Ribonucleoprotein Autoimmunity Drives Neurodegeneration in Multiple Sclerosis (MS) Models

Background: MS patients make autoantibodies to the RNA binding protein (RBP) heterogenous nuclear ribonucleoprotein A1 (A1), an RBP overexpressed in neurons. We’ve shown that A1 antibodies exacerbate A1 dysfunction and neurodegeneration in models of MS, but it is unknown whether A1 dysfunction triggers or occurs as a result of neurodegeneration.

Objectives: To determine the contribution of autoimmune induced RBP dysfunction to mechanisms of neurodegeneration in models of MS.

Methods: Mice with experimental autoimmune encephalomyelitis (EAE) were treated with A1 antibodies (overlapping with the immunodominant epitope of MS IgG), or saline (control). Spinal cords were analyzed for markers of RBP dysfunction and neurodegeneration over time (7-, 15- and 21-days post symptom onset). Mouse primary cortical neurons were treated with A1 or control IgG antibodies for 6, 12 or 24 hours and analyzed for markers of RBP dysfunction and neurodegeneration. RNA sequencing of EAE ventral spinal cord grey matter and primary neurons was performed to study A1 antibody induced changes in RNA expression in both in vivo and in vitro models.

Results: In EAE, A1 antibody treatment resulted in a statistically significant (i) increase in A1 mislocalization at days 7 and 15 (*p < .05), (ii) alteration in RNA expression at day 15, and (iii) increase in stress granule formation at days 15 and 21(**p < .01). RNA sequencing revealed enriched pathways related to regulation of neuronal projections, cell stress and programmed cell death. These molecular changes preceded worsening clinical disease at days 15 to 21, and an increase in necroptotic signalling (**p < .01) and neurodegeneration at day 21 (***p < .001).

Similarly, primary neurons treated with A1 antibodies (compared to controls) resulted in (i) increased A1 mislocalization at 6 and 12 hours (**p < .01), (ii) altered RNA expression at 12 hours (iii) increased stress granule formation at 12 and 24 hours (*p < .05), (iv) increased necroptotic signalling at 12 hours (***p < .001), which preceded (v) a reduction in neurite length (neurodegeneration) at 24 hours after antibody treatment (*p < .05). RNA sequencing revealed enriched pathways related to altered RNA processing, protein complex formation and neuronal cell death.

Conclusions: These data provide evidence that A1 antibodies induce A1 dysfunction, activation of necroptosis – a programmed cell death pathway, and subsequent neurodegeneration in both an in vitro and in vivo model of MS.