Skeletal Unloading Research Articles

Spinal Cord Injury Associated Disease of the Skeleton, an Unresolved Problem with Need for Multimodal Interventions.

Spinal cord injury is associated with skeletal unloading, sedentary behavior, decreases in skeletal muscle mass, and exercise intolerance, which results in rapid and severe bone loss. To date, monotherapy with physical interventions such as weight-bearing in standing frames, computer-controlled electrically stimulated cycling and ambulation exercise, and low-intensity vibration are unsuccessful in maintaining bone density after SCI. Strategies to maintain bone density with commonly used osteoporosis medications also fail to provide a significant clinical benefit, potentially due to a unique pathology of bone deterioration in SCI. In this review, the available data is discussed on evaluating and monitoring bone loss, fracture, and physical and pharmacological therapeutic approaches to SCI-associated disease of the skeleton. The treatment of SCI-associated disease of the skeleton, the implications for clinical management, and areas of need are considered for future investigation.

Reduced osseointegration in disuse and denervation rat models results from impaired cellular responses to multiscale microstructured titanium surfaces.

Immobilization-induced skeletal unloading results in muscle atrophy and rapid bone loss, thereby increasing the risk of falling and the need for implant therapy in patients with extended bed rest or neuromuscular injuries. Skeletal unloading causes bone loss by altering bone growth and resorption, suggesting that implant performance might be affected. To test this, we focused on early events in implant osseointegration. We used the rat sciatic neurectomy-induced disuse model under two different settings. In Study 1, 16 Sprague Dawley rats (SD) were separated into control, sham operated+cast immobilization, and sciatic neurectomy+casting groups; titanium implants with multiscale microtextured topography and hydrophilic chemistry (modSLA) were inserted in the distal femoral metaphysis. Neurectomy surgeries and casting were performed at the same surgical setting as implant placement; rats were euthanized 4 weeks post-implantation. In Study 2, we established the unloaded condition before implantation. A total of 12 SD rats were divided into control and sciatic+femoral neurectomy groups. A total of 24 days after sciatic and femoral neurectomy surgery, rats received implants. Study 2 rats were euthanized at 4 weeks post-implantation. MicroCT and histomorphometry showed that trabecular bone and osseointegration were reduced when disuse was established before implantation. Osteoblasts isolated from Study 1 sciatic neurectomy tibial bones exhibited impaired differentiation on modSLA culture disks, revealing a possible mechanism responsible for the decreased osseointegration observed in the Study 2 rats. This study addressed the importance of considering the mechanical unloading and muscle function history before implant insertion and suggests that implant performance was reduced due to poor cellular ability to regenerate.

PTH 1–34 reduced apoptosis of MLO-Y4 osteocyte-like cells by activating autophagy and inhibiting ER stress under RPM conditions

Osteocytes, as mechanosensitive cells residing within bone tissue, hold a pivotal role in averting the occurrence and progression of osteoporosis. The apoptosis of osteocytes induced by unloading is one of the contributing factors to osteoporosis, although the underlying molecular mechanisms have not been fully elucidated. PTH 1–34 is known to promote bone formation and inhibit bone loss by targeting osteoblasts and osteocytes. However, it is not known whether PTH 1–34 can inhibit osteocyte apoptosis under unloading conditions and the molecular mechanisms involved. In this study, we employed a Random Positioning Machine (RPM) to emulate unloading conditions and cultured MLO-Y4 osteocyte-like cells, in order to unravel the mechanisms through which PTH 1–34 constrains osteocyte apoptosis amidst unloading circumstances. Our findings revealed that PTH 1–34 activated autophagy while suppressing endoplasmic reticulum stress by curtailing the generation of reactive oxygen species (ROS) in MLO-Y4 osteocyte-like cells during unloading conditions. By shedding light on the osteoporosis triggered by skeletal unloading, this study contributes vital insights that may pave the way for the development of pharmacological interventions.

Recombinant irisin prevents cell death and mineralization defects induced by random positioning machine exposure in primary cultures of human osteoblasts: A promising strategy for the osteoporosis treatment.

