Lysophosphatidic acid induces hypertrophy of neonatal cardiac myocytes via activation of G i and Rho

Abstract

The effect of the lysophospholipid, lysophosphatidic acid (LPA), on signaling and hypertrophy of neonatal rat ventricular cardiomyocytes was examined. Myocytes express mRNA for all three G-protein-coupled LPA receptor subtypes (LPA 1/Edg-2, LPA 2/Edg-4, and LPA 3/Edg-7) as indicated by RT-PCR analysis. LPA inhibits isoproterenol-stimulated cyclic AMP accumulation with an IC 50 ~40 nM and promotes phosphorylation of ERK-1/2. LPA also elicits a small, slow onset, and activation of phosphoinositide hydrolysis with EC 50 ~400 nM, and stimulates a marked increase in the extent of Rho activation. Longer-term treatment with LPA induces a hypertrophic response in myocytes as indicated by increases in cell size, actin organization, ANF staining of the perinuclear region and activation of ANF promoter–luciferase gene expression. Pretreatment of myocytes with pertussis toxin (PTX) not only blocks the capacity of LPA to inhibit cyclic AMP formation and stimulate ERK phosphorylation, but also inhibits hypertrophic changes in cell morphology and ANF–luciferase gene expression. Neither phospholipase C nor Rho activation is PTX sensitive. The hypertrophic effects of LPA on myocytes are also inhibited by treatment with C3 exoenzyme or by transfection of plasmids expressing either C3 exoenzyme or dominant-negative Rho to block Rho function. Inhibition of ERK activation with PD98059 blocks LPA-induced hypertrophy while inhibitors of phospholipase C (U73122), PKC (GF109203X), or p38MAPK (SB203580) do not. These data suggest that LPA induces cardiomyocyte hypertrophy via a pathway different from the conventional G q pathway utilized by phenylephrine, endothelin, and PGF2α and involving activation of a PTX-sensitive G i/ERK pathway in conjunction with activation of Rho-mediated signals.