Human IgM antibody rHIgM22 promotes phagocytic clearance of myelin debris by microglia

Abstract

In multiple sclerosis (MS), demyelinated CNS lesions fail to sufficiently remyelinate, despite the presence of oligodendrocyte precursor cells (OPCs) capable of differentiating into mature oligodendrocytes. MS lesions contain damaged myelin debris that can inhibit OPC maturation and hinder repair. rHIgM22 is an experimental human recombinant IgM antibody that promotes remyelination in animal models and is being examined in patients with MS. rHIgM22 binds to CNS myelin and partially rescues OPC process outgrowth on myelin. Since rHIgM22 does not affect OPC process outgrowth in vitro on permissive substrate, we examined the possibility that it acts by enhancing phagocytic clearance of myelin debris by microglia. In this study, we tested if rHIgM22 binding could tag myelin for microglial phagocytosis. A mouse microglial cell line and primary rat microglia were treated with myelin and rHIgM22 and assayed for myelin phagocytosis. We found that: 1) rHIgM22 stimulates myelin phagocytosis in a dose-dependent manner; 2) rHIgM22-mediated myelin phagocytosis requires actin polymerization; and 3) rHIgM22-stimulation of myelin phagocytosis requires activity of rHIgM22 Fc domain and activation of Complement Receptor 3. Since myelin inhibits OPC differentiation, stimulation of phagocytic clearance of damaged myelin may be an important means by which rHIgM22 promotes remyelination.

Activated human astrocyte‐derived extracellular vesicles modulate neuronal uptake, differentiation and firing

“…For integrins inhibition experiment, final concentration of 0.1 or 0.1 μM RGD peptide was pre‐treated with the same amount of IL‐1β‐ADEVs at 37°C for 30 min, thereafter adding to DIV 10 neurons in EV‐depleted neuronal culture medium at a density of 50,000 cells/well in 24‐well plates. Time‐lapse images of ADEV uptake by neurons were obtained using a live cell imaging system (IncuCyte ZOOM system, Essen BioScience, Ann Arbor, MI) in a humidity chamber at 37°C and 5% CO 2 as previously described [24]. Images were acquired from 16 fields per culture well every 6 h for total 72 h and further processed in Incucyte software (2019A) for analysis.…”

“…Time-lapse images of ADEV uptake by neurons were obtained using a live cell imaging system (IncuCyte ZOOM system, Essen BioScience, Ann Arbor, MI) in a humidity chamber at 37°C and 5% CO 2 as previously described [24]. Images were acquired from 16 fields per culture well every 6 h for total 72 h and further processed in Incucyte software (2019A) for analysis.…”

Sphingosine 1-Phosphate Receptors and Metabolic Enzymes as Druggable Targets for Brain Diseases

“…It was shown to enter the CNS and to accumulate at the lesion sites in MS (Pirko et al, 2004) and to promote remyelination in Theiler’s murine encephalomyelitis virus (Warrington et al, 2000)-, lysolecithin (Bieber et al, 2002)-, and cuprizone-induced (Mullin et al, 2017) demyelination models of MS. A 16-site Phase 1 clinical trial in MS patients completed in 2015 (NCT0183867) showed no dose-limiting toxicities, no serious treatment-emergent adverse events, and the presence of the antibody in the CFS in all patients (Eisen et al, 2017). Although some studies suggest that the rHIgM22 remyelination-promoting effect is exerted directly on myelin-producing cells (Watzlawik et al, 2010; Watzlawik et al, 2013), others suggest that it acts on other cell types present in the lesion niche, including astrocytes (Paz Soldan et al, 2003) and microglia (Zorina et al, 2018). We recently showed that rHIgM22 stimulated the proliferation of astrocytes in mixed glial cells because of the increased production and release of S1P, suggesting that S1P signaling might be significant in the interplay of different cell types involved in the complex series of events eventually leading to myelin repair (Grassi et al, 2019).…”

Myelin Repair: From Animal Models to Humans

“…No drug is currently available for specifically preventing the aging-induced decrease in microglial phagocytosis, although several candidate molecules have been identified (Pinto and Fernandes, 2020). These molecules include two polyunsaturated fatty acids (DHA and EPA) (Chen et al, 2014), the endocannabinoid 2-AG (Mecha et al, 2019), and an experimental recombinant human antibody rhIGM22 (Zorina et al, 2018). Vitamin B 3 (niacin) also seems to be a promising compound for safely enhancing myelin phagocytosis by microglia (Rawji et al, 2020).…”