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Biomedical subjects

L E Lanyon

Publications and source records attributed to L E Lanyon.

At least 19 recordsLinked to original sources
PubMed2002

Growth rate rather than gender determines the size of the adaptive response of the growing skeleton to mechanical strain.

To determine whether male and female skeletons are equally responsive to mechanical load, the left ulnae in a group of juvenile male (n = 7), and age-matched female (n = 9) rats received a short daily period of controlled dynamic loading in vivo (1200 cycles at 2 Hz each day for 10 days) in addition to their normal exercise. Axial loads for each group were adjusted to engender a peak dynamic strain of -4000 microstrain at the medial face of the ulna midshaft, applied and released at a rate of +/-30,000 microstrain/sec. Fluorescent labels were administered at the start and finish of the loading period. Over the course of daily loading, the body mass of the male rats increased 2.5 times faster than that of the females (6.3 g/day vs. 2.5 g/day). The increase in periosteal interlabel bone area due to growth and normal exercise was also 2.5 times greater in the males than in the females. Both genders showed statistically significant (p < 0.05) increases in periosteal new bone deposition in the ulna of their loaded compared with their control limb. The pattern of osteogenic response was similar in males and females and featured increased mineral apposition rate on the lateral surface of the ulna, and arrest of modeling-drift-related resorption with its reversal to bone formation on the medial surface. In males, the absolute loading-related increase in bone area was six times greater than that in females. However, when the absolute size of the loading-related change in periosteal interlabel new bone deposition was expressed relative to that due to growth, there was no difference between males and females (Mean +/- SEM: 37 +/- 12% for males, 34 +/- 12% for females). These data confirm that the ulna of young actively growing rats of both genders responds to a short daily period of loading with an altered modeling response that involves increased bone formation and decreased resorption. Although the absolute amount of new bone formation stimulated by loading is greater in males than in females there is no difference between genders following correction for the higher rate of bone deposition seen in the males in association with their faster rate of growth.

Adaptation, Physiological↗
PubMed2002

Mechanical strain and fluid movement both activate extracellular regulated kinase (ERK) in osteoblast-like cells but via different signaling pathways.

Extracellular regulated kinases (ERKs)-1 and -2 are members of the MAPK family of protein kinases involved in the proliferation, differentiation, and apoptosis of bone cells. We have shown previously that ROS 17/2.8 cells show increased activation of ERK-1 or -2, which is sustained for 24 h, when the strips onto which they are seeded are subjected to a 10 min period of cyclic four point bending that produces physiological levels of mechanical strain along with associated fluid movement of the medium. Movement of the strips through the medium without bending causes fluid movement without strain. This also increases ERK-1/2 activation, but in a biphasic manner over the same time period. Our present study investigates the role of components of signaling pathways in the activation of ERK-1/2 in ROS 17/2.8 cells in response to these stimuli. Using a range of inhibitors we show specific differences by which ERK-1 and ERK-2 are activated in response to fluid movement alone, compared with those induced in response to strain plus its associated fluid movement. ERK-1 activation induced by fluid movement was markedly reduced by nifedipine, and therefore appears to involve L-type calcium channels, but was unaffected by either L-NAME or indomethacin. This suggests independence from prostacyclin (PGI(2)) and nitric oxide (NO) production. In contrast, ERK-1 activation induced by application of strain (and its associated fluid disturbance) was abrogated by TMB-8 hydrochloride, L-NAME, and indomethacin. This suggests that strain-induced ERK-1 activation is dependent upon calcium mobilization from intracellular stores and production of NO and PGI(2). ERK-2 activation appears to be mediated by a separate mechanism in these cells. Its activation by fluid movement alone involved both PGI(2) and NO production, but its activation by strain was not affected by any of the inhibitors used. The G protein inhibitor, pertussis toxin, did not cause a reduction in the activation of ERK-1 or -2 in response to either stimulus. These results are consistent with earlier observations of ERK activation in bone cells in response to both strain (with fluid movement) and fluid movement alone, and further demonstrate that these phenomena stimulate distinct signaling pathways.

