GCN2 is required to increase fibroblast growth factor 21 and maintain hepatic triglyceride homeostasis during asparaginase treatment

Abstract

The antileukemic agent asparaginase triggers the amino acid response (AAR) in the liver by activating the eukaryotic initiation factor 2 (eIF2) kinase general control nonderepressible 2 (GCN2). To explore the mechanism by which AAR induction is necessary to mitigate hepatic lipid accumulation and prevent liver dysfunction during continued asparaginase treatment, wild-type and Gcn2 null mice were injected once daily with asparaginase or phosphate buffered saline for up to 14 days. Asparaginase induced mRNA expression of multiple AAR genes and greatly increased circulating concentrations of the metabolic hormone fibroblast growth factor 21 (FGF21) independent of food intake. Loss of Gcn2 precluded mRNA expression and circulating levels of FGF21 and blocked mRNA expression of multiple genes regulating lipid synthesis and metabolism including Fas, Ppara, Pparg, Acadm, and Scd1 in both liver and white adipose tissue. Furthermore, rates of triglyceride export and protein expression of apolipoproteinB-100 were significantly reduced in the livers of Gcn2 null mice treated with asparaginase, providing a mechanistic basis for the increase in hepatic lipid content. Loss of AAR-regulated antioxidant defenses in Gcn2 null livers was signified by reduced Gpx1 gene expression alongside increased lipid peroxidation. Substantial reductions in antithrombin III hepatic expression and activity in the blood of asparaginase-treated Gcn2 null mice indicated liver dysfunction. These results suggest that the ability of the liver to adapt to prolonged asparaginase treatment is influenced by GCN2-directed regulation of FGF21 and oxidative defenses, which, when lost, corresponds with maladaptive effects on lipid metabolism and hemostasis.

General control nonderepressible 2 deletion predisposes to asparaginase-associated pancreatitis in mice

“…Activation of the AAR by GCN2 is essential for adaptation and survival during asparaginase treatment. In the absence of GCN2, failure to induce the AAR augments immunosuppression (8) and hepatotoxicity (64,65). These disease outcomes are in agreement with human genetic studies that report a correlation between single-nucleotide polymorphisms (SNPs) in the AAR genes asparagine synthetase (ASNS) and ATF5 and worse treatment outcome to asparaginase (6,49).…”

“…Serum amylase concentrations were measured in mouse serum by ELISA using a commercial kit. Triglyceride concentrations were measured from frozen prepared pancreas tissue lysates (ϳ20 mg) using a commercial kit as previously described (65). Circulating amino acid concentrations were measured in the serum of mice killed 8 h after the last injection of asparaginase or saline excipient.…”

“…The amino acid depletion also instigates a cellular stress response in nontumor tissues that we and others have previously described (4,9,29,46,55,64,65). In the liver and spleen, asparaginase corresponds with increased phosphorylation of eukaryotic initiation factor 2 (eIF2) by the general control nonderepressible 2 (GCN2) protein kinase (46).…”

A liver stress-endocrine nexus promotes metabolic integrity during dietary protein dilution

“…Evidence is emerging, however, that hepatic FGF21 can also be regulated by NEAA supply. For instance, mice with relative hepatic asparagine/glutamine (48,49) or alanine (50) insufficiency also have higher hepatic and circulating FGF21 levels. Consistent with these observations, our data provide evidence that hepatocyte FGF21 induction following DPD occurs in response to an insufficiency of NEAAs, specifically Ala, Gln/Glu, and Asn/Asp.…”

Nutritional regulation of fibroblast growth factor 21: from macronutrients to bioactive dietary compounds

“…The absence of slc6a19 (neutral amino acid transporter) causes a lack of systemic neutral amino acids, resulting in an increase in FGF21 transcription [108]. The treatment with the antileukemic agent asparaginase depletes circulating asparagine and glutamine levels, promoting FGF21 expression [109], and the skeletal muscle-specific knockout mice for glucocorticoid receptor (GR) show reduced alanine flux from skeletal muscle during fasting, resulting in an increase in FGF21 plasma levels [110]. Hence, it is likely that many other situations that reduce amino acid availability also lead to an induction of FGF21 expression.…”