File Download
  Links for fulltext
     (May Require Subscription)
Supplementary

postgraduate thesis: Toll-like receptor-4 mediates obesity-induced nonalcoholic steatohepatitis through activation of X-box binding protein-1 in mice

TitleToll-like receptor-4 mediates obesity-induced nonalcoholic steatohepatitis through activation of X-box binding protein-1 in mice
Authors
Advisors
Advisor(s):Xu, AWang, Y
Issue Date2012
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Ye, D. [叶得伟]. (2012). Toll-like receptor-4 mediates obesity-induced nonalcoholic steatohepatitis through activation of X-box binding protein-1 in mice. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4775291
AbstractBackground and objectives: Nonalcoholic steatohepatitis (NASH), which is characterized by concurrent existence of hepatic steatosis and predominantly lobular necroinflammation, represents the more advanced stage in the spectrum of nonalcoholic fatty liver disease (NAFLD). NASH exhibits dramatically increased risk of progression to end-stage liver diseases than simple steatosis. Therefore, the progression of hepatic steatosis to steatohepatitis is the crucial step in the development of obesity-related NASH. Toll like receptor 4 (TLR4), a master regulator of innate immunity, is the principal receptor for endotoxin, which is a central mediator of liver inflammation associated with both alcoholic and nonalcoholic liver disease. However, due to a lack of suitable animal models which fully recapitulate the natural history of obesity-induced NASH, the precise pathophysiological function of TLR4 signaling in the development of this disease remains poorly understood. The objective of this study is to investigate the role of TLR4 in mediating inflammatory responses in obesity-induced NASH using both in vivo and ex vivo approaches, and to unveil cellular and molecular mechanisms responsible for TLR4 actions. Key findings: 1. To address the role of TLR4 in the pathogenesis of NASH, we crossed ApoEdeficient mice (ApoE-/-) with TLR4 mutant mice (TLR4-/-) to generate ApoE-/- /TLR4 wild type mice (ApoE-/-/TLR4-WT) and ApoE-/-/TLR4-/- mice. Noticeably, when fed with high fat high cholesterol (HFHC) diet, ApoE-/-/TLR4-WT mice developed the typical pathology of NASH (hepatic steatosis, lobular inflammation, and hepatocyte ballooning) in the context of obesity and metabolic syndrome, suggesting HFHC-fed ApoE-/- mice as a suitable animal model for NASH. 2. TLR4 inactivation protected ApoE-/- mice against HFHC diet-induced liver injury, as indicated by a significant improvement in liver histology, a a marked reduction in serum ALT activity, a dramatic repression of inflammatory infiltrates, as well as an obvious decrease in hepatic production of pro-inflammatory cytokines. 3. In ApoE-/-/TLR4-WT mice, TLR4 expression was selectively elevated in Kupffer cells in response to HFHC diet feeding. 4. The activation of XBP1, a transcription factor involved in endoplasmic reticulum stress, was markedly elevated in liver of ApoE-/-/TLR4-WT mice fed with HFHC diet, whereas this change was abrogated in HFHC diet-fed ApoE-/-/TLR4-/- mice. 5. In rat primary Kupffer cells, treatment with anti-oxidants blocked endotoxininduced activation of XBP1 and NF-κB, leading to decreased cytokine production. In addition, siRNA-mediated knockdown of XBP1 inhibited NF-κB activation and cytokine production resulted from the treatment with the TLR4 agonist LPS. 6. In ApoE-/-/TLR4-WT mice, adenovirus-mediated expression of dominant negative XBP1 had no obvious effect on HFHC diet-induced hepatic steatosis and ROS production, but markedly decreased lobular inflammation, NF-κB activation, cytokine production in the liver and significantly reduced serum levels of ALT. Conclusions: These findings support the role of TLR4 in Kupffer cells as a key player in mediating the progression of simple steatosis to NASH, by inducing ROS-dependent activation of XBP1. In light of the obligatory role of XBP1 in TLR4-induced liver inflammation and injury, therapeutic interventions that inhibit TLR4/XBP1 activation may represent a promising strategy for treatment of NASH.
DegreeDoctor of Philosophy
SubjectCell receptors.
Fatty liver - Pathogenesis.
Fatty liver - Pathophysiology.
Fatty liver - Animal models.
Transcription factors.
Dept/ProgramMedicine

 

