Scavenger receptor of class B expressed by osteoblastic cells are implicated in the uptake of cholesteryl ester and estradiol from LDL and HDL3

RETRACTED: Deletion of the scavenger receptor Scarb1 in myeloid cells does not affect bone mass

The scavenger receptor class B member 1 (SR-B1 or Scarb1) is a glycosylated cell surface receptor for high density lipoproteins (HDL), oxidized low density lipoproteins (OxLDL), and phosphocholine-containing oxidized phospholipids (PC-OxPLs). Scarb1 is expressed in macrophages and has been shown to have both pro- and anti-atherogenic properties. It has been reported that global deletion of Scarb1 in mice leads to either high or low bone mass and that PC-OxPLs decrease osteoblastogenesis and increase osteoclastogenesis. PC-OxPLs decrease bone mass in 6-month-old mice and are critical pathogenetic factors in the bone loss caused by high fat diet or aging. We have investigated here whether Scarb1 expression in myeloid cells affects bone mass and whether PC-OxPLs exert their anti-osteogenic effects via activation of Scarb1 in macrophages. To this end, we generated mice with deletion of Scarb1 in LysM-Cre expressing cells and found that lack of Scarb1 did not affect bone mass in vivo. These results indicate that Scarb1 expression in cells of the myeloid/osteoclast lineage does not contribute to bone homeostasis. Based on this evidence, and earlier studies of ours showing that Scarb1 expression in osteoblasts does not affect bone mass, we conclude that Scarb1 is not an important mediator of the adverse effects on PC-OxPLs in osteoclasts or osteoblasts in 6-month-old mice.

Oxidative-Stress-Related Genes in Osteoporosis: A Systematic Review

Osteoporosis is characterized by a decline in bone mineral density (BMD) and increased fracture risk. Free radicals and antioxidant systems play a central role in bone remodeling. This study was conducted to illustrate the role of oxidative-stress-related genes in BMD and osteoporosis. A systematic review was performed following the PRISMA guidelines. The search was computed in PubMed, Web of Sciences, Scopus, EBSCO, and BVS from inception to November 1st, 2022. The risk of bias was evaluated using the Joanna Briggs Institute Critical Appraisal Checklist tool. A total of 427 potentially eligible articles exploring this search question were detected. After removing duplicates (n = 112) and excluding irrelevant manuscripts based on screenings of their titles and abstracts (n = 317), 19 articles were selected for full-text review. Finally, 14 original articles were included in this systematic review after we applied the exclusion and inclusion criteria. Data analyzed in this systematic review indicated that oxidative-stress-related genetic polymorphisms are associated with BMD at different skeletal sites in diverse populations, influencing the risk of osteoporosis or osteoporotic fracture. However, it is necessary to look deep into their association with bone metabolism to determine if the findings can be translated into the clinical management of osteoporosis and its progression.

Prevalence and Risk Factors of Low Bone Mineral Density in HIV/AIDS Patients: A Chinese Cross-Sectional Study

INTRODUCTION

Our study aimed to investigate the prevalence and risk factors of low bone mineral density (BMD) among HIV/AIDS patients in China.

METHODS

We performed a cross-sectional analysis of HIV-infected patients from October 2017 to August 2020. Demographic information, clinical data, and serum parameters were obtained. Univariable and multiple logistic regression analyses were performed.

RESULTS

A total of 1143 patients were included. In the ART-naive group, low BMD was diagnosed in 19.2% (117/608), including osteoporosis in 1.0% (6/608) and osteopenia in 18.3% (111/608). In the ART group, low BMD was diagnosed in 32.2% (231/717), including osteoporosis in 2.4% (17/717) and osteopenia in 29.8% (214/717). Using multivariate analysis, we identified age older than 50 years, body mass index < 18.5 kg/m2, and treatment based on tenofovir disoproxil fumarate as independent risk factors for low BMD. Low high-density lipoprotein cholesterol was a protective factor for low BMD. Among low BMD participants, the most common number of low BMD sites for a patient to have was 4 (33.6%, 117/348).

CONCLUSION

We confirmed a high prevalence of low BMD and osteoporosis in HIV/AIDS patients, and we identified age older than 50 years, low body mass index, and a treatment based on tenofovir disoproxil fumarate as risk factors for low BMD. Low high-density lipoprotein cholesterol had a protective effect against low BMD. Among low BMD patients, patients most commonly had 4 sites with low BMD, which has been associated with fracture risk. In addition, bone changes to L1 can present before low BMD diagnosis and may be a potentially useful indicator that low BMD is developing.

Deletion of the scavenger receptor Scarb1 in osteoblast progenitors does not affect bone mass

The scavenger receptor class B member 1 (SR-B1 or Scarb1) is a cell surface receptor for high density lipoproteins. It also binds oxidized low density lipoproteins and phosphocholine-containing oxidized phospholipids (PC-OxPL), which adversely affect bone homeostasis. Overexpression of a single chain form of the antigen-binding domain of E06 IgM-a natural antibody that recognizes PC-OxPL-increases trabecular and cortical bone mass in female and male mice by stimulating bone formation. We have previously reported that Scarb1 is the most abundant scavenger receptor for PC-OxPL in calvaria-derived osteoblastic cells. Additionally, bone marrow- and calvaria-derived osteoblasts from Scarb1 knockout mice (Scarb1 KO) are protected from the pro-apoptotic and anti-differentiating effects of OxPL. Previous skeletal analysis of Scarb1 KO mice has produced contradictory results, with some studies reporting elevated bone mass but another study reporting low bone mass. To clarify the role of Scarb1 in osteoblasts, we deleted Scarb1 specifically in cells of the osteoblast lineage using Osx1-Cre transgenic mice. We observed no difference in bone mineral density measured by DXA in either female or male Osx1-Cre;Scarb1fl/fl mice compared to wild type (WT), Osx1-Cre, or Scarb1fl/fl littermate controls. Additionally, microCT analysis of 6-month-old females and 7-month-old males did not detect any difference in trabecular or cortical bone mass between genotypes. These results indicate that expression of Scarb1 in cells of the osteoblast lineage does not play an important role in bone homeostasis and, therefore, it is not essential for the effects of PC-OxPL on these cells.

Positive association between high-density lipoprotein cholesterol and bone mineral density in U.S. adults: the NHANES 2011-2018

Background

Serum lipids are highly inheritable and play a major role in bone health. However, the relationship between high-density lipoprotein cholesterol (HDL-C) and bone mineral density (BMD) remains uncertain. The goal of this study was to see if there was a link between HDL-C levels and BMD in persons aged 20–59.

Methods

Multivariate logistic regression models were used to determine the link between HDL-C and lumbar BMD using data from the National Health and Nutrition Examination Survey (NHANES) 2011–2018. Generalized additive models and fitted smoothing curves were also used.

Results

The analysis included a total of 10,635 adults. After controlling for various variables, we discovered that HDL-C was positively linked with lumbar BMD. The favorable connection of HDL-C with lumbar BMD was maintained in subgroup analyses stratified by sex and race in women, but not in men, and in blacks, but not in whites. The relationship between HDL-C and lumbar BMD in men and whites was a U-shaped curve with the same inflection point: 0.98 mmol/L.

Conclusions

In people aged 20 to 59, our research discovered a positive relationship among HDL-C and lumbar BMD. Among males and whites, this relationship followed a U-shaped curve (inflection point: 0.98 mmol/L). HDL-C measurement might be used as a responsive biomarker for detecting osteoporosis early and guiding therapy.

Geniposide Ameliorated Dexamethasone-Induced Cholesterol Accumulation in Osteoblasts by Mediating the GLP-1R/ABCA1 Axis

Background: Overexposure to glucocorticoid (GC) produces various clinical complications, including osteoporosis (OP), dyslipidemia, and hypercholesterolemia. Geniposide (GEN) is a natural iridoid compound isolated from Eucommia ulmoides. Our previous study found that GEN could alleviate dexamethasone (DEX)-induced differentiation inhibition of MC3T3-E1 cells. However, whether GEN protected against Dex-induced cholesterol accumulation in osteoblasts was still unclear. Methods: DEX was used to induce rat OP. Micro-CT data was obtained. The ALP activity and mineralization were determined by the staining assays, and the total intracellular cholesterol was determined by the ELISA kits. The protein expression was detected by western blot. Results: GEN ameliorated Dex-induced micro-structure damages and cell differentiation inhibition in the bone trabecula in rats. In MC3T3-E1 cells, Dex enhanced the total intracellular cholesterol, which reduced the activity of cell proliferation and differentiation. Effectively, GEN decreased DEX-induced cholesterol accumulation, enhanced cell differentiation, and upregulated the expression of the GLP-1R/ABCA1 axis. In addition, inhibition of ABAC1 expression reversed the actions of GEN. Treatment with Exendin9-39, a GLP-1R inhibitor, could abrogate the protective activity of GEN. Conclusions: GEN ameliorated Dex-induced accumulation of cholesterol and inhibition of cell differentiation by mediating the GLP-1R/ABCA1 axis in MC3T3-E1 cells.

