Transcriptome Profiling of Fast-Glycolytic and Slow-Oxidative Muscle Fibers in Chickens under Short- and Long-Term High-Fat Diets

Skeletal muscle fiber composition influences meat quality and metabolic regulation in poultry, yet fiber-type–specific responses to high-fat diet (HFD) remain poorly understood. This study examined the effects of short-term (SHFD) and long-term (LHFD) HFD feeding on fast/glycolytic (pectoralis major, PEM) and slow/oxidative (soleus, SOL) muscles in Guangyuan grey chickens. Histological analysis showed SOL fibers underwent oxidative-to-glycolytic transition under LHFD, accompanied by mitochondrial disruption. PEM accumulated more lipids and showed early metabolic stress. Transcriptome profiling revealed 3840 differentially expressed genes between PEM and SOL, with 1761 constitutively different. Under SHFD, SOL activated protective pathways including PPAR and autophagy, while PEM showed limited adaptation. LHFD induced further downregulation of fatty acid metabolism and structural genes (e.g., ALPK1, CA12, PM20D2, SLC27A1, and GADD45G) in PEM, but SOL maintained or enhanced expression of genes (e.g., NR4A3, PRKAG2, NOCT, PPARA, and SLC6A6) involved in muscle organization and lipid processing. Temporal clustering highlighted progressive divergence in transcriptional responses. These results suggest SOL fibers exhibit greater resilience to lipid overload than PEM fibers. Our findings provide insight into the molecular basis of muscle-type–specific adaptations to dietary fat and offer targets for improving metabolic health and meat quality in poultry. Overall design: This study aimed to investigate the muscle-type–specific transcriptional responses to different durations of high-fat diet (HFD) feeding in Guangyuan Grey chickens. A total of 270 150-day-old hens with similar body weights were randomly assigned to three dietary groups: long-term high-fat diet (LHFD, 60 days), short-term high-fat diet (SHFD, 15 days), and a normal control diet (CONT). Each group included 9 replicates with 10 birds per replicate. At 210 days of age, nine birds per group were randomly selected and humanely euthanized after 12 hours of fasting. Immediately postmortem, the pectoralis major muscle (PEM) and soleus muscle (SOL) were dissected from the same birds. Tissue blocks (~0.5 × 0.5 × 1.0 cm) were excised from the ventral (skin-facing) side of PEM and from the widest region of SOL, excluding the superficial layer. Each sample was divided into two portions: one was fixed for histological analysis, and the other was rapidly snap-frozen in liquid nitrogen and stored at -80 °C for RNA extraction and transcriptomic analysis. PEM is composed primarily of fast-twitch glycolytic fibers, whereas SOL contains a mixture of oxidative and glycolytic fibers, making them ideal models for studying muscle fiber type–specific metabolic adaptations. RNA sequencing was conducted to compare gene expression profiles across the six sample groups (CONT-PEM, SHFD-PEM, LHFD-PEM, CONT-SOL, SHFD-SOL, LHFD-SOL). This design allowed for the identification of core transcriptional differences between muscle types and diet-induced transcriptional remodeling, particularly focusing on lipid metabolism, mitochondrial function, and fiber-type transformation.