Spaceflight exposure, like prolonged skeletal unloading, is known to result in significant bone loss, but the molecular mechanisms responsible are still partly unknown. This impairment, characterizing both conditions, suggests the possibility of identifying common signalling pathways and developing innovative treatment strategies to counteract the bone loss typical of astronauts and osteoporotic patients. In this context, primary cell cultures of human osteoblasts derived from healthy subjects and osteoporotic patients were exposed to random positioning machine (RPM) to reproduce the absence of gravity and to exacerbate the pathological condition, respectively. The duration of exposure to RPM was 3 or 6days, with the aim of determining whether a single administration of recombinant irisin (r-irisin) could prevent cell death and mineralizing capacity loss. In detail, cellular responses were assessed both in terms of death/survival, by MTS assay, analysis of oxidative stress and caspase activity, as well as the expression of survival and cell death proteins, and in terms of mineralizing capacity, by investigating the pentraxin 3 (PTX3) expression. Our results suggest that the effects of a single dose of r-irisin are maintained for a limited time, as demonstrated by complete protection after 3days of RPM exposure and only partial protection when RPM exposure was for a longer time. Therefore, the use of r-irisin could be a valid strategy to counteract the bone mass loss induced by weightlessness and osteoporosis. Further studies are needed to determine an optimal treatment strategy based on the use of r-irisin that is fully protective even over very long periods of exposure and/or to identify further approaches to be used in a complementary manner.

Glucose- and glutamine-dependent bioenergetics sensitize bone mechanoresponse after unloading by modulating osteocyte calcium dynamics.

Disuse osteoporosis is a metabolic bone disease resulting from skeletal unloading (e.g., during extended bed rest, limb immobilization, and spaceflight), and the slow and insufficient bone recovery during reambulation remains an unresolved medical challenge. Here, we demonstrated that loading-induced increase in bone architecture/strength was suppressed in skeletons previously exposed to unloading. This reduction in bone mechanosensitivity was directly associated with attenuated osteocytic Ca2+ oscillatory dynamics. The unloading-induced compromised osteocytic Ca2+ response to reloading resulted from the HIF-1α/PDK1 axis-mediated increase in glycolysis, and a subsequent reduction in ATP synthesis. HIF-1α also transcriptionally induced substantial glutaminase 2 expression and thereby glutamine addiction in osteocytes. Inhibition of glycolysis by blockade of PDK1 or glutamine supplementation restored the mechanosensitivity in those skeletons with previous unloading by fueling the tricarboxylic acid cycle and rescuing subsequent Ca2+ oscillations in osteocytes. Thus, we provide mechanistic insight into disuse-induced deterioration of bone mechanosensitivity and a promising therapeutic approach to accelerate bone recovery after long-duration disuse.

Bone Metabolism During Strict Head-Down Tilt Bed Rest and CO2 Exposure

ObjectivesCarbon dioxide (CO2) levels on board the International Space Station reach 10× those of outdoor terrestrial levels. We report here studies assessing whether increased levels of ambient CO2 contribute to elevated bone resorption characteristically observed with bed rest as an analog for skeletal unloading during spaceflight.MethodsData are reported from two ground-based studies which included 12 male and 7 female subjects placed in a strict −6° head-down tilt (HDT) position for 30 days at 0.5% ambient CO2 or 60 days with nominal environment (0.04% CO2). Subjects were neither afforded a pillow nor allowed to use an elbow while eating to increase headward fluid pressure. Bone mineral density (BMD) and bone mineral content (BMC) were measured with dual-energy X-ray absorptiometry. Blood and urine were collected before and during HDT for analysis.ResultsThere was no change in BMD or BMC. Excretion of collagen crosslinks increased during HDT (p < 0.001) with no additive effect of CO2. Serum and urine mineral concentrations were not affected by CO2. Serum PTH and 1,25-deoxyhydroxyvitamin D were both reduced during bed rest (p < 0.0001), likely secondary to calcium efflux from bone, but with no additive effect of CO2 exposure. These changes reinforce the impact of decreased mechanical loading on bone and mineral homeostasis and the efficacy of the strict HDT model.ConclusionsExposure to 0.5% CO2 for 30 days did not exacerbate bone resorption during strict HDT bed rest. Future research on bone metabolism at varied CO2 levels is needed to clarify a risk ceiling for bone resorption, especially as missions progress beyond low-Earth orbit.Funding SourcesThe data reported here were from the NASA Human Research Program Standard Measures Cross-Cutting Project. Funding was provided by the NASA Human Research Program's Human Health Countermeasures Element. ERM was funded through a NASA Summer Science Institute Fellowship.

