Research ArticleFragile X Syndrome

Selective inhibition of glycogen synthase kinase 3α corrects pathophysiology in a mouse model of fragile X syndrome

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Science Translational Medicine  20 May 2020:
Vol. 12, Issue 544, eaam8572
DOI: 10.1126/scitranslmed.aam8572

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Blocking GSK3α in a fragile X mouse model

Fragile X syndrome is a heritable cause of autism and intellectual disability. Inhibitors of glycogen synthase kinase 3 (GSK3), including lithium, have shown promise in correcting disease phenotypes in a mouse model of fragile X syndrome, but various toxicities have precluded further development of these compounds. McCamphill et al. now report that a major toxicity of GSK3 inhibition, stabilization of β-catenin, could be avoided by selective pharmacological inhibition of the α paralog of GSK3. Furthermore, the authors found that selective inhibition of GSK3α was sufficient to correct a range of disease phenotypes in a mouse model of fragile X syndrome, whereas inhibition of GSK3β was ineffective.

Abstract

Fragile X syndrome is caused by FMR1 gene silencing and loss of the encoded fragile X mental retardation protein (FMRP), which binds to mRNA and regulates translation. Studies in the Fmr1−/y mouse model of fragile X syndrome indicate that aberrant cerebral protein synthesis downstream of metabotropic glutamate receptor 5 (mGluR5) signaling contributes to disease pathogenesis, but clinical trials using mGluR5 inhibitors were not successful. Animal studies suggested that treatment with lithium might be an alternative approach. Targets of lithium include paralogs of glycogen synthase kinase 3 (GSK3), and nonselective small-molecule inhibitors of these enzymes improved disease phenotypes in a fragile X syndrome mouse model. However, the potential therapeutic use of GSK3 inhibitors has been hampered by toxicity arising from inhibition of both α and β paralogs. Recently, we developed GSK3 inhibitors with sufficient paralog selectivity to avoid a known toxic consequence of dual inhibition, that is, increased β-catenin stabilization. We show here that inhibition of GSK3α, but not GSK3β, corrected aberrant protein synthesis, audiogenic seizures, and sensory cortex hyperexcitability in Fmr1−/y mice. Although inhibiting either paralog prevented induction of NMDA receptor–dependent long-term depression (LTD) in the hippocampus, only inhibition of GSK3α impaired mGluR5-dependent and protein synthesis–dependent LTD. Inhibition of GSK3α additionally corrected deficits in learning and memory in Fmr1−/y mice; unlike mGluR5 inhibitors, there was no evidence of tachyphylaxis or enhanced psychotomimetic-induced hyperlocomotion. GSK3α selective inhibitors may have potential as a therapeutic approach for treating fragile X syndrome.

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