Anemia of immobility: caused by adipocyte accumulation in bone marrow

Musculoskeletal perturbations of deep space radiation: Assessment using a Gateway MRI

Human space exploration expansion from Low-Earth Orbit to deep space is accelerating the need to monitor and address the known health concerns related to deep space radiation. The human musculoskeletal system is vulnerable to these risks (alongside microgravity) and its health reflects the well-being of other body systems. Multiparametric magnetic resonance imaging (MRI) is an important approach for assessing temporal physiological changes in the musculoskeletal system. We propose that ultra-low-field MRI provides an optimal low Size Weight and Power (SwaP) solution for non-invasively monitoring muscle and bone changes on the planned Gateway lunar space station. Our proposed ultra-low-field Gateway MRI meets low SWaP design specifications mandated by limited room in the lunar space station. This review summarizes the current state of our knowledge on musculoskeletal consequences of spaceflight, especially with respect to radiation, and then elaborates how MRI can be used to monitor the deleterious effects of space travel and the efficacy of putative countermeasures. We argue that an ultra-low-field MRI in cis-lunar space on the Gateway can provide valuable research and medical insights into the effects of deep space radiation exposure on astronauts. Such an MRI would also allow the development of imaging protocols that would facilitate Earth-bound teams to monitor space personnel musculoskeletal changes during future interplanetary spaceflight. It will especially have a role in monitoring countermeasures, such as the use of melanin, in protecting space explorers.

Metformin increases bone marrow adipose tissue by promoting mesenchymal stromal cells apoptosis

Bone marrow adipose tissue (MAT) has the potential to exert both local and systemic effects on metabolic homeostasis. As a first-line drug used to treat type 2 diabetes mellitus, metformin has conflicting effects on MAT and bone marrow mesenchymal stem cell (BM-MSC) differentiation. Through a series of experiments in vivo and in vitro, we found that except improving the glucose and lipid metabolism disorder in ob/ob mice, 200 mg/kg metformin increased MAT in mice tibia, and prompted osteogenic genes (RunX2, OPN, OCN) and lipogenic genes (Ppar-γ, Cebpα, Scd1) expression in mice bone marrow. However, metformin promoted osteogenesis and inhibited lipogenesis of MSC in vitro, which is inconsistent with the results in vivo. Given MAT being considered the "filler" of the space after the apoptosis of bone marrow stroma, the effect of metformin on MSC apoptosis was examined. We discovered that metformin induces MSC apoptosis in vivo and in vitro. Therefore, we speculated that the increased MAT in mice tibia may be attributed to the filling of adipose tissue after apoptosis of bone marrow stromal cells induced by metformin. The increased MAT may be involved in the regulation of metformin on glucose, lipid, and bone metabolism in diabetic mice, providing a new way to understand the metabolic regulation of metformin. While increased MAT-associated insulin resistance and metabolic disorders may account for the poorer clinical benefits in patients with intensive glucose control.

Factors associated with mobility decrease leading to disability: a cross-sectional nationwide study in Japan, with results from 8681 adults aged 20-89 years

Background

Mobility decrease leading to disability can gradually develop during early life, however, its related factors are not well clarified. Therefore, we investigate the related factors of mobility decrease at various levels, using nationwide data in Japan.

Methods

In total, 8681 independent community dwellers aged 20-89 years were analysed (average age, 51.6 years; 58.5% women). Three stages of mobility decrease were based on the locomotive syndrome risk test: Stage 1, emerging; Stage 2, progressing; Stage 3, progressed to restrict social engagement. Age was analysed using a simple quadratic function model.

