Gene expression profiling of human epidermal keratinocytes in simulated microgravity and recovery cultures

Simulated microgravity (SMG) bioreactors and DNA microarray technology are powerful tools to identify "space genes" that play key roles in cellular response to microgravity. We applied these biotechnology tools to investigate SMG and post-SMG recovery effects on human epidermal keratinocytes by exposing cells to SMG for 3,4,9, and 10d using the high aspect ratio vessel bioreactor followed by recovery culturing for 15,50, and 60d in normal gravity. As a result, we identified 162 differentially expressed genes, 32 of which were "center genes" that were most consistently affected in the time course experiments. Eleven of the center genes were from the integrated stress response pathways and were coordinately down regulated. Another seven of the center genes, which are all metallothionein MT-Ⅰ and MT-Ⅱ isoforms, were coordinately up-regulated. In addition, HLA-G, a key gene in cellular immune response suppression, was found to be significantly upregulated during the recovery phase. Overall, more than 80% of the differentially expressed genes from the shorter exposures (≤4d) recovered in 15d; for longer (≥9d) exposures, more than 50d were needed to recover to the impact level of shorter exposures. The data indicated that shorter SMG exposure duration would lead to quicker and more complete recovery from the microgravity effect.