The accretion of skeletal muscle mass is a dominant component of neonatal growth. The long-term objective of this research is to define the mechanisms by which nutrients and hormones regulate the high rate of skeletal muscle protein deposition in neonates, with the goal of identifying new strategies to optimize the nutritional management of low birth weight infants. Our previous work showed that the high rate of muscle protein synthesis in the neonate is due largely to an enhanced activation of mRNA translation after a meal. This heightened response is mediated by amino acids and insulin and is due to enhanced activation of nutrient and insulin signaling pathways and translation initiation factors. Orogastric feeding, using either continuous or intermittent bolus delivery, is a common clinical practice for low birth weight infants with impaired sucking, swallowing, or breathing. There is controversy as to which nutritional support mechanism is optimal. There is strong evidence that intermittent bolus feeding promotes greater weight gain and small intestinal growth than continuous feeding, but whether this is true for skeletal muscle growth is unknown. Preliminary studies suggest that the modest increase in amino acid and insulin levels during continuous feeding, compared to intermittent bolus feeding, may not be sufficient to maximally stimulate muscle protein synthesis due to inadequate activation of translation initiation. This proposal tests the overall hypothesis that intermittent bolus feeding promotes greater rates of skeletal muscle protein synthesis and accretion than continuous feeding and that this response is mediated by amino acids and insulin and their activation of amino acid and insulin signaling components and regulators of translation. The following aims are proposed to address this hypothesis.
In Aim 1, the impact of intermittent bolus vs. continuous feeding on rates of muscle protein synthesis and activation of intracellular regulatory proteins will be determined using in vivo kinetic measurements of muscle protein synthesis and determination of indices of nutrient and insulin signaling, translation initiation and elongation, and ribosomal protein translation in skeletal muscle of neonatal pigs.
In Aim 2, the role of amino acids and insulin in mediating the response of muscle protein synthesis to intermittent bolus and continuous feeding will be assessed using pancreatic-substrate clamps and measurements of protein synthesis and activation of nutrient and insulin signaling proteins and regulators of translation.
In Aim 3, the long-term effects of intermittent bolus vs. continuous feeding on muscle growth in neonatal pigs will be determined and the regulatory mechanisms identified. This research will contribute fundamental new knowledge about the mechanism by which different types of nutritional support influence neonatal growth. The proposed studies are unique in that they bring basic research on the molecular mechanisms by which nutrients and hormones regulate protein synthesis closer to the translational level of improving the bedside nutritional support of low birth weight infants.
Tube feeding, either as a continuous drip or intermittent bolus delivery, is a common clinical practice for low birth weight infants, but the consequence of these different feeding modalities for muscle growth is unknown. We propose to test the hypothesis that intermittent bolus feeding promotes greater rates of synthesis of skeletal muscle proteins than continuous feeding, and that this response is mediated by insulin and amino acids through their activation of intracellular signaling components that regulate protein synthesis. The work will contribute fundamental new knowledge about the mechanism by which different types of nutritional support influence neonatal growth and in so doing brings basic research closer to the translational level of improving the bedside nutritional management of low birth weight infants.
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