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Activation of AMP-activated protein kinase reduces cAMP-mediated epithelial chloride secretion
John Walker1, Humberto B Jijon, Thomas Churchill
1Univ. of Alberta, 6146 Dentistry Pharmacy Bldg., Edmonton, AB, Canada T6G 2C2.
Abstract:
AMP-activated protein kinase (AMPK) is activated in response to fluctuations in cellular energy status caused by oxidative stress. One of its targets is the cystic fibrosis transmembrane conductance regulator (CFTR), which is the predominant Cl- secretory channel in colonic tissue. The aim of this study was to determine the role of AMPK in the modulation of colonic chloride secretion under conditions of oxidative stress and chronic inflammation. Chloride secretion and AMPK activity were examined in colonic tissue from adult IL-10-deficient and wild-type 129 Sv/Ev mice in the presence and absence of pharmacological AMPK inhibitors and activators, respectively. Apical levels of CFTR were measured in brush-border membrane vesicles. Cell culture studies in human colonic T84 monolayers examined the effect of hydrogen peroxide and pharmacological activation of AMPK on forskolin-stimulated chloride secretion. Inflamed colons from IL-10-deficient mice exhibited hyporesponsiveness to forskolin stimulation in association with reductions in surface CFTR expression and increased AMPK activity. Inhibition of AMPK restored tissue responsiveness to forskolin, whereas stimulation of AMPK with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) induced tissue hyporesponsivness in wild-type mice. T84 cells exposed to hydrogen peroxide demonstrated a time-dependent increase in AMPK activity and reduction of forskolin-stimulated chloride secretion. Inhibition of AMPK prevented the reduction in chloride secretion. Treatment of cells with the AMPK activator, AICAR, resulted in a decreased chloride secretion. In conclusion, AMPK activation is linked with reductions in cAMP-mediated epithelial chloride flux and may be a contributing factor to the hyporesponsiveness seen under conditions of chronic inflammation.
Insights
AMP-activated protein kinase (AMPK) activation reduces colonic chloride secretion by affecting cystic fibrosis transmembrane conductance regulator (CFTR). This finding may explain hyporesponsiveness in chronic inflammation.
Area of Science:
- Cellular biology
- Gastroenterology
- Molecular medicine
Background:
- AMP-activated protein kinase (AMPK) regulates cellular energy and targets cystic fibrosis transmembrane conductance regulator (CFTR).
- CFTR is crucial for chloride secretion in colonic tissue.
Purpose of the Study:
- To investigate AMPK's role in modulating colonic chloride secretion during oxidative stress and chronic inflammation.
- To explore the relationship between AMPK, CFTR, and chloride secretion in inflamed colons.
Main Methods:
- Examined chloride secretion and AMPK activity in colonic tissues from IL-10-deficient and wild-type mice.
- Measured apical CFTR levels and conducted cell culture studies with human colonic T84 monolayers.
- Utilized pharmacological AMPK inhibitors and activators, including AICAR, and hydrogen peroxide exposure.
Main Results:
- Inflamed colons from IL-10-deficient mice showed reduced forskolin response, lower surface CFTR, and higher AMPK activity.
- AMPK inhibition restored responsiveness, while AMPK activation (AICAR) caused hyporesponsiveness in wild-type mice.
- Hydrogen peroxide increased AMPK activity and reduced chloride secretion in T84 cells; AMPK inhibition prevented this reduction.
Conclusions:
- AMPK activation is associated with decreased cAMP-mediated epithelial chloride flux.
- AMPK may contribute to the hyporesponsiveness observed in chronic inflammatory conditions of the colon.