• Alternative splicing dysregulation in mental disorders

      Glatt, Stephen; Cohen, Ori S (2014)
      The brain's ability to adapt ultimately depends on the efficiency with which neuronal connections are made, destroyed, or manipulated. This connectivity is largely controlled by synaptic plasticity, which creates, strengthens, or weakens signals that are necessary for appropriate functioning of the organism. This constant rewiring allows an organism to learn, mature, and cope with the ever-changing environment. However, this rewiring is dependent on the ability to make new proteins, which highlights the importance of transcription, translation, and post-translational modification in the process of synaptic plasticity. Among these cellular functions, transcription plays a key role in providing the necessary variability that is required to regulate neurodevelopment and cognitive behaviors. During transcription, alternative splicing regulates the contents of transcriptomic elements by cutting and stitching the transcribed pre-mRNA and adjusting the configuration of the mature mRNA(s) to meet the necessary cellular requirements. Therefore, it is conceivable that alternative splicing abnormalities can result in inappropriate adjustment of the transcriptome and result in pathological adaptation. In this dissertation, I review the evidence of dysfunctional gene splicing in neuropsychiatric disorders. Then I evaluate the extent of alternative splicing in an animal model for social interaction. This model utilizes valproic acid exposure at a critical developmental period to illicit significant and long-lasting changes in social interaction behavior. Next, I explore the abundance and types of alternative-splicing dysregulationin postmortembrain tissue samples from schizophrenia patients as compared to non-psychotic comparison subjects. Finally, I describe the mechanisms by which a schizophrenia-associated polymorphism in a strong candidate gene (DRD2, which encodes the D2 dopamine receptor) disrupts alternative splicing and leads to inappropriate transcription that is associated with cognitive dysfunction. Collectively, these results reinforce the notion that consideration of genetic variants that dysregulate particular mRNA isoforms and understanding the biological consequence of expressing such isoforms is a crucial step in our efforts to understand human behavior and to develop therapeutic interventions for mental disorders.
    • ANTIVIRAL ACTIVITY AND MECHANISM OF ACTION OF A NOVEL URACIL ANALOG FOR VARICELLA-ZOSTER VIRUS

      Moffat, Jennifer; DE, CHANDRAV (2015)
      The alphaherpesvirus varicella-zoster virus (VZV) is widespread in humans. VZV causes primary and recurrent diseases that are preventable with live vaccines and are treatable with antiviral drugs. New antiviral drugs for varicella-zoster virus (VZV) with increased potency are needed, especially to prevent post-herpetic neuralgia. The purpose of this project was to evaluate β-L-1-[5-(E-2-Bromovinyl)-2-(hydroxymethyl)-1,3-dioxolan-4- yl)] uracil (L-BHDU) and 5′-O-valyl-L-BHDU for efficacy, safety, resistance, and mechanism of action in three models of VZV replication: primary human foreskin fibroblasts (HFFs), skin organ culture (SOC) and in SCID-Hu mice with skin xenografts. We found that L-BHDU and valyl-L-BHDU were safe and effective against VZV in culture and in a mouse model. Herpes simplex virus Type 1 was also sensitive to LBHDU in cultured cells. The mechanism of action of L-BHDU and its effect on drugdrug interactions were not known. Given its similar structure to brivudine (BVdU), we addressed whether L-BHDU, like BVdU, inhibits 5-fluorouracil (5-FU) metabolism. LBHDU did not interfere with 5FU metabolism, indicating that L-BHDU is a safer drug than BVdU. However, L-BHDU antagonized the activity of acyclovir (ACV), BVdU and foscarnet (PFA) in cultured cells, which was due to competition for phosphorylation by VZV thymidine kinase (TK). The mechanism of action of L-BHDU was studied by evaluating its activity against related α-herpesviruses and by analyzing resistant VZV viii strains. VZV strains resistant to L-BHDU (L-BHDUR ) were cross-resistant to ACV and BVdU but not to PFA and cidofovir (CDV). Whole genome sequencing of L-BHDUR strains identified mutations in ATP-binding (G22R) and nucleoside binding (R130Q) domains of VZV TK. The purified L-BHDUR TKs were enzymatically inactive and failed to phosphorylate the drug. In wild type VZV- infected cells, L-BHDU was converted to L-BHDU mono- and diphosphate forms; cells infected with L-BHDUR virus did not phosphorylate the drug. We also investigated whether addition of nucleosides reversed LBHDU inhibition of VZV in dividing and quiescent HFFs. Excess thymidine and uridine, but not purines, in proportion to L-BHDU restored VZV replication only in dividing cells, suggesting that the active form of L-BHDU interfered with pyrimidine biosynthesis. Like other herpesviruses, VZV infection induced thymidine triphosphate (dTTP) in confluent cells while L-BHDU treatment decreased the dTTP pool. Some herpesviruses raise dNTP pools by inducing cellular enzymes. However, VZV infection did not increase cellular thymidylate synthase (TS) expression to facilitate viral replication. Furthermore, the active form of L-BHDU did not interfere with cellular metabolism, suggesting a viral target. Further studies are required to identify the target(s) of L-BHDU active form(s).
    • ANTIVIRAL ACTIVITY AND MECHANISM OF ACTION OF A NOVEL URACIL ANALOG FOR VARICELLA-ZOSTER VIRUS

