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Despite their importance, many crucial networks for protein quality control within cells diminish with age. The resulting loss of proteostasis, the process by which the health of a cell's proteins is monitored and maintained, is associated with a wide range of age-related human diseases. Costa-Mattioli and Walter review the integrated stress response (ISR), a central signaling network that responds to proteostasis defects by tuning protein synthesis. The ISR is activated in a wide range of pathological conditions, so a mechanistic understanding of its pathway may help in the development of therapeutic tools through which it can be modulated. Science , this issue p. eaat5314 Protein quality control is essential for the proper function of cells and the organisms that they make up. The resulting loss of proteostasis, the processes by which the health of the cell’s proteins is monitored and maintained at homeostasis, is associated with a wide range of age-related human diseases. Here, we highlight how the integrated stress response (ISR), a central signaling network that responds to proteostasis defects by tuning protein synthesis rates, impedes the formation of long-term memory. In addition, we address how dysregulated ISR signaling contributes to the pathogenesis of complex diseases, including cognitive disorders, neurodegeneration, cancer, diabetes, and metabolic disorders. The development of tools through which the ISR can be modulated promises to uncover new avenues to diminish pathologies resulting from it for clinical benefit.

Memory and associated plasticity mechanisms span different timescales, from fleeting to enduring. This study shows that, across species, mTORC2's control of actin dynamics is critical for long-term forms of memory and synaptic plasticity. A major goal of biomedical research is the identification of molecular and cellular mechanisms that underlie memory storage. Here we report a previously unknown signaling pathway that is necessary for the conversion from short- to long-term memory. The mammalian target of rapamycin (mTOR) complex 2 (mTORC2), which contains the regulatory protein Rictor (rapamycin-insensitive companion of mTOR), was discovered only recently and little is known about its function. We found that conditional deletion of Rictor in the postnatal murine forebrain greatly reduced mTORC2 activity and selectively impaired both long-term memory (LTM) and the late phase of hippocampal long-term potentiation (L-LTP). We also found a comparable impairment of LTM in dTORC2-deficient flies, highlighting the evolutionary conservation of this pathway. Actin polymerization was reduced in the hippocampus of mTORC2-deficient mice and its restoration rescued both L-LTP and LTM. Moreover, a compound that promoted mTORC2 activity converted early LTP into late LTP and enhanced LTM. Thus, mTORC2 could be a therapeutic target for the treatment of cognitive dysfunction.

Traumatic brain injury (TBI) is a leading cause of long-term neurological disability, yet the mechanisms underlying the chronic cognitive deficits associated with TBI remain unknown. Consequently, there are no effective treatments for patients suffering from the long-lasting symptoms of TBI. Here, we show that TBI persistently activates the integrated stress response (ISR), a universal intracellular signaling pathway that responds to a variety of cellular conditions and regulates protein translation via phosphorylation of the translation initiation factor eIF2α. Treatment with ISRIB, a potent drug-like small-molecule inhibitor of the ISR, reversed the hippocampaldependent cognitive deficits induced by TBI in two different injury mouse models—focal contusion and diffuse concussive injury. Surprisingly, ISRIB corrected TBI-induced memory deficits when administered weeks after the initial injury and maintained cognitive improvement after treatment was terminated. At the physiological level, TBI suppressed long-term potentiation in the hippocampus, which was fully restored with ISRIB treatment. Our results indicate that ISR inhibition at time points late after injury can reverse memory deficits associated with TBI. As such, pharmacological inhibition of the ISR emerges as a promising avenue to combat head traumainduced chronic cognitive deficits.

Down syndrome (DS) is the most common genetic cause of intellectual disability. Protein homeostasis is essential for normal brain function, but little is known about its role in DS pathophysiology. In this study, we found that the integrated stress response (ISR)—a signaling network that maintains proteostasis—was activated in the brains of DS mice and individuals with DS, reprogramming translation. Genetic and pharmacological suppression of the ISR, by inhibiting the ISR-inducing double-stranded RNA–activated protein kinase or boosting the function of the eukaryotic translation initiation factor eIF2-eIF2B complex, reversed the changes in translation and inhibitory synaptic transmission and rescued the synaptic plasticity and long-term memory deficits in DS mice. Thus, the ISR plays a crucial role in DS, which suggests that tuning of the ISR may provide a promising therapeutic intervention.

