SPP1 and myocarditis: OPN is overexpressed in the heart coincident with myocardial infarction (Trueblood et al., 2001), hypertrophy (Graf et al., 1997; Li et al., 2017), and myocarditis (Szalay et al., 2009) in a cell type- and stimulant-dependent manner (Singh et al., 2010).