An in vivo Caenorhabditis elegans model for therapeutic research in human prion diseases.

Human prion diseases are fatal neurodegenerative disorders that include sporadic, infectious and genetic forms. Inherited Creutzfeldt-Jakob disease due to the E200K mutation of the prion protein-coding gene is the most common form of genetic prion disease. The phenotype resembles that of sporadic Creutzfeldt-Jakob disease at both the clinical and pathological levels, with a median disease duration of 4 months. To date, there is no available treatment for delaying the occurrence or slowing the progression of human prion diseases. Existing in vivo models do not allow high-throughput approaches that may facilitate the discovery of compounds targeting pathological assemblies of human prion protein or their effects on neuronal survival. Here, we generated a genetic model in the nematode Caenorhabditis elegans, which is devoid of any homologue of the prion protein, by expressing human prion protein with the E200K mutation in the mechanosensitive neuronal system. Expression of E200K prion protein induced a specific behavioural pattern and neurodegeneration of green fluorescent protein-expressing mechanosensitive neurons, in addition to the formation of intraneuronal inclusions associated with the accumulation of a protease-resistant form of the prion protein. We demonstrated that this experimental system is a powerful tool for investigating the efficacy of anti-prion compounds on both prion-induced neurodegeneration and prion protein misfolding, as well as in the context of human prion protein. Within a library of 320 compounds that have been approved for human use and cross the blood-brain barrier, we identified five molecules that were active against the aggregation of the E200K prion protein and the neurodegeneration it induced in transgenic animals. This model breaks a technological limitation in prion therapeutic research and provides a key tool to study the deleterious effects of misfolded prion protein in a well-described neuronal system.

Doxycycline Interferes With Tau Aggregation and Reduces Its Neuronal Toxicity.

Tauopathies are neurodegenerative disorders with increasing incidence and still without cure. The extensive time required for development and approval of novel therapeutics highlights the need for testing and repurposing known safe molecules. Since doxycycline impacts α-synuclein aggregation and toxicity, herein we tested its effect on tau. We found that doxycycline reduces amyloid aggregation of the 2N4R and K18 isoforms of tau protein in a dose-dependent manner. Furthermore, in a cell free system doxycycline also prevents tau seeding and in cell culture reduces toxicity of tau aggregates. Overall, our results expand the spectrum of action of doxycycline against aggregation-prone proteins, opening novel perspectives for its repurposing as a disease-modifying drug for tauopathies.

Doxycycline inhibits α-synuclein-associated pathologies in vitro and in vivo.

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are neurodegenerative disorders characterized by the misfolding and aggregation of alpha-synuclein (aSyn). Doxycycline, a tetracyclic antibiotic shows neuroprotective effects, initially proposed to be due to its anti-inflammatory properties. More recently, an additional mechanism by which doxycycline may exert its neuroprotective effects has been proposed as it has been shown that it inhibits amyloid aggregation. Here, we studied the effects of doxycycline on aSyn aggregation in vivo, in vitro and in a cell free system using real-time quaking induced conversion (RT-QuiC). Using H4, SH-SY5Y and HEK293 cells, we found that doxycycline decreases the number and size of aSyn aggregates in cells. In addition, doxycycline inhibits the aggregation and seeding of recombinant aSyn, and attenuates the production of mitochondrial-derived reactive oxygen species. Finally, we found that doxycycline induces a cellular redistribution of aggregates in a C.elegans animal model of PD, an effect that is associated with a recovery of dopaminergic function. In summary, we provide strong evidence that doxycycline treatment may be an effective strategy against synucleinopathies.