Cardiac allograft vasculopathy (CAV) limits survival after heart transplantation. CAV is caused by damage to the allograft endothelium, resulting in occlusive intimal lesions. Administration of ex vivo cultured early endothelial progenitor cells (eEPCs) enhances endothelial repair and inhibits intimal hyperplasia. However, engraftment rates of eEPCs remain low. We examined changes in eEPC adhesion molecule expression during ex vivo cultivation, and how these changes affect their ability to adhere. Compared to their parent cell population (freshly isolated peripheral blood mononuclear cells, PBMCs), eEPCs had decreased expression of integrins necessary to form firm adhesions with endothelial cells. Despite this eEPCs showed an enhanced ability to adhere under static conditions compared to PBMCs. However, under conditions of physiological flow, eEPC rolling adhesion was reduced compared to PBMCs. We hypothesize that low eEPC retention rates observed in vivo may be due to impaired eEPC rolling resulting from ex vivo culture.

Liver failure, which is the result of liver injury and pathological inflammation, is currently only successfully treated by organ transplantation. However donor organ shortages preclude transplantation for many patients in need. Thus, bioartificial liver systems (BALS) are being developed as a bridge to transplantation, or to create an environment conducive to liver regeneration. Hepatocytes, the main functional cells of the liver, are the cells of choice for BALSs, but in standard conditions ex vivo, they rapidly suffer from a reduction of their functionality and viability. Coculture with stromal cells, for example bone marrow mesenchymal stromal cells (BM-MSC), has been shown to improve, and extend, hepatocyte function ex vivo up to 21 days. But, only small numbers of BM-MSCs can be harvested from adult volunteers. We have previously described an alternative, more plentiful, source of MSCs — human umbilical cord perivascular cells (HUCPVC) — that are easily expanded and non-alloreactive. Our hypothesis was that HUCPVCs are putative stromal cells for hepatocytes. Our results show that HUCPVCs improved hepatocyte albumin secretion, urea synthesis and maintained hepatocyte cytochrome activity and the expression of hepato-specific genes. Furthermore, there was a net proliferation of hepatocytes, which were polarized in coculture with HUCPVCs, as judged by functional bile canaliculi that were present for up to 40 days. We found that both soluble and non-soluble factors contributed to these effects, while neither was able to allow net proliferation individually. Moreover, HUCPVCs expressed both hepato-trophic and anti-inflammatory factors, at different levels to BM-MSCs, indicating the potential for differential hepato-therapeutics. We conclude that HUCPVCs are putative stromal cells for hepatocytes; they improve hepatocyte functionality, polarity, morphology and net proliferation, and thus present an opportunity for the improvement of both BALS function and liver therapy.

Despite advances in investigating functional aspects of osteoblast (OB) differentiation, especially studies on how bone proteins are deposited and mineralized, there has been little research on the intracellular trafficking of bone proteins during OB differentiation. Collagen synthesis and secretion is the major function of OBs and is markedly upregulated upon ascorbic acid (AA) stimulation, significantly more so than in fibroblast cells. Understanding the mechanism by which collagen is mobilized in specialized OB cells is important for both basic cell biology and bone disease studies. Cellular organelles and vesicles in the exocytic and endocytic pathways have a distinctive spatial distribution and their trafficking is aided by many molecules, Rab GTPases being a master regulator. In this work, I identified the Rab GTPases that are upregulated during OB differentiation using microarray analysis, namely Rab1, Rab3d, and Rab27b, and investigated their role in regulating the trafficking of collagen from the site of synthesis in the ER to the Golgi and ultimately to the plasma membrane (PM) utilizing their dominant negative (DN) expression. The experimental halting of biosynthetic trafficking by these mutant Rabs initiated proteasome-mediated degradation of procollagen and ceased global protein translation. Acute expression of Rab1 and Rab3d DN constructs resulted in impaired ER to Golgi trafficking of procollagen. Similar expression of Rab27b DN constructs resulted in dispersed collagen vesicles which may represent failed secretory vesicles sequestered in the cytosol. A significant and strong reduction in extracellular collagen levels also was observed showing roles of Rab1, Rab3d and Rab27b in the specific function of these major collagen producing cells in the body. I further observed that a fraction of procollagen colocalized with lysosomes which was markedly increased when procollagen was experimentally misfolded. Lysosomes, essential organelles for intracellular degradation, are generally sequestered near the cell centre to receive vesicles with contents targeted for destruction. During AA-induced differentiation of OB cells, I saw a marked increase in total degradative lysosome organelles in addition to an enhanced endocytic rate. Interestingly, lysosomes were dispersed toward the cell periphery in differentiating OBs without being secreted. This required intact microtubules for long range transport and was kinesin motor-dependent but did not involve cytosolic acidification. Moreover, impairment of lysosome dispersion markedly reduced AA-induced OB differentiation. Taken together, this study provides an important general mechanism for cell secretion phenomena that may ultimately lead to clinical targets for treatments of diseases driven by aberrant collagen processing and secretion including Osteogenesis Imperfecta (OI).

