Age-induced gene expression in Thoroughbred horse skeletal muscle highlights genes that enhance muscle architecture and function.

Overview

• This study investigates how gene expression in skeletal muscle changes between the ages of two and three years in Thoroughbred horses.
• The research identifies key genes and biological pathways involved in muscle development, which are crucial for enhancing muscle structure and function during this critical growth period.

Background and Importance

• Early skeletal muscle development in racehorses is vital for their athletic performance and career longevity.
• Despite its importance, limited research has focused on the transcriptional or gene expression changes occurring in young horses’ muscles during this period.
• Understanding how age affects gene expression and how muscles adapt at the molecular level can help in designing better training and care strategies for juvenile horses.

Methodology

• The study used transcriptome-wide analysis — examining the complete set of RNA transcripts — from skeletal muscle biopsies of untrained Thoroughbred horses.
• Samples were collected from the same horses at two time points: at two years old (UR2) and three years old (UR3), both at rest.
• Differentially expressed genes (DEGs) were identified by comparing gene expression levels between these two time points.

Key Findings: Differential Gene Expression

• A total of 136 genes showed significant changes in expression with age.
• 95 genes showed increased expression at three years old compared to two years old, while 41 showed decreased expression.
• These genes are particularly involved in muscle structure, growth, and development processes.

Functional Analyses: Gene Ontology (GO) and Pathways

• Gene Ontology enrichment analysis pointed to muscle assembly and system development as key functional groups, including:
• Developmental process (biological processes related to growth and differentiation)
• Anatomical structure development (formation and maintenance of body structure)
• Actin cytoskeleton (a critical framework for muscle fiber structure and function)
• Growth factor binding (important for cell communication and muscle growth)
• KEGG pathway analysis revealed significant involvement of pathways such as:
• ECM-receptor interaction (extracellular matrix interactions critical for muscle integrity and repair)
• Protein digestion and absorption (important for nutrient availability and muscle metabolism)
• Focal adhesion (cell attachment points influencing muscle cell signaling)
• PI3K-Akt signalling pathway (key in muscle growth, survival, and metabolism)

Protein-Protein Interaction (PPI) and Hub Genes

• Network analysis identified seven hub or key regulatory genes that may control muscle development:
• COL1A1, COL1A2, COL3A1: genes coding for collagen proteins that form the muscle’s extracellular matrix and provide structural support.
• S100A4: protein involved in cell growth and motility.
• NOTCH1: a receptor involved in regulation of muscle cell fate and differentiation.
• THY1: a surface glycoprotein implicated in cell adhesion and development.
• MT-ND2: a mitochondrial gene important in energy metabolism, essential for muscle function.
• Additional genes such as MSTN (myostatin), COL4A1, COL4A2, SPEN, NOTCH3, also play pivotal roles in functional muscle development.

Conclusions and Implications

• The transcriptomic changes between two and three years indicate a critical window where muscle architecture and function are actively being enhanced.
• This underlying molecular remodeling supports the muscle adaptation necessary for the physical demands placed on young racing horses.
• These insights might guide better timing and design of training regimens, nutritional support, and medical interventions tailored to the developmental stage of young Thoroughbreds.
• The study contributes valuable data toward understanding equine muscle biology and could inform breeding, management, and health strategies for racehorses.