Human α-defensin regulates smooth muscle cell contraction: a role for low-density lipoprotein receptor–related protein/α2-macroglobulin receptor

• Published in: Blood 2002-12, Vol.100 (12), p.4026-4032
• Main Authors: Nassar, Taher, Akkawi, Sa’ed, Bar-Shavit, Rachel, Haj-Yehia, Abdullah, Bdeir, Khalil, Al-Mehdi, Abu-Bakr, Tarshis, Mark, Higazi, Abd Al-Roof
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Blood and lymphatic vessels; Cardiology. Vascular system; Medical sciences; Miscellaneous
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2002-04-1080

We have previously identified α-defensin in association with medial smooth muscle cells (SMCs) in human coronary arteries. In the present paper we report that α-defensin, at concentrations below those found in pathological conditions, inhibits phenylephrine (PE)–induced contraction of rat aortic rings. Addition of 1 μM α-defensin increased the half-maximal effective concentration (EC50) of PE on denuded aortic rings from 32 to 630 nM. The effect of α-defensin was dose dependent and saturable, with a half-maximal effect at 1 μM. α-Defensin binds to human umbilical vein SMCs in a specific manner. The presence of 1 μM α-defensin inhibited the PE-mediated Ca++ mobilization in SMCs by more than 80%. The inhibitory effect of α-defensin on contraction of aortic rings and Ca++ mobilization was completely abolished by anti–low-density lipoprotein receptor–related protein/α2-macroglobulin receptor (LRP) antibodies as well as by the antagonist receptor-associated protein (RAP). α-Defensin binds directly to isolated LRP in a specific and dose-dependent manner; the binding was inhibited by RAP as well as by anti-LRP antibodies. α-Defensin is internalized by SMCs and interacts with 2 intracellular subtypes of protein kinase C (PKC) involved in muscle contraction, α and β. RAP and anti-LRP antibodies inhibited the binding and internalization of α-defensin by SMCs and its interaction with intracellular PKCs. These observations suggest that binding of α-defensin to LRP expressed in SMCs leads to its internalization; internalized α-defensin binds to PKC and inhibits its enzymatic activity, leading to decreased Ca++mobilization and SMC contraction in response to PE.