PPARγ: a circadian transcription factor in adipogenesis and osteogenesis

Melatonin as a promising modulator of aging related neurodegenerative disorders: Role of microRNAs

One of the host risk factors involved in aging-related diseases is coupled with the reduction of endogenous melatonin (MLT) synthesis in the pineal gland. MLT is considered a well-known pleiotropic regulatory hormone to modulate a multitude of biological processes such as the regulation of circadian rhythm attended by potent anti-oxidant, anti-inflammatory, and anti-cancer properties. It has also been established that the microRNAs family, as non-coding mRNAs regulating post-transcriptional processes, also serve a crucial role to promote MLT-related advantageous effects in both experimental and clinical settings. Moreover, the anti-aging impact of MLT and miRNAs participation jointly are of particular interest, recently. In this review, we aimed to scrutinize recent advances concerning the therapeutic implications of MLT, particularly in the brain tissue in the face of aging. We also assessed the possible interplay between microRNAs and MLT, which could be considered a therapeutic strategy to slow down the aging process in the nervous system.

Beneficial effect of dietary geranylgeraniol on glucose homeostasis and bone microstructure in obese mice is associated with suppression of proinflammation and modification of gut microbiome

Geranylgeraniol (GGOH) is found in edible oils such as olive, linseed, and sunflower oils, which have favorable metabolic effects. However, it is unknown whether these physiological benefits are mediated through the gut microbiome. Thus, the purpose of this study was to test the hypothesis that GGOH supplementation would improve glucose homeostasis and benefit the bone microstructure in obese mice through suppression of inflammation and modification of gut microbiota composition. Thirty-six male C57BL/6J mice were divided into 3 groups: a low-fat diet, a high-fat diet (HFD), and an HFD supplemented with 800 mg GGOH/kg diet (GG) for 14 weeks. Glucose and insulin tolerance tests were measured at baseline and end of study. The concentrations of adipokine cytokines (resistin, leptin, monocyte chemoattractant protein-1, interleukin-6) were measured via ELISA. Bone microarchitecture and quality were measured by micro-CT. Microbiome analysis was performed using 16S rRNA amplicon sequencing on cecal content. Relative to the HFD group, the GG group: (1) improved glucose tolerance and insulin sensitivity; (2) reduced production of pro-inflammatory adipokines, (3) increased serum procollagen I intact N-terminal propeptide (bone formation marker) concentrations, while decreasing serum collagen type 1 cross-linked C-telopeptide (bone resorption marker) levels, and (4) increased stiffness at both femur and LV-4 and cortical thickness at femoral midshaft. Compared to the HFD group, the GG group had an increased abundance of Butyricicoccus pullicaecorum and decreased Dorea longicatena in the cecal microbiome. Collectively, GGOH improves glucose homeostasis and bone microstructure in obese mice, probably via suppression of pro-inflammation and modification of microbiome composition.

Potential modulatory mechanisms of action by long-chain polyunsaturated fatty acids on bone cell and chondrocyte metabolism

Long-chain polyunsaturated fatty acids (LCPUFAs) and their metabolites are considered essential factors to support bone and joint health. The n-6 PUFAs suppress the osteoblasts differentiation via increasing peroxisome proliferator-activated receptor gamma (PPARγ) expression and promoting adipogenesis while n-3 PUFAs promote osteoblastogenesis by down-regulating PPARγ and enhancing osteoblastic activity. Arachidonic acid (AA) and its metabolite prostaglandin E2 (PGE2) are key regulators of osteoclast differentiation via induction of the receptor activator of nuclear factor kappa-Β ligand (RANKL) pathway. Marine-derived n-3 LCPUFAs have been shown to inhibit osteoclastogenesis by decreasing the osteoprotegerin (OPG)/RANKL signalling pathway mediated by a reduction of pro-inflammatory PGE2 derived from AA. Omega-3 PUFAs reduce the expression of cartilage degrading enzyme matrix metalloproteinase-13 (MMP-13) and a disintegrin and metalloprotease with thrombospondin motifs-5 (ADAMTS-5) protein, oxidative stress and thereby apoptosis via nuclear factor kappa-betta (NF-kβ) and inducible nitric oxide synthase (iNOS) pathways. In this review, a diverse range of important effects of LCPUFAs on bone cells and chondrocyte was highlighted through different mechanisms of action established by cell cultures and animal studies. This review allows a better understanding of the possible role of LCPUFAs in bone and chondrocyte metabolism as potential therapeutics in combating the pathological complications such as osteoporosis and osteoarthritis.

Metabolomics in Bone Research

Identifying the changes in endogenous metabolites in response to intrinsic and extrinsic factors has excellent potential to obtain an understanding of cells, biofluids, tissues, or organisms' functions and interactions with the environment. The advantages provided by the metabolomics strategy have promoted studies in bone research fields, including an understanding of bone cell behaviors, diagnosis and prognosis of diseases, and the development of treatment methods such as implanted biomaterials. This review article summarizes the metabolism changes during osteogenesis, osteoclastogenesis, and immunoregulation in hard tissue. The second section of this review is dedicated to describing and discussing metabolite changes in the most relevant bone diseases: osteoporosis, bone injuries, rheumatoid arthritis, and osteosarcoma. We consolidated the most recent finding of the metabolites and metabolite pathways affected by various bone disorders. This collection can serve as a basis for future metabolomics-driven bone research studies to select the most relevant metabolites and metabolic pathways. Additionally, we summarize recent metabolic studies on metabolomics for the development of bone disease treatment including biomaterials for bone engineering. With this article, we aim to provide a comprehensive summary of metabolomics in bone research, which can be helpful for interdisciplinary researchers, including material engineers, biologists, and clinicians.

PAR2 Deficiency Induces Mitochondrial ROS Generation and Dysfunctions, Leading to the Inhibition of Adipocyte Differentiation

Protease-activated receptor 2 (PAR2) is a member of G-protein-coupled receptors and affects ligand-modulated calcium signaling. Although PAR2 signaling promotes obesity and adipose tissue inflammation in high fat- (HF-) fed conditions, its role in adipocyte differentiation under nonobesogenic conditions needs to be elucidated. Here, we used several tissues and primary-cultured adipocytes of mice lacking PAR2 to study its role in the development of adipose tissues. C57BL/6J mice with PAR2 deficiency exhibited a mild lipodystrophy-like phenotype in a chow diet-fed condition. When adipocyte differentiation was examined using primary-cultured preadipocytes, PAR2 deficiency led to a notable decrease in adipocyte differentiation and related protein expression, and PAR2 agonist treatment elevated adipocyte differentiation. Regarding the mechanism, PAR2-deficient preadipocytes exhibited impaired mitochondrial energy consumption. Further studies indicated that calcium-related signaling pathways for mitochondrial biogenesis are disrupted in the adipose tissues of PAR2-deficient mice and PAR2-deficient preadipocytes. Also, a PAR2 antagonist elevated mitochondrial reactive oxygen species and reduced the MitoTracker fluorescent signal in preadipocytes. Our studies revealed that PAR2 is important for the development of adipose tissue under basal conditions through the regulation of mitochondrial biogenesis and adipocyte differentiation.

PPARγ Mediates the Anti-Epithelial-Mesenchymal Transition Effects of FGF1ΔHBS in Chronic Kidney Diseases via Inhibition of TGF-β1/SMAD3 Signaling

Podocytes are essential components of the glomerular basement membrane. Epithelial-mesenchymal-transition (EMT) in podocytes results in proteinuria. Fibroblast growth factor 1 (FGF1) protects renal function against diabetic nephropathy (DN). In the present study, we showed that treatment with an FGF1 variant with decreased mitogenic potency (FGF1^ΔHBS) inhibited podocyte EMT, depletion, renal fibrosis, and preserved renal function in two nephropathy models. Mechanistic studies revealed that the inhibitory effects of FGF1^ΔHBS podocyte EMT were mediated by decreased expression of transforming growth factor β1 via upregulation of PPARγ. FGF1^ΔHBS enhanced the interaction between PPARγ and SMAD3 and suppressed SMAD3 nuclei translocation. We found that the anti-EMT activities of FGF1^ΔHBS were independent of glucose-lowering effects. These findings expand the potential uses of FGF1^ΔHBS in the treatment of diseases associated with EMT.