Accumulation of LDL/ox-LDL in the necrotic region participates in osteonecrosis of the femoral head: a pathological and in vitro study

Background

Osteonecrosis of the femoral head (ONFH) is a common but intractable disease that appears to involve lipid metabolic disorders. Although numerous studies have demonstrated that high blood levels of low-density lipoprotein (LDL) are closely associated with ONFH, there is limited evidence to explain the pathological role of LDL. Pathological and in vitro studies were performed to investigate the role of disordered metabolism of LDL and oxidized LDL (ox-LDL) in the femoral head in the pathology of ONFH.

Methods

Nineteen femoral head specimens from patients with ONFH were obtained for immunohistochemistry analysis. Murine long-bone osteocyte Y4 cells were used to study the effects of LDL/ox-LDL on cell viability, apoptosis, and metabolism process of LDL/ox-LDL in osteocytes in normoxic and hypoxic environments.

Results

In the pathological specimens, marked accumulation of LDL/ox-LDL was observed in osteocytes/lacunae of necrotic regions compared with healthy regions. In vitro studies showed that ox-LDL, rather than LDL, reduced the viability and enhanced apoptosis of osteocytes. Pathological sections indicated that the accumulation of ox-LDL was significantly associated with impaired blood supply. Exposure to a hypoxic environment appeared to be a key factor leading to LDL/ox-LDL accumulation by enhancing internalisation and oxidation of LDL in osteocytes.

Conclusions

The accumulation of LDL/ox-LDL in the necrotic region may contribute to the pathology of ONFH. These findings could provide new insights into the prevention and treatment of ONFH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01601-x.

Caspase-1 Inhibition Impacts the Formation of Chondrogenic Nodules, and the Expression of Markers Related to Osteogenic Differentiation and Lipid Metabolism

Caspase-1, as the main pro-inflammatory cysteine protease, was investigated mostly with respect to inflammation-related processes. Interestingly, caspase-1 was identified as being involved in lipid metabolism, which is extremely important for the proper differentiation of chondrocytes. Based on a screening investigation, general caspase inhibition impacts the expression of Cd36 in chondrocytes, the fatty acid translocase with a significant impact on lipid metabolism. However, the engagement of individual caspases in the effect has not yet been identified. Therefore, the hypothesis that caspase-1 might be a candidate here appears challenging. The primary aim of this study thus was to find out whether the inhibition of caspase-1 activity would affect Cd36 expression in a chondrogenic micromass model. The expression of Pparg, a regulator Cd36, was examined as well. In the caspase-1 inhibited samples, both molecules were significantly downregulated. Notably, in the treated group, the formation of the chondrogenic nodules was apparently disrupted, and the subcellular deposition of lipids and polysaccharides showed an abnormal pattern. To further investigate this observation, the samples were subjected to an osteogenic PCR array containing selected markers related to cartilage/bone cell differentiation. Among affected molecules, Bmp7 and Gdf10 showed a significantly increased expression, while Itgam, Mmp9, Vdr, and Rankl decreased. Notably, Rankl is a key marker in bone remodeling/homeostasis and thus is a target in several treatment strategies, including a variety of fatty acids, and is balanced by its decoy receptor Opg (osteoprotegerin). To evaluate the effect of Cd36 downregulation on Rankl and Opg, Cd36 silencing was performed using micromass cultures. After Cd36 silencing, the expression of Rankl was downregulated and Opg upregulated, which was an inverse effect to caspase-1 inhibition (and Cd36 upregulation). These results demonstrate new functions of caspase-1 in chondrocyte differentiation and lipid metabolism-related pathways. The effect on the Rankl/Opg ratio, critical for bone maintenance and pathology, including osteoarthritis, is particularly important here as well.

The atherogenic index of plasma is related to a degraded bone microarchitecture assessed by the trabecular bone score in postmenopausal women: The Camargo Cohort Study

OBJECTIVE

To assess the association between the atherogenic index of plasma (AIP) and the trabecular bone score (TBS) in postmenopausal women. Furthermore, to analyze its relationship with bone mineral density (BMD), and serum concentrations of 25OHD, PTH, and bone turnover markers.

STUDY DESIGN

Cross-sectional study nested in a population-based cohort of 1,367 postmenopausal women aged 44-94 years. Participants were classified according to TBS values (<1.230, between 1.230-1.310 and >1.310) and regarding a widely accepted cut-off point of ≥0.11 for AIP. We analyzed TBS, BMD, serum levels of 25OHD, PTH, P1NP, CTX, and clinical covariates. A multivariate analysis was performed to assess the adjusted association between AIP and TBS.

RESULTS

The mean age of participants was 63±10 years. Women with TBS values <1.230 were older, had greater BMI, greater prevalence of fractures after the age of 40 years, more years since menopause, higher values of AIP, and significantly lower levels of HDL-C, serum phosphate, and 25OHD. AIP values ≥0.11 were not associated with the presence of densitometric osteoporosis (OR=0.83, 95%CI 0.58-1.18; p = 0.30) but, in multivariate analysis, AIP values ≥0.11 were related to a degraded microarchitecture after controlling for age, BMI, smoking, diabetes status, ischemic heart disease, statin use, GFR, a fragility fracture at over 40 years of age and lumbar osteoporosis by DXA, with an adjusted OR=1.61 (95%CI 1.06-2.46; p = 0.009).

CONCLUSIONS

AIP is significantly and independently associated with a degraded bone microarchitecture as measured by TBS. In this sense, AIP might be a useful tool in the overall assessment of bone metabolism in postmenopausal women.

A Neutralizing Antibody Targeting Oxidized Phospholipids Promotes Bone Anabolism in Chow-Fed Young Adult Mice

Oxidized phospholipids containing phosphocholine (OxPL) are pro-inflammatory lipid peroxidation products that bind to scavenger receptors (SRs), such as Scarb1, and toll-like receptors (TLRs). Excessive OxPL, as found in oxidized low-density lipoprotein (OxLDL), overwhelm these defense mechanisms and become pathogenic in atherosclerosis, nonalcoholic steatohepatitis (NASH), and osteoporosis. We previously reported that the innate IgM natural antibody E06 binds to OxPL and neutralizes their deleterious effects; expression of the single-chain (scFv) form of the antigen-binding domain of E06 (E06-scFv) as a transgene increases trabecular bone in male mice. We show herein that E06-scFv increases trabecular and cortical bone in female and male mice by increasing bone formation and decreasing osteoblast apoptosis in vivo. Homozygous E06-scFv mice have higher bone mass than hemizygous, showing a dose effect of the transgene. To investigate how OxPL restrain bone formation under physiologic conditions, we measured the levels of SRs and TLRs that bind OxPL. We found that osteoblastic cells primarily express Scarb1. Moreover, OxLDL-induced apoptosis and reduced differentiation were prevented in bone marrow-derived or calvaria-derived osteoblasts from Scarb1 knockout mice. Because Scarb1-deficient mice are reported to have high bone mass, our results suggest that E06 may promote bone anabolism in healthy young mice, at least in part, by neutralizing OxPL, which in turn promote Scarb1-mediated apoptosis of osteoblasts or osteoblast precursors. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR)..

Wetting properties of blood lipid fractions on different titanium surfaces

Background

Blood is the first tissue contacting the implant surface and starting the biological interactions to enhance osseointegration and stimulate bone formation with the progenitor cytokines, chemokines, and growth factors. The coagulation cascade initiates the first step of osseointegration between implant and neighboring tissues. The wound healing may be inadequate unless the blood wets the implant surface properly. Wettability is one of the most important features of the implant surface while lipid level constitutes a milestone that may change the energy of blood, which determines its distribution on implant material. Thus, the aim of this study was to evaluate the effect of lipid component of blood as cholesterol and its treatment on their wetting behavior of titanium surfaces.

Methods

Five surface groups were formed including grade 4 titanium-machined, grade 4 titanium-SLA, grade 4 titanium-SLActive, Roxolid-SLA, and Roxolid-SLActive. In healthy, hyperlipidemic, and treatment situations, blood was taken from eight rabbits and dropped to the disc surfaces. Contact angles were measured between the blood samples and disc surfaces.

Results

A significant difference was found between both machined and SLActive surfaces, SLA and SLActive surfaces in the hyperlipidemic period, and only Roxolid-SLA and SLActive surfaces during the treatment period. When evaluated according to time, only grade 4-machined and Grade 4-SLA surfaces showed a significant difference.

