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Mechanotransduction in bone cells via oscillating flow
16S
Abstracts
013 MECHAN( )I'RANSI)IICTION IN BONE CELLS VIA OSCILLATINGFLOW CR Jacobs J You, CE Yellowley, HJ Donahue Musculoskeletal Research Lab, Penn State University, USA External mechanical loading of bone results in a variety of biophysical signals that may affect cellular metabolism and gene expression Furthermore, loading induced fluid flow is oscillatory in nature and has not been studied previously as a potentially important cellular physical signal in bone. The goal of this study was to determine what role oscillatory fluid flow plays in a variety of physiological responses linked to bone formation including early (intracellular calcium signalling), intermediate (MAP kinase activity), and late (osteopontin gene regulation) in osteoblastic, MC3T3-E1, cells Flow was delivered to the cells in a parallel plate flow chamber with a computer controlled flow delivery system. The llow profile was sinusoidal at l H z and a peak wall shear stress of 2Pa Cytosolic Ca 2+ was quantified in real-time with fura-2 and a microspectrofluorometer. Activity of three major MAP kinases, p38, ERK, and JNK, was determined by immunoprecipitation. MRNA levels of osteopontin were determined with quantitative realtime RT-PCR Within thirty seconds of flow onset cells dramatically increased their intracellular Ca 2+ levels. Furthermore, blocker studies indicated that the increase involved release from intracellular Ca 2 stores ERK and p38 (but not JNK) increased their activity within 90 minutes of flow onset Osteopontin mRNA levels were increased approximately four-fold within 24 hours of flow exposure Finally, it was found that the osteopontin expression increase involved both the early calcium signal and both of the MAPK's. Our esuhs suggest that oscillating flow may be an important physiological signal in bone cell mechanotransduction of external applied load. Oscillating flow as a physical signal induces intracellular calcium release that is required for osteopontin gene expression involving the p38 and ERK MAPK pathways.
015 THE RELATIONSHIP BETWEEN BONE VOLUMES AND BONE MASS DURING DIFFERENT STAGES OF PUBERTY S Bass*~ L Saxon*, R Daly*, S Stuckeyt *School of Health Sciences. Deakin University, Burwood, Australia *Dept. Nuclear Medicine, Alfred Hospital. Malvem, Australia Cortical bone density is a measure of bone volume and the mass contained within the periosteal and endosteal envelopes. The relative contribution of each trait is an important component of peak bone density. We asked: what are the changes in cortical bone volumes and bone mass (BMC) during different stages of growth? We studied the non-playnig arm of 17 pre-, 11 peri- and 18 post- pubertal (age menarche 12.5 _+0.3 .~rs) female tennis players (age 10B _+0.3. 125 _+ 0.4 and 14.4 _+ 0.5 yrs respectively). Bone volumes (total, cortical and medullary') and BMC at a site 25% to 60% of the humeral length from the distal end were determined using magnetic resonance imaging (MRI) and DEXA respectively. Tanner stage was self-assessed. Bone volumes m~d BMC increased with advancing age (range r=0.6 to 0.8, p < 0 0 1 ) MedullaD' vohmle was larger in the post- compared with the prepubertal group (86 vs 5.9 mm~, p<0.001). There was no detectable contraction of the medullary, volume with advancing age or pubertal maturation. Age at menarche correlated with total bone, and medullary volumes betbre and after adjusting for years post menarche (r=0.52 0.54. respectively p<0.05), in the pre-pubertal girls, bone mass was further from peak than bone volume, and bone volume was further from peak than bone length (48% vs 59% p=0.07 and 59% vs 84% p<0001. respectively). In the peri-pubertal girls, bone mass was further from peak thma bone length (67% vs 90%, respectively, p<0.03). In summary_, contraction of the medullary cavity after menarche was not detected. In addition, a later age ofmenarche was associated with a bigger bone and a larger medullaD, cavity, not a greater cortical bone volume Bone length, mass and volume track towards the peak for each trait at different rates. These results highlight the need to study the chm~ges in bone volume and bone mass when investigating factors that affect the attainment of peak bone densi~'
