Dynamics and mediators of acute graft attrition after myoblast transplantation to the heart

Abstract

Survival and proliferation of skeletal myoblasts within the cardiac environment are crucial to the therapeutic efficacy of myoblast transplantation to the heart. We have analyzed the early dynamics of myoblasts implanted into the myocardium and investigated the mechanisms underlying graft attrition. At 10 min after implantation of [14C]thymidine-labeled male myoblasts into female mice hearts, 14C measurement showed that 39.2 +/- 3.0% of the grafted cells survived, and this steadily decreased to 16.0 +/- 1.7% by 24 h and to 7.4 +/- 0.9% by 72 h. PCR of male-specific Smcy gene calculated that the total (surviving plus proliferated) number of donor-derived cells was 18.3 +/- 1.6 and 23.3 +/- 1.3% at 24 and 72 h, respectively, indicating that proliferation of the surviving cells began after 24 h. Acute inflammation became prominent by 24 h and was reduced by 72 h as indicated by myeloperoxidase activity and histological findings. Multiplex RT-PCR revealed corresponding changes in IL-1beta, TGF-beta, IL-6, and TNF-alpha expression. Treatment with CuZn-superoxide dismutase attenuated the initial rapid death and resulted in enhanced cell numbers afterward, giving a twofold increased total number at 72 h compared with the nontreatment. This effect was associated with reduced inflammatory response, suggesting a causative role for superoxide in the initial rapid graft death and subsequent inflammation. These data describe the early dynamics of myoblasts implanted into the myocardium and suggest that initial oxidative stress and following inflammatory response may be important mechanisms contributing to acute graft attrition, both of which could be potential therapeutic targets to improve the efficiency of cell transplantation to the heart.

Anoikis: an emerging hallmark in health and diseases

“…In addition, the survival rate of transplanted human mesenchymal stem cells in a mouse heart reaches <0.5% at 4 days after transplantation [165]. These discouraging results were also reported using different cell types, such as skeletal myoblasts, smooth muscle cells and unfractionated bone marrow cells, which can survive only few days after transplantation [166][167][168]. In vivo, bone marrow-derived circulating mesenchymal stem cells are able to repopulate damaged tissues, leading to reconstruction of their function, due to the secretion of soluble factors exerting proliferative and anti-apoptotic actions [169].…”

“…To further increase the damage, ROS can increase the anoikis signals during transplantation of myocardial precursors, since they are dramatically increased in the ischaemic heart and hinder cell adhesion [171]. Hence, co-injection of skeletal myoblasts with ROS scavengers increases cell survival by about two-fold after the engraftment [168]. Therefore, knowledge of molecules able to enhance the viability of the transplanted cells is crucial.…”

Systems approaches to preventing transplanted cell death in cardiac repair

“…In the context of injury, cells can be exposed to large concentrations of free radical species, especially from inflammatory leukocytes [73] and improper metabolite washout from ischemia. Coinjecting the free radical scavenger superoxide dismutase with skeletal myoblasts yielded a 2-fold increase in graft survival [53] three days after engraftment. This effect was concurrent with a reduced inflammatory response, suggesting that superoxide is an important factor in the initial graft death and in mediating recruitment of inflammatory cells.…”

“…Several interventions are already known to enhance survival of transplanted cells in the heart, and these are summarized in Table 1. We identified heat shock as a potent strategy to enhance survival of neonatal cardiomyocyte grafts [44], and heat shock treatment has subequently been shown to be effective for skeletal myoblast survival [53,54] and hESC-derived cardiomyocytes [21,22]. Heat shock is typically achieved by heating cells to 43°C for 30-60 minutes one day before transplantation, and this results in induction of the heat shock proteins (hsps) 60, 70 and 90 [21,44].…”

Stem Cell Therapy for Heart Disease

“…29 Suitable candidates include chronic ischemic HF patients, because chronically infarcted tissue does not release the necessary post-AMI physiological signals to attract and mobilize cells to the infarct zone. 19,28 However, only a small amount of cells survive more than three days, 30 because the microenvironment is problematic for cell survival secondary to inflammation and insufficient blood supply. 2,28 This is further complicated by mechanical leakage 2 and arrhythmia potential.…”