      Moffat, Jennifer; DE, CHANDRAV (2015)
      The alphaherpesvirus varicella-zoster virus (VZV) is widespread in humans. VZV causes primary and recurrent diseases that are preventable with live vaccines and are treatable with antiviral drugs. New antiviral drugs for varicella-zoster virus (VZV) with increased potency are needed, especially to prevent post-herpetic neuralgia. The purpose of this project was to evaluate β-L-1-[5-(E-2-Bromovinyl)-2-(hydroxymethyl)-1,3-dioxolan-4-yl)] uracil (L-BHDU) and 5′-O-valyl-L-BHDU for efficacy, safety, resistance, and mechanism of action in three models of VZV replication: primary human foreskin fibroblasts (HFFs), skin organ culture (SOC) and in SCID-Hu mice with skin xenografts. We found that L-BHDU and valyl-L-BHDU were safe and effective against VZV in culture and in a mouse model. Herpes simplex virus Type 1 was also sensitive to LBHDU in cultured cells. The mechanism of action of L-BHDU and its effect on drugdrug interactions were not known. Given its similar structure to brivudine (BVdU), we addressed whether L-BHDU, like BVdU, inhibits 5-fluorouracil (5-FU) metabolism. LBHDU did not interfere with 5FU metabolism, indicating that L-BHDU is a safer drug than BVdU. However, L-BHDU antagonized the activity of acyclovir (ACV), BVdU and foscarnet (PFA) in cultured cells, which was due to competition for phosphorylation by VZV thymidine kinase (TK). The mechanism of action of L-BHDU was studied by evaluating its activity against related α-herpesviruses and by analyzing resistant VZV strains. VZV strains resistant to L-BHDU (L-BHDUR) were cross-resistant to ACV and BVdU but not to PFA and cidofovir (CDV). Whole genome sequencing of L-BHDUR strains identified mutations in ATP-binding (G22R) and nucleoside binding (R130Q) domains of VZV TK. The purified L-BHDUR TKs were enzymatically inactive and failed to phosphorylate the drug. In wild type VZV- infected cells, L-BHDU was converted to L-BHDU mono- and diphosphate forms; cells infected with L-BHDUR virus did not phosphorylate the drug. We also investigated whether addition of nucleosides reversed LBHDU inhibition of VZV in dividing and quiescent HFFs. Excess thymidine and uridine, but not purines, in proportion to L-BHDU restored VZV replication only in dividing cells, suggesting that the active form of L-BHDU interfered with pyrimidine biosynthesis. Like other herpesviruses, VZV infection induced thymidine triphosphate (dTTP) in confluent cells while L-BHDU treatment decreased the dTTP pool. Some herpesviruses raise dNTP pools by inducing cellular enzymes. However, VZV infection did not increase cellular thymidylate synthase (TS) expression to facilitate viral replication. Furthermore, the active form of L-BHDU did not interfere with cellular metabolism, suggesting a viral target. Further studies are required to identify the target(s) of L-BHDU active form(s).
    • Biological importance of TIMP-2 phosphorylation on MMP-2 activity

      Bourboulia, Dimitra; Bullard, Renee (2016)
      Matrix metalloproteinases (MMPs) are proteolytic enzymes that are secreted from the cell and play an important role in embryonic development and tissue remodeling. In cancer, MMPs are hyperactive, promoting degradation of the ex-tracellular matrix. Enhancement of MMP proteolytic activity allows tumor cells to migrate and invade surrounding tissues, increasing the chance of metastasis. Tissue inhibitor of metalloproteinases (TIMPs) are also known to act extracellu-larly, and are the endogenous inhibitors of MMPs. To inhibit the protease activi-ty of MMPs, the N-terminus of the TIMP protein binds to the catalytic domain of MMP at a ratio of 1:1. Studies from our lab have found that TIMP-2 is phosphor-ylated on three tyrosine residues, and this phosphorylation increases the inter-action with MMP-2. This is the first time that phosphorylation of TIMP-2 has been reported. Fascinatingly, the proto-oncogene tyrosine kinase c-Src was found to phosphorylate TIMP-2. This is significant in that c-Src has not yet been shown to act extracellularly, and there are no details within the current lit-erature describing how this protein may function outside of the cell. In this the-sis, we usedmammalian cells as a model to decipher whether TIMP-2 phosphor-ylation wasable to occur extracellularly,as well as the effect that phosphoryla-tion of TIMP-2 hadon its functionto both inhibit/activate MMP-2. We found that(1) c-Src is able to phosphorylate TIMP-2 extracellularly in conditioned me-vidia; and (2) phosphorylation of TIMP-2 enhances its function of inhibiting MMP-2 proteolytic activity, as well as assisting in the activation of pro-MMP-2. Our results suggest the presence of anovel mechanismin whichphosphoryla-tion of TIMP-2is able to regulate the extracellular environment through en-hanced interaction with MMP-2. The information gained from this research couldlead to development of novel therapies that use phosphorylated TIMP-2 as a means of decreasing cellular migration and invasion with the overall goal of preventing metastasis.
    • BRAIN SPECIFIC NEURAL EXTRACELLULAR MATRIX EXPRESSION AND MODIFICATIONS IN NEUROLOGICAL DISEASE AND DISORDERS

