A tetracationic porphyrin with dual anti-prion activity

Therapeutic targeting of cellular prion protein: toward the development of dual mechanism anti-prion compounds

PrP Sc , a misfolded, aggregation-prone isoform of the cellular prion protein (PrP C ), is the infectious prion agent responsible for fatal neurodegenerative diseases of humans and other mammals. PrP Sc can adopt different pathogenic conformations (prion strains), which can be resistant to potential drugs, or acquire drug resistance, posing challenges for the development of effective therapies. Since PrP C is the obligate precursor of any prion strain and serves as the mediator of prion neurotoxicity, it represents an attractive therapeutic target for prion diseases. In this minireview, we briefly outline the approaches to target PrP C and discuss our recent identification of Zn(II)-BnPyP, a PrP C -targeting porphyrin with an unprecedented bimodal mechanism of action. We argue that in-depth understanding of the molecular mechanism by which Zn(II)-BnPyP targets PrP C may lead toward the development of a new class of dual mechanism anti-prion compounds.

AlphaFold prediction of structural ensembles of disordered proteins

Deep learning methods of predicting protein structures have reached an accuracy comparable to that of high-resolution experimental methods. It is thus possible to generate accurate models of the native states of hundreds of millions of proteins. An open question, however, concerns whether these advances can be translated to disordered proteins, which should be represented as structural ensembles because of their heterogeneous and dynamical nature. To address this problem, we introduce the AlphaFold-Metainference method to use AlphaFold-derived distances as structural restraints in molecular dynamics simulations to construct structural ensembles of ordered and disordered proteins. The results obtained using AlphaFold-Metainference illustrate the possibility of making predictions of the conformational properties of disordered proteins using deep learning methods trained on the large structural databases available for folded proteins.

Prion protein promotes copper toxicity in Wilson disease

Copper (Cu) is a vitally important micronutrient, whose balance between essential and toxic levels requires a tightly regulated network of proteins. Dysfunction in key components of this network leads to the disruption of Cu homeostasis, resulting in fatal disorders such as Wilson disease, which is caused by mutations in the hepatic Cu efflux transporter ATP7B. Unfortunately, the molecular targets for normalizing Cu homeostasis in Wilson disease remain poorly understood. Here, using genome-wide screening, we identified the cellular prion protein (PrP) as an important mediator of Cu toxicity in WD. Loss of ATP7B stimulates hepatic expression of PrP, which promotes endocytic Cu uptake, leading to toxic Cu overload. Suppression of PrP significantly reduces Cu toxicity in cell and animal models of Wilson disease. These findings highlight the critical regulatory role of PrP in copper metabolism and open new avenues for exploring the therapeutic potential of PrP suppression in Wilson disease.

Tau oligomers impair memory and synaptic plasticity through the cellular prion protein

Deposition of abnormally phosphorylated tau aggregates is a central event leading to neuronal dysfunction and death in Alzheimer's disease (AD) and other tauopathies. Among tau aggregates, oligomers (TauOs) are considered the most toxic. AD brains show significant increase in TauOs compared to healthy controls, their concentration correlating with the severity of cognitive deficits and disease progression. In vitro and in vivo neuronal TauO exposure leads to synaptic and cognitive dysfunction, but their mechanisms of action are unclear. Evidence suggests that the cellular prion protein (PrPC) may act as a mediator of TauO neurotoxicity, as previously proposed for β-amyloid and α-synuclein oligomers. To investigate whether PrPC mediates TauO detrimental activities, we compared their effects on memory and synaptic plasticity in wild type (WT) and PrPC knockout (Prnp0/0) mice. Intracerebroventricular injection of TauOs significantly impaired recognition memory in WT but not in Prnp0/0 mice. Similarly, TauOs inhibited long-term potentiation in acute hippocampal slices from WT but not Prnp0/0 mice. Surface plasmon resonance indicated a high-affinity binding between TauOs and PrPC with a KD of 20-50 nM. Immunofluorescence analysis of naïve and PrPC-overexpressing HEK293 cells exposed to TauOs showed a PrPC dose-dependent association of TauOs with cells over time, and their co-localization with PrPC on the plasma membrane and in intracellular compartments, suggesting PrPC-may play a role in TauO internalization. These findings support the concept that PrPC mediates the detrimental activities of TauOs through a direct interaction, suggesting that targeting this interaction might be a promising therapeutic strategy for AD and other tauopathies.

Creutzfeldt-Jakob disease and other prion diseases

Prion diseases share common clinical and pathological characteristics such as spongiform neuronal degeneration and deposition of an abnormal form of a host-derived protein, termed prion protein. The characteristic features of prion diseases are long incubation times, short clinical courses, extreme resistance of the transmissible agent to degradation and lack of nucleic acid involvement. Sporadic and genetic forms of prion diseases occur worldwide, of which genetic forms are associated with mutations in PRNP. Human to human transmission of these diseases has occurred due to iatrogenic exposure, and zoonotic forms of prion diseases are linked to bovine disease. Significant progress has been made in the diagnosis of these disorders. Clinical tools for diagnosis comprise brain imaging and cerebrospinal fluid tests. Aggregation assays for detection of the abnormally folded prion protein have a clear potential to diagnose the disease in peripherally accessible biofluids. After decades of therapeutic nihilism, new treatment strategies and clinical trials are on the horizon. Although prion diseases are relatively rare disorders, understanding their pathogenesis and mechanisms of prion protein misfolding has significantly enhanced the field in research of neurodegenerative diseases.

Sigma receptor ligands are potent anti-prion compounds that act independently of sigma receptor binding

Prion diseases are invariably fatal neurodegenerative diseases of humans and other animals for which there are no treatment options. Previous work from our laboratory identified phenethyl piperidines as novel class of anti-prion compounds. While working to identify the molecular target(s) of these molecules, we unexpectedly discovered ten novel anti-prion compounds based on their known ability to bind to the sigma receptors, σ 1 R and 2 R, which are currently being tested as therapeutic or diagnostic targets for cancer and neuropsychiatric disorders. Surprisingly, however, knockout of the respective genes encoding σ 1 R and σ 2 R ( Sigmar1 and Tmem97 ), in prion infected N2a cells did not alter the anti-prion activity of these compounds, demonstrating that these receptors are not the direct targets responsible the anti-prion effects of their ligands. Further investigation of the most potent molecules established that they are efficacious against multiple prion strains and protect against downstream prion-mediated synaptotoxicity. While the precise details of the mechanism of action of these molecules remains to be determined, the present work forms the basis for further investigations of these compounds in pre-clinical studies. Given the therapeutic utility of several of the tested compounds, including rimcazole and haloperidol for neuropsychiatric conditions, (+)-pentazocine for neuropathic pain, and the ongoing clinical trials of SA 4503 and ANAVEX2-73 for ischemic stroke and Alzheimer's disease, respectively, this work has immediate implications for the treatment of human prion disease.