Sphingolipids are important signaling molecules regulating cell growth, cell death and differentiation, thus making them important molecules in determining the fate of a cell and in the pathogenesis of chronic illnesses. The sphingolipid signaling pathway can be initiated by reactive oxygen species (ROS) and inflammatory molecules, both of which are believed to be upregulated in a state of obesity. The hypothesis tested in this dissertation is that due to the inflammatory state of obese animals, the sphingolipid pathway is altered, shifting the balance of pro- and anti-apoptotic proteins and contributing to the pathogenesis of diseases associated with an obese state. The specific aims were to compare, 1) key sphingolipid signaling enzymes; 2) levels of sphingolipid signaling molecules and 3) pro and anti-apoptotic protein levels, in hepatic and colonic tissues procured from lean and obese animals. Obese animals are susceptible to various diseases, including colon cancer and hepatic steatosis. To assess the effect of obesity on sphingolipid signaling, and to provide insight as to the pathogenesis of diseases in a state of obesity, liver and colon tissues from Zucker obese female rats (fa/fa) were compared to tissues from their lean counterparts (Fa/fa or Fa/Fa Zucker rats). Enzyme analyses included an assay of sphingomyelinase (SMase) activity and quantification of ceramidase and sphingosine kinase-1 (SK1) protein expression by western blot. Also, sphingomyelin (SM), ceramide, ceramide-1 phosphate (C1P), sphingosine and sphingosine-1-phosphate (S1P) levels were determined by high-performance liquid chromatography (HPLC) -tandem mass spectroscopy (MS). Representative apoptotic proteins, Bax and Bcl-2 were quantified by western blot. Obese liver demonstrates hepatic steatosis in the Zucker animal model. Among the major differences noted between obese and lean liver were significantly upregulated ceramidase, and downregulated SK1 and C1P levels (P<0.05), as well as a difference in ceramide and SM species composition. Bax was overexpressed while Bcl-2 level was lower in obese compared to lean liver (P<0.05). Taken together, the results indicate a shift toward higher apoptotic signaling in obese liver tissue and correspond with the diseased state of the steatotic liver. Analysis of the sphingolipid pathway in colon revealed upregulation of ceramidase and downregulation of SK1 (P<0.05), similar to liver tissue. C1P levels were lower (P<0.05) but no changes were observed for ceramide, SM or sphingosine levels. A trend toward higher SMase activity in obese colon was observed. Bax was overexpressed in obese colon tissue (P< 0.05), while Bcl-2 results were inconclusive. The liver expressed lower level of molecules associated with sphingolipid signaling than the colons. This study is first to demonstrate tissue-specific differences in the sphingolipid signaling pathway, regardless of genotype. Nevertheless, overall the genotype of Zucker model was found to be a factor altering the expression levels of various sphingolipid enzymes and metabolites in both colon and liver. The findings of the present research provide incentive to further understand the role and modulation of sphingolipid signaling pathway in causation and prevention of chronic diseases prevalent in obese state.

ABSTRACT CAMP factor is a 25kDa extracellular protein from Streptococcus agalactiae (Group B streptococci) that contains 226 amino acid residues. CAMP factor has been characterized as a pore-forming toxin (PFT). The typical mechanism of pore formation of PFTs involves three main stages, namely binding of toxin monomers to the membrane surface, oligomerization of the monomers on the cell membrane, and finally the insertion of oligomers into the membrane. This study focused on second stage, and investigates the oligomerisation of CAMP factor on sheep red blood cell membranes. It is known that the hemolytic activity of CAMP factor is greatly enhanced by interaction with sphingomyelinase from Staphylococcus aureus. We here focused on understanding the role of sphingomyelinase in the oligomerisation step. Experimental data were obtained using Förster resonance energy transfer (FRET) studies. The fluorescence dyes IAEDANS and Fluorescein-5-maleimide were used as donor/acceptor fluorophores and attached to mutant single cysteine residues in CAMP factor. Samples of donor- and acceptor-labelled protein were mixed and incubated with red cell membranes that had or had not been pre-treated with sphingomyelinase. Energy transfer was monitored with time-resolved and steady-state fluorescence measurements. In the time-resolved experiments, the fluorescence lifetime of the donor was measured in the presence and the absence of the acceptor, on membrane samples that were or were not treated with sphingomyelinase. We observed a decrease in the fluorescence lifetime of the donor with the presence of the acceptor. The decrease in lifetime due to acceptor interaction signifies the occurrence of energy transfer between the donor and acceptor fluorophores, which indicates proximity due to oligomerisation of the CAMP factor protein on the cell membrane. This was only observed when the membranes had been treated with sphingomyelinase. When membranes were used that had not been treated with sphingomyelinase, the donor lifetimes are very low, suggesting the inability of the CAMP factor to undergo membrane insertion and oligomerisation.