Results

The prevalence of Stages 1-3 was 31.6% (n = 2746), 5.8% (n = 504), and 3.2% (n = 278), respectively. On the multivariable logistic regression, increased age in participants aged ≥40 years (stage 1: odds ratio[OR] 1.05-1.20, stage 2: OR 1.04-1.22, stage 3: OR 1.05-1.22), female (stage 1: OR 2.28, 95% confidence interval [CI] 1.99-2.61, stage 2: OR 2.40, 95% CI 1.77-3.25, stage 3: OR 1.80, 95% CI 1.19-2.72), overweight status (stage 1: OR 1.56, 95% CI 1.34-1.82, stage 2: OR 3.19, 95% CI 2.38-4.27, stage 3: OR 2.87, 95% CI 1.90-4.32), hypertension (stage 1: OR 1.20, 95% CI 1.01-1.41, stage 2: OR 1.99, 95% CI 1.49-2.64, stage 3: OR 2.10, 95% CI 1.44-3.05), and diabetes mellitus (stage 1: OR 1.62, 95% CI 1.17-2.24, stage 2: OR 1.57, 95% CI 0.93-2.66, stage 3: OR 2.10, 95% CI 1.13-3.90) were positively associated. The frequency of physical activity/sports, even a few per month, was inversely associated with all stages (stage 1: OR 0.59-0.72, stage 2: OR 0.50-0.67, stage 3: 0.36-0.53). A one-year increase in age had a stronger impact on mobility decrease in older adults than in younger ones. Increased age in participants aged < 40 years and smoking were associated with Stage 1, while intake of various foods was inversely associated with Stages 1 and 2.

Conclusion

Increased age (< 40 years) was associated with emerging mobility decrease, while that (≥ 40 years) was associated with any levels of mobility decrease. Female, lifestyle habits, including physical activities and overweight status, were associated with mobility decrease at every level.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-021-02600-4.

Six degrees head-down tilt bed rest caused low-grade hemolysis: a prospective randomized clinical trial

This study aimed to measure hemolysis before, during and after 60 days of the ground-based spaceflight analog bed rest and the effect of a nutritional intervention through a prospective randomized clinical trial. Twenty male participants were hospitalized for 88 days comprised of 14 days of ambulatory baseline, 60 days of 6° head-down tilt bed rest and 14 days of reambulation. Ten participants each received a control diet or daily polyphenol associated with omega-3, vitamin E, and selenium supplements. The primary outcome was endogenous carbon monoxide (CO) elimination measured by gas chromatography. Hemolysis was also measured with serial bilirubin, iron, transferrin saturation blood levels and serial 3-day stool collections were used to measure urobilinoid excretion using photometry. Total hemoglobin mass (tHb) was measured using CO-rebreathing. CO elimination increased after 5, 11, 30, and 57 days of bed rest: +289 ppb (95% CI 101-477 ppb; p = 0.004), +253 ppb (78-427 ppb; p = 0.007), +193 ppb (89-298 ppb; p = 0.001) and +858 ppb (670-1046 ppb; p < 0.000), respectively, compared to baseline. Bilirubin increased after 20 and 49 days of bed rest +0.8 mg/l (p = 0.013) and +1.1 mg/l (p = 0.012), respectively; and iron increased after 20 days of bed rest +10.5 µg/dl (p = 0.032). The nutritional intervention did not change CO elimination. THb was lower after 60 days of bed rest -0.9 g/kg (p = 0.001). Bed rest enhanced hemolysis as measured through all three by-products of heme oxygenase. Ongoing enhanced hemolysis over 60 days contributed to a 10% decrease in tHb mass. Modulation of red blood cell control towards increased hemolysis may be an important mechanism causing anemia in astronauts.

