James P. Fabisiak - Research
Of primary current interest is the role of oxidative stress, not only as a mediator of cellular damage, but also as a physiologic signaling mechanism that can dictate numerous cellular responses.
For example, oxidative events have been implicated in executing the final common pathway of apoptosis (programmed cell death). Cell death in numerous diseases such as stroke, Alzheimer's disease, atherosclerosis, and exposure to various environmental toxins is characterized by apoptosis. Therefore, agents that specifically inhibit apoptosis may be of therapeutic use in these degenerative diseases. On the other hand, apoptosis plays an important physiological role in embryologic development, tissue repair, immune surveillance, and removal of potentially cancerous cells. Therefore, inappropriate inhibition of cell death may by detrimental to human health. In collaboration with Dr. Valerian Kagan's laboratory, we have demonstrated that selective oxidation of one particular membrane phospholipid, phosphatidylserine (PS) is an early and universal hallmark of apoptosis. Since the translocation of this same phospholipid to the external surface of the plasma membrane serves to mark apoptotic cells for efficient recognition and elimination by phagocytic macrophages it is likely that specific lipid peroxidation events play a role in the regulation of this process. In conjunction with Dr. Kagan's laboratory, we are currently pursuing the functional significance of PS oxidation as it may provide an important locus for targeting agents to modify apoptotic signaling and clearance processes.
In addition, my laboratory is also conducting a project funded by the U.S.E.P.A. to study the roles metallothionein (MT) in mediating transition metal-dependent oxidative stress upon exposure to metal/metal and metal/nitric oxide mixtures. Metallothioneins (MTs) are small molecular weight cysteine-rich peptides that confer resistance to metal toxicity and oxidative stress. However, we hypothesize that MTs can exert a bifunctional role with protection or enhancement of oxidative stress depending on the composition of the cellular milieu. For example, displacement of MT-bound Cu by other metal ions or nitrosative/oxidative modification of the metal-binding thiols may promote the release of redox-active Cu within cells and potentiate Cu toxicity. Using cell-free model systems we have shown that optimal binding of Cu to MT (12 moles Cu/1 mole MT) can be achieved under reducing conditions, but a significant portion of this Cu was released and was capable of redox-cycling under oxidizing/nitrosating conditions. Similarly, exposure of MT-overexpressing Cu-challenged cells with an NO-donor gave rise to substantial apoptosis with greater cytotoxicity than that observed in cells without MT challenged with the same concentration of Cu-alone. Thus, it appears that MT can act as a "double-edged sword" that protects cells from Cu toxicity under basal conditions on one hand, but provides a large intracellular reservoir of releasable redox-active Cu under conditions of oxidative/nitrosative stress. We also speculate that this redox-regulation of metal binding and release by MT can function in the safe and coordinated physiological delivery of Cu to specific proteins that require this metal for activity, such as Cu/Zn-superoxide dismutase.
In the future, we wish to combine these recent concepts in oxidative stress and signaling with our background in pulmonary cell biology and environmental diseases of the lung. Atmospheric particulate matter (PM) are chemically and physically diverse components of air pollution whose adverse health effects are gaining increasing interest. Undoubtedly many environmental and genetic factors converge to ultimately determine the degree to which PM ultimately cause or aggravate lung disease. We are hypothesizing that numerous latent/subclinical “pathogens” or commensal microorganisms often present within the lung can act as potent modulators of environmental disease. Using deliberate infection of human lung cells as an in vitro model system, my lab is beginning to explore the synergistic interactions between microbial infection and chemical stress like PM exposure in regulating inflammatory response signal transduction pathways at the cellular and molecular level.