Absence of P2Y2 Receptor Does Not Prevent Bone Destruction in a Murine Model of Muscle Paralysis-Induced Bone Loss.

Increased incidence of bone fractures in the elderly is associated with gradual sarcopenia. Similar deterioration of bone quality is seen with prolonged bed rest, spinal cord injuries or in astronauts exposed to microgravity and, preceded by loss of muscle mass. Signaling mechanisms involving uridine-5′-triphosphate (UTP) regulate bone homeostasis via P2Y2 receptors on osteoblasts and osteoclasts, whilst dictating the bone cells’ response to mechanical loading. We hypothesized that muscle paralysis-induced loss of bone quality would be prevented in P2Y2 receptor knockout (KO) mice. Female mice injected with botulinum toxin (BTX) in the hind limb developed muscle paralysis and femoral DXA analysis showed reduction in bone mineral density (<10%), bone mineral content (<16%) and bone area (<6%) in wildtype (WT) compared to KO littermates (with <13%, <21%, <9% respectively). The femoral metaphyseal strength was reduced equally in both WT and KO (<37%) and <11% in diaphysis region of KO, compared to the saline injected controls. Tibial micro-CT showed reduced cortical thickness (12% in WT vs. 9% in KO), trabecular bone volume (38% in both WT and KO), trabecular thickness (22% in WT vs. 27% in KO) and increased SMI (26% in WT vs. 19% in KO) after BTX. Tibial histomorphometry showed reduced formation in KO (16%) but unchanged resorption in both WT and KO. Furthermore, analyses of DXA and bone strength after regaining the muscle function showed partial bone recovery in the KO but no difference in the bone recovery in WT mice. Primary osteoblasts from KO mice displayed increased viability and alkaline phosphatase activity but, impaired bone nodule formation. Significantly more TRAP-positive osteoclasts were generated from KO mice but displayed reduced resorptive function. Our data showed that hind limb paralysis with a single dose of BTX caused profound bone loss after 3 weeks, and an incomplete reversal of bone loss by week 19. Our findings indicate no role of the P2Y2 receptor in the bone loss after a period of skeletal unloading in mice or, in the bone recovery after restoration of muscle function.

Dissociation of Bone Resorption and Formation in Spaceflight and Simulated Microgravity: Potential Role of Myokines and Osteokines?

The dissociation of bone formation and resorption is an important physiological process during spaceflight. It also occurs during local skeletal unloading or immobilization, such as in people with neuromuscular disorders or those who are on bed rest. Under these conditions, the physiological systems of the human body are perturbed down to the cellular level. Through the absence of mechanical stimuli, the musculoskeletal system and, predominantly, the postural skeletal muscles are largely affected. Despite in-flight exercise countermeasures, muscle wasting and bone loss occur, which are associated with spaceflight duration. Nevertheless, countermeasures can be effective, especially by preventing muscle wasting to rescue both postural and dynamic as well as muscle performance. Thus far, it is largely unknown how changes in bone microarchitecture evolve over the long term in the absence of a gravity vector and whether bone loss incurred in space or following the return to the Earth fully recovers or partly persists. In this review, we highlight the different mechanisms and factors that regulate the humoral crosstalk between the muscle and the bone. Further we focus on the interplay between currently known myokines and osteokines and their mutual regulation.

The Role of Histone Deacetylases I and IIa (HDAC1, HDAC4/5) and the MAPK38 Signaling Pathway in the Regulation of Atrophic Processes under Skeletal Muscle Unloading

The Role of Histone Deacetylases I and IIa (HDAC1, HDAC4/5) and the MAPK38 Signaling Pathway in the Regulation of Atrophic Processes under Skeletal Muscle Unloading

Bone Aging, Cellular Senescence, and Osteoporosis.

