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Research Project: Pediatric Clinical Nutrition

Location: Children's Nutrition Research Center

Title: Preovulatory exposure to a protein-restricted diet disrupts amino acid kinetics and alters mitochondrial structure and function in the rat oocyte and is partially rescued by folic acid

Author
item SCHUTT, AMY - Baylor College Of Medicine
item BLESSON, CHELLAKKAN - Baylor College Of Medicine
item HSU, JEAN - Children'S Nutrition Research Center (CNRC)
item VALDES, CECILIA - Baylor College Of Medicine
item GIBBONS, WILLIAM - Baylor College Of Medicine
item JAHOOR, FAROOK - Children'S Nutrition Research Center (CNRC)
item YALLAMPALLI, CHANDRA - Baylor College Of Medicine

Submitted to: Reproductive Biology and Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2019
Publication Date: 1/17/2019
Citation: Schutt, A.K., Blesson, C.S., Hsu, J.W., Valdes, C.T., Gibbons, W.E., Jahoor, F., Yallampalli, C. 2019. Preovulatory exposure to a protein-restricted diet disrupts amino acid kinetics and alters mitochondrial structure and function in the rat oocyte and is partially rescued by folic acid. Reproductive Biology and Endocrinology. 17(1):12. https://doi.org/10.1186/s12958-019-0458-y.
DOI: https://doi.org/10.1186/s12958-019-0458-y

Interpretive Summary: There is evidence that if a woman (or female animal) does not get enough nutrition and is malnourished during pregnancy that the growing baby in her womb develops permanent changes in how its body works and these changes increase the risk for developing diseases such as high blood pressure, heart disease, and diabetes. It is believed that these permanent changes take place in the womb because the growing baby has to adapt to the decreased amount of nutrition that it is receiving from the mother. There is also evidence from studies in female rats and mice that malnutrition, especially if the animal is not getting enough protein in her diet, can cause bad alterations to the quality of the egg produced by her ovary even before she becomes pregnant. In this case it is very likely that the alterations in the quality of the egg produced by the ovary of the animal that is not getting enough protein in the diet can cause its offspring to develop abnormalities when it is growing in the womb. It has been shown in rats and mice that these undesirable changes caused by insufficient protein in the mother's diet can be prevented if a type of B vitamin called folate is added to her protein deficient diet. Because folate is needed for the body to produce a very important compound called "one-carbon" that is necessary for new tissues and organs to grow, it is believed that insufficient protein has a negative effect on the mother's ovary and egg and the growth of her baby in the womb because she is not producing enough one-carbon. This makes sense because in order to make one-carbon in her body the mother needs three compounds called amino acids, named methionine, serine and glycine, and she gets these compounds from the protein in her diet. Methionine is also important because it makes another compound called cysteine which protects the cell against poisonous compounds called oxidants. Therefore, a diet low in protein will not supply enough methionine, serine and glycine for the mother to make adequate amounts of one-carbon. In this study in female rats we investigated the effects of a low protein diet on the availability of methionine, serine and glycine for the production of one-carbon compound in the egg, liver, and whole body of the female rat. We also examined the ovary and egg to look at how the structure and function of a component of the egg called the mitochondrion is affected. Mitochondria are important because they produce energy for the egg to grow in the ovary. Finally, we looked at whether adding folate to the low protein diet will prevent any negative effects on the egg and its mitochondria. We found that a diet low in protein decreased the supply of some but not all of the amino acids and one-carbon production was not decreased in the whole body. In the egg both serine and cysteine were decreased. However, the addition of folate prevented these changes. The structure of the mitochondria in the egg were abnormal and they were not able to increase in number and size in a normal rate. Because mitochondria supply energy to the egg, this means that the egg was not getting sufficient energy to develop in a normal way. The lower cysteine also means that the ovary and egg was not being adequately protected from poisonous compounds.

Technical Abstract: Detrimental exposures during pregnancy have been implicated in programming offspring to develop permanent changes in physiology and metabolism, increasing the risk for developing diseases in adulthood such as hypertension, diabetes, heart disease and obesity. This study investigated the effects of protein restriction on the metabolism of amino acids within the oocyte, liver, and whole organism in a rat model as well as effects on mitochondrial ultrastructure and function in the cumulus oocyte complex. Wistar outbred female rats 8-11 weeks of age (n=24) were assigned to three isocaloric dietary groups, including control (C), low protein (LP) and low protein supplemented with folate (LPF). Animals were superovulated and 48h later underwent central catheterization. Isotopic tracers of 1-13C-5C2H3-methionine, 2H2-cysteine, U-13C3-cysteine and U-13C3-serine were administered by a 4h prime-constant rate infusion. After sacrifice, oocytes were denuded of cumulus cells and liver specimens were obtained. Oocytes demonstrated reduced serine flux in LP vs. LPF (p<0.05), reduced cysteine flux in LP and LPF vs. C (p<0.05), and a trend toward reduced transsulfuration in LP vs. C and LPF. Folic acid supplementation reversed observed effects on serine flux and transsulfuration. Preovulatory protein restriction increased whole-body methionine transmethylation, methionine transsulfuration and the flux of serine in LP and LPF vs. C (p=0.003, p=0.002, p=0.005). The concentration of glutathione was increased in erythrocytes and liver in LP and LPF vs. C (p=0.003 and p=0.0003). Oocyte mitochondrial ultrastructure in LP and LPF had increased proportions of abnormal mitochondria vs. C (p<0.01 and p<0.05). Cumulus cell mitochondrial ultrastructure in LP and LPF groups had increased proportions of abnormal mitochondria vs. C (p<0.001 and p<0.05). Preovulatory protein restriction altered oocyte expression of Drp1, Opa-1, Mfn1/2, Parl and Ndufb6 (p<0.05) and Hk2 (p<0.01), which are genes involved in mitochondrial fission (division) and fusion, mitochondrial apoptotic mechanisms, respiratory electron transport and glucose metabolism. Preovulatory protein restriction resulted in altered amino acid metabolism, abnormal cumulus oocyte complex mitochondrial ultrastructure and differential oocyte expression of genes related to mitochondrial biogenesis.