Huntingtin polyQ Mutation Impairs the 17β-Estradiol/Neuroglobin Pathway Devoted to Neuron Survival

Among several mechanisms underlying the well-known trophic and protective effects of 17β-estradiol (E2) in the brain, we recently reported that E2 induces the up-regulation of two anti-apoptotic and neuroprotectant proteins: huntingtin (HTT) and neuroglobin (NGB). Here, we investigate the role of this up-regulation. The obtained results indicate that E2 promotes NGB-HTT association, induces the localization of the complex at the mitochondria, and protects SK-N-BE neuroblastoma cells and murine striatal cells, which express wild-type HTT (i.e., polyQ⁷), against H₂O₂-induced apoptosis. All E2 effects were completely abolished in HTT-knocked out SK-N-BE cells and in striatal neurons expressing the mutated form of HTT (mHTT; i.e., polyQ¹¹¹) typical of Huntington's disease (HD). As a whole, these data provide a new function of wild-type HTT which drives E2-induced NGB in mitochondria modulating NGB anti-apoptotic activity. This new function is lost by HTT polyQ pathological expansion. These data evidence the existence of a novel E2/HTT/NGB neuroprotective axis that may play a relevant role in the development of HD therapeutics.