Over 49% of elderly patients with heart failure exhibit left ventricular (LV) diastolic dysfunction, characterised by preserved LV ejection fraction, impaired relaxation and increased myocardial stiffness. Two major determinants of myocardial stiffness are i) the turnover and organisation of the extracellular matrix (ECM) and ii) the mechanical properties of the giant sarcomeric protein titin. We have previously reported that during heart failure, reduction in collagen content is correlated with a simultaneous increase in the activity of the collagen-degrading matrix metalloproteinase MMP-9.

Aim: 

In order to determine if titin contributes to altered compliance in diseased hearts, we have applied molecular combing techniques to characterise the nano-mechanical properties of isolated native cardiac titin molecules¹.

Methods: 

Following extraction from ferret LV², titin molecules were exposed to tensile forces ~110-160 pN.

Results: 

Visualisation of uncombed titin molecules by atomic force microscopy revealed a highly coiled, spring-like conformation. In contrast, combed molecules were both straightened and aligned. Fitting Gaussian curves to measured contour length distributions from combed and uncombed molecules revealed a tensile force induced 40% increase in titin monomer length from 1.2 to 1.7 mm. Mean axial heights were also reduced following combing (0.62 ± 0.21nm uncombed vs. 0.58 ± 0.2 nm, n = 40-42 molecules, p < 0.01) which may indicate the unfolding of domains.

Conclusion: 

The molecular combing technique is capable of aligning and stretching isolated titin molecules and has the potential to provide valuable information on the role of titin mechanical properties in disease processes.

References: 

(1) Sherratt MJ. et al. J Mol Biol 2003; 332(1):183 – 93;

(2) Soteriou A. et al. J Cell Sci 1993; 104:119 - 23.