The low molecular weight fraction of commercial human serum albumin induces acetylation of α-tubulin and reduces transcytosis in retinal endothelial cells

• LMWF5A rapidly induces the acetylation of α-tubulin in retinal endothelial cells.
• Inhibition of PI3 kinase reduces LMWF5A-induced acetylation.
• Inhibition of p38 MAPK potentates LMWF5A-induced acetylation.
• Calcium chelation reduces LMWF5A-induced acetylation.
• LMWF5A reduces the transcytosis of macromolecules across endothelial cells.

It has long been appreciated that the microtubule network plays a critical role in endothelial cell function. Chemical inhibition of tubulin polymerization has been shown to drastically increases endothelial permeability via interactions with the actin cytoskeleton. Conversely, stabilization of microtubules significantly decreases vascular permeability. The purpose of this investigation was to determine if the low molecular weight fraction of commercial 5% human serum albumin (LMWF5A) alters endothelial cell cytoskeletal dynamics and function. To investigate this, human retinal endothelial cells (HREC) were treated with LMWF5A and the acetylation of α-tubulin was determined by immunofluorescent staining and immunoblotting. In addition, permeability assays were performed to evaluate functional changes. We found that HREC treated with LMWF5A exhibit a rapid increase in the amount and distribution of acetylated α-tubulin. This was accompanied by a reduction in macromolecular permeability. Calcium depletion and inhibition of PI3-kinase reduced LMWF5A-induced acetylation while p38 MAPK inhibition potentiated this effect. These findings suggest that LMWF5A mediates changes in the microtubule network and reduces transcytosis in HREC.