|
YI-PING LI, PHD
Senior Member of the Staff (equivalent to Tenured Professor)
Department of Cytokine Biology
IABMR
email: ypli at forsyth.org
Zhejiang University, China, B.S., 1979, Chemistry
Shanghai Institute of Biochemistry, The Academy of Sciences of China, Ph.D., 1988, Molecular Genetics
Craniofacial abnormalities constitutes a major porportion of human birth defects. There are over one hundred human genetic syndromes known to result in craniofacial abnormalities. Although hundreds of thousands of children are affected each year, the genes responsible for these inherited diseases remain largely unknown. Osteoporosis is the most common human bone disease, leading to hip and vertebral fractures. Research in Dr. Li's laboratory is directed toward understanding the molecular basis of craniofacial development, as well as mechanisms of bone formation and bone resorption.
Bone formation and bone resorption are physiologically controlled by the activities of osteoblasts and osteoclasts. Imbalances in these activities can arise from a variety of hormonal or inflammatory perturbations, resulting in skeletal abnormalities characterized by decreased bone mass, as in osteoporosis, or increased bone mass, in osteopetrosis. Increased osteoclast activity is seen in many osteopenic disorders, including postmenopausal osteoporosis, Paget's disease, bone metastases, periodontitis, and rheumatoid arthritis. Major objectives of research in the Li laboratory are to elucidate the molecular mechanisms that control bone formation and bone resorption. We are also studying mechanisms of head formation during embryonic development and identifying genes that are important for craniofacial development. Results of our work will aid in developing therapeutic interventions in diseases involving craniofacial abnormalities and bone disorders.
Molecular Basis of Bone Formation
We are investigating genes that control the differentiation of mesenchymal stem cells to osteoblasts. Using the bone-specific osteocalcin gene as a model, we have studied the control of osteoblast differentiation by cytokines and transcription factors. Using subtractive differential screening, we recently identified several novel genes that are specifically expressed in osteoblasts. Sequence analysis of one novel clone identified a basic helix-loop-helix (bHLH) DNA binding domain, indicating that it may be a novel transcription factor, which we have designated osteoblast transcription factor-2 (OBTF2). We confirmed its role as a transcription factor by cotransfection of an OBTF2 cDNA expression construct and an osteocalcin promoter-CAT reporter construct into the osteoblast cell line ROS 17/2.8 and the nonosteoblastic cell line C3H10T1/2. Constitutive expression of OBTF2 in chicken embryos enhances bone. We are characterizing the functions of these novel genes in vitro by RNAi approach and in vivo by mouse gene knockout approach in our laboratory.
Mechanisms of Bone Resorption
In collaboration with Dr. Stashenko's laboratory, we cloned and characterized the genes encoding ATP6i and cathepsin K, through differential screening of a human osteoclastoma cDNA library. Using a gene knockout approach, we have studied in vivo functions of these two genes. We demonstrated that ATP6i is an osteoclast-specific subunit of a proton pump, while cathepsin K is a key osteoclast-specific cysteine protease involved in degradation of bone matrix proteins. Recent reports indicate that mutations of ATP6i and cathepsin K are responsible for some forms of osteopetrosis in humans. We have established an osteoclast precursor cell line, MOCP-5, to facilitate the study of osteoclast gene transcriptional regulation and differentiation, and have characterized the mouse cathepsin K gene promoter and expression in MOPC-5 cells. Based on its high and specific expression in osteoclasts and the physiological significance of cathepsin K, we chose cathepsin K as the gene model and MOCP-5 as the cell model to characterize how the cathepsin K gene is regulated during osteoclast differentiation. The critical cis-regulatory elements (CCREs) of the mouse cathepsin K gene are being mapped by mutagenesis of the promoter, and the CCRE-binding protein(s) are being characterized. We characterize RANKL-induced signaling proteins by Microarray genome-wide screening. Regulator of G-Signaling Protein 10 (RGS10) was found to be prominently expressed in RAN KL-induced mouse osteoclast-like cells (OLCs) and human osteoclasts. We generated RGS10 knockout mice. The mutant mice exhibit severe osteopetrosis owing to impaired osteoclast differentiation. Ectopic expression of RGS10 dramatically increased the sensitivity of osteoclast differentiation to RANKL signaling. Our results thus, for the first time, reveal the role of RGS10 in vivo as a critical regulator in the RANKL evoking RAN KL- PLC7-{Ca2+] i oscillation-N FAT2 signaling pathway for terminal differentiation of osteoclasts.
