Limits...
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 is an inhibitor of NF-kB through the MyD88 pathway. a Macrophages isolated from Cx3cr1cre-Lrp1fl/fl (LRP1-) and Lrp1fl/fl (LRP1+) mice were treated with LPS (1 μg/ml) and the expression of p-p65, p65, LRP1 and actin were determined by immunoblot. Representative of 3 independent experiments). b LRP1+ and LRP1- macrophages were treated with TLR ligands and expression of IL-6 was determined by qPCR analysis. *p < 0.05; Student’s t-test, mean ± s.e.m
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4940960&req=5

Fig7: LRP1 is an inhibitor of NF-kB through the MyD88 pathway. a Macrophages isolated from Cx3cr1cre-Lrp1fl/fl (LRP1-) and Lrp1fl/fl (LRP1+) mice were treated with LPS (1 μg/ml) and the expression of p-p65, p65, LRP1 and actin were determined by immunoblot. Representative of 3 independent experiments). b LRP1+ and LRP1- macrophages were treated with TLR ligands and expression of IL-6 was determined by qPCR analysis. *p < 0.05; Student’s t-test, mean ± s.e.m

Mentions: Production of cytokines, like TNF-α, IL-6 and IL-1β, is tightly controlled via signaling through NF-kB, a transcriptional master regulator of the inflammatory response [39]. Indeed, recent studies have demonstrated that blocking NF-kB activation specifically in microglia is sufficient to offer protection during EAE [9]. Previous reports have highlighted the fact that LRP1 can act as an inhibitor of inflammation through regulation of NF-kB activity [15]. We therefore hypothesized that LRP1 may function as a regulator of NF-kB mediated inflammatory response in microglia. Because the inflammatory mediator production appears similar in cultured microglia and BMDM lacking LRP1 (Fig. 6), we began by treating Lrp1fl/fl and Cx3cr1cre-Lrp1fl/fl BMDM with LPS and collecting protein extracts at several time points after stimulation. Protein extracts were analyzed for the phosphorylation status of the NF-kB subunit p65. As is shown in Fig. 7a, LPS stimulated LRP1 deficient macrophages have increased levels of phosphorylated p65 (p-p65), in comparison to control cells. LPS is the only Toll-like receptor (TLR) ligand known to activate two different signaling pathways: the MyD88 and the TRIF pathway [39]. To elucidate which arm of the signaling cascade is regulated by LRP1, we treated BMDM with a panel of TLR ligands that are associated with the TRIF (TLR3 ligand: PolyI:C), or the MyD88 adaptor response (TLR1 and 2 ligand: Pam3CSK4; TLR5 ligand: FLA-ST; TLR6 ligand: FSL-1; TLR9 ligand: ODN1826) [40]. BMDM were treated for 3 h and IL-6 expression was determined by qPCR analysis. IL-6 expression was increased in LRP1 deficient macrophages when the MyD88 pathway was engaged by the activation of TLR 1, 2, 4, 5, 6, and 9. On the contrary, TLR3-mediated production of IL-6 was not affected by the status of LRP1, showing that LRP1 may inhibit the NF-kB signaling pathway in a MyD88, but not TRIF dependent manner (Fig. 7b). Together, these results suggest that LRP1 functions as a regulator of NF-kB activity through modulation of the MyD88 dependent arm of the inflammatory response. This function of LRP1 might explain why its removal in the microglial compartment is detrimental during CNS autoimmunity.Fig. 7


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 is an inhibitor of NF-kB through the MyD88 pathway. a Macrophages isolated from Cx3cr1cre-Lrp1fl/fl (LRP1-) and Lrp1fl/fl (LRP1+) mice were treated with LPS (1 μg/ml) and the expression of p-p65, p65, LRP1 and actin were determined by immunoblot. Representative of 3 independent experiments). b LRP1+ and LRP1- macrophages were treated with TLR ligands and expression of IL-6 was determined by qPCR analysis. *p < 0.05; Student’s t-test, mean ± s.e.m
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4940960&req=5

Fig7: LRP1 is an inhibitor of NF-kB through the MyD88 pathway. a Macrophages isolated from Cx3cr1cre-Lrp1fl/fl (LRP1-) and Lrp1fl/fl (LRP1+) mice were treated with LPS (1 μg/ml) and the expression of p-p65, p65, LRP1 and actin were determined by immunoblot. Representative of 3 independent experiments). b LRP1+ and LRP1- macrophages were treated with TLR ligands and expression of IL-6 was determined by qPCR analysis. *p < 0.05; Student’s t-test, mean ± s.e.m
Mentions: Production of cytokines, like TNF-α, IL-6 and IL-1β, is tightly controlled via signaling through NF-kB, a transcriptional master regulator of the inflammatory response [39]. Indeed, recent studies have demonstrated that blocking NF-kB activation specifically in microglia is sufficient to offer protection during EAE [9]. Previous reports have highlighted the fact that LRP1 can act as an inhibitor of inflammation through regulation of NF-kB activity [15]. We therefore hypothesized that LRP1 may function as a regulator of NF-kB mediated inflammatory response in microglia. Because the inflammatory mediator production appears similar in cultured microglia and BMDM lacking LRP1 (Fig. 6), we began by treating Lrp1fl/fl and Cx3cr1cre-Lrp1fl/fl BMDM with LPS and collecting protein extracts at several time points after stimulation. Protein extracts were analyzed for the phosphorylation status of the NF-kB subunit p65. As is shown in Fig. 7a, LPS stimulated LRP1 deficient macrophages have increased levels of phosphorylated p65 (p-p65), in comparison to control cells. LPS is the only Toll-like receptor (TLR) ligand known to activate two different signaling pathways: the MyD88 and the TRIF pathway [39]. To elucidate which arm of the signaling cascade is regulated by LRP1, we treated BMDM with a panel of TLR ligands that are associated with the TRIF (TLR3 ligand: PolyI:C), or the MyD88 adaptor response (TLR1 and 2 ligand: Pam3CSK4; TLR5 ligand: FLA-ST; TLR6 ligand: FSL-1; TLR9 ligand: ODN1826) [40]. BMDM were treated for 3 h and IL-6 expression was determined by qPCR analysis. IL-6 expression was increased in LRP1 deficient macrophages when the MyD88 pathway was engaged by the activation of TLR 1, 2, 4, 5, 6, and 9. On the contrary, TLR3-mediated production of IL-6 was not affected by the status of LRP1, showing that LRP1 may inhibit the NF-kB signaling pathway in a MyD88, but not TRIF dependent manner (Fig. 7b). Together, these results suggest that LRP1 functions as a regulator of NF-kB activity through modulation of the MyD88 dependent arm of the inflammatory response. This function of LRP1 might explain why its removal in the microglial compartment is detrimental during CNS autoimmunity.Fig. 7

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