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Mitochondrial and Purinergic Dysregulation Promote Abnormal Behavior in Mice
TREIMM 1645 No. of Pages 2
Trends in Immunology
Spotlight
Mitochondrial and Purinergic Dysregulation Promote Abnormal Behavior in Mice Ping Fang1,* and Elaine Y. Hsiao1 Increasing evidence implicates immune dysregulation in the development of neurological disorders. Recent research by Fan and colleagues deepens our understanding of how physical stress alters the immune system to promote anxiety-like behavior. Physical and psychological stressors induce widespread alterations across the immune, endocrine, and nervous systems, predisposing to neurological conditions such as major depression and anxiety disorder [1]. Foundational studies have revealed that stress alters brain function and behavior, leukocyte distribution and cytokine production [2], neurotransmitter and hormone concentrations [3,4], and a variety of biochemicals involved in core metabolism [5]. While both immune and metabolic alterations have been implicated in the risk for anxiety and depression, the molecular and cellular mechanisms for how stresstriggered immune and metabolic pathways lead to long-term brain and behavioral abnormalities remain elusive. A recent study led by Fan et al. highlights a novel role for stress-induced metabolic alterations in peripheral CD4 + T cells in the development of behaviors related to anxiety in mice [6].
prevent the ES-induced behavioral abnormalities in the open field test and elevated plus maze, where reduced exploratory behavior is referred to as ‘anxiety-like behavior’ (Figure 1). This effect was also seen in another physical stress paradigm based on restraint stress (RS), where depletion of CD4+ T cells protected against the development of abnormal stress-induced behavior. To determine whether pathogenic CD4+ T cells were sufficient in promoting abnormal behavior, the authors adoptively transferred splenic CD4+ or CD8+ T cells from ES-treated mice or nontreated controls into Rag1−/mice, which lack T and B cells. Rag1−/mice that received CD4 + T cells from ES-treated mice exhibited elevated anxiety-like behavior relative to controls receiving wild-type (WT) CD4+ T cells. To specify the subset of CD4+ T cells involved, naïve CD4+ T cells or effector CD4+ T cells from ES donors were transferred to Rag1−/- mice. The findings indicated that behavioral abnormalities were sufficiently conferred by naïve CD4+ T cells, but not effector T cells, from EStreated donors [6].
To gain further insight into the molecular features of the pathogenic CD4+ T cells, the authors next compared the transcriptomes between ES-experienced CD4+ T cells relative to CD8+ T cells as negative controls. Numerous genes were differentially expressed, many of which encoded mitochondrial proteins. Consistent with this, ES- and RSexperienced CD4+ T cells exhibited metabolic dysfunction and increased mitochondrial fission relative to nontreated CD4+ T cells, as indicated by reduced glycolysis and oxidative phosphorylation, the presence of punctate mitochondrial morphology, and To evaluate the role of T cells in mediating degraded mitochondrial outer membrane the detrimental effects of physical stress proteins, such as Mitoguardin 2 (Miga2) on behavior, the authors first depleted and Mitofusin 2 (Mfn2). To evaluate a causal CD4+ or CD8+ T cells in mice exposed to relationship between mitochondrial dysfuncelectronic foot shock (ES) for eight con- tion and abnormal behavior, the authors secutive days. Deficiency in CD4+ T cells, found that Miga2−/- mice, which harbor but not CD8+ T cells, was sufficient to highly fragmented mitochondria, exhibited
anxiety-like behavioral abnormalities. In line with their previous findings, depletion of CD4+ T cells prevented anxiety-like symptoms in Miga2−/- mice, again suggesting a role for CD4+ T cells in mediating abnormal behavior. To determine whether mitochondrial abnormalities specifically in CD4+ T cells were sufficient to promote anxietylike behavior, the authors generated CD4+ T-cell-specific conditional knockout (cKO) mice harboring Miga2 (Miga2TKO) or Mfn (MfnTKO) deficiency. Similar to the Miga2−/mice, both cKO mouse strains exhibited anxiety-like behavior relative to their WT littermate controls. Overall, these findings reveal that mitochondrial dysfunction in CD4+ T cells can contribute to the development of anxiety-like behavior in mice [6]. Given that mitochondrial dynamics can regulate cellular metabolism [7], the authors next applied metabolomic profiling to identify likely pathways involved in the ability of CD4+ T cell mitochondrial dysfunction to elicit alterations in animal behavior. Compared with WT littermate controls, Miga2TKO mice displayed elevations in many serum purines, including xanthine, which also accumulated highly in the brain. This