Kupffer cells mediate leptin-induced liver fibrosis.
OBJECTIVE
Leptin has profibrogenic effects in liver, although the mechanisms of this process are unclear. We sought to elucidate the direct and indirect effects of leptin on hepatic stellate cells (HSCs).


METHODS
HSCs from Sprague-Dawley rats were exposed to leptin and expression of collagen-I, tissue inhibitor of matrix metalloproteinases-1 (TIMP1), transforming growth factor beta1 (TGF-beta1), and connective tissue growth factor (CTGF/CCN2) was assessed. The effects of medium from Kupffer cells (KCs) and sinusoidal endothelial cells (SECs) following leptin were evaluated in HSCs; alpha-smooth muscle actin (alphaSMA) production and KC signaling were analyzed.


RESULTS
HSCs were not activated by incubation with leptin. However, HSCs cultured with medium taken from KCs that were incubated with leptin had increased expression of collagen I, TIMP1, TGF-beta1, and CTGF/CCN2, as well as alphaSMA protein levels and proliferation. These effects were leptin receptor dependent because conditioned medium from KCs isolated from leptin receptor-deficient Zucker (fa/fa) rats did not activate HSCs. In KCs incubated with leptin, messenger RNA and protein expression of TGF-beta1 and CTGF/CCN2 increased. Leptin potentiated signal transducer and activator of transcription 3, AKT, and extracellular signal-related kinase 1/2 phosphorylation in KCs and increased AP-1 and nuclear factor-kappaB DNA binding. Finally, addition of anti-TGF-beta to KC-conditioned medium inhibited HSC expression of collagen I, TIMP1, and CTGF/CCN2, whereas signal transducer and activator of transcription 3 inhibitor attenuated TGF-beta1 production by KC.


CONCLUSIONS
Leptin mediates HSC activation and liver fibrosis through indirect effects on KC; these effects are partly mediated by TGF-beta1.
Storr Liver Unit, Westmead Millennium Institute, University of Sydney and Westmead Hospital, Westmead, Australia.
Jianhua
J
Wang
Isabelle
I
Leclercq
Joanne M
JM
Brymora
Ning
N
Xu
Mehdi
M
Ramezani-Moghadam
Roslyn M
RM
London
David
D
Brigstock
Jacob
J
George
D000818:Animals; D049109:Cell Proliferation; D002478:Cells, Cultured; D004195:Disease Models, Animal; D055166:Hepatic Stellate Cells / Q000166:cytology* / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D015151:Immunoblotting; D007150:Immunohistochemistry; D007728:Kupffer Cells / Q000166:cytology* / Q000378:metabolism; D020738:Leptin / Q000494:pharmacology*; D008103:Liver Cirrhosis / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*; D008297:Male; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D053773:Transforming Growth Factor beta1 / Q000378:metabolism; D015854:Up-Regulation
D020738:Leptin; D053773:Transforming Growth Factor beta1; D006861:Hydrogen Peroxide