MMP9 and nervous system disorder: The above findings, along with the finding that aggrecan, which is an important component of PNNs, is a direct target of MMP9 (Madsen et al., 2010), have tempted us to explore the key regulators that can orchestrate MMP9-mediated pruning of PNNs, thereby warranting and potentially paving the way for novel therapeutic treatment strategies for neurological disorders.