Quantitative Trait Locus Analysis, Pathway

Coxsackievirus B3 (CVB3) infection is the most common cause of viral myocarditis. The pathogenesis of viral myocarditis is strongly controlled by host genetic factors. Although certain indispensable components of immunity have been identified, the genes and pathways underlying natural variation between individuals remain unclear. Previously, we isolated the viral myocarditis susceptibility 1 (Vms1) locus on chromosome 3, which influences pathogenesis. We hypothesized that confirmation and further study of Vms1 controlling CVB3-mediated pathology, combined with pathway analysis and consomic mapping approaches, would elucidate both pathological and protective mechanisms accounting for natural variation in response to CVB3 infection. Vms1 was originally mapped to chromosome 3 using a segregating cross between susceptible A/J and resistant B10.A mice. To validate Vms1, C57BL/ 6J-Chr 3 A /NaJ (a chromosome substitution strain that carries a diploid A/J chromosome 3) were used to replicate susceptibility compared with resistant C57BL/6J (B6). A second segregating F2 cross was generated between these, confirming both the localization and effects of Vms1. Microarray analysis of the four strains (A/J, B10.A, C57BL/6J, and C57BL/6J-Chr 3 A /NaJ) illuminated a core program of response to CVB3 in all strains that is comprised mainly of IFN-stimulated genes. Microarray analysis also revealed strain-specific differential expression programs and genes that may be prognostic or diagnostic of susceptibility to CVB3 infection. A combination of analyses revealed very strong evidence for the existence and location of Vms1. Differentially expressed pathways were identified by microarray, and candidate gene analysis revealed Fpgt, H28, and Tnni3k as likely candidates for Vms1. V iral myocarditis and its long-term sequela, dilated car-diomyopathy (DC), are a common cause of morbidity and mortality (1). Adenoviruses, influenza, and herpes-viruses have been implicated; however, enteroviruses, particularly coxsackievirus B3 (CVB3) strains, are the most prominent etiol-ogy (2). In mice, experimental infection with CVB3 has served to elucidate three distinct clinical aspects of human disease progression: 1) an initial phase of viral replication and cytolytic damage of cardiomyocytes; 2) a phase of intense myocardial infiltration by immune effectors, which may resolve infection or persist indefinitely in susceptible animals (3); and 3) a delayed phase in which initial infiltration and response may transition into autoimmune or inflammatory cardiomyopathy (4). Furthermore, different individuals or inbred mouse strains display variable degrees of cardiomyopathy, likely influenced by their genetic background. Myocarditis and DC can also be induced experimentally in the absence of virus by administration of cardiac myosin with adjuvant. As with viral myocarditis, …