Sean W Limesand

Sean W Limesand

Professor, Animal and Comparative Biomedical Sciences
Professor, Physiological Sciences - GIDP
Director, Agriculture Research Complex
Professor, Obstetrics and Gynecology
Chair, Institutional Animal Care-USE Committee
Professor, BIO5 Institute
Department Affiliations
(520) 626-8903

Work Summary

Our current research program use an integrative approach at the whole animal, isolated organ, cellular and molecular levels to investigate developmental adaptations in pancreatic β-cells and insulin sensitivity that result from early life risk factors, such as intrauterine growth restriction, and increase risk of glucose intolerance and Diabetes in later life.

Research Interest

Sean W. Limesand, PhD, is an Associate Professor in the School of Animal and Comparative Biomedical Sciences at the University of Arizona in the College of Agriculture and Life Sciences. He is also a member of the UA’s BIO5 Institute and Department of Obstetrics and Gynecology. Dr. Limesand is nationally and internationally recognized for his work studying fetal endocrinology and metabolism in pregnancy and in pregnancies compromised by pathology such as intrauterine growth restriction and diabetes. His research is focused on defining developmental consequences resulting from a compromised intrauterine environment. Specifically, he is focused on fetal adaptations in insulin secretion and action that when altered in utero create lifelong metabolic complications. Dr. Limesand has lead the charge on prenatal origins of –cell dysfunction as the Principal Investigator for a number of federal and foundation grant awards and published more than 40 peer-reviewed articles on topics related to this research. Keywords: Diabetes, Pregnancy, Perinatal Biology


Cole, L., Anderson, M., Antin, P. B., & Limesand, S. W. (2009). One process for pancreatic beta-cell coalescence into islets involves an epithelial-mesenchymal transition. The Journal of endocrinology, 203(1), 19-31.
BIO5 Collaborators
Parker B Antin, Sean W Limesand

Islet replacement is a promising therapy for treating diabetes mellitus, but the supply of donor tissue for transplantation is limited. To overcome this limitation, endocrine tissue can be expanded, but this requires an understanding of normal developmental processes that regulate islet formation. In this study, we compare pancreas development in sheep and human, and provide evidence that an epithelial-mesenchymal transition (EMT) is involved in beta-cell differentiation and islet formation. Transcription factors know to regulate pancreas formation, pancreatic duodenal homeobox factor 1, neurogenin 3, NKX2-2, and NKX6-1, which were expressed in the appropriate spatial and temporal pattern to coordinate pancreatic bud outgrowth and direct endocrine cell specification in sheep. Immunofluorescence staining of the developing pancreas was used to co-localize insulin and epithelial proteins (cytokeratin, E-cadherin, and beta-catenin) or insulin and a mesenchymal protein (vimentin). In sheep, individual beta-cells become insulin-positive in the progenitor epithelium, then lose epithelial characteristics, and migrate out of the epithelial layer to form islets. As beta-cells exit the epithelial progenitor cell layer, they acquire mesenchymal characteristics, shown by their acquisition of vimentin. In situ hybridization expression analysis of the SNAIL family members of transcriptional repressors (SNAIL1, -2, and -3; listed as SNAI1, -2, -3 in the HUGO Database) showed that each of the SNAIL genes was expressed in the ductal epithelium during development, and SNAIL-1 and -2 were co-expressed with insulin. Our findings provide strong evidence that the movement of beta-cells from the pancreatic ductal epithelium involves an EMT.

Rozance, P. J., Limesand, S. W., & Hay Jr., W. W. (2006). Decreased nutrient-stimulated insulin secretion in chronically hypoglycemic late-gestation fetal sheep is due to an intrinsic islet defect. American Journal of Physiology - Endocrinology and Metabolism, 291(2), E404-E411.

PMID: 16569758;Abstract:

We measured in vivo and in vitro nutrient-stimulated insulin secretion in late gestation fetal sheep to determine whether an intrinsic islet defect is responsible for decreased glucose-stimulated insulin secretion (GSIS) in response to chronic hypoglycemia. Control fetuses responded to both leucine and lysine infusions with increased arterial plasma insulin concentrations (average increase: 0.13 ± 0.05 ng/ml leucine; 0.99 ± 0.26 ng/ml lysine). In vivo lysine-stimulated insulin secretion was decreased by chronic (0.37 ± 0.18 ng/ml) and acute (0.27 ± 0.19 ng/ml) hypoglycemia. Leucine did not stimulate insulin secretion following acute hypoglycemia but was preserved with chronic hypoglycemia (0.12 ± 0.09 ng/ml). Isolated pancreatic islets from chronically hypoglycemic fetuses had normal insulin and DNA content but decreased fractional insulin release when stimulated with glucose, leucine, arginine, or lysine. Isolated islets from control fetuses responded to all nutrients. Therefore, chronic late gestation hypoglycemia causes defective in vitro nutrient-regulated insulin secretion that is at least partly responsible for diminished in vivo GSIS. Chronic hypoglycemia is a feature of human intrauterine growth restriction (IUGR) and might lead to an islet defect that is responsible for the decreased insulin secretion patterns seen in human IUGR fetuses and low-birth-weight human infants. Copyright © 2006 the American Physiological Society.

