• Mechanisms of Homocysteine-Induced Retinal Ganglion Cell Death

      Ganapathy, Preethi S.; Department of Cellular Biology and Anatomy (2010-12)
      The purpose of these studies was to determine the effect of excess homocysteine on retinal ganglion cell viability. An overview of homocysteine metabolism and the literature concerning homocysteine-induced neurotoxicity is given below, followed by detailed descriptions of the eye, the retina, and retinal ganglion cells.
    • The Mechanobiology of Cranial Sutures

      Byron, Craig D.; Department of Cellular Biology and Anatomy (2005-07)
      A central hypothesis that cranial suture growth and modeling vary with respect to the mechanical loading environment is tested in a mouse sagittal suture model using three Specific Aims. Experiments within these aims were designed to elucidate mechanisms of bone formation and bone resorption at the cellular level and to determine how these processes influence the morphology and performance of cranial suture connective tissues. It is argued that suture waveform complexity (measured using fractal analysis) is generated by the positive coupling of osteogenesis along convex bone margins and bone resorption along concave bone margins and that this turnover cycle is regulated in large part by mechanical forces acting on the suture bone-ligament interface. This suture formfunction relationship is believed to operate via mechanosensing mechanisms within skeletal connective tissues. Although mechanically-induced cell wounding appears to be involved in normal suture biology, it does not occur in the fashion predicted. Apoptosis is not directly implicated. Thus, it is predicted that bone resorption in cranial sutures does not localize according to regions of shear-induced cell death but rather to regions adjacent to osteoblastic activity. Tension rather than shear is most likely to be the driving force in this system.
    • Modulation of a Conserved Cathepsin B-Like Extracellular Matrix Protein Impacts Wing and Egg Formation in Drosphila Melanogaster

      Dinkins, Michael B; Department of Cellular Biology and Anatomy (2011-03)
      Conserved in Bilaterian species, the tubulointerstitial nephritis antigen (TIN-ag) family of cathepsin B-like extracellular matrix proteins has been proposed to have roles in cell adhesion and regulation of basement membrane assembly based on in vitro studies of mammalian family members. Here we examined the single Drosophila ortholog, CG3074, and found conservation of its basement membrane localization as well as a role in cell adhesion. RNAi knockdown resulted in wing blistering and held-out wings following eclosion, consistent with defects in adhesion of wing epithelia and tendon cells to the underlying extracellular matrix, but no defects were detected during pupal development. We were unable to demonstrate a genetic or physical interaction with laminin and CG3074 but did detect genetic interactions with integrins and dystroglycan in the wing. A serine substitutes for cysteine in all TIN-ag family members at the 'active site' of the cathepsin B-like domain and is predicted to render the protein inactive as a protease. Overexpression of the mutant CG3074 S213C, in which the 'catalytic' cysteine of cathepsin is restored, resulted in gain-of-function defects in egg formation and larval development. We provide genetic and biochemical evidence that these defects arise from a neomorphic activity of the S213C protein that supports a role of this highly conserved domain in wildtype CG3074 function. These studies broaden our understanding of TINag family function and identify tissue and pathway models for future studies.
    • Murine CD19+ Plasmacytoid Dendritic Cells Expressing Indoleamine 2,3 Dioxygenase

