| Cardiovascular disease is the leading cause of death in the United States and many other countries. Atherosclerosis is initiated at focal points of unstable flow, such as branches, bifurcations, and curves, rather than throughout the vasculature. The endothelial layer at the vessel wall responds to fluid flow induced shear stress by initiating or inhibiting signaling pathways leading to gene expression. Caveolae play a role in mechanotransduction of shear stress in endothelial cells.; It was not known if caveolae formation and localization or if caveolin-1 and -2 expression and localization were affected by shear. Here we show that BAEC exposed to chronic shear (1 day) increase caveolae density specifically at the luminal surface. In addition, the caveolin-1 mRNA level is rapidly down-regulated while protein expression requires more than 1 day before decreases are seen. Caveolin-1 protein was seen as a peri-nuclear pool that colocalized with the cis-Golgi under static culture but translocated to the plasma membrane and caveolae upon shear exposure. Here we show that BAEC subject to chronic shear, then an additional step increase, exhibit little activation of ERK while Akt is phosphorylated robustly for the entire experiment.; We cloned the bovine caveolin-2 cDNA and developed an antibody that specifically recognized bovine caveolin-2. We used this antibody to show caveolin-2 co-localizes with the cis-Golgi in static control but, unlike caveolin-1, does not significantly diminish under shear conditions. Caveolin-2 demonstrated a familiar punctate pattern as well as a peri-nuclear pattern that may indicate nuclear membrane attachment after shear exposure. We established that in BAEC, caveolin-2 and caveolin-1 form a complex in caveolae fractions, however, caveolin-2 protein expression was not substantially affected by shear.; We also demonstrated caveolin-1 mRNA shear down-regulation may be controlled through the MAP kinase ERK pathway. In contrast, oscillatory shear, while still producing a down-regulation compared to static culture, maintained caveolin-1 mRNA on average 2.5 fold more than uni-directional laminar shear (ULS).; In conclusion, these results point to a direct dependence on shear for the function of caveolae and both caveolin-1 and caveolin-2 supporting a role in mechano-transduction. |
