Medical College of Georgia’s Research Institute – Dr. Robert K. Yu
For a number of years, Dr. Yu’s laboratory has engaged in research, with the generous support of the Children’s Medical Research Foundation, Inc., Chicago, for an effective and safe therapy for Sanfilippo disease. This disease is also known as mucopolysaccharidosis III (MPS III), a rare and catastrophic genetic disorder occurring in 1 out of 24,000 births. It belongs to a broader group of genetic disorders known as Lysosomal Storage Diseases. These diseases share a common feature in that a certain enzymatic defect can cause the accumulation of biological materials in the cells of the body. In MPS, these materials are collectively known as mucopolysacchrides or heparin sulfates, sugar-containing substances that are essential for the body to develop and function normally. Children afflicted with Sanfilippo Syndrome, however, are missing certain essential enzymes that break down these substances. As a result, these substances accumulate in the body, especially in the brain, causing progressive damage to tissues. A Sanfilippo child may appear normal at birth and seems to develop normally for the first year or two, but as more and more cells become damaged clinical symptoms begin to appear. These symptoms include hyperactivity, sleep disorders, loss of speech, mental retardation, dementia, and finally death. Life expectancy for a child with Sanfilippo Syndrome is between 10 to 15 years. To date, four different enzyme deficiencies have been found to cause Sanfilippo disease.
Despite the tremendous knowledge we have gained in understanding the etiology and pathogenic mechanism of the disease, development of a treatment strategy is still eluding us. A major difficulty is the presence of a barrier, known as the blood-brain barrier, that exists between brain tissues and blood circulation. The blood-brain barrier prevents therapeutic agents from entering from the blood into the nerve tissues to break down those accumulated materials inside the brain. Recently, there has been a strong interest in applying normal, healthy cells from the bone marrow or stem cells that can migrate into the nerve tissues to achieve the enzyme delivery. For this reason, Dr. Yu and his co-workers have been focusing on transplanting neural stem cells that are enriched in the missing enzyme into the affected brain in an attempt to supplement the tissues with the missing enzymes. They envision that the transplanted cells with an enriched dose of degradative enzymes can correct the lysosomal storage defects of MPS III affected brains. This technique is also known as enzyme-replacement therapy.
For this purpose, Dr. Yu has been actively engaged in studying the properties of neural stem cells in the hope to harness them for transplantation. This is particularly important as it has been shown that some neural stem cells that are engrafted into the brain can result in the formation of undesirable teratomas. Therefore, success in the evaluation and optimization of neural stem cells for the treatment of lysosomal disorders, such as Sanfilippo disease, should have tremendous impact on future research in devising an effective treatment of this disorder.
More recently, Dr. Yu and his team also realized that enzyme-replacement therapy can only achieve limited success for MPS and is not sufficiently effective for treating Sanfilippo patients. Gene transfer has the potential to treat innumerable genetic and acquired diseases. Adeno-associated virus-mediated gene therapy appears promising in correcting CNS pathology in MPS animal studies. However, potential complications may be caused by viral-based vectors in treating humans. For this reason, the use of plasmid-based vectors becomes an attractive alternative. In fact, transposon-based nonviral gene transfer is gaining momentum as a viable alternative approach for long-term therapy due to its low immunogenicity and the ability of integrating the therapeutic genes into host chromosomes. Sleeping Beauty, a reconstituted transposon, has been extensively explored for its potential use as a gene delivery system in animal models. Their recent study demonstrates that piggyBac, isolated from moth, is the most active transposon in various mammalian cells as compared to two other mammalian active transposons, Tol2 and Sleeping Beauty. This strategy has recently been thoroughly evaluated with support from CMRF (Meir et al. 2011). As compared with viral gene transfer vectors that favor transgene integration into active genes, piggyBac provides a much safer means for gene transfer because of its unbiased target site selection. Dr. Yu believes that ultimately it will be feasible to establish effective and safe methods, with little or no side effects, to treat these disorders in MPS III using a piggyBac-based gene delivery system. The ultimate goal of their research is to develop this therapeutic strategy for clinical use.
The above studies have been supported in main by CMRF and in part by a USPHS/NIH grant to RKY. The productivity of Dr. Yu’s group has been outstanding as can be seen from the following publications that have appeared in the literature during the past funding period:
Meir, Y.-J. J., Weirauch, M. T., Yang, H.-S., Chung, P-C., Yu, R. K., and Wu, S. C.-Y., Genome-wide target profiling of piggyBac and Tol2 in HEK 293: pros and cons for gene discovery and gene therapy. BMC Biotechnology 11:28, 2011, (http:/www.biomedcentral.com/1472-6750/11-28).
Nakatani, Y., Yanagisawa, M., Suzuki, Y., and Yu, R. K. Characterization of GD3 ganglioside as a novel biomarker for neural stem cells. Glycobiology 20: 78-86, 2010. PMID: 19776077; PMCID: 2782183. doi:10.1093/glycob/cwp149.
Yu, R. K., Suzuki, Y., and Yanagisawa, M. Membrane Glycolipids in Stem Cells. FEBS lett. 584: 1694-9, 2010. PMID: 19716368. doi: 10.1016/j.febslet.2009.08.026; NIHMS141765.
Yanagisawa, M., Ariga, T., and Yu, R. K. Cytotoxic effects of GM1 ganglioside and amyloid beta-peptide on mouse embryonic neural stem cells. ASN Neuro, 2: e00029, 2010. PMID: 20305711; PMCID: 2838405. doi:10,1042/AN20090063.
Suzuki, Y., Yanagisawa, M, Yagi, H., Nakatani, Y., and Yu, R. K. Involvement of β1-integrin up-regulation in basic fibroblast growth factor- and epidermal growth factor-induced proliferation of mouse neuroepithelial cells. J. Biol. Chem. 285: 18443-18451, 2010. PMID: 20371608; PMCID:2881770.
Yagi, H., Yanagisawa, M., Kato, K., and Yu, R. K. Lysosome-associated membrane protein-1 is a major SSEA-1-carrier protein in mouse neural stem cells. Glycobiology, 20: 976-981, 2010. PMID: 20360060. doi:10.1093/glycob/cwq054; PMCID: PMC2902283.
Yagi, H., Yanagisawa, M., Suzuki, Y., Nakatani, Y., Ariga, T., Kato, K., and Yu, R. K. An HNK-1 epitope-carrying tenascin-C spliced variant regulates the proliferation of mouse embryonic neural stem cells. J. Biol. Chem. 285: 37293-37301, 2010. PMID: 20855890.
Suzuki, Y., Yanagisawa, M., Ariga, T., and Yu, R. K. Histone acetylation-mediated glycosyltransferase gene regulation in mouse brain during development, J. Neurochem. 113: 351-362, 2011. doi: 10.1111/j.1471-4159.2010.07042.x.; PMID: 21214566.
Yanagisawa, M., Yoshimura, S., and Yu, R. K. Expression of GD2 and GD3 gangliosides in human embryonic neural stem cells, ASN Neuro (2011) doi:10.1042/AN20110006. PMC3072763.
