Oleic Acid Induces Adherens Junction Disassembly in Rat Neonatal Cardiomyocytes through Mechanisms Involving Fyn Kinase and Casein Kinase 1

Backgrounds: Accumulation of oleic acid (OA) and other nonesterified fatty acids in heart tissue during ischemia and reperfusion contribute to myocardial damage. OA has been shown to induce accumulation of intracellular lipid droplets and to disrupt adherens junctions (AJs). Cardiac N-cadherin is the major cadherin of AJs. This study investigated the role of N-cadherin in OA-induced junctional disassembly in neonatal cardiomyocytes. Methods: cardiomyocyte cultures from 2-day-old Wistar rats were used. Immunocytochemistry was performed to detect junctional N-cadherin. The binding of Fyn, phosphotyrosine, or phosphoserine with N-cadherin was assayed by immunopricipitation. Results: OA caused the disruption of AJs. In addition, OA promoted the association of N-cadherin with Fyn kinase, a member of Src family kinase, and increased tyrosine phosphorylation of N-cadherin without affecting the protein expression of Fyn and N-cedherin. The Src family kinase inhibitor, PP2, prevented the OA-induced tyrosine phosphorylation of N-cadherin and the loss of N-cadherin from AJs. Moreover, OA increased the expression of casein kinase (CK) 1α and 1δ in a time-dependent manner and the serine phosphorylation of N-cadherin. The CK1 inhibitor, IC261, prevented OA-induced serine phosphorylation of N-cadherin, and this modification is known to accelerate the turnover of N-cadherin. Double-labeling experiment showed partial colocalization of these N-cadherin punctate structures with early endosomes. Either MG132 (a proteasome inhibitor) or NH4Cl (a lysosomal inhibitor) inhibited OA-induced junctional N-cadherin disruption indicating that OA decreases junctional N-cadherin by the proteasomal and lysosomal degradation. Conclusions: OA activates CK1 and Fyn kinases, which modify N-cadherin by serine phosphorylation and tyrosine phosphorylation, respectively, and results in AJ disruption. This study provides an insight into the mechanism of OA-induced junctional abnormality.