Human mesangial cells express inducible macrophage scavenger receptor.
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.
Ruan
X Z
XZ
Center for Nephology, Royal Free and University College Medical School, Royal Free Campus, London, England, United Kingdom. rxz@rfhsm.ac.uk
Varghese
Z
Z
Powis
S H
SH
Moorhead
J F
JF
D000804:Angiotensin II / Q000494:pharmacology; D001161:Arteriosclerosis / Q000378:metabolism; D002232:Carbocyanines; D002273:Carcinogens / Q000494:pharmacology; D015815:Cell Adhesion Molecules / Q000235:genetics; D002460:Cell Line; D008078:Cholesterol, LDL / Q000493:pharmacokinetics; D015342:DNA Probes; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes; D005487:Foam Cells / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D005920:Glomerular Mesangium / Q000737:chemistry* / Q000166:cytology* / Q000502:physiology; D005923:Glomerulosclerosis, Focal Segmental / Q000378:metabolism; D006801:Humans; D016296:Mutagenesis / Q000502:physiology; D010957:Plasmids; D011388:Prolactin / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D011971:Receptors, Immunologic / Q000235:genetics*; D051116:Receptors, Scavenger; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
C101089:CM-DiI; D002232:Carbocyanines; D002273:Carcinogens; D015815:Cell Adhesion Molecules; D008078:Cholesterol, LDL; D015342:DNA Probes; D005456:Fluorescent Dyes; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D051116:Receptors, Scavenger; D018808:Transcription Factor AP-1; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D011388:Prolactin; D013755:Tetradecanoylphorbol Acetate