Memories are assumed to be formed by sets of synapses changing their structural or functional performance. The efficacy of forming new memories declines with advancing age, but the synaptic changes underlying age-induced memory impairment remain poorly understood. Recently, we found spermidine feeding to specifically suppress age-dependent impairments in forming olfactory memories, providing a mean to search for synaptic changes involved in age-dependent memory impairment. Here, we show that a specific synaptic compartment, the presynaptic active zone (AZ), increases the size of its ultrastructural elaboration and releases significantly more synaptic vesicles with advancing age. These age-induced AZ changes, however, were fully suppressed by spermidine feeding. A genetically enforced enlargement of AZ scaffolds (four gene-copies of BRP) impaired memory formation in young animals. Thus, in the Drosophila nervous system, aging AZs seem to steer towards the upper limit of their operational range, limiting synaptic plasticity and contributing to impairment of memory formation. Spermidine feeding suppresses age-dependent memory impairment by counteracting these age-dependent changes directly at the synapse.

Neuronal communication across synapses relies on neurotransmitter release from presynaptic active zones (AZs) followed by postsynaptic transmitter detection. Synaptic plasticity homeostatically maintains functionality during perturbations and enables memory formation. Postsynaptic plasticity targets neurotransmitter receptors, but presynaptic mechanisms regulating the neurotransmitter release apparatus remain largely enigmatic. By studying Drosophila neuromuscular junctions (NMJs) we show that AZs consist of nano-modular release sites and identify a molecular sequence that adds modules within minutes of inducing homeostatic plasticity. This requires cognate transport machinery and specific AZ-scaffolding proteins. Structural remodeling is not required for immediate potentiation of neurotransmitter release, but necessary to sustain potentiation over longer timescales. Finally, mutations in Unc13 disrupting homeostatic plasticity at the NMJ also impair short-term memory when central neurons are targeted, suggesting that both plasticity mechanisms utilize Unc13. Together, while immediate synaptic potentiation capitalizes on available material, it triggers the coincident incorporation of modular release sites to consolidate synaptic potentiation.

Highlights d Presynaptic active zone plasticity as a molecular signature of sleep loss d Core active zone scaffold protein BRP drives presynaptic upscaling d Global BRP promotes sleep and arousal threshold in a dosage-dependent manner d BRP-driven synaptic plasticity-encoded sleep need impairs learning via R2 neurons

Ageing constitutes the most important risk factor for all major chronic ailments, including malignant, cardiovascular and neurodegenerative diseases. However, behavioural and pharmacological interventions with feasible potential to promote health upon ageing remain rare. Here we report the identification of the flavonoid 4,4′-dimethoxychalcone (DMC) as a natural compound with anti-ageing properties. External DMC administration extends the lifespan of yeast, worms and flies, decelerates senescence of human cell cultures, and protects mice from prolonged myocardial ischaemia. Concomitantly, DMC induces autophagy, which is essential for its cytoprotective effects from yeast to mice. This pro-autophagic response induces a conserved systemic change in metabolism, operates independently of TORC1 signalling and depends on specific GATA transcription factors. Notably, we identify DMC in the plant Angelica keiskei koidzumi, to which longevity- and health-promoting effects are ascribed in Asian traditional medicine. In summary, we have identified and mechanistically characterised the conserved longevity-promoting effects of a natural anti-ageing drug.

Highlights d Spermidine supplementation age-protects Drosophila brain mitochondria d Brain hypusination levels decay with age but are boosted by spermidine supplementation d Mitochondrial functionality is defective after genetic attenuation of hypusination d Defective hypusination compromises spermidine effects on locomotion and memory