Conclusions

Our findings indicated that each period has its own characteristics and showed the importance of cholesterol in blood structure on applicability of implant surfaces.

Fucoidan Inhibition of Osteosarcoma Cells Is Species and Molecular Weight Dependent

Fucoidan is a brown algae-derived polysaccharide having several biomedical applications. This study simultaneously compares the anti-cancer activities of crude fucoidans from Fucus vesiculosus and Sargassum filipendula, and effects of low (LMW, 10-50 kDa), medium (MMW, 50-100 kDa) and high (HMW, >100 kDa) molecular weight fractions of S. filipendula fucoidan against osteosarcoma cells. Glucose, fucose and acid levels were lower and sulphation was higher in F. vesiculosus crude fucoidan compared to S. filipendula crude fucoidan. MMW had the highest levels of sugars, acids and sulphation among molecular weight fractions. There was a dose-dependent drop in focal adhesion formation and proliferation of cells for all fucoidan-types, but F. vesiculosus fucoidan and HMW had the strongest effects. G1-phase arrest was induced by F. vesiculosus fucoidan, MMW and HMW, however F. vesiculosus fucoidan treatment also caused accumulation in the sub-G1-phase. Mitochondrial damage occurred for all fucoidan-types, however F. vesiculosus fucoidan led to mitochondrial fragmentation. Annexin V/PI, TUNEL and cytochrome c staining confirmed stress-induced apoptosis-like cell death for F. vesiculosus fucoidan and features of stress-induced necrosis-like cell death for S. filipendula fucoidans. There was also variation in penetrability of different fucoidans inside the cell. These differences in anti-cancer activity of fucoidans are applicable for osteosarcoma treatment.

Lipidomic architecture shared by subclinical markers of osteoporosis and atherosclerosis: The Cardiovascular Risk in Young Finns Study

BACKGROUND

Studies have shown that osteoporosis and atherosclerosis are comorbid conditions sharing common risk factors and pathophysiological mechanisms. Understanding these is crucial in order to develop shared methods for risk stratification, prevention, diagnosis and treatment. The aim of this study was to apply a system-level bioinformatics approach to lipidome-wide data in order to pinpoint the lipidomic architecture jointly associated with surrogate markers of these complex comorbid diseases.

SUBJECTS AND METHODS

The study was based on the Cardiovascular Risk in Young Finns Study cohort from the 2007 follow-up (n = 1494, aged 30-45 years, women: 57%). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to analyse the serum lipidome, involving 437 molecular lipid species. The subclinical osteoporotic markers included indices of bone mineral density and content, measured using peripheral quantitative computer tomography from the distal and shaft sites of both the tibia and the radius. The subclinical atherosclerotic markers included carotid and bulbus intima media thickness measured with high-resolution ultrasound. Weighted co-expression network analysis was performed to identify networks of densely interconnected lipid species (i.e. lipid modules) associated with subclinical markers of both osteoporosis and atherosclerosis. The levels of lipid species (lipid profiles) of each of the lipid modules were summarized by the first principal component termed as module eigenlipid. Then, Pearson's correlation (r) was calculated between the module eigenlipids and the markers. Lipid modules that were significantly and jointly correlated with subclinical markers of both osteoporosis and atherosclerosis were considered to be related to the comorbidities. The hypothesis that the eigenlipids and profiles of the constituent lipid species in the modules have joint effects on the markers was tested with multivariate analysis of variance (MANOVA).

RESULTS

Among twelve studied molecular lipid modules, we identified one module with 105 lipid species significantly and jointly associated with both subclinical markers of both osteoporosis (r = 0.24, p-value = 2 × 10^-20) and atherosclerosis (r = 0.16, p-value = 2 × 10^-10). The majority of the lipid species in this module belonged to the glycerolipid (n = 60), glycerophospholipid (n = 13) and sphingolipid (n = 29) classes. The module was also enriched with ceramides (n = 20), confirming their significance in cardiovascular outcomes and suggesting their joint role in the comorbidities. The top three of the 37 statistically significant (adjusted p-value < 0.05) lipid species jointly associated with subclinical markers of both osteoporosis and atherosclerosis within the module were all triacylglycerols (TAGs) - TAG(18:0/18:0/18:1) with an adjusted p-value of 8.6 × 10^-8, TAG(18:0/18:1/18:1) with an adjusted p-value of 3.7 × 10^-6, and TAG(16:0/18:0/18:1) with an adjusted p-value of 8.5 × 10^-6.

CONCLUSION

This study identified a novel lipid module associated with both surrogate markers of both subclinical osteoporosis and subclinical atherosclerosis. Alterations in the metabolism of the identified lipid module and, more specifically, the TAG related molecular lipids within the module may provide potential new biomarkers for testing the comorbidities, opening avenues for the emergence of dual-purpose prevention measures.

Dual Effects of Lipid Metabolism on Osteoblast Function

The skeleton is a dynamic and metabolically active organ with the capacity to influence whole body metabolism. This newly recognized function has propagated interest in the connection between bone health and metabolic dysfunction. Osteoblasts, the specialized mesenchymal cells responsible for the production of bone matrix and mineralization, rely on multiple fuel sources. The utilization of glucose by osteoblasts has long been a focus of research, however, lipids and their derivatives, are increasingly recognized as a vital energy source. Osteoblasts possess the necessary receptors and catabolic enzymes for internalization and utilization of circulating lipids. Disruption of these processes can impair osteoblast function, resulting in skeletal deficits while simultaneously altering whole body lipid homeostasis. This article provides an overview of the metabolism of postprandial and stored lipids and the osteoblast's ability to acquire and utilize these molecules. We focus on the requirement for fatty acid oxidation and the pathways regulating this function as well as the negative impact of dyslipidemia on the osteoblast and skeletal health. These findings provide key insights into the nuances of lipid metabolism in influencing skeletal homeostasis which are critical to appreciate the extent of the osteoblast's role in metabolic homeostasis.

Causal link between lipid profile and bone mineral density: A Mendelian randomization study

The level of serum lipids is associated with bone mineral density (BMD), an important skeletal trait. Yet the causality has not been determined. Here we performed a Mendelian randomization (MR) analysis to test potential causal links between BMD and lipid profile, i.e., low-density lipoprotein cholesterol (LDC-c), total cholesterol (TC), triglyceride (TG) and high-density lipoprotein cholesterol (HDL-c). We observed causal effect of LDL-c, TC and TG to BMD, and reversely the effect of BMD to HDL-c. We further explored the effect of body mass index (BMI) in these causalities and found that the effect of LDL-c, TC and TG to BMD is independent of BMI. Our findings provided useful information in the clinical relevance of blood lipids on BMD variation and osteoporosis risk.

oxLDL inhibits differentiation of mesenchymal stem cells into osteoblasts via the CD36 mediated suppression of Wnt signaling pathway

Bone abnormalities as a consequence of osteoblast deregulation are associated with several diseases such as diabetes and chronic kidney disease. Important role for oxidized low density lipoproteins (oxLDL) in the pathophysiology of bone disorders has been reported. However, little is known about the effects and mechanisms of oxLDL on the process of osteoblastogenesis in human mesenchymal stem cells (MSCs). We show that oxLDL concentrations of ~ 10-25 µg protein (0.43-1.0 µM MDA/mg protein) inhibited the differentiation of MSCs to osteoblasts. We demonstrate that the underlying mechanism entails the suppression of the Wnt signaling through the down-regulation of β-catenin. Further, we show the association of scavenger receptor CD36 with the receptors LRP5/6 and Frizzled in mediating the oxLDL effects on the differentiation of MSCs to pre-osteoblasts. Inhibiting CD36 restored osteoblasts differentiation in the presence of oxLDL. Our findings suggest that oxLDL interferes with the canonical Wnt signaling pathway in a CD36 dependent manner leading to an inhibition of osteoblastogenesis.

Physiologic and pathologic effects of dietary free fatty acids on cells of the joint

Fatty acids (FAs) are potent organic compounds that not only can be used as an energy source during nutrient deprivation but are also involved in several essential signaling cascades in cells. Therefore, a balanced intake of different dietary FAs is critical for the maintenance of cellular functions and tissue homeostasis. A diet with an imbalanced fat composition creates a risk for developing metabolic syndrome and various musculoskeletal diseases, including osteoarthritis (OA). In this review, we summarize the current state of knowledge and mechanistic insights regarding the role of dietary FAs, such as saturated FAs, omega-6 polyunsaturated FAs (PUFAs), and omega-3 PUFAs on joint inflammation and OA pathogeneses. In particular, we review how different types of dietary FAs and their derivatives distinctly affect a variety of cells within the joint, including chondrocytes, osteoblasts, osteoclasts, and synoviocytes. Understanding the molecular mechanisms underlying the effects of FAs on metabolic behavior, anabolic, and catabolic processes, as well as the inflammatory response of joint cells, may help identify therapeutic targets for the prevention of metabolic joint diseases.