      Matthews, Rick; Dwyer, Chrissa (2013)
      The central nervous system (CNS) is extraordinarily complex in both structure and function. The neural extracellular matrix (ECM) is one of the key classes ofmolecules that regulates thedevelopment of the CNS and maintains its structure and function in the adult.Thereby understanding the function of the neural ECMis key to understanding the CNS. The neural ECM is composed of several nervous-system specificproteins, which are hypothesized to uniquely contribute to the defining physiological functions of the CNS. However,work in this area has been hindered by the highly complex molecular properties of the neural ECM, which stem from alterations in expressionand modifications (resulting from glycosylation and proteolytic cleavage) of its constituents. Further defining mechanisms that alter the expression and modifications of neural ECM constituents are critical to fully understanding its complex array of functions. Often in neuropathologies, the neural ECM undergoes dynamic changes providing a valuable tool to further understand its function andthe opportunity to explore its contribution to disease pathology and utility as a therapeutic target. The work presented herein investigates the role of altered expression of the nervous-system specific ECM constituent, Brain Enriched Hyaluronan Binding (BEHAB)/ brevican(B/b), in glioma,and altered glycosylation of the nervous system enriched ECM constituent, RPTPζ/phosphacan, in O-mannosylrelated congenital muscular dystrophies (CMDs). Our work suggests that increased expression of B/b in the glioma tumor microenvironment (TEM) contributes to the pathological progression of these tumors, and reducing its expression is a valuable therapeutic strategy. Additionally, our work evaluates the transcriptional regulatory mechanisms leading to increases inB/b expression in glioma and highlights the potential value of these mechanisms as therapeutic targets. Our work also identifies the absence of O-mannosyl linked carbohydrates on RPTPζ/phosphacan in the brains of CMD models and suggests that altered glycosylation of RPTPζ/phosphacan may have a role in the neuropathologies underlying these disorders. Overall this work provides valuable insight intothe molecular complexities of the neural ECM stemming from changes in the expression and glycosylation of its constituents and furthers our understanding of its function in the normal CNS and in neuropathologies.
    • Bundling of cytoskeletal actin by the formin FMNL1 contributes to celladhesion and migration

      Blystone, Scott; Miller, Eric (2018)
      Metastasis is one of the leading causes of death in the world, affecting thousands every year. This is especially true of breast cancer, which can often result in the formation of secondary metastatic sites in the lung, liver, and bone marrow. There are many aspects to metastasis and an innumerable amount of molecular, biochemical, and cellular interactions contribute to its pathology. The ability of primary tumor cells to disseminate from the primary tumor, degrade the basement membrane, invade through the ECM, and eventually intravasate across the endothelial cell lining of the circulatory system or lymphatics requires a plethora of proteins, all working together in concert to achieve this. Nowhere in the cell is this more apparent than the actin cytoskeleton.Locomotion of cells requires several alterations in the actin cytoskeleton component of the cellular machinery. Generally speaking, cells must be able to polarize, form protrusions, adhere to the substratum, translocate, and then retract their tail, repeating this process as they continue to navigate to their destination. While there are many underlying aspects to this activity, spatiotemporal rearrangements of the actin cytoskeleton are key to the successful cellular motility. The mechanics behind dynamic actin cytoskeletal modifications are varied and complex, demonstrating the requirement for a variety of actin-associated, regulatory proteins.A crucial family of proteins involved in this process is the formin family of proteins. Formins are a relatively “new” group of actin modifiers which possess the unique ability to modify and generate linear actin filaments. While the members of this protein family all share some of the same actin modifying processes, many of these proteins also have functions exclusive to themselves. As a result, research into this field has blossomed and several novel features of different formins have been identified. Furthermore, alternative splice isoforms of several formins are often expressed in a variety of cell types, with specific functions attributed to each.The formin FMNL1 was originally identified in cells of a myeloid lineage and for many years was mostly thought to be involved in leukocyte adhesion and migration. Indeed, our lab has characterized many of the functions of this protein in both human and murine macrophages. However, as a result of the work in this dissertation, we have generated sufficient evidence suggesting that FMNL1 not only plays a role in breast cancer migration, but also exhibits functions unique to a specific alternative splice isoform of this protein.Our work on FMNL1 has pushed the field of study into this protein family in new directions. Herein, we have demonstrated that all three alternative splice isoforms of FMNL1 are expressed in a variety of cell types and the FMNL1ɣalternative splice isoform distinguishes itself from these isoforms via its ability to bundle linear actin filaments. Additionally, our data indicates that this is accomplished independently of the trademark FH2 domain, often thought to be the essential component of all formins. More specifically, we have identified a unique amino acid sequence in the C-terminal region of this isoform that most likely regulates this function. As a result, we have not only identified a potential therapeutic target for the treatment of metastasis via inhibition of cellular locomotion, but also pushed the field of formin research into a novel direction by providing insight which may foster new hypotheses and challenge classical theories regarding the relationship between formins and actin.
    • Characterization of Hic-5 in Cancer Associated Fibroblasts: A Role in Extracellular Matrix Deposition and Remodeling

