👤 Hervé Guillou

Regardless of its mechanism, hyperammonemia can cause coma and death, and requires urgent management. This study aims at describing the landscape of causes of hyperammonemia in adults and at evaluating the performance of targeted next-generation sequencing (NGS) in this setting. We analyzed two cohorts. The first included patients aged ≥15 years presenting with hyperammonemia ≥100 μmol/L at Necker-Enfants Malades (NEM) University Hospital for 10 years and at Toulouse University Hospital for 1.5 years. The second cohort included patients who underwent genetic testing for inherited metabolic disease (IMD) via targeted NGS at NEM hospital over a 5 year-period, regardless of their inclusion in the first cohort, all with hyperammonemia ≥100 μmol/L after age 15. We included 184 patients in the first cohort, with a median peak ammonia concentration of 155 μmol/L. Among them, 61 patients (33 %) presented with coma. Non-genetic liver failure or portosystemic shunt was present in 133 patients. Twenty-three patients had received asparaginase treatment (none with coma despite a median ammonia level of 257 μmol/L), 7 had received valproic acid, 3 had undergone surgical ureterorectal anastomosis, 2 had multiple myeloma, 1 was receiving 5-Fluorouracil (5FU) for metastatic gastrointestinal cancer, 1 had disseminated atypical mycobacteriosis with Mycobacterium genavense (urease-producing bacteria) in a renal transplant setting and 13 had a genetically confirmed IMD diagnosed in adulthood. In the second cohort of 17 patients, genetic testing was positive in 5 of 6 patients with IMD-suggestive biochemical profiles (2 CPS1 deficiencies, 1 OTC deficiency, 1 multiple acyl-coA dehydrogenase deficiency, and 1 lysinuric protein intolerance), and negative in patients without biochemical profile suggesting an IMD. Among them, four patients suffered from protein malnutrition related to various severe conditions (gastric bypass, metastatic colorectal adenocarcinoma, Duchenne muscular dystrophy, and short bowel syndrome). The causes of hyperammonemia in adults are varied. In cases of acute episodes without unequivocal metabolic profiles (when unwell) and with an acquired identified cause of hyperammonemia, genetic investigations had a low yield. Show less

In hepatocytes, the peroxisome proliferator-activated receptor (PPAR)-α and insulin receptor (IR) are critical for transcriptional responses to fasting and feeding, respectively. The present report analyzes the effects of nutritional status (fasting vs feeding) on the expression of a large panel of hepatokines in hepatocyte-specific PPAR-α (Pparα Pparα Our data confirmed that PPAR-α is essential for regulating fasting-induced Fgf21 and Angptl4 expression. In mice lacking PPAR-α, fasting led to increased Igfbp1 and Gdf15 gene expression. In the absence of hepatic IR, feeding induced overexpression of Igfbp1, follistatin (Fst) and adropin (Enho), and reduced activin E (Inhbe) expression. Gender had only a modest influence on hepatokine gene expression in the liver. The present results highlight the potential roles of hepatokines as a class of hormones that substantially influence nutritional regulation in both female and male mice. Show less

Impaired adipose tissue insulin signalling is a critical feature of insulin resistance. Here we identify a pathway linking the lipolytic enzyme hormone-sensitive lipase (HSL) to insulin action via the glucose-responsive transcription factor ChREBP and its target, the fatty acid elongase ELOVL6. Genetic inhibition of HSL in human adipocytes and mouse adipose tissue results in enhanced insulin sensitivity and induction of ELOVL6. ELOVL6 promotes an increase in phospholipid oleic acid, which modifies plasma membrane fluidity and enhances insulin signalling. HSL deficiency-mediated effects are suppressed by gene silencing of ChREBP and ELOVL6. Mechanistically, physical interaction between HSL, independent of lipase activity, and the isoform activated by glucose metabolism ChREBPα impairs ChREBPα translocation into the nucleus and induction of ChREBPβ, the isoform with high transcriptional activity that is strongly associated with whole-body insulin sensitivity. Targeting the HSL-ChREBP interaction may allow therapeutic strategies for the restoration of insulin sensitivity. Show less

