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 prote in component affected is the dipeptidyl peptidase I (DPP II). The incr ease of DPP II activity is dose- and time-dependent and can also be el icited by the second messenger cAMP. More mature astrocytes express hi gher 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 w ithin the catabolic processes of cellular differentiation. To assess w hether the in vitro results may reflect in vivo conditions, we investi gated the postnatal development of DPP II in the rat brain. Differenti ating astrocytes in vivo are especially found early postnatally and, i ndeed, during this period high specific activities are found in brain. Depending on the region investigated DPP II activities decrease withi n 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 hypo thalamus, where the activity is generally 1.5- to 3-fold higher than e lsewhere in brain, and pons and mesencephalon, where the perinatal act ivity peak is lacking. The bulk activity of DPP II in immature rat bra ins is attributed to differentiating astrocytes loosing it in later po stnatal stages due to a neuronal influence.