Neuropeptide Y is expressed by osteocytes and can inhibit osteoblastic activity

Osteocytes are the most abundant osteoblast lineage cells within the bone matrix. They respond to mechanical stimulation and can participate in the release of regulatory proteins that can modulate the activity of other bone cells. We hypothesize that neuropeptide Y (NPY), a neurotransmitter with regulatory functions in bone formation, is produced by osteocytes and can affect osteoblast activity. To study the expression of NPY by the osteoblast lineage cells, we utilized transgenic mouse models in which we can identify and isolate populations of osteoblasts and osteocytes. The Col2.3GFP transgene is active in osteoblasts and osteocytes, while the DMP1 promoter drives green fluorescent protein (GFP) expression in osteocytes. Real‐time PCR analysis of RNA from the isolated populations of cells derived from neonatal calvaria showed higher NPY mRNA in the preosteocytes/osteocytes fraction compared to osteoblasts. NPY immunostaining confirmed the strong expression of NPY in osteocytes (DMP1GFP⁺), and lower levels in osteoblasts. In addition, the presence of NPY receptor Y1 mRNA was detected in cavaria and long bone, as well as in primary calvarial osteoblast cultures, whereas Y2 mRNA was restricted to the brain. Furthermore, NPY expression was reduced by 30–40% in primary calvarial cultures when subjected to fluid shear stress. In addition, treatment of mouse calvarial osteoblasts with exogenous NPY showed a reduction in the levels of intracellular cAMP and markers of osteoblast differentiation (osteocalcin, BSP, and DMP1). These results highlight the potential regulation of osteoblast lineage differentiation by local NPY signaling. J. Cell. Biochem. 108: 621–630, 2009. © 2009 Wiley‐Liss, Inc.     

Involvement of neuropeptide Y and its Y1 and Y5 receptors in maintaining self‐renewal and proliferation of human embryonic stem cells

Neuropeptide Y (NPY) and NPY receptors are widely expressed in various organs and cell types and have been shown to have pleiotropic functions. However, their presence or role in human embryonic stem cells (hESCs) remains unknown. We now show that undifferentiated hESCs primarily express NPY and its Y1 and Y5 receptors. Inhibition of NPY signalling using either the selective NPY Y1 or Y5 receptor antagonist reduces the maintenance of self‐renewal and proliferation of undifferentiated hESCs. We also provide compelling evidence that exogenous NPY supports the long‐term growth of undifferentiated hESCs in the absence of feeder cell factors using only knockout serum replacement media. Further, NPY facilitates the use of chemically defined medium made up of N2/B27 supplement and basic fibroblast growth factor (bFGF) for hESC feeder‐free culture. Our results indicate that both Y1 and Y5 receptors appear to be involved in the NPY‐mediated activation of AKT/protein kinase B and extracellular signal‐regulated kinase 1/2 (ERK1/2) in hESCs. Notably, only Y1 receptor, but not Y5 receptor, is responsible for the NPY‐induced activation of cAMP‐response element binding (CREB) in hESCs. These results provide the first evidence that NPY and its Y1 and Y5 receptors have potential role in maintaining hESC self‐renewal and pluripotency. We demonstrate the underlying importance of NPY signalling and its usefulness in the development of a defined and xeno‐free culture condition for the large‐scale propagation of undifferentiated hESCs.     

大鼠NPY Y2受体基因的克隆及C端肽的表达和纯化

Y2受体亚型是早期发现的NPY的两种主要受体亚型之一,参与NPY所介导的多种生理和病理功能.为了制备Y2受体抗体和开展Y2受体的定位研究,用RT-PCR方法从大鼠海马的总RNA扩增NPY的Y2受体全长基因,接着PCR扩增Y2受体的C端片段,克隆入表达载体中,建立了重组NPY Y2受体C端肽的表达菌株,并对表达产物进行纯化.     

Neuropeptide Y regulates the hematopoietic stem cell microenvironment and prevents nerve injury in the bone marrow

Many reports have revealed the importance of the sympathetic nervous system (SNS) in the control of the bone marrow environment. However, the specific role of neuropeptide Y (NPY) in this process has not been systematically studied. Here we show that NPY‐deficient mice have significantly reduced hematopoietic stem cell (HSC) numbers and impaired regeneration in bone marrow due to apoptotic destruction of SNS fibers and/or endothelial cells. Furthermore, pharmacological elevation of NPY prevented bone marrow impairments in a mouse model of chemotherapy‐induced SNS injury, while NPY injection into conditional knockout mice lacking the Y1 receptor in macrophages did not relieve bone marrow dysfunction. These results indicate that NPY promotes neuroprotection and restores bone marrow dysfunction from chemotherapy‐induced SNS injury through the Y1 receptor in macrophages. They also reveal a new role of NPY as a regulator of the bone marrow microenvironment and highlight the potential therapeutic value of this neuropeptide.     

