Dezhi Liao - US grants

[unreadable] DESCRIPTION (provided by applicant): Chronic opiate abuse impairs neuronal development and causes cognitive deficits in addicts. In addition to acting on inhibitory GABAergic synapses, our recent study revealed that mu-opioid receptors (MOR) could regulate the stability of the dendritic spines, which are mainly excitatory glutamatergic synapses. Since morphine tolerance and dependence have been reported to decrease in transgenic mice lacking AMPA receptor subunits, changes in the stability of such dendritic spines may contribute to opiate addiction. The overall objective of this proposed project is to clarify the intracellular signaling pathways that are involved in opioid regulation of dendritic spines. Based on our and other's previous studies, we proposed the following central hypothetical model: Activation of the postsynaptic opioid receptors in excitatory synapses inhibits the activities of protein kinases and Rho GTPases. Particularly, the inhibition of Rac 1, a Rho GTPase, causes the subsequent collapse of dendritic protrusions and spines by altering actin cytoskeleton. Combined genetic, living imaging and electrophysiological techniques will be used to test this model in cultured dissociated neurons. We will test this model by pursuing three specific aims. 1. We will further characterize the roles of MORs and their internalization in postsynaptic modulation of dendritic spines. Both receptor internalization and spine plasticity have been proposed to be important for drug addiction and tolerance development. The elucidation of the mechanistic links between these two critical cellular events may shed new light on our understanding of opiate addiction. We will also determine why some clinical relevant opiates, such as methadone, cause concentration-dependent biphasic changes in dendritic spines. The dosage-response studies of clinical relevant opiates may potentially reduce addictive liability of these opiates in the future. 2. We will identify and determine the Rho GTPase that mediates opioid modulation of dendritic spines. This aim will determine how morphine induces plasticity of spines by altering the actin cytoskeleton. 3. We will identify and determine the protein kinase(s) that mediates opioid modulation of dendritic spines. This aim will determine the signaling link between MOR and Rac1. By completing these specific aims, we will have determined three major signaling steps that mediate morphine-induced collapse of spines: the receptor that mediates morphine's effect; the protein kinase(s) that mediates the morphine response; and the actin-interacting proteins that contribute to morphine's effect. The determination of these signaling steps will provide a major framework of the signaling pathway that is responsible for opioid-induced changes in the excitatory synapses, and thus will provide new information about opiate abuse at a molecular and cellular level. [unreadable] [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): Drug addiction is a neurological and psychological disorder characterized by compulsive intake, craving and seeking of drugs with negative impacts that adversely affect the lives of the drug abusers. Addiction has recently been proposed to be a pathological form of learning and memory, which requires long-term changes of neural circuits. Consistent with this proposal, our recent studies reveal that chronic treatment with opioids alters the stability of dendritic spines in cultured dissociated neurons. The ultimate goal of my scientific career is to significantly advance our integrated understanding of drug addiction at both system and cellular levels. The scientific objective of my research is to determine the cellular mechanism underlying opioid modulation of dendritic spines. My present research is funded by a National Institute on Drug Abuse (NIDA) R01 grant (DA020582) which contains three Specific Aims: (1) to further characterize the roles of MORs and their internalization in postsynaptic modulation of dendritic spines. (2) To identify and determine the Rho GTPase that mediates opioid modulation of dendritic spines. (3) To identify and determine the protein kinase(s) that mediate opioid modulation of dendritic spines. This K02 award will allow me to significantly reduce my teaching hours so that I can devote more of my effort to research (increased from 50% to 75% of total effort). I will use the extra 25% effort to strengthen and broaden the R01 project in two ways: (1) enhancing the Specific Aims 1 and 3 with newly proposed experiments using brain slices prepared from different regions of the brain including the striatum, ventral tegmental area (VTA), frontal neocortex and hippocampus: Our recent unexpected results reveal that MORs could exist in either pre or post-synaptic sites depending upon the types of neurons and the region of the brain. Therefore, to better understand drug addiction, we will investigate how opioids modulate excitatory synaptic transmissions in different regions of the brain. (2) Learning and using the two-photon microscopic technique to investigate AMPA receptor trafficking during chronic opioid exposure: Chronic treatment of morphine decreases the amplitude of miniature EPSCs, suggesting a removal of post-synaptic AMPA receptors. The objective of this approach is to lay a solid foundation for the next future research plan when my funded R01 grant is up for competitive renewal. This next future research plan is to clarify the cellular mechanism underlying the trafficking of AMPA receptors during opioid exposure. In addition, this K02 award will also allow me to devote extra effort to my training in opioid pharmacology. I will attend seminars and meetings in the Department of Neuroscience and the NIDA funded Basic Center for Molecular and Cellular Biology of Drug Abuse at the University of Minnesota. I will regularly attend the NIDA funded summer courses at Cold Spring Harbor and participate in national and international scientific meetings of neuroscience and pharmacology. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Dementia in Parkinson's disease (PD) patients is often associated with pathological changes in a-synuclein, Amyloid ? (A?) and tau proteins. In our new preliminary study, the CA1 and CA3 regions of the hippocampus are highly vulnerable to ?-synuclein pathology as well as tau deposits in the brains from PD patients. Clarifying the cellular interaction between ?-synuclein and tau will help better understand the pathogenesis of PD dementia. Interestingly, in our preliminary studies, the expression of PD-related A53T mutant a-synuclein proteins drives tau proteins to dendritic spines, causes loss of AMPA receptors in spines and results in memory loss. To find a postsynaptic link between ?-synuclein and tau, we will test the central hypothesis that A53T a-synuclein impairs post-synaptic structures and/or functions by causing tau mislocalization to dendritic spines, which subsequently leads to calcineurin- and GluR1 S845 dephosphorylation-dependent AMPA receptor internalization. The central hypothesis will be tested by two specific aims: In Specific Aim 1, we will perform biochemical, live imaging, immunocytochemical and electrophysiological experiments to determine the role of tau mislocalization and/or tau hyperphosphorylation in postsynaptic dysfunction caused by ?-synuclein. We will test the hypothesis that a-synuclein induces synaptic dysfunction by causing loss of AMPA receptor through tau mislocalization and tau hyperphosphorylation. In Specific Aim 2, we will use pharmacological, molecular biological, genetic, imaging and electrophysiological approaches to determine the roles of calcineurin and tau in ?-synuclein- induced AMPA receptor internalization. We will test the hypothesis that ?-synuclein induces AMPA receptor internalization via tau- and calcineurin-dependent dephosphorylation of Serine 845 at the C-terminus of GluR1 subunits. The completion of the proposed project will unravel a new final postsynaptic cascade that leads to functional deficits after a-synuclein initiation, which may occur at either a pre- or post-synaptic location. The unraveled signaling steps may be targeted in future AD and PD therapeutic strategies.