DC FieldValueLanguage
dc.contributor.advisorXu, A-
dc.contributor.advisorWang, Y-
dc.contributor.authorYe, Dewei.-
dc.contributor.author叶得伟.-
dc.date.issued2012-
dc.identifier.citationYe, D. [叶得伟]. (2012). Toll-like receptor-4 mediates obesity-induced nonalcoholic steatohepatitis through activation of X-box binding protein-1 in mice. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4775291-
dc.description.abstractBackground and objectives: Nonalcoholic steatohepatitis (NASH), which is characterized by concurrent existence of hepatic steatosis and predominantly lobular necroinflammation, represents the more advanced stage in the spectrum of nonalcoholic fatty liver disease (NAFLD). NASH exhibits dramatically increased risk of progression to end-stage liver diseases than simple steatosis. Therefore, the progression of hepatic steatosis to steatohepatitis is the crucial step in the development of obesity-related NASH. Toll like receptor 4 (TLR4), a master regulator of innate immunity, is the principal receptor for endotoxin, which is a central mediator of liver inflammation associated with both alcoholic and nonalcoholic liver disease. However, due to a lack of suitable animal models which fully recapitulate the natural history of obesity-induced NASH, the precise pathophysiological function of TLR4 signaling in the development of this disease remains poorly understood. The objective of this study is to investigate the role of TLR4 in mediating inflammatory responses in obesity-induced NASH using both in vivo and ex vivo approaches, and to unveil cellular and molecular mechanisms responsible for TLR4 actions. Key findings: 1. To address the role of TLR4 in the pathogenesis of NASH, we crossed ApoEdeficient mice (ApoE-/-) with TLR4 mutant mice (TLR4-/-) to generate ApoE-/- /TLR4 wild type mice (ApoE-/-/TLR4-WT) and ApoE-/-/TLR4-/- mice. Noticeably, when fed with high fat high cholesterol (HFHC) diet, ApoE-/-/TLR4-WT mice developed the typical pathology of NASH (hepatic steatosis, lobular inflammation, and hepatocyte ballooning) in the context of obesity and metabolic syndrome, suggesting HFHC-fed ApoE-/- mice as a suitable animal model for NASH. 2. TLR4 inactivation protected ApoE-/- mice against HFHC diet-induced liver injury, as indicated by a significant improvement in liver histology, a a marked reduction in serum ALT activity, a dramatic repression of inflammatory infiltrates, as well as an obvious decrease in hepatic production of pro-inflammatory cytokines. 3. In ApoE-/-/TLR4-WT mice, TLR4 expression was selectively elevated in Kupffer cells in response to HFHC diet feeding. 4. The activation of XBP1, a transcription factor involved in endoplasmic reticulum stress, was markedly elevated in liver of ApoE-/-/TLR4-WT mice fed with HFHC diet, whereas this change was abrogated in HFHC diet-fed ApoE-/-/TLR4-/- mice. 5. In rat primary Kupffer cells, treatment with anti-oxidants blocked endotoxininduced activation of XBP1 and NF-κB, leading to decreased cytokine production. In addition, siRNA-mediated knockdown of XBP1 inhibited NF-κB activation and cytokine production resulted from the treatment with the TLR4 agonist LPS. 6. In ApoE-/-/TLR4-WT mice, adenovirus-mediated expression of dominant negative XBP1 had no obvious effect on HFHC diet-induced hepatic steatosis and ROS production, but markedly decreased lobular inflammation, NF-κB activation, cytokine production in the liver and significantly reduced serum levels of ALT. Conclusions: These findings support the role of TLR4 in Kupffer cells as a key player in mediating the progression of simple steatosis to NASH, by inducing ROS-dependent activation of XBP1. In light of the obligatory role of XBP1 in TLR4-induced liver inflammation and injury, therapeutic interventions that inhibit TLR4/XBP1 activation may represent a promising strategy for treatment of NASH.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.source.urihttp://hub.hku.hk/bib/B47752919-
dc.subject.lcshCell receptors.-
dc.subject.lcshFatty liver - Pathogenesis.-
dc.subject.lcshFatty liver - Pathophysiology.-
dc.subject.lcshFatty liver - Animal models.-
dc.subject.lcshTranscription factors.-
dc.titleToll-like receptor-4 mediates obesity-induced nonalcoholic steatohepatitis through activation of X-box binding protein-1 in mice-
dc.typePG_Thesis-
dc.identifier.hkulb4775291-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplineMedicine-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_b4775291-
dc.date.hkucongregation2012-

Export via OAI-PMH Interface in XML Formats


OR


Export to Other Non-XML Formats