Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Biologically active 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) binds the vitamin D receptor (VDR) to exert its effect on target cells. VDR expression is found in a number of immune cells including professional antigen-presenting cells such as dendritic cells. It has been found that the actions of 1,25-(OH)2D3 on the immune system are mainly immunosuppressive. The cross-presentation pathway allows for exogenously derived antigens to be presented by pAPCs on MHC-I molecules to CD8+ T cells. CD8+ T cell activation results in the expansion of epitope-specific T cell populations that confer host protection. These epitopes can be organized into an immunodominance hierarchy. Previous work demonstrated that introducing LCMV-NP via the cross-priming pathway significantly alters the immunodominance hierarchy of a subsequent LCMV infection. Building upon these observations, our study assessed the effects of LCMV-NP cross priming in the presence of a single dose of 1,25-(OH)2D3. Treatment with 1,25-(OH)2D3 was found to have biological effects in our model system. In vitro pAPCs were demonstrated to up-regulate IL-10 and CYP24A1 mRNA, in addition to the transactivation of cellular VDR, as demonstrated by a relocalization to the nuclear region. Mice treated with 1,25-(OH)2D3 were found to produce up-regulated IL-10 and CYP24A1 transcripts. Expression of VDR was increased at both the transcript and protein level. Our results demonstrate that a single dose of 1,25-(OH)2D3 does not affect the cross-priming pathway in this system. Treatment with 1,25-(OH)2D3 did not influence the ability of differentiated pAPCs to phagocytose or cross-present exogenous antigen to epitope-specific CD8+ T cells. Furthermore, 1,25-(OH)2D3 did not alter cross-priming or the establishment of the LCMV immunodominance hierarchy in vivo. By confirming that 1,25-(OH)2D3 does not suppress cross-priming in our model, our study helps to expand the understanding of the immunomodulatory role of exogenous 1,25-(OH)2D3 on the outcome of virus infection. Collectively, our data supports the observation that the role of 1,25-(OH)2D3 in the immune system is not always associated with suppressive effects. / Thesis (Master, Microbiology & Immunology) -- Queen's University, 2011-08-29 14:53:18.766

