Involvement of NLRP3 Inflammasome in Methamphetamine Augmentation of SARS-CoV-2 N-Protein-Induced Neuroinflammation in Rat Microglial Cells

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes an immune-mediated neurological syndrome, which persists long after infection. Mechanisms for SARS-CoV-2-associated neurological complications are multifactorial, with an increased risk of drug abuse such as methamphetamine (meth). SARS-CoV-2 infection and its viral proteins play pivotal roles in coronavirus disease 2019 (COVID-19)-associated neuroinflammation, which can lead to long COVID. We hypothesize that meth augments activation of the microglial NOD-, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome by the SARS-CoV-2 nucleocapsid (N) protein, resulting in neuroinflammation. To test this hypothesis, we investigated the effect of N-protein and meth on NLRP3 inflammasome activation in primary rat microglial cultures using enzyme-linked immunosorbent assay (ELISA), Reverse Transcription quantitative Polymerase Chain reaction (RT-qPCR), western blot (WB), and immunofluorescence assay (IFA). Our results showed that meth augmented N-protein-induced microglial activation, as evidenced by increased ionized calcium-binding adapter 1 (Iba-1) expression. The addition of meth to the microglial cultures treated with N-protein increased proinflammatory cytokine production. Meth augmentation of N-protein-induced neuroinflammation was further supported by increased inducible nitric oxide synthase (iNOS)-mediated nitric oxide (NO) production. The effects of meth on N-protein-associated inflammatory responses were significantly attenuated by MCC950, a specific NLRP3 inhibitor. Moreover, meth-associated NLRP3 activation was either blocked by the opioid sigma1-receptor (σ1-R) inhibitor BD1047 or by σ1R siRNA knockdown. Taken together, these results demonstrated that meth augmented SARS-CoV-2 N-protein-induced neuroinflammation via microglial σ1-R and the NLRP3 inflammasome, which may underlie the pathogenesis of neurological manifestations in COVID-19, such as long COVID with meth abuse. These results may also underscore the impact of drug abuse on long COVID and provide targets for the development of therapeutic strategies to control the neurological outcomes of long COVID.