Missense variant in insulin receptor (Y1355H) segregates in family with fatty liver disease

A missense variant in the cytoplasmic domain of the insulin receptor (INSR) was identified by exome sequencing in affected members of a four-generation family with fatty liver disease (FLD). The variant (rs766457461, c.4063T>C, p.Y1355H) results in the substitution of histidine for a tyrosine that undergoes autophosphorylation in response to insulin stimulation in vitro. Because insulin promotes lipogenesis in hepatocytes, we hypothesized that the variant was causally linked to FLD in the family. To test this hypothesis, we used CRISPR/Cas9 technology to replace the corresponding tyrosine in mouse INSR with histidine (Y1345H). No significant differences were found in hepatic insulin signaling, as assessed by phosphorylation of INSR or AKT levels or in activation of the insulin-responsive transcription factor SREBP-1c. Glucose tolerance and hepatic triglyceride (TG) content in Insr^1345H/H mice fed a chow diet or diets rich in fat, sucrose or fructose did not differ significantly from WT littermates. Thus, our studies in mice failed to support the notion that INSR (Y1355H) is causally related to FLD in the family or that phosphorylation of this residue alters hepatic TG metabolism.

Suppression of uric acid and lactate production by sodium acetate ameliorates hepatic triglyceride accumulation in fructose-insulin resistant pregnant rats

High fructose intake has been associated with perturbed lipid, uric acid and lactate homeostasis. However, consumption of fructose-sweetened beverages is not usually regulated during pregnancy. The effect of short-chain fatty acid (acetate) on the metabolic effects of high fructose intake during pregnancy is not known. We hypothesized that acetate prevents gestational fructose-induced hepatic triglyceride (TG) accumulation by suppressing uric acid and lactate production. Pregnant Wistar rats were randomly separated into three groups (n = 6/group) receiving drinking water (CON), 10 % (w/v) fructose drink (FRU) and 10 % (w/v) fructose with 200 mg/kg (w/w; p.o.) sodium acetate (FRU + ACE) daily for nineteen days. Fructose intake resulted in increased body weight gain, liver weight, fluid intake, visceral fat, insulin resistance, fasting blood glucose, insulin, plasma and hepatic TG, total cholesterol, free fatty acid, lipid peroxidation, adenosine deaminase, xanthine oxidase, uric acid, lactate, lactate dehydrogenase, and liver injury marker enzymes. However, gestational high fructose intake led to depressed plasma and hepatic glucose-6-phosphate dehydrogenase (G6PD)-dependent antioxidant barrier, adenosine and food intake. All these effects except water intake and food intake were abated by sodium acetate. These results demonstrate that maternal fructose-enriched drink would cause hepatic TG accumulation that is associated with perturbed glucose, uric acid, lactate homeostasis, and G6PD-dependent antioxidant barrier. These results also demonstrate that acetate protects the liver against gestational fructose-induced TG accumulation by inhibiting uric acid and lactate production. Thus, acetate may be useful in the treatment of hyperuricemia- and hyperlactatemia-related disorders.