Question: 

Shear stress induces the release of proteases from the endothelium. The mechanism of release has not yet been identified, but proteases are known as typical constituents of lysosomes which have been shown to fuse with the cell membrane. Therefore, we studied whether shear stress induces release of lysosomal contents.

Methods: 

Cultures of porcine aortic endothelial cells were loaded with the lysosomal marker LysoTracker Red (LTR) and were exposed to laminar shear stress (cone-plate apparatus or flow chamber) for up to 60 min.

Results: 

Confocal microscopy of living cells showed LTR in vesicles concentrated in the perinuclear area. Fluorescent lysosomes represented 75% of total cellular fluorescence as determined by quantitative microscopy. Mean lysosomal fluorescence intensity in endothelial cells decreased by 20% during 10 min in the absence of flow. Application of continuous shear stress (15 dyn/cm² for 10 min) enhanced the decline of fluorescence to 48%. Release of the tracer was confirmed by its accumulation in the supernatant of labelled endothelial cells during a 1 h exposure to arterial levels of shear stress (15 dyn/cm², 0.28 pmol/min LTR). No significant increase of fluorescence was observed under low shear stress (5 dyn/cm²), no flow (< 0.06 pmol/min LTR), or in the absence of LTR.

Conclusion: 

These results suggest that laminar shear stress can trigger the release of lysosomal contents from the endothelium, indicating its role in translating hemodynamic influences to extracellular degradation processes.