Current studies include roles of microglia in brain injury and development; anti-inflammatory and immuno-suppressive roles of lipocortin 1 and regulation of eicosanoids in brain and kidney.
Epidermal growth factor (EGF) stimulates the tyrosine kinase activity of transmembrane receptors and apparently enhances the proliferative rate of cells in vitro. However, it seems unlikely that regulation of proliferation is the only, or even the major, activity of EGF in intact organisms. With the objective of gaining clues to the role of EGF in situ, we have developed methods to localize a preferential substrate for the EGF receptor kinase known as lipocortin 1 (LC1) during morphogenesis and recovery from trauma. In most cells of embryonic and adult mammals LC1 is undetectable, but with methods developed in our laboratory LC1 expression has been demonstrated in restricted loci, and it often co-localizes with phosphotyrosine.
LC1 belongs to a family of proteins known as annexins that share Ca++-dependent affinity for membrane phospholipids based on four homologous Ca++-binding domains that are novel; i.e., the sequences show no homology to the EF-hand binding sites of calmodulin-like proteins. Annexins are highly conserved regulatory proteins that are detected in human placenta, Drosophilia, plants and the slime mold Dictyostelium. Anti-inflammatory and immuno-suppressive activities have been demonstrated for LC1.
Our laboratory has shown that regulation of LC1 expression is associated with the development of sensory commissures in the CNS and with the morphogenesis of branched tubular organs including kidney, lung, salivary glands, placenta and inner ear. In the adult kidney, LC1 levels increase more than five-fold during recovery from ischemia, and studies are underway to examine the relationship of LC1 to EGF and prostaglandins in renal pathophysiology.
Most recently, we have demonstrated that LC1 identifies microglia, the immuo-surveillance cells of the CNS. LC1 is useful as a marker to study the roles of microglia in the normal adult and developing nervous system, and following damage to the brain. Specifically, these studies focus on (1) the degree to which LC1 co-localizes with other glia markers under normal conditions and following CNS damage; (2) whether ramified mature microglia are progeny of LC1-positive floor plate glia; (3) phosphotyrosine signals in microglia, phosphotyrosylated-LC1 and the phosphotyrosine phosphatase CD-45 that also is present in microglia; and (4) the characteristics of microglia in vitro in brain slices and cell cultures under different conditions and in response to stimulation by cytokines. These studies should provide new insights into the origin and roles of microglia in both normal and challenged CNS.