Sphingolipids are important signaling molecules regulating cell growth, cell death and differentiation, thus making them important molecules in determining the fate of a cell and in the pathogenesis of chronic illnesses. The sphingolipid signaling pathway can be initiated by reactive oxygen species (ROS) and inflammatory molecules, both of which are believed to be upregulated in a state of obesity. The hypothesis tested in this dissertation is that due to the inflammatory state of obese animals, the sphingolipid pathway is altered, shifting the balance of pro- and anti-apoptotic proteins and contributing to the pathogenesis of diseases associated with an obese state. The specific aims were to compare, 1) key sphingolipid signaling enzymes; 2) levels of sphingolipid signaling molecules and 3) pro and anti-apoptotic protein levels, in hepatic and colonic tissues procured from lean and obese animals. Obese animals are susceptible to various diseases, including colon cancer and hepatic steatosis. To assess the effect of obesity on sphingolipid signaling, and to provide insight as to the pathogenesis of diseases in a state of obesity, liver and colon tissues from Zucker obese female rats (fa/fa) were compared to tissues from their lean counterparts (Fa/fa or Fa/Fa Zucker rats). Enzyme analyses included an assay of sphingomyelinase (SMase) activity and quantification of ceramidase and sphingosine kinase-1 (SK1) protein expression by western blot. Also, sphingomyelin (SM), ceramide, ceramide-1 phosphate (C1P), sphingosine and sphingosine-1-phosphate (S1P) levels were determined by high-performance liquid chromatography (HPLC) -tandem mass spectroscopy (MS). Representative apoptotic proteins, Bax and Bcl-2 were quantified by western blot. Obese liver demonstrates hepatic steatosis in the Zucker animal model. Among the major differences noted between obese and lean liver were significantly upregulated ceramidase, and downregulated SK1 and C1P levels (P<0.05), as well as a difference in ceramide and SM species composition. Bax was overexpressed while Bcl-2 level was lower in obese compared to lean liver (P<0.05). Taken together, the results indicate a shift toward higher apoptotic signaling in obese liver tissue and correspond with the diseased state of the steatotic liver. Analysis of the sphingolipid pathway in colon revealed upregulation of ceramidase and downregulation of SK1 (P<0.05), similar to liver tissue. C1P levels were lower (P<0.05) but no changes were observed for ceramide, SM or sphingosine levels. A trend toward higher SMase activity in obese colon was observed. Bax was overexpressed in obese colon tissue (P< 0.05), while Bcl-2 results were inconclusive. The liver expressed lower level of molecules associated with sphingolipid signaling than the colons. This study is first to demonstrate tissue-specific differences in the sphingolipid signaling pathway, regardless of genotype. Nevertheless, overall the genotype of Zucker model was found to be a factor altering the expression levels of various sphingolipid enzymes and metabolites in both colon and liver. The findings of the present research provide incentive to further understand the role and modulation of sphingolipid signaling pathway in causation and prevention of chronic diseases prevalent in obese state.

ABSTRACT CAMP factor is a 25kDa extracellular protein from Streptococcus agalactiae (Group B streptococci) that contains 226 amino acid residues. CAMP factor has been characterized as a pore-forming toxin (PFT). The typical mechanism of pore formation of PFTs involves three main stages, namely binding of toxin monomers to the membrane surface, oligomerization of the monomers on the cell membrane, and finally the insertion of oligomers into the membrane. This study focused on second stage, and investigates the oligomerisation of CAMP factor on sheep red blood cell membranes. It is known that the hemolytic activity of CAMP factor is greatly enhanced by interaction with sphingomyelinase from Staphylococcus aureus. We here focused on understanding the role of sphingomyelinase in the oligomerisation step. Experimental data were obtained using Förster resonance energy transfer (FRET) studies. The fluorescence dyes IAEDANS and Fluorescein-5-maleimide were used as donor/acceptor fluorophores and attached to mutant single cysteine residues in CAMP factor. Samples of donor- and acceptor-labelled protein were mixed and incubated with red cell membranes that had or had not been pre-treated with sphingomyelinase. Energy transfer was monitored with time-resolved and steady-state fluorescence measurements. In the time-resolved experiments, the fluorescence lifetime of the donor was measured in the presence and the absence of the acceptor, on membrane samples that were or were not treated with sphingomyelinase. We observed a decrease in the fluorescence lifetime of the donor with the presence of the acceptor. The decrease in lifetime due to acceptor interaction signifies the occurrence of energy transfer between the donor and acceptor fluorophores, which indicates proximity due to oligomerisation of the CAMP factor protein on the cell membrane. This was only observed when the membranes had been treated with sphingomyelinase. When membranes were used that had not been treated with sphingomyelinase, the donor lifetimes are very low, suggesting the inability of the CAMP factor to undergo membrane insertion and oligomerisation.

