Striatin knock out induces a gain of function of INa and impaired Ca2+ handling in mESC-derived cardiomyocytes

Aim

Striatin (Strn) is a scaffold protein expressed in cardiomyocytes (CMs) and alteration of its expression are described in various cardiac diseases. However, the alteration underlying its pathogenicity have been poorly investigated.

Methods

We studied the role(s) of cardiac Strn gene (STRN) by comparing the functional properties of CMs, generated from Strn-KO and isogenic WT mouse embryonic stem cell lines.

Results

The spontaneous beating rate of Strn-KO CMs was faster than WT cells, and this correlated with a larger fast I_Na conductance and no changes in I_f. Paced (2–8 Hz) Strn-KO CMs showed prolonged action potential (AP) duration in comparison with WT CMs and this was not associated with changes in I_CaL and I_Kr. Motion video tracking analysis highlighted an altered contraction in Strn-KO CMs; this was associated with a global increase in intracellular Ca²⁺, caused by an enhanced late Na⁺ current density (I_NaL) and a reduced Na⁺/Ca²⁺ exchanger (NCX) activity and expression. Immunofluorescence analysis confirmed the higher Na⁺ channel expression and a more dynamic microtubule network in Strn-KO CMs than in WT. Indeed, incubation of Strn-KO CMs with the microtubule stabilizer taxol, induced a rescue (downregulation) of I_Na conductance toward WT levels.

Conclusion

Loss of STRN alters CMs electrical and contractile profiles and affects cell functionality by a disarrangement of Strn-related multi-protein complexes. This leads to impaired microtubules dynamics and Na⁺ channels trafficking to the plasma membrane, causing a global Na⁺ and Ca²⁺ enhancement.