Extensive Alternative Splicing in the 5'-Untranslated Region of the Rat and Human Neuropeptide Y Y5 Receptor Genes Regulates Receptor Expession

Neuropeptide Y (NPY) elicits a plethora of physiological effects by interacting with several distinct G protein-coupled receptors. Activation of one of these receptors, the NPY Y5 receptor, is thought to result in increased food intake, anticonvulsant effects, attenuation of opiate withdrawal, inhibition of neuronal activity, and alteration of renal function. Several alternatively spliced human and rat NPY Y5 receptor cDNAs have been isolated that use different combinations of exons in the 5'-untranslated region. The various human NPY Y5 receptor cDNAs appear to be differentially expressed in different brain regions. The level of human NPY Y5 receptor expressed transiently in COS1 cells was significantly influenced by the sequence of the 5'-untranslated region. These results indicate that alternative splicing in the 5'-untranslated region of the human and rat NPY Y5 receptor genes occurs in a tissue-specific manner and is one mechanism by which cells control the level of NPY Y5 receptor expression.     

神经肽Y及其受体Y1、Y2对痛觉调制的研究进展

神经肽Y（neuropeptide Y,NPY）是一种由36个氨基酸残基组成的肽类激素,属胰多肽家族,广泛分布于中枢及外周神经组织的神经元中。NPY主要参与摄食行为、心血管活动、垂体分泌等生理功能的调节。NPY还参与了痛觉调制。NPY受体有Y1、Y2、Y3、Y4、Y5和Y6六种亚型。目前对Y1受体和Y2受体的研究较多,显示Y1受体和Y2受体参与痛觉调制。但现在对NPY在痛觉中的具体作用机制还不清楚。该文对NPY及其Y1受体、Y2受体在痛觉调制中的作用作一概述。     

Prolactin decreases the expression ratio of receptor activator of nuclear factor kappaB ligand/osteoprotegerin in human fetal osteoblast cells

Prolactin (PRL) enhanced bone remodeling leading to net bone loss in adult and net bone gain in young animals. Studies in PRL-exposed osteoblasts derived from adult humans revealed an increase in the expression ratio of receptor activator of nuclear factor kappaB ligand (RANKL) and osteoprotegerin (OPG), thus supporting the previous finding of PRL-induced bone loss in adults. This study thus investigated the effects of PRL on the osteoblast functions and the RANKL/OPG ratio in human fetal osteoblast (hFOB) cells which strongly expressed PRL receptors. After 48h incubation, PRL increased osteocalcin expression, but had no effect on cell proliferation. However, the alkaline phosphatase activity was decreased in a dose-response manner within 24h. The effect of PRL on alkaline phosphatase was abolished by LY294002, a phosphoinositide 3-kinase (PI3K) inhibitor. PRL also decreased the RANKL/OPG ratio by downregulating RANKL and upregulating OPG expression, implicating a reduction in the osteoblast signal for osteoclastic bone resorption. It could be concluded that, unlike the osteoblasts derived from adult humans, PRL-exposed hFOB cells exhibited indices suggestive of bone gain, which could explain the in vivo findings in young rats. The signal transduction of PRL in osteoblasts involved the PI3K pathway.     

Evidence for direct effects of prolactin on human osteoblasts: Inhibition of cell growth and mineralization

Hyperprolactinemia is one of the risk factor of decrease in bone mass which has been believed to be mediated by hypogonadism. However, the presence of prolactin receptor in human osteosarcoma cell line and primary bone cell culture from mouse calvariae supported the hypothesis of a direct prolactin (PRL) action on bone cells. Therefore, the aim of this study was to investigate the role of PRL and its signal transduction pathway in the regulation of bone metabolism via osteoblast differentiation. Human pre‐osteoblasts (SV‐HFO) that differentiate in a 3‐week period from proliferating pre‐osteoblasts (days 2–7) to extracellular matrix producing cells (days 7–14) which is eventually mineralized (days 14–21) were used. Concentration of PRL mimicked a lactating period (100 ng/ml) was used to incubate SV‐HFO for 21 days in osteogenic medium. Human prolactin receptor mRNA and protein are expressed in SV‐HFO. PRL significantly decreased osteoblast number (DNA content) which was due to a decrease in proliferation. PRL increased osteogenic markers, RUNX2 and ALP in early stage of osteoblast differentiation while decreasing it later suggesting a bi‐directional effect. Calcium measurement and Alizarin red staining showed a reduction of mineralization by PRL while having neither an effect on osteoblast activity nor RANKL/OPG mRNA ratio. We also demonstrated that PRL action on mineralization was not via PI‐3 kinase pathway. The present study provides evidence of a direct effect of prolactin on osteoblast differentiation and in vitro mineralization. J. Cell. Biochem. 107: 677–685, 2009. © 2009 Wiley‐Liss, Inc.     