Phorbol 12-myristate 13-acetate (PMA) suppresses high Ca2+-enhanced adipogenesis in bone marrow stromal cells

We have previously reported that increased extracellular and intracellular Ca2+ lead to adipocyte accumulation in bone marrow stromal cells (BMSCs). However, strategies to suppress high Ca2+-enhanced adipocyte accumulation have not been reported. We examined the effects of the diacylglycerol analog phorbol 12-myristate 13-acetate (PMA) on proliferation and adipogenesis of mouse primary BMSCs. We used 9 mM CaCl2 and 100 nM ionomycin to increase extracellular Ca2+ and intracellular Ca2+, respectively. PMA suppressed the expression of both C/EBPα and PPARγ under normal adipogenesis, adipogenesis + CaCl2, and adipogenesis + ionomycin conditions. PMA enhanced proliferation under normal adipogenesis conditions but suppressed proliferation under adipogenesis + CaCl2 and adipogenesis + ionomycin conditions. PMA did not affect the accumulation of adipocytes under normal adipogenesis conditions but suppressed adipocyte accumulation under adipogenesis + CaCl2 and adipogenesis + ionomycin conditions. These results suggest that the PMA-dependent pathway is an important signaling pathway to suppress high Ca2+-enhanced adipocyte accumulation.

Specific Modulation of Vertebral Marrow Adipose Tissue by Physical Activity

Marrow adipose tissue (MAT) accumulation with normal aging impacts the bone, hemopoiesis, and metabolic pathways. We investigated whether exercise was associated with lower MAT, as measured by vertebral marrow fat fraction (VFF) on magnetic resonance imaging. A total of 101 healthy individuals (54 females) aged 25 to 35 years without spine or bone disease but with distinct exercise histories were studied. Long-distance runners (67 km/wk, n = 25) exhibited lower mean lumbar VFF (27.9% [8.6%] versus 33.5% [6.0%]; p = 0.0048) than non-sporting referents (n = 24). In habitual joggers (28 km/wk, n = 30), mean lumbar VFF was 31.3% (9.0%) (p = 0.22 versus referents) and 6.0 percentage points lower than referents at vertebrae T₁₀ , T₁₁ , and T₁₂ (p ≤ 0.023). High-volume road cycling (275 km/wk, n = 22) did not impact VFF. 3D accelerations corresponding to faster walking, slow jogging, and high-impact activities correlated with lower VFF, whereas low-impact activities and sedentary time correlated with higher mean lumbar VFF (all p ≤ 0.05). Given an estimated adipose bone marrow conversion of 7% per decade of life, long distance runners, with 5.6 percentage points lower VFF, showed an estimated 8-year younger vertebral marrow adipose tissue phenotype. Regression analysis showed a 0.7 percentage point reduction in mean lumbar VFF with every 9.4 km/wk run (p = 0.002). This study presents the first evidence in humans or animals that specific volumes and types of exercise may influence the age-determined adipose marrow conversion and result in low MAT. These results identify a potentially modifiable risk factor for prevalent chronic conditions related to bone metabolism, hemopoietic production, and other metabolic functions with potential global health applications. © 2017 American Society for Bone and Mineral Research.

Bone Marrow Fat and Hematopoiesis

Bone marrow fat cells comprise the largest population of cells in the bone marrow cavity, a characteristic that has attracted the attention of scholars from different disciplines. The perception that bone marrow adipocytes are "inert space fillers" has been broken, and currently, bone marrow fat is unanimously considered to be the third largest fat depot, after subcutaneous fat and visceral fat. Bone marrow fat (BMF) acts as a metabolically active organ and plays an active role in energy storage, endocrine function, bone metabolism, and the bone metastasis of tumors. Bone marrow adipocytes (BMAs), as a component of the bone marrow microenvironment, influence hematopoiesis through direct contact with cells and the secretion of adipocyte-derived factors. They also influence the progression of hematologic diseases such as leukemia, multiple myeloma, and aplastic anemia, and may be a novel target when exploring treatments for related diseases in the future. Based on currently available data, this review describes the role of BMF in hematopoiesis as well as in the development of hematologic diseases.

