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. Author manuscript; available in PMC: 2016 Jul 11.
Published in final edited form as: Cell Metab. 2014 Dec 2;20(6):1059–1068. doi: 10.1016/j.cmet.2014.11.003

Figure 6. NR prevents neurite retraction from inner hair cells in a SIRT3-dependent manner.

Figure 6

(a) Neurite retraction from inner hair cells is reduced following noise exposure in mice treated with NR. To determine whether NR treatment also reduced spiral ganglia neurite degeneration, C57BL6 mice were treated for 5 d with NR (1,000 mg/kg by intraperitoneal injection, twice daily) or vehicle prior to noise exposure. Cochlea were then harvested either 24 hr or 14 d after noise exposure and neurite retraction from inner hair cells was measured by staining with an anti-NF200 antibody (red, spiral ganglia neurites) and actin (green, inner hair cells). DAPI staining (blue) was used to identify the nucleus of the inner hair cells, which defines the base of these cells. Representative immunofluorescence staining is shown for control mice that were not exposed to noise, noise-exposed mice treated with vehicle, noise-exposed mice treated with NR, and noise-exposed SIRT3−/− mice treated with NR. Neurite retraction (indicated with a white bracket) is seen in vehicle-treated mice both 24 hr and 14 d following noise exposure. Neurite retraction is considerably reduced in NR-treated mice at both time points (the junction between the neurites and hair cells is indicated with a white arrow). The protective effect of NR against neurite retraction is lost in SIRT3−/− animals. This suggests that NR stabilizes spiral ganglia neurites and prevents their retraction following noise exposure in a SIRT3-dependent manner. Scale bar, 25 μm.

(b) Quantification of results in (a). The distance between the tips of the spiral ganglia neurites to the nucleus at the base of the inner hair cell (IHC) was measured to determine the degree of neurite retraction. Reduced neurite retraction is seen in noise-exposed mice that were treated with NR compared to those treated with vehicle alone. This reduction in neurite retraction is dependent on SIRT3. Shown are the average measurements obtained from a minimum of 5 cochlea from 3 mice for each group. Statistical analysis was performed using a one-way ANOVA followed by T-test (*P < 0.05, **P < 0.01). Error bars represent SD.