Les macrophages sont une cible cellulaire du VIH-1, et jouent un rôle important dans la pathogenèse virale. Au cours de ma thèse, je me suis intéressée au rôle des macrophages dans la pathogenèse du VIH-1, mais aussi au cours de la co-infection avec Mycobacterium tuberculosis (Mtb), l'agent étiologique de la tuberculose. J'ai tout d'abord participé à une étude mettant en évidence que l'infection par le VIH-1 reprogramme la migration des macrophages, favorisant notamment le mode migratoire protéolytique. Cet effet est médié par l'interaction de la protéine virale Nef avec les protéines de l'hôte Hck et WASP, ce qui conduit à une modification de l'organisation et de la fonction des podosomes, structures impliquées dans la dégradation de la matrice extracellulaire et la migration dépendante des protéases. La meilleure capacité à migrer des macrophages infectés par le VIH-1 in vitro se traduit in vivo par une augmentation du recrutement des macrophages dans différents tissus de souris transgéniques qui expriment la protéine Nef. Ces travaux ont ainsi révélé un nouveau mécanisme par lequel le VIH-1 dissémine dans les tissus, via l'action de Nef dans les macrophages. L'association fréquente du VIH-1 avec Mtb complique le problème de santé publique posé par l'infection virale. En effet, Mtb aggrave la pathogenèse du VIH-1 chez les patients co-infectés. L'étude des mécanismes impliqués et le rôle des macrophages dans ce phénomène constituent les objectifs principaux de ma thèse. J'ai révélé que les macrophages infectés par Mtb génèrent un microenvironnement qui active les macrophages voisins vers un programme de polarisation anti-inflammatoire dit M(IL-10). J'ai mis en évidence que ces macrophages M(IL-10) sont particulièrement efficaces pour la production de VIH-1. J'ai démontré que le microenvironnement associé à la tuberculose entraîne la formation de nanotubes entre les macrophages, grâce à l'activation de la signalisation cellulaire médiée par l'axe IL-10/STAT3. Ces nanotubes, qui favorisent le transfert du virus d'un macrophage à un autre, sont à l'origine de la spectaculaire production de VIH-1 par les macrophages. Nous avons également constaté que ces cellules M(IL-10) s'accumulent dans la circulation sanguine des patients co-infectés ainsi que dans les poumons de primates non-humains co-infectés. Dans l'ensemble, mes travaux identifient les nanotubes comme des acteurs clés dans l'aggravation de la pathogenèse du VIH-1 lors de la co-infection avec Mtb. Ainsi, les nanotubes et la voie de signalisation IL-10/STAT3 pourraient représenter des cibles pour développer de nouvelles thérapies de lutte contre la comorbidité VIH/Mtb. Les résultats obtenus lors de ma thèse contribuent à une meilleure compréhension du rôle des macrophages dans la pathogenèse et la dissémination du VIH-1 dans un contexte de mono-infection, ou lors d'une co-infection avec Mtb. / Macrophages are both crucial host effector cells for HIV-1 and important leukocytes involved in viral pathogenesis. For my doctoral thesis, I was interested in further characterizing the role of macrophages in HIV-1 pathogenesis, and during co-infection with Mycobacterium tuberculosis (Mtb), the etiological agent for tuberculosis (TB). I first participated in a study that provided evidence that HIV-1 infection reprograms the migration of macrophages, particularly by triggering the protease-dependent migration mode. This effect was mediated by the interaction of the viral protein Nef with the host proteins Hck and WASP, which leads to modification in the organization and proteolytic activity of podosomes, important structures for protease-dependent migration. The higher migration capacity of HIV-1-infected macrophages translated in vivo by an increase in the recruitment of macrophages in several tissues of Nef-transgenic mice. This work revealed a novel mechanistic understanding of how HIV-1 infection drives macrophages into tissues, contributing to viral dissemination and possibly creating a hidden cellular reservoir of virus. Worsening this public health issue posed by the HIV-1 epidemic is the frequent association of the virus with Mtb. Indeed, Mtb aggravates HIV-1 pathogenesis in co-infected individuals. Yet, the mechanisms involved in this process are still poorly understood, including the contribution of macrophages. To investigate how Mtb exacerbates the HIV-1 infection in human macrophages was the main focus of my thesis. First, I revealed that Mtb-infected macrophages generate a microenvironment that drives bystander macrophages towards