- Assistant Professor of Pediatrics at University of Pennsylvania School of Medicine (1996 – 2005)
- Hallam Hurt Professor in Neonatology at University of Pennsylvania School of Medicine (2014– present)
- Associate Professor of Pediatrics at University of Pennsylvania School of Medicine (2005 – 2012)
- Professor of Pediatrics at University of Pennsylvania School of Medicine (2012 – 2014)
- Associate Professor of Obstetrics and Gynecology at University of Pennsylvania School of Medicine (2008 – 2011)
Developmental Origins of Adult Disease, epigenetics, ß-cell function and development
The principal goal of our research program is to elucidate the underlying molecular mechanisms that link fetal growth retardation to the later development of obesity and type 2 diabetes in adulthood. We currently have 3 major projects and several smaller projects. The first project focuses on the relationship between oxidative stress and ß-cell dysfunction and insulin resistance. We have developed a model of fetal growth retardation in the rodent (mice and rats) which leads to the later development of diabetes and obesity in adult animals. We have established that fetal growth retardation induces progressive mitochondrial dysfunction, oxidative stress, mtDNA mutations, and electron transport defects. These defects cause abnormal ß-cell function and development, and hepatic and muscle insulin resistance. Oxidative stress decreases transcription of key genes related to ß-cell development, induces modifications of proteins of the Krebs cycle in the liver, and muscle. Pdx-1 is a critical transcription factor that regulates ß-cell function and development. Transcription of this gene is permanently down-regulated in ß-cells of IUGR rats leading to a gradual reduction in ß-cell function and ß-cell replication. We have determined that oxidative stress induced by uteroplacental insufficiency in IUGR fetal pancreas induces aberrant methylation and chromatin remodeling at the Pdx-1 promoter, which in turn induces transcription silencing. The focus of the second project is to determine whether the effects of an aberrant intrauterine milieu can be reversed after birth, we have designed a number of therapeutic modalities including diet modifications and antioxidant treatment. In collaboration with Dr. Doris Stoffers, we have successfully prevented the development of diabetes in IUGR rats with several of these treatments. Administration of a pancreatic ß-cell trophic factor, Exendin-4, during the neonatal period dramatically prevents the development of diabetes in our model. Neonatal Exendin-4 treatment prevents the progressive reduction in ß-cell mass that is observed in IUGR rats over time. Expression of Pdx-1 is restored to normal levels, and islet ß-cell proliferation rates are normalized by the neonatal Exendin-4 treatment. Of major clinical significance is our finding that Exendin-4 treatment in the newborn period prevents the onset of obesity in IUGR rats. This surprising finding has stimulated a new direction for this project and we are currently determining the mechanisms by which Exendin-4 treatment reverses epigenetic modifications such as DNA methylation and histone modifications of key genes related to ß-cell development. The third project is focused on the effects of obesity during pregnancy and the long-term outcome in the offspring. The specific aims of this project are to determine the window of susceptibility of the developing organism to the effects of obesity during gestation, determining whether regulation of the adipogenic pathway is altered in offspring, and defining the molecular mechanisms responsible for enhanced adipogenesis observed in offspring of obese mothers.
1. Cell culture and animal models to study fetal programming (the effect of an abnormal in-utero environment- IUGR, obesity, diabetes-upon fetal growth and development and the later development of obesity and diabetes).
2. Epigenetic regulation of gene expression (DNA methylation and histone acetylation and methylation) using bisulfite sequencing and ChIP assays
3. Measures of Mitochondrial function-oxidative phosphorylation and electron transport chain activity.
- M.D., University of Arizona (1983)
- B. S., University of Arizona, Tucson (with Distinction and Honors) (1978)
- Stoffers DA, Desai BM, DeLeon DD, Simmons RA. Neonatal exendin-4 prevents the development of diabetes in the intrauterine growth retarded rat. Diabetes. Vol 52(3) . 2003 Mar:734-740.
- Selak MA, Storey BT, Peterside IE, Simmons RA. Impaired oxidative phosphorylation in skeletal muscle of intrauterine growth-retarded rats. Am J Physiol Endocrinol Metab. Vol 285(1) . 2003 Jul:E130-E137.
- Chennathukuzhi V, Stein JM, Abel T, Donlon S, Yang S, Miller JP, Allman DM, Simmons RA, Hecht NB. Mice deficient for testis-brain RNA-binding protein exhibit a coordinate loss of TRAX, reduced fertility, altered gene expression in the brain, and behavioral changes. Mol Cell Biol. Vol 23(18) . 2003 Sep:6419-6434.
- Peterside IE, Selak MA, Simmons RA. Impaired oxidative phosphorylation in hepatic mitochondria in growth-retarded rats. Am J Physiol. Vol 285(6) . 2003 Dec:E1258-1264.
- Pallotto EK, Macones GA, Simmons R. Small for gestational age infants at risk for prolonged hypoglycemia. Epidemiology. 2003.
- Pallotto EK, Woelnerhanssen B, Macones G, Simmons RA. Hypoglycemia in small for gestational age infants: How extensive is the problem and what are the risks?. Pediatr Res. Vol 53. 2003:499A.
- Simmons RA, Selak MA. Intrauterine growth retardation increases oxidative stress and induces mitochondrial DNA deletions in rat ß-cells. Pediatr Res. Vol 53. 2003:804A.
- Vuguin P, Raab B, Xiaohui-Ma, Liu B, Barzilai N, Stoffers DA, Simmons RA. Exendin-4 decreases body weight and improves insulin action in intrauterine growth retarded rats.. Pediatr Res. Vol 53. 2003:877A.
- Simmons RA, Crutchlow M, Desai BM, Stoffers DA. Reduced islet vascularity in intrauterine growth retarded rats. Endocrinology. 2003:PI-295.
- Simmons, RA. Cell glucose transport handling during fetal and neonatal development. Fetal and Neonatal Physiol. W.B. Saunders, Philadelphia; 2003.