Knockdown of the putative Lifeguard homologue CG3814 in neurons of Drosophila melanogaster.

Lifeguard is an integral transmembrane protein that modulates FasL-mediated apoptosis by interfering with the activation of caspase 8. It is evolutionarily conserved, with homologues present in plants, nematodes, zebra fish, frog, chicken, mouse, monkey, and human. The Lifeguard homologue in Drosophila, CG3814, contains the Bax inhibitor-1 family motif of unknown function. Downregulation of Lifeguard disrupts cellular homeostasis and disease by sensitizing neurons to FasL-mediated apoptosis. We used bioinformatic analyses to identify CG3814, a putative homologue of Lifeguard, and knocked down CG3814/LFG expression under the control of the Dopa decarboxylase (Ddc-Gal4) transgene in Drosophila melanogaster neurons to investigate whether it possesses neuroprotective activity. Knockdown of CG3814/LFG in Ddc-Gal4-expressing neurons resulted in a shortened lifespan and impaired locomotor ability, phenotypes that are strongly associated with the degeneration and loss of dopaminergic neurons. Lifeguard interacts with anti-apoptotic Bcl-2 proteins and possibly pro-apoptotic proteins to exert its neuroprotective function. The co-expression of Buffy, the sole anti-apoptotic Bcl-2 gene family member in Drosophila, and CG3814/LFG by stable inducible RNA interference, suppresses the shortened lifespan and the premature age-dependent loss in climbing ability. Suppression of CG3814/LFG in the Drosophila eye reduces the number of ommatidia and increases disruption of the ommatidial array. Overexpression of Buffy, along with the knockdown of CG3814/LFG, counteracts the eye phenotypes. Knockdown of CG3814/LFG in Ddc-Gal4-expressing neurons in Drosophila diminishes its neuroprotective ability and results in a shortened lifespan and loss of climbing ability, phenotypes that are improved upon overexpression of the pro-survival Buffy.