Mauro Costa-Mattioli

The endoplasmic reticulum (ER) coordinates protein folding and lipid biosynthesis, while peroxisomes govern fatty-acid catabolism and redox balance. However, little is known about the mechanisms by which these organelles communicate. Here we show that activating transcription factor 6 (ATF6α), a cytoprotective ER-resident sensor of the unfolded protein response (UPR) ^1–4 , forms a molecular tether that zippers the ER and peroxisomes together at a 23-nm intermembrane distance. ATF6α achieves this by inserting a short segment of its unstructured N-terminal cytosolic tail into the solvated transmembrane cavity of the peroxisomal ABC-type lipid transporter ABCD3, trapping it in an off-state. This interaction is reinforced by Ceapin, a previously identified small molecule molecular-glue ligand, which promotes ER–peroxisome contact formation ^5–7 . The junctions serve as a scaffold that can initiate peroxisome turnover by p62-triggered autophagy (pexophagy), as enhanced lipid processing resulting from organelle zippering leads to peroxisome damage due to excessive reactive oxygen species (ROS) accumulation. These findings define ATF6α as a non-transcriptional regulator of organelle quality control and provide a template for engineering Ceapin analogues against ATF6α/ABCD3-dependent colorectal and hepatocellular cancers and related diseases.

The integrated stress response (ISR) is essential for cellular homeostasis and cognitive function. We investigated how persistent ISR activation affects cognitive performance by studying the PPP1R15B ^R658C genetic variant associated with intellectual disability. To model this condition, we generated a mouse line with the pathogenic allele inserted. This variant destabilized the PPP1R15B•PP1 phosphatase complex, causing persistent ISR activation, impaired protein synthesis, and long-term memory deficits. We demonstrated that the cognitive and synaptic impairments in Ppp1r15b ^R658C mice arise directly from ISR activation. Furthermore, we characterized DP71L, a viral ortholog of PPP1R15B, which acted as a potent pan-ISR inhibitor. DP71L reversed the cognitive and synaptic deficits across mouse models of Down syndrome, Alzheimer’s disease, and aging, and enhanced synaptic plasticity and memory in healthy mice.

SUMMARY: Alterations in the gut microbiome are associated with neurodevelopmental disorders, but causal mechanisms and therapeutic strategies remain undefined. Here, we demonstrate that human infant microbiomes isolated during the first six months of life drive behavioral impairments in mice and that microbiota-based interventions restore mice to normal behavior. Early-life microbiomes from twelve infants who later exhibited cognitive deficits at 2 years old (low-scoring) transferred adverse metabolic, brain, and behavioral phenotypes to mice, in contrast to microbiomes from twenty-three cognitively typical or high-scoring infants. Deficits in mice were rescued by fecal microbiota transplant from high-scoring infants or a rationally designed consortium that promoted amino acid levels. We confirmed lower fecal amino acid concentrations in low-scoring infants and replicated the association between early-life microbiome composition and cognitive outcomes in a second geographically independent infant cohort. Altogether, we discovered an early-life microbiome-mediated metabolic state causally linked to cognitive deficits and amenable to microbial intervention.

The Integrated Stress Response (ISR) couples cellular stress sensing to translational control, playing a critical role in the homeostatic regulation of cell health. However, prolonged and unmitigated ISR activation becomes maladaptive and drives the progression of a wide range of pathologies, including cognitive decline. Pharmacological inhibition of the ISR with the small, drug-like molecule ISRIB has proven remarkably effective in reversing cognitive deficits and pathology in animal models, highlighting its potential for therapeutic intervention in humans. We engineered an allele-specific ISRIB analog (mISRIB) that selectively targets a mutant form of eIF2B, the molecular target of ISRIB, without affecting wild-type eIF2B. Notably, mISRIB treatment in mice homozygous for the eIF2B mutant allele enhances synaptic plasticity and long-term memory, confirming the on-target mechanism underlying ISRIB’s cognitive benefits. Our results provide a framework for dissecting the ISR’s contributions within complex cellular networks, such as those governing brain function, with precise temporal and spatial resolution.

Summary: Persistent activation of the integrated stress response (ISR) is a major driver of cognitive decline in both neurodevelopmental and neurodegenerative disorders. Using a new mouse model ( Ppp1r15b ^R658C mice) that mimics the persistent ISR activation and cognitive decline observed in humans, we generated the first single-cell ISR atlas of the brain. By integrating single-cell RNA-seq and single-cell ATAC-seq with proteomics, we discovered that distinct brain cell types respond differently to persistent ISR activation and elicit cell-type-specific ISR programs. Interestingly, chromatin accessibility analyses revealed that the ISR downstream factor ATF4 is a key ISR effector in GABAergic neurons, while AP-1 (JUNB) is implicated in glutamatergic neurons. More importantly, selective deletion of ATF4 in GABAergic neurons—but not in glutamatergic neurons—impacts ISR-mediated cognitive decline in Ppp1r15b ^R658C mice, demonstrating that different neuronal subtypes rely on unique ISR downstream effectors to regulate mnemonic processes. Furthermore, we defined a comprehensive molecular signature of persistent ISR activation, which we showed could serve as a biomarker for cognitive dysfunction across neurodevelopmental, neurodegenerative disorders and normal aging. This multi-omic framework provides a key platform for exploring and validating new scientific hypotheses, significantly advancing our understanding of ISR-related brain disorders.

Summary: The integrated stress response (ISR) is a highly conserved network essential for maintaining cellular homeostasis and cognitive function. Here, we investigated how persistent ISR activation impacts cognitive performance, primarily focusing on a PPP1R15B ^R658C genetic variant associated with intellectual disability. By generating a novel mouse model that mimics this human condition, we revealed that this variant destabilizes the PPP1R15B•PP1 phosphatase complex, resulting in chronic ISR activation, impaired protein synthesis, and deficits in long-term memory. Importantly, we found that the cognitive and synaptic deficits in Ppp1r15b ^R658C mice are directly due to ISR activation. Leveraging insights from evolutionary biology, we characterized DP71L, a viral orthologue of PPP1R15B, through detailed molecular and structural analyses, uncovering its mechanism of action as a potent pan-ISR inhibitor. Remarkably, we found that DP71L not only buffers cognitive decline associated with a wide array of conditions—including Down syndrome, Alzheimer’s disease and aging—but also enhances long-term synaptic plasticity and memory in healthy mice. These findings highlight the promise of utilizing evolutionary insight to inform innovative therapeutic strategies.

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.