Are multiple sclerosis and amyotrophic lateral sclerosis autoimmune disorders of endogenous vasoactive neuropeptides?
Autoimmune dysfunction of endogenous vasoactive neuropeptides (VNs) such as vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) has been postulated as a cause for some fatigue-related conditions. VN receptors are class II G protein-coupled receptors (GPCRs) which couple primarily to the adenylate cyclase (AC)-cyclic AMP (cAMP) pathway and cAMP has a central role in neurological metabolism including influencing blood-brain barrier (BBB) and blood-spinal barrier (BSB) permeability, coordinating neuroregulatory pathways, and protecting against neuronal apoptosis. Complex clinical signs occur in multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). While traditionally viewed as diseases of the motor system, the clinical picture of these conditions is considerably more complex. Disturbances of cognition and memory, as well as emotional lability occur along with fatigue and motor dysfunction. This paper explores the hypothesis that autoimmune dysfunction of VNs may contribute to MS and ALS. While MS and ALS differ in important respects, they have common pathogenic features including inflammation, oxidative stress and mitochondrial dysfunction. Apoptotic mechanisms are associated with activation of caspase pathways and functional interplay between proinflammatory cytokines, interferon gamma and nitric oxide is suggested associated with oxidative stress and glial activation. Diseases such as MS and ALS may represent related conditions resulting from variation in expression of different receptor subtypes of the VN family. Anatomical differences of these receptors, perhaps in areas overly dependent on a specific VN receptor sub-type, may predispose to autoimmune susceptibility to these conditions, either in impaired expression of receptors or antibody and cellular immune targeting of them. Further studies are required to determine if such VN receptor sub-types of significant specificity exist and if they are susceptible to compromise. This hypothesis, if proven, may have implications for the development of treatment and preventive strategies.