TIGAR Inhibition Rescues Dopaminergic Neurons in Common Forms of Early Onset Parkinson's' Disease (I5-2.003)

OBJECTIVE: To identify novel mechanisms which lead to dopaminergic cell death in early onset PD (EOPD) and determine whether genetic manipulation of these mechanisms rescues the otherwise dying dopaminergic neurons.BACKGROUND: Loss of function mutations in PINK1 and parkin lead to EOPD. The precise mechanisms leading to cell death in PINK1 and Parkin deficiency are still poorly understood. Zebrafish (Danio rerio) are emerging as a powerful new vertebrate model to study neurodegenerative diseases. We had previously identified inhibition of the TP53 inducible glycolysis and apoptosis regulator (TIGAR) as a novel rescue mechanism in pink1 mutant zebrafish.METHODS: We applied the novel zinc finger nuclease (ZFN) technology to establish the first stable Parkin-deficient zebrafish line (parkin-/-). The effect of Parkin deficiency on embryonic survival, gross morphology, spontaneous motor behaviour and number of dopaminergic neurons was assessed. Morpholino antisense oligos (MO) inactivating TIGAR were injected into parkin-/- embryos to determine whether shared or distinct mechanisms lead to neuronal cell loss in PINK1 and Parkin deficiency.RESULTS: parkin-/- zebrafish embryos develop normally and do not display any gross morphological or behavioural abnormalities. The number of dopaminergic neurons in parkin-/- larvae was reduced by approx. 25% at 3 days post fertilization (dpf). Lysosomal and TUNEL staining did not reveal any differences between parkin-/- zebrafish embryos and controls. Antisense-mediated inactivation of TIGARgave rise to complete rescue of dopaminergic neurons in parkin-/- larvae. The observed rescue effect was not due to an upregulation of key transcription factors regulating the development and differentiation of DA neurons, namely OtpA, OtpB or Nurr1.CONCLUSION: We have identified a novel, shared pathogenic mechanism leading to dopaminergic neuronal loss in both PINK1 and Parkin deficiency. TIGAR inactivation is a promising novel target for disease-modifying therapy in EOPD. Study supported by: Parkinson’s UK, BBSRC/Lilly CASE PhD studentship.