Munchkin
Full of Fairy Dust
Seriously, I want to get rid of my EP2 right now! I had to shorten this to get it to post so use the link for the whole article!
http://www.jci.org/articles/view/77487
Prostaglandin signaling suppresses beneficial microglial function in Alzheimer’s disease models
Jenny U. Johansson1, Nathaniel S. Woodling1,2, Qian Wang1,Maharshi Panchal1, Xibin Liang1, Angel Trueba-Saiz3, Holden D. Brown1,Siddhita D. Mhatre1, Taylor Loui1 and Katrin I. Andreasson1
1Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California, USA.
2Neurosciences Graduate Program, Stanford University, Stanford, California, USA.
3Functional and Systems Neurobiology Department, Cajal Institute, CSIC, Madrid, Spain.
Address correspondence to: Katrin I. Andreasson, Stanford University School of Medicine, 1201 Welch Road, MSLS P210, Stanford, California 94305, USA. Phone: 650.498.5855; E-mail: [email protected].
First published December 8, 2014
Submitted: June 10, 2014; Accepted: October 30, 2014.
Microglia, the innate immune cells of the CNS, perform critical inflammatory and noninflammatory functions that maintain normal neural function. For example, microglia clear misfolded proteins, elaborate trophic factors, and regulate and terminate toxic inflammation. In Alzheimer’s disease (AD), however, beneficial microglial functions become impaired, accelerating synaptic and neuronal loss. Better understanding of the molecular mechanisms that contribute to microglial dysfunction is an important objective for identifying potential strategies to delay progression to AD. The inflammatory cyclooxygenase/prostaglandin E2 (COX/PGE2) pathway has been implicated in preclinical AD development, both in human epidemiology studies and in transgenic rodent models of AD. Here, we evaluated murine models that recapitulate microglial responses to Aβ peptides and determined that microglia-specific deletion of the gene encoding the PGE2 receptor EP2 restores microglial chemotaxis and Aβ clearance, suppresses toxic inflammation, increases cytoprotective insulin-like growth factor 1 (IGF1) signaling, and prevents synaptic injury and memory deficits. Our findings indicate that EP2 signaling suppresses beneficial microglia functions that falter during AD development and suggest that inhibition of the COX/PGE2/EP2 immune pathway has potential as a strategy to restore healthy microglial function and prevent progression to AD.
1). The widely considered “amyloid hypothesis” of AD causation posits that accumulation of amyloid β42 (Aβ42) triggers inflammation, tau hyperphosphorylation, and synaptic and neuronal loss, leading to cognitive decline (2, 3). Recent studies, however, indicate that brain Aβ42 accumulates in subjects that do not exhibit dementia, which suggests that Aβ42 accumulation may be necessary but not sufficient for development of cognitive impairment (4) and that additional factors are required to tip the balance toward progression to AD dementia.
Recent genetic studies of late-onset AD have identified AD-associated genes that are involved in the innate immune response and are expressed in microglia, the resident myeloid cells of the CNS. Microglial genes associated with AD include CD33 (5–7), TREM2 (8, 9), and CR1 (10,11); together with additional studies (12), these findings are indicative of an important role of microglia in maintaining local brain homeostasis and preventing Aβ42-mediated synaptic and inflammatory injury. Notably, clearance of accumulating Aβ42 is dependent on effective sensing by microglia (mediated by chemokines), followed by Aβ42 degradation. Moreover, prolonged exposure to proinflammatory cytokines or accumulating Aβ42 peptides cause microglia to lose their normal abilities to clear toxic proteins and control inflammation (13,14), a detrimental phenotype in the context of age-associated Aβ42 accumulation. Thus, microglia are emerging as critical regulators of innate immune responses in AD and, more broadly, in other neurodegenerative disorders, and understanding the molecular and cellular mechanisms that cause microglial dysfunction may help identify strategies to restore healthy microglial function and prevent development of AD.
A longstanding observation in epidemiological studies of normal aging populations has been that NSAIDs, which inhibit cyclooxygenase-1 (COX-1) and COX-2 and prostaglandin (PG) production, prevent development of AD (15–18). In addition, early-stage AD is characterized by increased cerebrospinal fluid levels of PGE2 (19, 20), supporting the hypothesis that inflammatory actions of brain COX/PGE2 may underlie preclinical development of AD. Consistently, studies in AD model mice demonstrate reduced amyloid pathology with global deletion of individual PGE2 G protein–coupled receptors (21–23), and additional studies have shown a suppressive signaling effect of the PGE2 receptor EP2 on Aβ42 phagocytosis (24, 25). These studies, along with the recent demonstration of a broad regulatory function of EP2 signaling on cell cycle, cytoskeletal, and immune genes in quiescent microglia (26), suggest that microglial EP2 signaling may be a general suppressor of immune and nonimmune processes that protect against onset and progression of AD pathology. To investigate this hypothesis, we used in vitro and in vivo mouse models that recapitulate acute and chronic aspects of microglial responses to Aβ peptides. Our findings demonstrate that microglial EP2 signaling suppresses multiple processes critical to microglial maintenance of homeostasis in vivo, notably microglial chemokine generation and chemotaxis, clearance of Aβ peptides, resolution of innate inflammatory responses to Aβ42, and trophic factor generation and signaling. We further demonstrate that ablation of microglial EP2 signaling prevents cognitive impairment and loss of synaptic proteins in AD model mice.
