Alterations of the expression levels of glucose, inflammation, and iron metabolism related miRNAs and their target genes in the hypothalamus of STZ-induced rat diabetes model.

BACKGROUND: The hypothalamus of the central nervous system is implicated in the development of diabetes due to its glucose-sensing function. Dysregulation of the hypothalamic glucose-sensing neurons leads to abnormal glucose metabolism. It has been described that fractalkine (FKN) is involved in the development of hypothalamic inflammation, which may be one of the underlying causes of a diabetic condition. Moreover, iron may play a role in the pathogenesis of diabetes via the regulation of hepcidin, the iron regulatory hormone synthesis. MicroRNAs (miRNAs) are short non-coding molecules working as key regulators of gene expression, usually by inhibiting translation. Hypothalamic miRNAs are supposed to have a role in the control of energy balance by acting as regulators of hypothalamic glucose metabolism via influencing translation. METHODS: Using a miRNA array, we analysed the expression of diabetes, inflammation, and iron metabolism related miRNAs in the hypothalamus of a streptozotocin-induced rat type 1 diabetes model. Determination of the effect of miRNAs altered by STZ treatment on the target genes was carried out at protein level. RESULTS: We found 18 miRNAs with altered expression levels in the hypothalamus of the STZ-treated animals, which act as the regulators of mRNAs involved in glucose metabolism, pro-inflammatory cytokine synthesis, and iron homeostasis suggesting a link between these processes in diabetes. The alterations in the expression level of these miRNAs could modify hypothalamic glucose sensing, tolerance, uptake, and phosphorylation by affecting the stability of hexokinase-2, insulin receptor, leptin receptor, glucokinase, GLUT4, insulin-like growth factor receptor 1, and phosphoenolpyruvate carboxykinase mRNA molecules. Additional miRNAs were found to be altered resulting in the elevation of FKN protein. The miRNA, mRNA, and protein analyses of the diabetic hypothalamus revealed that the iron import, export, and iron storage were all influenced by miRNAs suggesting the disturbance of hypothalamic iron homeostasis. CONCLUSION: It can be supposed that glucose metabolism, inflammation, and iron homeostasis of the hypothalamus are linked via the altered expression of common miRNAs as well as the increased expression of FKN, which contribute to the imbalance of energy homeostasis, the synthesis of pro-inflammatory cytokines, and the iron accumulation of the hypothalamus. The results raise the possibility that FKN could be a potential target of new therapies targeting both inflammation and iron disturbances in diabetic conditions.

Effect of aromatic ring-containing drugs on carnitine biosynthesis in rats with special regard to p-aminomethylbenzoic acid.

Secondary carnitine deficiencies are associated with metabolic disorders or may be the consequence of the side effects of some drugs. The mechanisms may be either a facilitated urinary excretion or an inhibited biosynthesis. Based on our earlier findings with drugs and benzoic acid analogue metabolites, in the present study, we studied the possible inhibitory effect of some benzoic acid analogue drugs. In the pathway of carnitine biosynthesis, we tested the last step, the hydroxylation of gamma-butyrobetaine (Bu) to carnitine in the liver. (Liver is the only organ in rats where this step takes place.) Of the 5 tested compounds, the p-aminomethylbenzoic acid (PAMBA) was found to be inhibitory. In tracer experiments with radioactive Bu, PAMBA (a single injection of 1.2 mmol/kg) reduced the conversion of [Me-(3)H]Bu to [Me-(3)H]carnitine from 62.6% +/- 5.11% to 46.8% +/- 5.02% (means +/- SEM, P < .02). This single dose also markedly reduced the conversion of loading amount of exogenous unlabeled Bu, as measured by enzymatic analysis of carnitine. The conversion of endogenous Bu was also hampered by long-term administration of PAMBA, as indicated by increased Bu and decreased carnitine levels. Furthermore, single injection of PAMBA markedly reduced the Glu level in the liver from 2.87 +/- 0.17 to 1.42 +/- 0.11 mumol/g (P < .001). Trying to get closer to a mechanism by which the flux through the Bu hydroxylase was depressed, we supposed that alfa-ketoglutarate (alpha-KG), an obligatory cofactor of the enzyme, was also be depressed. It was expected because alpha-KG is a reversible copartner of l-glutamate through the Glu-dehydrogenase reaction. We found that PAMBA reduced the alpha-KG level from 207 +/- 17.5 to 180 +/- 19.1 nmol/g (means +/- SEM, P < .02). Considering the conditions of the enzyme in vitro and in vivo, this decrease may contribute to the decreased in vivo flux through the butyrobetaine hydroxylase enzyme.

Cooperation between BAT and WAT of rats in thermogenesis in response to cold, and the mechanism of glycogen accumulation in BAT during reacclimation.

Rats were exposed to cold and then reacclimated at neutral temperature. Changes related to fatty acid and glucose metabolism in brown and white adipose tissues (BAT and WAT) and in muscle were then examined. Of the many proteins involved in the metabolic response, two lipogenic enzymes, acetyl-coenzyme A carboxylase (ACC) and ATP-citrate lyase, were found to play a pervasive role and studied in detail. Expression of the total and phosphorylated forms of both lipogenic enzymes in response to cold increased in BAT but decreased in WAT. Importantly, in BAT, only the phosphorylation of the ACC1 isoenzyme was enhanced, whereas that of ACC2 remained unchanged. The activities of these enzymes and the in vivo rate of FFA synthesis together suggested that WAT supplies BAT with FFA and glucose by decreasing its own synthetic activity. Furthermore, cold increased the glucose uptake of BAT by stimulating the expression of components of the insulin signaling cascade, as observed by the enhanced expression and phosphorylation of Akt and GSK-3. In muscle, these changes were observed only during reacclimation, when serum insulin also increased. Such changes may be responsible for the extreme glycogen accumulation in the BAT of rats reacclimated from cold.