Engineered Human Cardiac Tissue from Muscle Derived Stem Cells

Heart failure results in significant cardiomyocyte (CM) loss, and post-natal mammalian heart has limited regenerative capacity. Cellular cardiomyoplasty has emerged as a novel therapy to restore contractile function. A number of cell types illicit functional benefits through paracrine mechanisms, but cardiac stem cells are unique in their ability to preferentially differentiate down a cardiac lineage to replace lost CMs. However, cardiac stem cell isolation is highly invasive. Alternatively, skeletal myoblasts can be safely isolated and showed some benefits in clinical trials as donor muscle cells, but arrhythmias occurred due to lack of electric coupling with host cells. This limitation could be overcome by differentiating cells toward a cardiomyogenic lineage. Multipotent muscle derived stem cells (MDSC) are different from skeletal myoblasts and possess greater phenotypic plasticity. Our studies showed that cardiac and skeletal muscle share major genes/proteins during development in rodents, so it may be possible for human MDSCs to differentiate into CM-like cells under the appropriate conditions. My dissertation aims to develop approaches to differentiate human MDSCs into CM-like cells. Specifically, my work focuses on three aims: (I) to characterize the biochemical and functional properties of human MDSCs cultured in a 3-dimensional engineered muscle tissue (EMT) and examine whether it recapitulates properties of developing striated muscle; (II) to determine the potential for further CM differentiation under defined biophysical and chemical conditions; (III) to evaluate the potential of human MDSC derived cardiac progenitors to improve cardiac function in a human-rat xenograft model. The results of my studies showed that human MDSCs in EMT beat spontaneously, displayed calcium transients, expressed cardiac-specific genes/proteins, and exhibited pharmacological responses similar to iPS cell-derived CMs. They also possessed characteristics of skeletal muscle including expression of MyoD, myogenin, and sk-fMHC. Their electrical coupling also remained immature. By temporally treating EMT with 4 chemical factors (4CF: miR-206 inhibitor, IWR-1, BMP4, and LiCl) and improving aggregation conditions, 4F-AEMT showed better muscle tissue formation and cardiac-like morphology with improved contractility, pharmacological responses, and electrical coupling. Although 4F-AEMT expressed MyoD and myogenin, it exhibited more cardiac-like function. Finally, human MDSC-aggregates showed evidence of survival and improved cardiac function in vivo

Developing cardiac and skeletal muscle share fast-skeletal myosin heavy chain and cardiac troponin-I expression

Skeletal muscle derived stem cells (MDSCs) transplanted into injured myocardium can differentiate into fast skeletal muscle specific myosin heavy chain (sk-fMHC) and cardiac specific troponin-I (cTn-I) positive cells sustaining recipient myocardial function. We have recently found that MDSCs differentiate into a cardiomyocyte phenotype within a three-dimensional gel bioreactor. It is generally accepted that terminally differentiated myocardium or skeletal muscle only express cTn-I or sk-fMHC, respectively. Studies have shown the presence of non-cardiac muscle proteins in the developing myocardium or cardiac proteins in pathological skeletal muscle. In the current study, we tested the hypothesis that normal developing myocardium and skeletal muscle transiently share both sk-fMHC and cTn-I proteins. Immunohistochemistry, western blot, and RT-PCR analyses were carried out in embryonic day 13 (ED13) and 20 (ED20), neonatal day 0 (ND0) and 4 (ND4), postnatal day 10 (PND10), and 8 week-old adult female Lewis rat ventricular myocardium and gastrocnemius muscle. Confocal laser microscopy revealed that sk-fMHC was expressed as a typical striated muscle pattern within ED13 ventricular myocardium, and the striated sk-fMHC expression was lost by ND4 and became negative in adult myocardium. cTn-I was not expressed as a typical striated muscle pattern throughout the myocardium until PND10. Western blot and RT-PCR analyses revealed that gene and protein expression patterns of cardiac and skeletal muscle transcription factors and sk-fMHC within ventricular myocardium and skeletal muscle were similar at ED20, and the expression patterns became cardiac or skeletal muscle specific during postnatal development. These findings provide new insight into cardiac muscle development and highlight previously unknown common developmental features of cardiac and skeletal muscle. © 2012 Clause et al

RT-PCR analysis of cardiac and skeletal muscle transcription factors, sk-fMHC, cTn-I mRNA expression.

<p><b>Lane 1</b>: ED13 ventricle, <b>Lane 2</b>: ED20 ventricle; <b>Lane 3</b>: ND0 ventricle; <b>Lane 4</b>: ND4 ventricle; <b>Lane 5</b>: PND10 ventricle; <b>Lane 6</b>: Adult ventricle; <b>Lane 7</b>: ED13 hind limbs; <b>Lane 8</b>: ED20 hind limbs, <b>Lane 9</b>: ND0 hind limbs; <b>Lane 10</b>: ND4 hind-limbs; <b>Lane 11</b>: PND10 gastrocnemius muscle; <b>Lane 12</b>: Adult gastrocnemius muscle. We note that ED20 skeletal muscle (hind limbs) mRNA expression patterns are similar to ED20 ventricular myocardium.</p

sk-fMHC (green color) and cardiac troponin-I (red color) expression within developing ventricular myocardium and skeletal muscle.

