Doppel-induced cerebellar degeneration in transgenic mice.

Doppel (Dpl) is a paralog of the mammalian prion protein (PrP); it is abundant in testes but expressed at low levels in the adult central nervous system. In two Prnp-deficient (Prnp(0/0)) mouse lines (Ngsk and Rcm0), Dpl overexpression correlated with ataxia and death of cerebellar neurons. To determine whether Dpl overexpression, rather than the dysregulation of genes neighboring the Prn gene complex, was responsible for the ataxic syndrome, we placed the mouse Dpl coding sequence under the control of the Prnp promoter and produced transgenic (Tg) mice on the Prnp(0/0)-ZrchI background (hereafter referred to as ZrchI). ZrchI mice exhibit neither Dpl overexpression nor cerebellar degeneration. In contrast, Tg(Dpl)ZrchI mice showed cerebellar granule and Purkinje cell loss; the age of onset of ataxia was inversely proportional to the levels of Dpl protein. Crosses of Tg mice overexpressing wild-type PrP with two lines of Tg(Dpl)ZrchI mice resulted in a phenotypic rescue of the ataxic syndrome, while Dpl overexpression was unchanged. Restoration of PrP expression also rendered the Tg(Dpl) mice susceptible to prion infection, with incubation times indistinguishable from non-Tg controls. Whereas the rescue of Dpl-induced neurotoxicity by coexpression of PrP argues for an interaction between the PrP and Dpl proteins in vivo, the unaltered incubation times in Tg mice overexpressing Dpl in the central nervous system suggest that Dpl is unlikely to be involved in prion formation.

A protease-resistant 61-residue prion peptide causes neurodegeneration in transgenic mice.

An abridged prion protein (PrP) molecule of 106 amino acids, designated PrP106, is capable of forming infectious miniprions in transgenic mice (S. Supattapone, P. Bosque, T. Muramoto, H. Wille, C. Aagaard, D. Peretz, H.-O. B. Nguyen, C. Heinrich, M. Torchia, J. Safar, F. E. Cohen, S. J. DeArmond, S. B. Prusiner, and M. Scott, Cell 96:869-878, 1999). We removed additional sequences from PrP106 and identified a 61-residue peptide, designated PrP61, that spontaneously adopted a protease-resistant conformation in neuroblastoma cells. Synthetic PrP61 bearing a carboxy-terminal lipid moiety polymerized into protease-resistant, beta-sheet-enriched amyloid fibrils at a physiological salt concentration. Transgenic mice expressing low levels of PrP61 died spontaneously with ataxia. Neuropathological examination revealed accumulation of protease-resistant PrP61 within neuronal dendrites and cell bodies, apparently causing apoptosis. PrP61 may be a useful model for deciphering the mechanism by which PrP molecules acquire protease resistance and become neurotoxic.

Selective neuronal vulnerability during experimental scrapie infection: insights from an ultrastructural investigation.

The goal was to test whether all neurons are equally susceptible to degeneration in response to PrP(Sc) scrapie infection. We tested this by immunogold GABA labeling. Our ultrastructural results indicates that GABAergic neurons are less vulnerable than other neuronal populations. This conclusion is supported by our findings: (1) reversal of the normal ratio of non-GABAergic to GABAergic neurons in the terminal stages, which implies that non-GABAergic neurons degenerated earlier, and (2) that the degeneration of GABAergic neurons occurs late in the disease after reactive astrogliosis, a response to nerve cell death.

Modification of tritiated gamma-amino-n-butyric acid transport in rabies virus-infected primary cortical cultures.

The role of brain neurotransmitter transport processes in rabies virus infection of neurons was examined. The uptake and release of gamma-amino-n-butyric acid (GABA) in rabies virus-infected embryonic rat cortical neurons was assayed using tritiated ligands. A 45% reduction of [3H]GABA uptake was observed 3 days post-infection, when a maximum level of infectious particle release occurs. At this time, kinetic analysis revealed significant changes in Vmax, whereas no changes were found in Km values in comparison with the control values. K+ and veratridine-induced [3H]GABA release was increased in infected cultures (98% and 35%, respectively) as compared with control values. The results obtained from rabies virus-infected cultures provide some preliminary evidence of the involvement of GABA in the pathogenesis of rabies.

Alteration of potassium-evoked 5-HT release from virus-infected rat cortical synaptosomes.

Potassium-evoked 3H-serotonin (5-HT) release from rat cerebrocortical synaptosomes was performed after peripheral inoculation with fixed rabies virus CVS (challenge virus strain). At the onset of clinical symptoms, the rats were sacrificed, synaptosomes were prepared from dissected cortices and assayed for K+ evoked 5-HT release. The results show a decrease in evoked 5-HT release from virus-infected synaptosomes. Alterations in serotoninergic transmission in rabies virus infected brain cortex indicate a possible involvement in the triggering of pathogenetic mechanisms relating to the clinicopathological manifestations of the viral disease.