MerTK-mediated regulation of myelin phagocytosis by macrophages generated from patients with MS

Healy, Luke M.; Jang, Jeong Ho; Won, So-Yoon; Lin, Yun Hsuan; Touil, Hanane; Aljarallah, Salman; Bar‐Or, Amit; Antel, Jack P.

doi:10.1212/nxi.0000000000000402

Cited by 55 publications

(61 citation statements)

References 26 publications

(32 reference statements)

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“…As mentioned again below, products of human lymphoid cells enhance differentiation of fetal human spinal cord OPCs (Zhang et al, ). Optimal myelin repair also requires myeloid cells to clear (phagocytose) myelin debris released as a result of the initial injury process (Healy et al, ). While many of these processes are conserved across species, the comparison of phagocytic activity and repair‐promoting capacity of microglia and astrocytes requires consideration of age‐related changes.…”

Section: Comparison Of the Role Of Inflammation In Physiologic And Pamentioning

confidence: 99%

Species differences in immune‐mediated CNS tissue injury and repair: A (neuro)inflammatory topic

Healy

Yaqubi

Ludwin

et al. 2019

Glia

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Cells of the adaptive and innate immune systems in the brain parenchyma and in the meningeal spaces contribute to physiologic functions and disease states in the central nervous system (CNS). Animal studies have demonstrated the involvement of immune constituents, along with major histocompatibility complex (MHC) molecules, in neural development and rare genetic disorders (e.g., colony stimulating factor 1 receptor [CSF1R] deficiency). Genome wide association studies suggest a comparable role of the immune system in humans. Although the CNS can be the target of primary autoimmune disorders, no current experimental model captures all of the features of the most common human disorder placed in this category, multiple sclerosis (MS). Such features include spontaneous onset, environmental contributions, and a recurrent/progressive disease course in a genetically predisposed host. Numerous therapeutic interventions related to antigen and cytokine specific therapies have demonstrated effectiveness in experimental autoimmune encephalomyelitis (EAE), the animal model used to define principles underlying immune‐mediated mechanisms in MS. Despite the similarities in the two diseases, most treatments used to ameliorate EAE have failed to translate to the human disease. As directly demonstrated in animal models and implicated by correlative studies in humans, adaptive and innate immune constituents within the systemic compartment and resident in the CNS contribute to the disease course of neurodegenerative and neurobehavioral disorders. The expanding knowledge of the molecular properties of glial cells provides increasing insights into species related variables. These variables affect glial bidirectional interactions with the immune system as well as their own production of “immune molecules” that mediate tissue injury and repair.

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Section: Comparison Of the Role Of Inflammation In Physiologic And Pamentioning

confidence: 99%

Species differences in immune‐mediated CNS tissue injury and repair: A (neuro)inflammatory topic

Healy

Yaqubi

Ludwin

et al. 2019

Glia

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“…MerTK, which is associated with phagocytosis of apoptotic cells and cellular debris 30,46 , was modestly increased in Dex microparticle-treated cells compared to untreated controls (p<0.07). Contrary to our expectation, we did not observe a significant increase in expression of CCR2, a homing-associated receptor, in cells treated with free Dex or Dex microparticles ( Fig.…”

Section: Intracellular Dex Microparticles Modulate and Maintain Macromentioning

confidence: 93%

Non-Genetic Reprogramming of Monocytes via Microparticle Phagocytosis for Sustained Modulation of Macrophage Phenotype

Wofford

Singh

Cullen

et al. 2019

Preprint

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Monocyte-derived macrophages orchestrate tissue regeneration by homing to sites of injury, phagocytosing pathological debris, and stimulating other cell types to repair the tissue. Accordingly, monocytes have been investigated as a translational and potent source for cell therapy, but their utility has been hampered by their rapid acquisition of a pro-inflammatory phenotype in response to the inflammatory injury microenvironment. To overcome this problem, we designed a cell therapy strategy where we collect and exogenously reprogram monocytes by intracellularly loading the cells with biodegradable microparticles containing an anti-inflammatory drug in order to modulate and maintain an anti-inflammatory phenotype over time. To test this concept, poly(lactic-co-glycolic) acid microparticles were loaded with the anti-inflammatory drug dexamethasone (Dex) and administered to primary human monocytes for four hours to facilitate phagocytic uptake. After removal of non-phagocytosed microparticles, microparticle-loaded monocytes differentiated into macrophages and stored the microparticles intracellularly for several weeks in vitro, releasing drug into the extracellular environment over time. Cells loaded with intracellular Dex microparticles showed decreased expression and secretion of inflammatory factors even in the presence of pro-inflammatory stimuli up to 7 days after microparticle uptake compared to untreated cells or cells loaded with blank microparticles. This study represents a new strategy for long-term maintenance of anti-inflammatory macrophage phenotype using a translational monocyte-based cell therapy strategy without the use of genetic modification. Because of the ubiquitous nature of monocytederived macrophage involvement in pathology and regeneration, this strategy holds potential as a treatment for a vast number of diseases and disorders. RESULTS Microparticle Characteristics and Intracellular StabilityPoly(lactic-co-glycolic) acid (PLGA) microparticles were fabricated with dexamethasone (Dex) or with tetramethylrhodamine (TRITC) as a fluorescent model drug. Microparticles ranged in diameter from 0.98 to 2.05 µm with polydispersity indices between 0.08 and 0.28 ( Fig. 2A).Microparticles were administered to primary human monocytes for 4 hours followed by removal of non-phagocytosed microparticles. Thereafter, monocytes were cultured in macrophage colony stimulating factor (MCSF)-containing media to induce differentiation into macrophages and were imaged at regular intervals (Fig. 2B). Cell area increased over time for both untreated and microparticle-loaded cells, indicating that that monocyte-to-macrophage differentiation was not hindered by intracellular microparticle loading (Fig. 2C). Intracellular fluorescent microparticles were detected for up to 16 days in vitro (detection and quantification methods outlined in Sup. Fig. 1). Interestingly, the number of microparticles ( Fig. 2D) and their intensity per cell ( Fig. 2E) increased in the first three days, which may be due to cell death, phagocytosi...