Low density lipoprotein adsorption on a titanium surface and its effect on osteoblast behaviors

Objective: This study aims to investigate the adsorption of low density lipoprotein (LDL) on a titanium surface and to explore its effect on osteoblast behaviors. Materials and methods: LDL adsorption on a titanium surface was analyzed using LDL assay and X-ray photoelectron spectroscopy (XPS). Physical properties, including topography, surface roughness and wettability of a control smooth titanium surface and a LDL pre-adsorbed titanium surface, were assessed. Subsequently, the adhesion, proliferation and differentiation abilities of MC3T3-E1 cells (an osteoblast-like cell line) on the surfaces of control titanium and LDL pre-adsorbed titanium were investigated. Results: LDL assay and XPS confirmed LDL adsorption on the titanium surface. The maximum adsorption of LDL on the titanium surfaces was observed after 150 minutes of incubation. In comparison with the control smooth titanium surface, the roughness and hydrophilicity of the LDL pre-adsorbed titanium surface were significantly altered. Furthermore, in vitro studies demonstrated that LDL adsorption obviously attenuated the adhesion, proliferation and differentiation of MC3T3-E1 cells on the titanium surface. Conclusion: LDL could adsorb on a titanium surface. Meanwhile, LDL adsorption changed the characteristics of the titanium surface, which, in turn, negatively regulated osteoblast behaviors.

This study aims to investigate the adsorption of low density lipoprotein (LDL) on a titanium surface and to explore its effect on osteoblast behaviors.

Fatty acid metabolism by the osteoblast

The emergence of bone as an endocrine organ able to influence whole body metabolism, together with comorbid epidemics of obesity, diabetes, and osteoporosis, have prompted a renewed interest in the intermediary metabolism of the osteoblast. To date, most studies have focused on the utilization of glucose by this specialized cell, but the oxidation of fatty acids results in a larger energy yield. Osteoblasts express the requisite receptors and catabolic enzymes to take up and then metabolize fatty acids, which appears to be required during later stages of differentiation when the osteoblast is dedicated to matrix production and mineralization. In this article, we provide an overview of fatty acid β-oxidation and highlight studies demonstrating that the skeleton plays a significant role in the clearance of circulating lipoproteins and non-esterified fatty acids. Additionally, we review the requirement for long-chain fatty acid metabolism during post-natal bone development and the effects of anabolic stimuli on fatty acid utilization by osteoblasts. These recent findings may help to explain the skeletal manifestations of human diseases associated with impaired lipid metabolism while also providing additional insights into the metabolic requirements of skeletal homeostasis.

Oxidation-specific epitopes restrain bone formation

Atherosclerosis and osteoporosis are epidemiologically linked and oxidation specific epitopes (OSEs), such as phosphocholine (PC) of oxidized phospholipids (PC-OxPL) and malondialdehyde (MDA), are pathogenic in both. The proatherogenic effects of OSEs are opposed by innate immune antibodies. Here we show that high-fat diet (HFD)-induced bone loss is attenuated in mice expressing a single chain variable region fragment of the IgM E06 (E06-scFv) that neutralizes PC-OxPL, by increasing osteoblast number and stimulating bone formation. Similarly, HFD-induced bone loss is attenuated in mice expressing IK17-scFv, which neutralizes MDA. Notably, E06-scFv also increases bone mass in mice fed a normal diet. Moreover, the levels of anti-PC IgM decrease in aged mice. We conclude that OSEs, whether produced chronically or increased by HFD, restrain bone formation, and that diminished defense against OSEs may contribute to age-related bone loss. Anti-OSEs, therefore, may represent a novel therapeutic approach against osteoporosis and atherosclerosis simultaneously.

Synthetic lipoprotein as nano-material vehicle in the targeted drug delivery

High-density lipoprotein (HDL) and low-density lipoprotein (LDL), as human endogenous lipoprotein particles, have low toxicity, high selectivity, and good safety. They can avoid the recognition and clearance of human reticuloendothelial system. These synthetic lipoproteins (sLPs) have been attracted extensive attention as the nanovectors for tumor-targeted drug and gene delivery. Herein, recent advances in the field of anticancer based on these two lipid proteins and recombinant lipoproteins (rLPs) as target delivery vectors were analyzed and discussed.

Bone Cell Bioenergetics and Skeletal Energy Homeostasis

The rising incidence of metabolic diseases worldwide has prompted renewed interest in the study of intermediary metabolism and cellular bioenergetics. The application of modern biochemical methods for quantitating fuel substrate metabolism with advanced mouse genetic approaches has greatly increased understanding of the mechanisms that integrate energy metabolism in the whole organism. Examination of the intermediary metabolism of skeletal cells has been sparked by a series of unanticipated observations in genetically modified mice that suggest the existence of novel endocrine pathways through which bone cells communicate their energy status to other centers of metabolic control. The recognition of this expanded role of the skeleton has in turn led to new lines of inquiry directed at defining the fuel requirements and bioenergetic properties of bone cells. This article provides a comprehensive review of historical and contemporary studies on the metabolic properties of bone cells and the mechanisms that control energy substrate utilization and bioenergetics. Special attention is devoted to identifying gaps in our current understanding of this new area of skeletal biology that will require additional research to better define the physiological significance of skeletal cell bioenergetics in human health and disease.

Obesity-associated Breast Cancer: Analysis of risk factors

Several studies show that a significantly stronger association is obvious between increased body mass index (BMI) and higher breast cancer incidence. Furthermore, obese women are at higher risk of all-cause and breast cancer specific mortality when compared to non-obese women with breast cancer. In this context, increased levels of estrogens due to excessive aromatization activity of the adipose tissue, overexpression of pro-inflammatory cytokines, insulin resistance, hyperactivation of insulin-like growth factors (IGFs) pathways, adipocyte-derived adipokines, hypercholesterolemia and excessive oxidative stress contribute to the development of breast cancer in obese women. While higher breast cancer risk with hormone replacement therapy is particularly evident among lean women, in postmenopausal women who are not taking exogenous hormones, general obesity is a significant predictor for breast cancer. Moreover, increased plasma cholesterol leads to accelerated tumor formation and exacerbates their aggressiveness. In contrast to postmenopausal women, premenopausal women with high BMI are inversely associated with breast cancer risk. Nevertheless, life-style of women for breast cancer risk is regulated by avoiding the overweight and a high-fat diet. Estrogen-plus-progestin hormone therapy users for more than 5 years have elevated risks of both invasive ductal and lobular breast cancer. Additionally, these cases are more commonly node-positive and have a higher cancer-related mortality. Collectively, in this chapter, the impacts of obesity-related estrogen, cholesterol, saturated fatty acid, leptin and adiponectin concentrations, aromatase activity, leptin and insulin resistance on breast cancer patients are evaluated. Obesity-related prognostic factors of breast cancer also are discussed at molecular basis.

Isoflavone supplementation in postmenopausal women does not affect leukocyte LDL receptor and scavenger receptor CD36 expression: A double-blind, randomized, placebo-controlled trial

SCOPE

Isoflavones are discussed to improve serum lipoproteins and body composition and to reduce cardiovascular disease risk in postmenopausal women (PMW). LDL receptors (LDLR) and scavenger receptor CD36 (CD36) play a pivotal role in the regulation of plasma LDL-cholesterol concentrations (LDL-chol). We investigated the impact of isoflavones on the receptor expression of both receptors in leukocytes of PMW.

METHODS AND RESULTS

A randomized, double-blind, placebo-controlled trial in parallel design was conducted to assess the effects of an isoflavone-enriched soy extract (117.4 mg/day isoflavone aglycone equivalents) for 12 weeks on serum LDL-chol, LDLR, and CD36 expression on leukocytes in 170 healthy PMW. Baseline and after 12 weeks, blood lipid concentrations, anthropometric data and body composition were determined. Receptor expression on leukocytes was measured by means of flow cytometry. After the intervention, no significant differences were found for LDLR and CD36 expression on leukocytes. A significant increase of serum LDL-chol was shown for the isoflavone group (p = 0.03) after 12 weeks. Body fat content and VAT were not affected.

CONCLUSION

Isoflavone supplementation for 12 weeks did not change LDLR and CD36 expression on leukocytes of PMW and did not affect body fat content and visceral adipose tissue (VAT), but slightly increased serum LDL-chol.

Optimal serum cholesterol concentrations are associated with accelerated bone loss in African ancestry men

We tested if serum lipid and lipoprotein cholesterol levels are associated with longitudinal measures of bone mineral density (BMD) in 1289 African ancestry men. After 6 years of mean follow-up, men with clinically optimal levels of low-density lipoprotein (LDL), high-density lipoprotein (HDL), or triglycerides at baseline experienced the greatest BMD loss, independent of potential confounding factors (all p < 0.05).

