Extensive elimination of acinar cells during normal postnatal pancreas growth

Summary: While programmed cell death plays important roles during morphogenetic stages of development, post-differentiation organ growth is considered an efficient process whereby cell proliferation increases cell number. Here we demonstrate that early postnatal growth of the pancreas unexpectedly involves massive acinar cell elimination. Measurements of cell proliferation and death in the human pancreas in comparison to the actual increase in cell number predict daily elimination of 0.7% of cells, offsetting 88% of cell formation over the first year of life. Using mouse models, we show that death is associated with mitosis, through a failure of dividing cells to generate two viable daughters. In p53-deficient mice, acinar cell death and proliferation are reduced, while organ size is normal, suggesting that p53-dependent developmental apoptosis triggers compensatory proliferation. We propose that excess cell turnover during growth of the pancreas, and presumably other organs, facilitates robustness to perturbations and supports maintenance of tissue architecture

DNA methylation-based assessment of cell composition in human pancreas and islets

Assessment of pancreas cell type composition is crucial to the understanding of the genesis of diabetes. Current approaches use immunodetection of protein markers, for example insulin as a marker of beta-cells. A major limitation of these methods is that protein content varies in physiological and pathological conditions, complicating the extrapolation to actual cell number. Here we demonstrate the use of cell type-specific DNA methylation markers for determining the fraction of specific cell types in human islet and pancreas specimens. We identified genomic loci that are uniquely demethylated in specific pancreatic cell types and applied targeted PCR to assess the methylation status of these loci in tissue samples, enabling inference of cell type composition. In islet preparations, normalization of insulin secretion to beta-cell DNA revealed similar beta-cell function in pre-T1D, T1D and T2D , which was significantly lower than in non-diabetic donors. In histological pancreas specimens from recent-onset T1D this assay showed beta-cell fraction within the normal range, suggesting a significant contribution of beta-cell dysfunction. In T2D pancreata we observed increased alpha-cell fraction and normal beta-cell fraction. Methylation-based analysis provides an accurate molecular alternative to immune detection of cell types in the human pancreas, with utility in the interpretation of insulin secretion assays and the assessment of pancreas cell composition in health and disease.</p