Transcriptomic evaluation in racehorses
Background: The molecular mechanisms underlying adaptation to physical exertion and racing stress in horses remain incompletely understood. Peripheral blood transcriptomics offers a minimally invasive method to monitor systemic responses to exercise and identify biomarkers of adaptation or overload. Objectives: To evaluate transcriptomic changes in peripheral blood of racehorses during different phases of training and competition, and to identify molecular markers of physiological adaptation and race-induced stress. Study design: Prospective transcriptomic profiling of trained racehorses across three exercise conditions. Methods: Forty racehorses (29 Arabian, 11 Thoroughbred) were sampled before (p0) and after (p1) exercise at three stages: initial training (T1), mid-season training (T2), and racing (R). RNA-seq was performed, followed by differential expression analysis (DESeq2) and pathway enrichment (g:Profiler, DAVID). Results: Distinct molecular programs were identified at each stage. At T1, immediate-early response genes such as FOS, FOSB, and HSPA6 were strongly up-regulated, reflecting acute stress and immune activation. At T2, immune-related transcripts (KLRD1, CCL4, PRF1) remained enriched, but genes linked to remodeling and adaptation, including DNAJA1, HSPH1, and CXCR4, became prominent, suggesting a shift toward recovery and regulatory processes. Post-race, chemokines such as CCL5 and stress markers (HSP90 family, JUN) were highly induced, accompanied by widespread transcriptomic divergence and down-regulation of certain immune regulators (IL18, ARHGAP44), indicating both heightened innate activation and transient immune suppression. Main limitations: Transcriptomic profiling was limited to peripheral blood, which may not reflect tissue-specific responses. Only three sampling points were included, potentially overlooking transient transcriptomic changes. Conclusions: Transcriptomic dynamics in blood reflect the transition from early immune activation (T1), through adaptation (T2), to stress-related activation post-race (R). This approach offers promising molecular biomarkers for monitoring training adaptation and detecting physiological overload in equine athletes.