ABSTRACTChanges in aging bone that lead to osteoporosis are mediated at multiple levels, including hormonal alterations, skeletal unloading, and accumulation of senescent cells. This pathological interplay is superimposed upon medical conditions, potentially bone‐wasting medications, modifiable and unmodifiable personal risk factors, and genetic predisposition that accelerate bone loss with aging. In this study, the focus is on bone hemostasis and its dysregulation with aging. The major physiological changes with aging in bone and the role of cellular senescence in contributing to age‐related osteoporosis are summarized. The aspects of bone aging are reviewed including remodeling deficits, uncoupling phenomena, inducers of cellular senescence related to bone aging, roles of the senescence‐associated secretory phenotype, radiation‐induced bone loss as a model for bone aging, and the accumulation of senescent cells in the bone microenvironment as a predominant mechanism for age‐related osteoporosis. The study also addresses the rationale and potential for therapeutic interventions based on the clearance of senescent cells or suppression of the senescence‐associated secretory phenotype. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Bone and visceral adipose tissue - a literature review

The potential associations between obesity and bone health have long been discussed, but the results of the clinical trials remain controversial. It is known that adipose tissue affects bone metabolism through mechanical, hormonal and inflammatory factors, but it is still debated whether the total effect is positive or negative for the bone. Higher body mass is associated with greater mechanical load, which in turn can stimulate the increase in bone mass. Fat accumulation is also associated with increased production of estrogen, which has a positive effect on bone metabolism. Increased secretion of insulin and amylin further suggests a greater anabolic effect on bone tissue. On the other hand, obesity is associated with low-grade inflammation and increased secretion of cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α). However, these cytokines have a negative effect on bone tissue. In addition, decreased circulating levels of 25-hydroxyvitamin D (25OHD) have been observed in obese individuals, which may lead to impaired bone formation with altered quantitative and qualitative bone characteristics. Lower levels of vitamin D further lead to increased levels of parathyroid hormone (PTH), which can separately adversely affect bone metabolism. Additional discussions arise in connection with weight reduction, as dietary restrictions and mechanical changes caused by skeletal unloading during weight loss, as well as the resulting hormonal changes can increase the risk of fractures.

Endoplasmic reticulum stress mediates osteocyte death under oxygen-glucose deprivation in vitro

As a vascularized organ, bone is known to be susceptible to ischemia. Ischemic osteonecrosis or skeletal unloading lead to ischemia in bone microenvironment that causes osteocytes to suffer hypoxia and nutrition deprivation. ObjectiveTo explore the effects of Oxygen-glucose deprivation (OGD) on osteocytes and the potential mechanism. MethodsOGD model was established in cultured MLO-Y4 cell. Cell damage, intracellular oxidative stress and cell apoptosis were detected at different OGD times (0, 2, 4, 8, 12, 24 h), and the changes in endoplasmic reticulum (ER) stress-related indicators were observed. Furthermore, cells were treated with 4-phenylbutyrate sodium (4-PBA) to inhibit ER stress, and cell damage and oxidative stress level were detected. ResultsThe cell viability under OGD exhibited a significantly reduced in a time-dependent manner, and the level of intracellular reactive oxygen species (ROS) were increased, cell apoptosis and ER stress was induced. Inhibition of ER stress can reduce cell death and intracellular ROS levels. ConclusionOur study demonstrated that ER stress regulates OGD-induced apoptotic cell death in MLO-Y4 cells via intracellular ROS.

The Skeletal Consequences of Bariatric Surgery.

This review outlines the recent findings regarding the impact of bariatric surgery on bone. It explores potential mechanisms for skeletal changes following bariatric surgery and strategies for management. Bone loss following bariatric surgery is multifactorial. Probable mechanisms include skeletal unloading, abnormalities in calciotropic hormones, and changes in gut hormones. Skeletal changes that occur after bariatric surgery are specific to procedure type and persist for several years post-operatively. Studies suggest that while bone loss begins early, fracture risk may be increased later in the post-operative course, particularly after Roux-en-Y gastric bypass (RYGB). Further research is needed to assess the extent to which skeletal changes following bariatric surgery result in fragility. Current management should be geared toward prevention of bone loss, correction of nutritional deficiencies, and incorporation of weight bearing exercise. Pharmacologic treatment should be considered for high-risk patients.