Mutations in the chloride-proton antiporter, ClC-5, cause Dent’s disease, a kidney disease defined by excessive loss of proteins in the urine. ClC-5 resides on early endosomal membranes in proximal tubule epithelial cells, where it facilitates protein receptor-mediated endocytosis. Loss-of-function mutations in ClC-5 produce proximal tubule defects in protein reabsorption. This study characterized an epithelial cell phenotype for nonsense ClC-5 mutations, R648X and R704X. Both ClC-5 mutants displayed defective biosynthesis, mistrafficking and ER localization. This study showed that ClC-5 mutations, R718X and C221R, which are also misprocessed and ER retained, are targeted for proteasomal degradation as a means to be efficiently eliminated from the ER. In addition, we have shown that a missense mutation in ClC- 5, C221R, causes a global conformational change in the antiporter, which likely reflects protein misfolding, as evident by enhanced susceptibility to trypsin proteolysis. We have characterized ClC-5 disease-causing mutations in an epithelial cell model of the proximal tubule.

Tie2 is a receptor tyrosine kinase (RTK) involved in numerous aspects of both normal and pathological angiogenesis. Proper functioning of this receptor is essential for normal development of the vasculature in the embryo as well as vessel maintenance and at sites of active angiogenesis in the adult. A growing list of pathological states has been attributed to a disruption of the angiogenic ‘balance’ including psoriasis, arthritis, atherosclerosis and diabetic retinopathy. Elucidating the molecular mechanisms behind this important biological process will provide insight into the various molecules involved as well as provide potential targets for novel angiogenic therapies. In an attempt to better understand the signaling pathways downstream of the Tie2 receptor we have studied tyrosine residues on the receptor believed to play an important role in Tie2 function. Of these, we have identified Y1111 as a negative regulatory site on Tie2. Mutation of this site affects receptor phosphorylation and kinase activity. Furthermore, protease digestion studies indicate that mutation of Y1111 may alter receptor conformation and potentially relieve negative inhibition imparted by the C-tail of Tie2. As well, we examined potential Tie2 downstream binding partners, specifically the novel Grb7 family of proteins. This work describes for the first time tyrosine phosphorylation of Grb14, an adaptor molecule previously shown to bind Tie2 in vitro. Moreover, our data suggests a role for this adaptor in Tie2 signal transduction involving two tyrosine residues in the receptor C-terminal tail; Y1100 and Y1106. These studies provide important insight into both signal transduction downstream of Tie2 as well as help us understand some of the molecular mechanisms behind the intrinsic ability of this RTK to regulate its own activity.

Liver failure, which is the result of liver injury and pathological inflammation, is currently only successfully treated by organ transplantation. However donor organ shortages preclude transplantation for many patients in need. Thus, bioartificial liver systems (BALS) are being developed as a bridge to transplantation, or to create an environment conducive to liver regeneration. Hepatocytes, the main functional cells of the liver, are the cells of choice for BALSs, but in standard conditions ex vivo, they rapidly suffer from a reduction of their functionality and viability. Coculture with stromal cells, for example bone marrow mesenchymal stromal cells (BM-MSC), has been shown to improve, and extend, hepatocyte function ex vivo up to 21 days. But, only small numbers of BM-MSCs can be harvested from adult volunteers. We have previously described an alternative, more plentiful, source of MSCs — human umbilical cord perivascular cells (HUCPVC) — that are easily expanded and non-alloreactive. Our hypothesis was that HUCPVCs are putative stromal cells for hepatocytes. Our results show that HUCPVCs improved hepatocyte albumin secretion, urea synthesis and maintained hepatocyte cytochrome activity and the expression of hepato-specific genes. Furthermore, there was a net proliferation of hepatocytes, which were polarized in coculture with HUCPVCs, as judged by functional bile canaliculi that were present for up to 40 days. We found that both soluble and non-soluble factors contributed to these effects, while neither was able to allow net proliferation individually. Moreover, HUCPVCs expressed both hepato-trophic and anti-inflammatory factors, at different levels to BM-MSCs, indicating the potential for differential hepato-therapeutics. We conclude that HUCPVCs are putative stromal cells for hepatocytes; they improve hepatocyte functionality, polarity, morphology and net proliferation, and thus present an opportunity for the improvement of both BALS function and liver therapy.

