Figure 2.

Mechanisms of peptidylarginine deiminases PADs) in central nervous system (CNS injury and neurodegenerative pathologies and the proposed effect of PAD-inhibitors. Upon CNS injury (hypoxic ischaemic encephalopathy, HIE), Ca²⁺ entry is facilitated via the reversal of the Na⁺/Ca²⁺ exchanger due to over activation of the Na⁺/H⁺ exchanger (NHE). Ca²⁺ entry can also be facilitated due to membranolytic pathways including the complement membrane attack complex (MAC) and perforin. Increased cytosolic Ca²⁺ triggers the neurotoxic cascade, which includes activation of the Ca²⁺ dependent PAD enzymes. Neurodegenerative disease mutations cause protein aggregation and impaired calcium buffering, which activates the downstream PAD-cascade. Both in CNS acute injury and neurodegeneration, PAD activation causes protein deimination and further protein misfolding, affecting cell motility, autophagy, phagoptosis, and mictochondrial function, leading to neurotoxic events. Deiminated neo-epitopes and leakage of deiminated proteins from dying cells contribute to neuroinflammation that in turn may upregulate TNFα, which causes nuclear translocation of PADs, leading to histone deimination and also formation of neutrophil extracellular traps (NETosis). PAD-mediated cytoskeletal protein deimination and nuclear PAD translocation, which can affect histone deimination, contribute to EMV release, resulting in export of misfolded proteins, DNA, RNA, miRNAs, enzymes, and other EMV cargo that can contribute to pathologies. PAD-inhibitior Cl-Amidine targets PAD activation and reduces deimination of target proteins and neuroinflammatory responses. Cl-Amidine also significantly reduces EMV shedding, resulting in decreased transport of noxious EMV cargo (red arrows emphasise the main events associated to PAD activation and PAD inhibition that affect EMV release. Blue arrows indicate additional downstream changes due to PAD-mediated protein misfolding; based on [26,129]).