Indiana University-Purdue University Indianapolis (IUPUI) / Key regulatory decisions of protein synthesis and autophagy are controlled by the lysosomal nutrient sensing complex (LYNUS). To engage protein synthesis signaling, LYNUS requires cellular availability of amino acids, adenosine triphosphate (ATP), growth factors, and docking at the lysosomal membrane. The molecular determinants of LYNUS signaling and docking are not completely elucidated and may involve regulators of the lipid membrane structure and function of the lysosome. Since ceramides are both bioactive second messengers and determinants of lipid membrane stiffness, we investigated the role of the ceramide-producing lysosomal acid sphingomyelinase (ASM) in the homeostatic function of mammalian target of rapamycin (mTOR) signaling and autophagy. Using ASM inhibition with either imipramine or siRNA against SMPD1, in primary human lung cells or Smpd1+/- mice, we demonstrated that ASM is an endogenous inhibitor of autophagy. ASM was necessary for physiological mTOR signaling and maintenance of sphingosine levels. Whereas overstimulation of ASM has been shown to trigger autophagy with impaired flux, inhibition of ASM activity during homeostatic, non-stressed conditions triggered autophagy with degradative potential, associated with enhanced transcription factor EB (TFEB), a master regulator of autophagy and lysosomal biogenesis genes, translocation to the nucleus and decreased sphingosine levels. These findings suggest LYNUS signaling and autophagy are partially regulated by ASM.

No description available.

Acid Sphingomyelinase (ASMase) activity has been proposed to mediate LPS signaling in various cell types. This study shows that in macrophages, ASMase is a negative regulator of LPS-induced TNFα secretion. ASMasedeficient (asm-/-) mice and isolated peritoneal macrophages produce several fold more TNFα than their wild-type (asm+/+) counterparts when stimulated with LPS. The mechanism for these differences however is not transcriptional but post-translational. The TNFα converting enzyme (TACE) catalyzes the maturation of the 26kD precursor (proTNFα) to the active 17kD form (sTNFα). In mouse peritoneal macrophages, the activity of TACE rather than the rate of TNFα mRNA synthesis was the rate-limiting factor regulating TNFα production. Substantial portion of the translated proTNFα was not processed to sTNFα; instead it was rapidly internalized and degraded in the lysosomes. TACE activity was 2 to 3 fold higher in asm-/- macrophages as compared to asm+/+ macrophages and was suppressed when cells were treated with exogenous ceramide and SMase. In asm-/- but not in asm+/+macrophages, indirect immunofluorescence experiments revealed distinct TNFα-positive structures in close vicinity of the plasma membrane. Asm-/- cells also had higher number of EEA1-positive early endosomes. Co-localization experiments that involved inhibitors of TACE and/or lysosomal proteolysis suggest that in asm-/-cells a significant portion of proTNFα is sequestered within the early endosomes, and instead of undergoing lysosomal proteolysis it is recycled to the plasma membrane and processed to sTNFα.

