Expression and Tissue Localization of Soluble Guanylyl Cyclase in the Human Placenta Using Novel Antibodies Directed against the {alpha}2 Subunit

Ana-Maria Bamberger, Markus Koglin, Jörg Kempfert, Thomas Löning, Hasso Scholz and Sönke Behrends

Departments of Gynecopathology (A.-M.B., T.L.) and Pharmacology (M.K., J.K., H.S., S.B.), University clinic Eppendorf, 20246 Hamburg, Germany

The cytoplasmic or soluble forms of guanylyl cyclase (sGC) are heme-containing heterodimeric enzymes that are regulated by nitric oxide (NO) and carbon monoxide (CO). These gaseous messenger molecules are produced in the human placenta and are potential regulators of vasodilation and trophoblast invasion. The {alpha}2-subunit of sGC has only recently been shown to naturally occur in placental extracts. In the present study, two novel antibodies directed against different epitopes of the {alpha}2 subunit, were generated. Western Blot analysis confirmed the presence of a 82 kDa protein, identical with {alpha}2 protein overexpressed in Sf9 cells. According to RNase protection analysis the alternatively spliced {alpha}2i variant was absent from human placenta. Immunohistochemical analysis showed the presence of {alpha}2 protein in syncytiotrophoblast and villous and umbilical blood vessels, which are known sites of NO production. Strong expression was observed in the extravillous (intermediate) trophoblast, where the expression of CO-generating hemeoxygenases has recently been documented. Localization of {alpha}2 subunit expression suggests a role for sGC in mediating the actions of both NO and CO. The novel antibodies characterized in the present study will be powerful tools to further elucidate the role of the NO/CO/cGMP signaling pathways in pathologic states such as preeclampsia and intrauterine growth retardation.