Microglial Keratan Sulfate Epitope Elicits in Central Nervous Tissues of Transgenic Model Mice and Patients with Amyotrophic Lateral Sclerosis

The functional role of 5D4 antibody-reactive keratan sulfate (KS) in the pathogenesis of neurodegenerative diseases is unknown. We therefore studied the expression of 5D4-reactive KS in amyotrophic lateral sclerosis (ALS), a motor neuron-degenerative disease, with the use of SOD1G93A ALS model mice and patients with ALS. Histochemical and immunoelectron microscopic characterizations showed that the 5D4-reactive KS is expressed in Mac2/galectin-3–positive activated or proliferating microglia of SOD1G93A ALS model mice at disease end stage and that the KS is an O-linked glycan modified with sialic acid and fucose, which was thus far shown to exist in cartilage. Intriguingly, microglial KS was detected in the spinal cord and brainstem but not in the cerebral cortex of SOD1G93A mice. We found that KSGal6ST, a galactose-6-sulfotransferase, is required for biosynthesis of the microglial 5D4-reactive KS by generating SOD1G93A/KSGal6ST−/− mice. The requirement of GlcNAc6ST1 for this synthesis was corroborated by analyzing SOD1G93A/GlcNAc6ST1−/− mice. These results indicate that both galactose-6– and N acteylglucosamine-6–sulfated KS elicited in the spinal cord and brainstem are associated with the degeneration of spinal and bulbar lower motor neurons in ALS pathology and may play a role in disease progression via microglial activation and proliferation.