Drosophila Nrf2/Keap1 Mediated Redox Signaling Supports Synaptic Function and Longevity and Impacts on Circadian Activity

Abstract

Many neurodegenerative conditions and age-related neuropathologies are associated with increased levels of reactive oxygen species (ROS). The cap “n” collar (CncC) family of transcription factors is one of the major cellular system that fights oxidative insults, becoming activated in response to oxidative stress. This transcription factor signaling is conserved from metazoans to human and has a major developmental and disease-associated relevance. An important mammalian member of the CncC family is nuclear factor erythroid 2-related factor 2 (Nrf2) which has been studied in numerous cellular systems and represents an important target for drug discovery in different diseases. CncC is negatively regulated by Kelch-like ECH associated protein 1 (Keap1) and this interaction provides the basis for a homeostatic control of cellular antioxidant defense. We have utilized the Drosophila model system to investigate the roles of CncC signaling on longevity, neuronal function and circadian rhythm. Furthermore, we assessed the effects of CncC function on larvae and adult flies following exposure to stress. Our data reveal that constitutive overexpression of CncC modifies synaptic mechanisms that positively impact on neuronal function, and suppression of CncC inhibitor, Keap1, shows beneficial phenotypes on synaptic function and longevity. Moreover, supplementation of antioxidants mimics the effects of augmenting CncC signaling. Under stress conditions, lack of CncC signaling worsens survival rates and neuronal function whilst silencing Keap1 protects against stress-induced neuronal decline. Interestingly, overexpression and RNAi-mediated downregulation of CncC have differential effects on sleep patterns possibly via interactions with redox-sensitive circadian cycles. Thus, our data illustrate the important regulatory potential of CncC signaling in neuronal function and synaptic release affecting multiple aspects within the nervous system.

A Crosstalk between the Biorhythms and Gatekeepers of Longevity: Dual Role of Glycogen Synthase Kinase-3

“…It has been revealed recently that constitutive overexpression of CncC proteins in Drosophila positively influences neuronal functions by modifying synaptic mechanisms. Suppression of Keap1, a CncC inhibitor, promotes synaptic function and increases the lifespan [ 38 ]. The results obtained by Hansen et al indicate that the ratio between glutathione reduced and oxidized forms (GSH/GSSG) controls Nrf2 in the cytoplasm, but does not affect Nrf2 binding to AREs in the nucleus [ 39 ].…”

Modulated Expression of the Protein Kinase GSK3 in Motor and Dopaminergic Neurons Increases Female Lifespan in Drosophila melanogaster

“…In particular, NRF2 mediates neuronal damage by modulating the expression of antioxidant enzymes (Tavakkoli et al, 2019). The activation of NRF2 due to suppression of the NRF2 repressor Keap1 extended the lifespan of D. melanogaster (Sykiotis and Bohmann, 2008;Spiers et al, 2019), and both Keap1 suppression and the constitutive overexpression of NRF2 positively modified neuronal function (Spiers et al, 2019). Another upstream regulator of NRF2 is GSK3, which also negatively controls NRF2 activity through phosphorylation and nuclear exclusion (Salazar et al, 2006;Jain and Jaiswal, 2007;Rada et al, 2011).…”

Evolutionary Conservation of Transcription Factors Affecting Longevity

“…Highlighting their importance, similar processes can be activated by other longevity-promoting TFs. These include nuclear factor erythroid 2-related factor 2(NRF2) orthologues, which are known to be involved in xenobiotic detoxification [35][36][37][38], as well as the endoplasmic reticulum unfolded protein response mediator, X-box binding protein 1 (XBP1) [39,40] . This consistent presence of pathways that limit or repair molecular damage in transcriptional programmes that promote longevity has reinforced the view that ageing results from accumulation of age-related molecular damage.…”

“…ELT-2 [55,106] ELT-3/5/6 [107,108] Srp [80] GATAe [80] ETS LIN-1 [33] ETS-4 [43] Aop [34], Pnt [33], Eip74EF [33], Ets21C [33], Ets97D [33] Nrf2 SKN-1 [109] CncC [35,36] NRF2 [110] CREB CRH-1 [111] CREB [112] Myc Myc-Mondo-like complexes [88] dMyc [83,84] MYC [44] Maf1…”