Osmolality controls the expression of cathelicidin antimicrobial peptide in human macrophages

Abstract An imbalance between extracellular and intracellular fluid osmolality causes osmotic stress and affects cellular homeostasis. Recent research suggests that osmotic stress is also associated with various innate and adaptive immune responses. Here we present the surprising finding that osmolality tightly controls the expression of cathelicidin antimicrobial peptide (CAMP) in human macrophages. CAMP expression is strongly upregulated under hyperosmotic conditions and downregulated under hypoosmotic conditions. We also provide evidence that this osmolality-mediated antimicrobial response is dependent on nuclear factor of activated T-cells 5 (NFAT5) and mitogen-activated protein kinase (MAPK) p38. Finally, Toll-like receptor (TLR) activation inhibits osmolality-mediated expression of CAMP in human macrophages, suggesting that this osmolality-dependent regulation of CAMP is more relevant under homeostatic conditions, rather than during acute infections. This study expands our knowledge of the regulation of human antimicrobial peptides and highlights osmolality as an important and independent factor shaping host innate immune homeostasis.