INTRODUCTION

Studies of lipid and lipoprotein cholesterol associations with bone mineral density (BMD) and bone loss have been inconclusive, and longitudinal data are sparse. Therefore, the aim of this study was to test if fasting serum lipid and lipoprotein cholesterol levels are associated with areal and volumetric BMD and BMD change.

METHODS

We determined the association of serum triglycerides, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) cholesterol concentrations with cross-sectional and longitudinal (mean follow-up, 6.1 years) measures of BMD in a cohort of 1289 in African ancestry men (mean age, 56.4 years). Fasting serum triglycerides, HDL, and LDL were measured at baseline concurrent with BMD assessments. Dual-energy X-ray absorptiometry was used to quantify integral hip BMD, and peripheral quantitative computed tomography at the radius and tibia was used to quantify volumetric BMD. Men were categorized as optimal, borderline, or high risk for triglyceride, HDL, and LDL concentrations based on Adult Treatment Panel III guidelines.

RESULTS

Lower serum triglyceride or LDL and higher HDL concentrations were associated with lower trabecular BMD at baseline (all p < 0.05). Similarly, men classified as having optimal levels of LDL, HDL, or triglycerides at baseline experienced the greatest integral BMD loss at the hip and trabecular BMD loss at the tibia (all p < 0.05), independent of potential confounding factors.

CONCLUSIONS

We found that clinically optimal serum lipid and lipoprotein cholesterol concentrations were associated with accelerated bone loss among Afro-Caribbean men. Further studies are needed to better understand the mechanisms involved and potential clinical significance of these findings.

Apolipoprotein D Internalization Is a Basigin-dependent Mechanism

Apolipoprotein D (apoD), a member of the lipocalin family, is a 29-kDa secreted glycoprotein that binds and transports small lipophilic molecules. Expressed in several tissues, apoD is up-regulated under different stress stimuli and in a variety of pathologies. Numerous studies have revealed that overexpression of apoD led to neuroprotection in various mouse models of acute stress and neurodegeneration. This multifunctional protein is internalized in several cells types, but the specific internalization mechanism remains unknown. In this study, we demonstrate that the internalization of apoD involves a specific cell surface receptor in 293T cells, identified as the transmembrane glycoprotein basigin (BSG, CD147); more particularly, its low glycosylated form. Our results show that internalized apoD colocalizes with BSG into vesicular compartments. Down-regulation of BSG disrupted the internalization of apoD in cells. In contrast, overexpression of basigin in SH-5YSY cells, which poorly express BSG, restored the uptake of apoD. Cyclophilin A, a known ligand of BSG, competitively reduced apoD internalization, confirming that BSG is a key player in the apoD internalization process. In summary, our results demonstrate that basigin is very likely the apoD receptor and provide additional clues on the mechanisms involved in apoD-mediated functions, including neuroprotection.

Chrysin inhibits foam cell formation through promoting cholesterol efflux from RAW264.7 macrophages

CONTEXT

Chrysin, a natural flavonoid, has been shown to possess multiple pharmacological activities including anti-atherosclerosis.

OBJECTIVE

The effects of chrysin on foam cell formation and cholesterol flow in RAW264.7 macrophages were investigated in this work to explore the potential mechanism underlying its anti-atherogenic activity.

MATERIALS AND METHODS

The inhibitive effect of chrysin on foam cell formation and cholesterol accumulation induced by oxidized low-density lipoprotein cholesterol (ox-LDL) was assessed by oil red O staining and intracellular total cholesterol and triglyceride quantification in RAW264.7 macrophages. The action of chrysin on cholesterol efflux and influx was tested by fluorescent assays. Real-time quantitative PCR was used to quantify the relative expression of cholesterol flow-associated genes and luciferase assay was applied to test the transcription activity of peroxisome proliferator-activated receptor gamma (PPARγ).

RESULTS

Chrysin dose dependently inhibited the formation of foam cells and prevented the enhanced cholesterol accumulation by ox-LDL. Treatment with chrysin (10 μM) significantly enhanced cholesterol efflux and substantially inhibited cholesterol influx. Simultaneously, chrysin significantly increased the mRNA levels of PPARγ, liver X receptor alpha (LXRα), ATP-binding cassette, sub-family A1 (ABCA1), and sub-family G1 (ABCG1), decreased scavenger receptor A1 (SR-A1) and SR-A2, and increased the transcriptional activity of PPARγ.

DISCUSSION AND CONCLUSION

Chrysin is a new inhibitor of foam cell formation that may stimulate cholesterol flow. Up-regulation of the classical PPARγ-LXRα-ABCA1/ABCG1 pathway and down-regulation of SR-A1 and SR-A2 may participate in its suppressive effect on intracellular cholesterol accumulation.

Scavenger receptor class B, type I (Scarb1) deficiency promotes osteoblastogenesis but stunts terminal osteocyte differentiation

Scavenger receptor class B type I (SR-BI), the Scarb1 gene product, is a high-density lipoprotein (HDL) receptor which was shown to influence bone metabolism. Its absence in mice is associated with alterations of the glucocorticoid/adrenocorticotropic hormone axis, and translated in high bone mass and enhanced bone formation. Since the cellular alterations underlying the enhanced bone formation remain unknown, we investigated Scarb1-deficient marrow stromal cells (MSC) behavior in vitro. No difference in HDL3, cholesteryl ester (CE) or estradiol (E) association/binding was measured between Scarb1-null and wild-type (WT) cells. Scarb1 genic expression was down-regulated twofold following osteogenic treatment. Neither WT nor null cell proliferation was influenced by HDL3 exposure whereas this condition decreased genic expression of osteoblastic marker osterix (Sp7), and osteocyte markers sclerostin (Sost) and dentin matrix protein 1 (Dmp1) independently of genotype. Sost and Dmp1 basal expression in null cells was 40% and 50% that of WT cells; accordingly, osteocyte density was 20% lower in vertebrae from Scarb1-null mice. Genic expression of co-receptors for Wnt signaling, namely LDL-related protein (Lrp) 5 and Lrp8, was increased, respectively, by two- and threefold, and of transcription target-genes axis inhibition protein 2 (Axin2) and lymphoid enhancer-binding factor 1 (Lef1) over threefold. Gene expression of Wnt signaling agonist Wnt5a and of the antagonist dickkopfs-related protein 1 (Dkk1) were found to be increased 10- to 20-fold in null MSC. These data suggest alterations of Wnt pathways in Scarb1-deficient MSC potentially explaining their enhanced function, hence contributing to the high bone mass observed in these mice.

Gender- and region-specific alterations in bone metabolism in Scarb1-null female mice

A positive correlation between plasma levels of HDL and bone mass has been reported by epidemiological studies. As scavenger receptor class B, type I (SR-BI), the gene product of Scarb1, is known to regulate HDL metabolism, we recently characterized bone metabolism in Scarb1-null mice. These mice display high femoral bone mass associated with enhanced bone formation. As gender differences have been reported in HDL metabolism and SR-BI function, we investigated gender-specific bone alterations in Scarb1-null mice by microtomography and histology. We found 16% greater relative bone volume and 39% higher bone formation rate in the vertebrae from 2-month-old Scarb1-null females. No such alteration was seen in males, indicating gender- and region-specific differences in skeletal phenotype. Total and HDL-associated cholesterol levels, as well as ACTH plasma levels, were increased in both Scarb1-null genders, the latter being concurrent to impaired corticosterone response to fasting. Plasma levels of estradiol did not differ between null and WT females, suggesting that the estrogen metabolism alteration is not relevant to the higher vertebral bone mass in female Scarb1-null mice. Constitutively, high plasma levels of leptin along with 2.5-fold increase in its expression in white adipose tissue were measured in female Scarb1-null mice only. In vitro exposure of bone marrow stromal cells to ACTH and leptin promoted osteoblast differentiation as evidenced by increased gene expression of osterix and collagen type I alpha. Our results suggest that hyperleptinemia may account for the gender-specific high bone mass seen in the vertebrae of female Scarb1-null mice.

