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The challenges of discovery and translation inspire my biomedical research. I am fascinated by the creative process of identifying novel molecules that regulate signal transduction and gene expression. My achievements focus in 5 main areas: NFkB regulation, G protein signaling, neurogenesis/neuronal polarization and HIV cure. In my early studies I discovered that TRAIL receptors induce apoptosis and activate NFkB and JNK, and discovered the potent NFkB-activating roles of the apoptosis-inducing proteins FADD, Casper and Caspase-8. My current and planned researches are catalyzed by my discovery of 3 novel proteins (NIBP, TNAP and TALL-1) that modulate NFkB signaling. NIBP enhances, while TNAP suppresses, NFkB activation by cytokines. NIBP regulates neuronal differentiation and neurodevelopment, perhaps contributing to newly-identified neurodevelopmental diseases (NIBP Syndrom). TALL-1 strongly modulates B-cell proliferation through non-classical NFkB pathway, as later discovered by others. NIMP, a novel mitochondrial protein I discovered, interacts with nerve growth inhibitor Nogo. I tested astrocytic NFkB roles in neuropathogenesis by creating GFAP-dnIkBa transgenic mice, revealing reduced disease severity and improved functional recovery in nerve injury models. I discovered that RGS4 is a novel target gene regulated by NFkB signaling, that is differentially modified by MAPKs and PI3K/Akt/GSK3β signaling, and that RGS4 mRNA stability is regulated by HuR. I identified a new function of NFkB signaling that initiates early differentiation of neural stem cells, by repressing C/EBPβ. These findings have advanced the fields of neuroinflammation and neurogenesis, and positioned me as a visionary leader to continue driving discovery of novel roles and applications of NIBP/NFkB signaling in the nervous system.

 

I. CRISPR/Cas9-mediated HIV excision and reactiation

For a cure of HIV-1 patients, there is an urgent need of developing a novel strategy that is capable of eradicating the integrated viral genome or eliminate HIV latent cells. We utilized a newly-developed and easy-to-use CRISPR/Cas9 technology to specifically cut the long term repeat (LTR) regions at multiple sites within HIV-1. We identified highly specific targets within LTR U3 region that inactivate viral gene expression and replication in latently infected microglial, promonocytic, and T cells [Huge global media response with the Altmetric score 391: http://www.altmetric.com/details.php?domain=www.pnas.org&citation_id=2526844. Ranked 2014 discovery at #86 among 100 top stories by “Discover” magazine. http://news.temple.edu/news/2015-01-08/temple-aids-discovery-among-top-100-science-stories-2014]. Cas9/gRNAs caused neither genotoxicity nor off-target editing to the host cells. Furthermore, a combination of sgRNAs targeting LTRs and the viral structural genes provides a more efficient means of HIV-1 eradication in cultured cells. AAV9-mediated saCas9/duplex sgRNA can be used to excise the integrated HIV-1 genome in HIV-1 transgenic mice and rat. AAVDJ8-mediated saCas9/quadruplex sgRNA excised HIV-1 genome in humanized BLT mice and EcoHIV-infected mice. Our results suggest that Cas9/gRNA can be engineered to provide a specific, efficacious prophylactic and therapeutic approach against AIDS. We also identified a hotspot near to the enhancer of HIV LTR promoter that can be targeted by dCas9-SAM/msgRNA system to induce robust and persistent reactivation of HIV latency leading to suicide death of latent cells. This targeted latency-reversing approach adds a new therapeutic to the “shock and kill” strategy to cure HIV/AIDS.

