HEAT SHOCK PRE-TREATMENT OF EXPLANT-DERIVED CARDIAC STEM CELLS PROTECTS AGAINST ISCHEMIC STRESS

Abstract

Transplant of explant-derived cardiac stem cells (EDCs) provides therapeutic regeneration of ischemic cardiomyopathy (ICM) through stimulation of angiogenesis and the generation of new cardiomyocytes- despite negligible long-term engraftment of transplanted cells. To offset the relentless ongoing loss of transplanted cells in ICM hearts, we investigated the ability of heat shock proteins (HSPs) to protect EDCs from cellular stress. Increasing EDCs exposure to heat shock culture conditions (43°C at 5% oxygen) progressively enhanced HSP70 transcript expression while HSP90 transcript expression remained unchanged. HSP70 expression plateaued 2012±736 fold above baseline after exposure to 3 hours of heat shock conditions and this pre-treatment duration was used for subsequent experiments. Heat shock treatment increased EDC proliferation within ischemic (1% oxygen) serum free conditions designed to mimic the ICM heart (population doubling time: 75±4 vs. 103±7 hours with no heat shock treatment, p=0.01, n=4). After 48 hours of exposure to hypoxic serum free conditions, heat shock pre-treatment increased the number of proliferating (Ki-67+) EDCs by 60±13% (p < 0.0001, n=6). Heat shock pre-treatment also conferred resistance to direct noxious stimuli. After 18 hours of exposure to 2ul of 100mM staurosporine, heat shock pre-treatment reduced cell death by 45±7% (p=0.03 vs. non heat shock pre-treated cells, n=5) and annexin V+ cells by 27±6% (p=0.04 vs. non heat shock pre-treated cells, n=5). Heat shock pre-treatment provides a simple inexpensive strategy to increase EDC survival in conditions mirroring the inhospitable remodeled ICM heart. We anticipate this strategy will synergize with biomaterial-based approaches that boost acute engraftment without supporting long-term cell survival.