Altered insulin receptor processing and function in scrapie-infected neuroblastoma cell lines

Prion protein modulates glucose homeostasis by altering intracellular iron

The prion protein (PrP^C), a mainly neuronal protein, is known to modulate glucose homeostasis in mouse models. We explored the underlying mechanism in mouse models and the human pancreatic β-cell line 1.1B4. We report expression of PrP^C on mouse pancreatic β-cells, where it promoted uptake of iron through divalent-metal-transporters. Accordingly, pancreatic iron stores in PrP knockout mice (PrP^-/-) were significantly lower than wild type (PrP^+/+) controls. Silencing of PrP^C in 1.1B4 cells resulted in significant depletion of intracellular (IC) iron, and remarkably, upregulation of glucose transporter GLUT2 and insulin. Iron overloading, on the other hand, resulted in downregulation of GLUT2 and insulin in a PrP^C-dependent manner. Similar observations were noted in the brain, liver, and neuroretina of iron overloaded PrP^+/+ but not PrP^-/- mice, indicating PrP^C-mediated modulation of insulin and glucose homeostasis through iron. Peripheral challenge with glucose and insulin revealed blunting of the response in iron-overloaded PrP^+/+ relative to PrP^-/- mice, suggesting that PrP^C-mediated modulation of IC iron influences both secretion and sensitivity of peripheral organs to insulin. These observations have implications for Alzheimer's disease and diabetic retinopathy, known complications of type-2-diabetes associated with brain and ocular iron-dyshomeostasis.

Loss of prion protein is associated with the development of insulin resistance and obesity

Prion protein (PrP^C) was initially described due to its involvement in transmissible spongiform encephalopathies. It was subsequently demonstrated to be a cell surface molecule involved in many physiological processes, such as vesicle trafficking. Here, we investigated the roles of PrP^C in the response to insulin and obesity development. Two independent PrP^C knockout (KO) and one PrP^C overexpressing (TG20) mouse models were fed high-fat diets, and the development of insulin resistance and obesity was monitored. PrP^C KO mice fed high-fat diets presented all of the symptoms associated with the development of insulin resistance: hyperglycemia, hyperinsulinemia, and obesity. Conversely, TG20 animals fed high-fat diets showed reduced weight and insulin resistance. Accordingly, the expression of peroxisome proliferator-activated receptor gamma (PPARγ) was reduced in PrP^C KO mice and increased in TG20 animals. PrP^C KO cells also presented reduced glucose uptake upon insulin stimulation, due to reduced translocation of the glucose transporter Glut4. Thus, our results suggest that PrP^C reflects susceptibility to the development of insulin resistance and metabolic syndrome.

Unaltered Prion Pathogenesis in a Mouse Model of High-Fat Diet-Induced Insulin Resistance

Epidemiological, clinical, and experimental animal studies suggest a strong correlation between insulin resistance and Alzheimer’s disease. In fact, type-2 diabetes is considered an important risk factor of developing Alzheimer’s disease. In addition, impaired insulin signaling in the Alzheimer’s disease brain may promote Aβ production, impair Aβ clearance and induce tau hyperphosphorylation, thereby leading to deterioration of the disease. The pathological prion protein, PrP^Sc, deposits in the form of extracellular aggregates and leads to dementia, raising the question as to whether prion pathogenesis may also be affected by insulin resistance. We therefore established high-fat diet-induced insulin resistance in tga20 mice, which overexpress the prion protein. We then inoculated the insulin-resistant mice with prions. We found that insulin resistance in tga20 mice did not affect prion disease progression, PrP^Sc deposition, astrogliosis or microglial activation, and had no effect on survival. Our study demonstrates that in a mouse model, insulin resistance does not significantly contribute to prion pathogenesis.

