Research note: Effect of a biotechnologically produced Pleurotus sapidus mycelium on expression of genes involved in protein synthesis and degradation in breast muscle of broilers.

Recently, feeding a fungal mycelium from Pleurotus sapidus was found to reduce relative breast muscle weight of broilers. The present study tested the hypothesis that dietary inclusion of P. sapidus mycelium modulates the expression of genes involved in protein anabolic and protein catabolic pathways in breast muscle of broilers. The study included 72 male, 1-day-old Cobb 500 broilers which were randomly assigned to three groups fed three different diets containing either 0 (PSA-0), 25 (PSA-25) and 50 (PSA-50) g/kg diet P. sapidus mycelium in a three-phase feeding system for 35 days. Within the somatropic axis, the mRNA level of GHR was higher and that of IGF1R was lower in group PSA-25 than in group PSA-0 (P < 0.05). Within the mTOR signaling pathway, the mRNA level of S6K1 was higher in group PSA-25 than in group PSA-0 (P < 0.05). Within muscle growth-related genes, the mRNA level of MYOG was lower in groups PSA-25 and PSA-50 than in group PSA-0 (P < 0.05). The relative phosphorylation of proteins involved in protein anabolic pathways (S6K1, RPS6, eIF2a, AKT) did not differ across the three groups. The mRNA of most genes involved in molecular pathways of protein degradation and inhibition of protein synthesis, such as the GCN/eIF2a pathway, the ubiquitin-proteasome pathway, and the autophagy-lysosomal pathway, showed no differences across the three groups. Only the mRNA level of ATG9A was higher in group PSA-25 compared to group PSA-0 (P < 0.05). These observations suggest that a modulation of these signaling pathways is unlikely to explain the reduced relative breast muscle weight in broilers. Nevertheless, future studies are necessary to exclude an effect of feeding P. sapidus mycelium on other less prominent pathways affecting skeletal muscle mass.