Growth Hormone Effects on Bone Loss-Induced by Mild Traumatic Brain Injury and/or Hind Limb Unloading

Growth hormone (GH) deficiency and loss of physical activity are common features in traumatic brain injury (TBI) patients that may contribute to bone loss. Therefore, we tested the hypothesis that GH treatment will rescue the hind limb unloading (UL)-induced skeletal deficit in TBI mice. Mild TBI was induced once per day for four consecutive days. UL (right hind limb) and treatment (3 mg/day GH or vehicle) began two weeks after the first TBI episode and lasted for four weeks. GH treatment increased femur BMD and lean body mass but decreased the % fat measured by DXA in the Control group. Micro-CT analysis revealed that the TBI, UL and TBI-UL groups showed reduced tibia trabecular (Tb) bone mass by 15%, 70%, and 75%, respectively compared to Control mice and that GH treatment significantly increased Tb. bone mass in all four groups. Vertebra also showed reduced Tb. bone mass in TBI, UL and TBI-UL groups. GH treatment increased vertebral Tb. bone mass in Control and UL groups but not in the TBI or TBI-UL group. GH treatment increased serum IGF-I levels similarly in TBI, UL and TBI-UL groups at day 14, suggesting the GH effect on liver IGF-I production was unaffected by skeletal UL. In contrast, GH effect on expression of ALP, IGFBP5 and axin2 in bone were compromised by UL. In conclusion, skeletal UL caused a greater Tb. bone deficit than mild TBI alone and that GH anabolic effects in the TBI and UL groups vary depending on the skeletal site.

Effects of skeletal unloading on the bone marrow antibody repertoire of tetanus toxoid and/or CpG treated C57BL/6J mice

Spaceflight is known to impact the immune system in multiple ways. However, its effect on the antibody repertoire, especially in response to challenge, has not been well characterized. The development of the repertoire has multiple steps that could be affected by spaceflight, including V-(D-)J-gene segment rearrangement and the selection of complementarity determining regions (CDRs); specifically, CDR3, responsible for much of the diversity in the repertoire. We used skeletal unloading with the antiorthostatic suspension (AOS) model to simulate some of the physiological effects associated with spaceflight. Animals ± AOS were challenged with tetanus toxoid (TT) and/or CpG, an adjuvant. Two weeks after challenge, bone marrow was collected and sequenced using the Illumina MiSeq 2 × 300 platform. The resulting antibody repertoire was characterized, including V-, D- (heavy only), and J-gene segment usage, constant region usage, CDR3 length, and V(D)J combinations. We detected changes in gene-segment usage in response to AOS, TT, and CpG treatment in both the heavy and light chains. Additionally, changes were seen in the class-switched VH-gene repertoire. Alterations were also detected in V/J pairing for both the heavy and light chains, and changes in CDR3 length. We also detected lower levels of CDR3 AA overlap than detected in the splenic repertoire. These results demonstrate that AOS, TT, and CpG alter the bone marrow antibody repertoire however, it is still unclear from the data whether there is a loss of host antigen-specific responsiveness because of the change in gene use.

Skeletal unloading reduces cluster of differentiation (CD) 38 expression in the bone marrow and osteoblasts of mice