Loss of KDM4B exacerbates bone-fat imbalance and mesenchymal stromal cell exhaustion in skeletal aging

Skeletal aging is a complex process, characterized by a decrease in bone formation, an increase in marrow fat, and stem cell exhaustion. Loss of H3K9me3, a heterochromatin mark, has been proposed to be associated with aging. Here, we report that loss of KDM4B in mesenchymal stromal cells (MSCs) exacerbated skeletal aging and osteoporosis by reducing bone formation and increasing marrow adiposity via increasing H3K9me3. KDM4B epigenetically coordinated β-catenin/Smad1-mediated transcription by removing repressive H3K9me3. Importantly, KDM4B ablation impaired MSC self-renewal and promoted MSC exhaustion by inducing senescence-associated heterochromatin foci formation, providing a mechanistic explanation for stem cell exhaustion with aging. Moreover, while KDM4B was required for parathyroid hormone-mediated bone anabolism, KDM4B depletion accelerated bone loss and marrow adiposity induced by a high-fat diet. Our results suggest that the epigenetic rejuvenation and reversing bone-fat imbalance might be new strategies for preventing and treating skeletal aging and osteoporosis by activating KDM4B in MSCs.

Adrenomedullin 2 improves bone regeneration in type 1 diabetic rats by restoring imbalanced macrophage polarization and impaired osteogenesis

BACKGROUND

Both advanced glycation end products (AGEs) and AGE-mediated M1 macrophage polarization contribute to bone marrow mesenchymal stem cell (BMSC) dysfunction, leading to impaired bone regeneration in type 1 diabetes mellitus (T1DM). Adrenomedullin 2 (ADM2), an endogenous bioactive peptide belonging to the calcitonin gene-related peptide family, exhibits various biological activities associated with the inhibition of inflammation and reduction of insulin resistance. However, the effects and underlying mechanisms of ADM2 in AGE-induced macrophage M1 polarization, BMSC dysfunction, and impaired bone regeneration remain poorly understood.

METHODS

The polarization of bone marrow-derived macrophages was verified using flow cytometry analysis. Alkaline phosphatase (ALP) staining, ALP activity detection, and alizarin red staining were performed to assess the osteogenesis of BMSCs. Quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, and immunofluorescence staining were used to assess polarization markers, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling, and osteogenic markers. In vivo, a distraction osteogenesis (DO) rat model with T1DM was established, and tibia samples were collected at different time points for radiological, biomechanical, and histological analyses, to verify the effects of ADM2 on bone regeneration and M2 polarization under diabetic conditions.

RESULTS

ADM2 treatment reversed AGE-induced M1 macrophage polarization towards the M2 phenotype, which was partially achieved by the peroxisome proliferator-activated receptor γ (PPARγ)-mediated inhibition of NF-κB signaling. The PPARγ inhibitor GW9662 significantly attenuated the effects of ADM2. Besides, ADM2 treatment improved the AGE-impaired osteogenic potential of BMSCs in vitro. Furthermore, ADM2 accelerated bone regeneration, as revealed by improved radiological and histological manifestations and biomechanical parameters, accompanied by improved M2 macrophage polarization in diabetic DO rats, and these effects were partially blocked by GW9662 administration.

CONCLUSIONS

These results indicate that ADM2 enhances diabetic bone regeneration during DO, by attenuating AGE-induced imbalances in macrophage polarization, partly through PPARγ/NF-κB signaling, and improving AGE-impaired osteogenic differentiation of BMSCs simultaneously. These findings reveal that ADM2 may serve as a potential bioactive factor for promoting bone regeneration under diabetic conditions, and imply that management of inflammation and osteogenesis, in parallel, may present a promising therapeutic strategy for diabetic patients during DO treatment.

Tributyltin perturbs femoral cortical architecture and polar moment of inertia in rat

Background

Tributyltin, a well-known endocrine disruptor, is widely used in agriculture and industry. Previous studies have shown that tributyltin could cause deleterious effects on bone health by impairing the adipo-osteogenic balance in bone marrow.

Methods

To investigate further the effects of tributyltin on bone, weaned male SD rats were treated with tributyltin (0.5, 5 or 50 μg·kg^− 1) or corn oil by gavage once every 3 days for 60 days in this study. Then, we analyzed the effects of tributyltin on geometry, the polar moment of inertia, mineral content, relative abundances of mRNA from representative genes related to adipogenesis and osteogenesis, serum calcium ion and inorganic phosphate levels.

Results

Micro-computed tomography analysis revealed that treatment with 50 μg·kg^− 1 tributyltin caused an obvious decrease in femoral cortical cross sectional area, marrow area, periosteal circumference and derived polar moment of inertia in rats. However, other test results showed that exposure to tributyltin resulted in no significant changes in the expression of genes detected, femoral cancellous architecture, ash content, as well as serum calcium ion and inorganic phosphate levels.

Conclusions

Exposure to a low dose of tributyltin from the prepubertal to adult stage produced adverse effects on skeletal architecture and strength.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04298-2.

Histone modifications centric-regulation in osteogenic differentiation

Histone modification critically contributes to the epigenetic control of gene expression by changing the configuration of chromatin and modifying the access of transcription factors to gene promoters. Recently, we observed that histone acetylation and crotonylation mediated the expression of endocytosis-related genes and tumor-related immune checkpoint genes by regulating the enrichment of signal transducer and activator of transcription 3 on these gene promoters in Alzheimer's disease and tumorigenesis, suggesting that histone modification plays an important role in disease development. Furthermore, studies performed in the past decade revealed that histone modifications affect osteogenic differentiation by regulating the expression of osteogenic marker genes. In this review, we summarize and discuss the histone modification-centric regulation of osteogenic gene expression. This review improves the understanding of the role of histone modifications in osteogenic differentiation and describes its potential as a therapeutic target for osteogenic differentiation-related diseases.

Lack of Adiponectin Drives Hyperosteoclastogenesis in Lipoatrophic Mice

Long bones from mammals host blood cell formation and contain multiple cell types, including adipocytes. Physiological functions of bone marrow adipocytes are poorly documented. Herein, we used adipocyte-deficient PPARγ-whole body null mice to investigate the consequence of total adipocyte deficiency on bone homeostasis in mice. We first highlighted the dual bone phenotype of PPARγ null mice: one the one hand, the increased bone formation and subsequent trabecularization extending in the long bone diaphysis, due to the well-known impact of PPARγ deficiency on osteoblasts formation and activity; on the other hand, an increased osteoclastogenesis in the cortical bone. We then further explored the cause of this unexpected increased osteoclastogenesis using two independent models of lipoatrophy, which recapitulated this phenotype. This demonstrates that hyperosteoclastogenesis is not intrinsically linked to PPARγ deficiency, but is a consequence of the total lipodystrophy. We further showed that adiponectin, a cytokine produced by adipocytes and mesenchymal stromal cells is a potent inhibitor of osteoclastogenesis in vitro and in vivo. Moreover, pharmacological activation of adiponectin receptors by the synthetic agonist AdipoRon inhibited mature osteoclast activity both in mouse and human cells by blocking podosome formation through AMPK activation. Finally, we demonstrated that AdipoRon treatment blocks bone erosion in vivo in a murine model of inflammatory bone loss, providing potential new approaches to treat osteoporosis.

Knockout of NOS2 Promotes Adipogenic Differentiation of Rat MSCs by Enhancing Activation of JAK/STAT3 Signaling

Mesenchymal stromal cells (MSCs) are a heterogeneous population of cells that possess multilineage differentiation potential and extensive immunomodulatory properties. In mice and rats, MSCs produce nitric oxide (NO), as immunomodulatory effector molecule that exerts an antiproliferative effect on T cells, while the role of NO in differentiation was less clear. Here, we investigated the role of NO synthase 2 (NOS2) on adipogenic and osteogenic differentiation of rat MSCs. MSCs isolated from NOS2-null (NOS2^–/–) and wild type (WT) Sprague–Dawley (SD) rats exhibited homogenous fibroblast-like morphology and characteristic phenotypes. However, after induction, adipogenic differentiation was found significantly promoted in NOS2^–/– MSCs compared to WT MSCs, but not in osteogenic differentiation. Accordingly, qRT-PCR revealed that the adipogenesis-related genes PPAR-γ, C/EBP-α, LPL and FABP4 were markedly upregulated in NOS2^–/– MSCs, but not for osteogenic transcription factors or marker genes. Further investigations revealed that the significant enhancement of adipogenic differentiation in NOS2^–/– MSCs was due to overactivation of the STAT3 signaling pathway. Both AG490 and S3I-201, small molecule inhibitors that selectively inhibit STAT3 activation, reversed this adipogenic effect. Furthermore, after high-fat diet (HFD) feeding, knockout of NOS2 in rat MSCs resulted in significant obesity. In summary, NOS2 is involved in the regulation of rat MSC adipogenic differentiation via the STAT3 signaling pathway.