Mesenchymal Stem Cell Benefits Observed in Bone Marrow Failure and Acquired Aplastic Anemia

Acquired aplastic anemia (AA) is a type of bone marrow failure (BMF) syndrome characterized by partial or total bone marrow (BM) destruction resulting in peripheral blood (PB) pancytopenia, which is the reduction in the number of red blood cells (RBC) and white blood cells (WBC), as well as platelets (PLT). The first-line treatment option of AA is given by hematopoietic stem cell (HSCs) transplant and/or immunosuppressive (IS) drug administration. Some patients did not respond to the treatment and remain pancytopenic following IS drugs. The studies are in progress to test the efficacy of adoptive cellular therapies as mesenchymal stem cells (MSCs), which confer low immunogenicity and are reliable allogeneic transplants in refractory severe aplastic anemia (SAA) cases. Moreover, bone marrow stromal cells (BMSC) constitute an essential component of the hematopoietic niche, responsible for stimulating and enhancing the proliferation of HSCs by secreting regulatory molecules and cytokines, providing stimulus to natural BM microenvironment for hematopoiesis. This review summarizes scientific evidences of the hematopoiesis improvements after MSC transplant, observed in acquired AA/BMF animal models as well as in patients with acquired AA. Additionally, we discuss the direct and indirect contribution of MSCs to the pathogenesis of acquired AA.

The effects of knee immobilization on marrow adipocyte hyperplasia and hypertrophy at the proximal rat tibia epiphysis

Marrow adipose deposition is observed during aging and in association with extended periods of immobility. The objective of this study was to determine the contribution of adipocyte hypertrophy and hyperplasia to bone marrow fat deposition induced by immobilization of the rat knee joint for 2, 4, 16 or 32 weeks. Histomorphometric analyses compared immobilized to sham-operated proximal tibia from age and gender matched rats to assess the contribution of aging and duration of immobilization on the number and size of marrow adipocytes. Results indicated that marrow adipose tissue increased with the duration of immobilization and was significant larger at 16 weeks compared to the sham-operated group (0.09956±0.13276mm² vs 0.01990±0.01100mm², p=0.047). The marrow adipose tissue was characterized by hyperplasia of adipocytes with a smaller average size after 2 and 4 weeks of immobilization (at 2 weeks hyperplasia: 68.86±33.62 vs 43.57±24.47 adipocytes/mm², p=0.048; at 4 weeks hypotrophy: 0.00036±0.00019 vs 0.00046±0.00023mm², p=0.027), and by adipocyte hypertrophy after 16 weeks of immobilization (0.00083±0.00049 vs 0.00046±0.00028mm², p=0.027) compared to sham-operated. Both immobilized and sham-operated groups showed marrow adipose conversion with age; immobilized (p=0.008; sham: p=0.003). Overall, fat deposition in the bone marrow of the proximal rat tibia epiphysis and induced by knee joint immobilization was characterized by hyperplasia of small adipocytes in the early phase and by adipocyte hypertrophy in the later phase. Mediators of marrow fat deposition after immobilization and preventive countermeasures need to be investigated.

High extracellular Ca2+ enhances the adipocyte accumulation of bone marrow stromal cells through a decrease in cAMP

Bone marrow stromal cells (BMSCs) are common progenitors of both adipocytes and osteoblasts. We recently suggested that increased [Ca²⁺]_o caused by bone resorption might accelerate adipocyte accumulation in response to treatment with both insulin and dexamethasone. In this study, we investigated the mechanism by which high [Ca²⁺]_o enhances adipocyte accumulation. We used primary mouse BMSCs and evaluated the levels of adipocyte accumulation by measuring Oil Red O staining. CaSR agonists (both Ca²⁺ and Sr²⁺) enhanced the accumulation of adipocytes among BMSCs in response to treatment with both insulin and dexamethasone. We showed that high [Ca²⁺]_o decreases the concentration of cAMP using ELISA. Real-time RT-PCR revealed that increasing the intracellular concentration of cAMP (both chemical inducer (1μM forskolin and 200nM IBMX) and a cAMP analog (10μM pCPT-cAMP)) suppressed the expression of PPARγ and C/EBPα. In addition, forskolin, IBMX, and pCPT-cAMP inhibited the enhancement in adipocyte accumulation under high [Ca²⁺]_o in BMSCs. However, this inhibited effect was not observed in BMSCs that were cultured in a basal concentration of [Ca²⁺]_o. We next observed that the accumulation of adipocytes in the of bone marrow of middle-aged mice (25-40 weeks old) is higher than that of young mice (6 weeks old) based on micro CT. ELISA results revealed that the concentration of cAMP in the bone marrow mononuclear cells of middle-aged mice is lower than that of young mice. These data suggest that increased [Ca²⁺]_o caused by bone resorption might accelerate adipocyte accumulation through CaSR following a decrease in cAMP.