Lysophosphatidylcholine-induced cytotoxicity in osteoblast-like MG-63 cells: involvement of transient receptor potential vanilloid 2 (TRPV2) channels

Epidemiological studies indicate that patients suffering from atherosclerosis are predisposed to develop osteoporosis. Accordingly, atherogenic determinants such as oxidized low density lipoprotein (OxLDL) particles have been shown to alter bone cell functions. In this work, we investigated the cytotoxicity of lysophosphatidylcholine (lysoPC), a major phospholipid component generated upon LDL oxidation, on bone-forming MG-63 osteoblast-like cells. Cell viability was reduced by lysoPC in a concentration-dependent manner with a LC50 of 18.7±0.7 μM. LysoPC-induced cell death was attributed to induction of both apoptosis and necrosis. Since impairment of intracellular calcium homeostasis is often involved in mechanism of cell death, we determined the involvement of calcium in lysoPC-induced cytotoxicity. LysoPC promoted a rapid and transient increase in intracellular calcium attributed to mobilization from calcium stores, followed by a sustained influx. Intracellular calcium mobilization was associated to phospholipase C (PLC)-dependent mobilization of calcium from the endoplasmic reticulum since inhibition of PLC or calcium depletion of reticulum endoplasmic with thapsigargin prevented the calcium mobilization. The calcium influx induced by lysoPC was abolished by inhibition of transient receptor potential vanilloid (TRPV) channels with ruthenium red whereas gadolinium, which inhibits canonical TRP (TRPC) channels, was without effect. Accordingly, expression of TRPV2 and TRPV4 were shown in MG-63 cells. The addition of TRPV2 inhibitor Tranilast in the incubation medium prevent the calcium influx triggered by lysoPC and reduced lysoPC-induced cytotoxicity whereas TRPV4 inhibitor RN 1734 was without effect, which confirms the involvement of TRPV2 activation in lysoPC-induced cell death.

Phosphatidylcholine metabolism and choline kinase in human osteoblasts

There is a paucity of information about phosphatidylcholine (PC) biosynthesis in bone formation. Thus, we characterized PC metabolism in both primary human osteoblasts (HOB) and human osteosarcoma MG-63 cells. Our results show that the CDP-choline pathway is the only de novo route for PC biosynthesis in both HOB and MG-63 cells. Both CK activity and CKα expression in MG-63 cells were significantly higher than those in HOB cells. Silencing of CKα in MG-63 cells had no significant effect on PC concentration but decreased the amount of phosphocholine by approximately 80%. The silencing of CKα also reduced cell proliferation. Moreover, pharmacological inhibition of CK activity impaired the mineralization capacity of MG-63 cells. Our data suggest that CK and its product phosphocholine are required for the normal growth and mineralization of MG-63 cells.

The atherogenic Scarb1 null mouse model shows a high bone mass phenotype

Scavenger receptor class B, type I (SR-BI), the Scarb1 gene product, is a receptor associated with cholesteryl ester uptake from high-density lipoproteins (HDL), which drives cholesterol movement from peripheral tissues toward the liver for excretion, and, consequently, Scarb1 null mice are prone to atherosclerosis. Because studies have linked atherosclerosis incidence with osteoporosis, we characterized the bone metabolism in these mice. Bone morphometry was assessed through microcomputed tomography and histology. Marrow stromal cells (MSCs) were used to characterize influence of endogenous SR-BI in cell functions. Total and HDL-associated cholesterol in null mice were increased by 32-60%, correlating with its role in lipoprotein metabolism. Distal metaphyses from 2- and 4-mo-old null mice showed correspondingly 46 and 37% higher bone volume fraction associated with a higher number of trabeculae. Histomorphometric analyses in 2-mo-old null male mice revealed 1.42-fold greater osteoblast surface, 1.37-fold higher percent mineralizing surface, and 1.69-fold enhanced bone formation rate. In vitro assays for MSCs from null mice revealed 37% higher proliferation rate, 48% more alkaline phosphatase activity, 70% greater mineralization potential and a 2-fold osterix (Sp7) expression, yet a 0.5-fold decrease in caveolin-1 (Cav1) expression. Selective uptake levels of HDL-associated cholesteryl oleate and estradiol were similar between MSC from wild-type and Scarb1 null mice, suggesting that its contribution to this process is not its main role in these cells. However, Scarb1 knockout stunted the HDL-dependent regulation of Cav1 genic expression. Scarb1 null mice are not prone to osteoporosis but show higher bone mass associated with enhanced bone formation.

Low-bone-mass phenotype of deficient mice for the cluster of differentiation 36 (CD36)

Bone tissue is continuously remodeled by bone cells and maintenance of its mass relies on the balance between the processes of resorption and formation. We have reported the expression of numerous scavenger receptors, namely scavenger receptor (SR) class B type I and II (SR-BI and SR-BII), and CD36, in bone-forming osteoblasts but their physiological roles in bone metabolism are still unknown. To unravel the role of CD36 in bone metabolism, we determined the bone phenotype of CD36 knockout (CD36KO) mice and characterized the cell functions of osteoblasts lacking CD36. Weights of CD36KO mice were significantly lower than corresponding wild-type (WT) mice, yet no significant difference was found in femoral nor tibial length between CD36KO and WT mice. Analysis of bone architecture by micro-computed tomography revealed a low bone mass phenotype in CD36KO mice of both genders. Femoral trabecular bone from 1 to 6 month-old CD36KO mice showed lower bone volume, higher trabecular separation and reduced trabeculae number compared to WT mice; similar alterations were noticed for lumbar vertebrae. Plasma levels of osteocalcin (OCN) and N-terminal propeptide of type I procollagen (PINP), two known markers of bone formation, were significantly lower in CD36KO mice than in WT mice, whereas plasma levels of bone resorption markers were similar. Accordingly, histology highlighted lower osteoblast perimeter and reduced bone formation rate. In vitro functional characterization of bone marrow stromal cells and osteoblasts isolated from CD36KO mice showed reduced cell culture expansion and survival, lower gene expression of osteoblastic Runt-related transcription factor 2 (Runx2) and osterix (Osx), as well as bone sialoprotein (BSP) and osteocalcin (OCN). Our results indicate that CD36 is mandatory for adequate bone metabolism, playing a role in osteoblast functions ensuring adequate bone formation.

Evidence for sodium metasilicate receptors on the human osteoblast cell surface; spatial localization and binding properties

We report details of the interaction of sodium metasilicate with osteoblast cellular membranes using Fluoresceinphosphatidylethanolamine (FPE) as a fluorescent indicator of membrane interactions. Fluorescence imaging studies of the FPE-based indicator system revealed areas of localized binding that would be consistent with the presence of a structure with 'receptor-like' properties. From these results, it seems unlikely that silica binds 'non-specifically' to the osteoblast surface. Moreover, the receptors are localized into membrane domains. Such regions of the cell membrane could well be structures such as 'rafts' or other such localized domains within the membrane. The binding profile of silica with the osteoblast cell surface takes place with all the characteristics of a receptor-mediated process best represented by a cooperativity (sigmoidal) binding model with a Hill coefficient of 3.6.

Two neglected biologic risk factors in bone grafting and implantology: high low-density lipoprotein cholesterol and low serum vitamin D

Following a failure of a bone graft or an implant placement, the hypothesis of a biological abnormality is rarely considered as a possible cause. A systematic search of peer-reviewed literature for dyslipidemia or vitamin D deficiency may explain this lack of consideration. Excess low-density lipoprotein cholesterol (dyslipidemia) is responsible for a slower bone metabolism or lower dental implant osseointegration. In addition, vitamin D is a key factor for linking innate and adaptive immunity. Both of these factors are compromised under the conditions of vitamin D deficiency. Therefore, vitamin D deficiency slows implant osseointegration and increases the risk of graft infection. Vitamin D is also involved in immune function and therefore allergic reactions.

Caveolar endocytosis is required for human PSGL-1-mediated enterovirus 71 infection

Enterovirus 71 (EV71) causes hand, foot, and mouth disease and severe neurological disorders in children. Human scavenger receptor class B member 2 (hSCARB2) and P-selectin glycoprotein ligand-1 (PSGL-1) are identified as receptors for EV71. The underling mechanism of PSGL-1-mediated EV71 entry remains unclear. The endocytosis required for EV71 entry were investigated in Jurkat T and mouse L929 cells constitutively expressing human PSGL-1 (PSGL-1-L929) or human rhabdomyosarcoma (RD) cells displaying high SCARB2 but no PSGL-1 by treatment of specific inhibitors or siRNA. We found that disruption of clathrin-dependent endocytosis prevented EV71 infection in RD cells, while there was no influence in Jurkat T and PSGL-1-L929 cells. Disturbing caveolar endocytosis by specific inhibitor or caveolin-1 siRNA in Jurkat T and PSGL-1-L929 cells significantly blocked EV71 infection, whereas it had no effect on EV71 infection in RD cells. Confocal immunofluorescence demonstrated caveola, and EV71 was directly colocalized. pH-dependent endosomal acidification and intact membrane cholesterol were important for EV71 infection, as judged by the pretreatment of inhibitors that abrogated the infection. A receptor-dominated endocytosis of EV71 infection was observed: PSGL-1 initiates caveola-dependent endocytosis and hSCARB2 activates clathrin-dependent endocytosis.

