Browsing by Subject "Brain-Derived Neurotrophic Factor"
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Item BDNF-Producing B Cells Mediate Plasticity in the Recovering Brain After Stroke(2021-11-29) Torres, Vanessa; Monson, Nancy L.; Stowe, Ann; Goldberg, Mark P.; Vitetta, Ellen S.; Volk, Lenora J.; Satterthwaite, Anne B.Neuronal networks require significant neurotrophic support for functional plasticity after stroke, but the delivery of neurotrophins has failed thus far in clinical trials. Therefore, identifying endogenous mechanisms that could enhance neurotrophic support in the recovering brain after stroke is essential. B cells, a lymphocyte known to infiltrate the post-stroke brain, possess the ability to produce neurotrophins, including brain-derived neurotrophic factor (BDNF). Depleting B cells after stroke results in motor and cognitive deficits that are mediated by specific brain regions (e.g., hippocampus) outside the initial infarct. We propose that B cells migrate to specific brain regions after stroke and respond to local signals that enhance their neurotrophic capacities to promote neuroplasticity. To investigate whether B cells are a potential source of endogenous BDNF support after stroke, we must identify 1.) the spatial distribution of B cells within the post-stroke brain, 2.) the type of neurotrophic support B cells provide to ischemic-injured neurons and 3.) the impact that the post-stroke microenvironment exerts on the neurotrophic capacity of B cells. Using whole brain microscopy, we discovered that B cells migrate to specific remote brain regions areas outside of the initial infarct that regulate motor and cognitive function after stroke. To understand how B cells support ischemic-injured neurons, we used ex vivo electrophysiology and in vitro models of ischemic injury to assess functional and structural neuroplasticity in the presence or absence of B cells. We discovered that B cells support synaptic transmission in the dentate gyrus region of the hippocampus after stroke and through the production of BDNF, B cells protect against the ischemic-induced loss of neurons and neuronal dendrites. After stroke, neuronal BDNF production is dependent on glutamate-induced activity of the N-methyl-D-aspartate receptor (NMDAR) downstream of the GluN2A subunit. Given that B cells also express NMDARs, we investigated whether glutamate can similarly upregulate BDNF in B cells downstream of their NMDARs. Using microscopy, flow cytometry and qPCR, we discovered that stroke and glutamate differentially regulate B cell gene and surface expression of GluN2A. Additionally, both mouse and human B cells elicit a functional response to glutamate and can induce autocrine BDNF signaling. Collectively, the data presented in this thesis are the first to demonstrate a glutamate-induced neurotrophic role for B cells in the ischemic brain. Understanding the mechanisms by which neuroinflammation supports neuroplasticity after stroke enables the development of immune-based therapeutics that harness endogenous neurotrophic support from B cells to ameliorate pathology.Item Exploring Mechanisms of Depression-Related Behavior and Rapid Antidepressant Action(2011-12-12) Autry, Anita Ellen; Monteggia, LisaMajor Depressive Disorder is a serious mental disorder with a profound disease burden, particularly in the United States. Intriguingly, this disease is almost twice as prevalent in females compared to males. Presently, antidepressant treatment for patients with Major Depressive Disorder requires chronic use and first-line treatment is often ineffective. The neurotrophic hypothesis of depression suggests that a) neurotrophins, in particular brain-derived neurotrophic factor, are necessary for maintaining normal mood states and that b) increases in neurotrophin signaling mediate therapeutic effects of clinical antidepressants. In the laboratory, we have explored aspects of the neurotrophic hypothesis of depression and made progress toward understanding the role of brain-derived neurotrophic factor in depression-related animal models as well as its role in the cellular mechanisms underlying antidepressant efficacy. First, we examined whether loss of brain-derived neurotrophic factor in forebrain neurons impacted susceptibility to chronic stress, an animal model of depression, in a gender-specific manner. Next we examined the contribution of dorsal raphe nucleus brain-derived neurotrophic factor signaling on traditional antidepressant efficacy. Finally, we uncovered a novel role for brain-derived neurotrophic factor in mediating effects of rapid antidepressant efficacy. In the course of my studies, we have found that brain-derived neurotrophic factor expression may be more important for protecting females from negative behavioral effects of chronic stress; that brain-derived neurotrophic factor receptor activation in dorsal raphe is essential for traditional antidepressant efficacy; and finally that