Metabolic disorders are characterized by the inability to properly use and/or store energy. The burdens of metabolic disease, such as obesity or diabetes, are believed to arise through a complex interplay between genetics and epigenetics predisposition, environment and nutrition. Therefore, understanding the molecular mechanisms for the onset of metabolic disease will provide new insights for prevention and treatment. There is growing concern about the dysregulation of micro-RNAs (miRNAs) in metabolic diseases. MiRNAs are short non-coding RNA molecules that post-transcriptionally repress the expression of genes by binding to untranslated regions and coding sequences of the target mRNAs. This review aims to provide recent data about the potential involvement of miRNAs in metabolic diseases, particularly obesity and type 2 diabetes.

Endocrine-disrupting chemicals (EDCs) are diverse natural and synthetic chemicals that may alter various mechanisms of the endocrine system and produce adverse developmental, reproductive, metabolic, and neurological effects in both humans and wildlife. Research on EDCs has revealed that they use a variety of both nuclear receptor-mediated and non-receptor-mediated mechanisms to modulate different components of the endocrine system. The molecular mechanisms underlying the effects of EDCs are still under investigation. Interestingly, some of the effects of EDCs have been observed to pass on to subsequent unexposed generations, which can be explained by the gametic transmission of deregulated epigenetic marks. Epigenetics is the study of heritable changes in gene expression that occur without a change in the DNA sequence. Epigenetic mechanisms, including histone modifications, DNA methylation, and specific micro-RNAs (miRNAs) expression, have been proposed to mediate transgenerational transmission and can be triggered by environmental factors. MiRNAs are short non-coding RNA molecules that post-transcriptionally repress the expression of genes by binding to 3′-untranslated regions of the target mRNAs. Given that there is mounting evidence that miRNAs are regulated by hormones, then clearly it is important to investigate the potential for environmental EDCs to deregulate miRNA expression and action.

CH-Pi stacking interactions between carbohydrates and aromatic compounds play a central role in biomolecular recognition, especially in lectin-sugar and protein-glycolipid systems. In the present study, we have measured the solubility of the sparingly soluble aromatic base adenine in presence of various saccharides as an approach to investigate the interaction between adenine and sugars. Above 82.5 mM, adenine solutions gradually formed a crystalline precipitate which could be quantified by spectrophotometric turbidity measurements. Precipitation of adenine was increased by salts (NaCl and NaF) whereas it was prevented by DMSO, in agreement with the involvement of hydrophobic interactions (pi-pi stacking) in the vertical stacking of adenine molecules. Several monosaccharides and disaccharides were found to increase adenine solubility, with the following order: D-galactose = D-lactose > D-sucrose > D-glucose = D-maltose > D-ribose > D-fructose. Molecular mechanics simulations indicated that the potent cosolvent effect of beta-D-galactopyranose was probably mediated by CH-pi stacking interactions between its apolar surface and the aromatic structure of adenine. The polar OH groups of the sugars interacted with surrounding water molecules, ensuring the solubility of sugar-adenine complexes. In contrast, beta-D-fructofuranose, which has two polar faces, did not stack onto adenine and had a weak cosolvent effect. CH-pi stacking interactions were also demonstrated between 6-methylpurine and the sugar head group of glycolipids (glucosyl-, galactosyl- and lactosylceramide) but not with the charged head group of phosphatidylinositol-4,5-diphosphate. These data indicate that galactose-containing molecules have a high stacking propensity for aromatic compounds such as adenine, due to the specific structure of the galactose cycle.

The central nervous system (CNS) monitors modifications in metabolic parameters or hormone levels and elicits adaptive responses such as food intake regulation. Particularly, within the hypothalamus, leptin modulates the activity of pro-opiomelanocortin (POMC) neurons which are critical regulators of energy balance. Consistent with a pivotal role of the melanocortin system in the control of energy homeostasis, disruption of the POMC gene causes hyperphagia and obesity. MicroRNAs (miRNAs) are short noncoding RNA molecules that post-transcriptionally repress the expression of genes by binding to 3′-untranslated regions (3′UTR) of the target mRNAs. However, little is known regarding the role of miRNAs that target POMC 3′UTR in the central control energy homeostasis. Particularly, their interaction with the leptin signaling pathway remain unclear. First, we used common prediction programs to search for potential miRNAs target sites on 3′UTR of POMC mRNA. This screening identified a set of conserved miRNAs seed sequences for mir-383, mir-384-3p, and mir-488. We observed that mir-383, mir-384-3p, and mir-488 are up-regulated in the hypothalamus of leptin deficient ob/ob mice. In accordance with these observations, we also showed that mir-383, mir-384-3p, and mir-488 were increased in db/db mice that exhibit a non-functional leptin receptor. The intraperitoneal injection of leptin down-regulated the expression of these miRNAs of interest in the hypothalamus of ob/ob mice showing the involvement of leptin in the expression of mir-383, mir-384-3p, and mir-488. Finally, the evaluation of responsivity to intracerebroventricular administration of leptin exhibited that a chronic treatment with leptin decreased mir-488 expression in hypothalamus of C57BL/6 mice. In summary, these results suggest that leptin modulates the expression of miRNAs that target POMC mRNA in hypothalamus.