Elena Quaglio

Molecular Distinction between Pathogenic and Infectious Properties of the Prion Protein

ABSTRACT Tg(PG14) mice express a prion protein (PrP) with a nine-octapeptide insertion associated with a human familial prion disease. These animals spontaneously develop a fatal neurodegenerative disorder characterized by ataxia, neuronal apoptosis, and accumulation in the brain of an aggregated and weakly protease-resistant form of mutant PrP (designated PG14spon). Brain homogenates from Tg(PG14) mice fail to transmit disease after intracerebral inoculation into recipient mice, indicating that PG14spon, although pathogenic, is distinct from PrPSc, the infectious form of PrP. In contrast, inoculation of Tg(PG14) mice with exogenous prions of the RML strain induces accumulation of PG14RML, a PrPSc form of the mutant protein that is infectious and highly protease resistant. Like PrPSc, both PG14spon and PG14RML display conformationally masked epitopes in the central and octapeptide repeat regions. However, these two forms differ profoundly in their oligomeric states, with PG14RML aggregates being much larger and more resistant to dissociation. Our analysis provides new molecular insight into an emerging puzzle in prion biology, the discrepancy between the infectious and neurotoxic properties of PrP.

The neurotoxicity of prion protein (PrP) peptide 106-126 is independent of the expression level of PrP and is not mediated by abnormal PrP species

A synthetic peptide homologous to region 106-126 of the prion protein (PrP) is toxic to cells expressing PrP, but not to PrP knockout neurons, arguing for a specific role of PrP in mediating the peptides activity. Whether this is related to a gain of toxicity or a loss of function of PrP is not clear. We explored the possibility that PrP106-126 triggered formation of PrP(Sc) or other neurotoxic PrP species. We found that PrP106-126 did not induce detergent-insoluble and protease-resistant PrP, nor did it alter its membrane topology or cellular distribution. We also found that neurons expressing endogenous or higher level of either wild-type PrP or a nine-octapeptide insertional mutant were equally susceptible to PrP106-126, and that sub-physiological PrP expression was sufficient to restore vulnerability to the peptide. These results indicate that PrP106-126 interferes with a PrP function that requires only low protein levels, and is not impaired by a pathogenic insertion in the octapeptide region.

Preventive study in subjects at risk of fatal familial insomnia: Innovative approach to rare diseases.

Abstract The text describes a preventive clinical trial with drug treatment in a very rare neurodegenerative disease (Fatal familial Insomnia, FFI) designed with the help of individuals at genetic risk of developing the disease, asymptomatic carriers, who have agreed to be exposed over a 10-year period to doxycycline, an antibiotic with anti-prion activity. At least 10 carriers of the FFI mutation over 42 y old will be treated with doxycycline (100 mg/die) and the incidence of the disease will be compared to that of an historical dataset. For ethical reasons a randomized, double-blind, placebo-controlled trial was not feasible, however the study design and the statistical analysis ensure the scientific value of the results. This approach might represent an important breakthrough in terms of potential therapy and knowledge of rare diseases that could give some hopes to these neglected patients.

Role of Plasminogen in Propagation of Scrapie

ABSTRACT To investigate whether plasminogen may feature in scrapie infection, we inoculated plasminogen-deficient (Plg−/−), heterozygous plasminogen-deficient (Plg+/−), and wild-type (Plg+/+) mice by the intracerebral or intraperitoneal (i.p.) route with the RML scrapie strain and monitored the onset of neurological signs of disease, survival time, brain, and accumulation of scrapie disease-associated forms of the prion protein (PrPSc). Only after i.p. inoculation, a slight, although significant, difference in survival (P < 0.05) between Plg−/− and Plg+/+ mice was observed. Neuropathological examination and Western blot analysis were carried out when the first signs of disease appeared in Plg+/+ animals (175 days after i.p. inoculation) and when mice reached the terminal stage of illness. At the onset of symptoms, PrPSc accumulation was higher in the brain and spleen of Plg+/+ and Plg+/− mice than in those of Plg−/− mice, and these differences were paralleled by differences in the severity of spongiform changes and astrogliosis in the cerebral cortex and subcortical gray structures. Immunohistochemical analysis of the spleens before inoculation did not show any impairment of the immune system affecting follicular dendritic or lymphoid cells in Plg−/− mice. Once the disease progressed and mice began to die of infection, differences were no longer apparent in either brains or spleens. In conclusion, our data indicate that plasminogen has no major effect on the survival of scrapie agent-infected mice.

A murine model of a familial prion disease

We have produced a mouse model of a familial prion disorder by introduction of a transgene that encodes the moPrP homolog of a nine-octapeptide insertional mutant associated with an inherited form of CJD in humans. These mice develop progressive neurologic symptoms, display neuropathologic changes, and accumulate a form of mutant PrP in their brains and peripheral tissues that displays some of the biochemical properties of PrPSc. These mice have been extremely valuable for analyzing the cellular and biochemical mechanisms involved in inherited prion disorders and correlating the appearance of the PrPSc-like form with clinical and neuropathologic findings. Because the mutant protein in the mice is highly neurotoxic but appears to lack infectivity, further analysis of its properties promises to shed new light on the molecular distinction between pathogenic and infectious forms of PrP.

A transgenic model of a familial prion disease

We have generated lines of transgenic mice that express a mutant prion protein containing 14 octapeptide repeats whose human homologue is associated with an inherited prion dementia. These mice develop an ataxic illness that begins at 65 days of age when the transgene array is homozygous, and results in death by 115-138 days. Starting from birth, mutant PrP is converted into a protease-resistant and detergent-insoluble form that resembles PrP(Sc), and this form accumulates dramatically in many brain regions throughout the lifetime of the mice. As PrP accumulates, there is massive apoptosis of cerebellar granule cells, as well as astrocytosis and deposition of PrP in a punctate pattern. These results establish a new transgenic animal model of an inherited human prion disease, and provide important insights into the molecular pathogenesis of these disorders.