The molecular mechanism(s) by which Toll-like receptors become activated are not well understood. For the majority of TLR receptors, dimerization is a prerequisite to facilitate MyD88-TLR complex formation and subsequent cellular signaling to activate NF-κB. However, the parameters controlling interactions between the receptors and their ligands still remain poorly defined. Previous reports have identified that neuraminidase-1 (NEU1) is an important intermediate in the initial process of TLR ligand induced receptor activation and subsequent cell function. What we do not yet understand is how NEU1 is activated following TLR ligand binding. In this thesis, the findings disclose a receptor signaling paradigm involving a process of receptor ligand-induced GPCR-signaling via neuromedin-B (NMBR) Gα-proteins, matrix metalloproteinase-9 (MMP-9) activation, and the induction of Neu1 activation. Central to this process is that NEU1–MMP-9-NMBR complex is associated with TLR-4 receptors on the cell surface of naive primary macrophages and TLR-expressing cell lines. Ligand binding to the receptor initiate GPCR-signaling via GPCR Gα subunit proteins and MMP-9 activation to induce NEU1. Activated NEU1 targets and hydrolyzes sialyl α-2-3-linked to β-galactosyl residues at the ectodomain of TLRs, enabling the removal of steric hindrance to receptor association, activation of receptors and cellular signaling. Furthermore, a novel glycosylation model is uncovered for the activation of nucleic acid sensing intracellular TLR-7 and TLR-9 receptors. It discloses an identical signaling paradigm as described for the cell-surface TLRs. NEU1 and MMP9 cross-talk in alliance with neuromedin-B receptors tethered to TLR-7 and -9 receptors at the ectodomain is essential for ligand activation of the TLRs and pro-inflammatory responses. However, the mechanism(s) behind this GPCR and TLR cross-talk has not been fully defined. Here, GPCR agonists mediate GPCR-signaling via membrane Gα subunit proteins to induce NEU1 and MMP-9 cross-talk at the TLR ectodomain on the cell surface. This molecular organizational GPCR signaling platform is proposed to be an initial processing stage for GPCR agonist-induced transactivation of TLRs and subsequent cellular signaling. Collectively, these novel findings radically redefine the current dogma(s) governing the mechanism(s) of the interaction of TLRs and their ligands, which may provide important pioneering approaches to disease intervention strategies. / Thesis (Ph.D, Microbiology & Immunology) -- Queen's University, 2013-04-30 12:23:42.429

Receptor glycosylation is critical in receptor-ligand interactions in immune cells, but the exact role of glycosylation in receptor activation upon ligand binding has not been elucidated. In neuronal cells, we have shown that when neurotrophic factors bind their respective Trk tyrosine kinase receptors, receptor activation and subsequent neurotrophin-mediated signaling is dependent upon the induction and activity of an endogenous sialidase enzyme. In this thesis, we report that toll-like receptor (TLR) activation upon ligand binding is similarly dependent on the induction of a cellular sialidase, which we have identified as Neu1 sialidase, which specifically targets and hydrolyses alpha-2,3-linked sialic acid residues on the receptor. Blocking Neu1 sialidase activity with specific inhibitor Tamiflu detrimentally impacts ligand-induced TLR4/MyD88 interaction, NFkappaB activation and TLR-mediated effector responses like nitric oxide and pro-inflammatory cytokine production. Diminished cytokine production is also seen in vivo in Neu1-deficient mice. We propose a mechanism for the induction of Neu1 sialidase, upon ligand binding to TLR, that involves the activation of heterotrimeric G-alpha protein-dependent G-protein coupled receptor (GPCR) signaling to activate a matrix metalloproteinase (MMP) enzyme, likely MMP-9. It is suggested that MMP-(9) targets the cell surface elastin receptor complex of Neu1/protective protein cathepsinA/elastin binding protein (EBP), which potentially catalytically activates Neu1. In addition, we report an association between Neu1 and TLR2, TLR3 and TLR4 on the plasma membrane that has not previously been described. The idea that the multiple