Browsing by Subject "Microglia"

Now showing 1 - 4 of 4
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    Antigen presenting cells In the retina
    (2010-10) Lehmann, Ute
    The presence and activity of dendritic cells (DC) in retina is controversial. This is in part due to the limited number of DC in the retina and the small number of reliable DC markers. In addition, functions ascribed to DC in other parts of the body are thought to be done by microglia in the central nervous system. CD11c is the cellular marker most associated with DC. In order to study the nature of retinal DC, transgenic mice that express green fluorescent protein (GFP) on the CD11c promoter were used to visualize, quantify, and characterize DC in both quiescent and injured retinas. In the quiescent retina it was found that compared to the number of neurons and microglial cells there were relatively few DC located in the nerve fiber layer and the outer plexiform layer. Upon retinal injury by either optic nerve crush or exposure to continuous bright light, the numbers of DC increased significantly and translocated to retinal layers associated with the injury. Surprisingly, the retinas of the eyes contralateral to the optic nerve crush also showed a significant increase in DC. The potential origin of the DC in retina was examined using a chimeric mouse paradigm. Most of the retinal DC were found to originate from circulating precursors, and a smaller number from a local progenitor cell population. This study suggests that retinal DC are a previously overlooked population, distinct from microglia, and may be important in the injury response and maintenance of homeostasis in the retina.
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    Diet induced neuroinflammation and cognitive decline
    (2017-12) Duffy, Cayla
    The prevalence of obesity in the U.S. is over 50%, and midlife obesity is a clinical risk factor for cognitive impairment and the onset of neurodegenerative diseases such as Alzheimer’s disease (1-3). Inflammation of the brain (neuroinflammation), a state associated with progressive neuronal loss, is heightened in cognitive decline and obesity (4-7). Consumption of high fat diets (HFD), specifically those high in the saturated fatty acid palmitic acid (C16:0; PA), exacerbate neuroinflammation, neurodegeneration, and cognitive impairment (8-16). The research presented within this thesis seeks to define the role of microglia in the context of obesity and cognition. The central hypothesis of my thesis is that high fat diets induce microglial activation resulting in altered immunometabolic response, neuroinflammation, and subsequent cognitive decline. While neuroinflammation normally increases with age, risk of neuroinflammation and cognitive impairment is exacerbated by obesogenic diets (14). The findings from this work will provide a deeper understanding of diet-induced neuroinflammation, and will facilitate the development of novel therapeutics for cognitive disorders. This research has focused on utilizing basic science approaches to understand the effects of high fat diets on the central nervous system. Highlighted below are the major findings from my dissertation research. 1) Orexin A-induced neuroprotection: Excess intake of dietary PA increases the risk for developing obesity (17, 18). PA is known to induce neuronal cell death in the hypothalamus, a region of the brain important in regulating feeding behaviors (11, 19-21). One potential target to prevent this is orexin A, a hypothalamic signaling protein important in promoting obesity resistance that also has neuroprotective properties (22). I hypothesized that orexin A would protect against PA-induced hypothalamic cell death. To test this, I evaluated the response of hypothalamic neurons to orexin A and PA. I demonstrated that orexin A decreases PA-induced programmed cell death and stabilizes expression of the pro-survival gene Bcl-2. I also demonstrated that orexin A protects against PA-induced damage to the mitochondria (measured via changes in reactive oxygen species (ROS) and mitochondrial respiration). These data support that orexin A protects against PA-induced hypothalamic cell death. 2) Orexin A signaling in PA-activated microglia: Obesity is associated with chronic low-grade inflammation, characterized by increased circulating pro-inflammatory signals and immune cell activation (8, 11, 23). Microglia are highly responsive to changes throughout the brain, and communication between neurons and microglia depends in part on pro- or anti-inflammatory secreted signals (cytokines and chemokines). Furthermore, PA promotes microglia to release pro-inflammatory signaling cascades (9, 24-26). My next goal was to determine how PA and orexin A treatment influences microglial secretion and activation states. To test this, I exposed microglial cells to orexin A and PA and measured changes in secreted signals. I demonstrated that orexin A treatment reduces PA-induced upregulation of pro-inflammatory markers and increases anti-inflammatory markers in microglia. Next, I sought to determine if the factors secreted by the activated microglia influenced neuronal survival. To test this, I filtered the microglial cell culture media to remove excess orexin A and PA while retaining the secreted cytokines, exposed neurons to this filtered supernatant, and determined neuronal cell death. I found that neurons exposed to media from orexin A-treated microglia have increased cell survival compared to those treated with media from PA-activated microglia. This result demonstrated that microglia exposed to orexin secreted protective signals that protected neurons, whereas microglia exposed to PA alone secreted harmful cytokines that resulted in neuronal cell death. My findings are the first to demonstrate that orexin A modulates PA-activated microglial cells. 