The goals of this project are to study the gene expression of growth factors, myelin-related proteins and other glial proteins by glial cells during myelin breakdown and regeneration. This year, we compared relative levels of insulin-like growth factor-I (IGF-I) and of glial fibrillary acidic protein (GFAP) mRNAs and peptides produced by astrocytes in demyelinating lesions induced by the copper chelator, cuprizone. Hybridization studies of lesions using specific nucleic acid probes and immunostaining with cell-specific markers showed that levels of GFAP mRNA in hypertrophic astrocytes rose earlier and persisted longer during the recovery period than IGF-I mRNA levels. This suggested that in this demyelinative process, astrocytic production of IGF-I and GFAP are independently regulated. Two additional models of CNS myelin breakdown and regeneration were selected for new studies of possible growth factor production by reactive glial cells. When focal lesions are produced in the dorsal columns of rat thoracic spinal cords by cryogenic injury, lesion margins are known to contain hypertrophic astrocytes and regenerating, remyelinated axons 30 - 60 days after injury (Collins and West, 1989). Dr. West produced these cryogenic lesions in groups of rats and preliminary examination of spinal cords removed and examined in LENP 7- 14 days later showed dramatic increases in astrocytic GFAP mRNA and peptide levels and levels of IGF-I mRNA significantly above those seen in sham-operated control spinal cords. Localization studies and examination of later intervals are in progress. The second model is experimental autoimmune encephalomyelitis (EAE), a disease characterized by perivascular mononuclear cell infiltrates, myelin breakdown, relative sparing of axons and subsequent regeneration of myelin. Studies of astrocyte responses in these demyelinating lesions have just begun.
