Previous studies revealed that exposure of mesangial cells to high glucose concentration induces the production of matrix proteins mediated by TGF-beta1. We tested if structural analogues of D-glucose may mimic the high glucose effect and found that D-glucosamine was strikingly more potent than D-glucose itself in enhancing the production of TGF-beta protein and subsequent production of the matrix components heparan sulfate proteoglycan and fibronectin in a time- and dose-dependent manner. D-Glucosamine also promoted conversion of latent TGF-beta to the active form. Therefore, we suggested that the hexosamine biosynthetic pathway (the key enzyme of which is glutamine:fructose-6-phosphate amidotransferase [GFAT]) contributes to the high glucose-induced TGF-beta1 production. Inhibition of GFAT by the substrate analogue azaserine or by inhibition of GFAT protein synthesis with antisense oligonucleotide prevented the high glucose-induced increase in cellular glucosamine metabolites and TGF-beta1 expression and bioactivity and subsequent effects on mesangial cell proliferation and matrix production. Overall, our study indicates that the flux of glucose metabolism through the GFAT catalyzed hexosamine biosynthetic pathway is involved in the glucose-induced mesangial production of TGF-beta leading to increased matrix production.
Previous investigations have demonstrated that growing mesangial cells in high glucose concentration stimulates extracellular matrix synthesis and also increases the expression of transforming growth factor-beta (TGF-beta). We examined the effects of hyperglycemia on mesangial proliferation and heparan sulfate proteoglycan (HSPG) and fibronectin production. Prolonged exposure of mesangial cells to increasing glucose concentrations resulted in dose-dependent effects on growth inhibition and stimulation of matrix production. Treatment of mesangial cells with high glucose-conditioned medium or with TGF-beta 1 mimicked the effects of high-glucose incubation. Furthermore, TGF-beta 1 caused a dose-dependent increase in HSPG mRNA levels. The high-glucose effects on mesangial cells were preceded by an increase in total TGF-beta 1 protein. The presence of TGF-beta 1 antisense oligonucleotide attenuated the glucose-mediated effects on mesangial proliferation and matrix production. The data show that even moderately elevated glucose concentrations appear to affect the mesangial cells. The results indicate that 1) TGF-beta 1 protein production is necessary to obtain the high glucose-induced effects and 2) TGF-beta 1 stimulates mesangial HSPG expression and production. Because these effects may be attenuated by oligonucleotides antisense to TGF-beta 1, the results suggest a possible way for effective intervention in TGF-beta-mediated glomerulosclerosis.
Recent in vitro and in vivo studies suggested that the increased flux of glucose through the hexosamine biosynthetic pathway may contribute to glucose-induced insulin resistance and to the induction of the synthesis of growth factors. Because glutamine:fructose-6-phosphate amidotransferase (GFAT) catalyzes the first and rate-limiting step in the formation of hexosamine products, this enzyme is the key regulator in this pathway and is therefore possibly also involved in the alterations occurring in preclinical or manifest diabetic patients. To study the expression of GFAT in human tissues, we produced and characterized a peptic antiserum specifically recognizing GFAT protein and a riboprobe for the detection of GFAT mRNA. Immunohistochemical and nonradioactive in situ hybridization analysis revealed high levels of expression of GFAT protein and mRNA in adipocytes and skeletal muscle. Furthermore, a marked GFAT expression was found in vascular smooth muscle cells with unexpectedly high variability and lower levels in other cells, e.g., peripheral nerve sheath cells or endocrine-active cells, including the pancreatic islet cell. GFAT protein expression was below detection level in endothelium, osteocytes, lymphocytes, granulocytes, and in most quiescent fibroblasts. In renal tissue, GFAT was expressed in tubular epithelial cells, while glomerular cells remained essentially unstained. Renal sections obtained from patients with diabetic nephropathy showed significant GFAT expression in some glomerular epithelial and mesangial cells, indicating that GFAT expression may be induced by manifest diabetes. Our data indicate that GFAT is expressed in most tissues involved in the development of diabetic late complications. Furthermore, the results suggest that GFAT gene expression is highly regulated.
We have used laser capture microdissection (LCM) and fluorescence microscopy to isolate genetically labeled neurons from the Drosophila melanogaster brain. From native thin sections, regions of interest could be analyzed with a spatial resolution better than 50 μm. To exploit the specificity of LCM for lipidomics, catapulted tissue patches were directly collected on a reversed phase column and analyzed using an on-column extraction (OCE) that was directly coupled with liquid chromatography-multistage mass spectrometry (LC-MS(n)). With this approach, more than 50 membrane lipids belonging to 9 classes were quantified in tissue regions equivalent to a sample amount of 50 cells. Using this method, the limit of quantitation and the extraction efficiency could be estimated enabling a reliable evaluation of acquired lipid profiles. The lipid profiles of cell body- and synapse-enriched regions of the Drosophila brain were determined and found to be distinct. We argue that this workflow represents a tremendous improvement for tissue lipidomics by integrating genetics, fluorescence microscopy, LCM and LC-MS(n).
The expression of matrix metalloproteinases (MMPs) with type IV collagenase activity has been associated with tumour invasion and metastatic potential in experimental models. We studied whether the cellular localization of MMP expression provides useful information on tumour behaviour in human breast cancer. Immunohistochemistry and non-radioisotopic-detected in situ hybridization were used to study protein and mRNA expression profiles for MMPs-2, -3 and -9 in paraffin sections of 70 invasive breast carcinomas. Protein and mRNA expression of the MMPs was observed in tumour as well as in peritumoural stromal cells. MMP protein expression was increased at the invasive border (p < 0.05). Grade 3 carcinomas expressed MMP-2 mRNA in significantly more tumour cells than grade 2 carcinomas (p = 0.006). Ductal carcinomas with an extensive intraductal component were characterized by the lowest percentages of MMPs-2 and -3 mRNA expressing peritumoural stromal cells (p < 0.05). No correlation was observed between MMP protein/mRNA expression and pTNM classification. In conclusion our results indicate that the expression of MMPs is associated with tumour behaviour. The correlation of MMPs-2 and -3 expression in peritumoural stromal cells with tumour type, shown for the first time, suggests that transcriptional regulation of these MMPs in stromal cells is important for the growth pattern of breast cancer.
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