Bone loss during energy restriction: mechanistic role of leptin

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Title: Bone loss during energy restriction: mechanistic role of leptin
Author: Baek, Kyunghwa
Abstract: Mechanical unloading and food restriction (FR ) are leading causes of bone loss , which increase the risk of fracture later in life . Leptin , a 16kDa cytokine like hormone principally produced by white adipocytes , may be involved in bone metabolism with physiological or mechanical changes causing bone loss . The hypotheses of the first study were aimed at determining if serum leptin is reduced by unloading or FR . The serum leptin level reduced by unloading or by global FR , is associated with the decline in bone formation rate . It was conjectured that decreased serum leptin may be due to reduced adipocyte number /size and /or sympathetic nervous system (SNS ) activation of betaadrenoreceptors with unloading or FR , inhibiting the release of leptin from adipocytes . In the second experiment , we tested whether leptin or beta -adrenoreceptor blockade attenuates bone loss during unloading and whether such an effect due to beta blockade is associated with changes in serum leptin level . Beta -blockade mitigated unloading induced reduction in serum leptin and also beta blockade was as effective as leptin administration in mitigating a reduction in cancellous bone mineral density with unloading through both stimulation of bone formation and suppression of resorption . It was previously demonstrated that energy restriction (ER ) is a major contributor to the bone loss during global FR . In the third study , we tested whether beta - blockade attenuates bone loss during ER and whether such an effect is associated with changes in serum leptin level and leptin localization in bone tissues . Beta blockade attenuated the ER induced reduction in serum leptin level , cancellous bone mineral density and bone formation rate , and also abolished the ER induced increase in bone resorption . Reduction in leptin expression in bone marrow adipocytes observed with ER was attenuated by beta -blockade . Reduction in the number of cells (bone lining cells , osteocytes and chondrocytes in cartilage ) which are stained positive for leptin was also attenuated by beta -blockade . Collectively , these data identify circulating leptin effects on preventing bone loss during mechanical unloading or energy restriction . Also beta blockade is associated with mitigating reduction in serum leptin and subsequently with mitigating reduction in bone mass with unloading or ER .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2561
Date: 2009-05-15

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Bone loss during energy restriction: mechanistic role of leptin. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2561 .

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