BackgroundMechanical unloading induces bone loss in human weight-loaded bones. The findings of recent studies have revealed that cluster of differentiation 38 knockout mice display bone loss similar to that observed in osteoporosis. This study aimed to determine whether the expression of cluster of differentiation 38 is implicated in skeletal unloading and reloading. MethodsEight-week-old male C57BL/6J mice were assigned to control, tail-suspension, or reloading after tail-suspension groups. In the tail-suspension group, tail suspension elevated the hind limbs for 1 week. The bilateral femurs and tibias from the groups were evaluated for cluster of differentiation 38 immunocytochemistry, and the cluster of differentiation 38 messenger ribonucleic acid levels and the expression of cluster of differentiation 38 and other cell-surface antigens were evaluated using quantitative real-time polymerase chain reaction and flow cytometric analyses. ResultsIn the tail-suspension group, the alkaline phosphatase reactivity, cluster of differentiation 38 immunoreactivity in the bone marrow and osteoblasts, and the expression of cluster of differentiation 38 messenger ribonucleic acid and that of other cell-surface antigens were significantly lower than those in the control group. In the reloading after tail-suspension group, the level of cluster of differentiation 38 expression was restored to the same level as that in the control group. ConclusionsCluster of differentiation 38 expression declined after skeletal unloading and recovered to normal levels after reloading. In the bone marrow, cluster of differentiation 38 expression plays a crucial role in bone formation in response to mechanical stress.

SAT-518 Long-term Impact of Gastric Bypass on Bone Density &gt;10 years after Bariatric Surgery: Exceeding Physiologic Expectations

Introduction: In the initial years after bariatric surgery, Roux-en-Y gastric bypass (RYGB) leads to high-turnover bone loss and an increased risk of fractures. The long-term effects of RYGB on bone density and microarchitecture have not been defined beyond 5 years. Furthermore, there remains an open question of whether bone loss exceeds physiologic expectations for surgical weight loss. Thus, we evaluated bone mineral density (BMD) and bone microarchitecture in adults who received RYGB at least 10 years ago compared to BMI-matched controls. Methods: In this ongoing study, we recruited 24 adults who received RYGB ≥10 years ago, along with nonsurgical controls who were matched 1:1 by age, sex, race/ethnicity, and current BMI. Total body composition and areal BMD (aBMD) of the lumbar spine and proximal femur were assessed by dual energy x-ray absorptiometry (DXA). Volumetric BMD (vBMD) and bone microarchitecture at the distal radius and tibia were evaluated with high resolution peripheral QCT. Serum calcium, 25-OH vitamin D, and PTH were available in 2/3 of subjects; additional analyses are ongoing. Paired t-tests were used to compare outcomes between groups. Results: By design, the RYGB group was well-matched with controls for BMI (33 ± 6 kg/m2), age (56 ± 10 yr), sex (88% female), and race (65% white). Fat mass and lean mass were similar between RYGB and controls. Mean time since surgery was 13.7 ± 2.2 yrs in the RYGB group, and self-reported weight loss was 45 ± 19 kg. As compared to BMI-matched controls, RYGB patients had 17% lower femoral neck aBMD (p<0.001) and 13% lower total hip aBMD (p<0.001), but lumbar spine aBMD was not significantly different between groups. RYGB patients had lower cortical and trabecular vBMD than BMI-matched controls at both the radius and tibia (p≤0.02 for all), leading to a total vBMD that was 27% lower at the radius (p<0.001) and 20% lower at the tibia (p<0.001). Cortical area and thickness were significantly lower in the RYGB group at the radius and tibia (p<0.05 for all). In addition, the RYGB group had lower trabecular number and thickness, wider trabecular separation, and increased trabecular heterogeneity at both the radius and tibia (p≤0.02 for all). Serum calcium and 25-OH vitamin D levels were similar to BMI-matched controls, although PTH levels tended to be higher in the RYGB group (71 vs 52 pg/mL, p=0.07). Conclusions: Adults who received RYGB at least 10 years ago have femoral and peripheral BMD that is lower than expected given their new weight set point, despite comparable serum calcium and vitamin D levels as BMI-matched controls. Furthermore, both the radius and tibia showed a similar magnitude of deterioration in bone microarchitecture, suggesting that bone loss is driven by a systemic process rather than confined to weight-bearing sites. These data indicate that the effects of RYGB on bone are pathophysiologic, and may be attributed to factors beyond skeletal unloading.

Effects of skeletal unloading on the antibody repertoire of tetanus toxoid and/or CpG treated C57BL/6J mice.

