Project Number: 6250-51000-054-10
Project Type: Specific Cooperative Agreement

Start Date: Apr 01, 2009
End Date: Mar 31, 2014

Objective:
Objective 1: Differentiate the effects of fetal versus postnatal maternal dietary protein restriction on satellite cell accretion and skeletal muscle mass. Sub-objective 1.A. Determine in vivo the number of skeletal muscle satellite cells undergoing division, apoptosis, and differentiation in term fetuses of mouse dams that are fed a protein-restricted (PR) or a control (C) diet ad libitum during gestation. Sub-objective 1.B. Determine in vivo the number of skeletal muscle satellite cells undergoing division, differentiation, and apoptosis in 21-d-old mouse pups that are suckled by dams fed either a PR or a C diet ad libitum from birth. Sub-objective 1.C. Determine satellite cell and myonuclear numbers, myofiber cross-sectional area, and muscle mass in the 15-wk-old and 18-mo-old offspring of dams fed a PR diet either during gestation or during the suckling period, and then refed from birth (suckled on C dams) or after weaning (C diet, ad libitum), respectively. Objective 2: Determine if impaired catch-up growth upon nutritional rehabilitation is due to aberrant epigenetic mechanisms intrinsic to the satellite cell and/or an absence of the extracellular cues necessary to sufficiently accelerate satellite cell division. Sub-objective 2.A.1. Quantify and compare the in vitro replicative, differentiation, and fusion capacities of satellite cells isolated from muscles of 21-d-old offspring that were suckled on C or PR dams when they are cultured in vitro under identical conditions. Sub-objective 2.A.2. Quantify and compare the in vitro replicative, differentiation, and fusion capacities of satellite cells isolated from muscles of 21-d-old offspring of dams fed the PR or C diet during pregnancy and then suckled on C dams when they are cultured in vitro under identical conditions. Sub-objective 2.B. Determine the regenerative capacity of whole skeletal muscles transplanted from 21-d-old PR and C pups into 10-d-old C pups. Objective 3: Develop novel techniques to study amino acid metabolism in conscious mouse models, with special emphasis on hepatic and enteral metabolism. Sub-Objective 3.A. Determine the effect of a loss of small intestinal function on arginine availability. Sub-Objective 3.B. Verify the function of arginase II in first pass metabolism of arginine by the small intestine. Objective 4: Determine the role of urea cycle intermediates in maintaining nitric oxide and ureagenesis during different physiological and pathophysiological conditions. Sub-objective 4A: Determine the role of arginine availability in sustaining nitric oxide production during conditions of increased arginine demand. Sub-objective 4B: Determine the liver requirements of urea cycle intermediates for ureagenesis in urea cycle transgenic mice.

Approach:
Children's Nutrition Research Center researchers will study the offspring of mouse dams that have been protein malnourished during pregnancy and/or lactation, and then nutritionally rehabilitated by suckling on well-nourished dams or by feeding on a control diet after weaning. In vivo satellite cell responses and skeletal muscle growth will be assessed primarily by immunohistofluorescence imaging with morphometry to assess cell division, apoptosis, differentiation, and muscle mass. To assess the role of epigenetic mechanisms intrinsic to the satellite cell, cells will be harvested from mice with different nutritional histories and their activity studied in vitro. Additionally, we will use different transgenic mouse models, including conditional knockout models, and stable isotope tracer infusions to explore various pathways. Mice will also have surgical implantation of intravenous or intragastric catheters for the delivery of nutrients and tracers. These infusions will be performed to further explore the transorgan metabolism of arginine and related molecules.