Protein deimination in the rat brain: Generation of citrulline-containing proteins in cerebrum perfused with oxygen-deprived media

The central nervous system contains the posttranslational modification enzy me, peptidylarginine deiminase (PAD; EC 3.5.3.15) type II. This enzyme cata lyzes the deimination of arginine residues of proteins in a calcium ion-dep endent manner, thereby, forming citrulline residues. Previously, we found p ostmortem deimination of glial fibrillary acidic protein in rat spinal cord . In the present study, therefore, we studied the deimination further as a possible cause of neurodegeneration in cerebrum. Additionally, as a model o f tissue damage, the effect of oxygen deprivation on protein deimination in rat cerebral tissue was also analyzed by applying systemic perfusion with an emulsion of perfluorochemicals. In the presence of sufficient oxygen, su ch perfusion caused only negligible formation of citrullinated proteins. Ho wever, deprivation of oxygen produced by the perfusion medium resulted in p referential deimination of many kinds of high-molecular-weight (>55 kDa) pr oteins. Deiminated protein immunoreactivity was found in all regions of the cerebrum but was relatively more intense in the hypothalamus and the later al amygdaloid nucleus. Most of the deiminated protein-positive cells seemed to be astrocytes. Some neuronal cells in the lateral amygdaloid nucleus be came positive after prolonged perfusion with oxygen-deprived medium, althou gh the PAD immunoreactivity appeared only in astrocytes. These results indi cate that PAD type II localizes mainly in astrocytes of the cerebrum and th at a consequence of hypoxia is enzyme activation that deiminates proteins i n astrocytes and some neurons. Such deimination of proteins may be a useful marker of nerve cell degeneration.