title: AMP-activated protein kinase (AMPK) activation inhibits nuclear translocation of Smad4 in mesangial cells and diabetic kidneys.
abstract: Diabetic nephropathy is characterized by diffuse mesangial matrix expansion and is largely dependent on the TGF-β/Smad signaling pathway. Smad4 is required for TGF-β signaling; however, its regulation has not been well characterized in diabetic kidney disease. Here, we report that high glucose is sufficient to stimulate nuclear translocation of Smad4 in mesangial cells and that stimulation of the major energy sensor AMP-activated protein kinase (AMPK) has a potent effect to block Smad4 nuclear translocation. Activation of AMPK by 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) inhibited high glucose-induced and TGF-β stimulation of nuclear Smad4. To identify which of the catalytic α-subunits may be involved, small interfering (si) RNA-based inhibition of AMPK α1- or α2-subunit was employed. Inhibition of either subunit reduced overall AMPK activity and contributed to Smad4 nuclear accumulation. In an animal model of early diabetic kidney disease, induction of diabetes was found to markedly stimulate Smad4 protein levels and enhance nuclear accumulation. AMPK activation with AICAR completely prevented the upregulation of Smad4 and reduced mesangial matrix accumulation. We conclude that stimulation of Smad4 in cell culture and in in vivo models of early diabetic kidney disease is dependent on AMPK.
authors.affiliation: Center for Renal Translational Medicine, Division of Nephrology-Hypertension, University of California, La Jolla, California; Institute of Nephrology of Chongqing and Department of Nephrology, Xinqiao Hospital, Third Military Medical University, Chongqing, China; and.
authors.forename: Jinghong
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Center for Renal Translational Medicine, Division of Nephrology-Hypertension, University of California, La Jolla, California; Veterans Administration San Diego HealthCare System, La Jolla, California.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Miyamoto
authors.affiliation: Center for Renal Translational Medicine, Division of Nephrology-Hypertension, University of California, La Jolla, California; Veterans Administration San Diego HealthCare System, La Jolla, California.
authors.forename: Young-Hyun
authors.initials: YH
authors.lastname: You
authors.affiliation: Center for Renal Translational Medicine, Division of Nephrology-Hypertension, University of California, La Jolla, California; Veterans Administration San Diego HealthCare System, La Jolla, California kumarsharma@ucsd.edu.
authors.forename: Kumar
authors.initials: K
authors.lastname: Sharma
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000150:complications*; D003928:Diabetic Nephropathies / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D005947:Glucose / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D050527:Mesangial Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D051901:Smad4 Protein / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism*; D013311:Streptozocin / Q000009:adverse effects; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology
chemical_list: D007004:Hypoglycemic Agents; D012265:Ribonucleotides; D051901:Smad4 Protein; C490810:Smad4 protein, mouse; D016212:Transforming Growth Factor beta; D000620:Aminoimidazole Carboxamide; D013311:Streptozocin; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide; D005947:Glucose
keywords: AICAR; AMP-activated protein kinase; Smad4; diabetic nephropathy; high glucose