Animals↗
PubMed2002

Validation of a technique for studying functional adaptation of the mouse ulna in response to mechanical loading.

Functional adaptation of the mouse ulna in response to artificial loading in vivo was assessed using a technique previously developed in the rat. Strain gauge recordings from the mouse ulnar midshaft during locomotion showed peak strains of 1680 muepsilon and maximum strain rates of 0.03 sec(-1). During falls from 20 cm these reached 2620 muepsilon and 0.10 sec(-1). Axial loads of 3.0 N and 4.3 N, applied through the olecranon and flexed carpus, engendered peak strains at the lateral ulnar midshaft of 2000 muepsilon and 3000 muepsilon, respectively. The left ulnae of 17, 17-week-old female CD1 mice were loaded for 10 min with a 4 Hz trapezoidal wave engendering a strain rate of 0.1 sec(-1) for 5 days/week for 2 weeks. The mice were killed 3 days later. The response of the cortical bone of the diaphysis was assessed histomorphometrically using double calcein labels administered on days 3 and 12 of the loading period. Loading to peak strains of 2000 muepsilon stimulated lamellar periosteal bone formation, but no response endosteally. The greatest increase in cortical bone area was 4 mm distal to the midshaft (5 +/- 0.4% compared with 0.1 +/- 0.1% in controls [p < 0.01]). Periosteal bone formation rate (BFR) at this site was 0.73 +/- 0.06 microm(2)/microm per day, compared with 0.03 +/- 0.02 microm(2)/microm per day in controls (p < 0.01). Loading to peak strains of 3000 muepsilon induced a mixed woven/lamellar periosteal response and lamellar endosteal bone formation. Both of these were greatest 3-4 mm distal to the ulnar midshaft. At this level, the loading-induced periosteal response increased cortical bone area by 21 +/- 4% compared with 0.03 +/- 0.02% in controls, and resulted in a BFR of 2.84 +/- 0.42 microm(2)/microm per day, compared with 0.01 +/- 0.01 microm(2)/microm per day in controls (p < 0.05). Endosteal new bone formation resulted in a 2 +/- 0.4% increase in cortical bone area, compared with 0.4 +/- 0.3% in controls, and a BFR of 1.05 +/- 0.23 microm(2)/microm per day, compared with 0.22 +/- 0.15 microm(2)/microm per day in controls (p < 0.05). These data show that the axial ulna loading technique developed in the rat can be used successfully in the mouse. As in the rat, a short daily period of loading results in an osteogenic response related to peak strain magnitude. One important advantage in using mice over rats involves the potential for assessing the effects of loading in transgenics.

Adaptation, Physiological↗
PubMed2002

The effect of in vivo mechanical loading on estrogen receptor alpha expression in rat ulnar osteocytes.

The presence of estrogen receptor alpha (ER alpha) in osteocytes was identified immunocytochemically in transverse sections from 560 to 860 microm distal to the midshaft of normal neonatal and adult male and female rat ulnas (n = 3 of each) and from adult male rat ulnas that had been exposed to 10 days of in vivo daily 10-minute periods of cyclic loading producing peak strains of either -3000 (n = 3) or -4000 microstrain (n = 5). Each animal ambulated normally between loading periods, and its contralateral ulna was used as a control. In animals in which limbs were subject to normal locomotor loading alone, 14 +/- 1.2% SEM of all osteocytes in each bone section were ER alpha positive. There was no influence of either gender (p = 0.725) or age (p = 0.577) and no interaction between them (p = 0.658). In bones in which normal locomotion was supplemented by short periods of artificial loading, fewer osteocytes expressed ER alpha (7.5 +/- 0.91% SEM) than in contralateral control limbs, which received locomotor loading alone (14 +/- 1.68% SEM; p = 0.01; median difference, 6.43; 95% CI, 2.60, 10.25). The distribution of osteocytes expressing ER alpha was uniform across all sections and thus did not reflect local peak strain magnitude. This suggests that osteocytes respond to strain as a population, rather than as individual strain-responsive cells. These data are consistent with the hypothesis that ER alpha is involved in bone cells' responses to mechanical strain. High strains appear to decrease ER alpha expression. In osteoporotic bone, the high strains assumed to accompany postmenopausal bone loss may reduce ER alpha levels and therefore impair the capacity for appropriate adaptive remodeling.

