The Nitric Oxide-Cyclic GMP Pathway Regulates FoxO and Alters Dopaminergic Neuron Survival in Drosophila

Abstract

Activation of the forkhead box transcription factor FoxO is suggested to be involved in dopaminergic (DA) neurodegeneration in a Drosophila model of Parkinson's disease (PD), in which a PD gene product LRRK2 activates FoxO through phosphorylation. In the current study that combines Drosophila genetics and biochemical analysis, we show that cyclic guanosine monophosphate (cGMP)-dependent kinase II (cGKII) also phosphorylates FoxO at the same residue as LRRK2, and Drosophila orthologues of cGKII and LRRK2, DG2/For and dLRRK, respectively, enhance the neurotoxic activity of FoxO in an additive manner. Biochemical assays using mammalian cGKII and FoxO1 reveal that cGKII enhances the transcriptional activity of FoxO1 through phosphorylation of the FoxO1 S319 site in the same manner as LRRK2. A Drosophila FoxO mutant resistant to phosphorylation by DG2 and dLRRK (dFoxO S259A corresponding to human FoxO1 S319A) suppressed the neurotoxicity and improved motor dysfunction caused by co-expression of FoxO and DG2. Nitric oxide synthase (NOS) and soluble guanylyl cyclase (sGC) also increased FoxO's activity, whereas the administration of a NOS inhibitor L-NAME suppressed the loss of DA neurons in aged flies co-expressing FoxO and DG2. These results strongly suggest that the NO-FoxO axis contributes to DA neurodegeneration in LRRK2-linked PD.

Feeding-Related Traits Are Affected by Dosage of theforagingGene inDrosophila melanogaster

“…Without knowing the precise tissues or cells where foraging expression is required to alter its associated behaviors, it is difficult to speculate on the nature of the gene networks in which it resides. That being said, previous genetic evidence has suggested possible interaction with insulin-signaling and foxo-signaling (Kent et al 2009;Kanao et al 2012).…”

<i>Pink1 </i>and <i>parkin</i> demonstrate multifaceted roles when co-expressed with <i>Foxo</i>

“…The Foxo-induced phenotype of developmental defects in the Drosophila eye is likely due to the transcription of pro-apoptotic gene targets. Drosophila studies link phosphorylation of Foxo to neurodegeneration, and have identified the pro-apoptotic Hid gene as one responsible target, where overexpression of Hid causes dramatic eye degeneration [29,30,37]. In contrast, Foxo has also been shown to prevent mitochondrial dysfunction and neurodegeneration, and is proposed to function downstream of Pink1 [26].…”

“…In addition to genes that promote stress resistance, under conditions of oxidative stress or starvation, Foxo transcription factors may also target genes that promote cell cycle arrest and apoptosis [27,28]. Overexprssion of Foxo has been linked to neurotoxicity [29,30] and overexpression in the developing Drosophila eye results in a characteristic phenotype with reductions in cell number and area [31]. Genetic expression studies using the fly eye have been enormously successful in the study of neurodegeneration.…”

Why is nitric oxide important for our brain?

“…The fact that, among the myriad processes and factors involved, oxidative stress and NO have a key role in neurodegenerative processes suggests that they could be potential targets of novel therapeutic strategies (Foley and Riederer, 2000;Džoljić et al, 2005) New results, more precisely, show signaling pathways underpinning synapse loss in PD. Paracrine/retrograde NO action activates the soluble guanylyl cyclase/PKG pathway and RhoA/Rho kinase (ROCK) signaling resulting in loss of synapses (Kanao et al, 2012). In addition, NO, through the cGMP pathway, regulates the activity of transcriptional factor FoxO and alters dopaminergic neuron survival, potentiating its neurotoxicity (Kanao et al, 2012).…”

“…Paracrine/retrograde NO action activates the soluble guanylyl cyclase/PKG pathway and RhoA/Rho kinase (ROCK) signaling resulting in loss of synapses (Kanao et al, 2012). In addition, NO, through the cGMP pathway, regulates the activity of transcriptional factor FoxO and alters dopaminergic neuron survival, potentiating its neurotoxicity (Kanao et al, 2012). Moehle et al (2012) revealed the role of iNOS-derived NO in PD neurodegeneration, showing effects of microglial secretion of iNOS-derived NO on leucine-rich repeat kinase 2 (Moehle et al, 2012).…”