The TLR-chaperone CNPY3 is a critical regulator of NLRP3-Inflammasome activation

Toll like receptors (TLRs) mediate the recognition of microbial and endogenous insults to orchestrate the inflammatory response. TLRs localize to the plasma membrane or endomembranes, depending on the member, and rely critically on endoplasmic reticulum-resident chaperones to mature and reach their subcellular destinations. The chaperone canopy FGF signaling regulator 3 (CNPY3) is necessary for the proper trafficking of multiple TLRs including TLR1/2/4/5/9 but not TLR3. However, the exact role of CNPY3 in inflammatory signalling downstream of TLRs has not been studied in detail. Consistent with the reported client specificity, we report here that functional loss of CNPY3 in engineered macrophages impairs downstream signalling by TLR2 but not TLR3. Unexpectedly, CNPY3-deficient macrophages show reduced interleukin-1β (IL-1ß) and IL-18 processing and production independent of the challenged upstream TLR species, demonstrating a separate, specific role for CNPY3 in inflammasome activation. Mechanistically, we document that CNPY3 regulates caspase-1 localization to the apoptosis speck and auto-activation of caspase-1. Importantly, we were able to recapitulate these findings in macrophages from an early infantile epileptic encephalopathy (EIEE) patient with a novel CNPY3 loss-of-function variant. Summarizing, our findings reveal a hitherto unknown, TLR-independent role of CNPY3 in inflammasome activation, highlighting a more complex and dedicated role of CNPY3 to the inflammatory response than anticipated. This article is protected by copyright. All rights reserved.

Biallelic Variants in CNPY3, Encoding an Endoplasmic Reticulum Chaperone, Cause Early-Onset Epileptic Encephalopathy

Early-onset epileptic encephalopathies, including West syndrome (WS), are a group of neurological disorders characterized by developmental impairments and intractable seizures from early infancy. We have now identified biallelic CNPY3 variants in three individuals with WS; these include compound-heterozygous missense and frameshift variants in a family with two affected siblings (individuals 1 and 2) and a homozygous splicing variant in a consanguineous family (individual 3). All three individuals showed hippocampal malrotation. In individuals 1 and 2, electroencephalography (EEG) revealed characteristic fast waves and diffuse sharp- and slow-wave complexes. The fast waves were clinically associated with seizures. CNPY3 encodes a co-chaperone in the endoplasmic reticulum and regulates the subcellular distribution and responses of multiple Toll-like receptors. The amount of CNPY3 in lymphoblastoid cells derived from individuals 1 and 2 was severely lower than that in control cells. Cnpy3-knockout mice exhibited spastic or dystonic features under resting conditions and hyperactivity and anxiolytic behavior during the open field test. Also, their resting EEG showed enhanced activity in the fast beta frequency band (20-35 Hz), which could mimic the fast waves in individuals 1 and 2. These data suggest that CNPY3 and Cnpy3 perform essential roles in brain function in addition to known Toll-like receptor-dependent immune responses.

Unique features of chicken Toll-like receptors

Toll-like receptors (TLRs) are a major class of innate immune pattern recognition receptors that have a key role in immune homeostasis and the defense against infections. The research explosion that followed the discovery of TLRs more than a decade ago has boosted fundamental knowledge on the function of the immune system and the resistance against disease, providing a rational for clinical modulation of the immune response. In addition, the conserved nature of the ancient TLR system throughout the animal kingdom has enabled a comparative biology approach to understand the evolution, structural architecture, and function of TLRs. In the present review we focus on TLR biology in the avian species, and, especially, on the unique functional properties of the chicken TLR repertoire.