brain-derived neurotrophic factor is required for the action of novel rapid antidepressant ketamine.Item Interaction of Quantal Inhibitory and Excitatory Neurotransmission in Regulation of Synaptic Homeostasis via Molecular Signaling(August 2021) Horvath, Patricia Mary; Chahrour, Maria; Monteggia, Lisa; Cobb, Melanie H.; Kavalali, Ege T.; Konopka, GenevieveThe processing and flow of information through brain circuits is undeniably shaped by individual neurons and synapses. The type of synapse between any two given neurons determines the reliability, speed, and strength of signal transfer. Therefore, studying the organization and signaling capacity of the variety of synapses present in our nervous system is critical to understanding how information is shaped and communicated between neurons. Neurotransmission can be classified into two broad types: spontaneous and evoked. Much of the work examining these types of neurotransmission and their properties has been done in excitatory synapses. Yet the variety of inhibitory neurons is so vast that Ramon y Cajal referred to them as the "Butterflies of the Soul." In order to help paint a more complete picture of the brain, this PhD thesis is focused on the structure, function, and regulation of synapses and neurotransmission, with a focus on inhibitory synapses. We first expanded the tools available to study synapses by demonstrating that lentiviral CRISPR could be used in postmitotic cells to knockout synaptic proteins and study non-cell autonomous phenotypes. Next, we took advantage of the use-dependent properties of the GABAA receptor antagonist picrotoxin, demonstrating that this drug could be used to interrogate inhibitory synapse parameters, such as presynaptic release probability. By utilizing picrotoxin, we were able to examine the postsynaptic organization of spontaneous and evoked neurotransmission at inhibitory synapses, and discovered a partial segregation of the postsynaptic receptors activated by evoked and spontaneous neurotransmission. This result implied that spontaneous and evoked neurotransmission at inhibitory synapses may have partially non-overlapping functions. Because the function of inhibitory spontaneous neurotransmission is largely unknown, we next examined the signaling capacity of inhibitory spontaneous neurotransmission. We discovered that modulation of inhibitory, but not excitatory, spontaneous neurotransmission alters transcription of certain activity-induced genes, including Bdnf. Furthermore, blockade of inhibitory spontaneous neurotransmission leads to downscaling of excitatory synapses through a BDNF-dependent mechanism. Finally, we examined the regulation of synapse function by miRNAs regulated by MeCP2, a gene in which loss of function mutations are the primary cause of Rett Syndrome. We characterized the effects of two candidate miRNAs on synapse function. One of these miRNAs, miR-101a, has opposing impacts on excitatory and inhibitory synapses, suggesting a role in regulating excitatory/inhibitory balance, a feature that is often altered in ASD and ASD-like disorders such as Rett Syndrome. In summary, we have contributed to the study of synapses by expanding the tools available, improving understanding of inhibitory synapse structure and function, and examining the broad regulatory capacity of certain miRNAs over synaptic function.Item Molecular Mechanisms Underlying Fast-Acting Antidepressant Efficacy(2015-04-09) Szabla, Kristen Lynn; Kim, Tae-Kyung; Kavalali, Ege T.; Cobb, Melanie H.; Monteggia, LisaMajor Depressive Disorder is a devastating mental illness with a profound disease burden, particularly in the United States. Major Depressive Disorder is a heterogeneous disorder that is characterized by dysregulated mood and/or anhedonia with intense feelings of despair and sadness, agitation, self-deprecation, and suicidal ideation. Antidepressants, such as selective serotonin reuptake inhibitors, are the most common form of treatment for Major Depressive Disorder, however the precise mechanism by which these drugs work is largely unknown. Moreover, the time they take to reach clinical effect can take weeks to months, and some patients never truly respond, leaving a critical need for more rapidly acting antidepressants with sustained efficacy. In the laboratory, we have explored aspects of the neurotrophic hypothesis of depression and have made progress toward understanding the role of brain-derived neurotrophic factor in animal models. We have also made progress in understanding the role of brain-derived neurotrophic factor in cellular and molecular mechanisms which underlie fast-acting antidepressant efficacy. First, we examined whether ketamine, a novel fast acting antidepressant, functioned in a dose dependent manner to elicit its antidepressant effects. We found that only low, nonpsychomimetic doses of ketamine produce antidepressant effects, whereas high, psychomimetic doses did not produce antidepressant