Role of white adipose lipolysis in the development of NASH induced by methionine- and choline-deficient diet

Abstract

Methionine- and choline-deficient diet (MCD) is a model for nonalcoholic steatohepatitis (NASH) in rodents. However, the mechanism of NASH development by dietary methionine/choline deficiency remains undetermined. To elucidate the early metabolic changes associated with MCD-NASH, serum metabolomic analysis was performed using mice treated with MCD and control diet for three days and one week, revealing significant increases in oleic and linoleic acids after MCD treatment. These increases were correlated with reduced body weight and white adipose tissue (WAT) mass, increased phosphorylation of hormone-sensitive lipase, and up-regulation of genes encoding carboxylesterase 3 and β2-adrenergic receptor in WAT, indicating accelerated lipolysis in adipocytes. The changes in serum fatty acids and WAT by MCD treatment were reversed by methionine supplementation, and similar alterations were detected in mice fed a methionine-deficient diet (MD), thus demonstrating that dietary methionine deficiency enhances lipolysis in WAT. MD treatment decreased glucose and increased fibroblast growth factor 21 in serum, thus exhibiting a similar metabolic phenotype as the fasting response. Comparison between MCD and choline-deficient diet (CD) treatments suggested that the addition of MD-induced metabolic alterations, such as WAT lipolysis, to CD-induced hepatic steatosis promotes liver injury. Collectively, these results demonstrate an important role for dietary methionine deficiency and WAT lipolysis in the development of MCD-NASH.

Role of fibroblast growth factor 21 in the early stage of NASH induced by methionine- and choline-deficient diet

“…The MCD was purchased from Dyets Inc. (#58810; Bethlehem, PA) and methionine- and choline-supplemented MCD diet (MCS, #518754; Dyets) was used as a control diet. The compositions of these diets were described previously [29, 30]. Before starting the experiments, regular chow was replaced with MCS for acclimatization.…”

“…Total RNA was extracted using a TRIzol Reagent (Invitrogen, Carlsbad, CA) and cDNA was generated from 1 μg RNA with a SuperScript II ™ Reverse Transcriptase kit and random oligonucleotides (Invitrogen). Quantitative PCR was performed using SYBR green PCR master mix and ABI Prism 7900HT Sequence Detection System (Applied Biosystems, Foster City, CA) [29, 30]. The primer pairs were designed using qPrimerDepot (http://mouseprimerdepot.nci.nih.gov/) and listed in Supplementary Table 1.…”

“…Serum alanine aminotransferase (ALT) concentrations were measured with an assay kit for ALT (Catachem, Bridgeport, CT) [29, 30]. Hepatic TG contents were determined as described previously [29, 30] using a kit purchased from Wako Chemicals USA, Inc. (Richmond, VA).…”

“…While hepatic Fgf21 mRNA and serum FGF21 were robustly increased after 2-week MCD feeding [29], the significance of FGF21 induction in the early stage of MCD-induced NASH (MCD-NASH) remains unclear. In the present study, MCD was used to treat Fgf21 -null and wild-type mice for 1 week and the phenotypical changes were examined.…”

Adipocyte-specific Disruption of Fat-specific Protein 27 Causes Hepatosteatosis and Insulin Resistance in High-fat Diet-fed Mice

“…Immunoblot Analysis-Immunoblot analysis was carried out as described elsewhere (18). Briefly, ϳ40 mg of epididymal WAT (eWAT) or liver was homogenized in radioimmune precipitation assay buffer containing a proteinase inhibitor mixture.…”