Faculty Bibliography

The expression of forms of synaptic plasticity, such as the phenomenon of long-term potentiation, requires the activity-dependent regulation of synaptic proteins and synapse composition. Here we show that ARMS (ankyrin repeat-rich membrane spanning protein)/Kidins220, a transmembrane scaffold molecule and BDNF TrkB substrate, is significantly reduced in hippocampal neurons after potassium chloride depolarization. The activity-dependent proteolysis of ARMS/Kidins220 was found to occur through calpain, a calcium-activated protease. Moreover, hippocampal long-term potentiation in ARMS/Kidins220(+/-) mice was enhanced, and inhibition of calpain in these mice reversed these effects. These results provide an explanation for a role for the ARMS/Kidins220 protein in synaptic plasticity events and suggest that the levels of ARMS/Kidins220 can be regulated by neuronal activity and calpain action to influence synaptic function

Scaffolding proteins play a critical role in the proper development and function of neural circuits. In contrast to the case for excitatory circuits, in which the role of several scaffolding proteins has been characterized, less is known about the scaffolding proteins that regulate inhibitory neurotransmission. The ankyrin repeat-rich membrane spanning (ARMS)/kinase D-interacting substrate of 220 kDa (Kidins220) scaffolding protein is expressed during the establishment of gamma-aminobutyric acid (GABA) neurotransmission and is highly regulated by activity. To evaluate whether ARMS/Kidins220 expression affects GABAergic neurotransmission, we modified the ARMS/Kidins220 levels during the period of its maximum expression in culture (DIV 1-10). Whereas a decrease in ARMS/Kidins220 levels suppressed GABAergic neurotransmission, overexpression of ARMS/Kidins220 produced an increase in GABAergic neurotransmission in hippocampal neurons. In addition, we found that ARMS/Kidins220 regulates GABAergic neurotransmission by a presynaptic mechanism. Our results suggest that the ARMS/Kidins220 scaffold protein plays a critical role in the regulation of inhibitory transmission in hippocampal neurons. (c) 2010 Wiley-Liss, Inc

BACKGROUND: Endocytic dysfunction and neurotrophin signaling deficits may underlie the selective vulnerability of hippocampal neurons during the progression of Alzheimer's disease (AD), although there is little direct in vivo and biochemical evidence to support this hypothesis. METHODS: Microarray analysis of hippocampal CA1 pyramidal neurons acquired via laser capture microdissection was performed using postmortem brain tissue. Validation was achieved using real-time quantitative polymerase chain reaction and immunoblot analysis. Mechanistic studies were performed using human fibroblasts subjected to overexpression with viral vectors or knockdown via small interference RNA. RESULTS: Expression levels of genes regulating early endosomes (rab5) and late endosomes (rab7) are selectively upregulated in homogeneous populations of CA1 neurons from individuals with mild cognitive impairment and AD. The levels of these genes are selectively increased as antemortem measures of cognition decline during AD progression. Hippocampal quantitative polymerase chain reaction and immunoblot analyses confirmed increased levels of these transcripts and their respective protein products. Elevation of select rab GTPases regulating endocytosis paralleled the downregulation of genes encoding the neurotrophin receptors TrkB and TrkC. Overexpression of rab5 in cells suppressed TrkB expression, whereas knockdown of TrkB expression did not alter rab5 levels, suggesting that TrkB downregulation is a consequence of endosomal dysfunction associated with elevated rab5 levels in early AD. CONCLUSIONS: These data support the hypothesis that neuronal endosomal dysfunction is associated with preclinical AD. Increased endocytic pathway activity, driven by elevated rab GTPase expression, may result in long-term deficits in hippocampal neurotrophic signaling and represent a key pathogenic mechanism underlying AD progression

The refinement of neural circuits during development depends on a dynamic process of branching of axons and dendrites that leads to synapse formation and connectivity. The neurotrophin brain-derived neurotrophic factor (BDNF) is essential for the outgrowth and activity-dependent remodeling of axonal arbors in vivo. However, the mechanisms that translate extracellular signals into the formation of axonal branches are incompletely understood. We found that MAP kinase phosphatase-1 (MKP-1) controls axon branching. MKP-1 expression induced by BDNF signaling caused spatiotemporal deactivation of c-jun N-terminal kinase (JNK), which reduced the phosphorylation of JNK substrates that destabilize microtubules. Indeed, neurons from mkp-1 null mice could not produce axon branches in response to BDNF. Our results identify a signaling mechanism that regulates axonal branching and provide a framework for studying the molecular mechanisms of innervation and axonal remodeling under normal and pathological conditions

Herpes simplex virus-1 (HSV-1) establishes life-long latency in peripheral neurons where productive replication is suppressed. While periodic reactivation results in virus production, the molecular basis of neuronal latency remains incompletely understood. Using a primary neuronal culture system of HSV-1 latency and reactivation, we show that continuous signaling through the phosphatidylinositol 3-kinase (PI3-K) pathway triggered by nerve growth factor (NGF)-binding to the TrkA receptor tyrosine kinase (RTK) is instrumental in maintaining latent HSV-1. The PI3-K p110alpha catalytic subunit, but not the beta or delta isoforms, is specifically required to activate 3-phosphoinositide-dependent protein kinase-1 (PDK1) and sustain latency. Disrupting this pathway leads to virus reactivation. EGF and GDNF, two other growth factors capable of activating PI3-K and PDK1 but that differ from NGF in their ability to persistently activate Akt, do not fully support HSV-1 latency. Thus, the nature of RTK signaling is a critical host parameter that regulates the HSV-1 latent-lytic switch