<p>The skeletal muscle fast myosin heavy chain (sk-fMHC) and cardiac troponin-I (cTn-I) expression within the embryonic day (ED13) heart (ED13 Ventricle insert, scale indicates 500 µm). The sk-fMHC was expressed as a typical striated muscle pattern in the developing ventricle and cTn-I expression was near background level at ED13. Somites also express sk-fMHC as a fiber structure and cTn-I was also expressed very weakly similar to the heart (ED13 somite panel). Scales in ED13 ventricle and somite panels indicate 20 µm. At ED20, both heart muscle (ED20 Left Vent Pap M) and skeletal muscle (not shown) express sk-fMHC and cTn-I as a striated muscle pattern. Scales in ED20 and ND4 Vent Pap M panels indicate 20 µm. In the heart, sk-fMHC expression is significantly decreased, and cTn-I expression was increased with striation pattern after neonate day 4, and skeletal muscle significantly decreases its cTn-I expression after neonate day 4 (data not shown). At postnatal day 10 (PND10), left ventricular myocardium does not express sk-fMHC and cTn-I displayed a typical striation pattern (PND10 Left Ventricle panel). Conversely, gastrocnemius muscle expressed sk-fMHC as a typical striation pattern and cTn-I was negative (PND10 skeletal muscle panel). Scales in PND10 panels indicate 20 µm.</p

Changes in mRNA levels of sk-fMHC, cTn-I, and cardiac α-MHC within ventricular myocardium and skeletal muscle.

<p>Data are expressed as average ± SD. The sk-fMHC mRNA level was significantly decreased and cTn-I and α-MHC levels were significantly increased in ventricular myocardium (<i>P</i><0.05, ANOVA). Conversely, sk-fMHC mRNA level was significantly increased and cTn-I and α-MHC were significantly decreased in skeletal muscle. Log₁₀RQ: Relative Quantification of mRNA level compared to the value in ED13. The ratio is expressed as logarithm with base value of 10 (Log₁₀).</p

Western blot analysis of developing myocardium and skeletal muscle.

<p><b>Lane 1</b>: ED13; <b>Lane 2</b>: ED20; <b>Lane 3</b>: ND0; <b>Lane 4</b>: ND4; <b>Lane 5</b>: PND10; <b>Lane 6</b>: Adult (8 week-old). <b>Top panel</b>: Left ventricular myocardium, <b>Bottom panel</b>: hind limbs at ED13, ED20, ND0, and ND4, and gastrocnemius muscle in PND10 and adult. At ED13 and ED20, left ventricular myocardium expressed sk-fMHC and cTn-I expression was very weak while skeletal muscle expressed sk-fMHC. During development, sk-fMHC expression in the left ventricular myocardium decreased and increased in skeletal muscle, whereas cTn-I is expressed in the left ventricular myocardium and was negative in skeletal muscle. α-sarcomeric actinin (α-sarcActn) was used to adjust the total protein loading for the electrophoresis.</p

Changes in mRNA levels of cardiac and skeletal muscle specific transcription factors within ventricular myocardium and skeletal muscle.

<p>Data are expressed as average ± SD. Cardiac transcription factors, Nkx2.5 and GATA4, and skeletal muscle transcription factor MyoD expression did not change in ventricular myocardium in adulthood, whereas myogenin expression was significantly decreased in ventricular myocardium (<i>P</i><0.05, ANOVA). Nkx2.5 and GATA4 were significantly decreased during development, and MyoD and myogenin were significantly increased in skeletal muscle during the development (<i>P</i><0.05). Log₁₀RQ: Relative Quantification of mRNA level compared to the mRNA level in ED13. The ratio is expressed as logarithm with base value of 10 (Log₁₀).</p

Cycle to threshold (Ct) Values of cardiac and skeletal muscle transcription factor and structural muscle protein gene expression of Embryonic day 13 (ED13) ventricular myocardium and skeletal muscle (limbs).

<p>Although expression levels vary between both types of tissue, their transcriptional and structural gene profiles overlap.</p

sk-fMHC (green color) and cardiac troponin-I (red color) expression (Panel A) and gene expression (Panel B) of skeletal muscle derived stem cell 3D collagen gel bioreactor (MDSC-3DGB).

<p>MDSC-3DGB showed co-localized expression of sk-fMHC and cardiac troponin I. Transcription factor and structural gene expression was increased compared to 2D undifferentiated MDSCs. Scale in panel A indicates 20 µm.</p