Anti-adipogenic effects of sesamol on human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) from adult bone marrow are able to differentiate into adipocytes, osteoblasts, chondrocytes and neuronal cells. Adipocytes in bone marrow are primarily responsible for the maintenance of bone structure by maintaining cell number balance with other stromal cells. However, the number of adipocytes in the bone marrow increases with age, leading to an imbalance of the bone marrow microenvironment, which results in a disruption of bone structure. In addition, the excessive number of adipocytes in bone marrow can cause diseases, such as osteoporosis or anemia. In this study, we investigated the effect of sesamol, a major natural phenolic compound of sesame oil, on the adipogenic differentiation of hMSCs. Numerous studies have reported the anti-oxidant property of sesamol, but its effect on cell differentiation has not yet been shown. We first found that sesamol treatment during adipogenic differentiation of hMSCs reduced intracellular lipid accumulation, which was unrelated to lipolysis. Interestingly, sesamol diminished the expression of genes responsible for adipogenesis, but increased the expression of osteogenic genes. In addition, sesamol decreased the expression of genes necessary for adipocyte maturation without affecting the expression of hMSC-specific genes. Studies concerning intracellular signaling in hMSCs showed that the extracellular signal-regulated kinase 1/2 (ERK1/2) was decreased by sesamol, which was similar with the effect of an ERK1/2 inhibitor. Overall, this study demonstrates that sesamol can attenuate the adipogenic differentiation of hMSCs without affecting its characteristics through the inhibition of ERK1/2 pathway. Herein, this study reports for the first time the effect of sesamol on hMSC differentiation and suggests the possibility of using sesamol as a therapeutic agent to treat intraosseous disruption triggered by the excessive adipogenesis of hMSCs.

Influence of early zoledronic acid administration on bone marrow fat in ovariectomized rats

Although the primary target cell of bisphosphonates is the osteoclast, increasing attention is being given to other effector cells influenced by bisphosphonates, such as osteoblasts and marrow adipocytes. Early zoledronic acid (ZA) treatment to ovariectomized (OVX) rats has been found to fully preserve bone microarchitecture over time. However, little is known regarding the influence of ZA on marrow adipogenesis. The purpose of this study was to monitor the ability of early administration of ZA in restoring marrow adiposity in an estrogen-deficient rat model. Thirty female Sprague-Dawley rats were randomly divided into sham-operated (SHAM), OVX + vehicle, and OVX + ZA groups (n=10/group). Dual-energy x-ray absorptiometry and water/fat magnetic resonance imaging were performed at baseline, 6 weeks, and 12 weeks after treatment to assess bone mineral density and marrow fat fraction. Serum biochemical markers, bone remodeling, and marrow adipocyte parameters were analyzed using biochemistry, histomorphometry, and histopathology, respectively. The expression levels of osteoblast, adipocyte, and osteoclast-related genes in bone marrow were assessed using RT-PCR. The OVX rats showed marked bone loss, first detected at 12 weeks, but estrogen deficiency resulted in a remarked increase in marrow fat fraction, first detected at 6 weeks compared with the SHAM rats (all P < .001). Similarly, the OVX rats had a substantially larger percent adipocyte area (+163.0%), mean diameter (+29.5%), and higher density (+57.3%) relative to the SHAM rats. Bone histomorphometry, levels of osteoclast-related gene expression, and a serum resorption marker confirmed that ZA significantly suppressed bone resorption activities. Furthermore, ZA treatment returned adipocyte-related gene expression and marrow adipocyte parameters toward SHAM levels. These data suggest that a single dose of early ZA treatment acts to reverse marrow adipogenesis occurring during estrogen deficiency, which may contribute to its capacity to reduce bone loss.

