Phospholipase D signaling in serotonin-induced mitogenesis of pulmonary artery smooth muscle cells

Abstract

(7), has been increasingly associated with pulmonary hypertension (2, 4, 9, 30), and it is recognized that hyperplasia of SMCs accompanies the pathology of pulmonary hypertension (5, 10, 22). 5-HT initiates its SMC mitogenic action through both 5-HT receptors and the 5-HT transporter (5-HTT) (7) that are present on the cell membrane in close proximity to membrane structural lipids that include phosphatidylcholine. Through the receptor and transporter ligands, 5-HT produces SMC proliferation via combinatorial actions on the small G protein Rho, p 42/44 mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3-kinase)/protein kinase B (Akt), and platelet-derived growth factor-␤ receptor signaling pathways (17-20).Lipid-derived second messengers generated by the action of phospholipases on membrane-associated phospholipids play an important role in cellular signal transduction in general (3). Phospholipase D (PLD), which catalyzes the hydrolysis of phosphotidylcholine to phosphatidic acid (PA) and choline, has been recognized to be an intermediate in the actions of a wide variety of agonists on cellular functions, including those that cause proliferation (8,33). Agonists identified to activate PLD include neurotransmitters, growth factors, hormones, calcium ionophores, and reactive oxygen species (6, 24). The cell signaling associated with PLD activation occurs at least in part through actions of PA (14).It previously was reported that 5-HT activates PLD in rat mesangial cells (15) and mesenteric SMCs, which associates the activation of PLD with contraction (11). Plevin and coworkers (27) demonstrated in 1994 that 5-HT activates PLD in cultured sheep pulmonary artery SMCs. However, there is no information currently available about the relationship between 5-HT, its receptors and transporter, and PLD in pulmonary artery SMC signaling and proliferation. In the present study, we show that 5-HT activates PLD of pulmonary artery SMCs via the 5-HT 2A receptor, leading to the generation of PA that promotes SMC proliferation through activations of mammalian target of rapamycin (mTOR), S6K1 and MAPK but not the Rho or PI3-kinase/Akt signaling pathways. We hypothesize that these observations link an important lipid component of the cell membrane, i.e., phosphatidyl choline, with cell signaling occurring via 5-HT ligands in SMCs.

JNK regulates serotonin-mediated proliferation and migration of pulmonary artery smooth muscle cells

“…This provides direct evidence that JNK regulates Akt. We (17) also have previously found that activation of PLD by 5-HT occurs through the 5-HT 2A receptor and, like JNK, requires a mechanism that is PI3K-independent. We do not presently know whether the JNK pathway might participate in the activation of PLD by 5-HT.…”

Psychedelics

“…Although all known classic psychedelics produce their behavioral effects through activation of 5-HT 2A receptors, they also have significant 5-HT 2B receptor agonist activity at the doses necessary for behavioral effects. Activation of 5-HT 2A receptors directly in certain tissues including vascular, placental, and cancers can also have a proliferative effect (Sonier et al, 2005;Göoz et al, 2006;Liu and Fanburg, 2008;Chen et al, 2014), suggesting that the classic psychedelics may also have an effect on these processes. The molecular mechanisms underlying the proliferative effects largely appear to involve activation of ERK/ MAPK signaling downstream from the receptor.…”

PLD1-dependent PKCγ activation downstream to Src is essential for the development of pathologic retinal neovascularization

“…33 In light of these findings, it can be anticipated that Src via recruitment of PKC or some other serine/threonine kinases mediates VEGF-induced PLD1 activation in stimulating HRMVEC angiogenic responses. Because PLD1 generates PA, a potent mitogen, 27 one could also expect that PA itself may be mediating the VEGF effects on HRMVEC proliferation, migration, and tube formation. However, this scenario appears unlikely as inhibition of PAP abrogated the VEGF-induced HRMVEC angiogenic responses.…”

“…In addition, either 1-butanol (0.25%), the pharmacologic inhibitor of PLD1, 26 or PLD1 depletion by its siRNA attenuated VEGF-induced HRMVEC DNA synthesis, migration, and tube formation ( Figure 1B-D). Because activation of PLD1 generates phosphatidic acid (PA), a potential mitogen, 27 we asked the question whether PA or its conversion to diacylglycerol (DAG) is needed for VEGF-induced HRMVEC DNA synthesis, migration, and tube formation. To After exposure to 75% oxygen, the mice pups were returned to normoxia, administered 1 g of Scr, Src, PLD1, or PKC␥ siRNA at P13, P14, and P15 by intravitreal injections, and at P17 pups were anesthetized, perfused with FITC-dextran, sacrificed, enucleated, retinas were isolated, and flat mounts of whole retina were examined for retinal neovascularization (B).…”