Abstract 542: Angiotensin II-Induced Leptin Secretion in Rat Neonatal Cardiomyocytes is Mediated by Two Different Mechanisms Involving JAk-STAT and NF-kB Activation
Introduction: Leptin is a 16 kDa protein produced primarily by adipose tissue but recently we demonstrated that it is also synthesized in heart and cardiomyocytes. In addition, we identified leptin as downstream target to carry out angiotensin II (Ang II)-induced hypertrophic effects in cardiomyocytes. To understand the molecular mechanisms involved, we determined the role of JAK-STAT and NF-kB in Ang II-induced leptin synthesis in rat neonatal cardiomyocytes.
Methods and Results: Ang II (100 nM) and leptin (3.1 nM) increased cell surface area by 44% (P<0.002) and 40% (P<0.002), respectively as measured by Sigma scan software. The increase in cell surface area was significantly blocked by NF-kB activation inhibitor (1μM) and JAK2 inhibitor AG490 (50 μM) whereas STAT3 inhibitor peptide (1 mM) blocked only partially (16%; P<0.07 vs Ang II and 20%; P<0.03) ELISA analysis demonstrated an increased leptin secretion into the medium induced by Ang II (40%; P<0.0003) and it was significantly abolished by NF-Kb activation inhibitor (1μM), JAK2 inhibitor AG490 (50 μM) and p38 MAPK inhibitor SB202190 (10 μM) whereas STAT3 inhibitor peptide (1 mM) had no effect. The AT1 receptor blocker [Sar1-Ile8)-Ang II but not the AT2 receptor blocker PD 123319 (P<0.14) significantly inhibited Ang II-induced leptin secretion suggesting that AT1 receptor is important for downstream signaling to induce leptin secretion. Moreover, Ang II stimulated leptin gene expression by 53% (P<0.01) as determined by real time PCR and this increase was significantly inhibited by NF-Kb inhibitor, AG490 and SB202190. Western blot analysis showed Ang II activated p38 MAPK and STAT3 by 27% (P<0.01) and 42% (P<0.04) respectively. The activation of these two molecules was significantly prevented by NF-kB inhibitor while AG490 did not. In addition, both NF-kB inhibitor and AG490 had no inhibitory effect on Ang II induced activation of JAK2 (34%; P<0.05) and NF-kB (26%; P<0.01), respectively.
Conclusion: Ang II-induced leptin secretion in rat neonatal cardiomyocytes is mediated at least in part by two different signaling mechanisms involving JAK2 and NF-kB pathways with p38MAPK and STAT3 as downstream targets for NF-kB.