Peak in matrix metaloproteinases-2 levels observed during recovery from olfactory nerve injury

Abstract

Matrix metalloproteineases are associated with extracellular remodeling that occurs in injury and repair processes in the central nervous system (CNS). We examined the role of MMP-2 in a model of olfactory nerve injury and found that MMP-2 levels increased several hours following injury, peaked at day 7 and then decreased rapidly. We previously reported a rapid increase in MMP-9, within 5 h after nerve injury, corresponding to neuronal degeneration and increased glial activity. In this study, we show that MMP-2 peaks later than MMP-9, at the onset of neuronal regeneration and repair. Using MMP-9 knockout mice, we determined that the MMP-2 increase is independent of MMP-9. Our data suggest that MMP-2 and MMP-9 may play different roles in the injury and repair processes.

Fig. 1

Analysis of MMP-2 expression in the olfactory bulb following olfactory nerve transection injury in P2 mice. (a) Representative Western blot illustrating changes in MMP-2 expression at different time points following injury. Lane 1 shows pro (upper band) and active forms (lower band) of purified murine MMP-2 standard. Lane 2 shows that MMP-2 is barely detectable in control mice (CTRL). Cyclophilin A (CPA) expression at each time point was used to adjust for differences in protein loading. (b) Plot of the relative amounts of MMP-2 (pro and active forms included in the quantification) from four separate experiments expressed as percentages of CPA. Each experiment represents data from nine separate mice. MMP-2 levels initially increased slowly, rose rapidly after day 3 to a maximum at day 7. MMP-2 levels declined rapidly between day 7 and day 10. CPA, Cyclophilin A; MMP, matrix metalloproteinases.

Fig. 2

Analysis of MMP-2 expression in the olfactory bulb following olfactory nerve transection injury in MMP-9 KO mice. (a) Representative Western blot illustrating changes in MMP-2 expression at different time points following injury. Lane 1 shows pro and active forms of purified murine MMP-2 standard. Lane 2 shows that MMP-2 is barely detectable in control mice (CTRL). Cyclophilin A (CPA) expression at each time point was used to adjust for differences in protein loading. (b) Plot of the relative amounts of MMP-2 (pro and active forms included in the quantification) from four separate experiments expressed as percentages of CPA. Each experiment represents data from nine separate mice. MMP-2 levels initially increased slowly, rose rapidly after day 3 to a maximum at day 7. MMP-2 levels declined equally as rapidly from day 7 to day 10 or 15. Elevation in the level of MMP-2 in the absence of MMP-9 (MMP-9 KO mice) illustrates that MMP-9 is not required for the increase in MMP-2 expression following olfactory nerve injury. KO, Knockout; MMP, matrix metaloproteinases.

Fig. 3

Summary of time course differences in MMP-2 and MMP-9 expression in the olfactory bulbs of P2 and MMP-9 KO mice following olfactory nerve transection injury. The MMP-9 data (filled circles) is from NeuroReport 2006; 17:1787−1791. The average MMP/ CPA ratio from four separate time course experiments were calculated and plotted as a percent of the maximum value. In P2 mice, MMP-9 peaked very rapidly (hours) after injury and remained elevated during olfactory neuron regeneration The MMP-2 expression data for both the P2 mice (filled diamonds) and MMP-9 KO mice (open squares) show nearly identical changes in the time course of expression following injury. MMP-2 levels peaked later than MMP-9, at day 7 and returned rapidly to the lower levels observed immediately following injury. KO, Knockout; MMP, matrix metaloproteinases.