Animals↗
PubMed2001

Mechanical strain and estrogen activate estrogen receptor alpha in bone cells.

Bone cells' early responses to estrogen and mechanical strain were investigated in the ROS 17/2.8 cell line. Immunoblotting with antiphosphorylated estrogen receptor a (ER-alpha) antibody showed that when these cells were exposed for 10 minutes to estrogen (10(-8) M) or a single period of cyclic dynamic strain (peak 3400 microepsilon, 1 Hz, 600 cycles), there was an increase in the intensity of a 66-kDa band, indicating phosphorylation of ser122 in the amino terminus of ER-alpha. Increased phosphorylation was detected within 5 minutes of exposure to estrogen and 5 minutes after the end of the period of strain. Estrogen and strain also activated the mitogen-activated protein kinase (MAPK) family member extracellular regulated kinase-1 (ERK-1). Increases in ERK activation coincided with increased ER-alpha phosphorylation. Activation of ERK-1 and the phosphorylation of ER-alpha, by both estrogen and strain, were prevented by the MAP kinase kinase (MEK) inhibitor U0126 and the protein kinase A (PKA) inhibitor (PKI). These data support previous suggestions that resident bone cells' early responses to strain and estrogen share a common pathway, which involves ER-alpha. This pathway also appears to involve PKA and ERK-mediated phosphorylation of ser122 within the amino terminus of ER-alpha. Reduced availability of this pathway when estrogen levels are reduced could explain diminished effectiveness of mechanically related control of bone architecture after the menopause.

Bone and Bones↗
PubMed2000

Cryptosporidia on dairy farms and the role these farms may have in contaminating surface water supplies in the northeastern United States.

The prevalence and risk factors for shedding of cryptosporidia by dairy cattle and calves and the prevalence and risk factors for cryptosporidia in surface waters associated with dairy farms were determined for a well-defined watershed in the northeastern United States. Eleven dairy farms were enrolled in the study and subjected to monthly sampling over a 6-month period. Animal-, water-, and manure-management practices were determined by survey and fecal, on-farm water, and stream samples were obtained monthly and evaluated for the presence of cryptosporidia. Ninety-one percent of the dairy farms in our study had Cryptosporidium on their premises. Fifteen percent of the sampled calves 0-3 weeks of age were shedding cryptosporidia. The risk factors for calves shedding cryptosporidia were contact between calves and frequent bedding changes. The probability of shedding cryptosporidia decreased with age. Nine percent of farm-associated stream samples were cryptosporidia-positive. The single risk factor for detecting cryptosporidia in surface water was increasing frequency of spreading of manure on fields. The probability of detecting cryptosporidia in streams decreased as 5-day cumulative precipitation increased. There were no animal-associated or barnyard-management features associated with detecting cryptosporidia in farm-impacted streams.

Agriculture↗
PubMed2000

Arachidonic acid for loading induced prostacyclin and prostaglandin E(2) release from osteoblasts and osteocytes is derived from the activities of different forms of phospholipase A(2).

