Glucose-6-phosphatase mRNA levels in kidney isolated tubule suspensions are increased by dexamethasone and decreased by insulin

Proinsulin C-peptide potentiates the inhibitory action of insulin on glucose synthesis in primary cultured rabbit kidney-cortex tubules: Metabolic studies

Effects of equimolar concentrations of proinsulin C-peptide and insulin on glucose synthesis were studied in primary cultures of rabbit kidney-cortex tubules grown in the presence of alanine, glycerol, and octanoate. The rhodamine-labeled C-peptide entered renal tubular cells and localized in nuclei, both in the presence and absence of insulin; preincubations with the unlabeled compound inhibited internalization. C-peptide did not affect glucose formation when added alone but potentiated the inhibitory action of insulin by about 20% due to a decrease in flux through glucose-6-phosphate isomerase (GPI) and (or) glucose-6-phosphatase (G6Pase). GPI inhibition was caused by: (i) increased intracellular contents of fructose-1,6-bisphosphate and fructose-1-phosphate, inhibitors of the enzyme and (ii) reduced level of the phosphorylated GPI, which exhibits higher enzymatic activity in the presence of casein kinase 2. A decrease in flux through G6Pase, due to diminished import of G6P by G6P-transporter from the cytoplasm into endoplasmic reticulum lumen, is also suggested. The data show for the first time that in the presence of insulin and C-peptide, both GPI and G6P-ase may act as regulatory enzymes of renal gluconeogenic pathway.

Altered gene expression profiles in the brain, kidney, and lung of one-month-old cloned pigs

Although numerous mammalian species have been successfully cloned by somatic cell nuclear transfer (SCNT), little is known about gene expression of cloned pigs by SCNT. In the present study, expression profiles of 1-month-old cloned pigs generated from fetal fibroblasts (n = 5) were compared to those of age-matched controls (n = 5) using a 13K oligonucleotide microarray. The brain, kidney, and lung were chosen for microarray analysis to represent tissues from endoderm, mesoderm, and ectoderm in origin. In clones, 179 and 154 genes were differentially expressed in the kidney and the lung, respectively (fold change >2, p < 0.05, false discovery rate = 0.05), whereas only seven genes were differentially expressed in the brain of clones. Functional analysis of the differentially expressed genes revealed that they were enriched in diabetic nephropathy in the kidney, delayed alveologenesis as well as downregulated MAPK signaling pathways in the lung, which was accompanied with collapsed alveoli in the histological examination of the lung. To evaluate whether the gene expression anomalies are associated with changes in DNA methylation, global concentration of the methylated cytosine was measured in lung DNA by HPLC. Clones were significantly hypermethylated (5.72%) compared to the controls (4.13%). Bisulfite-pyrosequencing analyses of the promoter regions of differentially expressed genes, MYC and Period 1 (PER1), however, did not show any differences in the degree of DNA methylation between controls and clones. Together, these findings demonstrate that cloned pigs have altered gene expression that may potentially cause organ dysfunction.

Actuality of Warburg’s views in our understanding of renal cancer metabolism

More than 50 years ago, Warburg proposed that the shift in glucose metabolism from oxidative phosphorylation (OXPHOS) to glycolysis occurring in spite of an adequate oxygen supply was at the root of cancer. This hypothesis often disregarded over the following years has recently stirred up much interest due to progress made in cancer genetics and proteomics. Studies related to renal cancers have been particularly informative to understand how abnormal use of glucose and decrease in OXPHOS are linked to cell proliferation in tumors. Indeed, in aggressive tumors such as clear cell renal carcinoma, the von Hippel-Lindau factor invalidation stabilizes the hypoxia-inducible factor (HIF) in the presence of oxygen. HIF stimulating glycolytic gene expression increases the glycolytic flux. Deficiencies in genes involved in oxidative phosphorylation that can explain the down-regulation of OXPHOS components also begin to be identified. These findings are important in the search for novel therapeutic approaches to cancer treatment.

