To understand the system of secreted proteins and receptors involved in cell-cell signaling, we produced a comprehensive set of recombinant secreted proteins and the extracellular domains of transmembrane proteins, which constitute most of the protein components of the extracellular space. Each protein was tested in a suite of assays that measured metabolic, growth, or transcriptional responses in diverse cell types. The pattern of responses across assays was analyzed for the degree of functional selectivity of each protein. One of the highly selective proteins was a previously undescribed ligand, designated interleukin-34 (IL-34), which stimulates monocyte viability but does not affect responses in a wide spectrum of other assays. In a separate functional screen, we used a collection of extracellular domains of transmembrane proteins to discover the receptor for IL-34, which was a known cytokine receptor, colony-stimulating factor 1 (also called macrophage colony-stimulating factor) receptor. This systematic approach is thus useful for discovering new ligands and receptors and assessing the functional selectivity of extracellular regulatory proteins.

There are many transmembrane receptor-like proteins whose ligands have not been identified. A strategy for finding ligands when little is known about their tissue source is to screen each extracellular protein individually expressed in an array format by using a sensitive functional readout. Taking this approach, we have screened a large collection (3,191 proteins) of extracellular proteins for their ability to activate signaling of an orphan receptor, leukocyte tyrosine kinase (LTK). Only two related secreted factors, FAM150A and FAM150B (family with sequence similarity 150 member A and member B), stimulated LTK phosphorylation. FAM150A binds LTK extracellular domain with high affinity (K D = 28 pM). FAM150A stimulates LTK phosphorylation in a ligand-dependent manner. This strategy provides an efficient approach for identifying functional ligands for other orphan receptors.leukocyte tyrosine kinase | extracellular protein | library screening | FAM150A | orphan receptor M any biological processes and pathogenic conditions involve ligand/receptor signaling. There are numerous transmembrane receptor-like proteins whose ligands have not been identified. Most known ligand-receptor interactions were discovered by painstaking protein purification, genetic approaches, or sequence homology. Strategies using cDNA library expressionsuch as secretion trapping (1), mammalian expression cloning (2), yeast signaling display (3), and λ phage binding display (4)-have also identified ligands for orphan receptors. However, these approaches are limited by the unknown comprehensiveness of the cDNA library and by the fact that the libraries are biased toward high-abundance transcripts and not focused on the extracellular proteome. An alternative strategy is to screen secreted factors that are individually expressed in an array format in which there is no bias in expression of each protein based on the abundance of its cDNA. The advantages of this approach for deorphanization of receptors are that it is extremely sensitive and selective and that it covers the majority of the extracellular proteome. Although arrayed proteins have been used to identify receptor partners with low-affinity, high-avidity interactions (5-7), few studies have used a cell-signaling measurement to study "classic" high-affinity ligandreceptor interactions.Leukocyte tyrosine kinase (LTK) is a receptor tyrosine kinase that was identified in 1988 (8). The extracellular domain (ECD) of LTK has no known domain structure except a glycine-rich region, leading to a proposal that LTK is not activated by a protein ligand. LTK has a close homolog named anaplastic lymphoma kinase (ALK) (9). The LTK pathway has been implicated in autoimmunity, neuronal development, and cancer. One study showed that gain-of-function polymorphism of Ltk has been associated with systemic lupus erythematosus (SLE) pathogenesis (10). Ltk is expressed throughout the adult hippocampus, and mouse knockout studies indicated that both Ltk and Alk are involved in adult neurogenesis with some functio...

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Psychostimulants are insufficiently studied as adjunctive or monotherapy in adults with mood disorders. Most published studies have significant methodological limitations (eg, heterogeneous samples, dependent measures, type/dose of agent). In addition to improvements in methodological factors, a testable hypothesis is that psychostimulants may be more appropriately tested in select domains of psychopathology (eg, cognitive emotional processing), rather than as "broad-spectrum" antidepressants.

Calcium phosphates like hydroxyapatite (HA), beta-tricalcium phosphate (beta-TCP), and their mixtures (biphasic calcium phosphates; BCP) are used clinically to repair bone defects. These materials can be difficult to handle and have no inherent biological activity. Handling properties of other bone substitute materials have been improved by combining them with an inert carrier such as Pluronic F-127 (Pluronic, BASF, Mt. Olive, NJ), while the addition of bone morphogenetic proteins (BMP) with such implants has also been shown to enhance bone repair. This study assessed the impact of adding Pluronic and BMPs to an HA (C-Graft) or a BCP (80/20 HA/beta-TCP ratio; Algisorb) implant's ability of promote bony repair in the rabbit calvarial defect model.Twenty-five New Zealand white rabbits were divided into 5 groups of 5 animals each. Bilateral calvarial defects were made in the parietal bones of each animal. HA or BCP alone or combined with Pluronic and/or BMP were implanted into the defect sites. Animals were euthanized at 6 weeks, postoperatively. Bone regeneration was evaluated quantitatively by histomorphometry. The amount of bone regeneration, which occurred in defects containing HA and BCP, was similar over the time period studied. Incorporating Pluronic increased handling and moldability without compromising osteoconductivity of either calcium phosphate. The addition of BMP significantly increased the amount of new bone formed with all calcium phosphates studied (P < 0.05). These results suggest that Pluronic can be added to calcium phosphates to enhance handling and moldability without any negative effects on their biocompatibility and that healing can be enhanced with the incorporation of BMPs.