Toll-like receptor 4 expression during cerebral aneurysm formation. Laboratory investigation.
OBJECTIVE
The pathophysiological origin of cerebral aneurysms is closely associated with chronic inflammation in arterial walls. Recently, the authors identified nuclear factor-kappa B (NF-κB) as a key mediator of cerebral aneurysm formation and progression. Because Toll-like receptor 4 (TLR4) stimulates NF-κB activation in arterial walls in atherosclerosis, the authors hypothesize that TLR4 expresses in cerebral aneurysms and contributes to the activation of NF-κB in cerebral aneurysm walls.


METHODS
Cerebral aneurysms were induced in male Sprague-Dawley rats. Expression of TLRs in cerebral aneurysm walls was assessed using reverse transcriptase polymerase chain reaction (RT-PCR). The expression of TLR4 was examined using RT-PCR, immunohistochemical studies, and Western blotting. To assess TLR4 dependency on NF-κB activation, double immunostaining and a study using NF-κB-deficient mice were done. Finally, TLR4 expression in human cerebral aneurysm walls was assessed using immunohistochemical studies.


RESULTS
In cerebral aneurysm walls, TLR1, -4, -5, -6, -10, and -11 were expressed. Among them, TLR4 and TLR10 expression changed during cerebral aneurysm formation. Expression of TLR4 was predominantly in the endothelial cell layer of cerebral aneurysm walls, and was transitionally upregulated at the early stage of cerebral aneurysm formation. The TLR4 expression coincided well with NF-κB activation. In human cerebral aneurysms, TLR4 was also expressed in the endothelial cell layer, as it was in rats.


CONCLUSIONS
Toll-like receptor 4 was expressed in cerebral aneurysm walls both in rats and humans. This receptor may play a crucial role in cerebral aneurysm formation through NF-κB activation in endothelial cells. The results of the present study will shed new light on the pathogenesis of cerebral aneurysm formation.
Aoki
Tomohiro
T
Department of Neurosurgery, Kyoto University Graduate School of Medicine, Sakyo-ku, Kyoto, Japan.
Nishimura
Masaki
M
Ishibashi
Ryota
R
Kataoka
Hiroharu
H
Takagi
Yasushi
Y
Hashimoto
Nobuo
N
D000818:Animals; D015153:Blotting, Western; D006801:Humans; D007150:Immunohistochemistry; D002532:Intracranial Aneurysm / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D052002:NF-kappa B p50 Subunit / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000302:isolation & purification; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051197:Toll-Like Receptor 4 / Q000096:biosynthesis*; D051193:Toll-Like Receptors / Q000096:biosynthesis
D052002:NF-kappa B p50 Subunit; D012333:RNA, Messenger; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors