Regulation of bone mass in mice by the lipoxygenase gene Alox15

Nanoplastic impact on bone microenvironment: A snapshot from murine bone cells

Our world is made of plastic. Plastic waste deeply affects our health entering the food chain. The degradation and/or fragmentation of plastics due to weathering processes result in the generation of nanoplastics (NPs). Only a few studies tested NPs effects on human health. NPs toxic actions are, in part, mediated by oxidative stress (OS) that, among its effects, affects bone remodeling. This study aimed to assess if NPs influence skeleton remodeling through OS. Murine bone cell cultures (MC3T3-E1 preosteoblasts, MLOY-4 osteocyte-like cells, and RAW264.7 pre-osteoclasts) were used to test the NPs detrimental effects on bone cells. NPs affect cell viability and induce ROS production and apoptosis (by caspase 3/7 activation) in pre-osteoblasts, osteocytes, and pre-osteoclasts. NPs impair the migration capability of pre-osteoblasts and potentiate the osteoclastogenesis of preosteoclasts. NPs affected the expression of genes related to inflammatory and osteoblastogenic pathways in pre-osteoblasts and osteocytes, related to the osteoclastogenic commitment of pre-osteoclasts. A better understanding of the impact of NPs on bone cell activities resulting in vivo in impaired bone turnover could give more information on the possible toxicity consequence of NPs on bone mass and the subsequent public health problems, such as bone disease.

The Multifarious Functions of Leukotrienes in Bone Metabolism

Leukotrienes (LTs) are derived from arachidonic acid metabolism by the 5-lipoxygenase (5-LO) enzyme. The production of LTs is stimulated in the pathogenesis of rheumatoid arthritis (RA), osteoarthritis, and periodontitis, with a relevant contribution to bone resorption. However, its role in bone turnover, particularly the suppression of bone formation by modulating the function of osteoclasts and osteoblasts, remains unclear. We investigated the effects of LTs on bone metabolism and their impact on osteogenic differentiation and osteoclastogenesis using a 5-LO knockout (KO) mouse model. Results from micro-computed tomography (μCT) analysis of femur from 8-week-old 5-LO-deficient mice showed increased cortical bone and medullary region in females and males and decreased trabecular bone in females. In the vertebra, we observed increased marrow area in both females and males 5-LO KO and decreased trabecular bone only in females 5-LO KO. Immunohistochemistry (IHC) analysis showed higher levels of osteogenic markers tissue-nonspecific alkaline phosphatase (TNAP) and osteopontin (OPN) and lower expression of osteoclastogenic marker tartrate-resistant acid phosphatase (TRAP) in the femurs of 5-LO KO mice versus wild-type (WT). Alkaline phosphatase activity and mineralization assay results showed that the 5-LO absence enhances osteoblasts differentiation and mineralization but decreases the proliferation. Alkaline phosphatase (ALP), Bglap, and Sp7 gene expression were higher in 5-LO KO osteoblasts compared to WT cells. Eicosanoids production was higher in 5-LO KO osteoblasts except for thromboxane 2, which was lower in 5-LO-deficient mice. Proteomic analysis identified the downregulation of proteins related to adenosine triphosphate (ATP) metabolism in 5-LO KO osteoblasts, and the upregulation of transcription factors such as the adaptor-related protein complex 1 (AP-1 complex) in long bones from 5-LO KO mice leading to an increased bone formation pattern in 5-LO-deficient mice. We observed enormous differences in the morphology and function of osteoclasts with reduced bone resorption markers and impaired osteoclasts in 5-LO KO compared to WT osteoclasts. Altogether, these results demonstrate that the absence of 5-LO is related to the greater osteogenic profile. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Genetic susceptibility to diabetic kidney disease is linked to promoter variants of XOR

The lifetime risk of kidney disease in people with diabetes is 10-30%, implicating genetic predisposition in the cause of diabetic kidney disease (DKD). Here we identify an expression quantitative trait loci (QTLs) in the cis-acting regulatory region of the xanthine dehydrogenase, or xanthine oxidoreductase (Xor), a binding site for C/EBPβ, to be associated with diabetes-induced podocyte loss in DKD in male mice. We examine mouse inbred strains that are susceptible (DBA/2J) and resistant (C57BL/6J) to DKD, as well as a panel of recombinant inbred BXD mice, to map QTLs. We also uncover promoter XOR orthologue variants in humans associated with high risk of DKD. We introduced the risk variant into the 5'-regulatory region of XOR in DKD-resistant mice, which resulted in increased Xor activity associated with podocyte depletion, albuminuria, oxidative stress and damage restricted to the glomerular endothelium, which increase further with type 1 diabetes, high-fat diet and ageing. Therefore, differential regulation of Xor contributes to phenotypic consequences with diabetes and ageing.

Polymorphisms in genes expressed during amelogenesis and their association with dental caries: a case–control study

Objectives

Dental caries is a widespread multifactorial disease, caused by the demineralization of hard dental tissues. Susceptibility to dental caries is partially genetically conditioned; this study was aimed at finding an association of selected single nucleotide polymorphisms (SNPs) in genes encoding proteins involved in amelogenesis with this disease in children.

Materials and methods

In this case–control study, 15 SNPs in ALOX15, AMBN, AMELX, KLK4, TFIP11, and TUFT1 genes were analyzed in 150 children with primary dentition and 611 children with permanent teeth with/without dental caries from the European Longitudinal Study of Pregnancy and Childhood (ELSPAC) cohort.

Results

Dental caries in primary dentition was associated with SNPs in AMELX (rs17878486) and KLK4 (rs198968, rs2242670), and dental caries in permanent dentition with SNPs in AMELX (rs17878486) and KLK4 (rs2235091, rs2242670, rs2978642), (p ≤ 0.05). No significant differences between cases and controls were observed in the allele or genotype frequencies of any of the selected SNPs in ALOX15, AMBN, TFIP11, and TUFT1 genes (p > 0.05). Some KLK4 haplotypes were associated with dental caries in permanent dentition (p ≤ 0.05).

Conclusions

Based on this study, we found that although the SNPs in AMELX and KLK4 are localized in intronic regions and their functional significance has not yet been determined, they are associated with susceptibility to dental caries in children.

Clinical relevance

AMELX and KLK4 variants could be considered in the risk assessment of dental caries, especially in permanent dentition, in the European Caucasian population.

Integrated RNA-Seq Analysis Uncovers the Potential Mechanism of the “Kidney Governing Bones” Theory of TCM

Background. As in philosophy of traditional Chinese medicine (TCM), the theory of “kidney governing bones” has been demonstrated by a series of scientific studies. Furthermore, many groups including ours have explored the molecular mechanisms related to bone development, growth, and regeneration using modern biology technologies, such as RNA sequencing (RNA-Seq) and isobaric tags for relative and absolute quantification (ITRAQ), and have demonstrated that the underlying molecular mechanisms were highly consistent with the “kidney governing bones” theory. Objective. Kidney-yang deficiency (YD), as a pathological condition, has a passive effect on the skeleton growth; more specifically, it is a state of skeletal metabolic disorder. However, the exact molecular mechanisms related to the “kidney governing bones” theory under the control of multiple organs and systems are still unknown. Methods. In this study, we performed RNA-Seq analysis to investigate and compare the gene expression patterns of six types of tissue (bone, cartilage, kidney, testicle, thyroid gland, and adrenal gland) from YD rats and normal rats and analyzed the interaction effects controlled by multiple functional genes and signaling pathways between those tissues. Results. Our results showed that, in the state of YD, the functions of bone and cartilage were inhibited. Furthermore, multiple organs involving the reproductive, endocrine, and urinary systems were also investigated, and our results showed that YD could cause dysfunctions of these systems by downregulating multiple functional genes and signaling pathways that positively regulate the homeostasis of these tissues. Conclusion. We ensure that “kidney governing bones” was not a simple change in a single gene but the changes in complex biological networks caused by functional changes in multiple genes. This also coincides with the holistic view of TCM, which holds that the human body itself is an organic whole and the functional activities of each organ coordinate with each other.

Association between ALOX15 gene polymorphism and brick-tea type skeletal fluorosis in Tibetans, Kazaks and Han, China

To evaluate the association between ALOX15 gene polymorphism and skeletal fluorosis (SF), a case-control study was conducted. A total of 1023 individuals, including 308 Tibetans, 290 Kazaks and 425 Han, were enrolled in this study, in which cases and controls were 278 and 745, respectively. SF was diagnosed by X-ray absorptiometry. SNPs were genotyped using the Sequenom Mass ARRAY system. The genotypes of ALOX15 rs7220870, rs2664593 and rs1107852 were not associated with the risk of SF. After reconstructing the haplotype of rs7220870 and rs11078528, the risk effect of haplotype CA was found in Han participants aged ≤45 years or with moderate fluoride intake. Diplotype of CC/CC had a protective effect on SF risk in Han participants; whereas, CA/CC diplotype showed a risk effect on SF risk in participants aged ≥65; Our results provide the first evidence of an association between ALOX15 gene polymorphism and SF risk in Han participants.Abbreviation: SF: Skeletal fluorosis; SNP: Single Nucleotide polymorphism.

