Somatic Stem Cell Transplantation for the Failing Heart

Bcl-2 Expression Enhances Myoblast Sheet Transplantation Therapy for Acute Myocardial Infarction

Myoblast sheet transplantation is a promising novel treatment modality for heart failure after an ischemic insult. However, low supply of blood and nutrients may compromise sheet survival. The aim of this study was to investigate the effect of mitochondria-protective Bcl-2-modified myoblasts in cell sheet transplantation therapy. In the Bcl-2-expressing rat L6 myoblast sheets (L6-Bcl2), increased expression of myocyte markers and angiogenic mediators was evident compared to wild-type (L6-WT) sheets. The L6-Bcl2 sheets demonstrated significant resistance to apoptotic stimuli, and their differentiation capacity in vitro was increased. We evaluated the therapeutic effect of Bcl-2-modified myoblast sheets in a rat model of acute myocardial infarction (AMI). Sixty-four Wistar rats were divided into four groups. One group underwent AMI ( n = 22), another AMI and L6-WT sheet transplantation ( n = 17), and a third AMI and L6-Bcl2 sheet transplantation ( n = 20). Five rats underwent a sham operation. Echocardiography was performed after 3, 10, and 28 days. Samples for histological analysis were collected at the end of the study. After AMI, the Bcl-2-expressing sheets survived longer on the infarcted myocardium, and significantly improved cardiac function. L6-Bcl2 sheet transplantation reduced myocardial fibrosis and increased vascular density in infarct and border areas. Moreover, the number of c-kit-positive and proliferating cells in the myocardium was increased in the L6-Bcl2 group. In conclusion, Bcl-2 prolongs survival of myoblast sheets, increases production of proangiogenic paracrine mediators, and enhances the therapeutic efficacy of cell sheet transplantation.

Heat shock enhances troponin expression and decreases differentiation-associated caspase-3 dependence in myoblasts under hypoxia

BACKGROUND

Myoblast transplantation can functionally restore muscle tissues damaged by ischemic or other insults. Despite promising results in clinical trials, however, myoblast transplantation still presents several challenges, with effective differentiation under harsh conditions of the host tissue being one of the most demanding. In keeping with a straightforward clinical application, heat shock (HS) pretreatment as a nonviral method can be utilized with promising results in cell therapy. The aim of this study was to demonstrate whether HS-pretreated cells would receive a differentiation benefit under hypoxic conditions.

MATERIALS AND METHODS

We studied HS preconditioning of C2C12 myoblasts in relation to their differentiation- and apoptosis-associated responses under normoxia or 1% hypoxia.

RESULTS

HS induced long-lasting expression of Hsp70/72 and Hsp90. Although myoblast differentiation proceeded in HS-pretreated and control cells under both normoxia and hypoxia, expression of differentiation-associated troponin was enhanced in HS-preconditioned cells under hypoxia. This effect persisted when differentiation was inhibited by Z-DEVD-FMK, a caspase-3 inhibitor.

CONCLUSIONS

HS preconditioning enhances expression of myoblast differentiation-associated troponin and may reduce dependence of differentiation on caspase-3.