SUMMARYNuclear factor kappa B (NF-k B) is a transcription factor pivotal for the development of inflammation. A dysregulation of NF-k B has been shown to play an important role in many chronic inflammatory diseases including rheumatoid arthritis, inflammatory bowel disease and psoriasis. Although classical NFk B, a heterodimer composed of the p50 and p65 subunits, has been well studied, little is known about gene regulation by other hetero-and homodimeric forms of NF-k B. While p65 possesses a transactivation domain, p50 does not. Indeed, p50/p50 homodimers have been shown to inhibit transcriptional activity. We have recently shown that Interleukin-10 exerts its anti-inflammatory activity in part through the inhibition of NF-k B by blocking I k B kinase activity and by inhibiting NF-k B already found in the nucleus. Since the inhibition of nuclear NF-k B could not be explained by an increase of nuclear I k B, we sought to further investigate the mechanisms involved in the inhibition of NF-k B by IL-10. We show here that IL-10 selectively induced nuclear translocation and DNA-binding of p50/p50 homodimers in human monocytic cells. TNF-a treatment led to a strong translocation of p65 and p50, whereas pretreatment with IL-10 followed by TNF-a blocked p65 translocation but did not alter the strong translocation of p50. Furthermore, macrophages of p105/p50-deficient mice exhibited a significantly decreased constitutive production of MIP-2 a and IL-6 in comparison to wild type controls. Surprisingly, IL-10 inhibited high constitutive levels of these cytokines in wt macrophages but not in p105/p50 deficient cells. Our findings suggest that the selective induction of nuclear translocation and DNA-binding of the repressive p50/p50 homodimer is an important anti-inflammatory mechanism utilized by IL-10 to repress inflammatory gene transcription.

Changes in whole body energy levels are closely linked to alterations in body weight and bone mass. Here, we show that hypothalamic signals contribute to the regulation of bone mass in a manner consistent with the central perception of energy status. Mice lacking neuropeptide Y (NPY), a well-known orexigenic factor whose hypothalamic expression is increased in fasting, have significantly increased bone mass in association with enhanced osteoblast activity and elevated expression of bone osteogenic transcription factors, Runx2 and Osterix. In contrast, wild type and NPY knockout (NPY −/−) mice in which NPY is specifically over expressed in the hypothalamus (AAV-NPY+) show a significant reduction in bone mass despite developing an obese phenotype. The AAV-NPY+ induced loss of bone mass is consistent with models known to mimic the central effects of fasting, which also show increased hypothalamic NPY levels. Thus these data indicate that, in addition to well characterized responses to body mass, skeletal tissue also responds to the perception of nutritional status by the hypothalamus independently of body weight. In addition, the reduction in bone mass by AAV NPY+ administration does not completely correct the high bone mass phenotype of NPY −/− mice, indicating the possibility that peripheral NPY may also be an important regulator of bone mass. Indeed, we demonstrate the expression of NPY specifically in osteoblasts. In conclusion, these data identifies NPY as a critical integrator of bone homeostatic signals; increasing bone mass during times of obesity when hypothalamic NPY expression levels are low and reducing bone formation to conserve energy under ‘starving’ conditions, when hypothalamic NPY expression levels are high.

Background & AimsGastrointestinal peptides are increasingly being linked to processes controlling the maintenance of bone mass. Peptide YY (PYY), a gut-derived satiety peptide of the neuropeptide Y family, is upregulated in some states that also display low bone mass. Importantly, PYY has high affinity for Y-receptors, particularly Y1R and Y2R, which are known to regulate bone mass. Anorexic conditions and bariatric surgery for obesity influence circulating levels of PYY and have a negative impact on bone mass, but the precise mechanism behind this is unclear. We thus examined whether alterations in PYY expression affect bone mass.MethodsBone microstructure and cellular activity were analyzed in germline PYY knockout and conditional adult-onset PYY over-expressing mice at lumbar and femoral sites using histomorphometry and micro-computed tomography.ResultsPYY displayed a negative relationship with osteoblast activity. Male and female PYY knockout mice showed enhanced osteoblast activity, with greater cancellous bone mass. Conversely, PYY over-expression lowered osteoblast activity in vivo, via a direct Y1 receptor mediated mechanism involving MAPK stimulation evident in vitro. In contrast to PYY knockout mice, PYY over expression also altered bone resorption, as indicated by greater osteoclast surface, despite the lack of Y-receptor expression in osteoclastic cells. While evident in both sexes, cellular changes were generally more pronounced in females.ConclusionsThese data demonstrate that the gut peptide PYY is critical for the control of bone remodeling. This regulatory axis from the intestine to bone has the potential to contribute to the marked bone loss observed in situations of extreme weight loss and higher circulating PYY levels, such as anorexia and bariatric obesity surgery, and may be important in the maintenance of bone mass in the general population.

