Monogalactosyl Diglyceride, a Marker for Myelination, Activates Oligodendroglial Protein Kinase C

: Protein kinase C (PKC) is activated by 1,2‐sn‐diacylglycerol (DAG), the source of which can either be phosphatidylinositol bisphosphate or phosphatidylcholine. Here, we show that monogalactosyl diglyceride (MGDG), a minor galactolipid present in oligodendrocytes (OLs) and myelin, which is designated as a marker for myelination, can enhance OL PKC activity. Based on different calcium and substrate requirements we conclude that MGDG and DAG activate different isoforms of PKC group A: MGDG primarily stimulates PKC‐α, and DAG primarily activates PKC‐γ. The presence of these PKC isoforms in OLs was confirmed by western blotting, whereas PKC‐β was only weakly stained, if at all. Addition of MGDG to the culture medium provided a higher density of regenerating OL fibers, which was not observed when membrane‐permeable DAG was used. These findings indicate that MGDG can modulate the OL PKC activity and that PKC‐α is the major PKC isoform involved in OL process formation.