Multi-organ phenotypes in mice lacking latent TGFβ binding protein 2 (LTBP2)

AUTHORS

Nicholas K. Bodmer, Russell H. Knutsen, Robyn A. Roth, Ryan M. Castile, Michael D. Brodt, Carrie M. Gierasch, Thomas J. Broekelmann, Mark A. Gibson, Jeffrey A. Haspel, Spencer P. Lake, Jeffrey R. Koenitzer, Steven L. Brody, Matthew J. Silva, Robert P. Mecham, David M. Ornitz

ABSTRACT

Background

Latent TGFβ binding protein-2 (LTBP2) is a fibrillin 1 binding component of the microfibril. LTBP2 is the only LTBP protein that does not bind any isoforms of TGFβ, although it may interfere with the function of other LTBPs or interact with other signaling pathways.

Results

Here, we investigate mice lacking Ltbp2 (Ltbp2−/−) and identify multiple phenotypes that impact bodyweight and fat mass, and affect bone and skin development. The alterations in skin and bone development are particularly noteworthy since the strength of these tissues is differentially affected by loss of Ltbp2. Interestingly, some tissues that express high levels of Ltbp2, such as the aorta and lung, do not have a developmental or homeostatic phenotype.

Conclusions

Analysis of these mice show that LTBP2 has complex effects on development through direct effects on the extracellular matrix (ECM) or on signaling pathways that are known to regulate the ECM.

The effect of low-frequency high-intensity ultrasound combined with aspirin on tooth movement in rats

AUTHORS

Jiao Xin, Xinxin Zhan, Fu Zheng, Huazhi Li, Yixiang Wang, Cuiying Li & Jiuhui Jiang

ABSTRACT

Background

Given the difficulties or incapacity of teeth movement in orthodontic treatment, the ways to speed tooth movement must be investigated. Besides, nonsteroidal anti-inflammatory drugs (NSAIDs) were utilized to treat pain caused by tooth movement during orthodontic treatment. The purpose of this study is to examine the impact of aspirin and low-frequency high-intensity ultrasound (LFHIU) on rat orthodontic tooth movement in rats.

Methods

Thirty-six male Sprague-Dawley rats were divided into three groups: orthodontic (O), ultrasound-treated orthodontic (OU), and ultrasound-treated orthodontic with aspirin gavage (OUA) group. In the OU and OUA group, LFHIU (44 W/cm2, 28 kHz) was applied to the buccal side of the maxillary first molar alveolar bone for 10 s every day. In the OUA group, aspirin was given by gavage every day. The rats were sacrificed on days 1, 3, 7, and 14.

Results

After ultrasonic treatment, the speed of tooth movement was increased by about 1.5 times. And the number of osteoclasts considerably increased by about 2 times. However, they decreased slightly after aspirin gavage. By Applying ultrasound therapy, Receptor Activator for Nuclear Factor-κ B Ligand (RANKL) levels in periodontal tissue were elevated. Aspirin was able to reduce these increases. Results from Micro Computed Tomography (Micro-CT) revealed that bone mineral density decreased by about 1/5 after ultrasound treatment on the compression side. The rate of bone mineral apposition indicated that bone was forming under tension, and that of the OU group increased by about 1.3 times that O group.

Conclusions

Although aspirin slowed this trend, LFHIU still enhanced overall tooth mobility in orthodontic treatment.

Nystagmus Associated With the Absence of MYOD Expression Across the Lifespan in Extraocular and Limb Muscles

AUTHORS

Laura L. Johnson; Sadie Hebert; Rachel B. Kueppers; Linda K. McLoon

ABSTRACT

Purpose: The extraocular muscles (EOMs) undergo significant levels of continuous myonuclear turnover and myofiber remodeling throughout life, in contrast to limb skeletal muscles. Activation of the myogenic pathway in muscle precursor cells is controlled by myogenic transcription factors, such as MYOD. Limb muscles from MyoD−/− mice develop normally but have a regeneration defect, and these mice develop nystagmus. We examined MyoD−/− mice to determine if they have an aging phenotype.

Methods: Eye movements of aging MyoD−/− mice and littermate controls (wild type) were examined using optokinetic nystagmus (OKN). We assessed limb muscle function, changes to myofiber number, mean cross-sectional area, and abundance of the PAX7 and PITX2 populations of myogenic precursor cells.

Results: Aging did not significantly affect limb muscle function despite decreased mean cross-sectional areas at 18+ months. Aging wild type mice had normal OKN responses; all aging MyoD−/− mice had nystagmus. With OKN stimulus present, the MyoD−/− mice at all ages had shorter slow phase durations compared to wild type age matched controls. In the dark, the MyoD−/− mice had a shorter slow phase duration with age. This correlated with significantly decreased fiber numbers and cross-sectional areas. The EOM in MyoD−/− mice had increased numbers of PAX7-positive satellite cells and significantly decreased PITX2-positive myonuclei.