Mechanical loading of bone stimulates resident bone cells to produce prostacyclin (PGI(2)) and prostaglandin (PG)E(2) by a mechanism that can be differentially regulated by ion channel blockers. We have investigated differences in the loading-related PG production mechanisms in rat ulnae explants loaded ex vivo. Loading and aluminium fluoride (AlF(3), a nonselective activator of G-proteins) both increased PGI(2) and PGE(2) release into culture medium. Pertussis toxin (PTX) blocked loading-related release of PGE(2), but not PGI(2), while isotetrandrine, an inhibitor of G-protein-mediated activation of phospholipase (PL)A(2), abolished the loading-related release of both PGs. This suggests both PTX-sensitive and -insensitive G-protein-dependent, PLA(2)-mediated mechanisms for loading-related PG production. Blockade of secretory (s)PLA(2) activity prevented loading-related release of PGE(2) and PGI(2), whereas inhibition of cytosolic (c)PLA(2) activity blocked loading-related release of PGE(2) alone. cPLA(2) was localized immuno-cytochemically to osteoblasts, but not to osteocytes. sPLA(2) was localized to osteocytes and osteoblasts. Exogenous type-IA sPLA(2) and type-IB sPLA(2) stimulated significant increases in PGE(2) and PGI(2) release. PTX reduced the release of both PGs stimulated by type IA PLA(2), but not type IB. Furthermore, inhibition of protein kinase C (PKC) activity blocked loading-related release of PGE(2), but not that of PGI(2). These data suggest that loading-related release of PGI(2) and PGE(2) utilizes arachidonic acid derived from the activity of different PLA(2)s. In osteocytes and osteoblasts, arachidonic acid for PGI(2) synthesis is liberated by PTX-insensitive G-protein-dependent sPLA(2) alone. In osteoblasts, arachidonic acid for PGE(2) synthesis is released by PTX-sensitive, G-protein-dependent, cPLA(2)-mediated activity, which also requires upstream sPLA(2) and PKC activities.

Alkaloids↗
PubMed2000

Mechanical strain activates estrogen response elements in bone cells.

The involvement of the estrogen receptor in the early responses of bone cells to mechanical strain was investigated by subjecting subconfluent monolayer cultures of ROS.SMER #14 cells (ROS 17/2.8 cells stably transfected with additional ER alpha) to 17 beta-estradiol or a single short period of dynamic mechanical strain (600 cycles, 1 Hz). The basal proliferation rate of ROS.SMER #14 cells was similar to ROS 17/2.8 cells, whose proliferative responsiveness to strain and estrogen is similar to that of primary cultures of rat long bone-derived osteoblasts. At peak strains of 3400 mu epsilon, strain-related proliferation in ROS.SMER #14 cells was 1.4 times that of ROS 17/2.8 cells. At 10(-8) mol/L, 17 beta-estradiol-related proliferation was nearly twice greater. The ROS.SMER #14 cells were transiently transfected with an estrogen-responsive reporter, 2ERE-pS2-CAT, containing two consensus estrogen response elements (ERE) linked to a chloroamphenicol acetyl transferase gene. Strain increased normalized ERE-CAT activity threefold and estradiol (10(-8) mol/L) sixfold. Both strain-related and estradiol-related increases in proliferation and ERE-CAT activity were blocked by the estrogen antagonist ICI 182,780 (10(-6) mol/L). These data show that strain as well as estrogen stimulates increased proliferation in ROS 17/2.8 cells and increased ER alpha-related ERE activity in ROS cells transfected with ER alpha. Proliferation is greater in the cells with more estrogen receptors. Both strain- and estrogen-related proliferation and ERE activity are blocked by the estrogen antagonist ICI 182,780. This indicates that ROS cells' early responses to mechanical strain involve ER alpha and estrogen-responsive genes.

Animals↗
PubMed2000

Mechanical strain stimulates osteoblast proliferation through the estrogen receptor in males as well as females.