Activity-dependent changes of synaptic connections are facilitated by a variety of scaffold proteins, including PSD-95, Shank, SAP97 and GRIP, which serve to organize ion channels, receptors and enzymatic activities and to coordinate the actin cytoskeleton. The abundance of these scaffold proteins raises questions about the functional specificity of action of each protein. Here we report that basal synaptic transmission is regulated in an unexpected manner by the ankyrin repeat-rich membrane-spanning (ARMS/Kidins220) scaffold protein. In particular, decreases in the levels of ARMS/Kidins220 in vivo led to an increase in basal synaptic transmission in the hippocampus, without affecting paired pulse facilitation. One explanation to account for the effects of ARMS/Kidins220 is an interaction with the AMPA receptor subunit, GluA1, which could be observed after immunoprecipitation. Importantly, shRNA and cell surface biotinylation experiments indicate that ARMS/Kidins220 levels have an impact on GluA1 phosphorylation and localization. Moreover, ARMS/Kidins220 is a negative regulator of AMPAR function, which was confirmed by inward rectification assays. These results provide evidence that modulation of ARMS/Kidins220 levels can regulate basal synaptic strength in a specific manner in hippocampal neurons

The neurotrophins are a family of trophic factors that have been shown to have neuroprotective effects after traumatic lesions of the nervous system and in animal models of neurodegenerative diseases. They mediate a broad spectrum of biological actions by interacting with tyrosine kinase receptors (Trk). While studies have demonstrated that neurotrophin administration may have beneficial effects, there were difficulties in delivering therapeutic quantities of these factors to spinal motor neurons. We now describe a strategy for applying transactivation of Trk receptors using small molecules, such as adenosine, which can penetrate the blood brain barrier and rescue motor neurons from cell death. Transactivation opens up the possibility of stimulating Trk receptors only in populations of neurons that co-express both Trk and adenosine receptors. We propose in this review to exploit transactivation to improve the survival of motor neurons in a transgenic mouse model of ALS and for other neurodegenerative diseases, such as Alzheimer's and Huntington's disease

Neurotrophin receptors utilize specific adaptor proteins to activate signaling pathways involved in various neuronal functions, such as neurite outgrowth and cytoskeletal remodeling. The Ankyrin-Repeat Rich Membrane Spanning (ARMS)/kinase D-interacting substrate-220 kDa (Kidins220) serves as a unique downstream adaptor protein of Trk receptor tyrosine kinases. To gain insight into the role of ARMS/Kidins220, a yeast two-hybrid screen of a rat dorsal root ganglion library was performed using the C-terminal region of ARMS/Kidins220 as bait. The screen identified a mammalian septin, Septin 5 (Sept5), as an interacting protein. Co-immunoprecipitation using lysates from transiently transfected HEK-293 cells revealed the specific interaction between ARMS/Kidins220 and Sept5. Endogenous ARMS/Kidins220 and Sept5 proteins were colocalized in primary hippocampal neurons and were also predominantly expressed at the plasma membrane and in the tips of growing neurites in nerve growth factor-treated PC12 cells. Mapping of Sept5 domains important for ARMS/Kidins220 binding revealed a highly conserved N-terminal region of Sept5. The direct interaction between ARMS/Kidins220 and Sept5 suggests a possible role of ARMS/Kidins220 as a functional link between neurotrophin receptors and septins to mediate neurotrophin-induced intracellular signaling events, such as neurite outgrowth and cytoskeletal remodeling

BACKGROUND: SIRT1, a NAD-dependent deacetylase, has diverse roles in a variety of organs such as regulation of endocrine function and metabolism. However, it remains to be addressed how it regulates hormone release there. METHODOLOGY/PRINCIPAL FINDINGS: Here, we report that SIRT1 is abundantly expressed in pituitary thyrotropes and regulates thyroid hormone secretion. Manipulation of SIRT1 level revealed that SIRT1 positively regulated the exocytosis of TSH-containing granules. Using LC/MS-based interactomics, phosphatidylinositol-4-phosphate 5-kinase (PIP5K)gamma was identified as a SIRT1 binding partner and deacetylation substrate. SIRT1 deacetylated two specific lysine residues (K265/K268) in PIP5Kgamma and enhanced PIP5Kgamma enzyme activity. SIRT1-mediated TSH secretion was abolished by PIP5Kgamma knockdown. SIRT1 knockdown decreased the levels of deacetylated PIP5Kgamma, PI(4,5)P(2), and reduced the secretion of TSH from pituitary cells. These results were also observed in SIRT1-knockout mice. CONCLUSIONS/SIGNIFICANCE: Our findings indicated that the control of TSH release by the SIRT1-PIP5Kgamma pathway is important for regulating the metabolism of the whole body