Conditional deletion of hypothalamic Y2 receptors reverts gonadectomy-induced bone loss in adult mice

Reduction in levels of sex hormones at menopause in women is associated with two common, major outcomes, the accumulation of white adipose tissue, and the progressive loss of bone because of excess osteoclastic bone resorption exceeding osteoblastic bone formation. Current antiresorptive therapies can reduce osteoclastic activity but have only limited capacity to stimulate osteoblastic bone formation and restore lost skeletal mass. Likewise, the availability of effective pharmacological weight loss treatments is currently limited. Here we demonstrate that conditional deletion of hypothalamic neuropeptide Y2 receptors can prevent ongoing bone loss in sex hormone-deficient adult male and female mice. This benefit is attributable solely to activation of an anabolic osteoblastic bone formation response that counterbalances persistent elevation of bone resorption, suggesting the Y2-mediated anabolic pathway to be independent of sex hormones. Furthermore, the increase in fat mass that typically occurs after ovariectomy is prevented by germ line deletion of Y2 receptors, whereas in male mice body weight and fat mass were consistently lower than wild-type regardless of sex hormone status. Therefore, this study indicates a role for Y2 receptors in the accumulation of adipose tissue in the hypogonadal state and demonstrates that hypothalamic Y2 receptors constitutively restrain osteoblastic activity even in the absence of sex hormones. The increase in bone formation after release of this tonic inhibition suggests a promising new avenue for osteoporosis treatment.

Hypothalamic regulation of cortical bone mass: Opposing activity of Y2 receptor and leptin pathways

NeuropeptideY-, Y2 receptor (Y2)-, and leptin-deficient mice show similar anabolic action in cancellous bone but have not been assessed in cortical bone. Cortical bone mass is elevated in Y2(-/-) mice through greater osteoblast activity. In contrast, leptin deficiency results in reduced bone mass. We show opposing central regulation of cortical bone.

Studies of the role of nf-κb in controlling osteoclast differentiation and bone loss

Increased osteoclast (OC) bone resorption and/or decreased osteoblast (OB) bone formation contribute to bone loss in osteoporosis and rheumatoid arthritis (RA). Findings of the basic and translational research presented in this thesis demonstrate a number of mechanisms by which cytokine-induced NF-κB activation controls bone resorption and formation: 1) Tumour necrosis factor-α (TNF) expands pool of OC precursors (OCPs) by promoting their proliferation through stimulation of the expression of macrophage colony stimulating factor (M-CSF) receptor, c-Fms, and switching M-CSF-induced resident (M2) to inflammatory (M1) macrophages with enhanced OC forming potential and increased production of inflammatory factors through induction of NF-κB RelB; 2) Similar to RANKL, TNF sequentially activates transcriptional factors NF-κB p50 and p52 followed by c-Fos and then NFATc1 to induce OC differentiation. However, TNF alone induces very limited OC differentiation. In contrast, it pre-activates OCPs to express cFos which cooperates with interleukin-1 (IL-1) produced by these OCPs in an autocrine mechanism by interacting with bone matrix to mediate the OC terminal differentiation and bone resorption from these pre-activated OCPs. 3) TNF-induced OC formation is independent of RANKL but it also induces NF-κB2 p100 to limit OC formation and bone resorption, and thus p100 deletion accelerates joint destruction and systemic bone loss in TNF-induced RA; 4) TNF receptor associated factor-3 (TRAF3) limits OC differentiation by negatively regulating non-canonical NF-κB activation and RANKL induces TRAF3 ubiquitination and lysosomal degradation to promote OC differentiation. Importantly, a lysosomal inhibitor that inhibits TRAF3 degradation prevents ovariectomy-induced bone loss; 5) RelB and Notch NICD bind RUNX2 to inhibit OB differentiation and RelB:p52 dimer association with NICD inhibit OB differentiation by enhancing the binding of RBPjκ to Hes1. These findings suggest that non-canonical NF- κB signaling could be targets to develop new therapies for RA or osteoporosis. For example 1) Agents that degrade TNF-induced RelB could block M1 macrophage differentiation to inhibit inflammation and joint destruction for the therapy of RA; 2)Agents that prevent p100 processing or TRAF3 degradation could inhibit bone resorption and also stimulate bone formation simultaneously for the therapy of osteoporosis.

