The mechanisms that mediate acute exacerbations in chronic inflammatory diseases such as periodontitis are not understood. IL-8 is a potent chemoattractant for neutrophils in acute inflammatory lesions. We investigated the role of fibroblast-mast cell interactions on short-term IL-8 release. Human gingival fibroblasts were co-cultured with human mast cells (HMC-1). After co-culture, the concentration of IL-8 was measured by ELISA. HMC co-cultured with fibroblasts increased IL-8 secretion by >6-fold, which required intercellular contact and was blocked by the gap junction inhibitor BGA. Thapsigargin-induced elevations of intracellular calcium increased IL-8 levels by 15-fold. Chemotaxis of human neutrophils was significantly enhanced in response to conditioned medium from co-cultures. Calcein-dye transfer showed intercellular, gap junction communication between HMC and fibroblasts that was dependent in part on β1 integrins. We conclude that mast cells adhere to fibroblasts and promote IL-8 secretion, thereby enhancing neutrophil chemotaxis and possibly the perpetuation of the inflammatory response.

Helicobacter pylori is a gram-negative bacterium that infects half the world population and is the etiological cause of numerous gastric pathologies. H. pylori possess numerous mechanisms to promote its survival and modulate host immunity. We propose that H. pylori can modulate intercellular communication by manipulating the host exosome pathway. Exosomes are secreted nanovesicles that contain different proteins and microRNAs that can be transferred between cells to alter cell signaling and gene expression. We demonstrate that H. pylori infection increases host exosome secretion. Furthermore, infection can alter exosome composition as VacA, a bacterial virulence factor, can be exported in exosomes and Argonaute 5, a miRNA effector protein, is upregulated in exosomes during infection. Lastly, we show preliminary evidence that infection-modulated exosomes can modulate immune-regulatory signaling in dendritic cells by activating STAT3. Together, these studies elucidate a novel mechanism by which H. pylori can modulate the host environment and promote its continued survival.

Inflammatory bone diseases like rheumatoid arthritis and periodontal disease lead to increased bone loss in the inflamed areas. The multinucleated bone resorbing cells, the osteoclasts, present in these diseases are larger than normal, and these larger osteoclasts (10+ nuclei) resorb more bone and more often than smaller osteoclasts (2-5 nuclei). Thus, the focus of this thesis was to determine if there are differences in mechanisms of osteoclast activation between large and small osteoclasts. Experiments using authentic rabbit osteoclasts and RAW 264.7-derived osteoclasts revealed differences in the expression of a number of activating factors; with large osteoclasts expressing higher levels of activating receptors (RANK, IL-1RI, TNFR1 and integrins αv and β3), as well as enzymes involved in cellular resorption, while small osteoclasts expressed higher levels of an alleged fusion receptor and the inhibitory receptor, IL-1RII. Further studies revealed that large osteoclasts more readily responded to stimulation by IL-1 compared to small osteoclasts and at lower concentrations suggesting this is a result of their higher expression of activating receptors. Differences in responses to the IL-1 isoforms, IL-1α and IL-1β, were also seen in large osteoclasts: IL-1α generated more large osteoclasts over the course of differentiation, while IL-1β induced changes in cell morphology and in the induction of integrin β3 phosphorylation. These observations suggested that differences in osteoclast responses are induced by IL-1α and IL-1β and it led to the hypothesis that there are differences in signaling between large and small osteoclasts. To elucidate differences in signaling mechanisms a signaling pathway microarray was used which revealed higher expression of Vegfa in large compared to small osteoclasts. Osteoclast differentiation with RANKL increased Vegfa gene expression in a time-dependent manner and VEGF-A secretion was elevated in populations enriched for large osteoclasts. Furthermore, mechanistic studies with inhibitors of transcription factors involved in differentiation revealed that RANKL-mediated Vegfa expression in large osteoclasts was regulated by the NF-κB pathway via induction of Hif1α. These results support the hypothesis that signaling differences exist between large and small osteoclasts and implicates VEGF-A in osteoclast hyperactivity in inflammatory conditions.

