Obesity is a growing disorder in the United States, affecting over 60% of the population. We previously defined sympathetic nervous system (SNS) outflow from brain to white adipose tissue (WAT) using a viral transneuronal tract tracer. SNS innervation of WAT is the principle initiator of lipolysis, whereas decreases in sympathetic drive promote lipid accumulation. Which of the many origins of SNS outflow from brain to WAT results in SNS-mediated changes in lipid mobilization (increases in drive) or accumulation (decrease in drive) is unknown. Previous research indicates that sympathetic denervation blocks lipid mobilization; thus, rostral sites in the neuroaxis connected to WAT via the SNS may promote WAT lipid mobilization. The hypothalamic paraventricular nucleus (PVN) may play a role via its descending projections to the intermediolateral horn of the spinal cord. Therefore, the consequences of PVN lesions (PVNx) on WAT mobilization or accumulation were tested. PVNx resulted in increased lipid accumulation, indicated by increases in retroperitoneal (RWAT) , epididymal (EWAT) , and inguinal WAT (IWAT) pad masses, in fed hamsters, but PVNx did not block fasting (56 h)-induced lipid mobilization. Because adrenal medullary catecholamines, especially epinephrine, also play a minor role in lipid mobilization, we tested the contribution of catecholamine release on lipid mobilization through adrenal demedullation (ADMEDx), with and without PVNx, and found fastinginduced lipid mobilization was not blocked. There was, however, a suggestion that distal denervation of IWAT, with and without ADMEDx, partially blocked lipid mobilization. In addition, evidence suggests SNS also may be an important controller of fat cell proliferation. Surgical denervation of WAT triggers increases in fat cell number (FCN), but have not determined if this FCN increase is due to preadipocyte proliferation or differentiation of preadipocytes into mature fat cells. We also have not demonstrated what role sensory innervation may have in regulating white adipocyte proliferation. Therefore, the role of WAT sympathetic or sensory innervation on adipocyte proliferation was tested. The SNS but not sensory denervation triggered bona fide proliferation as indicated by bromodeoxyuridine plus AD3, a specific adipocyte membrane protein, colabeling. These and previous data suggest that the SNS plays a role in regulating adiposity.

L’obésité est en croissance rapide à l’échelle mondiale et représente un facteur de risque important pour plusieurs pathologies, dont la dégénérescence maculaire liée à l’âge (DMLA). Dans l’obésité, le tissu adipeux blanc (WAT) subi un remodelage pathologique caractérisé par le recrutement de macrophages pro-inflammatoires facilitant l’établissement de l’inflammation stérile systémique. Contrairement au WAT, les tissus adipeux brun (BAT) et beige (BgAT) participent à la thermogénèse, un processus qui libère de la chaleur en métabolisant les lipides. En raison de leurs potentiels effets physiologiques bénéfiques, le recrutement d’adipocytes et l’activation de ces types spécifiques de tissu adipeux (AT) ont fait l’objet de multiples recherches et débats. Malgré les avancées considérables dans le domaine, les mécanismes impliqués dans l’activation du BAT et du BgAT ainsi que les mécanismes impliqués dans le développement de l’obésité et leur contribution à des maladies comme la DMLA, restent mal définis. Dans un premier temps, nous avons développé le protocole RELi pour permettre une extraction et une quantification fiable des protéines du AT murin saturé en lipides. Notre protocole élimine les lipides contaminants en excès, réduit la variabilité du chargement de protéines pour le western blot et l’usage de gènes de ménage standards (Article #1). Ensuite, nous avons étudié l’inflammation au niveau du BAT dans un modèle d’obésité induite par l’alimentation. La délétion de la Neuropiline 1 (NRP1) chez les macrophages résidents du tissu adipeux (ATMs) a provoqué une diminution des densités de la vasculature et de l’innervation. De plus ces souris sont devenues plus sensibles à l’exposition au froid suggérant un rôle des ATMs-Nrp1+ dans la régulation de l’homéostasie du BAT et de la température corporelle (Article #2). Finalement, nous avons exploré l’axe BgAT-DMLA; plus spécifiquement son impact potentiel sur la néovascularization choroïdienne (CNV) en utilisant des approches in vivo et in vitro. Nous avons démontré que la délétion génétique de PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16), un gène impliqué dans la thermogénèse, conduit à une réduction de la CNV, et que la réintroduction d’AT-PRDM16+ exacerbe la formation de CNV pathologique. Le traitement d’explants de choroïde avec du milieu conditionné par des adipocytes-PRDM16+ augmente la croissance des vaisseaux sanguins. Ensemble, les données suggèrent un rôle sécrétoire potentiel pour le BgAT-PRDM16+ capable d’influencer la formation distale de CNV qui pourrait être pertinente pour la DMLA (Article #3). Les travaux présentés dans cette thèse établissent les bases d’un protocole permettant l’obtention de résultats reproductibles dans l’étude du AT, soulignent l’importance des ATMs- Nrp1+ dans la régulation de l’homéostasie du BAT et explorent pour la première fois l’implication du BgAT-PRDM16+ chez la DMLA neovasculaire. Ce travail établit les bases de la compréhension des mécanismes moléculaires reliant la régulation du AT thermogénique et les pathologies caractérisées par un excès de gras. Ce travail souligne également l’importance d’évaluer l’activation du BgAT chez les patients atteints de la DMLA. / Obesity is rapidly growing worldwide and represents a significant risk factor to several pathologies, including age-related macular degeneration (AMD). In obesity, the white adipose tissue (WAT) undergoes a strong remodeling characterized by the recruitment of pro- inflammatory macrophages, facilitating low-grade chronic inflammation. Unlike WAT, brown (BAT) and beige (BgAT) adipose tissues participate in thermogenesis, a process that releases heat by metabolizing lipids. Due to the likely beneficial physiological effects of BAT and BgAT, the recruitment of adipocytes and activation of these specific types of adipose tissue (AT) has been the subject of much research and debate. Despite considerable advances in the field, the mechanisms involved in BAT- and BgAT-activation as well as mechanisms involved in the development of obesity and their contribution to diseases such as AMD, remain ill-defined. First, we developed the RELi protocol to allow a reliable extraction and quantification of proteins from murine AT saturated with lipids. Our protocol eliminates excess contaminating lipids, reduces the variability of protein loading in Western blot and stabilizes expression of housekeeping genes (Article #1). Next, we investigated the inflammatory component of BAT in a diet-induced obesity model. The deletion of NRP1 in resident adipose tissue macrophages (ATMs) led to the expansion of the BAT and affected the densities of the vasculature and the innervation. Moreover, these mice became more sensitive to cold exposure, suggesting a role of ATMs-Nrp1+ in the regulation of BAT homeostasis and body temperature (Article #2). Lastly, we explored the axis of BgAT and AMD; more specifically, its potential impact on choroidal neovascularization (CNV) using in vivo and in vitro approaches. We demonstrated that the genetic deletion in BgAT of PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16), a gene involved in thermogenesis, leads to a reduction of CNV, and that the reintroduction of BgAT-PRDM16+ via AT transplantation exacerbates the formation of pathological CNV. Treatment of choroid explants with PRDM16+-adipocyte-conditioned medium augmented blood vessel growth. Altogether, the data suggest a potential secretory role for BgAT-PRDM16+ to influence distal CNV formation that could be relevant to AMD (Article #3). The work presented in this thesis establishes the basis of a protocol allowing reproducible results in the study of AT, underlines the importance of ATMs-Nrp1+ in the regulation of BAT homeostasis and explores, for the first time, the involvement of BgAT-PRDM16+ in neovascular AMD. This work sets the basis for the understanding of the molecular mechanisms linking the regulation of thermogenic AT and pathologies characterized by an excess of fat. This work also highlights the importance of assessing the activation of BgAT in patients with AMD.