Aberrant histone methylation profile is reported to correlate with the development and progression of NAFLD during obesity. However, the identification of specific epigenetic modifiers involved in this process remains poorly understood. Here, we identify the histone demethylase Plant Homeodomain Finger 2 (Phf2) as a new transcriptional co-activator of the transcription factor Carbohydrate Responsive Element Binding Protein (ChREBP). By specifically erasing H3K9me2 methyl-marks on the promoter of ChREBP-regulated genes, Phf2 facilitates incorporation of metabolic precursors into mono-unsaturated fatty acids, leading to hepatosteatosis development in the absence of inflammation and insulin resistance. Moreover, the Phf2-mediated activation of the transcription factor NF-E2-related factor 2 (Nrf2) further reroutes glucose fluxes toward the pentose phosphate pathway and glutathione biosynthesis, protecting the liver from oxidative stress and fibrogenesis in response to diet-induced obesity. Overall, our findings establish a downstream epigenetic checkpoint, whereby Phf2, through facilitating H3K9me2 demethylation at specific gene promoters, protects liver from the pathogenesis progression of NAFLD. Show less

While the physiological benefits of the fibroblast growth factor 21 (FGF21) hepatokine are documented in response to fasting, little information is available on Fgf21 regulation in a glucose-overload context. We report that peroxisome-proliferator-activated receptor α (PPARα), a nuclear receptor of the fasting response, is required with the carbohydrate-sensitive transcription factor carbohydrate-responsive element-binding protein (ChREBP) to balance FGF21 glucose response. Microarray analysis indicated that only a few hepatic genes respond to fasting and glucose similarly to Fgf21. Glucose-challenged Chrebp Show less

The Constitutive Androstane Receptor (CAR, NR1I3) has been newly described as a regulator of energy metabolism. A relevant number of studies using animal models of obesity suggest that CAR activation could be beneficial on the metabolic balance. However, this remains controversial and the underlying mechanisms are still unknown. This work aimed to investigate the effect of CAR activation on hepatic energy metabolism during physiological conditions, i.e. in mouse models not subjected to metabolic/nutritional stress. Gene expression profiling in the liver of CAR knockout and control mice on chow diet and treated with a CAR agonist highlighted CAR-mediated up-regulations of lipogenic genes, concomitant with neutral lipid accumulation. A strong CAR-mediated up-regulation of the patatin-like phospholipase domain-containing protein 3 (Pnpla3) was demonstrated. Pnpla3 is a gene whose polymorphism is associated with the pathogenesis of nonalcoholic fatty liver disease (NAFLD) development. This observation was confirmed in human hepatocytes treated with the antiepileptic drug and CAR activator, phenobarbital and in immortalized human hepatocytes treated with CITCO. Studying the molecular mechanisms controlling Pnpla3 gene expression, we demonstrated that CAR does not act by a direct regulation of Pnpla3 transcription or via the Liver X Receptor but may rather involve the transcription factor Carbohydrate Responsive Element-binding protein. These data provide new insights into the regulation by CAR of glycolytic and lipogenic genes and on pathogenesis of steatosis. This also raises the question concerning the impact of drugs and environmental contaminants in lipid-associated metabolic diseases. Show less

