Proliferator-activated Receptor Alpha mRNA Research Articles

Dietary Alaska pollock protein attenuates liver steatosis and alters gut microbiota in leptin-deficient ob/ob mice

• Alaska pollock protein attenuated liver steatosis in leptin-deficient ob/ob mice. • Alaska pollock protein activated liver fatty acid oxidation through PPARα pathway. • Alaska pollock protein enhanced acetic acid production in cecal contents. • Alaska pollock protein improved the structure of the microbiota in cecal content. This study examined the effects of dietary Alaska pollock ( Theragra chalcogramma ) protein (APP) on nonalcoholic fatty liver disease (NAFLD) and gut microbiota in leptin-deficient ob/ob mice. Mice were fed with high-fat diet containing either casein or APP for six weeks. Then, lipid accumulation and mRNA expression levels in the liver and the composition and metabolites of the gut microbiota were evaluated. Dietary APP attenuated liver steatosis in part through the enhancement and suppression of gene expression involved in liver fatty acid oxidation and synthesis, respectively. The enhancement of liver peroxisome proliferator-activated receptor alpha mRNA expression level by APP consumption may be partly due to the high acetic acid content in cecal contents. Moreover, APP consumption modified the structure of the microbiota and high relative abundance of probiotic bacteria and low relative abundances of Bacteroides and Blautia in cecal content. Therefore, APP consumption could help prevent NAFLD development.

Aqueous Extract of Yerba Mate Tea Lowers Atherosclerotic Risk Factors in a Rat Hyperlipidemia Model

Yerba Mate tea (Mate) is believed to be a natural source of cardioprotective lipid-lowering and antioxidant compounds. In this study, the antihyperlipidemic and antioxidant effects of Mate tea in a rat hyperlipidemia model were investigated. Male Sprague-Dawley rats were divided randomly into five groups and fed varying diets: standard diet, hyperlipidemic diet, and hyperlipidemic diet supplemented with low, moderate, or high concentrations of Mate tea aqueous extract (1%, 2%, and 4% w/v, respectively). Compared to the hyperlipidemic control group, Mate tea reduced significantly the total body weight and lowered serum levels of total cholesterol, triglyceride, and low-density lipoprotein-cholesterol, and caused the elevation of serum levels of high-density lipoprotein-cholesterol. Moreover, activities of superoxide dismutase and glutathione peroxidase in serum were elevated significantly, whereas the levels of malondialdehyde decreased. In addition, Mate tea treatment ameliorated significantly the severe fatty degeneration of liver cells that occurred in the hyperlipidemic groups. The relative levels of sterol regulatory element binding protein 1 and its target fatty acid synthase, as well as acetyl-CoA carboxylase mRNA transcripts were reduced, whereas peroxisome proliferator-activated receptor alpha mRNA transcripts were elevated in the Mate tea groups. Our results suggest that Mate tea exerts strong antioxidant and lipid-lowering effects, prevents hepatic fatty deposition, and regulates the expression of lipid metabolic regulators. It can therefore be used to reduce the risk of atherosclerosis.

Consumption of plant sterols reduces plasma and hepatic triglycerides and modulates the expression of lipid regulatory genes and de novo lipogenesis in C57BL/6J mice

To investigate emerging clinical data suggesting a triglyceride (TAG)-lowering response to plant sterol (PS) therapy, we characterized changes in TAG metabolism in 16 C57BL/6J mice fed a basal control diet (CON) or the CON diet supplemented with 2% PS for 6 wk. PS consumption reduced (p<0.05) plasma (-28%) and hepatic (-30%) TAG concentrations compared with CON mice. PS consumption increased (p<0.05) hepatic lipogenic gene expression (sterol-regulatory-element-binding protein 1c, 2.4-fold of CON; fatty acid synthase, 6.5-fold of CON) and de novo lipogenesis (4.51+/-0.72 versus 2.82+/-0.61%/day) compared with CON. PS consumption increased (p<0.05) fecal palmitate and stearate excretion and reduced body weight gain compared with CON mice. Although no change in the transcription of intestinal fatty acid absorptive genes was observed, peroxisome proliferator-activated receptor alpha mRNA was reduced (p<0.05, 2.0-fold of CON) in the PS-fed mice. In conclusion, PS-fed C57BL/6J mice showed pronounced reductions in plasma and hepatic TAG concentrations despite increases in hepatic lipogenic gene expression and de novo lipogenesis. Interference with intestinal fatty acid/TAG metabolism as suggested by increased fecal fatty acid loss and reduced weight gain may be associated with the TAG-lowering response to PS consumption.

