Essential role of Rho/ROCK-dependent processes and actin dynamics in mediating leptin-induced hypertrophy in rat neonatal ventricular myocytes.

Obesity is associated with increased leptin production, which may contribute to cardiac hypertrophy. Although leptin has been shown to produce cardiomyocyte hypertrophy, its mechanism of action is far from clear. Rho proteins have been suggested as major contributors to cardiac hypertrophy, although their potential role in mediating the effect of leptin has not been studied. We determined the role of Rho and Rho-associated kinase (ROCK) as mediators of leptin-induced cell hypertrophy in cultured neonatal rat ventricular myocytes. Leptin (3.1 nmol/L) significantly increased cell surface area by 32+/-5% and leucine incorporation by 43 +/- 7%. These effects were associated with significant activation of RhoA to 450 +/- 40% of pre-leptin levels that was attenuated by pretreatment with an anti-leptin receptor (anti-OBR) antibody (166 ng/mL) to 120 +/- 20% of control values. Both the RhoA inhibitor C3 exoenzyme and ROCK inhibitor Y-27632 potently attenuated leptin-induced increased cell surface area and leucine incorporation. The hypertrophic effect of leptin was associated with an increase in phosphorylation of the actin binding protein cofilin to 290 +/- 20% of control values. In addition, the increase in polymerization of actin, as reflected by a decrease in the G/F-actin ratio, was significantly inhibited by both the anti-OBR antibody and Y-27632. Leptin-induced hypertrophy was also attenuated by disruption of actin filaments with 50 nmol/L latrunculin B. RhoA pathway inhibitors and latrunculin B also both attenuated leptin-induced ERK1/2 and p38 activation. Our results indicate that the activation of Rho and actin dynamics play a pivotal role in leptin signaling leading to the development of cardiomyocyte hypertrophy.