Microglial Response to Inflammatory Stimuli-Impact of Protein Acetylation and Phosphorylation

Inflammation and immune responses have been shown to contribute to a number pathological conditions including those neurodegenerative diseases which affect the brain. Microglial cells represent the resident immune cell population that constitute the immune system of the CNS. Acetylation of proteins is one of the chemical modifications by which microglial cells regulate the transcription of genes that respond to proand anti-inflammatory signals through multiple pathways. In addition to acetylation, the intensity and duration of the inflammatory response is regulated by changes in the phosphorylation state of the signaling pathways involved in the regulation of inflammation. One of the major intracellular cell-signaling pathways for inflammation, the NF-κB system, regulates the expression of many genes involved in immune responses. The transcriptional response of intranuclear NF-κB is also tightly regulated, not only by post-translational modifications of NF-κB itself but also by modification of histones. The dynamic switches between activity states of chromatin are modified by the interplay of two competing enzymatic activities, histone acetyltransferases (HATs) and histone deacetylases (HDACs), which regulate the acetylation state of proteins. By counteracting the effects of HATs at the site of inflammatory gene transcription, HDACs play a major role in the regulation of the NFκB-dependent inflammatory response. Our aim was to shed light on changes occurring in the regulation of the inflammatory response by manipulating the acetylation and phosphorylation status of different neural inflammation models. The proand anti-inflammatory responses were characterized using established cell culture models. The results show that an increase in the level of protein acetylation, as well as enhancement of protein phosphorylation, leads to a proinflammatory response. The potentiated response by hyperphosphorylation occurred earlier than the acetylation induced response. Moreover, the inflammatory response showed a synergistic potentiation when both acetylation and phosphorylation were enhanced simultaneously with compounds affecting separate pathways, indicating that different signaling pathways govern the overall acetylation and phosphorylation mediated immune responses. The proinflammatory responses could be inhibited by using specific blockers targeted against the different signaling pathways. This thesis provides more insight into the research, development and characterization of antiinflammatory drug candidates that are targeted to modulate the HAT-HDAC balance, phosphorylation status and the regulation of NF-κB pathway National Library of Medicine Classification: WL 300, QW 700, QW 504 Medical Subject Headings: Central Nervous System/immunology; Inflammation; Immune System; Microglia/immunology; Acetylation; Phosphorylation; NF-kappa B; Histone Deacetylases; Histone Acetyltransferases; Cells, Cultured "A man should keep his little brain attic stocked with all the furniture that he is likely to use, and the rest he can put away in the lumber-room of his library, where he can get it if he wants it. " -Sir Arthur Conan Doyle(Sherlock Holmes in "The Five Orange Pips")