phenotypic and functional features of the so-called M(IL-10) anti-inflammatory program. I found that these M(IL-10) macrophages are highly efficient for HIV-1 production. I demonstrated that the TB-associated microenvironment induces the formation of macrophage-to-macrophage connecting tunneling nanotubes (TNTs) through the IL- 10/STAT3 axis, a phenomenon that is responsible for the dramatic increase of HIV-1 production in M(IL-10) macrophages. Moreover, I provided evidence that M(IL-10) cells are expanded in the peripheral blood of co-infected patients and accumulate in the lungs of co-infected non-human primates. Altogether, this central part of my PhD thesis sheds light to TNTs as key players in the aggravation of HIV-1 pathogenesis in human macrophages during co-infection with Mtb. Thus, this cellular mechanism (together with the IL- 10/STAT3 axis) could represent an unexpected target to develop novel therapeutics against AIDS/TB co-morbidity. Collectively, the results obtained during my thesis contribute to a better understanding of the role of macrophages during HIV-1 pathogenesis and their ability to disseminate the virus in a mono-infection context, or during co-infection with Mtb.

L’ADN méthyltransférase 3a (DNMT3A) relie environnement et phénotype par la méthylation des dinucléotides CpG, qu’on les trouve en particulier dans les régions promotrices des gènes. Hypométhylation de ces CpG est associée à l’activation de la transcription, qui permet le contrôle de l'expression génique dans des états physiologiques et pathologiques. La plupart de nos connaissances sur l’implication de Dnmt3a en pathologie concernent le cancer, quelques données montrent sa contribution à d’autres pathologies. L’athérosclérose est la maladie cardiovasculaire la plus fréquente. Plusieurs facteurs de risque contribuant à son apparition, sont liés à L’environnement. En particulier, les dyslipidémies, largement influencées par le régime alimentaire. Par ailleurs, d’abondantes données décrivent la contribution des cellules inflammatoires à la physiopathologie de cette maladie. Jusqu'à présent, un nombre croissant de données suggère un rôle de la méthylation de l’ADN dans l'athérosclérose, mais à ce jour, le rôle de Dnmt3a dans la régulation du cholestérol et le développement initial des plaques n'a pas été étudié.Nos résultats suggèrent que l’inactivation de Dnmt3a dans les monocytes/macrophages ne modifie pas le développement initial des plaques d’athérome et n’a pas d’influence sur la polarisation des macrophages in vitro. En parallèle, nous avons démontré que l’inactivation de Dnmt3a dans les hépatocytes conduit à une différence significative de cholestérolémie plasmatique qui n’est pas liée à une dérégulation des gènes majeurs impliqués dans le métabolisme du cholestérol. En revanche, nous avons mis en évidence une activation des réponses inflammatoires. / DNA methyltransferase 3a (DNMT3A) links environment to phenotypes via catalysis of CpG dinucleotides, notably found in genes promoter regions, methylation and whose hypomethylation is associated with gene transcriptional activation thus enabling the control of gene expression in physiologic and pathologic states. Most of our knowledge about its’ role in disease occurrence are based on articles demonstrating its’ implication in human cancers. Limited data from mouse studies illustrates its’ contribution to certain pathologies. Atherosclerosis constitutes the single most important contributor to the growing burden of cardiovascular disease. Risk factors contribute to disease occurrence, where most are related to environmental influences, notably Dyslipidaemia, a key initiator of atherosclerosis. Abundant data link hypercholesterolemia to atherogenesis, on the other hand, contribution of inflammatory mechanisms that couple dyslipidaemia to atheroma formation has been also appreciated. So far, a growing number of data suggests a role of Dnmt3a in atherosclerosis but to date, its role in cholesterol regulation and early plaque formation has not been clearly elucidated. Our results suggested that deletion of Dnmt3a in monocyte/macrophages does not affect the formation of early atherosclerostic plaque nor does it impact the polarization of macrophages in vitro. In parallel, we have also demonstrated that the deletion of Dnmt3a in hepatocytes leads to significant elevation in TC levels. We were not able to relate this elevation to dysregulation of major genes involved in Cholesterol regulation. On the other hand, we noticed activation of hepatic inflammatory responses.