Induction of ligand-specific PrP (C) signaling in human neuronal cells

Cellular prion protein (PrP (C) ) has attracted considerable attention for its role in transmissible spongiform encephalopathies (TSEs). In spite of being a point of intense research effort critical questions still remain regarding the physiological function of PrP (C) and how these functions may change with the conversion of the protein into the infectious and pathological conformation (PrP (Sc) ). While emerging evidence suggests PrP (C/Sc) are involved in signal transduction there is little consensus on the signaling pathways associated with the normal and diseased states. The purported involvement of PrP (C) in signal transduction, and the association of TSEs with neural pathology, makes kinome analysis of human neurons an interesting and appropriate model to characterize patterns of signal transduction following activation of PrP (C) by two commonly employed experimental ligands; antibody-induced dimerization by 6H4 and the amino acids 106-126 PrP peptide fragment (PrP 106-126). Analysis of the induced kinome responses reveals distinct patterns of signaling activity following each treatment. Specifically, stimulation of human neurons with the 6H4 antibody results in alterations in mitogen activated protein kinase (MAPK) signaling pathways while the 106-126 peptide activates growth factor related signaling pathways including vascular endothelial growth factor (VEGF) signaling and the phosphoinositide-3 kinase (PI3K) pathway. These pathways were validated through independent functional assays. Collectively these results indicate that stimulation of PrP (C) with distinct ligands, even within the same cell type, results in unique patterns of signaling. While this investigation highlights the apparent functional versatility of PrP (C) as a signaling molecule and may offer insight into cellular mechanisms of TSE pathology it also emphasizes the potential dangers associated with attributing activation of specific intracellular events to particular receptors through artificial models of receptor activation.

Prion protein expression and functional importance in skeletal muscle

Skeletal muscle expresses prion protein (PrP) that buffers oxidant activity in neurons.

AIMS

We hypothesize that PrP deficiency would increase oxidant activity in skeletal muscle and alter redox-sensitive functions, including contraction and glucose uptake. We used real-time polymerase chain reaction and Western blot analysis to measure PrP mRNA and protein in human diaphragm, five murine muscles, and muscle-derived C2C12 cells. Effects of PrP deficiency were tested by comparing PrP-deficient mice versus wild-type mice and morpholino-knockdown versus vehicle-treated myotubes. Oxidant activity (dichlorofluorescin oxidation) and specific force were measured in murine diaphragm fiber bundles.

RESULTS

PrP content differs among mouse muscles (gastrocnemius>extensor digitorum longus, EDL>tibialis anterior, TA; soleus>diaphragm) as does glycosylation (di-, mono-, nonglycosylated; gastrocnemius, EDL, TA=60%, 30%, 10%; soleus, 30%, 40%, 30%; diaphragm, 30%, 30%, 40%). PrP is predominantly di-glycosylated in human diaphragm. PrP deficiency decreases body weight (15%) and EDL mass (9%); increases cytosolic oxidant activity (fiber bundles, 36%; C2C12 myotubes, 7%); and depresses specific force (12%) in adult (8-12 mos) but not adolescent (2 mos) mice.

INNOVATION

This study is the first to directly assess a role of prion protein in skeletal muscle function.

CONCLUSIONS

PrP content varies among murine skeletal muscles and is essential for maintaining normal redox homeostasis, muscle size, and contractile function in adult animals.

Growth hormone production and action in N1E-115 neuroblastoma cells

Neuroblastoma cells are undifferentiated cells derived from the neural crest and are commonly used as models for studying neural function. Mouse N1E-115 neuroblastoma cells are derived from cancerous tissue and provide a model for studying the oncogenesis of neural cells. As growth hormone (GH) has been implicated as an autocrine or paracrine involved in neural regulation and in the induction or progression of cancer, the possibility that N1E-115 cells are sites of GH production and GH action was assessed. Using RT-PCR, cultured N1E-115 cells were found to express the mouse GH and GH receptor (GHR) genes. Immunocytochemistry demonstrated that both of the translated proteins (GH and its receptor) were abundantly present in the cytoplasm of these cells and their co-localization was established by confocal cytochemistry. GH action in these cells was determined in cells cultured for 72 h in the presence or absence of 10(-6) M or 10(-9) M mouse GH, which induced neurite sprouting and increased axon growth. In summary, the expression of GH and its receptor in GH responsive tumor-derived N1E-115 neuroblastoma cells suggests they provide a useful experimental model to assess GH actions in neural function or neural oncogenesis.

