Erythropoietin and sonic hedgehog mediate the neuroprotective effects of brain-derived neurotrophic factor against mitochondrial inhibition

Brain-derived neurotrophic factor (BDNF) deficiency and mitochondrial dysfunction have been implicated in the pathogenesis of Huntington's disease (HD). 3-Nitropropionic acid (3-NP) is a mitochondrial inhibitor commonly used as a pharmacological model mimicking HD. We have recently reported that preconditioning of primary rat cortical cultures with BDNF induces sonic hedgehog (SHH), which contributes to the protective effects of BDNF against 3-NP neurotoxicity. Because carbamylated erythropoietin (EPO) may induce SHH, we investigated whether BDNF-dependent SHH expression and 3-NP resistance require prior induction of EPO. We found that BDNF induced EPO expression at both mRNA and protein levels. BDNF-mediated SHH induction and 3-NP resistance were abolished by the soluble EPO receptor (sEPO-R), an EPO inhibitor. Recombinant rat EPO (rEPO) induced SHH and attenuated 3-NP neurotoxicity. The rEPO-dependent neuroprotection was suppressed by the SHH inhibitor cyclopamine (CPM); however, sEPO-R failed to affect SHH neuroprotection. Furthermore, the rEPO-dependent neuroprotection was not suppressed by the BDNF neutralizing antibody, which completely abolished BDNF-mediated 3-NP resistance at the same dosage. Overall, our results demonstrate that BDNF-dependent SHH expression and 3-NP resistance require prior induction of EPO, thus establishing a signaling cascade of "BDNF → EPO → SHH → 3-NP resistance" in rat cortical neurons.