Scientific Report 2005

Molecular Biology

Molecular Neuroscience: Lysophospholipid Signaling, Neural Aneuploidy

J. Chun, B. Almeida, B. Anliker, E. Birgbauer, M. Fontanoz, S. Gardell, C. Paczkowski, D. Herr, D. Kaushal, G. Kennedy, M. Kingsbury, C.W. Lee, M. McConnell, M. McCreight, S. Peterson, S. Rehen, R. Rivera, M. Lu, W. Westra, A.H. Yang, X.Q. Ye, Y. Yung, L. Zhu

Understanding the nervous system—how it arises developmentally and how it carries out its myriad complex tasks in normal and diseased states—is a major challenge. We are studying 2 topics with both basic and potentially therapeutic relevance: the role of lysophospholipid signaling and the role of genomic alterations within individual neurons as manifested by aneuploidy.

Lysophospholipid Signaling

Lysophospholipids are simple phospholipids containing a glycerophosphate or glycerosphingoid backbone and single acyl chain of varied length and saturation. Two major forms of lysophospholipids are lysophosphatidic acid and sphingosine 1-phosphate (Fig. 1).

Fig. 1. Chemical structures of lysophosphatidic acid and sphingosine 1-phosphate.

It is now clear from our research and that of many others that most important actions of lysophospholipids are mediated by cognate G protein–coupled receptors. A growing range of neurobiological functions is being identified, particularly effects on Schwann cells and oligodendrocytes, which are involved in myelination, and on neuroprogenitor cells of the cerebral cortex. To determine receptor selectivity and actual neurobiological function, we are producing mice that lack the genes for single and multiple receptors. In collaboration with other scientists at Scripps Research, we are developing chemical tools to dissect the in vivo function of lysophosphatidic acid and sphingosine 1-phosphate.

During 2004, the range of new biological functions for receptor-mediated lysophospholipid signaling continued to grow. With collaborators from around the world, we showed that lysophospholipid signaling influences the cardiovascular system, the immune system, cancer cell motility, and, especially, neuropathic pain and multiple sclerosis.

Neuropathic pain is pain due to nerve damage or dysfunction. Mechanisms for the initiation of this type of pain are poorly understood. In a murine model of neuropathic pain, activation of a single lysophospholipid receptor was necessary for the initiation of pain; such pain did not develop in mice that lacked the gene for the receptor. Another medically important disease, multiple sclerosis, can be approximated in animals by immunization with myelin antigens to produce experimental autoimmune encephalomyelitis. Agonists for lysophospholipid receptors (specifically, sphingosine 1-phosphate receptor agonists) abrogated the disability normally produced by experimental autoimmune encephalomyelitis, suggesting a role for this signaling pathway in the medical biology and a possible therapy for multiple sclerosis. We are expanding these themes in previously identified and new biological systems.

Normal Neural Aneuploidy

Are all neurons of the brain genetically identical, as is widely assumed, or are differences encoded within individual genomes? Using a combination of spectral karyotyping, which “paints” chromosomes to allow their unambiguous detection, and fluorescence in situ hybridization, which uses labeled point-probes to identify discrete genetic loci in interphase cells, we detected a substantial degree of genomic variation in the normal brain. During neurogenesis, approximately one third of all cells are aneuploid, produced, at least in part, by chromosome missegregation mechanisms. In postmitotic neurons, in which spectral karyotyping cannot be used because neurons are in interphase, fluorescence in situ hybridization of sex chromosomes revealed a high percentage of aneuploidy, and the total number of aneuploid cells is certainly higher if the remaining autosomes are considered (Fig. 2).

Fig. Examples of neural aneuploidy in different regions of the brain in adult mice as revealed by fluorescence in situ hybridization.

During 2004, by analyzing mice deficient in DNA surveillance or repair molecules, we detected a new influence on the generation of aneuploidy. One of these molecules, the mutated protein ATM, is the cause of the rare genetic disease ataxia-telangiectasia. Elimination of the gene for ATM or the gene for XRCC5, another molecule involved in DNA surveillance and repair, resulted in major increases in the number and severity of aneuploid neural progenitor/stem cells, indicating a positive biological link between aneuploidy and molecules involved with genome integrity. Currently, we are exploring the basic phenomenologic aspects and functional importance of neural aneuploidy during development and in disease processes.