Rozance, P. J., Anderson, M., Martinez, M., Fahy, A., Macko, A. R., Kailey, J., Seedorf, G. J., Abman, S. H., Hay, W. W., & Limesand, S. W. (2015). Placental insufficiency decreases pancreatic vascularity and disrupts hepatocyte growth factor signaling in the pancreatic islet endothelial cell in fetal sheep. Diabetes, 64(2), 555-64.

Hepatocyte growth factor (HGF) and vascular endothelial growth factor A (VEGFA) are paracrine hormones that mediate communication between pancreatic islet endothelial cells (ECs) and β-cells. Our objective was to determine the impact of intrauterine growth restriction (IUGR) on pancreatic vascularity and paracrine signaling between the EC and β-cell. Vessel density was less in IUGR pancreata than in controls. HGF concentrations were also lower in islet EC-conditioned media (ECCM) from IUGR, and islets incubated with control islet ECCM responded by increasing insulin content, which was absent with IUGR ECCM. The effect of ECCM on islet insulin content was blocked with an inhibitory anti-HGF antibody. The HGF receptor was not different between control and IUGR islets, but VEGFA was lower and the high-affinity VEGF receptor was higher in IUGR islets and ECs, respectively. These findings show that paracrine actions from ECs increase islet insulin content, and in IUGR ECs, secretion of HGF was diminished. Given the potential feed-forward regulation of β-cell VEGFA and islet EC HGF, these two growth factors are highly integrated in normal pancreatic islet development, and this regulation is decreased in IUGR fetuses, resulting in lower pancreatic islet insulin concentrations and insulin secretion.

Brown, L. D., Green, A. S., Limesand, S. W., & Rozance, P. J. (2011). Maternal amino acid supplementation for intrauterine growth restriction. Frontiers in Bioscience - Scholar, 3 S(2), 428-444.

PMID: 21196387;PMCID: PMC3181118;Abstract:

Maternal dietary protein supplementation to improve fetal growth has been considered as an option to prevent or treat intrauterine growth restriction. However, in contrast to balanced dietary supplementation, adverse perinatal outcomes in pregnant women who received high amounts of dietary protein supplementation have been observed. The responsible mechanisms for these adverse outcomes are unknown. This review will discuss relevant human and animal data to provide the background necessary for the development of explanatory hypotheses and ultimately for the development therapeutic interventions during pregnancy to improve fetal growth. Relevant aspects of fetal amino acid metabolism during normal pregnancy and those pregnancies affected by IUGR will be discussed. In addition, data from animal experiments which have attempted to determine mechanisms to explain the adverse responses identified in the human trials will be presented. Finally, we will suggest new avenues for investigation into how amino acid supplementation might be used safely to treat and/or prevent IUGR.

Green, A. S., Macko, A. R., Rozance, P. J., Yates, D. T., Chen, X., Hay Jr., W. W., & Limesand, S. W. (2011). Characterization of glucose-insulin responsiveness and impact of fetal number and sex difference on insulin response in the sheep fetus. American Journal of Physiology - Endocrinology and Metabolism, 300(5), E817-E823.

PMID: 21343544;PMCID: PMC3093975;Abstract:

GSIS is often measured in the sheep fetus by a square-wave hyperglycemic clamp, but maximal β-cell responsiveness and effects of fetal number and sex difference have not been fully evaluated. We determined the dose-response curve for GSIS in fetal sheep (0.9 of gestation) by increasing plasma glucose from euglycemia in a stepwise fashion. The glucose- insulin response was best fit by curvilinear third-order polynomial equations for singletons (y = 0.018x3 - 0.26x2 + 1.2x - 0.64) and twins (y = -0.012x3 + 0.043x2 + 0.40x - 0.16). In singles, maximal insulin secretion was achieved at 3.4 ± 0.2 mmol/l glucose but began to plateau after 2.4 ± 0.2 mmol/l glucose (90% of maximum), whereas the maximum for twins was reached at 4.8 ± 0.4 mmol/l glucose. In twin (n = 18) and singleton (n = 49) fetuses, GSIS was determined with a square-wave hyperglycemic clamp >2.4 mmol/l glucose. Twins had a lower basal glucose concentration, and plasma insulin concentrations were 59 (P 0.01) and 43% (P 0.05) lower in twins than singletons during the euglycemic and hyperglycemic periods, respectively. The basal glucose/insulin ratio was approximately doubled in twins vs. singles (P 0.001), indicating greater insulin sensitivity. In a separate cohort of fetuses, twins (n = 8) had lower body weight (P 0.05) and β-cell mass (P 0.01) than singleton fetuses (n = 7) as a result of smaller pancreata (P 0.01) and a positive correlation (P 0.05) between insulin immunopositive area and fetal weight (P 0.05). No effects of sex difference on GSIS or β-cell mass were observed. These findings indicate that insulin secretion is less responsive to physiological glucose concentrations in twins, due in part to less β-cell mass. © 2011 the American Physiological Society.