      Turner, Christopher; Goreczny, Gregory (2017)
      Hic-5 (TGFβ1i1) is a focal adhesion scaffold protein that has previously been implicated in many cancer-related processes. However, the contribution of Hic-5 during tumor progression has never been evaluated, in vivo. In Chapter 2 of this thesis, I crossed our Hic-5 knockout mouse with the MMTV-PyMT breast tumor mouse model to assess the role of Hic-5 in breast tumorigenesis. Tumors from the Hic-5 -/-;PyMT mouse exhibited an increased latency and reduced tumor growth. Immunohistochemical analysis of the Hic-5 -/-;PyMT tumors revealed that the tumor cells were less proliferative. However isolated tumor cells exhibit no difference in growth rate. Surprisingly, Hic-5 expression was restricted to the tumor stroma. Further analysis showed that Hic-5 regulates Cancer Associated Fibroblast (CAF) contractility and differentiation which resulted in a reduced ability to deposit and reorganize the extracellular matrix (ECM) in two-and three-dimensions. Furthermore, Hic-5 dependent ECM remodeling supported the ability of tumor cells to metastasize and colonize the lungs.The molecular mechanisms by which CAFs mediate ECM remodeling remains incompletely understood. In Chapter 3 of this thesis, I show that Hic-5 is required to generate fibrillar adhesions, which are specialized structures that are critical for the assembly of fibronectin fibers. Hic-5 was found to promote fibrillar adhesion formation through a newly characterized interaction with tensin1, a scaffold protein that binds to β1 integrin and actin. Furthermore, this interaction was mediated by Src-dependent phosphorylation of Hic-5 in two and three-dimensional matrix environments to prevent β1 integrin internalization and subsequent degradation in the lysosome. This work highlights the importance of the focal adhesion protein, Hic-5 during breast tumorigenesis and provides insight into the molecular machinery driving CAF-mediated ECM remodeling.
    • Connexin43 and immunity : macrophage phagocytosis, cardiac calcinosis and autoimmune myocarditis

      Steven Taffet; Aaron Glass (2013)
      Connexin43 (Cx43) is a gap junction protein best known for coupling the cytoplasms of cardiac myocytes and allowing the efficient conduction of action potentials throughout the heart. In addition to the heart, Cx43 is also highly expressed in many immune cells and it has been attributed numerous roles in immunity. One such reported role was in macrophage phagocytosis. The first chapter in this dissertation explored the phagocytic activity of cultured and primary murine macrophages from wild type (WT) and Cx43-deleted (Cx43-/-) macrophages. No difference in phagocytic uptake was observed between the two groups using a series of target particles, indicating that Cx43 is dispensable for phagocytosis in macrophages. Given the spectrum of immune functions in which Cx43 has been ascribed a role, we set out to characterize its effect on a model of autoimmune myocarditis (EAM). Using the area of cardiac inflammatory infiltrate as a correlate of disease severity, we observed the progression of the disease to be independent of Cx43 status utilizing WT and Cx43-heterozygous (Cx43+/-) animals as well as radiation chimeric mice reconstituted with cells from donor WT, Cx43+/- and Cx43-/- mice. Although the severity of EAM did not measurably change when induced in animals with differing levels of Cx43 expression, substantial changes to ventricular Cx43 were noted in diseased hearts. Large foci were observed that completely lacked Cx43 immunofluorescence signal. Areas surrounding these foci exhibited disrupted Cx43 patterns such as internalization and lateralization. Similar alterations to Cx43 were also observed in the BALB/cByJ strain of laboratory mice that develop a spontaneous myocarditic disease. To investigate the electrophysiological ramifications of EAM, especially in the context of Cx43+/- mice, ECGs were recorded from animals over the course of EAM. Significant changes to the QRS interval were noted, including prolongation that was only observed in Cx43+/- animals.
    • EVALUATION OF THE ROLE OF THE CENTRAL PAIR IN CHLAMYDOMONAS REINHARDTII FLAGELLAR MOTILITY

