Research Paper Volume 8, Issue 9 pp 2081—2099

Age-related hearing loss: prevention of threshold declines, cell loss and apoptosis in spiral ganglion neurons


Figure 9. Apoptotic biomarker expression levels in modiolar tissue samples from young adult (2-3 mon), middle-aged (20-21 mon) ALD-treated and untreated CBA/CaJ mice. Panel (a) shows the key molecules (Bcl-2, Bax, caspase 3 & 8) for the apoptotic pathways being investigated. (b) Cleaved caspase-3 protein expression is elevated in middle age controls, but reduced in ALD-treated mice. Since caspase-3 is an executor of apoptosis and a common factor of the intrinsic and extrinsic pathways, its upregulation can induce apoptosis. Note: the antibody utilized here also recognizes the cleaved caspase-3 to a lesser degree. Statistical differences are relative to the young adult levels. (c) To further assess age-related changes in the apoptotic pathways, the extrinsic factor, caspase-8, and intrinsic factors, Bcl-2 and Bax, were examined using western blots (WB). All three biomarkers were activated as shown: caspase-8 cleavages including p43 and p18 were enhanced in the middle age mice compared to the young adults, but reduced in ALD-treated mice. Bax was increased, but Bcl-2 was decreased with aging in SGNs, and ALD treatment inhibited the age-related changes of both molecules. Lastly, the DNA ladder detected in aging SGNs, but ALD treatment prevented the genomic DNA to be digested by endonucleases, L-Ladder: DNA molecular weight. *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001.