Inhibition of MMP-2 but not MMP-9 Influences Inner Ear Spiral Ganglion Neurons In Vitro
Matrix metalloproteinases (MMPs) play an important role in modeling of the extracellular matrix. There is increasing evidence that these proteases are important in neurite elongation and axonal guidance during development in the central nervous system and retina. Moreover, they are also expressed after acute injury and can be the key mediators of pathogenesis. However, the role of MMPs in the inner ear is largely unknown. Our group recently demonstrated that general inhibition of MMPs resulted in auditory hair cell loss in vitro. In the present study, we investigated the role of MMPs in inner ear spiral ganglion neuron (SGN) survival, neuritogenesis and neurite extension by blocking MMPs known to be involved in axonal guidance, neurite elongation, and apoptosis in other neuronal systems. Spiral ganglion (SG) explants from 5-day-old Wistar rats were treated with different concentrations of the general MMP inhibitor GM6001, a specific MMP-2 inhibitor, and a specific MMP-9 inhibitor, in vitro. The general inhibitor of MMPs and the specific inhibition of MMP-2 significantly reduced both the number of neurites that extended from SG explants, as well as the length of individual neurites. However, neither the general inhibitor of MMPs nor the specific inhibition of MMP-2 influenced SGN survival. Inhibition of MMP-9 had no influence on SGNs. The data suggest that MMPs, and more specifically MMP-2, influence the growth of developing afferent neurites in the mammalian inner ear in vivo.
KeywordsExtracellular matrix Inner ear Matrix metalloproteinase Spiral ganglion neurons
This study is supported by Medizinische Abteilung der Margarete und Walter Lichtsteiner-Stiftung, Basel, Switzerland.
Conflict of interest
All authors report no conflicts of interest.
- Evans AR, Euteneuer S, Chavez E, Mullen LM, Hui EE, Bhatia SN, Ryan AF (2007) Laminin and fibronectin modulate inner ear spiral ganglion neurite outgrowth in an in vitro alternate choice assay. Dev Neurobiol 67:1721–1730Google Scholar
- Genepaint (2013) http://www.genepaint.org. Accessed 30 June 2013
- Hansen MR, Zha XM, Bok J, Green SH (2001) Multiple distinct signal pathways, including an autocrine neurotrophic mechanism, contribute to the survival-promoting effect of depolarization on spiral ganglion neurons in vitro. J Neuorosci 21:2256–2267Google Scholar
- Hertzano R, Puligilla C, Chan SL, Timothy C, Depireux DA, Ahmed Z, Wolf J, Eisenman DJ, Friedman TB, Riazuddin S, Kelley MW, Strome SE (2010) CD44 is a marker for the outer pillar cells in the early postnatal mouse inner ear. J Assoc Res Otolaryngol 11:407–418PubMedCrossRefPubMedCentralGoogle Scholar
- Reuter A, Nestl A, Zwacka RM, Tuckermann J, Waldherr R, Wagner EM, Meyer zum Gottesberge AM, Angel P, Weiher H (1998) Expression of the recessive glomerulosclerosis gene Mpv17 regulates MMP-2 expression in fibroblasts, the kidney, and the inner ear of mice. Mol Biol Cell 9:1675–1682PubMedCrossRefPubMedCentralGoogle Scholar
- Yang Y, Estrada EY, Thompson JF, Liu W, Rosemberg GA (2007) Matrix metalloproteinase-mediated disruption of tight junction proteins in cerebral vessels is reversed by synthetic matrix metalloproteinase inhibitor in focal ischemia in rat. J Cereb Blood Flow Metab 27:697–709PubMedCrossRefGoogle Scholar