Research Progress of Therapeutic Enzymes and Their Derivatives: Based on Herbal Medicinal Products in Rheumatoid Arthritis

Rheumatoid arthritis (RA) acts as one of the most common, agnogenic and chronic inflammatory-autoimmune disorder which is characterized by persistent synovitis, cartilage destruction, and joint deformities, leads to a wide range of disabilities, and increased mortality, thus imposing enormous burdens. Several drugs with anti-inflammatory and immunomodulatory properties such as celecoxib, diclofenac and methotrexate are being selected as conventional drugs in the allopathic system of medicine for the treatment of RA in clinic. However, there are some serious side effects more or less when using these drugs because of their short poor bioavailability and biological half-life for a long time. These shortcomings greatly promote the exploration and application of new low- or no-toxicity drugs for treating the RA. Meanwhile, a growing number of studies demonstrate that several herbs present certain anti-inflammatory and anti-arthritic activities through different enzymes and their derivatives, which indicate that they are promising therapeutic strategies when targeting these mediators based on herbal medicinal products in RA research. This review article summarizes the roles of the main enzymes and their derivatives during the pathogenesis of RA, and clearly clarifies the explicit and potential targeted actions of herbal medicinal products that have anti-RA activity. Our review provides timely and critical reference for the scientific rationale use of herbal medicinal products, with the increasing basic research and clinical application of herbal medicinal products by patients with RA.

Purification of Soluble Membrane-Bound Ambystoma mexicanum Epidermal Lipoxygenase from E. coli and Its Growth Effect on Human Fetal Foreskin Fibroblast

Lipoxygenases are non-heme iron-containing lipid dioxygenases enzymes that catalyze the hydroperoxidation of lipids. The Mexican axolotl (Ambystoma mexicanum) is a prominent source of the enzyme with a regeneration capacity in limbs. It has been shown that transfected human osteosarcoma and keratinocyte cells with epidermal lipoxygenase (LOXe) have an increased rate of cell migration. In the present study, LOXe, a peripheral membrane protein, was produced in Escherichia coli. The enzyme was purified using different detergents, anionic solutions, and gel filtration chromatography. Kinetic assay of the enzyme activity was carried out by the spectroscopy method using arachidonic acid as a substrate. Finally, the enzyme was characterized and its growth effect on human fibroblast cells was examined by MTT viability assay. Enzyme kinetic parameters including K_m of 90.4 µM and V_max of 2.63 IU were determined for LOXe. The enzyme with 0.1 nM end concentration promoted the growth of 5000 cells/well human fibroblast cells up to 11% (P < 0.01). In the present study, we introduce an E. coli expression system to produce an excessive amount of soluble LOXe and the efficient purification method to provide a soluble and active form of LOXe that is effective in stimulating human fibroblast cell proliferation.

Expression profile of lipoxygenases in gingival tissues of human periodontitis

OBJECTIVES

This study aimed to clarify the expression profile and significance of lipoxygenases in periodontitis.

MATERIALS AND METHODS

The mRNA levels of lipoxygenases in gingival tissues from 14 patients with periodontitis and 14 healthy individuals were determined by real-time PCR, and validated in datasets, GSE16134 and GSE10334, and by Western blotting. Correlation of differentially expressed lipoxygenases with clinical parameters and expression of tumor necrosis factor-α (TNF-α), interleukin-1β, matrix metalloproteinase (MMP)-8, MMP-9, and receptor activator of nuclear factor-κB ligand (RANKL) was investigated in patients with periodontitis by Spearman's correlation analysis.

RESULTS

The expression of ALOX5 (2.1-fold, p < .05), ALOX12B (2.9-fold, p < .001), and ALOX15B (9.4-fold, p < .001) was upregulated in gingival tissues from patients with periodontitis, which was validated by dataset analysis and Western blotting. Positive correlations were observed between ALOX5 and probing depth, and ALOX15B and probing depth and clinical attachment loss. Furthermore, ALOX5 expression was positively correlated with TNF-α, MMP-8, MMP-9, and RANKL expression, and ALOX15B was positively correlated with MMP-8 and RANKL.

CONCLUSIONS

Our findings indicated the upregulation of ALOX5 and ALOX15B in periodontitis and suggested that ALOX5 and ALOX15B may be involved in periodontitis pathogenesis, including inflammation, connective tissue destruction, and abnormal bone metabolism.

Deciphering the potential pharmaceutical mechanism of Guzhi Zengsheng Zhitongwan on rat bone and kidney based on the "kidney governing bone" theory

BACKGROUND

Guzhi Zengsheng Zhitongwan (GZZSZTW) is an effective Chinese medicinal formulation for the treatment of osteoarthritis (OA) designed according to the "kidney governing bone" theory, which has been widely used as a golden guide for treating bone and cartilage diseases in traditional Chinese medicine. The aim of this study was to explore the molecular mechanism underlying its effects on the bone and kidney.

METHODS

Preparation and quality control were performed as previously described. Since GZZSZTW is orally administered in the form of pills prepared in boiled water, the Chinese materia medica (CMM) mixture of this formula was extracted with distilled water by a reflux method and was then filtered through a 0.45-μm Hollow Fiber Cartridge (GE Healthcare, USA). The filtrate was freeze-dried by a Heto PowerDry LL3000 Freeze Dryer (Thermo, USA) and stored at - 80 °C. The effects of GZZSZTW on gene expression and regulation of both kidney and bone tissues were investigated using a state-of-the-art RNA-seq technology.

RESULTS

We demonstrated that GZZSZTW could enhance kidney function and suppress bone formation and resorption by modulating the activities of osteoblast and osteoclast, and might subsequently contribute to the inhibition of osteophyte formation during the process of OA. These effects might be achieved by the synergistic interactions of various herbs and their active components in GZZSZTW, which increased the expression levels of functional genes participating in kidney function, regulation, and repair, and then decreased the expression levels of genes involved in bone formation and resorption. Thus, our findings were consistent with the "kidney governing bone" theory, which has been widely used as a guide in clinical practice for thousands of years.

CONCLUSIONS

This study has deepened the current knowledge about the molecular effects of GZZSZTW on bone and kidney regulation. Furthermore, this study might be able to provide possible strategies to further prevent and treat joint diseases by using traditional Chinese medicinal formulations following the "kidney governing bone" theory.

Intestinal helminth infection enhances bacteria-induced recruitment of neutrophils to the airspace

Intestinal helminth infections elicit Th2-type immunity, which influences host immune responses to additional threats, such as allergens, metabolic disease, and other pathogens. Th2 immunity involves a shift of the CD4⁺ T-cell population from type-0 to type-2 (Th2) with increased abundance of interleukin (IL)-4 and IL-13. This study sought to investigate if existing gut-restricted intestinal helminth infections impact bacterial-induced acute airway neutrophil recruitment. C57BL/6 mice were divided into four groups: uninfected; helminth-Heligmosomoides polygyrus infected; Pseudomonas aeruginosa infected; and coinfected. Mice infected with H. polygyrus were incubated for 2 weeks, followed by P. aeruginosa intranasal inoculation. Bronchial alveolar lavage, blood, and lung samples were analyzed. Interestingly, infection with gut-restricted helminths resulted in immunological and structural changes in the lung. These changes include increased lung CD4⁺ T cells, increased Th2 cytokine expression, and airway goblet cell hyperplasia. Furthermore, coinfected mice exhibited significantly more airspace neutrophil infiltration at 6 hours following P. aeruginosa infection and exhibited an improved rate of survival compared with bacterial infected alone. These results suggest that chronic helminth infection of the intestines can influence and enhance acute airway neutrophil responses to P. aeruginosa infection.

Identification of genetic variants associated with skeletal muscle function deficit in childhood acute lymphoblastic leukemia survivors

Background: Although 80% of childhood acute lymphoblastic leukemia (ALL) cases are cured with current treatment protocols, exposure to chemotherapeutics or radiation therapy during a vulnerable period of child development has been associated with a high frequency of late adverse effects (LAE). Previous observations suggest important skeletal muscle size, density and function deficits in ALL survivors.

Purpose: Given that only a fraction of all patients will suffer from this particular complication, we investigated whether it could be predicted by genetic markers. 

Patients and methods: We analysed associations between skeletal muscle force (Fmax) and power (Pmax) and germline genetic variants from 1039 genes derived through whole-exome sequencing. Top-ranking association signals retained after correction for multiple testing were confirmed through genotyping, and further analysed through stratified analyses and multivariate models. 

Results: Our results show that skeletal muscle function deficit is associated with two common single nucleotide polymorphisms (SNPs) (rs2001616DUOX2, P=0.0002 (Pmax) and rs41270041ADAMTS4, P=0.02 (Fmax)) and two rare ones located in the ALOX15 gene (P=0.001 (Pmax)). These associations were further modulated by sex, body mass index and risk groups, which reflected glucocorticoid dose and radiation therapy (P≤0.02). 

Conclusion: Occurrence of muscle function deficit in childhood ALL is thus strongly modulated by variations in the DUOX2, ADAMTS4 and ALOX15 genes, which could lead to personalized prevention strategies in childhood ALL survivors.

Effect of the lipoxygenase inhibitor baicalein on bone tissue and bone healing in ovariectomized rats

BACKGROUND

Osteoporosis is one of the world's major medical burdens in the twenty-first century. Pharmaceutical intervention currently focusses on decelerating bone loss, but phytochemicals such as baicalein, which is a lipoxygenase inhibitor, may rescue bone loss. Studies evaluating the effect of baicalein in vivo are rare.