functionality and diversity of TLRs and TLR-mediated signaling may be an immunologic paradigm capable of explaining all human disease is provocative but plausible. Certainly, the structural integrity of TLRs, their ligand interactions and activation are essential for immunological protection. Thus, understanding the molecular mechanism of Neu1 sialidase regulation of TLR activation will provide important opportunities for disease control through TLR manipulation. The future directions of this research will also open a new area of glycobiology research (the glycomics of innate immune responses) and will widen the scope for the development of novel therapeutic drugs to combat infections and inflammatory diseases. / Thesis (Ph.D, Microbiology & Immunology) -- Queen's University, 2009-01-26 12:33:32.743

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

<p>Atherosclerosis is a complex multi-factorial disease that involves the interaction of many cell types and a plethora of molecular events. Initiation of the disease occurs when circulating LDL gets trapped in the sub-endothelial space of arteries, where LDL is oxidized causing inflammatory responses by endothelial cells. This results in recruitment and differentiation of monocytes into macrophages; macrophages in turn continue to take up cholesterol and propagate inflammation. Such a gloomy milieu of immune cells, lipids, and smooth muscle cells can give rise to atherosclerotic plaques, which then cause stenosis, vascular stiffening and eventually thrombosis. Common risk factors such as cholesterol levels, lifestyle and genetic predisposition can accelerate this potentially life threatening series of events. The downstream long-term effects of atherosclerosis, including heart disease and strokes, are now the number one cause of death in the world. While a large amount of knowledge and evidence is available in understanding this disease, prevention and treatment strategies remain somewhat ineffective. Sialylation of immune cells, lipoproteins and cellular receptors has been previously implicated in metabolic and molecular pathways relevant to atherosclerosis; however, little is known about the functional role of sialidase in these processes. Sialidase cleaves sialic acid, and is a ubiquitously expressed and evolutionarily conserved protein with essential functions in many life forms. In this study, we sought to investigate the impact of sialidase activity on atherosclerosis, emphasizing the interaction of lipid metabolism and inflammation. We have demonstrated a significant role for sialidase in cholesterol iv and lipoprotein metabolism in vivo. Specifically, hypomorphic sialidase mice have increased hepatic storage of lipids and triglycerides, decreased VLDL production, lower circulating LDL levels and alterations in regulation of LDLR. Mice over-expressing hepatic human sialidase have increased atherosclerotic lesion formation, higher serum cholesterol esters and lower levels of hepatic LDLR and SRB-1 protein. In vitro, we have shown that VLDL can induce differentiation and cytokine production in monocytes coupled with an up-regulation of Neu1. Inhibition of sialidase using DANA attenuated VLDL-induced monocyte differentiation and lipid uptake, as well as activation of macrophages, implicating Neu1 in inflammatory processes associated with initiation of atherosclerosis. Furthermore, we have shown that hypomorphic sialidase activity increases LDLR-dependent LDL uptake and cholesterol efflux to HDL in macrophages. We conclude that reduction of sialidase activity can lead to an atheroprotective phenotype with multiple effects on mechanisms involved in disease progression. This work represents novel contributions into delineating both metabolic and inflammatory processes of atherosclerosis and enables the advancement of future treatment strategies.</p> / Doctor of Philosophy (PhD)

