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Human mesangial cells express inducible macrophage scavenger receptor
X Z Ruan1, Z Varghese, S H Powis
1Center for Nephology, Royal Free and University College Medical School, Royal Free Campus, London, England, United Kingdom. rxz@rfhsm.ac.uk
Background:
Type A scavenger receptors (Scr) mediate the uptake of modified low-density lipoproteins by macrophages. The accumulation of lipids via this process is thought to lead to foam cell formation in atherosclerotic plaques. Human mesangial cells (HMCs) have not been previously shown to express Scr in normal culture. We therefore investigated whether there is an inducible form of Scr in a human mesangial cell line (HMCL).
Methods:
Scr activity was analyzed by cellular uptake of fluorescently labeled acetylated low-density lipoprotein using a flow cytometer. Scr mRNA expression was examined using reverse transcription-polymerase chain reaction, followed by Southern blotting. To investigate the molecular mechanism of Scr expression, several reporter gene constructs were designed. The first contained a full Scr promoter, the second a part of the Scr promoter that has both AP-1 and ets transcription factor binding sites. Other constructs were identical to the second, except that they contained either AP-1 or ets motif mutations.
Results:
Phorbol 12-Myristate 13-acetate (PMA) and angiotensin II (Ang II) increased both the percentage of Scr-positive cells and the Scr mean fluorescence intensity. PMA and Ang II also increased Scr mRNA and promoter activity in a time- and dose-responsive manner. Protein kinase C and calmodulin transduction pathways were involved in Scr up-regulation induced by PMA and Ang II. Additionally, a serine/threonine kinase was involved in PMA stimulation. Functional analysis showed that both AP-1 and ets motifs were specific response elements to PMA stimulation in HMCLs.
Conclusions:
This study suggests that HMCs may express an inducible Scr, by which cells can acquire lipids and convert to foam cells in developing glomerulosclerosis.
Insights
Human mesangial cells (HMCs) can be induced to express scavenger receptors (Scr), mediating lipid uptake and potentially leading to foam cell formation in glomerulosclerosis.
Area of Science:
- Cell biology
- Molecular biology
- Renal pathology
Background:
- Type A scavenger receptors (Scr) facilitate modified low-density lipoprotein uptake by macrophages.
- Lipid accumulation via Scr is implicated in foam cell formation within atherosclerotic plaques.
- Human mesangial cells (HMCs) have not been previously characterized for Scr expression in standard culture.
Purpose of the Study:
- To investigate the potential for an inducible form of scavenger receptors (Scr) in a human mesangial cell line (HMCL).
- To elucidate the molecular mechanisms regulating Scr expression in HMCs.
Main Methods:
- Scavenger receptor (Scr) activity assessed by fluorescently labeled acetylated low-density lipoprotein uptake via flow cytometry.
- Scr mRNA expression analyzed using reverse transcription-polymerase chain reaction and Southern blotting.
- Reporter gene constructs with wild-type and mutated AP-1 and ets transcription factor binding sites were used to probe promoter activity.
Main Results:
- Phorbol 12-Myristate 13-acetate (PMA) and angiotensin II (Ang II) significantly increased Scr-positive cells and mRNA levels in a dose- and time-dependent manner.
- Both PMA and Ang II enhanced Scr promoter activity, with AP-1 and ets motifs identified as key response elements for PMA.
- Protein kinase C and calmodulin signaling pathways were implicated in Scr up-regulation.
Conclusions:
- Human mesangial cells (HMCs) exhibit inducible scavenger receptor (Scr) expression.
- This inducible Scr pathway allows HMCs to acquire lipids, suggesting a role in foam cell formation during glomerulosclerosis development.