METHODS

We administered baicalein to sixty-one three-month-old female Sprague-Dawley rats. They were divided into five groups, four of which were ovariectomized (OVX) and one non-ovariectomized (NON-OVX). Eight weeks after ovariectomy, bilateral tibial osteotomy with plate osteosynthesis was performed and bone formation quantified. Baicalein was administered subcutaneously using three doses (C1: 1 mg/kg BW; C2: 10 mg/kg BW; and C3: 100 mg/kg BW) eight weeks after ovariectomy for four weeks. Finally, femora and tibiae were collected. Biomechanical tests, micro-CT, ashing, histological and gene expression analyses were performed.

RESULTS

Biomechanical properties were unchanged in tibiae and reduced in femora. In tibiae, C1 treatment enhanced callus density and cortical width and decreased callus area. In the C3 group, callus formation was reduced during the first 3 weeks after osteotomy, correlating to a higher mRNA expression of Osteocalcin, Tartrate-resistant acid phosphatase and Rankl. In femora, baicalein treatments did not alter bone parameters.

CONCLUSIONS

Baicalein enhanced callus density and cortical width but impaired early callus formation in tibiae. In femora, it diminished the biomechanical properties and calcium-to-phosphate ratio. Thus, it is not advisable to apply baicalein to treat early bone fractures. To determine the exact effects on bone healing, further studies in which baicalein treatments are started at different stages of healing are needed.

Expression of 15-lipoxygenase-1 in Merkel cell carcinoma is linked to advanced disease

BACKGROUND

The purpose of this study was to determine whether the expression of 15-lipoxygenase-1 (ALOX15) in primary tumour specimens predicts lymph node metastasis and subsequently clinical outcome in Merkel cell carcinoma (MCC) patients.

METHODS

A retrospective medical chart review of 33 patients was performed between 1994 and 2014. Eleven out of 33 (33%) Patients with primary MCC stages I and II were categorised as group I. Twenty two out of 33 (67%) Patients with regional lymph node metastases and/or distant metastases were defined as group II. All available tumour samples were immunostained for ALOX15, Podoplanin and MCPyV large T-protein antibody.

RESULTS

ALOX15 expression was observed in 19/23 (83%) primary tumour samples and in all lymph node metastasis. Primary tumours in patients with stage III and IV disease showed a higher expression rate of ALOX15 compared to patients with early stage disease (11/12 (92%) and 8/11 (73%), respectively). In group I, five patients (45%) were MCPyV positive, whereas in group II, 15 patients (68%) were MCPyV positive. The median lymphatic vessel density in ALOX15 negative group I primary tumour samples was lower compared to the median lymphatic vessel density in ALOX15 positive group I primary tumour probes (2.7 range, 1-4.3 vs 4.7 range, 4.0-7.3). Furthermore, all 17 samples of MCC metastases showed ALOX15 expression with a median lymphatic vessel density (not lymph node metastases) of 5.3 (range 2.0-7.3).

CONCLUSION

In the current study, we were able to show ALOX15 expression in the primary MCC sample and the metastasis sample. Based on the findings of the current study, expression rate of ALOX15 in primary MCC and metastases is possibly linked to an increased lymphatic vessel density.

Inhibition of Arachidonate 12/15-Lipoxygenase Improves α-Galactosidase Efficacy in iPSC-Derived Cardiomyocytes from Fabry Patients

(1) Background: A high incidence of intervening sequence (IVS)4+919 G>A mutation with later-onset cardiac phenotype have been reported in a majority of Taiwan Fabry cohorts. Some evidence indicated that conventional biomarkers failed to predict the long-term progression and therapeutic outcome; (2) Methods: In this study, we constructed an induced pluripotent stem cell (iPSC)-based platform from Fabry cardiomyopathy (FC) patients carrying IVS4+919 G>A mutation to screen for potential targets that may help the conventional treatment; (3) Results: The FC-patient-derived iPSC-differentiated cardiomyocytes (FC-iPSC-CMs) carried an expected IVS4+919 G>A genetic mutation and recapitulated several FC characteristics, including low α-galactosidase A enzyme activity and cellular hypertrophy. The proteomic analysis revealed that arachidonate 12/15-lipoxygenase (Alox12/15) was the most highly upregulated marker in FC-iPSC-CMs, and the metabolites of Alox12/15, 12(S)- and 15(S)-hydroxyeicosatetraenoic acid (HETE), were also elevated in the culture media. Late administration of Alox12/15 pharmacological inhibitor LOXBlock-1 combined with α-galactosidase, but not α-galactosidase alone, effectively reduced cardiomyocyte hypertrophy, the secretion of 12(S)- and 15(S)-HETE and the upregulation of fibrotic markers at the late phase of FC; (4) Conclusions: Our study demonstrates that cardiac Alox12/15 and circulating 12(S)-HETE/15(S)-HETE are involved in the pathogenesis of FC with IVS4+919 G>A mutation.

Deletion of 12/15-lipoxygenase accelerates the development of aging-associated and instability-induced osteoarthritis

OBJECTIVE

12/15-Lipoxygenase (12/15-LOX) catalyzes the generation of various anti-inflammatory lipid mediators, and has been implicated in several inflammatory and degenerative diseases. However, there is currently no evidence that 12/15-LOX has a role in osteoarthritis (OA). The aim of this study was to investigate the role of 12/15-LOX in the pathogenesis of OA.

METHODS

The development of aging-associated and destabilization of the medial meniscus (DMM)-induced OA were compared in 12/15-LOX-deficient (12/15-LOX-/-) and wild-type (WT) mice. The extent of cartilage damage was evaluated by histology. The expression of OA markers was evaluated by immunohistochemistry and RT-PCR. Cartilage explants were stimulated with IL-1α in the absence or presence of the 12/15-LOX metabolites, 15-hydroxyeicosatetraenoic acids (15-HETE), 13-hydroxyoctadecadienoic acid (13-HODE) or lipoxin A4 (LXA4), and the levels of matrix metalloproteinases-13 (MMP-13), Nitric oxide (NO) and prostaglandin E₂ (PGE₂) were determined. The effect of LXA4 on the progression of OA was evaluated in wild type (WT) mice.

RESULTS

The expression of 12/15-LOX in cartilage increased during the progression of DMM-induced OA and with aging in WT mice. Cartilage degeneration was more severe in 12/15-LOX-/- mice compared to WT mice in both models of OA, and this was associated with increased expression of MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs, aggrecanases (ADAMTS5), inducible NO synthases (iNOS), and mPGES-1. Treatment of cartilage explants with 12/15-LOX metabolites, suppressed IL-1α-induced production of MMP-13, NO and PGE₂, with LXA4 being the most potent. Intra-peritoneal injection of LXA4 reduced the severity of DMM-induced cartilage degradation.

CONCLUSIONS

These data suggest an important role of 12/15-LOX in the pathogenesis of OA. They also suggest that activation of this pathway may provide a novel strategy for prevention and treatment of OA.

Effect of zileuton on osteoporotic bone and its healing, expression of bone, and brain genes in rats

Estrogen deficiency and aging are associated with osteoporosis, impaired bone healing, and lower cognitive performance. Close functional and physical connections occur between bone and the central nervous system. An anti-inflammatory drug, zileuton (which is an inhibitor of arachidonate 5-lipoxygenase), is known to have a positive effect on bone tissue repair and brain ischemia. We studied the effect of zileuton on osteopenic bone and its healing and on the genes considered to be crucial for the cross talks between bone and brain. Three-month-old Sprague-Dawley rats were ovariectomized or left untreated. After 8 wk, bilateral metaphyseal tibia osteotomy with plate osteosynthesis was performed in all rats. Ovariectomized rats were fed with food containing zileuton (1, 10, or 100 mg/kg body wt) for 5 wk. In tibiae, bone volume, callus and cortical volume, and gene expression of osteocalcin and alkaline phosphatase were enhanced by zileuton (10 or 100 mg); biomechanical properties and bone density were not changed. In femur, zileuton enlarged cortical volume distal and trabecular volume proximal, decreasing their density. The expression level of brain Sema3a, known to regulate bone mass positively, was downregulated after ovariectomy. In contrast, bone Sema4d, a negative regulator of bone mass, was upregulated in the tibia callus after ovariectomy, whereas zileuton treatment (10 or 100 mg) resulted in reverse effects. Here, we describe for the first time the expression of Rbbp4 mRNA and its increase in tibia after ovariectomy. Zileuton caused downregulation of Rbbp4 in the hippocampus and had an effect on bone healing, changed the expression of genes involved in cross talk between bones and brain, and may be a potent drug for further examination in estrogen deficiency-related dysfunction(s). NEW & NOTEWORTHY Zileuton, a 5-lipoxygenase inhibitor, increased bone volume, callus and cortical volume in osteotomized tibia, and trabecular and cortical volume in femur. Although the expression of Sema3a (positively regulating bone mass) in brain was downregulated and Sema4d (negatively regulating bone mass) was upregulated in tibia callus after ovariectomy, zileuton could counteract these effects. Rbbp4 (involved in age-related memory loss) was increased in tibia callus after ovariectomy.

