Date of Award

January 2014

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Karl L. Insogna

Subject Area(s)

Medicine, Endocrinology

Abstract

IMPACT OF GAIN-OF-FUNCTION MUTATIONS IN THE LOW DENSITY LIPOPROTEIN RECEPTOR RELATED PROTEIN 5 (LRP5) ON GLUCOSE AND LIPID HOMEOSTASIS. Dinah Foer, Meiling Zhu, Christine Simpson, Grace Lee, Rebecca Sullivan, and Karl L. Insogna. Section of Endocrinology, Department of Internal Medicine, Yale University, School of Medicine, New Haven, CT.

Investigations in animal models suggest a physiologic link between LRP5 and glucose and lipid homeostasis. However, the data in human studies is far from consensus. While LRP5 has been shown to be critical to Wnt signaling, the molecular mechanism for the effect on metabolism is unknown. We hypothesize that a high bone mass (HBM) mutation in LRP5 will lead to improved glucose and lipid homeostasis. We aim to measure the impact of these mutated receptors on human glucose and lipid metabolism and to investigate the pathway(s) by which Wnt may affect glucose metabolism in vitro. Eleven subjects with HBM-causing LRP5 mutations were matched by gender, age, and body mass index (BMI) to 22 unrelated control subjects. Hemoglobin A1c (HbA1c), estimated average glucose (eAG), HOMA-B, HOMA-IR, and lipid panel were analyzed. An oral glucose tolerance test and 1HMRS study of liver and skeletal muscle were performed on a subset of affected patients. Primary hepatocytes and HepG2 cells were treated in vitro with Wnt3a, and PEPCK-C mRNA expression was measured by QPCR. INS-1 cells and human pancreatic islet beta-cells were assayed for glucose-stimulated insulin secretion using an ELISA technique. Statistical differences were analyzed using the unpaired Student t-test and one-way ANOVA. There were no statistically significant differences between affected and control populations for HbA1c, eAG, insulin, HOMA-B and HOMA-IR. Differences in total cholesterol, triglycerides, and HDL, were not significant. However, LDL levels were significantly lower in affected subjects (p=0.04). Wnt did not effect PEPCK-C expression. Wnt did not significantly effect glucose-stimulated insulin secretion in INS-1 cells and human islets. In summary, this is the first investigation on the metabolic consequences of LRP5 mutations in human kindreds with HBM-causing mutations. Our data does not support the hypothesis that LRP5 improves glucose metabolism in these individuals. The data does suggest that there may be a specific, beneficial effect of LRP5 on LDL cholesterol, however additional studies need to be done to confirm the effect and elucidate the mechanism.

Comments

This is an Open Access Thesis.

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