RESUMO
We investigated the effects of prolonged heat shock treatment on human embryonic stem cell (hESC) viability. The hESC viability steadily declined with longer exposure to heat shock treatment (43ºC). After 4 h of exposure to heat shock at 43ºC, only 56.2 ± 1.5% of cells were viable. Viability subsequently declined to 37.0 ± 3.3% and 3.5 ± 0.7% after 8 h and 16 h, respectively of heat shock treatment at 43ºC. Transmission electron micrographs showed that the morphology of the dead/dying cells after heat shock treatment was characteristic of cellular necrosis with an uncondensed chromatin and a non-intact plasma membrane. This was further confirmed by flow cytometry analysis which showed that the DNA of the dead/ dying cells was still mostly intact, unlike the characteristic DNA fragmentation observed with apoptotic cells. In conclusion, prolonged exposure to heat shock treatment was detrimental to hESC viability. Hence, any future protocols developed for either the heat shock pre-conditioning of hESC prior to transplantation or for the temporary expression of specific genes with heat shock-responsive promoters should take these results into account; to achieve an optimal balance between the duration of heat shock exposure and the attainment of the desired effects.