      Kahler, David J.; Department of Cellular Biology and Anatomy (2008-10)
      Indoleamine 2,3 Dioxygenase (IDO) is a potent immunomodulatory enzyme whose role has been described in diverse physiologic states including pregnancy, cancer, tissue transplants, autoimmune disease, chronic inflammation, and depression. IDO suppresses antigen specific T cell proliferation via mechanisms including tryptophan degradation and the production of toxic metabolites, and the activation of resting regulatory T cells (Tregs). IDO expression is tightly regulated in the murine spleen, as only rare dendritic cell (DC) subsets are competent to express IDO. Therefore, an accurate phenotype by which to identify IDO competent DCs in tissues is important when ascribing the role of IDO competent DCs in disease models. Here we show that IDO competent CD19+ pDCs (CD19+ pDCs) express high levels of costimulatory receptors (CD80 / CD86) under homeostatic conditions indicating a mature or activated phenotype and uniquely express the Class I MHC-like molecule CD1d, and the chemokine receptor CCR6. IDO competent pDCs do not share the same lineage as other murine splenic DCs as they were the only DC subset to express Pax5, and were present in reduced numbers in murine models of B cell development indicating that they develop from B cell precursors. Distinct signaling requirements regulate IDO induction in IDO competent pDCs as MyD88 was required for IDO induction and function in inflamed skin draining lymph nodes following phorbol myristate acetate application but not for IDO transcript expression or STAT1 or STAT2 protein phosphorylation following treatment with recombinant cytokines. CD19+ pDCs from WT mice but not mice genetically deficient for the IDO1 gene formed stress granules (SG) following treatment with IFNγ, which were not prevented by inhibitors of IDO activity indicating that SG formation was not IDO dependent. We hypothesize that IDO competent murine splenic pDCs uniquely expressing CD19 are phenotypically and functionally distinct from other splenic DC subsets and respond to inflammatory signals by expressing IDO. We further hypothesize that activated IDO causes distinct yet undefined biochemical changes within IDO competent pDCs following induction most probably by activating the integrated stress response and the eif2a kinases GCN2, PKR, and PERK.
    • NEUROVASCULAR DEGENERATION FOLLOWING RETINAL ISCHEMIA REPERFUSION INJURY: ROLE OF ARGINASE 2

      Shosha, Esraa; Department of Cellular Biology and Anatomy (2017)
      Ischemic retinopathies such as retinopathy of prematurity, central retinal artery occlusion and diabetic retinopathy are leading causes of visual impairment and blindness. These pathologies share common features of oxidative stress, activation of inflammatory pathways and neurovascular damage. There is no clinically effective treatment for these conditions because the underlying mechanisms are still not fully understood. In the current study, we used a mouse model of retinal ischemia reperfusion (I/R) insult to explore the underlying mechanisms of neurovascular degeneration in ischemic retinopathies. The arginase enzyme utilizes the L-arginine amino acid for the production of L-ornithine and urea. Here, we investigated the role of the mitochondrial arginase isoform, arginase 2 (A2) in retinal I/R induced neurovascular injury. We found that retinal I/R induced neurovascular degeneration, superoxide and nitrotyrosine formation, glial activation, cell death by necroptosis and impairment of inner retinal function in wild type (WT) mice. A2 homozygous deletion (A2-/-) significantly protected against the neurovascular degeneration after retinal I/R. That was attributed to decreased oxidative stress and glial activation. A2 deletion protected against I/R induced retinal function impairment. Using Optical coherence tomography (OCT), we evaluated the retinal structure in live animals and found that A2-/- retinas showed a more preserved structure and less retinal detachment. To investigate the underlying mechanisms of A2 induced vascular damage after I/R, we used an in vitro model of oxygen glucose deprivation/ reperfusion (OGD/R) in bovine retinal endothelial cells (BRECs). Analysis of oxidative metabolism showed impaired mitochondrial function. We also found an increase in dynamin elated protein 1 (Drp1), a mitochondrial fission marker. Mitochondria labeling studies showed fragmented mitochondria after OGD/R. Arginase inhibition reduced mitochondrial fragmentation in OGD/R insult. This dissertation presents A2 as a new therapeutic target in reducing neurovascular damage in ischemic retinopathies.
    • Oxidation of Dietary Amino Acids Disrupts their Anabolic Effects on Bone Marrow-Derived Mesenchymal Stem Cells