Role of 25-Hydroxyvitamin D3 and 1,25-Dihydroxyvitamin D3 in Chicken Embryo Osteogenesis, Adipogenesis, Myogenesis, and Vitamin D3 Metabolism

A study was conducted to understand the effects of 25-hydroxyvitamin D₃ (25OHD) and 1,25-dihydroxyvitamin D₃ (1,25OHD) administration on the expression of key genes related to osteogenesis, adipogenesis, myogenesis, and vitamin D₃ metabolism in the chicken embryo. A total of 120 fertilized Cobb 500 eggs were used in the current study and were reared under standard incubation conditions. On embryonic day 3 (ED 3), PBS (C), PBS with 40ng 1,25OHD (1,25D-L), 200ng 1,25OHD (1,25D-H), 40ng 25OHD (25D-L), or 200ng 25OHD (25D-H) were injected into the dorsal vein of developing embryos. Whole embryos were harvested at 1, 3, and 6h post-injection for gene expression analyses (n=8). Gene expression for key osteogenesis markers (RUNX2: runt-related transcription factor 2; BMP2: bone morphogenetic protein 2; COL1A2: collagen type I alpha 2 chain; BGLAP: bone gamma-carboxyglutamate protein; SPP1: secreted phosphoprotein 1; and ALP: alkaline phosphatese), adipogenesis markers (PPAR-γ: peroxisome proliferator-activated receptor gamma; FASN: fatty acid synthase; and FABP4: fatty acid binding protein 4), myogenesis markers (MYOG: myogenin; MYOD1: myogenic differentiation 1; and MYF5: myogenic factor 5), and the enzyme responsible for vitamin D₃ inactivation (CYP24A1: cytochrome P450 family 24 subfamily A member 1) were measured using real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). Data were normalized by the ΔΔCT method and analyzed using a one-way ANOVA. Results indicated that at 1h post-injection, no differences were found among treatments. At 3h, the early osteogenesis differentiation marker, ALP, was increased by 1,25D-H and 25D-H, and 25D-H also stimulated the expression of adipogenesis markers (FAPB4 and FASN). In contrast, the expression of myogenesis markers (MYOD1 and MYF5) was suppressed by 25OHD or 1,25OHD treatments, respectively. At 6h, a late osteogenic differentiation marker, SPP1, was increased by 25D-H. MYOD1 and MYF5 were continuously suppressed by 25OHD treatments or 1,25D-H. The evidence of vitamin D₃ metabolite retention was assessed by measuring CYP24A1 expression. At 1h, there were no differences in CYP24A1 expression. At 3h, all treatments upregulated CYP24A1 expression relative to control (PBS) embryos. However, at 6h, only the 25D-H group retained higher CYP24A1 expression compared to the other treatments. In conclusion, the results suggested both 1,25OHD and 25OHD induced chicken embryo osteogenesis and adipogenesis, but inhibited myogenesis during early chicken embryo development. The higher dosage of 25OHD showed a possibility of a longer retention time in the embryos.

Trends in osteoporosis and mean bone density among type 2 diabetes patients in the US from 2005 to 2014

This study aimed to examine how bone health changed among T2DM patients in the past decade. Continuous National Health and Nutrition Examination Survey (NHANES) data from 2005-2006 to 2013-2014 were analyzed to examine the trends of bone mineral density (BMD) and the prevalence trends of osteoporosis osteopenia among T2DM patients and non-diabetic people aged 40 years and older. The age- and BMI-adjusted mean BMD of the femur neck for the four NHANES cycles decreased linearly in both T2DM patients and non-diabetic people (both Plinear trend ≤ 0.009). Among women with T2DM, the mean BMD in 2013-2014 was significantly lower than that in 2005-2006, even after adjusting for multiple covariates. During 2005-2014, the prevalence of osteoporosis among T2DM patients and non-diabetic people increased but with no significant linear trend (both Plinear trend > 0.05), while the prevalence of osteopenia in the two populations increased linearly (both Plinear trend < 0.04). Age- and BMI-adjusted mean BMD decreased in 2013-2014 in patients with T2DM and non-diabetic people, while the prevalence of osteoporosis and osteopenia increased in both groups.

Pristimerin Suppresses RANKL-Induced Osteoclastogenesis and Ameliorates Ovariectomy-Induced Bone Loss

Osteoporosis is characterized by bone loss and destruction of trabecular architecture, which greatly increases the burden on the healthcare system. Excessive activation of osteoclasts is an important cause of osteoporosis, and suppression of osteoclastogenesis is helpful for the treatment of osteoporosis. Pristimerin, a natural compound, possesses numerous pharmacological effects via inactivating the NF-κB and MAPK pathways, which are closely related to osteoclastogenesis process. However, the relationship between Pristimerin and osteoclastogenesis requires further investigation. In this research, we examined the effect of Pristimerin on osteoclastogenesis and investigated the related mechanisms. Our results showed Pristimerin inhibited RANKL-induced osteoclast differentiation and osteoclastic bone resorption in vitro, with decreased expression of osteoclastogenesis-related markers including c-Fos, NFATc1, TRAP, Cathepsin K, and MMP-9 at both mRNA and protein levels. Furthermore, Pristimerin suppressed NF-κB and MAPK signaling pathways, reduced reactive oxygen species (ROS) production and activated the nuclear factor erythroid 2-related factor 2/heme oxygenase 1 (Nrf2/HO-1) signaling during osteoclastogenesis. Our in vivo experiments showed that Pristimerin remarkably ameliorated ovariectomy-induced bone loss, reduced serum levels of TNF-α, IL-1β, IL-6, and RANKL, and increased serum level of osteoprotegerin (OPG). Therefore, our research indicated that Pristimerin is a potential chemical for the treatment of osteoporosis.

Trb3 controls mesenchymal stem cell lineage fate and enhances bone regeneration by scaffold-mediated local gene delivery

Aberrant lineage commitment of mesenchymal stem cells (MSCs) in marrow contributes to abnormal bone formation due to reduced osteogenic and increased adipogenic potency. While several major transcriptional factors associated with lineage differentiation have been found during the last few decades, the molecular switch for MSC fate determination and its role in skeletal regeneration remains largely unknown, limiting creation of effective therapeutic approaches. Tribbles homolog 3 (Trb3), a member of tribbles family pseudokinases, is known to exert diverse roles in cellular differentiation. Here, we investigated the reciprocal role of Trb3 in the regulation of osteogenic and adipogenic differentiation of MSCs in the context of bone formation, and examined the mechanisms by which Trb3 controls the adipo-osteogenic balance. Trb3 promoted osteoblastic commitment of MSCs at the expense of adipocyte differentiation. Mechanistically, Trb3 regulated cell-fate choice of MSCs through BMP/Smad and Wnt/β-catenin signals. Importantly, in vivo local delivery of Trb3 using a novel gelatin-conjugated caffeic acid-coated apatite/PLGA (GelCA-PLGA) scaffold stimulated robust bone regeneration and inhibited fat-filled cyst formation in rodent non-healing mandibular defect models. These findings demonstrate Trb3-based therapeutic strategies that favor osteoblastogenesis over adipogenesis for improved skeletal regeneration and future treatment of bone-loss disease. The distinctive approach implementing a scaffold-mediated local gene transfer may further broaden the translational use of targeting specific therapeutic gene related to lineage commitment for clinical bone treatment.

