Browsing by Subject "Glia"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item HDL-Mimetic Peptides as Potential Therapeutics for Alzheimer's Disease(2018-08) Chernick, DustinAlzheimer’s disease (AD) is the leading cause of dementia worldwide, for which there currently exists no approved disease modifying treatment. A number of large scale human clinical studies have confirmed a robust connection between high density lipoprotein (HDL) – known as the ‘good cholesterol’ levels and AD. Low levels of HDL are associated with increased risk and severity of AD. The role of HDL in the brain is not fully established, however, the anti-inflammatory and anti-oxidative properties of HDL are thought to be critical for its beneficial effects. Apolipoprotein E (apoE) is a key constituent of HDL-like particles in the interstitial fluid (ISF) and cerebral spinal fluid (CSF) in the brain. ApoE exists in 3 common variants in the human population (apoE2, E3, and E4), and the apoE4 isoform is the strongest genetic risk factor for AD, accounting for 40-60% of cases. This risk allele is known to increase neuroinflammation and to promote the aggregation and deposition of amyloid beta (Aβ) in the brain, effects which are influenced by the poor lipidation status of apoE4 (incomplete or improper composition of HDL-like particles) in the brain. Previous studies in the laboratory of Dr. Ling Li have shown that overexpression of human apoA-I, the primary apolipoprotein associated with HDL in the periphery, mitigated amyloid pathology and rescued memory deficits in AD mice. However, a full-length, glycosylated protein is extremely difficult and costly to synthesize and to administer. Therefore, the goal of my research was to test the therapeutic potential of small HDL-mimetic peptides, designed to mimic the beneficial function of their parent apolipoproteins, in AD. My studies focused on 4F, an 18 amino acid HDL-mimetic peptide that has been shown to be safe and well tolerated in human clinical trials for cardiovascular disease. I have demonstrated that the lipidation state of apoE is negatively impacted by the addition of aggregated Aβ to astrocytes from mice and humans, in vitro, an effect that is reversed by the addition of 4F. In addition, I confirmed that apoE4 is less lipidated than apoE2 and E3 at baseline, and demonstrated that apoE4 is more susceptible to the detrimental effects of Aβ on lipidation than apoE2. Intriguingly, 4F was able to completely rescue this effect, bringing apoE4 lipidation levels on par with those of apoE2, even in the presence of Aβ. Preliminary in vivo studies in mice expressing the human apoE isoforms and in a mouse model of AD indicate that 4F reduces soluble amyloid levels in the brain and attenuates memory deficits. As chronic neuroinflammation is a key hallmark of AD pathology, another line of my research focused on a small molecule, called Minnelide. Minnelide is a water soluble, pro-drug of triptolide, which is an anti-inflammatory agent that has been shown in Dr. Li’s lab and in other labs to mitigate AD pathology and rescue memory deficits in animal models. Poor solubility hinders this agent’s prospects in the clinic, and so we sought to test the efficacy of Minnelide in AD. My studies show that Minnelide attenuated age-related cognitive decline in AD mice, independent of Aβ levels in the brains of these animals. These data, taken together, indicate that HDL mimetic peptides, and targeting of inflammatory pathways in the periphery and in the brain are promising avenues for continued efforts to find an effective treatment for AD.Item Mechanisms and functional consequences of glial signaling in the retina.(2009-07) Kurth-Nelson, Zebulun LloydTwenty years ago, glia were viewed as passive support cells for neurons. Since then, experiments have shown that glial cells have their own form of excitability with precise intracellular spatiotemporal dynamics, intercellular communication among themselves, a bidirectional dialog with neurons and synapses, and a key role in mediating blood flow changes in response to neuronal activity. Most of these experiments have been conducted in brain regions such as hippocampus, cortex, hypothalamus, and cerebellum. However, as work from our laboratory has shown, the mammalian retina is also an excellent preparation to study the active functions of glial cells. Here, we describe two forms of active glial signaling in the retina. First, we tested the hypothesis that glial cells modulate synaptic activity in the retina. We measured synaptic strength by evoking excitatory postsynaptic currents (EPSCs) in ganglion cells with either light or an electrical stimulus. We then excited glial cells through several methods, including agonist ejection, photolysis of caged Ca2+, and depolarization. The amplitude of the synaptic currents was altered by some, but not all, of these glial stimuli, leaving us unable to draw a definitive conclusion as to whether glial excitation alone is sufficient to modulate synaptic transmission in the retina. Second, we characterized spontaneous intercellular glial Ca2+ waves in the retina. Glial cell excitability takes the form of transient intracellular Ca2+ elevations. One of the first recognized active properties of glia was their ability to propagate these Ca2+ elevations from cell to cell in a wave-like pattern. In most previous experiments, glial Ca2+ waves were initiated by an experimenter-driven stimulus, raising doubts about whether these waves occurred naturally in the organism. We demonstrate here that these waves occur spontaneously both in intact tissue and in vivo, and that the rate of spontaneous wave generation increases as animals age. These spontaneous waves propagate by glial release of ATP and activation of ATP receptors on neighboring cells. Finally, spontaneous waves cause changes in blood vessel diameter. This is the first demonstration of a functional effect of spontaneous intercellular glial signaling. These results suggest a functional role for glial cell signaling in the retina and raise the possibility that glial signaling may actively participate in the aging of the nervous system.Item Mechanisms of Blood Flow Regulation in the Retina: Glial Calcium Signaling Regulates Capillary, but Not Arteriole Diameter(2016-12) Biesecker, KyleBlood flow is tightly regulated in the central nervous system to ensure neurons receive sufficient oxygen and glucose. When neuronal activity increases, nearby blood vessels dilate to increase local blood flow, a phenomenon termed functional hyperemia. Two key controversies have arisen concerning the mechanisms that underlie functional hyperemia. Firstly, the role of glial Ca2+ signaling in triggering vessel dilations is unclear. Some evidence suggests that glial Ca2+ signals precede vessel dilations, but blocking glial Ca2+ signaling does not alter functional hyperemia. Secondly, data has been presented arguing both for and against the ability of capillaries to actively dilate during functional hyperemia. Herein, I demonstrate that glial Ca2+ signaling does play a key role in regulating capillary diameter, but is not necessary for regulating arteriole diameter. Additionally, capillaries can actively dilate during functional hyperemia responses. These findings suggest that glial Ca2+ signaling contributes to blood flow regulation in the central nervous system by triggering capillary dilations during functional hyperemia.Item The Role of Microglia and Astrocyte in Spinocerebellar Ataxia Type 1(2020-11) Ferro, AustinSpinocerebellar 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.