Leptin-induced cardiomyocyte hypertrophy involves selective caveolae and RhoA/ROCK-dependent p38 MAPK translocation...

Leptin-induced cardiomyocyte hypertrophy is dependent on both RhoA and p38 mitogen-activated protein kinase (p38 MAPK) activation. The present study investigated the role of lipid raft/caveolae in these responses and assessed the nature of p38 MAPK activation in mediating leptin-induced hypertrophy.

Studies were carried out using cultured neonatal rat ventricular myocytes. Pharmacological, molecular, microscopy, and confocal imaging techniques were used to assess the role of caveolae in leptin-induced hypertrophy and to study the underlying cellular mechanisms. Leptin (3.1 nmol/L) treatment for 24 h significantly increased caveolae number two-fold and increased expression of caveolin-3 to 278 +/- 14% of control values. These effects were associated with increased cell surface area by 29 +/- 5% and leucine incorporation by 40 +/- 6%. The hypertrophic effect of leptin was associated with significant activation of RhoA (422 +/- 26%) and a decrease in the G-actin-to-F-actin ratio from 3.1 +/- 0.2 to 0.9 +/- 0.1. Caveolae disruption with methyl-beta-cyclodextrin (MbetaCD) potently attenuated leptin-induced cell hypertrophy and the associated signalling. RhoA was detected in caveolae fraction of a sucrose gradient after treatment with leptin for 5 min, indicating subcellular translocation of RhoA: this effect was inhibited by MbetaCD, the RhoA inhibitor C3 exoenzyme, and by disruption of actin filaments with latrunculin B. Furthermore, leptin-induced hypertrophy was associated with p38 MAPK but not with extracellular signal-regulated kinase (ERK1/2) translocation to nuclei, which was inhibited by MbetaCD, C3 exoenzyme, and the Rho kinase inhibitor Y-27632.

Our results indicate that p38 import into nuclei represents a key mechanism for leptin-induced hypertrophy acting through lipid raft/caveolae and a RhoA-dependent pathway.