Role of AKT in cyclic strain-induced endothelial cell proliferation and survival

Abstract

Endothelial cells (ECs) are exposed to repetitive cyclic strain (CS) in vivo by the beating heart. The aim of this study was to assess the influence of CS amplitude and/or frequency on EC proliferation and survival and to determine the role of AKT in CS-induced EC proliferation and survival. Cultured bovine aortic ECs were exposed to 10% strain at a frequency of 60 (60 cpm-10%) or 100 (100 cpm-10%) cycles/min or 15.6% strain at a frequency of 60 cycles/min (60 cpm-15.6%). AKT, glycogen synthase kinase (GSK)-3beta, BAD, and cleaved caspase-3 were activated by CS in ECs. Increasing the magnitude or frequency of strain resulted in an earlier phosphorylation of GSK-3beta, although the magnitude of phosphorylation was similar. After CS at 60 cpm-10% for 24 h, the number of nontransfected ECs was significantly increased by 8.5% (P < 0.05). We found that the number of apoptotic ECs was slightly decreased with exposure to CS. ECs transfected with kinase-dead AKT (KA179) as well as plasmids containing a point mutation in the pleckstrin homology domain of AKT (RC25) not only prevented AKT, GSK-3beta, and BAD phosphorylation but also inhibited the CS-induced increase in cell number as well as the CS-induced protection against apoptosis (both P < 0.05). The ratio of 5'-bromo-2'-deoxyuridine-positive cells was increased when ECs transfected with RC25 and KA179 as well as nontransfected ECs and ECs transfected with Lipofectamine 2000 were exposed to CS. We conclude that AKT is important in enhancing the survival of ECs exposed to CS but is not involved in EC proliferation.

Strain-induced Proliferation Requires the Phosphatidylinositol 3-Kinase/AKT/Glycogen Synthase Kinase Pathway

“…stimulates proliferation and differentiation via both AKT and ERK (48). Endothelial cells exposed to strain require AKT for enhanced cell survival, and AKT blockade prevents the strain-induced increase in endothelial cell number (26), whereas PI3K and AKT are both needed to stimulate angiogenesis in pulmonary cells subjected to strain (27). Our data suggest a divergent pathway that mediates the mitogenic effect of strain, involving parallel paths in which PI3K leads to the eventual activation of both ERK and AKT.…”

“…PI3K and AKT are required for increased extracellular pressure to stimulate colon cancer cell adhesion (23), although the pathway by which pressure stimulates colon cancer cells in suspension differs from the response of adherent intestinal epithelial cells to repetitive deformation (24), and GSK is not involved in this effect. 3 Repetitive strain also stimulates vascular endothelial cell proliferation via PI3K and AKT (25,26), whereas respiratory strain stimulates angiogenic responses via PI3K (27). We, therefore, hypothesized that the PI3K/ AKT/GSK axis would be involved in the mitogenic effects of repetitive deformation on a collagen matrix.…”

Cyclic Stretch Affects Pulmonary Endothelial Cell Control of Pulmonary Smooth Muscle Cell Growth

“…This device also delivers uniform strain across the membrane and was set to deliver 15% strain. Also, it has been used to study the effects of cyclic stretch on endothelial cells and type II epithelial cells (33,34).…”

Angiotensin II cell signaling: physiological and pathological effects in the cardiovascular system

“…Of importance, PD98059 (an inhibitor of MEK) and Tyrphostin A-23 (tyrosine kinase inhibitor) attenuate contraction caused by ANG II (192). ERK has also been implicated in anti-apoptotic and pro-mitogenic effects, and activation of ERK1/2 and Akt/PKB has been shown to inhibit apoptosis (4,111,137). Furthermore, ERK 1/2 has been implicated in ANG II-induced cellular growth and protein synthesis via regulation of PHAS-1 (inhibitor of eukaryotic initiation factor 4E).…”