[Involvement of TOLL-like receptors in the neuroimmunology of alcoholism]

Prolonged alcohol consumption influences microRNA expression in the nucleus accumbens of the rat brain

The microRNA (miR) species analyzed in this study are involved in molecular mechanisms of TLR4 and TLR7 signaling, mediating the development of neuroinflammation and neurodegeneration. We have investigated the expression levels of miR-let7b, miR-96, miR-182, miR-155, and the mRNA content of HMGB1, TLR3, TLR4 in the nucleus accumbens (NAc) of the brain of rats exposed to long-term alcoholization. The long-term alcoholization caused a decrease in miR-let7b, miR-96, miR-182, and TLR7 mRNA levels; this was accompanied by an increase in miR-155, TLR4, and Hmgb1 mRNA levels in the NAc of rat brain. TLR7 is functionally linked to miR-let7b. The data of a simultaneous decrease in miR-let7b and TLR7 mRNA are of interest for further studies; they may indicate on the lack of functionally significant links between Hmgb1 and the miR-let7b-TLR7 system in NAc. The existing evidence of a functional relationship between TLR4 with miR-155 and miR-182 and our observations on their expression changes during chronic alcoholization are very interesting and require further investigation. The suggestion about the development of neuroinflammatory process in NAc under prolonged alcohol exposure are relevant for studying the level of TLR gene expression in NAc, as well as the expression of miR species, which may have a functional relationship with the TLR system.

[The effect of rifampicin on the system of Toll-like receptors in the nucleus accumbens of the brain of long-term alcoholized rats during alcohol withdrawal]

Nucleus accumbens (NAc) is the ventral part of the striatum of the brain; it is an important part of the mesolimbic pathway involved in the reward system that mediates the formation of various forms of addiction, in particular alcohol addiction. Neuroimaging data and in vitro studies indicate the development of a pronounced neurodegenerative process in the NAc, with long-term alcohol use, but the key mechanisms mediating this process remain unknown. In recent years, the attention of researchers has been focused on studying the system of Toll-like receptors (TLRs), the increased activity of which is clearly shown in the cerebral cortex and hippocampus during prolonged alcohol exposure, but there is a need to study the role of this system in other brain structures. In this study, we have shown that prolonged alcohol exposure (2 months) with moderate doses of ethanol (2 g/kg) promotes a pronounced increase in the expression of the Tlr4 gene and its endogenous ligand Hmgb1 in NAc during the period of alcohol withdrawal in rats. Injections of rifampicin (100 mg/kg) reduced the elevated expression level of Hmgb1, Tlr4, as well as pro-inflammatory cytokine genes (IL1β, IL6), while the administration of the drug increased the reduced level of mRNA of anti-inflammatory cytokines (IL10, IL11).

[Prenatal exposure to alcohol alters TLR4 signaling in the prefrontal cortex in rats]

Prenatal alcohol exposure (PAE) can lead to developmental disorders of the central nervous system (CNS) and mental retardation. Toll-like receptor (TLR) 4 plays an important role in the development of defects in the nervous system caused by PAE. However, how PAE affects the TLR4 response in the brain remains unclear. Using the model of semi-forced alcoholization of pregnant rats, we investigated TLR4-mediated signaling on the 30th day of postnatal development in their offspring. Rats exposed to PAE showed a higher expression of proinflammatory cytokines in the prefrontal cortex, but TLR4-mediated signaling in response to lipopolysaccharide (LPS) was weakened. These data suggest that PAE can lead to neuroinflammation and suppression of the TLR4-mediated response to LPS in the prefrontal cortex of young rats. Since innate immunity plays an important role in brain development, PAE-induced suppression of the TLR4-mediated response may be one of the mechanisms for the development of CNS pathology.

[The TLR3 induction increases content of interferons in rat's brain by TRAIL signaling during long-term alcoholization]

The pathogenetic mechanisms associated with alcohol use include dysregulation of the innate immune system mechanisms in the brain. TLR3 expression is increased in the postmortem material of the prefrontal cortex of humans. An increase in the TLR3 signaling activity leads to the induction of interferons (IFN). IFN are associated with depressive symptoms and, therefore, may play a role in the pathogenesis of alcoholism; however, the exact mechanisms of intracellular signaling mediated by the influence of ethanol are not fully elucidated and their study was the purpose of this work. The experimental results showed that ethanol and the TLR3 agonist Poly (I:C) increased the content of TLR3, IFNβ, and IFNγ mRNA in the prefrontal cortex. In addition, expression of the TRAIL encoding gene also increased, and this increase positively correlaed with the mRNA content of TLR3, IFNβ and IFNγ both under alcoholization conditions and after injections of the TLR3 agonist. The data obtained may indicate that alcoholization is able to activate TLR3-TRAIL-IFN-signaling in the prefrontal cortex of the brain.

[HMGB1gene expression changes in the striatum and amigdal of the rat's brain under alcoholization and ethanol withdrawal]

Intracellular signaling mediated by the HMGB1 protein, an agonist of TLRs, is considered as a possible target for the correction of pathologies of the neuroimmune system, however, the expression level of the Hmgb1 gene has not been previously studied in various brain structures of rats exposed to prolonged alcoholization followed by ethanol withdrawal. The study showed that long-term use of ethanol caused to an increase in the level of Hmgb1 mRNA in the striatum of rat brain. Alcohol withdrawal changed the level Hmgb1 mRNA in the striatum and amygdala on the 1st and 14th day. The data obtained may indicate that in different structures of the brain there are multidirectional changes in the molecular mechanisms of the neuroimmune response with prolonged use of ethanol and its withdrawal.