Structural and molecular basis of choline uptake into the brain by FLVCR2.

Choline is an essential nutrient that the human body needs in vast quantities for cell membrane synthesis, epigenetic modification and neurotransmission. The brain has a particularly high demand for choline, but how it enters the brain remains unknown1-3. The major facilitator superfamily transporter FLVCR1 (also known as MFSD7B or SLC49A1) was recently determined to be a choline transporter but is not highly expressed at the blood-brain barrier, whereas the related protein FLVCR2 (also known as MFSD7C or SLC49A2) is expressed in endothelial cells at the blood-brain barrier4-7. Previous studies have shown that mutations in human Flvcr2 cause cerebral vascular abnormalities, hydrocephalus and embryonic lethality, but the physiological role of FLVCR2 is unknown4,5. Here we demonstrate both in vivo and in vitro that FLVCR2 is a BBB choline transporter and is responsible for the majority of choline uptake into the brain. We also determine the structures of choline-bound FLVCR2 in both inward-facing and outward-facing states using cryo-electron microscopy. These results reveal how the brain obtains choline and provide molecular-level insights into how FLVCR2 binds choline in an aromatic cage and mediates its uptake. Our work could provide a novel framework for the targeted delivery of therapeutic agents into the brain.

Radial glia promote microglial development through integrin αVß8 -TGFß1 signaling.

Microglia diversity emerges from interactions between intrinsic genetic programs and environment-derived signals, but how these processes unfold and interact in the developing brain remains unclear. Here, we show that radial glia-expressed integrin beta 8 (ITGB8) expressed in radial glia progenitors activates microglia-expressed TGFß1, permitting microglial development. Domain-restricted deletion of Itgb8 in these progenitors establishes complementary regions with developmentally arrested "dysmature" microglia that persist into adulthood. In the absence of autocrine TGFß1 signaling, we find that microglia adopt a similar dysmature phenotype, leading to neuromotor symptoms almost identical to Itgb8 mutant mice. In contrast, microglia lacking the TGFß signal transducers Smad2 and Smad3 have a less polarized dysmature phenotype and correspondingly less severe neuromotor dysfunction. Finally, we show that non-canonical (Smad-independent) signaling partially suppresses disease and development associated gene expression, providing compelling evidence for the adoption of microglial developmental signaling pathways in the context of injury or disease.

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.