27). In addition to their direct disruption of synaptic function, Aβ42 oligomers generate a robust NF-κB– and IFN-regulatory factor 1–dependent (IRF1-dependent) inflammatory response (28) that can secondarily injure synapses and neurons. To determine the function of EP2 signaling in young and aged immune responses to oligomeric Aβ42 peptides, we assayed the effects of the selective EP2 agonist butaprost in macrophages stimulated with Aβ42 oligomers; because yields of viable microglia suitable for culture experiments are very low when harvested from adult brain (29), we examined peritoneal macrophages (which share many properties with microglia) harvested from both young (4 months) and aged (21 months) C57B6/J mice. We found that Ep2 mRNA was significantly induced in aged but not young macrophages in response to Aβ42 oligomers (5 μM; Figure 1A). Consistently, Aβ42 oligomers induced a robust inflammatory transcriptional response in aged but not young macrophages that was further increased by costimulation with 1 μM butaprost (Figure 1B). Aβ42-induced increases in IL-1β generation and secretion were further amplified with butaprost (Figure 1C and Supplemental Figure 1A; supplemental material available online with this article; doi:10.1172/JCI77487DS1), which suggests that myeloid EP2 signaling increases inflammasome generation of IL-1β. Conversely, expression of the chemokines MCP-1 and MIP-1α, which are involved in myeloid cell recruitment to sites of injury, was suppressed with butaprost both basally and with Aβ42 stimulation (Figure 1D and Supplemental Figure 1, B and C). Finally, expression of Aβ peptide clearance enzymes, notablyNeprilysin, Insulysin, and Mmp9, was also suppressed with EP2 activation in Aβ42-stimulated macrophages (Figure 1E). Taken together, these findings demonstrate an age-dependent pattern of gene regulation by EP2 signaling in the context of Aβ42-induced innate immune responses, with induction of proinflammatory factors (including IL-1β, COX-2, iNOS, and NADPH oxidase subunits) and suppression of chemokines and proteases important in microglial migration and Aβ42 oligomer clearance.
http://www.jci.org/articles/view/77487
Prostaglandin signaling suppresses beneficial microglial function in Alzheimer’s disease models
Jenny U. Johansson1, Nathaniel S. Woodling1,2, Qian Wang1,Maharshi Panchal1, Xibin Liang1, Angel Trueba-Saiz3, Holden D. Brown1,Siddhita D. Mhatre1, Taylor Loui1 and Katrin I. Andreasson1
1Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California, USA.
2Neurosciences Graduate Program, Stanford University, Stanford, California, USA.
3Functional and Systems Neurobiology Department, Cajal Institute, CSIC, Madrid, Spain.
Address correspondence to: Katrin I. Andreasson, Stanford University School of Medicine, 1201 Welch Road, MSLS P210, Stanford, California 94305, USA. Phone: 650.498.5855; E-mail: [email protected].
First published December 8, 2014
Submitted: June 10, 2014; Accepted: October 30, 2014.
Microglia, the innate immune cells of the CNS, perform critical inflammatory and noninflammatory functions that maintain normal neural function. For example, microglia clear misfolded proteins, elaborate trophic factors, and regulate and terminate toxic inflammation. In Alzheimer’s disease (AD), however, beneficial microglial functions become impaired, accelerating synaptic and neuronal loss. Better understanding of the molecular mechanisms that contribute to microglial dysfunction is an important objective for identifying potential strategies to delay progression to AD. The inflammatory cyclooxygenase/prostaglandin E2 (COX/PGE2) pathway has been implicated in preclinical AD development, both in human epidemiology studies and in transgenic rodent models of AD. Here, we evaluated murine models that recapitulate microglial responses to Aβ peptides and determined that microglia-specific deletion of the gene encoding the PGE2 receptor EP2 restores microglial chemotaxis and Aβ clearance, suppresses toxic inflammation, increases cytoprotective insulin-like growth factor 1 (IGF1) signaling, and prevents synaptic injury and memory deficits. Our findings indicate that EP2 signaling suppresses beneficial microglia functions that falter during AD development and suggest that inhibition of the COX/PGE2/EP2 immune pathway has potential as a strategy to restore healthy microglial function and prevent progression to AD.