      El Refaey, Mona M.; Department of Cellular Biology and Anatomy (2016-07)
      Age-dependent bone loss has been well documented in both human and animal models. Since it has been proposed that aging is associated with an increase in the generation of damaging reactive oxygen species (ROS), our hypothesis was that the oxidized products of dietary amino acids could play a role in age-induced bone loss by altering osteoprogenitor cell differentiation and function or activating osteoclastic activity. We first examined the effects of the oxidized nutrients on the bone marrow-derived mesenchymal stem cells and our data showed a decrease in the protein and gene expression of osteogenic markers normally stimulated by nutrients. Aromatic amino acids activated signaling pathways involved in protein synthesis in vitro, and thus, in contrast, the oxidized metabolites of these aromatic amino acids had no effect on the activation of these anabolic pathways. We then examined the bone marrow concentration of the oxidized aromatic amino acids in mature (12 months) vs. aged (24 months) C57BL/6 mice and found that kynurenine, the oxidized product of the aromatic amino acid tryptophan, was found in the highest concentration in 12 months mice. Thus, we tested the effects of kynurenine, fed as a dietary supplement, on the bone mass of twelve-month-old C57BL/6 mice compared to a normal protein diet to see if the oxidized amino acid would induce a pattern consistent with age-related bone loss. Twelve-month-old, male C57BL/6 mice were fed one of four diets; 18% protein diet (normal protein diet); 8% protein diet + tryptophan; 8% protein diet + kynurenine (50 μM) and 8% protein diet + kynurenine (100 μM) for 8 wks. Bone densitometry and micro-CT analyses demonstrated bone loss following the kynurenine diet. Histological and histomorphometric studies showed a decreased bone formation and an increased MONA M. EL REFAEY Oxidation of Dietary Amino Acids Disrupts Their Anabolic Effects on Bone Marrow-Derived Mesenchymal Stem Cells (Under the direction of DR. CARLOS M. ISALES) osteoclastic activity in the kynurenine groups; these animals also exhibited an increase in serum pyridinoline, a marker of bone breakdown. Thus, these data demonstrate that feeding an oxidized product of an essential amino acid induces bone loss in a pattern consistent with accelerated aging, and we propose that one of the mechanisms involved in age-induced bone loss may be from alterations of dietary nutrients by the increased generation of ROS associated with aging.
    • PKC and ATR Mediated Regulation of Cisplatin-Induced Renal Tubular Cell Apoptosis

      Pabla, Navjotsingh; Department of Cellular Biology and Anatomy (2009-03)
      Cisplatin is one of the most widely used anti-cancer drug. However, its use and efficacy is limited due to nephrotoxicity. One fourth of patients treated with cisplatin develop varying degree of renal impairment, frequently resulting in acute kidney injury. Due to high mortality associated with acute kidney injury, effort has been made to understand the molecular basis of cisplatin nephrotoxicity and develop effective renoprotective strategies. In kidneys, cisplatin is accumulated in tubular cells; however the uptake mechanism that is responsible for high accumulation of cisplatin in renal cells is unclear. In tubular cell, cisplatin accumulation induces cell death by apoptosis. Mechanistically, our laboratory has demonstrated a critical role of p53 in tubular cell apoptosis during cisplatin nephrotoxicity. However, the proximal events that contribute to p53 activation and related signaling are unknown. The focus of my work was to decipher these early events during cisplatin nephrotoxicity. Firstly, my results suggest that the copper transporter Ctr1 is highly expressed in renal tubular cells and is responsible for renal uptake of cisplatin. Secondly, I show that DNA damage response involving ATR-Chk2 is responsible for p53 activation and consequent apoptosis during cisplatin-induced kidney injury and nephrotoxicity. Thirdly, I have identified that PKCd is a novel regulator of cisplatin nephrotoxicity. During cisplatin treatment PKCd is activated in a Src dependent manner and is responsible for activation of MAPKs, contributing to renal cell death. Most importantly, my results suggest that pharmacological inhibition of PKCd ameliorates renal injury without affecting the anticancer efficacy of cisplatin. These results have not only provided new insights into the 3 molecular mechanism of cisplatin nephrotoxicity, but have also identified a novel strategy to mitigate the side effects of cisplatin in normal renal tissues.
    • Progesterone Regulation of Proliferation and Regression of Rat Decidua Basalis

      Dai, Donghai; Department of Cellular Biology and Anatomy (1998-07)
      During implantation mesometrial cells o f the uterine stroma become decidualized under the coordinate actions of progesterone (P4 ) and estrogen (E) [1,2]. This process is characterized by transformation o f phenotype and stromal cell proliferation between Days 8-12 of gestation, resulting ultimately in the formation o f the decidua basalis (DB) [3,4], By Day 14. however, the DB begins to regress and a reduced layer o f stromal cells persists to the end of pregnancy [5.6]. The regression of DB is accompanied by development o f two other layers, namely junctional zone (JZ) and labyrinth zone (LZ), which are fetal parts of the placenta and morphologically become predominant at the end stages o f pregnancy. Although the morphological changes have been well documented and numerous functions have been revealed for DB [3-8], the mechanism and factors involved in the regulation of proliferation and regression o f DB have not been elucidated. The transition of DB from proliferation to regression occurs in such a delicate way that the morphological integrity and functional competence of the DB and placenta are maintained even though stromal cells are being lost. The objective o f this study was to identify the intracellular signals initially favoring proliferation and synthetic processes and those promoting remodeling and regression as pregnancy progresses.
    • Rapamycin, an evolving role in up-regulation of autophagy to improve stroke outcome and increase neuronal survival to stroke type injuries