Effect of the lipoxygenase-inhibitors baicalein and zileuton on the vertebra in ovariectomized rats

Osteoporosis is one of the most common diseases worldwide. In osteoporosis, vertebral fractures represent a major burden. Lipoxygenase (LOX) inhibitors such as baicalein and zileuton may represent a promising therapeutic option owing to their antioxidative effects and suppression of various inflammatory processes in muscle and bone. The effect of these LOX inhibitors on the spine was studied in osteopenic rats. Female Sprague-Dawley rats were divided two times into five groups: four groups each were ovariectomized (OVX) and one control group was non-ovariectomized (NON-OVX). Eight weeks after ovariectomy, three concentrations of baicalein (1mg/kg body weight [BW], 10mg/kgBW, and 100mg/kgBW) were administered subcutaneously daily in three OVX groups for 4weeks. Similarly, zileuton was administered in three concentrations via food for 5weeks. In vivo computed tomography (pQCT) of the spine was performed before the treatments and at the end of the experiment. Lumbar vertebrae were subjected to a compression test, micro-CT, and ashing analyses. After baicalein treatment, cortical bone mineral density (BMD) was improved; trabecular connectivity and trabecular BMD were diminished at high dose. After zileuton treatment, the total BMD, anorganic weight, trabecular nodes, and trabecular area were improved. The in vivo stress-strain index was increased and alkaline phosphatase activity in serum was enhanced after both treatments. A dose-dependent effect was not clearly observed after both treatments. The treatments using baicalein for 4 and zileuton for 5weeks were not sufficient to change the biomechanical properties and bone volume fraction (BV/TV). Overall, baicalein improved the cortical bone parameters whereas zileuton had a favorable effect on the trabecular structure. Moreover, both treatments increased the bone formation rate. Longer trials, a combination of both LOX inhibitors, and their effect at the cellular and molecular levels should be investigated in further studies.

Effect of Lipoxygenase Oxidation on Surface Deposition of Unsaturated Fatty Acids

We studied the interactions of lipid molecules (linoleic acid, glycerol trilinoleate and a complex mixture of wood extractives) with hydrophilic and hydrophobic surfaces (cellulose nanofibrils (CNFs) and polyethylene terephthalate (PET), respectively). The effect of lipoxygenase treatment to minimize the affinity of the lipids with the given surface was considered. Application of an electroacoustic sensing technique (QCM) allowed the monitoring of the kinetics of oxidation as well as dynamics of lipid deposition on CNF and PET. The effect of the lipoxygenase enzymes (LOX) was elucidated with regards to their ability to reduce the formation of soiling lipid layers. The results pointed to the fact that the rate of colloidal oxidation depended on the type of lipid substrate. The pretreatment of the lipids with LOX reduced substantially their affinity to the surfaces, especially PET. Surface plasmon resonance (SPR) sensograms confirmed the effect of oxidation in decreasing the extent of deposition on the hydrophilic CNF. QCM energy dissipation analyses revealed the possible presence of a loosely adsorbed lipid layer on the PET surface. The morphology of the deposits accumulated on the solids was determined by atomic force microscopy and indicated important changes upon lipid treatment with LOX. The results highlighted the benefit of enzyme as a biobased treatment to reduce hydrophobic interactions, thus providing a viable solution to the control of lipid deposition from aqueous media.

Polymorphisms and mutations in the melanocortin-3 receptor and their relation to human obesity

Inactivating mutations in the melanocortin 3 receptor (Mc3r) have been described as causing obesity in mice, but the physiologic effects of MC3R mutations in humans have been less clear. Here we review the MC3R polymorphisms and mutations identified in humans, and the in vitro, murine, and human cohort studies examining their putative effects. Some, but not all, studies suggest that the common human MC3R variant T6K+V81I, as well as several other rare, function-altering mutations, are associated with greater adiposity and hyperleptinemia with altered energy partitioning. In vitro, the T6K+V81I variant appears to decrease MC3R expression and therefore cAMP generation in response to ligand binding. Knockin mouse studies confirm that the T6K+V81I variant increases feeding efficiency and the avidity with which adipocytes derived from bone or adipose tissue stem cells store triglycerides. Other MC3R mutations occur too infrequently in the human population to make definitive conclusions regarding their clinical effects. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

Serum from postmenopausal women treated with a by-product of olive-oil extraction process stimulates osteoblastogenesis and inhibits adipogenesis in human mesenchymal stem-cells (MSC)

Aging may enhance both oxidative stress and bone-marrow mesenchymal stem-cell (MSC) differentiation into adipocytes. That reduces osteoblastogenesis, thus favoring bone-mass loss and fracture, representing an important worldwide health-issue, mainly in countries with aging populations. Intake of antioxidant products may help to retain bone-mass density. Interestingly, a novel olive-pomace physical treatment to generate olive oil also yields by-products rich in functional antioxidants. Thus, diet of postmenopausal women was supplemented for two months with one of such by-products (distillate 6; D6), being rich in squalene. After treatment, serum from such women showed reduced both lipidic peroxidation and oxidized low-density lipoprotein (LDL). Besides, vitamin E and coenzyme Q10 levels increased. Furthermore, culture medium containing 10% of such serum both increased osteoblastogenesis and reduced adipogenesis in human MSC from bone marrow. Therefore, highly antioxidant by-products like D6 may represent a relevant source for development of functional products, for both prevention and treatment of degenerative pathologies associated with aging, like osteoporosis.

Fine-mapping of genes determining extrafusal fiber properties in murine soleus muscle

Muscle fiber cross-sectional area (CSA) and proportion of different fiber types are important determinants of muscle function and overall metabolism. Genetic variation plays a substantial role in phenotypic variation of these traits; however, the underlying genes remain poorly understood. This study aimed to map quantitative trait loci (QTL) affecting differences in soleus muscle fiber traits between the LG/J and SM/J mouse strains. Fiber number, CSA, and proportion of oxidative type I fibers were assessed in the soleus of 334 genotyped female and male mice of the F₃₄ generation of advanced intercross lines (AIL) derived from the LG/J and SM/J strains. To increase the QTL detection power, these data were combined with 94 soleus samples from the F₂ intercross of the same strains. Transcriptome of the soleus muscle of LG/J and SM/J females was analyzed by microarray. Genome-wide association analysis mapped four QTL (genome-wide P < 0.05) affecting the properties of muscle fibers to chromosome 2, 3, 4, and 11. A 1.5-LOD QTL support interval ranged between 2.36 and 4.67 Mb. On the basis of the genomic sequence information and functional and transcriptome data, we identified candidate genes for each of these QTL. The combination of analyses in F₂ and F₃₄ AIL populations with transcriptome and genomic sequence data in the parental strains is an effective strategy for refining QTL and nomination of the candidate genes.

Novel association between bone mineral density scores and the prevalence of peripheral artery disease in both sexes

The purpose of the current study was to investigate the association between bone mineral density (BMD) scores and the prevalence of peripheral artery disease (PAD) in a large cohort of subjects who underwent arterial Doppler assessments and calcaneal bone densitometry. The study was performed using data obtained from Life Line Screening Inc. Subjects were self-selected and paid for screening tests. The prevalence of PAD was significantly higher in men with osteopenia (4.5%) and osteoporosis (10.9%) compared to men with normal BMD (3.0%) ( p<0.001). Osteopenia (odds ratio (OR) 1.3) and osteoporosis (OR 2.3) were found to be independent risk factors for the presence of PAD in men. The prevalence of PAD was significantly higher in women with osteopenia (4.8%) and osteoporosis (11.8%) compared to women with normal BMD (3.3%) ( p<0.001). Osteopenia (OR 1.15) and osteoporosis (OR 1.8) were found to be independent risk factors for the presence of PAD in women. The current study reports a strong association of abnormal BMD analysis with the prevalence of PAD, which persists even when controlling for age and associated atherosclerotic risk factors. Although the mechanism by which these two disease processes is related is not completely elucidated, the presence of osteoporosis should make clinicians aware of the possibility of occult PAD or associated atherosclerotic disease in appropriate patients.

Osteoporosis: the current status of mesenchymal stem cell-based therapy

Osteoporosis, or bone loss, is a progressive, systemic skeletal disease that affects millions of people worldwide. Osteoporosis is generally age related, and it is underdiagnosed because it remains asymptomatic for several years until the development of fractures that confine daily life activities, particularly in elderly people. Most patients with osteoporotic fractures become bedridden and are in a life-threatening state. The consequences of fracture can be devastating, leading to substantial morbidity and mortality of the patients. The normal physiologic process of bone remodeling involves a balance between bone resorption and bone formation during early adulthood. In osteoporosis, this process becomes imbalanced, resulting in gradual losses of bone mass and density due to enhanced bone resorption and/or inadequate bone formation. Several growth factors underlying age-related osteoporosis and their signaling pathways have been identified, such as osteoprotegerin (OPG)/receptor activator of nuclear factor B (RANK)/RANK ligand (RANKL), bone morphogenetic protein (BMP), wingless-type MMTV integration site family (Wnt) proteins and signaling through parathyroid hormone receptors. In addition, the pathogenesis of osteoporosis has been connected to genetics. The current treatment of osteoporosis predominantly consists of antiresorptive and anabolic agents; however, the serious adverse effects of using these drugs are of concern. Cell-based replacement therapy via the use of mesenchymal stem cells (MSCs) may become one of the strategies for osteoporosis treatment in the future.

A High-Saturated-Fat, High-Sucrose Diet Aggravates Bone Loss in Ovariectomized Female Rats

BACKGROUND

Estrogen deficiency in women and high-saturated fat, high-sucrose (HFS) diets have both been recognized as risk factors for metabolic syndrome. Studies on the combined actions of these 2 detrimental factors on the bone in females are limited.