Biological outputs of insulin/IGF signaling are regulated through essential mediators, such as IRSs, PI3-kinase, and PKB/Akt. These mediators serve critical roles in signal propagation, feedback, and as junctions for crosstalk with other pathways. Abnormal insulin/IGF signaling results in disease, such as obesity, diabetes, and cancer. Given the vital role of this signaling pathway to human health, unraveling its regulatory mechanisms is crucial. Components of this pathway are highly conserved throughout evolution. PTEN, one of the well-defined regulators of this pathway, functions as a lipid phosphatase that negatively regulates insulin/IGF-1 signaling at the PIP3 level, a phosphoinositol that is upregulated by activated PI3-kinase in both Drosophila and mammals. To discover genetic modulators of PTEN in Drosophila, we performed a loss-of-function genetic screen to identify molecules that modify the phenotype elicited by PTEN overexpression in the Drosophila eye. From this screen, we identified a member of the Dbl-family, the guanine nucleotide exchange factor DRhoGEF2, which suppresses the PTEN-overexpression eye phenotype via its effects on dPKB/dAkt activation. By conducting a genetic rescue, we established that PDZ-RhoGEF, a member of the regulator of G-protein signal (RGS)-like domain containing Rho GEFs (RGS-RhoGEFs) subfamily of Dbl-family GEFs, is the mammalian counterpart of DRhoGEF2. PDZ-RhoGEF is essential for cell proliferation and survival through ROCK-dependent activation of IRS/PI3-kinase signaling cascade, which has a major impact on adipose tissue homeostasis. Through an integrative approach, we have demonstrated that DRhoGEF2/PDZ-RhoGEF-dependent signaling has tissue-specific effects on insulin/IGF-signaling throughput in both Drosophila and mammals. Particularly, we have demonstrated the role played by PDZ-RhoGEF in diet related pathology, provides an alternative therapeutic opportunity in disease intervention.

The scaffolding protein anillin plays a crucial role during cytokinesis – the physical separation of daughter cells following chromosome segregation. Anillin binds filamentous F-actin, non-muscle myosin II and septins, and in cell culture models has been shown to restrict actomyosin contractility to the cleavage furrow. Whether anillin also serves this function during the incomplete cytokinesis that occurs in developing germ cells has remained unclear. Localization of anillin to several actin-rich structures in developing male germ cells also suggests potential roles for anillin outside of cytokinesis. In this study, I demonstrate that anillin is required for cytokinesis in dividing Drosophila spermatocytes. In addition, spermatid individualization is defective in anillin-depleted cells, although similarities to another cytokinesis mutant, four wheel drive, suggest this may be a secondary effect of failed cytokinesis. Anillin, septins and myosin II stably associate with the cleavage furrow in wild-type dividing spermatocytes. Anillin is necessary for recruitment of septins to the cleavage furrow, and for maintenance of Rho, F-actin and myosin II at the equator in late stages of cytokinesis. Membrane trafficking appears unaffected in anillin-depleted cells, although, unexpectedly, ectopic expression of one membrane trafficking marker, DE-cadherin-GFP, suppresses the cytokinesis defect. DE-cadherin-GFP recruits β-catenin (armadillo) and α-catenin to the cleavage furrow and stabilizes F-actin at the equator. Taken together, my results suggest that the anillin-septin and cadherin-catenin complexes can serve as alternative means to promote tight physical coupling of F-actin and myosin II to the cleavage furrow and successful completion of cytokinesis.

The lymphatic system complements the blood circulatory system in absorption and transport of nutrients, and in the maintenance of homeostasis. Historically, the angiogenesis field has advanced faster and farther than the field of lymphangiogenesis. The discovery of lymphatic markers and the emerging evidence implicating the lymphatic system as a central player in a variety of pathological conditions has attracted research interest and driven the field forward. Research efforts have produced the observation that regulators of the blood endothelium are frequently members of the same protein families of regulators of the lymphatic endothelium. More importantly, these regulators do not act discretely, restricting their regulatory activities to one endothelial cell (EC) type. Two examples of regulators that behave in this manner are the VEGF and the Angiopoietin families of proteins, which have cell-type-dependent effects on EC processes such as migration, proliferation and survival. The study of these regulators therefore requires an in vitro EC system capable of accommodating the simultaneous characterization of the signaling pathways downstream of these shared molecular regulators in venous, arterial and lymphatic endotheliums. To build such an in vitro system, I isolated and validated lymphatic, venous, and arterial ECs derived from vessels of bovine mesentery. The proteomes of the three cell types were comparatively studied using two-dimensional polyacrylamide gel electrophoresis followed by mass spectrometric identification. The three cell types were used in a subtractive immunization scheme for the production of a monoclonal antibody selectively reactive to a potentially novel surface protein marker of lymphatic ECs. The studies recorded herein all share the common goal of identifying and characterizing unique molecular signatures that distinguish lymphatic ECs from blood ECs, and that may underline the cellular biology of the lymphatic endothelium as distinct from the blood endothelium.

The clinical manifestations of hemolytic disease of the fetus and newborn mediated by anti-K, an antibody of the Kell blood group system, are distinguishable from the classical form of the disease. Affected fetuses have low numbers of circulating reticulocytes and antibody titers and bilirubin levels are not reliable predictors of anemia. These observations suggest that antibodies to Kell glycoprotein lead to anemia through suppression of erythropoiesis. This study established a liquid erythroid progenitor cell culture model in which to perform analyses on the mechanism of the suppressive growth effect of anti-Kell glycoprotein. Using this culture model, this study demonstrated the requirement for co-ligation of Kell glycoprotein by a bivalent antibody for growth suppression. The absence of markers of apoptosis in cell cultures treated with anti-Kell glycoprotein suggests that the mechanism of growth suppression is distinct from programmed cell death and necrosis. Furthermore, this growth suppression cannot be rescued by erythropoietin.

