Pharmacological matrix metalloproteinase (MMP) inhibition blocks axonal regeneration in the damaged retinotectal system of the adult zebrafish

Abstract

AbstractPurpose Complete restoration of the injured mammalian central nervous system (CNS) remains a challenge, making the search for regenerative molecules essential. Matrix metalloproteinases (MMPs), (non)‐matrix protein cleaving endopeptidases, are upregulated during CNS repair, reduce glial scar formation and potentially promote axonal regrowth. As such MMPs or their underlying molecules likely form potent regenerative molecules. One study already reported upregulated mRNA levels of specific MMPs in spontaneously regenerating eyes of adult zebrafish subjected to an optic nerve crush (ONC). Here, we intend to elucidate the role of these MMPs in zebrafish retinotectal regeneration.Methods Immunohistochemistry and Western blotting were used to determine the protein expression pattern of MMP‐2,‐9,‐13a and ‐14 after ONC in the regenerating zebrafish retina. To investigate the role of MMPs in retinal ganglion cell (RGC) axonal regeneration, a broad‐spectrum (GM6001) inhibitor was intravitreally injected at specific time points after ONC. Biocytin labeling was used to study tectal reinnervation.Results Our expression data show a spatiotemporal expression of these MMPs in the regenerating zebrafish retina and suggest an individual role in RGC survival, axonal regrowth and dendritic/synaptic remodeling. Moreover, broad‐spectrum MMP inhibition during the first week after ONC significantly reduces retinotectal regeneration without influencing RGC survival.Conclusion Our study reveals that MMPs are associated with zebrafish retinotectal regeneration and that these enzymes or their downstream targets might be of therapeutic value for the injured mammalian CNS.