Adipocyte-induced transdifferentiation of osteoblasts and its potential role in age-related bone loss.

Our preliminary findings have lead us to propose bone marrow adipocyte secretions as new contributors to bone loss. Indeed, using a coculture model based on human bone marrow stromal cells, we previously showed that soluble factors secreted by adipocytes induced the conversion of osteoblasts towards an adipocyte-like phenotype. In this study, microarray gene expression profiling showed profound transcriptomic changes in osteoblasts following coculture and confirmed the enrichment of the adipocyte gene signature. Double immunofluorescence microscopic analyses demonstrated the coexpression of adipogenic and osteoblastic specific markers in individual cells, providing evidence for a transdifferentiation event. At the molecular level, this conversion was associated with upregulated expression levels of reprogramming genes and a decrease in the DNA methylation level. In line with these in vitro results, preliminary immunohistochemical analysis of bone sections revealed adipogenic marker expression in osteoblasts from elderly subjects. Altogether, these data suggest that osteoblast transdifferentiation could contribute to decreased bone mass upon ageing.

Analysis of sterol-regulatory element-binding protein 1c target genes in mouse liver during aging and high-fat diet.

BACKGROUND: The sterol regulatory element-binding protein (SREBP) 1c contributes to the transcriptional coordination of cholesterol, fatty acid, and carbohydrate metabolisms. Alterations in these processes accelerate the progression of hepatic steatosis and insulin resistance during aging and obesity. METHODS: Using an ex vivo chromatin immunoprecipitation coupled to microarray (ChIP-on-chip) technique combined with genome-wide gene expression analysis, we analyzed the transcriptomic adaptations mediated by Srebp-1c binding to gene promoters in the liver of mice fed with a low-fat diet or a high-fat diet (HFD) for either 1 or 12 months. RESULTS: Aging had a higher transcriptional impact than HFD and modified the expression of genes involved in fatty acid oxidation and oxidative stress. HFD was associated with a marked induction of genes involved in lipid and cholesterol metabolism. The prolonged high-fat feeding together with the aging effects stimulates inflammatory pathways. ChIP-on-chip applied to aging and HFD analyses revealed that the binding of SREBP-1c to a series of promoters accompanied a paralleled modification of gene expression. Therefore, SREBP-1c could play a role in aging and high-fat feeding through the regulation of genes involved in lipid metabolism and inflammatory response. CONCLUSIONS: This study represents an original ex vivo experiment to elucidate the molecular events involved in metabolic disorders.

Pharmacometabonomic investigation of dynamic metabolic phenotypes associated with variability in response to galactosamine hepatotoxicity.

Galactosamine (galN) is widely used as an in vivo model of acute liver injury. We have applied an integrative approach, combining histopathology, clinical chemistry, cytokine analysis, and nuclear magnetic resonance (NMR) spectroscopic metabolic profiling of biofluids and tissues, to study variability in response to galactosamine following successive dosing. On re-challenge with galN, primary non-responders displayed galN-induced hepatotoxicity (induced response), whereas primary responders exhibited a less marked response (adaptive response). A systems-level metabonomic approach enabled simultaneous characterization of the xenobiotic and endogenous metabolic perturbations associated with the different response phenotypes. Elevated serum cytokines were identified and correlated with hepatic metabolic profiles to further investigate the inflammatory response to galN. The presence of urinary N-acetylglucosamine (glcNAc) correlated with toxicological outcome and reflected the dynamic shift from a resistant to a sensitive phenotype (induced response). In addition, the urinary level of glcNAc and hepatic level of UDP-N-acetylhexosamines reflected an adaptive response to galN. The unique observation of galN-pyrazines and altered gut microbial metabolites in fecal profiles of non-responders suggested that gut microfloral metabolism was associated with toxic outcome. Pharmacometabonomic modeling of predose urinary and fecal NMR spectroscopic profiles revealed a diverse panel of metabolites that classified the dynamic shift between a resistant and sensitive phenotype. This integrative pharmacometabonomic approach has been demonstrated for a model toxin; however, it is equally applicable to xenobiotic interventions that are associated with wide variation in efficacy or toxicity and, in particular, for prediction of susceptibility to toxicity.

