Endothelial cell activation of the smooth muscle cell phosphoinositide 3-kinase/Akt pathway promotes differentiation

Abstract

Interactions between endothelial cells (ECs) and smooth muscle cells (SMCs) are fundamental in diverse cardiovascular processes such as arteriogenesis, collateral blood vessel development, atherosclerosis, and restenosis. Alterations in SMC phenotype occur in each of these processes. Endothelial denudation has been suggested to contribute to the SMC proliferative response to vessel injury by angioplasty or other catheterization procedures. We have employed a co-culture approach to dissect the molecular signals that are dependent on the spatial relationship between ECs and SMCs, and have identified the importance of the PI3K/Akt pathway in EC-induced SMC differentiation. This pathway may suggest targets for therapeutic interventions for intimal hyperplasia and restenosis.

Serotonin passes through myoendothelial gap junctions to promote pulmonary arterial smooth muscle cell differentiation

“…Although paracrine signaling and direct cell-cell contact between arterial ECs and SMCs have been shown in numerous studies to regulate the phenotype of SMCs (4,10,15,18,19,26,27,31,32,34), the signals exchanged during the direct cell-cell contact have not been fully defined. Using the EC/ SMC coculture system established by Isakson communication between the cocultured cells was blocked by pharmacological inhibitors or genetic ablation of the gap junctional protein Cx-43, the differentiation of PASMCs was prevented.…”

Rapamycin Promotes Vascular Smooth Muscle Cell Differentiation through Insulin Receptor Substrate-1/Phosphatidylinositol 3-Kinase/Akt2 Feedback Signaling

“…Twenty-four hours prior to drug treatment, cells were transferred to media containing 0% or 2.5% FBS for the duration of the experiment as indicated in the figure legends. VSMCs cultured in 2.5% FBS proliferate slowly and do not spontaneously differentiate (7,16,22). VSMCs were treated with vehicle (ethanol for rapamycin) or drug (rapamycin (Calbiochem) or IGF-I (Upstate, Charlottesville, VA)) as indicated in the figure legends.…”

“…Western Blotting-Whole cell lysates were prepared and quantitated by Bradford assay as previously described (7,16,22). Equal amounts of protein per lane were subjected to SDS-PAGE, transferred to a membrane, and immunoblotted using antibodies against SM2-MHC (Seikagaku America, Cape Cod, MA), h-caldesmon, SM␣-actin, calponin 1 (Sigma), GAPDH, anti-phosphotyrosine (PY20), ␤-tubulin (Santa Cruz Biotechnology, Santa Cruz, CA), Akt1, Akt2, total Akt, phospho-Ser-473 Akt, phospho-Ser-9 GSK-3␤, total GSK3-␤, S6K1, total S6, phospho-S6 (Ser-235/236), IRS-1 phospho-Ser-636, or phospho-Ser302 (Cell Signaling, Boston, MA), or total IRS-1 (Upstate), horseradish peroxidase-conjugated secondary antibodies, and chemiluminescent detection and autoradiography as described (7,16,22).…”

“…The IGF-I differentiation signal is thought to be mediated by PI3K and Akt, because inhibition of this pathway with PI3K inhibitors or dominant negative Akt promotes dedifferentiation of vascular (14) or gizzard smooth muscle (15). We have shown that constitutively active myristoylated Akt is sufficient to promote VSMC differentiation (16). The unique ability of IGF-I to promote VSMC differentiation, as opposed to proliferation, has been attributed to its preferential activation of the PI3K pathway versus the strong ERK activation mediated by other growth factors (14).…”

Hypoxia and Pulmonary Hypertension

“…Speciically, dysregulated endothelial cells can cause alterations in AKT signalling in VSMCs, which in turn triggers their phenotypic switch [23]. This pathway is also afected by aberrant regulation of the mechanistic target of rapamycin (mTOR) pathway (discussed later in this chapter).…”