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# Partial deletion of titin's C-zone alters cardiac function by reducing the operating sarcomere length range

Preferred citation (DataCite format):

  Methawasin, Methajit; Farman, Gerrie P.; Granzier-Nakajima, Shawtaroh; Strom, 
  Joshua; Kiss, Balázs; Smith, John E.; et al. (2023).
  Partial deletion of titin's C-zone alters cardiac function by reducing the
  operating sarcomere length range.
  University of Arizona Research Data Repository.
  Dataset. https://doi.org/10.25422/azu.data.22239415


Corresponding Author:
  Mei Methawasin, Cellular Molecular Medicine, methajit@arizona.edu


License:
  CC BY 4.0


DOI:
  https://doi.org/10.25422/azu.data.22239415



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## Summary

Titin’s C-zone is an inextensible segment in titin, comprised of 11 super-
repeats and located in the cMyBP-C-containing region of the thick filament.
Previously we showed that deletion of titin’s super-repeats C1 and C2 (
_TtnΔC1-2_ model) results in shorter thick filaments and contractile
dysfunction of the left ventricular (LV) chamber but that unexpectedly LV
diastolic stiffness is normal. Here we studied the contraction-relaxation
kinetics from the time-varying elastance of the LV and intact cardiomyocyte,
cellular work loops of intact cardiomyocytes, Ca2+ transients, cross-bridge
kinetics, and myofilament Ca2+ sensitivity. Intact cardiomyocytes of
_TtnΔC1-2_ mice exhibit systolic dysfunction and impaired relaxation. The
time-varying elastance at both LV and single-cell levels showed that
activation kinetics are normal in _TtnΔC1-2_ mice, but that relaxation is
slower. The slowed relaxation is, in part, attributable to an increased
myofilament Ca2+ sensitivity and slower early Ca2+ reuptake. Cross-bridge
dynamics showed that cross-bridge kinetics are normal but that the number of
force-generating cross-bridges is reduced. In vivo sarcomere length (SL)
measurements revealed that in _TtnΔC1-2_ mice the operating SL range of the LV
is shifted towards shorter lengths. This normalizes the apparent cell and LV
diastolic stiffness but further reduces systolic force as systole occurs
further down on the ascending limb of the force-SL relation. We propose that
the reduced working SLs reflect titin’s role in regulating diastolic stiffness
by altering the number of sarcomeres in series. Overall, our study reveals
that thick filament length regulation by titin’s C-zone is critical for normal
cardiac function.



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## Files and Folders

The data was divided into multiple zip files according to the experimental 
techniques. Each zip file contains its own readme file (explaining the names 
of subfolder/files), protocol file, analyzed excel files, and the final 
figures corresponding to the final result. 



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## Materials and Methods

Some specialized software is required to view the raw data files:
Intact cardiomyocyte: IonWizard software 6.3  or higher version (Ion optix)
Myofilament Ca2+ sensitivity and crossbridge kinetic studies: 1200A (Aurora Scientific)
Pressure-volume analysis:LabScribe3 or higher version (iWorx)
The analysis software is available for download through the websites of the companies.



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## Contributor Roles

The roles are defined by the CRediT taxonomy http://credit.niso.org/

  - Mei Methawasin, University of Arizona:Conceptualization,Data curation,Formal Analysis,Funding acquisition,Methodology, Investigation,Writing – original draft
  - Gerrie P. Farman, University of Arizona:Data curation,Formal Analysis,Investigation,Methodology
  - Shawtaroh Granzier-Nakajima, University of Arizona:Software
  - Joshua Strom, University of Arizona:Data curation,Formal Analysis,Investigation
  - Balazs Kiss, University of Arizona:Software
  - John E Smith III, University of Arizona: Methodology
  - Henk Granzier, University of Arizona:Conceptualization,Funding acquisition,Writing – review & editing



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## Additional Notes

Abbreviation
LV (left ventricle)
SL (sarcomere length)
cMyBP-C (cardiac myosin-binding protein C)
ESPVR (end-systolic pressure-volume relation)
EDPVR (end-diastolic pressure-volume relation)
E(t) (elastance)
En(t) (normalized elastance)
Toe (time to the onset of ejection)
Tes (time to the end-systole)
Eoe (elastance at the onset of ejection)
Ees (elastance at end-systole)
dS/dtmax (maximal rate of stress rise) 
dS/dtmin (maximal rate of stress decline)
ES-SSLR (end-systolic stress-sarcomere length relation)
ED-SSLR (end-diastolic stress-sarcomere length relation)
LDA (length dependence of activation)
IVRT (Isovolumic relaxation time)