Di-(2-ethylhexyl) phthalate limits the pleiotropic effects of statins in chronic kidney disease patients undergoing dialysis and endothelial cells

The level of di-(2-ethylhexyl) phthalate (DEHP) is elevated in chronic kidney disease patients undergoing dialysis. However, statins are unable to reduce the cardiovascular events in chronic dialysis patients. In this study, we investigated the effects of DEHP on statin-conferred pleiotropic effects and the underlying molecular mechanism in peritoneal dialysis (PD) patients and endothelial cells (ECs). In PD patients with serum DEHP level ≥0.0687 μg/mL, statin treatment was not associated with lower risk of cardiovascular disease. In ECs, exposure to DEHP abrogated the simvastatin-induced NO bioavailability and EC-related functions. Additionally, DEHP abolished the anti-inflammatory effect of simvastatin on the tumor necrosis factor α-induced upregulation of adhesion molecules and monocyte adhesion to ECs. Mechanistically, DEHP blunted the activation of transient receptor potential vanilloid type 1 (TRPV1), which is required for NO production by simvastatin in ECs. Notably, DEHP increased the activity and expression of protein phosphatase 2B (PP2B), a negative regulator of TRPV1 activity. The effect of DEHP on PP2B activation was mediated by the activation of the NADPH oxidase/reactive oxygen species (NOX-ROS) pathway. Inhibition of PP2B activity by pharmacological antagonists prevented the inhibitory effects of DEHP on simvastatin-induced Ca²⁺ influx, NO bioavailability, and EC migration, proliferation, tube formation, and anti-inflammatory action. Collectively, DEHP activates the NOX-ROS-PP2B pathway, which in turns inhibits TRPV1/Ca²⁺-dependent signaling and abrogates the statin-conferred pleiotropic protection in ECs.

Impact of Type 2 Diabetes Mellitus and Antidiabetic Medications on Bone Metabolism

PURPOSE OF REVIEW

This review focuses on the complex interactions between hyperglycemia and bone fragility and the effects of antidiabetic medications on bone metabolism.

RECENT FINDINGS

Type 2 diabetes (T2D) is associated with increased risk of bone fracture even in those with increased or normal bone mineral density (BMD). The pathophysiology of diabetic bone disease is not completely understood, but it is thought to be multifactorial and associated with complex cross talk among factors such as AGEs, IGF-1, enteric hormones, and pro-inflammatory cytokines. Treatment for T2D may have an impact on bone metabolism. Diabetic bone disease should be considered a serious complication of long-standing T2D.

The Role of Omega-3 Polyunsaturated Fatty Acids from Different Sources in Bone Development

N-3 polyunsaturated fatty acids (PUFAs) are essential nutrients that must be obtained from the diet. We have previously showed that endogenous n-3 PUFAs contribute to skeletal development and bone quality in fat-1 mice. Unlike other mammals, these transgenic mice, carry the n-3 desaturase gene and thus can convert n-6 to n-3 PUFAs endogenously. Since this model does not mimic dietary exposure to n-3 PUFAs, diets rich in fish and flaxseed oils were used to further elucidate the role of n-3 PUFAs in bone development. Our investigation reveals that dietary n-3 PUFAs decrease fat accumulation in the liver, lower serum fat levels, and alter fatty acid (FA) content in liver and serum. Bone analyses show that n-3 PUFAs improve mechanical properties, which were measured using a three-point bending test, but exert complex effects on bone structure that vary according to its source. In a micro-CT analysis, we found that the flaxseed oil diet improves trabecular bone micro-architecture, whereas the fish oil diet promotes higher bone mineral density (BMD) with no effect on trabecular bone. The transcriptome characterization of bone by RNA-seq identified regulatory mechanisms of n-3 PUFAs via modulation of the cell cycle and peripheral circadian rhythm genes. These results extend our knowledge and provide insights into the molecular mechanisms of bone remodeling regulation induced by different sources of dietary n-3 PUFAs.

Nuclear receptors in osteoclasts

Osteoclasts are bone-resorbing cells that play an essential role in the remodeling of bone under physiological conditions and numerous pathological conditions, such as osteoporosis, bone metastasis, and inflammatory bone erosion. Nuclear receptors are crucial to various physiological processes, including metabolism, development and inflammation, and function as transcription factors to activate target genes. Synthetic ligands of nuclear receptors are also available for the treatment of metabolic and inflammatory diseases. However, dysregulated bone phenotypes have been documented in patients who take synthetic nuclear receptor ligands as a therapy. Therefore, the effect of nuclear receptors on bone cells has become an important area of exploration; additionally, the molecular mechanisms underlying the action of nuclear receptors in osteoclasts have not been completely understood. Here, we cover the recent progress in our understanding of the roles of nuclear receptors in osteoclasts.

Myotubularin-related protein 7 activates peroxisome proliferator-activated receptor-gamma

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a transcription factor drugable by agonists approved for treatment of type 2 diabetes, but also inhibits carcinogenesis and cell proliferation in vivo. Activating mutations in the Kirsten rat sarcoma viral oncogene homologue (KRAS) gene mitigate these beneficial effects by promoting a negative feedback-loop comprising extracellular signal-regulated kinase 1/2 (ERK1/2) and mitogen-activated kinase kinase 1/2 (MEK1/2)-dependent inactivation of PPARγ. To overcome this inhibitory mechanism, we searched for novel post-translational regulators of PPARγ. Phosphoinositide phosphatase Myotubularin-Related-Protein-7 (MTMR7) was identified as cytosolic interaction partner of PPARγ. Synthetic peptides were designed resembling the regulatory coiled-coil (CC) domain of MTMR7, and their activities studied in human cancer cell lines and C57BL6/J mice. MTMR7 formed a complex with PPARγ and increased its transcriptional activity by inhibiting ERK1/2-dependent phosphorylation of PPARγ. MTMR7-CC peptides mimicked PPARγ-activation in vitro and in vivo due to LXXLL motifs in the CC domain. Molecular dynamics simulations and docking predicted that peptides interact with the steroid receptor coactivator 1 (SRC1)-binding site of PPARγ. Thus, MTMR7 is a positive regulator of PPARγ, and its mimicry by synthetic peptides overcomes inhibitory mechanisms active in cancer cells possibly contributing to the failure of clinical studies targeting PPARγ.

Adipogenesis Inhibitory Activity of Hypersampsone P from Hypericum subsessile

Adamantane polycyclic polyprenylated acylphloroglucinols (PPAPs) with caged architecture, a special class of hybrid natural products, is specifically rich in the plant family Guttiferae, especially Hypericum or Garcinia genus. Hypersampsone P is one of Adamantane PPAPs compounds extracted from Hypericum subsessile. Here we have chosen, screened ten PPAPs and identified one of them showed an activity in inhibiting of adipocytes differentiation. Particularly, the compound, hypersampsone P, blunted the adipocyte differentiation dose-dependently. Moreover, hypersampsone P down-regulated the expressions of several key regulators for adipogenesis, including PPARγ and FABP4. The treatment of cells at the early stage of adipogenesis by hypersampsone P induced the greatest blunting of adipocyte differentiation and the effect might be involved in the LKB1-AMPK signaling pathway.

Myeloma cells shift osteoblastogenesis to adipogenesis by inhibiting the ubiquitin ligase MURF1 in mesenchymal stem cells

The suppression of bone formation is a hallmark of multiple myeloma. Myeloma cells inhibit osteoblastogenesis from mesenchymal stem cells (MSCs), which can also differentiate into adipocytes. We investigated myeloma-MSC interactions and the effects of such interactions on the differentiation of MSCs into adipocytes or osteoblasts using single-cell RNA sequencing, in vitro coculture, and subcutaneous injection of MSCs and myeloma cells into mice. Our results revealed that the α₄ integrin subunit on myeloma cells stimulated vascular cell adhesion molecule-1 (VCAM1) on MSCs, leading to the activation of protein kinase C β1 (PKCβ1) signaling and repression of the muscle ring-finger protein-1 (MURF1)-mediated ubiquitylation of peroxisome proliferator-activated receptor γ2 (PPARγ2). Stabilized PPARγ2 proteins enhanced adipogenesis and consequently reduced osteoblastogenesis from MSCs, thus suppressing bone formation in vitro and in vivo. These findings reveal that suppressed bone formation is a direct consequence of myeloma-MSC contact that promotes the differentiation of MSCs into adipocytes at the expense of osteoblasts. Thus, this study provides a potential strategy for treating bone resorption in patients with myeloma by counteracting tumor-MSC interactions.