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“…MerTK deficiency results in delayed remyelination in the cuprizone model of demyelination (7). MDMs derived from MS patients show impaired ability to phagocytose myelin, a defect linked to a reduction in MerTK expression (8). In addition to clearing myelin debris, MerTK mediates the process of efferocytosis, the removal of dead/dying cells, which is important for autoreactive T-cell fate determination in MS (9).…”

Section: Introductionmentioning

confidence: 99%

Vitamin D regulates MerTK-dependent phagocytosis in human myeloid cells

Clarke

Yaqubi

Futhey

et al. 2020

Preprint

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Vitamin D deficiency is a major environmental risk factor for the development of multiple 1 sclerosis (MS). The major circulating metabolite of vitamin D (25OHD) is converted to the 2 active form (calcitriol) by the hydroxylase enzyme CYP27B1. In MS lesions the tyrosine kinase 3MerTK expressed by microglia and macrophages regulates phagocytosis of myelin debris and 4 apoptotic cells that can accumulate and inhibit tissue repair and remyelination. We show that 5 calcitriol downregulates MerTK mRNA and protein expression in adult human microglia and 6 monocyte-derived macrophages, thereby inhibiting myelin phagocytosis and apoptotic cell 7 clearance. Proinflammatory myeloid cells express high levels of CYP27B1 compared to 8 homeostatic (TGFβ-treated) myeloid cells. Only proinflammatory cells in the presence of TNF-α 9 generate calcitriol from 25OHD, resulting in repression of MerTK expression and function. The 10 selective production of calcitriol in proinflammatory myeloid cells leading to downregulation of 11 MerTK-mediated phagocytosis has the potential to reduce the risk for auto-antigen presentation 12 while retaining the phagocytic ability of homeostatic myeloid cells, thereby contributing to 13 inflammation reduction and enhanced tissue repair. 14 cuprizone model of demyelination (7). MDMs derived from MS patients show impaired ability 38 to phagocytose myelin, a defect linked to a reduction in MerTK expression (8). In addition to 39 clearing myelin debris, MerTK mediates the process of efferocytosis, the removal of dead/dying 40 cells, which is important for autoreactive T-cell fate determination in MS (9). The functions of 41 myeloid cells are dependent on their state of activation. TGFβ, a key cytokine involved in CNS 42 homeostasis, has been shown to maintain cells in a homeostatic state characterized by high 43 expression of MerTK, TREM2, CSF1R and Mafb (10). In contrast, MerTK expression is 44 comparatively lower in proinflammatory myeloid cells, a population shown to contribute to MS 45 pathogenesis (6). Genome-wide association studies (GWAS) have explained much of MS 46 heritability. Single nucleotide polymorphisms (SNPs) in CYP24A1 and CYP27B1, which tightly 47 Methods 61Monocyte-derived macrophages -Human peripheral blood mononuclear cells (PBMCs) were 62 isolated from healthy donors by Ficoll-Hypaque density gradient centrifugation (GE healthcare). 63Monocytes were isolated from PBMCs using magnetic CD14+ isolation beads (Miltenyi). 64Proinflammatory (MØ GMcsf ) and alternative (M2) macrophages were generated by differentiating 65 monocytes for 6 days in the presence of 25ng/mL GM-CSF and M-CSF respectively. To 66 generate CNS homeostatic (MØ 0 ) macrophages, TGFβ (50ng/mL) was added to the M-CSF 67 culture conditions on days 3 and 6. 10 -7 M calcitriol (Selleckchem) was added to designated 68 macrophages on day 1 of culture and maintained throughout differentiation. Culture media was 69 replenished every 2-3 days. 70Microglia & astrocytes -Human adult microglia were isolated from brain tissue of ...

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MerTK-mediated regulation of myelin phagocytosis by macrophages generated from patients with MS

Cited by 55 publications

References 26 publications

Species differences in immune‐mediated CNS tissue injury and repair: A (neuro)inflammatory topic

Species differences in immune‐mediated CNS tissue injury and repair: A (neuro)inflammatory topic

Non-Genetic Reprogramming of Monocytes via Microparticle Phagocytosis for Sustained Modulation of Macrophage Phenotype

Vitamin D regulates MerTK-dependent phagocytosis in human myeloid cells

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