Occludin knockdown is not sufficient to induce transepithelial macromolecule passage

Area of Science:

• Epithelial biology
• Cellular physiology
• Membrane transport

Background:

• Tight junction proteins, like occludin, are implicated in regulating epithelial barrier function.
• The precise role of occludin in macromolecule passage at the single cell-cell junction level remains incompletely understood.

Purpose of the Study:

• To elucidate the specific function of occludin in the macromolecule leak pathway at individual cell-cell junctions.
• To investigate the relationship between occludin expression levels and macromolecule flux across epithelial barriers.

Main Methods:

• Generated a variance model of occludin expression using transient and stable knockdown in intestinal epithelial cells.
• Employed global and local analysis techniques to assess macromolecule flux and passage at single-cell junctions.
• Utilized a novel method for spatially resolving macromolecular permeation sites.

Main Results:

• Macromolecular flux across intestinal epithelial cells did not correlate with occludin expression levels.
• Leaky cell junctions were identified at the edge of Transwells, contributing significantly to overall macromolecule passage.
• Rare leaks, rather than widespread occludin dysfunction, were found to dictate net macromolecule flux.

Conclusions:

• Occludin expression alone is insufficient to determine the epithelial leak pathway activity.
• Local analysis of macromolecule passage is crucial for accurate interpretation of global flux data.
• The presence of occludin does not preclude the formation of leaky junctions, suggesting other factors are involved.