The Role of Integrins in Osteocyte Response to Mechanical Stimulus

2012 ◽  
Author(s):  
Matthew G. Haugh ◽  
Laoise M. McNamara
Keyword(s):  
Physical Activity ◽  
Bone Mass ◽  
Mechanical Strength ◽  
Mechanical Loading ◽  
Integrin Αvβ3 ◽  
Mechanical Stimulus ◽  
Mechanical Environment ◽  
Physiological Processes ◽  
Cell Processes

Bone is an exceptional material that is efficiently lightweight, possesses excellent mechanical strength and can also adapt itself in response to changes in physical activity by means of coordinated physiological processes known as modelling and remodelling. The response of bone to mechanical loading is thought to be regulated by mechanosensitive osteocyte cells that can direct the alteration of bone mass, by osteoblasts and osteoclasts, and thereby play an important role in optimizing bone strength. The mechanisms by which osteocytes sense their mechanical environment are not well understood. It has been proposed that integrin-based (αVβ3) attachments to ECM on osteocyte cell processes may facilitate mechanosensation in osteocytes [1,2]. While previous studies have shown that integrin beta;1 plays an important role in response to mechanical stimulus, the role of integrin αVβ3 in osteocyte mechanotransduction has yet to be investigated [3,4].

Role of Extracellular Matrix in Adaptation of Tendon and Skeletal Muscle to Mechanical Loading

2004 ◽  
Vol 84 (2) ◽  
pp. 649-698 ◽  
Author(s):  
MICHAEL KJÆR
Keyword(s):  
Physical Activity ◽  
Mechanical Properties ◽  
Skeletal Muscle ◽  
Extracellular Matrix ◽  
Connective Tissue ◽  
Mechanical Loading ◽  
Collagen Synthesis ◽  
Cross Linking ◽  
Collagen Turnover

Kjær, Michael. Role of Extracellular Matrix in Adaptation of Tendon and Skeletal Muscle to Mechanical Loading. Physiol Rev 84: 649–698, 2004; 10.1152/physrev.00031.2003.—The extracellular matrix (ECM), and especially the connective tissue with its collagen, links tissues of the body together and plays an important role in the force transmission and tissue structure maintenance especially in tendons, ligaments, bone, and muscle. The ECM turnover is influenced by physical activity, and both collagen synthesis and degrading metalloprotease enzymes increase with mechanical loading. Both transcription and posttranslational modifications, as well as local and systemic release of growth factors, are enhanced following exercise. For tendons, metabolic activity, circulatory responses, and collagen turnover are demonstrated to be more pronounced in humans than hitherto thought. Conversely, inactivity markedly decreases collagen turnover in both tendon and muscle. Chronic loading in the form of physical training leads both to increased collagen turnover as well as, dependent on the type of collagen in question, some degree of net collagen synthesis. These changes will modify the mechanical properties and the viscoelastic characteristics of the tissue, decrease its stress, and likely make it more load resistant. Cross-linking in connective tissue involves an intimate, enzymatical interplay between collagen synthesis and ECM proteoglycan components during growth and maturation and influences the collagen-derived functional properties of the tissue. With aging, glycation contributes to additional cross-linking which modifies tissue stiffness. Physiological signaling pathways from mechanical loading to changes in ECM most likely involve feedback signaling that results in rapid alterations in the mechanical properties of the ECM. In developing skeletal muscle, an important interplay between muscle cells and the ECM is present, and some evidence from adult human muscle suggests common signaling pathways to stimulate contractile and ECM components. Unaccostumed overloading responses suggest an important role of ECM in the adaptation of myofibrillar structures in adult muscle. Development of overuse injury in tendons involve morphological and biochemical changes including altered collagen typing and fibril size, hypervascularization zones, accumulation of nociceptive substances, and impaired collagen degradation activity. Counteracting these phenomena requires adjusted loading rather than absence of loading in the form of immobilization. Full understanding of these physiological processes will provide the physiological basis for understanding of tissue overloading and injury seen in both tendons and muscle with repetitive work and leisure time physical activity.

scholarly journals Muscle and bone mass in middle‐aged women: role of menopausal status and physical activity

2020 ◽  
Vol 11 (3) ◽  
pp. 698-709 ◽  
Author(s):  
Sarianna Sipilä ◽  
Timo Törmäkangas ◽  
Elina Sillanpää ◽  
Pauliina Aukee ◽  
Urho M. Kujala ◽  
...  
Keyword(s):  
Physical Activity ◽  
Bone Mass ◽  
Menopausal Status ◽  
Middle Aged

scholarly journals Endocrine Disorders in Adolescent and Young Female Athletes: Impact on Growth, Menstrual Cycles, and Bone Mass Acquisition

2014 ◽  
Vol 99 (11) ◽  
pp. 4037-4050 ◽  
Author(s):  
Laurent Maïmoun ◽  
Neoklis A. Georgopoulos ◽  
Charles Sultan
Keyword(s):  
Physical Activity ◽  
Adipose Tissue ◽  
Bone Mass ◽  
Peak Bone Mass ◽  
Female Athletes ◽  
Reproductive Function ◽  
Young Female ◽  
Menstrual Cycles ◽  
Intense Training

