The eIF2α/ATF4 pathway is essential for stress-induced autophagy gene expression.

In response to different environmental stresses, eIF2α phosphorylation represses global translation coincident with preferential translation of ATF4, a master regulator controlling the transcription of key genes essential for adaptative functions. Here, we establish that the eIF2α/ATF4 pathway directs an autophagy gene transcriptional program in response to amino acid starvation or endoplasmic reticulum stress. The eIF2α-kinases GCN2 and PERK and the transcription factors ATF4 and CHOP are also required to increase the transcription of a set of genes implicated in the formation, elongation and function of the autophagosome. We also identify three classes of autophagy genes according to their dependence on ATF4 and CHOP and the binding of these factors to specific promoter cis elements. Furthermore, different combinations of CHOP and ATF4 bindings to target promoters allow the trigger of a differential transcriptional response according to the stress intensity. Overall, this study reveals a novel regulatory role of the eIF2α-ATF4 pathway in the fine-tuning of the autophagy gene transcription program in response to stresses.

Hepatocyte FBXW7-dependent activity of nutrient-sensing nuclear receptors controls systemic energy homeostasis and NASH progression in male mice.

Nonalcoholic steatohepatitis (NASH) is epidemiologically associated with obesity and diabetes and can lead to liver cirrhosis and hepatocellular carcinoma if left untreated. The intricate signaling pathways that orchestrate hepatocyte energy metabolism and cellular stress, intrahepatic cell crosstalk, as well as interplay between peripheral tissues remain elusive and are crucial for the development of anti-NASH therapies. Herein, we reveal E3 ligase FBXW7 as a key factor regulating hepatic catabolism, stress responses, systemic energy homeostasis, and NASH pathogenesis with attenuated FBXW7 expression as a feature of advanced NASH. Multiomics and pharmacological intervention showed that FBXW7 loss-of-function in hepatocytes disrupts a metabolic transcriptional axis conjointly controlled by the nutrient-sensing nuclear receptors ERRα and PPARα, resulting in suppression of fatty acid oxidation, elevated ER stress, apoptosis, immune infiltration, fibrogenesis, and ultimately NASH progression in male mice. These results provide the foundation for developing alternative strategies co-targeting ERRα and PPARα for the treatment of NASH.

Integrated multi-omics analysis of adverse cardiac remodeling and metabolic inflexibility upon ErbB2 and ERRα deficiency.

Functional oncogenic links between ErbB2 and ERRα in HER2+ breast cancer patients support a therapeutic benefit of co-targeted therapies. However, ErbB2 and ERRα also play key roles in heart physiology, and this approach could pose a potential liability to cardiovascular health. Herein, using integrated phosphoproteomic, transcriptomic and metabolic profiling, we uncovered molecular mechanisms associated with the adverse remodeling of cardiac functions in mice with combined attenuation of ErbB2 and ERRα activity. Genetic disruption of both effectors results in profound effects on cardiomyocyte architecture, inflammatory response and metabolism, the latter leading to a decrease in fatty acyl-carnitine species further increasing the reliance on glucose as a metabolic fuel, a hallmark of failing hearts. Furthermore, integrated omics signatures of ERRα loss-of-function and doxorubicin treatment exhibit common features of chemotherapeutic cardiotoxicity. These findings thus reveal potential cardiovascular risks in discrete combination therapies in the treatment of breast and other cancers.

Divergent Role of Estrogen-Related Receptor α in Lipid- and Fasting-Induced Hepatic Steatosis in Mice.

Given the increasing prevalence of obesity and the metabolic syndrome, identification of intrinsic molecular programs responsible for ensuring fuel homeostasis and preventing metabolic disease is needed. We investigated whether the orphan nuclear receptor estrogen-related receptor α (ERRα), a major regulator of energy metabolism, plays a role in lipid homeostasis and the development of nonalcoholic fatty liver disease (NAFLD) in response to chronic high-fat diet (HFD) consumption and long-term fasting. Systemic ablation of ERRα in mice demonstrated clear beneficial effects for loss of ERRα function in protection from HFD-provoked body weight gain manifested not only from a reduction in white adipose tissue stores but also from an impediment in intrahepatic lipid accumulation. The prevention of HFD-induced NAFLD in ERRα-null mice was underscored by transcriptional repression of de novo lipogenesis, which was upregulated in wild-type mice, a known contributing factor to lipid-stimulated hepatic steatosis. Surprisingly, given these findings, ERRα deficiency had no significant impact on the degree of fasting-induced NAFLD, involving the mobilization of adipocyte triglyceride (TG) stores into the liver. However, the presence of ERRα was essential for acute refeeding-mediated reversal of fasting-induced hepatic TG accretion, underpinned by impaired downregulation of adipose TG lipolysis and reduced hepatic mitochondrial oxidative activity. Taken together, the regulation of lipid handling by ERRα depended on the nutritional state, suggesting that negative modulation of ERRα activity could be envisaged to prevent lipid-induced NAFLD, whereas inducing its activity would be useful to treat and reverse the instilled disease.

Activation of the EIF2AK4-EIF2A/eIF2α-ATF4 pathway triggers autophagy response to Crohn disease-associated adherent-invasive Escherichia coli infection.