particular finding also aligned with the increased abundance of xanthine reported in the sera of human patients with anxiety or depression. To test for a causal role of xanthine, the authors injected WT mice with xanthine intraperitoneally, which sufficiently triggered anxietylike behavior relative to vehicle-injected controls. By contrast, administering a chemical inhibitor of purine metabolism ameliorated the behavioral abnormalities in Miga2TKO mice and ES-treated mice. The authors further examined the potential effect of xanthine on the left amygdala, an area implicated in anxiety disorder. Having observed the accumulation of many nonneuronal cells in the left amygdala compared with the right amygdala of Miga2TKO mice, the authors performed singlecell RNA-seq (scRNA-seq) to define the relevant cell populations that could Trends in Immunology, Month 2019, Vol. xx, No. xx
1
Trends in Immunology
findings in this study warrant continued exploration into whether and how altered metabolites influence neuronal activity to promote the manifestation of behavioral abnormalities. The authors’ findings also raise the question of whether metabolic disruptions triggered by other risk factors, in addition to stress, can promote neurobehavioral abnormalities through a similar neuroimmune–metabolic pathway. While current interventions for depression and anxiety largely target select neurons in the brain itself, this study highlights a striking interaction between the immune system, core metabolism, and animal behavior, providing a foundation for the exploration of novel non-neuronal and peripheral targets for modulating behaviors that are Trends in Immunology + Figure 1. Mitochondrial Dysfunction and Altered Purine Metabolism in CD4 T Cells Can Mediate used to model neurological diseases the Development of Anxiety-like Behavioral Abnormalities in Response to Physical Stress in Mice. in mice. The present study by Fan and colleagues demonstrates that physical stress, including electronic foot shock and physical restraint, enhances mitochondrial fission in peripheral CD4+ T cells, which increases the accumulation of interferon regulatory factor 1 (IRF1) in the promoter region of genes that express purine synthesis enzymes. This mitochondrial dysregulation elevates the concentrations of purine metabolites in both serum and the brain. In particular, elevated xanthine signaling to AdorA1+ oligodendrocytes in the left amygdala leads to the development of anxiety-like behavior in the open field, elevated plus maze, tail suspension, and light-dark box tests [6]. This figure was created using BioRender (https://biorender.com/).
Acknowledgments P.F. and E.Y.H. are supported by the Chan Zuckerberg Initiative Ben Barres Career Acceleration Award. E.Y.H. is also supported by the New York Stem Cell Foundation – Robertson Investigator Award. 1
respond to xanthine. They identified that the xanthine receptor AdorA1 was mainly expressed by oligodendrocytes. An increased relative abundance of oligodendrocytes was confirmed by flow cytometry and scRNA-seq of the left amygdala of Miga2−/- mice, which was reversed by depletion of CD4+ T cells. To study the role of AdorA1+ oligodendrocytes in the development of anxiety-like behavior, the authors applied virally mediated knockdown of AdorA1 specifically in oligodendrocytes of the left amygdala. Prevention of AdorA1 expression by oligodendrocytes in the left amygdala significantly ameliorated anxiety-like behavior in Miga2−/- mice. Accordingly, the authors also observed that interferon regulatory factor 1 (IRF1), previously found to accumulate during mitochondrial fission [8], was elevated in CD4+ T cells from Miga2−/- mice and mice exposed to ES. Chromatin immunoprecipitation qPCR in 2
Trends in Immunology, Month 2019, Vol. xx, No. xx
Miga2−/- CD4+ T cells revealed that IRF1 was enriched in the promoter region of several purine synthesis enzymes. Depletion of IRF1 in Miga2TKO mice not only inhibited the expression of purine synthesis enzymes but also rescued the anxiety-like behavior. These series of experiments suggest that stress can disrupt mitochondrial fission in CD4+ T cells, leading to elevated xanthine production and xanthine signaling to amygdalar oligodendrocytes, ultimately promoting abnormal stress-related behaviors [6]. Overall, this tour de force study by Jin’s group provides new insights into the role of CD4+ T cells in mediating stresstriggered behavioral abnormalities in mice. The authors reveal a novel mechanism for neuroimmune interactions by illustrating that enhanced purine metabolism from CD4+ T cells can contribute to the development of anxiety-like behavior (Figure 1). The
Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, CA, USA *Correspondence: [email protected] (P. Fang). https://doi.org/10.1016/j.it.2019.12.007 © 2019 Elsevier Ltd. All rights reserved.
