Background—: Secreted factors from epicardial adipose tissue (EAT) have been implicated in the development of cardiomyocyte dysfunction. This study aimed to assess whether alterations in the secretory profile of EAT in patients with type 2 diabetes mellitus (DM2) affect contractile function and insulin action in cardiomyocytes. Methods and Results—: Contractile function and insulin action were analyzed in primary adult rat cardiomyocytes incubated with conditioned media (CM) generated from explants of EAT biopsies obtained from patients without and with DM2. CM from subcutaneous and pericardial adipose tissue biopsies from the same patients served as the control. Cardiomyocytes treated with CM (EAT) from DM2 patients showed reductions in sarcomere shortening, cytosolic Ca ²⁺ fluxes, expression of sarcoplasmic endoplasmic reticulum ATPase 2a, and decreased insulin-mediated Akt-Ser473-phosphorylation as compared with CM from the other groups. Profiling of the CM showed that activin A, angiopoietin-2, and CD14 selectively accumulated in CM-EAT-DM2 versus CM-EAT in patients without DM2 and CM from the other fat depots. Accordingly, EAT biopsies from DM2 patients were characterized by clusters of CD14-positive monocytes. Furthermore, SMAD2-phosphorylation, a downstream target of activin A signaling, was elevated in cardiomyocytes treated with CM (EAT) from DM2 patients, and the detrimental effects of CM (EAT) from DM2 patients were partially abolished in cardiomyocytes pretreated with a neutralizing antibody against activin A. Finally, both recombinant activin A and angiopoietin-2 reduced cardiomyocyte contractile function, but only activin A reduced the expression of sarcoplasmic endoplasmic reticulum ATPase 2a. Conclusions—: Collectively, our data implicate DM2-related alterations in the secretory profile of EAT in the pathogenesis of diabetes mellitus–related heart disease.

Decellularized cardiac extracellular matrix (ECM) has been introduced as a template for cardiac tissue engineering, providing the advantages of a prevascularized scaffold that mimics native micro- and macroarchitecture to a degree difficult to achieve with synthetic materials. Nonetheless, the decellularization protocols used to create acellular myocardial scaffolds vary widely throughout the literature. In this study we performed a direct comparison of three previously described protocols while introducing and evaluating a novel, specifically developed fourth protocol, by decellularizing whole rat hearts through software-controlled automatic coronary perfusion. Although all protocols preserved the macroarchitecture of the hearts and all resulting scaffolds could successfully be reseeded with C2C12 myoblasts, assessing their biocompatibility for three-dimensional in vitro studies, we found striking differences concerning the microcomposition of the ECM scaffolds on a histological and biochemical level. While laminin could still be detected in all groups, other crucial ECM components, like elastin and collagen IV, were completely removed by at least one of the protocols. Further, only three protocols maintained a glycosaminoglycan content comparable to native tissue, whereas the remaining DNA content within the ECM varied highly throughout all four tested protocols. This study showed that the degree of acellularity and resulting ECM composition of decellularized myocardial scaffolds strongly differs depending on the decellularization protocol.

Background Surgical repair of congenital and acquired cardiac defects may be enhanced by the use of autologous bioengineered muscle grafts. These tissue-engineered constructs are not optimal in their formation and function. We hypothesized that a mechanical stretch regimen applied to human heart cells that were seeded on a three-dimensional gelatin scaffold (Gelfoam) would improve tissue formation and enhance graft strength. Methods and Results Heart cells from children undergoing repair of Tetralogy of Fallot were isolated and cultured. Heart cells were seeded on gelatin-matrix scaffolds (Gelfoam) and subjected to cyclical mechanical stress (n=7) using the Bio-Stretch Apparatus (80 cycles/minute for 14 days). Control scaffolds (n=7) were maintained under identical conditions but without cyclical stretch. Cell counting, histology, and computerized image analysis determined cell proliferation and their spatial distribution within the tissue-engineered grafts. Collagen matrix formation and organization was determined with polarized light and laser confocal microscopy. Uniaxial tensile testing assessed tissue-engineered graft function. Human heart cells proliferated within the gelatin scaffold. Remarkably, grafts that were subjected to cyclical stretch demonstrated increased cell proliferation and a marked improvement of cell distribution. Collagen matrix formation and organization was enhanced by mechanical stretch. Both maximal tensile strength and resistance to stretch were improved by cyclical mechanical stretch. Conclusion The cyclical mechanical stretch regimen enhanced the formation of a three-dimensional tissue-engineered cardiac graft by improving the proliferation and distribution of seeded human heart cells and by stimulating organized matrix formation resulting in an order of magnitude increase in the mechanical strength of the graft.

More than a decade after the first reports on successful three-dimensional cardiac cell culture for experimental and potential therapeutic application, the interest and experimental efforts in the field of myocardial tissue engineering continues to grow. The hope that tissue cultures may one day act as graft substitute for malfunctioning myocardium continues to drive current scientific activity. Against this background interest seem to have progressively shifted towards the aim of engineering single tissue components. Accordingly, elements of the extracellular matrix (ECM) have gained increasing attention as potentially crucial mediators in developing and maintaining the characteristics of three-dimensional cardiac cell cultures. The ECM is now no longer regarded as merely a scaffold for developing tissue, a concept that is widely acknowledged in modern tissue engineering. The understanding of the role of precursor and stem cells has highlighted new complicated aspects of cell proliferation and differentiation and ECM proves to play an important role in providing essential signals to influence major intracellular pathways such as proliferation, differentiation and cell metabolism. Furthermore, progress in biochemical engineering has provided the perspective of application of synthetic ECM-linked molecules with bioactive potential. With the advent and continuous refinement of cell removal techniques, a new class of native acellular ECM has emerged with some striking advantages. The presently available ECM materials aim to closely resemble the in vivo microenvironment by acting as an active component of the developing tissue construct. It is therefore not surprising that most of the focus in myocardial tissue engineering has been on cell-matrix interaction, for both naturally derived and synthetic ECM. This article provides a review of established models of myocardial tissue engineering with respect to the employed ECM materials including current frontiers in material development.