Palmitate induces mRNA translation and increases ER protein load in islet β-cells via activation of the mammalian target of rapamycin pathway.
Saturated free fatty acids (FFAs) have complex effects on the islet β-cell, acutely promoting adaptive hyperplasia but chronically impairing insulin release. The acute effects of FFAs remain incompletely defined. To elucidate these early molecular events, we incubated mouse β-cells and islets with palmitate and then studied mRNA translation by polyribosomal profiling and analyzed signaling pathways by immunoblot analysis. We found that palmitate acutely increases polyribosome occupancy of total RNA, consistent with an increase in mRNA translation. This effect on translation was attributable to activation of mammalian target of rapamycin (mTOR) pathways via L-type Ca(2+) channels but was independent of insulin signaling. Longer incubations led to depletion of polyribosome-associated RNA, consistent with activation of the unfolded protein response (UPR). Pharmacologic inhibition of mTOR suppressed both the acute effects of palmitate on mRNA translation and the chronic effects on the UPR. Islets from mice fed a high-fat diet for 7 days showed increases in polyribosome-associated RNA and phosphorylation of S6K, both consistent with activation of mTOR. Our results suggest that palmitate acutely activates mRNA translation and that this increase in protein load contributes to the later UPR.
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN.
Masayuki
M
Hatanaka
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN.
Bernhard
B
Maier
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN.
Emily K
EK
Sims
Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN.
Andrew T
AT
Templin
Section on Islet Cell and Regenerative Biology, Joslin Diabetes Center, Department of Medicine, Harvard Medical School, Boston, MA.
Rohit N
RN
Kulkarni
Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN Department of Medicine, Indiana University School of Medicine, Indianapolis, IN Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN.
Carmella
C
Evans-Molina
Department of Pediatrics, Indiana University School of Medicine, Indianapolis, IN Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN Department of Medicine, Indiana University School of Medicine, Indianapolis, IN Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN rmirmira@iu.edu.
Raghavendra G
RG
Mirmira
D000818:Animals; D059305:Diet, High-Fat; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D019308:Palmitic Acid / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D007328:Insulin; D019308:Palmitic Acid; D058570:TOR Serine-Threonine Kinases