Conclusions: The absence of MYOD expression in aging mice causes a decrease in on-going myofiber remodeling, EOM fiber size, and number, and is associated with the development of spontaneous nystagmus. These results suggest that muscle-specific mutations can result in nystagmus, with increasing aging-related changes in the MyoD−/− EOM.

Inhibition of KIF11 ameliorates osteoclastogenesis via regulating mTORC1-mediated NF-κB signaling

AUTHORS

Jiansen Miao, Hanbing Yao, Jian Liu, Zhixian Huang, Chengge Shi, Xinyu Lu, Junchen Jiang, Rufeng Ren, Chenyu Wang, Youjin Pan, Te Wang, Haiming Jin

ABSTRACT

Osteoporosis, characterized by over-production and activation of osteoclasts, has become a major health problem especially in elderly women. In our study, we first tested the effect of Caudatin (Cau) in osteoclastogenesis, which is separated from Cynanchum auriculatum as a species of C-21 steroidal glyosides. The results indicated that Cau suppressed osteoclastogenesis in a time- and dose-dependent manner in vitro. Mechanistically, Cau was identified to inhibit NF-κB signaling pathway via modulation of KIF11-mediated mTORC1 activity. In vivo, by establishing an ovariectomized (OVX) mouse model to mimic osteoporosis, we confirmed that Cau treatment prevented OVX-induced bone loss in mice. In conclusion, we demonstrated that Cau inhibited NF-κB signaling pathway via modulation of KIF11-mediated mTORC1 activity to suppress osteoclast differentiation in vitro as well as OVX-induced bone loss in vivo. This provides the possibility of a novel prospective drug for osteoporosis remedies.

Inhibiting WNT secretion reduces high bone mass caused by Sost loss-of-function or gain-of-function mutations in Lrp5

AUTHORS

Cassandra R. Diegel, Ina Kramer, Charles Moes, Gabrielle E. Foxa, Mitchell J. McDonald, Zachary B. Madaj, Sabine Guth, Jun Liu, Jennifer L. Harris, Michaela Kneissel & Bart O. Williams

ABSTRACT

Proper regulation of Wnt signaling is critical for normal bone development and homeostasis. Mutations in several Wnt signaling components, which increase the activity of the pathway in the skeleton, cause high bone mass in human subjects and mouse models. Increased bone mass is often accompanied by severe headaches from increased intracranial pressure, which can lead to fatality and loss of vision or hearing due to the entrapment of cranial nerves. In addition, progressive forehead bossing and mandibular overgrowth occur in almost all subjects. Treatments that would provide symptomatic relief in these subjects are limited. Porcupine-mediated palmitoylation is necessary for Wnt secretion and binding to the frizzled receptor. Chemical inhibition of porcupine is a highly selective method of Wnt signaling inhibition. We treated three different mouse models of high bone mass caused by aberrant Wnt signaling, including homozygosity for loss-of-function in Sost, which models sclerosteosis, and two strains of mice carrying different point mutations in Lrp5 (equivalent to human G171V and A214V), at 3 months of age with porcupine inhibitors for 5–6 weeks. Treatment significantly reduced both trabecular and cortical bone mass in all three models. This demonstrates that porcupine inhibition is potentially therapeutic for symptomatic relief in subjects who suffer from these disorders and further establishes that the continued production of Wnts is necessary for sustaining high bone mass in these models.

Dlk2 interacts with Syap1 to activate Akt signaling pathway during osteoclast formation

AUTHORS

Xinwei Chen, Xuzhuo Chen, Rui Chao, Yexin Wang, Yi Mao, Baoting Fan, Yaosheng Zhang, Weifeng Xu, An Qin & Shanyong Zhang

ABSTRACT

Excessive osteoclast formation and bone resorption are related to osteolytic diseases. Delta drosophila homolog-like 2 (Dlk2), a member of the epidermal growth factor (EGF)-like superfamily, reportedly regulates adipocyte differentiation, but its roles in bone homeostasis are unclear. In this study, we demonstrated that Dlk2 deletion in osteoclasts significantly inhibited osteoclast formation in vitro and contributed to a high-bone-mass phenotype in vivo. Importantly, Dlk2 was shown to interact with synapse-associated protein 1 (Syap1), which regulates Akt phosphorylation at Ser473. Dlk2 deletion inhibited Syap1-mediated activation of the AktSer473, ERK1/2 and p38 signaling cascades. Additionally, Dlk2 deficiency exhibits increased bone mass in ovariectomized mice. Our results reveal the important roles of the Dlk2-Syap1 signaling pathway in osteoclast differentiation and osteoclast-related bone disorders.