Die saure Sphingomyelinase (Asm), ein Enzym des Sphingolipidmetabolismus, spaltet Sphingomyelin zu Ceramid und Phosopocholin. Aktiviert wird die Asm unter anderem durch Stimulation des CD28 Rezeptors. CD28 Signale werden auch für die Aktivierung von konventionellen T-Zellen (Tconv) und für die Kostimulation benötigt und sind essentiell für die Differenzierung von regulatorischen T-Zellen (Treg) im Thymus und deren Erhalt in der Peripherie. Wir konnten zeigen, dass sich Tconv und Treg Zellen hinsichtlich der Asm unterscheiden. Treg haben eine höhere "basale" Asm Aktivität, widergespiegelt im höheren Ceramidgehalt und haben eine niedrigere Lipidordnung als Tconv Zellen. Die Abwesenheit der Asm in defizienten Mäusen bewirkt einen relativen Anstieg der Treg-Frequenz innerhalb der CD4+ T-Zellen. Außerdem führt die Asm-Defizienz in Treg Zellen zu einer erhöhten Umsatzrate des immunsupprimierenden Moleküls CTLA-4 und zu einer verstärkten Suppressivität von Treg Zellen aus Asm-/- Mäusen gegenüber Wildtyp Zellen. Ein Anstieg in der Treg-Frequenz, äquivalent zur genetischen Defizienz, kann auch durch Inhibition der Asm, d. h. durch Wirkstoffe wie Amitriptylin und Desipramin erreicht werden. Es konnte gezeigt werden, dass die Inhibitorbehandlung die absolute Anzahl der Tconv Zellen selektiv verringert, da Treg Zellen gegenüber dem Asm Inhibitor-induzierten Zelltod resistenter sind. Mechanistisch erklärbar sind die Unterschiede gegenüber den proapoptotischen Inhibitoreffekten zwischen Tconv und Treg Zellen dadurch, dass Treg Zellen durch die Anwesenheit von IL-2 geschützt sind. In Abwesenheit von IL-2 sterben die Treg Zellen ebenfalls. Die gezielte Veränderung des Verhältnisses von Treg zu Tconv durch den Einsatz von Asm-inhibitorischen Medikamenten kann hilfreich bei der therapeutischen Behandlung von inflammatorischen- und Autoimmunerkrankungen sein. Inwiefern die Asm für die Funktion von T-Zellen in der anti-viralen Immunantwort entscheidend ist, wurde im Masernvirus-Infektionsmodell näher untersucht. In Asm-/- Mäusen und Amitriptylin-behandelten Mäusen konnte gezeigt werden, dass in Abwesenheit der Asm die Kontrolle der Masernvirusinfektion verschlechtert ist. Treg sind auch hier von entscheidender Bedeutung, da die Asm-abhängige, verstärkte Masernvirusinfektion bei Fehlen der Asm nur in Gegenwart von Treg auftritt. In der akuten Phase gibt es in Asm-/- Mäusen weniger masernvirusspezifische T-Zellen und dadurch eine verringerte Beseitigung der Viruslast. In der chronischen Phase ist die Anzahl masernvirusspezifischer T-Zellen zwischen WT und Asm-/- Mäusen vergleichbar. In Letzteren ist allerdings die Anzahl und Frequenz von T-Zellen im Gehirn infizierter Mäuse noch deutlich erhöht, was die verstärkte Maserninfektion widerspiegelt. Zusammenfassend zeigt sich, dass die Asm die Funktion von Treg moduliert und einen Einfluss auf das Verhältnis von Tconv und Treg zueinander hat. Im Masernvirus-Infektionsmodell kann die Veränderung des Tconv zu Treg Verhältnisses in Abwesenheit der Asm ursächlich für die verringerte Viruskontrolle sein. Die Asm Inhibitor-induzierte Treg-Aktivierung und die Beeinflussung des Treg zu Tconv Verhältnisses können wiederum für therapeutische Zwecke genutzt werden, wie beispielsweise bei Multipler Sklerose und Rheumatoider Arthritis. / The acid sphingomyelinase (Asm), an enzyme of the sphingolipid metabolism, hydrolyses sphingomyelin into ceramide and phosphocholine. Besides other stimuli the Asm is activated by ligation of the costimulatory molecule CD28. CD28 signaling is necessary to activate conventional T-cells (Tconv) and is crucial for the differentiation and maintenance of thymus-derived regulatory T-cells (Treg). We could demonstrate that Tconv and Treg cells differ with respect to Asm activity. Treg cells have an increased "basal" Asm activity resulting in an elevated level of ceramide and show a decreased lipid order compared to Tconv cells. The absence of Asm leads to a relative increase in Treg frequency among CD4+ T-cells in Asmdeficient mice. Furthermore, the Asm deficiency results in an increased turnover rate of the immunosuppressive molecule CTLA-4 and strengthens the suppressive capacity of Treg cells from Asm-/- mice compared to wild type Treg cells. An increase of the Treg cell frequency, equivalent to that seen with genetic deficiency, can be achieved by drugs like amitriptyline and desipramine too. The inhibitor treatment selectively decreases the absolute numbers of Tconv cells as Treg cells are more resistant towards Asm inhibitor induced cell death. The mechanistic explanation for the difference concerning the proapotptotic effects of Asm inhibitors between Treg and Tconv cells is that Treg cells are protected by IL-2. In the absence of IL-2 Treg cells die too. Therapeutically shifting the balance of Treg and Tconv cells by Asminhibiting drugs can be beneficial in inflammatory and autoimmune diseases. Whether the Asm is necessary for the function of T-cells during anti-viral immune responses was investigated in a measles virus infection model. In Asm-/- mice and amitriptyline treated mice control of the measles virus was impaired. Treg cells are of critical relevance as the Asm dependent boost in measles infection was only visible in the presence of Treg cells. During the acute phase of infection less measles virus specific T-cells were present leading to a decreased clearance of virus from the brains of Asm-/- mice. In the chronic phase the number of measles virus specific Tcell was comparable between wt and Asm-/- mice. But in the latter the number and frequency of T-cells in brains of infected mice was increased, which mirrors the enhanced measles virus infection. In conclusion, the Asm modulates the function of Treg cells and influences the Treg- Tconv ratio. The changed Treg-Tconv ratio in the absence of Asm expression might be responsible for the reduced virus control in the measles virus infection model. Additionally, the Asm inhibitor induced Treg cell activation and its effects on the Treg- Tconv ratio can be used for therapeutical approaches in diseases like multiple sclerosis or rheumatoid arthritis.