II. Transcription Factor 4 (TCF4) resitricts neurite branching and synapse formation

Proneural proteins of the class I/II basic-helix-loop-helix (bHLH) family are highly conserved transcription factors. Class I bHLH proteins are expressed in a broad number of tissues during development, whereas class II bHLH protein expression is more tissue restricted. Our understanding of the function of class I/II bHLH transcription factors in both invertebrate and vertebrate neurobiology is largely focused on their function as regulators of neurogenesis. TCF4 mutations have been reliably identified in genome-wide association studies as a susceptibility risk factor for schizophrenia and have also been associated with Pitt-Hopkins syndrome, Fuchs’ endothelial corneal dystrophy, and primary sclerosing. It is unknown whether these diseases are due to defects in neurogenesis, in mature differentiated cells, or both. Our collaborative studies show that the class I bHLH proteins Daughterless and Tcf4 are expressed in postmitotic neurons in Drosophila melanogaster and mice, respectively, where they function to restrict neurite branching and synapse formation by repressing the expression of the cell adhesion molecule Neurexin

III. NF-kB signaling: In my early studies I discovered that TRAIL receptors induce apoptosis and activate NFkB and JNK(Hu, Johnson et al. 1999), and apoptosis-inducing proteins FADD, Casper and Caspase-8 also activate NFkB signaling (Hu, Johnson et al. 2000). My current researches are catalyzed by the discovery of 3 novel proteins (NIBP, TNAP and TALL-1) that modulate NFkB signaling. NIBP enhances(Hu, Pendergast et al. 2005), while TNAP suppresses(Hu, Mo et al. 2004), NFkB activation by cytokines. NIBP regulates neuronal differentiation and neurodevelopment, perhaps contributing to newly-identified neurodevelopmental diseases including NIBP syndrome. TALL-1 strongly modulates B-cell proliferation through non-classical NFkB pathway. These early contributions have over 1100 citations.

1. Identification of three novel components of the NF-kB signaling pathway (TNAP, NIBP, TALL-1)

 1) TNAP.

Using yeast two-hybrid system with NIK (NFkB-inducing kinase) as bait to screen cDNA libraries from brain, spleen, leukocyte and HEK293T cells, several known proteins such as TRAF3, PAX6, CDC23 and proteasome subunit PSMA3, and two novel proteins, TNAP and NIBP; the latter were characterized in detail and shown to interact with NIK.  TNAP (TRAFs and NIK-Associated Protein) specifically inhibited TNF-a and IL-1b-induced NF-κB activation by interacting with NIK and TRAF2/3, and suppressing NIK kinase activity. Thus, TNAP regulated both classical (IkBa phosphorylation and degradation) and non-classical (p100 processing to p52) pathways of NF-kB activation. TNAP also suppressed TNFa-induced and NIK-mediated Ser536 phosphorylation of p65.

        2)  NIBP.  

NIBP (NIK and IKKb Binding Protein) was mainly expressed in brain, muscle, heart and kidney, and moderately expressed in immune tissues such as spleen, thymus and peripheral blood leukocytes, where NF-kB was known to modulate immune function. NIBP physically interacted with NIK, IKKb, but not IKKa or IKKg.  NIBP over-expression potentiated TNFa and IL-1b-induced NF-kB activation through increased phosphorylation of the IKK complex and its downstream IkBa and p65 substrates. Knockdown of NIBP expression by lentiviral vector-mediated small interfering RNA reduced TNFa-induced NF-kB activation, prevented NGF-induced neuronal differentiation and decreased the expression of NFkB-dependent gene, Bcl-xL, in PC12 cells. These data demonstrated that NIBP, by interacting with NIK and IKKb, was a novel enhancer of  cytokine-induced NF-kB signaling.

3)  TALL-1.

 Using amino acid homology analysis, another novel member of TNF ligand family was identified and designated TALL-1 (for TNF- and ApoL-related Leukocyte expressed Ligand 1).  Simultaneously, TALL-1 was discovered by others and designated BAFF, BLyS, and zTNF4. TALL-1 was a potent modulator of B-cell proliferation via its receptors BCMA (B cell maturation antigen) and TACI (transmembrane activator and CAML-interactor), and was expressed by monocytes/macrophages and dendritic cells.

 

2.  Characterization of NFkB signaling pathways

As shown above, TNAP suppressed and NIBP enhanced cytokine-induced NF-kB activation. Our earlier studies demonstrated that receptors for TRAIL (TNF-related apoptosis-inducing ligand) induced apoptosis, and NF-kB and JNK activation through distinct signaling pathways. The apoptosis-inducing adaptors FADD (Fas-associated via Death Domain), Casper and Caspase-8 potently activated NF-kB, whereas “activated” Caspase-8 blocked NF-kB activation by inactivating NIK. These data were corroborated by several other groups.

