Comparative effects of insulin and refeeding on DNA synthesis, HMP shunt and cholesterogenesis in diabetic and fasted rats

Transcriptional regulation of mouse 6-phosphogluconate dehydrogenase by ADD1/SREBP1c

6-Phosphogluconate dehydrogenase (6PGDH) constitutes the pentose phosphate pathway and produces NADPH. 6PGDH is also considered as a lipogenic gene since NADPH is a pivotal cofactor for lipogenesis. Thus, it is important to elucidate how 6PGDH is regulated by various signals related to energy homeostasis. Here, we provide several evidences that ADD1/SREBP1c regulates the expression of mouse 6PGDH gene. DNase I footprinting assay and point mutation studies revealed that the E-box (CANNTG) motif in the promoter of mouse 6PGDH is an important cis-regulatory element for ADD1/SREBP1c. 6PGDH mRNA is highly expressed in white adipose tissue and tightly modulated by nutritional status. Furthermore, we found that ADD1/SREBP1c mediates insulin-dependent 6PGDH expression and that PI3-kinase is an important linker for its regulation. Taken together, these data suggest that ADD1/SREBP1c is a key transcription factor for 6PGDH gene expression and would coordinate glucose metabolism and lipogenesis for energy homeostasis.

Cell growth and cholesterol metabolism in human glucose-6-phosphate dehydrogenase deficient lymphomononuclear cells

Atherosclerosis is an inflammatory-fibroproliferative response of the arterial wall involving a complex set of interconnected events where cell proliferation (lymphomonocytes, and endothelial and smooth-muscle cells) and substantial perturbations of intracellular cholesterol metabolism are considered to be among the main features. Glucose-6-phosphate dehydrogenase (G6PD), the key enzyme of the hexose-monophosphate shunt pathway, is an essential enzyme involved in both cell growth and cholesterol metabolism, raising the question as to whether G6PD deficiency may have metabolic and growth implications in a deficient population. In the present study, we investigated cell growth and cholesterol metabolism in peripheral blood lymphomononuclear cells (PBMC) from G6PD-normal (n = 5) and -deficient (n = 5) subjects stimulated with lectins (phytohaemoagglutinin and Concanavalin A). G6PD activity, DNA ([3H]-thymidine incorporation) cholesterol synthesis and esterification ([14C]-acetate and [14C]-oleate incorporation), and G6PD, HMGCoA reductase and low density lipoprotein (LDL) receptor mRNA levels (RT-PCR) all increased following lectin stimulation in both normal and G6PD-deficient cells. However, these parameters were significantly lower in G6PD-deficient cells (P < 0.05). It is of interest that G6PD-deficient PBMC, which showed lower expression of G6PD and higher expression of the LDL receptor gene than normal PBMC under basal conditions, exhibited an opposite pattern after stimulation: G6PD and HMGCoA reductase being expressed at significantly higher levels in deficient than in normal cells (P < 0.05). We conclude that the reduced capability of G6PD-deficient cells to respond to mitogenic stimuli and to synthesize cholesterol esters may represent favourable conditions for reducing the risk of cardiovascular diseases.

Relationship between DNA and cholesterol synthesis in kidney after refeeding

DNA and cholesterol synthesis were investigated in the kidneys of fasted-refed rats. Refeeding resulted in an increase in kidney DNA synthesis, as measured by 3H-thymidine incorporation, starting at 72 h. The increase in DNA synthesis was accompanied by a stimulation of cholesterol synthesis, as measured by 14C-acetate incorporation into cholesterol.