Stroke, a life-threatening condition, primarily resulting from ischemic events often caused by occlusion of the middle cerebral artery (MCA). Pre-existing leptomeningeal collateral (LMC) vessels connect MCA branches to anterior or posterior arteries, situated along the brain's cortical surface or meninges, under healthy conditions these vessels remain dormant due to their small diameters and relatively low flow velocity. LMCs serve as vascular redundancies that retrogradely re-supply blood to help salvage the penumbra following cerebral vascular occlusion. Their outward growth or remodeling (arteriogenesis) is essential for promoting cerebral reperfusion and preventing tissue damage after ischemic stroke. Increased fluid shear stress on collateral vessel wall activates arteriogenesis result in the activation of the endothelium and subsequent recruitment of peripheral-derived immune cells (PDICs), which have been shown to aid this unique adaptive process in other organ systems, however their role and mechanism(s) involved in LMC remodeling in stroke has not previously been evaluated. Initial findings suggest the EphA4, a well-established axonal growth and guidance receptors, plays a novel role in LMC arteriogenesis. This dissertation examined PDIC-specific functions of EphA4 using GFP labeled bone marrow chimeric mice subjected to permanent middle cerebral artery occlusion (pMCAO). We assessed immune cell population changes, infarct volume, functional recovery, characterized subtypes of infiltrated immune cell, and measured collateral vessel diameters. Additionally, we explored the Tie2-mediated PI3K signaling pathway in peripheral-derived monocyte/macrophages (PDM) treated with soluble Tie2-Fc and a PI3K p110α inhibitor. The results from this dissertation show that loss of PDIC-specific EphA4 led to increased collateral remodeling, associated with decreased infarct volume, improved cerebral blood flow, and functional recovery within 24 hours post-pMCAO. The crosstalk between EphA4-Tie2 signaling in PDMs, regulated through PI3K/Akt axis, inhibited pial collateral remodeling. In conclusion, our findings highlight the negative regulatory role of PDM-specific EphA4 in collateral growth and remodeling by inhibiting Tie2 function via the PI3K regulated pathway. Peripheral myeloid-derived EphA4 emerges as a new regulator of cerebral vascular injury and neuroinflammation following acute ischemic stroke. / Doctor of Philosophy / Stroke, a life-threatening condition, occurs when blood flow to part of the brain is disrupted due to the vascular occlusion of a major brain artery, such as the MCA. Within protective layers of our brain, there are pre-existing pial collateral vessels that act as backup connections. These vessels play an important role in increasing cerebral reperfusion and preventing tissue damage after stroke. One fascinating aspect of stroke recovery involves PDICs. These immune cells migrate into the blood hypo-perfused region of the brain and regulate the growth of collateral vessels. However, the specific functions of PDICs, particularly a receptor called EphA4, has remained unclear. Our research delved into the immune response following ischemic stroke using genetically modified mice. We examined immune cell populations, infarct volume (the damaged brain tissue), functional recovery, and collateral vessel diameters. Notably, we discovered that deletion of PDIC-specific EphA4 enhanced collateral vessel remodeling. This led to decreased infarct volume, better blood flow, and improved functional recovery within 24 hours after stroke. Furthermore, we explored a signaling pathway involving Tie2 and PI3K in PDM. This crosstalk between EphA4 and Tie2, mediated through PI3K regulation, played a critical role in suppressing collateral vessel remodeling. In summary, understanding how immune cells contribute to stroke recovery may pave the way for novel therapeutic approaches to enhance outcomes for stroke patients.

