DIPEPTIDYL PEPTIDASE-II IN ASTROCYTES OF THE RAT-BRAIN - MENINGEAL CELLS INCREASE ENZYMATIC-ACTIVITY IN CULTIVATED ASTROCYTES

Astrocytes grown in media conditioned by meningeal cells (MCM) develop cellular processes and markedly increased protein per cell. One protein component affected is the dipeptidyl peptidase I (DPP II). The increase of DPP II activity is dose- and time-dependent and can also be elicited by the second messenger cAMP. More mature astrocytes express higher levels of DPP II than immature proliferating astrocytes. The rate of proliferation of astrocytes is markedly enhanced by enriched MCM. These observations lead to the assumption that DPP II has a function within the catabolic processes of cellular differentiation. To assess whether the in vitro results may reflect in vivo conditions, we investigated the postnatal development of DPP II in the rat brain. Differentiating astrocytes in vivo are especially found early postnatally and, indeed, during this period high specific activities are found in brain. Depending on the region investigated DPP II activities decrease within the first ten days to one fourth of their P2 level and finally reach at about similar levels in all brain regions. Exceptions are the hypothalamus, where the activity is generally 1.5- to 3-fold higher than elsewhere in brain, and pons and mesencephalon, where the perinatal activity peak is lacking. The bulk activity of DPP II in immature rat brains is attributed to differentiating astrocytes loosing it in later postnatal stages due to a neuronal influence.