Abstract
Microglia are glial-immune cells that are essential for the function and survival of the central nervous system. Microglia not only protect neural tissues from immunological insults, but also play a critical role in neural development and repair. However, little is known about the biology of microglia in the cochlea, the auditory portion of the inner ear. In this study, we detected TMEM119+, CD11b+, CD45+ and Iba1+ populations of cells in the rat cochlea, particularly in Rosenthal's canal, inner sulcus and stria vascularis. Next, we isolated and enriched the population of CD11b+ cells from the cochlea and immortalized these cells with the 12S E1A gene of adenovirus in a replication-incompetent retroviral vector to derive a novel microglial cell line, designated Mocha (microglia of the cochlea). The resulting Mocha cells express a number of markers consistent with microglia and respond to lipopolysaccharide (LPS) stimulation by upregulation of genes (Cox2, ICAM-1, Il6r, Ccl2, Il13Ra and Il15Ra) as well as releasing cytokines (IL-1beta, IL-12, IL-13 and RANTES). As evidence of microglial function, Mocha cells phagocytose fluorescent beads at 37°C, but not at 4°C. The expression pattern of microglial markers in Mocha cells suggests that immortalization leads to a more primitive phenotype, a common phenomenon in immortalized cell lines. In summary, Mocha cells display key characteristics of microglia and are now available as a useful model system for the study of cochlear microglial behavior, both in vitro and in vivo.