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LRP1 expression in microglia is protective during CNS autoimmunity.

Chuang TY, Guo Y, Seki SM, Rosen AM, Johanson DM, Mandell JW, Lucchinetti CF, Gaultier A - Acta Neuropathol Commun (2016)

Bottom Line: While T cells are known orchestrators of the immune response leading to MS pathology, the precise contribution of CNS resident and peripheral infiltrating myeloid cells is less well described.We further show that the increased disease severity in experimental autoimmune encephalomyelitis is not due to haplodeficiency of the Cx3cr1 locus.At the cellular level, microglia lacking LRP1 adopt a pro-inflammatory phenotype characterized by amoeboid morphology and increased production of the inflammatory mediator TNF-α.

View Article: PubMed Central - PubMed

Affiliation: Center for Brain Immunology and Glia, Department of Neuroscience, University of Virginia, Charlottesville, VA, USA.

ABSTRACT
Multiple sclerosis is a devastating neurological disorder characterized by the autoimmune destruction of the central nervous system myelin. While T cells are known orchestrators of the immune response leading to MS pathology, the precise contribution of CNS resident and peripheral infiltrating myeloid cells is less well described. Here, we explore the myeloid cell function of Low-density lipoprotein receptor-related protein-1 (LRP1), a scavenger receptor involved in myelin clearance and the inflammatory response, in the context of Multiple sclerosis. Supporting its central role in Multiple sclerosis pathology, we find that LRP1 expression is increased in Multiple sclerosis lesions in comparison to the surrounding healthy tissue. Using two genetic mouse models, we show that deletion of LRP1 in microglia, but not in peripheral macrophages, negatively impacts the progression of experimental autoimmune encephalomyelitis, an animal model of Multiple sclerosis. We further show that the increased disease severity in experimental autoimmune encephalomyelitis is not due to haplodeficiency of the Cx3cr1 locus. At the cellular level, microglia lacking LRP1 adopt a pro-inflammatory phenotype characterized by amoeboid morphology and increased production of the inflammatory mediator TNF-α. We also show that LRP1 functions as a robust inhibitor of NF-kB activation in myeloid cells via a MyD88 dependent pathway, potentially explaining the increase in disease severity observed in mice lacking LRP1 expression in microglia. Taken together, our data suggest that the function of LRP1 in microglia is to keep these cells in an anti-inflammatory and neuroprotective status during inflammatory insult, including experimental autoimmune encephalomyelitis and potentially in Multiple sclerosis.

No MeSH data available.


Related in: MedlinePlus

LRP1 deficient microglia have an amoeboid morphology. Cx3cr1creER-Lrp1fl/fl and Lrp1fl/fl mice were injected daily with LPS (1 mg/kg) for 4 consecutive days. Brain sections were stained with Iba1 antibody, imaged by confocal microscopy and analyzed with ImageJ. a Representative images of microglia and b corresponding Sholl analyses. *p < 0.05; **p < 0.01; ***p < 0.001, 2-way ANOVA. (Scale bar = 60 μm). c Soma size of the microglia. 10 microglia per animal were quantified for each experimental group. **p < 0.01, Student’s t-test. d Quantification of area covered by Iba1+ microglia per image. *p < 0.05, Student’s t-test. e Numbers of microglia per unit area (n = 3–4 mice per condition). Values represent mean ± s.e.m
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Fig5: LRP1 deficient microglia have an amoeboid morphology. Cx3cr1creER-Lrp1fl/fl and Lrp1fl/fl mice were injected daily with LPS (1 mg/kg) for 4 consecutive days. Brain sections were stained with Iba1 antibody, imaged by confocal microscopy and analyzed with ImageJ. a Representative images of microglia and b corresponding Sholl analyses. *p < 0.05; **p < 0.01; ***p < 0.001, 2-way ANOVA. (Scale bar = 60 μm). c Soma size of the microglia. 10 microglia per animal were quantified for each experimental group. **p < 0.01, Student’s t-test. d Quantification of area covered by Iba1+ microglia per image. *p < 0.05, Student’s t-test. e Numbers of microglia per unit area (n = 3–4 mice per condition). Values represent mean ± s.e.m

