Palmitoleate attenuates palmitate-induced Bim and PUMA up-regulation and hepatocyte lipoapoptosis.
OBJECTIVE
Saturated free fatty acids induce hepatocyte lipoapoptosis. This lipotoxicity involves an endoplasmic reticulum stress response, activation of JNK, and altered expression and function of Bcl-2 proteins. The mono-unsaturated free fatty acid palmitoleate is an adipose-derived lipokine which suppresses free fatty acid-mediated lipotoxicity by unclear mechanisms. Herein we examined the mechanisms responsible for cytoprotection.


METHODS
We employed isolated human and mouse primary hepatocytes, and the Huh-7 and Hep 3B cell lines for these studies. Cells were incubated in presence and absence of palmitate (16:0), stearate (18:0), and or palmitoleate (16:1, n-7).


RESULTS
Palmitoleate significantly reduced lipoapoptosis by palmitate or stearate in both primary cells and cell lines. Palmitoleate accentuated palmitate-induced steatosis in Huh-7 cells excluding inhibition of steatosis as a mechanism for reduced apoptosis. Palmitoleate inhibited palmitate induction of the endoplasmic reticulum stress response as demonstrated by reductions in CHOP expression, eIF2-alpha phosphorylation, XBP-1 splicing, and JNK activation. Palmitate increased expression of the BH3-only proteins PUMA and Bim, which was attenuated by palmitoleate. Consistent with its inhibition of PUMA and Bim induction, palmitoleate prevented activation of the downstream death mediator Bax.


CONCLUSIONS
These data suggest palmitoleate inhibits lipoapoptosis by blocking endoplasmic reticulum stress-associated increases of the BH3-only proteins Bim and PUMA.
Akazawa
Yuko
Y
Division of Gastroenterology and Hepatology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
Cazanave
Sophie
S
Mott
Justin L
JL
Elmi
Nafisa
N
Bronk
Steven F
SF
Kohno
Shigeru
S
Charlton
Michael R
MR
Gores
Gregory J
GJ
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000235:genetics* / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism; D004347:Drug Interactions; D004721:Endoplasmic Reticulum / Q000502:physiology; D005229:Fatty Acids, Monounsaturated / Q000378:metabolism* / Q000494:pharmacology; D005234:Fatty Liver / Q000473:pathology / Q000503:physiopathology*; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D010168:Palmitates / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D013312:Stress, Physiological / Q000502:physiology; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D000071717:X-Box Binding Protein 1; D051028:bcl-2-Associated X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; C438378:BBC3 protein, human; C000606775:BCL2L11 protein, human; C494827:Bax protein, mouse; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; C497249:DDIT3 protein, human; D004268:DNA-Binding Proteins; D005229:Fatty Acids, Monounsaturated; D008565:Membrane Proteins; C488588:PUMA protein, mouse; D010168:Palmitates; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; D051028:bcl-2-Associated X Protein; D051742:Transcription Factor CHOP; C101003:ELF2 protein, human; C008757:palmitoleic acid; D048031:JNK Mitogen-Activated Protein Kinases