Areas of Expertise
Teaching Responsibilities: General Biology 1, Principles of Biology, Genetics, Molecular Cell Biology
Research Interests: Human genetics, Molecular and Genetic Mechnisms of Age-Related Skeletal Muscle Atrophy
B.S. (Genetics) University of California, Davis (1997)
Ph.D. (Molecular Cancer Biology) Duke University (2004)
Postdoctoral Training: University of California, Davis (Mentors: Dr. David Furlow and Dr. Sue Bodine)
My research interests are concerned with the molecular mechanisms of aging and in particular on a phenomenon called sarcopenia. Sacropenia is the gradual deterioration of skeletal muscle that accompanies the aging process and is a serious medical condition facing millions of elderly people. The sarcopenic muscle shows signs of atrophy as well as a reduced capacity to regenerate following damage. Muscle loss or atrophy occurs as the result of a number of different conditions including disuse, cachexia, inflammation, exposure to corticosteroids and aging. A number of studies aimed at identifying differentially expressed genes in atrophy and aging models have found a number of interesting genes, including the E3 Ubiquitin Ligase, MuRF1, which is expressed predominantly in skeletal muscle and is up-regulated in virtually all atrophy models. In addition to MuRF1, HDAC4, a class II Histone Deacetylase, is rapidly and significantly up-regulated only under neuromuscular damage-induced skeletal muscle atrophy. Furthermore, a targeted disruption of the MuRF1 gene in mice leads to a resistance in muscle wasting under atrophic conditions. These observations, among others, have led to the hypothesis that these genes may play a pivotal role in regulating a suite of other genes important in general skeletal muscle physiology, including the processes of sarcopenia and cellular stress handling. With this hypothesis in mind, my research is focused on understanding the molecular and genetic controls of longevity and the role that cellular stress may play in aging. In particular, I am interested in determining if an “aging signature” of skeletal muscle may exist and how this process may progress. Several projects will be undertaken in the lab, including: 1) identifying and analyzing genes that are differentially expressed in young and old muscle, 2) determining how these differently expressed genes may be regulated and if cellular stresses play a role in these changes, and 3) studying the epigenetic events (such as chromatin remodeling and DNA methylation) that may result from cellular stresses and ultimately contribute to long-term and irreversible changes in the heritable material. My lab will be using the mouse as a model organism, as well as cell culture and an array of molecular biological techniques to address the topics mentioned above and outlined below.
Project 1: Gene expression analysis of skeletal muscle from aged animals.
This project will involve performing a microarray analysis of aged skeletal muscle tissue. We will collect tissues from animals and perform an array comparing gene expression profiles in 6, 12, 18, and 24 month old mice. The hope is that we will identify an aging specific signature of gene expression in older animals compared to younger animals. Genes that show a differential expression profile will be further analyzed using cell culture and well established gene expression techniques, such as transfections and reporter assays. A long-term goal of this project will be to study animals with targeted disruption of the most promising gene(s) identified from the array that also show potential to be important aging effectors.
Project 2: Analysis of the role of cellular stresses, including Reactive Oxygen Species (ROS), in aged tissue using skeletal muscle as a model organ.
In addition to gene expression analysis of aged skeletal muscle tissue, the lab will also undertake a project to analyze the more specific role of ROS and other cellular stresses in the aging process. Preliminary evidence, from microarray data generated from MuRF1 null and wild-type mice following denervation, suggests that loss of muscle innervation leads to changes in expression of a collection of genes that play an important role in regulating ROS levels in the cell. Based on these observations, we will conduct research into the role of ROS in the aging process and determine if environmental and heritable differences may impact this role. It is known that as muscle ages, it shows a reduction in the number of neuromuscular junctions resulting in a decrease in innervation of the muscle. Based on preliminary results from the microarray mentioned above, it is reasonable to hypothesize that a reduction in innervation might lead to an increase in ROS, resulting in an increase in cellular stress and ultimately macromolecular, cellular and tissue damage. We will strive to employee a combinatorial approach to studying ROS by using biochemical techniques, tissue culture and animal models. In tissue culture, ROS stress can be mimicked by addition of hydrogen peroxide to cells, which will then be analyzed by determining transcriptional (via qPCR or Northern Blot analysis) and translational (via Western Blot analysis) responses of known ROS regulated genes. Identified transcriptional changes in expression of ROS responsive genes will then be further analyzed by use of reporter gene techniques in cell culture. A more long range goal of this research will be to use the SOD1 null mice, which have increased oxidative stress, and monitor both gene expression and epigenetic events induced by ROS as the animals age. This would be done by performing microarray and ChIP-CHIP or ChIP-Seq techniques to analyze changes in gene expression, DNA methylation and/or histone acetylation in SOD1 null mice compared to wild type, age-matched litter mates.