      Mitchell, David; Brandon, Smith (2013)
      Cilia and flagella are essential for the function of nearly all eukaryotes. This organelle is made up of nine outer doublet microtubules and two central singlet microtubules to form the canonical (9+2) ciliary structure. Cilia and flagella use this structure, as well as several protein complexes, such as the outer and inner dynein arms, the radial spokes, and the proteins that decorate the central pair to propagate the bending that produces motion. Flagellar motion is highly regulated, and each of these structures is necessary to regulate the dynein arms that generate the motile force. The central pair is one of the least understood of these structures. To date there are two major impediments hindering our understanding of the central pair: a lack of understanding as to how distinct central pair structures work in concert, and a general lack of available central pair mutant strains in the model organism Chlamydomonas reinhardtii. In order to further our understanding of how the central pair functions I have used multiple strategies. Firstly I have used previously characterized central pair mutants to study both structural interactions within the central pair and how the double mutant affects motility regulation. Secondly I provide evidence that a potential central pair mutant, H2, is indeed a central pair mutant and affects the C2b projection. Lastly I will attempt to characterize a new Chlamydomonas mutant, 10B5. Together these analyses will demonstrate that double mutants can have an additive effect on the structure of the central pair, and that double central pair mutants do not appear to suppress one another, but are at least ivepistatic to the most severe phenotype. I will also show evidence that 10B5 is not a central pair mutant, but with further study it may offer new insight into motilityregulation.
    • Expression and Function of Paxillin Genes in Zebrafish: A Role in Skeletal Muscle Development

      Turner, Chris; Amack, Jeffrey; Jacob, Andrew (2017)
      Paxillin is a key component of the Integrin adhesion complex, which regulates cellular signaling events in response to extracellular matrix interactions. Although the roles for Paxillin in cell migration have been extensively studied, less is understood about its role in vertebrate development. Depletion of Paxillin from mouse embryos results in early lethality due to impaired cardiovascular development and function, necessitating the development of alternative vertebrate genetic models for examining the role of Paxillin during embryogenesis. Zebrafish have emerged as an experimental vertebrate model amenable to genetic manipulation. The work compiled herein first characterizes the expression profiles for Paxillin genes in zebrafish, and then describes the embryonic phenotypes observed upon mutation of these genes. The identification of two Paxillin genes in zebrafish, pxnaand pxnb, provided new insight into the evolution of this gene family in the Teleost lineage. Both overlapping and unique expression profiles for these genes during zebrafish embryogenesis were uncovered. While both genes are expressed in developing skeletal muscle, pxnawas restricted to the notochord during earlier stages of embryogenesis and pxnbwas expressed in the developing heart. Targeted mutation of either gene alone did not impair embryonic development, suggesting partial functional redundancy between each gene during embryogenesis. Accordingly, combined mutations in pxnaand pxnbrevealed defects during the development ofseveral embryonic tissues. In particular, skeletal muscle morphogenesis iiiwas perturbed in these double mutant embryos. Further characterization revealed that Paxillin genes in zebrafish serve to regulate embryonic myotome shape and proper extracellular matrix composition during muscle development. The amount of Laminin was reduced, while the abundance of Fibronectin persisted, during myotome morphogenesis in Paxillin double mutant embryos. In addition, a role for cytoskeletal contractility in regulatingsubcellular localization of Paxillin in developing skeletal muscle was established. Defects in the development of the cardiovascular system were also apparent in Paxillin double mutant embryos, and future work will focus on characterizing these in further detail. Altogether, this work provides a new vertebrate model to use for understanding the role of Paxillin during embryonic development, and uncovers an unrecognized role for Paxillin in establishing the extracellular matrix of skeletal muscle.
    • Investigating the Role of Paxillin in Mammary Gland Morphogenesis and Breast Cancer Progression

      Turner, Christopher; Xu, Weiyi (2020)
      Breast cancer is one of the most invasive cancers among women. Understanding the mechanisms contributing to breast cancer progression may identify potential ways to prevent and cure the disease. Meanwhile, mammary gland morphogenesis shares similar mechanisms to allow the ducts to invade and occupy the fat pad. Thus, it is equally important to investigate the normal mammary gland development as breast tumor progression. Paxillin, as a focal adhesion scaffold protein, has previously been implicated in multiple types of cancer cell migration and invasion through its role in cell- ECM signaling. Herein, I utilized a novel paxillin conditional knockout mouse model and paxillin knockout mouse crossed with PyMT breast tumor mouse model to show that paxillin is critical for both mammary gland morphogenesis and breast tumor progression. In Chapter 2, by evaluating the developing mammary gland morphology with immunohistochemistry and the three-dimensional cultured mammary organoids and acini, a critical role of paxillin was shown in facilitating apical-basal polarity formation in the luminal epithelial cells in part, through its control of HDAC6 activity and associated microtubule acetylation. Correct polarization and columnar shape of the epithelial cells potentially contributes to lumen formation and branching of the ducts. Investigation in Chapter 3 highlights a crucial role of paxillin in breast cancer invasion and distant organ metastasis, but did not affect the primary tumor growth rate. Further analysis revealed that paxillin is required for the endocytosis and recycling of E- cadherin, which is important for the maintenance of Adherens junction equilibrium during cancer cell collective migration. This thesis characterizes the roles for paxillin in mammary gland morphogenesis and breast cancer progression and reveals the importance of paxillin-dependent apical trafficking in normal epithelial cells, and E-cadherin trafficking in collective migrating tumor cells. Together, this work highlights a trafficking-dependent mechanism for paxillin during both physiologic and pathologic processes in the mammary gland.
    • Laminins regulate retinal angiogenesis

