Enhanced Akt signaling is an early pro-survival response that reflects N-methyl-D-aspartate receptor activation in Huntington's disease knock-in striatal cells.
Huntington's disease features the loss of striatal neurons that stems from a disease process that is initiated by mutant huntingtin. Early events in the disease cascade, which predate overt pathology in Hdh CAG knock-in mouse striatum, implicate enhanced N-methyl-D-aspartate (NMDA) receptor activation, with excitotoxity caused by aberrant Ca2+ influx. Here we demonstrate in precise genetic Huntington's disease mouse and striatal cell models that these early phenotypes are associated with activation of the Akt pro-survival signaling pathway. Elevated levels of activated Ser(P)473-Akt are detected in extracts of Hdh(Q111/Q111) striatum and cultured mutant STHdh(Q111/Q111) striatal cells, compared with their wild type counterparts. Akt activation in mutant striatal cells is associated with increased Akt signaling via phosphorylation of GSK3beta at Ser9. Consequent decreased turnover of transcription co-factor beta-catenin leads to increased levels of beta-catenin target gene cyclin D1. Akt activation is phosphatidylinositol 3-kinase dependent, as demonstrated by increased levels of Ser(P)241-PDK1 kinase and decreased Ser(P)380-PTEN phosphatase. Moreover, Akt activation can be normally stimulated by treatment with insulin growth factor-1 and blocked by treatment with the phosphatidylinositol 3-kinase inhibitor LY294002. However, in contrast to wild type cells, Akt activation in mutant striatal cells can be blocked by the addition of the NMDA receptor antagonist MK-801. Akt activation in mutant striatal cells is Ca(2+)-dependent, because treatment with EGTA reduces levels of Ser(P)473-Akt. Thus, consistent with excitotoxicity early in the disease process, activation of the Akt pro-survival pathway in mutant knock-in striatal cells predates overt pathology and reflects mitochondrial dysfunction and enhanced NMDA receptor signaling.
Gines
Silvia
S
Molecular Neurogenetics Unit, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA. gines@helix.mgh.harvard.edu
Ivanova
Elena
E
Seong
Ihn-Sik
IS
Saura
Carlos A
CA
MacDonald
Marcy E
ME
D000483:Alleles; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D003342:Corpus Striatum / Q000378:metabolism; D019938:Cyclin D1 / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004789:Enzyme Activation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006816:Huntington Disease / Q000235:genetics*; D015151:Immunoblotting; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D014158:Transcription, Genetic; D051176:beta Catenin
D002867:Chromones; D019938:Cyclin D1; D003598:Cytoskeletal Proteins; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016194:Receptors, N-Methyl-D-Aspartate; D012694:Serine; D015534:Trans-Activators; D051176:beta Catenin; C495267:CTNNB1 protein, mouse; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C000605507:Gsk3b protein, mouse