Circadian Rhythms in the Pathogenesis and Treatment of Fatty Liver Disease

Circadian clock proteins are endogenous timing mechanisms that control the transcription of hundreds of genes. Their integral role in coordinating metabolism has led to their scrutiny in a number of diseases, including nonalcoholic fatty liver disease (NAFLD). Discoordination between central and peripheral circadian rhythms is a core feature of nearly every genetic, dietary, or environmental model of metabolic syndrome and NAFLD. Restricting feeding to a defined daily interval (time-restricted feeding) can synchronize the central and peripheral circadian rhythms, which in turn can prevent or even treat the metabolic syndrome and hepatic steatosis. Importantly, a number of proteins currently under study as drug targets in NAFLD (sterol regulatory element-binding protein [SREBP], acetyl-CoA carboxylase [ACC], peroxisome proliferator-activator receptors [PPARs], and incretins) are modulated by circadian proteins. Thus, the clock can be used to maximize the benefits and minimize the adverse effects of pharmaceutical agents for NAFLD. The circadian clock itself has the potential for use as a target for the treatment of NAFLD.

Site-Dependent Lineage Preference of Adipose Stem Cells

Adult stem cells have unique properties in both proliferation and differentiation preference. In this study, we hypothesized that adipose stem cells have a depot-dependent lineage preference. Four rabbits were used to provide donor-matched adipose stem cells from either subcutaneous adipose tissue (ScAT) or infrapatellar fat pad (IPFP). Proliferation and multi-lineage differentiation were evaluated in adipose stem cells from donor-matched ScAT and IPFP. RNA sequencing (RNA-seq) and proteomics were conducted to uncover potential molecular discrepancy in adipose stem cells and their corresponding matrix microenvironments. We found that stem cells from ScAT exhibited significantly higher proliferation and adipogenic capacity compared to those from donor-matched IPFP while stem cells from IPFP displayed significantly higher chondrogenic potential compared to those from donor-matched ScAT. Our findings are strongly endorsed by supportive data from transcriptome and proteomics analyses, indicating a site-dependent lineage preference of adipose stem cells.

PKM2 suppresses osteogenesis and facilitates adipogenesis by regulating β-catenin signaling and mitochondrial fusion and fission

Bone marrow mesenchymal stem cells (BMSCs) differentiation dysfunction is a common pathological phenotype of several prevalent metabolic and genetic bone diseases. Pyruvate kinase muscle isoenzyme 2 (PKM2) regulates the last step of glycolysis, and its role in BMSCs differentiation is still unknown. In this study, the influence of PKM2 on osteogenesis and adipogenesis was assessed in vitro and in vivo. We found that DASA-58 (the activator of PKM2) reduced the enzymatic activity of ALP, and inhibited the levels of osteogenic marker genes, especially RUNX2, which is a crucial transcription factor for osteogenesis. Besides, we provided evidence that C3k, an inhibitor of PKM2, caused increase in mitochondrial membrane potential and maintained low levels of ROS, and promoted mitochondrial fusion. Furthermore, after treatment with DASA-58, the level of active β-catenin gradually decreased, which also inhibited the transport of active β-catenin into the nucleus, but C3k obviously promoted its nuclear translocation. As for adipogenesis, PKM2 activation increased the expression of adipogenic related genes and decreased active-β-catenin expression, whereas treatment of C3k had the opposite effect. In addition, C3k significantly attenuated ovariectomy-induced trabecular bone loss in vivo. Our findings helped uncover the molecular mechanisms underlying PKM2 regulation of BMSCs differentiation.

Osteoporosis and Hepatic Steatosis: 2 Closely Related Complications in Short-Bowel Syndrome

BACKGROUND

Osteoporosis has scarcely been prospectively investigated in short-bowel syndrome (SBS). This prospective study was designed to evaluate incretins, adipokines, bone mass, and lipid deposits from marrow adipose tissue (MAT), visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and liver (IHLs).

METHODS

The study comprised 2 groups matched by gender, height, and age: the control group (CG) (9 males, 9 females) and the SBS group (SBSG) (6 males, 5 females). The SBSG was evaluated twice in an interval of 1 year (SBSG₀ and SBSG₁ ). The biochemical evaluation included incretins, leptin, and adiponectin. Dual-energy x-ray absorptiometry and magnetic resonance were, respectively, used to measure BMD and lipid deposits.

RESULTS

Bone mineral density (BMD) was lower in the SBSG than in the CG, but there was no difference between SBSG₀ and SBSG₁ . There was no difference in MAT, SAT, and VAT, but IHL was lower in CG than in SBSG₀ and SBSG₁ . A negative correlation between MAT and third lumbar vertebrae BMD was found in the CG but not in SBSG₀ or SBSG₁ . There was a negative association between IHL and bone mass considering all participants (CG and SBSG₀ ) (R² = 0.38; P < .05).

CONCLUSION

Appropriate nutrition assistance recovers body composition, reverts the relationship of bone mass and MAT, and mitigates bone loss in SBS. In spite of this, osteoporosis seems to be an early and persistent complication in SBS. Curiously, SBS seems to be a highly vulnerable condition for the development of hepatic steatosis and shows an association between bone mass and IHL.

Cyclin-Dependent Kinase 5 Inhibitor Butyrolactone I Elicits a Partial Agonist Activity of Peroxisome Proliferator-Activated Receptor γ

Adiponectin is an adipocyte-derived cytokine having an insulin-sensitizing activity. During the phenotypic screening of secondary metabolites derived from the marine fungus Aspergillus terreus, a poly cyclin-dependent kinase (CDK) inhibitor butyrolactone I affecting CDK1 and CDK5 was discovered as a potent adiponectin production-enhancing compound in the adipogenesis model of human bone marrow-derived mesenchymal stem cells (hBM-MSCs). CDK5 inhibitors exhibit insulin-sensitizing activities by suppressing the phosphorylation of peroxisome proliferator-activated receptor γ (PPARγ). However, the adiponectin production-enhancing activities of butyrolactone I have not been correlated with the potency of CDK5 inhibitor activities. In a target identification study, butyrolactone I was found to directly bind to PPARγ. In the crystal structure of the human PPARγ, the ligand-binding domain (LBD) in complex with butyrolactone I interacted with the amino acid residues located in the hydrophobic binding pockets of the PPARγ LBD, which is a typical binding mode of the PPARγ partial agonists. Therefore, the adiponectin production-enhancing effect of butyrolactone I was mediated by its polypharmacological dual modulator activities as both a CDK5 inhibitor and a PPARγ partial agonist.

Angiotensin receptor subtypes regulate adipose tissue renewal and remodelling

Obesity is often associated with high systemic and local renin-angiotensin system (RAS) activity in adipose tissue. Adipose-derived mesenchymal stem/stromal cells (ADSCs), responsible for adipose tissue growth upon high-fat diet, express multiple angiotensin II receptor isoforms, including angiotensin II type 1 receptor (AT₁ R), angiotensin II type 2 receptor (AT₂ R), Mas and Mas-related G protein-coupled receptor D. Although AT₁ R is expressed on most ADSCs, other angiotensin receptors are co-expressed on a small subpopulation of the cells, a phenomenon that results in a complex response pattern. Following AT₁ R activation, the effects are transient due to rapid receptor internalisation. This short-lived effect can be prevented by heteromerisation with AT₂ R, a particularly important strategy for the regulation of ADSC differentiation and secretory activity. Heteromeric AT₂ R might be especially important for the generation of thermogenic beige adipocytes. This review summarises current data regarding the regulation of adipose tissue renewal and particularly ADSC adipogenic differentiation and secretory activity by RAS, with an emphasis on AT₂ R and its effects. We reveal a new scheme that implicates AT₂ R into the regulation of ADSC hormonal sensitivity.

High-Energy Diet and Shorter Light Exposure Drives Markers of Adipocyte Dysfunction in Visceral and Subcutaneous Adipose Depots of Psammomys obesus

Dysfunctional adipose tissue phenotype underpins type 2 diabetes mellitus (T2DM) development. The disruption of circadian rhythms contributes to T2DM development. We investigated the effects of high-energy diet and photoperiod length on visceral and subcutaneous adipose tissue phenotype. Psammomys obesus sand rats exposed to neutral (12 light:12 dark) or short (5 light:19 dark) photoperiod were fed a low- (LE) or high- (HE) energy diet. The HE diet and/or short photoperiod reduced subcutaneous expression of adipocyte differentiation/function markers C/ebpα, Pparδ, Pparγ and Adipoq. Visceral Pparα levels were elevated in the 5:19HE group; however, the HE diet and/or short photoperiod decreased visceral Pparγ and Adipoq expression. 5:19HE animals had elevated Ucp1 yet lower Pgc-1α levels. The HE diet increased visceral Tgf-β1, Ccl2 and Cd68 levels, suggestive of a pro-inflammatory state. Daily visceral rhythms of these genes were affected by a short photoperiod and/or HE diet. The 12:12HE, 5:19LE or 5:19HE animals had a higher proportion of larger adipocytes, indicating increased adipocyte hypertrophy. Collectively, the HE diet and/or shorter light exposure drives a dysfunctional adipose tissue phenotype. Daily rhythms are affected by a short photoperiod and HE diet in a site-specific manner. These findings provide mechanistic insight on the influence of disrupted circadian rhythms and HE diet on adipose tissue phenotype.