Opposing effects of ERK and p38-JNK MAP kinase pathways on formation of prions in GT1-1 cells

Brain-derived neurotrophic factor, which activates the extracellular regulated kinase (ERK) pathway, increases formation of prions in scrapie-infected gonadotropin-releasing hormone (GT1-1) cells. This indicates that conversion of the cellular prion protein PrP(C) to its pathogenic isoform, PrP(Sc), can be regulated by physiological stimuli acting on specific signal transduction pathways. In the present study, we examined the involvement of different mitogen-activated protein (MAP) kinase cascades and the cAMP-PKA pathway in formation of proteinase K-resistant PrP(Sc) (rPrP(Sc)). Long-term depolarization of GT1-1 cells infected with the Rocky Mountain Laboratory strain of scrapie increased the formation of rPrP(Sc). This effect was associated to ERK activation and was blocked by the MAPK/ERK kinase (MEK) inhibitor U0126. Treatment with forskolin caused a similar increase in rPrP(Sc) formation that was prevented by the protein kinase A (PKA) inhibitor H89. Both depolarization and forskolin treatment were accompanied by increased phosphorylation of the S6 ribosomal protein, while phosphorylation of histone H3 occurred only after forskolin treatment. Inhibitors of p38- and c-Jun NH(2)-terminal kinase (JNK) promoted the formation of rPrP(Sc), in contrast to the clearance of rPrP(Sc) produced by inhibitors of the ERK pathway. Thus, the ERK and the p38-JNK MAP kinase pathways appear to exert opposing effects on rPrP(Sc) formation, suggesting that balances between these intracellular signaling cascades may regulate replication of prions.

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.

Prion infection of muscle cells in vitro

The prion agent has been detected in skeletal muscle of humans and animals with prion diseases. Here we report scrapie infection of murine C2C12 myoblasts and myotubes in vitro following coculture with a scrapie-infected murine neuroblastoma (N2A) cell line but not following incubation with a scrapie-infected nonneuronal cell line or a scrapie brain homogenate. Terminal differentiation of scrapie-infected C2C12 myoblasts into myotubes resulted in an increase in the expression of the disease-specific prion protein, PrP(Sc). The amount of scrapie infectivity or PrP(Sc) in C2C12 myotubes was comparable to the levels found in scrapie-infected N2A cells, indicating that a high level of infection was established in muscle cells. Subclones of scrapie-infected C2C12 cells produced high levels of PrP(Sc) in myotubes, and the C-terminal C2 polypeptide fragment of PrP(Sc) was found based on deglycosylation and PrP(Sc)-specific immunoprecipitation of cell lysates. This is the first report of a stable prion infection in muscle cells in vitro and of a long-term prion infection in a nondividing, differentiated peripheral cell type in culture. These in vitro studies also suggest that in vivo prion infection of skeletal muscle requires contact with prion-infected neurons or, possibly, nerve terminals.

Increased Src kinase level results in increased protein tyrosine phosphorylation in scrapie-infected neuronal cell lines

We have studied how prion infection may affect the Src kinase activity in three different neuronal cell lines, ScGT1 and ScN2a, where ScGT1 were generated in our laboratory. By immunoblotting, using clone 28 - a monoclonal antibody recognizing active Src, we have found a 32+/-6.3% and 75+/-7.7% elevation in Src activity in ScGT1 and ScN2a cells, respectively, compared to uninfected cells. Immunocomplex in vitro kinase assay confirmed the increased Src activity. The increased Src kinase activity in scrapie-infected cells was further shown to correlate to an increased level of Src protein. In addition, an important increase in the protein tyrosine phosphorylation signal was observed in ScGT1 and ScN2a cells, which was further shown to be Src-dependent, as treatment with PP2 - a Src family kinase specific inhibitor, reversed the protein tyrosine phosphorylation profile. Abnormal Src-kinase activation and subsequent protein tyrosine phosphorylation may be key elements in the neuropathology of the prion diseases.