This dissertation represents efforts to determine the functional consequences acquired by vascular smooth muscle cells (SMC) in response to CD40 ligation by activated CD154+ T cells, and to elucidate components of the signaling pathway(s) activated in response to CD40 signaling in both monocytes and SMC. To study the consequences of CD40 stimulation, primary human monocytes and aortic SMC were treated with plasma membranes purified from CD154 + , CD4+ T cells. The results presented in this dissertation demonstrate that SMC, like monocytes/macrophages, are capable of interacting with T cells in a manner that results in reciprocal activation events. SMC were shown to present antigen to, and activate T cells. In turn T cell stimulus resulted in the activation of proinflammatory function in SMC initiated through the CD154:CD40 interaction. CD40 stimulation of SMC resulted in the production of the chemokines interleukin 8 (IL-8) and macrophage chemotactic protein-1 (MCP-1), and the upregulation of intercellular adhesion molecule (ICAM). Examination of the intracellular signaling pathways activated through CD40 signaling revealed the involvement of MAPKs in the pathway leading to induction of proinflammatory activity. Evaluation of CD40 signaling in monocytes demonstrated the activation of the MAPK family members ERK1/2, but not the MAPK family members p38 or c-jun-N-terminal kinase (JNK). In contrast, CD40 signaling in SMC was shown to result in ERK1/2 and p38 activation, and both of these kinases were shown to play a critical role in the induction of chemokine synthesis. An examination of the ability of anti-inflammatory cytokines to modulate CD40 signaling in monocytes and SMC demonstrated that the anti-inflammatory cytokines IL-4 and IL-10 abrogate CD40-mediated induction of inflammatory cytokine production by monocytes. This inhibition was shown to be a result of a negative influence of IL-4 and IL-10 on CD40 mediated ERK1/2, activation in monocytes. However, IL-4 and IL-10 did not inhibit SMC proinflammatory responses indicating a difference in the intracellular responses to these cytokines by the two cell types. (Abstract shortened by UMI.)

The quality of marine bathing water is currently assessed by monitoring the levels of faecal indicator bacteria. Among other drawbacks, results are retrospective using the traditional culture based methods. A rapid method is thus needed as an early warning to bathers for bacterial contamination in marine bathing waters. Total lipopolysaccharide (LPS) was chosen here as a potential general biomarker for bacterial contamination. Levels of total LPS, measured using a Kinetic QCL™ Limulus Amebocyte Lysate (LAL) assay, highly correlated with enumerated Escherichia coli and Bacteroides species. Levels of LPS in excess of 50 EU mL-1 were found to equate with water that was unsuitable for bathing under the current European Union regulations. Results showed that monitoring the levels of total LPS has a potential applicability as a rapid method for screening the quality of marine bathing water. More importantly, the LAL assay overcome the retrospective results when using culture based assessment since the LAL assay takes less than 30 minutes. Although false positive events were not detected, the occurrence of a false positive has been hypothesised, hence a more specific faecal biomarker was also investigated. LPS of five Bacteroides species (B. fragilis, B. caccae, B. ovatus, B. xylanisolvens and B. finegoldii) isolated from marine bathing waters samples were successfully profiled and showed high similarity between isolates in LPS gel electrophoresis banding pattern. Similar results were shown when investigating the endotoxic activity of Bacteroides species with the Kinetic QCL™ LAL assay. The potential biological relevance of Bacteroides LPS was also investigated in cell culture models indicating that Bacteroides showed similar induction of proinflammatory cytokines (TNF-α, IL-6 and IL-1α) and generally the biological activity was approximately 100 fold less than E. coli LPS. In addition, an ELISA assay was designed for the detection of Bacteroides LPS. Results showed that the Bacteroides LPS has a high potential to be used as a faecal biomarker, however, further work is required to develop a fully functional assay. The potential biological relevance of LPS present in contaminated bathing waters was also investigated in cell culture models. Results showed that there is a significant difference in the production of proinflammatory cytokines in comparison to “clean” bathing waters. Thus, results suggest that the European Directive regulations should be extended to cover the levels of total LPS in bathing waters to assure safety to the users of marine recreational water.