Prematurity Alters the Feeding-Induced Activation of Signaling Components Towards AKT in Skeletal Muscle of Neonatal Piglets

Abstract

Abstract Objectives Postnatal growth faltering is a common complication of premature birth. Our recent study in a neonatal pig model of prematurity showed that preterm birth reduces weight gain and protein synthesis in skeletal muscle and this is associated with blunted insulin-induced activation of signaling components downstream of AKT. However, prematurity does not affect the activation of the IR/IRS-1/PI3K axis. In this study, we aimed to identify components in the AKT signaling pathway in skeletal muscle that underlie the differential response to insulin between preterm and term pigs. Methods Cesarean-derived piglets delivered 11 d (preterm) or 2 d (term) before term were fitted with a jugular vein catheter for delivery of total parenteral nutrition. On day 3, all piglets were fasted for 4 h and then assigned randomly to fast one additional h or to receive an elemental meal by oral gavage. Macronutrient content of the elemental meal mimicked sow milk composition at day 3 of lactation. Piglets were euthanized for tissue collection in the fasted state or 60 min after feeding. The longissimus dorsi muscle was collected and subjected to Western blot and immunoprecipitation assays for analyzing upstream regulators of AKT activity. Results Phosphorylation of PDK1 and mTORC2 was lower in preterm than term pigs (P < 0.05). The abundance of phosphatase PHLPP, but not PTEN, was significant higher in preterm than term pigs (P < 0.05). Preterm pigs had lower PP2A activation (P < 0.05), but its activation was not affected by feeding, unlike term pigs where feeding inhibited PP2A activation (P < 0.05). The abundance of Ubl4A, required for insulin-induced translocation of AKT to the plasma membrane, was reduced by prematurity (P < 0.05). While AKT1 abundance was higher in preterm than term pigs (P < 0.05), the abundances of both AKT2 and AKT3 were lower in preterm than term pigs (P < 0.05). Conclusions Our results demonstrate that prematurity reduces the abundance and/or activation of positive regulators of AKT such as Ubl4A, PDK1, and mTORC2. Conversely, prematurity increased the activation of AKT inhibitors such as PHLPP and PP2A. Our findings potentially pave the way for a better understanding of the mechanisms that underlie postnatal growth faltering in premature infants. Funding Sources NIH and USDA.