Lys184 deletion in troponin I impairs relaxation kinetics and induces hypercontractility in murine cardiac myofibrils.

Abstract

AIMS:

To understand the functional consequences of the Lys184 deletion in murine cardiac troponin I (mcTnI(DeltaK184)), we have studied the primary effects of this mutation linked to familial hypertrophic cardiomyopathy (FHC) at the sarcomeric level.

METHODS AND RESULTS:

Ca(2+) sensitivity and kinetics of force development and relaxation were investigated in cardiac myofibrils from transgenic mice expressing mcTnI(DeltaK184), as a model which co-segregates with FHC. Ca(2+)-dependent conformational changes (switch-on/off) of the fluorescence-labelled human troponin complex, containing either wild-type hcTnI or mutant hcTnI(DeltaK183), were investigated in myofibrils prepared from the guinea pig left ventricle. Ca(2+) sensitivity and maximum Ca(2+)-activated and passive forces were significantly enhanced and cooperativity was reduced in mutant myofibrils. At partial Ca(2+) activation, mutant but not wild-type myofibrils displayed spontaneous oscillatory contraction of sarcomeres. Both conformational switch-off rates of the incorporated troponin complex and the myofibrillar relaxation kinetics were slowed down by the mutation. Impaired relaxation kinetics and increased force at low [Ca(2+)] were reversed by 2,3-butanedione monoxime (BDM), which traps cross-bridges in non-force-generating states.

CONCLUSION:

We conclude that these changes are not due to alterations of the intrinsic cross-bridge kinetics. The molecular mechanism of sarcomeric diastolic dysfunction in this FHC model is based on the impaired regulatory switch-off kinetics of cTnI, which induces incomplete inhibition of force-generating cross-bridges at low [Ca(2+)] and thereby slows down relaxation of sarcomeres. Ca(2+) sensitization and impairment of the relaxation of sarcomeres induced by this mutation may underlie the enhanced systolic function and diastolic dysfunction at the sarcomeric level.

• Authors: Bogdan Iorga, Natascha Blaudeck, Johannes Solzin, Axel Neulen, Ina Stehle, Alfredo J Lopez Davila, Gabriele Pfitzer, Robert Stehle
• Journal: Cardiovascular research (Cardiovasc Res) Vol. 77 Issue 4 Pg. 676-86 (Mar 01 2008) ISSN: 0008-6363 [Print] England
• PMID: 18096573 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Troponin I
• diacetylmonoxime
• Diacetyl
• Lysine

Topics

• Animals
• Calcium Signaling
• Cardiomyopathy, Hypertrophic, Familial (genetics, metabolism, physiopathology)
• Diacetyl (analogs & derivatives, pharmacology)
• Disease Models, Animal
• Guinea Pigs
• Humans
• Kinetics
• Lysine
• Mice
• Mice, Inbred C57BL
• Mice, Transgenic
• Muscle Contraction (drug effects)
• Muscle Strength
• Myofibrils (metabolism, pathology)
• Papillary Muscles (drug effects, metabolism, pathology, physiopathology)
• Protein Conformation
• Sarcomeres (metabolism)
• Sequence Deletion
• Troponin I (chemistry, genetics, metabolism)
• Ventricular Dysfunction, Left (genetics, metabolism, physiopathology)