References 1. McEwen, B.S. et al. (2015) Mechanisms of stress in the brain. Nat. Neurosci. 18, 1353–1363 2. Dhabhar, F.S. (2014) Effects of stress on immune function: the good, the bad, and the beautiful. Immunol. Res. 58, 193–210 3. Glaser, R. and Kiecolt-Glaser, J.K. (2005) Stress-induced immune dysfunction: implications for health. Nat. Rev. Immunol. 5, 243–251 4. Bassett, S.A. et al. (2019) Metabolome and microbiome profiling of a stress-sensitive rat model of gut–brain axis dysfunction. Sci. Rep. 9, 14026 5. Miyajima, M. et al. (2017) Metabolic shift induced by systemic activation of T cells in PD-1-deficient mice perturbs brain monoamines and emotional behavior. Nat. Immunol. 18, 1342–1352 6. Fan, K.Q. et al. (2019) Stress-induced metabolic disorder in peripheral CD4+ T cells leads to anxiety-like behavior. Cell 179, 864–879.e19 7. Mishra, P. and Chan, D.C. (2016) Metabolic regulation of mitochondrial dynamics. J. Cell Biol. 212, 379–387 8. Gao, Z. et al. (2017) Mitochondrial dynamics controls antitumour innate immunity by regulating CHIP–IRF1 axis stability. Nat. Commun. 8, 1805
Trends in Immunology
Spotlight
Mitochondrial and Purinergic Dysregulation Promote Abnormal Behavior in Mice Ping Fang1,* and Elaine Y. Hsiao1 Increasing evidence implicates immune dysregulation in the development of neurological disorders. Recent research by Fan and colleagues deepens our understanding of how physical stress alters the immune system to promote anxiety-like behavior. Physical and psychological stressors induce widespread alterations across the immune, endocrine, and nervous systems, predisposing to neurological conditions such as major depression and anxiety disorder [1]. Foundational studies have revealed that stress alters brain function and behavior, leukocyte distribution and cytokine production [2], neurotransmitter and hormone concentrations [3,4], and a variety of biochemicals involved in core metabolism [5]. While both immune and metabolic alterations have been implicated in the risk for anxiety and depression, the molecular and cellular mechanisms for how stresstriggered immune and metabolic pathways lead to long-term brain and behavioral abnormalities remain elusive. A recent study led by Fan et al. highlights a novel role for stress-induced metabolic alterations in peripheral CD4 + T cells in the development of behaviors related to anxiety in mice [6].
prevent the ES-induced behavioral abnormalities in the open field test and elevated plus maze, where reduced exploratory behavior is referred to as ‘anxiety-like behavior’ (Figure 1). This effect was also seen in another physical stress paradigm based on restraint stress (RS), where depletion of CD4+ T cells protected against the development of abnormal stress-induced behavior. To determine whether pathogenic CD4+ T cells were sufficient in promoting abnormal behavior, the authors adoptively transferred splenic CD4+ or CD8+ T cells from ES-treated mice or nontreated controls into Rag1−/mice, which lack T and B cells. Rag1−/mice that received CD4 + T cells from ES-treated mice exhibited elevated anxiety-like behavior relative to controls receiving wild-type (WT) CD4+ T cells. To specify the subset of CD4+ T cells involved, naïve CD4+ T cells or effector CD4+ T cells from ES donors were transferred to Rag1−/- mice. The findings indicated that behavioral abnormalities were sufficiently conferred by naïve CD4+ T cells, but not effector T cells, from EStreated donors [6].
