knockdown phenotypes are suppressed by and exacerbate degeneration in a model of Parkinson disease.

BACKGROUND

Bax inhibitor-1 (BI-1) is an evolutionarily conserved cytoprotective transmembrane protein that acts as a suppressor of -induced apoptosis by regulation of endoplasmic reticulum stress-induced cell death. We knocked down in the sensitive () expressing neurons of to investigate its neuroprotective functions. We additionally sought to rescue the -induced phenotypes by co-expression with the pro-survival and determined the effect of knockdown on the neurodegenerative α--induced Parkinson disease (PD) model.

METHODS

We used organismal assays to assess longevity of the flies to determine the effect of the altered expression of in the -expressing neurons by employing two RNAi transgenic fly lines. We measured the locomotor ability of these RNAi lines by computing the climbing indices of the climbing ability and compared them to a control line that expresses the transgene. Finally, we performed biometric analysis of the developing eye, where we counted the number of ommatidia and calculated the area of ommatidial disruption.

RESULTS

The knockdown of in these neurons was achieved under the direction of the transgene and resulted in shortened lifespan and precocious loss of locomotor ability. The co-expression of , the Drosophila anti-apoptotic Bcl-2 homologue, with resulted in suppression of the reduced lifespan and impaired climbing ability. Expression of human α- in Drosophila dopaminergic neurons results in neuronal degeneration, accompanied by the age-dependent loss in climbing ability. We exploited this neurotoxic system to investigate possible BI-1 neuroprotective function. The co-expression of α- with results in a slight decrease in lifespan coupled with an impairment in climbing ability. In supportive experiments, we employed the neuron-rich Drosophila compound eye to investigate subtle phenotypes that result from altered gene expression. The knockdown of in the Drosophila developing eye under the direction of the transgene results in reduced ommatidia number and increased disruption of the ommatidial array. Similarly, the co-expression of with results in the suppression of the eye phenotypes. The expression of α- along with the knockdown of resulted in reduction of ommatidia number and more disruption of the ommatidial array.

CONCLUSION

Knockdown of in the dopaminergic neurons of Drosophila results in a shortened lifespan and premature loss in climbing ability, phenotypes that appear to be strongly associated with models of PD in Drosophila, and which are suppressed upon overexpression of and worsened by co-expression with α-. This suggests that is neuroprotective and its knockdown can be counteracted by the overexpression of the pro-survival homologue.