Peptidylarginine Deiminases (PADs) – Novel Drug Targets for the Amelioration of Neurodegenerative Disease Progression - Modelled in Human iPSCs.

Background: Progressive neurodegenerative diseases are often referred to as protein misfolding disorders, as common features are calcium dysregulation and accumulated misfolded protein aggregates that lead to fatal neuronal loss. Peptidylarginine deiminases (PADs) are a group of Ca+2 activated enzymes which cause irreversible post-translational conversions of protein bound arginines to citrullines in target proteins, changing their structure and function. Novel roles have been shown for PADs in acute CNS damage, where pharmacological PADinhibition resulted in significant dampening of neuroinflammatory microglial activation and neuroprotective effects in vivo. We have also shown a novel mechanistic role for PADs in the biogenesis of extracellular vesicle (EV) release, via deimination of cytoskeletal proteins and histones, which can be effectively targeted using PAD-inhibitors. Protein deimination and extracellular vesicle release are both Ca2+ mediated mechanisms which are increasingly associated to neurodegenerative diseases. Methods: We are currently using human induced pluripotent stem cell (iPSC) models to elucidate the involvement of PADs and post-translational protein deimination in neurodegenerative disease progression. We are testing neuronal cell lysates, generated from fibroblasts derived from patients carrying mutations for Parkinson’s disease (PD), frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) for expression of PAD isozymes, changes in deiminated target proteins and EV release. Results: We have found that protein deimination is increased in cell lines carrying certain FTD-ALS linked valosin-containing protein mutations (VCPR155C and VCPR191Q) and in the Parkinson Disease α¬ synuclein triplication. Specific targets identified include nuclear histone H3, which is involved in gene regulation and EV release. Conclusion: Human iPSC neurodegenerative disease models can be used to investigate PADmediated mechanisms involved in neurodegenerative pathologies and to test pharmacological PAD-inhibitors for intervention in neurodegenerative disease progression.