Growth potential of scrapie mouse brain in vitro

Cell culture models to unravel prion protein function and aberrancies in prion diseases

From an early stage of prion research, tissue cultures that could support and propagate the scrapie agent were sought after. The earliest attempts were explants from brains of infected mice, and their growth and morphological characteristics were compared with those from uninfected mice. Using the explant technique, several investigators reported increased cell growth in cultures established from scrapie-sick brain compared with cultures from normal mice. These are odd findings in the light of the massive neuronal cell death known to occur in scrapie-infected brains; however, the cell types responsible for the increased cell growth in the scrapie-explants most probably were not neuronal. The first successful cell culture established in this way, in which the scrapie agent was serially and continuously passaged beyond the initial explant, was in the scrapie mouse brain culture, which is still used today. This chapter describes the generation and use of chronically prion-infected cell lines as cell culture models of prion diseases. These cell lines have been crucial for the current understanding of the cell biology of both the normal (PrP(C)) and the pathogenic isoform (PrP(Sc)) of the prion protein. They also have been useful in the development of antiprion drugs, prospectively used for therapy of prion diseases, and they offer an alternative approach for transmission/infectivity assays normally performed by mouse bioassay. Cell culture models also have been used to study prion-induced cytopathological changes, which could explain the typical spongiform neurodegeneration in prion diseases.

Establishment of cell lines from bovine brain

As shown by immunocytochemistry, 16 cell lines of neuronal, oligodendroglial or neuronoglial origin have been established from bovine fetal brain by immortalization with SV40 virus and cloning in soft agar. The cell lines were characterized according to their cell surface markers using mono- and polyclonal antibodies.

Growth factor production by Creutzfeldt-Jakob disease cell lines

Creutzfeldt-Jakob disease (CJD), a progressive dementia of humans, is caused by an infectious agent that is closely related to the scrapie agent of sheep. Although the molecular nature of these "unconventional" agents is still a matter of speculation and controversy, even less is known concerning the mechanism(s) of their effects on the central nervous system. To gain insight into the cellular effects of these agents, we have examined a series of cell lines derived directly from CJD-infected hamster brain or produced from nontransformed rodent lines by exposure to CJD infectious fractions in vitro. These cell lines appear transformed by a variety of criteria and secrete growth factors into the culture medium. All CJD lines produce a factor that is like alpha-transforming growth factor (alpha-TGF). Conditioned medium from these CJD lines also stimulates the synthesis of glial fibrillary acidic protein in normal astrocytic cells in vitro. This effect is mimicked by purified alpha-TGF and platelet-derived growth factors. Further study of CJD-induced growth factor production may elucidate fundamental properties of these unconventional agents.

Immortality of cell cultures derived from brains of mice and hamsters infected with Creutzfeldt-Jakob disease agent

Isolates from six patients with Creutzfeldt-Jakob disease (CJD) were injected into various strains of hamsters and mice, and the infective agent was propagated. Serially passaged cultures were established from these CJD agent-infected brains and from uninfected control brains. All healthy cultures (21 out of 21) from CJD agent-infected brains became immortal and/or transformed. In contrast only 3 out of 13 normal brain cultures became immortal, and the rest died out with serial propagation in vitro. The fact that permanent cell lines were readily derived from multiple rodent strains and all CJD isolates tested suggests that a transforming capability is an intrinsic property of CJD agents. This conclusion is supported by demonstrations of in vitro cell transformation by CJD infectious brain fractions. Although the molecular mechanism of transformation events associated with the CJD agent is not presently known, a provocative possibility is that the CJD agent has a direct effect on the host genome by mechanisms analogous to those known for slowly oncogenic retroviruses.

Isolation from mouse spleen of cell populations with high specific infectivity for scrapie virus

Spleen cells from mice infected with scrapie virus were separated into subpopulations on the basis of buoyant density in discontinuous gradients of isotonic albumin or differential adherence of cells to plastic. At three different intervals after infection, a population of "less dense" cells was found in albumin gradients that had 40-to 60-fold higher specific infectivity (cells per median lethal dose) than the total cell suspension before gradient sedimentation. The class of cells associated with high relative specific infectivity has a density characteristic of lymphoblasts, myeloblasts, and macrophages. Separation of "macrophage rich" cells on the basis of adherence to plastic did not result in significant enrichment of scrapie virus-infected cells.