Aglycosylated extracellular loop of inwardly rectifying potassium channel 4.1 (KCNJ10) provides a target for autoimmune neuroinflammation

Abstract

Multiple sclerosis is an autoimmune disease of the central nervous system (CNS). Yet, the autoimmune targets are still undefined. The extracellular e1 sequence of KCNJ10, the inwardly rectifying potassium (Kir) channel 4.1, has been subject to fierce debate for its role as a candidate autoantigen in multiple sclerosis. Kir4.1 is expressed in the CNS but also in peripheral tissues, raising concerns about the CNS-specificity of such autoreactivity. Immunization of C57Bl6/J female mice with the e1 peptide (amino-acids 83-120 of Kir4.1) induced anti-e1 immunoglobulin G (IgG) and T cell responses, and promoted demyelinating encephalomyelitis with B cell CNS enrichment in leptomeninges and T cells/macrophages in CNS parenchyma from forebrain to spinal cord, mostly in the white matter. Within our cohort of multiple sclerosis patients (n = 252), six percent exhibited high anti-e1 IgG levels in serum as compared to 0.7% in the control cohort (n = 127; P = 0.015). Immunolabeling of Kir4.1-expressing white matter glia with the anti-e1 serum from immunized mice increased during murine autoimmune neuroinflammation and in multiple sclerosis white matter as compared with controls. Strikingly, the mouse and human anti-e1 sera labeled astrocytoma cells when N-glycosylation was blocked with tunicamycin. Western blot confirmed that neuroinflammation induces Kir4.1 expression, including its shorter aglycosylated form in murine experimental autoencephalomyelitis and multiple sclerosis. In addition, recognition of Kir4.1 using mouse anti-e1 serum in Western blot experiments under unreduced conditions or in cells transfected with the N-glycoslylation defective N104Q mutant as compared to the wild type further suggests that autoantibodies target an e1 conformational epitope in its aglycosylated form. These data highlight the e1 sequence of Kir4.1 as a valid CNS autoantigen with a disease/tissue-specific post-translational antigen modification as potential contributor to autoimmunity in some multiple sclerosis patients.

Potassium homeostasis during disease progression of Alzheimer’s Disease

“…3, 4). Interestingly, in our study of 5xFAD mice, we found a decrease of only one of the Kir4.1 isoforms, with a molecular weight corresponding to the glycosylated form of the Kir4.1 protein that is mainly expressed in astrocytes (51, 52, 63).…”

“…5). Kir4.1 protein can be expressed as a glycosylated (50 kDa) or aglycosylated protein (37 kDa) (51). However, while in astrocytes most Kir4.1 channels are highly glycosylated, oligodendrocytes predominantly express the aglycosylated form of Kir4.1 channels (52).…”