A neuraminidase-1 (Neu1) participa da regulação do catabolismo de sialoglicoconjugados nos lisossomos. A deficiência congênita da Neu1 é a base da sialidose, doença neurossomática grave associada a deformidades osteoesqueléticas, hipotonia e fraqueza muscular. Camundongos com deficiência de Neu1 (Neu1-/-) desenvolvem uma forma atípica de degeneração muscular caracterizada por expansão da matriz extracelular (MEC), invasão das fibras musculares por fibroblastos, fragmentação do citoplasma, formação vacuolar e atrofia muscular. Apesar de a degeneração muscular estar bem caracterizada nestes animais, a miogênese ainda não havia sido estudada. O objetivo desta pesquisa foi avaliar o envolvimento da Neu1 no processo de regeneração muscular, após aplicação de cardiotoxina (CTX) em camundongos Neu1-/-, em comparação com controles normais. A CTX foi administrada no músculo tibial anterior direito e os animais foram eutanasiados por deslocamento cervical 1, 3, 5, 7, 10, 14, 21 e 28 dias após a lesão. Os músculos foram analisados através de histologia; medição da área transversa das fibras musculares centronucleadas; verificação do potencial proliferativo celular por quantificação de marcação de BrdU; imunoistoquímica para inflamação, fibras regenerativas e fibrose; e expressão gênica e proteica de fatores de transcrição musculares. Os dados foram comparados estatisticamente e as variações significativas devem apresentar p <= 0,05. Nos animais com deficiência de Neu1, o processo inflamatório (especialmente a reação macrofágica) e o potencial proliferativo estavam aumentados nas fases iniciais, acompanhados da hiperexpressão de Pax7. Observamos atraso na maturação muscular caracterizado por maior expressão de miosina embrionária em estágios mais tardios da regeneração. Os genes MyoD e MyoG estavam com expressão aumentada no período de 5 a 10 dia após a lesão, embora a expressão destas proteínas estivesse reduzida. Ao final da regeneração, houve maior deposição de reticulina na MEC, indicando processo fibrótico. A Neu1 parece atuar em todos os estágios da regeneração muscular, desde a fase aguda da lesão através do controle da proliferação celular, até a maturação muscular e estágios finais em que regularia a deposição de componentes da MEC / Neuraminidase-1 (Neu1) participates in sialoglycoconjugates catabolism in lysosomes. Congenital Neu1 deficiency is the basis of sialidosis, a severe neurosomatic disorder associated with osteoskeletal deformities, hypotonia and muscle weakness. Mice with Neu1 deficiency (Neu1-/-) develop an atypical form of muscle degeneration characterized by abnormal fibroblast proliferation and expanded extracellular matrix (ECM), invasion of muscle fibers by fibroblast, cytosolic fragmentation, vacuolar formation and muscle atrophy. Despite muscle degeneration is well characterized in these animals, myogenesis has not been studied so far. The aim of this study was to evaluate the involvement of Neu1 in muscle regeneration process after cardiotoxin (CTX) injection in Neu1-/- mice and normal controls. CTX was applied in the right tibialis anterior muscle, and the animals were euthanized by cervical dislocation 1, 3, 5, 7, 10, 14, 21 and 28 days after injury. The muscles were analyzed through histology; cross-sectional area of regenerative muscle fibers; quantification of BrdU labeling; immunohistochemistry labelling for inflammation, regenerative fibers, and fibrosis; and gene and protein expression of muscle transcription factors. The data were compared and variances considered statistically significant in case p <= 0.05. In animals with Neu1 deficiency, both inflammatory process (mainly macrophagic response) and proliferative potential were increased in the initial stages, accompanied by overexpression of Pax7. We observed delay in muscle maturation characterized by higher expression of embryonic myosin later in muscle regeneration. MyoD and MyoG genes were overexpressed from 5 to 10 days after injury, though the expression of these proteins was reduced. At the end of muscle regeneration, reticulin deposition in ECM was increased, indicating fibrotic process. Neu1 seems to participate in all stages of muscle regeneration, since acute injury phase through the control of cell proliferation, towards muscle maturation, and at the final stages when it would regulate the deposition of ECM components