The Effects of a Fat- and Sugar-Enriched Diet and Chronic Stress on Nonalcoholic Fatty Liver Disease in Male Wistar Rats

The pathogenesis of nonalcoholic fatty liver disease (NAFLD) is still under debate. The aim of this study was to investigate the effects of a long-term fat- and sugar-enriched diet (FSED) and chronic stress (CS) on NAFLD. Male Wistar rats were fed on either a standard diet or a FSED and given CS, a random electric foot shock (2 hr/morning and afternoon per day), or not for 12 weeks. After the experimental period, epididymal adipose tissue weight, sign of visceral obesity (VO), and hepatic index (HI) were measured. At sacrifice blood samples and liver were obtained. Histology of the liver was blindly determined by a pathologist. Histopathologically, moderate to severe steatosis, ballooning hepatocytes, and portal or lobules inflammation were observed in the FSED+CS group. However, mild to moderate steatosis with a few portal inflammation in the FSED group and mild steatosis or not with a few portal inflammation in the CS group were found correspondingly. In addition, more severe blood-fat disorder, high HI, fatty metabolic dysfunction, oxidative stress, high expressions of C-reactive protein mRNA and low expressions of peroxisome proliferator-activated receptor alpha mRNA in the liver were also revealed in the FSED+CS group. But, the degree of VO was not different between the FSED and FSED+CS groups. The observations strongly suggest that chronic stress can aggravate fat- and sugar-enriched diet-induced NAFLD from steatosis to steatohepatitis in male Wistar rats, although VO is not changed.

Effects of ovariectomy on PPARα, SREBP-1c, and SCD-1 gene expression in the rat liver

To investigate whether estrogen deficiency modifies the expression of important genes involved in hepatic lipid regulation, PPAR alpha, SREBP-1c, and SCD-1, in association with fat accumulation in the liver of ovariectomized rats. Thirty female Sprague-Dawley rats were divided into three groups: sham-operated (n = 12), ovariectomized (n = 12), and ovariectomized with 17beta-estradiol replacement (n = 6). All animals were killed 8 weeks after surgery. In addition to liver triacylglycerol determination, transcripts levels and protein content of peroxisome proliferator-activated receptor alpha, liver sterol regulatory element-binding protein 1c, and stearoyl coenzyme Adesaturase 1 were quantified by quantitative real-time polymerase chain reaction and Western blot, respectively. As expected, liver triacylglycerol levels were higher (51%; 21.9 +/- 2.6 vs 14.5 +/- 1.2 mg/g; P < 0.01) in ovariectomized compared with sham-operated rats. Peroxisome proliferator-activated receptor alpha mRNA levels were 66% lower (P < 0.01), whereas sterol regulatory element-binding protein 1 and stearoyl coenzyme A desaturase 1 transcript levels were 80% and 41% higher (P < 0.05), respectively, after estrogen removal. Our data on gene expression obtained with quantitative real-time polymerase chain reaction for peroxisome proliferator-activated receptor alpha and sterol regulatory element-binding protein 1c were confirmed by Western blots. All the effects of ovariectomy were prevented by 17beta-estradiol replacement, indicating a role for estrogens in the prevention of hepatic fat accumulation. Our results suggest that a reduction in lipid oxidation and an increase in lipogenesis are defective mechanisms leading to lipid accumulation in the liver of ovariectomized rats. We conclude that estrogen deficiency induced by ovariectomy changes the expression of genes that favor the development of a steatotic phenotype.

