Claudin-derived peptides are internalized via specific endocytosis pathways

Claudins regulate paracellular barriers in epithelial and endothelial tissues. Their internalization is influenced by external signals like cytokines, enabling barrier modulation for cell movement or drug transport. However, the uptake of claudin-derived peptides remains poorly understood. Prior research has shown that claudins are essential for tight junction function, but no prior work had resolved how their extracellular domains might be internalized. This gap motivated the investigation into whether claudin-derived peptides can be taken up by cells and through which pathways. Understanding these mechanisms could clarify how paracellular barriers are dynamically regulated. The role of claudin peptides in this process had not been explored before. This uncertainty drove the current study to explore peptide internalization in epithelial and endothelial cells. The findings could contribute to broader efforts in drug delivery and barrier biology.

The study aimed to determine how claudin-derived peptides are internalized in epithelial and endothelial cells. Researchers focused on two specific peptides: TAMRA-claudin-1 and TAMRA-claudin-5. The goal was to identify the endocytosis pathways involved in their uptake. The motivation stemmed from the need to understand how claudin peptides interact with cellular machinery. By investigating these peptides, the researchers hoped to uncover whether their internalization is pathway-specific or nonspecific. The study also sought to compare uptake mechanisms between different cell types. The findings could inform future strategies for modulating paracellular barriers. This work addresses a gap in knowledge about claudin peptide behavior.

The researchers used TAMRA-labeled claudin-1 and claudin-5 peptides to track internalization in epithelial and endothelial cells. They applied inhibitors and fluorescent tracers to identify endocytosis pathways. Colocalization experiments were performed to determine which pathways were active. Claudin-1 peptide uptake was tested for clathrin, macropinocytosis, and caveolae pathways. Claudin-5 peptide uptake was similarly analyzed using specific markers. The experiments were conducted in controlled cell culture conditions. Fluorescence microscopy was used to observe peptide localization. The study design allowed for pathway-specific comparisons between the two peptides.

The claudin-1 peptide was internalized via clathrin-mediated endocytosis, as shown by colocalization with clathrin markers. Macropinocytosis and caveolae-mediated pathways also contributed to its uptake. Claudin-5 peptide uptake was primarily caveolae-mediated, with some involvement of macropinocytosis. Inhibitor experiments confirmed pathway specificity for both peptides. Claudin-1 showed stronger clathrin dependence than claudin-5. Claudin-5 exhibited less efficient macropinocytosis compared to claudin-1. The results suggest that each peptide uses distinct but overlapping pathways. These findings support the hypothesis that claudin peptides can be internalized through multiple routes.

The study supports the idea that claudin-derived peptides can be internalized through both specific and nonspecific pathways. Claudin-1 peptide uptake is mainly clathrin-mediated, with contributions from macropinocytosis and caveolae. Claudin-5 peptide uptake is primarily caveolae-mediated with minor macropinocytosis involvement. The findings suggest that each peptide follows a distinct uptake mechanism. The authors propose that these pathways may be relevant to paracellular barrier regulation. The results do not imply that these peptides are essential for barrier function. The study does not claim that these pathways are universally used for all claudin peptides. The authors suggest that further work is needed to explore functional implications.