ABSTRACT
BACKGROUND & AIMS: The adiponutrin/PNPLA3 (patatin-like phospholipase domain-containing protein 3) variant I148M has recently emerged as an important marker of human fatty liver disease. In order to understand the role of the adiponutrin/PNPLA3 protein, we investigated the regulation of its expression in both human and mouse hepatocytes. METHODS: Adiponutrin/PNPLA3 and lipogenic enzyme expression was determined by real-time PCR analysis in a wide panel of analysis in vivo in the mouse liver and in vitro in murine hepatocytes and human hepatocyte cell lines infected with ChREBP or SREBP1c-expressing adenoviruses. RESULTS: We show that in the mouse liver, adiponutrin/PNPLA3 gene expression is under the direct transcriptional control of ChREBP (carbohydrate-response element-binding protein) and SREBP1c (sterol regulatory element binding protein1c) in response to glucose and insulin, respectively. In silico analysis revealed the presence of a ChoRE (carbohydrate response element) and of a SRE (sterol response element) binding site on the mouse adiponutrin/PNPLA3 gene promoter. Point mutation analysis in reporter gene assays identified the functional response of these two binding sites in the mouse adiponutrin/PNPLA3 promoter. In contrast, in human immortalized hepatocytes and in HepG2 hepatoma cells, only SREBP1c was able to induce adiponutrin/PNPLA3 expression, whereas ChREBP was unable to modulate its expression. CONCLUSIONS: All together, our results suggest that adiponutrin/PNPLA3 is regulated by two key factors of the glycolytic and lipogenic pathways, raising the question of its implication in the metabolism of carbohydrates and lipids.
Subject(s)
Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/metabolism , Hepatocytes/metabolism , Lipase/genetics , Membrane Proteins/genetics , Nuclear Proteins/metabolism , Phospholipases A2, Calcium-Independent/genetics , Sterol Regulatory Element Binding Protein 1/metabolism , Transcription Factors/metabolism , Animals , Binding Sites/genetics , Fatty Liver/etiology , Fatty Liver/genetics , Fatty Liver/metabolism , Gene Expression Regulation/drug effects , Glucose/pharmacology , HEK293 Cells , Hep G2 Cells , Hepatocytes/drug effects , Humans , In Vitro Techniques , Insulin/pharmacology , Male , Mice , Mice, Inbred C57BL , Non-alcoholic Fatty Liver Disease , Nutritional Status , Promoter Regions, GeneticABSTRACT
Genome sequencing technologies led to tremendous breakthrough in biology uncovering numerous genes unknown so far and thus opening the field of deep investigations to understand their associated biological functions. As a matter of fact, functional genomics have been progressively replacing sequence genomics with as a main objective to yield insight into cellular physiology. Recently, an emerging group of genes coding for proteins bearing a common domain termed patatin (PNPLA domain) have been discovered. Members of this new enzymatic family displaying lipase and transacylase properties appeared to have major roles in the regulation of lipid metabolism. The aim of this review is to make an overview on the latest discoveries concerning this new family of proteins and their relationship with lipid metabolism, physiology of mammals and their potential involvement in human pathology.
Subject(s)
Carboxylic Ester Hydrolases/physiology , Catalytic Domain , Escherichia coli Proteins/physiology , Lipid Metabolism/physiology , Lipolysis/genetics , Multigene Family , Amino Acid Sequence , Animals , Arabidopsis Proteins/chemistry , Arabidopsis Proteins/physiology , Caenorhabditis elegans Proteins/chemistry , Caenorhabditis elegans Proteins/physiology , Carboxylic Ester Hydrolases/chemistry , Carboxylic Ester Hydrolases/classification , Carboxylic Ester Hydrolases/genetics , Catalytic Domain/genetics , Conserved Sequence , Drosophila Proteins/chemistry , Drosophila Proteins/physiology , Escherichia coli Proteins/chemistry , Humans , Lipase/chemistry , Lipase/physiology , Lipid Metabolism/genetics , Mammals/metabolism , Mice , Molecular Sequence Data , Phospholipases A2, Calcium-Independent/chemistry , Phospholipases A2, Calcium-Independent/physiology , Phylogeny , Plant Proteins/chemistry , Plant Proteins/physiology , Saccharomyces cerevisiae Proteins/chemistry , Saccharomyces cerevisiae Proteins/physiology , Sequence Alignment , Sequence Homology, Amino Acid , Species SpecificityABSTRACT
BACKGROUND: Preventing or slowing the progression of prediabetes to diabetes is a major therapeutic issue. OBJECTIVES: Our aim was to evaluate the effects of 4-month treatment with a dietary supplement containing cinnamon, chromium and carnosine in moderately obese or overweight pre-diabetic subjects, the primary outcome being change in fasting plasma glucose (FPG) level. Other parameters of plasma glucose homeostasis, lipid profile, adiposity and inflammatory markers were also assessed. METHODS: In a randomized, double-blind, placebo-controlled study, 62 subjects with a FPG level ranging from 5.55 to 7 mmol/L and a body mass index ≥ 25 kg/m(2), unwilling to change their dietary and physical activity habits, were allocated to receive a 4-month treatment with either 1.2 g/day of the dietary supplement or placebo. Patients were followed up until 6 months post-randomization. RESULTS: Four-month treatment with the dietary supplement decreased FPG compared to placebo (-0.24 ± 0.50 vs +0.12 ± 0.59 mmol/L, respectively, p = 0.02), without detectable significant changes in HbA1c. Insulin sensitivity markers, plasma insulin, plasma lipids and inflammatory markers did not differ between the treatment groups. Although there were no significant differences in changes in body weight and energy or macronutrient intakes between the two groups, fat-free mass (%) increased with the dietary supplement compared to placebo (p = 0.02). Subjects with a higher FPG level and a milder inflammatory state at baseline benefited most from the dietary supplement. CONCLUSIONS: Four-month treatment with a dietary supplement containing cinnamon, chromium and carnosine decreased FPG and increased fat-free mass in overweight or obese pre-diabetic subjects. These beneficial effects might open up new avenues in the prevention of diabetes. TRIAL REGISTRATION: ClinicalTrials.gov NCT01530685.