Immunomodulatory effect of lithium treatment on in vitro model of neuroinflammation

Bipolar disorder (BD) is psychiatric disorder of not fully acknowledged pathophysiology. Studies show the involvement of innate-immune system activation and inflammation in BD course and treatment efficiency. Microglia are crucial players in the inflammatory response possibly responsible for BD innate-immune activity. Lithium is a mood stabilizer used in treatment for 75 years. Immunomodulation was previously described as one of the potential modes of its action. We hypothesized that lithium might modulate the microglia response to innate-immune-associated cytokines (10 ng/mL TNF-α, 50 ng/mL IL-1β, 20 ng/mL IFN-γ). We aimed to investigate whether lithium treatment and pretreatment of microglia modify the expression of genes associated with NLRP3 inflammasome. We also aimed to verify lithium treatment effect on caspase activity and extracellular IL-1β concentration. For the first time, our study used human microglial cell line - HMC3, the cytokine stimuli and lithium in concentration corresponding to that in the brains of patients. To analyze lithium mode of action, we analyzed the short- and long-term treatment and pretreatment. To assess the influence on microglia responding to innate-immune cytokines, we analyzed the expression of genes involved in innate-immune and inflammasome (TSPO, TLR4, NFKB1, CASP1, CASP4, NLRP3, IL-1β, IL-6), caspase activity, extracellular IL-1β concentration, phospho-GSK-3β(Ser9) expression and lactate concentration. We found that lithium treatment significantly reduced NLRP3 inflammasome-related genes expression. We observed that lithium treatment reduces inflammasome activity, which may attenuate the inflammatory state. Interestingly, the lithium pretreatment resulted in significantly elevated inflammasome activity, suggesting that lithium does not impair the immune response to additional stimuli.