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

Abstract The aim of the present study was to examine associations between serum 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D[(1,25(OH)2D]—the circulating and active forms of vitamin D—and periodontal infection. The data were gathered from a case-control study (63 periodontitis patients and 30 periodontally healthy controls) and an intervention study among individuals with type 1 diabetes mellitus (T1DM, 80 patients at the baseline and 65 after periodontal treatment). The periodontal data and the levels of serum 25(OH)D, 1,25(OH)2D and parathyroid hormone (PTH) were available. A third data set included periodontal data and the serum level of 25(OH)D of 1262 non-smoking and non-diabetic 30–49-year-old individuals (Health 2000 Survey). Serum 25(OH)D analyses were done using enzyme-linked immunoassay and radioimmunoassay, 1,25(O)2D analyses using enzyme-immunoassay after purification of 1,25(OH)2D by immunoextraction and PTH analyses using electrochemiluminescence immunoassay. In the case-control study individuals with a low serum 1,25(O)2D level were more likely to belong to the periodontitis group than to the periodontally healthy group and an inverse association was observed between serum 1,25(OH)2D and severity of periodontitis at the baseline of the intervention study. Serum 1,25(OH)2D increased significantly after periodontal treatment in the T1DM patients; a finding that was considered suggestive of a causal relationship between serum 1,25(OH)2D and periodontal infection. Also, serum PTH increased after periodontal treatment; this increase, which was statistically significant (p = 0.016) in patients with moderate or severe periodontitis, may partly account for the earlier observed post-treatment increase in serum 1,25(OH)2D level. Possible explanations for low serum 1,25(OH)2D in periodontal infection may be increased degradation of 1,25(OH)2D, increased use of 1,25(OH)2D, or decreased hydroxylation of 25(OH)D The association between serum 25(OH)D level and periodontal infection was weak, if existent. An inverse association between serum 25(OH)D and the severity of periodontal infection was observed only in the T1DM patients. Among individuals with low plaque level, those in higher 25(OH)D quintiles tended to have fewer teeth with deepened periodontal pockets than those in lower quintiles; a finding which was interpreted to mean a slight protective role of 25(OH)D against periodontal infection. / Tiivistelmä Tutkimuksen tarkoituksena oli selvittää seerumin 25-hydroksivitamiini D:n [25(OH)D, D-vitamiinin varastomuoto] ja 1,25-dihydroksivitamiini D:n [1,25(OH)2D, D-vitamiinin aktiivinen muoto] tasojen yhteyttä parodontiumin alueen infektiosairauksiin. Tulokset perustuvat kolmeen tutkimusasetelmaan: tapaus-verrokki-tutkimus (63 parodontiitti-potilasta, 30 verrokkia), interventio-tutkimus [80 tyypin 1 diabetes mellitus (T1DM) potilasta, joista 65 osallistui seurantaan parodontologisen hoidon jälkeen] ja poikittaistutkimus Terveys 2000 tutkimuksen osa-aineistossa (1262 30-49 vuotiasta tupakoimatonta ei-diabeetikkoa). Tapaus-verrokki- ja interventiotutkimuksissa tutkittiin myös seerumin parathormoonin (PTH) yhteyttä parodontaali-infektioon sekä PTH:n vaikutusta seerumin 1,25(OH)2D tasoon infektion hoidon jälkeen. D-vitamiinin ja PTH:n tasot määritettiin immunologisin menetelmin. Yhteyksiä tutkittiin käyttäen vakioituja monimuuttujamalleja. Tapaus-verrokki-tutkimuksessa yksilöt, joilla seerumin 1,25(OH)2D taso oli alhainen, kuuluivat todennäköisemmin parodontiitti- kuin verrokkiryhmään. Interventiotutkimuksen alkutilanteessa seerumin 1,25(OH)2D:n ja parodontaali-infektion vaikeusasteen välillä vallitsi tilastollisesti merkittävä käänteinen yhteys ja taso nousi merkittävästi infektion hoidon jälkeen. Myös seerumin PTH taso nousi parodontaali-infektion hoidon jälkeen; nousu oli tilastollisesti merkittävä (p = 0.016) pitkälle edennyttä parodontiittia sairastavilla. Interventiotutkimuksen tulokset viittaavat kausaaliseen yhteyteen 1,25(OH)2D:n ja parodontaali-infektion välillä. Alhainen seerumin 1,25(OH)2D pitoisuus infektion vallitessa voi selittyä sen suurella käytöllä immuunipuolustukseen infektion aikana tai lisääntyneellä hajoamisella. Tason nousu hoidon jälkeen tukee edellä mainittua. PTH on 25(OH)D:n hydroksylaation pääsäätelijä ja 1,25(OH)2D:n nousua hoidon jälkeen voi osittain selittää myös seerumin PTH tason kohoaminen. Seerumin 25(OH)D:n ja parodontaali-infektion välillä havaittu yhteys oli heikko, mutta ei täysin sulje pois 25(OH)D:n suojaavaa vaikutusta. Käänteinen yhteys löytyi vain interventiotutkimuksen alkutilanteessa T1DM potilailla. Infektion hoito ei vaikuttanut 25(OH)D tasoon. Terveys 2000 tutkimuksen osa-aineistossa havaittiin hyvän suuhygienian omaavilla jonkin verran alhaisempi määrä syventyneitä ientaskuja ylemmissä kuin alemmissa 25(OH)D kvintiileissä.

Nuclear receptors play significant roles in the regulation of transporters and enzymes to balance the level of endogenous molecules and to protect the body from foreign molecules. The vitamin D receptor (VDR) and its natural ligand, 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3], was shown to upregulate rat ileal apical sodium dependent bile acid transporter (Asbt) to increase the reclamation of bile acids, ligands of the farnesoid X receptor (FXR). FXR is considered to be an important, negative regulator of the cholesterol metabolizing enzyme, Cyp7a1, which metabolizes cholesterol to bile acids in the liver. In rats, decreased Cyp7a1 and increased P-glycoprotein/multidrug resistance protein 1 (P-gp/Mdr1) expressions pursuant to 1,25(OH)2D3 treatment was viewed as FXR effects in which hepatic VDR protein is poorly expressed. In contrast, changes in rat intestinal and renal transporters such as multidrug resistance associated proteins (Mrp2, Mrp3, and Mrp4), Asbt, and P-gp after administration of 1,25(OH)2D3 were attributed directly as VDR effects due to higher VDR levels expressed in these tissues. Higher VDR expressions were found among mouse hepatocytes compared to those in rats. Hence, fxr(-/-) and fxr(+/+) mouse models were used to discriminate between VDR vs. FXR effects in murine livers. Hepatic Cyp7a1 in mice was found to be upregulated with 1,25(OH)2D3 treatment, via the derepression of the short heterodimer partner (SHP). Putative VDREs, identified in mouse and human SHP promoters, were responsible for the inhibitory effect on SHP. The increase in hepatic Cyp7a1 expression and decreased plasma and liver cholesterol were observed in mice prefed with a Western diet. A strong correlation was found between tissue Cyp7a1 and P-gp changes and 1,25(OH)2D3 plasma and tissue concentrations, confirming that VDR plays an important role in the disposition of xenobiotics and cholesterol metabolism. Moreover, renal and brain Mdr1a/P-gp were found to be directly upregulated by the VDR in mice, and concomitantly, increased renal and brain secretion of digoxin, a P-gp substrate, in vivo. The important observations: the cholesterol lowering and increased brain P-gp efflux activity properties suggest that VDR is a therapeutic target for treatment of hypercholesterolemia and Alzheimer’s diseases, since beta amyloid, precursors of plague, are P-gp substrates.