Despite advances in investigating functional aspects of osteoblast (OB) differentiation, especially studies on how bone proteins are deposited and mineralized, there has been little research on the intracellular trafficking of bone proteins during OB differentiation. Collagen synthesis and secretion is the major function of OBs and is markedly upregulated upon ascorbic acid (AA) stimulation, significantly more so than in fibroblast cells. Understanding the mechanism by which collagen is mobilized in specialized OB cells is important for both basic cell biology and bone disease studies. Cellular organelles and vesicles in the exocytic and endocytic pathways have a distinctive spatial distribution and their trafficking is aided by many molecules, Rab GTPases being a master regulator. In this work, I identified the Rab GTPases that are upregulated during OB differentiation using microarray analysis, namely Rab1, Rab3d, and Rab27b, and investigated their role in regulating the trafficking of collagen from the site of synthesis in the ER to the Golgi and ultimately to the plasma membrane (PM) utilizing their dominant negative (DN) expression. The experimental halting of biosynthetic trafficking by these mutant Rabs initiated proteasome-mediated degradation of procollagen and ceased global protein translation. Acute expression of Rab1 and Rab3d DN constructs resulted in impaired ER to Golgi trafficking of procollagen. Similar expression of Rab27b DN constructs resulted in dispersed collagen vesicles which may represent failed secretory vesicles sequestered in the cytosol. A significant and strong reduction in extracellular collagen levels also was observed showing roles of Rab1, Rab3d and Rab27b in the specific function of these major collagen producing cells in the body. I further observed that a fraction of procollagen colocalized with lysosomes which was markedly increased when procollagen was experimentally misfolded. Lysosomes, essential organelles for intracellular degradation, are generally sequestered near the cell centre to receive vesicles with contents targeted for destruction. During AA-induced differentiation of OB cells, I saw a marked increase in total degradative lysosome organelles in addition to an enhanced endocytic rate. Interestingly, lysosomes were dispersed toward the cell periphery in differentiating OBs without being secreted. This required intact microtubules for long range transport and was kinesin motor-dependent but did not involve cytosolic acidification. Moreover, impairment of lysosome dispersion markedly reduced AA-induced OB differentiation. Taken together, this study provides an important general mechanism for cell secretion phenomena that may ultimately lead to clinical targets for treatments of diseases driven by aberrant collagen processing and secretion including Osteogenesis Imperfecta (OI).

Mutations in the chloride-proton antiporter, ClC-5, cause Dent’s disease, a kidney disease defined by excessive loss of proteins in the urine. ClC-5 resides on early endosomal membranes in proximal tubule epithelial cells, where it facilitates protein receptor-mediated endocytosis. Loss-of-function mutations in ClC-5 produce proximal tubule defects in protein reabsorption. This study characterized an epithelial cell phenotype for nonsense ClC-5 mutations, R648X and R704X. Both ClC-5 mutants displayed defective biosynthesis, mistrafficking and ER localization. This study showed that ClC-5 mutations, R718X and C221R, which are also misprocessed and ER retained, are targeted for proteasomal degradation as a means to be efficiently eliminated from the ER. In addition, we have shown that a missense mutation in ClC- 5, C221R, causes a global conformational change in the antiporter, which likely reflects protein misfolding, as evident by enhanced susceptibility to trypsin proteolysis. We have characterized ClC-5 disease-causing mutations in an epithelial cell model of the proximal tubule.

The course of pathogenic bacterial infection is dependent on the interactions between the host immune response and the bacterial virulence mechanisms. Our lab previously discovered that the Survival of Motor Neuron (SMN) protein complex undergoes a change in subcellular localization during infection with invasive Shigella bacteria, forming novel cytoplasmic aggregates called "U bodies". Similar results were obtained with other intracellular bacterial pathogens suggesting that these U bodies are a fundamental entity in microbial pathogenesis. Notably, the SMN complex normally plays a key role in the assembly of the spliceosomal U snRNA. We have shown during infection that there are changes in U snRNA maturation and splicing patterns. Importantly, we have found that U bodies are downstream of a stress pathway involving the stress-inducible ATF3 protein. Altogether, intracellular bacterial infection induces novel cellular stress pathways that disrupt normal SMN complex function and leads to changes in U snRNA associated functions.

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.