Salubrinal

Abstract: Most protein phosphatases have little intrinsic substrate specificity, making selective pharmacological inhibition of specific dephosphorylation reactions a challenging problem. In a screen for small molecules that protect cells from endoplasmic reticulum (ER) stress, we identified salubrinal, a selective inhibitor of cellular complexes that dephosphorylate eukaryotic translation initiation factor 2 subunit alpha (eIF2alpha). Salubrinal also blocks eIF2alpha dephosphorylation mediated by a herpes simplex virus protein and inhibits viral replication. These results suggest that selective chemical inhibitors of eIF2alpha dephosphorylation may be useful in diseases involving ER stress or viral infection. More broadly, salubrinal demonstrates the feasibility of selective pharmacological targeting of cellular dephosphorylation events.

Abstract: The mechanisms underlying disease manifestations in neurodegeneration remain unclear, but their understanding is critical to devising effective therapies. We carry out a longitudinal analysis in vivo of identified motoneurons selectively vulnerable (VUL) or resistant (RES) to motoneuron disease (amyotrophic lateral sclerosis, ALS) and show that subtype-selective endoplasmic reticulum (ER) stress responses influence disease manifestations. VUL motoneurons were selectively prone to ER stress and showed gradually upregulated ER stress markers from birth on in three mouse models of familial ALS (FALS). 25-30 days before the earliest denervations, ubiquitin signals increased in both VUL and RES motoneurons, but an unfolded protein response coupled with microglial activation was initiated selectively in VUL motoneurons. This transition was followed by selective axonal degeneration and spreading stress. The ER stress-protective agent salubrinal attenuated disease manifestations and delayed progression, whereas chronic enhancement of ER stress promoted disease. Thus, whereas all motoneurons are preferentially affected in ALS, ER stress responses in specific motoneuron subtypes influence the progressive manifestations of weakening and paralysis.

Abstract: Accumulation of prion protein during prion replication causes persistent translational repression of global protein synthesis, which is mediated by eIF2α-P and is associated with synaptic failure and neuronal loss in prion-diseased mice; promoting translational recovery in hippocampi of prion-infected mice is neuroprotective. Despite extensive research, the mechanisms leading to neuronal loss in neurodegenerative disease are still little understood, and no treatments or promising treatment strategies exist. Using prion-diseased mice as a model, this study demonstrates that the accumulation of misfolded prion protein during prion replication causes persistent translational repression of global protein synthesis. This is mediated by eIF2α-P and is associated with synaptic failure and neuronal loss in prion-diseased mice. Promoting translational recovery in the hippocampi of prion-infected mice is neuroprotective, suggesting that a generic approach involving the fine-tuning of protein synthesis may be worth pursuing in prion diseases, and perhaps in other neurodegenerative disorders involving protein misfolding. The mechanisms leading to neuronal death in neurodegenerative disease are poorly understood. Many of these disorders, including Alzheimer’s, Parkinson’s and prion diseases, are associated with the accumulation of misfolded disease-specific proteins. The unfolded protein response is a protective cellular mechanism triggered by rising levels of misfolded proteins. One arm of this pathway results in the transient shutdown of protein translation, through phosphorylation of the α-subunit of eukaryotic translation initiation factor, eIF2. Activation of the unfolded protein response and/or increased eIF2α-P levels are seen in patients with Alzheimer’s, Parkinson’s and prion diseases1,2,3,4, but how this links to neurodegeneration is unknown. Here we show that accumulation of prion protein during prion replication causes persistent translational repression of global protein synthesis by eIF2α-P, associated with synaptic failure and neuronal loss in prion-diseased mice. Further, we show that promoting translational recovery in hippocampi of prion-infected mice is neuroprotective. Overexpression of GADD34, a specific eIF2α-P phosphatase, as well as reduction of levels of prion protein by lentivirally mediated RNA interference, reduced eIF2α-P levels. As a result, both approaches restored vital translation rates during prion disease, rescuing synaptic deficits and neuronal loss, thereby significantly increasing survival. In contrast, salubrinal, an inhibitor of eIF2α-P dephosphorylation5, increased eIF2α-P levels, exacerbating neurotoxicity and significantly reducing survival in prion-diseased mice. Given the prevalence of protein misfolding and activation of the unfolded protein response in several neurodegenerative diseases, our results suggest that manipulation of common pathways such as translational control, rather than disease-specific approaches, may lead to new therapies preventing synaptic failure and neuronal loss across the spectrum of these disorders.

Abstract: Accumulation of misfolded α-synuclein (αS) is mechanistically linked to neurodegeneration in Parkinson9s disease (PD) and other α-synucleinopathies. However, how αS causes neurodegeneration is unresolved. Because cellular accumulation of misfolded proteins can lead to endoplasmic reticulum stress/unfolded protein response (ERS/UPR), chronic ERS could contribute to neurodegeneration in α-synucleinopathy. Using the A53T mutant human αS transgenic ( A53T α S Tg) mouse model of α-synucleinopathy, we show that disease onset in the αS Tg model is coincident with induction of ER chaperones in neurons exhibiting αS pathology. However, the neuronal ER chaperone induction was not accompanied by the activation of phospho-eIF2α, indicating that α-synucleinopathy is associated with abnormal UPR that could promote cell death. Induction of ERS/UPR was associated with increased levels of ER/microsomal (ER/M) associated αS monomers and aggregates. Significantly, human PD cases also exhibit higher relative levels of ER/M αS than the control cases. Moreover, αS interacts with ER chaperones and overexpression of αS sensitizes neuronal cells to ERS-induced toxicity, suggesting that αS may have direct impact on ER function. This view is supported by the presence of ERS-activated caspase-12 and the accumulation of ER-associated polyubiquitin. More important, treatment with Salubrinal, an anti-ERS compound, significantly attenuates disease manifestations in both the A53T α S Tg mouse model and the adeno-associated virus-transduced rat model of A53T α S -dependent dopaminergic neurodegeneration. Our data indicate that the accumulation αS within ER leads to chronic ER stress conditions that contribute to neurodegeneration in α-synucleinopathies. Attenuating chronic ERS could be an effective therapy for PD and other α-synucleinopathies.