Molecular characterisation of the placental-pancreatic islet axis

Thesis

During pregnancy adaptive changes support foetal growth and prepare the mother for childbirth. This includes the pancreatic islets, in which insulin secretion from β cells doubles by the third trimester. When these adaptations fail, gestational diabetes mellitus can occur, negatively impacting outcomes. These islet adaptations are closely linked to placental growth, with insulin secretion increasing as the placenta develops and returning to normal post-delivery. In mouse models, placental signals, such as hormones and extracellular vesicles (EVs), enhance islet function and β-cell mass. However, it remains unclear if these mechanisms apply to humans. This thesis investigates islet changes during human pregnancy ex vivo, using rare pancreatic tissue from pregnant women, and explores the role of placental small EVs (psEVs) in β-cell biology using a human-based model system. In the first part of the study, human islets were isolated using laser capture microdissection and analysed via liquid chromatography-mass spectrometry (LC-MS/MS), generating the largest dataset of proteins from islets isolated from pregnant women to date with over 7,000 proteins detected. Comparative analysis between pregnant and non-pregnant samples identified differences in only four proteins. Immunohistochemistry, coupled with unbiased computational analysis, revealed that whole islet, α-, and β-cell areas increased during pregnancy due to an increase in cell number, similar to findings in mice. However, unlike in mice, serotonin 2B receptor was absent in human β cells, and prolactin receptor expression remained unchanged. A notable increase in glucagon-like peptide-1 (GLP-1) within α cells was observed, which may enhance β-cell function through paracrine signalling. In the second part of the study, psEVs were isolated from human placentae and their effects tested in vitro on a human β-cell line, EndoC-βH3. psEVs increased β-cell insulin gene expression and insulin content but did not enhance glucose-stimulated insulin secretion. Proteomic analysis via LC-MS/MS identified an increase in Annexin A1 (ANXA1) in psEV-treated Endoc-βH3 cells, suggesting a potential mechanistic role in psEV-mediated effects. In conclusion, islet adaptations in human pregnancy differ to those in mice and psEVs increase insulin content potentially through ANXA1.

Authors: Seedat, F

• DOI: 10.5287/ora-bdbxdngrx
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: extracellular vesicles; pancreatic islet cells; alpha cell; liquid chromatography mass spectrometry; gestational diabetes mellitus; beta cell; laser capture microdissection
• Subjects: Pancreatic alpha cells; Pancreatic beta cells; Extracellular vesicles; Molecular biology; Islands of Langerhans; Pregnancy; Gestational diabetes mellitus