Enhancing survival, engraftment, and osteogenic potential of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are promising candidates for bone regeneration therapies due to their plasticity and easiness of sourcing. MSC-based treatments are generally considered a safe procedure, however, the long-term results obtained up to now are far from satisfactory. The main causes of these therapeutic limitations are inefficient homing, engraftment, and osteogenic differentiation. Many studies have proposed modifications to improve MSC engraftment and osteogenic differentiation of the transplanted cells. Several strategies are aimed to improve cell resistance to the hostile microenvironment found in the recipient tissue and increase cell survival after transplantation. These strategies could range from a simple modification of the culture conditions, known as cell-preconditioning, to the genetic modification of the cells to avoid cellular senescence. Many efforts have also been done in order to enhance the osteogenic potential of the transplanted cells and induce bone formation, mainly by the use of bioactive or biomimetic scaffolds, although alternative approaches will also be discussed. This review aims to summarize several of the most recent approaches, providing an up-to-date view of the main developments in MSC-based regenerative techniques.

Effects of 4-Hydroxy-2,3,3',4',5-Pentachlorobiphenyl (4-OH-CB107) on Liver Transcriptome in Rats: Implication in the Disruption of Circadian Rhythm and Fatty Acid Metabolism

Polychlorinated biphenyls (PCBs) and their hydroxylated metabolites (OH-PCBs) have been detected in tissues of both wild animals and humans. Several previous studies have suggested adverse effects of OH-PCBs on the endocrine and nervous systems in mammals. However, there have been no studies on transcriptome analysis of the effects of OH-PCBs, and thus, the whole picture and mechanisms underlying the adverse effects induced by OH-PCBs are still poorly understood. We therefore investigated the mRNA expression profile in the liver of adult male Wistar rats treated with 4-hydroxy-2,3,3',4',5-pentachlorobiphenyl (4-OH-CB107) to explore the genes responsive to OH-PCBs and to understand the potential effects of the chemical. Next-generation RNA sequencing analysis revealed changes in the expression of genes involved in the circadian rhythm and fatty acid metabolism, such as nuclear receptor subfamily 1, group D, member 1, aryl hydrocarbon receptor nuclear translocator-like protein 1, cryptochrome circadian clock 1, and enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase, in 4-OH-CB107-treated rats. In addition, biochemical analysis of the plasma revealed a dose-dependent increase in the leucine aminopeptidase, indicating the onset of liver damage. These results suggest that OH-PCB exposure may induce liver injury as well as disrupt the circadian rhythm and peroxisome proliferator-activated receptor-related fatty acid metabolism.

Altered expression of leptin and leptin receptor in the development of immune-mediated aplastic anemia in mice

The current study aimed to explore the levels of leptin (LEP) and LEP receptor (LEP-R) on the progression of aplastic anemia (AA) with bone marrow fat conversion. An AA model was developed by infusing C57BL/6 lymph node cells into BALB/c mice. At 0, 3, 6, 9, 12, 15 and 18 days after modeling, routine blood counts, bone marrow biopsy slides, lymphocyte subsets (CD4⁺ and CD8⁺ T cells) and cytokine levels [including interleukin (IL)-2, IL-4, IL-5 and interferon-γ] were assessed. LEP and LEP-R levels in peripheral blood serum, mesenchymal stem cells (MSCs) and bone marrow were also analyzed by enzyme-linked immunosorbent assay, polymerase chain reaction and immunohistochemistry. The relevance of LEP, LEP-R and other factors was analyzed by Pearson's correlation analysis. Peripheral pancytopenia (reduced count of white blood cells, red blood cells, hemoglobin and platelets), abnormal immune factor levels and histological changes in bone marrow sections were detected in the AA model mice, suggesting that these mice mimicked the pathological changes commonly observed in AA. In addition, following the establishment of AA, the LEP level was gradually increased and the LEP-R level was reduced in the mice over time (P<0.05). The expression of adipogenic genes, including CCAAT/enhancer-binding protein (C/EBP)α, C/EBPβ and peroxisome proliferator-activated receptor γ, was markedly increased, while the expression of the osteogenic gene runt-related transcription factor 2 was reduced compared with the levels in the control group (P<0.05). Taken together, damage to LEP-R may lead to dysregulation of LEP and the enhancement of MSCs to differentiate into adipocytes, resulting in excessive fat in bone marrow of AA patients.

FK506 prevented bone loss in streptozotocin-induced diabetic rats via enhancing osteogenesis and inhibiting adipogenesis

Background

Type 1 diabetes mellitus (DM) is associated with severe osteoporosis, which is still a great challenge in the clinic. This work aimed to investigate the skeletal effects of FK506 in a rat model of streptozocin induced type 1 DM.

Methods

Rats were divided into three groups: control (CTL), DM rats and DM rats treated with FK506. Dual energy X-ray absorption, micro-computed tomography, bone mechanics and bone histology were used for skeletal analysis. Bone marrow adipocytes infiltrations were detected by oil red O stain and H&E stain. In addition, the protein expression of adipocyte-specific makers (PPAR-γ, C/EBP-αβ), osteoblast-specific markers (Runx2, Osterix) and nuclear translocation of β-catenin in femurs were determined by western blot.

Results

In the study, bone mineral density of femurs and lumbar vertebras in diabetic rats were increased after FK506 administration. FK506 treatment resulted in higher cancellous bone volume but had no significant effect on cortical bones in diabetic rats. The ultimate force and work to failure were increased in DM+FK506 group, while they were reduced in the DM group. Compared with the CTL, the infiltration of bone marrow adipocytes was significantly increased in the DM group, which was reduced after the treatment of FK506. Besides, the expression levels of Runx2 and Osterix were up-regulated, and that of PPAR-γ and C/EBP-α were down-regulated in diabetic rats after FK506 treatment. In addition, the nuclear translocation of β-catenin protein levels were increased in diabetic rats after the treatment of FK506.

Conclusions

Our study indicated that FK506 could alleviate bone loss in diabetic rats. This effects could be due to the results of enhancing osteogenesis and inhibiting adipogenesis, which might be regulated by activation the nuclear translocation of β-catenin.

Peroxisome Proliferator-Activated Receptor-γ Knockdown Impairs Bone Morphogenetic Protein-2-Induced Critical-Size Bone Defect Repair

The Food and Drug Administration-approved clinical dose (1.5 mg/mL) of bone morphogenetic protein-2 (BMP2) has been reported to induce significant adverse effects, including cyst-like adipose-infiltrated abnormal bone formation. These undesirable complications occur because of increased adipogenesis, at the expense of osteogenesis, through BMP2-mediated increases in the master regulatory gene for adipogenesis, peroxisome proliferator-activated receptor-γ (PPARγ). Inhibiting PPARγ during osteogenesis has been suggested to drive the differentiation of bone marrow stromal/stem cells toward an osteogenic, rather than an adipogenic, lineage. We demonstrate that knocking down PPARγ while concurrently administering BMP2 can reduce adipogenesis, but we found that it also impairs BMP2-induced osteogenesis and leads to bone nonunion in a mouse femoral segmental defect model. In addition, in vitro studies using the mouse bone marrow stromal cell line M2-10B4 and mouse primary bone marrow stromal cells confirmed that PPARγ knockdown inhibits BMP2-induced adipogenesis; attenuates BMP2-induced cell proliferation, migration, invasion, and osteogenesis; and escalates BMP2-induced cell apoptosis. More important, BMP receptor 2 and 1B expression was also significantly inhibited by the combined BMP2 and PPARγ knockdown treatment. These findings indicate that PPARγ is critical for BMP2-mediated osteogenesis during bone repair. Thus, uncoupling BMP2-mediated osteogenesis and adipogenesis using PPARγ inhibition to combat BMP2's adverse effects may not be feasible.