Bone Voh 27, No. 4, Supplement October 2000:1 S-54S
014 GROWTH HORMONE IS PERMISSIVE FOR SKELETAL ADAPTATION TO MECHANICAL LOADING MR Forwood. L Li, WL Kelly, MB Bennett Depamnent of Anatomical Sciences. The University of Queensland. Brisbane Qld 4072, Australia The Lewis dwarf rat (DW) was used as a model to test the hypothesis that grow'th hormone (GEl) is permissive for new bone formation induced b?, mechanical loading in vivo. Adult female Lewis Dwarf (DW) rats (187 ± 18 g) were allocated to 4 vehicle groups (DW), 4 GH-treatment groups at 325 lag. 100 g~ body mass (DW,;~H). and 4 GH-treatment groups at 65 p,g 100 g~ (DW~H2). Saline vehicle or GH were injected i.p at 1830 h and 0630 h prior to naechanical loading of tibiae at 0730 h A single period of 300 cycles of 4-point bending was applied to right tibiae at 2 0 Hz. and magnitudes of 24 N. 29 N. 38 N or 48 N. Separate strain gauge ,analyses in 5 DW rats validated the selection of loading magnitudes After loading, doublelabel histomorphometry was used to assess bone formation at the periosteal (Ps.S) and endocortical surfaces lEeS) of tibiae Comparing left (unloaded) tibiae among groups, GH treatment had no effect on bone formation. Bone formation in tibiae in DW rats was insensitive to mechanical loading At the Ec.S, mechanically-induced lamellar bone formation increased in the DWc;m group loaded at 48 N (P < 0.05). and no significant increases in bone formation were observed among other groups. The percentage of tibiae expressing woven bone formation (WoB) at the Ps.S was significantly greater in the DW~n groups compared to controls (P < 0.05). We conclude that GH influences loading related bone formation in a permissive manner, and modulales the responsiveness of bone tissue to mechanical stmmli by changing thresholds for bone formation
016 SKELETAL ADAPTATIONS TO INTENSE EXERCISE 1N PREPUBERTAL BOYS. HJ Woodhead, C Blimkie. A Kemp, J Briod?, S Garnett CT Coxxell The New Children's Hospital Sydney 2145, Australia. Evidence suggests that the pre-pubertal epoch may be the optimal period for m~cximising not only bone mass, but also bone strength, using exercise. We aimed to examine the influence of both weightsupported and weight-bearing intense exercise on the mineral. material and geometric properties of bone, in pre-pubertal boys. This is a longitudinal cohort stud?, incorporating 3 groups of 21) boys each: healthy controls (C:9.6_+l.5?'ears), swimmers (S: 10.0_+1.1 ) and tennis players (T: 10 2+0.9). Athletes were training at least 4 hrs/week and had participated at that lexel for at least 1 ?'ear. All groups p l ~ e d less than 2 hours of (other) organised sport/week. Bone density (BMD. DXA Lunar3.6), ultrasound (Cuba Clinical) and midfemur geometry (MRI Philips 1.5T with Analyze analysis : total, cortical and medullam' xolumes) were measured. Groups ~ere compared using ANOVA (SPSS). At baseline subjects ~xere matched for age, height, weight, hours of training (S: 6.4+2.5, T: 6.7+2.2 h/wk) and duration of sport (both 4.4+1.6y). There ~ere no significant differences between groups in mineral, material or geometry outcomes, except for femoral neck (FN) areal BMD (C:0 81_+0.09. S:0.84+0.09, T:0.88+008g/cm2). which was not present xxhen adjusted for bone size and age, although t test showed differences betx~een C and T FN volumetric B M D These findings suggesl that in prepubertal boys. intense exercise does not enhance bone mineral, material or geometric parameters Furthermore, athletes do not hme inherent genetic adxanlages in bone strength As studies in postpubertal athleles do show enhancements, p u b e m rather lhan pre-pubert3 may be the more critical period for optinnsmg bone health xxith ph?sical actix itx