Mechanical strain, testosterone, and estrogen all stimulate proliferation of primary cultures of male rat long bone (LOB)-derived osteoblast-like cells as determined by [3H]thymidine incorporation. The maximum proliferative effect of a single period of mechanical strain (3400 microepsilon, 1 Hz, and 600 cycles) is additional to that of testosterone (10(-8) M) or estrogen (10(-8) M). The cells' proliferative response to strain is abolished both by concentrations of tamoxifen that cause proliferation (10(-8) M) and by those that have no effect (10(-6) M). Strain-related proliferation also is reduced by the estrogen antagonist ICI 182,780 (10(-8) M) but is unaffected by the androgen receptor antagonist hydroxyflutamide (10(-7) M). Tamoxifen, ICI 182,780, and the aromatase inhibitor 4-dihydroandrostenedione, at concentrations that have no effect on basal proliferation, significantly reduce the proliferative effect of the aromatizable androgen testosterone but not that of the nonaromatizable androgen 5alpha-dihydrotestosterone. Hydroxyflutamide, at a concentration that has no effect on basal proliferation (10(-7) M), eliminates the proliferative effect of 5alpha-dihydro-testosterone but had no significant effect on that caused by testosterone. Proliferation associated with strain is blocked by neutralizing antibody to insulin-like growth factor II (IGF-II) but not by antibody to IGF-I. Proliferation associated with testosterone is blocked by neutralizing antibody to IGF-I but is unaffected by antibody to IGF-II. These data suggest that in rat osteoblast-like cells from males, as from females, strain-related proliferation is mediated through the estrogen receptor (ER) in a manner that does not compete with estrogen but that can be blocked by ER modulators. Proliferation associated with testosterone appears to follow its aromatization to estrogen and is mediated through the ER, whereas proliferation associated with 5alpha-dihydrotestosterone is mediated by the androgen receptor. Strain-related proliferation in males, as in females, is mediated by IGF-II, whereas proliferation associated with estrogen and testosterone is mediated by IGF-I.

Androgen Antagonists↗
PubMed1999

Mechanical strain stimulates ROS cell proliferation through IGF-II and estrogen through IGF-I.

The mechanism by which mechanical strain stimulates bone cell proliferation was investigated and compared with that of estrogen in ROS 17/2.8 cells. Similarity of strain-related responses between ROS cells and osteoblasts was established by demonstrating that ROS cells respond to a short single period of strain in their substrate (1000-3500 microepsilon, 600 cycles, 1 Hz) by a similar strain magnitude-related increase in glucose 6-phosphate dehydrogenase activity as rat osteoblasts and osteocytes in explants in situ. ROS17/2.8 cells also showed similar proliferative responses to strain and 17beta-estradiol, as assessed by [3H]thymidine incorporation and cell counting, as primary cultures of long bone-derived osteoblast-like cells. Strain-related increase in proliferation in ROS cells was accompanied by a 4-fold increase in levels of insulin-like growth factor-II (IGF-II) in conditioned medium. Neither strain nor estrogen had an effect on the conditioned medium levels of IGF-I. Exogenous truncated IGFs tIGF-I and tIGF-II both increased proliferation in a dose-dependent manner. The neutralizing monoclonal antibody (nMAb) to IGF-I blocked proliferation stimulated by tIGF-I but not that due to tIGF-II and vice versa. IGF-I receptor blocking antibody (IGF-IRBAb) blocked the proliferative effect of tIGF-I but not that to tIGF-II. The proliferative effect of estrogen was abolished by IGF-I nMAb and IGF-IRBAb, but these antibodies had no effect on the proliferative response to strain. In contrast IGF-II nMAb abolished the proliferative effect of strain but had no effect on that of estrogen. These data show that ROS17/2.8 cells have similar responses to strain and estrogen qualitatively and quantitatively as rat osteoblasts in situ and rat long bone-derived osteoblast-like cells in primary culture. Estrogen-related proliferation in ROS17/2.8 cells appears to be mediated by IGF-I acting through the IGF-I receptor and does not involve IGF-II. In contrast, strain-related proliferation appears to be mediated by IGF-II and does not involve either IGF-I or the IGF-I receptor.

Animals↗
PubMed1999

Bone's early responses to mechanical loading differ in distinct genetic strains of chick: selection for enhanced growth reduces skeletal adaptability.

