Tetanus toxin Hc fragment reduces neuronal MPP+ toxicity

The non-toxic carboxi-terminal domain of the heavy chain of tetanus toxin (H_C) elicits neuroprotection of cerebellar granule neurons against apoptotic death induced by potassium deprivation. In this study we sought to determine whether H_C also prevents the apoptosis induced by the mitochondrial poison 1-methyl-4-phenylpyridinium (MPP⁺), which induces a form of Parkinsonism. Pre-treatment of cultures with H_C prevented MPP⁺-induced cell death, as well as impaired the MPP⁺-triggered apoptotic cascade. Cytochrome c release from the mitochondria, procaspase-3 activation and chromatin condensation, were significantly reduced in H_C-pre-treated neurons. Moreover, H_C induced Ser¹¹² and Ser¹³⁶ BAD phosphorylation, which correlated with the detachment of BAD from Bcl-X_L and its association to 14-3-3. In turn, Bcl-X_L remained bound to Bax, impairing its translocation to mitochondria of stressed neurons. The use of Wortmannin or PD98059 demonstrated the involvement of the PI3K/Akt as well as the ERK1/2 transduction pathways in the H_C fragment effect. Interestingly, the H_C fragment also induces an increase in the DNA binding activity of NF-κB, a well-established transcription factor involved in the prevention of neuronal death. Taken together, our results strongly suggest that the recombinant H_C fragment of tetanus toxin can act as a neuroprotector in a model of MPP⁺-triggered apoptosis.