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Topic: Osteocyte

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	Osteocyte - Wikipedia, the free encyclopedia
		An osteocyte, a star-shaped cell, is the most abundant cell found in bone.
		Osteocytes are networked to each other via long processes that occupy tiny canals called canaliculi, which are used for exchange of nutrients and waste.
		The space that an osteocyte occupies is called a lacuna (Latin for a pit).
	en.wikipedia.org /wiki/Osteocyte (130 words)

	Below is the complete text without illustrations
		Osteocytes, differentiated osteoblasts regularly spaced throughout the mineralized matrix, are believed to detect bone microdamage and to transmit signals leading to its repair (17,18).
		Osteocyte experiments could have been performed in cortical bone, but osteocyte apoptosis is restricted to a narrow zone of the murine femoral metaphyseal cortex (21).
		Osteocytes evidently sense changes in interstitial fluid flow through canaliculi produced by mechanical forces (65), and detect changes in the levels of hormones such as estrogen and glucocorticoids that influence their survival and which circulate in the same fluid (21,66).
	www.uams.edu /info/OsteoArticle.html (5191 words)

	Fluoride & Osteocytes
		This specific exposure would hold for osteocytes and osteoclasts throughout bone, both of which would be subjected to a concentration of fluoride which would be approximately proportionate to the intensity of the resorptive process.
		Decline in osteocyte lacunar density in human cortical bone is associated with accumulation of microcracks with age.
		In contrast to osteoblasts or osteoclasts that must be signaled to appear, the omnipresent osteocytes are continually subject to the strain of the matrix and its derivatives such as strain-generated potentials and shear-induced fluid flow.
	www.fluoridealert.org /health/bone/cellular/osteocytes.html (1214 words)

	Osteoporosis and bone functional adaptation: Mechanobiological regulation of bone architecture in growing and adult ... (Site not responding. Last check: 2007-09-16)
		This difference in osteocyte responsiveness seems likely to reflect a difference in bone function, since the primarily protective purpose of the bones in the cranial vault is clearly different from that of the limb bones (2,3,54).
		Osteocyte apoptosis is known to occur in growing bones, as well as those undergoing remodelling (74,75).
		In normal rat ulnae, the distribution of apoptotic osteocytes is strongly related to the local strain magnitude, with the majority of apoptotic osteocytes clustered at the neutral axis, and in bone adjacent to the resorbing medial periosteal surface.
	www.vard.org /jour/00/37/2/mosley.htm (7283 words)

	Cells
		Osteocytes are formed by the incorporation of osteoblasts into the bone matrix.
		Osteocytes are highly differentiated cells with alkaline phosphatase activity, PTH receptors, and function as mechanosensory cells.
		However, the osteocyte is well adapted for its role in bone homeostasis and maintains intracellular signaling to respond to the unique demands of its location.
	www.btec.cmu.edu /tutorial/cells/cells.htm (1107 words)

	Osteocyte hypoxia: a novel mechanotransduction pathway -- Dodd et al. 277 (3): 598 -- AJP - Cell Physiology
		In bone, the osteocyte is an ideal cellular candidate to initiate biochemical responses culminating in tissue adaptation.
		Acute disuse (24 h) significantly elevated osteocyte hypoxia compared with negative (Neg) control bones (animals not injected with pimonidazole; * P = 0.03) and intact control bones (contralateral ulna of animals injected with pimonidazole; P = 0.03).
		Mean ± SE percent osteocyte hypoxia in experimental bones (Exp) subjected to 24 h of disuse (n = 4) or 24 h of disuse superimposed with a brief loading regimen (Disuse + Load; n = 2).
	ajpcell.physiology.org /cgi/content/full/277/3/C598 (2639 words)

	Bone
		The principal bone cells are the osteocyte, the osteoblast, and the osteoclast.
		The osteocyte, or bone cell proper, is found in lacunae lying in or between the lamellae.
		The osteocyte is derived from the osteoblast as it becomes surrounded by matrix.
	ect.downstate.edu /courseware/histomanual/bone.html (1980 words)

	Osteoblastic Responses to TGF-beta during Bone Remodeling -- Erlebacher et al. 9 (7): 1903 -- Molecular Biology of the ...
		The osteocyte density in D4 mice (n = 5; ) was significantly elevated compared with wild-type (n = 6; p < 0.0001), whereas the osteocyte* density in E1 mice (n = 5) was not significantly reduced compared with wild-type.
		Osteocyte densities in wild-type mice treated with vehicle and parathyroidectomy (n = 2), alendronate and sham operation (n = 3), or alendronate and parathyroidectomy (n = 6) were not significantly different from untreated wild-type mice (n = 6).
		Although the epiphyseal osteocyte density in D4/E1 mice is at the wild-type level (Figure 3A), the osteocyte formation rate in these mice is partially reduced compared with D4 mice since their epiphyseal mineral apposition rate is still elevated (Figure 7).
	www.molbiolcell.org /cgi/content/full/9/7/1903 (7559 words)

