Research Interests

05/01/2017

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My overarching research goal is to understand the molecular mechanisms of neurogenesis, neural metabolism and tumorigenesis. Specifically I aim to elucidate how NIBP, a novel family of proteins I discovered, directs these processes by regulating NFkB signaling and protein trafficking pathways. Three novel working hypotheses drive my research: 1) NIBP is a proneuronal factor that determines neuronal fate during a very early stage of neural induction or neurogenesis, and also maintains neuronal polarization and functional integrity by regulating protein trafficking; 2) NIBP is an adaptive host restriction factor that serves to eradicate/prevent encephalopathogenic latent HIV-1 infection of neural stem cells; 3) NIBP may provide a novel biomarker and target for cancer diagnosis and treatment, owing to its intense induction in highly invasive cancer cells and other preliminary findings. To test these hypotheses and elucidate NIBP's roles, I am establishing advantageous novel animal models and human induced pluripotent stem (iPS) cells. Elucidating NIBP's functions may drive discovery and broad translational advances in neural development, adult neurogenesis, neuronal polarization, neuroregeneration, neuroinflammation, metabolic syndrome and tumorigenesis. I have the vision, expertise, and leadership skills to accomplish these goals. My creativity and productivity are reflected by my achievements during the past years.

   Regulation of NF-kB signaling pathways: NIBP.

NF-kB can be stimulated by many stimuli through various pathways.  It regulates an array of genes important in immunity, inflammation, stress response, cell growth and plasticity. High basal activity of NF-kB is reported in cancer cells, lymphocytes, neurons and smooth muscle cells. Sustained activation of NF-kB is critical for inflammation-linked cancer and other chronic diseases. However, the origins and mechanisms of NF-kB activation (constitutive or inducible) are not well understood. In most cases, NF-kB is held in the cytoplasm via Inhibitor of NF-kB (IkB). After phosphorylation by IkB kinase (IKK), IkB is degraded, leading to NF-kB activation. How IKK is activated remains a focus of considerable research interest.

My previous research interests were focused on the identification of novel proteins regulating IKK and its upstream kinases. Several novel proteins have been identified. Their functions and mechanisms need characterized. One of the novel proteins, NIBP, is shown to enhance TNFa and IL-1b-induced NF-kB activation via increasing IKK2 kinase activity and be required for growth and differentiation of neuronal cell line PC12 (Hu, et al., 2005). However, it is not known whether NIBP is essential for neuronal differentiation and survival in primary neurons or neural stem cells from central, peripheral and enteric nervous system. In addition, much more functions of NIBP and their mechanisms remain to be elucidated.

It is also a key member of trafficking protein particle (TRAPP) complex II (Cox et al., 2007; Kummel et al., 2008; Zong et al., 2011, 2012), implying its importance in regulating cellular trafficking. New clinical data showed that homozygous NIBP non-sense mutation is closely correlated with autosomal recessive mental retardation and neonatal microcephaly (Mir et al., 2009; Mochida et al., 2009; Philippe et al., 2009; Marangi et al., 2012). Homozygous deletion of NIBP genome in human leads to severe developmental delay, retinal dystrophy, hearing loss and dismorphic facial features (Koifman et al., 2010). Genome-wide assay identified two SNPs (single nucleotide polymorphisms) in NIBP that contribute to maternal effects on human height (Yoshida et al., 2010). NIBP is highly expressed in various human tumors. These clinical findings highlight the importance of NIBP in neurogenesis, mental development, neural functional integrity and tumorigenesis.

Hypothesis I: NIBP may play an important role in neurogenesis. The important role of NF-κB in neural development has been well established. In addition, NIBP may have some functions other than NF-κB regulation. Our preliminary data demonstrated that NIBP-like immunoreactivity is extensively expressed in neurons and neural stem/progenitor cells (including enteric nervous system).  To study the developmental role of NIBP, we generated conditional NIBP knockout or knockin mice using Cre/LoxP system. We also use Zebrafish neurogenic model and human induced pluripotent stem cells to study the role of NIBP signaling in neural induction and neurogenesis.

Hypothesis II: NIBP mediates neural regeneration after CNS (central nervous system) injury and disorders. The rationale is that regenerative failure in adult CNS may be partially due to the reduction or loss of NIBP expression after CNS injury. Lentivirus-mediated long-term and neuron-selective delivery of NIBP gene after adult CNS injury may promote nerve growth and ultimately improve functional recovery. We will first address the questions whether endogenous NIBP is required for central nerve growth and whether CNS injury reduces endogenous NIBP expression. Then, the lentivirus-mediated NIBP-shRNA strategy will be used to knock down the endogenous NIBP expression both in vitro and in vivo. Finally, lentivirus-mediated Cre/LoxP system will be employed to induce neuron-selective controllable expression of NIBP after CNS injury. Alternatively, neural stem/progenitor cells or other candidate cells infected with NIBP lentivirus will be transplanted into CNS after injury. The selective and inducible expression of NIBP will compensate for the reduction of NIBP after CNS injury and promote nerve growth through neuronal NFκB signaling while non-neuronal NFκB signaling will not be intervened.

