Project description:Many neurodegenerative diseases are thought to be caused by impaired containment and/or disposal of neurotoxic material such as amyloid beta (Ab) and myelin debris. Indeed, recent human genome-wide association studies (GWAS) and animal model studies have begun to reveal critical roles for the brain’s professional phagocytes, microglia, as well as various innate immune receptors expressed by microglia in the control of neurotoxic material and subsequent neurodegenerative disease pathogenesis. Yet, the critical intracellular molecules that orchestrate the neuroprotective functions of microglia in degenerative disorders remain poorly understood. In our studies, we have identified the innate immune signaling molecule spleen tyrosine kinase (SYK) as a key regulator of microglial phagocytosis in neurodegenerative disease. We find that targeted deletion of SYK in microglia leads to exacerbated Ab deposition, aggravated neuropathology, and cognitive defects in the 5xFAD mouse model of Alzheimer’s disease (AD). Furthermore, disruption of SYK signaling in this AD model was also shown to impede the development of disease-associated microglia (DAMs), alter AKT/GSK3b-signaling in microglia, and to cause severe deficits in the ability of microglia to phagocytose Ab. Importantly, these critical neuroprotective functions of SYK in microglia were not only restricted to Ab-driven models of neurodegeneration, as we found that SYK is also a critical regulator of microglial phagocytosis and DAM phenotype acquisition in demyelinating disease. Collectively, these results help to break new ground in our understanding of the key innate immune signaling molecules that instruct beneficial microglial functions in response to neurotoxic material. Moreover, these findings suggest that targeting SYK may offer a therapeutic strategy to treat a spectrum of neurodegenerative disorders.
Project description:Many neurodegenerative diseases are thought to be caused by impaired containment and/or disposal of neurotoxic material such as amyloid beta (Ab) and myelin debris. Indeed, recent human genome-wide association studies (GWAS) and animal model studies have begun to reveal critical roles for the brain’s professional phagocytes, microglia, as well as various innate immune receptors expressed by microglia in the control of neurotoxic material and subsequent neurodegenerative disease pathogenesis. Yet, the critical intracellular molecules that orchestrate the neuroprotective functions of microglia in degenerative disorders remain poorly understood. In our studies, we have identified the innate immune signaling molecule spleen tyrosine kinase (SYK) as a key regulator of microglial phagocytosis in neurodegenerative disease. We find that targeted deletion of SYK in microglia leads to exacerbated Ab deposition, aggravated neuropathology, and cognitive defects in the 5xFAD mouse model of Alzheimer’s disease (AD). Furthermore, disruption of SYK signaling in this AD model was also shown to impede the development of disease-associated microglia (DAMs), alter AKT/GSK3b-signaling in microglia, and to cause severe deficits in the ability of microglia to phagocytose Ab. Importantly, these critical neuroprotective functions of SYK in microglia were not only restricted to Ab-driven models of neurodegeneration, as we found that SYK is also a critical regulator of microglial phagocytosis and DAM phenotype acquisition in demyelinating disease. Collectively, these results help to break new ground in our understanding of the key innate immune signaling molecules that instruct beneficial microglial functions in response to neurotoxic material. Moreover, these findings suggest that targeting SYK may offer a therapeutic strategy to treat a spectrum of neurodegenerative disorders.
Project description:Recent studies have begun to reveal critical roles for the brain's professional phagocytes, microglia, and their receptors in the control of neurotoxic amyloid beta (Aβ) and myelin debris accumulation in neurodegenerative disease. However, the critical intracellular molecules that orchestrate neuroprotective functions of microglia remain poorly understood. In our studies, we find that targeted deletion of SYK in microglia leads to exacerbated Aβ deposition, aggravated neuropathology, and cognitive defects in the 5xFAD mouse model of Alzheimer's disease (AD). Disruption of SYK signaling in this AD model was further shown to impede the development of disease-associated microglia (DAM), alter AKT/GSK3β-signaling, and restrict Aβ phagocytosis by microglia. Conversely, receptor-mediated activation of SYK limits Aβ load. We also found that SYK critically regulates microglial phagocytosis and DAM acquisition in demyelinating disease. Collectively, these results broaden our understanding of the key innate immune signaling molecules that instruct beneficial microglial functions in response to neurotoxic material.
