Endocrine Abstracts

JOINT1881

Introduction: Pregnancy requires pancreatic islet adaptations to maintain glucose homeostasis. Human studies show that β-cell mass increases in pregnancy, murine studies suggest that prolactin receptor (PRLR) and serotonin 2B (5-HT2B) receptor signalling are key to these adaptations. However, little is known about the islet proteome and α cells in human pregnancy. This study investigates pregnancy-associated islet changes using rare human pancreatic tissues from pregnant women, focusing on proteomic alterations, whole islet, α- and β-cell metrics, and the expression of the PRLR, 5-HT2B receptor, and glucagon-like peptide-1 (GLP-1).

Methods: Formalin-fixed paraffin-embedded pancreatic tissue from pregnant human donors (n=7, third trimester) and non-pregnant controls (n=7) best-matched by age, race, and BMI were obtained from the Network for Pancreatic Organ Donors with Diabetes. Islets were isolated using laser-capture microdissection, and proteomic profiling performed using liquid chromatography-mass spectrometry (LC-MS/MS). Islets were labelled by immunofluorescence, and images acquired using spinning disc confocal microscopy. Unbiased, automated computational image analysis of whole pancreatic tissue sections was used to quantify whole islet, α- and β-cell areas, and the abundance of PRLR, 5-HT2B receptor, and GLP-1. For each metric, values were normalised to total tissue area prior to comparisons to account for the size differences between tissue sections.

Results: LC-MS/MS identified 7,546 proteins in human islets, generating the largest dataset of islet proteins from pregnant women to date. Four proteins—cathepsin Z, β1,4-galactosyltransferase 4, cyclin-dependent kinase 5, and laminin subunit alpha 4—were significantly more abundant in third-trimester islets. In pregnancy, whole islet area increased 1.9-fold (3.0% vs. 1.6%, P=0.0145), α-cell area 4.3-fold (0.44% vs. 0.1%, P=0.0206), and β-cell area 1.9-fold (1.26% vs. 0.65%, P=0.0241), driven by increased cell numbers. In pregnant islets, PRLR expression was upregulated in α cells (302.3 vs. 267.7 AU/mm², P=0.0398) but not β cells (P=0.0610). The 5-HT2B receptor was absent in β cells, confirmed by colocalisation analysis and positive ductal staining as an internal control for antibody functionality. Additionally, GLP-1 abundance in α cells increased 2.9-fold (0.69% vs. 0.24%, P=0.0184).

Conclusion: Human islet adaptations in pregnancy differ from those in mice. While α- and β-cell areas expand, the absence of β-cell 5-HT2B receptor expression and minimal proteomic changes suggest alternative regulatory mechanisms. The increased α-cell area and GLP-1 expression highlight the potential role of α-cell-derived paracrine signals in supporting β-cell function. These findings underscore the need for human-based studies to further elucidate mechanisms driving islet plasticity in pregnancy and their relevance to gestational diabetes.