Objective To examine 20S proteasome activity and its expression in the subventricular zone (SVZ) of mice at different ages, then investigating the effects of proteasome inhibitor MG132 on the viability and proliferation potential of neural stem cells (NSCs), thus to establish the relationships between 20S proteasome activity and NSCs viability.This work aimed to unveil the underlying mechanism for NSCs dysfunction in aging brain, so as to develop a new treatment stratedgy for age-related neurodegenerative disorders.Methods In the present study, immuno-staining was used to check the expression of 20S proteasome in embryonic and adult mice SVZ.To test whether 20S proteasome deficiency and expression level display in an age-dependent manner in SVZ, proteasome peptidase assay and Western Blot assay were performed on mice at embryonic (embryonic day 14), neonatal (postnatal day 0), adult (postnatal day 90), aged (postnatal day 540) stages.Moreover, proteasome inhibitor MG132 was injected into lateral ventricles of adult mice to examine its effects on NSCs proliferation by BrdU labeling at day 3 post-injection.Furthermore, in vitro analyses were used to determine the effect of MGl32 on NSCs viability from SVZ by BrdU incorporation and Cell Counting Kit-8 (CCK-8) assay.Results (1) 20S proteasome was collocalized with NSCs marker nestin in SVZ of embryonic and aged mouse, 20S proteasome-positive cells were distributed along the ventricular wall.(2) Age-dependent decline in the activity and expression of 20S proteasome were found.in SVZ, the 20S proteasome activity was significantly reduced 3~4 times in aged mice verse embryonic or neonatal mice (P<0.05).Moreover, the decreased numbers of BrdU-positive cells were founded in SVZ of aged mice.These observations indicated that 20S proteasome is associated with neural stem cells maintenance.(3) After intracerebroventricular injection of MG132, the numbers of BrdU-positive cells were significantly decreased to 21+4 at post-injection day 3 compared to control group (P<0.05).(4) After treatment of NSCs with MG132, BrdU incorporation and CCK-8 assay showed that the proliferation and viability of NSCs was significantly inhibited at the concentration of 0.8 μM and this inhibition displayed in a dose-dependent manner.Conclusion The activity and expression level of 20S proteasome is decreased in SVZ of aged mice.Inhibition of proteasome activity by MG132 mimicks this age-related dysfunction of NSCs.Taken together, these data suggests that 20S proteasome may be involved in NSCs maintenance in SVZ.