Doctor of Philosophy / Department of Diagnostic Medicine and Pathobiology / Kyeong-Ok Chang / Caliciviruses are important pathogens of humans and animals. Noroviruses are major causes of foodborne gastroenteritis cases, but their research is hindered due to the inability to grow human noroviruses in cell culture. Detailed studies on entry events of caliciviruses are lacking and may be crucial for development of cell culture models. We examined the entry events of caliciviruses using porcine enteric calicivirus (PEC), feline calicivirus (FCV) and murine norovirus-1 (MNV-1). PEC replication in LLC-PK cells requires bile acid in the medium, but the mechanism is not well understood. Our studies showed that bile acids are required in the early stage of virus replication, and while internalization of PEC is not dependent of them, they are required for endosomal escape and successful replication. Further examination on virus entry, we demonstrated that endosomal acidification and cathepsin L activity are essential in the replication of PEC, FCV and MNV-1. The results showed that inhibition of endosomal acidification or cathepsin L activity led to retention of viruses in the endosomes. Also we demonstrated that recombinant cathepsin L cleaved structural protein of PEC, FCV or MNV-1, which suggests that the enzyme may facilitate uncoating viruses in endosomes. In addition to bile acids, we found that a cold shock treatment during virus entry supported PEC replication by facilitating the endosomal escape. While PEC alone did not induce ceramide formation, bile acids or cold shock treatment induce ceramide formation on endosomes through activation acid sphingomyelinase (ASM), and this event was crucial for virus replication because inhibition of ASM blocked ceramide formation and significantly reduced PEC replication. Incubation of FCV or MNV-1 with cells led to ceramide formation during virus entry, and inhibition of ASM also significantly reduced their replication. Inhibition of ASM led to endosomal retention of PEC, FCV or MNV-1 during virus entry, which may be the reason for the reduction of viral replication. These studies revealed the important and common events during calicivirus entry for successful replication, including virus endosomal escape, cathepsin L activity and ASM/ceramide formation. This detailed information may provide clues for understanding the replication of fastidious caliciviruses and for potential therapeutic targets.

A esquistossomose representa um grande problema de saúde pública em regiões tropicais, negligenciado pelas empresas farmacêuticas. Três genes foram selecionados a partir do transcriptoma do S. mansoni para serem caracterizados molecularmente e testados como vacinas. O gene da Carboxipeptidase apresentou altos níveis de transcrição no estágio de cercária e uma variável expressão protéica nos estágios intra-hospedeiros. A proteína recombinante renaturada apresentou baixa atividade. O gene da Esfingomielinase apresentou alto nível transcricional em ovos, sendo expresso em todos os estágios exceto em esquistossômulos de 7 dias e fêmeas. O gene da Fosfatase Alcalina apresentou elevada transcrição em cercária, mas a expressão da proteína se eleva somente no estágio de esquistossômulo. A imunização de camundongos com cada uma das três proteínas recombinantes expressas em E. coli não levou à redução da carga parasitária após desafio. Estes resultados demonstram que diversas características de um antígeno são necessárias para que este seja um bom candidato vacinal. / Schistosomiasis is a major public health problem in tropical areas and neglected by most of the pharmaceutical companies. Three genes were selected from S. mansoni transcriptome to be molecularly characterized and tested as vaccines. The Carboxypeptidase gene showed high transcription levels in cercariae stage and a variable protein expression in intra-host stages. The refolded recombinant protein showed limited activity. The Sphingomyelinase gene showed the highest level of transcriptional activity in the egg stage and the protein is expressed in all stages but 7-day old schistosomula and females. The Alkaline Phosphatase gene showed a high transcriptional activity in cercariae stage with most of the mRNA being translated into protein as soon as it penetrates its definitive host. Immunization of mice with each of the three proteins did not show reduction in worm burden recovery after challenge. These results demonstrate that several characteristics of an antigen are important for it to be considered a good vaccine candidate.