Inhibition of mitochondrial β-oxidation by miR-107 promotes hepatic lipid accumulation and impairs glucose tolerance in vivo.
Hepatic expression of microRNA-107 is ubiquitously upregulated in various metabolic diseases. In our previous study, we had demonstrated that fatty acid synthase (FASN) is a target of miR-107. miR-107-FASN interaction, by inducing endoplasmic reticulum (ER) stress, promotes lipid accumulation in hepatocytes. Here, we explore the possible mechanism(s) of the miR-107-FASN-ER stress on hepatic lipid metabolism.



HepG2 cells were transfected with the scramble or miR-107 and/or its inhibitor. Transcript levels of lipid droplet membrane proteins, apolipoproteins and β-oxidation genes were quantified by quantitative reverse transcription-PCR. Cells were treated with tunicamycin (Tm, 1 h) and 4-PBA (4-phenyl butyric acid, 8 h) or transfected with hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase, apha subunit (HADHA) short interfering RNA or its overexpression vector. Mice were injected with the scramble or mmu-miR-107 (2.5 mg kg(-1) body weight) and random glucose levels were measured and oral glucose tolerance test was performed. Serum levels of cholesterol, triglyceride and serum glutamic oxaloacetic transaminase/serum glutamic-pyruvic transaminase (SGOT/SGPT) were evaluated. Hepatic tissues were collected to estimate levels of miR-107 and mitochondrial β-oxidation genes. Six-micrometer-thick cryosections of hepatic tissues were prepared and stained with Oil Red O for lipid accumulation.



miR-107 does not alter the expression of lipid metabolism-related transcription factors, lipid droplet components and apolipiprotein B. miR-107 significantly decreased the levels of the mitochondrial β-oxidation enzyme, HADHA in HepG2 cells (P<0.01), which was prevented by the miR-107 inhibitor. Similar decrease was observed with Tm (P<0.001), suggesting that HADHA inhibition is promoted by ER stress induction. Interestingly, miR-107-mediated HADHA suppression was rescued by the ER stress inhibitor, 4-PBA (P<0.01). HADHA overexpression rescued miR-107-induced lipid accumulation (P<0.01). miR-107 injection in mice increased random blood glucose levels (P<0.05) and impaired glucose tolerance (P<0.05). Hepatic levels of Hadha were significantly decreased (P<0.001 and P<0.05) accompanied by increased lipid accumulation (P<0.001).



miR-107 promotes hepatic lipid accumulation by suppressing transcript levels of HADHA, induces hyperglycemia and impairs glucose tolerance. We conclude that miR-107 regulation of fatty acid oxidation is an important contributor toward hepatic lipid accumulation.
CSIR-Institute of Genomics and Integrative Biology, Delhi, India.
H
H
Bhatia
CSIR-Institute of Genomics and Integrative Biology, Delhi, India.
B R
BR
Pattnaik
CSIR-Institute of Genomics and Integrative Biology, Delhi, India.
M
M
Datta
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004195:Disease Models, Animal; D059865:Endoplasmic Reticulum Stress; D005227:Fatty Acids / Q000378:metabolism; D005234:Fatty Liver / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D005786:Gene Expression Regulation; D018149:Glucose Intolerance / Q000235:genetics / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D050356:Lipid Metabolism; D050155:Lipogenesis / Q000502:physiology; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism*; D010084:Oxidation-Reduction
D005227:Fatty Acids; C555365:MIRN107 microRNA, mouse; D035683:MicroRNAs