ABSTRACT
It is known that endogenous levels of the incretin hormone glucagon-like peptide 1 (GLP1) can be enhanced by various secretagogues, but the mechanism underlying GLP1 secretion is still not fully understood. We assessed the possible effect of uncoupling protein 2 (UCP2) on GLP1 secretion in mouse intestinal tract and NCI-H716 cells, a well-characterized human enteroendocrine L cell model. Localization of UCP2 and GLP1 in the gastrointestinal tract was assessed by immunofluorescence staining. Ucp2 mRNA levels in gut were analyzed by quantitative RT-PCR. Human NCI-H716 cells were transiently transfected with siRNAs targeting UCP2. The plasma and ileum tissue levels of GLP1 (7-36) amide were measured using an ELISA kit. UCP2 was primarily expressed in the mucosal layer and colocalized with GLP1 in gastrointestinal mucosa. L cells secreting GLP1 also expressed UCP2. After glucose administration, UCP2-deficient mice showed increased glucose-induced GLP1 secretion compared with wild-type littermates. GLP1 secretion increased after NCI-H716 cells were transfected with siRNAs targeting UCP2. UCP2 was markedly upregulated in ileum tissue from ob/ob mice, and GLP1 secretion decreased compared with normal mice. Furthermore, GLP1 secretion increased after administration of genipin by oral gavage. Taken together, these results reveal an inhibitory role of UCP2 in glucose-induced GLP1 secretion.
Subject(s)
Enteroendocrine Cells/drug effects , Enteroendocrine Cells/metabolism , Glucagon-Like Peptide 1/metabolism , Glucose/pharmacology , Intestinal Mucosa/drug effects , Intestinal Mucosa/metabolism , Ion Channels/metabolism , Mitochondrial Proteins/metabolism , Animals , Cell Line , Cholagogues and Choleretics/pharmacology , Enteroendocrine Cells/cytology , Humans , Ileum/cytology , Ileum/drug effects , Ileum/metabolism , Intestinal Mucosa/cytology , Ion Channels/genetics , Iridoids/pharmacology , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Obese , Mitochondrial Proteins/genetics , RNA, Small Interfering/metabolism , Uncoupling Protein 2ABSTRACT
Our previous studies have demonstrated that stable microRNAs (miRNAs) in mammalian serum and plasma are actively secreted from tissues and cells and can serve as a novel class of biomarkers for diseases, and act as signaling molecules in intercellular communication. Here, we report the surprising finding that exogenous plant miRNAs are present in the sera and tissues of various animals and that these exogenous plant miRNAs are primarily acquired orally, through food intake. MIR168a is abundant in rice and is one of the most highly enriched exogenous plant miRNAs in the sera of Chinese subjects. Functional studies in vitro and in vivo demonstrated that MIR168a could bind to the human/mouse low-density lipoprotein receptor adapter protein 1 (LDLRAP1) mRNA, inhibit LDLRAP1 expression in liver, and consequently decrease LDL removal from mouse plasma. These findings demonstrate that exogenous plant miRNAs in food can regulate the expression of target genes in mammals.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Gene Expression Regulation , MicroRNAs/metabolism , Oryza/genetics , RNA, Plant/metabolism , Adaptor Proteins, Signal Transducing/genetics , Adult , Animals , Asian People , Chromatin Immunoprecipitation , Computational Biology , Diet , Female , Hep G2 Cells , Herbivory , Humans , Liver/cytology , Liver/metabolism , Male , Mice , Mice, Inbred C57BL , MicroRNAs/blood , MicroRNAs/genetics , Middle Aged , Plasmids/genetics , Plasmids/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Plant/blood , RNA, Plant/genetics , RNA, Untranslated , Secretory Vesicles/metabolism , Substrate Specificity , Transfection , Young AdultABSTRACT
Despite years of effort, exact pathogenesis of nonalcoholic fatty liver disease (NAFLD) remains obscure. To gain an insight into the regulatory roles of microRNAs (miRNAs) in aberrant energy metabolic status and pathogenesis of NAFLD, we analyzed the expression of miRNAs in livers of ob/ob mice, streptozotocin (STZ)-induced type 1 diabetic mice, and normal C57BL/6 mice by miRNA microarray. Compared with normal C57BL/6 mice, ob/ob mice showed upregulation of eight miRNAs and downregulation of four miRNAs in fatty livers. Upregulation of miR-34a and downregulation of miR-122 was found in livers of STZ-induced diabetic mice. These results demonstrate that distinct miRNAs are strongly dysregulated in NAFLD and hyperglycemia. Comparison between miRNA expressions in livers of ob/ob mice and STZ-administered mice further revealed upregulation of four miRNAs and downregulation of two miRNAs in livers of ob/ob mice, indicating that these miRNAs may represent a molecular signature of NAFLD. A distinctive miRNA expression pattern was identified in ob/ob mouse liver, and hierarchical clustering of this pattern could clearly discriminate ob/ob mice from either normal C57BL/6 mice or STZ-administered mice. These findings suggest an important role of miRNAs in hepatic energy metabolism and implicate the participation of miRNAs in the pathophysiological processes of NAFLD.
Subject(s)
Energy Metabolism/genetics , Gene Expression Regulation , Liver/metabolism , MicroRNAs/genetics , Animals , Diabetes Mellitus, Experimental/complications , Diabetes Mellitus, Experimental/genetics , Diabetes Mellitus, Experimental/metabolism , Fatty Liver/complications , Fatty Liver/genetics , Fatty Liver/metabolism , Female , Humans , Hyperglycemia/complications , Hyperglycemia/genetics , Hyperglycemia/metabolism , Male , Mice , Oligonucleotide Array Sequence Analysis , Reproducibility of Results , Reverse Transcriptase Polymerase Chain Reaction , Sex CharacteristicsABSTRACT
BACKGROUND: Oleic acid (OA) stimulates vascular smooth muscle cell (VSMC) proliferation and migration. The precise mechanism is still unclear. We sought to investigate the effects of peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator-1 alpha (PGC-1alpha) on OA-induced VSMC proliferation and migration. PRINCIPAL FINDINGS: Oleate and palmitate, the most abundant monounsaturated fatty acid and saturated fatty acid in plasma, respectively, differently affect the mRNA and protein levels of PGC-1alpha in VSMCs. OA treatment resulted in a reduction of PGC-1alpha expression, which may be responsible for the increase in VSMC proliferation and migration caused by this fatty acid. In fact, overexpression of PGC-1alpha prevented OA-induced VSMC proliferation and migration while suppression of PGC-1alpha by siRNA enhanced the effects of OA. In contrast, palmitic acid (PA) treatment led to opposite effects. This saturated fatty acid induced PGC-1alpha expression and prevented OA-induced VSMC proliferation and migration. Mechanistic study demonstrated that the effects of PGC-1alpha on VSMC proliferation and migration result from its capacity to prevent ERK phosphorylation. CONCLUSIONS: OA and PA regulate PGC-1alpha expression in VSMCs differentially. OA stimulates VSMC proliferation and migration via suppression of PGC-1alpha expression while PA reverses the effects of OA by inducing PGC-1alpha expression. Upregulation of PGC-1alpha in VSMCs provides a potential novel strategy in preventing atherosclerosis.