On initial inspection, bone remodeling, the process whereby the skeleton adapts through time, appears to be relatively simple. Two cell types, the bone-forming osteoblasts and the bone-resorbing osteoclasts, interact to keep bone mass relatively stable throughout adult life. However, the complexity of the regulatory influences on these cells is continuing to expand our understanding of the intricacy of skeletal physiology and also the interactions between other organ systems and bone. One such example of the broadening of understanding in this field has occurred in the last decade with study of the central, neural regulation of bone mass. Initial studies of an adipose-derived hormone, leptin, helped define a direct, sympathetic pathway involving efferent neural signals from the hypothalamus to receptors on the osteoblast. Since the leptin-mediated pathway has been continuously modified to reveal a complex system involving neuromedin U, cocaineand amphetamine-related transcript and serotonin interacting within the hypothalamus and brainstem to regulate both bone formation and resorption in cancellous bone, a number of other systems have also been identified. Neuropeptide Y, acting through hypothalamic Y2 receptors, is capable of skeleton-wide modulation of osteoblast activity, with important coordination between body weight and bone mass. Cannabinoids, acting through central cannabinoid receptor 1 and bone cell cannabinoid receptor 2 receptors, modulate osteoclast activity, thereby identifying pathways active on both aspects of the bone remodeling process. This review explores the key central pathways to bone and explores the complexity of the interactions being revealed by this emergent field of research. Journal of Molecular Endocrinology (2010) 45, 175-181 Function of hypothalamusThe brain has long been appreciated as a pivotal regulator of homeostasis in peripheral tissues, including the skeleton. There is now clear evidence for crosstalk between the brain and bone through two distinct routes. The first pathway comprises welldefined hormonal signals arising from neuroendocrine neurons of the hypothalamus and subsequently processed within the pituitary. The second pathway consists of efferent neuronal discharges originating from the hypothalamus and processed through the brainstem. The hypothalamus, with its semipermeable blood-brain barrier, is thus one of the most powerful regulatory regions within the body, integrating signals not only from peripheral tissues but also from within the brain itself. These direct, neural pathways represent an emergent area of study that is identifying novel regulatory axes between the brain and the cells of bone. Moreover, this work is also providing insights into regulatory connections involving skeletal tissue, which are proving to be unexpected, thereby outlining a level of interconnectedness that has been previously unappreciated. This review examines the expanded understanding of the central, neural outputs to bone metabolism and remodeling.

Chronic stress and depression have adverse consequences on many organ systems, including the skeleton, but the mechanisms underlying stress-induced bone loss remain unclear. Here we demonstrate that neuropeptide Y (NPY), centrally and peripherally, plays a critical role in protecting against stress-induced bone loss. Mice lacking the anxiolytic factor NPY exhibit more anxious behavior and elevated corticosterone levels. Additionally, following a 6-week restraint, or cold-stress protocol, Npy-null mice exhibit three-fold greater bone loss compared to wild-type mice, owing to suppression of osteoblast activity. This stress-protective NPY pathway acts specifically through Y2 receptors. Centrally, Y2 receptors suppress corticotropin-releasing factor expression and inhibit activation of noradrenergic neurons in the paraventricular nucleus. In the periphery, they act to control noradrenaline release from sympathetic neurons. Specific deletion of arcuate Y2 receptors recapitulates the Npy-null stress response, coincident with elevated serum noradrenaline. Importantly, specific reintroduction of NPY solely in noradrenergic neurons of otherwise Npy-null mice blocks the increase in circulating noradrenaline and the stress-induced bone loss. Thus, NPY protects against excessive stress-induced bone loss, through Y2 receptor-mediated modulation of central and peripheral noradrenergic neurons.

