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Microglial NLRP3 Inflammasome Induces Excitatory Synaptic Loss Through IL-1β-Enriched Microvesicle Release: Implications for Sepsis-Associated Encephalopathy

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Abstract

Acute cerebral dysfunction is a pathological state common in severe infections and a pivotal determinant of long-term cognitive outcomes. Current evidence indicates that a loss of synaptic contacts orchestrated by microglial activation is central in sepsis-associated encephalopathy. However, the upstream signals that lead to microglial activation and the mechanism involved in microglial-mediated synapse dysfunction in sepsis are poorly understood. This study investigated the involvement of the NLRP3 inflammasome in microglial activation and synaptic loss related to sepsis. We demonstrated that septic insult using the cecal ligation and puncture (CLP) model induced the expression of NLRP3 inflammasome components in the brain, such as NOD-, LRR-, and pyrin domain–containing protein 3 (NLRP3), apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), caspase-1, and IL-1β. Immunostaining techniques revealed increased expression of the NLRP3 inflammasome in microglial cells in the hippocampus of septic mice. Meanwhile, an in vitro model of primary microglia stimulated with LPS exhibited an increase in mitochondrial reactive oxygen species (ROS) production, NLRP3 complex recruitment, and IL-1β release. Pharmacological inhibition of NLRP3, caspase-1, and mitochondrial ROS all decreased IL-1β secretion by microglial cells. Furthermore, we found that microglial NLRP3 activation is the main pathway for IL-1β-enriched microvesicle (MV) release, which is caspase-1-dependent. MV released from LPS-activated microglia induced neurite suppression and excitatory synaptic loss in neuronal cultures. Moreover, microglial caspase-1 inhibition prevented neurite damage and attenuated synaptic deficits induced by the activated microglial MV. These results suggest that microglial NLRP3 inflammasome activation is the mechanism of IL-1β-enriched MV release and potentially synaptic impairment in sepsis.

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Data Availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Abbreviations

CLP:

Cecal ligation and puncture

NLRP3:

NOD-, LRR-, and pyrin domain–containing 3

ASC:

Apoptosis-associated speck-like protein containing a CARD

IL-1β:

Interleukin-1β

Iba1:

Ionized calcium-binding adaptor molecule 1

ROS:

Reactive oxygen species

LPS:

Lipopolysaccharide

MV:

Microvesicle

IL-18:

Interleukin-18

ATP:

Adenosine triphosphate

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Acknowledgements

We thank Edson Fernandes Assis and Rose Branco Rodrigues for their technical assistance.

Funding

This work was supported by the National Institute of Science and Technology (CNPq), the Rio de Janeiro State Research Supporting Foundation (FAPERJ), and the Coordination for the Improvement of Higher Education Personnel (CAPES).

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Authors and Affiliations

  1. Laboratory of Immunopharmacology, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Fiocruz, Rio de Janeiro, RJ, Brazil

    Carolina A. Moraes, Eugenio D. Hottz, Joana C. d’Avila, Tatiana Maron-Gutierrez & Patricia Torres Bozza

  2. Laboratory of Immunothrombosis, Department of Biochemistry, Federal University of Juiz de Fora (UFJF), Juiz de Fora, MG, Brazil

    Eugenio D. Hottz

  3. Laboratory of Molecular and Cellular Physiology, Carlos Chagas Filho Biophysics Institute, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil

    Débora Dos Santos Ornellas

  4. Laboratory of Structural Biology, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Fiocruz, Rio de Janeiro, RJ, Brazil

    Daniel Adesse & Helene Santos Barbosa

  5. Laboratory of Inflammation, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Fiocruz, Rio de Janeiro, RJ, Brazil

    Carolina T. de Azevedo

  6. Laboratory of Pre-Clinical Research, Iguaçu University, Rio de Janeiro, RJ, Brazil

    Joana C. d’Avila

  7. Evandro Chagas National Institute of Infectious Diseases, Oswaldo Cruz Foundation, Fiocruz, Rio de Janeiro, RJ, Brazil

    Camila Zaverucha-do-Valle & Fernando Augusto Bozza

  8. D’Or Institute for Research and Education, Rio de Janeiro, RJ, Brazil

    Fernando Augusto Bozza

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  1. Carolina A. Moraes
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Contributions

C.A.M., E.D.H., D.D.S.O., D.A., C.T.A., T.M.G., H.S.B., P.T.B., and F.A.B. designed the research; C.A.M., E.D.H., D.D.S.O., D.A., C.T.A., T.M.G, C.Z.V., and J.C.D. performed the experiments; C.A.M., E.D.H., D.D.S.O., D.A., C.T.A., H.S.B., C.Z.V., J.C.D., P.T.B., and F.A.B. analyzed the data; C.A.M. and F.A.B. wrote the manuscript.

Corresponding author

Correspondence to Fernando Augusto Bozza.

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Ethics Approval

The Animal Welfare Committee of the Oswaldo Cruz Foundation (CEUA/FIOCRUZ) approved and covered (015/2015) the experiments in this study. The procedures described in this study were according to the local guidelines and guidelines published in the National Institutes of Health Guide for the Care and Use of Laboratory Animals. The study is reported in accordance with the ARRIVE guidelines for reporting experiments involving animals [42].

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Supplemental Fig. 1

DMSO does not affect microglial cells. ELISA for IL-1β in the culture supernatant of unstimulated microglial cells (MCM), microglial cells stimulated with LPS (MCM-LPS), or microglial cells incubated with the diluent of the drugs (dimethyl sulfoxide, DMSO) used in the in vitro experiments (MCM+DMSO; MCM-LPS+DMSO). DMSO (0.4%) did not affect microglial cells (MCM vs. MCM-DMSO and MCM-LPS vs. MCM-LPS+DMSO). t-test. N=4 per condition. (PNG 138 kb)

High resolution image (TIF 2906 kb)

Supplemental Fig. 2

Microglial-derived MV are increased by LPS and LPS+ATP in culture. (a) Annexin V fluorescence intensity histogram in microglia microvesicles from unstimulated control culture supernatant (MVM; gray), cultures activated with 1 μg/mL LPS for 24 hours (MVM-LPS; red), or cultures treated with 1 μg/mL LPS for 5 hours followed by 10 μM ATP for 50 minutes (MVM-LPS+ATP; black). (b) Quantitative flow cytometric analysis of annexin V from MVM, MVM-LPS, and MVM-LPS+ATP. *p<0.05; one-way ANOVA with Tukey’s for multiple comparisons. N=4 per condition. (PNG 95 kb)

High resolution image (TIF 128 kb)

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Moraes, C.A., Hottz, E.D., Dos Santos Ornellas, D. et al. Microglial NLRP3 Inflammasome Induces Excitatory Synaptic Loss Through IL-1β-Enriched Microvesicle Release: Implications for Sepsis-Associated Encephalopathy. Mol Neurobiol 60, 481–494 (2023). https://doi.org/10.1007/s12035-022-03067-z

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