OBJECTIVE

We sought to determine the interactive actions of estrogen deficiency and an HFS diet on bone properties and to investigate the underlying mechanisms.

METHODS

Six-month-old Sprague Dawley sham or ovariectomized (OVX) rats were pair fed the same amount of either a low-saturated-fat, low-sucrose (LFS) diet (13% fat calories; 15% sucrose calories) or an HFS diet (42% fat calories; 30% sucrose calories) for 12 wk. Blood, liver, and bone were collected for correspondent parameters measurement.

RESULTS

Ovariectomy decreased bone mineral density in the tibia head (TH) by 62% and the femoral end (FE) by 49% (P < 0.0001). The HFS diet aggravated bone loss in OVX rats by an additional 41% in the TH and 37% in the FE (P < 0.05). Bone loss in the HFS-OVX rats was accompanied by increased urinary deoxypyridinoline concentrations by 28% (P < 0.05). The HFS diet induced cathepsin K by 145% but reduced osteoprotegerin mRNA expression at the FE of the HFS-sham rats by 71% (P < 0.05). Ovariectomy significantly increased peroxisome proliferator-activated receptor γ mRNA expression by 136% and 170% at the FE of the LFS- and HFS-OVX rats, respectively (P < 0.05). The HFS diet aggravated ovariectomy-induced lipid deposition and oxidative stress (OS) in rat livers (P < 0.05). Trabecular bone mineral density at the FE was negatively correlated with rat liver malondialdehyde concentrations (R(2) = 0.39; P < 0.01).

CONCLUSIONS

The detrimental actions of the HFS diet and ovariectomy on bone properties in rats occurred mainly in cancellous bones and were characterized by a high degree of bone resorption and alterations in OS.

Skeletal inflammation and attenuation of Wnt signaling, Wnt ligand expression, and bone formation in atherosclerotic ApoE-null mice

ApoE-null (ApoE-KO) mice fed a high-fat diet (HFD) develop atherosclerosis, due in part to activation of vascular inflammation by oxidized low-density lipoprotein. Since bone loss also occurs in these mice, we used them to investigate the impact of oxidized lipids on bone homeostasis and to search for underlying pathogenic pathways. Four-month-old female ApoE-KO mice fed a HFD for three months exhibited increased levels of oxidized lipids in bone, as well as decreased femoral and vertebral trabecular and cortical bone mass, compared with ApoE-KO mice on normal diet. Despite HFD-induced increase in expression of Alox15, a lipoxygenase that oxidizes LDL and promotes atherogenesis, global deletion of this gene failed to ameliorate the skeletal impact of HFD. Osteoblast number and function were dramatically reduced in trabecular and cortical bone of HFD-fed mice, whereas osteoclast number was modestly reduced only in trabecular bone, indicating that an imbalance in favor of osteoclasts was responsible for HFD-induced bone loss. These changes were associated with decreased osteoblast progenitors and increased monocyte/macrophages in the bone marrow as well as increased expression of IL-1β, IL-6, and TNF. HFD also attenuated Wnt signaling as evidenced by reduced expression of Wnt target genes, and it decreased expression of pro-osteoblastogenic Wnt ligands. These results suggest that oxidized lipids decrease bone mass by increasing anti-osteoblastogenic inflammatory cytokines and decreasing pro-osteoblastogenic Wnt ligands.

Anti-osteoporosis effect of Epimedium via an estrogen-like mechanism based on a system-level approach

ETHNOPHARMACOLOGICAL RELEVANCE

Epimedium is a popular traditional herbal medicine worldwide that has long been used to relieve osteoporosis. The estrogenic properties of the herb are conferred by several phytoestrogens, such as flavonoids, lignans, and steroids. However, the poor understanding on the estrogen-like mechanism of Epimedium at the molecular and system levels limits the applications of this herb in osteoporosis treatment.

MATERIALS AND METHODS

In this study, systems pharmacology was established to investigate the relationship between Epimedium and estrogen against osteoporosis by integrating active component screening, drug-likeness evaluation, herb feature mapping, target prediction and validation, and network analysis.

RESULTS

A total of 77 active components that possessed similar structural features to estrogen as determined using herb feature mapping were selected from Epimedium by oral bioavailability prediction and drug-likeness evaluation. Twenty three osteoporosis-related targets were obtained from the active components of Epimedium as potential targets, 11 of which were common targets with estrogen. All osteoporosis-related targets were further mapped to compound-target and target-pathway networks. Results displayed that Epimedium can exert anti-osteoporosis effects by directly regulating the 11 estrogen-related targets and a set of target proteins on five estrogen-related pathways.

CONCLUSION

This study explained the estrogen-like mechanism of Epimedium in preventing and treating osteoporosis, and provided a new standpoint for exploring the traditional herbal medicine against osteoporosis.

Quantitative Trait Locus and Genetical Genomics Analysis Identifies Putatively Causal Genes for Fecundity and Brooding in the Chicken

Life history traits such as fecundity are important to evolution because they make up components of lifetime fitness. Due to their polygenic architectures, such traits are difficult to investigate with genetic mapping. Therefore, little is known about their molecular basis. One possible way toward finding the underlying genes is to map intermediary molecular phenotypes, such as gene expression traits. We set out to map candidate quantitative trait genes for egg fecundity in the chicken by combining quantitative trait locus mapping in an advanced intercross of wild by domestic chickens with expression quantitative trait locus mapping in the same birds. We measured individual egg fecundity in 232 intercross chickens in two consecutive trials, the second one aimed at measuring brooding. We found 12 loci for different aspects of egg fecundity. We then combined the genomic confidence intervals of these loci with expression quantitative trait loci from bone and hypothalamus in the same intercross. Overlaps between egg loci and expression loci, and trait–gene expression correlations identify 29 candidates from bone and five from hypothalamus. The candidate quantitative trait genes include fibroblast growth factor 1, and mitochondrial ribosomal proteins L42 and L32. In summary, we found putative quantitative trait genes for egg traits in the chicken that may have been affected by regulatory variants under chicken domestication. These represent, to the best of our knowledge, some of the first candidate genes identified by genome-wide mapping for life history traits in an avian species.

Modulation of unloading-induced bone loss in mice with altered ERK signaling

Genetic variations mediate skeletal responsiveness to mechanical unloading, with individual space travelers exhibiting large variations in the extent of bone loss. We previously identified genomic regions harboring several hundred genes that can modulate the magnitude of skeletal adaptation to mechanical unloading. Here, bioinformatic filters aided in shortlisting 30 genes with bone-related and mechanoregulatory roles. The genes CD44, FGF2, NOD2, and Fas, all associated with ERK signaling, were then functionally tested in hindlimb-unloaded (HLU) knockout (KO) mice. Compared to their respective normally ambulating wildtype (WT) controls, all KO strains, except Fas mice, had lower trabecular bone volume, bone volume fraction, and/or trabecular number. For cortical bone and compared to ambulatory WT mice, CD44(-/-) had impaired properties while FGF2(-/-) showed enhanced indices. NOD2(-/-) and Fas(-/-) did not have a cortical phenotype. In all KO and WT groups, HLU resulted in impaired trabecular and cortical indices, primarily due to trabecular tissue loss and mitigation of cortical bone growth. The difference in trabecular separation between HLU and ambulatory controls was significantly greater in CD44(-/-) and NOD2(-/-) mice than in WT mice. In cortical bone, differences in cortical thickness, total pore volume, and cortical porosity between HLU and controls were aggravated in CD44(-/-) mice. In contrast, deletion of NOD2 and Fas genes mitigated the differences in Po.V between HLU and control mice. Together, we narrowed a previous list of QTL-derived candidate genes from over 300 to 30, and showed that CD44, NOD2, and Fas have distinct functions in regulating changes in trabecular and cortical bone indices during unloading.

Polymorphisms in inflammation associated genes ALOX15 and IL-6 are associated with bone properties in young women and fracture in elderly

PURPOSE

ALOX12 and ALOX15 encode arachidonate lipoxygenases which produce lipid metabolites involved in inflammatory processes. Metabolites generated by ALOX12 and ALOX15 can activate the expression of the potent pro-inflammatory cytokine IL-6, and produce endogenous ligands for PPARG. In this study, polymorphisms in ALOX12, ALOX15, IL6 and PPARG were investigated for association with bone properties in young and elderly Swedish women.

METHODS

Three SNPs in ALOX12, five in ALOX15, one each in IL6 and PPARG were genotyped in the cohorts PEAK-25 (n=1061 women; all 25y) and OPRA (n=1044 women; all 75y). Bone mineral density (BMD) and quantitative ultrasound (QUS) were analyzed in both cohorts; trabecular bone score (TBS) in PEAK-25; bone loss, fracture incidence and serum C-reactive protein (CRP) were assessed in OPRA.

RESULTS

In the elderly women ALOX15 (rs2619112) was associated with CRP levels (p=0.004) and incident fracture of any type (p=0.014), although not with BMD or ultrasound. In young women, carrying the common T allele (ALOX 15 rs748694) was associated with lower QUS values (p=0.002-0.006). The IL6 SNP was associated with lower BMD in PEAK-25 (femoral neck p=0.034; hip p=0.012). TBS was not associated with variation in any gene. Variants in the ALOX12 and PPARγ were not associated with BMD in either cohort.