Abstracts
013 MECHAN( )I'RANSI)IICTION IN BONE CELLS VIA OSCILLATINGFLOW CR Jacobs J You, CE Yellowley, HJ Donahue Musculoskeletal Research Lab, Penn State University, USA External mechanical loading of bone results in a variety of biophysical signals that may affect cellular metabolism and gene expression Furthermore, loading induced fluid flow is oscillatory in nature and has not been studied previously as a potentially important cellular physical signal in bone. The goal of this study was to determine what role oscillatory fluid flow plays in a variety of physiological responses linked to bone formation including early (intracellular calcium signalling), intermediate (MAP kinase activity), and late (osteopontin gene regulation) in osteoblastic, MC3T3-E1, cells Flow was delivered to the cells in a parallel plate flow chamber with a computer controlled flow delivery system. The llow profile was sinusoidal at l H z and a peak wall shear stress of 2Pa Cytosolic Ca 2+ was quantified in real-time with fura-2 and a microspectrofluorometer. Activity of three major MAP kinases, p38, ERK, and JNK, was determined by immunoprecipitation. MRNA levels of osteopontin were determined with quantitative realtime RT-PCR Within thirty seconds of flow onset cells dramatically increased their intracellular Ca 2+ levels. Furthermore, blocker studies indicated that the increase involved release from intracellular Ca 2 stores ERK and p38 (but not JNK) increased their activity within 90 minutes of flow onset Osteopontin mRNA levels were increased approximately four-fold within 24 hours of flow exposure Finally, it was found that the osteopontin expression increase involved both the early calcium signal and both of the MAPK's. Our esuhs suggest that oscillating flow may be an important physiological signal in bone cell mechanotransduction of external applied load. Oscillating flow as a physical signal induces intracellular calcium release that is required for osteopontin gene expression involving the p38 and ERK MAPK pathways.
015 THE RELATIONSHIP BETWEEN BONE VOLUMES AND BONE MASS DURING DIFFERENT STAGES OF PUBERTY S Bass*~ L Saxon*, R Daly*, S Stuckeyt *School of Health Sciences. Deakin University, Burwood, Australia *Dept. Nuclear Medicine, Alfred Hospital. Malvem, Australia Cortical bone density is a measure of bone volume and the mass contained within the periosteal and endosteal envelopes. The relative contribution of each trait is an important component of peak bone density. We asked: what are the changes in cortical bone volumes and bone mass (BMC) during different stages of growth? We studied the non-playnig arm of 17 pre-, 11 peri- and 18 post- pubertal (age menarche 12.5 _+0.3 .~rs) female tennis players (age 10B _+0.3. 125 _+ 0.4 and 14.4 _+ 0.5 yrs respectively). Bone volumes (total, cortical and medullary') and BMC at a site 25% to 60% of the humeral length from the distal end were determined using magnetic resonance imaging (MRI) and DEXA respectively. Tanner stage was self-assessed. Bone volumes m~d BMC increased with advancing age (range r=0.6 to 0.8, p < 0 0 1 ) MedullaD' vohmle was larger in the post- compared with the prepubertal group (86 vs 5.9 mm~, p<0.001). There was no detectable contraction of the medullary, volume with advancing age or pubertal maturation. Age at menarche correlated with total bone, and medullary volumes betbre and after adjusting for years post menarche (r=0.52 0.54. respectively p<0.05), in the pre-pubertal girls, bone mass was further from peak than bone volume, and bone volume was further from peak than bone length (48% vs 59% p=0.07 and 59% vs 84% p<0001. respectively). In the peri-pubertal girls, bone mass was further from peak thma bone length (67% vs 90%, respectively, p<0.03). In summary_, contraction of the medullary cavity after menarche was not detected. In addition, a later age ofmenarche was associated with a bigger bone and a larger medullaD, cavity, not a greater cortical bone volume Bone length, mass and volume track towards the peak for each trait at different rates. These results highlight the need to study the chm~ges in bone volume and bone mass when investigating factors that affect the attainment of peak bone densi~'