	Bone idol: Uncovering the secrets of the mineralized osteocyte remnant
		Osteocytes are what some bone-forming cells (osteoblasts) turn into during bone formation.
		The ‘mineralised osteocyte remnant’ is formed by a process akin to fossilisation as the cell dies.
		The process is usually triggered by age, although osteocytes can survive for up to 18 years – a ripe old age for a cell.
	www.wellcome.ac.uk /doc_WTX024080.html (1245 words)

	Prevention of osteocyte and osteoblast apoptosis by bisphosphonates and calcitonin -- Plotkin et al. 104 (10): 1363 -- ...
		Apoptotic, TUNEL-positive osteocytes (a) and osteoblasts (b) are indicated by the arrows.
		A normal osteocyte (a) and a normal osteoblast (b) are indicated by arrowheads.
		Anatomic juxtaposition of apoptotic osteocytes and avascular necrosis in femurs from patients with glucocorticoid excess.
	www.jci.org /cgi/content/full/104/10/1363 (6663 words)

	APStracts 6:0157C, 1999. (Site not responding. Last check: 2007-09-16)
		Because osteocytes reside distant from the blood supply, their metabolic needs are met by a combination of passive diffusion and enhanced diffusion arising when the tissue is loaded during functional activity.
		Additionally, we present preliminary data suggesting that a brief loading regimen is sufficient to rescue osteocytes from this fate.
		The rapid onset of the observed osteocyte hypoxia, the inhibition of hypoxia by brief loading, and the cellular consequences of oxygen deprivation are suggestive of a novel mechanotransduction pathway with implications across organ systems.
	www.uth.tmc.edu /apstracts/1999/cell/June/157c.html (210 words)

	APStracts 10:0015C, 2003. (Site not responding. Last check: 2007-09-16)
		There is increasing evidence that osteocytes modulate this targeting by their apoptosis, which is associated with locally increased bone resorption.
		To investigate the role of osteocytes in the control of loading- related modeling or remodeling, we studied the effects on osteocyte viability of short periods of mechanical loading applied to the ulnae of rats.
		This increase in osteocyte apoptosis was transient and preceded both intracortical remodeling and death of half of the osteocytes (P < 0.01).
	www.uth.tmc.edu /apstracts/2003/cell/January/15c.html (350 words)

	Apoptosis of Osteocytes in Glucocorticoid-Induced Osteonecrosis of the Hip -- Weinstein et al. 85 (8): 2907 -- Journal ...
		in 28% of the osteocytes in metaphyseal cortical bone (7).
		Apoptotic osteocytes (arrow) were rare in osteonecrosis due to alcohol abuse (B, E, and H) and were absent in traumatic osteonecrosis (C, F, and I).
		The devastating skeletal impact of glucocorticoids is shown by the intensely luminescent, apoptotic osteocytes (arrows) recently buried in a new packet of bone (outlined by the yellow tetracycline markers).
	jcem.endojournals.org /cgi/content/full/85/8/2907 (3248 words)

	Arthritis Research & Therapy \| Full text \| Bisphosphonates prevent osteocyte apoptosis
		Bone quality is maintained by the concerted action of osteoclasts (bone-resorbing cells), osteoblasts (bone-forming cells), and osteocytes, which appear to have a mechanosensory function and respond to microdamage.
		The osteocytic cell line MLO-Y4 or calvarial osteoblasts were treated in vitro with calcitonin or bisphosphonates (etidronate, pamidronate, alendronate, olpadronate or an amino-derivative of olpadronate) for 1 h.
		Apoptosis of osteocytes and osteoblasts was also quantitated, using TUNEL assay, on undecalcified sections of vertebral bone from prednisolone-treated mice.
	arthritis-research.com /paperreport/ar-1999-66755 (562 words)

	Mechanical loading: biphasic osteocyte survival and targeting of osteoclasts for bone destruction in rat cortical bone ...
		and the apoptotic death of osteocytes in regions of cortical bone.
		The number of osteocytes in the entire bone cross section was determined by combining maps of propidium iodide-stained sections.
		Osteocytes were plotted radially around the cortex in 11 zones of equal perimeter length.
	ajpcell.physiology.org /cgi/content/full/284/4/C934 (6435 words)

	The metalloproteinase MT1-MMP is required for normal development and maintenance of osteocyte processes in bone -- ...
		The osteocyte is the terminally differentiated state of the
		(A) Osteocytes are surrounded by many well-defined cell processes emanating from the lacunae and extending into the pericellular bone matrix to generate a mesh-like appearance in this 30-day-old wild-type mouse.
		Isolated osteocytes in the bone cortex (c) likewise display signal indicating expression of MT1-MMP.
	jcs.biologists.org /cgi/content/full/118/1/147 (5294 words)

	Osteocyte viability with glucocorticoid treatment: relation to histomorphometry -- Sambrook et al. 62 (12): 1215 -- ...
		Osteocyte viability with glucocorticoid treatment: relation to histomorphometry -- Sambrook et al.
		on osteocyte lifespan independent of apoptosis is unknown.
		Apoptosis of osteocytes in glucocorticoid induced osteonecrosis of the hip.
	ard.bmjjournals.com /cgi/content/full/62/12/1215 (1921 words)

