Abstract 15312: The Inflammatory and Osteogenic Responses to Tlr4 Stimulation in Human Aortic Valve Interstitial Cells is Greater in Adults Than Children: The Role of Stat3 as a Negative Regulatory Mechanism
Calcific aortic valve stenosis is characterized by progressive valvular inflammation and calcification. It is a disease of aging; the aortic valves of children almost never calcify.
We have previously demonstrated that stimulation of Toll-like receptor 4 (TLR4) induces inflammatory and osteogenic responses in aortic valve interstitial cells (AVICs) isolated from the leaflets of normal aortic valves from adults. We therefore hypothesized that adult AVICs have greater inflammatory and osteogenic responses to TLR4 stimulation than do pediatric AVICs.
Methods and Results: AVICs were isolated from leaflets of pediatric (2 months to 16 years old) and adult (48 to 65 years old) heart transplant recipients without aortic valve abnormalities.
Cells were treated with TLR4 agonist lipopolysaccharide (LPS). Cellular levels of TLR4, intercellular adhesion molecule 1 (ICAM-1), bone morphogenetic protein 2 (BMP-2) and alkaline phosphatase (ALP), as well as phosphorylation of p-38, NF-κB and Stat3, were analyzed by immunoblotting. While TLR4 protein levels were comparable between adult and pediatric AVICs, adult cells had markedly higher levels of ICAM-1, BMP-2 and ALP following TLR4 stimulation. The greater inflammatory and osteogenic responses in adult cells were associated with higher levels of phosphorylation of p-38 and NF-κB, two important signaling molecules that mediate the inflammatory and osteogenic responses in human AVICs. Interestingly, pediatric cells exhibited markedly higher levels of phosphorylated Stat3. Inhibition of Stat3 enhanced p-38 and NF-κB phosphorylation, and exaggerated the expression of ICAM-1, BMP-2 and ALP in pediatric AVICs following TLR4 stimulation.
Conclusion: Adult AVICs have greater inflammatory and osteogenic responses to TLR4 stimulation. The enhanced responses in adult AVICs are not due to higher TLR4 levels, but correlate to lower Stat3 activation in response to TLR4 stimulation in adult cells relative to pediatric cells. The results suggest that Stat3 negatively regulates the inflammatory and osteogenic responses in human AVICs and is a potential therapeutic target for suppression of the progression of calcific aortic valve disease.
- © 2013 by American Heart Association, Inc.