De novo expression of lipocortin-1 in reactive microglia and astrocytes inkainic acid lesioned rat cerebellum

An understanding of the role of reactive glia in the neurodegenerative/rege nerative process requires a knowledge of the molecules synthesised by these cells following trauma. We investigated the cellular localisation of lipoc ortin-1 (LC-1), a putative neuroprotective agent, in cryostat sections of n ormal and kainic acid lesioned rat cerebellum. In the normal cerebellum lip ocortin-1 immunoreactivity was detected in Purkinje cell bodies and molecul ar layer interneurons. Following kainic acid (1 mu g) induced lesions, it w as rapidly upregulated in activated microglia, from which it appeared to be secreted. At later time points it was detected in activated astrocytes. LC -1 protein levels were quantified by a sensitive and specific ELISA. Compar ed to control cerebellum, LC-1 levels were dramatically elevated following lesion, peaking at 3 days: 760% of basal (unlesioned) levels. In situ hybri disation studies revealed a marked upregulation of LC-1 mRNA at 1 and 3 day s following the lesion, indicating the transient de novo synthesis of this protein, consistent with a localisation to microglia. In vitro studies, on cultured astrocytes and microglia, demonstrated high levels of intracellula r LC-1 in both cell types. LC-1 was detected in microglial but not astrocyt ic, conditioned media, confirming the in vivo observations that activated m icroglia may secrete LC-1. Our data show that at early time points followin g excitotoxic lesion to the cerebellum, it is activated microglia that synt hesise and possibly secrete this protein, suggesting an important role of t his cell type in immunosuppression and neuroprotection following damage to the central nervous system. GLIA 26:333-343, 1999. a 1999 (C) Wiley-Liss, I nc.