Intracisternal A-particles in genetically diabetic mice: Identification in pancreas and induction in cultured beta cells

Abstract

Sucrose density gradient analysis of purified pancreatic homogenates from glycaemic C57BL/Ks diabetes (db/db) mice and their normoglycaemic controls have revealed the presence in the diabetics of increased Mg++-dependent RNA-directed DNA polymerase activity sedimenting with a density of approximately 1.21 g/cm3. Electron microscopy revealed that this fraction contained typical intracisternal A-particles. Purified cultures of pancreatic islet cells 4--7 day old postnatal "misty diabetic" mice and normal siblings were established and then maintained in Eagle's minimal essential medium without serum. Under these conditions, the presence of intracisternal A-particles in beta cells of both mutant and control genotypes was very rare. No change in numbers of intracisternal A-particles was seen after 2--4 days of incubation in Dulbecco's-modified minimal essential medium containing 5.5 mmol/l glucose. However, when the glucose concentration of Dulbecco's medium was elevated to 16.5 mmol/l, ultrastructural changes specific to the beta cell population occurred that were reminiscent of those alterations observed in situ. Intracisternal A-particles were commonly seen in cultured beta cells showing hypersecretion-stress morphology. Since equal numbers of intracisternal A-particles were present in cultured beta cells from normal and mutant mice, it was concluded that the db gene itself was not required for intracisternal A-particle expression. The cell culture results suggest that elevated intracisternal A-particle activity observed in vivo may be produced directly or indirectly by the ambient high blood glucose levels characteristic of this mutant.

Glucose induces intracisternal type A retroviral gene transcription and translation in pancreatic beta cells.

“…4). Again, this observation is consistent with our previous work showing increased numbers of IAP at the ultrastructural level in glucose-stressed BKs beta cells in culture (2). It is relevant to note here that p73 and the p 114-120 proteins may differ markedly in turnover rate in the cultured beta cells.…”

“…4). This biochemical demonstration that glucose-stressed B6 beta cells are induced poorly or not at all for the IAP structural protein corroborates our previous report of the absence of morphologically identifiable IAP in B6 beta cells at the ultrastructural level (2). In contrast, BKs islets synthesized p117 and p78 (a variant form of the main structural protein), and incorporation into both of these components was stimulated at elevated glucose concentrations (Fig.…”

“…The beta cell was the only islet endocrine cell type observed to express IAP; cell necrosis was limited to this cell type as well. In chronically hyperglycemic db/db mice, prenecrotic beta cells showed increased numbers of morphologically identifiable IAP, as well as increased immunoreactivity against a rabbit antiserum detecting both a 73 kD IAP group-specific internal structural protein (p73) and highermolecular mass proteins containing p73 determinants (1)(2)(3). The glucose-dependent nature of this induction was demonstrated in vitro using cultures of normal beta cells from diabetes-susceptible inbred strains, such as C57BL/KsJ (BKs) or CBA/LtJ.…”

Biphasic Development of the Postnatal Mouse Pancreas

“…One current approach of these studies is work with isolated islets of Langcrhans and their cultured cells [4], However, this work has not developed rapidly, since isolation of intact islets or their component cells from 'normal' adult mice is more difficult than islet isola tion from rats or hamsters. We have ob served that young postnatal mice provide the best source for intact islets as have others [5;Leiter,Yoon,Crowell,personal commun. ].…”

No effect of superoxide dismutase on spontaneous development of diabetes in db/db mice

“…Collections of chronic inflammatory cells, capillary endothelial cells, and presumptive fibroblasts have been noted around islets involved in the inflammatory pro¬ cess (Like & Chick 1970a). Furthermore, within B-cells from these mice, virus-like bodies have been shown (Like & Chick 1970b;Leiter & Bedigan 1979;Leiter & Kuff 1984). The observed decrease in number of B-cells and the inability of B-cell proliferation (Like & Chick 1970a) are lethal for this mouse, but how the damage to the B-cells is mediated is still unclear.…”