Neuromedin U (NMU) regulates osteoblast differentiation and activity.

Osteoporosis is a disease of low bone mass that places individuals at enhanced risk for fracture, disability, and death. Osteoporosis rates are expected to rise significantly in the coming decades yet there are limited pharmacological treatment options, particularly for long-term management of this chronic condition. The drug development pipeline is relatively bereft of new strategies, causing an urgent and unmet need for developing new strategies and targets for treating osteoporosis. Here, we examine a lesser-studied bone remodeling pathway, Neuromedin U (NMU), which is expressed in the bone microenvironment along with its cognate receptors NMU receptor 1 (NMUR1) and 2 (NMUR2). We independently corroborate a prior report that global loss of NMU expression leads to high bone mass and test the hypothesis that NMU negatively regulates osteoblast differentiation. Consistent with this, in vitro studies reveal NMU represses osteoblastic differentiation of osteogenic precursors but, in contrast, promotes osteoblastic marker expression, proliferation and activity of osteoblast-like cells. Phospho-profiling arrays were used to detail differential signaling outcomes that may underlie the opposite responses of these cell types. Collectively, our findings indicate that NMU exerts cell-type-specific responses to regulate osteoblast differentiation and activity.

Estrogen levels influence medullary bone quantity and density in female house finches and pine siskins.

Medullary bone, a non-structural osseous tissue, serves as a temporary storage site for calcium that is needed for eggshell production in a number of avian species. Previous research focusing primarily on domesticated species belonging to the Anseriformes, Galliformes, and Columbiformes has indicated that rising estrogen levels are a key signal stimulating medullary bone formation; Passeriformes (which constitute over half of extant bird species and are generally small) have received little attention. In the current study, we examined the influence of estrogen on medullary bone and cortical bone in two species of Passeriformes: the Pine Siskin (Spinus pinus) and the House Finch (Haemorhous mexicanus). Females of these species received either an estradiol implant or were untreated as a control. After 4.5-5months, reproductive condition was assessed and leg (femora) and wing (humeri) bones were collected for analysis using high-resolution (10µm) micro-computed tomography scanning. We found that in both species estradiol-treated females had significantly greater medullary bone quantity in comparison to untreated females, but we found no differences in cortical bone quantity or microarchitecture. We were also able to examine medullary bone density in the pine siskins and found that estradiol treatment significantly increased medullary bone density. Furthermore, beyond the effect of the estradiol treatment, we observed a relationship between medullary bone quantity and ovarian condition that suggests that the timing of medullary bone formation may be related to the onset of yolk deposition in these species. Further research is needed to better understand the precise timing and endocrine regulation of medullary bone formation in Passerines and to determine the extent to which female Passerines rely on medullary bone calcium during the formation of calcified eggshells.

Examining the Role of Hypothalamus-Derived Neuromedin-U (NMU) in Bone Remodeling of Rats.

Global loss of the neuropeptide Neuromedin-U (NMU) is associated with increased bone formation and high bone mass in male and female mice by twelve weeks of age, suggesting that NMU suppresses osteoblast differentiation and/or activity in vivo. NMU is highly expressed in numerous anatomical locations including the skeleton and the hypothalamus. This raises the possibility that NMU exerts indirect effects on bone remodeling from an extra-skeletal location such as the brain. Thus, in the present study we used microinjection to deliver viruses carrying short-hairpin RNA designed to knockdown Nmu expression in the hypothalamus of 8-week-old male rats and evaluated the effects on bone mass in the peripheral skeleton. Quantitative RT-PCR confirmed approximately 92% knockdown of Nmu in the hypothalamus. However, after six weeks, micro computed tomography on tibiae from Nmu-knockdown rats demonstrated no significant change in trabecular or cortical bone mass as compared to controls. These findings are corroborated by histomorphometric analyses which indicate no differences in osteoblast or osteoclast parameters between controls and Nmu-knockdown samples. Collectively, these data suggest that hypothalamus-derived NMU does not regulate bone remodeling in the postnatal skeleton. Future studies are necessary to delineate the direct versus indirect effects of NMU on bone remodeling.

NMUR1 in the NMU-Mediated Regulation of Bone Remodeling.

Neuromedin-U (NMU) is an evolutionarily conserved peptide that regulates varying physiologic effects including blood pressure, stress and allergic responses, metabolic and feeding behavior, pain perception, and neuroendocrine functions. Recently, several lines of investigation implicate NMU in regulating bone remodeling. For instance, global loss of NMU expression in male and female mice leads to high bone mass due to elevated bone formation rate with no alteration in bone resorption rate or observable defect in skeletal patterning. Additionally, NMU treatment regulates the activity of osteoblasts in vitro. The downstream pathway utilized by NMU to carry out these effects is unknown as NMU signals via two G-protein-coupled receptors (GPCRs), NMU receptor 1 (NMUR1), and NMU receptor 2 (NMUR2), and both are expressed in the postnatal skeleton. Here, we sought to address this open question and build a better understanding of the downstream pathway utilized by NMU. Our approach involved the knockdown of Nmur1 in MC3T3-E1 cells in vitro and a global knockout of Nmur1 in vivo. We detail specific cell signaling events (e.g., mTOR phosphorylation) that are deficient in the absence of NMUR1 expression yet trabecular bone volume in femora and tibiae of 12-week-old male Nmur1 knockout mice are unchanged, compared to controls. These results suggest that NMUR1 is required for NMU-dependent signaling in MC3T3-E1 cells, but it is not required for the NMU-mediated effects on bone remodeling in vivo. Future studies examining the role of NMUR2 are required to determine the downstream pathway utilized by NMU to regulate bone remodeling in vivo.

