Tachycardia-induced CD44/NOX4 signaling is involved in the development of atrial remodeling

Atrial fibrillation (AF) is associated with oxidative stress and Ca²⁺-handling abnormalities in atrial myocytes. Our prior study has demonstrated the involvement of CD44, a membrane receptor for hyaluronan (HA), in the pathogenesis of AF. This study further evaluated whether CD44 and its related signaling mediate atrial tachycardia-induced oxidative stress and Ca²⁺-handling abnormalities. Tachypacing in atrium-derived myocytes (HL-1 cell line) induced the activation of CD44-related signaling, including HA and HA synthase (HAS) expression. Blocking HAS/HA/CD44 signaling attenuated tachypacing-induced oxidative stress (NADPH oxidase [NOX] 2/4 expression) and Ca²⁺-handling abnormalities (oxidized Ca²⁺/calmodulin-dependent protein kinase II [ox-CaMKII] and phospho-ryanodine receptor type 2 [p-RyR2] expression) in HL-1 myocytes. Furthermore, a direct association between CD44 and NOX4 was documented in tachy-paced HL-1 myocytes and atrial tissues from AF patients. In vitro, Ca²⁺ spark frequencies in atrial myocytes isolated from CD44^−/− mice were lower than those from wild-type mice. Furthermore, administration of an anti-CD44 blocking antibody in atrial myocytes isolated from wild-type mice diminished the frequency of Ca²⁺ spark. Ex vivo tachypacing models of CD44^−/− mice exhibited a lower degree of oxidative stress and expression of ox-CaMKII/p-RyR2 in their atria than those of wild-type mice. In vivo, burst atrial pacing stimulated a less inducibility of AF in CD44^−/−mice than in wild-type mice. In conclusion, atrial tachypacing-induced Ca²⁺-handling abnormalities are mediated via CD44/NOX4 signaling, which provides a possible explanation for the development of AF.