Glycogen synthase kinase-3 (GSK-3) inhibition attenuates hepatocyte lipoapoptosis

Samar C Ibrahim, Yuko Akazawa, Sophie C. Cazanave, Steven F. Bronk, Nafisa A. Elmi, Nathan W. Werneburg, Daniel D Billadeau, Gregory James Gores

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

Backgrounds & Aims: Saturated free fatty acids induce hepatocyte lipoapoptosis, a key pathologic feature of non-alcoholic steatohepatitis. The saturated free fatty acid palmitate induces hepatocyte lipoapoptosis via an endoplasmic reticulum stress pathway resulting in c-Jun-N-terminal (JNK) activation. Glycogen synthase kinase (GSK)-3 is a serine/threonine kinase which may also promote JNK activation. Thus, our aim was to determine if GSK-3 inhibition suppresses palmitate induced JNK activation and lipoapoptosis. Methods: For these studies, we employed mouse primary hepatocytes, Huh-7 and Hep3B cell lines. Results: Palmitate-induced GSK-3 activation was identified by phosphorylation of its substrate glycogen synthase. GSK-3 pharmacologic inhibition, by GSK-3 inhibitor IX and enzastaurin, significantly reduced PA-mediated lipoapoptosis. More importantly, Huh-7 cells, in which either GSK-3α or GSK-3β isoforms were stably and selectively knocked down by shRNA, displayed resistance to palmitate-induced cytotoxicity. GSK-3 pharmacological inhibitors and shRNA-targeted knockdown of GSK-3α or GSK-3β also suppressed JNK activation by palmitate. JNK activation, in part, promotes lipoapotosis by inducing expression of the pro-apoptotic effector p53-upregulated modulator of apoptosis (PUMA). Consistent with this concept, GSK-3 pharmacologic inhibition also reduced PUMA cellular protein levels during exposure to palmitate. On the other hand, the GSK-3 inhibitors did not prevent PA induction of ER stress. Conclusions: Our results suggest that GSK-3 activation promotes a JNK-dependent cytotoxic signaling cascade culminating in lipoapoptosis.

Original languageEnglish (US)
Pages (from-to)765-772
Number of pages8
JournalJournal of Hepatology
Volume54
Issue number4
DOIs
StatePublished - Apr 2011

Fingerprint

Glycogen Synthase Kinase 3
Hepatocytes
Palmitates
Nonesterified Fatty Acids
Small Interfering RNA
Fatty Acids
Apoptosis
Glycogen Synthase
Endoplasmic Reticulum Stress
Protein-Serine-Threonine Kinases
Fatty Liver

Keywords

  • Endoplasmic reticulum stress
  • Glycogen synthase kinase
  • JNK
  • Lipoapoptosis
  • Non-alcoholic steatohepatitis
  • PUMA

ASJC Scopus subject areas

  • Hepatology

Cite this

Glycogen synthase kinase-3 (GSK-3) inhibition attenuates hepatocyte lipoapoptosis. / Ibrahim, Samar C; Akazawa, Yuko; Cazanave, Sophie C.; Bronk, Steven F.; Elmi, Nafisa A.; Werneburg, Nathan W.; Billadeau, Daniel D; Gores, Gregory James.

In: Journal of Hepatology, Vol. 54, No. 4, 04.2011, p. 765-772.

Research output: Contribution to journalArticle

Ibrahim, Samar C ; Akazawa, Yuko ; Cazanave, Sophie C. ; Bronk, Steven F. ; Elmi, Nafisa A. ; Werneburg, Nathan W. ; Billadeau, Daniel D ; Gores, Gregory James. / Glycogen synthase kinase-3 (GSK-3) inhibition attenuates hepatocyte lipoapoptosis. In: Journal of Hepatology. 2011 ; Vol. 54, No. 4. pp. 765-772.
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abstract = "Backgrounds & Aims: Saturated free fatty acids induce hepatocyte lipoapoptosis, a key pathologic feature of non-alcoholic steatohepatitis. The saturated free fatty acid palmitate induces hepatocyte lipoapoptosis via an endoplasmic reticulum stress pathway resulting in c-Jun-N-terminal (JNK) activation. Glycogen synthase kinase (GSK)-3 is a serine/threonine kinase which may also promote JNK activation. Thus, our aim was to determine if GSK-3 inhibition suppresses palmitate induced JNK activation and lipoapoptosis. Methods: For these studies, we employed mouse primary hepatocytes, Huh-7 and Hep3B cell lines. Results: Palmitate-induced GSK-3 activation was identified by phosphorylation of its substrate glycogen synthase. GSK-3 pharmacologic inhibition, by GSK-3 inhibitor IX and enzastaurin, significantly reduced PA-mediated lipoapoptosis. More importantly, Huh-7 cells, in which either GSK-3α or GSK-3β isoforms were stably and selectively knocked down by shRNA, displayed resistance to palmitate-induced cytotoxicity. GSK-3 pharmacological inhibitors and shRNA-targeted knockdown of GSK-3α or GSK-3β also suppressed JNK activation by palmitate. JNK activation, in part, promotes lipoapotosis by inducing expression of the pro-apoptotic effector p53-upregulated modulator of apoptosis (PUMA). Consistent with this concept, GSK-3 pharmacologic inhibition also reduced PUMA cellular protein levels during exposure to palmitate. On the other hand, the GSK-3 inhibitors did not prevent PA induction of ER stress. Conclusions: Our results suggest that GSK-3 activation promotes a JNK-dependent cytotoxic signaling cascade culminating in lipoapoptosis.",
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AU - Ibrahim, Samar C