Diet-induced obesity modulates epigenetic responses to ionizing radiation in mice

Both exposure to ionizing radiation and obesity have been associated with various pathologies including cancer. There is a crucial need in better understanding the interactions between ionizing radiation effects (especially at low doses) and other risk factors, such as obesity. In order to evaluate radiation responses in obese animals, C3H and C57BL/6J mice fed a control normal fat or a high fat (HF) diet were exposed to fractionated doses of X-rays (0.75 Gy ×4). Bone marrow micronucleus assays did not suggest a modulation of radiation-induced genotoxicity by HF diet. Using MSP, we observed that the promoters of p16 and Dapk genes were methylated in the livers of C57BL/6J mice fed a HF diet (irradiated and non-irradiated); Mgmt promoter was methylated in irradiated and/or HF diet-fed mice. In addition, methylation PCR arrays identified Ep300 and Socs1 (whose promoters exhibited higher methylation levels in non-irradiated HF diet-fed mice) as potential targets for further studies. We then compared microRNA regulations after radiation exposure in the livers of C57BL/6J mice fed a normal or an HF diet, using microRNA arrays. Interestingly, radiation-triggered microRNA regulations observed in normal mice were not observed in obese mice. miR-466e was upregulated in non-irradiated obese mice. In vitro free fatty acid (palmitic acid, oleic acid) administration sensitized AML12 mouse liver cells to ionizing radiation, but the inhibition of miR-466e counteracted this radio-sensitization, suggesting that the modulation of radiation responses by diet-induced obesity might involve miR-466e expression. All together, our results suggested the existence of dietary effects on radiation responses (especially epigenetic regulations) in mice, possibly in relationship with obesity-induced chronic oxidative stress.

Mechanisms of palmitate-induced cell death in human osteoblasts

Lipotoxicity is an overload of lipids in non-adipose tissues that affects function and induces cell death. Lipotoxicity has been demonstrated in bone cells in vitro using osteoblasts and adipocytes in coculture. In this condition, lipotoxicity was induced by high levels of saturated fatty acids (mostly palmitate) secreted by cultured adipocytes acting in a paracrine manner. In the present study, we aimed to identify the underlying mechanisms of lipotoxicity in human osteoblasts. Palmitate induced autophagy in cultured osteoblasts, which was preceded by the activation of autophagosomes that surround palmitate droplets. Palmitate also induced apoptosis though the activation of the Fas/Jun kinase (JNK) apoptotic pathway. In addition, osteoblasts could be protected from lipotoxicity by inhibiting autophagy with the phosphoinositide kinase inhibitor 3-methyladenine or by inhibiting apoptosis with the JNK inhibitor SP600125. In summary, we have identified two major molecular mechanisms of lipotoxicity in osteoblasts and in doing so we have identified a new potential therapeutic approach to prevent osteoblast dysfunction and death, which are common features of age-related bone loss and osteoporosis.

