scholarly journals Cyclic AMP stimulates the synthesis and function of the low-density lipoprotein receptor in human vascular smooth-muscle cells and fibroblasts

1992 ◽  
Vol 282 (3) ◽  
pp. 853-861 ◽  
Author(s):  
B Middleton ◽  
A Middleton
Keyword(s):  
Smooth Muscle ◽  
Cyclic Amp ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Free Cholesterol ◽  
Low Density Lipoprotein ◽  
Ldl Receptor ◽  
Density Lipoprotein ◽  
Muscle Cells

1. Cyclic AMP-elevating agents stimulate low-density lipoprotein (LDL) receptor activity in human vascular smooth-muscle cells by increasing the rate of receptor protein synthesis. The stimulation is not secondary to the decrease in the regulatory pool of free cholesterol, since it is unaffected, or even enhanced, by inhibition of cholesterol synthesis and esterification, or inhibition of the conversion of cholesterol into its repressor metabolites. The cyclic AMP-mediated up-regulation of the receptor is maintained at low concentrations of inhibitory sterols, but is eventually over-ridden at high concentrations of these sterols. 2. Cyclic AMP-elevating agents also stimulate the hydrolysis of lysosomal cholesterol esters, thus increasing the cellular cholesterol pool and repressing the expression of the LDL receptor. This cholesterol-mediated repressive effect of cyclic AMP can be prevented by chloroquine, which inhibits lysosomal actions, or by ketoconazole, which inhibits conversion of free cholesterol into its repressor metabolite. Thus the cyclic AMP stimulation of the LDL receptor can be masked by the rapid mobilization of free cholesterol from existing cholesterol esters within cultured cells. 3. We have observed that elevated cyclic AMP concentrations will up-regulate the LDL receptor in cholesterol-depleted human vascular smooth-muscle cells, skin fibroblasts and foetal-lung fibroblasts. We propose that our results are evidence for a cyclic AMP-stimulated, sterol-independent, control of LDL-receptor synthesis which is of widespread occurrence in human cells.

scholarly journals sLRP1 (Soluble Low-Density Lipoprotein Receptor-Related Protein 1)

2020 ◽  
Vol 40 (6) ◽  
Author(s):  
Jiefang Chen ◽  
Shulan Pi ◽  
Cheng Yu ◽  
Hanqing Shi ◽  
Yuxiao Liu ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Muscle Cells ◽  
P2y12 Receptor ◽  
Density Lipoprotein Receptor ◽  
Lipoprotein Receptor Related Protein

Objective: Recent studies suggest that the P2Y12 (P2Y purinoceptor 12) receptor of vascular smooth muscle cells in atherosclerotic plaques aggravates atherosclerosis, and P2Y12 receptor inhibitors such as CDL (clopidogrel) may effectively treat atherosclerosis. It is imperative to identify an effective biomarker for reflecting the P2Y12 receptor expression on vascular smooth muscle cells in plaques. Approach and Results: We found that there was a positive correlation between the level of circulating sLRP1 (soluble low-density lipoprotein receptor-related protein 1) and the number of LRP1 + α-SMA + (α-smooth muscle actin), P2Y12 + , or P2Y12 + LRP1 + cells in plaques from apoE −/− mice fed a high-fat diet. Furthermore, activation of the P2Y12 receptor increased the expression and shedding of LRP1 in vascular smooth muscle cells by inhibiting cAMP (3'-5'-cyclic adenosine monophosphate)/PKA (protein kinase A)/SREBP-2 (sterol regulatory element binding transcription factor 2). Conversely, genetic knockdown or pharmacological inhibition of the P2Y12 receptor had the opposite effects. Additionally, CDL decreased the number of lesional LRP1 + α-SMA + cells and the levels of circulating sLRP1 by activating cAMP/PKA/SREBP-2 in apoE −/− mice fed a high-fat diet. Conclusions: Our study suggests that sLRP1 may be a biomarker that reflects the P2Y12 receptor level in plaques and has the potential to be an indicator for administering P2Y12 receptor inhibitors for patients with atherosclerosis.

scholarly journals Agents which increase cyclic AMP have diverse effects on low-density-lipoprotein-receptor function in human vascular smooth-muscle cells and skin fibroblasts

1990 ◽  
Vol 267 (3) ◽  
pp. 607-614 ◽  
Author(s):  
A Middleton ◽  
B Middleton
Keyword(s):  
Smooth Muscle ◽  
Cyclic Amp ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Ldl Receptor ◽  
Muscle Cells ◽  
Skin Fibroblasts ◽  
Receptor Expression ◽  
Low Density

Receptor-mediated binding and metabolism of low-density lipoproteins (LDL) in cultured human vascular smooth-muscle cells and skin fibroblasts are altered by increased cellular cyclic AMP concentrations. However, the LDL receptor does not respond to changes in cyclic AMP concentration in a simple manner. The activation of adenylate cyclase with forskolin, or the addition of membrane-permeant cyclic AMP analogues, initially decreases the expression of the LDL receptor, but is followed by a substantial increase in receptor expression after 24 h. This increase does not occur in the presence of inhibitors of RNA or protein synthesis, and is due to doubling of the Bmax. of the LDL receptor, without alteration of its affinity for LDL. By contrast, elevation of cyclic AMP concentration by inhibition of phosphodiesterases results in decreased receptor expression throughout the 24 h period. These two response patterns are reproducible phenomena, consistently observed in low-passaged cells derived from seven unrelated individuals.

Atherosclerosis and thrombosis

2015 ◽  
Author(s):  
Lina Badimon ◽  
Gemma Vilahur
Keyword(s):  
Smooth Muscle ◽  
Inflammatory Response ◽  
Vascular Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Vascular Smooth Muscle Cells ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Muscle Cells ◽  
Low Density ◽  
Atherosclerosis Progression

Atherosclerosis is the main underlying cause of heart disease. The continuous exposure to cardiovascular risk factors induces endothelial activation/dysfunction which enhances the permeability of the endothelial layer and the expression of cytokines/chemokines and adhesion molecules. This results in the accumulation of lipids (low-density lipoprotein particles) in the extracellular matrix and the triggering of an inflammatory response. Accumulated low-density lipoprotein particles suffer modifications and become pro-atherogenic, enhancing leucocyte recruitment and further transmigration across the endothelium into the intima. Infiltrated monocytes differentiate into macrophages which acquire a specialized phenotypic polarization (protective or harmful), depending on the stage of the atherosclerosis progression. Once differentiated, macrophages upregulate pattern recognition receptors capable of engulfing modified low-density lipoprotein, leading to foam cell formation. Foam cells release growth factors and cytokines that promote vascular smooth muscle cell migration into the intima, which then internalize low-density lipoprotein via low-density lipoprotein receptor-related protein-1 receptors. As the plaque evolves, the number of vascular smooth muscle cells decline, whereas the presence of fragile/haemorrhagic neovessels increases, promoting plaque destabilization. Disruption of this atherosclerotic lesion exposes thrombogenic surfaces that initiate platelet adhesion, activation, and aggregation, as well as thrombin generation. Both lipid-laden vascular smooth muscle cells and macrophages release the procoagulant tissue factor, contributing to thrombus propagation. Platelets also participate in progenitor cell recruitment and drive the inflammatory response mediating the atherosclerosis progression. Recent data attribute to microparticles a potential modulatory effect in the overall atherothrombotic process. This chapter reviews our current understanding of the pathophysiological mechanisms involved in atherogenesis, highlights platelet contribution to thrombosis and atherosclerosis progression, and provides new insights into how atherothrombosis may be modulated.

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