Mentions: Since our results suggested that T cell and BBB function is normal in the absence of LRP1 expression in CX3CR1 positive cells, we hypothesized that the increased disease severity is due to an intrinsic function of LRP1 in microglia. Therefore, we analyzed the morphology of microglia in the cortex of Cx3cr1creER-Lrp1fl/fl and control mice at both the resting state, and after inducing microgliosis via peripheral administration of LPS for 4 consecutive days, as described [37]. LRP1 status in microglia did not affect the weight of the animals injected with LPS (Additional file 1: Figure S4). We chose this model instead of EAE because of the lack of good markers to differentiate microglia from peripheral myeloid cells by immunochemistry. Because this model of neuroinflammation lacks recruitment of peripheral immune cells, a more focused analysis of microglia morphology is possible [37]. Brain sections were stained with Iba1 specific antibody and microglial ramifications were quantified by Sholl analysis in the cortex (Fig. 5a-b). In the healthy control mice, microglia appear thin and ramified (Fig. 5b, grey curve) [37]. Surprisingly, microglia lacking LRP1 expression appeared more amoeboid than the control cells at baseline, with a denser cell body and thickened proximal dendrites (Fig. 5b, grey vs. orange curves). Whereas LPS administration in control mice leads to the transition of microglial morphology into the bushy and thickened appearance (Fig. 5b, grey vs black curves), LPS had no effect on the appearance and branching of LRP1 deficient microglia (Fig. 5b, orange vs red curves). LPS administration significantly increased the soma size of control microglia, but not the microglia lacking LRP1 expression (Fig. 5c). Quantification of the area covered by Iba1+ cells confirms that LRP1 deletion leads to microglial hypertrophy. The morphology of these LRP1 deficient microglia are similar in appearance to the microglia observed in LPS treated control mice (Fig. 5d). These morphological changes were not associated with an overall change in numbers of microglia (Fig. 5e). Our results suggest that the removal of LRP1 alters microglial morphology in a manner similar to treatment with LPS, a potent neuroinflammatory stimulus.Fig. 5


LRP1 expression in microglia is protective during CNS autoimmunity.

Chuang TY, Guo Y, Seki SM, Rosen AM, Johanson DM, Mandell JW, Lucchinetti CF, Gaultier A - Acta Neuropathol Commun (2016)

