Human Micro- and Macrovascular Endothelial Cells Exposed to Simulated Microgravity Upregulate hsp70

Microgravity is known to have adverse effects on the eukaryotic cells. Here we report that microgravity affects the behaviour of human micro- and macro-vascular endothelial cells. To simulate microgravity we have utilized a NASA-developed bioreactor, the Rotating Wall Vessel (RWV). Macrovascular cells proliferate faster in the RWV than controls and, accordingly, downregulate p21, which inhibits the transition from the G1 to the S phase. On the contrary, microvascular cells are growth retarded in simulated microgravity and upregulate p21. No apoptosis was detected in both the cell types. In parallel, upregulation of heat shock protein (hsp) 70 was observed in the two cell types. Because it is reported the hsp70 increases endothelial survival, we hypothesize that hsp70 induction might protect against apoptosis. Hsp70 upregulation might therefore represent an important adaptive response of human endothelial cells to simulated microgravity.