      Brunken, William J.; Biswas,Saptarshi (2017)
      Vascular pathologies are the leading causes of acquired blindness in the developed world. While many studies sought to unravel cell-intrinsic and growth factor-mediated regulations of angiogenesis, it is only recently that the role of the basement membrane (BM) components in angiogenesis began to be explored. Several diseases with ocular manifestations are known to alter vascular BM compositions. Therefore, a detailed knowledge of the BM-mediated signals that regulate angiogenesis is of great importance. Laminins, a critical component of the BM, have been shown to regulate several aspects of angiogenesis in the retina. Our laboratory previously demonstrated that the laminin composition of the inner limiting membrane (ILM) regulates astrocyte migration, and consequently vascular expansion along the retinal surface. Here, I examined the role of γ3- and β2-containing laminins in two specific aspects of angiogenesis: 1) vascular branching and endothelial cell proliferation in the nascent vascular plexus, and 2) arterial morphogenesis in the remodeling zone. Results presented in Chapter 2 and Appendix 1 demonstrate that laminin composition of the BM is a critical regulator of microglial recruitment to the growing nascent plexus, where microglia facilitate vascular branching. Furthermore, microglia interact with the astrocyte-derived layer of the vascular BM, and that this interaction regulates iii microglial activation. The activation state of microglia, in turn, regulates endothelial cell proliferation. Results presented in Chapter 3 and Appendix 2 demonstrate that vascular BM laminins are critical regulators of arterial morphogenesis. Specifically, my results reveal a novel mechanism where γ3- containing laminins signal through dystroglycan to induce Dll4/Notch signaling in arterial endothelial cells, regulating proper arterial morphogenesis. Finally, in Appendix 3, I examined the coordinated expression of different laminin chains in the vascular BM. My preliminary results suggest that expressions of laminin α2-, α5- and γ3-chains in the retinal vascular BM are coordinately regulated with the expression of laminin β2-chain. In conclusion, this study sheds light on hitherto unexplored mechanisms by which BM laminins regulate retinal vascular development.
    • A matter of life and death: human cytomegalovirus induction of monocyte survival and differentiation into macrophages through manipulation of the PI3K/Akt pathway

      Chan, Gary; Cojohari, Olesea (2017)
      Human cytomegalovirus (HCMV) is a ubiquitous β-herpesvirus infecting up to 80% of the US population and reaching 100% seroprevalence in many parts of the world. In mostindividuals HCMV infection is usually asymptomatic. In contrast, in immunodeficient or immunonaive people, such as transplant recipients and the developing fetus, the virus is a major cause of morbidity and mortality. During a primary infection, HCMVcan spread very effectively in the body infecting many organ types and monocytes are believed to be the principal cell type responsible for HCMV dissemination throughout the body. Monocytes, however, are naturally programmed to undergo apoptosis after 48h in the circulation and are not permissive for viral replication. Our lab has shown that in order to combat these biological hurdles, HCMV promotes survival of these short-lived cells past their 48h “viability gate”. Besides inducing survival, the virus also mediates the differentiation of monocytes into macrophages skewed towards an M1 pro-inflammatory phenotype with select M2 anti-inflammatory features, which are long-lived cells, permissive for viral replication. However, the mechanisms used by HCMV to concomitantly induce survival and macrophage differentiation -two linked but separate processes, are not fully understood. The studies in this thesis reveal that upon binding and entry, HCMV initiates a survival program in monocytes by inducing a rapid and sustained activation of the PI3K/Akt pathway, which isdifferent from that induced by myeloid growth factors. Moreover, after inducing cellular survival across the 48-h viability gate, the virus also employsthe PI3K/Akt pathway to regulate caspase 3 activation which mediatesthe atypical M1/M2 polarization. Our work suggests that virus not only makes use of the PI3K/Akt pathway, but manipulates it at multiple levels toallow for viral-specific downstream functional changes.Deciphering how the virus uniquely maneuvers signaling pathways in monocytes to drive their survival and differentiation might allow us to develop new treatments targeting HCMV-infected monocytes and preventing viral spread and disease.
    • Mechanisms of aseptic loosening in total knee arthroplasty

