sham-operated mice treated with vehicle (Sham-Vehicle), OVX mice subjected to UCB-MSCs (OVX-MSC), or human dermal fibroblast (OVX-DFB) transplantation, OVX mice treated with UCB-MSC CM (OVX-CM), zoledronate (OVX-Zol), or vehicle (OVX-Vehicle). Although the OVX-Vehicle group exhibited significantly less bone mineral density (BMD) gain compared with the Sham-Vehicle group, transplantation of hUCB-MSCs (OVX-MSC group) has effectively prevented OVX-induced bone mass attenuation. Notably, the OVX-CM group also showed BMD preservation comparable to the OVX-MSC group. In addition, microcomputed tomography analysis demonstrated improved trabecular parameters in both the OVX-MSC and OVX-CM groups compared to the OVX-Vehicle or OVX-DFB group. Histomorphometric analysis showed increased bone formation parameters, accompanied by increased serum procollagen type-I N-telopeptide levels in OVX-MSC and OVX-CM mice. However, cell-trafficking analysis failed to demonstrate engraftment of MSCs in bone tissue 48 h after cell infusion. In vitro, hUCB-MSC CM increased alkaline phosphatase (ALP) activity in human bone marrow-derived MSCs and mRNA expression of collagen type 1, Runx2, osterix, and ALP in C3H10T1/2 cells. Furthermore, hUCB-MSC CM significantly increased survival of osteocyte-like MLO-Y4 cells, while it inhibited osteoclastic differentiation. To summarize, transplantation of hUCB-MSCs could effectively prevent OVX-mediated bone loss in nude mice, which appears to be mediated by a paracrine mechanism rather than direct engraftment of the MSCs.

Link to Article

http://dx.doi.org/10.1089/ten.tea.2012.0047

Orthodontic mini-implant diameter does not affect in-situ linear microcrack generation in the mandible or the maxilla

Authors

Sean Shih-Yao Liu, Enrique Cruz-Marroquin, Jun Sun, Kelton T. Stewart, Matthew R. Allen

Abstract

Microdamage reduces bone mechanical properties and thus could contribute to implant failure. The objective of this study was to investigate whether the diameter of mini-implants affects linear microcrack generation and whether this differs between the mandible and the maxilla because of their contrasting cortical thicknesses. Maxillary and mandibular quadrants of 5 dogs were randomly assigned to receive, in situ, no pilot drilling or mini-implant insertion (control), pilot drilling only without mini-implants, or pilot drilling plus a mini-implant of 1 of 3 diameters: 1.4 mm (n = 18), 1.6 mm (n = 18), and 2.0 mm (n = 18). Linear microcracks were assessed on basic fuchsin-stained sections by using epifluorescence microscopy. Pilot drilling without mini-implant insertion produced significantly higher linear microcrack burdens in the mandible compared with the maxilla. In the both the mandible and the maxilla, all implants produced higher linear microcrack burdens than did the controls, yet there were no differences between the 3 implant diameters. Neither the diameter of the mini-implant nor the site of insertion (mandible vs maxilla) had a significant effect on the amount of linear microdamage adjacent to the implant when the implants were inserted after pilot drilling in situ.

Link to Article

http://dx.doi.org/10.1016/j.ajodo.2012.07.014

Low-dose Risedronate Sodium Protects Bone Cells after Abrupt Oestrogen Withdrawal

Authors

Wang, G.; Zhu, Z.; Lei, C.; Li, M.; Liu, F.; Mao, Y.; Yu, Z.; Liu, M.; Zhao, X.; Tang, T

Abstract

To investigate the effects of low-dose risedronate sodium on the in vitro cellular profile of osteoblasts, adipocytes, osteocytes and osteoclasts in a rat model of abrupt oestrogen deficiency. Oestrogen deficiency was induced by ovariectomy in 24 female rats. The rats were treated with low-dose (0.24 μg/kg) or high-dose (2.4 μg/kg) risedronate sodium for 4 days presurgery, continuing every 3 days until 15 days postsurgery. Osteogenic and adipogenic differentiation were determined in cultured bone marrow cells by alkaline phosphatase and Oil Red O staining, respectively, and by osteogenic and adipogenic gene expression. Osteoclast formation was measured in bone marrow cells stimulated with macrophage colony-stimulating factor and receptor activator of nuclear factor κB ligand, and stained with tartrate-resistant acid phosphatase. Osteocyte apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling assay and B-cell lymphoma-2 (Bcl-2) immunohistochemistry. Low-dose risedronate sodium enhanced osteoblast differentiation, suppressed adipocyte differentiation and osteoclast formation, and reduced osteocyte apoptosis through regulation of Bcl-2 and Bcl-2-associated X protein. Low-dose risedronate sodium may have clinical benefit in protecting against bone loss after abrupt oestrogen deficiency.

Link to Article

http://www.ingentaconnect.com/content/field/jimr/2012/00000040/00000005/art00015

β-catenin promotes bone formation and suppresses bone resorption in postnatal growing mice

Authors

Jianquan Chen, Fanxin Long

Abstract

Genetic studies in the mouse have demonstrated multiple roles for β-catenin in the skeleton. In the embryo, β-catenin is critical for the early stages of osteoblast differentiation. Postnatally, β-catenin in mature osteoblasts and osteocytes indirectly suppresses osteoclast differentiation. However, a direct role for β-catenin in regulating osteoblast number and/or function specifically in the postnatal life has not been demonstrated. Addressing this knowledge gap is important because LRP5, a co-receptor for WNT signaling proposed to function through β-catenin, controls osteoblast number and function in postnatal mice or humans. To overcome the neonatal lethality caused by embryonic deletion of β-catenin in early-stage osteoblast-lineage cells, we utilize Osx-CreERT2 to remove β-catenin in Osx-expressing cells by administering tamoxifen (TM) temporarily to postnatal mice. Lineage-tracing experiments in the long bones demonstrate that Osx-CreERT2 targets predominantly osteoblast-lineage cells on the bone surface, but also transient progenitors that contribute to bone marrow stromal cells and adipocytes. Deletion of β-catenin by this strategy greatly reduces the bone formation activity of the targeted osteoblasts. However, the targeted osteoblasts rapidly turn over and are replaced by an excessive number of non-targeted osteoblasts, causing an unexpected increase in bone formation, but an even greater increase in osteoclast number and activity produces a net effect of severe osteopenia. With time, the mutant mice also exhibit a marked increase in bone marrow adiposity. Thus, β-catenin in postnatal Osx-lineage cells critically regulates bone homeostasis by promoting osteoblast activity and suppressing osteoblast turnover, while restraining osteoclast and marrow fat formation.

Link to Article

http://dx.doi.org/10.1002/jbmr.1834