Carbohydrate responsive element binding protein (ChREBP) is central for de novo fatty acid synthesis under physiological conditions and in the context of nonalcoholic fatty liver disease. We explored its contribution to alcohol-induced steatosis in a mouse model of binge drinking as acute ethanol (EtOH) intoxication has become an alarming health problem. Within 6 hours, ChREBP acetylation and its recruitment onto target gene promoters were increased in liver of EtOH-fed mice. Acetylation of ChREBP was dependent on alcohol metabolism because inhibition of alcohol dehydrogenase (ADH) activity blunted ChREBP EtOH-induced acetylation in mouse hepatocytes. Transfection of an acetylation-defective mutant of ChREBP (ChREBP(K672A) ) in HepG2 cells impaired the stimulatory effect of EtOH on ChREBP activity. Importantly, ChREBP silencing in the liver of EtOH-fed mice prevented alcohol-induced triglyceride accumulation through an inhibition of the lipogenic pathway but also led, unexpectedly, to hypothermia, increased blood acetaldehyde concentrations, and enhanced lethality. This phenotype was associated with impaired hepatic EtOH metabolism as a consequence of reduced ADH activity. While the expression and activity of the NAD(+) dependent deacetylase sirtuin 1, a ChREBP-negative target, were down-regulated in the liver of alcohol-fed mice, they were restored to control levels upon ChREBP silencing. In turn, ADH acetylation was reduced, suggesting that ChREBP regulates EtOH metabolism and ADH activity through its direct control of sirtuin 1 expression. Indeed, when sirtuin 1 activity was rescued by resveratrol pretreatment in EtOH-treated hepatocytes, a significant decrease in ADH protein content and/or acetylation was observed. our study describes a novel role for ChREBP in EtOH metabolism and unravels its protective effect against severe intoxication in response to binge drinking. Show less

Nonalcoholic fatty liver disease (NAFLD) is associated with all features of the metabolic syndrome. Although deposition of excess triglycerides within liver cells, a hallmark of NAFLD, is associated with a loss of insulin sensitivity, it is not clear which cellular abnormality arises first. We have explored this in mice overexpressing carbohydrate responsive element-binding protein (ChREBP). On a standard diet, mice overexpressing ChREBP remained insulin sensitive, despite increased expression of genes involved in lipogenesis/fatty acid esterification and resultant hepatic steatosis (simple fatty liver). Lipidomic analysis revealed that the steatosis was associated with increased accumulation of monounsaturated fatty acids (MUFAs). In primary cultures of mouse hepatocytes, ChREBP overexpression induced expression of stearoyl-CoA desaturase 1 (Scd1), the enzyme responsible for the conversion of saturated fatty acids (SFAs) into MUFAs. SFA impairment of insulin-responsive Akt phosphorylation was therefore rescued by the elevation of Scd1 levels upon ChREBP overexpression, whereas pharmacological or shRNA-mediated reduction of Scd1 activity decreased the beneficial effect of ChREBP on Akt phosphorylation. Importantly, ChREBP-overexpressing mice fed a high-fat diet showed normal insulin levels and improved insulin signaling and glucose tolerance compared with controls, despite having greater hepatic steatosis. Finally, ChREBP expression in liver biopsies from patients with nonalcoholic steatohepatitis was increased when steatosis was greater than 50% and decreased in the presence of severe insulin resistance. Together, these results demonstrate that increased ChREBP can dissociate hepatic steatosis from insulin resistance, with beneficial effects on both glucose and lipid metabolism. Show less

Liver X receptor alpha (LXRalpha), also referred to as nuclear receptor subfamily 1, group H, member 3 is a member of the nuclear hormone receptor superfamily, and has recently been shown to act as a master transcription factor governing hepatic lipogenesis in mammals. Liver X receptor alpha directly regulates both the expression of other lipogenic transcription factors and the expression of lipogenic enzymes, thereby enhancing hepatic fatty acid synthesis (FASN). In birds, like in humans, fatty acid synthesis primarily occurs in the liver. Whether LXRalpha is involved in hepatic regulation of lipogenic genes remained to be investigated in this species. Here we show that fatty acid synthase and the expression of other lipogenic genes (sterol regulatory element binding protein 1 and steroyl coenzyme A desaturase 1) are induced in chicken hepatoma cells in response to a pharmacological liver X receptor agonist, T0901317. A detailed analysis of the chicken FASN promoter revealed a functional liver X response element. These data define the chicken FASN gene as a direct target of LXRalpha and further expand the role of LXRalpha as a regulator of lipid metabolism in this species. Show less