Progenitor and bihormonal cells in neuroinsular complexes of the developing human pancreas

BACKGROUND: The development of effective treatments for diabetes mellitus directly depends on a comprehensive understanding of the mechanisms underlying endocrine cell differentiation and pancreatic islet morphogenesis. Experimental studies have demonstrated that the nervous system plays an important role in regulating these processes. In the developing human pancreas, neural structures closely interact with hormone-containing cells, forming neuroinsular complexes, as well as with epithelial cells, suggesting a potential involvement of the nervous system in pancreatic islet development. To support this hypothesis, data on interactions between neural structures and cells exhibiting a progenitor immunophenotype are essential; however, such data are currently lacking in the scientific sources. AIM: To investigate the distribution of cells expressing the transcription factor PDX1 and bihormonal cells within neuroinsular complexes during human pancreatic development. METHODS: The study was performed on autopsy specimens of the pancreas obtained from 15 human fetuses (gestational age of 9–25 weeks). Multiple immunofluorescence staining and confocal microscopy were used. To assess the cellular composition of neuroinsular complexes, various combinations of antibodies were applied: against endocrine cell hormones (insulin, glucagon, somatostatin), against the transcription factor PDX1 (pancreatic and duodenal homeobox 1), and against the neural marker neuron-specific β3-tubulin. RESULTS: Triple immunofluorescence staining with antibodies against insulin, PDX1, and β3-tubulin revealed cells with a progenitor immunophenotype characteristic of ductal epithelial cells within neuroinsular complexes: insulin−/PDX1+/β3-tubulin− and insulin−/PDX1+/β3-tubulin+ cells. Starting from the 9th week of gestation, such cells were detected in isolated ganglia, and from the 14th week onward, in ganglia integrated with pancreatic islets within neuroinsular complexes. In specimens stained with insulin/glucagon/β3-tubulin and insulin/somatostatin/β3-tubulin antibody combinations, bihormonal insulin+/glucagon+ and insulin+/somatostatin+ cells were identified within neuroinsular complexes. CONCLUSION: The present study demonstrates spatial integration of neural structures with cells exhibiting a progenitor immunophenotype and with bihormonal cells in the developing human pancreas. These bihormonal cells are regarded by most authors as endocrine cells at a stage of differentiation and maturation. Such integration may be necessary for the regulation of β-cell mass and maturation, as well as for modulation of pancreatic islet morphogenesis, as previously shown in experimental studies in animal models and cell cultures.