Transcriptional Regulation in Craniofacial Development
Another area of research addresses factors controlling craniofacial development. To understand the genetic mechanisms involved in regulation, we have cloned genes that are specifically expressed at the anterior ends of developing mouse embryos. We are characterizing the head formation functions of those genes that encode putative novel transcription factors in chicken and mouse models. We are also studying mouse mutants with developmental defects that resemble the craniofacial abnormalities seen in a variety of human genetic disorders. Through misexpression, dominant negative inactivation, and targeted mutation, we are investigating the actions of a network of transcription factors in controlling craniofacial development in both the mouse and chicken. We showed that targeted disruption of the gene encoding a cellular nucleic-acid binding protein (CNBP) in mice results in severe craniofacial defects. The defects include lack of anterior head structures, such as the mandible and eyes, and are reminiscent of the effects of otocephalic mutations reported in humans. We are characterizing the origin of these abnormalities in CNBP mutant embryos to facilitate dissection of the mechanisms governing craniofacial development. We are defining the role of CNBP in forebrain development using a tissue-specific targeted disruption (gene conditional knock out) approach and the role of CNBP in craniofacial development using a neural crest cell (NCC)-specific targeted disruption approach.
Fields of Interest and Description of Dr. Li’s Laboratory
Major research objectives in the Li laboratory are divided in six well-defined goals:
1. To reveal the mechanisms underlying the transcription factors that regulates osteoclast lineage commitment, differentiation, and function. We have determined the essential role of RUNX1 in dose dependent osteoclast lineage commitment, differentiation, activation, and function.
2. To discover the role of subunits of the osteoclast proton pump (SOPP) in osteoclast functions (e.g., osteoclast-mediated extracellular acidification, membrane trafficking, exocytosis) and to elucidate their potential role in developing a means to cure or alleviate human osteolytic diseases. Previously, we showed that inactivation of subunit a3 (also known as ATP6V0A3 or TCIRG1) leads to osteopetrosis in mice because of nonfunctional osteoclasts that are incapable of acidifying the extracellular resorption lacuna. Knockdown of subunits d2 (ATP6V0D2), C1 (ATP6V1C1), and Ac45 (ATP6AP1) resulted in defects in osteoclast function. We have characterized the unique isoform of the proton pump responsible for osteoclastic bone resorption. We also found certain subunits have more functions than others (Biochemistry J . 2009; J. Bone Miner. Res. 2009)
3. To understand signal transduction and the ways in which it controls osteoclast differentiation and function. We characterized the response of osteoclast signaling pathways to RANKL and revealed the role of RGS10 as a critical regulator in the RANKL-evoked RGS10/calmodulin-PLCγ-[Ca2+]i oscillation-NFATc1 signaling pathway for osteoclast differentiation. This RGS10 work was published (Genes & Development, 2007; JCS. 2007).
4. To elucidate the mechanism of bone formation and develop a means to cure or alleviate bone abnormalities, such as osteoporosis. Attractive targets are osteoblast cells, which increase bone formation. Our previous work shows that cellular nucleic acid binding protein (CNBP) is expressed in all stages of osteoblast lineage. Furthermore, we have demonstrated that CNBP is located in both the nucleus and the cytoplasm, which indicates that it may be a dual regulator of transcription and translation.
5. To identify how cellular nucleic acid binding protein (CNBP) and other transcription factors regulate craniofacial development and disease and to expand our understanding of the biological and molecular basis of craniofacial morphogenesis. We have characterized the functions of CNBP in head formation in chicken and mouse models through gene knockout misexpression and tissue-specific targeted disruption approaches (Development, 2003;Developmental Biology, 2006).
6. To develop novel means of tissue regeneration treatment that will simultaneously prevent tissue damage and bone loss by reducing the inflammation and bone resorption caused by oral infectious and inflammatory diseases, such as periodontal and endodontic diseases.
7. To define the role of Znf9 in myotonic dystrophy type 2 (DM2) and muscle development. We characterized Znf9 mice and found that their phenotype reflects many of the features in myotonic dystrophy. Znf9 is highly expressed in skeletal and heart muscle. Our data demonstrated that Znf9 haploinsufficiency might contribute to the myotonic dystrophy phenotype in Znf9 mice (J. Molecular Biology, 2007).
Selected Publications
Soltanoff CS, Chen W, Yang S, Li Y-P. 2009. The signaling networks that control the lineage commitment and differentiation of bone cells. Crit. Rev. Eukaryot. Gene Expr. 19:1-46
Wu H, Xu G, Li YP. 2009. Atp6vOd2 is an essential component of the osteoclast-specific proton pump that mediates extracellular acidification in bone resorption. J. Bone Miner. Res.
Feng S, Deng, L, Chen W, Shao J, Xu G Li YP. 2009. Atp6v1c1 is an essential component of the osteoclast proton pump and in F-actin ring formation in osteoclasts. Biochem J. 417(1):195-203.
Tu Q, Zhang J, Fix A, Brewer E, Li YP, Zhang ZY, Chen J. 2009. Targeted overexpression of BSP in osteociasts promotes bone metastasis of breast cance cells. J Cell Physiol. 218(1):135-45.