Increased susceptibility to oxidative stress in scrapie-infected neuroblastoma cells is associated with intracellular iron status

The molecular mechanism of neurodegeneration in prion diseases remains largely uncertain, but one of the features of infected cells is higher sensitivity to induced oxidative stress. In this study, we have investigated the role of iron in hydrogen peroxide (H(2)O(2))-induced toxicity in scrapie-infected mouse neuroblastoma N2a (ScN 2 a) cells. ScN 2 a cells were significantly more susceptible to H(2)O(2) toxicity than N2a cells as revealed by cell viability (MTT) assay. After 2h exposure, significant decrease in cell viability in ScN 2 a cells was observed at low concentrations of extracellular H(2)O(2) (5-10 microM), whereas N2a cells were not affected. The increased H(2)O(2) toxicity in ScN 2 a cells may be related to intracellular iron status since ferrous iron (Fe(2+)) chelator 2,2'-bipyridyl (BIP) prevented H(2)O(2)-induced decrease in cell viability. Further, the level of calcein-sensitive labile iron pool (LIP) was significantly increased in ScN 2 a cells after H(2)O(2) treatment. Finally, the production of reactive oxygen species (ROS) was inhibited by 30% by iron chelators desferrioxamine (DFO) and BIP in ScN 2 a cells, whereas no significant effect of iron chelators on basal ROS production was observed in N2a cells. This study indicates that cellular resistance to oxidative stress in ScN 2 a cells is associated with intracellular status of reactive iron.

Activation of mitogen-activated protein kinases in hamster brains infected with 263K scrapie agent

We investigated the expression, activation and distribution of c-Jun N-terminal kinases (JNKs), p38 mitogen-activated protein kinases (p38 MAPKs) and extracellular signal-regulated kinases (ERKs), using western blotting and immunohistochemistry, in the brains of hamsters infected with 263K scrapie agent, to clarify the role of these kinases in the pathogenesis of prion disease. The immunoblot analysis demonstrated that activation of JNK, p38 MAPK and ERK in whole brain homogenates was increased in infected animals. Phosphorylation of cAMP/calcium responsive element binding protein (CREB), a downstream transcription factor of active ERK, was significantly increased in scrapie-infected hamsters. The immunohistochemical study showed that active ERK was enhanced in infected hamsters compared with controls. Active ERK immunoreactivity was observed within neurons in the dentate gyrus and in glial fibrillary acidic protein (GFAP)-positive reactive astrocytes of infected animals. The expression level of c-Jun mRNA as well as protein, a substrate of active JNK, was increased in infected animals. A significant increase in JNK activity upon glutathione S-transferase (GST)-c-Jun was observed in infected compared with control animals. Phospho-c-Jun immunoreactivity was observed only in neurons of the thalamus in infected groups. These findings indicated that the JNK pathway was activated in the scrapie-infected group. The chronological activation of MAPKs using immunoblot analysis indicates that the kinases are sequentially activated during the pathophysiology of prion disease. Taken together, these results lend credence to the notion that MAPK pathways are dysregulated in prion disease, and also indicate an active role for this pathway in disease pathogenesis.

Increased iron-induced oxidative stress and toxicity in scrapie-infected neuroblastoma cells

The mechanisms behind the pathology of prion diseases are still unknown, but accumulating evidence suggests oxidative impairment along with metal imbalances in scrapie-infected brains. In this study, we have investigated iron-induced oxidative stress in scrapie-infected mouse neuroblastoma N2a (ScN2a) cells. Uninfected N2a and ScN2a cells were treated with ferric ammonium citrate (FAC) for 1-16 h, and the levels of labile iron pool (LIP), the formation of reactive oxygen species (ROS), cell viability and ferritin protein levels were measured. The increase in LIP in N2a cells was transient with a quick recovery to normal levels within 4h accompanied by a moderate increase of formation of ROS after 3h followed by the decrease to the basal level. In ScN2a cells, the increase in LIP was lower, but the process of recovery was prolonged and accompanied by high ROS formation and decreased cell viability. Ferritin protein levels were significantly lower in ScN2a cells than in wild-type cells in all iron treatments. These results suggest that ScN2a cells are more sensitive to iron treatment as compared to wild-type cells with respect to ROS formation and cell viability, and that ferritin deficiency in infected cells may contribute to iron-induced oxidative stress in scrapie-infected cells.

