Mithieux, Gilles, Isabelle Bady, Amandine Gautier, Martine Croset, Fabienne Rajas, and Carine Zitoun. Induction of control genes in intestinal gluconeogenesis is sequential during fasting and maximal in diabetes. Am J Physiol Endocrinol Metab 286: E370-E375, 2004. First published October 14, 2003 10.1152/ ajpendo.00299.2003.-We studied in rats the expression of genes involved in gluconeogenesis from glutamine and glycerol in the small intestine (SI) during fasting and diabetes. From Northern blot and enzymatic studies, we report that only phosphoenolpyruvate carboxykinase (PEPCK) activity is induced at 24 h of fasting, whereas glucose-6-phosphatase (G-6-Pase) activity is induced only from 48 h. Both genes then plateau, whereas glutaminase and glycerokinase strikingly rebound between 48 and 72 h. The two latter genes are fully expressed in streptozotocin-diabetic rats. From arteriovenous balance and isotopic techniques, we show that the SI does not release glucose at 24 h of fasting and that SI gluconeogenesis contributes to 35% of total glucose production in 72-h-fasted rats. The new findings are that 1) the SI can quantitatively account for up to one-third of glucose production in prolonged fasting; 2) the induction of PEPCK is not sufficient by itself to trigger SI gluconeogenesis; 3) G-6-Pase likely plays a crucial role in this process; and 4) glutaminase and glycerokinase may play a key potentiating role in the latest times of fasting and in diabetes.glucose-6-phosphatase; phosphoenolpyruvate carboxykinase; glutaminase; glycerokinase AT VARIANCE WITH THE PREVIOUS VIEW that only the liver and kidney are gluconeogenic organs because both are the only organs to express glucose-6-phosphatase (G-6-Pase) (1, 29, 32), we recently demonstrated (35) that the small intestine (SI) also expresses the enzyme in humans and rats. In addition, the SI G-6-Pase gene is strongly induced in 48-h-fasted and streptozotocin-induced diabetic rats (35), just as it is in both the liver and the kidney (31). We then showed that this confers on the SI the capacity to contribute to ϳ20% of total glucose production in 48-h-fasted rats (11). We further demonstrated that glutamine is the main precursor of glucose synthesized in the SI (11), making glutaminase and phosphoenolpyruvate carboxykinase (PEPCK) two major control genes in SI gluconeogenesis (30,36). On the other hand, the expression, without induction in insulinopenia, of the glycerokinase gene may account for the lesser role of glycerol as a possible glucose precursor in the SI (11). In contrast, alanine and lactate, i.e., the two major liver gluconeogenic substrates, are not glucose precursors in the rat SI (11).In previous studies related to fasting, we reported that, after a period of induction lasting 48 h, G-6-Pase activity is surprisingly decreased at 72 h in the liver of rats, whereas in contrast it continuously increases in the kidney during the same time (28). This suggests that the liver might have a decreasing role and/or that other sources of glucose, e.g., the kidney...

Glucose-6-phosphatase confers on gluconeogenic tissues the capacity to release endogenous glucose in blood. The expression of its gene is modulated by nutritional mechanisms dependent on dietary fatty acids, with specific inhibitory effects of polyunsaturated fatty acids (PUFA). The presence of consensus binding sites of hepatocyte nuclear factor 4 (HNF4) in the ؊1640/؉60 bp region of the rat glucose-6-phosphatase gene has led us to consider the hypothesis that HNF4␣ could be involved in the regulation of glucose-6-phosphatase gene transcription by long chain fatty acid (LCFA). Our results have shown that the glucose-6-phosphatase promoter activity is specifically inhibited in the presence of PUFA in HepG2 hepatoma cells, whereas saturated LCFA have no effect. In HeLa cells, the glucose-6-phosphatase promoter activity is induced by the co-expression of HNF4␣ or HNF1␣. PUFA repress the promoter activity only in HNF4␣-cotransfected HeLa cells, whereas they have no effects on the promoter activity in HNF1␣-cotransfected HeLa cells. From gel shift mobility assays, deletion, and mutagenesis experiments, two specific binding sequences have been identified that appear able to account for both transactivation by HNF4␣ and regulation by LCFA in cells. The binding of HNF4␣ to its cognate sites is specifically inhibited by polyunsaturated fatty acyl coenzyme A in vitro. These data strongly suggest that the mechanism by which PUFA suppress the glucose-6-phosphatase gene transcription involves an inhibition of the binding of HNF4␣ to its cognate sites in the presence of polyunsaturated fatty acyl-CoA thioesters.Glucose-6-phosphatase (Glc6Pase 1 ; EC 3.1.3.9) confers on gluconeogenic tissues, i.e. the liver, the kidney, and the small intestine, the capacity to release endogenous glucose in blood (1, 2). The expression of its gene is increased during diabetes and fasting and normalized upon insulin treatment and refeeding, respectively, in all three gluconeogenic tissues (3,4). An increase in the Glc6Pase flux (5, 6) and maximal velocity (7) has also been strongly suggested to account for increased glucose production and hepatic insulin resistance in type 2 diabetes mellitus.The Glc6Pase gene expression is also modulated by nutritional mechanisms dependent on dietary fatty acids. In the liver of rats, Glc6Pase mRNA and protein contents are increased upon high fat feeding (8) and upon elevation in plasma fatty acid levels (9). Under these nutritional conditions, the suppression of hepatic glucose production by insulin is impaired (10). This suggests that a high plasma fatty acid level may contribute increased production of glucose via increased expression of Glc6Pase, resulting in the development of liver insulin resistance (9,11,12). In vitro, the treatment of fetal hepatocytes with a high concentration (500 M) of long chain fatty acids (LCFA), such as oleic and linoleic acids, increases the Glc6Pase mRNA content (13). We have shown that the likely mechanism involves a stabilizing effect on Glc6Pase mRNA (13). On the other han...

Malaria is caused by the unicellular parasite Plasmodium which is transmitted to humans through the bite of infected female Anopheles mosquitoes. To initiate sexual reproduction and to infect the midgut of the mosquito, Plasmodium gametocytes are able to recognize the intestinal environment after being ingested during blood feeding. A shift in temperature, pH change and the presence of the insect-specific compound xanthurenic acid have been shown to be important stimuli perceived by gametocytes to become activated and proceed to sexual reproduction. Here we report that the salivary protein Saglin, previously proposed to be a receptor for the recognition of salivary glands by sporozoites, facilitates Plasmodium colonization of the mosquito midgut, but does not contribute to salivary gland invasion. In mosquito mutants lacking Saglin, Plasmodium infection of Anopheles females is reduced, resulting in impaired transmission of sporozoites at low infection densities. Interestingly, Saglin can be detected in high amounts in the midgut of mosquitoes after blood ingestion, possibly indicating a previously unknown host-pathogen interaction between Saglin and midgut stages of Plasmodium. Furthermore, we were able to show that saglin deletion has no fitness cost in laboratory conditions, suggesting this gene would be an interesting target for gene drive approaches.