A novel NDUFS4 frameshift mutation causes Leigh disease in the Hutterite population.

Leigh disease is a progressive, infantile-onset, neurodegenerative disorder characterized by feeding difficulties, failure to thrive, hypotonia, seizures, and central respiratory compromise. Metabolic and neuroimaging investigations typically identify abnormalities consistent with a disorder of mitochondrial energy metabolism. Mutations in more than 35 genes affecting the mitochondrial respiratory chain encoded from both the nuclear and mitochondrial genomes have been associated with Leigh disease. The clinical presentations of five individuals of Hutterite descent with Leigh disease are described herein. An identity-by-descent mapping and candidate gene approach was used to identify a novel homozygous c.393dupA frameshift mutation in the NADH dehydrogenase (ubiquinone) Fe-S protein 4 (NDUFS4) gene. The carrier frequency of this mutation was estimated in >1,300 Hutterite individuals to be 1 in 27. © 2017 Wiley Periodicals, Inc.

Hepatitis C virus genotype-3a core protein enhances sterol regulatory element-binding protein-1 activity through the phosphoinositide 3-kinase-Akt-2 pathway.

Hepatitis C virus genotype-3a (HCV-3a) is directly linked to the development of steatosis. We previously showed that, through sterol regulatory element binding protein-1 (SREBP-1), HCV-3a core protein upregulates the promoter activity of fatty acid synthase, a major enzyme involved in de novo lipid synthesis. In this study, we investigated whether HCV-3a core can activate SREBP-1 and studied the role of phosphoinositide 3-kinase (PI3K)-Akt-2 pathway in modulating SREBP-1 activity by HCV-3a core. To determine whether HCV-3a core could activate SREBP-1, the level of mature SREBP-1 was analysed by Western blotting. Our results showed that the level of mature SREBP-1 was enhanced by HCV-3a core protein after transient expression and in the chimeric HCV-3a core/1b replicon cells in comparison to controls. To investigate the role of the PI3K-Akt-2 pathway in SREBP-1 activation by HCV-3a core, PI3K and Akt-2 activity was inhibited by using the chemical inhibitor LY294002, a dominant-negative Akt-2 plasmid, or knockdown of Akt-2 by small hairpin RNA. Our results showed that inhibition of PI3K and Akt-2 was associated with reduced SREBP-1 activation by HCV-3a core. These results indicate a role for PI3K and Akt-2 in increasing SREBP-1 activity by HCV-3a core protein and provide a mechanism of steatosis caused by HCV.

Activation of sterol regulatory element-binding protein 1c and fatty acid synthase transcription by hepatitis C virus non-structural protein 2.

Transcriptional factor sterol regulatory element-binding protein 1c (SREBP-1c) activates the transcription of lipogenic genes, including fatty acid synthase (FAS). Hepatitis C virus (HCV) infection is often associated with lipid accumulation within the liver, known as steatosis in the clinic. The molecular mechanisms of HCV-associated steatosis are not well characterized. Here, we showed that HCV non-structural protein 2 (NS2) activated SREBP-1c transcription in human hepatic Huh-7 cells as measured by using a human SREBP-1c promoter-luciferase reporter plasmid. We further showed that sterol regulatory element (SRE) and liver X receptor element (LXRE) in the SREBP-1c promoter were involved in SREBP-1c activation by HCV NS2. Furthermore, expression of HCV NS2 resulted in the upregulation of FAS transcription. We also showed that FAS upregulation by HCV NS2 was SREBP-1-dependent since deleting the SRE sequence in a FAS promoter and expressing a dominant-negative SREBP-1 abrogated FAS promoter upregulation by HCV NS2. Taken together, our results suggest that HCV NS2 can upregulate the transcription of SREBP-1c and FAS, and thus is probably a contributing factor for HCV-associated steatosis.

Up-regulation of fatty acid synthase promoter by hepatitis C virus core protein: genotype-3a core has a stronger effect than genotype-1b core.

BACKGROUND/AIMS: Hepatitis C virus genotype-3a (HCV-3a) is directly linked to steatosis development. We studied the effects of HCV-3a core protein on the promoter activity of fatty acid synthase (FAS), a major enzyme involved in de novo lipid synthesis. METHODS AND RESULTS: HCV-3a and -1b core genes were cloned and expressed. Using a FAS promoter-luciferase reporter, we demonstrated that both HCV-3a and -1b core proteins up-regulated the FAS promoter. However, HCV-3a core protein expression induced significantly higher FAS promoter activity than HCV-1b core. We further showed that FAS up-regulation by HCV core was dependent on transcription factor sterol response element binding protein-1. Mutational analysis showed that processing of HCV core protein of different genotypes was differentially involved in FAS promoter up-regulation. Although lipid droplet localization of HCV core protein was not important for FAS up-regulation, a specific amino acid residue (Phe(164)) within the FATG lipid droplet localization sequence of HCV-3a core protein played a major role in the stronger FAS activation by HCV-3a core. CONCLUSIONS: The stronger effect of HCV-3a core protein on FAS activation in comparison to HCV-1b core could contribute to the higher prevalence and severity of steatosis in HCV-3a infections.