Both the formation of long-term memory (LTM) and late-long-term potentiation (L-LTP), which is thought to represent the cellular model of learning and memory, require de novo protein synthesis. The mammalian target of Rapamycin (mTOR) complex I (mTORC1) integrates information from various synaptic inputs and its best characterized function is the regulation of translation. Although initial studies have shown that rapamycin reduces L-LTP and partially blocks LTM, recent genetic and pharmacological evidence indicating that mTORC1 promotes L-LTP and LTM is controversial. Thus, the role of mTORC1 in L-LTP and LTM is unclear. To selectively inhibit mTORC1 activity in the adult brain, we used a \"pharmacogenetic\" approach that relies on the synergistic action of a drug (rapamycin) and a genetic manipulation (mTOR heterozygotes, mTOR⁺/⁻ mice) on the same target (mTORC1). Although L-LTP and LTM are normal in mTOR⁺/⁻ mice, application of a low concentration of rapamycin--one that is subthreshold for WT mice--prevented L-LTP and LTM only in mTOR⁺/⁻ mice. Furthermore, we found that mTORC1-mediated translational control is required for memory reconsolidation. We provide here direct genetic evidence supporting the role of mTORC1 in L-LTP and behavioral memory.

Bloodborne infections with Candida albicans are an increasingly recognized complication of modern medicine. Here, we present a mouse model of low-grade candidemia to determine the effect of disseminated infection on cerebral function and relevant immune determinants. We show that intravenous injection of 25,000  C. albicans cells causes a highly localized cerebritis marked by the accumulation of activated microglial and astroglial cells around yeast aggregates, forming fungal-induced glial granulomas. Amyloid precursor protein accumulates within the periphery of these granulomas, while cleaved amyloid beta (Aβ) peptides accumulate around the yeast cells. CNS-localized C. albicans further activate the transcription factor NF-κB and induce production of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor (TNF), and Aβ peptides enhance both phagocytic and antifungal activity from BV-2 cells. Mice infected with C. albicans display mild memory impairment that resolves with fungal clearance. Our results warrant additional studies to understand the effect of chronic cerebritis on cognitive and immune function. The potential links between infections and neurodegenerative disorders are unclear. Here, Wu et al. present a mouse model of low-grade candidemia characterized by highly localized cerebritis, accumulation of amyloid precursor protein and beta peptides, and mild memory impairment that resolves with fungal clearance.

Transcriptional activation of cytokines, such as type-I interferons (interferon (IFN)-α and IFN-β), constitutes the first line of antiviral defence. Here we show that translational control is critical for induction of type-I IFN production. In mouse embryonic fibroblasts lacking the translational repressors 4E-BP1 and 4E-BP2, the threshold for eliciting type-I IFN production is lowered. Consequently, replication of encephalomyocarditis virus, vesicular stomatitis virus, influenza virus and Sindbis virus is markedly suppressed. Furthermore, mice with both 4E- and 4E-BP2 genes (also known as Eif4ebp1 and Eif4ebp2 , respectively) knocked out are resistant to vesicular stomatitis virus infection, and this correlates with an enhanced type-I IFN production in plasmacytoid dendritic cells and the expression of IFN-regulated genes in the lungs. The enhanced type-I IFN response in 4E-BP1 -/-   4E-BP2 -/- double knockout mouse embryonic fibroblasts is caused by upregulation of interferon regulatory factor 7 ( Irf7 ) messenger RNA translation. These findings highlight the role of 4E-BPs as negative regulators of type-I IFN production, via translational repression of Irf7 mRNA. Found in translation Transcriptional control of interferon-mediated gene expression plays a major role in the activation of the innate immune response, but little is known about the role of translational control — the control exerted at the stage at which mRNA is converted into a protein. Colina et al . show that in mice lacking the translational repressors 4E-BP1 and 4E-BP2, the threshold for eliciting type-I interferon in response to challenge by various viruses is lowered and virus replication is dramatically suppressed. The 4E-BP repressors appear to act by the synthesis of the protein IRF-7, the master regulator of interferon production. By targeting 4E-BP1 and 4E-BP2 with drugs, it may be possible to boost innate immunity against virus infection. Production of type-I interferon is regulated by the transcription factor IRF-7. This paper shows that IRF-7 is negatively regulated by translational repressor proteins 4E-BP1 and 4E-BP2. Viral infection promotes mTOR-mediated phosphorylation of the repressor proteins and allows type-I interferon production to proceed.