Pathological Prion Protein Exposure Switches on Neuronal Mitogen-activated Protein Kinase Pathway Resulting in Microglia Recruitment

Transmissible spongiform encephalopathies are accompanied by the recruitment of microglial cells in the vicinity of amyloid aggregates of the pathological prion protein (PrPres). We previously showed that PrPres itself triggered the recruitment of microglia by interacting with neurons leading to the up-regulation of the expression level of chemokines, mainly RANTES (regulated on activation normal T cell expressed and secreted). The intracellular mechanisms underlying the PrPres-inducible expression of chemokines in this setting are not clear. Here we demonstrate that the mitogen-activated protein kinase pathway is switched on shortly after PrPres exposure to neurons leading to the expression of early growth response factor-1 (Egr-1), a transcription factor initially linked to differentiation and growth and to up-regulation of RANTES mRNA expression. PD98059, a selective inhibitor of extracellular signal-regulated kinase1/2 activation, resulted in a decrease of RANTES mRNA expression and as a consequence to the lowering of microglial cell migration. Neuronal overexpression of Nab2, a corepressor of Egr-1, produced similar effects. PrPres-induced chemoattraction is independent of the presence of PrPc and the laminin receptor on the neuronal cell surface. Our report is the first demonstration that PrPres exposure on neurons results in the activation of the MAP kinase signaling pathway that acts as a master switch to trigger neuronal expression of regulators of chemoattraction.

Prion-associated Increases in Src-family Kinases

The prion diseases result from the generation and propagation of an abnormal conformer of the prion protein. It is unclear how this molecular event disrupts neuronal function and viability. Current evidence argues it is not due to loss of normal prion protein activity or direct toxic effects of the abnormal conformer. Both the normal and abnormal prion proteins are glycosylphosphatidylinositol-linked membrane proteins. Conversion to the abnormal isoform results in the formation and accumulation of prion protein aggregates. Because aggregation of glycosylphosphatidylinositol-linked proteins activates Src-family kinases, the activation status and levels of the Src-family kinases in prion disease were investigated. Elevations of Src-family kinases were found in a cell culture model and two separate animal models of prion disease. The elevations in Src kinases preceded the onset of symptoms and occurred concurrently with the appearance of detergent-insoluble prion protein. In addition, the total level of kinases phosphorylated at tyrosine residues associated with activation was increased. Similar alterations were not present in brain homogenates from presymptomatic animals early in the disease course, prion protein-ablated animals, or end-stage Tg2576 mice overexpressing mutant amyloid precursor protein. Identification of similar elevations in cell culture and animal model systems suggests the elevations are a specific response to the presence of the disease-associated conformer. Abnormal regulation of these signal transduction cascades may be a key element in the cellular pathology of the prion diseases.

Increased levels of insulin and insulin-like growth factor-1 hybrid receptors and decreased glycosylation of the insulin receptor alpha- and beta-subunits in scrapie-infected neuroblastoma N2a cells

We have previously shown that ScN2a cells (scrapie-infected neuroblastoma N2a cells) express 2-fold- and 4-fold-increased levels of IR (insulin receptor) and IGF-1R (insulin-like growth factor-1 receptor) respectively. In addition, the IR alpha- and beta-subunits are aberrantly processed, with apparent molecular masses of 128 and 85 kDa respectively, as compared with 136 and 95 kDa in uninfected N2a cells. Despite the 2-fold increase in IR protein, the number of (125)I-insulin-binding sites was slightly decreased in ScN2a cells [Ostlund, Lindegren, Pettersson and Bedecs (2001) Brain Res. 97, 161-170]. In order to determine the cellular localization of IR in ScN2a cells, surface biotinylation was performed, showing a correct IR trafficking and localization to the cell surface. The present study shows for the first time that neuroblastoma N2a cells express significant levels of IR-IGF-1R hybrid receptors, and in ScN2a cells the number of hybrid receptors was 2-fold higher than that found in N2a cells, potentially explaining the apparent loss of insulin-binding sites due to a lower affinity for insulin compared with the homotypic IR. Furthermore, the decreased molecular mass of IR subunits in ScN2a cells is not caused by altered phosphorylation or proteolytic processing, but rather by altered glycosylation. Enzymic deglycosylation of immunoprecipitated IR from N2a and ScN2a cells with endoglycosidase H, peptide N-glycosidase F and neuraminidase all resulted in subunits with increased electrophoretic mobility; however, the 8-10 kDa shift remained. Combined enzymic or chemical deglycosylation using anhydrous trifluoromethane sulphonic acid treatment ultimately showed that the IR alpha- and beta-subunits from ScN2a cells are aberrantly glycosylated. The increased formation of IR-IGF-1R hybrids in ScN2a cells may be part of a neuroprotective response to prion infection. The degree and functional significance of aberrantly glycosylated proteins in ScN2a cells remain to be determined.

