Myocyte-Depleted Engineered Cardiac Tissues Support Therapeutic Potential of Mesenchymal Stem Cells

Abstract

The therapeutic potential of mesenchymal stem cells (MSCs) for restoring cardiac function after cardiomyocyte loss remains controversial. Engineered cardiac tissues (ECTs) offer a simplified three-dimensional in vitro model system to evaluate stem cell therapies. We hypothesized that contractile properties of dysfunctional ECTs would be enhanced by MSC treatment. ECTs were created from neonatal rat cardiomyocytes with and without bone marrow-derived adult rat MSCs in a type-I collagen and Matrigel scaffold using custom elastomer molds with integrated cantilever force sensors. Three experimental groups included the following: (1) baseline condition ECT consisting only of myocytes, (2) 50% myocyte-depleted ECT, modeling a dysfunctional state, and (3) 50% myocyte-depleted ECT plus 10% MSC, modeling dysfunctional myocardium with intervention. Developed stress (DS) and pacing threshold voltage (VT) were measured using 2-Hz field stimulation at 37°C on culture days 5, 10, 15, and 20. By day 5, DS of myocyte-depleted ECTs was significantly lower than baseline, and VT was elevated. In MSC-supplemented ECTs, DS and VT were significantly better than myocyte-depleted values, approaching baseline ECTs. Findings were similar through culture day 15, but lost significance at day 20. Trends in DS were partly explained by changes in the cell number and alignment with time. Thus, supplementing myocyte-depleted ECTs with MSCs transiently improved contractile function and compensated for a 50% loss of cardiomyocytes, mimicking recent animal studies and clinical trials and supporting the potential of MSCs for myocardial therapy.

Cardiac Tissue Engineering

“…One study added mesenchymal stem cell to heart tissue constructs that were, compared with control, depleted of 50% cardiac myocytes, mimicking a disease state. 83 This nonmyocyte substitution of myocytes restored force to almost control values, interestingly only for the first 15 days, similar to the transient benefit observed in some cell therapy studies. Others injected ESCs or ESCderived progenitor cells into 3D engineered tissues and observed both beneficial, paracrine, and unwanted effects, such as conduction block and teratoma formation with undifferentiated ESC.…”

Construction of Defined Human Engineered Cardiac Tissues to Study Mechanisms of Cardiac Cell Therapy

“…While many of the initial results have been promising 21,23,25 , the initial benefit often diminishes over time 26–29 . A similar trend has been reported in murine engineered cardiac tissues, which display a significant functional benefit due to MSC supplementation, but the benefit is not sustained during long-term culture 1 . Underlying the sub-optimal performance is our limited knowledge of the mechanisms governing cell therapies.…”

“…Cardiac tissue engineering has advanced greatly in the last decade, with multiple groups publishing results of fully functional, beating tissues made from both murine cardiomyocytes 1–6 and, more recently, human stem cell-derived cardiac myocytes 7–12 . The cardiac tissue engineering field is driven by two primary and essentially independent goals: 1) to develop exogenous grafts that can be transplanted into failing hearts to improve function 4–6 ; and 2) to develop in vitro models for studying physiology and disease, or as screening tools for therapeutic development 2,7 .…”

Mesenchymal Stem Cells for Cardiac Therapy: Practical Challenges and Potential Mechanisms

“…Formation of functional gap junctions between MSCs and cardiomyocytes has been documented in cultured cells [46]. While some studies claim this may improve conduction [47] and tissue excitability [48], others have cautioned about possible arrhythmogenic sodium channel inactivation in cardiomyocytes coupled to MSCs due to the mismatched resting membrane potential [49]. Optical mapping of engrafted MSCs in a rat cryoinjury model showed evidence of electrical coupling and action potential activity; however, this was apparently not MSC-generated but rather a passive effect of coupling to adjacent viable myocardium [50].…”

“…For example, our lab recently reported three-dimensional engineered cardiac tissues in which MSC co-culture increased the force generation capacity of neonatal rat cardiomyocytes and effectively compensated for a 50% reduction in myocyte content [48], with a transient benefit that mimicked animal studies and clinical trials described above. Engineered cardiac tissues using human-derived cell sources [57, 58] offer additional species-specific advantages as in vitro preclinical models of human myocardium.…”