A neuraminidase-1 (Neu1) participa da regulação do catabolismo de sialoglicoconjugados nos lisossomos. A deficiência congênita da Neu1 é a base da sialidose, doença neurossomática grave associada a deformidades osteoesqueléticas, hipotonia e fraqueza muscular. Camundongos com deficiência de Neu1 (Neu1-/-) desenvolvem uma forma atípica de degeneração muscular caracterizada por expansão da matriz extracelular (MEC), invasão das fibras musculares por fibroblastos, fragmentação do citoplasma, formação vacuolar e atrofia muscular. Apesar de a degeneração muscular estar bem caracterizada nestes animais, a miogênese ainda não havia sido estudada. O objetivo desta pesquisa foi avaliar o envolvimento da Neu1 no processo de regeneração muscular, após aplicação de cardiotoxina (CTX) em camundongos Neu1-/-, em comparação com controles normais. A CTX foi administrada no músculo tibial anterior direito e os animais foram eutanasiados por deslocamento cervical 1, 3, 5, 7, 10, 14, 21 e 28 dias após a lesão. Os músculos foram analisados através de histologia; medição da área transversa das fibras musculares centronucleadas; verificação do potencial proliferativo celular por quantificação de marcação de BrdU; imunoistoquímica para inflamação, fibras regenerativas e fibrose; e expressão gênica e proteica de fatores de transcrição musculares. Os dados foram comparados estatisticamente e as variações significativas devem apresentar p <= 0,05. Nos animais com deficiência de Neu1, o processo inflamatório (especialmente a reação macrofágica) e o potencial proliferativo estavam aumentados nas fases iniciais, acompanhados da hiperexpressão de Pax7. Observamos atraso na maturação muscular caracterizado por maior expressão de miosina embrionária em estágios mais tardios da regeneração. Os genes MyoD e MyoG estavam com expressão aumentada no período de 5 a 10 dia após a lesão, embora a expressão destas proteínas estivesse reduzida. Ao final da regeneração, houve maior deposição de reticulina na MEC, indicando processo fibrótico. A Neu1 parece atuar em todos os estágios da regeneração muscular, desde a fase aguda da lesão através do controle da proliferação celular, até a maturação muscular e estágios finais em que regularia a deposição de componentes da MEC / Neuraminidase-1 (Neu1) participates in sialoglycoconjugates catabolism in lysosomes. Congenital Neu1 deficiency is the basis of sialidosis, a severe neurosomatic disorder associated with osteoskeletal deformities, hypotonia and muscle weakness. Mice with Neu1 deficiency (Neu1-/-) develop an atypical form of muscle degeneration characterized by abnormal fibroblast proliferation and expanded extracellular matrix (ECM), invasion of muscle fibers by fibroblast, cytosolic fragmentation, vacuolar formation and muscle atrophy. Despite muscle degeneration is well characterized in these animals, myogenesis has not been studied so far. The aim of this study was to evaluate the involvement of Neu1 in muscle regeneration process after cardiotoxin (CTX) injection in Neu1-/- mice and normal controls. CTX was applied in the right tibialis anterior muscle, and the animals were euthanized by cervical dislocation 1, 3, 5, 7, 10, 14, 21 and 28 days after injury. The muscles were analyzed through histology; cross-sectional area of regenerative muscle fibers; quantification of BrdU labeling; immunohistochemistry labelling for inflammation, regenerative fibers, and fibrosis; and gene and protein expression of muscle transcription factors. The data were compared and variances considered statistically significant in case p <= 0.05. In animals with Neu1 deficiency, both inflammatory process (mainly macrophagic response) and proliferative potential were increased in the initial stages, accompanied by overexpression of Pax7. We observed delay in muscle maturation characterized by higher expression of embryonic myosin later in muscle regeneration. MyoD and MyoG genes were overexpressed from 5 to 10 days after injury, though the expression of these proteins was reduced. At the end of muscle regeneration, reticulin deposition in ECM was increased, indicating fibrotic process. Neu1 seems to participate in all stages of muscle regeneration, since acute injury phase through the control of cell proliferation, towards muscle maturation, and at the final stages when it would regulate the deposition of ECM components