 Neurons and their neighboring cells employ the NF-κB pathway for distinctive functions, ranging from development to neuronal plasticity and coordination of cellular responses to injury.  As part of our studies,  IκBa-dominant mutant transgenic mice were generated which stably expressed mutant IκBa under the control of an astrocyte-specific promoter, GFAP (glial fibrillary acidic Protein) or a neuron-specific promoter, synapsin.  Selective inactivation of astroglial NF-kB in transgenic mice led to marked improvement in function 8 weeks after contusive spinal cord injury.  The mice showed reduced expression of pro-inflammatory chemokines and cytokines, such as CXCL10, CCL2, and TGF-b2.  Inactivation of astroglial NF-kB in transgenic mice led to a significant deficit in learning and memory.

 

3.  NFkB signaling pathway initiates early neurogenesis

 Both NFκB signaling and neurogenesis are currently two hot topics in modern biomedical science. The epigenic and transcriptional regulation in embryonic and adult neurogenesis is drawing wide attention. NFκB signaling regulates neurite outgrowth and neural plasticity, as well as the proliferation/apoptosis and terminal differentiation of neural stem cells (NSCs). Early neurogenesis from NSCs produces identical progeny through symmetric division and committed daughter neural progenitor cells (NPCs) through asymmetric division. Whether NFκB signaling regulates initial differentiation and asymmetric division of NSCs and the factors involved still remains largely unknown. In this study, we employed multiple systems to demonstrate for the first time that NFκB signaling initiates the differentiation of the quiescent NSCs at the very early stage of both embryonic and adult neurogenesis. The canonical IKK2/IκBα/p65 pathway is activated during the initial stage of neural differentiation. NSC-specific inhibition of NFκB in transgenic mice causes an accumulation of NSCs. Inhibition of NFκB signaling in vitro blocks differentiation and asymmetric division and maintains NSCs in an undifferentiated state. This key finding may explain a previous observation that the proliferation of NSCs but not intermediate NPCs is significantly reduced by stress-induced NFκB activation in the adult brain (Koo et al., 2010). Our finding also supports a recent report showing that PEDF enhances NSC self-renewal through the promotion of p65 nucleo-cytoplasmic export (Andreu-Agullo et al., 2009). In addition, we found that C/EBPβ is one of the key effectors of NFκB signaling for the modulation of early asymmetric division and differentiation of NSCs. Our findings will advance our understanding of the molecular mechanisms not only for neural development and endogenous neurogenesis under normal conditions, but also for the inducible regulation of neurogenesis after injuries or diseases in the nervous system. Enrichment of NSCs by NFκB inhibition may provide an invaluable tool to expand neurospheres.

 

4. NFκB and MAPK signaling regulates RGS4

Regulator of G-protein Signaling 4 (RGS4) regulates the strength and duration of Gai/Gαq signaling and plays an important role in regulating smooth muscle contraction/relaxation, cardiac development, neural plasticity and psychiatric disorder. However, the underlying regulatory mechanisms remain elusive. Our studies showed that pro-inflammatory cytokine IL-1b up-regulates Rgs4 expression in rabbit colonic smooth muscle cells through the canonical IKK2/IκBα pathway of NFκB activation as well as ERK1/2 and p38 MAPK pathways. This up-regulation of Rgs4 is negatively regulated by the activation of PI3K/Akt/GSK3β pathway and MEKK1-MKK4-JNK-AP1 pathway. RGS4 mRNA stability is regulated by HuR. GATA-6 transcriptional factor is essential for RGS4 transcriptional regulation. These findings provide a novel and comprehensive understanding of the signaling regulation on RGS4 expression. The positive and negative regulatory mechanisms of RGS4 expression reflect an intricate and delicate system for gene regulation. Such orchestral regulation may aid in maintaining the transient function of RGS4 for smooth muscle contraction/relaxation as well as cardiovascular and neuronal functions.

