Pancreatic islet of Langerhans' cytoarchitecture and ultrastructure in normal glucose tolerance and in type 2 diabetes mellitus.

While a number of structural and cellular abnormalities occur in the islet of Langerhans in diabetes, and in particular in type 2 diabetes, the focus has been mostly on the insulin producing ß-cells and only more recently on glucagon producing α- and δ-cells. There is ample evidence that in type 2 diabetes mellitus (T2DM), in addition to a progressive decline in ß-cell function and associated insulin resistance in a number of insulin-sensitive tissues, alterations in glucagon secretion are also present and may play an important role in the pathogenesis of hyperglycemia both in the fasting and in the postprandial state. Recently, a number of studies have showed that there are also functional and structural alterations in glucagon-producing α-cells and somatostatin-producing δ-cells. Thus, it is becoming increasingly clear that multiple cellular alterations of multiple cell types occur, which adds even more complexity to our understanding of the pathophysiology of this common and severe disease. We believe that persistent efforts to increase the understanding of the pathophysiology of hormone secretion in the islets of Langerhans will also improve our capability to better prevent and treat diabetes mellitus.

Intranuclear rodlets in human pancreatic islet cells.

OBJECTIVES: Intranuclear rodlets (INRs) are rod-shaped intranuclear inclusions that we have described in neurons of the human brain. We recently identified these structures in pancreatic islet cells. The objectives of this study are to describe the light microscopic features and cellular pattern of distribution of INRs in human pancreatic islet cells. METHODS: Double immunofluorescence staining was performed on 5 human pancreatic tissue samples for the detection of class III beta tubulin (C3T) to detect INRs and for promyelocytic leukemia (PML) protein to examine the relationship between PML and INRs. RESULTS: Intranuclear rodlets were detected in 22.99% of pancreatic B cells compared with only 3.11%, 1.80%, and 1.60% of A, D, and PP cells, respectively. Twenty-four percent of C3T-immunoreactive INRs showed partial or complete immunoreactivity for PML. Promyelocytic leukemia staining within the nuclei of B cells was confined to INRs and was not present in the typical PML bodies present in other cell types. Spatially, PML and C3T staining of islet cell INRs appeared to be mutually exclusive within individual INRs. CONCLUSIONS: Intranuclear rodlets are present within the nuclei of pancreatic islet cells, where they reside predominantly but not exclusively in B cells. Immunoreactivity of B-cell INRs for PML suggests that the functional significance of INRs may be related to that of PML and/or PML bodies. Conversely, the exclusive localization of PML staining to INRs in B cells indicates that PML's function in B cells is selectively associated with INRs. The mutually exclusive pattern of PML and C3T staining suggests dynamic interactions between these 2 proteins in B-cell INRs. In light of evidence for the involvement of INRs and of PML bodies in disease, it will be of interest to investigate these structures in animal models of diabetes and in human diabetes.