Z. Dave Sharp, PhD
|1968||BBA||Accounting||University of Arkansas
Monticello , AR
|1975||BS||Biology||University of Arkansas
Little Rock , AR
|1981||PhD||Cell Biology and Human Anatomy||University of Arkansas for Medical Sciences
Little Rock , AR
|Postdoctoral Fellowship||Biology and Biochemistry||Rice University
Houston , TX
The major research interest of my laboratory is cancer and aging and the role played by the mechanistic target of rapamycin (mTOR) signaling system.
Our published work on the long-lived (in the vivarium) hypopituitary Ames dwarf mouse showed an inhibition of the mTOR complex 1 (mTORC1) effectors such as 4E-BP1 and S6K1 in liver and skeletal muscle. This is consistent with numerous lines of evidence in yeast, worms and flies that the TOR signaling system has an evolutionarily conserved role in the regulation of longevity.
These observations and those showing that diet restriction (DR) extended life and health span, prompted me to propose that chronic treatment of mice with an mTORC1 inhibitor, such as rapamycin, would mimic growth factor and/or diet restriction and would also extend life- and health-span in mice. This proposal was rigorously tested in three separate geographically located vivaria by the NIA funded Intervention Testing Program (ITP), whose site directors are Drs. Randy Strong at the UTHCSA, Rich Miller at the University of Michigan and David Harrison, Jackson Labs.
The trial was made possible by the development of a novel microencapsulated enterically-released formulation of rapamycin (called eRapa) by Dr. Randy Strong, which stabilized it in food and delivered rapamycin to the lower GI tract. The results of the first trial showed that mice starting encapsulated rapamycin when they are twenty months of age (equivalent to 60 in human years) live an additional 28% (males) to 38% (females) time. Importantly, and like the gold standard invention calorie restriction, both median and maximum life span was observed. These results were published in Nature.
The second rapamycin trial by the ITP was completed and published in Journal of Gerontology Biological Sciences, which showed that mice starting eRapa at nine months of age also showed similar extensions of median and maximum life spans for both males and females. These results also showed that chronic rapamycin treatment delayed the age-related decline in mobility of mice, and a reduction of cancer, which was the first strong indication of an improved health span.
Current efforts in our lab are directed toward determining if chronic rapamycin will prevent, delay, and/or reduce the severity of one of the most feared diseases of aging – cancer. Toward this end and in collaboration with Drs. Livi, Hasty and Christy, we are testing three mouse models. The first is mice deficient for the tumor suppressor p53, which is defective in most human cancers. DR was previously shown to extend the life span of this short-lived mouse (due to numerous types of cancers), and the prediction is that chronic rapamycin treatment will mimic CR. In a paper being prepared for publication, we show that the ability of chronic rapamycin treatment to extend life and health span is dependent on the number of good copies of p53 gene present in the mouse.
The second model is mice with tumors deficient for another famous suppressor of tumorigenesis, the retinoblastoma protein (pRb1). We published data showing that DR is minimally effective in delaying the development or growth of spontaneous neuroendocrine tumors (pituitary and thyroid) in Rb1+/- mice. Based on this, we predicted that eRapa treatment starting at 8-9 weeks of age would also be minimally effective in extending longevity and preventing tumor development and growth. We showed the exact opposite – eRapa is very effective in extending the life span of both male and female due to a reduction of thyroid tumors and a delay in the development and slower growth of pituitary tumors.
The third is a mouse model of intestinal adenomas called ApcMin/+. Since our formulation of rapamycin is delivered to the gut, we predicted it would be efficacious in this model. In a paper ready for submission, we show that eRapa starting at 8 weeks of age extends their life span to almost that of wild type mice (mid dose) or exceeds that of wild type (high dose).
In summary, eRapa is the first anticancer prophylactic drug, which could have a large impact on the amelioration of age-associated cancer and, at the same tiem, extend the healthy portion of our lives. The mTOR system like aging is woven into the very fabric of life. It is no wonder that its regulation has a profound effect on the length and quality of life. We are just beginning to understand this very deep connection and the exciting possibilities at hand.
High throughput/content screening technology – Using automated fluorescent microscopy (aka image cytometery), we are developing cell based assays that can be adapted for large scale screens using small interfering RNAs (siRNAs), or chemical libraries. Cell based assays are more amenable in academic-based laboratories for purposes of discovering new targets and drugs. An example is our prolactin array-containing cell line below, which has been used to identify estrogen-like compounds in a chemical library. Our goal is development of a center to promote the discovery of new biological targets and drugs by providing assistance and expertise to UTHSC investigators.
Pituitary-specific gene transcription – This involves the discovery and study of a pituitary-specific transcription factor called PUF-I, which later became known as Pit-1. Our approaches include cell-free transcription and more recently cell biological assays.
Single cell transcription factor dynamics – I designed a chromosomally integrated array of DNA-binding sites using the prolactin enhancer/promoter as the prototype. In collaboration with Michael A. Mancini’s laboratory at Baylor College of Medicine, we have shown that the array binds Pit-1 and estrogen receptor and is visible as a bright focus in living and fixed cells that express these transcription factor translationally fused to the green fluorescent protein. The array is transcriptionally fused to a gene encoding dsRed-SKL protein, which reports estrogen and anti-estrogen responsiveness as cytoplasmic (peroxisome) red fluorescent foci. The array also provides multiplex data regarding large-scale changes in chromatin (expansion with agonist, and contraction with antagonist), co-localization with RNA polymerase and co-activators/repressors, and dynamics of Pit-1 and ER? exchange at array chromatin. The cell line will be useful in providing data in tests of stochastic models of mammalian transcription factor function.
mTOR inhibition as anti-aging – Mechanistic target of rapamycin (mTOR) inhibition by our novel formulation, encapsulated (enteric) rapamycin (eRapa) as an effective intervention to treat aging and associated diseases.