Background: A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) proteoglycanases are specialized in the degradation of chondroitin sulfate proteoglycans and participate in mechanisms mediating neuroplasticity. Despite the beneficial effect of ADAMTS-4 on neurorepair after spinal cord injury, the functions of ADAMTS proteoglycanases in other CNS disease states have not been studied. Therefore, we investigated the expression, effects and associated mechanisms of ADAMTS-4 during amyotrophic lateral sclerosis (ALS) in the SOD1(G93A) mouse model.
Results: ADAMTS-4 expression and activity were reduced in the spinal cord of SOD1(G93A) mice at disease end-stage when compared to WT littermates. To counteract the loss of ADAMTS-4, SOD1(G93A) and WT mice were treated with saline or a recombinant ADAMTS-4 before symptom onset. Administration of ADAMTS-4 worsened the prognosis of SOD1(G93A) mice by accelerating clinical signs of neuromuscular dysfunctions. The worsened prognosis of ADAMTS-4-treated SOD1(G93A) mice was accompanied by increased degradation of perineuronal nets enwrapping motoneurons and increased motoneuron degeneration in the lumbar spinal cord. Motoneurons of ADAMTS-4-treated SOD1(G93A) mice were more vulnerable to degeneration most likely due to the loss of their extracellular matrix envelopes. The decrease of neurotrophic factor production induced by ADAMTS-4 in vitro and in vivo may also contribute to a hostile environment for motoneuron especially when devoid of a net.
Conclusions: This study suggests that the reduction of ADAMTS-4 activity during the progression of ALS pathology may be an adaptive change to mitigate its neurodegenerative impact in CNS tissues. Therapies compensating the compromized ADAMTS-4 activity are likely not promising approaches for treating ALS.