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Human mesangial cells express inducible macrophage scavenger receptor: an Ap-1 and ets mediated response
X Z Ruan1, Z Varghese, S H Powis
1Center for Nephrology, Royal Free and University College Medical School, London, England, United Kingdom. rxz@rfhsm.ac.uk
Background:
Type A scavenger (SR) mediate the uptake of modified low-density lipoproteins by macrophages. The accumulation of lipid via this process is thought to lead to foam cell formation in atherosclerotic plaques. Human mesangial cells (HMC), which can be converted to foam cells in vivo, have not previously been shown to express SR in normal culture. We investigated whether or not there was an inducible form of SR in a human mesangial cell line (HMCL).
Methods:
SR activity was analyzed by cellular uptake of fluorescently labeled acetylated low-density lipoprotein using a flow cytometer. SR mRNA expression was examined using RT-PCR followed by Southern blotting. To investigate the molecular mechanism of SR expression, several reporter gene constructs were designed. The first contained a full SR promoter, the second a part of the SR promoter that has both activated protein-1 (AP-1) and ets transcriptional factor binding sites. Other constructs were identical to the second except they contained either AP-1 or ets motif mutations.
Results:
Phorbol 12-myristate 13-acetate (PMA) increased both the percentage of SR positive cells and SR mean fluorescence intensity. PMA also increased SR mRNA and promoter activity in a time and dose responsive manner. Function analysis showed that both AP-1 and ets motifs were specific response elements to PMA stimulation in HMCL.
Conclusions:
The present study suggests that the combination of interaction between AP-1 and ets transcriptional factors may mediate the inducible expression of the SR gene in HMCL, which may contribute to foam cell formation.
Insights
Human mesangial cells (HMC) can form foam cells. This study found that phorbol 12-myristate 13-acetate (PMA) induces scavenger receptor (SR) expression in HMC, potentially contributing to foam cell formation.
Area of Science:
- Cell Biology
- Molecular Biology
- Cardiovascular Research
Background:
- Scavenger receptors (SR) mediate modified low-density lipoprotein uptake by macrophages, leading to foam cell formation in atherosclerosis.
- Human mesangial cells (HMC) can become foam cells in vivo but have not been shown to express SR in normal culture.
- This study investigated inducible SR expression in a human mesangial cell line (HMCL).
Purpose of the Study:
- To determine if human mesangial cell lines express inducible scavenger receptors (SR).
- To investigate the molecular mechanisms regulating SR gene expression in response to stimulation.
- To explore the potential role of SR in foam cell formation in HMC.
Main Methods:
- Analyzed SR activity via cellular uptake of fluorescently labeled acetylated low-density lipoprotein using flow cytometry.
- Examined SR mRNA expression using RT-PCR and Southern blotting.
- Investigated SR promoter activity using reporter gene constructs with wild-type and mutated AP-1 and ets transcriptional factor binding sites.
Main Results:
- Phorbol 12-myristate 13-acetate (PMA) significantly increased SR-positive cells and SR mean fluorescence intensity in HMCL.
- PMA treatment dose- and time-dependently elevated SR mRNA levels and promoter activity.
- Functional analysis confirmed that AP-1 and ets motifs are critical response elements for PMA-induced SR expression in HMCL.
Conclusions:
- Inducible scavenger receptor (SR) expression in human mesangial cells (HMCL) is mediated by phorbol 12-myristate 13-acetate (PMA).
- The interaction between AP-1 and ets transcriptional factors appears to regulate inducible SR gene expression in HMCL.
- This inducible SR expression may play a role in the development of foam cells in the context of atherosclerosis.