To gain further insight into the molecular features of the pathogenic CD4+ T cells, the authors next compared the transcriptomes between ES-experienced CD4+ T cells relative to CD8+ T cells as negative controls. Numerous genes were differentially expressed, many of which encoded mitochondrial proteins. Consistent with this, ES- and RSexperienced CD4+ T cells exhibited metabolic dysfunction and increased mitochondrial fission relative to nontreated CD4+ T cells, as indicated by reduced glycolysis and oxidative phosphorylation, the presence of punctate mitochondrial morphology, and To evaluate the role of T cells in mediating degraded mitochondrial outer membrane the detrimental effects of physical stress proteins, such as Mitoguardin 2 (Miga2) on behavior, the authors first depleted and Mitofusin 2 (Mfn2). To evaluate a causal CD4+ or CD8+ T cells in mice exposed to relationship between mitochondrial dysfuncelectronic foot shock (ES) for eight con- tion and abnormal behavior, the authors secutive days. Deficiency in CD4+ T cells, found that Miga2−/- mice, which harbor but not CD8+ T cells, was sufficient to highly fragmented mitochondria, exhibited
anxiety-like behavioral abnormalities. In line with their previous findings, depletion of CD4+ T cells prevented anxiety-like symptoms in Miga2−/- mice, again suggesting a role for CD4+ T cells in mediating abnormal behavior. To determine whether mitochondrial abnormalities specifically in CD4+ T cells were sufficient to promote anxietylike behavior, the authors generated CD4+ T-cell-specific conditional knockout (cKO) mice harboring Miga2 (Miga2TKO) or Mfn (MfnTKO) deficiency. Similar to the Miga2−/mice, both cKO mouse strains exhibited anxiety-like behavior relative to their WT littermate controls. Overall, these findings reveal that mitochondrial dysfunction in CD4+ T cells can contribute to the development of anxiety-like behavior in mice [6]. Given that mitochondrial dynamics can regulate cellular metabolism [7], the authors next applied metabolomic profiling to identify likely pathways involved in the ability of CD4+ T cell mitochondrial dysfunction to elicit alterations in animal behavior. Compared with WT littermate controls, Miga2TKO mice displayed elevations in many serum purines, including xanthine, which also accumulated highly in the brain. This particular finding also aligned with the increased abundance of xanthine reported in the sera of human patients with anxiety or depression. To test for a causal role of xanthine, the authors injected WT mice with xanthine intraperitoneally, which sufficiently triggered anxietylike behavior relative to vehicle-injected controls. By contrast, administering a chemical inhibitor of purine metabolism ameliorated the behavioral abnormalities in Miga2TKO mice and ES-treated mice. The authors further examined the potential effect of xanthine on the left amygdala, an area implicated in anxiety disorder. Having observed the accumulation of many nonneuronal cells in the left amygdala compared with the right amygdala of Miga2TKO mice, the authors performed singlecell RNA-seq (scRNA-seq) to define the relevant cell populations that could Trends in Immunology, Month 2019, Vol. xx, No. xx
1
Trends in Immunology
findings in this study warrant continued exploration into whether and how altered metabolites influence neuronal activity to promote the manifestation of behavioral abnormalities. The authors’ findings also raise the question of whether metabolic disruptions triggered by other risk factors, in addition to stress, can promote neurobehavioral abnormalities through a similar neuroimmune–metabolic pathway. While current interventions for depression and anxiety largely target select neurons in the brain itself, this study highlights a striking interaction between the immune system, core metabolism, and animal behavior, providing a foundation for the exploration of novel non-neuronal and peripheral targets for modulating behaviors that are Trends in Immunology + Figure 1. Mitochondrial Dysfunction and Altered Purine Metabolism in CD4 T Cells Can Mediate used to model neurological diseases the Development of Anxiety-like Behavioral Abnormalities in Response to Physical Stress in Mice. in mice. The present study by Fan and colleagues demonstrates that physical stress, including electronic foot shock and physical restraint, enhances mitochondrial fission in peripheral CD4+ T cells, which increases the accumulation of interferon regulatory factor 1 (IRF1) in the promoter region of genes that express purine synthesis enzymes. This mitochondrial dysregulation elevates the concentrations of purine metabolites in both serum and the brain. In particular, elevated xanthine signaling to AdorA1+ oligodendrocytes in the left amygdala leads to the development of anxiety-like behavior in the open field, elevated plus maze, tail suspension, and light-dark box tests [6]. This figure was created using BioRender (https://biorender.com/).
