Titin strain contributes to the Frank-Starling law of the heart by structural rearrangements of both thin- and thick-filament proteins

Younss Ait-Mou, Karen Hsu, Gerrie P. Farman, Mohit Kumar, Marion L. Greaser, Thomas C. Irving, Pieter P. De Tombe, J. G. Seidman

Research output: Contribution to journalArticle

51 Citations (Scopus)

Abstract

The Frank-Starling mechanism of the heart is due, in part, to modulation of myofilament Ca2+ sensitivity by sarcomere length (SL) [length-dependent activation (LDA)]. The molecular mechanism(s) that underlie LDA are unknown. Recent evidence has implicated the giant protein titin in this cellular process, possibly by positioning the myosin head closer to actin. To clarify the role of titin strain in LDA, we isolated myocardium from either WT or homozygous mutant (HM) rats that express a giant splice isoform of titin, and subjected the muscles to stretch from 2.0 to 2.4 μm of SL. Upon stretch, HM compared with WT muscles displayed reduced passive force, twitch force, and myofilament LDA. Time-resolved small-angle X-ray diffraction measurements of WT twitching muscles during diastole revealed stretch-induced increases in the intensity of myosin (M2 and M6) and troponin (Tn3) reflections, as well as a reduction in cross-bridge radial spacing. Independent fluorescent probe analyses in relaxed permeabilized myocytes corroborated these findings. X-ray electron density reconstruction revealed increased mass/ordering in both thick and thin filaments. The SL-dependent changes in structure observed in WT myocardium were absent in HM myocardium. Overall, our results reveal a correlation between titin strain and the Frank-Starling mechanism. The molecular basis underlying this phenomenon appears not to involve interfilament spacing or movement of myosin toward actin but, rather, sarcomere stretch-induced simultaneous structural rearrangements within both thin and thick filaments that correlate with titin strain and myofilament LDA.

Original languageEnglish
Pages (from-to)2306-2311
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume113
Issue number8
DOIs
Publication statusPublished - 23 Feb 2016
Externally publishedYes

Fingerprint

Connectin
Starlings
Sarcomeres
Myofibrils
Myosins
Myocardium
Proteins
Muscles
Actins
Troponin
Diastole
Fluorescent Dyes
X-Ray Diffraction
Muscle Cells
Protein Isoforms
X-Rays
Electrons

Keywords

  • Fluorescent probes
  • Myofilament length-dependent activation
  • Passive force
  • Rat
  • Small-angle X-ray diffraction

ASJC Scopus subject areas

  • General

Cite this

Titin strain contributes to the Frank-Starling law of the heart by structural rearrangements of both thin- and thick-filament proteins. / Ait-Mou, Younss; Hsu, Karen; Farman, Gerrie P.; Kumar, Mohit; Greaser, Marion L.; Irving, Thomas C.; De Tombe, Pieter P.; Seidman, J. G.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 113, No. 8, 23.02.2016, p. 2306-2311.

Research output: Contribution to journalArticle

Ait-Mou, Younss ; Hsu, Karen ; Farman, Gerrie P. ; Kumar, Mohit ; Greaser, Marion L. ; Irving, Thomas C. ; De Tombe, Pieter P. ; Seidman, J. G. / Titin strain contributes to the Frank-Starling law of the heart by structural rearrangements of both thin- and thick-filament proteins. In: Proceedings of the National Academy of Sciences of the United States of America. 2016 ; Vol. 113, No. 8. pp. 2306-2311.
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AU - Ait-Mou, Younss

AU - Hsu, Karen

AU - Farman, Gerrie P.

AU - Kumar, Mohit

AU - Greaser, Marion L.

AU - Irving, Thomas C.

AU - De Tombe, Pieter P.

AU - Seidman, J. G.

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N2 - The Frank-Starling mechanism of the heart is due, in part, to modulation of myofilament Ca2+ sensitivity by sarcomere length (SL) [length-dependent activation (LDA)]. The molecular mechanism(s) that underlie LDA are unknown. Recent evidence has implicated the giant protein titin in this cellular process, possibly by positioning the myosin head closer to actin. To clarify the role of titin strain in LDA, we isolated myocardium from either WT or homozygous mutant (HM) rats that express a giant splice isoform of titin, and subjected the muscles to stretch from 2.0 to 2.4 μm of SL. Upon stretch, HM compared with WT muscles displayed reduced passive force, twitch force, and myofilament LDA. Time-resolved small-angle X-ray diffraction measurements of WT twitching muscles during diastole revealed stretch-induced increases in the intensity of myosin (M2 and M6) and troponin (Tn3) reflections, as well as a reduction in cross-bridge radial spacing. Independent fluorescent probe analyses in relaxed permeabilized myocytes corroborated these findings. X-ray electron density reconstruction revealed increased mass/ordering in both thick and thin filaments. The SL-dependent changes in structure observed in WT myocardium were absent in HM myocardium. Overall, our results reveal a correlation between titin strain and the Frank-Starling mechanism. The molecular basis underlying this phenomenon appears not to involve interfilament spacing or movement of myosin toward actin but, rather, sarcomere stretch-induced simultaneous structural rearrangements within both thin and thick filaments that correlate with titin strain and myofilament LDA.

AB - The Frank-Starling mechanism of the heart is due, in part, to modulation of myofilament Ca2+ sensitivity by sarcomere length (SL) [length-dependent activation (LDA)]. The molecular mechanism(s) that underlie LDA are unknown. Recent evidence has implicated the giant protein titin in this cellular process, possibly by positioning the myosin head closer to actin. To clarify the role of titin strain in LDA, we isolated myocardium from either WT or homozygous mutant (HM) rats that express a giant splice isoform of titin, and subjected the muscles to stretch from 2.0 to 2.4 μm of SL. Upon stretch, HM compared with WT muscles displayed reduced passive force, twitch force, and myofilament LDA. Time-resolved small-angle X-ray diffraction measurements of WT twitching muscles during diastole revealed stretch-induced increases in the intensity of myosin (M2 and M6) and troponin (Tn3) reflections, as well as a reduction in cross-bridge radial spacing. Independent fluorescent probe analyses in relaxed permeabilized myocytes corroborated these findings. X-ray electron density reconstruction revealed increased mass/ordering in both thick and thin filaments. The SL-dependent changes in structure observed in WT myocardium were absent in HM myocardium. Overall, our results reveal a correlation between titin strain and the Frank-Starling mechanism. The molecular basis underlying this phenomenon appears not to involve interfilament spacing or movement of myosin toward actin but, rather, sarcomere stretch-induced simultaneous structural rearrangements within both thin and thick filaments that correlate with titin strain and myofilament LDA.

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