Systems approaches to preventing transplanted cell death in cardiac repair

Abstract

Stem cell transplantation may repair the injured heart, but tissue regeneration is limited by death of transplanted cells. Most cell death occurs in the first few days post-transplantation, likely from a combination of ischemia, anoikis and inflammation. Interventions known to enhance transplanted cell survival include heat shock, over-expressing anti-apoptotic proteins, free radical scavengers, anti-inflammatory therapy and co-delivery of extracellular matrix molecules. Combinatorial use of such interventions markedly enhances graft cell survival, but death still remains a significant problem. We review these challenges to cardiac cell transplantation and present an approach to systematically address them.Most anti-death studies use histology to assess engraftment, which is time-and labor-intensive. To increase throughput, we developed two biochemical approaches to follow graft viability in the mouse heart. The first relies on LacZ enyzmatic activity to track genetically modified cells, and the second quantifies human genomic DNA content using repetitive Alu sequences. Both show linear relationships between input cell number and biochemical signal, but require correction for the time lag between cell death and loss of signal. Once optimized, they permit detection of as few as 1 graft cell in 40,000 host cells. Pro-survival effects measured biochemically at three days predict long-term histological engraftment benefits. These methods permitted identification of carbamylated erythropoietin (CEPO) as a pro-survival factor for human embryonic stem cell-derived cardiomyocyte grafts. CEPO's effects were additive to heat shock, implying independent survival pathways. This system should permit combinatorial approaches to enhance graft viability in a fraction of the time required for conventional histology.

Physiological function and transplantation of scaffold-free and vascularized human cardiac muscle tissue

“…To rapidly determine whether human cardiac tissue patches could engraft in muscle in vivo, we established a model of patch transplantation into skeletal muscle. Our previous work with direct injection of enzymatically dispersed cells demonstrated that death of cells during transplantation was multifactorial and that a ''cocktail'' of prosurvival interventions was required to achieve engraftment (1,18). Patches containing 3 ϫ 10 6 human cardiomyocytes cultured in the optimal RPMI-B27 media were therefore heat shocked 1 day before transplantation, bathed in prosurvival cocktail, and then implanted into the skeletal muscle of nude rats.…”

Proangiogenic scaffolds as functional templates for cardiac tissue engineering

“…Scaffolds may promote oriented tissue architectures that facilitate diffusion-based mass transfer to reduce the ischemic injury often encountered in cell aggregates or cell transplantation (9). A scaffold can also promote survival and integration by enhancing neovascularization while minimizing fibrotic encapsulation (10).…”

Bimodal in vivo imaging provides early assessment of stem-cell-based photoreceptor engraftment

“…Here we show, for the first time, that graft architecture can be highly variable at the time of transplantation, which could represent a considerable source of treatment variation among recipients and across the fundus. In this regard, bimodal imaging allows for early detection of a central problem inherent to cellsuspension therapeutics: undesired graft aggregation resulting in ischemia (reviewed by Robey et al 26 ) and/or spatial inhibition of functional connections, such as the highly limited contact observed between bolus PPC-grafts and host RPE 9 -a common architecture seen here and in other studies 7,9,27 ). Conversely, bimodal imaging can also detect extensive graft dispersion, which can leave insufficient density of cells for functional benefit, as small quantities of integrating PPCs are unlikely to rescue vision.…”