Interleukin-6 inhibits human peroxisome proliferator activated receptor alpha gene expression via CCAAT/enhancer-binding proteins in hepatocytes

Peroxisome proliferator activated receptor alpha has been implicated as a regulator of acute phase response genes in hepatocytes. Interleukin-6 is widely known as a major cytokine responsible in the regulation of acute phase proteins and, therefore, acute phase response. Unfortunately, to date, very little is understood about the molecular mechanisms by which interleukin-6 regulates the gene expression of peroxisome proliferator activated receptor alpha. Here, we report the molecular mechanisms by which peroxisome proliferator activated receptor alpha was regulated by interleukin-6 in human HepG2 cells. Interleukin-6 was shown to down-regulate the peroxisome proliferator activated receptor alpha gene expression at the level of gene transcription. Functional dissection of human peroxisome proliferator activated receptor alpha promoter B revealed the role of predicted CCAAT/enhancer-binding protein binding site (−164/+34) in mediating the interleukin-6 inhibitory effects on peroxisome proliferator activated receptor alpha mRNA expression and electrophoretic mobility shift assay showed the binding of CCAAT/enhancer-binding protein isoforms to this cis-acting elements was increased in interleukin-6-treated HepG2 cells. Co-transfection experiments, then, demonstrated that CCAAT/enhancer-binding protein beta either in homodimer or heterodimer with CCAAT/enhancer-binding protein alpha and CCAAT/enhancer-binding protein delta plays a predominant role in inhibiting the transcriptional activity of peroxisome proliferator activated receptor alpha promoter B, thus, reducing the peroxisome proliferator activated receptor alpha mRNA expression. These studies, therefore, suggest a novel mechanism for interleukin-6-mediated inhibition of peroxisome proliferator activated receptor alpha gene expression that involves the activation of CCAAT/enhancer-binding protein isoforms with CCAAT/enhancer-binding protein beta may play a major role.

CDNA cloning and analysis of tissue-specific expression of mouse peroxisomal straight-chain acyl-CoA oxidase.

Straight-chain acyl-CoA oxidase is the first and rate limiting enzyme in the peroxisomal beta-oxidation pathway catalysing the desaturation of acyl-CoAs to 2-trans-enoyl-CoAs, thereby producing H2O2. To study peroxisomal beta-oxidation we cloned and characterized the cDNA of mouse peroxisomal acyl-CoA oxidase. It consists of 3778 bp, including a 1983-bp ORF encoding a polypeptide of 661 amino-acid residues. Like the rat and human homologue the C-terminus contains an SKL motif, an import signal present in several peroxisomal matrix proteins. Sequence analysis revealed high amino-acid homology with rat (96%) and human (87%) acyl-CoA oxidase in addition to minor homology ( approximately 40%) with other related proteins, such as rabbit trihydroxy-cholestanoyl-CoA oxidase, human branched chain acyl-CoA oxidase and rat trihydroxycoprostanoyl-CoA oxidase. Acyl-CoA oxidase mRNA and protein expression were most abundant in liver followed by kidney, brain and adipose tissue. During mouse brain development acyl-CoA oxidase mRNA expression was highest during the suckling period indicating that peroxisomal beta-oxidation is most critical during this developmental stage. Comparing tissue mRNA levels of peroxisome proliferator-activated receptor alpha and acyl-CoA oxidase, we noticed a constant relationship in all tissues investigated, except heart and adipose tissue in which much more, and respectively, much less, peroxisome proliferator-activated receptor alpha mRNA in proportion to acyl-CoA oxidase mRNA was found. Our data show that acyl-CoA oxidase is an evolutionary highly conserved enzyme with a distinct pattern of expression and indicate an important role in lipid metabolism.