Human BIN1 isoforms grow, maintain, and regenerate excitation–contraction couplons in adult rat and human stem cell-derived cardiomyocytes

Abstract

Aims In ventricular myocytes, Transverse-tubules (T-tubules) are instrumental for excitation-contraction (EC) coupling and their disarray is a hallmark of cardiac diseases. BIN1 is a key contributor to their biogenesis. Our study set out to investigate the role of human BIN1 splice variants in the maintenance and regeneration of EC-coupling in rat adult ventricular myocytes and human induced pluripotent stem cell-derived cardiac myocytes (hiPS-CMs). Methods and Results In heart samples from healthy human donors expression patterns of 5 BIN1 splice variants were identified. Following viral transduction of human BIN1 splice variants in cellular models of T-tubular disarray we employed high-speed confocal calcium imaging and Ca-CLEAN analysis to identify functional EC-coupling sites and T-tubular architecture. Adult rat ventricular myocytes were used to investigate the regeneration after loss and maintenance of EC-coupling while we studied the enhancement of EC-coupling in hiPS-CMs. All five human BIN1 splice variants induced de novo generation of T-tubules in both cell types. Isoforms with the phosphoinositide binding motif (PI) were most potent in maintenance and regeneration of T-tubules and functional EC-coupling in adult rat myocytes. In hiPSC-CMs, BIN1 variants with PI motiv induced de-novo generation of T-tubules, functional EC-coupling sites and enhanced calcium handling. Conclusion(s) BIN1 is essential for the maintenance, regeneration, and de-novo generation of functional T-tubules, especially isoforms with PI motifs. These T-tubules trigger the development of functional EC couplons resulting in enhanced calcium handling. Translational Perspective Cardiomyopathy and heart failure are among the most frequent causes of death in modern societies. Gene therapies and hiPSC technology are becoming increasingly promising, both for treatment and therapy development. On the cellular level, one of the common denominators of cardiac diseases is the concurrent loss of T-tubules essential for efficient EC-coupling. While initial approaches in animal models employing gene therapy with BIN1 have depicted encouraging improvements the expression pattern of BIN1 isoforms in the human heart is still elusive. The present study identifies a unique set of five distinct BIN1 isoforms in healthy human hearts and demonstrates their potency in both, T-tubule maintenance and re-generation after loss resulting in efficient EC-coupling. Noteworthy, PI-motif containing isoforms were potent trigger of de-novo generation of T-tubules and establishment of efficient EC-coupling in hiPSC-CMs. Therefore, the expression of BIN1 might be novel and promising for pharmaceutical treatment and gene therapy.

BIN1, Myotubularin, and Dynamin-2 Coordinate T-Tubule Growth in Cardiomyocytes

“…19 There are, however, likely important species differences, as previous reports have identified BIN1+11+17 in human, sheep, and rat hearts. 18,33,34 During postnatal development in mice, we observed that all 4 BIN1 isoforms and total BIN1 showed bell-shape expression patterns in both mRNA and protein levels, with highest levels observed during the initiation of t-tubule growth between 10 and 20 days of age. Notably, the 2 ubiquitous BIN1 variants (BIN1 and BIN1+17) showed comparable predicted and estimated molecular weights by immunoblotting.…”

Membrane remodelling triggers maturation of excitation–contraction coupling in 3D-shaped human-induced pluripotent stem cell-derived cardiomyocytes

“…The localization of LTCCs and RyR2s switched from a diffuse distribution to a more organised and striated expression pattern in cuboid BIN1-overexpressing hiPSC-CM leading to increased formation of dyads, i.e. subcellular microdomains where LTCCs and RyR2s are enriched for better functional interaction [ 11 , 3 ]. In contrast to non-patterned control cells, the distance between both types of Ca 2+ channel was reduced to less than 40 nm in 3D-reshaped BIN1-overexpressing hiPSC-CM, reminiscent of the narrow dyadic cleft of adult, i.e.…”

Phosphatidylinositol-4,5-Bisphosphate Binding to Amphiphysin-II Modulates T-Tubule Remodeling: Implications for Heart Failure

“…It is also important to note that recent work has also identified the presence of exon 11-containing isoform 8 in rat ( Li et al, 2020 ) but not apparently in mouse ( Hong et al, 2014 ) myocardium. Furthermore, Guo et al (2021) have shown that at least two different exon 11-containing isoforms 8 and 13 (i.e., Bin1+11 and Bin1+11+17, respectively) are also present in human heart. These results indicate that there are indeed exon 11-containing isoforms in hearts other than mouse that are likely to interact with PIP2 through this motif as well as possible additional binding sites described here that do not rely on the presence of exon 11.…”