The importance of gut microbiota in human health and pathophysiology is undisputable. Despite the abundance of metagenomics data, the functional dynamics of gut microbiota in human health and disease remain elusive. Urolithin A (UroA), a major microbial metabolite derived from polyphenolics of berries and pomegranate fruits displays anti-inflammatory, anti-oxidative, and anti-ageing activities. Here, we show that UroA and its potent synthetic analogue (UAS03) significantly enhance gut barrier function and inhibit unwarranted inflammation. We demonstrate that UroA and UAS03 exert their barrier functions through activation of aryl hydrocarbon receptor (AhR)- nuclear factor erythroid 2–related factor 2 (Nrf2)-dependent pathways to upregulate epithelial tight junction proteins. Importantly, treatment with these compounds attenuated colitis in pre-clinical models by remedying barrier dysfunction in addition to anti-inflammatory activities. Cumulatively, the results highlight how microbial metabolites provide two-pronged beneficial activities at gut epithelium by enhancing barrier functions and reducing inflammation to protect from colonic diseases.

Gephyrin is a bi-functional modular protein involved in molybdenum cofactor biosynthesis and in postsynaptic clustering of inhibitory glycine receptors (GlyRs). Here, we show that full-length gephyrin is a trimer and that its proteolysis in vitro causes the spontaneous dimerization of its C-terminal region (gephyrin-E), which binds a GlyR b-subunit-derived peptide with high and low affinity. The crystal structure of the tetra-domain gephyrin-E in complex with the b-peptide bound to domain IV indicates how membrane-embedded GlyRs may interact with subsynaptic gephyrin. In vitro, trimeric full-length gephyrin forms a network upon lowering the pH, and this process can be reversed to produce stable full-length dimeric gephyrin. Our data suggest a mechanism by which induced conformational transitions of trimeric gephyrin may generate a reversible postsynaptic scaffold for GlyR recruitment, which allows for dynamic receptor movement in and out of postsynaptic GlyR clusters, and thus for synaptic plasticity.

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Gephyrin is a bifunctional modular protein that, in neurons, clusters glycine receptors and ␥-aminobutyric acid, type A receptors in the postsynaptic membrane of inhibitory synapses. By x-ray crystallography and cross-linking, the N-terminal G-domain of gephyrin has been shown to form trimers and the C-terminal E-domain dimers, respectively. Gephyrin therefore has been proposed to form a hexagonal submembranous lattice onto which inhibitory receptors are anchored. Here, crystal structure-based substitutions at oligomerization interfaces revealed that both G-domain trimerization and E-domain dimerization are essential for the formation of higher order gephyrin oligomers and postsynaptic gephyrin clusters. Insertion of the alternatively spliced C5 cassette into the G-domain inhibited clustering by interfering with trimerization, and mutation of the glycine receptor ␤-subunit binding region prevented the localization of the clusters at synaptic sites. Together our findings show that domain interactions mediate gephyrin scaffold formation.The precise localization and a high density of neurotransmitter receptors at postsynaptic sites is a prerequisite for proper synaptic transmission. During the development of inhibitory synapses, the peripheral membrane protein gephyrin accumulates beneath the postsynaptic plasma membrane and plays a key role in recruiting inhibitory receptors under the contacting nerve terminals (1, 2). Both attenuation of gephyrin expression by antisense oligonucleotides and targeted disruption of the gephyrin gene prevent the synaptic clustering of glycine receptors (GlyRs) 4 (3, 4) and ␥2-subunit-containing GABA A R subtypes (5-7). Although a direct interaction with GABA A Rs has not yet been demonstrated, gephyrin binding to the large intracellular loop of GlyR␤ has been shown to be of high affinity (8, 9). Additional interaction partners of gephyrin include proteins implicated in the regulation of the cytoskeleton, intracellular trafficking, and protein synthesis (1, 10). Gephyrin is a modular protein consisting of an N-terminal G-domain, a C-terminal E-domain, and a connecting linker region (1, 11). The G-and E-domains of gephyrin show significant homology to Escherichia coli, Drosophila, and plant proteins and are involved in the synthesis of a coenzyme of oxidoreductases, the molybdenum cofactor (4,11,12). This enzymatic activity explains the widespread expression of the gephyrin gene also in non-neuronal tissues (11). Crystallographic analysis of the isolated G-and E-domains indicates that they have trimeric and dimeric structures, respectively (13-16). Bacterially expressed full-length gephyrin forms trimers that can assemble into higher order structures (15). This oligomerization behavior of gephyrin and its subdomains is thought to provide the basis for the formation of submembranous hexagonal gephyrin scaffolds that cluster inhibitory neurotransmitter receptors at postsynaptic membrane specializations (1, 15) by reducing their lateral mobility (17,18).In this study, we investigated whe...

BackgroundPlethora of efforts fails to yield a single drug to reverse the pathogenesis of Parkinson's disease (PD) and related α-synucleopathies.MethodsUsing chemical biology, we identified a small molecule inhibitor of c-abl kinase, PD180970 that could potentially clear the toxic protein aggregates. Genetic, molecular, cell biological and immunological assays were performed to understand the mechanism of action. In vivo preclinical disease model of PD was used to assess its neuroprotection efficacy.FindingsIn this report, we show the ability of a small molecule inhibitor of tyrosine kinases, PD180970, to induce autophagy (cell lines and mice midbrain) in an mTOR-independent manner and ameliorate the α-synuclein mediated toxicity. PD180970 also exerts anti-neuroinflammatory potential by inhibiting the release of proinflammatory cytokines such as IL-6 (interleukin-6) and MCP-1 (monocyte chemoattractant protein-1) through reduction of TLR-4 (toll like receptor-4) mediated NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation. In vivo studies show that PD180970 is neuroprotective by degrading the toxic protein oligomers through induction of autophagy and subsiding the microglial activation.InterpretationThese protective mechanisms ensure the negation of Parkinson's disease related motor impairments.FundThis work was supported by Wellcome Trust/DBT India Alliance Intermediate Fellowship (500159-Z-09-Z), DST-SERB grant (EMR/2015/001946), DBT (BT/INF/22/SP27679/2018) and JNCASR intramural funds to RM, and SERB, DST (SR/SO/HS/0121/2012) to PAA, and DST-SERB (SB/YS/LS-215/2013) to JPC and BIRAC funding to ETA C-CAMP.