Protective effect of Rhizoma drynariae extract on osteoporosis in ovariectomized rat model

Purpose: To investigate the therapeutic effect of Rhizoma drynariae extract (RDE) on ovariectomyinduced osteoporosis in rats. Methods: Female Sprague-Dawley rats were randomly assigned to a sham-operated group (control) and five ovariectomy (OVX) subgroups: OVX with vehicle (OVX), OVX with 17ß-estradiol (E2, 25 μg/kg/day), and OVX with RDE doses (40, 80, and 160 mg/kg/day). Daily oral administration of E2 or RDE started 4 weeks after OVX and lasted for 16 weeks. The bone mineral density (BMD) of the L4 vertebrae and right femurs was estimated. The length of each femur was measured with a micrometer gauge, and the center of the diaphysis determined. Three representatives L4 vertebrae were selected to evaluate the trabecular microarchitecture. Serum alkaline phosphatase (ALP), urinary calcium (U-Ca), urinary phosphorus (U-P), urinary creatinine (Cr) and osteocalcin (OC) levels were measured. Results: The study showed that high-dose of RDE significantly inhibited the bone mineral density (BMD) reduction of L4 vertebrae (0.20 ± 0.02 g/cm3, p < 0.05) and femurs (0.18 ± 0.02 g/cm3, p < 0.05) caused by OVX and prevented the deterioration of trabecular microarchitecture (p < 0.05), which were accompanied by a significant decrease in skeletal remodeling (p < 0.05) as evidenced by the lower levels of bone turnover markers. High-dose of RDE improved morphometric parameters, namely, Tb-N (3.8 ± 0.2 mm, p < 0.05), Tb-Th (0.083 ± 0.011 mm, p < 0.05) and Tb-Sp (0.19 ± 0.01 mm, p < 0.05) in L4 vertebrae significantly. The present study indicates that the administration of RDE at higher doses over a 16-week period can prevent OVX-induced osteoporosis in rats without hyperplastic effects on the uterus. Conclusion: Thus, RDE is a potential natural alternative for postmenopausal osteoporosis treatment in elderly women.

Anti-osteoporosis activity of Astragalus membranaceus Bunge extract in experimental rats

Purpose: To investigate the anti-osteoporosis effect of Astragalus membranaceus (Fisch.) Bunge. extract (AMBE) in experimental rats. Method: Female Sprague-Dawley rats were randomly divided into six groups: control group, ovariectomy (OVX) with vehicle group, OVX with 17β-estradiol (E2, 25 μg/kg/day) group, and OVX with AMBE doses (60, 120 and 240 mg/kg/day) groups. Daily oral administration of AMBE or E2 was started 4 weeks after OVX and lasted for 16 weeks. The bone mineral density (BMD) of L4 vertebrae and right femurs was evaluated. The length of each femur was measured with a micrometer, and the center of diaphysis was determined. Three representative L4 vertebrae were selected to evaluate trabecular microarchitecture. Serum alkaline phosphatase (ALP), urinary calcium (U-Ca), urinary phosphorus (UP), urinary creatinine (Cr) and osteocalcin (OC) levels were measured. Results: AMBE dose-dependently inhibited the bone mineral density (BMD) reduction of L4 vertebrae (0.27 ± 0.03 g/cm2, p < 0.05) and femurs (0.23 ± 0.03 g/cm2, p < 0.05) caused by OVX and prevented the deterioration of trabecular microarchitecture (p < 0.05), which were accompanied by a significant decrease in skeletal remodeling (p < 0.05) as evidenced by the lower levels of bone turnover markers. A higher dosage of AMBE treatment (240 mg/kg/day) increased U-Ca/Cr (0.27 ± 0.03 mmol/mmol), ALP (137.23 ± 16.72 U/L), U-P/Cr (4.18 ± 0.27 mmol/mmol) and OC (8.47 ± 0.26 mmol/L) levels (both p < 0.05). Conclusion: The findings of this study indicate that AMBE prevents OVX-induced osteoporosis in rats.

Anti-osteoporosis effect of Cistanche deserticola Ma extract in ovariectomized rats

Purpose: To investigate the therapeutic effects of Cistanche deserticola Ma. extract (CDME) on ovariectomy-induced osteoporosis in rats. Methods: Female Sprague-Dawley rats were randomly assigned to a control group and five ovariectomy (OVX) subgroups, that is, OVX with vehicle (OVX), OVX with 17ß-estradiol (E2, 25 μg/kg/day), and OVX with CDME doses (40, 80, or 160 mg/kg/day). Daily oral administration of E2 or CDME started 4 weeks after OVX and lasted for 16 weeks. Bone mineral density (BMD) of L4 vertebrae and right femur of rats was estimated, The length of each femur was measured, and biochemical analysis of serum and urine specimens were performed. Results: CDME dose-dependently inhibited the reduction in BMD of L4 vertebrae (0.23 ± 0.02 g/cm3, p < 0.05) and femurs (0.20 ± 0.03 g/cm3, p < 0.05) caused by OVX and prevented the deterioration of trabecular microarchitecture (p < 0.05), which were accompanied by a significant decrease in skeletal remodeling (p < 0.05) as evidenced by the lower levels of bone turnover markers. Conclusion: This study indicates that CDME prevents OVX-induced osteoporosis in rats, and could be used for treating osteoporosis in elderly women.