Bone's functional competence is established and maintained, at least partly, by mechanisms involving appropriate adaptation to mechanical loading. These appear to fail in chickens selectively bred either for maximum egg (Egg-type) or meat (Meat-type) production, which show high rates of fracture and skeletal abnormality, respectively. By measuring several early strain-induced responses in cultured embryonic tibiotarsi from commercially bred (Egg-type and Meat-type) and wild-type (Wild-type) chicks, we have investigated the possibility that these skeletal failures are the product of a compromised ability to respond appropriately to loading-induced mechanical strain. Axial loads engendering peak dynamic (1 Hz) longitudinal strains of between -1300 microepsilon and -1500 microepsilon (for 10 minutes) in vitro in tibiotarsi from the three types of 18-day-old chicks increased periosteal osteoblast glucose 6-phosphate dehydrogenase (G6PD) activity in both Wild-type (26%, p < 0.01) and Egg-type (49%, p < 0.001) chicks in situ, while Meat-type chicks did not show any significant changes (11%). Load-induced increases in medium nitrite accumulation (stable nitric oxide [NO] metabolite) were produced in Egg-type and Wild-type tibiotarsi (82 +/- 12%, p < 0.01; 39 +/- 8%, p < 0.01), respectively. In contrast, loading produced no change in NO release from Meat-type chick tibiotarsi. These changes in NO release correlated with load-related increases in G6PD activity (R2 = 0.98, p < 0.05) in the different chick types. Wild-type and Meat-type tibiotarsal periosteal osteoblasts responded in a biphasic manner to exogenous prostacyclin (PGI2), with maximal stimulation of G6PD activity at 10(-7) M and 10(-6) M PGI2. However, Egg-type chick osteoblasts showed smaller, progressive increases up to 10(-5) M PGI2. These results indicate that early phases of the adaptive response to loading differ in different genetic strains of embryonic chick; that skeletal abnormalities which develop in genetically selected, high growth rate chicks may reflect a compromised ability to respond to load; and that load-induced increases in osteoblastic G6PD activity appear to be closely associated with increased rates of NO release. It is probable that similar genetically related differences in bones' responsiveness to mechanical loading occur in other species.

Adaptation, Physiological↗
PubMed1999

Mechanical strain stimulates nitric oxide production by rapid activation of endothelial nitric oxide synthase in osteocytes.

Previous studies have indicated that physiological levels of dynamic mechanical strain produce rapid increases in nitric oxide (NO) release from rat ulna explants and primary cultures of osteoblast-like cells and embryonic chick osteocytes derived from long bones. To establish the mechanism by which loading-induced NO production may be regulated, we have examined: nitric oxide synthase (NOS) isoform mRNA and protein expression, the effect of mechanical loading in vivo on NOS mRNA expression, and the effect of mechanical strain on NO production by bone cells in culture. Using Northern blot analyses, in situ hybridization, and immunocytochemistry we have established that the predominant NOS isoform expressed in rat long bone periosteal osteoblasts and in a distinct population of cortical bone osteocytes is the endothelial form of NOS (eNOS), with little or no expression of the inducible NOS or neuronal NOS isoforms. In contrast, in non-load-bearing calvariae there are no detectable levels of eNOS in osteocytes and little in osteoblasts. Consistent with these observations, ulnar explants release NO rapidly in response to loading in vitro, presumably through the activation of eNOS, whereas calvarial explants do not. The relative contribution of different bone cells to these rapid increases in strain-induced NO release was established by assessment of medium nitrite (stable NO metabolite) concentration, which showed that purified populations of osteocytes produce significantly greater quantities of NO per cell in response to mechanical strain than osteoblast-like cells derived from the same bones. Using Northern blot hybridization, we have also shown that neither a single nor five consecutive daily periods of in vivo mechanical loading produced any significant effect on different NOS isoform mRNA expression in rat ulnae. In conclusion, our results indicate that eNOS is the prevailing isoform expressed by cells of the osteoblast/osteocyte lineage and that strain produces increases in the activity of eNOS without apparently altering the levels of eNOS mRNA.