Yang, S., Chen, W., Stashenko, P. and Li, Y-P (2007) RGS 10A is an essential factor in RANKL evoking signaling of osteoclast differentiation. Journal of Cell Science. 120:3362-71
Yang S, Li Y-P. 2007. RGS10 null mutation impairs osteoclast differentiation resulting from the loss of [Ca2+]i oscillation regulation. Genes Dev. 21(14):1803-16.
Chen W, Wang Y, Abe Y, Cheney L, Udd B, Li Y-P. 2007. Haploinsufficiency for Znf9 in Znf9 mice is associated with multiorgan abnormalities resembling myotonic dystrophy. J. Mol. Biol. 368:8-17.
Chen W, Yang S, Abe Y, Li M, Wang Y, Shao J, Li E, Li YP. 2007. Novel pycnodysostosis mouse model uncovers cathepsin K function as a potential regulator of osteoclast apoptosis and senescence. Hum. Mol. Genet. 16:410-423.
Yang S, Li YP. 2007. RGS12 is essential for RANKL: evoked signaling for terminal differentiation of osteo-clasts in vitro. J. Bone Miner. Res. 22:45-54.
Abe Y, Chen W, Huang W, Nishino M, Li YP. 2006. CNBP regulates forebrain formation at organogenesis stage in chick embryos. Dev. Biol. 295:116-127., 2006
Kamolmatyakul S, Chen W, Yang S, Abe Y, Moroi R, Ashique AM, Li Y-P. 2004. IL-1á stimulates Cathep-sin K expression in osteoclasts via the tyrosine kinase-NF-kB pathway. J. Dent. Res. 83:791-796.
Chen W, Liang Y, Deng W, Shimizu K, Ashique AM, Li E, Li Y-P. 2003. The zinc-finger protein CNBP is required for forebrain development. Development 130:1367-1379.
Shimizu K, Chen W, Liang Y, Deng W, Li Y-P. 2003. Molecular cloning, developmental expression, promoter analysis and functional characterization of the mouse CNBP gene. Gene. 307:51-62.
Kamolmatyakul S, Chen W, Li Y-P. 2001. Interferon-g down-regulates gene expression of Cathepsin K osteoclasts and inhibits osteoclast formation. J. Dent Res. 80:351-355.
Deng W, Stashenko P, Chen W, Liang Y, Shimizu K, Li Y-P. 2001. Characterization of mouse Atp6i gene, the gene promoter and the gene expression. J. Bone Miner. Res. 16:1136-1146.
Li Y-P, Chen W. 1999. Characterization of Cathepsin K gene structure, promoter and expression. J. Bone Miner. Res. 14:487-499.
Li Y-P, Chen W, Liang Y, Li E, Stashenko P. 1999. Atp6i-deficient mice exhibit severe osteopetrosis due to loss of osteoclast-mediated extracellular acidification. Nat. Genet. 23:447-451.
Chen W, Li Y-P. 1998. Generation of osteoclastogenic cell lines immortalized with SV-40 large T antigen. J. Bone Miner. Res. 13:1112-1123.
Li Y-P, Chen W, Stashenko P. 1996. Molecular cloning and characterization of a putative novel human osteoclast-specific 116-KDa vacuolar proton pump subunit. Biochem. Biophys. Res. Comm. 218:813-821.
Li Y-P, Alexander M, Yelick P, Wucherpfennig A, Chen W, Stashenko P. 1995. Cloning and complete cDNA sequence of a novel human Cathepsin expressed in osteoclast. J. Bone Miner. Res. 10:1197-1202.
Li Y-P, Chen W, Stashenko P. 1995. Characterization of a silencer element in the first exon of the human osteocalcin gene. Nucleic Acids Res. 23:5064-5072.
Wucherpfennig AL, Li Y-P, Stetler-Stevenson WG, Rosenberg AE, Stashenko P. 1994. Expression of 92- kDa type IV collagenase/gelatinase B in human osteoclasts. J. Bone Miner. Res. 9:549-556.
Li Y-P, Stashenko P. 1993. Characterization of a tumor necrosis factor-responsive element which down-regulates human osteocalcin. Mol. Biol. Cell. 13:3714.
Li Y-P, Stashenko P. 1992. TNFa and IL-6, but not IL-1, down-regulate the osteocalcin promoter. J. Immunol. 148:788-794.
Feng Z, Li Y-P, Chen C. 1989. Analysis of the 5'-flanking region of rat inhibin a- and b-subunit genes reveals two different regulation mechanisms. Mol. Endocrinol. (USA) 3:1914-1925.
Staff
Assistant Reseach Investigator
Wei Chen, M.D.
Staff Associate
Wei Tang, Ph.D.
Research Assistant
Christie Taylor
|