Anti-Ca ²⁺ channel antibody attenuates Ca ²⁺ currents and mimics cerebellar ataxia in vivo

Abstract

Voltage-gated Ca 2؉ channels (VGCCs) are membrane proteins that determine the activity and survival of neurons, and mutations in the P/Q-type VGCCs are known to cause cerebellar ataxia. VGCC dysfunction may also underlie acquired peripheral and central nervous system diseases associated with small-cell lung cancer, including Lambert-Eaton myasthenic syndrome (LEMS) and paraneoplastic cerebellar ataxia (PCA). The pathogenic role of anti-VGCC antibody in LEMS is well established. Although anti-VGCC antibody is also found in a significant fraction of PCA patients, its contribution to PCA is unclear. Using a polyclonal peptide antibody against a major immunogenic region in P/Q-type VGCCs (the extracellular Domain-III S5-S6 loop), we demonstrated that such antibody was sufficient to inhibit VGCC function in neuronal and recombinant VGCCs, alter cerebellar synaptic transmission, and confer the phenotype of cerebellar ataxia. Our data support the hypothesis that anti-VGCC antibody may play a significant role in the pathogenesis of cerebellar dysfunction in PCA.Lambert-Eaton myasthenic syndrome ͉ paraneoplastic ͉ P/Q-type ͉ N-type ͉ neurotransmission T he association between anti-voltage-gated Ca 2ϩ channel (VGCC) antibody and paraneoplastic cerebellar ataxia (PCA) dates back several decades to clinical observations of the coexistence of small-cell lung cancer with either cerebellar ataxia, Lambert-Eaton myasthenic syndrome (LEMS), or both (1, 2). The majority of these cancer patients with neurological symptoms have antibody against different types of VGCCs, especially P/Q-and N-type (3-5). The presence of different antibodies may be the consequence of an autoimmune response against the cancer cells (6, 7), known to express different VGCCs (8). There is conclusive evidence that the peripheral disease LEMS is caused by anti-VGCC antibodies, which diminish the availability of P/Q-type channels of the motor nerve terminals (9, 10).In contrast, much less is known about the origin of cerebellar ataxia associated with anti-VGCC antibody, although VGCCs are prominent in cerebellar neurons (11,12), and mutations in the P/Q-type VGCC cause ataxia (13). PCA patients have a high titer of anti-VGCC antibody (14-17) and undergo a selective loss of P/Q-type VGCC-containing cerebellar neurons (2, 18). Sera from LEMS patients, known to contain anti-VGCC antibodies, reduce P/Q-type VGCC surface expression in cerebellar granule and Purkinje neurons (19), consistent with an overlap of clinical syndromes between LEMS and PCA and, possibly, of pathogenic mechanism. There is no evidence to date that passive transfer of sera from LEMS or PCA patients is sufficient to cause central nervous system disease. Based on epitope mapping of antibody repertoire in patients with paraneoplastic neurological syndromes and small-cell lung cancer, we generated an antibody against a major epitope in the P/Q-type VGCC and evaluated its ability to affect cerebellar VGCC function and motor behavior. ResultsFunctional Effects of Anti-VGCC Antibody. We looked for...

Extracellular Ion Channel Inhibitor Antibodies

“…Furthermore NESOpAb has proved useful in studies of native channels, demonstrating an involvement of neonatal Na V 1.5 in the enhancement of invasive behaviour of breast cancer cells, a result confirmed using RNA interference [18]. A further example is the D-III polyclonal antibody, which was developed as a blocker of P/Q-type voltage-gated Ca 2+ channels in cerebellar granule cells [17]. D-III was used to demonstrate a direct link between voltage-gated Ca 2+ channel antibodies and the pathogenesis of para-neoplastic cerebellar ataxia, suggesting that normal channel function and neurophysiology could be restored in patients by removal of damaging antibodies directed against these channels [17].…”

“…The first study used polyclonal antibodies targeted to the voltagegated K + channels K V 1.2 and K V 3.1 which inhibited whole cell currents and helped establish that K V 1.2 is functional in neuronal cells [14]. Polyclonal antibodies also proved successful as inhibitors of the voltage gated sodium channel Na V 1.5 [13,16], and of N-and P/Q-type voltage-gated Ca 2+ channels [17]. NESOpAb is a polyclonal antibody designed to recognise the 'neonatal' splice variant form of Na V 1.5, and is an efficient blocker of current conducted by the channel [16].…”

“…A further example is the D-III polyclonal antibody, which was developed as a blocker of P/Q-type voltage-gated Ca 2+ channels in cerebellar granule cells [17]. D-III was used to demonstrate a direct link between voltage-gated Ca 2+ channel antibodies and the pathogenesis of para-neoplastic cerebellar ataxia, suggesting that normal channel function and neurophysiology could be restored in patients by removal of damaging antibodies directed against these channels [17].…”

Antibody therapeutics targeting ion channels: are we there yet?

“…When tested at neuromuscular junctions, this antibody attenuated excitatory postsynaptic currents. Moreover, cerebellum infusion caused cerebellar ataxia in mice, establishing a link between anti-voltage-gated calcium channel antibodies and pathogenesis [19] . Besides regulating neural excitability, some E3-targeted antibodies could modulate store-operated or agonist-evoked Ca 2+ entry [20][21][22][23][24][25] , oligodendrocyte proliferation and migration [26] , and tumor growth [27,28] .…”

PTPRR, Cerebellum, and Motor Coordination

“…Furthermore, silencing of small-conductance calcium-activated potassium channels, regulators of firing frequency, in the CNS has proved that a purely electrical alteration is sufficient to cause cerebellar ataxia [11]. Even an anti-Ca 2+ channel antibody was sufficient to inhibit voltage-gated Ca 2+ channels, alter cerebellar synaptic transmission, and confer the phenotype of cerebellar ataxia [12].…”