Skeletal effects of whole-body vibration in adult and aged mice

Authors

Michelle A. Lynch, Michael D. Brodt, Matthew J. Silva

Abstract

Low-amplitude, whole-body vibration (WBV) may be anabolic for bone. Animal studies of WBV have not evaluated skeletal effects in aged animals. We exposed 75 male BALB/c mice (7 month/young-adult; 22 month/aged) to 5 weeks of daily WBV (15 min/day, 5 day/wk; 90 Hz sine wave) at acceleration amplitudes of 0 (sham), 0.3, or 1.0 g. Whole-body bone mineral content (BMC) increased with time in 7 month (p < 0.001) but not 22 month (p = 0.34) mice, independent of WBV (p = 0.60). In 7 month mice, lower-leg BMC increased with time in 0.3 and 1.0 g groups (p < 0.005) but not in the sham group (p = 0.09), indicating a positive WBV effect. In 22 month mice, there were no changes with time in lower-leg BMC (p = 0.11). WBV did not affect tibial trabecular or cortical bone structure (by µCT), dynamic indices of trabecular or cortical bone formation, trabecular osteoclast surface, or the mass of the reproductive fat pad (p > 0.05). Each of these outcomes was diminished in 7 month versus 22 month animals (p < 0.05). In summary, 5 weeks of daily exposure to low-amplitude WBV had no skeletal effects in aged male mice. The potential of WBV to enhance bone mass in age-related osteoporosis is not supported in this preclinical study.

Link to Article

http://dx.doi.org/10.1002/jor.20965

Exposure-dependent increases in IL-1β, substance P, CTGF, and tendinosis in flexor digitorum tendons with upper extremity repetitive strain injury

Authors

Jane M. Fedorczyk, Ann E. Barr, Shobha Rani, Helen G. Gao, Mamta Amin, Shreya Amin, Judith Litvin, Mary F. Barbe

Abstract

Upper extremity tendinopathies are associated with performance of forceful repetitive tasks. We used our rat model of repetitive strain injury to study changes induced in forelimb flexor digitorum tendons. Rats were trained to perform a high repetition high force (HRHF) handle-pulling task (12 reaches/min at 60 ± 5% maximum pulling force [MPF]), or a low repetition negligible force (LRNF) reaching and food retrieval task (three reaches/min at 5 ± 5% MPF), for 2 h/day in 30 min sessions, 3 days/week for 3–12 weeks. Forelimb grip strength was tested. Flexor digitorum tendons were examined at midtendon at the level of the carpal tunnel for interleukin (IL)-1β, neutrophil, and macrophage influx, Substance P, connective tissue growth factor (CTGF), and periostin-like factor (PLF) immunoexpression, and histopathological changes. In HRHF rats, grip strength progressively decreased, while IL-1β levels progressively increased in the flexor digitorum peritendon (para- and epitendon combined) and endotendon with task performance. Macrophage invasion was evident in week 6 and 12 HRHF peritendon but not endotendon. Also in HRHF rats, Substance P immunoexpression increased in week 12 peritendon as did CTGF- and PLF-immunopositive fibroblasts, the increased fibroblasts contributing greatly to peritendon thickening. Endotendon collagen disorganization was evident in week 12 HRHF tendons. LRNF tendons did not differ from controls, even at 12 weeks. Thus, we observed exposure-dependent changes in flexor digitorum tendons within the carpal tunnel, including increased inflammation, nociceptor-related neuropeptide immunoexpression, and fibrotic histopathology, changes associated with grip strength decline.

Link to Article

http://dx.doi.org/10.1002/jor.20984

Role of TNF alpha and PLF in bone remodeling in a rat model of repetitive reaching and grasping

Authors

Shobha Rani, Mary F Barbe, Ann E Barr, Judith Litivn

Abstract

We have previously developed a voluntary rat model of highly repetitive reaching that provides an opportunity to study effects of non-weight bearing muscular loads on bone and mechanisms of naturally occurring inflammation on upper limb tissues in vivo. In this study, we investigated the relationship between inflammatory cytokines and matricellular proteins (Periostin-like-factor, PLF, and connective tissue growth factor, CTGF) using our model. We also examined the relationship between inflammatory cytokines, PLF and bone formation processes. Rats underwent initial training for 5 weeks, and then performed a high repetition high force (HRHF) task (12 reaches/min, 60% maximum grip force, 2 h/day, 3 days/week) for 6 weeks. We then examined the effect of training or task performance with or without treatment with a rat specific TNFα antibody on inflammatory cytokines, osteocalcin (a bone formation marker), PLF, CTGF, and behavioral indicators of pain or discomfort. The HRHF task decreased grip strength and induced forepaw mechanical hypersensitivity in both trained control and 6-week HRHF animals. Two weeks of anti-TNFα treatment improved grip strength in both groups, but did not ameliorate forepaw hypersensitivity. Moreover, anti-TNFα treatment attenuated task-induced increases in inflammatory cytokines (TNFα, IL-1α, and MIP2 in serum; TNFα in forelimb bone and muscles) and serum osteocalcin in 6-week HRHF animals. PLF levels in forelimb bones and flexor digitorum muscles increased significantly in 6-week HRHF animals, increases attenuated by anti-TNFα treatment. CTGF levels were unaffected by task performance or anti-TNFα treatment in 6-week HRHF muscles. In primary osteoblast cultures, TNFα, MIP2 and MIP3a treatment increased PLF levels in a dose dependent manner. Also in primary osteoblast cultures, increased PLF promoted proliferation and differentiation, the latter assessed by measuring Runx2, alkaline phosphatase (ALP) and osteocalcin mRNA levels; ALP activity; as well as calcium deposition and mineralization. Increased PLF also promoted cell adhesion in MC3T3-E1 osteoblast-like cell cultures. Thus, tissue loading in vivo resulted in increased TNFα, which increased PLF, which then induced anabolic bone formation, the latter results confirmed in vitro.