CONCLUSIONS

This study suggests that variation in inflammation related genes ALOX15 and IL6 was associated with bone microarchitecture and density in young adult women, but appears to be less important in the elderly, despite an observed association with CRP as a marker of inflammation and incident fracture.

Establishing biomechanical mechanisms in mouse models: practical guidelines for systematically evaluating phenotypic changes in the diaphyses of long bones

Mice are widely used in studies of skeletal biology, and assessment of their bones by mechanical testing is a critical step when evaluating the functional effects of an experimental perturbation. For example, a gene knockout may target a pathway important in bone formation and result in a "low bone mass" phenotype. But how well does the skeleton bear functional loads; eg, how much do bones deform during loading and how resistant are bones to fracture? By systematic evaluation of bone morphological, densitometric, and mechanical properties, investigators can establish the "biomechanical mechanisms" whereby an experimental perturbation alters whole-bone mechanical function. The goal of this review is to clarify these biomechanical mechanisms and to make recommendations for systematically evaluating phenotypic changes in mouse bones, with a focus on long-bone diaphyses and cortical bone. Further, minimum reportable standards for testing conditions and outcome variables are suggested that will improve the comparison of data across studies. Basic biomechanical principles are reviewed, followed by a description of the cross-sectional morphological properties that best inform the net cellular effects of a given experimental perturbation and are most relevant to biomechanical function. Although morphology is critical, whole-bone mechanical properties can only be determined accurately by a mechanical test. The functional importance of stiffness, maximum load, postyield displacement, and work-to-fracture are reviewed. Because bone and body size are often strongly related, strategies to adjust whole-bone properties for body mass are detailed. Finally, a comprehensive framework is presented using real data, and several examples from the literature are reviewed to illustrate how to synthesize morphological, tissue-level, and whole-bone mechanical properties of mouse long bones.

Genetic regulation of bone metabolism in the chicken: similarities and differences to Mammalian systems

Birds have a unique bone physiology, due to the demands placed on them through egg production. In particular their medullary bone serves as a source of calcium for eggshell production during lay and undergoes continuous and rapid remodelling. We take advantage of the fact that bone traits have diverged massively during chicken domestication to map the genetic basis of bone metabolism in the chicken. We performed a quantitative trait locus (QTL) and expression QTL (eQTL) mapping study in an advanced intercross based on Red Junglefowl (the wild progenitor of the modern domestic chicken) and White Leghorn chickens. We measured femoral bone traits in 456 chickens by peripheral computerised tomography and femoral gene expression in a subset of 125 females from the cross with microarrays. This resulted in 25 loci for female bone traits, 26 loci for male bone traits and 6318 local eQTL loci. We then overlapped bone and gene expression loci, before checking for an association between gene expression and trait values to identify candidate quantitative trait genes for bone traits. A handful of our candidates have been previously associated with bone traits in mice, but our results also implicate unexpected and largely unknown genes in bone metabolism. In summary, by utilising the unique bone metabolism of an avian species, we have identified a number of candidate genes affecting bone allocation and metabolism. These findings can have ramifications not only for the understanding of bone metabolism genetics in general, but could also be used as a potential model for osteoporosis as well as revealing new aspects of vertebrate bone regulation or features that distinguish avian and mammalian bone.

In this work we seek to further the understanding of bone genetics by mapping bone traits and gene expression in the chicken. Bone in female birds is special due to egg production. In this study, we combine the genetic mapping of bone traits with bone gene expression to find candidate quantitative trait genes that explain the differences between wild and domestic chickens in terms of bone production. The concept of combining genetic mapping and gene expression mapping is not new, and has already been successful in isolating bone-related genes in mammals, however this is the first time it has been applied to an avian system with such unique bone modelling processes. We aim to reveal new molecular mechanisms of bone regulation, and many of the candidates we find are new, highlighting the potential this technique has to identify the potential differences between avian and mammalian bone biology.

Pros and cons of fatty acids in bone biology

Despite the growing interest in deciphering the causes and consequences of obesity-related disorders, the mechanisms linking fat intake to bone behaviour remain unclear. Since bone fractures are widely associated with increased morbidity and mortality, most notably in elderly and obese people, bone health has become a major social and economic issue. Consistently, public health system guidelines have encouraged low-fat diets in order to reduce associated complications. However, from a bone point of view, mechanisms linking fat intake to bone alteration remain quite controversial. Thus, after more than a decade of dedicated studies, this timely review offers a comprehensive overview of the relationships between bone and fatty acids. Using clinical evidences as a starting-point to more complex molecular elucidation, this work highlights the complexity of the system and reveals that bone alteration that cannot be solved simply by taking ω-3 pills. Fatty acid effects on bone metabolism can be both direct and indirect and require integrated investigations. Furthermore, even at the level of a single cell, one fatty acid is able to trigger several different independent pathways (receptors, metabolites…) which may all have a say in the final cellular metabolic response.

Expression of inactive glutathione peroxidase 4 leads to embryonic lethality, and inactivation of the Alox15 gene does not rescue such knock-in mice

AIMS

Glutathione peroxidases (Gpx) and lipoxygenases (Alox) are functional counterplayers in the metabolism of hydroperoxy lipids that regulate cellular redox homeostasis. Gpx4 is a moonlighting protein that has been implicated not only as an enzyme in anti-oxidative defense, gene expression regulation, and programmed cell death, but also as a structural protein in spermatogenesis. Homozygous Gpx4 knock-out mice are not viable, but molecular reasons for intrauterine lethality are not completely understood. This study was aimed at investigating whether the lack of catalytic activity or the impaired function as structural protein is the dominant reason for embryonic lethality. We further explored whether the pro-oxidative enzyme mouse 12/15 lipoxygenase (Alox15) plays a major role in embryonic lethality of Gpx4-deficient mice.

RESULTS

To achieve these goals, we first created knock-in mice, which express a catalytically inactive Gpx4 mutant (Sec46Ala). As homozygous Gpx4-knock-out mice Sec46Ala-Gpx4(+/+) knock-in animals are not viable but undergo intrauterine resorption between embryonic day 6 and 7 (E6-7). In contrast, heterozygous knock-in mice (Sec46Ala-Gpx4(-/+)) are viable, fertile and do not show major phenotypic alterations. Interestingly, homozygous Alox15 deficiency did not rescue the U46A-Gpx4(+/+) mice from embryonic lethality. In fact, when heterozygous U46A-Gpx4(-/+) mice were stepwise crossed into an Alox15-deficent background, no viable U46A-Gpx4(+/+)+Alox15(-/-) individuals were obtained. However, we were able to identify U46A-Gpx4(+/+)+Alox15(-/-) embryos in the state of resorption around E7.

INNOVATION AND CONCLUSION

These data suggest that the lack of catalytic activity is the major reason for the embryonic lethality of Gpx4(-/-) mice and that systemic inactivation of the Alox15 gene does not rescue homozygous knock-in mice expressing catalytically silent Gpx4.

Arachidonate 15-lipoxygenase is required for chronic myeloid leukemia stem cell survival

Cancer stem cells (CSCs) are responsible for the initiation and maintenance of some types of cancer, suggesting that inhibition of these cells may limit disease progression and relapse. Unfortunately, few CSC-specific genes have been identified. Here, we determined that the gene encoding arachidonate 15-lipoxygenase (Alox15/15-LO) is essential for the survival of leukemia stem cells (LSCs) in a murine model of BCR-ABL-induced chronic myeloid leukemia (CML). In the absence of Alox15, BCR-ABL was unable to induce CML in mice. Furthermore, Alox15 deletion impaired LSC function by affecting cell division and apoptosis, leading to an eventual depletion of LSCs. Moreover, chemical inhibition of 15-LO function impaired LSC function and attenuated CML in mice. The defective CML phenotype in Alox15-deficient animals was rescued by depleting the gene encoding P-selectin, which is upregulated in Alox15-deficient animals. Both deletion and overexpression of P-selectin affected the survival of LSCs. In human CML cell lines and CD34+ cells, knockdown of Alox15 or inhibition of 15-LO dramatically reduced survival. Loss of Alox15 altered expression of PTEN, PI3K/AKT, and the transcription factor ICSBP, which are known mediators of cancer pathogenesis. These results suggest that ALOX15 has potential as a therapeutic target for eradicating LSCs in CML.

Bicc1 is a genetic determinant of osteoblastogenesis and bone mineral density

Patient bone mineral density (BMD) predicts the likelihood of osteoporotic fracture. While substantial progress has been made toward elucidating the genetic determinants of BMD, our understanding of the factors involved remains incomplete. Here, using a systems genetics approach in the mouse, we predicted that bicaudal C homolog 1 (Bicc1), which encodes an RNA-binding protein, is responsible for a BMD quantitative trait locus (QTL) located on murine chromosome 10. Consistent with this prediction, mice heterozygous for a null allele of Bicc1 had low BMD. We used a coexpression network-based approach to determine how Bicc1 influences BMD. Based on this analysis, we inferred that Bicc1 was involved in osteoblast differentiation and that polycystic kidney disease 2 (Pkd2) was a downstream target of Bicc1. Knock down of Bicc1 and Pkd2 impaired osteoblastogenesis, and Bicc1 deficiency-dependent osteoblast defects were rescued by Pkd2 overexpression. Last, in 2 human BMD genome-wide association (GWAS) meta-analyses, we identified SNPs in BICC1 and PKD2 that were associated with BMD. These results, in both mice and humans, identify Bicc1 as a genetic determinant of osteoblastogenesis and BMD and suggest that it does so by regulating Pkd2 transcript levels.

