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Mechanical Adaptations (mechanical + adaptation)
Selected AbstractsPulsating fluid flow modulates gene expression of proteins involved in Wnt signaling pathways in osteocytesJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 10 2009Ana Santos Abstract Strain-derived flow of interstitial fluid activates signal transduction pathways in osteocytes that regulate bone mechanical adaptation. Wnts are involved in this process, but whether mechanical loading modulates Wnt signaling in osteocytes is unclear. We assessed whether mechanical stimulation by pulsating fluid flow (PFF) leads to functional Wnt production, and whether nitric oxide (NO) is important for activation of the canonical Wnt signaling pathway in MLO-Y4 osteocytes. MC3T3-E1 osteoblasts were studied as a positive control for the MLO-Y4 osteocyte response to mechanical loading. MLO-Y4 osteocytes and MC3T3-E1 osteoblasts were submitted to 1-h PFF (0.7,±,0.3 Pa, 5 Hz), and postincubated (PI) without PFF for 0.5,3 h. Gene expression of proteins related to the Wnt canonical and noncanonical pathways were studied using real-time polymerase chain reaction (PCR). In MLO-Y4 osteocytes, PFF upregulated gene expression of Wnt3a, c-jun, connexin 43, and CD44 at 1,3-h PI. In MC3T3-E1 osteoblasts, PFF downregulated gene expression of Wnt5a and c-jun at 0.5,3-h PI. In MLO-Y4 osteocytes, gene expression of PFF-induced Wnt target genes was suppressed by the Wnt antagonist sFRP4, suggesting that loading activates the Wnt canonical pathway through functional Wnt production. The NO inhibitor L-NAME suppressed the effect of PFF on gene expression of Wnt target genes, suggesting that NO might play a role in PFF-induced Wnt production. The response to PFF differed in MC3T3-E1 osteoblasts. Because Wnt signaling is important for bone mass regulation, osteocytes might orchestrate loading-induced bone remodeling through, among others, Wnts. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1280,1287, 2009 [source] A comparative view on mechanisms and functions of skeletal remodelling in teleost fish, with special emphasis on osteoclasts and their functionBIOLOGICAL REVIEWS, Issue 2 2009P. Eckhard Witten ABSTRACT Resorption and remodelling of skeletal tissues is required for development and growth, mechanical adaptation, repair, and mineral homeostasis of the vertebrate skeleton. Here we review for the first time the current knowledge about resorption and remodelling of the skeleton in teleost fish, the largest and most diverse group of extant vertebrates. Teleost species are increasingly used in aquaculture and as models in biomedical skeletal research. Thus, detailed knowledge is required to establish the differences and similarities between mammalian and teleost skeletal remodelling, and between distantly related species such as zebrafish (Danio rerio) and medaka (Oryzias latipes). The cellular mechanisms of differentiation and activation of osteoclasts and the functions of teleost skeletal remodelling are described. Several characteristics, related to skeletal remodelling, distinguish teleosts from mammals. These characteristics include (a) the absence of osteocytes in most species; (b) the absence of haematopoietic bone marrow tissue; (c) the abundance of small mononucleated osteoclasts performing non-lacunar (smooth) bone resorption, in addition to or instead of multinucleated osteoclasts; and (d) a phosphorus- rather than calcium-driven mineral homeostasis (mainly affecting the postcranial dermal skeleton). Furthermore, (e) skeletal resorption is often absent from particular sites, due to sparse or lacking endochondral ossification. Based on the mode of skeletal remodelling in early ontogeny of all teleosts and in later stages of development of teleosts with acellular bone we suggest a link between acellular bone and the predominance of mononucleated osteoclasts, on the one hand, and cellular bone and multinucleated osteoclasts on the other. The evolutionary origin of skeletal remodelling is discussed and whether mononucleated osteoclasts represent an ancestral type of resorbing cells. Revealing the differentiation and activation of teleost skeletal resorbing cells, in the absence of several factors that trigger mammalian osteoclast differentiation, is a current challenge. Understanding which characters of teleost bone remodelling are derived and which characters are conserved should enhance our understanding of the process in fish and may provide insights into alternative pathways of bone remodelling in mammals. [source] Compensatory bone remodelling in moose: a study of age, sex, and cross-sectional cortical bone dimensions in moose at Isle Royale National ParkINTERNATIONAL JOURNAL OF OSTEOARCHAEOLOGY, Issue 5 2002Mary Hindelang Abstract We studied interrelationships among age, sex, and cross-sectional cortical bone dimensions using quantitative computed tomography (QCT) scans of metatarsal bones of 180 moose (Alces alces) that died in Isle Royale National Park, Michigan. As a large-bodied quadruped with demanding ecological constraints on movement and behaviour, a moose experiences different weight-bearing and mechanical stressors than humans, to whom most existing studies of mechanical adaptations of bone pertain. In moose, both sexes showed significant subperiosteal expansion and an increase in medullary area, with an overall increase in cortical bone area over time. Female moose did not exhibit cortical thinning or reduction in cross-sectional area with age, rather they showed an increase in cortical bone area with periosteal apposition exceeding endosteal resorption, similar to the males. We also found that moose undergo changes in bone geometry through remodelling of bone similar to humans, suggesting a compensatory mechanism for increasing bone strength under conditions of decline in bone mineral density with age. Copyright © 2002 John Wiley & Sons, Ltd. [source] Enamel ridge alignment in upper molars of ruminants in relation to their natural dietJOURNAL OF ZOOLOGY, Issue 1 2010T. M. Kaiser Abstract Although it is generally thought that dental design reflects mechanical adaptations to particular diets, concrete concepts of such adaptations beyond the evolution of hypsodonty are largely missing. We investigated the alignment of enamel ridges in the occlusal molar surface of 37 ruminant species and tested for correlations with the percentage of grass in the natural diet. Independent of phylogenetic lineage, species that were either larger and/or included more grass in their natural diet showed a higher proportion of enamel ridges aligned at low angles to the direction of the chewing stroke. Possible explanations for this design are a potential alignment of grass blades in parallel to the molar tooth row, a potential increased proportion of a propalinal (anterior,posterior) chewing movement in grazers as opposed to a strictly transversal chewing stroke in browsers and the general distribution of forces along the occlusal surface during the chewing stroke. The latter will be less heterogenous (with less force peaks) with an increasing proportion of low-angle enamel ridges. While the validity of these explanations will have to be tested in further studies, the enamel ridge alignment represents a clear signal that deviates from an arbitrary distribution and hence most likely represents a functional adaptation. [source] Mechanical ventilatory constraints during incremental cycle exercise in human pregnancy: implications for respiratory sensationTHE JOURNAL OF PHYSIOLOGY, Issue 19 2008Dennis Jensen The aim of this study was to identify the physiological mechanisms of exertional respiratory discomfort (breathlessness) in pregnancy by comparing ventilatory (breathing pattern, airway function, operating lung volumes, oesophageal pressure (Poes)-derived indices of respiratory mechanics) and perceptual (breathlessness intensity) responses to incremental cycle exercise in 15 young, healthy women in the third trimester (TM3; between 34 and 38 weeks gestation) and again 4,5 months postpartum (PP). During pregnancy, resting inspiratory capacity (IC) increased (P < 0.01) and end-expiratory lung volume decreased (P < 0.001), with no associated change in total lung capacity (TLC) or static respiratory muscle strength. This permitted greater tidal volume (VT) expansion throughout exercise in TM3, while preserving the relationship between contractile respiratory muscle effort (tidal Poes swing expressed as a percentage of maximum inspiratory pressure (PImax)) and thoracic volume displacement (VT expressed as a percentage of vital capacity) and between breathlessness and ventilation . At the highest equivalent work rate (HEWR = 128 ± 5 W) in TM3 compared with PP: , tidal Poes/PImax and breathlessness intensity ratings increased by 10.2 l min,1 (P < 0.001), 8.8%PImax (P < 0.05) and 0.9 Borg units (P < 0.05), respectively. Pulmonary resistance was not increased at rest or during exercise at the HEWR in TM3, despite marked increases in mean tidal inspiratory and expiratory flow rates, suggesting increased bronchodilatation. Dynamic mechanical constraints on VT expansion (P < 0.05) with associated increased breathlessness intensity ratings (P < 0.05) were observed near peak exercise in TM3 compared with PP. In conclusion: (1) pregnancy-induced increases in exertional breathlessness reflected the normal awareness of increased and contractile respiratory muscle effort; (2) mechanical adaptations of the respiratory system, including recruitment of resting IC and increased bronchodilatation, accommodated the increased VT while preserving effort,displacement and breathlessness, relationships; and (3) dynamic mechanical ventilatory constraints contributed to respiratory discomfort near the limits of tolerance in late gestation. [source] | ||||||||||