Molecular characterization of the AMPA-receptor potentiator S70340 in rat primary cortical culture: whole-genome expression profiling.

To improve our understanding of the molecular events underlying the effects of positive allosteric modulators of the alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (S)-AMPA-type glutamate receptors, gene expression profiles of primary cortical culture were measured by Agilent-Microarray technique under (S)-AMPA (1µM) stimulation for 0.5, 6, 24 and 48h in the presence or absence of S70340 (30µM), an allosteric potentiator of AMPA receptors. (S)-AMPA and S70340 treatment alone have little effect on gene expression whereas as early as 6h, their combination induced a large number of genes known to decrease apoptosis and mediate cell survival. Pathway analyses of (S)-AMPA+S70340 treatment-mediated gene expression from 6 to 48h further suggested the activation of cellular functions including neuron differentiation and neurite outgrowth. A proportion of genes implicated in these functions encode proteins involved in environmental cues and are expressed in growth cones, such as extracellular matrix component proteins and filopodia microfilament-associated proteins. Time course analysis of mRNA expression combined with in silico promoter analysis revealed an enrichment in the cAMP response element (CRE) among co-regulated genes. This study demonstrated that S70340-mediated AMPA potentialisation activated genes and functional processes involved in neuroprotective and cognitive effects and describes putative new functional biomarkers.

Only a subset of Met-activated pathways are required to sustain oncogene addiction.

Tumor onset and progression require the accumulation of many genetic and epigenetic lesions. In some cases, however, cancer cells rely on only one of these lesions to maintain their malignant properties, and this dependence results in tumor regression upon oncogene inactivation ("oncogene addiction"). Determining which nodes of the many networks operative in the transformed phenotype specifically mediate this response to oncogene neutralization is crucial to identifying the vulnerabilities of cancer. Using the Met receptor as the major model system, we combined multiplex phosphoproteomics, genome-wide expression profiling, and functional assays in various cancer cells addicted to oncogenic receptor tyrosine kinases. We found that Met blockade affected a limited subset of Met downstream signals: Little or no effect was observed for several pathways downstream of Met; instead, only a restricted and pathway-specific signature of transducers and transcriptional effectors downstream of Ras or phosphoinositide 3-kinase (PI3K) was inactivated. An analogous signature was also generated by inhibition of epidermal growth factor receptor in a different cellular context, suggesting a stereotyped response that likely is independent of receptor type or tissue origin. Biologically, Met inhibition led to cell-cycle arrest. Inhibition of Ras-dependent signals and PI3K-dependent signals also resulted in cell-cycle arrest, whereas cells in which Met was inhibited proliferated when Ras or PI3K signaling was active. These findings uncover "dominant" and "recessive" nodes among the numerous oncogenic networks regulated by receptor tyrosine kinases and active in cancer, with the Ras and PI3K pathways as determinants of therapeutic response.

Only a subset of Met-activated pathways are required to sustain oncogene addiction.

