Post‐Myocardial Infarction T‐tubules Form Enlarged Branched Structures With Dysregulation of Junctophilin‐2 and Bridging Integrator 1 (BIN‐1)

Abstract

BackgroundHeart failure is a common secondary complication following a myocardial infarction (MI), characterized by impaired cardiac contraction and t‐tubule (t‐t) loss. However, post‐MI nano‐scale morphological changes to the remaining t‐ts are poorly understood.Method and ResultsWe utilized a porcine model of MI, using a nonlethal microembolization method to generate controlled microinfarcts. Using serial block face scanning electron microscopy, we report that post‐MI, after mild left‐ventricular dysfunction has developed, t‐ts are not only lost in the peri‐infarct region, but also the remnant t‐ts form enlarged, highly branched disordered structures, containing a dense intricate inner membrane. Biochemical and proteomics analyses showed that the calcium release channel, ryanodine receptor 2 (RyR2), abundance is unchanged, but junctophilin‐2 (JP2), important for maintaining t‐t trajectory, is depressed (−0.5×) in keeping with the t‐ts being disorganized. However, immunolabeling shows that populations of RyR2 and JP2 remain associated with the remodeled t‐ts. The bridging integrator 1 protein (BIN‐1), a regulator of tubulogensis, is upregulated (+5.4×), consistent with an overdeveloped internal membrane system, a feature not present in control t‐ts. Importantly, we have determined that t‐ts, in the remote region, are narrowed and also contain dense membrane folds (BIN‐1 is up‐regulated +3.4×), whereas the t‐ts have a radial organization comparable to control JP2 is upregulated +1.7×.ConclusionsThis study reveals previously unidentified remodeling of the t‐t nano‐architecture in the post‐MI heart that extends to the remote region. Our findings highlight that targeting JP2 may be beneficial for preserving the orientation of the t‐ts, attenuating the development of hypocontractility post‐MI.

Remodeling of the transverse tubular system after myocardial infarction in rabbit correlates with local fibrosis: A potential role of biomechanics

“…In two-dimensional images, they can easily be mistaken for longitudinally oriented t-tubules (Kaprielian et al, 2000; Kostin et al, 1998; Seidel et al, 2017). T-system remodeling in failing rodent hearts has been studied extensively, but t-system components as found in human heart failure or in a porcine infarct model (Pinali et al, 2017) have not been identified. In contrast, images of remodeled t-tubules published by others (Driesen et al, 2007) and us (Seidel et al, 2016), including the present study, indicate that t-system remodeling in rabbit resembles the human phenotype.…”

“…It still remains unclear if t-sheets are also present in animal models of heart failure, but most likely not in mice or rats because these species have already been studied extensively. In a porcine model of MI “enlarged, highly branched disordered structures” of the t-system were described in a recent study using three-dimensional electron microscopy (Pinali et al, 2017). These structures may correspond to the “sheet-like” components observed by confocal microscopy in human heart failure.…”

New Insights in Cardiac Calcium Handling and Excitation-Contraction Coupling

“…On the side of plasma membrane, along T-tubules, there are voltage-gated Ca 2+ channels (T-Type and L-type, also known as dihydropyridine receptors, DHPRs), whereas on the side of SR cisternae there are intracellular Ca 2+ release channels (ryanodine receptors, RyRs) (Pinali et al 2017; Crocini et al 2016; Li et al 2015; Fameli et al 2014). …”

“…These anomalies could also be related to impaired function of junctophilins, proteins that are responsible for appropriate positioning of voltage-gated Ca 2+ channels on T- tubules (Pinali et al 2017; Schobesberger et al 2017). …”

Junctophilins emerge as novel therapeutic targets

“…Decline of myocardial JP2 expression in patients with heart failure has been reported , and in other heart diseases such as ischemia/reperfusion injury (Guo et al, 2015), elevated wall stress (Frisk et al, 2016), transverse aortic constriction (Bryant et al, 2018;Reynolds et al, 2016), myocardial infarction (Pinali et al, 2017), and premature ventricular contraction-induced cardiomyopathy (Jiang et al, 2016).…”