Characterising the Effects of a Peptide Directed Against the L-Type Ca2+ Channel on Mitochondrial Function in Hypertrophic Cardiomyopathy

Abstract

Mutations in cardiac troponin I (cTnI) or β-myosin heavy chain (MHC) account for approximately 45% of genotyped families with hypertrophic cardiomyopathy (HCM). HCM is characterised by disorganisation of cytoskeletal proteins and altered energy metabolism. The L-type Ca2+ channel (LTCC) plays a critical role in cardiac excitation and contraction. We have demonstrated that activation of LTCC can also regulate mitochondrial function. HCM mouse models cTnI-G203S and αMHC403/+ exhibit a faster LTCC inactivation rate and altered mitochondrial responses after LTCC activation. This results in a “hypermetabolic” mitochondrial state. We examined the efficacy of in vitro and in vivo exposure of cTnI-G203S and αMHC403/+ mice to a peptide derived against the alpha-interacting domain (AID-TAT) on mitochondrial function by assessing alterations in mitochondrial membrane potential (Ψm, JC-1 fluorescence) and mitochondrial oxygen consumption (flavoprotein autofluorescence). In vitro exposure of cTnI-G203S cardiomyocytes to 10µM AID-TAT attenuated the increase in JC-1 fluorescence in response to activation of LTCC with channel agonist BayK(-) (cTnI-G203S+AID-TAT=4.4±0.36% increase, n=6 versus cTnI-G203S=29.2±1.8% increase, n=15, p<0.05). AID-TAT also attenuated increases in flavoprotein autofluorescence in response to BayK(-) (cTnI-G203S+AID-TAT=4.0±0.4% increase, n=6 versus cTnI-G203S=24.4±6.5% increase, n=8, p<0.05). In vivo treatment of cTnI-G203S mice with IP injection of 10µM AID-TAT attenuated JC-1 fluorescence in response to BayK(-) compared to untreated mice (JC-1: cTnI-G203S+AID-TAT=19.7±3.6% increase, n=6 versus cTnI-G203S=29.2±1.8% increase, n=15, p<0.05). Similar results were observed in αMHC403/+ mice. These data suggest that treatment of cTnI-G203S and αMHC403/+ mice with AID-TAT restores mitochondrial function. Normalising mitochondrial function with AID-TAT may be effective in preventing development of the cardiomyopathy.