      Buckley, Kathleen; Department of Cellular Biology and Anatomy (2015-10)
      Rapamycin was shown to reduce infarct size in a non-reperfusion and a slow reperfusion model of murine stroke; it also improved neurological score and survival in the slow-reperfusion model. The rapamycin improvement was 50 percent greater than that observed with chloroquine. In HT22 mouse hippocampal neurons, rapamycin was shown to improve survival to an oxidative/reperfusion injury with H2O2 and a hypoxic/ischemic injury with oxygen and glucose deprivation to a larger degree than chloroquine. Rapamycin treatment increased punctate microtubule light chain associated protein 3, LC3, in the HT22 neurons in an uninjured and oxygen and glucose deprivation injured HT22 neurons compared to untreated neurons. Finally, genetic knockdown of autophagy with shRNA to autophagy protein 5, ATG5, abrogated the rapamycin’s positive effect on survival to injury.
    • Regulation of Reduced-Folate Transporter-1 in Retinal Pigment Epithelium

      Naggar, Hany A.; Department of Cellular Biology and Anatomy (2003-04)
      (First Paragraph) The purpose of these studies was to analyze the regulation of the folate transport protein, reduced-folate transporter (RFT-1) in the retinal pigment epithelium (RPE) under conditions o f hyperglycemia, hyperhomocysteinemia and folate deficiency. A detailed description o f the retina, followed by information regarding folate and regulation o f RFT-1, is provided below.
    • Role of Autophagy and Apoptosis in the Pathogenesis of Murine Cytomegalovirus Retinitis

      Mo, Juan; Department of Cellular Biology and Anatomy (2014-05)
      This study focused on the roles o f autophagy and apoptosis in the pathogenesis of murine cytomegalovirus (MCMV) retinitis. An overview of MCMV retinitis and the literature concerning autophagy, apoptosis and viral infection are given below, followed by detailed descriptions o f the eye, the retina, MCMV, autophagy and apoptosis.
    • ROLE OF CLASS III PHOSPHATIDYLINOSITOL 3-KINASE IN THE RENAL PROXIMAL TUBULE

      Liu, Ting; Department of Cellular Biology and Anatomy (Augusta University, 2020-05)
      Yeast only has a single phosphatidylinositol 3-kinase (PI3K) known as vacuolar protein sorting 34 (VPS34); however, mammals have evolved to express three structurally different classes of PI3Ks: class I, II, and III. Although the class III PI3K (Pik3c3) is the only PI3K evolutionarily conserved from yeast to man, its distribution in the mammalian kidney is unknown, and its role in the renal proximal tubule, especially under certain pathophysiological conditions such as nephron loss-induced Compensatory Nephron Hypertrophy (CNH), remains undefined. The goal of Aim 1 was to define the expression pattern and relevant biological function of Pik3c3 in the kidney. We found that the glomerular podocyte expresses the highest level of Pik3c3 in the kidney. Among all renal tubular cells, the specialized distal convoluted tubular epithelial cells called macula densa cells express the highest level of Pik3c3, and the renal proximal tubular cells (RPTC) express the second highest level of Pik3c3. This prompted us to perform additional experiments for Aim 1 that led to the demonstration of an essential function of Pik3c3 in regulating the degradation of epidermal growth factor (EGF) receptor (EGFR) and the termination of EGFR signaling in RPTC following EGF binding with EGFR. The goal of Aim 2 was to determine whether Pik3c3 is essential in mediating uninephrectomy (UNX)-induced compensatory nephron hypertrophy. We generated a global Pik3c3-hypomorphic mouse model and two slightly different proximal tubule-specific Pik3c3 knockout mouse models: Pik3c3Neo-ptKO and Pik3c3ptKO. Interestingly, CNH was markedly inhibited in the global Pik3c3-hypomorphic mouse model and proximal tubule-specific Pik3c3 knockout models. The goal of Aim 3 was to determine the effect and underlying mechanism of complete Pik3c3 deletion in renal proximal tubule cells. We found that complete Pik3c3 deletion in some renal proximal tubule cells resulting in marked cell death that subsequently progressed to tubulointerstitial fibrosis. My project has, for the first time, determined the expression pattern of Pik3c3 in the kidney and provided the first definitive evidence that Pik3c3 controls the degree of CNH and functions upstream of the mTORC1-S6K1-rpS6 pathway in the regulation of CNH. In addition, my project reveals an essential role of Pik3c3 in maintaining the homeostasis and survival of proximal tubule cells.
    • Role of microtubules and motor proteins in mRNA localization

