Leptin as a novel profibrogenic cytokine in hepatic stellate cells: mitogenesis and inhibition of apoptosis mediated by extracellular regulated kinase (Erk) and Akt phosphorylation.
A key feature in the molecular pathogenesis of liver fibrosis requires maintenance of the activated hepatic stellate cell (HSC) phenotype by both proliferation and inhibition of apoptosis. We provide evidence that leptin is a potent HSC mitogen and dramatically inhibits stellate cell apoptosis. Leptin proved to be as potent an HSC mitogen as platelet-derived growth factor (PDGF) as assessed by bromodeoxyuridine (BrdU) incorporation in isolated primary HSCs; data using fluorescent propidium iodide (PI) uptake revealed that leptin, like PDGF, increased HSC populations in the S- and G2/M-phases of the cell cycle. Leptin resulted in a robust increase in cyclin D1 expression. Using the chemical inhibitor of Janus kinase 2 (Jak2) activity, AG 490, and overexpression of the suppressor of cytokine signaling 3 (SOCS-3), we show that blockade of leptin receptor (Ob-Rb) phosphorylation blocks leptin-induced HSC proliferation. Leptin-associated phosphorylation of both extracellular regulated kinase (p44/p42, Erk) and Akt is also prohibited. Further, the PI-3 kinase inhibitor LY294002 and MAPK inhibitor PD98059 were found to significantly reduce leptin-induced HSC proliferation, thereby indicating that leptin induced HSC proliferation is Akt- and Erk-dependent. Akt was also protective against HSC apoptosis. Leptin abolished both cycloheximide-induced and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, demonstrated by reduced caspase-3 activity, HSC-TUNEL staining, and DNA fragmentation. We conclude that leptin acts as a direct hepatic stellate cell survival agonist. Importantly, we have demonstrated that leptin-induced HSC proliferation and survival by Ob-Rb phosphorylation are both Erk- and Akt-dependent.
Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA.
Neeraj K
NK
Saxena
Mark A
MA
Titus
Xiaokun
X
Ding
Jeffrey
J
Floyd
Shanthi
S
Srinivasan
Shanthi V
SV
Sitaraman
Frank A
FA
Anania
D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D019938:Cyclin D1 / Q000096:biosynthesis; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D020738:Leptin / Q000378:metabolism* / Q000494:pharmacology*; D008099:Liver / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000494:pharmacology; D008934:Mitogens / Q000494:pharmacology; D008938:Mitosis / Q000187:drug effects; D009025:Morpholines / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000378:metabolism; D054411:Receptors, Leptin; D012097:Repressor Proteins / Q000378:metabolism; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; D014157:Transcription Factors / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D051017:Apoptosis Regulatory Proteins; D002867:Chromones; D005419:Flavonoids; C515448:LEPR protein, human; D020738:Leptin; D008562:Membrane Glycoproteins; D008934:Mitogens; D009025:Morpholines; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D054411:Receptors, Leptin; D012097:Repressor Proteins; C106644:SOCS3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D019938:Cyclin D1; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D004247:DNA; D003513:Cycloheximide; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one