Determinants of bone marrow adiposity: the modulation of peroxisome proliferator-activated receptor-γ2 activity as a central mechanism

Although the presence of adipocytes in the bone marrow is a normal physiological phenomenon, the role of these cells in bone homeostasis and during pathological states has not yet been fully delineated. As osteoblasts and adipocytes originate from a common progenitor, with an inverse relationship existing between osteoblastogenesis and adipogenesis, bone marrow adiposity often negatively correlates with osteoblast number and bone mineral density. Bone adiposity can be affected by several physiological and pathophysiological factors, with abnormal, elevated marrow fat resulting in a pathological state. This review focuses on the regulation of bone adiposity by physiological factors, including aging, mechanical loading and growth factor expression, as well as the pathophysiological factors, including diseases such as anorexia nervosa and dyslipidemia, and pharmacological agents such as thiazolidinediones and statins. Although these factors regulate bone marrow adiposity via a plethora of different intracellular signaling pathways, these diverse pathways often converge on the modulation of the expression and/or activity of the pro-adipogenic transcription factor peroxisome proliferator-activated receptor (PPAR)-γ2, suggesting that any factor that affects PPAR-γ2 may have an impact on the fat content of bone.

Hematopoietic recovery following chemotherapy is improved by BADGE-induced inhibition of adipogenesis

This study was designed to investigate the role of increased adipocytes in the bone marrow (BM) niche induced by high-dose chemotherapy in hematopoietic recovery. Arabinosylcytosine (Ara-C) was administered to adult C57BL/6J mice to induce adipogenesis in the BM. We investigated the effects of adipogenesis on hematopoietic recovery following chemotherapy, using the peroxisome proliferator-activated receptor gamma inhibitor, bisphenol A diglycidyl ether (BADGE). Adipocyte hyperplasia could be induced by Ara-C treatment in BM and inhibited by BADGE. The accelerated recovery of leukocyte counts, increased colony forming units, and a higher proportion of Ki67(+)CD45(+) BM cells and Ki67(+)Lin(-)Sca1(+)c-kit(+) hematopoietic stem cells were observed in the long bone marrow of adipocyte-inhibited mice, as well as an increase in the number of CD45(+) BM cells in the tail fatty marrow compared to controls. Adipocytes participated in creating a distinctive niche for hematopoietic cells. In addition, lower expression of stromal cell-derived factor-1α and hypoxia-inducible factor-1 alpha were detected in the BADGE-treated group. These results indicate that hematopoietic recovery is improved following chemotherapy in adipogenesis-inhibited mice. In addition, adipocytes may create an individual niche that affects the proliferation and migration of hematopoietic cells in vitro and in vivo.

New insights into osteoporosis: the bone-fat connection

Osteoporosis and obesity are chronic disorders that are both increasing in prevalence. The pathophysiology of these conditions is multifactorial and includes genetic, environmental and hormonal determinants. Although it has long been considered that these are distinct disorders rarely found in the same individual, emerging evidence from basic and clinical studies support an important interaction between adipose tissue and the skeleton. It is proposed that adiposity may influence bone remodelling through three mechanisms: (i) secretion of cytokines that directly target bone, (ii) production of adipokines that influence the central nervous system thereby changing sympathetic impulses to bone and (iii) paracrine influences on adjacent skeletal cells. Here we focus on the current understanding of bone-fat interactions and the clinical implications of recent studies linking obesity to osteoporosis.

Effects of exercise training on red blood cell production: implications for anemia

Exercise training can increase total Hb and red cell mass, which enhances oxygen-carrying capacity. The possible underlying mechanisms are proposed to come mainly from bone marrow, including stimulated erythropoiesis with hyperplasia of the hematopoietic bone marrow, improvement of the hematopoietic microenvironment induced by exercise training, and hormone- and cytokine-accelerated erythropoiesis. Anemia is one of the most common medical conditions in chronic disease. The effects of exercise training on counteracting anemia have been explored and evaluated. The results of the research available to date are controversial, and it seems that significant methodological limitations exist. However, exercise training might be a promising, additional, safe and economical method to help improve anemia. There is a need for further investigation into the effects of and guidelines for exercise interventions (especially strength training) in this population of patients, particularly among cancer patients who are undergoing or have undergone chemotherapy or radiation treatments. As the available data are limited, additional research to uncover the underlying mechanisms associated with the effects of exercise training on anemia is clearly warranted.