Glucose transporter GLUT8 translocation in neurons is not insulin responsive

We examined the subcellular distribution of a novel glucose transporter isoform (GLUT8) in murine N2A neuroblastoma cells. Exogenous expression of GLUT8-green fluorescent protein (GFP) DNA constructs mimicked the endogenous GLUT8 localization to intracellular vesicles and minimally to the Giantin-positive Golgi. This distribution was unlike the distributions of endogenous GLUT1 and GLUT3 (predominant neuronal isoform), which were limited predominantly to the plasma membrane and minimal in the cytoplasm. Although GLUT4-GFP (insulin responsive isoform) was expressed transiently, no endogenous GLUT4 was detected in N2A cells. By employing stable transfectants that expressed GLUT8-GFP, the effect of insulin and insulin-like growth factor-I, potassium chloride (depolarized state), and 3% oxygen on translocation of GLUT8 to the plasma membrane of N2A cells was examined immunohistochemically and by subfractionation, followed by Western blot analysis. None of these agents translocated GLUT8 to the plasma membrane. However, when the internalization dileucine motif (L(12,13)) of GLUT8 was mutated to a dialanine motif (A(12,13)), GLUT8 colocalized with GLUT3 in the plasma membrane. We conclude that GLUT8 translocation to the N2A cellular plasma membrane is not observed secondary to the various stimuli investigated. Mutation of the N-terminal dileucine motif led to constitutive GLUT8 localization in the plasma membrane. The endogenous stimulus required for translocating neuronal GLUT8 is unknown. This stimulus, which is necessary for uncoupling the "cytoplasmic vesicular anchor" of GLUT8, would be crucial for its glucose-transporting function.

Loss of lipopolysaccharide-induced nitric oxide production and inducible nitric oxide synthase expression in scrapie-infected N2a cells

In scrapie-infected cells, the conversion of the cellular prion protein to the pathogenic prion has been shown to occur in lipid rafts, which are suggested to function as signal transduction platforms. Neuronal cells may respond to bacterial lipopolysaccharide (LPS) treatment with a sustained and elevated nitric oxide (NO) release. Because prions and the major LPS receptor CD14 are colocalized in lipid rafts, the LPS-induced NO production in scrapie-infected neuroblastoma cells was studied. This study shows that LPS induces a dose- and time-dependent increase in NO release in the murine neuroblastoma cell line N2a, with a 50-fold increase in NO production at 1 microg/ml LPS after 96 hr, as measured by nitrite in the medium. This massive NO release was not caused by activation of the neuronal NO synthase (nNOS), but by increased expression of the inducible NOS (iNOS) mRNA and protein. However, in scrapie-infected N2a cells (ScN2a), the LPS-induced NO production was completely abolished. The absence of LPS-induced NO production in ScN2a was due not to abolished enzymatic activity of iNOS but to a complete inhibition of the LPS-induced iNOS gene expression as measured by Western blot and RT-PCR. These results indicate that scrapie infection inhibits the LPS-mediated signal transduction upstream of the transcriptional step in the signaling cascade and may reflect the important molecular and cellular changes induced by scrapie infection.

Prion propagation in cultured cells

Cell cultures represent relevant and useful experimental models of transmissible spongiform encephalopathies (TSEs). They are able to promote, upon subpassaging, stable and persistent replication of PrP(Sc) as well as infectivity. To date, only a few cell culture models permissive to prion replication are available. Among them, mouse neuroblastoma cell lines (N2a) are most commonly used. While they correspond to homologous models supporting propagation of mouse-adapted scrapie strains, recent studies have reported heterologous models sensitive to natural occurring disease. Infected cell culture models have provided some valuable insights into the biogenesis of PrP(Sc) in terms of conversion, subcellular localisations, physiopathological consequences and species-barrier determinants. They have also contributed to the screening and the study of possible therapeutic compounds and to the development of new strategies for the investigation of TSE-specific diagnostic markers.