Fig. 4.
Leptin and CNTFAx15 activate STAT3 and ERK pathways. (a) Western blot analysis demonstrates time-dependent STAT3 phosphorylation in isolated adult mouse cardiomyocytes after exposure to leptin (■; 50 ng/μl) or CNTFAx15. (○; 50 ng/μl). STAT3 phosphorylation occurred within 15 min and subsided over time. (b) Similar activation occurred in the ERK1/2 pathway, with the effect of CNTFAx15 being more prolonged. [∗, P < 0.05; †, P < 0.01; ‡, P < 0.001 vs. time 0; §, P < 0.05 between groups (two-way ANOVA).] (c and d) Immunoblots from ob/ob mice (filled bars) and db/db mice (hatched bars) demonstrate increased abundance in both phosphorylated STAT3 and STAT3 expression with 4 weeks of CNTFAx15 (CNTF) treatment. Leptin (LEP) increased STAT3 abundance in ob/ob but not db/db mice. CR, calorie restriction. [∗, P < 0.05; †, P < 0.01 vs. ad libitum (AL).]