title: Activation of the Stress Response Kinase JNK (c-Jun N-terminal Kinase) Attenuates Insulin Action in Retina through a p70S6K1-dependent Mechanism.
abstract: Despite recent advances in therapeutics, diabetic retinopathy remains a leading cause of vision impairment. Improvement in the treatment of diabetic retinopathy requires a better understanding of the molecular mechanisms that cause neurovascular complications, particularly in type 2 diabetes. Recent studies demonstrate that rodents fed a high fat diet exhibit retinal dysfunction concomitant with attenuated Akt phosphorylation. The purpose of the present study was to evaluate the impact of a high fat/high sucrose diet on retinal insulin signaling and evaluate the mechanism(s) responsible for the changes. Mice fed a high fat/sucrose diet exhibited attenuated Akt phosphorylation in the retina as compared with mice fed normal chow. Retinas of mice fed a high fat/sucrose diet also exhibited elevated levels of activated JNK as well as enhanced p70S6K1 autoinhibitory domain phosphorylation. In cells, JNK activation enhanced p70S6K1 phosphorylation and mTORC1-dependent activation of the kinase, as evidenced by enhanced phosphorylation of key substrates. Rictor phosphorylation by p70S6K1 was specifically enhanced by the addition of phosphomimetic mutations in the autoinhibitory domain and was more sensitive to inhibition of the kinase as compared with rpS6. Notably, rictor and IRS-1 phosphorylation by p70S6K1 attenuate insulin action through a negative feedback pathway. Indeed, p70S6K1 inhibition prevented the repressive effect of JNK activation on insulin action in retinas. Overall, the results identify the JNK/S6K1 axis as a key molecular mechanism whereby a high fat/sucrose diet impairs insulin action in retina.
authors.affiliation: From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
authors.forename: William P
authors.initials: WP
authors.lastname: Miller
authors.affiliation: From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
authors.forename: Suhana
authors.initials: S
authors.lastname: Ravi
authors.affiliation: From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
authors.forename: Tony D
authors.initials: TD
authors.lastname: Martin
authors.affiliation: From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.affiliation: From the Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033. Electronic address: mdennis@psu.edu.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Dennis
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D003930:Diabetic Retinopathy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D004041:Dietary Fats / Q000009:adverse effects / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D048670:MAP Kinase Kinase 4 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D020125:Mutation, Missense; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D000072417:Protein Domains; D012160:Retina / Q000378:metabolism* / Q000473:pathology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000235:genetics / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D013395:Sucrose / Q000009:adverse effects / Q000494:pharmacology
chemical_list: D004041:Dietary Fats; D007328:Insulin; D013395:Sucrose; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; C448901:ribosomal protein S6 kinase, 70kD, polypeptide 1; D048670:MAP Kinase Kinase 4
keywords: Type 2 diabetes; c-Jun N-terminal kinase (JNK); insulin action; insulin resistance; mammalian target of rapamycin (mTOR); retina; retinopathy