? DESCRIPTION (provided by applicant): Widespread tau-containing neurofibrillary tangles and A? plaque pathologies are present in the brains of patients with repetitive mild human traumatic brain injuries (TBI) and of patients many years after a single severe TBI. The overall goal of the proposed project is to build a novel in vitro TBI model in order to clarify the intracellular pathways that link mechanical neuronal injuries to tau abnormalities. To achieve this goal, we will test the central hypothesis that neuronal injuries caused by mechanical forces lead to tau hyperphosphorylation, which induces subsequent tau mislocalization and tau-mediated synaptic deficits. We will pursue two Specific aims: In Aim 1, we determine the cellular mechanism underlying mechanical injury- induced tau-mediated morphological deficits in dendritic spines. Neurons will be stretched using three TBI protocols to mimic one single severe TBI, repeated mild injuries and bomb blast waves. We will determine whether the tau mislocalization caused by the stretching protocols depends upon tau hyperphosphorylation, activation of tau kinases (CDK5 and GSK3) and the production of A? oligomers. We will also test the roles of tau and Fyn in spine loss caused by neuronal injuries. In Aim 2, we will clarify the cellular mechanism underlying mechanical injury-induced tau-mediated functional deficits in dendritic spines. We will characterize pre- and/or post-synaptic deficits caused by mechanical injuries in our in vitro model and will determine whether these deficits are mediated by endogenous tau, tau hyperphosphorylation, the production of A? oligomers and the activation of calcineurin. This will be the first in vitro TBI model that can replicate DAI and tau abnormalities. Using this novel model, we will clarify the tau-mediated link between TBI, AD, and FTD at a cellular level, opening a new area to the field of TBI research.

Summary/Abstract: Parkinson?s disease (PD) is the second most common late-onset neurodegenerative disease with the largest relative increase in mortality rates among all neurological disorders. PD is traditionally considered a motor disorder, characterized by the loss of dopaminergic neurons of the SNpc, and the presence of fibrillar cytoplasmic inclusions called Lewy bodies and Lewy neurites. However, a more global perspective on the PD is developing, motivated by pathological and clinical findings that extend beyond the basal ganglia. In particular, the majority of PD patients meet criteria for a secondary diagnosis of mild cognitive impairment that progresses dementia, a significant contributor to disease morbidity and mortality. The emerging view is that the abnormalities in ?-synuclein (?S) may be responsible for motor and non-motor symptoms in PD and Dementia with Lewy Bodies (DLB). Significantly, we recently found that abnormal ?S can cause post-synaptic deficits in vitro and in vivo via a microtubule associated protein tau (MAPT) dependent mechanism. In this proposal, we will directly determine the following hypothesis: 1) Pathogenic ?S species produce cognitive decline tau-dependent post-synaptic mechanisms and 2) MAPT-dependent postsynaptic deficits caused by exogenous ?S fibrils/oligomers contribute to cognitive deficits in sporadic PD and DLB. To determine the mechanistic basis for cognitive deficits in ?-synucleinopathy, we propose following aims: 1) Determine whether tau is required for ?S dependent synaptic and cognitive deficits; 2) Determine if mutant ?S-dependent AMPAR deficits and memory deficits are caused by multiple pathways; 3) Determine whether hippocampal ?S pathology and somatodendritic tau mislocalization correlates with dementia in PD; 4) Determine if exogenous pathogenic ?S induces pre- and/or post-synaptic deficits; and 5) Determine if pathogenic ?S induces defects in synaptic plasticity and memory in a tau dependent manner.