Abstract
Purpose: :
Elevated levels of dietary histidine have previously been shown to prevent or mitigate cataract formation in farmed Atlantic salmon (Salmo salar). The aim of this study was to shed light on the mechanisms by which histidine acts. Applying microarray analysis to the lens transcriptome, we screened for differentially expressed genes in search for a model explaining cataract development in fish.
Methods: :
Atlantic salmon were fed diets only differing in the histidine content. Cataract score was assessed by slit lamp biomicroscopy. Lens N-acetylhistidine contents were measured by HPLC. Total RNA from whole lenses was analysed using the GRASP 16K salmonid microarray. The microarray data were analysed using J-Express Pro 2.8 and validated by qRT-PCR.
Results: :
Fish developed cataracts with different severity in response to dietary histidine levels. Lens N-acetylhistidine contents reflected the dietary histidine levels and were negatively correlated to cataract scores. Significance analysis of microarrays (SAM) revealed 248 significantly up-regulated and 266 significantly down-regulated genes in fish fed low levels of histidine compared to fish fed higher histidine levels. Among those were genes involved in stress-response, lipid metabolism, carbohydrate metabolism, ion homeostasis regulation, and proteolysis. Hierarchical clustering and correspondence analysis plot confirmed differences in gene expression between the feeding groups. The differentially expressed genes could be categorised as "early" and "late" responsive, according to their expression pattern relative to progression in cataract formation.
Conclusions: :
Dietary histidine levels affect cataract formation in Atlantic salmon and gene expression in the lens. The results of this screening study might be used to establish genes as markers for early cataract diagnosis.
Keywords: cataract • gene microarray • nutritional factors