Selective clearance of macrophages in atherosclerotic plaques by autophagy.
OBJECTIVE
The purpose of this study was to investigate whether stent-based delivery of an inhibitor of mammalian target of rapamycin (mTOR) can selectively clear macrophages in rabbit atherosclerotic plaques.


BACKGROUND
Current pharmacologic approaches to stabilize atherosclerotic plaques have only partially reduced the incidence of acute coronary syndromes and sudden death. Macrophages play a pivotal role in plaque destabilization, whereas smooth muscle cells (SMC) promote plaque stability.


METHODS
Stents eluting the mTOR inhibitor everolimus were implanted in atherosclerotic arteries of cholesterol-fed rabbits. In addition, in vitro experiments using explanted atherosclerotic segments and cultured macrophages as well as SMC were performed.


RESULTS
Stents eluting everolimus led to a marked reduction in macrophage content without altering the amount of SMC compared with polymer control stents. In vitro studies showed that everolimus treatment induced inhibition of translation in both cultured macrophages and SMC. However, cell death occurred only in macrophages and was characterized by bulk degradation of long-lived proteins, processing of microtubule-associated protein light chain 3, and cytoplasmic vacuolization, which are all markers of autophagy. Everolimus-induced autophagy was mediated by mTOR inhibition, because cell viability was not affected using tacrolimus, an mTOR-independent everolimus analog. Moreover, mTOR gene silencing was associated with selective induction of macrophage cell death. Autophagic macrophage cell death was confirmed by transmission electron microscopy both in cultured cells and in atherosclerotic explants.


CONCLUSIONS
Stent-based delivery of everolimus selectively cleared macrophages in rabbit atherosclerotic plaques by autophagy, an mTOR inhibition-dependent and novel mechanism to induce cell death in mammalian cells.
Verheye
Stefan
S
Antwerp Cardiovascular Institute Middelheim, Antwerp, Belgium. stefan.verheye@pandora.be
Martinet
Wim
W
Kockx
Mark M
MM
Knaapen
Michiel W M
MW
Salu
Koen
K
Timmermans
Jean-Pierre
JP
Ellis
Jeffrey T
JT
Kilpatrick
Deborah L
DL
De Meyer
Guido R Y
GR
D000818:Animals; D050197:Atherosclerosis / Q000276:immunology*; D001343:Autophagy; D002460:Cell Line; D016503:Drug Delivery Systems; D000068338:Everolimus; D020868:Gene Silencing; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D008264:Macrophages / Q000276:immunology*; D011494:Protein Kinases; D011817:Rabbits; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology; D015607:Stents; D058570:TOR Serine-Threonine Kinases
D007166:Immunosuppressive Agents; D000068338:Everolimus; D011494:Protein Kinases; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus