The M2 Gene Is a Determinant of Reovirus-Induced Myocarditis

Dina Zita, Marcelle; Phillips, Matthew B.; Stuart, Johnasha D.; Kumarapeli, Asangi R.; Sridharan, Vijayalakshmi; Boerma, Marjan; Snyder, Anthony J.; Danthi, Pranav; Boehme, Karl W.

Although a broad range of viruses cause myocarditis, the mechanisms that underlie viral myocarditis are poorly understood. Here, we report that the M2 gene is a determinant of reovirus myocarditis. The reovirus M2 gene encodes outer capsid protein μ1, which influences both cell entry and cell death. We infected newborn C57BL/6 mice with reovirus strain type 1 Lang (T1L) or a reassortant reovirus in which the M2 gene from strain type 3 Dearing (T3D) was substituted into the T1L genetic background (T1L/T3DM2). T1L was non-lethal in wild-type mice, whereas greater than 90% of mice succumbed to T1L/T3DM2 infection. T1L/T3DM2 produced higher viral loads than T1L at the site of inoculation. In secondary organs, T1L/T3DM2 was detected with more rapid kinetics and reached higher peak titers than T1L. We found that hearts from T1L/T3DM2-infected mice were grossly abnormal, with large lesions corresponding to substantial cardiac injury with inflammatory infiltrates. Lesions in T1L/T3DM2-infected mice contained aggregates of necrotic cardiomyocytes with pyknotic debris, and prominent lymphocyte and histiocyte infiltration. In contrast, T1L induced the formation of smaller lesions in a subset of animals, consistent with T1L being mildly myocarditic. Finally, more activated caspase-3-positive cells were observed in hearts from animals infected with T1L/T3DM2 compared to T1L. Together, our findings indicate that substitution of the T3D M2 allele into an otherwise T1L genetic background is sufficient to change a non-lethal infection into a lethal infection. Our results further indicate that T3D M2 enhances T1L replication and dissemination in vivo, which potentiates the capacity of reovirus to cause myocarditis. IMPORTANCE Reovirus is a non-enveloped virus with a segmented double-stranded RNA genome that serves as a model for studying virus-induced injury to the heart. However, the mechanisms by which reovirus affects heart disease are not fully elucidated. We found that substituting a single gene from reovirus strain type 3 Dearing (T3D) into an otherwise type 1 Lang (T1L) genetic background (T1L/T3DM2) was sufficient to convert the non-lethal T1L strain into a lethal infection in neonatal mice. In comparison to T1L, T1L/T3DM2 reached distal organs such as the heart more efficiently. Furthermore, it replicated to higher levels at those sites. Hearts from mice infected with T1L resulted in limited recruitment of immune cells. In contrast, hearts from mice infected with T1L/T3DM2 contained substantially more immune cell invasion and cell death. Together, our findings identify the reovirus M2 gene as a new determinant of reovirus induced heart disease.