Project 3: Analysis of chromatin remodeling in aged skeletal muscle tissue.
This project will focus on the global epigenetic changes that appear to occur naturally in aged individuals. In particular, the fact that HDAC4, a class II histone deacetylase, shows increased expression in skeletal muscle of aged rodents and humans suggests that remodeling of the chromatin structure might be one important factor that results in loss of plasticity of this tissue in older individuals. Furthermore, previous studies have shown that HDAC4 expression increases significantly during denervation and is accompanied by a rapid translocation to the nucleus. In light of these findings, it is not unreasonable to speculate that in aged muscle, in which innervation is reduced and HDAC4 levels are increased, HDAC4 may play a role in global chromatin remodeling and alterations in gene expression. Therefore, I am particularly interested in identifying regulatory regions of genes that are either bound by HDAC4 and/or have undergone significant changes in histone acetylation in aged muscle when compared to tissue from younger animals. This work will again entail the use of several advanced molecular techniques including ChIP-CHIP or ChIP-Seq analysis of skeletal muscle tissue in hopes of identifying global changes in DNA that occur during the aging process. This powerful and relatively new technique would allow us to analyze samples from aged rodents and potentially identify regulatory regions that might be important in the progression of aging. A long term objective of this project will be to eventually analyze identified regions of the genome using cell culture, advanced molecular techniques and animal models in hopes of elucidating the importance of these regions in the aging process.
Publications & Presentations
Waddell, D.S., Baehr, L.M., van den Brandt, J., Johnsen, S.A., Reichardt, H.M., Furlow, J.D. and Bodine, S.C. The Glucocorticoid Receptor and FoxO1 Synergistically Activate the Skeletal Muscle Atrophy Associated MuRF1 Gene. Am J Physiol Endocrinol Metab. 295(4) 2008: 785-797.
Guo, X., Waddell, D.S.*, Wang, W., Liberati, N.T., Yong, S., Liu, X. and Wang, X-F. Ligand-dependent ubiquitination of Smad3 is regulated by casein kinase 1 gamma 2, an inhibitor of TGF-b signaling.Oncogene 27(58) 2008: 7235-47. *Co-First Author.
Guo, X., Ramirez, A., Waddell, D.S., Liu, X., and Wang, X-F. Axin and GSK3-β control Smad3 protein stability and modulate TGF-β signaling. Genes and Development 22(1) 2008: 106-120.
Cohen, T.J., Waddell, D.S., Barrientos, T., Lu, Z., Feng, G., Cox, G.A., Bodine, S.C. and Yao, T-P. The Histone Deacetylase HDAC4 Connects Neural Activity to Muscle Transcriptional Reprogramming. J. Biol. Chem. 282(46) 2007: 33752-33759.
Weidner, W.J., Waddell, D.S. and Furlow, J.D. Measurement of the filtration coefficient (Kfc) in the lung of Gallus domesticus and the effects of increased microvascular permeability. J. Comp. Physiol. [B]. 176(6) 2006: 567-74.
Waddell, D.S., Liberati, N.T., Guo, X., Frederick, J.P. and Wang, X-F. A Functional Role for Casein Kinase Iε in the TGF-β Signaling Pathway. J. Biol. Chem. 279(28) 2004: 29236-29246.
Frederick, J.P., Liberati, N.T., Waddell, D.S., Shi, Y. and Wang, X-F. TGF-β Mediated Transcriptional Repression of c-myc is Dependent on Direct Binding of Smad3 to a Novel Repressive Smad Binding Element. Mol. Cell. Biol. 24(6) 2004: 2546-59.
Shen, X., Li, J., Hu, P. P-C., Waddell, D.S., Zhang, J. and Wang, X-F. The Activity of Guanine Exchange Factor Net1 is Essential for TGF-b Mediated Stress Fiber Formation. J. Biol. Chem. 276(18) 2001: 15362-15368.
Weidner, W.J., Waddell, D.S. and Sillman, A.J. Low Levels of Cadmium Chloride Alter the Immunoprecipitation of Corneal Cadherin-Complex Proteins. Archives of Toxicology. Arch. Toxicol. 74(10) 2000: 578-581.