In Vitro Grown Micro-Tissues for Cardiac Cell Replacement Therapy in Vivo.

BACKGROUND/AIMS: Different approaches have been considered to improve heart reconstructive medicine and direct delivery of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) appears to be highly promising in this context. However, low cell persistence post-transplantation remains a bottleneck hindering the approach. Here, we present a novel strategy to overcome the low engraftment of PSC-CMs during the early post-transplantation phase into the myocardium of both healthy and cryoinjured syngeneic mice. METHODS: Adult murine bone marrow mesenchymal stem cells (MSCs) and PSC-CMs were co-cultured on thermo-responsive polymers and later detached through temperature reduction, resulting in the protease-free generation of cell clusters (micro-tissues) composed of both cells types. Micro-tissues were transplanted into healthy and cryo-injured murine hearts. Short term cell retention was quantified by real-time-PCR. Longitudinal cell tracking was performed by bioluminescence imaging for four weeks. Transplanted cells were further detected by immunofluorescence staining of tissue sections. RESULTS: We demonstrated that in vitro grown micro-tissues consisting of PSC-CMs and MSCs can increase cardiomyocyte retention by >10fold one day post-transplantation, but could not fully rescue a further cell loss between day 1 and day 2. Neutrophil infiltration into the transplanted area was detected in healthy hearts and could be attributed to the cellular implantation rather than tissue damage exerted by the transplantation cannula. Injected PSC-CMs were tracked and successfully detected for up to four weeks by bioluminescence imaging. CONCLUSION: This approach demonstrated that in vitro grown micro-tissues might contribute to the development of cardiac cell replacement therapies.

The influence of physiological matrix conditions on permanent culture of induced pluripotent stem cell-derived cardiomyocytes.

Cardiomyocytes (CMs) from induced pluripotent stem (iPS) cells mark an important achievement in the development of in vitro pharmacological, toxicological and developmental assays and in the establishment of protocols for cardiac cell replacement therapy. Using CMs generated from murine embryonic stem cells and iPS cells we found increased cell-matrix interaction and more matured embryoid body (EB) structures in iPS cell-derived EBs. However, neither suspension-culture in form of purified cardiac clusters nor adherence-culture on traditional cell culture plastic allowed for extended culture of CMs. CMs grown for five weeks on polystyrene exhibit signs of massive mechanical stress as indicated by α-smooth muscle actin expression and loss of sarcomere integrity. Hydrogels from polyacrylamide allow adapting of the matrix stiffness to that of cardiac tissue. We were able to eliminate the bottleneck of low cell adhesion using 2,5-Dioxopyrrolidin-1-yl-6-acrylamidohexanoate as a crosslinker to immobilize matrix proteins on the gels surface. Finally we present an easy method to generate polyacrylamide gels with a physiological Young's modulus of 55 kPa and defined surface ligand, facilitating the culture of murine and human iPS-CMs, removing excess mechanical stresses and reducing the risk of tissue culture artifacts exerted by stiff substrates.