MAPK3 and aneurysm: Additionally, accumulation of phosphorylated ERK1/2 (pERK1/2), the active form of ERK1/2, was associated with aneurysm growth in Fbn1C1041G+ mice, and both a TGF-β neutralizing antibody and losartan were able to reduce pERK1/2 levels and to attenuate aneurysm expansion [37].