Project description:Genetic studies have highlighted microglia as pivotal in orchestrating Alzheimer’s disease (AD). Microglia that adhere to Aβ plaques acquire a transcriptional signature, “diseaseassociated microglia” (DAM), which largely emanates from the TREM2-DAP12 receptor complex that transmits intracellular signals through the protein tyrosine kinase SYK. The human TREM2R47H variant associated with high AD risk fails to activate microglia via SYK. We found that SYK-deficient microglia cannot encase Aβ plaques, accelerating brain pathology and behavioral deficits. SYK deficiency impaired the PI3K-AKT-GSK3β-mTOR pathway, incapacitating anabolic support required for attaining the DAM profile. However, SYK-deficient microglia proliferated and advanced to an Apoe-expressing prodromal stage of DAM; this pathway relied on the adaptor DAP10, which also binds TREM2. Thus, microglial responses to Aβ involve non-redundant SYK- and DAP10-pathways. Systemic administration of an antibody against CLEC7A, a receptor that directly activates SYK, rescued microglia activation in mice expressing the TREM2R47H allele, unveiling new options for AD immunotherapy.
Project description:INTRODUCTION: Gain-of-function mutations in INPP5D, which encodes for the SH2-domain-containing inositol phosphatase SHIP-1, have recently been linked to an increased risk of developing late-onset Alzheimer’s disease (LOAD). Yet, little is currently known in regards to how SHIP-1 affects neurobiology or neurodegenerative disease pathogenesis. METHODS: To bridge this knowledge gap, we generated 5xFAD Inpp5dfl/flCx3cr1Ert2Cre mice to investigate the function of microglial SHIP-1 signaling in response to amyloid beta (Aβ)-mediated pathology. RESULTS: In our studies, we found that SHIP-1 deletion in microglia leads to substantially enhanced recruitment of microglia to Aβ plaques, altered microglial gene expression, and marked improvements in neuronal health. Further, SHIP-1 loss enhanced microglial plaque containment and Aβ engulfment when compared to microglia from Cre-negative 5xFAD Inpp5dfl/fl littermate controls. DISCUSSION: These results define SHIP-1 as a pivotal regulator of microglial responses during Aβ-driven neurological disease.
Project description:The intrinsic mechanisms that regulate neurotoxic versus neuroprotective astrocyte phenotypes and their effects on central nervous system (CNS) degeneration and repair remain poorly understood. Here, we show injured white matter astrocytes differentiate into two distinct C3-positive and C3-negative reactive populations, previously simplified as neurotoxic (A1) and neuroprotective (A2)1,2, which can be further subdivided into unique subpopulations defined by proliferation and differential gene expression signatures. We find the balance of neurotoxic versus neuroprotective astrocytes is regulated by discrete pools of compartmented cAMP derived from soluble adenylyl cyclase (sAC) and show proliferating neuroprotective astrocytes inhibit microglial activation and downstream neurotoxic astrocyte differentiation to promote retinal ganglion cell (RGC) survival. Finally, we report a new, therapeutically tractable viral vector to specifically target optic nerve head astrocytes and show elevating nuclear or depleting cytoplasmic cAMP in reactive astrocytes inhibits deleterious immune cell infiltration and promotes RGC survival after optic nerve injury. Thus, soluble adenylyl cyclase and compartmented, nuclear- and cytoplasmic-localized cAMP in reactive astrocytes act as a molecular switch for neuroprotective astrocyte reactivity that can be targeted to inhibit microglial activation and neurotoxic astrocyte differentiation to therapeutic effect. These data expand upon and define new reactive astrocyte subtypes and represents a novel step towards the development of gliotherapeutics for the treatment of glaucoma and other optic neuropathies.
Project description:Genetic studies have highlighted microglia as pivotal in orchestrating Alzheimer’s disease (AD). Microglia that adhere to Aβ plaques acquire a transcriptional signature, “diseaseassociated microglia” (DAM), which largely emanates from the TREM2-DAP12 receptor complex that transmits intracellular signals through the protein tyrosine kinase SYK. The human TREM2R47H variant associated with high AD risk fails to activate microglia via SYK. We found that SYK-deficient microglia cannot encase Aβ plaques, accelerating brain pathology and behavioral deficits. SYK deficiency impaired the PI3K-AKT-GSK3β-mTOR pathway, incapacitating anabolic support required for attaining the DAM profile. However, SYK-deficient microglia proliferated and advanced to an Apoe-expressing prodromal stage of DAM; this pathway relied on the adaptor DAP10, which also binds TREM2. Thus, microglial responses to Aβ involve non-redundant SYK- and DAP10-pathways. Systemic administration of an antibody against CLEC7A, a receptor that directly activates SYK, rescued microglia activation in mice expressing the TREM2R47H allele, unveiling new options for AD immunotherapy.