The Scavenger Receptor Class B Type I Adaptor Protein PDZK1 Maintains Endothelial Monolayer Integrity

Abstract

Abstract-Circulating levels of high-density lipoprotein (HDL) cholesterol are inversely related to the risk of cardiovascular disease, and HDL and the HDL receptor scavenger receptor class B type I (SR-BI) initiate signaling in endothelium through src that promotes endothelial NO synthase activity and cell migration. Such signaling requires the C-terminal PDZ-interacting domain of SR-BI. Here we show that the PDZ domain-containing protein PDZK1 is expressed in endothelium and required for HDL activation of endothelial NO synthase and cell migration; in contrast, endothelial cell responses to other stimuli, including vascular endothelial growth factor, are PDZK1-independent. Coimmunoprecipitation experiments reveal that Src interacts with SR-BI, and this process is PDZK1-independent. PDZK1 also does not regulate SR-BI abundance or plasma membrane localization in endothelium or HDL binding or cholesterol efflux. Alternatively, PDZK1 is required for HDL/SR-BI to induce Src phosphorylation. Paralleling the in vitro findings, carotid artery reendothelialization following perivascular electric injury is absent in PDZK1 Ϫ/Ϫ mice, and this phenotype persists in PDZK1Ϫ/Ϫ mice with genetic reconstitution of PDZK1 expression in liver, where PDZK1 modifies SR-BI abundance. Thus, PDZK1 is uniquely required for HDL/SR-BI signaling in endothelium, and through these mechanisms, it is critically involved in the maintenance of endothelial monolayer integrity. Key Words: PDZK1 Ⅲ high-density lipoprotein Ⅲ SR-BI Ⅲ endothelium T he risk of atherosclerosis is inversely related to circulating high-density lipoprotein (HDL) cholesterol levels, 1,2 and there is also evidence that a lower HDL level is associated with a greater likelihood of restenosis after a vascular intervention. 3,4 HDL classically functions in reverse cholesterol transport, removing cholesterol from peripheral tissues and delivering it to the liver and to steroidogenic organs by binding of the major HDL apolipoprotein, apolipoprotein (apo)A-I, to the high-affinity HDL receptor scavenger receptor B type I (SR-BI). 5,6 In mouse models of atherosclerosis, apoA-I and SR-BI both provide atheroprotection, 7,8 and in the context of experimental hypercholesterolemia, the provision of apoA-I or HDL attenuates neointima formation after artery injury. 9,10 The protective nature of HDL has been previously attributed to its role in reverse cholesterol transport. However, evidence is accumulating that HDL has a number of additional actions that also afford cardiovascular protection, and many of these entail direct modulation of endothelial cell phenotype. 11 The direct actions of HDL on the endothelium are multiple. In particular, HDL promotes the production of the atheroprotective signaling molecule NO by upregulating endothelial NO synthase (eNOS) expression, 12 by maintaining the lipid environment in caveolae, where eNOS is colocalized with partner signaling molecules, 13 and by stimulating eNOS enzymatic activity. 14,15 As importantly, HDL protects endothelial cells from...

Prostacyclin receptors: Transcriptional regulation and novel signalling mechanisms

“…In brief, key amongst those findings include: (i) PDZK1 directly interacts with the IP involving a Class I PDZ ligand at its C-terminus; (ii) while the interaction occurs constitutively, it is dynamically regulated in response to agonist (cicaprost)-activation of the IP ( Figure 7A); (iii) while PDZK1 did not influence overall levels of the IP, it increases its functional expression at the plasma membrane enhancing agonist binding and cAMP generation; (iv) specifically, in the context of the role of prostacyclin in re-endothelialization, both cicaprost and HDL were confirmed to promote substantial EC migration and in vitro angiogenesis, and in an augmentative manner (Figure 7B), while (v) similar to that previously reported for the HDL/SR-B1-mediated EC responses 117 , siRNA-disruption of PDZK1 abolished cicaprost-induced EC migration and in vitro angiogenesis, and without affecting VEGFmediated responses 106 . A number of studies have suggested that prostacyclin-induced endothelial migration and angiogenesis occurs through its regulation of PPARδ, rather than through the IP per se 22,23 .…”

“…PDZK1 contains 4 PDZ domains, facilitating its binding to highly specific interacting partners [114][115][116] . Most notably, in the context of the CV system, through its interaction with the high density lipoprotein (HDL) scavenger receptor class B, type 1 (SR-B1), PDZK1 is essential for both reverse cholesterol transport (RCT) and for HDL-mediated vascular reendothelialization 112,117 . Similar to prostacyclin and the IP, through its activation of SR-B1, HDL also plays an essential protective role within the CV system where it regulates re-endothelialization as well as RCT, maintaining endothelial integrity and protecting against atherosclerosis and restenosis 118,119 .…”

“…Similar to prostacyclin and the IP, through its activation of SR-B1, HDL also plays an essential protective role within the CV system where it regulates re-endothelialization as well as RCT, maintaining endothelial integrity and protecting against atherosclerosis and restenosis 118,119 . By binding to its C-terminal PDZ ligand, PDZK1 plays an essential role in maintaining SR-BI expression levels in the liver, thereby controlling HDL cholesterol levels, and is now also known to play a key role in HDL/SR-BI-regulation of EC migration, promoting re-endothelialization 117,120,121 …”

Dysfunctional high-density lipoproteins in coronary heart disease: implications for diagnostics and therapy

“…HDL induces endothelium-dependent vascular relaxation via increased endothelial nitric oxide synthase (eNOS) phosphorylation and nitric oxide production, 20 and maintains endothelial barrier stability by promoting endothelial cell survival, 21,22 stimulating endothelial junction closure via HDL-bound sphingosine-1-phosphate (S1P), 23,24 and accelerating endothelial cell migration and re-endothelialization of injured arteries. 25,26 Moreover, antiinflammatory activities of HDL in atherosclerosis have been documented. HDL attenuates the adhesion of monocytes to the vascular endothelial lining and subsequent monocyte transendothelial migration by decreasing the expression of adhesion molecules on endothelial cells 27, 28 and monocytes 29 as well as by suppressing the expression of chemokines and chemokine receptors.…”

Noncanonical Role of the PDZ4 Domain of the Adaptor Protein PDZK1 in the Regulation of the Hepatic High Density Lipoprotein Receptor Scavenger Receptor Class B, Type I (SR-BI)

“…steroidogenic organs or endothelial cells) (8,21,22). As a result, PDZK1 KO mice show an increase of plasma cholesterol (ϳ1.7-fold) in the form of abnormally large HDL particles that is similar to, but not as severe as, that seen in SR-BI KO mice (8).…”