Pro-osteogenic phenotype of human aortic valve interstitial cells is associated with higher levels of Toll-like receptors 2 and 4 and enhanced expression of bone morphogenetic protein 2.
OBJECTIVE
Our aim was to determine whether aortic valve interstitial cells (AVICs) and pulmonary valve interstitial cells (PVICs) differ in expression of Toll-like receptor (TLR)2 and TLR4, response to TLR agonists, and osteogenic phenotypic changes.


BACKGROUND
Calcific stenosis occurs frequently in aortic valves but rarely in pulmonary valves. Studies have implicated AVICs in the inflammation associated with calcification and progression to stenosis. We previously reported that human AVICs express functional TLR2 and TLR4 and that stimulation of these receptors induces pro-osteogenic factor expression.


METHODS
Human aortic and pulmonary valve leaflets from the same heart were collected and interstitial cells isolated.


RESULTS
Aortic valves express more TLR2 and TLR4, in both tissue and isolated interstitial cells, than pulmonary valves. After stimulation with TLR2 and TLR4 agonists, AVICs express higher levels of pro-inflammatory and pro-osteogenic mediators (bone morphogenetic protein [BMP]-2, runt-related transcription factor 2) and greater osteogenic phenotypic changes (alkaline phosphatase [ALP] activity, calcified nodule formation) than PVICs. Silencing TLR2 and TLR4 in AVICs reduced BMP-2 expression and ALP activity to PVIC levels. ALP activity in AVICs induced by TLR2 and TLR4 agonists was abolished by BMP antagonism with Noggin and mimicked by stimulation with recombinant BMP-2. AVICs isolated from stenotic valves had greater expression of TLR2 and TLR4 and a greater BMP-2 response than AVICs from normal valves.


CONCLUSIONS
Greater expression of TLR2 and TLR4 and greater pro-inflammatory and pro-osteogenic responses to TLR2 and TLR4 agonists in AVICs than PVICs are associated with osteogenic phenotypic changes. These innate immune receptors may play a critical role in aortic valve calcification and stenosis.
Yang
Xiaoping
X
Division of Cardiothoracic Surgery, Department of Surgery, University of Colorado Denver, Denver, CO, USA.
Fullerton
David A
DA
Su
Xin
X
Ao
Lihua
L
Cleveland
Joseph C
JC
Meng
Xianzhong
X
D001021:Aortic Valve / Q000378:metabolism*; D001024:Aortic Valve Stenosis / Q000235:genetics*; D055396:Bone Morphogenetic Protein 2 / Q000096:biosynthesis*; D002114:Calcinosis / Q000235:genetics*; D005260:Female; D015870:Gene Expression; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D011664:Pulmonary Valve / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000235:genetics*; D051197:Toll-Like Receptor 4 / Q000235:genetics*
C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4