      Sanghavi, Paulomi; Department of Cellular Biology and Anatomy (2015-08)
      Establishment of polarity is essential for many cell types to perform their functions. A common mechanism that is used to establish polarity is localization of mRNAs at specific sites. This results in spatial restriction of protein expression. mRNA localization is a widespread phenomenon, occurring in most species. However, the mechanism by which mRNAs are localized is poorly understood. Using Drosophila as the model system, we investigated the localization of one such localized transcript, oskar mRNA. Studying the mechanism by which oskar mRNA is localized is important because many factors involved in localizing this transcript also function in localizing mRNAs in mammalian neurons. oskar mRNA localizes at the posterior pole of the Drosophila oocyte. This results in the posterior restriction of Oskar protein, which is turn functions in establishment of polarity in the oocyte and the future embryo. Localization of oskar mRNA is microtubule-dependent. We, therefore, characterized the polarity of microtubules in the oocyte. Our findings suggest that the posterior region is highly enriched in microtubule plus ends. However, this polarization is not essential for oskar mRNA localization. Secondly, the posterior localization of oskar mRNA was shown to be mediated primarily by the Kinesin-1 motor. Our findings demonstrate the role of an additional motor, Dynein, in this pathway. We found that Dynein associates with oskar mRNA in vivo and depletion of Dynein caused a significant delocalization of oskar mRNA. Next, we examined the role of a Dynein adaptor, Egalitarian (Egl), in the oskar mRNA localization pathway. Egl has been shown to recruit localized mRNAs to the Dynein motor in Drosophila embryos. Our results suggest that Egl associates with oskar mRNA in vivo and is required for the posterior localization of this transcript. Interestingly, one of the mechanisms by which Egl affects the localization of oskar mRNA is by affecting the microtubule polarity in the oocyte. Additionally, depletion of Egl caused precocious translation of oskar mRNA in the oocyte. Thus, our findings revealed a novel function for Egl in organizing oocyte microtubules and in regulating the translation of a localized mRNA.
    • Role of NEK1 in VHL and Cell Cycle Regulation

      Patil, Mallikarjun; Department of Cellular Biology and Anatomy (2013)
      Nekl is the member of NIMA (Never in mitosis gene A) related protein kinase family that is widely expressed in mammals. Nekl is an essential protein because loss of function in Nekl gene causes polycystic kidney disease in mice, which is similar to ADPKD (Autosomal Dominant Polycystic Kidney Disease) in humans. In Humans Nekl mutations also cause short rib polydactyl syndrome characterized by renal cysts and other developmental defects. At the cellular level Nekl thought to regulate ciliogenesis, centrosome duplication and DNA damage response.Nekl mutations leading to PKD have long been attributed to its role in ciliogenesis. Interestingly, VHL (Von hippel lindau) protein a known tumor suppressor is also involved in ciliogenesis.VHL mutations cause cystic kidney disease and renal clear cell carcinoma. Since Nekl and VHL are involved in ciliogenesis and cystic kidney disease, my overall goal was to investigate if Nekl and VHL are part of common regulatory pathway and also to investigate the role of Nekl in cell cycle regulation. My results indicate that Nekl phosphorylates VHL and this has important role in cilia regulation. Nekl phosphorylates VHL on multiple sites and S168 of VHL a site phosphorylated by Nekl significantly affects its stability. Importantly renal cells expressing S168A VHL that cannot be phosphorylated by Nekl grow cilia that are resistant to serum stimulation and Nocodazole treatment. Surprisingly I also found that Nekl is an essential regulator of S phase. Nekl knockdown in HEK cells blocks cell cycle progression. Further characterization Nekl showed that Nekl is needed for S phase progression and DNA replication. Nekl deficient cells have replication stress and activate cell cycle check point. Nekl loads on to chromatin and this increases during replication stress. We have also identified that Nekl interacts with and affects Ku80 loading on to chromatin. These findings have provided novel insights into the Nekl functions, which help in understanding the pathophysiology and development of polycystic kidney disease in mice and short rib polydactyl syndrome mejawski in humans.
    • The role of stromal cell-derived factor-1 in cell mobilization, cell homing and neovascularization following stroke

      Walker, Aisha L.; Department of Cellular Biology and Anatomy (2007-11)
      Stroke is the 3rd leading cause of death and the leading cause of long-term disability in the U.S. With only one approved drug presently used in clinics, there is a great need for the development for new therapeutic targets. Stromal cell derived factor-1 (SDF-1) is a small chemokine that may aid in cerebral repair following stroke. Acting primarily through the CXCR4 receptor, SDF-1 is known to be chemotactic for neuroblasts, endothelial cells, and bone marrow derived (BMD) cells including stem and progenitor cells found in the bone marrow. Recently, BMD stem/progenitor cells have become widely studied for their potential role in tissue repair following ischemia. SDF-1 is under hypoxic regulation and is highly expressed in ischemic brain tissue for at least 30 days following ischemia suggesting it may play role in long term repair or remodeling. The goal of these studies is to determine the role of SDF-1 in cerebral repair following stroke. I hypothesize that SDF-1 upregulaton during brain ischemia contributes to tissue repair and neurological recovery by inducing the homing of bone marrow-derived cells to the site of injury and neovascularization. In a mouse middle cerebral artery ligation (MCAL) permanent occlusion stroke model, I investigated mobilization, homing, and differentiation of adult bone marrow derived (BMD) cells in response to SDF-1 induced by cerebral ischemia. Results presented in this dissertation show that SDF-1 induces mobilization of BMD cells following stroke. Once mobilized, BMD cells homed to the brain and either retained their blood cell phenotypes (i.e. monocytes and neutrophils) or they differentiated mostly into microglia cells. Many BMD cells migrated to a perivascular location with a subset becoming pericytes. Additionally, I found that SDF-1 induced neovascularization and this occurs through a combination of angiogenic and vasculogenic processes in the in vivo stroke model as well as in an in vitro tube formation assay. However, we did not detect beneficial preservation of brain tissue or augmented functional recovery with treatment of SDF-1, but it remains to be determined if altering timing, delivery, or isoform-specificity of SDF-1 may be therapeutically beneficial.
    • The Role of Stromal Cell-Derived Factor-1Β in Osteogenic Differentiation of Bone Marrow-Derived Mesenchymal Stem/Stromal Cells and Bone Formation