Tumor onset and progression require the accumulation of many genetic and epigenetic lesions. In some cases, however, cancer cells rely on only one of these lesions to maintain their malignant properties, and this dependence results in tumor regression upon oncogene inactivation ("oncogene addiction"). Determining which nodes of the many networks operative in the transformed phenotype specifically mediate this response to oncogene neutralization is crucial to identifying the vulnerabilities of cancer. Using the Met receptor as the major model system, we combined multiplex phosphoproteomics, genome-wide expression profiling, and functional assays in various cancer cells addicted to oncogenic receptor tyrosine kinases. We found that Met blockade affected a limited subset of Met downstream signals: Little or no effect was observed for several pathways downstream of Met; instead, only a restricted and pathway-specific signature of transducers and transcriptional effectors downstream of Ras or phosphoinositide 3-kinase (PI3K) was inactivated. An analogous signature was also generated by inhibition of epidermal growth factor receptor in a different cellular context, suggesting a stereotyped response that likely is independent of receptor type or tissue origin. Biologically, Met inhibition led to cell-cycle arrest. Inhibition of Ras-dependent signals and PI3K-dependent signals also resulted in cell-cycle arrest, whereas cells in which Met was inhibited proliferated when Ras or PI3K signaling was active. These findings uncover "dominant" and "recessive" nodes among the numerous oncogenic networks regulated by receptor tyrosine kinases and active in cancer, with the Ras and PI3K pathways as determinants of therapeutic response.

Nox4 mediates the expression of plasminogen activator inhibitor-1 via p38 MAPK pathway in cultured human endothelial cells.

INTRODUCTION: Plasminogen Activator Inhibitor-1 (PAI-1) is the most potent endogenous inhibitor of fibrinolysis which is implicated in the pathogenesis of myocardial infarction and metabolic syndrome. The formation of reactive oxygen species (ROS) plays an important role in the pathology of vascular disorders and has been shown to increase PAI-1 expression by endothelial cells. Growing evidence indicates that NADPH oxidase and in particular the constitutively active Nox4-p22(phox) complexes are major sources of ROS in endothelial cells. The aim of the present study was to characterize the role of NADPH oxidase and in particular Nox4 in the regulation of PAI-1 expression in cultured Human Umbilical Venous Endothelial Cells (HUVECs). METHODS AND RESULTS: N-acetylcysteine (NAC, scavenger of ROS), diphenylene iodonium chloride (DPI, inhibitor of flavoproteins), M40403 (superoxyde dismutase mimic) and S17834 (inhibitor of NADPH oxidase) inhibited PAI-1 release and promoter activity in HUVECs. Specific knock down of Nox4 mRNA by siRNA caused a decrease in ROS production and NADPH oxidase activity. Moreover, Nox4 silencing decreased PAI-1 expression, release and activity as well as p38 MAPK pathways and NFkappaB activation. These signalling pathways are also involved in PAI-1 release. CONCLUSIONS: The NADPH oxidase inhibitors DPI and S 17834 as well as Nox4 silencing decreased PAI-1 synthesis in human cultured endothelial cells demonstrating the involvement of the constitutively active Nox4-containing NADPH oxidase in ROS-mediated PAI-1 transcription via p38 MAPK pathways. NADPH oxidase targeting with inhibitors such as S17834 could be an interesting strategy to decrease both oxidative stress and PAI-1 synthesis.

Synthesis and in vitro evaluation of targeted tetracycline derivatives: effects on inhibition of matrix metalloproteinases.

Among other non-antibiotic properties, tetracyclines inhibit matrix metalloproteinases and are currently under study for the treatment of osteoarthritis. Quaternary ammonium conjugates of tetracyclines were synthesized by direct alkylation of the amine function at the 4-position with methyl iodide. When tested in vitro, they inhibited cytokine-induced MMP expression to a lesser extent than parent tetracyclines. This was compensated by an improved inhibition of MMP catalytic activity. Since inhibition of collagen degradation was maintained these derivatives could be potent drug candidates for cartilage-targeted chondroprotective treatment.

Semiquantitative analysis of gene expression in cultured chondrocytes by RT-PCR.

Reverse transcriptase-polymerase chain reaction (RT-PCR) is a powerful, sensitive, and rapid method to monitor small amounts of nucleic acids. This is of particular interest for small amounts of cells, as in cartilage. We present here two protocols to isolate total RNA and a protocol to study matrix metalloproteinase and type II collagen gene expression from chondrocytes of human origin. Specific gene expression is revealed on an ethidium bromide-containing agarose gel on an ultraviolet plate and normalized to that of a housekeeping gene.