LRP1 deficient microglia have an amoeboid morphology. Cx3cr1creER-Lrp1fl/fl and Lrp1fl/fl mice were injected daily with LPS (1 mg/kg) for 4 consecutive days. Brain sections were stained with Iba1 antibody, imaged by confocal microscopy and analyzed with ImageJ. a Representative images of microglia and b corresponding Sholl analyses. *p < 0.05; **p < 0.01; ***p < 0.001, 2-way ANOVA. (Scale bar = 60 μm). c Soma size of the microglia. 10 microglia per animal were quantified for each experimental group. **p < 0.01, Student’s t-test. d Quantification of area covered by Iba1+ microglia per image. *p < 0.05, Student’s t-test. e Numbers of microglia per unit area (n = 3–4 mice per condition). Values represent mean ± s.e.m
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Fig5: LRP1 deficient microglia have an amoeboid morphology. Cx3cr1creER-Lrp1fl/fl and Lrp1fl/fl mice were injected daily with LPS (1 mg/kg) for 4 consecutive days. Brain sections were stained with Iba1 antibody, imaged by confocal microscopy and analyzed with ImageJ. a Representative images of microglia and b corresponding Sholl analyses. *p < 0.05; **p < 0.01; ***p < 0.001, 2-way ANOVA. (Scale bar = 60 μm). c Soma size of the microglia. 10 microglia per animal were quantified for each experimental group. **p < 0.01, Student’s t-test. d Quantification of area covered by Iba1+ microglia per image. *p < 0.05, Student’s t-test. e Numbers of microglia per unit area (n = 3–4 mice per condition). Values represent mean ± s.e.m
Mentions: Since our results suggested that T cell and BBB function is normal in the absence of LRP1 expression in CX3CR1 positive cells, we hypothesized that the increased disease severity is due to an intrinsic function of LRP1 in microglia. Therefore, we analyzed the morphology of microglia in the cortex of Cx3cr1creER-Lrp1fl/fl and control mice at both the resting state, and after inducing microgliosis via peripheral administration of LPS for 4 consecutive days, as described [37]. LRP1 status in microglia did not affect the weight of the animals injected with LPS (Additional file 1: Figure S4). We chose this model instead of EAE because of the lack of good markers to differentiate microglia from peripheral myeloid cells by immunochemistry. Because this model of neuroinflammation lacks recruitment of peripheral immune cells, a more focused analysis of microglia morphology is possible [37]. Brain sections were stained with Iba1 specific antibody and microglial ramifications were quantified by Sholl analysis in the cortex (Fig. 5a-b). In the healthy control mice, microglia appear thin and ramified (Fig. 5b, grey curve) [37]. Surprisingly, microglia lacking LRP1 expression appeared more amoeboid than the control cells at baseline, with a denser cell body and thickened proximal dendrites (Fig. 5b, grey vs. orange curves). Whereas LPS administration in control mice leads to the transition of microglial morphology into the bushy and thickened appearance (Fig. 5b, grey vs black curves), LPS had no effect on the appearance and branching of LRP1 deficient microglia (Fig. 5b, orange vs red curves). LPS administration significantly increased the soma size of control microglia, but not the microglia lacking LRP1 expression (Fig. 5c). Quantification of the area covered by Iba1+ cells confirms that LRP1 deletion leads to microglial hypertrophy. The morphology of these LRP1 deficient microglia are similar in appearance to the microglia observed in LPS treated control mice (Fig. 5d). These morphological changes were not associated with an overall change in numbers of microglia (Fig. 5e). Our results suggest that the removal of LRP1 alters microglial morphology in a manner similar to treatment with LPS, a potent neuroinflammatory stimulus.Fig. 5

Bottom Line: While T cells are known orchestrators of the immune response leading to MS pathology, the precise contribution of CNS resident and peripheral infiltrating myeloid cells is less well described.We further show that the increased disease severity in experimental autoimmune encephalomyelitis is not due to haplodeficiency of the Cx3cr1 locus.At the cellular level, microglia lacking LRP1 adopt a pro-inflammatory phenotype characterized by amoeboid morphology and increased production of the inflammatory mediator TNF-α.

View Article: PubMed Central - PubMed

Affiliation: Center for Brain Immunology and Glia, Department of Neuroscience, University of Virginia, Charlottesville, VA, USA.

ABSTRACT
Multiple sclerosis is a devastating neurological disorder characterized by the autoimmune destruction of the central nervous system myelin. While T cells are known orchestrators of the immune response leading to MS pathology, the precise contribution of CNS resident and peripheral infiltrating myeloid cells is less well described. Here, we explore the myeloid cell function of Low-density lipoprotein receptor-related protein-1 (LRP1), a scavenger receptor involved in myelin clearance and the inflammatory response, in the context of Multiple sclerosis. Supporting its central role in Multiple sclerosis pathology, we find that LRP1 expression is increased in Multiple sclerosis lesions in comparison to the surrounding healthy tissue. Using two genetic mouse models, we show that deletion of LRP1 in microglia, but not in peripheral macrophages, negatively impacts the progression of experimental autoimmune encephalomyelitis, an animal model of Multiple sclerosis. We further show that the increased disease severity in experimental autoimmune encephalomyelitis is not due to haplodeficiency of the Cx3cr1 locus. At the cellular level, microglia lacking LRP1 adopt a pro-inflammatory phenotype characterized by amoeboid morphology and increased production of the inflammatory mediator TNF-α. We also show that LRP1 functions as a robust inhibitor of NF-kB activation in myeloid cells via a MyD88 dependent pathway, potentially explaining the increase in disease severity observed in mice lacking LRP1 expression in microglia. Taken together, our data suggest that the function of LRP1 in microglia is to keep these cells in an anti-inflammatory and neuroprotective status during inflammatory insult, including experimental autoimmune encephalomyelitis and potentially in Multiple sclerosis.

No MeSH data available.


Related in: MedlinePlus