Environmental Arginine Controls Multinuclear Giant Cell Metabolism and Formation

Multinucleated giant cells (MGCs) are implicated in many diseases including schistosomiasis, sarcoidosis and arthritis. Formation of MGCs is energy intensive to enforce membrane fusion and cytoplasmic expansion. Here we used receptor activator of nuclear factor kappa-Β ligand (RANKL) induced osteoclastogenesis to model MGC formation. We found amino acid (AA) scarcity controls MGC formation and reveal specific requirements for extracellular arginine in RANKL cellular programming. Systemic arginine restriction improved outcome in multiple murine arthritis models and its removal induced preosteoclast metabolic quiescence, associated with impaired tricarboxylic acid (TCA) cycle function and metabolite induction. Effects of arginine deprivation on osteoclastogenesis were independent of mTORC1 activity or global transcriptional and translational inhibition. Arginine scarcity also dampened generation of IL-4 induced polykaryons, another form of MGCs. Strikingly, in the absence of extracellular arginine, both cell types displayed flexibility as their formation could be restored with select arginine precursors. These data establish how environmental amino acids control the metabolic fate of polykaryons and suggest metabolic ways to manipulate MGC-associated pathologies and bone remodelling.