Background: Lysosomal storage diseases (LSD) often manifest with cherry red macular spots. Diagnosis is based on clinical features and specific biochemical and enzymatic patterns. In uncertain cases, genetic testing with next generation sequencing can establish a diagnosis, especially in milder or atypical phenotypes. We report on the diagnostic work-up in a boy with sialidosis type I, presenting initially with marked cherry red macular spots but non-specific urinary oligosaccharide patterns and unusually mild excretion of bound sialic acid. Methods: Biochemical, enzymatic and genetic tests were performed in the patient. The clinical and electrophysiological data was reviewed and a genotype-phenotype analysis was performed. In addition a systematic literature review was carried out. Case report and results: Cherry red macular spotswere first noted at 6 years of age after routine screening myopia. Physical examination, psychometric testing, laboratory investigations aswell as cerebralMRIwere unremarkable at 9 years of age. So far no clinical myoclonic seizures occurred, but EEG displays generalized epileptic discharges and visual evoked potentials are prolonged bilaterally. Urine thin layer chromatography showed an oligosaccharide pattern compatible with different LSD including sialidosis, galactosialidosis, GM1 gangliosidosis or mucopolysaccharidosis type IV B. Urinary bound sialic acid excretion was mildly elevated in spontaneous and 24 h urine samples. In cultured fibroblasts, α-sialidase activity was markedly decreased to b1%; however, bound and free sialic acid were within normal range. Diagnosis was eventually established by multigene panel next generation sequencing of genes associated to LSD, identifying two novel, compound heterozygous variants in NEU1 gene (c.699CNA, p.S233R in exon 4 and c.803ANG; p.Y268C in Exon 5 in NEU1 transcriptNM_000434.3), leading to amino acid changes predicted to impair protein function. Discussion: Sialidosis should be suspected in patients with cherry red macular spots, even with non-significant urinary sialic acid excretion. Multigene panel next generation sequencing can establish a definite diagnosis, allowing for counseling of the patient and family.

Background: Lysosomal storage diseases (LSD) often manifest with cherry red macular spots. Diagnosis is based on clinical features and specific biochemical and enzymatic patterns. In uncertain cases, genetic testing with next generation sequencing can establish a diagnosis, especially in milder or atypical phenotypes. We report on the diagnostic work-up in a boy with sialidosis type I, presenting initially with marked cherry red macular spots but non-specific urinary oligosaccharide patterns and unusually mild excretion of bound sialic acid. Methods: Biochemical, enzymatic and genetic tests were performed in the patient. The clinical and electrophysiological data was reviewed and a genotype-phenotype analysis was performed. In addition a systematic literature review was carried out. Case report and results: Cherry red macular spotswere first noted at 6 years of age after routine screening myopia. Physical examination, psychometric testing, laboratory investigations aswell as cerebralMRIwere unremarkable at 9 years of age. So far no clinical myoclonic seizures occurred, but EEG displays generalized epileptic discharges and visual evoked potentials are prolonged bilaterally. Urine thin layer chromatography showed an oligosaccharide pattern compatible with different LSD including sialidosis, galactosialidosis, GM1 gangliosidosis or mucopolysaccharidosis type IV B. Urinary bound sialic acid excretion was mildly elevated in spontaneous and 24 h urine samples. In cultured fibroblasts, α-sialidase activity was markedly decreased to b1%; however, bound and free sialic acid were within normal range. Diagnosis was eventually established by multigene panel next generation sequencing of genes associated to LSD, identifying two novel, compound heterozygous variants in NEU1 gene (c.699CNA, p.S233R in exon 4 and c.803ANG; p.Y268C in Exon 5 in NEU1 transcriptNM_000434.3), leading to amino acid changes predicted to impair protein function. Discussion: Sialidosis should be suspected in patients with cherry red macular spots, even with non-significant urinary sialic acid excretion. Multigene panel next generation sequencing can establish a definite diagnosis, allowing for counseling of the patient and family.