April 27, 2007

Aliquots — Research highlights from VUMC laboratories

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From stem cells to bladder cells

Harnessing the promise of embryonic stem cells for regenerative therapies will require a full understanding of how these cells “mature” into functional tissues. A report in the April 15 issue of Developmental Biology by Siam Oottamasathien, M.D., and colleagues describes a model of bladder development from stem cells. The investigators combined mouse embryonic stem cells with a layer of rat embryonic bladder mesenchyme and transplanted the combo under the kidney capsule in nude mice. The mouse stem cells produced “endodermal” cells and then mature bladder cell types and structures.

The model is the first to capture protein expression patterns at early times in bladder development, and it opens avenues for exploring the molecular events that give rise to bladder-specific stem cells and then to mature bladder cells. The characterization of these events is key to using stem cells to regenerate and restore bladder tissue in disease states.

— Leigh MacMillan

Light receptor regulation in sight

Rod cells in the eye are chock full of rhodopsin, the receptor for light, making them a preferred system for studying how receptors like rhodopsin work. Rhodopsin is a G protein-coupled receptor (GPCR), one of a large family of signaling proteins that are targets for about half of all pharmaceuticals.

Proteins called arrestins bind to GPCRs to regulate their signaling. There has been some controversy about how many arrestins bind — one to each receptor or one to a pair of receptors? Vsevolod Gurevich, Ph.D., and colleagues studied the interaction of rhodopsin and arrestin in vivo, by genetically manipulating their expression levels in mice, and in vitro, by combining purified proteins. They report in the Proceedings of the National Academy of Sciences, that each rhodopsin molecule binds its own arrestin. The findings have implications for how arrestin regulates GPCRs, including their potential to interact with molecules mediating a second round of receptor signaling.

— Leigh MacMillan

HIV drug-resistance mutations

The immunosuppressive drug cyclosporine A and its nonimmunosuppressive analogs seem counterintuitive adjuncts to antiviral medications for combating HIV infection. These drugs inhibit HIV replication by interfering with the interaction between HIV's capsid protein and the host cell protein, cyclophilin A — an interaction that normally enhances viral replication. However, two mutations in the cyclophilin-binding loop of the capsid protein confer resistance to — and, in some cases, a dependence on — the drug.

In the April issue of the Journal of Virology, Ruifeng Yang and Christopher Aiken, Ph.D., report that another capsid protein mutation outside of the cyclophilin-binding loop also reduces HIV infectivity in vitro and renders HIV dependent on cyclosporine A. An additional mutation in another part of the viral capsid protein counteracted this effect. The results suggest that mutations outside the capsid protein's cyclophilin-binding loop modulate viral resistance to and dependence on cyclosporine, a finding that may aid in the understanding of HIV resistance to cyclosporine in humans.

— Melissa Marino

Rapid bacteria ID method

Blood infections can quickly become life threatening. Traditional methods for identifying the causative organism and antibiotic susceptibility can take 24-72 hours, which can delay appropriate treatment.

Yi-Wei Tang, M.D., Ph.D., and colleagues at Vanderbilt, Genaco Biomedical Products and the CDC developed and validated a new system, called StaphPlex, to rapidly identify and test antibiotic susceptibility of Gram-positive cocci in clusters (GPCC), which are mainly staphylococci, from blood cultures. The procedure, based on molecular methods, can be completed within five hours from the initial observation of GPCC under the microscope. While the system had a high overall accuracy in identifying the organism, the error rate in determining antibiotic susceptibility proved too high for clinical use. However, the system was effective at identifying highly virulent strains of methicillin-resistant Staphylococcus aureus (MRSA) — a major concern in health care settings and increasingly in the community. The results, reported online in the Journal of Clinical Microbiology, suggest that with refinement of susceptibility testing, such a rapid identification method could potentially improve patient care and prevent inappropriate antibiotic use.

— Melissa Marino

Past Aliquots

June 22, 2012
June 8, 2012
May 11, 2012
April 27, 2012
April 13, 2012
March 30, 2012
March 16, 2012