Montserrat Arrasate

Background and Purpose The integrated stress response (ISR) regulates translation in response to diverse stresses. ISR activation has been documented in amyotrophic lateral sclerosis (ALS) patients and ALS experimental models. In experimental models, both ISR stimulation and inhibition prevented ALS neurodegeneration; however, which mode of ISR regulation would work in patients is still debated. We previously demonstrated that the ISR modulator ISRIB (Integrated Stress Response InhiBitor, an eIF2B activator) enhances survival of neurons expressing the ALS neurotoxic allele SOD1 G93A. Here, we tested the effect of two ISRIB‐like eIF2B activators (2BAct and PRXS571) in the disease progression of transgenic SOD1 G93A mice. Experimental Approach After biochemical characterization in primary neurons, SOD1 G93A mice were treated with 2BAct and PRXS571. Muscle denervation of vulnerable motor units was monitored with a longitudinal electromyographic test. We used a clinical score to document disease onset and progression; force loss was determined with the hanging wire motor test. Motor neuronal survival was assessed by immunohistochemistry. Key Results In primary neurons, 2BAct and PRXS571 relieve the ISR‐imposed translational inhibition while maintaining high ATF4 levels. Electromyographic recordings evidenced an earlier and more dramatic muscle denervation in treated SOD1 G93A mice that correlated with a decrease in motor neuron survival. Both compounds anticipated disease onset and shortened survival time. Conclusion and Implications 2BAct and PRXS571 anticipate disease onset, aggravating muscle denervation and motor neuronal death of SOD1 G93A mice. This study reveals that the ISR works as a neuroprotective pathway in ALS motor neurons and reveals the toxicity that eIF2B activators may display in ALS patients.

Inflammation is a common feature in neurodegenerative diseases that contributes to neuronal loss. Previously, we demonstrated that the basal inflammatory tone differed between brain regions and, consequently, the reaction generated to a pro‐inflammatory stimulus was different. In this study, we assessed the innate immune reaction in the midbrain and in the striatum using an experimental model of Parkinson's disease. An adeno‐associated virus serotype 9 expressing the α‐synuclein and mCherry genes or the mCherry gene was administered into the substantia nigra. Myeloid cells (CD11b + ) and astrocytes (ACSA2 + ) were purified from the midbrain and striatum for bulk RNA sequencing. In the parkinsonian midbrain, CD11b + cells presented a unique anti‐inflammatory transcriptomic profile that differed from degenerative microglia signatures described in experimental models for other neurodegenerative conditions. By contrast, striatal CD11b + cells showed a pro‐inflammatory state and were similar to disease‐associated microglia. In the midbrain, a prominent increase of infiltrated monocytes/macrophages was observed and, together with microglia, participated actively in the phagocytosis of dopaminergic neuronal bodies. Although striatal microglia presented a phagocytic transcriptomic profile, morphology and cell density was preserved and no active phagocytosis was detected. Interestingly, astrocytes presented a pro‐inflammatory fingerprint in the midbrain and a low number of differentially displayed transcripts in the striatum. During α‐synuclein‐dependent degeneration, microglia and astrocytes experience context‐dependent activation states with a different contribution to the inflammatory reaction. Our results point towards the relevance of selecting appropriate cell targets to design neuroprotective strategies aimed to modulate the innate immune system during the active phase of dopaminergic degeneration.