AU - Akazawa, Yuko

AU - Cazanave, Sophie C.

AU - Bronk, Steven F.

AU - Elmi, Nafisa A.

AU - Werneburg, Nathan W.

AU - Billadeau, Daniel D

AU - Gores, Gregory James

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N2 - Backgrounds & Aims: Saturated free fatty acids induce hepatocyte lipoapoptosis, a key pathologic feature of non-alcoholic steatohepatitis. The saturated free fatty acid palmitate induces hepatocyte lipoapoptosis via an endoplasmic reticulum stress pathway resulting in c-Jun-N-terminal (JNK) activation. Glycogen synthase kinase (GSK)-3 is a serine/threonine kinase which may also promote JNK activation. Thus, our aim was to determine if GSK-3 inhibition suppresses palmitate induced JNK activation and lipoapoptosis. Methods: For these studies, we employed mouse primary hepatocytes, Huh-7 and Hep3B cell lines. Results: Palmitate-induced GSK-3 activation was identified by phosphorylation of its substrate glycogen synthase. GSK-3 pharmacologic inhibition, by GSK-3 inhibitor IX and enzastaurin, significantly reduced PA-mediated lipoapoptosis. More importantly, Huh-7 cells, in which either GSK-3α or GSK-3β isoforms were stably and selectively knocked down by shRNA, displayed resistance to palmitate-induced cytotoxicity. GSK-3 pharmacological inhibitors and shRNA-targeted knockdown of GSK-3α or GSK-3β also suppressed JNK activation by palmitate. JNK activation, in part, promotes lipoapotosis by inducing expression of the pro-apoptotic effector p53-upregulated modulator of apoptosis (PUMA). Consistent with this concept, GSK-3 pharmacologic inhibition also reduced PUMA cellular protein levels during exposure to palmitate. On the other hand, the GSK-3 inhibitors did not prevent PA induction of ER stress. Conclusions: Our results suggest that GSK-3 activation promotes a JNK-dependent cytotoxic signaling cascade culminating in lipoapoptosis.

AB - Backgrounds & Aims: Saturated free fatty acids induce hepatocyte lipoapoptosis, a key pathologic feature of non-alcoholic steatohepatitis. The saturated free fatty acid palmitate induces hepatocyte lipoapoptosis via an endoplasmic reticulum stress pathway resulting in c-Jun-N-terminal (JNK) activation. Glycogen synthase kinase (GSK)-3 is a serine/threonine kinase which may also promote JNK activation. Thus, our aim was to determine if GSK-3 inhibition suppresses palmitate induced JNK activation and lipoapoptosis. Methods: For these studies, we employed mouse primary hepatocytes, Huh-7 and Hep3B cell lines. Results: Palmitate-induced GSK-3 activation was identified by phosphorylation of its substrate glycogen synthase. GSK-3 pharmacologic inhibition, by GSK-3 inhibitor IX and enzastaurin, significantly reduced PA-mediated lipoapoptosis. More importantly, Huh-7 cells, in which either GSK-3α or GSK-3β isoforms were stably and selectively knocked down by shRNA, displayed resistance to palmitate-induced cytotoxicity. GSK-3 pharmacological inhibitors and shRNA-targeted knockdown of GSK-3α or GSK-3β also suppressed JNK activation by palmitate. JNK activation, in part, promotes lipoapotosis by inducing expression of the pro-apoptotic effector p53-upregulated modulator of apoptosis (PUMA). Consistent with this concept, GSK-3 pharmacologic inhibition also reduced PUMA cellular protein levels during exposure to palmitate. On the other hand, the GSK-3 inhibitors did not prevent PA induction of ER stress. Conclusions: Our results suggest that GSK-3 activation promotes a JNK-dependent cytotoxic signaling cascade culminating in lipoapoptosis.

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