MES-DERIVED CARDIOMYOCYTES AS CELLULAR MODEL TO STUDY CARDIAC DISEASES: ALTERATIONS IN STRN AND GNB5 GENES

Striatin (Strn), a scaffold protein expressed in many tissues, among which in cardiomyocytes (CMs), whose altered expression has been found in various cardiac diseases. Here we studied the role(s) of cardiac STRN by comparing the electrophysiological properties of CMs, generated from STRN-KO and isogenic WT mouse embryonic stem cell (mESC) lines. 10-12-day old beating mESC-CMs were analyzed by Patch-clamp, motion video tracking, Ca2+ dynamics and immunofluorescence analysis. STRN-KO cells have a higher spontaneous beating rate and faster action potential depolarization (dV/dt) than WT, correlated with a larger fast INa conductance. Since in HEK cells downregulation of STRN was reported to destabilize microtubules and increase INa, immunofluorescence analysis confirmed the higher Na+ channel expression and a more dynamic microtubule network in KO CMs. Motion video tracking analysis highlighted an altered contraction in STRN-KO CMs, and this was associated with a global increase in intracellular Ca2+. This was likely due to an increased late Na+ current (INaL) and a reduction of Ca2+extrusion through the Na+/Ca2+ exchanger (NCX). Other currents such as ICaL, If and IKr were not altered in STRN-KO cells. Incubation of STRN-KO CMs with the microtubule stabilizer Taxol, induced a reduction of INa conductance toward WT levels. In conclusion, loss of STRN alters CMs electrical and contractile profile and affects cell functionality by a disarrangement of multi-protein complexes leading to the impairment of microtubules dynamics and trafficking of Na+ channels.