IV. Secondary spinal cord injury and neural growth inhibition

Around twenty years ago, the pathophysiologic mechanism of the secondary spinal cord injury was a hot spot in the field of central nervous system injury. Using evoked potentials to evaluate spinal cord function and biomicrosphere technique to measure spinal cord blood flow, my studies demonstrated that ischemia in the white matter is closely correlated with spinal cord dysfunction after balloon compressive injury in dogs. My further works together with my colleagues corroborated the important role of excitotoxicity and lipoxidation in secondary spinal cord injury. These studies were awarded a Second Prize of Military Science and Technology Achievement in 1998.

During my PhD study, I continued the research on the excitotoxic mechanism of spinal cord injury using pharmacological animal model, focusing on the role of NMDA-Ca2+-NOS/NO pathway. NO was a "molecule of the year 1992 in science". My research demonstrated for the first time that neurotoxic dose of dynorphin (an endogenous opioid peptide) induces high expression of both neuronal and inducible nitric oxide synthases (nNOS and iNOS) in the spinal cord of rats. Selective inhibition of either nNOS or iNOS is neuroprotective while non-selective NOS inhibition aggravates dynorphin-induced spinal cord injury. NMDA receptor functional activity is significantly elevated in the ventral spinal cord of rats with dynorphin spinal neurotoxicity. In cultured spinal cord neurons, high concentration of dynorphin produces persistent calcium overload, which is antagonized by pretreatment with both NMDA receptor antagonist and kappa opioid receptor antagonist. These data were granted a Second Prize of Beijing Science and Technology Achievement in 2000.

Excitatory amino acids transporters (EAAT) are essential to prevent excitotoxicity and to terminate glutamatergic neurotransmission. During my postdoctoral training in Miami Project to Cure Paralysis, I observed, unexpectedly, that EAAT4 immunoreactivity is highly enriched in the spinal cord. Further studies demonstrated that EAAT4 is expressed in the astrocytes of spinal cord at both protein and mRNA levels. This astrocytic localization of EAAT4 may reveal some new function of EAAT4 in the spinal cord.

To develop a better understanding of the mechanisms responsible for the functions of Nogo, an important myelin-derived nerve growth inhibitor after spinal cord injury, I performed a yeast two-hybrid screen of human brain cDNA library using Nogo-66 as bait.  A novel mitochondrial protein designated NIMP (for Nogo-Interacting Mitochondrial Protein) is highly conserved and ubiquitously expressed in neurons and astrocytes. Other two-mitochondrial proteins UQCRC1/2 also interact with Nogo, indicating that Nogo may affect mitochondrial functions.

 

V. Receptor mechanism for S1P signaling

Sphingosine-1-phosphate (S1P) regulates diverse biological processes through five receptor types, S1P1-5. S1P induces an initial Ca2+)-dependent contraction followed by a sustained Ca2+-independent, RhoA-mediated contraction in rabbit gastric smooth muscle cells. The cells coexpress S1P1 and S1P2 receptors, but the signaling pathways initiated by each receptor type and the involvement of one or both receptors in contraction are not known. Lentiviral vector-mediated siRNA silencing of S1P1 receptors abolished S1P-stimulated activation of Gai3 and partially inhibited activation of Gai1, whereas silencing of S1P2 receptors abolished activation of Gaq, Ga13, and Gai2 and partially inhibited activation of Gai1. Silencing of S1P2 but not S1P1 receptors suppressed S1P-stimulated PLC-b and Rho kinase activities, implying that both signaling pathways were mediated by S1P2 receptors. The results obtained by receptor silencing were corroborated by receptor inactivation. The selective S1P1 receptor agonist SEW2871 did not stimulate PLC-b or Rho kinase activity or induce initial and sustained contraction; when this agonist was used to protect S1P1 receptors so as to enable chemical inactivation of S1P2 receptors, S1P did not elicit contraction, confirming that initial and sustained contraction was mediated by S1P2 receptors. Thus S1P1 and S1P2 receptors are coupled to distinct complements of G proteins. Only S1P2 receptors activate PLC-b and Rho kinase and mediate initial and sustained contraction.


 

TUSOM CMDR SFNAGADDWASBMB

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