A novel long noncoding RNA PGC1β-OT1 regulates adipocyte and osteoblast differentiation through antagonizing miR-148a-3p

Long noncoding RNAs (LncRNAs) have been implicated in the regulation of adipocyte and osteoblast differentiation. However, the functional contributions of LncRNAs to adipocyte or osteoblast differentiation remain largely unexplored. In the current study we have identified a novel LncRNA named peroxisome proliferator-activated receptor γ coactivator-1β-OT1 (PGC1β-OT1). The expression levels of PGC1β-OT1 were altered during adipogenic and osteogenic differentiation from progenitor cells. 5'- and 3'-rapid amplification of cDNA ends (RACE) revealed that PGC1β-OT1 is 1759 nt in full length. Overexpression of PGC1β-OT1 in progenitor cells inhibited adipogenic differentiation, whereas silencing of endogenous PGC1β-OT1 induced adipogenic differentiation. By contrast, overexpression of PGC1β-OT1 in progenitor cells stimulated, whereas silencing of PGC1β-OT1 inhibited osteogenic differentiation. In vivo experiment showed that silencing of endogenous PGC1β-OT1 in marrow stimulated fat accumulation and decreased osteoblast differentiation in mice. Mechanism investigations revealed that PGC1β-OT1 contains a functional miR-148a-3p binding site. Overexpression of the mutant PGC1β-OT1 with mutation at the binding site failed to regulate either adipogenic or osteogenic differentiation. In vivo crosslinking combined with affinity purification studies demonstrated that PGC1β-OT1 physically associated with miR-148a-3p through the functional miR-148a-3p binding site. Furthermore, PGC1β-OT1 affected the expression of endogenous miR-148a-3p and its target gene lysine-specific demethylase 6b (KDM6B). Supplementation of miR-148a-3p in progenitor cells blocked the inhibitory effect of PGC1β-OT1 on adipocyte formation. Moreover, overexpression of Kdm6b restored the osteoblast differentiation which was inhibited by silencing of endogenous PGC1β-OT. Our studies provide evidences that the novel LncRNA PGC1β-OT1 reciprocally regulates adipogenic and osteogenic differentiation through antagonizing miR-148a-3p and enhancing KDM6B effect.

Sialoglycoprotein isolated from Carassius auratus eggs promotes osteogenesis by stimulating mesenchymal stem cells to commit to osteoblast differentiation

In this study, we explore whether the pro-osteogenic effects of sialoglycoprotein from Carassius auratus eggs (Ca-SGP) involve mesenchymal stem cells (MSCs). Ovariectomized osteoporotic mice treated with Ca-SGP had increased bone formation and reduced bone marrow adipose tissue. As MSCs are common progenitors of osteoblasts and adipocytes, we isolated MSCs from Ca-SGP-treated mice and found that they tended to differentiate into osteoblasts over adipocytes confirmed by Alizarin red and Oil red O staining. This change was seen at the gene and protein level. To further explore the effect of Ca-SGP on MSCs, we isolated MSCs from healthy mice and treated them with Ca-SGP in vitro. We discovered that Ca-SGP promoted MSC differentiation to osteoblasts. In addition, Ca-SGP promoted osteogenesis and reduced the fat in marrow cavity of adolescent mice. For the first time, our results demonstrate that Ca-SGP promotes osteogenesis via stimulating MSCs to commit to osteoblasts. Graphical Abstract ᅟ.

miR-181a modulates circadian rhythm in immortalized bone marrow and adipose derived stromal cells and promotes differentiation through the regulation of PER3

miRNAs are important regulators of diverse cellular processes including proliferation, apoptosis, and differentiation. In the context of bone marrow derived stromal cell and adipose derived stromal cell differentiation, miRNAs are established regulators of both differentiation or stemness depending on their target. Furthermore, miRNA dysregulation can play a key role in various disease states. Here we show that miR-181a is regulated in a circadian manner and is induced during both immortalized bone marrow derived stromal cell (iBMSC) as well as primary patient adipose derived stromal cell (PASC) adipogenesis. Enhanced expression of miR-181a in iBMSCs  and PASCs produced a robust increase in adipogenesis through the direct targeting of the circadian factor period circadian regulator 3 (PER3). Furthermore, we show that knocking down endogenous miR-181a expression in iBMSC has a profound inhibitory effect on iBMSC adipogenesis through its regulation of PER3. Additionally, we found that miR-181a regulates the circadian dependency of the adipogenesis master regulator PPARγ. Taken together, our data identify a previously unknown functional link between miR-181a and the circadian machinery in immortalized bone marrow stromal cells and adipose derived stromal cells highlighting its importance in iBMSC and ASC adipogenesis and circadian biology.

BM-MSC-derived exosomes alleviate radiation-induced bone loss by restoring the function of recipient BM-MSCs and activating Wnt/β-catenin signaling

Background

Radiotherapy to cancer patients is inevitably accompanied by normal tissue injury, and the bone is one of the most commonly damaged tissues. Damage to bone marrow mesenchymal stem cells (BM-MSCs) induced by radiation is thought to be a major cause of radiation-induced bone loss. Exosomes exhibit great therapeutic potential in the treatment of osteoporosis, but whether exosomes are involved in radiation-induced bone loss has not been thoroughly elucidated to date. The main purpose of this study is to investigate the role of exosomes derived from BM-MSCs in restoring recipient BM-MSC function and alleviating radiation-induced bone loss.

Methods

BM-MSC-derived exosomes were intravenously injected to rats immediately after irradiation. After 28 days, the left tibiae were harvested for micro-CT and histomorphometric analysis. The effects of exosomes on antioxidant capacity, DNA damage repair, proliferation, and cell senescence of recipient BM-MSCs were determined. Osteogenic and adipogenic differentiation assays were used to detect the effects of exosomes on the differentiation potential of recipient BM-MSCs, and related genes were measured by qRT-PCR and Western blot analysis. β-Catenin expression was detected at histological and cytological levels.

Results

BM-MSC-derived exosomes can attenuate radiation-induced bone loss in a rat model that is similar to mesenchymal stem cell transplantation. Exosome-treated BM-MSCs exhibit reduced oxidative stress, accelerated DNA damage repair, and reduced proliferation inhibition and cell senescence-associate protein expression compared with BM-MSCs that exclusively received irradiation. Following irradiation, exosomes promote β-catenin expression in BM-MSCs and restore the balance between adipogenic and osteogenic differentiation.

Conclusions

Our findings indicate that BM-MSC-derived exosomes take effects by restoring the function of recipient BM-MSCs. Therefore, exosomes may represent a promising cell-free therapeutic approach for the treatment of radiation-induced bone loss.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1121-9) contains supplementary material, which is available to authorized users.

Histone demethylase KDM7A reciprocally regulates adipogenic and osteogenic differentiation via regulation of C/EBPα and canonical Wnt signalling

Recent emerging evidences revealed that epigenetic methylation of histone and DNA regulates the lineage commitment of mesenchymal progenitor cells. This study was undertaken to delineate the actions of histone lysine demethylase 7A (KDM7A) on osteogenic and adipogenic differentiation. Kdm7a expression was up‐regulated in primary marrow stromal cells and established stromal ST2 line after adipogenic and osteogenic treatment. Silencing of endogenous Kdm7a in the cells blocked adipogenic differentiation whereas promoted osteogenic differentiation. Conversely, overexpression of wild‐type Kdm7a in the progenitor cells enhanced adipogenic differentiation whereas inhibited osteogenic differentiation. However, the effect of KDM7A on cell differentiation was largely attenuated when the point mutation was made that abolishes enzymatic activity of KDM7A. Mechanism investigations revealed that silencing of Kdm7a down‐regulated the expression of the CCAAT/enhancer binding protein α (C/EBPα) and secreted frizzled‐related protein 1 (Sfrp1). Chromatin immunoprecipitation (ChIP) assay revealed that KDM7A directly binds to the promoters of C/EBPα and Sfrp1 and removes the histone methylation marks H3K9me2 and H3K27me2. Furthermore, silencing of Kdm7a activated canonical Wnt signalling. Thereafter, activation of canonical Wnt signalling through silencing of Sfrp1 in ST2 attenuated the stimulation of adipogenic differentiation and inhibition of osteogenic differentiation by KDM7A. Our study suggests that KDM7A balances adipogenic and osteogenic differentiation from progenitor cells through epigenetic control of C/EBPα and canonical Wnt signalling and implicates that control of KDM7A action has an epigenetic perspective of curtailing metabolic disorders like osteoporosis.

