Oleic Acid–Induced Mitogenic Signaling in Vascular Smooth Muscle Cells

Abstract

As an initial step in testing the hypothesis that high oleic acid concentrations contribute to vascular remodeling in obese hypertensive patients by activating protein kinase C (PKC), the effects of oleic acid on primary cultures of rat aortic smooth muscle cells (RASMCs) were studied. Oleic acid, an 18-carbon cis-monounsaturated fatty acid (18:1 [cis]), from 25 to 200 mumol/L significantly increased [3H]thymidine uptake in RASMCs with an EC50 of 41.0 mumol/L and a maximal response of 196 +/- 15% of control (P < .01). Oleic acid from 25 to 200 mumol/L caused a concentration-dependent increase in the number of RASMCs in culture at 6 days, reaching a maximum of 210 +/- 13% of control at 100 mumol/L (P < .001). PKC inhibition with 4 mumol/L bisindolyImaleimide I and PKC depletion (alpha, mu, iota, and zeta) with 24-hour exposure to 200 nmol/L phorbol 12-myristate 13-acetate in RASMCs eliminated the mitogenic effects of oleic acid but did not reduce responses to 10% FBS. Stimulation of intact cells with oleic acid induced a peak increase of cytosolic PKC activity, reaching 328 +/- 8% of control (P < .001), but did not enhance PKC activity in the membrane fraction (105 +/- 4%, P = NS). The oleic acid-induced increase of PKC activity in cell lysates was similar in the presence and absence of Ca2+, phosphatidylserine, and diolein (maximum response, 360 +/- 4% versus 342 +/- 9% of control, P = NS). Unlike phorbol 12-myristate 13-acetate, oleic acid over 24 hours did not downregulate any of the four PKC isoforms detected in RASMCs. Oleic acid treatment activated mitogen-activated protein (MAP) kinase. PKC depletion in RASMCs eliminated the rise in thymidine uptake, activation of PKC, and activation of MAP kinase in response to oleic acid. In contrast to oleic acid, 50 to 200 mumol/L stearic (18:0) and elaidic (18:1 [trans]) acids, which are less effective activators of PKC than oleic acid, did not enhance thymidine uptake. These data suggest that oleic acid induces proliferation of RASMCs by activating PKC, particularly one or more of the Ca(2+)-independent isoforms, and raise the possibility that the higher oleic acid concentrations observed in obese hypertensive patients may contribute to vascular remodeling.

Effects of authentic and VLDL hydrolysis‐derived fatty acids on vascular smooth muscle cell growth

“…In short, it has been shown (Rao et al, 1995) that a weak increase in DNA synthesis and a moderate increase in VSMC number occur after a 96 h incubation with 20 mM linoleic acid. Similarly, others (Lu et al, 1996; have found that oleic acid at concentrations from 25 ± 200 mM signi®cantly increased [ 3 H]-thymidine uptake and cell number in rat VSMC after a 6 day stimulation period. Furthermore, it has been shown that linoleic acid (50 mM) induced a signi®cant increase in VSMC DNA synthesis and cell number over a 4 day incubation period (Hu et al, 1998).…”

“…There are contradictory ®ndings regarding the e ects of free fatty acids on VSMC growth. Some investigators have observed growth stimulation (Hu et al, 1998;Lu et al, 1996;Rao et al, 1995) while others suppression (Huttner et al, 1977;Olsson et al, 1999). In short, it has been shown (Rao et al, 1995) that a weak increase in DNA synthesis and a moderate increase in VSMC number occur after a 96 h incubation with 20 mM linoleic acid.…”

“…On the other hand, others found that exposure of human arterial smooth muscle cells to 100 ± 300 mM linoleic acid lowered their proliferation rate and altered cell morphology . Moreover, it has been described that oleic acid (Lu et al, 1996; and linoleic acid (Hu et al, 1998;Rao et al, 1995) stimulate the extracellular response kinases 1 and 2 (ERK1/2, also known as p44 mapk /p42 mapk ) but not the p38 mitogen-activated protein (MAP) kinase (Lu et al, 1998).…”

Non-esterified fatty acids and blood pressure elevation: a mechanism for hypertension in subjects with obesity/insulin resistance?

“…53,54 In vitro studies have reported that unsaturated NEFAs, including oleic and linoleic acid, can directly activate the typical and atypical isoforms of protein kinase C (PKC) in various cell types, including VSMCs. [55][56][57][58] Among other deleterious effects on human vasculature, PKC has been shown to play a central role in mitogenic processes in VSMCs. 59,60 Several studies have clearly shown that NEFAs induce proliferation of VSMCs via PKC activation, [55][56][57] implicating a potential involvement of plasma NEFA elevation in vascular remodelling and hypertension in obese subjects.…”

“…[55][56][57][58] Among other deleterious effects on human vasculature, PKC has been shown to play a central role in mitogenic processes in VSMCs. 59,60 Several studies have clearly shown that NEFAs induce proliferation of VSMCs via PKC activation, [55][56][57] implicating a potential involvement of plasma NEFA elevation in vascular remodelling and hypertension in obese subjects. In addition, oleic and linoleic acid were reported to increase the trophic action on VSMC of other growth factors, for example insulin-like growth factor-1 (IGF-1).…”