Effects of resistance training on biomarkers of bone formation and association with red blood cell variables

We previously showed that resistance training significantly increased the red blood cell count (RBC) and hematocrit (Hct) and decreased the mean cell hemoglobin concentration (MCHC) in physically inactive men. Since the enhanced hematopoiesis may result, at least partly, from bone metabolism, the purpose of this study was to further investigate the effect of resistance training on serum bone-specific alkaline phosphatase activity (B-ALP), a biomarker of bone formation, and focus on the relationship between the change in B-ALP from baseline to 20-week follow-up and the corresponding changes in RBC, Hct and MCHC. Seventy-four men aged 20-45 years were randomly assigned to training and control groups. The training group underwent a 20-week progressive resistance training. Fasting blood samples were analyzed for serum B-ALP at baseline, and at 10-week and 20-week follow-up. B-ALP in the control group exhibited no significant change. In contrast, the training group increased its B-ALP from baseline at 10-week and 20-week follow-up (both P<0.01 compared to control group). Within the training group, B-ALP was elevated at 10-week and 20-week follow-up when compared to baseline (both P<0.001). A significant correlation was found between change in B-ALP from baseline to 20-week follow-up and the corresponding changes in RBC, Hct and MCHC in the training group (r=0.49, P<0.01; r=0.56, P<0.01, and r = -0.38, P<0.05, respectively). We concluded that resistance training increased biomarkers of bone formation, which had association with RBC turnover. Adaptive changes of bone metabolism induced by resistance training might facilitate erythropoiesis.

Bed rest in health and critical illness: a body systems approach

Bed rest is a common intervention for critically ill adults. Associated with both benefits and adverse effects, bed rest is undergoing increasing scrutiny as a therapeutic option in the intensive care unit. Bed rest has molecular and systemic effects, ultimately affecting functional outcomes in healthy individuals as well as in those with acute and critical illnesses. Using empirical sources, the purpose of this article was to describe the consequences of bed rest and immobility, especially consequences with implications for critically ill adults in the intensive care unit. This review uses body systems to cluster classic and current results of bed rest studies, beginning with cardiovascular and including pulmonary, renal, skin, nervous, immune, gastrointestinal/ metabolic, and skeletal systems. It concludes with effects on muscles, a system profoundly affected by immobility and bed rest.

Adipose-immune interactions during obesity and caloric restriction: reciprocal mechanisms regulating immunity and health span

Increasing evidence suggests a tight coupling of metabolic and immune systems. This cross-talk mediated by neuroendocrine peptides as well as numerous cytokines and chemokines is believed to be responsible for integrating energy balance to immune function. These neuroendocrine-immune interactions are heightened during the state of chronic positive energy balance, as seen during obesity, and negative energy balance caused by caloric restriction (CR). Emerging evidence suggests that obesity may be associated with an immunodeficient state and chronic inflammation, which contribute to an increased risk of premature death. The direct interactions between expanded leukocyte populations within the adipose tissue during obesity and an increased number of adipocytes within an aging lymphoid microenvironment may constitute an important adaptive or pathological response as a result of change in energy balance. In stark contrast to obesity, CR causes negative energy balance and robustly prolongs a healthy lifespan in all of the species studied to date. Therefore, the endogenous neuroendocrine-metabolic sensors elevated or suppressed as a result of changes in energy balance may offer an important mechanism in understanding the antiaging and potential immune-enhancing nature of CR. Ghrelin, one such sensor of negative energy balance, is reduced during obesity and increased by CR. Ghrelin also regulates immune function by reducing proinflammatory cytokines and promotes thymopoiesis during aging and thus, may be a new CR mimetic target. The identification of immune effects and molecular pathways used by such orexigenic metabolic factors could offer potentially novel approaches to enhance immunity and increase healthy lifespan.