Retinoic acid increases the length and volume density of ducts in the rat embryonic pancreas

Abstract

In this study, the role of all-trans retinoic acid (RA) on the proliferation of rat embryonic pancreas ducts and on the proportion of insulin cells was investigated. All-trans RA (10-6 m) was added to Ham's F12.ITS serum-free medium in which 12.5 day rat dorsal pancreatic buds were cultured on Matrigel. Control explants were cultured on Matrigel in Ham's F12.ITS alone or in Ham's F12.ITS containing ethanol (the diluent for RA). After a 7 day culture period, explants were incubated with bromodeoxyuridine (BrdU) for assessment of cell proliferation. Explants were processed for both morphometry and immunocytochemistry. The length density and volume density of the pancreatic ducts were assessed using an image analysis system. Cells positive for insulin, BrdU and glucagon were localized on adjacent serial sections. RA treatment caused a statistically significant increase in the volume density (P < 0.007) and length density (P < 0.008) of the ducts, as well as a 1.2-fold increase (P < 0.0001) in the proportion of insulin to glucagon cells, compared to both control groups. Few insulin cells were BrdU positive, indicating that cells had a low proliferation rate. The increased proportion of insulin cells may relate to the increased volume density and length density of the ducts in RA-treated explants. It is suggested that RA stimulated the production of additional progenitor cells and not proliferation of existing insulin cells.

Effect of All‐Trans Retinoic Acid on the Pancreas of Streptozotocin‐Induced Diabetic Rat

“…The ductal epithelial cells regress into a least differentiated state and acquire characteristics of progenitor cells, since external signals were able to direct their differentiation to an endocrine, acinar or mature duct phenotype (Bounwens and De Blay, , Kritzik et al, , Song et al, ). RA has been reported to enhance proliferation and survival of cells (Erasmus et al, , Lin and Wu, , Noy, ). In line with our findings, Erasmus et al () reported that atRA increased the branching of ductal cells during which some cells broke away from the duct epithelium and lost their attachment to the basement membrane to form islets.…”

“…RA has been reported to enhance proliferation and survival of cells (Erasmus et al, , Lin and Wu, , Noy, ). In line with our findings, Erasmus et al () reported that atRA increased the branching of ductal cells during which some cells broke away from the duct epithelium and lost their attachment to the basement membrane to form islets. Also, Penny and Kramer () found that atRA in vitro caused a significant increase in the proportion of insulin‐secreting cells in the pancreas of the chick accompanied with an increase in duct profiles.…”

“…RA induces cultured embryonic mouse pancreas to form clusters of endocrine cells resembling mature islets (Tulachan et al, ). RA significantly increased the proportion of insulin secreting cells in both chick and rat embryonic dorsal pancreatic buds in vitro (Penny and Kramer, ; Erasmus et al, ). It was documented that ductal pancreatic adenocarcinoma cells were transdifferentiated into functional insulin‐secreting cells after treatment with atRA in vitro (El‐Metwally et al, ).…”

Cellular pathways to β‐cell replacement

“…Pancreatic ductal cells isolated from pre‐diabetic non‐obese diabetic (NOD) mice can be induced to form functional islets, which are able to reverse diabetes when transplanted into the diabetic counterparts of these donor mice 44, 45. Furthermore, more recent in vitro work performed on ductal cells from the rat suggests that clusterin may induce the differentiation of β‐cells 46, and another study has suggested that all‐trans retinoic acid can act to induce the differentiation of β‐cells from rat ductal cells 47.…”

Effects of high dose retinoic acid on TGF-β2 expression during pancreatic organogenesis

“…However, administration after neurulation did not affect development of Langerhans islets. Retinoic acid increased insulin secreting cells by stimulating production of extra progenitor cells (Erasmus et al 2003). Exogenous retinoic acid can increase insulin secretion both the fetal and adult islets.…”