Elevated ERK/p90 ribosomal S6 kinase activity underlies audiogenic seizure susceptibility in fragile X mice.
Fragile X syndrome (FXS) is the most common heritable cause of intellectual disability and a leading genetic form of autism. The Fmr1 KO mouse, a model of FXS, exhibits elevated translation in the hippocampus and the cortex. ERK (extracellular signal-regulated kinase) and mTOR (mechanistic target of rapamycin) signaling regulate protein synthesis by activating downstream targets critical to translation initiation and elongation and are known to contribute to hippocampal defects in fragile X. Here we show that the effect of loss of fragile X mental retardation protein (FMRP) on these pathways is brain region specific. In contrast to the hippocampus, ERK (but not mTOR) signaling is elevated in the neocortex of fragile X mice. Phosphorylation of ribosomal protein S6, typically a downstream target of mTOR, is elevated in the neocortex, despite normal mTOR activity. This is significant in that S6 phosphorylation facilitates translation, correlates with neuronal activation, and is altered in neurodevelopmental disorders. We show that in fragile X mice, S6 is regulated by ERK via the "alternative" S6 kinase p90-ribosomal S6 kinase (RSK), as evidenced by the site of elevated phosphorylation and the finding that ERK inhibition corrects elevated RSK and S6 activity. These findings indicate that signaling networks are altered in the neocortex of fragile X mice such that S6 phosphorylation receives aberrant input from ERK/RSK. Importantly, an RSK inhibitor reduces susceptibility to audiogenic seizures in fragile X mice. Our findings identify RSK as a therapeutic target for fragile X and suggest the therapeutic potential of drugs for the treatment of FXS may vary in a brain-region-specific manner.
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY 10461 ksawicka@rockefeller.edu suzanne.zukin@einstein.yu.edu michael.bennett@einstein.yu.edu.
Kirsty
K
Sawicka
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY 10461.
Alexander
A
Pyronneau
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY 10461.
Miranda
M
Chao
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY 10461 ksawicka@rockefeller.edu suzanne.zukin@einstein.yu.edu michael.bennett@einstein.yu.edu.
Michael V L
MV
Bennett
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, NY 10461 ksawicka@rockefeller.edu suzanne.zukin@einstein.yu.edu michael.bennett@einstein.yu.edu.
R Suzanne
RS
Zukin
D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism / Q000503:physiopathology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D020195:Epilepsy, Reflex / Q000188:drug therapy / Q000209:etiology* / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics / Q000378:metabolism; D005600:Fragile X Syndrome / Q000150:complications*; D051379:Mice; D018345:Mice, Knockout; D009474:Neurons / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012640:Seizures / Q000209:etiology / Q000378:metabolism; D015398:Signal Transduction; D013569:Synapses / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
D004268:DNA-Binding Proteins; D048049:Extracellular Signal-Regulated MAP Kinases; D051860:Fragile X Messenger Ribonucleoprotein 1; D019869:Phosphatidylinositol 3-Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors; C491779:Elf4 protein, mouse; C497684:Fmr1 protein, mouse
FMRP; RSK; autism; intellectual disability; mTOR
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