An In Vitro Comparison Study of Two Cell Therapies for Cardiac Repair

Abstract

Cardiovascular disease continues to be the leading cause of death in New Zealand and throughout the world. Apart from orthotopic heart transplantation, no current treatment can prevent the progression of disease. Due to long waiting lists, heart transplantation is not a viable option for most patients. As a result, cell-therapies have garnered attention due to their potential to replace lost cardiac cells, repairing and regenerating the damaged myocardium. Despite recent advances in regenerative medicine, one of the biggest challenges remaining in translating cell-based therapies to the clinic is determining the best cell type to use.

Many different cell types have been investigated for their potential in cardiac repair. Cardiac progenitor cells (CPCs) and adipose derived stromal cells (ASCs) both show potential to promote cardiac repair. CPCs have been shown to greatly promote cardiac repair while ASCs increase angiogenesis and can be isolated in greater numbers through a relatively easy procedure. Despite advantages and disadvantages being known for various cell types, few studies exist directly comparing different cell types for cardiac repair. As both ASCs and CPCs have regenerative potential, this study aimed to directly compare these cells for in vitro cardiac repair.

ASCs and CPCs were successfully isolated from epicardial adipose tissue (EAT) and right atrial appendage (RAA) samples from the same patients through explant culture. Flow cytometry analysis showed the ASC population to be heterogeneous for mesenchymal cell marker CD90 and positive for CD29, CD73 and CD105 while CPCs were negative for the circulating haematopoietic cell marker CD34, positive for CD105 and heterogeneous for CD90. ASCs and CPCs showed comparable CD90 expression and combined CD90/CD105 expression, but CPCs showed significantly higher CD105 expression.

A wound healing assay over 24 hours to determine the migration potential of the cells showed CPCs to have significantly higher wound coverage at 6-, 12- and 18-hour time points compared to ASCs. However, after the 24-hour period, the wound coverage was comparable between both cell types. This showed both cells were able to migrate to the site of injury, but CPCs were able to do so faster.

ASCs and CPCs were then cultured in serum deprived hypoxia (1% O2) to mimic ischaemic conditions. Normoxic conditions (20% O2) were used as a control. Proliferation was measured and no significant difference was observed between ASC and CPC proliferation in normoxia and hypoxia. Gene expression of HIF1A, AKT1, FGF2 and PDGFA were measured to assess the cell responses to ischaemic conditions. No significant difference was found between either cell type or oxygen condition for any mRNA expression. To compare the paracrine effects of ASCs and CPCs, conditioned media (CM) was collected following serum deprived normoxic and hypoxic culture. IGF-1 and VEGF-A concentrations were measured. IGF-1 concentration was significantly higher in both normoxic and hypoxic ASC CM compared to CPC CM. VEGF-A concentration was comparable across all groups. AC16 cardiomyocytes cultured in hypoxia and treated with CPC CM had significantly lower levels of apoptosis compared to ASC CM. CPC normoxia CM was also able to significantly increase HIF1- protein expression in AC16 cardiomyocytes cultured in hypoxia. However, CM-treated HUVECs showed no significant change in angiogenesis between each group or compared to the untreated control.

In conclusion, several differences were found between CPCs and ASCs with CPCs having a marginal improvement in therapeutic effects compared to ASCs for cardiac repair. Hence, this study has provided evidence that there could be a difference between using these two cell types as therapy for cardiovascular disease. However, further in vitro and in vivo studies are required to adequately determine which cell type is more appropriate for cardiac repair.