Human remyelination promoting antibody inhibits apoptotic signaling and differentiation through Lyn kinase in primary rat oligodendrocytes

Abstract

Purpose-Human remyelination promoting IgM mAbs target oligodendrocytes (OLs) and function in animal models of multiple sclerosis (MS). However, their mechanism of action is unknown. This study seeks to identify the cellular mechanism of action of a recombinant human IgM on OL survival.Methods-Binding of rHIgM22 to the surface of rat OLs was studied by co-localization with various markers. RHIgM22-mediated effects on apoptotic signaling in OLs, differentiation markers and signaling molecules were detected by Western blotting and immunoprecipitation.Results-RHIgM22 co-localized with integrin β3 but not other integrin β-chains in OLs. Downstream of integrin β3 we identified Src family kinase (SFK) Lyn as a key player of rHIgM22-mediated actions in OLs. Lyn immunoprecipitated in a complex together with integrin αvβ3 and PDGFαR. Lyn expression was 9 fold up-regulated and Lyn activation was 3 fold higher in rHIgM22-treated OL cultures compared to controls. RHIgM22 inhibited apoptotic signaling by greater than 10 fold reduction of caspase-3 and capsase-9 cleavage and reduced by 4 fold expression of differentiation markers MBP and MOG in OLs. SFK inhibitors PP2 and SU6656 inhibited Lyn activity and restored caspase-cleavage in OLs. A human IgM that did not promote remyelination and medium were used as controls.Conclusions-rHIgM22 prevented apoptotic signaling and inhibited OL differentiation by Lyn implying that IgM-mediated remyelination is due to protection of OPC and OLs rather than promotion of OPC differentiation.

Human-derived natural antibodies: biomarkers and potential therapeutics

“…However, it is clear that the antigen(s) of IgM22 can be presented to activate natural IgM production without inducing autoimmunity. As previously mentioned, HIgM22 can mediate signaling to promote oligodendrocyte precursor cell proliferation in cultured mixed glia [86] and accelerate myelin repair in vivo [4]. This finding has provided evidence that, in addition to regulating the immune system, natural IgMs signal the neural cells directly and/or indirectly to mediate a novel CNS function distinctive to the traditional view of natural IgMs in maintaining homeostasis.…”

Adult oligodendrocyte progenitor cells – Multifaceted regulators of the CNS in health and disease

“…The impact of these molecules on OPCs remains controversial, with reports suggesting both a beneficial outcome on myelination and induction of OPC death. For example, TNFα is highly expressed in demyelinating MS lesions and has been shown to potentiate IFN-γ-induced cell death in vitro (Andrews et al, 1998; Watzlawik et al, 2010). Arnett et al showed a modest delay in cuprizone-induced oligodendrocyte death in TNF-α knockout mice, implicating it as a potentially harmful cytokine (Arnett et al, 2001).…”

Treatment with a recombinant human IgM that recognizes PSA-NCAM preserves brain pathology in MOG-induced experimental autoimmune encephalomyelitis

“…rHIgM22 is a true human monoclonal antibody that crosses the blood brain barrier [23,24] and targets demyelinating lesions [25]. This antibody increases Ca 2+ signaling in oligodendrocytes and astrocytes [26] stimulates proliferation of progenitor oligodendrocytes by reorganizing plasma membranes of oligodendrocyte surfaces and inducing a signaling complex [27]. In contrast, rHIgM12 binds to neurons and protects against axonal injury in chronic TMEV murine model and ALS model [12].…”