Physiological regulation of epithelial tight junctions is associated with myosin light-chain phosphorylation.
Level 5 - mechanism / opinion, no new human data
In vitro cell line model and ex vivo tissue bench study
PubMed 9357784 · doi:10.1152/ajpcell.1997.273.4.C1378
What was done
Researchers developed a cell model using Caco-2 intestinal epithelial cells transfected with the Na+-glucose cotransporter SGLT1 to investigate tight junction regulation. They measured changes in transepithelial resistance (TER) and size-selective solute flux (mannitol vs. inulin) upon SGLT1 activation and inhibition (using phloridzin). They also measured myosin light-chain (MLC) phosphorylation and assessed the effect of myosin light-chain kinase (MLCK) inhibitors (20 µM ML-7, 40 µM ML-9) in cell monolayers and intact small intestinal mucosa.
What was found
Activation of SGLT1 decreased TER by 22 ± 5% (P < 0.001), whereas SGLT1 inactivation with phloridzin increased TER by 24 ± 2% (P < 0.001). The resulting permeability increase was size-selective, permitting flux of small molecules like mannitol but not larger molecules like inulin. SGLT1 activation increased MLC phosphorylation by 2.08-fold (P < 0.01). MLCK inhibitors (ML-7 and ML-9) blocked both the permeability increase and the rise in MLC phosphorylation (P < 0.01), and ML-9 also inhibited SGLT1-mediated tight junction changes in intact small intestinal mucosa (P < 0.01).
Why it matters
This study delineates the intracellular pathway linking nutrient transport to tight junction remodeling, demonstrating that SGLT1-driven paracellular permeability changes are directly mediated by epithelial MLCK activation and MLC phosphorylation.
Limits
The study is an in vitro and ex vivo model using transfected adenocarcinoma cells (Caco-2) and isolated mucosa, which may not fully replicate in vivo human intestinal physiology. The abstract does not report the number of independent experimental replicates (n).
Cited by
- supports Intestinal epithelial tight junctions transiently open and close during normal meal consumption.