1 Synaptic transmission is mediated by neurotransmitter release at presynaptic active zones (AZs) 2 followed by postsynaptic neurotransmitter detection. Plastic changes in transmission maintain 3 functionality during perturbations and enable memory formation. Postsynaptic plasticity targets 4 neurotransmitter receptors, but presynaptic plasticity mechanisms directly regulating the 5 neurotransmitter release apparatus remain largely enigmatic. Here we describe that AZs consist 6 of nano-modular release site units and identify a molecular sequence adding more modules 7 within minutes of plasticity induction. This requires cognate transport machinery and a discrete 8 subset of AZ scaffold proteins. Structural remodeling is not required for the immediate 9 potentiation of neurotransmitter release, but rather necessary to sustain this potentiation over 10 longer timescales. Finally, mutations in Unc13 that disrupt homeostatic plasticity at the 11 neuromuscular junction also impair shot-term memory when central neurons are targeted, 12 suggesting that both forms of plasticity operate via Unc13. Together, while immediate synaptic 13 potentiation capitalizes on available material, it triggers the coincident incorporation of modular 14 release sites to consolidate stable synapse function. 16Neurotransmitter-laden synaptic vesicles (SVs) release their content at presynaptic active zones 17 (AZs) in response to Ca 2+ influx through voltage gated channels that respond to action-potential 18 (AP) depolarization. Neurotransmitter binding to postsynaptic receptors subsequently leads to 19 their activation for synaptic transmission. Modulation of transmission strength is called synaptic 20 plasticity. Long-term forms of synaptic plasticity are major cellular substrates for learning, 21 memory, and behavioral adaptation 1, 2 . Mechanisms of long-term synaptic plasticity modify the 22 structure and function of the presynaptic terminal and/or the postsynaptic apparatus. AZs are 23 covered by complex scaffolds composed of a conserved set of extended structural proteins. 24 ELKS/Bruchpilot (BRP), RIM, and RIM-binding protein (RBP) functionally organize the 25 coupling between Ca 2+ -channels and release machinery by immobilizing the critical (M)Unc13 26 release factors in clusters close to presynaptic Ca 2+ -channels and thus generate SV release sites, 27 at both mammalian and Drosophila synapses 3-12 . Whether and how discrete AZ release sites and 28 the associated release machinery are reorganized during plastic changes remains unknown. 29 One crucial form of presynaptic plasticity is the homeostatic control of neurotransmitter 30 release. This process, referred to as presynaptic homeostatic potentiation (PHP), is observed in 31 organisms ranging from invertebrates to humans, but is perhaps best illustrated at the larval 32 neuromuscular junction (NMJ) of Drosophila melanogaster 13, 14 . Here, PHP requires the core 33 AZ-scaffolding proteins RIM, RBP and Fife 15-17 and physiologically coincides with the 34 upregulat...

Macroautophagy is an evolutionarily conserved cellular maintenance program, meant to protect the brain from premature aging and neurodegeneration. How neuronal autophagy, usually loosing efficacy with age, intersects with neuronal processes mediating brain maintenance remains to be explored. Here, we show that impairing autophagy in the Drosophila learning center (mushroom body, MB) but not in other brain regions triggered changes normally restricted to aged brains: impaired associative olfactory memory as well as a brain-wide ultrastructural increase of presynaptic active zones (metaplasticity), a state non-compatible with memory formation. Mechanistically, decreasing autophagy within the MBs reduced expression of an NPY-family neuropeptide, and interfering with autocrine NPY signaling of the MBs provoked similar brain-wide metaplastic changes. Our results in an exemplary fashion show that autophagy-regulated signaling emanating from a higher brain integration center can execute high-level control over other brain regions to steer life-strategy decisions such as whether or not to form memories.

At presynaptic active zones, arrays of large conserved scaffold proteins mediate fast and temporally precise release of synaptic vesicles (SVs). SV release sites could be identified by clusters of Munc13, which allow SVs to dock in defined nanoscale relation to Ca2+ channels. We here show in Drosophila that RIM-binding protein (RIM-BP) connects release sites physically and functionally to the ELKS family Bruchpilot (BRP)-based scaffold engaged in SV recruitment. The RIM-BP N-terminal domain, while dispensable for SV release site organization, was crucial for proper nanoscale patterning of the BRP scaffold and needed for SV recruitment of SVs under strong stimulation. Structural analysis further showed that the RIM-BP fibronectin domains form a “hinge” in the protein center, while the C-terminal SH3 domain tandem binds RIM, Munc13, and Ca2+ channels release machinery collectively. RIM-BPs’ conserved domain architecture seemingly provides a relay to guide SVs from membrane far scaffolds into membrane close release sites.