Gene expression analysis of Atlantic salmon gills reveals mucin 5 and interleukin 4/13 as key molecules during amoebic gill disease

Abstract

Amoebic gill disease (AGD) is one of the main diseases affecting Atlantic salmon (Salmo salar L.) mariculture. Hallmarks of AGD are hyperplasia of the lamellar epithelium and increased production of gill mucus. This study investigated the expression of genes involved in mucus secretion, cell cycle regulation, immunity and oxidative stress in gills using a targeted 21-gene PCR array. Gill samples were obtained from experimental and natural Neoparamoeba perurans infections, and sampling points included progressive infection stages and post-freshwater treatment. Up-regulation of genes related to mucin secretion and cell proliferation, and down-regulation of pro-inflammatory and pro-apoptotic genes were associated with AGD severity, while partial restoration of the gill homeostasis was detected post-treatment. Mucins and Th2 cytokines accoun ted for most of the variability observed between groups highlighting their key role in AGD. Two mucins (muc5, muc18) showed differential regulation upon disease. Substantial up-regulation of the secreted muc5 was detected in clinical AGD, and the membrane bound muc18 showed an opposite pattern. Th2 cytokines, il4/13a and il4/13b2, were significantly up-regulated from 2 days post-infection onwards, and changes were lesion-specific. Despite the differences between experimental and natural infections, both yielded comparable results that underline the importance of the studied genes in the respiratory organs of fish, and during AGD progression.

Characterising the mechanisms underlying genetic resistance to amoebic gill disease in Atlantic salmon using RNA sequencing

“…Another highly expressed transcript is involved in T-cell function, T-cell specific surface glycoprotein CD28 ( CD28 ; logFC = 1.60). CD28 promotes T-cell survival and proliferation, and enhances the production of multiple cytokines including IL4 (Blotta et al 1996) IL4 has been found to be up-regulated in response to AGD (Marcos-López et al 2018), and this gene induces differentiation of naïve helper T cells to Th2 cells. The Th2 pathway was found to be up-regulated in late stages of AGD (Benedicenti et al 2015).…”

“…This gene inhibits apoptosis by suppressing the activity of caspase-8 (You et al 2001). The down-regulation of pro-apoptotic genes has been connected to AGD severity (Marcos-López et al 2018). The lack of a clear picture in head kidney might reflect the relative importance of the local and systemic immune responses in response to AGD.…”

“…using CRISPR/Cas9) in future aquaculture breeding programmes, understanding the functional mechanisms underlying disease resistance traits is key to identifying target genes and variants for editing. Previous studies into AGD-infected Atlantic salmon have suggested that the amoebae might elicit an immunosuppressive effect on the innate response of the host, with a concurrent up-regulation of the adaptive Th2-mediated response (Benedicenti et al 2015; Marcos-López et al 2017, 2018). Th2 cytokines were also found consistently up-regulated when comparing AGD infected and non-infected samples, and lesion and non-lesion areas (Marcos-López et al 2018).…”

“…Previous studies into AGD-infected Atlantic salmon have suggested that the amoebae might elicit an immunosuppressive effect on the innate response of the host, with a concurrent up-regulation of the adaptive Th2-mediated response (Benedicenti et al 2015; Marcos-López et al 2017, 2018). Th2 cytokines were also found consistently up-regulated when comparing AGD infected and non-infected samples, and lesion and non-lesion areas (Marcos-López et al 2018). The heritability of resistance to AGD has been shown to increase after successive cycles of disease challenge / treatment (Taylor et al 2009), which could suggest that the ability to elicit a successful adaptive immune response is partly under genetic control.…”

Methacarn preserves mucus integrity and improves visualization of amoebae in gills of Atlantic salmon (Salmo salar L.)

“…More recently, study of immunological responses within the gill has highlighted the potential role of secreted IgT responses, in part delivered through mucus, as well as gene expression reflecting production of other defensins carried in mucus and acting against gill pathogens (Brinchmann, 2016;Xu et al, 2016) and their correlated pathology (Benhamed, Guardiola, Mars, & Esteban, 2014;Hishida, Ishimatsu, & Oda, 1997). Additionally, mucins have been investigated as reliable markers of prognostic and diagnostic value of fish intestinal health (Estensoro, Calduch-giner, Pe, Kaushik, & Sitja, 2013;Marcos-López et al, 2018). Is therefore a need to maintain the mucous coat in order to identify the pathogens embedded in it and potentially study their relationship with the mucus secretions.…”