Animals↗
PubMed1999

Alpha-particle doses to cells of the bone remodeling cycle from alpha-particle-emitting bone-seekers: indications of an antiresorptive effect of actinides.

There are indications that alpha-particle-emitting bone-seekers such as plutonium or americium could enhance bone mass by suppressing bone resorption. To assess this possibility, this study calculates doses from alpha-particle emitters to the cells involved in trabecular bone turnover. Alpha-particle energy deposition in tissue from a bone surface source was calculated by Monte Carlo modeling. This was combined with bone surface cellular geometry to yield dose rates to cells during the remodeling cycle. Bone-resorbing osteoclasts receive on average 50 times the dose rate that bone-forming osteoblasts receive. Newly formed bone shields osteoblasts from alpha particles emitted by the buried deposit of alpha-particle emitters. However, at alpha-particle bone-seeking radionuclide intakes known to cause changes in remodeling (about 3700 Bq/kg body weight), the alpha-particle dose to osteoclasts corresponds to an extremely low rate of cell traversals (0.07% per cycle). It is therefore unlikely that perturbation of bone remodeling by alpha-particle bone-seeking radionuclides is directly caused by alpha-particle traversals of remodeling cells; some other indirect mechanism might be involved.

Actinoid Series Elements↗
PubMed1998

RoBo-1, a novel member of the urokinase plasminogen activator receptor/CD59/Ly-6/snake toxin family selectively expressed in rat bone and growth plate cartilage.

Using differential display polymerase chain reaction, we cloned a novel cDNA named RoBo-1 from rat tibia. RoBo-1 is abundantly expressed in bone, including the hypertrophic chondrocytes of the growth plate where cartilage is remodeled into bone. RoBo-1 mRNA expression increased in response to two modulators of bone metabolism, estradiol and intermittent mechanical loading, suggesting a role in bone homeostasis. The 1.6-kilobase cDNA encodes a 240-amino acid protein with a cysteine spacing pattern, suggesting that RoBo-1 is a novel member of the urokinase plasminogen activator receptor/CD59/Ly-6/snake toxin family. Furthermore, the C-terminal contains a glycosyl-phosphatidylinositol attachment site, suggesting that it is a cell surface protein similar to other mammalian members of this family. The strongest homology of RoBo-1 is to the snake serum-derived phospholipase A2 inhibitors, which uniquely contain two of the cysteine domains but are secreted proteins. Interestingly, RoBo-1 is likely the first membrane-anchored member of this family containing two cysteine domains. Thus, the tissue specificity, responsiveness to bone protective mediators, along with its relationship to the multifunctional urokinase plasminogen activator receptor/CD59/Ly-6/snake toxin family suggests that RoBo-1 may play a novel role in the growth or remodeling of bone.

Amino Acid Sequence↗
PubMed1998

Strain rate as a controlling influence on adaptive modeling in response to dynamic loading of the ulna in growing male rats.

To test the hypothesis that the rate of change of strain to which a bone is subjected is an important determinant to the subsequent functionally adaptive modeling response, the ulnae of growing male rats were subjected to dynamic axial loading in vivo for a short period each day over 2 weeks. Due to the longitudinal curvature of the ulna, such axial loading leads to both compression and bending. The left ulna in three groups of rats was loaded cyclically between 1 and 20 N in a trapezoidal pattern to produce dynamic, longitudinal compressive strains of -0.004 (-4000 microstrain) at the medial midshaft with one of three strain rates: low (+/-0.018 sec(-1); n = 7); moderate (+/-0.030 sec(-1); n = 7); and high (+/-0.100 sec(-1); n = 8). These strain rates span the range recorded from strain gauges bonded to the bone at this site during a variety of normal activities. At the end of the experiment, the loaded ulnae were slightly, but significantly, shorter than their contralateral controls (2.7% to 5.6% mean change in length; p < 0.0001). This effect was most marked at lower strain rates, associated with an increased load-bearing time. The pattern of adaptive modeling along the bone shaft was similar for all groups, each showing a reduced rate of periosteal expansion proximally, and increased periosteal new bone production distally. This distal increase was achieved through enhanced periosteal bone formation on the lateral (tension) cortex, and arrest of resorption, with conversion to formation on the medial (compression) surface. The modeling response to axial loading therefore involves complex location-dependent increases and decreases in both formation and resorption. The high-strain-rate group demonstrated a 54% greater osteogenic response than the moderate-strain-rate group, which in turn showed a 13% larger response than the low-strain-rate group. Rate of strain change is therefore a major determinant of the adaptive osteogenic/antiresorptive response to mechanical load. Across the physiological range, a high rate of strain change provides a greater osteogenic stimulus than the same peak strain achieved more slowly.

