Fernandez-Arjona, Maria Del MarGrondona, Jesus MFernandez-Llebrez, PedroLopez-Avalos, Maria Dolores2023-02-082023-02-082019-12-02Fernández-Arjona MDM, Grondona JM, Fernández-Llebrez P, López-Ávalos MD. Microglial activation by microbial neuraminidase through TLR2 and TLR4 receptors. J Neuroinflammation. 2019 Dec 2;16(1):245.http://hdl.handle.net/10668/14780Neuraminidase (NA) is a sialidase present, among various locations, in the envelope/membrane of some bacteria/viruses (e.g., influenza virus), and is involved in infectiveness and/or dispersion. The administration of NA within the brain lateral ventricle represents a model of acute sterile inflammation. The relevance of the Toll-like receptors TLR2 and TLR4 (particularly those in microglial cells) in such process was investigated. Mouse strains deficient in either TLR2 (TLR2-/-) or TLR4 (TLR4-/-) were used. NA was injected in the lateral ventricle, and the inflammatory reaction was studied by immunohistochemistry (IBA1 and IL-1β) and qPCR (cytokine response). Also, microglia was isolated from those strains and in vitro stimulated with NA, or with TLR2/TLR4 agonists as positive controls (P3C and LPS respectively). The relevance of the sialidase activity of NA was investigated by stimulating microglia with heat-inactivated NA, or with native NA in the presence of sialidase inhibitors (oseltamivir phosphate and N-acetyl-2,3-dehydro-2-deoxyneuraminic acid). In septofimbria and hypothalamus, IBA1-positive and IL-1β-positive cell counts increased after NA injection in wild type (WT) mice. In TLR4-/- mice, such increases were largely abolished, while were only slightly diminished in TLR2-/- mice. Similarly, the NA-induced expression of IL-1β, TNFα, and IL-6 was completely blocked in TLR4-/- mice, and only partially reduced in TLR2-/- mice. In isolated cultured microglia, NA induced a cytokine response (IL-1β, TNFα, and IL-6) in WT microglia, but was unable to do so in TLR4-/- microglia; TLR2 deficiency partially affected the NA-induced microglial response. When WT microglia was exposed in vitro to heat-inactivated NA or to native NA along with sialidase inhibitors, the NA-induced microglia activation was almost completely abrogated. NA is able to directly activate microglial cells, and it does so mostly acting through the TLR4 receptor, while TLR2 has a secondary role. Accordingly, the inflammatory reaction induced by NA in vivo is partially dependent on TLR2, while TLR4 plays a crucial role. Also, the sialidase activity of NA is critical for microglial activation. These results highlight the relevance of microbial NA in the neuroinflammation provoked by NA-bearing pathogens and the possibility of targeting its sialidase activity to ameliorate its impact.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/MicrogliaN-acetyl-2,3-dehydro-2-deoxyneuraminic acidNeuraminidaseNeuroinflammationOseltamivirTLR2TLR4AnimalsCells, CulturedEnzyme InhibitorsInjections, IntraventricularMiceMice, Inbred C57BLMice, KnockoutMicrogliaNeuraminidaseToll-Like Receptor 2Toll-Like Receptor 4research article31791382open accessNeuraminidasaReceptor Toll-like 4Receptor Toll-like 2MicroglíaNeuroinflamaciónCitoquinasInhibidores de sialidasaModelos de ratones knockout10.1186/s12974-019-1643-91742-2094PMC6889729https://doi.org/10.1186/s12974-019-1643-9https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6889729/pdf