Fracture healing and lipid mediators

Lipid mediators regulate bone regeneration during fracture healing. Prostaglandins and leukotrienes are well-known lipid mediators that regulate inflammation and are synthesized from the Ω-6 fatty acid, arachidonic acid. Cyclooxygenase (COX-1 or COX-2) and 5-lipoxygenase (5-LO) catalyze the initial enzymatic steps in the synthesis of prostaglandins and leukotrienes, respectively. Inhibition or genetic ablation of COX-2 activity impairs fracture healing in animal models. Genetic ablation of COX-1 does not affect the fracture callus strength in mice, suggesting that COX-2 activity is primarily responsible for regulating fracture healing. Inhibition of cyclooxygenase activity with nonsteroidal anti-inflammatory drugs (NSAIDs) is performed clinically to reduce heterotopic ossification, although clinical evidence that NSAID treatment impairs fracture healing remains controversial. In contrast, inhibition or genetic ablation of 5-LO activity accelerates fracture healing in animal models. Even though prostaglandins and leukotrienes regulate inflammation, loss of COX-2 or 5-LO activity appears to primarily affect chondrogenesis during fracture healing. Prostaglandin or prostaglandin analog treatment, prostaglandin-specific synthase inhibition and prostaglandin or leukotriene receptor antagonism also affect callus chondrogenesis. Unlike the Ω-6-derived lipid mediators, lipid mediators derived from Ω-3 fatty acids, such as resolvin E1 (RvE1), have anti-inflammatory activity. In vivo, RvE1 can inhibit osteoclastogenesis and limit bone resorption. Although Ω-6 and Ω-3 lipid mediators have clear-cut effects on inflammation, the role of these lipid mediators in bone regeneration is more complex, with apparent effects on callus chondrogenesis and bone remodeling.

Modulation of strain-specific differences in gene expression by cannabinoid type 2 receptor deficiency

Previous studies have shown that the skeletal consequences of cannabinoid receptor deficiency differ in different strains of mice. In order to explore the mechanisms responsible, we analysed global gene expression in bone from wild-type CD1 mice and littermates with targeted inactivation of the type 2 cannabinoid receptor (Cnr2 (-/-)) and compared the results with those obtained from a similar analysis of wild-type and Cnr2 (-/-) C57BL/6 mice. Trabecular bone volume was increased in Cnr2 (-/-) CD1 mice compared with wild-type littermates but decreased in Cnr2 (-/-) C57BL/6 mice. Microarray analysis identified 354 genes in which substantial differences in gene expression (>1.5-fold) were observed that were specifically affected by Cnr2 deficiency. Bioinformatic analysis of data from wild-type mice of each strain revealed Cnr2-dependent differences in expression of genes clustering within the gene ontology (GO) terms immune response (p < 0.0001), positive regulation of response to stimulus (p < 0.0001), nucleotide binding (p = 0.002), and ribonucleotide binding (p = 0.003). Bioinformatic analysis of data from Cnr2 (-/-) mice of each strain revealed associations between GO terms corresponding to the extracellular region (p = 0.002), the cell surface (p = 0.02), antigen binding (p = 0.03), external side of plasma membrane (p = 0.04), and regulation of the force of heart contraction (p = 0.04). We conclude that Cnr2 deficiency affects expression of a large number of genes in different strains of mice, and that these differences are likely to be responsible in part for the differences in skeletal phenotype that we and others have observed in mice with defective cannabinoid receptor signalling in different genetic backgrounds.

New vitamin D less-calcemic analog affect human bone cell line and cultured vascular smooth muscle cells similar to other less-calcemic analogs

Primary cultures of human bone and vascular cells respond to vitamin D treatment by modulation of cell proliferation measured by DNA synthesis (DNA) and energy metabolism measured by creatine kinase specific activity (CK) via binding to vitamin D receptors (VDR) which are expressed in these cells. Vitamin D compounds also modulate the response to estradiol-17β (E₂) and the expression mRNAs of estrogen receptors (ERα and ERβ), VDR, 25-hydroxy vitamin D₃ 1-α hydroxylase (1OHase) and lipoxygenases (12LO and 15LO). We now compared our newly synthesized analog: 1α,25-dihydroxy-9-methylene-19-norvitamin D₃ JK152 (JK), on bone and vascular cells compared to other analogs. Human bone cell line SaOS₂ respond to JK by increased DNA and stimulated CK dose-dependently, similar to the less-calcemic analogs CB 1093 (CB) and EB 1089 (EB). JK also up-regulated the response to E₂ in terms of DNA and CK. JK inhibited DNA synthesis and increased CK in primary human vascular smooth muscle cells (VSMC) dose-dependently similar to EB and CB. JK up regulated the response to E₂ in terms of CK with no effect on DNA. JK similar to CB and EB stimulated mRNA expression of VDR and ERα, 12LO and 15LO, with no effect on ERβ and 1OHase mRNA expression in SaOS₂ measured by real time PCR. Similar treatments of VSMC with JK, CB and EB stimulated 12LO and 15LO, VDR and ERα mRNA expression with no effect on ERβ and 1OHase mRNA expression. The results presented here demonstrate that the new vitamin D less-calcemic analog JK is similar to other analogs in its effects on human cultured cells and therefore may be used in combined hormone replacement treatment (HRT) both in vitro and in vivo.

Genetic ablation of 12/15-lipoxygenase but not 5-lipoxygenase protects against denervation-induced muscle atrophy

Skeletal muscle atrophy is a debilitating outcome of a number of chronic diseases and conditions associated with loss of muscle innervation by motor neurons, such as aging and neurodegenerative diseases. We previously reported that denervation-induced loss of muscle mass is associated with activation of cytosolic phospholipase A2 (cPLA2), the rate-limiting step for the release of arachidonic acid from membrane phospholipids, which then acts as a substrate for metabolic pathways that generate bioactive lipid mediators. In this study, we asked whether 5- and 12/15-lipoxygenase (LO) lipid metabolic pathways downstream of cPLA2 mediate denervation-induced muscle atrophy in mice. Both 5- and 12/15-LO were activated in response to surgical denervation; however, 12/15-LO activity was increased ~2.5-fold versus an ~1.5-fold increase in activity of 5-LO. Genetic and pharmacological inhibition of 12/15-LO (but not 5-LO) significantly protected against denervation-induced muscle atrophy, suggesting a selective role for the 12/15-LO pathway in neurogenic muscle atrophy. The activation of the 12/15-LO pathway (but not 5-LO) during muscle atrophy increased NADPH oxidase activity, protein ubiquitination, and ubiquitin-proteasome-mediated proteolytic degradation. In conclusion, this study reveals a novel pathway for neurogenic muscle atrophy and suggests that 12/15-LO may be a potential therapeutic target in diseases associated with loss of innervation and muscle atrophy.

Interactions between α-tocopherol, polyunsaturated fatty acids, and lipoxygenases during embryogenesis

α-Tocopherol is a lipid-soluble antioxidant that is specifically required for reproduction and embryogenesis. However, since its discovery, α-tocopherol's specific biologic functions, other than as an antioxidant, and the mechanism(s) mediating its requirement for embryogenesis remain unknown. As an antioxidant, α-tocopherol protects polyunsaturated fatty acids (PUFAs) from lipid peroxidation. α-Tocopherol is probably required during embryonic development to protect PUFAs that are crucial to development, specifically arachidonic (ARA) and docosahexaenoic (DHA) acids. Additionally, ARA and DHA are metabolized to bioactive lipid mediators via lipoxygenase enzymes, and α-tocopherol may directly protect, or it may mediate the production and/or actions of, these lipid mediators. In this review, we discuss how α-tocopherol (1) prevents the nonspecific, radical-mediated peroxidation of PUFAs, (2) functions within a greater antioxidant network to modulate the production and/or function of lipid mediators derived from 12- and 12/15-lipoxygenases, and (3) modulates 5-lipoxygenase activity. The application and implication of such interactions are discussed in the context of α-tocopherol requirements during embryogenesis.

Effects of phytoestrogens and other plant-derived compounds on mesenchymal stem cells, bone maintenance and regeneration

Phytoestrogens and other plant-derived compounds and extracts have been developed for the treatment of menopause-related complaints and disorders, e.g. hot flushes and osteoporosis. Since estrogens have been discussed to enhance the risk for hormone-sensitive cancers, research activities try to find alternatives. Phytoestrogens like genistein and resveratrol as well as other plant-derived compounds are capable of substituting for estrogens to some extent. Their effects on mesenchymal stem cells and the tissues derived therefrom have been investigated in vitro and in preclinical settings. Besides their well-known estrogenic, i.e. mainly antiresorptive effects on bone via estrogen receptor (ER) signalling, they also directly or indirectly affect osteogenic and adipogenic pathways. As a novel mechanism, phytoestrogens and plant-derived saponins and flavonoids like kaempferol and xanthohumol have been described to reciprocally affect the osteogenic versus the adipogenic differentiation pathway. Both, ER-mediated and other pathways mediate a shift towards osteogenesis by inhibiting PPARγ and C/EBPα, the key adipogenic transcription factors (TFs), while stimulating the key osteogenic TFs Runx2 and Sp7. Besides ER signalling, the broad spectrum of molecular mechanisms supporting osteogenesis comprises the modulation of PPARγ, Wnt/β-catenin, and Sirt1 signalling, which inversely influence the transcription or transactivation of osteogenic versus adipogenic TFs. Preventing the age- and hormone deficiency-related shift towards adipogenesis without provoking adverse estrogenic effects represents a very promising strategy for treating bone loss and other metabolic diseases beyond bone. Research on plant-derived compounds will have to be pursued in vitro as well as in preclinical studies and controlled clinical trials in humans are urgently needed. This article is part of a Special Issue entitled 'Phytoestrogens'.