The Unique Metabolic Characteristics of Bone Marrow Adipose Tissue

Bone marrow adipose tissue (MAT) is distinct from white adipose tissue (WAT) or brown adipose tissue (BAT) for its location, feature and function. As a largely ignored adipose depot, it is situated in bone marrow space and resided with bone tissue side-by-side. MAT is considered not only as a regulator of bone metabolism through paracrine, but also as a functionally particular adipose tissue that may contribute to global metabolism. Adipokines, inflammatory factors and other molecules derived from bone marrow adipocytes may exert systematic effects. In this review, we summary the evidence from several aspects including development, distribution, histological features and phenotype to elaborate the basic characteristics of MAT. We discuss the association between bone metabolism and MAT, and highlight our current understanding of this special adipose tissue. We further demonstrate the probable relationship between MAT and energy metabolism, as well as glucose metabolism. On the basis of preliminary results from animal model and clinical studies, we propose that MAT has its unique secretory and metabolic function, although there is no in-depth study at present.

An ameloblastin C-terminus variant is present in human adipose tissue

Objective

Transcriptional regulatory elements in the ameloblastin (AMBN) promoter indicate that adipogenesis may influence its expression. The objective here was to investigate if AMBN is expressed in adipose tissue, and have a role during differentiation of adipocytes.

Design

AMBN expression was examined in adipose tissue and adipocytes by real-time PCR and ELISA. Distribution of ameloblastin was investigated by immunofluorescence in sections of human subcutaneous adipose tissue. The effect of recombinant proteins resembling AMBN and its processed products on proliferation of primary human pre-adipocytes and murine 3T3-L1 cell lines was measured by [³H]-thymidine incorporation. The effect on adipocyte differentiation was evaluated by the expression profile of the adipogenic markers PPARγ and leptin, and the content of lipids droplets (Oil-Red-O staining).

Results

AMBN was found to be expressed in human adipose tissue, human primary adipocytes, and in 3T3-L1 cells. The C-terminus of the AMBN protein and a 45 bp shorter splice variant was identified in human subcutaneous adipose tissue. The expression of AMBN was found to increase four-fold during differentiation of 3T3-L1 cells. Administration of recombinant AMBN reduced the proliferation, and enhanced the expression of PPARγ and leptin in 3T3-L1 and human pre-adipocytes, respectively.

Conclusions

The AMBN C-terminus variant was identified in adipocytes. This variant may be encoded from a short splice variant. Increased expression of AMBN during adipogenesis and its effect on adipogenic factors suggests that AMBN also has a role in adipocyte development.

The GDF11-FTO-PPARγ axis controls the shift of osteoporotic MSC fate to adipocyte and inhibits bone formation during osteoporosis

During osteoporosis, the shift of bone mesenchymal stem cell (BMSC) lineage commitment to adipocyte leads to the imbalance between bone mass and fat, which increases the risk of fracture. The mechanism underlying this process is not fully understood. Fat mass and obesity-associated protein (FTO) is an RNA demethylase that demethylates various methylated nucleic acids and participates in various physiological and pathological processes. Here we identified FTO as a regulator for BMSC fate determination during osteoporosis. FTO was up-regulated in bone marrow during aging or osteoporosis in human and mice in a GDF11(growth differentiation factor 11)-C/EBPα-dependent mechanism. The expression of FTO was also up-regulated during adipocyte differentiation of BMSCs whereas its expression was down-regulated during osteoblast differentiation. Gain-of-function and loss-of-function experiments showed that FTO favored the BMSCs to differentiate to adipocytes rather than osteoblasts. Further mechanism study demonstrated that FTO bound and demethylated the mRNA of the Peroxisome proliferator-activated receptor gamma (Pparg), leading to the increase in the expression of Pparg mRNA. Reversely, Pparg knockdown blocked the function of GDF11-FTO during osteoblast differentiation of BMSCs. Furthermore, conditionally genetic knockout of Fto in osteoblasts inhibited the development of osteopenia in mice. Collectively, our findings demonstrated that GDF11-FTO-Pparg axis promoted the shift of osteoporotic BMSC fate to adipocyte and inhibited bone formation during osteoporosis.

Oil from Antarctic krill (Euphausia superba) facilitates bone formation in dexamethasone-treated mice

Glucocorticoids are the leading cause of secondary osteoporosis. In the current study, the in vivo effects of Antarctic krill (Euphausia superba) oil (AKO) on dexamethasone-treated mice were investigated. Results showed that AKO significantly prevents bone loss, as evidenced by improved bone mineral density, biomechanical strength, and cancellous bone microstructure. Fluorescence double-labeling of femur showed that AKO induces new bone formation. Toluidine blue staining of marrow cavity indicated that AKO increases the number of trabecula, and decreases the generation of adipose cells. Runt-related transcription factor 2 (Runx2) and Peroxisome proliferator-activated receptor γ (PPARγ) are the switches for osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells, respectively. AKO significantly promoted the expression of Runx2 protein, and reduced PPARγ expression in bone tissue. Furthermore, AKO increased the mRNA expression of osteogenesis-related genes and decreased the expression of adipogenesis-related genes. In conclusion, AKO improved glucocorticoid-induced osteoporosis via promoting bone formation.

PGC-1α Controls Skeletal Stem Cell Fate and Bone-Fat Balance in Osteoporosis and Skeletal Aging by Inducing TAZ

Aberrant lineage specification of skeletal stem cells (SSCs) contributes to reduced bone mass and increased marrow adipose tissue (MAT) in osteoporosis and skeletal aging. Although master regulators of osteoblastic and adipogenic lineages have been identified, little is known about factors that are associated with MAT accumulation and osteoporotic bone loss. Here, we identify peroxisome-proliferator-activated receptor γ coactivator 1-α (PGC-1α) as a critical switch of cell fate decisions whose expression decreases with aging in human and mouse SSCs. Loss of PGC-1α promoted adipogenic differentiation of murine SSCs at the expense of osteoblastic differentiation. Deletion of PGC-1α in SSCs impaired bone formation and indirectly promoted bone resorption while enhancing MAT accumulation. Conversely, induction of PGC-1α attenuated osteoporotic bone loss and MAT accumulation. Mechanistically, PGC-1α maintains bone and fat balance by inducing TAZ. Our results suggest that PGC-1α is a potentially important therapeutic target in the treatment of osteoporosis and skeletal aging.

Maintenance of Kidney Metabolic Homeostasis by PPAR Gamma

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors that control the transcription of specific genes by binding to regulatory DNA sequences. Among the three subtypes of PPARs, PPARγ modulates a broad range of physiopathological processes, including lipid metabolism, insulin sensitization, cellular differentiation, and cancer. Although predominantly expressed in adipose tissue, PPARγ expression is also found in different regions of the kidney and, upon activation, can redirect metabolism. Recent studies have highlighted important roles for PPARγ in kidney metabolism, such as lipid and glucose metabolism and renal mineral control. PPARγ is also implicated in the renin-angiotensin-aldosterone system and, consequently, in the control of systemic blood pressure. Accordingly, synthetic agonists of PPARγ have reno-protective effects both in diabetic and nondiabetic patients. This review focuses on the role of PPARγ in renal metabolism as a likely key factor in the maintenance of systemic homeostasis.

The obesity paradox and osteoporosis

Overweight and obesity according to the definition of the WHO are considered as an abnormal or excessive fat accumulation that may impair health. Studies comparing fracture incidence in obese and non-obese individuals have demonstrated that obesity, defined on the basis of body mass index (BMI), is associated with increased risk of fracture at some sites but seems to be protective at others. The results of the studies are influenced by the distribution of BMI in the population studied; for example, in cohorts with a low prevalence of obesity, a predilection for certain fracture sites in obese individuals becomes difficult to detect, whereas, in populations with a high prevalence of obesity, previously unreported associations may emerge. Furthermore, obesity can bring with itself many complications (Type 2 diabetes mellitus, vitamin D deficiency, and motor disability) which, in the long run, can have a definite influence in terms of overall risk and quality of life, as well. This is a narrative review focusing on the relationship between bone metabolism and overweight/obesity and dealing with the fundamental dilemma of a disease (obesity) apparently associated with improved values of bone mineral density, part of a complicated relationship which revolves around obesity called "the obesity paradox".