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Abstract
Background and aims: Myofibroblast-like cells, originating from activation of hepatic stellate cells (HSC/MFs), play a key role in liver fibrosis, a potentially reversible process that may rely on induction of HSC/MFs apoptosis. While this possibility has been shown in cultured rat HSC, very limited data are currently available for human HSC/MFs.
Methods: Cultured human HSC/MFs were exposed to several proapoptotic stimuli, including those known to induce apoptosis in rat HSC/MFs, and induction of cell death and related mechanisms were investigated using morphology, molecular biology, and biochemical techniques.
Results: In this study we report that fully activated human HSC/MFs did not undergo spontaneous apoptosis and survived to prolonged serum deprivation, Fas activation, or exposure to nerve growth factor, tumour necrosis factor α (TNF-α), oxidative stress mediators, doxorubicin, and etoposide. Induction of caspase dependent, mitochondria driven apoptosis in HSC/MFs was observed only when protein synthesis or transcription were inhibited. Importantly, the process of HSC activation was accompanied by changes in expression of a set of genes involved in apoptosis control. In particular, activated human HSC/MFs in culture overexpressed Bcl-2. The role of Bcl-2 was crucial as Bcl-2 silenced cells became susceptible to TNF-α induced apoptosis. Finally, Bcl-2 was markedly expressed in HSC/MFs present in liver tissue obtained from patients with hepatitis C virus related cirrhosis.
Conclusions: Human activated HSC/MFs are resistant to most proapoptotic stimuli due to Bcl-2 overexpression and this feature may play a key role in the progression of fibrosis in chronic liver diseases.
- CLDs, chronic liver diseases
- DAPI, 4,6-diamidine-2-phenylindole di-hydrochloride
- Δψm, mitochondrial membrane potential
- ECL, enhanced chemiluminescence
- ERK, extracellular regulated kinase
- FasL, Fas ligand
- HCV, hepatitis C virus
- HSC, hepatic stellate cells
- HSC/MFs, activated hepatic stellate cells in myofibroblast-like phenotype
- JC-1, J-aggregate forming lipophilic cation
- LDH, lactate dehydrogenase
- mAb, monoclonal antibody
- NGF, nerve growth factor
- NFκB, nuclear factor κB
- PARP, poly (ADP ribose) polymerase
- SFI medium, serum free Iscove’s medium
- α-SMA, α smooth muscle actin
- siRNA, small interfering RNA
- TBS, Tris buffered saline
- h-TERT, human telomerase catalytic subunit
- TIMP, tissue inhibitor of metalloproteinases
- TNF-α, tumour necrosis factor α
- TrkA, tyrosine kinase A
- activated human hepatic stellate cells
- liver fibrosis
- apoptosis
- Bcl-2
- induction of cell death
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- CLDs, chronic liver diseases
- DAPI, 4,6-diamidine-2-phenylindole di-hydrochloride
- Δψm, mitochondrial membrane potential
- ECL, enhanced chemiluminescence
- ERK, extracellular regulated kinase
- FasL, Fas ligand
- HCV, hepatitis C virus
- HSC, hepatic stellate cells
- HSC/MFs, activated hepatic stellate cells in myofibroblast-like phenotype
- JC-1, J-aggregate forming lipophilic cation
- LDH, lactate dehydrogenase
- mAb, monoclonal antibody
- NGF, nerve growth factor
- NFκB, nuclear factor κB
- PARP, poly (ADP ribose) polymerase
- SFI medium, serum free Iscove’s medium
- α-SMA, α smooth muscle actin
- siRNA, small interfering RNA
- TBS, Tris buffered saline
- h-TERT, human telomerase catalytic subunit
- TIMP, tissue inhibitor of metalloproteinases
- TNF-α, tumour necrosis factor α
- TrkA, tyrosine kinase A
Footnotes
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Published online first 19 January 2006
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Conflict of interest: None declared.