EFFECTS OF TOLL-LIKE RECEPTOR 3 – DEPENDENT IMMUNE ACTIVATION IN MICE ARE SEX- AND TISSUE- SPECIFIC: IMPLICATIONS FOR ALCOHOL USE DISORDER
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Background
Alcohol use disorder (AUD) is linked to increased neuroinflammation. Alcohol (ethanol) may activate toll-like receptors, which leads to the release of inflammatory molecules that could influence AUD-related behaviors, such as increased alcohol intake. Activation of toll-like receptor 3 (TLR3) by Polyinosinic:polycytidylic acid (Poly(I:C) or PIC) is associated with escalation of alcohol consumption in male, but not female F1 hybrid mice from reciprocal crosses between FVB/NJ (FVB) and C57BL/6J (B6) strains. Little is known about the underlying mechanisms of these sex-specific behavioral effects. In this study, we investigated the effects of TLR3 activation by PIC on temporal profiles of several pro- and anti-inflammatory molecules in the blood and brain of FVB/B6 F1 hybrid male and female mice at multiple time points. We hypothesized that TLR3 – dependent immune profiles would differ between males and females, which may, at least in part, explain the observed differences in drinking behavior.
Methods
Male and female FVB/B6 F1 hybrid alcohol-naive mice were injected intraperitoneally with PIC (10 mg/kg) or saline. Blood and perfused brain tissues from the prefrontal cortex (PFC) and striatum were collected at 6-, 24-, and 48-hours post-injection. The expressions of Ccl2, Ccl5, Tnf, Il-6, Il-1β, Ifng, Ifnb1 , and Mmp9 genes were analyzed using qPCR. Protein levels of a subset of these molecules and IL-17r/a, IL-4, and IL-10 were measured in striatal samples from the same animals using ELISA.
Results
Activation of TLR3 by PIC triggered time-dependent, sex- and tissue-specific responses in immune genes and their proteins. PIC induced a time-dependent increase in expression of majority of the genes peaking at the 6 hr time point. Temporal immune profiles for pro-inflammatory chemokines, Ccl2 and Ccl5 differed between males and females in the PFC and striatum, suggesting possible sex-specific effects of these molecules on behavior. Protein levels of CCL2, CCL5, and IL-6 increased in the striatum of both sexes and correlated strongly with gene expression, with females showing somewhat higher protein fold changes. MMP-9, a key regulator of blood–brain barrier (BBB) permeability and synaptic plasticity, showed an increase in protein levels, but not mRNA levels in striatum. This pattern suggests altered blood–brain barrier (BBB) permeability, although this would require further investigation.
Conclusion
Our results revealed distinct TLR3-dependent immune gene and protein expression profiles in blood and brain between males and females and suggested different roles for these molecules in regulating alcohol consumption. We identified CCL2, CCL5 and MMP-9 as target molecules for investigating sex-specific behavior in the immune modulation of alcohol consumption.