responses. We also demonstrated that only low dose ketamine triggered robust increases in BDNF translation, which our lab has previously shown to be required for ketamine's fast acting antidepressant effects. Next we examined the role of calcineurin in relation to our model of ketamine action, and we uncovered a parallel L-type calcium channel mediated calcium signaling pathway that dephosphorylates eukaryotic elongation factor 2 and competes with the previously identified n-methyl-d-aspartate receptor dependent signaling that activates eukaryotic elongation factor 2 kinase function. The balance between these two calcium signaling pathways determines the degree of eukaryotic elongation factor 2 phosphorylation and the extent of BDNF protein translation, which in turn gauges the efficacy of ketamine-mediated rapid antidepressant responses in preclinical mouse models. Finally, we investigated the molecular mechanisms underlying scopolamine's fast acting antidepressant effect and discovered that scopolamine mediated antidepressant effects require brain-derived neurotrophic factor transcription.Item Regulation of Brain-Derived Neurotrophic Factor in the Adult Mouse Brain(2005-08-11) Malkovska, Irena; Parada, Luis F.In the adult central nervous system (CNS) brain-derived neurotrophic factor (BDNF) has been implicated in neuroprotection and synaptic plasticity among other functions. However, relatively little is known of its regulation. In this thesis, we attempted to learn more about BDNF regulation by means of: an in situ hybridization study of the four distinct untranslated exons in the adult mouse brain; use of transgenic animals to define BDNF promoter regions; and use of comparative genomics to identify evolutionarily conserved regions of BDNF. The in situ hybridization study suggests that the four distinct BDNF promoters are differentially regulated and that neighboring promoters are coregulated. Also it appears that all four promoters function in most of the same nuclei of the adult CNS. Inspite of the large size of the transgenic constructs used in this study specific to exons 1/2 and 3/4 (11.4 kb and 16 kb respectively), they were insufficient to mediate endogenous-like BDNF expression in the adult CNS. However, this study suggests that these regions may drive endogenous-like expression in a subset of nuclei (random chance integration cannot however be ruled out). The bioinformatics study revealed 9 highly conserved elements that are good candidates for cis-regulatory elements of BDNF. In conclusion, the regulation of the BDNF gene appears far more complicated than was previously predicted.Item A Role for BDNF-Trkb Signaling in the Modulation of Superoxide Dismutase-1 Expression(2014-04-15) Day, Cameron E.; Elliott, Jeffrey L.; Thomas, Philip J.; Cobb, Melanie H.; Kavalali, Ege T.Superoxide dismutase-1 (SOD1) has been implicated in the pathogenesis of familial amyotrophic lateral sclerosis (fALS), a degenerative motor neuron disease more commonly known as Lou Gehrig’s disease. The mechanism by which it causes degeneration and the extent of its involvement are currently unknown, although the present consensus is that a toxic gain-of-function mutation is involved. Our lab has previously demonstrated, via a cDNA expression screen, that the TrkB receptor and the guanine nucleotide exchange factor, RasGRF-1, modulate SOD1 expression at the protein level, suggesting that cell signaling pathways associated with TrkB signaling are involved in regulating the expression of SOD1. Overexpressing these proteins for long or ‘chronic’ time periods of 24-48 hours in a motor neuron-like cell line lead to a significant decrease in SOD1 protein levels. Subsequent experiments using TrkB mutants and pharmacological inhibitors of pathways known to be associated with TrkB revealed that the kinase activity of the receptor is necessary and that partial TrkB signaling is sufficient for suppression. Conversely, treatment with brain-derived neurotrophic factor (BDNF), an activator of this pathway, over shorter or ‘acute’ time periods increased SOD1 protein levels. Further analyses using qPCR, a human SOD1 promoter Lucifersase assay, and inhibitors of the proteasome and translation machinery provide evidence that in both the acute and chronic phase, BDNF-TrkB signaling is modulating SOD1 expression at the level of translation. Taken as a whole, these data demonstrate that BDNF-TrkB signaling is involved in the regulation of SOD1 expression via translation and that the expression pattern of SOD1 is bi-phasic in response to the duration of the stimulus. These findings may have implications for therapeutic modification of mutant SOD1 levels in ALS patients.Item Role of BDNF-TrkB Signaling in Cocaine Addiction(2014-04-14) Buzin, Nicole Renee; Goldberg, Matthew S.; Monteggia, Lisa; Rothenfluh, Adrian; Self, David W.Cocaine addiction results in neuroadaptations and drug-induced neuroplasticity that promote changes in protein