Bone Voh 27, No. 4, Supplement October 2000:1 S-54S
014 GROWTH HORMONE IS PERMISSIVE FOR SKELETAL ADAPTATION TO MECHANICAL LOADING MR Forwood. L Li, WL Kelly, MB Bennett Depamnent of Anatomical Sciences. The University of Queensland. Brisbane Qld 4072, Australia The Lewis dwarf rat (DW) was used as a model to test the hypothesis that grow'th hormone (GEl) is permissive for new bone formation induced b?, mechanical loading in vivo. Adult female Lewis Dwarf (DW) rats (187 ± 18 g) were allocated to 4 vehicle groups (DW), 4 GH-treatment groups at 325 lag. 100 g~ body mass (DW,;~H). and 4 GH-treatment groups at 65 p,g 100 g~ (DW~H2). Saline vehicle or GH were injected i.p at 1830 h and 0630 h prior to naechanical loading of tibiae at 0730 h A single period of 300 cycles of 4-point bending was applied to right tibiae at 2 0 Hz. and magnitudes of 24 N. 29 N. 38 N or 48 N. Separate strain gauge ,analyses in 5 DW rats validated the selection of loading magnitudes After loading, doublelabel histomorphometry was used to assess bone formation at the periosteal (Ps.S) and endocortical surfaces lEeS) of tibiae Comparing left (unloaded) tibiae among groups, GH treatment had no effect on bone formation. Bone formation in tibiae in DW rats was insensitive to mechanical loading At the Ec.S, mechanically-induced lamellar bone formation increased in the DWc;m group loaded at 48 N (P < 0.05). and no significant increases in bone formation were observed among other groups. The percentage of tibiae expressing woven bone formation (WoB) at the Ps.S was significantly greater in the DW~n groups compared to controls (P < 0.05). We conclude that GH influences loading related bone formation in a permissive manner, and modulales the responsiveness of bone tissue to mechanical stmmli by changing thresholds for bone formation
016 SKELETAL ADAPTATIONS TO INTENSE EXERCISE 1N PREPUBERTAL BOYS. HJ Woodhead, C Blimkie. A Kemp, J Briod?, S Garnett CT Coxxell The New Children's Hospital Sydney 2145, Australia. Evidence suggests that the pre-pubertal epoch may be the optimal period for m~cximising not only bone mass, but also bone strength, using exercise. We aimed to examine the influence of both weightsupported and weight-bearing intense exercise on the mineral. material and geometric properties of bone, in pre-pubertal boys. This is a longitudinal cohort stud?, incorporating 3 groups of 21) boys each: healthy controls (C:9.6_+l.5?'ears), swimmers (S: 10.0_+1.1 ) and tennis players (T: 10 2+0.9). Athletes were training at least 4 hrs/week and had participated at that lexel for at least 1 ?'ear. All groups p l ~ e d less than 2 hours of (other) organised sport/week. Bone density (BMD. DXA Lunar3.6), ultrasound (Cuba Clinical) and midfemur geometry (MRI Philips 1.5T with Analyze analysis : total, cortical and medullam' xolumes) were measured. Groups ~ere compared using ANOVA (SPSS). At baseline subjects ~xere matched for age, height, weight, hours of training (S: 6.4+2.5, T: 6.7+2.2 h/wk) and duration of sport (both 4.4+1.6y). There ~ere no significant differences between groups in mineral, material or geometry outcomes, except for femoral neck (FN) areal BMD (C:0 81_+0.09. S:0.84+0.09, T:0.88+008g/cm2). which was not present xxhen adjusted for bone size and age, although t test showed differences betx~een C and T FN volumetric B M D These findings suggesl that in prepubertal boys. intense exercise does not enhance bone mineral, material or geometric parameters Furthermore, athletes do not hme inherent genetic adxanlages in bone strength As studies in postpubertal athleles do show enhancements, p u b e m rather lhan pre-pubert3 may be the more critical period for optinnsmg bone health xxith ph?sical actix itx