Investigating the metabolic changes that accompany skeletal muscle maturation

Abstract

Skeletal muscle plasticity is imperative for our overall health but diminishes with inactivity and age. As we reach maturity, a shift in nutrient allocation from supporting skeletal muscle hypertrophy to adipogenesis occurs. This pivotal intersection in tissue growth marks the start of a metabolic decline in skeletal muscle and an accumulation of adipose tissue in inactive individuals. If left uncorrected, a loss of skeletal muscle metabolic flexibility can lead to a myriad of metabolic diseases. To define the metabolic changes in skeletal muscle that accompany maturation, samples were collected from the longissimus dorsi (LD, glycolytic muscle), latissimus dorsi (LAT, mixed muscle), and masseter (MS, oxidative muscle) at 20, 53, 87, 120, and 180 days of age from DNA 600 x 241 (DNA Genetics) castrated male pigs that weighed an average of 5.7, 20.8, 42.2, 83.4, and 130.5 kg, respectively. These ages were selected to correspond to tissue growth phases characterized by vital organ growth, intensive muscle hypertrophy, cessation of muscle hypertrophy, and the beginning of unrestricted adipose deposition. Samples were analyzed to determine the abundance of key metabolic enzymes through Western blotting and assess mitochondrial content through real-time PCR. Glucose-6-phosphate dehydrogenase decreased at 87, 120, and 180 d in MS compared to LAT and LD ( P < 0.01), which suggested glycolytic muscles increased nutrient allocation to the pentose phosphate pathway at this time whereas oxidative muscles did not. Moreover, pyruvate dehydrogenase ( P < 0.01) and citrate synthase ( P < 0.01) increased at 120 d, which indicated an increase in metabolites entering oxidative pathways. This increase was accompanied by an increase in mitochondrial DNA at 87 and 120 d ( P < 0.01). Further, glutamic-oxaloacetic transaminase 2 increased between 20 d to 120 d ( P < 0.01) indicating amino acid synthesis peaks at 120 d. These findings have established a metabolic fingerprint associated with the termination of muscle growth and the beginning of adipose tissue growth, which provides the framework for uncovering the regulatory mechanism that modulates nutrient allocation between muscle and fat. Elucidating this mechanism will aid in the discovery of metabolic interventions to combat metabolic diseases. Kansas State University Global Food Systems Seed Grant Program This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.