Interleukin-27 expression modifies prostate cancer cell crosstalk with bone and immune cells in vitro

Prostate cancer is frequently associated with bone metastases, where the crosstalk between tumor cells and key cells of the bone microenvironment (osteoblasts, osteoclasts, immune cells) amplifies tumor growth. We have explored the potential of a novel cytokine, interleukin-27 (IL-27), for inhibiting this malignant crosstalk, and have examined the effect of autocrine IL-27 on prostate cancer cell gene expression, as well as the effect of paracrine IL-27 on gene expression in bone and T cells. In prostate tumor cells, IL-27 upregulated genes related to its signaling pathway while downregulating malignancy-related receptors and cytokine genes involved in gp130 signaling, as well as several protease genes. In both undifferentiated and differentiated osteoblasts, IL-27 modulated upregulation of genes related to its own signaling pathway as well as pro-osteogenic genes. In osteoclasts, IL-27 downregulated several genes typically involved in malignancy and also downregulated osteoclastogenesis-related genes. Furthermore, an osteogenesis-focused real-time PCR array revealed a more extensive profile of pro-osteogenic gene changes in both osteoblasts and osteoclasts. In T-lymphocyte cells, IL-27 upregulated several activation-related genes and also genes related to the IL-27 signaling pathway and downregulated several genes that could modulate osteoclastogenesis. Overall, our results suggest that IL-27 may be able to modify interactions between prostate tumor and bone microenvironment cells and thus could be used as a multifunctional therapeutic for restoring bone homeostasis while treating metastatic prostate tumors.

HDL cholesterol and bone mineral density: is there a genetic link?

Overwhelming evidence has linked cardiovascular disease and osteoporosis, but the shared root cause of these two diseases of the elderly remains unknown. Low levels of high density lipoprotein cholesterol (HDL) and bone mineral density (BMD) are risk factors for cardiovascular disease and osteoporosis respectively. A number of correlation studies have attempted to determine if there is a relationship between serum HDL and BMD but these studies are confounded by a number of variables including age, diet, genetic background, gender and hormonal status. Collectively, these data suggest that there is a relationship between these two phenotypes, but that the nature of this relationship is context specific. Studies in mice plainly demonstrate that genetic loci for BMD and HDL co-map and transgenic mouse models have been used to show that a single gene can affect both serum HDL and BMD. Work completed to date has demonstrated that HDL can interact directly with both osteoblasts and osteoclasts, but no direct evidence links bone back to the regulation of HDL levels. Understanding the genetic relationship between BMD and HDL has huge implications for understanding the clinical relationship between CVD and osteoporosis and for the development of safe treatment options for both diseases.

CD36 genetics and the metabolic complications of obesity

PURPOSE OF REVIEW

The review summarizes our current understanding of the function of the fatty acid translocase, CD36, in lipid metabolism with an emphasis on the influence of CD36 genetic variants and their potential contribution to obesity-related complications.

RECENT FINDINGS

Studies in rodents implicate CD36 in a number of metabolic pathways with relevance to obesity and its associated complications. These include pathways related to fat utilization such as taste perception, intake, intestinal processing, and storage in adipose tissue. Dysfunction in these pathways, coupled with the ability of CD36 to transduce intracellular signals that initiate inflammation in response to excess fat supply, promotes metabolic pathology. In the last few years, the relevance of discoveries in rodents to humans has been highlighted by genetic studies, which identified common CD36 variants that influence circulating lipid levels and cardiometabolic phenotypes.

SUMMARY

Recent genetic studies suggest that CD36 plays an important role in lipid metabolism in humans and may be involved in obesity-related complications. These findings may accelerate the translation of CD36 metabolic functions determined in rodents to humans. Importantly, these studies highlight the potential utility of assessing CD36 expression and common single-nucleotide polymorphism genotypes.

Size-dependent transfection efficiency of PEI-coated gold nanoparticles

Gold nanoparticles (Au NPs) are promising vectors for gene delivery applications. In order to gain insight on the influence of particle size on cell transfection, Au NPs were combined with poly(ethylenimine) (PEI) to prepare two sets of PEI-coated Au NPs having particle-size distributions centered at about 6 nm (<10nm Au-PEI NPs) or 70 nm (<100 nm Au-PEI NPs), respectively. Au-PEI NPs were coupled to a variety of plasmids carrying reporter or suicide genes to prepare Au-PEI NPs/DNA complexes, and human osteosarcoma Saos-2 cells were used to investigate the performance of the Au-PEI NPs as transfection vectors in serum-containing media. The conjugates of DNA with both types of Au-PEI NPs were found to be negatively charged. In spite of the electrostatic repulsion that occurs between the surface of the cell and the surface of the plasmid-conjugated NPs, cell internalization was observed for both kinds of Au-PEI NPs. Cells were efficiently transfected with complexes derived from <10 nm Au-PEI NPs, but not with the <100 nm Au-PEI NPs. Large aggregates of NPs associated with DNA were found in endocytic vesicles of cells incubated with <100 nm Au-PEI NPs, while the success of the smaller Au-PEI NPs as transfection vectors was related to their lower agglomeration state inside cells and to endosomal escape of DNA.

Fatty acid esters of steroids: synthesis and metabolism in lipoproteins and adipose tissue

At the end of the last century ideas concerning the physiological role of the steroid fatty acid ester family were emerging. Estrogens, fatty acylated at C-17 hydroxyl group and incorporated in lipoproteins were proposed to provide antioxidative protection to these particles. A large number of studies involving non-estrogenic adrenal steroids, and their fatty acylated forms, demonstrated their lipoprotein-mediated transport into cells and subsequent intracellular activation, suggesting a novel transport mechanism for lipophilic steroid derivatives. After these important advances the main focus of interest has shifted away from C-19 and C-21 steroids to fatty acylated estrogens. However, interest in their lipoprotein-mediated transport has decreased because only minute amounts of these derivatives were detected in circulating lipoproteins, and their antioxidative activity remained unconfirmed under physiological circumstances. It now appears that the overwhelming majority of estradiol in postmenopausal women resides in adipose tissue, most of it in esterified form. This is poorly reflected in plasma levels which are very low. Recent data suggest that estrogen fatty acid esters probably represent a storage form. The future focus of investigation is likely to be on firstly, the enzymatic mechanisms regulating the esterification and de-esterification of estradiol and other steroids residing in adipose tissue and secondly, on the role of insulin and other hormones in the regulation of these enzymatic mechanisms. Thirdly, as a large proportion of fatty acid esterified C-19 and C-21 non-estrogenic steroids is transported in lipoproteins and as they are important precursors of androgens and estrogens, this field should be investigated further.

Dehydroepiandrosterone fatty acyl esters in high density lipoprotein: interaction with human vascular endothelial cells and vascular responses ex vivo

Dehydroepiandrosterone (DHEA) fatty acyl esters once incorporated in high density lipoprotein (HDL) induce a stronger vasodilatory response in rat mesenteric arteries ex vivo compared to native HDL. We studied the role of HDL receptor, scavenger receptor class B, type 1 (SR-B1), as well as estrogen and androgen receptors in the vasodilatory response of HDL-associated DHEA fatty acyl esters. Using cultured human vascular endothelial cells (HUVEC), we investigated the possible internalization and cellular response of HDL-associated DHEA esters. We prepared DHEA ester-enriched HDL by incubating human plasma in the presence of DHEA. After isolation and purification, HDL was added in cumulative doses to arterial rings precontracted with noradrenaline. Inhibition of the function of SR-B1 almost completely abolished maximal vasorelaxation by DHEA-enriched HDL while estrogen or androgen receptor blockage had no significant effect. When HUVECs were incubated in the presence of [³H]DHEA ester-enriched HDL, the amount of intracellular [³H]-radioactivity increased steadily during 24 h. Blocking of SR-B1 reduced this uptake by a mean of 30%. The proportion of unesterified [³H]DHEA, as analyzed by thin-layer chromatography, increased intracellularly and in the cell culture media after several hours of incubation of the cells in the presence of [³H]DHEA ester-enriched HDL. This indicated slow hydrolysis of DHEA fatty acyl esters and subsequent excretion of unesterified DHEA by the cells. In conclusion, DHEA-enriched HDL induced vasorelaxation via the SR-B1-facilitated pathway. However, this vasodilation is not likely to be attributed to rapid hydrolysis of HDL-associated DHEA esters by the vascular endothelium.

Vitamin D intestinal absorption is not a simple passive diffusion: evidences for involvement of cholesterol transporters

SCOPE

It is assumed that vitamin D is absorbed by passive diffusion. However, since cholecalciferol (vitamin D(3) ) and cholesterol display similar structures, we hypothesized that common absorption pathways may exist.