Context: Puberty is a crucial period of dramatic hormonal changes, accelerated growth, attainment of reproductive capacity, and acquisition of peak bone mass. Participation in recreational physical activity is widely acknowledged to provide significant health benefits in this period. Conversely, intense training imposes several constraints, such as training stress and maintenance of very low body fat to maximize performance. Adolescent female athletes are therefore at risk of overtraining and/or poor dietary intake, which may have several consequences for endocrine function. The “adaptive” changes in the hypothalamic-pituitary-gonadal, -adrenal, and somatotropic axes and the secretory role of the adipose tissue are reviewed, as are their effects on growth, menstrual cycles, and bone mass acquisition. Design: A systematic search on Medline between 1990 and 2013 was conducted using the following terms: “intense training,” “physical activity,” or “exercise” combined with “hormone,” “endocrine,” and “girls,” “women,” or “elite female athletes.” All articles reporting on the endocrine changes related to intense training and their potential implications for growth, menstrual cycles, and bone mass acquisition were considered. Results and Conclusion: Young female athletes present a high prevalence of menstrual disorders, including delayed menarche, oligomenorrhea, and amenorrhea, characterized by a high degree of variability according to the type of sport. Exercise-related reproductive dysfunction may have consequences for growth velocity and peak bone mass acquisition. Recent findings highlight the endocrine role of adipose tissue and energy balance in the regulation of homeostasis and reproductive function. A better understanding of the mechanisms whereby intense training affects the endocrine system may orient research to develop innovative strategies (ie, based on nutritional or pharmacological approaches and individualized modalities of training and competition) to improve the medical care of these adolescents and protect their reproductive function.

scholarly journals Theories of mechanically induced tissue differentiation and adaptation in the musculoskeletal system

2015 ◽  
Vol 20 (1) ◽  
Author(s):  
Daniel R. Suárez
Keyword(s):  
Mechanical Loading ◽  
Musculoskeletal System ◽  
Predictive Power ◽  
Biological Tissues ◽  
Tissue Differentiation ◽  
Mechanical Stimuli ◽  
Mechanical Environment ◽  
Adaptation Processes ◽  
Growth Adaptation

<p>It is well known that the mechanical environment affects biological tissues. The importance of theories and models that aim at explaining the role of the mechanical stimuli in process such as differentiation and adaptation of tissues is highlighted because if those theories can explain the tissue’s response to mechanical loading and to its environment, it becomes possible to predict the consequences of mechanical stimuli on growth, adaptation and ageing of tissues. This review aims to present an overview of the various theories and models on tissue differentiation and adaptation of tissues and their mathematical implementation.</p>Although current models are numerically well defined and are able to resemble the tissue differentiation and adaptation processes, they are limited by (1) the fact that some of their input parameters are likely to be site- and species-dependent, and (2) their verification is done by data that may make the model results redundant. However, some theories do have predictive power despite the limitations of generalization. It seems to be a matter of time until new experiments and models appear with predictive power and where rigorous verification can be performed.

scholarly journals Associations between physical activity and bone mass in black and white South African children at age 9 yr

2004 ◽  
Vol 97 (3) ◽  
pp. 1006-1012 ◽  
Author(s):  
J. A. McVeigh ◽  
S. A. Norris ◽  
N. Cameron ◽  
J. M. Pettifor
Keyword(s):  
Physical Activity ◽  
Bone Mass ◽  
South African ◽  
Black Children ◽  
Whole Body ◽  
Protective Mechanism ◽  
White Children ◽  
Black And White ◽  
Reaction Forces

We investigated differences in physical activity (PA) levels between black and white South African 9-yr-old children and their association with bone mineral content (BMC) and density (BMD) by using dual-energy X-ray absorptiometry. PA was analyzed in terms of a metabolic (METPA; weighted metabolic score of intensity, frequency, and duration) and a mechanical (MECHPA; sum of all ground reaction forces multiplied by duration) component. There were significant ethnic differences in patterns of activity. White children expended a significantly greater energy score (METPA of 21.7 ± 2.9) than black children (METPA of 9.5 ± 0.5) ( P < 0.001). When children were divided into quartiles according to the amount and intensity of sport played, the most active white children (using METPA scores) had significantly higher whole body BMD and higher hip and spine BMC and BMD than less active children. White children in the highest MECHPA quartile also showed significantly higher whole body, hip, and spine BMC and BMD than those children in the lowest quartile. No association between exercise and bone mass of black children was found. In this population, PA has an osteogenic association with white children, but not black children, which may be explained by the lower levels of PA in the black children. Despite this, black children had significantly greater bone mass at the hip and spine (girls only) ( P < 0.001) even after adjustment for body size. The role of exercise in increasing bone mass may become increasingly critical as a protective mechanism against osteoporosis in both ethnic groups, especially because the genetic benefit exhibited by black children to higher bone mass may be weakened with time, as environmental influences become stronger.

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