      Cyndari, Karen (2017)
      Introduction: Cemented Total Knee Arthroplasty (TKA) is the gold standard of care for end-stage, multi-etiologic arthritis. While the longevity of these devices may now reach or even surpass 15 years in service, a minority (~10%) will fail prematurely due to a process called aseptic loosening. Historically, this process has been attributed to an inflammatory reaction against wear debris from the TKA polyethylene (PE) insert. However, we have previously estimated supraphysiologic fluid shear stress (FSS) (exceeding 900 Pa) at the cement-bone interface of cemented joint replacements, and examined this as a possible alternative cause of increased osteoclast activity. Methods: We analyzed the cement-bone interlock of tibial and femoral components from en-bloc, postmortem-retrieved, non-revised TKAs to explore the process of loss of fixation, prior to any clinical loosening. For the tibial components, we used a novel protocol wherein whole undecalcified bone+PMMA cement segments from the proximal tibia were embedded in Spurr’s resin and thinly sectioned. Polarized light microscopy was used to identify and quantify co-located PE debris. Using a novel bioreactor developed by our lab called the Multi-Well Fluid Loading (MFL) System, we examined static, subphysiologic, physiologic, and supraphysiologic FSS on RAW 264.7 osteoclast activity and morphology, with and without PE particle treatment. Results: We found no association been the amount or presence of PE debris and the amount or location of loss of interlock in retrieved TKAs. FSS up to 17 Pa increased the ability of osteoclasts to resorb mineral, and FSS up to 4.4 Pa induced the formation of larger osteoclasts. FSS and fluid shear rate interacted together to increase the area of actin rings, while PE treatment increased the number of actin rings and TRAP production. FSS up to 4.4 Pa decreased expression of Ctsk and Il1a, but PE co-treatment abolished this effect. Conclusions: These results indicate there may be alternative factors leading to aseptic loosening apart from PE debris. We demonstrated that osteoclasts are mechanosensitive and able to adjust activity, morphology, and gene expression based on FSS. Further, PE interferes with osteoclast gene downregulation in response to FSS, indicating PE could be a potentiator of osteoclast activity or differentiation.
    • MECHANISMS OF WISKOTT ALDRICH SYNDROME PROTEIN WSP1 POSITIONING AND REGULATION AT SITES OF ENDOCYTOSIS IN S. POMBE

      Sirotkin, Vladimir; Macquarrie, Cameron Dale (2020-12-30)
      Branched actin networks nucleated by the Arp2/3 complex provide force needed to carry out endocytosis. The Arp2/3 complex is activated by Nucleation Promoting Factors (NPFs) including Wiskott-Aldrich Syndrome protein WASp. The WASp Interacting Protein WIP binds WASp, protecting it from degradation. Humans with mutations disrupting this interaction develop a serious immune disorder, Wiskott-Aldrich Syndrome. However, in the fission yeast S. pombe WASp homolog Wsp1 remains stable in the absence of WIP homolog Vrp1, providing an ideal environment to study additional WASp and WIP functions. In fission yeast, Wsp1, Vrp1, and the class-1 myosin Myo1 localize to sites of endocytosis, known as actin patches. Wsp1 and Myo1 play an important role in activating the Arp2/3 complex and initiating the actin network needed to internalize endocytic vesicles. S. pombe endocytosis is a rapid, reproducible event involving over 40 proteins. While several of these proteins are throught to regulate branched actin assembly, many still have poorly defined functions. Importantly, how WASp proteins are regulated at sites of endocytosis remains unclear. The following studies explore mechanisms of Wsp1 regulation using quantitative live cell imaging. In Chapter 2, we observed Wsp1, Vrp1, and Myo1 forming a transient complex near the membrane, positioning branched filaments in a way that optimizes force generation. In Chapter 3, we explored the role of WIP homolog Vrp1 in actin assembly and discovered the Vrp1-Wsp1 interaction is essential for Wsp1-mediated branched actin assembly. In Chapter 4, we examined how a separate module of endocytic coat proteins contributes to actin patch assembly and discovered the coat protein Sla1 inhibits Wsp1 NPF activity, after the endocytic vesicle begins to internalize. In Chapter 5, we examined how Wsp1 and Myo1 impact additional endocytic modules and discovered Wsp1 plays an important role in expediating endocytosis and Myo1 contributes to the localization of several proteins. Lastly, in Chapter 6, we observed that blocking the fastgrowing end of actin filaments does not impact actin assembly in patches. These studies provide key insight into how WASp family proteins are regulated in vivo.
    • MITOCHONDRIAL ELECTRON TRANSPORT CHAIN ACTIVITY IN SYSTEMIC LUPUS ERYTHEMATOSUS