Dikkopf-1 promotes matrix mineralization of osteoblasts by regulating Ca+-CAMK2A-CREB1 pathway

Dickkopf-1 (DKK1) is a secreted protein that acts as an antagonist of the canonical WNT/β-catenin pathway, which regulates osteoblast differentiation. However, the role of DKK1 on osteoblast differentiation has not yet been fully clarified. Here, we investigate the functional role of DKK1 on osteoblast differentiation. Primary osteoprogenitor cells were isolated from human spinal bone tissues. To examine the role of DKK1 in osteoblast differentiation, we manipulated the expression of DKK1, and the cells were differentiated into mature osteoblasts. DKK1 overexpression in osteoprogenitor cells promoted matrix mineralization of osteoblast differentiation but did not promote matrix maturation. DKK1 increased Ca⁺ influx and activation of the Ca⁺/calmodulin-dependent protein kinase II Alpha (CAMK2A)-cAMP response element-binding protein 1 (CREB1) and increased translocation of p-CREB1 into the nucleus. In contrast, stable DKK1 knockdown in human osteosarcoma cell line SaOS2 exhibited reduced nuclear translocation of p-CREB1 and matrix mineralization. Overall, we suggest that manipulating DKK1 regulates the matrix mineralization of osteoblasts by Ca⁺-CAMK2A-CREB1, and DKK1 is a crucial gene for bone mineralization of osteoblasts.     

Novel role of Y1 receptors in the coordinated regulation of bone and energy homeostasis

The importance of neuropeptide Y (NPY) and Y2 receptors in the regulation of bone and energy homeostasis has recently been demonstrated. However, the contributions of the other Y receptors are less clear. Here we show that Y1 receptors are expressed on osteoblastic cells. Moreover, bone and adipose tissue mass are elevated in Y1(-/-) mice with a generalized increase in bone formation on cortical and cancellous surfaces. Importantly, the inhibitory effects of NPY on bone marrow stromal cells in vitro are absent in cells derived from Y1(-/-) mice, indicating a direct action of NPY on bone cells via this Y receptor. Interestingly, in contrast to Y2 receptor or germ line Y1 receptor deletion, conditional deletion of hypothalamic Y1 receptors in adult mice did not alter bone homeostasis, food intake, or adiposity. Furthermore, deletion of both Y1 and Y2 receptors did not produce additive effects in bone or adiposity. Thus Y1 receptor pathways act powerfully to inhibit bone production and adiposity by nonhypothalamic pathways, with potentially direct effects on bone tissue through a single pathway with Y2 receptors.     

Ligands of the neuropeptide Y Y2 receptor

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the mammalian brain and exerts a variety of physiological processes in humans via four different receptor subtypes Y1, Y2, Y4 and Y5. Y2 receptor is the most abundant Y subtype receptor in the central nervous system and implicated with food intake, bone formation, affective disorders, alcohol and drugs of abuse, epilepsy, pain, and cancer. The lack of small molecule non-peptidic Y2 receptor modulators suitable as in vivo pharmacological tools hampered the progress to uncover the precise pharmacological role of Y2. Only in recent years, several potent, selective and non-peptidic Y2 antagonists have been discovered providing the tools to validate Y2 receptor as a therapeutic target. This Letter reviews Y2 receptor modulators mainly non-peptidic antagonists and their structure–activity relationships.     

BMP‐2 modulates β‐catenin signaling through stimulation of Lrp5 expression and inhibition of β‐TrCP expression in osteoblasts

Canonical BMP and Wnt signaling pathways play critical roles in regulation of osteoblast function and bone formation. Recent studies demonstrate that BMP‐2 acts synergistically with β‐catenin to promote osteoblast differentiation. To determine the molecular mechanisms of the signaling cross‐talk between canonical BMP and Wnt signaling pathways, we have used primary osteoblasts and osteoblast precursor cell lines 2T3 and MC3T3‐E1 cells to investigate the effect of BMP‐2 on β‐catenin signaling. We found that BMP‐2 stimulates Lrp5 expression and inhibits the expression of β‐TrCP, the F‐box E3 ligase responsible for β‐catenin degradation and subsequently increases β‐catenin protein levels in osteoblasts. In vitro deletion of the β‐catenin gene inhibits osteoblast proliferation and alters osteoblast differentiation and reduces the responsiveness of osteoblasts to the BMP‐2 treatment. These findings suggest that BMP‐2 may regulate osteoblast function in part through modulation of the β‐catenin signaling. J. Cell. Biochem. 108: 896–905, 2009. © 2009 Wiley‐Liss, Inc.