ORIGINAL: Chromogranin A is a global marker of endocrine cells. Most endocrine cells in the pancreas, in addition to Chromogranin A, also express other hormones, Insulin and Glucagon being most frequent, with Pancreatic Polypeptide, Somatostatin and Ghrelin in smaller numbers of endocrine cells. We have found that in adult human pancreas a small number of pancreatic endocrine cells (<1% of the total number) express Chromogranin A but not any of the other known pancreatic hormones; we have termed these cells Chromogranin Positive Hormone Negative [CPHN] cells.
We found that there is a very high percentage of CPHN cells in sections from human fetus and newborn pancreas, which suggests that these cells are a precursor of mature endocrine cells. We also found that the percentage of CPHN cells is higher in pancreas from both type 1 and type 2 diabetic subjects, suggesting that this may be an attempt at restoring the beta cells lost as a consequence of disease.
Our initial observations are that these cells occur mostly in small clusters of 1-3 cells rather than in established islets, suggesting that these cells may be newly formed endocrine cells. The source of these CPHN cells is of great interest, as they could potentially occur de novo (neogenesis), by transformation of existing cells (transdifferentiation) such as from cells in the ducts or exocrine pancreas, or by replication of existing endocrine cells.
Our goal is to characterize these cells by looking at the frequency of replication and apoptosis , and the transcription factors Nkx6.1 and Nkx2.2, in the CPHN cell population. Our findings will have significance with regard to the regenerative capacity of human endocrine cells in human pancreas.
ADDENDUM: Both type 1 and type 2 diabetes result from loss of functional beta-cell mass. Functional defects in evolving T1D and T2D are marked by the uncoupling of ambient glucose and insulin secretion, reminiscent of functionally immature beta cells in early pancreatic development. To develop successful beta-cell replacement for reversal of beta-cell dysfunction in diabetes, it is therefore critical to understand mechanisms that regulate beta cell maturity. Beta cells are formed during embryonic life, but acquire function only after birth, in a process called beta cell maturation. We have identified Neuropeptide Y (NPY) as a marker of functionally immature, neonatal beta cells. NPY is known to inhibit insulin secretion, and we show its co-localization to the insulin secretory granules in neonatal human beta cells. Our preliminary data show that NPY is down-regulated in adult beta cells, and re-expressed in beta cell in mouse models of type 2 diabetes. Thus, we propose to examine NPY in human beta cell maturation and diabetes pathogenesis.