METHODS AND RESULTS

Cholecalciferol apical transport was first examined in human Caco-2 and transfected Human embryonic kidney (HEK) cells. Cholecalciferol uptake was then valuated ex vivo and in vivo, using either wild-type mice, mice overexpressing Scavenger Receptor class B type I (SR-BI) at the intestinal level or mice treated or not with ezetimibe. Cholecalciferol uptake was concentration-, temperature- and direction-dependent, and was significantly impaired by a co-incubation with cholesterol or tocopherol in Caco-2 cells. Moreover Block Lipid Transport-1 (SR-BI inhibitor) and ezetimibe glucuronide (Niemann-Pick C1 Like 1 inhibitor) significantly decreased cholecalciferol transport. Transfection of HEK cells with SR-BI, Cluster Determinant 36 and Niemann-Pick C1 Like 1 significantly enhanced vitamin D uptake, which was significantly decreased by the addition of Block Lipid Transport-1, sulfo-N-succinimidyl oleate (Cluster Determinant 36 inhibitor) or ezetimibe glucuronide, respectively. Similar results were obtained in mouse intestinal explants. In vivo, cholecalciferol uptake in proximal intestinal fragments was 60% higher in mice overexpressing SR-BI than in wild-type mice (p<0.05), while ezetimibe effect remained non-significant.

CONCLUSION

These data show for the first time that vitamin D intestinal absorption is not passive only but involves, at least partly, some cholesterol transporters.

Role of cholesterol in the development and progression of breast cancer

Diet and obesity are important risk factors for cancer development. Many studies have suggested an important role for several dietary nutrients in the progression and development of breast cancer. However, few studies have specifically addressed the role of components of a Western diet as important factors involved in breast cancer initiation and progression. The present study examined the role of cholesterol in the regulation of tumor progression in a mouse model of mammary tumor formation. The results suggest that cholesterol accelerates and enhances tumor formation. In addition, tumors were more aggressive, and tumor angiogenesis was enhanced. Metabolism of cholesterol was also examined in this mouse model. It was observed that plasma cholesterol levels were reduced during tumor development but not prior to its initiation. These data provide new evidence for an increased utilization of cholesterol by tumors and for its role in tumor formation. Taken together, these results imply that an increase in plasma cholesterol levels accelerates the development of tumors and exacerbates their aggressiveness.

The administration of demethyl fruticulin A from Salvia corrugata to mammalian cells lines induces "anoikis", a special form of apoptosis

Recently demethyl fruticulin A was identified as the major diterpenoid component of the exudates produced by the trichomes of Salvia corrugata leafs. Given the documented apoptotic effects of some of the other known components of the exudates from Salvia species, we assessed if demethyl fruticulin A, once administered to mammalian cells, was involved in the onset of apoptosis and if its biological effects were exerted through the participation of a scavenger membrane receptor, CD36. Three model cell lines were chosen, one of which lacking CD36 expression. Functional availability of the receptor, or its transcriptional rate, were blocked/reduced with a specific antibody or by the administration of vitamin E. Immunodetection of cell cytoskeletal components and tunel analysis revealed that demethyl fruticulin A triggers the onset of anoikis, a special form of apoptosis induced by cell detachment from the substrate. Impairment of CD36 availability/transcription confirmed the receptor partial involvement in the intake of the substance and in anoikis, as also sustained by FACS analysis and by the downregulation of p95, a marker of anoikis, upon blockade of CD36 transcription. However, experiments with CD36-deficient cells suggested that alternate pathways, still to be determined, may take part in the biological effects exerted by demethyl fruticulin A.

Human enterovirus 71 and hand, foot and mouth disease

Hand, foot and mouth disease (HFMD) is generally a benign febrile exanthematous childhood disease caused by human enteroviruses. The route of transmission is postulated to be faeco-oral in developing areas but attributed more to respiratory droplet in developed areas. Transmission is facilitated by the prolonged environmental survival of these viruses and their greater resistance to biocides. Serious outbreaks with neurological and cardiopulmonary complications caused by human enterovirus 71 (HEV-71) seem to be commoner in the Asian Pacific region than elsewhere in the world. This geographical predilection is unexplained but could be related to the frequency of intra- and inter-typic genetic recombinations of the virus, the host populations' genetic predisposition, environmental hygiene, and standard of healthcare. Vaccine development could be hampered by the general mildness of the illness and rapid genetic evolution of the virus. Antivirals are not readily available; the role of intravenous immunoglobulin in the treatment of serious complications should be investigated. Monitoring of this disease and its epidemiology in the densely populated Asia Pacific epicentre is important for the detection of emerging epidemics due to enteroviruses.

Human macrophage cholesterol efflux potential is enhanced by HDL-associated 17beta-estradiol fatty acyl esters

High-density lipoprotein (HDL) and 17beta-estradiol independently provide protection against atherosclerosis. Estradiol fatty acyl esters incorporate into HDL and whether this association enhances the atheroprotective properties of HDL is unclear. The study objective was to clarify the role that HDL-associated estradiol fatty acyl esters play in mediating the initial steps of reverse cholesterol transport. Cholesterol efflux potential from cholesterol loaded macrophage cells to HDL-associated estradiol ester or between HDL from premenopausal women and age-matched males and the cellular receptors involved were examined. Human THP-1 macrophages, loaded with [(3)H]cholesterol oleate, acetylated low-density lipoprotein, were pretreated with or without SR-BI inhibitors or an estrogen receptor antagonist and incubated with either HDL-associated estradiol oleate, HDL lacking estradiol oleate, or isolated HDL from females and males, and cholesterol efflux was measured. Cellular internalization and hydrolysis of HDL-associated [(3)H]estradiol ester were determined. HDL-associated estradiol oleate and premenopausal female HDL demonstrated significantly higher cholesterol efflux capacity to media than male HDL. SR-BI and estrogen receptor inhibition significantly reduced this effect. Cells internalized and subsequently hydrolyzed HDL-associated [(3)H]estradiol ester to [(3)H]estradiol and again SR-BI inhibition reduced this internalization. These results demonstrate that HDL-mediated macrophage cholesterol efflux potential is enhanced by HDL-associated estradiol esters.

Antagonistic roles for BRM and BRG1 SWI/SNF complexes in differentiation

The mammalian SWI/SNF chromatin-remodeling complex is essential for the multiple changes in gene expression that occur during differentiation. However, the basis within the complex for specificity in effecting positive versus negative changes in gene expression has only begun to be elucidated. The catalytic core of the complex can be either of two closely related ATPases, BRM or BRG1, with the potential that the choice of alternative subunits is a key determinant of specificity. Short hairpin RNA-mediated depletion of the ATPases was used to explore their respective roles in the well characterized multistage process of osteoblast differentiation. The results reveal an unexpected role for BRM-specific complexes. Instead of impeding differentiation as was seen with BRG1 depletion, depletion of BRM caused accelerated progression to the differentiation phenotype. Multiple tissue-specific differentiation markers, including the tightly regulated late stage marker osteocalcin, become constitutively up-regulated in BRM-depleted cells. Chromatin immunoprecipitation analysis of the osteocalcin promoter as a model for the behavior of the complexes indicates that the promoter is a direct target of both BRM- and BRG1-containing complexes. BRG1 complexes, which are required for activation, are associated with the promoter well before induction, but the concurrent presence of BRM-specific complexes overrides their activation function. BRM-specific complexes are present only on the repressed promoter and are required for association of the co-repressor HDAC1. These findings reveal an unanticipated degree of specialization of function linked with the choice of ATPase and suggest a new paradigm for the roles of the alternative subunits during differentiation.

HDL3 reduces the association and modulates the metabolism of oxidized LDL by osteoblastic cells: a protection against cell death

Oxidized low density lipoproteins (OxLDL) are known to promote atherosclerosis, but it is only recently that OxLDL have been associated with alterations of the functions of bone-forming osteoblasts and osteoporosis. Although high density lipoproteins (HDL) are recognized for their anti-atherogenic action, there is less information about their ability to protect against osteoporosis. Therefore, we investigated the capacity of HDL3 to prevent the cell death induced by OxLDL in human osteoblastic cells. Simultaneous exposure of the cells to HDL3 and OxLDL abolished the reduction of cell viability monitored by MTT activity measurement and the induction of apoptosis determined by annexin V staining indicating that HDL3 prevent the apoptosis of osteoblasts induced by OxLDL. This protection correlated with the displacement by HDL3 of OxLDL association to osteoblasts, signifying that OxLDL binding and/or internalization are/is necessary for their cytotoxic effects. We also found that exposition of osteoblastic cells to HDL3 prior to incubation with OxLDL reduced cell death and preserved the lysosomal integrity. This protection was correlated with an increase of SR-BI expression, a modification of OxLDL metabolism with less global uptake of OxLDL and greater selective uptake of cholesterol from OxLDL. These results strongly suggest that, as for atherosclerosis, HDL may exert beneficial actions on bone metabolism.