Publications

Anliker, B., Chun, J. Cell surface receptors in lysophospholipid signaling. Semin. Cell Dev. Biol. 15:457, 2004.

Anliker, B., Chun, J. Lysophospholipid G protein-coupled receptors. J. Biol. Chem. 279:20555, 2004.

Baudhuin, L.M., Jiang, Y., Zaslavsky, A., Ishii, I., Chun, J., Xu, Y. S1P₃-mediated Akt activation and cross-talk with platelet-derived growth factor receptor (PDGFR). FASEB J. 18:341, 2004.

Chun, J. Choices, choices, choices. Nat. Neurosci. 7:323, 2004.

Girkontaite, I., Sakk, V., Wagner, M., Borggrefe, T., Tedford, K., Chun, J., Fischer, K.-D. The sphingosine-1-phosphate (S1P) lysophospholipid receptor S1P₃ regulates MAdCAM-1⁺ endothelial cells in splenic marginal sinus organization. J. Exp. Med. 200:1491, 2004.

Hama, K., Aoki, J., Fukaya, M., Kishi, Y., Sakai, T., Suzuki, R., Ohta, H., Yamori, T., Watanabe, M., Chun, J., Arai, H. Lysophosphatidic acid and autotaxin stimulate cell motility of neoplastic and non-neoplastic cells through LPA1. J. Biol. Chem. 279:17634, 2004.

Inoue, M., Rashid, M.H., Fujita, R., Contos, J.J., Chun, J., Ueda, H. Initiation of neuropathic pain requires lysophosphatidic acid receptor signaling [published correction appears in Nat. Med. 10:755, 2004]. Nat. Med. 10:712, 2004.

Ishii, I., Fukushima, N., Ye, X., Chun, J. Lysophospholipid receptors: signaling and biology. Annu. Rev. Biochem. 73:321, 2004.

Kingsbury, M.A., Rehen, S.K., Ye, X., Chun, J. Genetics and cell biology of lysophosphatidic acid receptor-mediated signaling during cortical neurogenesis. J. Cell. Biochem. 92:1004, 2004.

Levkau, B., Hermann, S., Theilmeier, G., van der Giet, M., Chun, J., Schober, O., Schäfers, M. High-density lipoprotein stimulates myocardial perfusion in vivo. Circulation 110:3355, 2004.

McConnell, M.J., Kaushal, D., Yang, A.H., Kingsbury, M.A., Rehen, S.K., Treuner, K., Helton, R., Annas, E.G., Chun, J., Barlow, C. Failed clearance of aneuploid embryonic neural progenitor cells leads to excess aneuploidy in ATM-deficient but not the Trp53-deficient adult cerebral cortex. J. Neurosci. 24:8090, 2004.

Nofer, J.-R., van der Giet, M., Tölle, M., Wolinska, I., von Wnuck-Lipinski, K., Baba, H.A., Gödecke, A., Tietge, U.J., Ishii, I., Kleuser, B., Schäfers, M., Fobker, M., Zidek, W., Assmann, G., Chun, J., Levkau, B. HDL induces NO-dependent vasorelaxation via the lysophospholipid receptor S1P₃. J. Clin. Invest. 113:569, 2004.

Rao, T.S., Lariosa-Willingham, K.D., Lin, F.-F. Yu, N., Tham, C.-S., Chun, J., Webb, M. Growth factor pre-treatment differentially regulates phosphoinositide turnover downstream of lysophospholipid receptor and metabotropic glutamate receptors in cultured rat cerebrocortical astrocytes. Int. J. Dev. Neurosci. 22:131, 2004.

Sanna, M.G., Liao, J., Jo, E., Alfonso, C., Ahn, M.Y., Peterson, M.S., Webb, B., Lefebvre, S., Chun, J., Gray, N., Rosen, H. Sphingosine 1-phosphate (S1P) receptor subtypes S1P₁ and S1P₃, respectively, regulate lymphocyte recirculation and heart rate. J. Biol. Chem. 279:13839, 2004.

Webb, M., Tham, C.-S., Lin, F.-F., Lariosa-Willingham, K., Yu, N., Hale, J., Mandala, S., Chun, J., Rao, T.S. Sphingosine 1-phosphate receptor agonists attenuate relapsing-remitting experimental autoimmune encephalitis in SJL mice. J. Neuroimmunol. 153:108, 2004.