Osteocytes represent the most abundant cellular component of mammalian bones with important functions in bone mass maintenance and remodeling. To elucidate the differential gene expression between osteoblasts and osteocytes we completed a comprehensive analysis of their gene profiles. Selective identification of these two mature populations was achieved by utilization of visual markers of bone lineage cells. We have utilized dual GFP reporter mice in which osteocytes are expressing GFP (topaz) directed by the DMP1 promoter, while osteoblasts are identified by expression of GFP (cyan) driven by 2.3kb of the Col1a1 promoter. Histological analysis of 7-day-old neonatal calvaria confirmed the expression pattern of DMP1GFP in osteocytes and Col2.3 in osteoblasts and osteocytes. To isolate distinct populations of cells we utilized fluorescent activated cell sorting (FACS). Cells suspensions were subjected to RNA extraction, in vitro transcription and labeling of cDNA and gene expression was analyzed using the Illumina WG-6v1 BeadChip.Following normalization of raw data from four biological replicates, 3444 genes were called present in all three sorted cell populations: GFP negative, Col2.3cyan + (osteoblasts), and DMP1topaz + (preosteocytes and osteocytes). We present the genes that showed in excess of a 2-fold change for gene expression between DMP1topaz + and Col2.3cyan + cells. The selected genes were classified and grouped according to their associated gene ontology terms. Genes clustered to osteogenesis and skeletal development such as Bmp4, Bmp8a, Dmp1, Enpp1, Phex and Ank were highly expressed in DMP1topaz + cells. Most of the genes encoding extracellular matrix components and secreted proteins had lower expression in DMP1topaz + cells, while most of the genes encoding plasma membrane proteins were increased. Interestingly a large number of genes associated with muscle development and function and with neuronal phenotype were increased in DMP1topaz + cells, indicating some new aspects of osteocyte biology. Although a large number of genes differentially expressed in DMP1topaz + and Col2.3cyan + cells in our study have already been assigned to bone Contact Information: Ivo Kalajzic, Department of Reconstructive Sciences, MC 3705, University of Connecticut Health Center, 263 Farmington Ave., Farmington, CT 06032. Tel.: 860-679-6051; Fax: 860-679-2910; ikalaj@neuron.uchc.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptBone. Author manuscript; available in PMC 2010 October 1. NIH-PA Author ManuscriptNIH-PA Author Manuscript NI...

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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. KeywordsNeuropeptide Y; Osteocytes; Osteoblasts; GFP; Bone Neuropeptide Y (NPY) is a 36-amino acid polypeptide that belongs to the larger family of neuropeptides, which also includes the pancreatic polypeptide and the peptide YY Allen et al., 1992]. NPY signals through a class of receptors known as Y receptors, members of the G-protein-coupled receptors [Lemos et al., 1997;Raimondi et al., 2002]. The Y receptor system consists of five Y receptors; Y1, Y2, Y4, Y5, and Y6 (which is present only in the mouse). NPY is highly expressed in the hypothalamus, and its receptors Y1, Y2, and Y5 are found in the central nervous system, including the hypothalamus [Sar et al., 1990;Parker and Herzog, 1999].Functionally, NPY is a potent orexigenic peptide; its expression is up-regulated in the hypothalamus of experimental diabetic rats la Fleur et al., 2003]. NPY acts through the Y2 receptor in the hypothalamus to centrally regulate bone mass [Baldock et al., 2002]. This observation was reinforced using germline deletion of Y2 or Y1 receptors in mice, resulting in a higher trabecular bone volume and elevated cortical bone mass [Baldock et al., 2005]. Moreover, targeted deletion of Y2 in the hypothalamus revealed an increased bone volume comparable to the effect of germ line deletion of Y1 or Y2 in mice, thus confirming the Y2-mediated central regulation of bone mass [Baldock et al., 2005]. In...

Aortic valve stenosis is the most common cardiac valve disease, and with current trends in the population demographics, its prevalence is likely to rise, thus posing a major health and economic burden facing the worldwide societies. Over the past decade, it has become more than clear that our traditional genetic views do not sufficiently explain the well-known link between AS, proatherogenic risk factors, flow-induced mechanical forces, and disease-prone environmental influences. Recent breakthroughs in the field of epigenetics offer us a new perspective on gene regulation, which has broadened our perspective on etiology of aortic stenosis and other aortic valve diseases. Since all known epigenetic marks are potentially reversible this perspective is especially exciting given the potential for development of successful and non-invasive therapeutic intervention and reprogramming of cells at the epigenetic level even in the early stages of disease progression. This review will examine the known relationships between four major epigenetic mechanisms: DNA methylation, posttranslational histone modification, ATP-dependent chromatin remodeling, and non-coding regulatory RNAs, and initiation and progression of AS. Numerous profiling and functional studies indicate that they could contribute to endothelial dysfunctions, disease-prone activation of monocyte-macrophage and circulatory osteoprogenitor cells and activation and osteogenic transdifferentiation of aortic valve interstitial cells, thus leading to valvular inflammation, fibrosis, and calcification, and to pressure overload-induced maladaptive myocardial remodeling and left ventricular hypertrophy. This is especcialy the case for small non-coding microRNAs but was also, although in a smaller scale, convincingly demonstrated for other members of cellular epigenome landscape. Equally important, and clinically most relevant, the reported data indicate that epigenetic marks, particularly certain microRNA signatures, could represent useful non-invasive biomarkers that reflect the disease progression and patients prognosis for recovery after the valve replacement surgery.

ses of ischemic stroke. The risk of ischemic stroke increases with the degree of carotid stenosis and plaque vulnerability. The aim of this study was to investigate the association of circulating and plaque resistin levels with plaque vulnerability and ischemic stroke events in patients with moderate- to high-grade carotid artery stenosis. Methods: 40 patients with ischemic stroke events and 38 neurologically asymptomatic patients scheduled for carotid endarterectomy were recruited for this study. Fasting blood samples for laboratory analysis were collected preoperatively and serum resistin levels were measured by enzyme-linked immunosorbent assays. Carotid endarterectomy specimens were analyzed according to the gold-standard procedure of histological classification. Plaque resistin expression was determined by standard immunohistochemical procedure. Results: Serum resistin levels and resistin plaque expression were found to be significantly higher in subjects with unstable carotid plaque (P < .001) while significantly higher serum resistin levels were also present in patients with ischemic stroke events (P < .001). In univariate stepwise logistic regression analysis, higher serum resistin levels were significantly associated with plaque instability (OR 2.223, 95% CI 1.488-3.320, P < .0001) and ischemic stroke events (OR 1.237, 95% CI 1.079-1.420, P = .002). There was also a significant association between higher serum and plaque resistin expression (OR 1.663, 95% CI1.332-2.077, P < .0001). These associations remained significant in all models of multivariate logistic regression analysis. High serum and plaque resistin levels were also significantly associated with specific histological features of plaque instability. Conclusion: The results suggests that serum resistin levels may be used as a potential biomarker of plaque vulnerability and ischemic stroke events in patients with moderate- to high-grade carotid artery stenosis and highlight the possible relationship that plaque resistin expression has with histological features of plaque vulnerability.