Downregulation of protein citrullination reduces myelin protein aggregation and protects motor neurons and axons

Protein citrullination (PC) is a posttranslational modification that involves the irreversible conversion of protein-arginine to protein-citrulline and is catalyzed by a family of enzymes known as protein arginine deiminases (PADs). Mammals encode five PADs, and PAD2 is the most dominant form in the central nervous system. Previously, we have shown that PAD2 dysregulation and aberrant PC accumulate in reactive astrocytes and in myelin protein aggregates in amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease characterized by motor neurons loss, paralysis, and death. We hypothesized that dysregulated PAD2 and PC contribute to ALS pathogenesis. To test this hypothesis, we generated PAD2 knockout (PAD2KO)-SOD1G93A ALS mice and examined the consequent modulation on the clinical symptoms and pathology, using behavioral, molecular biology, and proteomics approaches. Significant (p< 0.05) increase in lifespan was observed in male PAD2KO ALS mice. Detailed analysis revealed that the body weight peaked about 3 weeks earlier than the SOD1G93A ALS mice, suggesting that the PAD2KO accelerated the disease. However, the disease progression was slowed, leading to longer survival in males and similar survival in females. At the cellular level, PAD2KO preserved myelin, axons, neuromuscular junctions (NMJs), and motor neurons. Furthermore, PAD2KO reduced protein citrullination and myelin protein MBP aggregation. Using antibodies against different MBP citrullinated sites, we found that citrullination at arginine residue 24 (R24) was enriched in the myelin aggregates in ALS mice. PAD2KO eliminated R24 citrullination and dramatically reduced MBP aggregation, suggesting PAD2 citrullinate R24, which in turn facilitates MBP aggregation. Moreover, proteomics from isolated spinal cord myelin showed an increase in energy metabolic proteins in PAD2KO ALS mice, suggesting that PAD2KO improve energy metabolism. Taken together, our results demonstrate that PAD2 mediated citrullination plays a role in ALS pathogenesis in part through MBP aggregation and myelin degeneration. Funding Sources: NIH/NINDS RO1-NS118145; Angel Fund for ALS Research This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.