	Physiological and Genomic Consequences of Intermittent Hypoxia: Selected Contribution: Osteocytes upregulate ...
		that osteocyte cell death is exacerbated in a variety of conditions,
		Sun, YQ, McLeod KJ, and Rubin CT. Mechanically induced periosteal bone formation is paralleled by the upregulation of collagen type one mRNA in osteocytes as measured by in situ reverse transcript-polymerase chain reaction.
		Loss of osteocyte integrity in association with microdamage and bone remodeling after fatigue in vivo.
	jap.physiology.org /cgi/content/full/90/6/2514 (2917 words)

	Osteocyte - Wheeless' Textbook of Orthopaedics (Site not responding. Last check: 2007-09-16)
		- osteocyte is mentioned as possibly having resorptive capabilities;
		- osteocytes were once considered to be dormant, metabolically inactive cells;
		or disuse osteoporosis, osteocytes may be involved in the excessive bone
	www.wheelessonline.com /ortho/osteocyte (77 words)

	Mechanotransduction in bone—role of the lacuno-canalicular network -- BURGER and KLEIN-NULEND 13 (9001): 101 -- The ...
		Scanning electron micrograph of a group of osteocytes, isolated from embryonic chicken calvariae, after 3 days of culture as monolayer.
		This basal flow keeps the osteocytes viable and also ensures basal osteocyte activation and signaling, thereby suppressing osteoblastic activity as well as osteoclastic attack.
		B)During (local) overuse, the osteocytes are over-activated by enhanced fluid flow (indicated by double arrowheads), leading to release of osteoblast-recruiting signals.
	www.fasebj.org /cgi/content/full/13/9001/S101 (7134 words)

	CD40 Ligand Blocks Apoptosis Induced by Tumor Necrosis Factor {alpha}, Glucocorticoids, and Etoposide in Osteoblasts ...
		The data are presented as histograms of cell number on the y-axis plotted against log fluorescence intensity on the x-axis.
		occurs with growth, osteocyte cell death is observed (49).
		Weinstein RS, Nicholas RW, Manolagas SC 2000 Apoptosis of osteocytes in glucocorticoid-induced osteonecrosis of the hip.
	endo.endojournals.org /cgi/content/full/144/5/1761 (4771 words)

	eMedicine - Histology of Bone : Article by Yi Jun Yang, MD, PhD (Site not responding. Last check: 2007-09-16)
		Although osteocytes have reduced synthetic activity and are not capable of mitotic division, they are actively involved with the maintenance of bony matrix.
		Some of the osteocytes die during remodeling, but most probably return to the state of osteoprogenitor cell or persist as osteocytes for a long time.
		Inactive osteocytes also are present on the bone surface with a flattened shape.
	www.emedicine.com /orthoped/topic403.htm (4889 words)

	The Death of Osteocytes via Apoptosis Accompanies Estrogen Withdrawal in Human Bone -- Tomkinson et al. 82 (9): 3128 -- ...
		Results are expressed as the percentage of total osteocytes displaying positive staining for LDH activity and thus considered viable.
		To distinguish viable osteocytes in situ, cryostat sections of undemineralized transiliac biopsy were reacted for the presence of LDH activity in cells.
		Osteocyte nuclear morphology using PI to determine nuclear fragmentation.
	jcem.endojournals.org /cgi/content/full/82/9/3128 (5615 words)

	Sclerostin Is an Osteocyte-expressed Negative Regulator of Bone Formation, But Not a Classical BMP Antagonist -- van ... (Site not responding. Last check: 2007-09-16)
		Sclerostin staining of human bone biopsy of a 12-yr-old girl shows that sclerostin is expressed by osteocytes, but not by multinuclear osteoclasts on the bone surface (D).
		Sclerostin produced by osteocytes may be transported through lacunae to the bone surface, where it inhibits osteoblastic bone formation.
		to osteocytes in bone nodules remains to be established.
	www.jem.org /cgi/content/full/199/6/805 (6424 words)

	BioEd Online Slides: haversian system, osteocyte, human systems
		Nearly two-thirds of bone is made of various salts, primarily compounds containing phosphorus and calcium, which provide rigidity and hardness.
		After the calcium phosphate is deposited in the matrix, some of the osteoblasts become trapped in their own secretion and then are called osteocytes (osteo = bone, cyte = cell).
		Compact bone consists of concentric rings of calcium and other minerals (lamellae) surrounding a haversian canal (containing blood vessels and nerves that support the osteocytes).
	www.bioedonline.org /slides/slide01.cfm?q=haversian+system (152 words)

	Targeted Disruption of the Osteoblast/Osteocyte Factor 45 Gene (OF45) Results in Increased Bone Formation and Bone Mass ...
		Immunohistochemical analysis of OF45 protein localization in bone sections of mouse tibia indicated OF45 expression in the osteocytes embedded in mineralized bone of wild type animals.
		Arrows indicate positive staining osteocytes with the cortical bone of a wild type mouse.
		OF45 immunoreactivity was absent in bones from knockout mice.
	www.jbc.org /cgi/content/full/278/3/1998 (6386 words)

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