A variety of evidence suggests that endothelial cell functions are impaired in altered gravity conditions. Nevertheless, the effects of hypergravity on endothelial cell physiology remain unclear. In this study we cultured primary human endothelial cells under mild hypergravity conditions for 24-48 h, then we evaluated the changes in cell cycle progression, caveolin1 gene expression and in the caveolae status by confocal microscopy. Moreover, we analyzed the activity of enzymes known to be resident in caveolae such as endothelial nitric oxide synthase (eNOS), cycloxygenase 2 (COX-2), and prostacyclin synthase (PGIS). Finally, we performed a three-dimensional in vitro collagen gel test to evaluate the modification of the angiogenic responses. Results indicate that hypergravity shifts endothelial cells to G(0)/G(1) phase of cell cycle, reducing S phase, increasing caveolin1 gene expression and causing an increased distribution of caveolae in the cell interior. Hypergravity also increases COX-2 expression, nitric oxide (NO) and prostacyclin (PGI2) production, and inhibits angiogenesis as evaluated by 3-D collagen gel test, through a pathway not involving apoptosis. Thus, endothelial cell caveolae may be responsible for adaptation of endothelium to hypergravity and the mechanism of adaptation involves an increased caveolin1 gene expression coupled to upregulation of vasodilators as NO and PGI2.

Studies on the transmission from man to animals of Creutzfeld-Jacob disease (CJD) led Prusiner to identify a proteinaceous infectious particle lacking nucleic acid, which was called prion. The identification of the infectious prion (PrPsc) then led to the discovery of the normal cellular counterpart (PrPc). One of the still enigmatic aspects regarding prion diseases is actually how, where, and when the transformation PrPc/PrPsc is occurring, this being due to the result of a large extent to the fact that so far most studies have been dedicated to the formation and transmission of PrPsc, whereas the understanding of physiologic roles of PrPc are in their infancy. In this review, we hope to identify the most reliable hypotheses for future experiments on PrPc. This is relevant not only for the understanding of PrPc functions but also to unravel the enigmatic nature of PrPc/PrPsc conversion.