3) Loss of orexin and high fat diet increases cognitive impairment: Obesity is recognized as a risk factor for development of cognitive disorders such as Alzheimer’s disease (3). Moreover, deficiencies in orexin signaling have been linked to neurodegenerative diseases. My overall hypothesis was that reduced orexin signaling will increase diet-induced cognitive decline through a microglial-mediated pathway. To test this, I used wild type (WT) mice or a mouse model of orexin loss to determine differences in a cognitive task. I found that mice lacking orexin showed significant impairments in cognition vs. WT mice. Next, to determine the effects of HFD on microglia and cognition, mice were placed on a HFD or remained on normal chow, and the cognitive task was retested at 2 and 4 weeks. I demonstrated that cognition was impaired and microglial activation was increased in mice lacking orexin given a HFD vs. WT mice. Collectively, my results show that orexin loss impairs cognition, and that HFD accelerate cognitive deficits and the onset of neuroinflammation in orexin-deficient mice. 4) Fatty acid binding protein 4-uncoupling protein 2 axis in modulating microglia and cognition: Fatty acid binding proteins (FABP) are lipid chaperones regulating metabolic and inflammatory pathways in response to fatty acids (27, 28). To further define a mechanism for diet-induced microglial activation and cognitive decline, I sought to determine if the FABP4-UCP2 (uncoupling protein 2) axis is involved in neuroinflammation. I hypothesized that inhibition of microglial FABP4 would upregulate UCP2 and attenuate PA-induced inflammation. To test this, I measured hypothalamic gene expression changes in WT mice and mice lacking FABP4 (AKO mice) fed a HFD. I found hypothalamic tissue from AKO mice exhibit increased UCP2 expression and reduced pro-inflammatory makers compared to WT mice. Next, I pharmacologically inhibited FABP4 in microglia and demonstrated increased UCP2 expression and reduced PA-induced pro-inflammatory response and ROS production. Further, this effect is negated in microglia lacking UCP2, indicating the FABP4-UCP2 axis is pivotal in obesity-induced neuroinflammation. Finally, to determine if the FABP4-UCP2 axis was involved in attenuating diet-induced cognitive decline, WT and AKO mice were fed a HFD for 12 weeks and tested in a panel of cognitive tasks. I found that mice maintained on a HFD had reduced locomotor activity. Further, WT mice maintained on HFD had impaired memory, and AKO had attenuated HFD-induced memory impairment. Collectively, these results indicate that the FABP4-UCP2 axis is a link between HFD, neuroinflammation, and cognitive impairment.
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    A Dual Investigation of Questions in Drug Addiction: Exploring the Role of Neuroinflammation in Opioid Withdrawal and A Novel Measure of Reward-Seeking Behavior in Rodents
    (2016-08) Kennedy, Bruce
    Substance abuse disorders are extremely disruptive to the lives and relationships of those who suffer from them and are a burden on society and the healthcare system. Effective treatments are currently lacking and our understanding of the neurobiology driving addictive behaviors remains incomplete. The following animal studies aimed to advance the drug addiction field by 1) investigating neuroimmune interactions as a potential mechanism in opioid withdrawal in mice as well as 2) introducing a novel behavioral test in order to expand the repertoire of tools available to researchers investigating drug or reward-seeking behaviors in rats. Microglia, the immune cells of the brain have been recently recognized as being important contributors in a wide variety of neuropsychiatric disorders, including drug addiction. Although current views support a microglia role in the physical drug dependence experienced by opioids addicts, it is thought that the emotional effects of withdrawal, such as anxiety and depression, are better predictors of relapse. In the first series of experiment, a genetic mouse model lacking the key microglia immune receptor TLR4 was used to determine the involvement of this protein in the molecular and behavioral responses to opioid withdrawal, in particular those related to negative emotions. Although technological advances in behavioral testing techniques have improved our ability to model drug addiction in rodents, the low-tech behavioral assays used most frequently have remained largely unchanged over the last several decades. The second set of experiments introduced and validated a novel behavioral task based on the classic measure of reward, conditioned place preference. In the modified test, objects rather than contexts were used as a conditioned cue, which potentially allows for greater flexibility and opens up new ways of analyzing conditioned approach, a commonly used measure for assessing the reward value of a given substance.
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    The Role of Microglia and Astrocyte in Spinocerebellar Ataxia Type 1
    (2020-11) Ferro, Austin
    Spinocerebellar ataxia type 1 (SCA1) is a fatal dominantly inherited neurodegenerative disease. Even though there has been illuminating work on the effect of the disease-causing protein, a polyQ expanded ATAXIN-1 (ATXN1) on neurons, the relative contribution to disease of glia has been unknown. Here I present my work on glial-neuron interactions in the context of SCA1; focusing on the neuroinflammatory and activation of microglia as well as the previously undiscovered cell-autonomous effect of polyQ expanded ATXN1 on astrocytes. Using the Lysm-Cre Ikkβflx/tlx line to assess the role of microglial activation in the transgenic ATXN1[82Q] mouse model of SCA1, I show that inhibition of microglial reactivity does not have a large effect on SCA1 disease pathology. Instead, we found that the Lysm-Cre Ikkβflx/tlx line itself had motor performance deficits in the absence of Purkinje cell degeneration. Correlating with this motor performance deficiency, Lysm-Cre Ikkβflx/tlx mice had a prominent deficiency in climbing fiber removal onto Purkinje cells. Due to the low impact of microglia on SCA1 pathology, I then focus on astrocytes and in particular, astrocytic Kir4.1/Kcnj10. Astrocytic Kcnj10 was downregulated throughout the brain of the knock-in Atxn1154Q/2Q mouse line. To investigate the potential role of cell-autonomous effects of Atxn1 on astrocytic transcription, I used the novel conditional humanized ATXN1floxed 146Q/2Q line to delete polyQ expanded ATXN1 from astrocytes. Conditional astrocytic deletion of polyQ ATXN1 did not influence failure to gain weight nor a prominent effect on rotarod pathology. Yet, there was a trending rescue of Kcnj10 expression in the medulla, suggesting a cell-autonomous effect of ATXN1 on astrocytic transcription. In conclusion, my thesis work concerning the role of both microglia and astrocyte in the pathogenesis of SCA1 has revealed the importance of NFᴋB signaling in cerebellar development as well as the potential cell-autonomous effect of polyQ ATXN1 on astrocytes.