Gene expression profiling in blood cells of endurance horses completing competition or disqualified due to metabolic disorder

Abstract

Reasons for performing study: Genomics using cDNA microarrays could provide useful information about physiological adaptations and metabolic disorders in endurance horses. Objectives: In order to show that genes are modulated in leucocytes in relationship with performance and clinical status of the horses, gene expression in leucocytes, haematological and biochemical parameters were compared between successful and disqualified endurance horses. Methods: Blood samples were collected at rest (T0) and just after a 140-160 km endurance race (T1) in 2 groups of horses: 10 continuing successful (S) and 10 disqualified horses stopped at a vet-gate for metabolic disorders (D). Total RNA was extracted from the blood cells (leucocytes), checked for purity, amplified and hybridised using mouse cDNA microarrays including 15,264 unique genes. Differential gene expressions were studied by hybridisation of each sample T1 vs. a control sample collected at T0 (pool of 20 sound horses). Results: Some significant differences were observed in the haematology and biochemistry of the 2 groups (S vs. D). In Group D, rhadomyolysis was confirmed with CK 13,124 u/***l and AST 1242 u/***l. The list of 726 (including 603 annotated genes) significant genes was filtered according to a high P-value cut-off (P<0.00001). Among them, 130 were up-regulated (expression ratio>1.5) and 288 were down-regulated (<1/1.5). Analysis of variance revealed 62 genes differentially expressed (P<0.05) in Groups D and S. The expression levels of 28 and 50 genes were significantly correlated (r>0.75) with CK and AST level in Group D, respectively. The gene ontology classification showed that more genes were up-regulated in S than in the D. More genes were down-regulated in the disqualified horses. Conclusions: Long exercise induced many significant gene modulations in leucocytes. Some genes were expressed in relationship with the clinical phenotype observed in Group D: rhabdomyolysis and haemolysis. Potential relevance: Some of these genes could be candidates to explain poor performance or pathologies. Further association studies with a greater number of genes should be conducted. © 2006 EVJ Ltd.