Aldosterone induces myofibroblast EGF secretion to regulate epithelial colonic permeability

Area of Science:

• Gastroenterology
• Endocrinology
• Cell Biology

Background:

• Raised aldosterone (Aldo) is known to regulate colonic epithelial barrier function and myofibroblast growth during low-sodium adaptation.
• Understanding the in vitro mechanisms of aldosterone's effects on colonic cells is crucial for elucidating its role in gut physiology.

Purpose of the Study:

• To replicate in vitro the in vivo condition of increased aldosterone using human myofibroblast (CCD-18Co) and colonic epithelial (T84) cells.
• To measure the effects of aldosterone on myofibroblast and epithelial cell proliferation and the expression of intercellular junction proteins.

Main Methods:

• Quantification of cell proliferation using 5-bromo-2'-deoxyuridine incorporation.
• Measurement of myofibroblast gene expression (EGF, VEGFa, TGF-β1) via real-time PCR.
• Assessment of junctional complex protein expression using Western blot analysis.

Main Results:

• Aldosterone significantly increased myofibroblast proliferation (70%) and EGF mRNA expression (30%), effects blocked by spironolactone.
• Aldosterone-stimulated myofibroblasts secreted increased EGF, which enhanced T84 cell proliferation (40%) and β-catenin/claudin IV expression.
• In vivo studies confirmed increased EGF and EGFR expression in the colonic mucosa of rats on a low-salt diet.

Conclusions:

• Aldosterone promotes colonic myofibroblast proliferation and EGF secretion, which subsequently enhances epithelial cell barrier function and proliferation.
• The EGF-EGFR pathway plays a key role in mediating aldosterone's effects on colonic epithelial cells.
• These findings support the hypothesis that EGF secreted by myofibroblasts mediates colonic permeability changes during low-sodium adaptation.