Expression and tissue localization of soluble guanylyl cyclase in the human placenta using novel antibodies directed against the alpha(2) subunit.

The cytoplasmic or soluble forms of guanylyl cyclase (sGC) are heme-contain ing heterodimeric enzymes that are regulated by nitric oxide (NO) and carbo n monoxide (CO). These gaseous messenger molecules are produced in the huma n placenta and are potential regulators of vasodilation and trophoblast inv asion. The ar subunit of sGC has only recently been shown to naturally occu r in placental extracts. In the present study, two novel antibodies directe d against different epitopes of the alpha (2) subunit, were generated. West ern Blot analysis confirmed the presence of a 82 kDa protein, identical wit h alpha (2) protein overexpressed in Sf9 cells. According to RNase protecti on analysis the alternatively spliced alpha (2i) variant was absent from hu man placenta. Immunohistochemical analysis showed the presence of alpha (2) protein in syncytiotrophoblast and villous and umbilical blood vessels, wh ich are known sites of NO production. Strong expression was observed in the extravillous (intermediate) trophoblast, where the expression of GO-genera ting hemeoxygenases has recently been documented. Localization of alpha (2) subunit expression suggests a role for sGC in mediating the actions of bot h NO and CO. The novel antibodies characterized in the present study will b e powerful tools to further elucidate the role of the NO/CO/cGMP signaling pathways in pathologic states such as preeclampsia and intrauterine growth retardation.