Anna G. Orr

Summary: TAR DNA-binding protein-43 (TDP-43) alterations are a key hallmark of amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and other neurodegenerative disorders. Increasing evidence links these conditions to viral infections, but it is not known if and how viral pathogens may be affected by disease-associated TDP-43. We found that ALS/FTD-linked forms of human TDP-43 prevent infection by herpes simplex virus type-1 (HSV-1), a common neurotropic virus. This cell-autonomous protective effect was conserved across different TDP-43 mutations, sporadic ALS, and C9ORF72 -ALS, in neural and non-neural cell types, and in patient-derived cells and animal models. In addition to restricting infection, TDP-43 mutation prevented inflammatory and cell stress-related responses to HSV-1 exposure. TDP-43 knockdown but not overexpression was sufficient to protect cells from HSV-1 infection, implicating a loss-of-function mechanism. Neurons with TDP-43 mutation had disruptions in adhesion-related pathways and, accordingly, had reduced early-stage viral binding and entry. Further analyses revealed alternative RNA splicing and impairment of focal adhesion kinase (FAK/PTK2), a key mediator of cell-adhesion pathways. Inhibition of FAK was sufficient to decrease HSV-1 infection, and genetic enhancement of functional but not inactive FAK promoted infectivity in cells with TDP-43 mutation. Together, these data indicate that TDP-43 affects virus-host interactions by influencing adhesion pathways required for viral infection.

Neurodegenerative disorders alter mitochondrial functions, including the production of reactive oxygen species (ROS). Mitochondrial complex III (CIII) generates ROS implicated in redox signalling, but its triggers, temporal dynamics, targets and disease relevance are not clear. Here, using site-selective suppressors and genetic manipulations together with live mitochondrial ROS imaging and multiomic profiling, we show that CIII is a dominant source of ROS production in astrocytes exposed to neuropathology-related stimuli. Astrocytic CIII ROS production is dependent on nuclear factor-κB and the mitochondrial sodium-calcium exchanger (NCLX) and causes oxidation of select cysteines within immune- and metabolism-associated proteins linked to neurological disease. CIII ROS amplify metabolomic and pathology-associated transcriptional changes in astrocytes, with STAT3 activity as a major mediator, and facilitate neuronal toxicity. Therapeutic suppression of CIII ROS in mice decreases dementia-linked tauopathy and neuroimmune cascades and extends lifespan. Our findings establish CIII ROS as an important immunometabolic signal transducer and tractable therapeutic target in neurodegenerative disease.

Neurodegenerative disorders alter mitochondrial functions, including the production of reactive oxygen species (ROS). Mitochondrial complex III (CIII) generates ROS implicated in redox signaling, but its triggers, targets, and disease relevance are not clear. Using site-selective suppressors and genetic manipulations together with mitochondrial ROS imaging and multiomic profiling, we found that CIII is the dominant source of ROS production in astrocytes exposed to neuropathology-related stimuli. Astrocytic CIII-ROS production was dependent on nuclear factor-κB (NF-κB) and the mitochondrial sodium-calcium exchanger (NCLX) and caused oxidation of select cysteines within immune and metabolism-associated proteins linked to neurological disease. CIII-ROS amplified metabolomic and pathology-associated transcriptional changes in astrocytes, with STAT3 activity as a major mediator, and facilitated neuronal toxicity in a non-cell- autonomous manner. As proof-of-concept, suppression of CIII-ROS in mice decreased dementia-linked tauopathy and neuroimmune cascades and extended lifespan. Our findings establish CIII-ROS as an important immunometabolic signal transducer and tractable therapeutic target in neurodegenerative disease.

Astrocytes are emerging as key regulators of cognitive function and behavior. This review highlights some of the latest advances in the understanding of astrocyte roles in different behavioral domains across lifespan and in disease. We address specific molecular and circuit mechanisms by which astrocytes modulate behavior, discuss their functional diversity and versatility, and highlight emerging astrocyte-targeted treatment strategies that might alleviate behavioral and cognitive dysfunction in pathologic conditions. Converging evidence across different model systems and manipulations is revealing that astrocytes regulate behavioral processes in a precise and context-dependent manner. Improved understanding of these astrocytic functions may generate new therapeutic strategies for various conditions with cognitive and behavioral impairments.

Transactivating response region DNA binding protein 43 (TDP-43) pathology is prevalent in dementia, but the cell type–specific effects of TDP-43 pathology are not clear, and therapeutic strategies to alleviate TDP-43–linked cognitive decline are lacking. We found that patients with Alzheimer’s disease or frontotemporal dementia have aberrant TDP-43 accumulation in hippocampal astrocytes. In mouse models, induction of widespread or hippocampus-targeted accumulation in astrocytic TDP-43 caused progressive memory loss and localized changes in antiviral gene expression. These changes were cell-autonomous and correlated with impaired astrocytic defense against infectious viruses. Among the changes, astrocytes had elevated levels of interferon-inducible chemokines, and neurons had elevated levels of the corresponding chemokine receptor CXCR3 in presynaptic terminals. CXCR3 stimulation altered presynaptic function and promoted neuronal hyperexcitability, akin to the effects of astrocytic TDP-43 dysregulation, and blockade of CXCR3 reduced this activity. Ablation of CXCR3 also prevented TDP-43–linked memory loss. Thus, astrocytic TDP-43 dysfunction contributes to cognitive impairment through aberrant chemokine-mediated astrocytic-neuronal interactions.

Cognitive processes and neurocognitive disorders are regulated by astrocytes and have prominent sex differences. However, the contribution of astrocytes to sex differences is not known. We leveraged astrocyte-targeted gene editing and chemogenetics in adult mice to reveal that astrocytic glutamate receptors and other G protein-coupled receptors (GPCRs) modulate hippocampus-dependent cognitive function in a sexually dimorphic manner. In females, spatial memory was improved by increasing metabotropic glutamate receptor 3 (mGluR3) in astrocytes or stimulating astrocytic G _i/o -coupled signaling, whereas stimulating G _s -coupled signaling impaired memory. However, in males, memory was improved by reducing mGluR3 or stimulating G _s -coupled signaling, whereas stimulating G _i/o -coupled signaling impaired memory. Thus, memory requires a sex-specific balance of astrocytic G _s -coupled and G _i/o -coupled receptor activities, and disease-associated alterations or therapeutic targeting of these pathways may cause opposing sex-dependent effects on cognitive function. Summary: Glia cause sex-specific changes in cognition