Physiological oxygenation status is required for fully differentiated phenotype in kidney cortex proximal tubules

Hypoxia has been suspected to trigger transdifferentiation of renal tubular cells into myofibroblasts in an epithelial-to-mesenchymal transition (EMT) process. To determine the functional networks potentially altered by hypoxia, rat renal tubule suspensions were incubated under three conditions of oxygenation ranging from normoxia (lactate uptake) to severe hypoxia (lactate production). Transcriptome changes after 4 h were analyzed on a high scale by restriction fragment differential display. Among 1,533 transcripts found, 42% were maximally expressed under severe hypoxia and 8% under mild hypoxia (Po2 = 48 mmHg), suggesting two different levels of oxygen sensing. Normoxia was required for full expression of the proximal tubule-specific transcripts 25-hydroxyvitamin D 1-hydroxylase ( Cyp27b1) and l-pyruvate kinase ( Pklr), transcripts involved in tissue cohesion such as fibronectin ( Fn1) and N-cadherin ( Cdh2), and non-muscle-type myosin transcripts. Mild hypoxia increased myogenin transcript level. Conversely, severe hypoxia increased transcripts involved in extracellular matrix remodeling, those of muscle-type myosins, and others involved in creatine phosphate synthesis and lactate transport ( Slc16a7). Accordingly, microscopy showed loss of tubule aggregation under hypoxia, without tubular disruption. Hypoxia also increased the levels of kidney-specific transcripts normally restricted to the less oxygenated medullary zone and others specific for the distal part of the nephron. We conclude that extensive oxygen supply to the kidney tubule favors expression of its differentiated functions specifically in the proximal tubule, whose embryonic origin is mesenchymal. The phenotype changes could potentially permit transient adaptation to hypoxia but also favor pathological processes such as tissue invasion.

Natural antisense transcripts of HIF-1alpha are conserved in rodents

A natural antisense transcript (aHIF), which sequence is strictly complementary to the 3' untranslated region (3'UTR) of HIF-1alpha mRNA, has been identified in human and shown to be overexpressed in renal carcinomas. We searched for aHIF in different rodent tissues. Two candidate expressed sequence tag (EST) were identified in silico and their PCR products (1.1 and 1.0 kb) were cloned and sequenced in mouse and rat, respectively. These transcripts were rigorously complementary to the 3'UTR of rodent HIF-1alpha mRNA and were broadly expressed in all mouse and rat tissues we tested. The conservation of aHIF in rodents underlined its potential importance in cell regulations. Therefore the responses of aHIF and HIF-1alpha transcripts were investigated in various types of hypoxic conditions. In freshly isolated rat renal tubules, aHIF RNA level was increased by acute hypoxia and low in normal supply of oxygen. In a rat strain raised in chronic hypobaric altitude hypoxia, aHIF transcript was greatly induced in the oxidative-type soleus and heart muscles of 3 month-old animals. By contrast, in the glycolytic-type extensor digitorum longus muscle aHIF transcript amount was lowered by hypoxia whereas HIF-1alpha transcript was highly expressed. In brain, where oxidative glycolysis takes place, HIF-1alpha mRNA and its antisense transcript levels were high and not significantly changed by altitude. Tumour cell lines cultured for 6 h in conditions mimicking hypoxia expressed lower amounts of HIF-1alpha mRNA. In two rat cell lines, aHIF transcript levels were greatly augmented after a 6-h incubation in these conditions, whereas in a mouse cell line, aHIF level was significantly reduced.

Differential expression of the subunits of the glucose-6-phosphatase system in the clear cell type of human renal cell carcinoma - no evidence for an overexpression of protein kinase B

The expression of two components of the glucose-6-phosphatase system, the catalytic subunit (G6PaseC) and the glucose-6-phosphate transporter, was analyzed in the clear cell type of human renal cell carcinoma. The expression of G6PaseC was decreased in tumours compared with non-tumourous tissue of the same patient. The expression of G6PaseT varied with no general trend between tumours and control tissue. The expression of protein kinase B (PKB) was unchanged in the tumours, suggesting that the down-regulation of G6PaseC in clear cells and the maintenance of the transformed phenotype are not predominantly caused by an overexpression of PKB.