Activation of a novel microglial gene encoding a lysosomal membrane protein in response to neuronal apoptosis

In an attempt to understand the molecular mechanism of microglial activatio n in response to neuronal death or degeneration, we have employed cerebella r cell cultures prepared from P7 rats and grown in normal K+ (5.4 mM) mediu m. Under this condition, glial cells respond to degeneration and cell death of granule neurons that begins to occur at 4 days in vitro (DIV). Here we describe a novel gene, granule cell death-10 (gcd-10) that is expressed in microglia and up-regulated in an early period of granule cell death. gcd-10 is homologous to the mouse lysosomal-associated multispanning membrane pro tein (LAPTm5) with hematopoietic origin. Immunocytochemistry and vital stai ning with acridine orange revealed that GCD-10 was localized at the perinuc lear area of cultured microglia and COS 1 cells infected with a GCD-10-expr essing adenoviral vector. In cerebellar cell cultures, however, GCD-10 was markedly up-regulated and widely distributed to the cytoplasm, which parall eled the localization of the ED1 antigen, the lysosomal marker. In vivo, gc d-10 is expressed mainly in the brain and the spleen, and was up-regulated upon nerve injury in retina 7 days after optic nerve transection. These fin dings suggest that gcd-10 is involved in the dynamics of lysosomal membrane s associated with microglial activation both in vitro and in vivo. (C) 2001 Elsevier Science B.V. All rights reserved.