Objective This study was designed to investigate the expression and potential role of the protein phosphatase 1 (PP1) impairment in D -galactose-induced inner ear aging mouse model .Methods Forty Kunming mice were randomly divided into two groups :the control group and D -galactose group ,20 mice for each .The D-galactose group mice were treated with a daily subcutaneous injection of the D -galactose solutions (800 mg · kg -1 · d-1 ) or an equal volume of normal saline(for the control group) in the nape back for 8 weeks .Eight weeks after D-galactose administration ,the effects of were measured by total Superoxide Dismutase (SOD) activity and Malon-dialdehyde (MDA) level in plasma .Immunofluoresence was performed to detect the location of the PP1 expression in the cochlea .Real-time PCR was performed to detect the level of PP1 mRNA in cochlea .A Western blot analysis was performed to analyze the protein levels of protein phosphates 1 nuclear targeting subunit (PNUTS) ,PP1 and caspase-3 in the inner ear .Results The MDA level was more significantly increased in the D -galactose group than in the control group ;however ,the total SOD activity was significantly decreased in the plasma of D -galactose- induced aging mice(P<0 .01) .The results showed that PP1 was predominantly localized in the nucleus and cyto-plasm of the hair cell ,spiral ganglion cell and stria vascularis cell .And the protein levels of PP1 and caspase-3 sig-nificantly increased ,and the level of PNUTS was decreased in the cochlea of the D -galactose group when compared to the control group .Conclusion PP1 contributes to the development of D -galactose-induced aging mice .

Objective To observe the expression of protein phosphates 1 nuclear targeting subunit (PNUTS) in the cochlea of D-galactose induced ageing mice. Methods Twenty Kunming mice, six weeks old, cleaning degree, were randomly divided into two groups, control group and D-galactose group, ten mice for each group. Mice in D-galactose group were administrated with D-galactose at a dose of 800 mg/(kg · d) by subcutaneous injection for eight weeks. Mice in control group were injected with the same volume of saline. After eight weeks, auditory brainstem responses (ABR) were collected to test the hearing thresholds of mice. Western blot assay was used to detect expressions of PNUTS and p53 protein. The expression and distribution of PNUTS in the cochlear Corti, spiral ganglion and striavascularis cells were observed by immunohistochemical (IHC) staining. Results There were no significant differences in ABRs at 8, 12 and 24 kHz between two groups. Protein expressions of PNUTS were located in the cochlear hair cells, spiral ganglion cells and striavascularis cells, and the expression level of cochlea was significantly decreased in D-galactose group than that in control group ( P<0.05). The expression level of p53 protein was significantly increased in D-galactose group than that in control group (P<0.01). Conclusion PNUTS is expressed in the normal mouse cochlea, and which is down-regulated in the cochlea of ageing mice induced by D-galactose.