Calponin is a family of actin filament-associated proteins which regulate smooth muscle cell contraction. Three isoforms of calponin exist: calponin h1 (CNN1) ,calponin h2 (CNN2) and calponin 3 (CNN3). Calponin 1 and calponin 2 are predominately expressed in smooth muscle cells and cardiac muscle cells,respectively. Calponin 3 is highly expressed in many tissues including articular cartilage and brain.