Research Article 1465Introduction A reciprocal interaction between bone and energy metabolism has been described, whereby a hormone secreted by adipocytes influences bone formation and a factor produced by osteoblasts regulates fat metabolism (Lieben et al., 2009;Rosen, 2008). The crucial factor in this systemic loop is leptin, because its deficiency causes obesity and increases bone formation in the mouse (Ducy et al., 2000). Leptin is produced by white adipocytes and acts via the hypothalamus to regulate appetite and to favor energy expenditure. Bone formation is also negatively regulated by leptin through a second hypothalamic pathway, the -adrenergic sympathetic nervous system (Takeda et al., 2002). This pathway increases ATF-4-dependent expression of Esp (protein tyrosine phosphatase, receptor type, V; Ptprv) in osteoblasts, which leads to an inhibition of osteocalcin bioactivity. By contrast, insulin signaling in osteoblasts promotes the production of bioactive osteocalcin via acidification of the extracellular bone matrix as a consequence of increased bone resorption by osteoclasts (Ferron et al., 2010;Fulzele et al., 2010). In turn, osteocalcin, a hormone secreted by osteoblasts, modulates fat metabolism via the stimulation of pancreatic -cell proliferation and insulin secretion and thus, can indirectly, via adiponectin, lower insulin resistance (Hinoi et al., 2008;Yoshizawa et al., 2009). Thus, a common neuroendocrine systemic co-regulation of bone and adipose mass is established.In addition to this systemic regulation of bone and fat metabolism, a local control of cell fates balancing osteoblast and adipocyte differentiation, which is still poorly understood, must exist to integrate the systemic messages. Indeed, osteoblasts share with adipocytes a common mesenchymal progenitor, the mesenchymal stromal or stem cell (MSC) from which also arise other mesenchymal cell lineages such as chondrocytes, fibroblasts and myoblasts (Caplan, 2007). Mesenchymal cell fate decisions are driven by key transcription factors that confer identity to the cell. The major transcription factors regulating MSC differentiation to osteoblasts are -catenin and Runx2, both of which are required for the differentiation to pre-osteoblasts and osterix that drives osteoblast maturation (Karsenty, 2008;Komori, 2006). Similarly, adipocyte differentiation occurs first by activation of C/EBP and C/EBP, resulting in expression of PPAR2 and C/EBP, which then regulate late stages of adipogenesis (Lefterova and Lazar, 2009). Furthermore, a number of additional factors such as bone morphogenic proteins (BMPs) and signaling, for instance through the WNT pathway, have been described to regulate cell fate decisions between osteoblasts and adipocytes by promoting commitment or differentiation into one lineage at the expense of the other (Takada et al., 2007). All these observations strongly argue in favor of a cell-autonomous locally controlled relationship between osteoblastogenesis and adipogenesis. SummaryA shift from osteoblastogenesis...

Y-receptors control energy homeostasis, but the role of Npy6 receptors (Npy6r) is largely unknown. Young Npy6r-deficient (Npy6r(-/-)) mice have reduced body weight, lean mass, and adiposity, while older and high-fat-fed Npy6r(-/-) mice have low lean mass with increased adiposity. Npy6r(-/-) mice showed reduced hypothalamic growth hormone releasing hormone (Ghrh) expression and serum insulin-like growth factor-1 (IGF-1) levels relative to WT. This is likely due to impaired vasoactive intestinal peptide (VIP) signaling in the suprachiasmatic nucleus (SCN), where we found Npy6r coexpressed in VIP neurons. Peripheral administration of pancreatic polypeptide (PP) increased Fos expression in the SCN, increased energy expenditure, and reduced food intake in WT, but not Npy6r(-/-), mice. Moreover, intraperitoneal (i.p.) PP injection increased hypothalamic Ghrh mRNA expression and serum IGF-1 levels in WT, but not Npy6r(-/-), mice, an effect blocked by intracerebroventricular (i.c.v.) Vasoactive Intestinal Peptide (VPAC) receptors antagonism. Thus, PP-initiated signaling through Npy6r in VIP neurons regulates the growth hormone axis and body composition.

Purpose The anticipated emergence of hemophilia gene therapy will present people with hemophilia (PWH) and treating clinicians with increasingly complex treatment options. It will be critical that PWH and their families be empowered to participate fully in decision-making through transparent communication and the development of targeted educational resources. Methods The Council of Hemophilia Community (CHC) convened across a series of roundtable meetings to define the patient journey for hemophilia gene therapy, and to develop a question-and-answer style resource to guide discussion between healthcare professionals (HCPs) and their patients. Patient groups were also consulted during the development of this tool. Results The CHC defined 5 key stages in the hemophilia gene therapy patient journey: pre-gene therapy (information-seeking and decision-making), treatment initiation, short- and long-term post-gene therapy follow-up. PWH will have different questions and concerns at each stage of their journey, which should be discussed with their HCP to aid decision-making. The resulting patient journey infographic and Q&A resource (see Supplementary Materials ) has been developed for HCPs and PWH to provide a novel and practical roadmap of key issues and considerations throughout all stages. Conclusion These resources support a collaborative, patient-centric, shared decision-making approach to inform treatment decision discussions between HCPs and PWH. The value of such discussions will be influenced by the language adopted; health literacy is a particularly important consideration, and these discussions should be accessible and tailored to PWH. HCPs and PWH can benefit from awareness of the common questions and uncertainties as they progress together along the patient journey. While the contents of this article are specific to hemophilia gene therapy, the concepts developed here could be adapted to aid patients in other disease states.