Leptin-dose dependently increases activation of STAT3, PI3K, Akt, and ERK1/2. The Sca-1+/CD45-/CD34+ cells from ob/ob mice were seeded as 1 × 107/10ml/dish in a 100 mm × 20 mm culture dish. The cells were incubated with various dose of leptin (0, 250, 500 and 1000 ng/ml) for 30 min. Total cellular proteins were extracted and subjected to western blot analysis with antibodies specific for (A). anti-phospho-STAT3, (B). anti-phospho-PI3K p85(Tyr458), (C). anti-phospho-Akt, and (D). anti-phospho-p44/42 ERK (Thr202/Tyr204) as indicated. Bands were detected using the ECL system. Afterward, blots were stripped and reprobed with anti-STAT3, anti-PI3K p85, anti-Akt (pan), and anti-p44/42 ERK antibody for assessment of protein loading. Results shown are representative of three independent experiments.