Trends in Gender Authorship and Collaborations: A 30-Year Comparative Bibliometric Analysis of Manuscripts from The Journal of Bone and Joint Surgery and The Bone and Joint Journal.

Publishing original peer-reviewed research is essential for advancement through all career stages. Fewer women than men hold senior-level positions in academic medicine and, therefore, examining publication trends relative to gender is important. The goal of this study was to examine and compare publication trends in The Journal of Bone and Joint Surgery (JBJS) and The Bone and Joint Journal (BJJ) with a particular emphasis on trends regarding author gender. Data was collected and analyzed for manuscripts published in JBJS and BJJ over the past 30 years. For manuscripts published in 1986, 1996, 2006, and 2016, we recorded the numbers of authors, manuscript pages, references, collaborating institutions, the position in the byline of the corresponding author, the country of the corresponding author, and the names of the first and corresponding author. We also calculated the normalized number of citations and corresponding author position. The number of authors, institutions, and countries collaborating on manuscripts published in both JBJS and BJJ increased over time. JBJS published more manuscripts from North America and BJJ published more manuscripts from Europe. In both journals, the percentage of women as first and/or corresponding author increased over time. Trends over the past 30 years have shown increased collaborations with greater citations in manuscripts published in JBJS and BJJ. In the same time period, both journals demonstrated a rise in the percentage of manuscripts with women first and/or corresponding authors, suggesting a decrease in the gender gap.

Gene expression patterns in bone after 4 days of hind-limb unloading in two inbred strains of mice.

INTRODUCTION: An improved understanding of the interdependence of transcriptional and genomic control of bone loss is critical for the design of effective and safe countermeasures for osteoporosis in space and on Earth. In an effort to test whether molecular pathways modulating the loss of functional weight bearing are dependent on genetic makeup, we quantified the differential expression of genes critical to the early stages of bone remodeling in two different strains of mice. METHODS: Adult (4-mo-old) female BALB/cByJ (BALB) and C3H/HeJ (C3H) mice, strains with different sensitivities to unloading, were subjected to hind-limb unloading (HLU) or normal cage activities. RNA was extracted from the tibia following 4 d of HLU and expression levels were determined. RESULTS: In the BALB mice, HLU significantly altered transcriptional levels of osterix (-36%), alkaline phosphatase (-36%), osteonectin (-44%), collagen type 1 (-55%), MMP2 (-36%), osteocalcin (-68%), and osteopontin (+28%). This expression pattern was highly correlated (R2 = 0.75) with altered expression levels in the C3H mice, but the magnitude of altered mRNA levels was less than half of those in the BALB mice. These strain-specific changes in gene expression were consistent with the differential changes in bone formation, as determined in a second group of BALB and C3H mice. DISCUSSION AND CONCLUSIONS: These data indicate that genetics may influence the absolute changes in gene expression of genes during spaceflight, but that the molecular pathways targeted by countermeasures of bone loss may not need to be specific to an individual's genetic makeup.

Mechanical modulation of molecular signals which regulate anabolic and catabolic activity in bone tissue.

Identifying the molecular mechanisms that regulate bone's adaptive response to alterations in load bearing may potentiate the discovery of interventions to curb osteoporosis. Adult female mice (BALB/cByJ) were subjected to catabolic (disuse) and anabolic (45 Hz, 0.3g vibration for 10 min/day) signals, and changes in the mRNA levels of thirteen genes were compared to altered indices of bone formation. Age-matched mice served as controls. Following 4 days of disuse, significant (P = 0.05) decreases in mRNA levels were measured for several genes, including collagen type I (-55%), osteonectin (-44%), osterix (-36%), and MMP-2 (-36%) all of which, after 21 days, had normalized to control levels. In contrast, expression of several genes in the vibrated group, which failed to show significant changes at 4 days, demonstrated significant increases after 21 days, including inducible nitric oxide synthase (iNOS) (39%, P = 0.07), MMP-2 (54%), and receptor activator of the nuclear factor kB ligand (RANKL) (32%). Correlations of gene expression patterns across experimental conditions and time points allowed the functional clustering of responsive genes into two distinct groups. Each cluster's specific regulatory role (formation vs. resorption) was reinforced by the 60% suppression of formation rates caused by disuse, and the 55% increase in formation rates stimulated by mechanical signals (P < 0.05). These data confirm the complexity of the bone remodeling process, both in terms of the number of genes involved, their interaction and coordination of resorptive and formative activity, and the temporal sensitivity of the processes. More detailed spatial and temporal correlations between altered mRNA levels and tissue plasticity may further delineate the molecules responsible for the control of bone mass and morphology.