Hypothesis III:  NIBP regulates tumorigenesis. Unigene assay indicated that NIBP EST (Expression Sequence Tag) is widely present in various human tumors. Gene Expression Omnibus (GEO) profiles from many microarray experiments suggested that NIBP is highly expressed in cancer cells. The preliminary studies demonstrated that NIBP is selectively expressed in various cancer cell lines, and a similar interaction between endogenous NIBP and IKK2 is present in MCF7 and HCT116 cells. Immunohistochmistry and TissueScan real-time PCR analysis showed that NIBP is highly expressed in various human tumors. IKK2 is critical in regulating NF-kB activation and tumorigenesis. IKK2-specific inhibitors have been targeted for therapeutic development and clinical application. Thus, NIBP highly expressed in tumor cells may retain the constitutive activation of IKK2 and contribute to the proliferation, tumorigenesis, metastasis and drug-resistance of cancer cells. The expression pattern of NIBP in a number of cancer cell lines and human tumors will be profiled. In vivo studies using nude mice and cell-specific conditional NIBP knockout mice will be performed. The mechanisms for NIBP regulation and function in tumorigenesis will be investigated. Results from these studies will not only establish the novel role of NIBP in cancer development and progression but also provide an important insight into the mechanism of IKK2-mediated activation of NF-kB in tumor cells. NIBP may represent a novel adaptor protein or regulator that controls the activities of IKK complex and NF-kB.

   Regulation of gastrointestinal motility and inflammation by NIBP/NFκB signaling.

 

The enteric nervous system (ENS) regulates contraction/relaxation, secretion/absorption and mucosal homeostasis in the gastrointestinal (GI) tract. In debilitating GI diseases including inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), gastroparesis and chronic constipation/diarrhea, adult ENS exhibits morphological and functional abnormalities. Because immune and inflammatory responses play critical roles in the pathogenesis of these GI diseases, and most such deleterious immune responses are mediated via NκB signaling, suppression of NFκB signaling is a promising candidate target for new GI disease therapies. However, such a strategy has been limited by opposing, cell type-specific actions of NFκB signaling. For example, in immune cells NFκB signaling generates pro-inflammatory mediators that may worsen GI inflammation, but in intestinal epithelial cells it maintains intestinal mucosal integrity. In colonic smooth muscle cells, NFκB mediates inflammation-induced contractile inhibition. The roles of NFκB signaling within the ENS are largely unknown. NIBP is highly expressed at both mRNA and protein levels in neurons of brain and gut alike. NIBP knockdown in an enteric neuronal cell line inhibits cytokine-induced NFκB activation and neuronal differentiation. We hypothesize that NIBP is a pivotal regulator of enteric neuronal NFkB signaling, and thereby modulates GI motility. Enteric glial cells (EGCs) play a key role in protecting enteric neurons and mucosal integrity. EGCs may also become reactive after inflammation, acting as both source and target of pro-inflammatory mediators, but the molecular mechanisms and signaling pathways of reactive enteric astrogliosis are poorly understood. To test the role of NFκB in EGCs, we analyzed the transgenic mice (GFAP-dnIκBα) having astrocyte-targeted NFκB inhibition2,3, and found that inhibiting NFκB within enteric astroglia protects against chronic colitis. Also, to selectively augment glial NFκB activity, we used conditional stop-floxed mice carrying a constitutively active form of IKK2 (IKK2CA) to generate GFAP-IKK2CA mice with astrocyte-selective NFκB hyperactivity. GFAP-IKK2CA mice developed spontaneous colitis, enteric gliosis and neuronal loss. Therefore, we hypothesize that NFkB signaling in EGCs may mediate inflammation-induced enteric neuropathy and smooth muscle dysmotility. We expect that enteric neuronal NIBP/NFκB signaling maintains enteric neuron survival and functional integrity, while enteric astroglial NFκB signaling predominantly mediates inflammatory responses.

·   CRISPR/Cas9 (epi)genome editing and HIV cure
Although the combined antiretroviral therapy (cART) has saved the life and reduced the severity of neurocognitive impairment in HIV patients, the prevalence of the milder/moderate HIV-associated neurocognitive disorders (HAND) continues to increase . The cART can sufficiently eradicate the HIV production reservoir but does not eradicate the latent cellular and tissue reservoir including the brain and the gut. Several types of cells have been proposed as potential latent reservoir, such as resting memory T cells, microglia/macrophages and astrocytes, though these cells are known to serve primarily as productive reservoir. The quiescent NSCs may serve as a novel cellular reservoir for latent and persistent HIV infection. My research aims to identify the latent HIV reservoir in NSCs and define the molecular mechanisms underlying the reactivation and cell-selective elimination of HIV latent provirus.
Guide RNA (gRNA)-mediated CRISPR/Cas9 technology remains continuously expanded due to its rapid, easy and efficient application to manipulating endogenous genes/genomes in a wide variety of cell types and species. The CRISPR/Cas9-mediated gene/cell therapy may be a promising cure for HIV/AIDS. My research interest is focused on the “knockout” of the latent HIV provirus from host cells using Cas9 genome editing and the “shock and kill” of HIV latent cells using dCas9-mediated synergistic activator or the permanent silencing of the latent reservoir using dCas9-mediated epigenome suppressor.

·   Transcription factor 4 regulates spinogenesis and synaptogenesis
The 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. Current 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. My research interest aims to decipher the cytoplasmic functions of Tcf4 in regulating spinogenesis and synaptogenesis of postmitotic neurons.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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