beta-Amyloid Clustering around ASC Fibrils Boosts Its Toxicity in Microglia

Alzheimer\u27s disease is the world\u27s most common neurodegenerative disorder. It is associated with neuroinflammation involving activation of microglia by beta-amyloid (Abeta) deposits. Based on previous studies showing apoptosis-associated speck-like protein containing a CARD (ASC) binding and cross-seeding extracellular Abeta, we investigate the propagation of ASC between primary microglia and the effects of ASC-Abeta composites on microglial inflammasomes and function. Indeed, ASC released by a pyroptotic cell can be functionally built into the neighboring microglia NOD-like receptor protein (NLRP3) inflammasome. Compared with protein-only application, exposure to ASC-Abeta composites amplifies the proinflammatory response, resulting in pyroptotic cell death, setting free functional ASC and inducing a feedforward stimulating vicious cycle. Clustering around ASC fibrils also compromises clearance of Abeta by microglia. Together, these data enable a closer look at the turning point from acute to chronic Abeta-related neuroinflammation through formation of ASC-Abeta composites

Alternative splicing regulates stochastic NLRP3 activity

Leucine-rich repeat (LRR) domains are evolutionarily conserved in proteins that function in development and immunity. Here we report strict exonic modularity of LRR domains of several human gene families, which is a precondition for alternative splicing (AS). We provide evidence for AS of LRR domain within several Nod-like receptors, most prominently the inflammasome sensor NLRP3. Human NLRP3, but not mouse NLRP3, is expressed as two major isoforms, the full-length variant and a variant lacking exon 5. Moreover, NLRP3 AS is stochastically regulated, with NLRP3. exon 5 lacking the interaction surface for NEK7 and hence loss of activity. Our data thus reveals unexpected regulatory roles of AS through differential utilization of LRRs modules in vertebrate innate immunity

Structure of the NLRP3 decamer bound to the cytokine release inhibitor CRID3

NLRP3 is an intracellular sensor protein that when activated by a broad spectrum of exogenous and endogenous stimuli leads to inflammasome formation and pyroptosis(1,2). The conformational states of NLRP3 and the way antagonistic small molecules act at the molecular level remain poorly understood(2,3). Here we report the cryo-electron microscopy structures of full-length human NLRP3 in its native form and complexed with the inhibitor CRID3 (also named MCC950)(4). Inactive, ADP-bound NLRP3 is a decamer composed of homodimers of intertwined leucine-rich repeat (LRR) domains that assemble back-to-back as pentamers. The NACHT domain is located at the apical axis of this spherical structure. One pyrin domain dimer is in addition formed inside the LRR cage. Molecular contacts between the concave sites of two opposing LRR domains are mediated by an acidic loop that extends from an LRR transition segment. Binding of CRID3 considerably stabilizes the NACHT and LRR domains relative to each other. CRID3 binds into a cleft, connecting four subdomains of the NACHT with the transition LRR. Its central sulfonylurea group interacts with the Walker A motif of the NLRP3 nucleotide-binding domain and is sandwiched between two arginine residues, which explains the specificity of NLRP3 for this chemical entity. With the determination of the binding site of this key therapeutic agent, specific targeting of NLRP3 for the treatment of autoinflammatory and autoimmune diseases and rational drug optimization is within reach

Alternative splicing regulates stochastic NLRP3 activity

Leucine-rich repeat (LRR) domains are evolutionarily conserved in proteins that function in development and immunity. Here we report strict exonic modularity of LRR domains of several human gene families, which is a precondition for alternative splicing (AS). We provide evidence for AS of LRR domain within several Nod-like receptors, most prominently the inflammasome sensor NLRP3. Human NLRP3, but not mouse NLRP3, is expressed as two major isoforms, the full-length variant and a variant lacking exon 5. Moreover, NLRP3 AS is stochastically regulated, with NLRP3 exon 5 lacking the interaction surface for NEK7 and hence loss of activity. Our data thus reveals unexpected regulatory roles of AS through differential utilization of LRRs modules in vertebrate innate immunity

Alternative splicing regulates stochastic NLRP3 activity.

Leucine-rich repeat (LRR) domains are evolutionarily conserved in proteins that function in development and immunity. Here we report strict exonic modularity of LRR domains of several human gene families, which is a precondition for alternative splicing (AS). We provide evidence for AS of LRR domain within several Nod-like receptors, most prominently the inflammasome sensor NLRP3. Human NLRP3, but not mouse NLRP3, is expressed as two major isoforms, the full-length variant and a variant lacking exon 5. Moreover, NLRP3 AS is stochastically regulated, with NLRP3 ∆ exon 5 lacking the interaction surface for NEK7 and hence loss of activity. Our data thus reveals unexpected regulatory roles of AS through differential utilization of LRRs modules in vertebrate innate immunity