TITLE: Mitochondrial Manganese-superoxide dismutase prevents activation of stellate cells
AUTHORS (FIRST NAME, LAST NAME): Marjolein Tiebosch1, Floris Haijer1, Adil Tagdou1,
Manon Buist-Homan1, Klaas Nico Faber1, Han Moshage1
Institutional Author(s):
INSTITUTIONS (ALL): 1 Gastroenterology and Hepatology, University Medical Center
Groningen, University of Groningen, Groningen, Netherlands.
ABSTRACT BODY:
Introduction: Liver fibrosis and cirrhosis are listed in the top 10 causes of death in the Western
world. Currently, no effective therapy is available. To develop an effective anti-fibrotic therapy,
mechanisms of fibrogenesis need to be elucidated. Liver fibrosis is characterized by increased
production of extracellular matrix (ECM) by myofibroblasts-like cells from different origins in
the liver, such as the hepatic stellate cells (HSCs) and the portal myofibroblasts (PMFs), that
transdifferentiate during fibrogenesis, with increased expression of Transforming Growth Factor
β1 (TGF-β1), collagen type I and α-Smooth Muscle Actin (α-SMA). The mechanisms of this
transdifferentiation and activation are not completely known. Superoxide anions are claimed to
promote HSC activation. Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme
exclusively located in mitochondria, the major source of superoxide anions. CuZnSOD is mainly
responsible for dismutation of superoxide anions in the cytosol. The role of SODs in the
activation of HSCs and PMF’s has not been investigated yet.
Aim of the study: to determine the expression and role of superoxide dismutases in HSC and
PMF activation.
Methods: Experiments were performed in the human HSC cell line (LX-2), in rat hepatic stellate
cells, and in rat portal myofibroblasts. MnSOD and CuZnSOD were downregulated in LX-2 cells,
in rat HSCs, and in PMF’s using siRNA. Expression of mRNA levels was determined using
qPCR. Protein was quantified using Western Blot and localized by immunofluorescence.
Results: MnSOD expression in cultured rat HSCs declined rapidly during activation, while
CuZnSOD expression remained constant. MnSOD and CuZnSOD mRNA levels were effectively
downregulated from 24 up to 96 hrs after transfection in all cell types. Reduced expression of
MnSOD was also confirmed at protein level. mRNA levels of activation markers (α-SMA, TGF-β
and collagen type 1) were induced in rat HSCs and LX-2 cells after downregulation of MnSOD,
but not after downregulation of CuZnSOD.
Conclusion: Our results suggest that downregulation of MnSOD is linked to the activation of
HSC’s. Apparently, mitochondria-derived superoxide anions are the most important for HSC
activation, since downregulating CuZnSOD shows no effect on LX-2 activation. As the reduced
expression of MnSOD may be the driving force of HSC activation, interventions to increase
MnSOD levels in HSCs may be considered as a therapeutic target for liver fibrosis.