Nod2 Promotes Sepsis-Induced Neuroinflammation by Increasing Brain Endoplasmic Reticulum Stress Mediated by Lacc1

Abstract

1. Abstract Background Neuroinflammation is a primary pathological process in most neurological diseases, however, the genetic factors that make individuals prone to its occurrence and development were poorly understood. In preliminary studies, it was indicated that in C57BL/6 mice with neuroinflammation induced by cecal ligation puncture (CLP), the expression level of nucleotide-binding oligomerization domain-containing protein 2 (NOD2) increased in the periventricular white matter (PWM). However, its role in regulating sepsis-induced neuroinflammation has not been assessed. This study aimed to determine the role of NOD2 in modulating sepsis-induced neuroinflammation and to elucidate its potential mechanisms. Methods mRNA and protein expression levels of NOD2 were measured in the PWM of C57BL/6 mice and the microglia. NOD2-/- mice were generated using the CRISPR/Cas9 technology, and the mouse model was established using CLP. Microglia were transfected with siRNA specific to NOD2 or laccase domain-containing protein 1 (LACC1) or treated with the endoplasmic reticulum stress (ER stress) inhibitor 4-phenylbutyrate (4-PBA) in vitro under muramyl dipeptide (MDP)-induced neuroinflammation. Immunofluorescence staining, Western blotting, and quantitative reverse transcription polymerase chain reaction were performed to evaluate neuroinflammation and ER stress. The ER structure was observed using transmission electron microscopy. Results NOD2 expression level was upregulated in the mouse model of sepsis-induced neuroinflammation established by CLP. The lack of NOD2 resulted in a protective effect against neuroinflammation, which was correlated with ER stress both in vitro and in vivo. LACC1 was identified as a notable mediator of ER stress, contributing to the exacerbation of neuroinflammation. Mechanistically, elevated NOD2 expression level promoted neuroinflammation by enhancing ER stress through LACC1. Notably, these effects were partially mitigated by LACC1 downregulation. Conclusions These findings highlight the pivotal role of NOD2 in driving sepsis-induced neuroinflammation via regulating ER stress mediated by LACC1, providing a new potential strategy for treating human neuroinflammation.

Note:
Funding declaration: This research was financially supported by the National Natural Science Foundation of China (Grant Nos. 82272189, 82072230, and 8240081322), Medical Scientific Research Foundation of Guangdong Province, China (Grant No. A2024436), Science and Technology Program of Guangzhou, China (Grant No. 2024A04J4577), and Project of Guangdong Provincial Medical Science and Technology Research Foundation (Grant No. B2024067).

Conflict of Interests: The authors declare that there is no conflict of interest.

Ethical Approval: All animal experiments were approved by the Ethics Committee of Guangdong Provincial People's Hospital (Approval No. KY2020-267-01).

Keywords: Nucleotide-binding oligomerization domain-containing protein 2 (NOD2), Sepsis-induced neuroinflammation, Endoplasmic reticulum stress, Laccase domain-containing protein 1 (LACC1), Microglia