on April 3, 2008
Published online before print April 3, 2008, doi: 10.1161/ATVBAHA.108.164350
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Submitted on February 4, 2008
Accepted on March 21, 2008
Regulation of Endogenous Apolipoprotein E Secretion by Macrophages
Maaike Kockx ;
From the Macrophage Biology Group (M.K., W.J., L.K.), Centre for Vascular Research, University of New South Wales, Sydney; and the Department of Cardiology (L.K.), Concord Repatriation General Hospital, Sydney South Western Area Health Service, University of Sydney, Australia.
* To whom correspondence should be addressed. E-mail: l.kritharides{at}unsw.edu.au.
Abstract—Apolipoprotein E has critical roles in the protection against atherosclerosis and is understood to follow the classical constitutive secretion pathway. Recent studies have indicated that the secretion of apoE from macrophages is a regulated process of unexpected complexity. Cholesterol acceptors such as apolipoprotein A-I, high density lipoprotein, and phospholipid vesicles can stimulate apoE secretion. The ATP binding cassette transporter ABCA1 is involved in basal apoE secretion and in lipidating apoE-containing particles secreted by macrophages. However, the stimulation of apoE secretion by apoA-I is ABCA1-independent, indicating the existence of both ABCA1-dependent and -independent pathways of apoE secretion. The release of apoE under basal conditions is also regulated, requiring intact protein kinase A activity, intracellular calcium, and an intact microtubular network. Mathematical modeling of apoE turnover indicates that whereas some pools of apoE are committed to either secretion or degradation, other pools can be diverted from degradation toward secretion. Targeted inhibition or stimulation of specific apoE trafficking pathways will provide unique opportunities to regulate the biology of this important molecule.