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Methionine‐Restriction Decreases Non‐Electrolyte Tight Junction Permeability in a Renal Epithelial Cell Line

The principal function of an epithelial tissue is to act as a barrier, separating luminal and anti‐luminal compartments. Breakdown of epithelial barriers is involved in many diseases, often due to compromised tight junctional integrity. Caloric‐restricted or methionine‐restricted animals experience both prolonged lifespan and decreased age‐related morbidity. This study focuses on whether improved epithelial barrier function may be one mechanism responsible for the lifespan‐enhancing effect of these nutritional regimens. Using the renal epithelial cell culture, LLC‐PK1, we mimicked a methionine‐restricted diet by decreasing sulfur‐containing amino acids in culture medium. Cystine was eliminated completely; cysteine was reduced to 50%; methionine was reduced to 10%. These levels still supported cell division and differentiation. Whereas electrical resistance across methionine‐restricted cell sheets remained unchanged when compared to controls, transepithelial (paracellular) diffusion of D‐mannitol decreased significantly by nearly forty percent. Transepithelial diffusion of polyethyleneglycol (4000) also decreased significantly (by 30%). Tight junction protein expression was altered significantly, with claudin‐3 decreasing by nearly 50% whereas claudin‐5 increased nearly 300%.