Acknowledgments P.F. and E.Y.H. are supported by the Chan Zuckerberg Initiative Ben Barres Career Acceleration Award. E.Y.H. is also supported by the New York Stem Cell Foundation – Robertson Investigator Award. 1
respond to xanthine. They identified that the xanthine receptor AdorA1 was mainly expressed by oligodendrocytes. An increased relative abundance of oligodendrocytes was confirmed by flow cytometry and scRNA-seq of the left amygdala of Miga2−/- mice, which was reversed by depletion of CD4+ T cells. To study the role of AdorA1+ oligodendrocytes in the development of anxiety-like behavior, the authors applied virally mediated knockdown of AdorA1 specifically in oligodendrocytes of the left amygdala. Prevention of AdorA1 expression by oligodendrocytes in the left amygdala significantly ameliorated anxiety-like behavior in Miga2−/- mice. Accordingly, the authors also observed that interferon regulatory factor 1 (IRF1), previously found to accumulate during mitochondrial fission [8], was elevated in CD4+ T cells from Miga2−/- mice and mice exposed to ES. Chromatin immunoprecipitation qPCR in 2
Trends in Immunology, Month 2019, Vol. xx, No. xx
Miga2−/- CD4+ T cells revealed that IRF1 was enriched in the promoter region of several purine synthesis enzymes. Depletion of IRF1 in Miga2TKO mice not only inhibited the expression of purine synthesis enzymes but also rescued the anxiety-like behavior. These series of experiments suggest that stress can disrupt mitochondrial fission in CD4+ T cells, leading to elevated xanthine production and xanthine signaling to amygdalar oligodendrocytes, ultimately promoting abnormal stress-related behaviors [6]. Overall, this tour de force study by Jin’s group provides new insights into the role of CD4+ T cells in mediating stresstriggered behavioral abnormalities in mice. The authors reveal a novel mechanism for neuroimmune interactions by illustrating that enhanced purine metabolism from CD4+ T cells can contribute to the development of anxiety-like behavior (Figure 1). The
Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, CA, USA *Correspondence: [email protected] (P. Fang). https://doi.org/10.1016/j.it.2019.12.007 © 2019 Elsevier Ltd. All rights reserved.
References 1. McEwen, B.S. et al. (2015) Mechanisms of stress in the brain. Nat. Neurosci. 18, 1353–1363 2. Dhabhar, F.S. (2014) Effects of stress on immune function: the good, the bad, and the beautiful. Immunol. Res. 58, 193–210 3. Glaser, R. and Kiecolt-Glaser, J.K. (2005) Stress-induced immune dysfunction: implications for health. Nat. Rev. Immunol. 5, 243–251 4. Bassett, S.A. et al. (2019) Metabolome and microbiome profiling of a stress-sensitive rat model of gut–brain axis dysfunction. Sci. Rep. 9, 14026 5. Miyajima, M. et al. (2017) Metabolic shift induced by systemic activation of T cells in PD-1-deficient mice perturbs brain monoamines and emotional behavior. Nat. Immunol. 18, 1342–1352 6. Fan, K.Q. et al. (2019) Stress-induced metabolic disorder in peripheral CD4+ T cells leads to anxiety-like behavior. Cell 179, 864–879.e19 7. Mishra, P. and Chan, D.C. (2016) Metabolic regulation of mitochondrial dynamics. J. Cell Biol. 212, 379–387 8. Gao, Z. et al. (2017) Mitochondrial dynamics controls antitumour innate immunity by regulating CHIP–IRF1 axis stability. Nat. Commun. 8, 1805