title: The antiadipogenic effect of macrophage-conditioned medium depends on ERK1/2 activation.
abstract: The proatherogenic state of obesity is associated with hypertrophied adipocytes that may arise because of deficient adipogenesis. Macrophages infiltrate adipose tissue as a function of obesity and may release factors that attenuate adipogenesis. Macrophage-conditioned medium inhibits human and 3T3-L1 adipocyte differentiation in culture, but underlying molecular mechanisms have yet to be defined. Exposure of 3T3-L1 cells throughout the 8-day period of differentiation to medium conditioned by THP-1 macrophages (THP-1-MacCM) blocked adipogenesis. Triacylglycerol (TG) accumulation and induction of peroxisome proliferator-activated receptor gamma and fatty acid synthase protein levels were inhibited by 59% (n = 4, P < .001), 29% (n = 4, P < .01), and 47% (n = 4, P < .01), respectively. THP-1-MacCM had no effect when added after the first 2 days of differentiation, indicating that early exposure of its targets must be needed to inhibit 3T3-L1 adipogenesis. Cell enumeration revealed a 44% decrease in clonal expansion compared with standard differentiation (n = 3, P < .01). Addition of THP-1-MacCM to 3T3-L1 preadipocytes increased ERK1/2 phosphorylation by 6.5-fold (n = 3, P < .01). PD98059 (an inhibitor of the ERK1/2 pathway) impaired the negative effect of THP-1-MacCM on TG accumulation, indicated by an inhibition of 25% vs 69% (n = 3, P < .001), without altering fatty acid synthase or peroxisome proliferator-activated receptor gamma levels. Our data implicate ERK1/2 as an important signaling mediator for the inhibitory effect of THP-1-MacCM on TG accumulation during 3T3-L1 adipogenesis.
authors.affiliation: Department of Medicine, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Vanessa A
authors.initials: VA
authors.lastname: Constant
authors.forename: Annemarie
authors.initials: A
authors.lastname: Gagnon
authors.forename: Michelle
authors.initials: M
authors.lastname: Yarmo
authors.forename: Alexander
authors.initials: A
authors.lastname: Sorisky
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology; D050156:Adipogenesis; D000818:Animals; D002454:Cell Differentiation; D017077:Culture Media, Conditioned; D004789:Enzyme Activation; D006801:Humans; D008264:Macrophages / Q000502:physiology*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000502:physiology*; D048052:Mitogen-Activated Protein Kinase 3 / Q000502:physiology*; D010766:Phosphorylation; D014280:Triglycerides / Q000378:metabolism
chemical_list: D017077:Culture Media, Conditioned; D014280:Triglycerides; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3