The intestinal mucosa of Crohn disease (CD) patients is abnormally colonized by adherent-invasive E. coli (AIEC). Upon AIEC infection, autophagy is induced in host cells to restrain bacterial intracellular replication. The underlying mechanism, however, remains unknown. Here, we investigated the role of the EIF2AK4-EIF2A/eIF2α-ATF4 pathway in the autophagic response to AIEC infection. We showed that infection of human intestinal epithelial T84 cells with the AIEC reference strain LF82 activated the EIF2AK4-EIF2A-ATF4 pathway, as evidenced by increased phospho-EIF2AK4, phospho-EIF2A and ATF4 levels. EIF2AK4 depletion inhibited autophagy activation in response to LF82 infection, leading to increased LF82 intracellular replication and elevated pro-inflammatory cytokine production. Mechanistically, EIF2AK4 depletion suppressed the LF82-induced ATF4 binding to promoters of several autophagy genes including MAP1LC3B, BECN1, SQSTM1, ATG3 and ATG7, and this subsequently inhibited transcription of these genes. LF82 infection of wild-type (WT), but not eif2ak4(-/-), mice activated the EIF2AK4-EIF2A-ATF4 pathway, inducing autophagy gene transcription and autophagy response in enterocytes. Consequently, eif2ak4(-/-) mice exhibited increased intestinal colonization by LF82 bacteria and aggravated inflammation compared to WT mice. Activation of the EIF2AK4-EIF2A-ATF4 pathway was observed in ileal biopsies from patients with noninflamed CD, and this was suppressed in inflamed CD, suggesting that a defect in the activation of this pathway could be one of the mechanisms contributing to active disease. In conclusion, we show that activation of the EIF2AK4-EIF2A-ATF4 pathway upon AIEC infection serves as a host defense mechanism to induce functional autophagy to control AIEC intracellular replication.

Estrogen-related receptor-α coordinates transcriptional programs essential for exercise tolerance and muscle fitness.

Muscle fitness is an important determinant of health and disease. However, the molecular mechanisms involved in the coordinate regulation of the metabolic and structural determinants of muscle endurance are still poorly characterized. Herein, we demonstrate that estrogen-related receptor α (ERRα, NR3B1) is essential for skeletal muscle fitness. Notably, we show that ERRα-null animals are hypoactive and that genetic or therapeutic disruption of ERRα in mice results in reduced exercise tolerance. Mice lacking ERRα also exhibited lactatemia at exhaustion. Gene expression profiling demonstrates that ERRα plays a key role in various metabolic processes important for muscle function including energy substrate transport and use (Ldhd, Slc16a1, Hk2, and Glul), the tricarboxylic acid cycle (Cycs, and Idh3g), and oxidative metabolism (Pdha1, and Uqcrq). Metabolomics studies revealed impairment in replenishment of several amino acids (eg, glutamine) during recovery to exercise. Moreover, loss of ERRα was found to alter the expression of genes involved in oxidative stress response (Hmox1), maintenance of muscle fiber integrity (Trim63, and Hspa1b), and muscle plasticity and neovascularization (Vegfa). Taken together, our study shows that ERRα plays a key role in directing transcriptional programs required for optimal mitochondrial oxidative potential and muscle fitness, suggesting that modulation of ERRα activity could be used to manage metabolic myopathies and/or promote the adaptive response to physical exercise.

Dual role for CHOP in the crosstalk between autophagy and apoptosis to determine cell fate in response to amino acid deprivation.

CHOP encodes a ubiquitous transcription factor that is one of the most important components in the network of stress-inducible transcription. In particular, this factor is known to mediate cell death in response to stress. The focus of this work is to study its pivotal role in the control of cell viability according to the duration of a stress like amino acid starvation. We show that during the first 6h of starvation, CHOP upregulates a number of autophagy genes but is not involved in the first steps of the autophagic process. By contrast, when the amino acid starvation is prolonged (16-48h), we demonstrated that CHOP has a dual role in both inducing apoptosis and limiting autophagy through the transcriptional control of specific target genes. Overall, this study reveals a novel regulatory role for CHOP in the crosstalk between autophagy and apoptosis in response to stress.

Requirement for lysosomal localization of mTOR for its activation differs between leucine and other amino acids.

The mammalian target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth and metabolism. It controls many cell functions by integrating nutrient availability and growth factor signals. Amino acids, and in particular leucine, are among the main positive regulators of mTORC1 signaling. The current model for the regulation of mTORC1 by amino acids involves the movement of mTOR to the lysosome mediated by the Rag-GTPases. Here, we have examined the control of mTORC1 signaling and mTOR localization by amino acids and leucine in serum-fed cells, because both serum growth factors (or, e.g., insulin) and amino acids are required for full activation of mTORC1 signaling. We demonstrate that mTORC1 activity does not closely correlate with the lysosomal localization of mTOR. In particular, leucine controls mTORC1 activity without any detectable modification of the lysosomal localization of mTOR, indicating that the signal(s) exerted by leucine is likely distinct from those exerted by other amino acids. In addition, knock-down of the Rag-GTPases attenuated the inhibitory effect of amino acid- or leucine-starvation on the phosphorylation of mTORC1 targets. Furthermore, data from cells where Rag expression has been knocked down revealed that leucine can promote mTORC1 signaling independently of the lysosomal localization of mTOR. Our data complement existing models for the regulation of mTORC1 by amino acids and provide new insights into this important topic.

Hypothalamic eIF2α signaling regulates food intake.

The reversible phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) is a highly conserved signal implicated in the cellular adaptation to numerous stresses such as the one caused by amino acid limitation. In response to dietary amino acid deficiency, the brain-specific activation of the eIF2α kinase GCN2 leads to food intake inhibition. We report here that GCN2 is rapidly activated in the mediobasal hypothalamus (MBH) after consumption of a leucine-deficient diet. Furthermore, knockdown of GCN2 in this particular area shows that MBH GCN2 activity controls the onset of the aversive response. Importantly, pharmacological experiments demonstrate that the sole phosphorylation of eIF2α in the MBH is sufficient to regulate food intake. eIF2α signaling being at the crossroad of stress pathways activated in several pathological states, our study indicates that hypothalamic eIF2α phosphorylation could play a critical role in the onset of anorexia associated with certain diseases.