Decellularized extracellular matrix (dECM) based scaffolds are increasingly used in a wide range of regenerative medicine applications, as they maintain the complex microarchitecture and ultracomposition of native tissues and hence provide ideal cues for tissue regeneration (Taylor et al., 2018). In the cardiovascular field, dECM based scaffolds have already been successfully employed in many pre-clinical and clinical models, with decellularized heart valves being at the verge of changing paradigms of heart valve therapy (Horke et al., 2020). Decellularized ECM scaffolds may also offer great potential for regeneration and repair of damaged myocardium, as composition and organization of cardiac ECM - critical for cell support and tissue function–can be reproduced by decellularization of cardiac ECM (Bejleri and Davis, 2019). Although whole-heart tissue engineering approaches have impressively shown the prospects of cardiac-based ECM scaffolds, the generation of a bioartificial heart replacement is still very far afield due to biological and technical complexity (Tang-Quan et al., 2018). Hence, efforts in the field should concentrate on exploring strategies to support, repair and/or regenerate the damaged myocardium instead of replacing it. Such therapies are strongly warranted, as for today, the only viable options for the treatment of end-stage heart failure (HF) consist in the implantation of a permanent mechanical assist device or heart transplantation (McDonagh et al., 2021). Other surgical and experimental approaches that have been explored in the past, such as surgical cardiomyoplasty or stem cell therapy, have been mostly abandoned due to disappointing outcomes (Hetzer et al., 2021).

Here, we introduce a new therapy concept using a customized, decellularized cardiac ECM-based scaffold (cdECM-scaffold) in form of a tissue engineered myocardial sleeve (TEMS) for ventricular stabilization after myocardial infarction, hypothesizing that this might stimulate myocardial regeneration, hinder adverse cardiac remodeling and improve cardiac hemodynamics. This proof-of-concept study focuses on the effect on myocardial gene-expression after ventricular stabilization via TEMS in a standardized rodent LAD-ligation in vivo model.

All animal experiments and surgical procedures were performed in compliance with the Guide for the Care and Use of Laboratory Animals as published by the US National Institutes of Health (NIH Publication 85-23, revised 1996) and approved by the local animal care committees (Registration No. 84-01.04.2012. A335).

This proof-of concept study demonstrates that ventricular stabilization after myocardial infarction with a customized, decellularized cardiac ECM-based scaffold (TEMS) significantly alters myocardial gene expression in a rodent LAD-ligation model. Further, orientating analysis shows improved functional echocardiographic parameters as well as biological integration of the TEMS scaffold after 4 and 8 weeks of ventricular stabilization in vivo.

In the past, different surgical and experimental approaches have used the concept of cardiomyoplasty in terms of functional left ventricular restoration in order to treat end-stage heart failure. This concept was first introduced in 1985 by Carpentier and Chaques as dynamic cardiomyoplasty, by wrapping the M. latissimus dorsi circumferentially around the heart in order to support systolic contraction (Carpentier and Chachques, 1985). Another surgical approach was the implantation of a mesh-like woven polyester jacket circumferentially around the heart (Acorn CorCap cardiac support device, Acorn Cardiovascular, Inc., St Paul, Minn.) to provide support during diastole (Starling and Jessup, 2004). Although those surgical cardiomyoplasty approaches were used in thousands of patients, they were ultimately abandoned, as outcomes were disappointing with questionable improvement of cardiac hemodynamics and concerns regarding adverse effects such as pericardial constrictions (Acker, 1999; Power et al., 2001). However, one of the main effects of surgical cardiomyoplasty was its ability to prevent adverse left ventricular remodeling, such as attenuation of cardiac enlargement and specific reduction of left ventricular end-diastolic dimensions.

As shown in this study ventricular stabilization via TEMS implantation prevents progressive left ventricular dilatation after myocardial infarction. Rats with supported ventricles via TEMS implantation after LAD-ligation did not only present with significantly smaller LVEDDs after 8 weeks as compared to their controls, but also showed LVEDDs comparable to the values at the time-point of TEMS implantation 14 days after myocardial infarction. Together with the other functional echocardiographic parameters, this demonstrates the potential of the TEMS concept to prevent adverse cardiac remodeling. It is still unclear what triggers this effect. Decellularized cardiac ECM still has a certain stiffness which might offer passive mechanical support during diastole (Brazile et al., 2021), leading to similar effects as with above-mentioned Acorn CorCap device. However, as demonstrated by the orientating histological analysis the TEMS scaffold is not only largely infiltrated by host cells, but also seems to integrate into the scar zone after myocardial infarction. Hence, a biological interaction with the host tissue is likely to play a mechanistic role.

