Grants

5R01AI040384 - Regulation of HIV-Mediated CD4 T Cell Apoptosis

Identification of the mechanism(s) through which HIV leads to depletion of both CD4 and CD8 T cells has been elusive. A multitude of mechanisms have been postulated, generally falling into two broad categories; direct killing of the HIV infected cell or indirect death of HIV of uninfected T cells by HIV dependent mechanisms. The envelope of HIV(env) can mediate death of both infected and uninfected T cells. The discovery of chemokine receptors as HIV co-receptors has provided the opportunity to study their potential role in mediating env-triggered T cell death. A number of preliminary data have been obtained indicating that R5 and X4HIV, and their corresponding receptors exert T cell death through distinct molecular mechanisms.

R5env leads to a Fas- and caspase-dependent death of uninfected CD4 T cells. On the contrary, X4env leads to a Fas- and caspase-independent death of not only uninfected CD4 but also CD8 T cells, as well as HIV infected CD4 T cells. This has prompted us to hypothesize that env can mediate death of both uninfected and HIV infected T cells (including CD8 T cells) and that the molecular mechanism mediating such death is ultimately dependent on the type of chemokine receptor engaged by env. To address this hypothesis we propose the following three specific aims:

1. Study the signal transduction pathways whereby X4env leads to the death of uninfected CD4 and CD8 T cells via CXCR4.
2. Determine how the R5env interaction with CD4 and CCR- leads to Fas dependent apoptosis.
3. Document the necessary role of env in mediating killing of HIV infected T cells through its interaction with the corresponding chemokine receptor and translate such findings to lymphoid tissue from HIV infected patients.

Identification of the molecular mechanisms and second messengers whereby CCR- and CXCR4 mediate T cell death will help in determining how HIV infection ultimately ravages the immune system. The implications derived from chemokine receptor mediated death can also be expanded to other non CD4 T cells known to be targeted during the course of HIV infection and to express chemokine receptors such as neurons, epithelial cells, and NK cells.

1R01AI062261- Procaspase 8 Activation by HIV Protease

It remains controversial as to how CD4+ T cells directly infected with HIV die following infection. Numerous mechanisms have been proposed to account for infected cell killing, however none of the proposed mechanisms are universally accepted. It has long been recognized that one HIV protein, HIV protease, is intrinsically cytotoxic as its expression causes the death of bacteria, yeast, and mammalian cells, however it remains unclear how HIV protease kills these cells. Experimental data now demonstrate that HIV protease cleaves host cell proteins in addition to viral proteins.

Our laboratory has recently defined one mechanism by which HIV protease can kill cells; specifically HIV protease can cleave the apoptosis initiating protein, procaspase 8, to result in its activation. Thereafter, a traditional apoptosis cascade is initiated, ultimately resulting in the structural, nuclear, and morphologic changes associated with apoptosis. While we have demonstrated that this mechanism of HIV protease mediated killing can occur, we have yet to determine whether or not this mechanism does occur, particularly in vivo. The focus of the current proposal is to define the relevance of this form of cell killing both in infections, which occur in the test tube, as well as in patients.

The clinical significance of this research may be reflected in recent clinical observations, suggesting an altered diseased course of patients who have infections with HIV that contain mutations within the HIV protease gene as compared to those that do not. We will explore the potential impact of these mutations by assessing the differential impact of wild type HIV protease versus mutant protease on procaspase 8 activation and cell killing.

Burroughs Wellcome - “Novel Antiapoptotic Therapies for Sepsis”

Sepsis is the leading cause of death in critically ill patients in the United States. It develops in 750,000 Americans annually, and more than 210,000 of them die. Despite improvements in supportive treatment, mortality has changed very little, and until recently, no sepsis-specific treatments were available. Current treatments for sepsis are suboptimal. However, sepsis is associated with increased lymphoid and other target cell apoptosis, which raises the possibility that therapies designed to reduce apoptosis may improve survival during sepsis. Our proposed studies will evaluate the effect of PI on animal models of sepsis, and SIRS induced by non-infectious stimuli (e.g., pancreatitis) and we will conduct a pilot study in severe sepsis.