Polyoxygenated cholesterol ester hydroperoxide activates TLR4 and SYK dependent signaling in macrophages

Oxidation of low-density lipoprotein (LDL) is one of the major causative mechanisms in the development of atherosclerosis. In previous studies, we showed that minimally oxidized LDL (mmLDL) induced inflammatory responses in macrophages, macropinocytosis and intracellular lipid accumulation and that oxidized cholesterol esters (OxCEs) were biologically active components of mmLDL. Here we identified a specific OxCE molecule responsible for the biological activity of mmLDL and characterized signaling pathways in macrophages in response to this OxCE. Using liquid chromatography – tandem mass spectrometry and biological assays, we identified an oxidized cholesteryl arachidonate with bicyclic endoperoxide and hydroperoxide groups (BEP-CE) as a specific OxCE that activates macrophages in a TLR4/MD-2-dependent manner. BEP-CE induced TLR4/MD-2 binding and TLR4 dimerization, phosphorylation of SYK, ERK1/2, JNK and c-Jun, cell spreading and uptake of dextran and native LDL by macrophages. The enhanced macropinocytosis resulted in intracellular lipid accumulation and macrophage foam cell formation. Bone marrow-derived macrophages isolated from TLR4 and SYK knockout mice did not respond to BEP-CE. The presence of BEP-CE was demonstrated in human plasma and in the human plaque material captured in distal protection devices during percutaneous intervention. Our results suggest that BEP-CE is an endogenous ligand that activates the TLR4/SYK signaling pathway. Because BEP-CE is present in human plasma and human atherosclerotic lesions, BEP-CE-induced and TLR4/SYK-mediated macrophage responses may contribute to chronic inflammation in human atherosclerosis.

Effects of arachidonic acid on the concentration of hydroxyeicosatetraenoic acids in culture media of mesenchymal stromal cells differentiating into adipocytes or osteoblasts

Metabolites derived from the polyunsaturated fatty acids (PUFA) may modulate the mesenchymal stromal cell (MSC) differentiation. Such cells can differentiate into different cellular types, including adipocytes and osteoblasts. Aging favors the bone marrow MSC differentiation toward the former, causing a loss of bone density associated with pathologies like osteoporosis. The omega-6 arachidonic acid (AA) favors MSC adipogenesis to a greater extent than omega-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In this work, we study the joint action of both PUFA. Thus, not induced and induced to adipocyte or osteoblast MSC were treated with 20 μM of each PUFA (either AA, AA + DHA or AA + EPA). The expression of osteogenic and adipogenic molecular markers, the alox15b lipoxygenase gene expression and the 5-, 8-, 11-, 12- and 15-hydroxyeicosatetraenoic acids (HETE) derived from the AA metabolism in the culture media were determined. The results show that the adipogenesis induction of AA is not suppressed by the joint presence of EPA and DHA. In fact, both increased the adipogenic effect of AA on MSC differentiated into osteoblasts. The different HETE concentrations increased in cultures supplemented with AA, albeit such concentrations were lower in the cultures induced to differentiate, mainly at day 21 after the induction. Furthermore, the reduction in the HETE concentration was correlated with a higher expression of the alox15b gene. These results highlight the PUFA metabolism differences between uninduced and induced MSC to differentiate into adipocytes and osteoblasts, besides the relevant role of the lipoxygenase gene expression in adipogenesis induction.

Haploinsufficiency of osterix in chondrocytes impairs skeletal growth in mice

Osterix (Osx) is essential for both intramembranous or endochondral bone formation. Osteoblast-specific ablation of Osx using Col1α1-Cre resulted in osteopenia, because of impaired osteoblast differentiation in adult mice. Since Osx is also known to be expressed in chondrocytes, we evaluated the role of Osx expressed in chondrocytes by examining the skeletal phenotype of mice with conditional disruption of Osx in Col2α1-expressing chondrocytes. Surprisingly, Cre-positive mice that were homozygous for Osx floxed alleles died after birth. Alcian blue and alizarin red staining revealed that the lengths of skeleton, femur, and vertebrae were reduced by 21, 26, and 14% (P < 0.01), respectively, in the knockout (KO) compared with wild-type mice. To determine if haploid insufficiency of Osx in chondrocytes influenced postnatal skeletal growth, we compared skeletal phenotype of floxed heterozygous mice that were Cre-positive or Cre-negative. Body length was reduced by 8% (P < 0.001), and areal BMD of total body, femur, and tibia was reduced by 5, 7, and 8% (P < 0.05), respectively, in mice with conditional disruption of one allele of Osx in chondrocytes. Micro-CT showed reduced cortical volumetric bone mineral density and trabecular bone volume to total volume in the femurs of Osx(flox/+);col2α1-Cre mice. Histological analysis revealed that the impairment of longitudinal growth was associated with disrupted growth plates in the Osx(flox/+);col2α1-Cre mice. Primary chondrocytes isolated from KO embryos showed reduced expression of chondral ossification markers but elevated expression of chondrogenesis markers. Our findings indicate that Osx expressed in chondrocytes regulates bone growth in part by regulating chondrocyte hypertrophy.

Basic biology of skeletal aging: role of stress response pathways

Although a decline in bone formation and loss of bone mass are common features of human aging, the molecular mechanisms mediating these effects have remained unclear. Evidence from pharmacological and genetic studies in mice has provided support for a deleterious effect of oxidative stress in bone and has strengthened the idea that an increase in reactive oxygen species (ROS) with advancing age represents a pathophysiological mechanism underlying age-related bone loss. Mesenchymal stem cells and osteocytes are long-lived cells and, therefore, are more susceptible than other types of bone cells to the molecular changes caused by aging, including increased levels of ROS and decreased autophagy. However, short-lived cells like osteoblast progenitors and mature osteoblasts and osteoclasts are also affected by the altered aged environment characterized by lower levels of sex steroids, increased endogenous glucocorticoids, and higher oxidized lipids. This article reviews current knowledge on the effects of the aging process on bone, with particular emphasis on the role of ROS and autophagy in cells of the osteoblast lineage in mice.

Genetic loci that control the loss and regain of trabecular bone during unloading and reambulation

Changes in trabecular morphology during unloading and reloading are marked by large variations between individuals, implying that there is a strong genetic influence on the magnitude of the response. Here, we subjected more than 350 second-generation (BALBxC3H) 4-month-old adult female mice to 3 weeks of hindlimb unloading followed by 3 weeks of reambulation to identify the quantitative trait loci (QTLs) that define an individual's propensity to either lose trabecular bone when weight bearing is removed or to gain trabecular bone when weight bearing is reintroduced. Longitudinal in vivo micro-computed tomography (µCT) scans demonstrated that individual mice lost between 15% and 71% in trabecular bone volume fraction (BV/TV) in the distal femur during unloading (average: -43%). Changes in trabecular BV/TV during the 3-week reambulation period ranged from a continuation of bone loss (-18%) to large additions (56%) of tissue (average: +10%). During unloading, six QTLs accounted for 21% of the total variability in changes in BV/TV whereas one QTL accounted for 6% of the variability in changes in BV/TV during reambulation. QTLs were also identified for changes in trabecular architecture. Most of the QTLs defining morphologic changes during unloading or reambulation did not overlap with those QTLs identified at baseline, suggesting that these QTLs harbor genes that are specific for sensing changes in the levels of weight bearing. The lack of overlap in QTLs between unloading and reambulation also emphasizes that the genes modulating the trabecular response to unloading are distinct from those regulating tissue recovery during reloading. The identified QTLs contain the regulatory genes underlying the strong genetic regulation of trabecular bone's sensitivity to weight bearing and may help to identify individuals that are most susceptible to unloading-induced bone loss and/or the least capable of recovering.

Cyclic AMP signaling in bone marrow stromal cells has reciprocal effects on the ability of mesenchymal stem cells to differentiate into mature osteoblasts versus mature adipocytes

Stimulatory G protein-mediated cAMP signaling is intimately involved in skeletal homeostasis. However, limited information is available on the role of the cAMP signaling in regulating the differentiation of mesenchymal stem cells into mature osteoblasts and adipocytes. To investigate this, we treated primary mouse bone marrow stromal cells (BMSCs) with forskolin to stimulate cAMP signaling and determined the effect on osteoblast and adipocyte differentiation. Exposure of differentiating osteoblasts to forskolin markedly inhibited progression to the late stages of osteoblast differentiation, and this effect was replicated by continuous exposure to PTH. Strikingly, forskolin activation of cAMP signaling in BMSCs conditioned mesenchymal stem cells (MSCs) to undergo increased osteogenic differentiation and decreased adipogenic differentiation. PTH treatment of BMSCs also enhanced subsequent osteogenesis, but promoted an increased adipogenesis as well. Thus, activation of cAMP signaling alters the lineage commitment of MSCs, favoring osteogenesis at the expense of adipogenesis.