Manipulating L-Type Calcium Channel Activity Alters Mitochondrial Function and Prevents Hypertrophic Cardiomyopathy in a Troponin I Mutant Mouse Model

Abstract

Hypertrophic cardiomyopathy (HCM) affects 1:200 of the general population. It is associated with altered metabolic activity and hypercontractile function. Mitochondrial function can be regulated by alterations in L-type Ca2+ channel (LTCC) activity, and the cytoskeletal network plays an important role in this response. We have previously demonstrated that human HCM causing cardiac troponin I mutation Gly203Ser leads to a faster LTCC inactivation rate, impaired functional communication between LTCC and mitochondria, and a “hypermetabolic” mitochondrial state in a mouse model of the mutation (cTnI-G203S). These alterations precede development of the cardiomyopathy. A peptide derived against the LTCC alpha-interacting domain (AID-TAT) slows LTCC inactivation rate and decreases metabolic function in wt cardiomyocytes. Here we examined the efficacy of in vitro and in vivo exposure of cTnI-G203S to AID-TAT on normalising mitochondrial function in response to activation of the channel, assessed as changes in mitochondrial membrane potential (Ψm, JC-1 fluorescence) and mitochondrial oxygen consumption (flavoprotein autofluorescence). Acute in vitro exposure of cTnI-G203S cardiomyocytes to AID-TAT normalises Ψm in response to activation of LTCC with channel agonist BayK(-) (cTnI-G203S+AID-TAT = 4.4±0.4% increase, n = 6 versus cTnI-G203S+ inactive scrambled AID-TAT, AID(S)-TAT = 28.4±2.6% increase, n = 5, p<0.05) and flavoprotein autofluorescence (cTnI-G203S+AID-TAT = 4.0±0.3% increase, n=6 versus cTnI-G203S+AID(S)-TAT = 19.2±1.7% increase, n = 3, p<0.05). In vivo treatment of cTnI-G203S mice with AID-TAT via intraperitoneal injection (10µM tri-weekly for 5wks) also normalised Ψm (cTnI-G203S+AID-TAT = 20.1±2.2% increase, n = 18 versus cTnI-G203S+AID(S)-TAT = 30.3±1.8% increase, n = 18, p<0.05), and flavoprotein autofluorescence (cTnI-G203S+AID-TAT = 17.8±2.1% increase, n = 29 versus cTnI-G203S+AID(S)-TAT = 42.3±5.0% increase, n = 26, p<0.05). Treatment also reversed hypertrophy as evidenced by changes on echocardiography. We conclude that treatment of cTnI-G203S mice with AID-TAT appears to restore mitochondrial function and prevent development of hypertrophic cardiomyopathy.