A Matched-Filter-Based Algorithm for Subcellular Classification of T-System in Cardiac Tissues

Abstract

In mammalian ventricular cardiomyocytes, invaginations of the surface membrane form the transverse tubular system (T-system), which consists of transverse tubules (TTs) that align with sarcomeres and Z-lines as well as longitudinal tubules (LTs) that are present between Z-lines in some species. In many cardiac disease etiologies, the T-system is perturbed, which is believed to promote spatially heterogeneous, dyssynchronous Ca 2þ release and inefficient contraction. In general, T-system characterization approaches have been directed primarily at isolated cells and do not detect subcellular T-system heterogeneity. Here, we present MatchedMyo, a matched-filter-based algorithm for subcellular T-system characterization in isolated cardiomyocytes and millimeter-scale myocardial sections. The algorithm utilizes ''filters'' representative of TTs, LTs, and T-system absence. Application of the algorithm to cardiomyocytes isolated from rat disease models of myocardial infarction (MI), dilated cardiomyopathy induced via aortic banding, and sham surgery confirmed and quantified heterogeneous T-system structure and remodeling. Cardiomyocytes from post-MI hearts exhibited increasing T-system disarray as proximity to the infarct increased. We found significant (p < 0.05, Welch's t-test) increases in LT density within cardiomyocytes proximal to the infarct (12 5 3%, data reported as mean 5 SD, n ¼ 3) versus sham (4 5 2%, n ¼ 5), but not distal to the infarct (7 5 1%, n ¼ 3). The algorithm also detected decreases in TTs within 5 of the myocyte minor axis for isolated aortic banding (36 5 9%, n ¼ 3) and MI cardiomyocytes located intermediate (37 5 4%, n ¼ 3) and proximal (34 5 4%, n ¼ 3) to the infarct versus sham (57 5 12%, n ¼ 5). Application of bootstrapping to rabbit MI tissue revealed distal sections comprised 18.9 5 1.0% TTs, whereas proximal sections comprised 10.1 5 0.8% TTs (p < 0.05), a 46.6% decrease. The matched-filter approach therefore provides a robust and scalable technique for T-system characterization from isolated cells through millimeter-scale myocardial sections.

PGC-1α deficiency reveals sex-specific links between cardiac energy metabolism and EC-coupling during development of heart failure in mice

“…Images were analysed using FluoView 4.0 (Olympus, Japan), ImageJ 1.5 ( https://imagej.nih.gov/ij/ ), and MatchedMyo software. 34 …”

Tubulator : an automated approach to analysis of t-tubule and dyadic organization in cardiomyocytes

“…In addition, the plugin relies on continuous structures, thereby limiting its use on tissue where t-tubules or dyadic proteins are more sparsely distributed. Another approach has used matched-filter-based algorithms to circumvent the pitfalls of thresholding [8]. However, this method also relies on t-tubule regularity.…”