Transcriptome profiling of immune responses to cardiomyopathy syndrome (CMS) in Atlantic salmon

Abstract

BackgroundCardiomyopathy syndrome (CMS) is a disease associated with severe myocarditis primarily in adult farmed Atlantic salmon (Salmo salar L.), caused by a double-stranded RNA virus named piscine myocarditis virus (PMCV) with structural similarities to the Totiviridae family. Here we present the first characterisation of host immune responses to CMS assessed by microarray transcriptome profiling.ResultsUnvaccinated farmed Atlantic salmon post-smolts were infected by intraperitoneal injection of PMCV and developed cardiac pathology consistent with CMS. From analysis of heart samples at several time points and different tissues at early and clinical stages by oligonucleotide microarrays (SIQ2.0 chip), six gene sets representing a broad range of immune responses were identified, showing significant temporal and spatial regulation. Histopathological examination of cardiac tissue showed myocardial lesions from 6 weeks post infection (wpi) that peaked at 8-9 wpi and was followed by a recovery. Viral RNA was detected in all organs from 4 wpi suggesting a broad tissue tropism. High correlation between viral load and cardiac histopathology score suggested that cytopathic effect of infection was a major determinant of the myocardial changes. Strong and systemic induction of antiviral and IFN-dependent genes from 2 wpi that levelled off during infection, was followed by a biphasic activation of pathways for B cells and MHC antigen presentation, both peaking at clinical pathology. This was preceded by a distinct cardiac activation of complement at 6 wpi, suggesting a complement-dependent activation of humoral Ab-responses. Peak of cardiac pathology and viral load coincided with cardiac-specific upregulation of T cell response genes and splenic induction of complement genes. Preceding the reduction in viral load and pathology, these responses were probably important for viral clearance and recovery.ConclusionsBy comparative analysis of gene expression, histology and viral load, the temporal and spatial regulation of immune responses were characterised and novel immune genes identified, ultimately leading to a more complete understanding of host-virus responses and pathology and protection in Atlantic salmon during CMS.

Effects of functional feeds on the lipid composition, transcriptomic responses and pathology in heart of Atlantic salmon (Salmo salar L.) before and after experimental challenge with Piscine Myocarditis Virus (PMCV)

“…In addition, there were correlations between the expression of genes related with immune responses, viral load and heart lesions, in agreement with Timmerhaus et al [10]. Importantly, however, the temporal differences observed between the different dietary treatments in the present study strengthened these correlations.…”

“…The time-courses for the development and resolution of histopathology and immune gene responses were similar to those observed previously [10, 11]. In addition, there were correlations between the expression of genes related with immune responses, viral load and heart lesions, in agreement with Timmerhaus et al [10].…”

Comparative cardiac pathological changes of Atlantic salmon (Salmo salar L.) affected with heart and skeletal muscle inflammation (HSMI), cardiomyopathy syndrome (CMS) and pancreas disease (PD)

“…These findings were pointing the high cell turn over in the hearts where DNA damage/repair might be the case (as identified by PCNA, caspase 3 and TUNEL reactivity) (Table 2) (Ferguson et al, 1986;Poppe and Ferguson, 2006;Kongtorp et al, 2004Kongtorp et al, , 2006. In addition, the transcriptomic profile of CMS-affected fish has shown the upregulation of apoptosis genes, supporting the strong to moderate levels of apoptosis staining in diseased hearts (Timmerhaus et al, 2011).…”

“…The common regulatory mechanisms have been suggested for the expression of MHC class I and II in Atlantic salmon (Koppang et al, 1999). Recently, a CMS transcriptomic study identified the up-regulation of T-lymphocytes (CD3 and CD8), MHC and apoptotic genes, and also correlated with histopathological changes (Timmerhaus et al, 2011). The increased presence of MHC class II + cells have been described in granulomatous uveitis and amoebic gill disease of Atlantic salmon (Koppang et al, 2004;Morrison et al, 2006).…”

Risk factors for cardiomyopathy syndrome (CMS) in Norwegian salmon farming

“…Later years have shown a breakthrough in establishing the etiology of CMS: in 2009, 2 studies were published independently, both reporting successful experimental transmission of CMS in Atlantic salmon using tissue homogenates from fish collected during outbreaks of CMS in the field (Bruno & Noguera 2009, Fritsvold et al 2009). Subsequently, additional challenges have been performed where homogenates were filtered through 0.22 μm filters before successfully transmitting CMS to healthy fish, indicating that the infectious agent is a virus (Timmerhaus et al 2011). In 2010, a major breakthrough was achieved when 2 independent research groups both identified the causal agent for CMS, a hitherto unknown virus belonging to the family Totiviridae, which was subsequently named piscine myocarditis virus (PMCV).…”