      Herberg, Samuel A.; Department of Cellular Biology and Anatomy (2013-03)
      The experiments performed for this dissertation tested the hypotheses that SDF-1β enhances osteogenic differentiation of BMSCs, promotes engraftment and bone formation following whole-body irradiation, and potentiates suboptimal BMP-2 osteoinduction in a model of acute bone injury. We used multipotent primary BMSCs from 18-month-old C57BL/6J mice, genetically modified to overexpress SDF-1β, to ask whether SDF-1β played a role in cell survival and osteogenic differentiation of BMSCs in vitro. Our studies revealed that SDF-1β protected BMSCs from oxidative stress through increasing autophagy and decreasing apoptosis, independent from potential effects on cell proliferation. In support of the hypothesis we also found that SDF-1β enhanced calcium mineral deposition (independent of BMP-2 co-stimulation), upregulated key osteogenic markers, and increased phosphorylation of intracellular Erk1/2 and Smad1/5/8, thereby potentiating BMP-2 signal transduction during osteogenic differentiation, which was attenuated by blocking CXCR4 signaling. We next inquired whether SDF-1β promotes BMSC engraftment and new bone formation. Using direct tibial transplantation in irradiation-preconditioned animals, we found that SDF-1β enhanced new trabecular bone formation upon local BMSC transplantation. The data furthermore suggested that the differential proteolytic clearance of SDF-1 splice variants in the systemic and local environment following myeloablative injury may be an important determinant in the success of stem cell therapy protocols. The suggestion that SDF-1β could regulate BMP-2 osteoinduction through regulating CXCR4 signaling was compelling because several studies have reported a comparable effect using SDF-1α. We examined the direct contribution of SDF-1β to BMP-2 osteoinduction in a critical-size calvaria osteotomy model and found a dose-dependent ability of SDF-1β to potentiate suboptimal BMP-2-induced bone formation to levels comparable to those obtained with the 10-fold higher optimal/benchmark BMP-2 dose, which was blunted by perturbing CXCR4 signaling. These in vitro and in vivo findings expand our understanding of BMP-2 osteoinduction and implicate osteogenesis-enhancing properties of SDF-1β pointing towards its translational potential for cell therapy and regenerative medicine applications. It appears feasible for SDF-1β to improve bone regeneration in a variety of orthopaedic situations and ultimately reduce the burden of musculoskeletal injuries.
    • Signaling Mechanism of Blood-Retinal Barrier Regulation: Role of Mitogen-Activated

      Yang, Jinling; Department of Cellular Biology and Anatomy (2011-03)
      Breakdown of the blood-retinal barrier (BRB) is an early hallmark of diabetic retinopathy. A critical component in retinal vascular hyper-permeability is increased production of vascular endothelial growth factor (VEGF). VEGF is a potent permeability factor that activates mitogen-activated protein (MAP) kinases. Pigment epithelium-derived factor (PEDF), an endogenous anti-permeability factor, blocks VEGF-induced vascular permeability increase. However, the mechanisms underlying the actions of VEGF and PEDF in regulating endothelial permeability are not yet clear. Previous studies in our laboratory have shown that VEGF induces paracellular permeability via beta-catenin nuclear translocation/transcriptional activation and subsequent upregulation of urokinase plasminogen activator receptor (uPAR). This current study tests the role of two MAP kinases, p38 and extracellular-signal regulated kinase (ERK), in regulating VEGFinduced beta-catenin signaling, uPAR expression and BRB breakdown. We also evaluate the effects of PEDF on this VEGF permeability inducing pathway. The role of MAP kinase in this VEGF permeability inducing pathway was first evaluated using inhibitors of p38 and ERK. These inhibitors preserve the endothelial barrier function upon VEGF treatment. In confluent endothelial cells, cytosolic beta-catenin is phosphorylated by glycogen synthase kinase (GSK) then ubiquitinated and degraded. With VEGF treatment, GSK is phosphorylated/inactive followed by beta-catenin cytosolic accumulation, nuclear translocation and subsequent uPAR expression. These effects were blocked by MAP kinases inhibitors. This indicates p38 and ERK as mediators of VEGF-induced beta-catenin signaling, uPAR expression and endothelial barrier breakdown. Next, it was found that PEDF not only blocks VEGF-induced endothelial permeability increase and MAP kinase activation but also prevents the activation of GSK/beta-catenin signaling as well as uPAR expression. However, PEDF did not block VEGF receptor-2 (VEGFR-2) phosphorylation suggesting that PEDF acts downstream of VEGFR-2 and upstream of MAP kinase level. To further evaluate the role of p38 in regulating VEGF-induced permeability, adenovirusmediated delivery of p38alpha mutants was used. One p38alpha mutant has an altered ATP-binding site thus looses its activity. It is more efficient in blocking VEGF-induced GSK/beta-catenin signaling, uPAR expression and paracellular permeability increase. This study identifies p38alpha and ERK as mediators of VEGF permeability-inducing signaling. They could also serve as potential therapeutic targets for diseases featured by blood-retinal barrier dysfunction.
    • Studies on NF-kB Activation During Reperfusion Injury Following Reversible Acute Ischemic Stroke

