Causal association between mTOR-dependent EIF-4E and EIF-4A circulating protein levels and type 2 diabetes: a Mendelian randomization study

www.nature.com/scientificreports OPEN Causal association between mTOR‑dependent EIF‑4E and EIF‑4A circulating protein levels and type 2 diabetes: a Mendelian randomization study Ghada A. Soliman1* & C. Mary Schooling1,2 The mammalian Target of Rapamycin complex 1 (mTORC1) nutrient-sensing pathway is a central regulator of cell growth and metabolism and is dysregulated in diabetes. The eukaryotic translation initiation factor 4E (EIF-4E) protein, a key regulator of gene translation and protein function, is controlled by mTORC1 and EIF-4E Binding Proteins (EIF4EBPs). Both EIF4EBPs and ribosomal protein S6K kinase (RP-S6K) are downstream effectors regulated by mTORC1 but converge to regulate two independent pathways. We investigated whether the risk of type 2 diabetes varied with genetically predicted EIF-4E, EIF-4A, EIF-4G, EIF4EBP, and RP-S6K circulating levels using Mendelian Randomization. We estimated the causal role of EIF-4F complex, EIF4EBP, and S6K in the circulation on type 2 diabetes, based on independent single nucleotide polymorphisms strongly associated (p = 5 × 10–6) with EIF-4E (16 SNPs), EIF-4A (11 SNPs), EIF-4G (6 SNPs), EIF4EBP2 (12 SNPs), and RP-S6K (16 SNPs). The exposure data were obtained from the INTERVAL study. We applied these SNPs for each exposure to publically available genetic associations with diabetes from the DIAbetes Genetics Replication And Meta-analysis (DIAGRAM) case (n = 26,676) and control (n = 132,532) study (mean age 57.4 years). We meta-analyzed SNP-specific Wald-estimates using inverse variance weighting with multiplicative random effects and conducted sensitivity analysis. Mendelian Randomization (MR-Base) R package was used in the analysis. The PhenoScanner curated database was used to identify disease associations with SNP gene variants. EIF-4E is associated with a lowered risk of type 2 diabetes with an odds ratio (OR) 0.94, 95% confidence interval (0.88, 0.99, p = 0.03) with similar estimates from the weighted median and MR-Egger. Similarly, EIF-4A was associated with lower risk of type 2 diabetes with odds ratio (OR) 0.90, 95% confidence interval (0.85, 0.97, p = 0.0003). Sensitivity analysis using MR-Egger and weighed median analysis does not indicate that there is a pleiotropic effect. This unbiased Mendelian Randomization estimate is consistent with a protective causal association of EIF-4E and EIF-4A on type 2 diabetes. EIF-4E and EIF-4A may be targeted for intervention by repurposing existing therapeutics to reduce the risk of type 2 diabetes. Abbreviations SNPs Single nucleotide polymorphism mTOR Mammalian target of rapamycin EIF-4E Eukaryotic translation initiation factor 4E EIF4EBP2 Eukaryotic translation initiation factor 4E binding protein 2 (4E-BP) mTORC1 Mammalian target of rapamycin complex 1 mTORC2 Mammalian target of rapamycin complex 2 1 Department of Environmental, Occupational and Geospatial Health Sciences, The City University of New York, Graduate School of Public Health and Health Policy, 55 West 125th St, New York, NY 10027, USA. 2School of Public Health, Li Ka Shing, Faculty of Medicine, The University of Hong Kong, 7 Sassoon Road, Hong Kong, China. *email: Scientific Reports | (2020) 10:15737 | https://doi.org/10.1038/s41598-020-71987-8 1 Vol.:(0123456789) www.nature.com/scientificreports/ GWAS Genome-wide association studies IVW Inverse variance weighted WM Weighted median MR Mendelian randomization RP-S6K Ribosomal protein S6K kinase Diabetes is one of the most prevalent chronic diseases globally and in the US and is associated with several co-morbidities. In 2015, it was estimated that 9.4% of the US population, or approximately 30.3 million people have diabetes1. Among those, only 23.1 million people are diagnosed, and about 7.2 million are undiagnosed. Type 2 diabetes represents approximately 90 to 95% of all diabetes cases. The estimated direct medical costs of diagnosed diabetes in 2017 was $237 billion in the US with an average medical expenditure of diagnosed person of $13,700 per year2. It is further estimated that 33.9% of US adults have prediabetes. To date, the causes of type 2 diabetes are not fully understood. Diabetes is also associated with multiple co-morbidities and complications, including obesity. Thus, there is an urgent need to determine causal associations and develop new strategies for prevention, early detection, diagnosis, and treatment of type 2 diabetes. The mechanistic Target of Rapamycin (mTOR) is a highly conserved serine/threonine kinase and a key regulator of cell growth and m etabolism3–5. As such, mTOR protein is a central metabolic integrator and is dysregulated in type 2 diabetes and diabetes-associated co-morbidities6–8. Importantly, mTOR is a druggable protein and therefore is a potential target for type 2 diabetes interventions. It nucleates two functionally-distinct and mutually-exclusive complexes, namely mTOR Complex 1 (mTORC1) and mTOR Complex 2 (mTORC2). Both mTORC1 and mTORC2 regulate cellular metabolism, survival, proliferation, and growth. mTORC1 is a central hub for nutrient-sensing and energy metabolism and, as such, coordinates anabolic protein and nucleotide synthesis and catabolic a utophagy9–16. On the other hand, mTORC2 drives insulin signaling by phosphorylating Akt (Ser473)/PKB downstream of the phosphoinositide 3-kinase (PI3K)/insulin p athway17–20. The mTORC1, which binds exclusively to Raptor protein and other partners (Fig. 1), regulates two downstream effectors, namely, Ribosomal Protein-S6 kinase 1 (RP-S6K 1) and eukaryotic translation initiation factor 4E-binding protein (EIF4EBP). The first mTORC1 target, RP-S6K1 phosphorylates eukaryotic translation initiation factor 4B (EIF-4B), which is a positive regulator of EIF-4F c omplex21. In addition, RP-S6K also phosphorylates the programmed cell death protein 4 (PDCD4), which is a negative regulator of EIF-4A and targets it to degradation via the ubiquitin pathway22. The second mTORC1 downstream target, EIF4EBP, is a repressor of the translation initiation complex (EIF-4F), which is required for 5′cap-dependent translation of mRNA (Fig. 1). Once phosphorylated by mTORC1, EIF4EBP dissociates from EIF-4E, allowing for the assembly of the EIF-4F complex and initiation of 5′cap-dependent translation. The EIF-4F complex consists of EIF-4E, EIF-4G, and EIF4A. EIF-4E binds to 7-methylguanosine cap at the 5′-UTR of eukaryotic mRNA and mediates the recruitment of mRNA on ribosomes to start protein translation. As mentioned earlier, the mTOR kinase attracts different protein partners to generate two functionally distinct complexes, namely, mTORC1 and mTORC2. While mTORC1 integrates inputs from nutrients and growth factors and coordinates cellular growth and m etabolism23–25; mTORC2 is activated by growth factor signals only and responds by phosphorylating the C-terminal hydrophobic motif of Akt/PKB on serine 47317,26–29. As such, mTOR complexes and their downstream targets ar (...truncated)