A conformational switch controlling the toxicity of the prion protein

SummaryPrion infections cause conformational changes of PrPC and lead to progressive neurological impairment. Here we show that toxic, prion-mimetic ligands induce an intramolecular R208-H140 hydrogen bond (“H-latch”) altering the flexibility of the α2-α3 and β2-α2 loops of PrPC. Expression of a PrP2Cys mutant mimicking the H-latch was constitutively toxic, whereas a PrPR207A mutant unable to form the H-latch conferred resistance to prion infection. High-affinity ligands that prevented H-latch induction repressed prion-related neurodegeneration in organotypic cerebellar cultures. We then selected phage-displayed ligands binding wild-type PrPC, but not PrP2Cys. These binders depopulated H-latched conformers and conferred protection against prion toxicity. Finally, brain-specific expression of an antibody rationally designed to prevent H-latch formation, prolonged the life of prion-infected mice despite unhampered prion propagation, confirming that the H-latch is causally linked to prion neurotoxicity.

Δ 9 -Tetrahydrocannabinol Promotes Functional Remyelination in the Mouse Brain

Background: Research on demyelinating disorders aims to find novel molecules able to induce oligodendrocyte precursor cell differentiation to promote CNS remyelination and functional recovery. Δ9-Tetrahydrocannabinol (THC), the most prominent active constituent of the hemp plant Cannabis sativa, confers neuroprotection in animal models of demyelination. However, the possible effect of THC on myelin repair has never been studied. Methods: By using oligodendroglia-specific reporter mouse lines in combination with 2 models of toxin-induced demyelination, we analyzed the effect of THC on the processes of oligodendrocyte regeneration and functional remyelination. Results: We show that THC administration enhanced oligodendrocyte regeneration, white matter remyelination, and motor function recovery. THC also promoted axonal remyelination in organotypic cerebellar cultures. THC remyelinating action relied on the induction of oligodendrocyte precursor differentiation upon cell cycle exit and via CB1 cannabinoid receptor activation. Conclusions: Overall, our study identifies THC administration as a promising pharmacological strategy aimed to promote functional CNS remyelination in demyelinating disorders.

Brain-Derived Neurotrophic Factor Is Required for the Neuroprotective Effect of Mifepristone on Immature Purkinje Cells in Cerebellar Slice Culture

Endogenous γ-aminobutyric acid (GABA)-dependent activity induces death of developing Purkinje neurons in mouse organotypic cerebellar cultures and the synthetic steroid mifepristone blocks this effect. Here, using brain-derived neurotrophic factor (BDNF) heterozygous mice, we show that BDNF plays no role in immature Purkinje cell death. However, interestingly, BDNF haploinsufficiency impairs neuronal survival induced by mifepristone and GABAA-receptors antagonist (bicuculline) treatments, indicating that the underlying neuroprotective mechanism requires the neurotrophin full expression.

Astrocytes restore connectivity and synchronization in dysfunctional cerebellar networks

Evidence suggests that astrocytes play key roles in structural and functional organization of neuronal circuits. To understand how astrocytes influence the physiopathology of cerebellar circuits, we cultured cells from cerebella of mice that lack the ATM gene. Mutations in ATM are causative of the human cerebellar degenerative disease ataxia-telangiectasia. Cerebellar cultures grown from Atm−/− mice had disrupted network synchronization, atrophied astrocytic arborizations, reduced autophagy levels, and higher numbers of synapses per neuron than wild-type cultures. Chimeric circuitries composed of wild-type astrocytes and Atm−/− neurons were indistinguishable from wild-type cultures. Adult cerebellar characterizations confirmed disrupted astrocyte morphology, increased GABAergic synaptic markers, and reduced autophagy in Atm−/− compared with wild-type mice. These results indicate that astrocytes can impact neuronal circuits at levels ranging from synaptic expression to global dynamics.