4-Phenylbutyrate Induces Functional Elongation of the Microglial Process Through Activation of Akt

Conversion of microglia to a branching state is considered a potential strategy to ameliorate neuroinflammation. Inhibition of histone deacetylases (HDACs) may convert microglia to a branching state and thus prevent neuroinflammation. Drugs that inhibit HDACs could be used to alleviate neuroinflammation. Here, we hypothesize that 4-phenylbutyric acid (4-PBA), an HDAC inhibitor, could shift microglia to an anti-inflammatory phenotype by promoting microglial process elongation. As expected, our results showed that 4-PBA induced reversible elongation of branching processes in primary cultured mouse microglia and in microglia in the prefrontal cortex of mice. Pretreatment with 4-PBA also prevented lipopolysaccharide (LPS)-induced shortening of branching processes in microglia under both in vitro and ex vivo conditions, LPS-induced pro-inflammatory responses in cultured microglia and prefrontal cortex, and LPS-induced sickness behavior in mice. Short-term incubation with 4-PBA led to a significant increase in phosphorylation levels of protein kinase B (Akt) in cultured microglia. 4-PBA did not induce microglial process elongation in vitro or ex vivo when cultured microglia or mice were treated with the Akt signaling inhibitor LY294002, suggesting that the pro-elongation effect of 4-PBA on microglial processes require activation of Akt signaling. Moreover, 4-PBA did not prevent LPS-induced inflammatory responses in cultured microglia and prefrontal cortex or LPS-induced sickness behaviors when cultured microglia or mice were treated with LY294002. Altogether, these results indicate that 4-PBA induces microglial process elongation in an Akt-dependent manner, which may underlie the anti-neuroinflammatory properties of 4-PBA.