      Perl, Andras; Doherty, Edward (2014)
      Systemic lupus erythematosus (SLE) is an autoimmune disorder, characterized by T cell and B cell dysfunction. SLE mitochondria have been shown to be dysfunctional with increased mass, mitochondrial potential, decreased ATP, elevated reactive oxygen species (ROS) and reactive nitrogen species (RNS) concentrations, and altered Ca2+ stores. Drug treatments that target the mitochondria have shown efficacy in treating SLE. Here we have investigated electron transport chain (ETC) activity in SLE, to better understand the causes of mitochondrial dysfunction in SLE. We have found that mitochondrial complexes I and IV of the ETC have elevated respiration in SLE compared to healthy controls after both overnight resting and anti-CD3/CD28 stimulation. We have also shown that SLE complex I is resistant to NO inhibition of respiration. SLE peripheral blood lymphocytes (PBL) have increased S-nitrosylation (SNO) while immunoprecipitated complex I had decreased SNO of proteins compared to healthy controls. The drug Nacetylcysteine (NAC) was able to inhibit complex I activity in SLE, and was found to reduce the amount of complex I protein NDUFS3 after 15 minutes as measured by western blotting. These results have led us to the conclusion that SLE mitochondrial complex I is in an active form which is resistant to SNO and is driving the production of ROS and RNS that are associated with SLE. The drug NAC is able to inhibit complex I respiration which may have therapeutic efficacy by reducing the ROS and RNS stress in SLE.
    • The p53-Zn2+ Energy Landscape and Metallochaperone Hypothesis

      Loh, Stewart; Blanden, Adam (2017)
      p53 is a tumor suppressor protein found mutated in essentially half of human cancers, and dysfunctional in nearly all human cancers. Each DNA-binding domain of the protein contains a critical tetrahedrally coordinated Zn2+. In this work, we present a quantitative thermodynamic model describing the energetics of the p53-Zn2+ interaction, as well as the mechanism of action of a new class of therapeutic compounds we call synthetic zinc metallochaperones (ZMC) that restore proper structure and function to many mutant p53s by delivering Zn2+ to the protein in the cell. We combine recombinant protein expression and in vitrobiophysical characterization with cell biology, molecular biology, medicinal chemistry, and live cell imaging to address these issues. Our model for both the mechanism of action of ZMCs and the p53-Zn2+interaction are broadly based on the Metallochaperone Hypothesis originally proposed by our group in 2010. We find that the core tenants of the Metallochaperone Hypothesis are accurate, and have expanded that model to quantitatively describe the link between p53-Zn2+ binding and protein stability noted for decades in the field. We find that at physiological temperature and Zn2+ concentrations, wild-type p53 has a folding energy of ~0 kcal mol-1, and as such is exquisitely sensitive to inactivation by mutation, and rapidly changes the fraction folded in response to changes in Zn2+ concentration. We demonstrate that ZMCs are ionophores, transport Zn2+ from the extracellular space into cells, and rescue mutant p53 by increasing the intracellular free Zn2+ concentration. This increase in Zn2+ stabilizes the mutant proteins via the same mechanism previously described for substrate stabilization of enzymes, and is only seen in a "Goldilocks Zone" of Zn2+ concentrations and ZMC Kds. This presents a fundamentally new way to interact with and reactivate mutant p53s, and raises questions about the potential for biological exploitation of this interaction for signaling or other functions.
    • PHOSPHORYLATION AND UBIQUITINATION REGULATE PROTEIN PHOSPHATASE 5 ACTIVITY AND ITS PROSURVIVAL ROLE IN KIDNEY CANCER

      Mollapour, Mehdi; Dushukyan, Natela (2018)
      Protein Phosphatase 5 (PP5) is a serine/threonine phosphatase known to regulate many essential cellular functions including steroid hormone signaling, stress response, proliferation, apoptosis, and DNA repair. PP5 is a knownco-chaperone of the molecular chaperone heat shock protein 90 (Hsp90), and its regulation of Hsp90aidswiththe proper activation of Hsp90 clients and withsteroid hormone signaling.Hsp90 is also one of the strongest activators of PP5, as it releases the auto-inhibition of PP5 by interacting with the N-terminal tetratricopeptide repeat (TPR) domain of PP5. Our lab has recently shown that PP5 is phosphorylated at T362, and that this phosphorylation acts as an “on switch” resultingin the hyperactivation of PP5. Misregulation of this key phosphatase has been shown to aid in the tumor progression of ER-dependent and independent breast cancer. Elevated PP5 levels have also been linked to colorectalcancer, hepatocellular carcinoma (HCC), lymphoma, and prostate cancer. The work presented here reveals the pro-survival role that PP5 plays in kidney cancer. Clear cell renal cell carcinomas (ccRCC) are most often driven by mutations in the von Hippel-Lindau tumor suppressor (VHL). The data in this thesis shows that VHL binds and multi mono-ubiquitinates PP5 at two lysine residues K185 and K199. This post-translational modification negatively regulates PP5 likean “off switch” and ultimately leads to its degradation bythe proteasome. Mutations in the VHLgene that result in inactive mutants or a lack of VHL protein expression lead to ccRCC tumors. The data in this thesis shows that these VHL-nulltumors become dependent on elevated levels of PP5, and that both PP5 knockdown and inhibition lead to cancer cell death. The data further shows that the decrease in PP5 activity in VHL-null cells results in the induction of the extrinsic apoptotic pathway with a dramatic increase in the cleavage of PARP and caspases 3, 7, and 8.