The alteration of the gene expression pattern of the infarcted myocardium depending on whether the LV was supported by TEMS implantation or not, as well as the different gene expression pattern of the cells infiltrating the TEMS scaffold depending on whether it was placed on healthy or infarcted myocardium, seem to demonstrate a high degree of biological interdependency. TEMS implantation seemingly inhibited an up-regulation of infarction-related NPPA and NPPB, while promoting a down-regulation of pro-angiogenic PDGFB and immunomodulatory TGFBR2 and an up-regulation of pro-survival IGF1 and immunomodulatory IL-10 after 4 weeks of ventricular stabilization. Multiple pathophysiological factors converge after myocardial infarction leading to adverse remodeling and ischemic cardiomyopathy (Prabhu and Frangogiannis, 2016). Alteration of gene expression, as shown in this study, might enhance the post myocardial infarction regenerative process attenuating deteriorative effects of cardiac remodeling. For instance, platelet-derived growth factors as well as transforming growth factor-beta are involved in the negative inflammatory and fibrogenic response in the infarcted myocardium (Myocardial Remodeling, 2011; Dobaczewski et al., 2011) while IL-10 is a potent anti-inflammatory agent suppressing the synthesis of proinflammatory cytokines (Fiorentino et al., 1991), and activation of IGF-1 protects from the detrimental effects of myocardial infarction (Troncoso et al., 2014). On the other hand, down-regulation of NPPB, which is mainly secreted by the myocardium due to increased transmural pressure or volume overload and is considered a hallmark for maladaptive LV remodeling, could be a consequence of the TEMS capacity to prevent LV dilatation 4 weeks after myocardial infarction (Fu et al., 2018). Further, significant differences in gene expression could still be demonstrated 8 weeks after TEMS implantation with an up-regulation of remodeling-associated MMP9 and pro-angiogenic PDGFB and down-regulation of FGF2. Together with the echocardiographic findings demonstrating improved functional parameters and a further decrease in LV dimensions, our results advocate for beneficial long-term effects of ventricular stabilization via a cdECM scaffold.

Since in this proof-of-concept study only an orientating histological analysis of the explanted TEMS specimens was conducted, it remains unclear which cells infiltrate the TEMS scaffold and what role they play in the observed effects with regards to cardiac remodeling and improved cardiac function. Interestingly though, gene expression patterns of those cells significantly varied depending on whether the TEMS was placed on infarcted or healthy myocardium. During implantation the TEMS scaffold is only loosely placed on the epicardium, therefore the cdECM-scaffold seems to inherently attract resident cells, which possess the ability to integrate the scaffold into the myocardial tissue especially in the region of infarcted myocardium. Recent research efforts are increasingly demonstrating the importance of epicardial-myocardial signaling and epicardial stem cells in cardiac repair (Pellegrini et al., 2020). Therefore, a cdECM scaffold such as the TEMS might provide an ideal environment for recruitment, activation and differentiation of epicardial cells, which might enhance the regenerative capacity of the heart (Moroni and Mirabella, 2014). Targeted biofunctionalization of cdECM with specific biological cues, could further modulate TEMS-cell interaction by specific cell recruitment and activation enhancing the TEMS effects (Aubin et al., 2016).

Further, cardiac-derived decellularized ECM scaffolds can be repopulated ex vivo offering the possibility to enhance the TEMS concept with appropriate pro-regenerative cell populations potentially further increasing cardiac repair (Aubin et al., 2013b; Hülsmann et al., 2013). This would follow the cellular cardiomyoplasty approach, which aims at employing stem cell technologies in order to induce cardiac repair (Lamb et al., 2013). Although in the past cellular cardiomyplasty has shown the potential to decrease fibrosis of infarcted myocardium, to prevent adverse post-ischemic remodeling and to some extent improve systolic cardiac function, clinical outcomes have been disappointing so far, with low rates of cell survival and shortage of donor cells limiting further translation into the routine clinical practice (Broughton et al., 2018). Here, the TEMS platform could offer a promising delivery strategy that could be combined with induced pluripotent stem cell (iPSC) technology, which now allows for the derivation of large numbers of autologous cardiomyocytes from patient-specific iPSCs (Duran et al., 2018). In fact, engineered heart tissue patches generated from fibrinogen-thrombin and human iPSCs have already shown potential for remuscularization and improvement of cardiac function in a pre-clinical large animal model (Querdel et al., 2021).

In conclusion, ventricular stabilization of the heart via a cdECM-scaffold in form of a TEMS stimulates myocardial regeneration, attenuates cardiac remodeling and improves cardiac hemodynamics in a rodent model. Hence, the TEMS approach might be a promising therapy strategy for inducing cardiac regeneration in diseased hearts following a novel bioactive cardiomyoplasty concept. However, further studies are warranted in order to confirm those findings and translate the concept into a clinical setting.