Adaptation, Physiological↗
PubMed1998

Heme oxygenase isozymes in bone: induction of HO-1 mRNA following physiological levels of mechanical loading in vivo.

Heme oxygenases (HO) are responsible for the production of carbon monoxide, which has been suggested to act similarly to nitric oxide as a signaling molecule. Inducible HO-1 and constitutive HO-2 were located in sections of weight-bearing ulnae of the rat by immunocytochemistry. Intense HO-1 localization was restricted to peri- and endosteal sites, whereas HO-2 staining occurred in osteoblasts and osteocytes throughout the cortex. Northern blot hybridization of mRNA levels for HO-1 and HO-2 extracted from bones was also performed. Six hours after a single 10 min period of noninvasive mechanical loading of the ulna in vivo, generating physiological levels of strain sufficient to initiate an osteogenic response, the level of mRNA for the inducible HO-1 isoform was increased, but that of HO-2 was unchanged. The presence of a constitutive and strain-related upregulation of an inducible enzyme capable of producing carbon monoxide suggests that carbon monoxide may participate not only in bone cells' basal metabolism but also in their adaptive response to mechanical load.

Animals↗
PubMed1998

The estrogen receptor's involvement in osteoblasts' adaptive response to mechanical strain.

The estrogen receptor's role in bone cells' response to mechanical strain was investigated by studying the effect of the estrogen receptor modulators ICI 182, 780 and tamoxifen on the proliferation of primary cultures of rat long bone-derived osteoblasts stimulated by the independent and combined effects of 17beta-estradiol, mechanical strain, and the mitogens basic fibroblast growth factor (bFGF), truncated insulin-like growth factor (tIGF)-I and tIGF-II, and epidermal growth factor (EGF). 17Beta-estradiol (10(-10) M to 10(-8) M) increased [3H]thymidine incorporation equally in cells from males and females, as did a single period of cyclical strain in the plastic strips onto which the cells had been seeded (peak strain 3,400 microepsilon, 600 cycles, 1 Hz). At 10(-8) M, neither ICI 182,780 nor tamoxifen had any effect on basal [3H]thymidine incorporation in these cells, but both compounds prevented their proliferative responses to 10(-8) M 17beta-estradiol. Tamoxifen eliminated and ICI 182,780 substantially reduced the proliferation stimulated by strain. 17Beta-estradiol partially rescued the strain-related response from the effect of tamoxifen but not that of ICI 182,780. Both tamoxifen and ICI 182,780 reduced proliferation stimulated by 10(-8) M EGF but had no effect on that by 10(-7) M bFGF or tIGF-I and tIGF-II. That both ICI 182,780 and tamoxifen, which in other tissues act as estrogen antagonists, should reduce osteoblast proliferation stimulated by 17beta-estradiol and EGF, but not that by FGF or the IGFs, was expected since the mitogenic effects of estrogen and EGF involve the estrogen receptor, whereas those of FGF and the IGFs do not. That these compounds should prevent osteoblasts' proliferative response to strain suggests that strain also stimulates mitogenesis by a mechanism involving the estrogen receptor. If this is so, bones' reduced ability to maintain their structural strength after the menopause could be explained by less effective strain-related (re)modeling when estrogen is absent and, among other changes, the estrogen receptor could be down-regulated.

Animals↗