1). The widely considered “amyloid hypothesis” of AD causation posits that accumulation of amyloid β42 (Aβ42) triggers inflammation, tau hyperphosphorylation, and synaptic and neuronal loss, leading to cognitive decline (2, 3). Recent studies, however, indicate that brain Aβ42 accumulates in subjects that do not exhibit dementia, which suggests that Aβ42 accumulation may be necessary but not sufficient for development of cognitive impairment (4) and that additional factors are required to tip the balance toward progression to AD dementia.
Recent genetic studies of late-onset AD have identified AD-associated genes that are involved in the innate immune response and are expressed in microglia, the resident myeloid cells of the CNS. Microglial genes associated with AD include CD33 (5–7), TREM2 (8, 9), and CR1 (10,11); together with additional studies (12), these findings are indicative of an important role of microglia in maintaining local brain homeostasis and preventing Aβ42-mediated synaptic and inflammatory injury. Notably, clearance of accumulating Aβ42 is dependent on effective sensing by microglia (mediated by chemokines), followed by Aβ42 degradation. Moreover, prolonged exposure to proinflammatory cytokines or accumulating Aβ42 peptides cause microglia to lose their normal abilities to clear toxic proteins and control inflammation (13,14), a detrimental phenotype in the context of age-associated Aβ42 accumulation. Thus, microglia are emerging as critical regulators of innate immune responses in AD and, more broadly, in other neurodegenerative disorders, and understanding the molecular and cellular mechanisms that cause microglial dysfunction may help identify strategies to restore healthy microglial function and prevent development of AD.
A longstanding observation in epidemiological studies of normal aging populations has been that NSAIDs, which inhibit cyclooxygenase-1 (COX-1) and COX-2 and prostaglandin (PG) production, prevent development of AD (15–18). In addition, early-stage AD is characterized by increased cerebrospinal fluid levels of PGE2 (19, 20), supporting the hypothesis that inflammatory actions of brain COX/PGE2 may underlie preclinical development of AD. Consistently, studies in AD model mice demonstrate reduced amyloid pathology with global deletion of individual PGE2 G protein–coupled receptors (21–23), and additional studies have shown a suppressive signaling effect of the PGE2 receptor EP2 on Aβ42 phagocytosis (24, 25). These studies, along with the recent demonstration of a broad regulatory function of EP2 signaling on cell cycle, cytoskeletal, and immune genes in quiescent microglia (26), suggest that microglial EP2 signaling may be a general suppressor of immune and nonimmune processes that protect against onset and progression of AD pathology. To investigate this hypothesis, we used in vitro and in vivo mouse models that recapitulate acute and chronic aspects of microglial responses to Aβ peptides. Our findings demonstrate that microglial EP2 signaling suppresses multiple processes critical to microglial maintenance of homeostasis in vivo, notably microglial chemokine generation and chemotaxis, clearance of Aβ peptides, resolution of innate inflammatory responses to Aβ42, and trophic factor generation and signaling. We further demonstrate that ablation of microglial EP2 signaling prevents cognitive impairment and loss of synaptic proteins in AD model mice.
27). In addition to their direct disruption of synaptic function, Aβ42 oligomers generate a robust NF-κB– and IFN-regulatory factor 1–dependent (IRF1-dependent) inflammatory response (28) that can secondarily injure synapses and neurons. To determine the function of EP2 signaling in young and aged immune responses to oligomeric Aβ42 peptides, we assayed the effects of the selective EP2 agonist butaprost in macrophages stimulated with Aβ42 oligomers; because yields of viable microglia suitable for culture experiments are very low when harvested from adult brain (29), we examined peritoneal macrophages (which share many properties with microglia) harvested from both young (4 months) and aged (21 months) C57B6/J mice. We found that Ep2 mRNA was significantly induced in aged but not young macrophages in response to Aβ42 oligomers (5 μM; Figure 1A). Consistently, Aβ42 oligomers induced a robust inflammatory transcriptional response in aged but not young macrophages that was further increased by costimulation with 1 μM butaprost (Figure 1B). Aβ42-induced increases in IL-1β generation and secretion were further amplified with butaprost (Figure 1C and Supplemental Figure 1A; supplemental material available online with this article; doi:10.1172/JCI77487DS1), which suggests that myeloid EP2 signaling increases inflammasome generation of IL-1β. Conversely, expression of the chemokines MCP-1 and MIP-1α, which are involved in myeloid cell recruitment to sites of injury, was suppressed with butaprost both basally and with Aβ42 stimulation (Figure 1D and Supplemental Figure 1, B and C). Finally, expression of Aβ peptide clearance enzymes, notablyNeprilysin, Insulysin, and Mmp9, was also suppressed with EP2 activation in Aβ42-stimulated macrophages (Figure 1E). Taken together, these findings demonstrate an age-dependent pattern of gene regulation by EP2 signaling in the context of Aβ42-induced innate immune responses, with induction of proinflammatory factors (including IL-1β, COX-2, iNOS, and NADPH oxidase subunits) and suppression of chemokines and proteases important in microglial migration and Aβ42 oligomer clearance.
