Gedunin Inhibits Oligomeric Aß1-42-Induced Microglia Activation Via Modulation of Nrf2-NF-κB Signaling.

Alzheimer's disease (AD) is a neurodegenerative disorder and the leading cause of dementia in aged populations worldwide. The deposition of toxic protein aggregates such as amyloid beta (Aß) is a hallmark of AD, and there is growing awareness that a key driver of AD pathogenesis is the neuroinflammatory cascade triggered and sustained by these proteins. Consequently, interventions that suppress prolonged neuroinflammation represent viable therapeutic approaches for AD. In this context, we tested the natural product gedunin which is an anti-inflammatory molecule, found in the seeds of the neem tree (Azadirachta indica), whose mechanism of action remains to be fully elucidated. Using a mouse microglia cell line (IMG), we show that gedunin suppresses neuroinflammation arising from Aß1-42 oligomer exposure. Our results demonstrate that gedunin suppresses Aß1-42-induced NF-κB activation and its targets, including nitric oxide (NO) and IL-1ß, known proinflammatory molecules. Further, we show that gedunin inhibits neuroinflammation by activating nuclear factor 2 erythroid-related factor 2 (Nrf2) and its downstream targets γ-glutamylcysteine synthetase, heme oxygenase 1, and NADPH quinone dehydrogenase 1, which are involved in quenching reactive oxygen and nitrogen species (NO) generated by NF-κB activation. Nrf2 activation appears essential for the anti-inflammatory effect because when silenced, the proinflammatory effects of Aß1-42 are enhanced and the protective effect of gedunin against NO production is reduced. Additionally, using human neuronal cells (SH-SY5Y), we show that gedunin prevents neurotoxicity secondary to Aß-induced microglial activation. In conclusion, our findings highlight a potential therapeutic role of gedunin in neurodegenerative diseases.

Ontogenetic and Experience-Dependent Changes in Defensive Behavior in Captive-Bred Hawaiian Bobtail Squid, Euprymna scolopes.

Cephalopod molluscs are known for their extensive behavioral repertoire and their impressive learning abilities. Their primary defensive behaviors, such as camouflage, have received detailed study, but knowledge is limited to intensive study of relatively few species. A considerable challenge facing cephalopod research is the need to establish new models that can be captive bred, are tractable for range of different experimental procedures, and that will address broad questions in biological research. The Hawaiian Bobtail Squid (Euprymna scolopes) is a small, tropical cephalopod that has a long history of research in the field of microbial symbiosis, but offers great promise as a novel behavioral and neurobiological model. It can be bred in the laboratory through multiple generations, one of the few species of cephalopod that can meet this requirement (which is incorporated in regulations such as EU directive 2010/63/EU). Additionally, laboratory culture makes E. scolopes an ideal model for studying ontogeny- and experience-dependent behaviors. In this study, we show that captive bred juvenile and adult E. scolopes produce robust, repeatable defensive behaviors when placed in an exposed environment and presented with a visual threat. Further, adult and juvenile squid employ different innate defensive behaviors when presented with a size-matched model predator. When a 10-min training procedure was repeated over three consecutive days, defensive behaviors habituated in juvenile squid for at least 5 days after training, but memory did not appear to persist for 14 days. In contrast, adult squid did not show any evidence of long-term habituation memory. Thus we conclude that this species produces a range of quantifiable, modifiable behaviors even in a laboratory environment where ecologically-relevant, complex behavioral sequences may not reliably occur. We suggest that the lack of long-term memory in adult squid may be related to their less escalated initial response to the mimic, and thus indicates less motivation to retain memory and not necessary inability to form memory. This is the first demonstration of age-related differences in defensive behaviors in Euprymna, and the first record of habituation in this experimentally tractable genus of squid.