      Chen, Qiang; Department of Cellular Biology and Anatomy (1998-10)
      Specific Aim # 1. To investigate whether reoxvsenation o f hypoxic cells results in the activation o f NF-kB in the HBMEC model. I f NF-kB is activated, identify the Rel family proteins in the activated NF-kB. Specific Aim # 2: To investigate whether reperfusion o f the ischemic brain tissue results in the activation o f NF-kB in the rat stroke model. I f NF-kB is activated, identify the Rel family proteins in the activated NF-kB. Specific Aim # 3: To test the efficacy o f antioxidants /NAC. PDTC) on the inhibition o f NF-kB activation following TNF-a-treatment or kwoxiaJreperfusion in the HBMEC model.
    • T-Type Calcium Current and Calcium-Induced Calcium-Release in Developing Chick Myocardium

      Kitchens, Susan A.; Department of Cellular Biology and Anatomy (2002-02)
      HYPOTHESES 1. The contribution of T-type calcium currents to the calcium transient are greater at young developmental ages, but decline with chick heart development. The decrease in contribution of T-type calcium current to the calcium transient mirrors the normal developmental reduction in magnitude of T-type current in the chick heart. 2. T-type calcium current plays a role in calcium-induced calcium-release during chick heart development. T-type current plays a significant role in the calcium-induced calcium-release process in younger embryos due to the greater magnitude of the current at earlier developmental stages. 3. More than one isoform of the T-type calcium channel is present in developing chick myocardium. The multiple isoforms will function concomitantly to provide sufficient T-type calcium current for proper development. 4. The expression of the T-type calcium channel in ventricle decreases with development. There is a concomitant decrease in T-type Ca2* current stimulation of CICR. SPECIFIC AIMS 1. To determine the contribution of T-type calcium current to the calcium transient during development in chick ventricular myocytes. The approach is to use a fluorescent calcium indicator to measure the transients from myocytes at embryonic day (ED) 5, EDI 1 andED15. 2. To determine the contribution of T-type calcium current to calcium-induced calciumrelease during chick heart development. The approach is to use pharmacological agents to quantify the contribution to the Ca3* transient from T-type Ca3* current stimulated CICR. 3. To determine which isoforms of the T-type calcium channel are likely to be present in chick myocardium. The approach is to use PCR methods to identify any T-type channel isoform mRNA expressed in chick ventricle. 4. To determine the level of expression of T-type calcium channel isoforms during the development of chick ventricle. The approach is to use molecular quantitation methods to examine the expression pattern of T-type channel isoforms in chick ventricle during development.
    • Targeting cyclic GMP signaling for the treatment of gastrointestinal diseases

      Sharman, Sarah Kristen; Department of Biochemistry and Molecular Biology / Cancer Center (2017)
      Continual renewal of the luminal epithelium in the gut is essential for the maintenance of a healthy intestine as it sustains the barrier that protects underlying tissue from infiltration of material passing through the lumen. Dysregulation of homeostatic processes involved in maintenance of the barrier have been implicated in numerous gastrointestinal diseases. The cGMP signaling axis has emerged as an important regulator of homeostasis in the intestinal mucosa, and has been implicated in the suppression of visceral pain, colitis, and colon cancer. While there is considerable interest in exploiting this pathway, until recently the approaches used to increase cGMP have been limited. The present study sought to test the hypothesis that elevation of cGMP in the intestinal epithelium using PDE5 inhibitors will alter epithelial homeostasis and be therapeutic for constipation and preventative for colon cancer. Healthy mice treated with the PDE5 inhibitor sildenafil or the GC-C agonist linaclotide exhibited reduced proliferation and apoptosis, and increased numbers of differentiated secretory cells in the intestinal epithelium. In addition to these homeostatic effects, both drugs normalized intestinal transit and fecal water content in two mouse models of constipation. Furthermore, administration of sildenafil to mice treated with dextran sulfate sodium tightened the disrupted epithelial barrier. Treatment of ApcMin/+ mice with sildenafil or linaclotide significantly reduced the number of polyps per mouse (67% and 50%, respectively). The effect of these cGMP-elevating agents was not on the polyps themselves but was rather on the pre-neoplastic tissue, which was less proliferative and more apoptotic in the presence of the drugs. Taken together, the results of this study demonstrate that increasing cGMP with a pediatric dose of PDE5 inhibitors could be a potential alternative to GC-C agonists for the treatment of gastrointestinal diseases.