Link to Article

http://dx.doi.org/10.1002/jcp.22208

Is there an optimal force level for sutural expansion?

Authors

Sean Shih-Yao Liu, Lynne A. Opperman, Hee-Moon Kyung, Peter H. Buschang

Abstract

The purpose of this study was to establish the causal relationships between expansion force magnitudes, sutural separation, and sutural bone formation. Thirty-seven 6-week-old rabbits were randomly assigned to 4 force groups (0, 50, 100, or 200 g). Constant forces were delivered for 42 days by nickel-titanium open-coil springs to miniscrew implants (MSIs) placed in the frontal bone on both sides of the midsagittal suture. Inter-MSI and bone marker widths were measured biweekly to quantify sutural separation and MSI movements. Sutural bone formation was quantified based on the incorporation of fluorescent bone labels administered at days 18, 28, and 38. Nine of 74 MSIs failed between days 0 and 14, including 4 in the controls and 5 in the 50-g group. A decelerating curvilinear pattern of sutural separation was evident in the 50-g, 100-g, 200-g groups. Bone markers showed that sutural widths increased by 0.6, 3.2, 5.1, and 6.2 mm in the control, 50-g, 100-g, and 200-g groups, respectively. Except for the 200-g group, significantly greater amounts of bone formation were observed between days 18 and 28 than between days 28 and 38. Sutural bone formation also increased with increasing forces up to 100 g; there was no difference between the 100-g and the 200-g groups. Sutural separation explained 71% and 53% of the variations in bone formation between days 18 and 28 and days 28 and 38, respectively. Within the limits of this study, sutural bone formation is directly related to the amount of sutural separation, which is in turn related to the amount of force applied. The results suggest that there is a level of induced sutural separation that provides the greatest amount of bone formation.

Link to Article

http://dx.doi.org/10.1016/j.ajodo.2009.03.056

The presence of extracellular matrix alters the chondrocyte response to endoplasmic reticulum stress

Authors

Ashleigh E. Nugent, Denise L. McBurney, Walter E. Horton Jr.

Abstract

The objective of this study was to test the hypothesis that extracellular matrix (ECM) would alter the endoplasmic reticulum (ER) stress response of chondrocytes. Chondrocytes were isolated from calf knees and maintained in monolayer culture or suspended in collagen I to form spot cultures (SCs). Our laboratory has shown that bovine chondrocytes form cartilage with properties similar to native cartilage after 2–4 weeks in SCs. Monolayer cultures treated with ER stressors glucose withdrawal (–Glu), tunicamycin (TN), or thapsigargin (TG) up-regulated Grp78 and Gadd153, demonstrating a complete ER stress response. SCs were grown at specific times from 1 day to 6 weeks before treatment with ER stressors. Additionally, SCs grown for 1, 2, or 6 weeks were treated with increasing concentrations of TN or TG. Western blotting of SCs for Grp78 indicated that increased ECM accumulation results in delayed expression; however, Grp78 mRNA is up-regulated in response to ER stressors even after 6 weeks in culture. SCs treated with ER stressors did not up-regulate Gadd153, suggesting that the cells experienced ER stress but would not undergo apoptosis. In fact, SCs undergo apoptosis upon ER stress treatment after 0–1 day of growth; however, after 4 days and to 6 weeks, apoptosis in treated samples was not different than controls. Pro-survival molecules Bcl-2 and Bag-1 were up-regulated upon ER stress in SCs. These results suggest that presence of ECM confers protection from ER stressors. Future studies involving chondrocyte physiology should focus on responses in conditions more closely mimicking the in vivo cartilage environment.

Link to Article

http://dx.doi.org/10.1002/jcb.23025

Ovariectomy stimulates and bisphosphonates inhibit intracortical remodeling in the mouse mandible

Authors

DJ Kubek, DB Burr, MR Allen

Abstract

The pathophysiology of osteonecrosis of the jaw (ONJ) is thought to be linked to suppression of intracortical remodeling. The aim of this study was to determine whether mice, which normally do not undergo appreciable amounts of intracortical remodeling, could be stimulated by ovariectomy to remodel within the cortex of the mandible and if bisphosphonates (BPs) would suppress this intracortical remodeling. Skeletally mature female C3H mice were either ovariectomized (OVX) or SHAM operated and treated with two intravenous doses of zoledronic acid (ZOL, 0.06 mg/kg body weight) or vehicle (VEH). This ZOL dose corresponds to the dose given to patients with cancer on a mg/kg basis, adjusted for body weight. Calcein was administered prior to sacrifice to label active formation sites. Dynamic histomorphometry of the mandible and femur was performed. Vehicle-treated OVX animals had significantly higher (eightfold) intracortical remodeling of the alveolar portion of the mandible compared to sham – this was significantly suppressed by ZOL treatment. At all skeletal sites, overall bone formation rate was lower with ZOL treatment compared to the corresponding VEH group. Under normal conditions, the level of intracortical remodeling in the mouse mandible is minimal but in C3H mice it can be stimulated to appreciable levels with ovariectomy. Based on this, if the suppression of intracortical remodeling is found to be part of the pathophysiology of ONJ, the ovariectomized C3H mouse could serve as a useful tool for studying this condition.

Link to Article

http://dx.doi.org/10.1111/j.1601-6343.2010.01497.x