Nuclear receptors play significant roles in the regulation of transporters and enzymes to balance the level of endogenous molecules and to protect the body from foreign molecules. The vitamin D receptor (VDR) and its natural ligand, 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3], was shown to upregulate rat ileal apical sodium dependent bile acid transporter (Asbt) to increase the reclamation of bile acids, ligands of the farnesoid X receptor (FXR). FXR is considered to be an important, negative regulator of the cholesterol metabolizing enzyme, Cyp7a1, which metabolizes cholesterol to bile acids in the liver. In rats, decreased Cyp7a1 and increased P-glycoprotein/multidrug resistance protein 1 (P-gp/Mdr1) expressions pursuant to 1,25(OH)2D3 treatment was viewed as FXR effects in which hepatic VDR protein is poorly expressed. In contrast, changes in rat intestinal and renal transporters such as multidrug resistance associated proteins (Mrp2, Mrp3, and Mrp4), Asbt, and P-gp after administration of 1,25(OH)2D3 were attributed directly as VDR effects due to higher VDR levels expressed in these tissues. Higher VDR expressions were found among mouse hepatocytes compared to those in rats. Hence, fxr(-/-) and fxr(+/+) mouse models were used to discriminate between VDR vs. FXR effects in murine livers. Hepatic Cyp7a1 in mice was found to be upregulated with 1,25(OH)2D3 treatment, via the derepression of the short heterodimer partner (SHP). Putative VDREs, identified in mouse and human SHP promoters, were responsible for the inhibitory effect on SHP. The increase in hepatic Cyp7a1 expression and decreased plasma and liver cholesterol were observed in mice prefed with a Western diet. A strong correlation was found between tissue Cyp7a1 and P-gp changes and 1,25(OH)2D3 plasma and tissue concentrations, confirming that VDR plays an important role in the disposition of xenobiotics and cholesterol metabolism. Moreover, renal and brain Mdr1a/P-gp were found to be directly upregulated by the VDR in mice, and concomitantly, increased renal and brain secretion of digoxin, a P-gp substrate, in vivo. The important observations: the cholesterol lowering and increased brain P-gp efflux activity properties suggest that VDR is a therapeutic target for treatment of hypercholesterolemia and Alzheimer’s diseases, since beta amyloid, precursors of plague, are P-gp substrates.

Indiana University-Purdue University Indianapolis (IUPUI) / Multiple sclerosis (MS) is a disabling disease that afflicts an estimated two million people worldwide. The disease is characterized by degradation of the myelin sheath that insulates neurons of the central nervous system manifesting as a heterogeneous collection of symptoms. Two enzymes, protein arginine deaminases type 2 and 4 (PAD2 and PAD4) have been implicated to play an etiologic role in demyelination and neurodegeneration by catalyzing a post-translational modification of arginine peptide residues to citrulline. The pathogenesis of MS is poorly understood, though vitamin D deficiency is a well-associated risk factor for developing the disorder. Using the experimental autoimmune encephalomyelitis (EAE) model of MS we demonstrate vitamin D treatment to attenuate over-expression of PAD 2 and 4 in the brain and spine during EAE. In addition, we identify two molecules produced by peripheral immune cells, IFNɣ and IL-6, as candidate signaling molecules that induce PAD expression in the brain. We demonstrate vitamin D treatment to inhibit IFNɣ mediated up regulation of PAD2 and PAD4 both directly within the brain and by modulating PAD-inducing cytokine production by infiltrating immune cells. These results provide neuroprotective rational for the supplementation of vitamin D in MS patients. More importantly, these results imply an epigenetic link between vitamin D deficiency and the pathogenesis of MS that merits further investigation.