Spaceflight affects the immune system, but the effects on the antibody repertoire, responsible for humoral immunity, has not been well explored. In particular, the complex gene assembly and expression process; including mutations, might make this process vulnerable. Complementarity determining region 3 (CDR3), composed of parts of the V-(D-)J-gene segments, is very important for antigen binding and can be used as an important measure of variability. Skeletal unloading, and the physiological effects of it, parallel many impacts of space flight. Therefore, we explored the impact of skeletal unloading using the antiorthostatic suspension (AOS) model. Animals were experimentally challenged with tetanus toxoid (TT) and/or the adjuvant CpG. Blood was analyzed for anti-TT antibody and corticosterone concentrations. Whole spleen tissue was prepared for repertoire characterization. AOS animals showed higher levels of corticosterone levels, but AOS alone did not affect anti-TT serum antibody levels. Administration of CpG significantly increased the circulating anti-TT antibody concentrations. AOS did alter constant gene usage resulting in higher levels of IgM and lower levels of IgG. CpG also altered constant gene region usage increasing usage of IgA. Significant changes could be detected in multiple V-, D-, and J-gene segments in both the heavy and light chains in response to AOS, TT, and CpG treatments. Analysis of class-switched only transcripts revealed a different pattern of V-gene segment usage than detected in the whole repertoire and also showed significant alterations in gene segment usage after challenge. Alterations in V/J pairing were also detected in response to challenge. CDR3 amino acid sequence overlaps were similar among treatment groups, though the addition of CpG lowered overlap in the heavy chain. We isolated 3,045 whole repertoire and 98 potentially TT-specific CDR3 sequences for the heavy chain and 569 for the light chain. Our results demonstrate that AOS alters the repertoire response to challenge with TT and/or CpG.

Cortical bone loss due to skeletal unloading in aldehyde dehydrogenase 2 gene knockout mice is associated with decreased PTH receptor expression in osteocytes

Aldehyde dehydrogenase 2 (ALDH2) is the enzyme that degrades and detoxifies the acetaldehyde produced by alcohol metabolism. In our previous study, we found that compared with wild-type mice (WT), climbing exercises did not increase trabecular bone mass in Aldh2 knockout mice (KO). The purpose of this study was to clarify the effect of the Aldh2 gene on cortical bone structure and on the dynamics of skeletal unloading. Eight-week-old male KO and WT were divided into ground control (GC) or tail suspension (TS) groups for one week (i.e., the KOGC, KOTS, WTGC and WTTS groups). We measured the bone mineral density (BMD) of the femur using dual-energy X-ray absorptiometry. We assessed the femoral morphometry using peripheral quantitative computed tomography (pQCT) and evaluated the femoral cortex histomorphometry, and cortical mRNA using quantitative RT-PCR and cortical bone immunohistostaining. No significant differences were found between the femoral BMD of WTGC and that of WTTS, but the BMD in KOTS was significantly lower than that of KOGC. The pQCT results revealed that the cortical BMD of the femoral diaphysis in KOTS was significantly lower than that of KOGC. Furthermore, the cortical bone area and cortical thickness were significantly lower in KOTS than in the other three groups. Cortical histomorphometric analysis revealed that the endosteal and periosteal bone formation parameters were significantly lower in KOTS than in KOGC. Bone formation signals such as parathyroid hormone receptor (PTHR) were significantly decreased in KOTS compared with the levels in KOGC. Cortical bone immunohistostaining revealed a significantly decreased expression of PTHR in the osteocytes of KOTS compared with the expression level in KOGC. Thus, we concluded that when the Aldh2 gene is disrupted, skeletal unloading suppresses bone formation to decrease cortical bone mass, which may be mediated by a decreased expression of PTH receptors in osteocytes.

Body weight and bone/calcium metabolism. Response of bone metabolism after bariatric surgery.

While bariatric surgery is an effective treatment for severe obesity, these procedures may have unfavorable effects on bone and mineral metabolism. The most pronounced abnormalities are disorders of calcium/vitamin D metabolism, bone loss, as well as increased risk of bone fracture. These changes that occur after surgery vary by procedure type. Proposed mechanisms include skeletal unloading, malabsorption, secondary hyperparathyroidism and changes in gut hormones. This review explores bone response to bariatric surgery, potential mechanisms for these changes.