Inhibition of Foxo1 protects pancreatic islet beta-cells against fatty acid and endoplasmic reticulum stress-induced apoptosis.
OBJECTIVE
beta-Cells are particularly susceptible to fatty acid-induced apoptosis associated with decreased insulin receptor/phosphatidylinositol-3 kinase/Akt signaling and the activation of stress kinases. We examined the mechanism of fatty acid-induced apoptosis of mouse beta-cells especially as related to the role played by endoplasmic reticulum (ER) stress-induced Foxo1 activation and whether decreasing Foxo1 activity could enhance cell survival.


METHODS
Mouse insulinoma (MIN6) cells were administered with fatty acids, and the role of Foxo1 in mediating effects on signaling pathways and apoptosis was examined by measuring Foxo1 activity and using dominant-negative Foxo1.


RESULTS
Increasing fatty acid concentrations (100-400 micromol/l palmitate or oleate) led to early Jun NH(2)-terminal kinase (JNK) activation that preceded induction of ER stress markers and apoptosis. Foxo1 activity was increased with fatty acid administration and by pharmacological inducers of ER stress, and this increase was prevented by JNK inhibition. Fatty acids induced nuclear localization of Foxo1 at 4 h when Akt activity was increased, indicating that FoxO1 activation was not mediated by JNK inhibition of Akt. In contrast, fatty acid administration for 24 h was associated with decreased insulin signaling. A dominant-negative Foxo1 adenovirus (Adv-DNFoxo) conferred cells with protection from ER stress and fatty acid-mediated apoptosis. Microarray analysis revealed that fatty acid induction of gene expression was in most cases reversed by Adv-DNFoxo, including the proapoptotic transcription factor CHOP (C/EBP [CCAAT/enhancer binding protein] homologous protein).


CONCLUSIONS
Early induction of JNK and Foxo1 activation plays an important role in fatty acid-induced apoptosis. Expressing a dominant-negative allele of Foxo1 reduces expression of apoptotic and ER stress markers and promotes beta-cell survival from fatty acid and ER stress, identifying a potential therapeutic target for preserving beta-cells in type 2 diabetes.
Martinez
Sara C
SC
Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8127, St. Louis, MO 63110, USA.
Tanabe
Katsuya
K
Cras-Méneur
Corentin
C
Abumrad
Nada A
NA
Bernal-Mizrachi
Ernesto
E
Permutt
M Alan
MA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics*; D017930:Genes, Reporter; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007340:Insulinoma; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D019301:Oleic Acid / Q000494:pharmacology; D019308:Palmitic Acid / Q000494:pharmacology; D010957:Plasmids; D011419:Propidium / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013314:Stress, Mechanical
D005230:Fatty Acids, Nonesterified; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D019301:Oleic Acid; D019308:Palmitic Acid; D011419:Propidium