Long-term exposure from perinatal life to food-grade TiO2 alters intestinal homeostasis and predisposes to food allergy in young mice.

BACKGROUND: Food allergy (FA) is an inappropriate immunological response to food proteins resulting from an impaired induction of oral tolerance. Various early environmental factors can affect the establishment of intestinal homeostasis, predisposing to FA in early life. In this context, we aimed to assess the effect of chronic perinatal exposure to food-grade titanium dioxide (fg-TiO2 ), a common food additive. METHODS: Dams were fed a control versus fg-TiO2 -enriched diet from preconception to weaning, and their progeny received the same diet at weaning. A comprehensive analysis of baseline intestinal and systemic homeostasis was performed in offspring 1 week after weaning by assessing gut barrier maturation and microbiota composition, and local and systemic immune system and metabolome. The effect of fg-TiO2 on the susceptibility of progeny to develop oral tolerance versus FA to cow's milk proteins (CMP) was performed starting at the same baseline time-point, using established models. Sensitization to CMP was investigated by measuring ß-lactoglobulin and casein-specific IgG1 and IgE antibodies, and elicitation of the allergic reaction by measuring mouse mast cell protease (mMCP1) in plasma collected after an oral food challenge. RESULTS: Perinatal exposure to fg-TiO2 at realistic human doses led to an increased propensity to develop FA and an impaired induction of oral tolerance only in young males, which could be related to global baseline alterations in intestinal barrier, gut microbiota composition, local and systemic immunity, and metabolism. CONCLUSIONS: Long-term perinatal exposure to fg-TiO2 alters intestinal homeostasis establishment and predisposes to food allergy, with a clear gender effect.

Substitutions at residue 211 in the prion protein drive a switch between CJD and GSS syndrome, a new mechanism governing inherited neurodegenerative disorders.

Human prion diseases are a heterogeneous group of fatal neurodegenerative disorders, characterized by the deposition of the partially protease-resistant prion protein (PrP(res)), astrocytosis, neuronal loss and spongiform change in the brain. Among inherited forms that represent 15% of patients, different phenotypes have been described depending on the variations detected at different positions within the prion protein gene. Here, we report a new mechanism governing the phenotypic variability of inherited prion diseases. First, we observed that the substitution at residue 211 with either Gln or Asp leads to distinct disorders at the clinical, neuropathological and biochemical levels (Creutzfeldt-Jakob disease or Gerstmann-Sträussler-Scheinker syndrome with abundant amyloid plaques and tau neurofibrillar pathology). Then, using molecular dynamics simulations and biophysical characterization of mutant proteins and an in vitro model of PrP conversion, we found evidence that each substitution impacts differently the stability of PrP and its propensity to produce different protease resistant fragments that may contribute to the phenotypical switch. Thus, subtle differences in the PrP primary structure and stability are sufficient to control amyloid plaques formation and tau abnormal phosphorylation and fibrillation. This mechanism is unique among neurodegenerative disorders and is consistent with the prion hypothesis that proposes a conformational change as the key pathological event in prion disorders.

Prion fibrillization is mediated by a native structural element that comprises helices H2 and H3.

Aggregation and misfolding of the prion protein (PrP) are thought to be the cause of a family of lethal neurodegenerative diseases affecting humans and other animals. Although the structures of PrP from several species have been solved, still little is known about the mechanisms that lead to the misfolded species. Here, we show that the region of PrP comprising the hairpin formed by the helices H2 and H3 is a stable independently folded unit able to retain its secondary and tertiary structure also in the absence of the rest of the sequence. We also prove that the isolated H2H3 is highly fibrillogenic and forms amyloid fibers morphologically similar to those obtained for the full-length protein. Fibrillization of H2H3 but not of full-length PrP is concomitant with formation of aggregates. These observations suggest a "banana-peeling" mechanism for misfolding of PrP in which H2H3 is the aggregation seed that needs to be first exposed to promote conversion from a helical to a beta-rich structure.

The oligomerization properties of prion protein are restricted to the H2H3 domain.

The propensity of the prion protein (PrP) to adopt different structures is a clue to its pathological behavior. The determination of the region involved in the PrP(C) to PrP(Sc) conversion is fundamental for the understanding of the mechanisms underlying this process at the molecular level. In this paper, the polymerization of the helical H2H3 domain of ovine PrP (OvPrP) was compared to the full-length construct (using chromatography and light scattering). We show that the oligomerization patterns are identical, although the H2H3 domain has a higher polymerization rate. Furthermore, the depolymerization kinetics of purified H2H3 oligomers compared to those purified from the full-length PrP reveal that regions outside H2H3 do not significantly contribute to the oligomerization process. By combining rational mutagenesis and molecular dynamics to investigate the early stages of H2H3 oligomerization, we observe a conformationally stable beta-sheet structure that we propose as a possible nucleus for oligomerization; we also show that single point mutations in H2 and H3 present structural polymorphisms and oligomerization properties that could constitute the basis of species or strain variability.

Emergence of two prion subtypes in ovine PrP transgenic mice infected with human MM2-cortical Creutzfeldt-Jakob disease prions.

INTRODUCTION: Mammalian prions are proteinaceous pathogens responsible for a broad range of fatal neurodegenerative diseases in humans and animals. These diseases can occur spontaneously, such as Creutzfeldt-Jakob disease (CJD) in humans, or be acquired or inherited. Prions are primarily formed of macromolecular assemblies of the disease-associated prion protein PrP(Sc), a misfolded isoform of the host-encoded prion protein PrP(C). Within defined host-species, prions can exist as conformational variants or strains. Based on both the M/V polymorphism at codon 129 of PrP and the electrophoretic signature of PrP(Sc) in the brain, sporadic CJD is classified in different subtypes, which may encode different strains. A transmission barrier, the mechanism of which remains unknown, limits prion cross-species propagation. To adapt to the new host, prions have the capacity to 'mutate' conformationally, leading to the emergence of a variant with new biological properties. Here, we transmitted experimentally one rare subtype of human CJD, designated cortical MM2 (129 MM with type 2 PrP(Sc)), to transgenic mice overexpressing either human or the VRQ allele of ovine PrP(C). RESULTS: In marked contrast with the reported absence of transmission to knock-in mice expressing physiological levels of human PrP, this subtype transmitted faithfully to mice overexpressing human PrP, and exhibited unique strain features. Onto the ovine PrP sequence, the cortical MM2 subtype abruptly evolved on second passage, thereby allowing emergence of a pair of strain variants with distinct PrP(Sc) biochemical characteristics and differing tropism for the central and lymphoid tissues. These two strain components exhibited remarkably distinct replicative properties in cell-free amplification assay, allowing the 'physical' cloning of the minor, lymphotropic component, and subsequent isolation in ovine PrP mice and RK13 cells. CONCLUSIONS: Here, we provide in-depth assessment of the transmissibility and evolution of one rare subtype of sporadic CJD upon homologous and heterologous transmission. The notion that the environment or matrix where replication is occurring is key to the selection and preferential amplification of prion substrain components raises new questions on the determinants of prion replication within and between species. These data also further interrogate on the interplay between animal and human prions.