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Neuroscience Graduate Program at UCSF
Transcriptional Programs in Neuronal Survival and Differentiation
Following neurogenesis, neurons are faced with the decision to survive, differentiate and connect with its targets, or to undergo apoptotic cell death. Multiple mechanisms can regulate this important decision, including neurotrophic factors that activate a variety of signal transduction events. One major focus in our lab has been to understand the role of a transcriptional cofactor, homeodomain protein kinase 2 (HIPK2), in trophic factor-dependent survival and cell death in sensory and midbrain dopamine (DA) neurons. HIPK2 was isolated by virtue of its ability to interact with and regulate the activity of several transcription factors, including Brn3a and Smad2. In the past few years, we have used an array of interdisciplinary approaches to demonstrate that HIPK2 regulates programmed cell death during development of sensory, sympathetic and DA neurons. We show that HIPK2 is required for TGFb-dependent survival of DA neurons and that HIPK2 regulates cellular response to TGFb by promoting phosphorylation of Smad2 in the C-terminal transactivation domain. These results suggest that the pro-survival function of TGFb in DA neuron may depend on HIPK2 to maintain a higher level of Samd2 phosphorylation.
Due to the implications of trophic factor in treating patients with Parkinson’s disease, we also ask if loss of HIPK2 influences the survival of DA neurons under toxin-induced degeneration of DA neurons. Interestingly, DA neurons in adult Hipk2-/- mutants show considerable resistance to toxin-induced cell death. Indeed, control experiments demonstrate that the resistance of Hipk2-/- mutant DA neurons to toxin-induced cell death is not due to poor bioavailability of toxin in the mutant brains. Furthermore, the effect of HIPK2 in toxin-induced cell death can be recapitulated in cultured DA neurons and cell lines. While surprising, these results are not entirely unexpected since HIPK2 has been shown to promote cell death under UV or hypoxia-induced injury. Taken together, these results lead to the model that HIPK2 regulates survival and cell death in DA neurons in a context-dependent manner. During the development of DA neurons, HIPK2 is required for survival of DA neurons because of its role in promoting TGFb-Smad2 signaling pathway. In contrast, under toxin-induced injury conditions, HIPK2 can be “recruited” to activate JNK-dependent cell death. To test this hypothesis, we are in the process to (1) characterize the role of HIPK2 in phosphorylating the C-terminal transactivation domain of Smad2 in DA neurons, (2) characterize the functional redundancy of HIPK1 and HIPK2 in regulating the development of DA neurons, and (3) characterize the signaling mechanism of HIPK2 in toxin-induced cell death in DA neurons. Our studies will provide further insights into the signaling mechanisms of TGFb-dependent survival of DA neurons under physiological as well as pathological conditions.
In addition to the decision of neuronal survival and cell death, we are also interested in the molecular mechanisms that regulate the early stage of neurogenesis in DA neurons. It is well-established that ventral midbrain (vMB) contains the neurogenic niche that produces DA neurons. However, it is unclear how microenvironment within this niche controls DA neurogenesis. We show that Wnt-b-catenin controls DA neurogenesis by maintaining the integrity of neurogenic niche and the progression from progenitors to DA neurons. Using conditional gene targeting approaches, we show that regional deletion of b-catenin in vMB using Shh-Cre disrupts adherent junctions of progenitors and the integrity of radial glia in vMB, which lead to severe reduction in DA neurogenesis and perturb the migration and segregation of DA neurons. In contrast, TH-IRES-Cre removes b-catenin in a subset of neural progenitor cells without perturbing the cellular and structural integrity of vMB. Interestingly, loss of b-catenin in TH-IRES-Cre;b-Ctnfl/fl mutants negatively regulates neurogenesis by interfering with the progression of committed progenitors to DA neurons. Conversely, our recent results indicate that stabilization of Wnt-b-catenin signaling mechanisms leads to expansion of DA progenitors and promotes the differentiation of DA neurons. Taken together, these results provide new insights to the indispensable functions of b-catenin at multiple stages during DA neurogenesis. They also suggest that b-catenin-mediated signaling pathways can be targeted to promote and expand DA neurons in cell-based therapy.
Signaling mechanisms of HIPK2 in TGFb-dependent survival of DA neurons
Mechanisms of HIPK2 in genetic and toxin-induced models of degeneration in dopamine neurons
Cooperative roles of HIPK1 and HIPK2 in neural development
Roles of Wnt-b-catenin mechanisms in neurogenesis of DA neurons and its implications in cell-based therapy for Parkinson’s disease
Ku, Stephen
UCSF Medical Student
B.S., Stanford University
Pho, Vanee
Postdoctoral Fellow
Ph.D., Boston University
Tang, Amy
Staff Research Associate
B.S., UC Berkeley
Tang, Mike
Lab Technician
B.S., UC Berkeley
Wei, Guangwei
Postdoctoral Fellow
Ph.D., Fudan University
Wiggins, Amanda
Postdoctoral Fellow
Ph.D., University of Melbourne
Zhang, Jiasheng
Postdoctoral Fellow
Ph.D., Kanazawa University
Wiggins, A.K., Wei, G., Doxakis, E., Wong, C., Tang, A.A., Luo, E.J., Zang, K., Neve, R.L., Reichardt, L.F. and Huang, E.J. Interaction of Brn3a and HIPK2 mediates transcriptional repression of sensory neuron survival. J Cell Biol 167: 257-267, 2004.
Doxakis, E., Huang, E.J. and Davies, A.M. Homeodomain-interacting protein kinase-2 regulates apoptosis in developing sensory and sympathetic neurons. Curr Biol 14: 1761-1765, 2004.
Zhang, J. and Huang, E.J. Dynamic expression of neurotrophic factor receptors in postnatal spinal motoneurons and in mouse model of ALS. J Neurobiol 66(8), 882-895, 2006.
Zhang, J., Pho, V., Bonasera, S.J., Holzmann, J., Helmuth, J., Tang, A.A., Tang, S., Janak, P.H., Tecott, L.H. and Huang, E.J. Essential role of HIPK2 in TGFb-dependent survival of midbrain dopamine neurons. Nature Neurosci 10: 77-86, 2007.
Wei, G., Ku, S., Saito, S., Tang, A.A., Mao, J.H., Appella, E., Balmain, A. and Huang, E.J. HIPK2 represses b-catenin-mediated transcription, epidermal stem cell expansion, and skin tumorigenesis. Proc Natl Acad Sci (USA) 104: 13040-13045, 2007.
Laposa, R.R., Huang, E.J. and Cleaver, J.E. Increased apoptosis, p53 upregulation and cerebellar neuronal degeneration in a mouse model of Cockayne Syndrome. Proc Natl Acad Sci (USA) 104: 1389-1394, 2007.
Tang, M., Miyamoto, Y. and Huang, E.J. Multiple roles of b-catenin in controlling the neurogenic niche for midbrain dopamine neurons. Development 136: 2027-2038, 2009.
Eric J. Huang, M.D./Ph.D.
Phone
415-221-4810 x2620
Physical Address
VA Medical Center,
Bldg 2, Rm 355B
4150 Clement Street
San Francisco, CA 94121
Mailing Address
Pathology Service 113B VAMC
4150 Clement Street
San Francisco, CA 94121
Other Websites
Lab website (under construction)
PIBS Website (coming soon)