The HECT E3 ubiquitin ligase Nedd4-1 was previously shown to regulate diverse processes such as cell and animal growth, insulin signaling, and lysosomal trafficking. To further elucidate the cellular functions of Nedd4-1, Nedd4-1 knockout mouse embryonic fibroblasts were characterized relative to their wild type counterparts. Immunofluorescence experiments revealed an altered lysosomal distribution in the knockout cells, although their lysosomal proteolytic function appeared normal. Transmission Electron Microscopy revealed striking morphological differences, especially regarding the lysosome and endoplasmic reticulum of the knockout cells. Another aspect of my studies examined the interaction between Nedd4-1 and Angiomotin (p130-AMOT), which involves the same motifs required to sequester transcriptional co-activators YAP and TAZ in the cytoplasm. To test either a competitive or non-competitive mode of binding, co-immunoprecipitation experiments involving p130-AMOT, the Nedd4 proteins, and YAP or TAZ were performed, with results not supporting a competitive mode of interaction. Overall, my results demonstrate new Nedd4-1 cellular functions.

Specialized cells of the innate immune system, such as macrophages, employ lysosomal enzymes, together with cationic peptides and reactive oxygen intermediates, to eliminate invading microorganisms ensnared within phagosomes. The effectiveness of this impressive armamentarium is potentiated by the acid pH generated by the vacuolar-type ATPase (V-ATPase). The determinants of the luminal pH of phagosomes and of the lysosomes they fuse with are not completely understood, but the V-ATPase is known to be electrogenic and net accumulation of protons requires charge compensation. For this reason, counter-ion pathways are thought to serve a central role in the control of acidification. It has generally been assumed that a parallel anion influx accompanies proton pumping to dissipate the voltage that tends to build up. In fact, impaired chloride channel activity in cystic fibrosis has been proposed to underlie the defective phagolysosome acidification and microbial killing reported in lung macrophages. In the first part of this thesis, I devised methods to dialyze the lumen of lysosomes in intact cells, while monitoring lysosomal pH, in order to assess the individual contribution of counter-ions to acidification. Surprisingly, anions were found to be completely dispensable for proton pumping, whereas the presence of permeant cations in the lysosomal lumen was essential. Accordingly, defects in lysosomal anion permeability cannot explain the impaired microbicidal capacity of phagocytes in cystic fibrosis. Even though counter-ion permeation pathways exist, dissipation of the electrical contribution of the V-ATPase may not be complete. If present, a transmembrane potential would alter the rate and extent of proton accumulation in phagosomes and lysosomes. However, no estimates of the voltage across the phagosomes were available. To overcome this deficiency, in the second part of this thesis, I describe a noninvasive procedure to estimate the voltage across the phagosome using fluorescence resonance energy transfer. This novel approach, in combination with organellar pH measurements, demonstrated that proton pumping is not limited by counter-ion permeability.

There is a growing need for bone cells to be used in the generation and repair of bone tissues that have become destroyed as a result of disease (e.g. osteoporosis), injuries and genetic deficiencies. Human umbilical cord blood has been a source of cells that is being investigated for its ability to generate cells for repair of various tissues including bone, which is the focus of this investigation. Similarly cord blood can also be used as a source of progenitors for osteoclasts that might be used for management of other diseases of bone characterized by defects in these cells (e.g. osteopetrosis). Moreover, there are few reliable in vitro models for human osteoclasts and so the ability to develop a cell model for human osteoclasts will also permit more meaningful studies on regulation of these cells than possible in the past. One of the setbacks suffered by researchers in designing therapeutic uses for stem cells is that in laboratory animals tumours can arise from these transplanted and pleuripotential cells. This suggests that stem cells might also have a dysregulated apoptosis pathway, which is critically important to understand before the safe use of stem cells can be assured. In order to increase our understanding of apoptosis in bone cells in particular, studies were done to try to understand the role of harakiri, a pro-apoptotic gene, in the development of osteoblasts and osteoclasts. Therefore, this series of study had two main foci; the development of human bone cells, particularly osteoclasts and osteoblasts, from human umbilical cord blood, and to understand further the mechanisms regulating apoptosis in bone cells. This study showed that osteoblasts could not be derived easily from human cord blood cells while it was possible to generate fully functional osteoclasts, which demonstrated unique properties. Studies done on harakiri deficient mice showed that absence of this gene caused an increase in osteoblast formation and a decrease in osteoclast formation. These findings can be exploited when considering the development of pharmacological agents that might be used in the future to modulate osteoclast cell development, function, and apoptosis.