expression and neuron morphology. Cocaine-induced increases in dopamine ultimately alter dopamine signaling in brain regions modulating reward and motivation, specifically the nucleus accumbens (NAc), and downstream proteins. One protein of particular interest is brain-derived neurotrophic factor (BDNF), a modulator of cell survival, viability, and plasticity. Cocaine has been shown to increase BDNF mRNA and protein levels in the NAc shell. In addition, intra-NAc infusions of BDNF have been demonstrated to increase cocaine intake and motivation for cocaine. These increases in BDNF also lead to activation of its receptor, tropomyosin receptor kinase B (TrkB). Studies indicate that the loss of TrkB specifically in the NAc shell reduced the reinforcing effects of cocaine using a self-administration paradigm, and also psychomotor effects of cocaine on activity; however, the contributions of each signaling pathway are unknown. Chapter 3 examined the creation of a cell-type specific herpes simplex viral (HSV) vector system to over-express wildtype TrkB or its docking mutants. In vivo and cell culture experiments indicated very weak viral expression, while cocaine self-administration testing produced inconsistent and inconclusive results. Chapter 4 examined cocaine-induced BDNF-TrkB receptor signaling using an adeno-associated viral vector system to over-express wildtype TrkB and its signaling mutants, more generally across NAc cell types. Initial self-administration testing suggested that overexpression of kinase dead TrkB (TrkB K571N) in the NAc shell increased the threshold dose required to maintain self-administration on the dose-response test and reduced motivation for cocaine. Subsequent behavioral testing did not confirm these results. Preliminary tissue staining demonstrated similar levels of viral infectivity between AAV-GFP and AAV-TrkB WT; however, subsequent tissue staining demonstrated very weak to no viral expression, consistent with the lack of consistent behavioral results. Finally, Chapter 5 utilized a transient but efficacious HSV vector system to over-express wildtype TrkB and its signaling mutants during cocaine-induced activation of the BDNF-TrkB receptor signaling pathway. Self-administration testing suggested that the kinase dead TrkB viral mutant (HSV-TrkB K571N) inversely affected cocaine taking and motivation for cocaine. In contrast to the cell-specific HSV vectors tested earlier, immunohistochemical techniques indicated stronger and consistent expression of these HSV-TrkB viruses; however, TrkB signaling-specific protein expression was not found. These findings indicate an inconsistency between behavioral results and viral expression, yet suggest that further experimentation is warranted.Item Role of Tyrosine Receptor Kinase B in the Development and Function of the Central Nervous System(2009-01-14) Li, Yun; Parada, Luis F.Tyrosine Receptor Kinase B (TrkB) was initially identified as the high-affinity receptor for Brain-Derived Neurotrophic Factor (BDNF) in regulating the survival of sympathetic and sensory neurons. In the CNS, however, BDNF-TrkB interaction has been shown to regulate diverse aspects of development, physiology and pathology. In the current studies we focus on the roles of TrkB and its downstream signaling pathways in the progression and amelioration of CNS diseases. Though the nature of the diseases diverges, they share a common molecular regulatory mechanism. First we report that TrkB is required cell-autonomously to regulate the generation of new neurons. Mice lacking TrkB in hippocampal neural progenitor cells had impaired proliferation and neurogenesis, and are behaviorally insensitive to antidepressive treatments. Specific deletion of NF1, an antagonist of Ras, in adult neural progenitor cells enabled rapid proliferative and behavioral responses to sub-chronic antidepressants, and led to spontaneous antidepressive-like behaviors in the long run. Thus, our findings demonstrate impairment of the neural precursor niche as an etiological factor for refractory responses to antidepressive regimen, and the activation of adult neurogenesis as an approach to modulate depression and anxiety-like behaviors. In the second half, we report that ablation of Bdnf from the cortex and the substantia nigra leads to depletion of BDNF protein in the striatum. Mice lacking BDNF-TrkB signaling in the corticostriatal and nigrostriatal circuits displayed severe motor deficits and striatal degeneration reminiscent of the Huntington?disease. In contrast, specific ablation of TrkB from the striatal medium spiny neurons resulted in late-onset neuronal loss and spine degeneration, without causing obvious movement abnormalities. Thus, our results establish an essential role for TrkB in regulating the normal maturation and maintenance of striatal medium spiny neurons.Item [Southwestern News](1995-12-04) Martinez, EmilyItem [UT Southwestern Medical Center News](2006-02-09) McKenzie, Aline