Vincent Cw Chen

The cardiomyocyte lineage is critical for optimization of stem cell therapy in a mouse model of myocardial infarction

We recently described a murine embryonic stem cell (ESC) line engineered to express the activated Notch 4 receptor in a tetracycline (doxcycline; Dox) regulated fashion (tet‐notch4 ESCs). Notch 4 induction in Flk1+ hematopoietic and vascular progenitors from this line respecified them to a cardiovascular fate. We reasoned that these cells would be ideal for evaluating the contribution of the cardiomyocyte and vascular lineages to the functional improvement noted following stem cell transplantation in infarcted hearts. Flk‐1+ Tet‐notch4 cells from d 3 embryoid bodies exposed to doxycycline (Dox+) were compared to uninduced (Dox−) Flk‐1+ cells. Mice underwent transplantation of 5 × 105 Dox+ cells, Dox− cells, or an equal volume of serum‐free medium after surgically induced myocardial infarction. The mean ejection fraction was 59 ± 15, 46 ± 17, and 39 ± 13% in the Dox+, Dox−, and serum‐free medium groups, respectively (P<0.05 for the differences among all 3 groups). Immunohistochemistry of hearts injected with Dox+ grafts expressed myocardial and vascular markers, whereas grafts of Dox−cells expressed primarily vascular markers. We conclude that cardiovascular progenitors are more effective than vascular progenitors in improving function after myocardial infarction. The transplantation of appropriate cell types is critical for maximizing the benefit of cardiovascular cell therapy.—Adler, E. D., Chen, V. C., Bystrup, A., Kaplan, A. D., Giovannone, S., Eriley‐Saebo, K., Young, W., Kattman, S., Mani, V., Laflamme, M., Zhu, W.‐Z., Fayad, Z., Keller, G. The cardiomyocyte lineage is critical for optimization of stem cell therapy in a mouse model of myocardial infarction. FASEB J. 24, 1073–1081 (2010). www.fasebj.org

Passive Stretch Induces Structural and Functional Maturation of Engineered Heart Muscle as Predicted by Computational Modeling

The ability to differentiate human pluripotent stem cells (hPSCs) into cardiomyocytes (CMs) makes them an attractive source for repairing injured myocardium, disease modeling, and drug testing. Although current differentiation protocols yield hPSC‐CMs to >90% efficiency, hPSC‐CMs exhibit immature characteristics. With the goal of overcoming this limitation, we tested the effects of varying passive stretch on engineered heart muscle (EHM) structural and functional maturation, guided by computational modeling. Human embryonic stem cells (hESCs, H7 line) or human induced pluripotent stem cells (IMR‐90 line) were differentiated to hPSC‐derived cardiomyocytes (hPSC‐CMs) in vitro using a small molecule based protocol. hPSC‐CMs were characterized by troponin+ flow cytometry as well as electrophysiological measurements. Afterwards, 1.2 × 106 hPSC‐CMs were mixed with 0.4 × 106 human fibroblasts (IMR‐90 line) (3:1 ratio) and type‐I collagen. The blend was cast into custom‐made 12‐mm long polydimethylsiloxane reservoirs to vary nominal passive stretch of EHMs to 5, 7, or 9 mm. EHM characteristics were monitored for up to 50 days, with EHMs having a passive stretch of 7 mm giving the most consistent formation. Based on our initial macroscopic observations of EHM formation, we created a computational model that predicts the stress distribution throughout EHMs, which is a function of cellular composition, cellular ratio, and geometry. Based on this predictive modeling, we show cell alignment by immunohistochemistry and coordinated calcium waves by calcium imaging. Furthermore, coordinated calcium waves and mechanical contractions were apparent throughout entire EHMs. The stiffness and active forces of hPSC‐derived EHMs are comparable with rat neonatal cardiomyocyte‐derived EHMs. Three‐dimensional EHMs display increased expression of mature cardiomyocyte genes including sarcomeric protein troponin‐T, calcium and potassium ion channels, β‐adrenergic receptors, and t‐tubule protein caveolin‐3. Passive stretch affects the structural and functional maturation of EHMs. Based on our predictive computational modeling, we show how to optimize cell alignment and calcium dynamics within EHMs. These findings provide a basis for the rational design of EHMs, which enables future scale‐up productions for clinical use in cardiovascular tissue engineering. Stem Cells 2018;36:265–277

Cholesterol and Skeletal Muscle Health

In the United States, more than 400,000 people die every year directly due to physical inactivity and poor nutrition [1]. This accounts for 1/3 of all preventable deaths and 1/6 of all deaths. Increasingly, skeletal muscle has been identified as playing a central role in the modifiable risk associated with modern chronic disease with physical activity/muscle contraction being the central control point. The common link between more than 20 diseases and conditions affected by physical inactivity [2] is skeletal muscle. Skeletal muscle comprises 40–50% of the body mass, more than 50% of overall metabolism and only skeletal muscle activity can increase whole body metabolism 10-fold or greater, making the impact of caloric, fat and cholesterol intake on disease dependent, or at least interactive, with muscle activity. Skeletal muscle is the site of the largest glucose disposal, becomes insulin resistant with inactivity and skeletal muscle dysfunction, and correction of the dysfunction is the best predictor of diabetes outcomes. Skeletal muscle use and proper function contribute to cardiovascular health partly through accelerated metabolism, weight control, increased vascularization, cholesterol regulation, anti-inflammatory effects and pro-vasodilatory control. Skeletal muscle contraction directly stimulates growth or maintenance to prevent or treat the debilitating loss of muscle (sarcopenia) and bone (osteoporosis) associated with aging. Although it appears not to be widely known, it has been reported that 1/3 of cancer deaths are due to cachexia, disease-associated muscle loss, and not the cancer itself, perhaps due to the many downstream effects of inactivity, skeletal muscle’s role as a systemic amino acid buffer or due to the underlying mechanism (currently unknown) for the strong link between muscle activity and several cancers. Thus, optimal skeletal muscle function would appear to have a substantial impact on modern chronic diseases.