Age-dependent reduction in sialidase activity of nuclear membranes from mouse brain

Sialidase is an enzyme that cleaves alpha-linked sialic acid residues from sialoglycoconjugates and participates in various cellular functions. In the present study, we characterized sialidase activity in nuclear membranes from mouse brain and examined its age-related changes. A highly purified nuclear membrane preparation from 4-week-old mouse brain contained sialidase activity that hydrolyzed both 4-methylumbelliferyl-alpha-D-N-acetylneuraminic acid (4MU-Neu5Ac) and ganglioside GM3. The specific activities directed toward both substrates were 6.33+/-0.77 and 13.4+/-1.1pmol/mgprotein/min, respectively. Nuclear localization of sialidase activity was confirmed by fluorescent cytochemistry of intact nuclei using 5-bromo-4-chloro-3-indolyl-alpha-D-N-acetylneuraminic acid (X-Neu5Ac) as the substrate. Age-related changes in nuclear sialidase activity in brain tissue were investigated using mice of different ages (i.e. 2-week-, 4-week-, 14-month-, and 26-month-old). Sialidase activity toward 4MU-Neu5Ac had almost identical levels at 2nd and 4th weeks, but thereafter decreased rapidly; the activity at 26 months was about one third of the young levels. Sialidase activity toward GM3 also showed a similar developmental pattern, though the reduction at advancing ages was less than that of activity toward 4MU-Neu5Ac. The present study demonstrates that the activity of nuclear sialidase decreases with aging. The reduced activity of nuclear sialidase may be implicated with alterations of neural cell function during aging.