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by maternal deficiency of the imprinted gene UBE3A. Individuals with AS suffer from intellectual disability, speech impairment, and motor dysfunction. Currently there is no cure for the disease. Here, we evaluated the phenotypic effect of activating the silenced paternal allele of Ube3a by depleting its antisense RNA Ube3a-ATS in mice. Premature termination of Ube3a-ATS by poly(A) cassette insertion activates expression of Ube3a from the paternal chromosome, and ameliorates many disease-related symptoms in the AS mouse model, including motor coordination defects, cognitive deficit, and impaired long-term potentiation. Studies on the imprinting mechanism of Ube3a revealed a pattern of biallelic transcription initiation with suppressed elongation of paternal Ube3a, implicating transcriptional collision between sense and antisense polymerases. These studies demonstrate the feasibility and utility of unsilencing the paternal copy of Ube3a via targeting Ube3a-ATS as a treatment for Angelman syndrome.

Epilepsy is a neurological disorder that poses a major threat to public health. Hyperactivation of mTOR complex 1 (mTORC1) is believed to lead to abnormal network rhythmicity associated with epilepsy, and its inhibition is proposed to provide some therapeutic benefit. However, mTOR complex 2 (mTORC2) is also activated in the epileptic brain, and little is known about its role in seizures. Here we discover that genetic deletion of mTORC2 from forebrain neurons is protective against kainic acid-induced behavioral and EEG seizures. Furthermore, inhibition of mTORC2 with a specific antisense oligonucleotide robustly suppresses seizures in several pharmacological and genetic mouse models of epilepsy. Finally, we identify a target of mTORC2, Nav1.2, which has been implicated in epilepsy and neuronal excitability. Our findings, which are generalizable to several models of human seizures, raise the possibility that inhibition of mTORC2 may serve as a broader therapeutic strategy against epilepsy. A loss of neuronal network resilience results in epilepsy. In this study, the authors show that inhibition of mTORC2 suppresses seizures in animal models with multiple aetiologies, thus enhancing neuronal resilience to the pathological hypersynchrony associated with epilepsy.

Traumatic brain injury (TBI) causes extensive neural damage, often resulting in long-term cognitive impairments. Unfortunately, effective treatments for TBI remain elusive. The RhoA-ROCK signaling pathway is a potential therapeutic target since it is activated by TBI and can promote the retraction of dendritic spines/synapses, which are critical for information processing and memory storage. To test this hypothesis, RhoA-ROCK signaling was blocked by RhoA deletion from postnatal neurons or treatment with the ROCK inhibitor fasudil. We found that TBI impairs both motor and cognitive performance and inhibiting RhoA-ROCK signaling alleviates these deficits. Moreover, RhoA-ROCK inhibition prevents TBI-induced spine remodeling and mature spine loss. These data argue that TBI elicits pathological spine remodeling that contributes to behavioral deficits by altering synaptic connections, and RhoA-ROCK inhibition enhances functional recovery by blocking this detrimental effect. As fasudil has been safely used in humans, our results suggest that it could be repurposed to treat TBI.