Peptidylarginine deiminases: novel drug targets for prevention of neuronal damage following hypoxic ischemic insult (HI) in neonates

<jats:title>Abstract</jats:title><jats:p>Neonatal hypoxic ischaemic (<jats:styled-content style="fixed-case">HI</jats:styled-content>) injury frequently causes neural impairment in surviving infants. Our knowledge of the underlying molecular mechanisms is still limited. Protein deimination is a post‐translational modification caused by Ca<jats:sup>+2</jats:sup>‐regulated peptidylarginine deiminases (<jats:styled-content style="fixed-case">PAD</jats:styled-content>s), a group of five isozymes that display tissue‐specific expression and different preference for target proteins. Protein deimination results in altered protein conformation and function of target proteins, and is associated with neurodegenerative diseases, gene regulation and autoimmunity. In this study, we used the neonatal <jats:styled-content style="fixed-case">HI</jats:styled-content> and <jats:styled-content style="fixed-case">HI</jats:styled-content>/infection [lipopolysaccharide (LPS) stimulation] murine models to investigate changes in protein deimination. Brains showed increases in deiminated proteins, cell death, activated microglia and neuronal loss in affected brain areas at 48 h after hypoxic ischaemic insult. Upon treatment with the pan‐<jats:styled-content style="fixed-case">PAD</jats:styled-content> inhibitor Cl‐amidine, a significant reduction was seen in microglial activation, cell death and infarct size compared with control saline or <jats:styled-content style="fixed-case">LPS</jats:styled-content>‐treated animals. Deimination of histone 3, a target protein of the <jats:styled-content style="fixed-case">PAD</jats:styled-content>4 isozyme, was increased in hippocampus and cortex specifically upon <jats:styled-content style="fixed-case">LPS</jats:styled-content> stimulation and markedly reduced following Cl‐amidine treatment. Here, we demonstrate a novel role for <jats:styled-content style="fixed-case">PAD</jats:styled-content> enzymes in neural impairment in neonatal HI Encephalopathy, highlighting their role as promising new candidates for drug‐directed intervention in neurotrauma. <jats:boxed-text content-type="graphic" position="anchor"><jats:graphic xmlns:xlink="http://www.w3.org/1999/xlink" mimetype="image/png" position="anchor" specific-use="enlarged-web-image" xlink:href="graphic/jnc12744-fig-0005-m.png"><jats:alt-text>image</jats:alt-text></jats:graphic></jats:boxed-text></jats:p><jats:p>Hypoxic Ischaemic Insult (HI) results in activation of peptidylarginine deiminases (PADs) because of calcium dysregulation. Target proteins undergo irreversible changes of protein bound arginine to citrulline, resulting in protein misfolding. Infection in synergy with HI causes up‐regulation of TNFα, nuclear translocation of PAD4 and change in gene regulation as a result of histone deimination. Pharmacological PAD inhibition significantly reduced HI brain damage.</jats:p>