Caveolae in mechanotransduction
K. Fiedler, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
A tissue-culture assay for receptor-mediated transcytosis of LDL previously showed that poly (ethylene glycol)-modified cholesterol did not inhibit the
majority of transcytosis in endothelial cells derived from mice lymph nodes. Incubation of cells at 4°C led to a twofold reduction in receptor-mediated transport
suggesting that protein-protein interactions and enzymology in direct transcytosis are unusual and that additional non-clathrin- and non-caveolae-mediated pathways exist
in endothelia. In a biochemical analysis of caveolae by immunoisolation from rat lung microvascular endothelial luminal plasma membrane the 11 major proteins corresponded
to caveolin-1 α and β, ESA/reggie-1/flotillin-2, annexin V and ATP synthase β subunit and unidentified components as analyzed by 2D-IPG-SDS-PAGE, tandem mass
spectroscopy and western blotting. Immunoprecipitation experiments of caveolin-1 α from octylglucoside extracts from this source demonstrated that caveolin-1 α
associated with 12 major proteins identified by silver-staining and tandem mass spectroscopy, these were caveolin-1 β, caveolin-2, actin, the microsomal form of NADH
cytochrome B5 reductase and additional factors. I propose that caveolae are involved in blood vessel compliance regulation by pressure integration by ATP synthase
alternatively targeted to the plasma membrane. ATP synthesis in the exoplasm activates purinergic receptors via ATP or ADP generated by CD39 in caveolae to downmodulate basal
nitric oxide production. Pressure stimuli exerted on the blood vessel by orthostatic changes drive the muscle cell layer to constrict, triggered by endothelial tensegrity
and second messengers such as ATP released from the abluminal membrane. NADH cytochrome B5 reductase as part of a ternary chain of enzymes of reductase, cytochrome B5 and
desaturases is implicated in fatty acyl-CoA/lipid desaturation and cholesterol biosynthesis, may adapt channels involved in the trigger cascade of mechanosensation to
pressure changes and conduct protons to the cytoplasm via integral membrane protein desaturases to stimulate ATP synthesis and allow for metabolic input.
