Douglas Craig Hooper

Research Interests

The role of peroxynitrite in pathogenesis and immunity
The primary focus of the laboratory is on the role of peroxynitrite (ONOO-) in pathogenesis and immunity. ONOO-, the product of the free radicals nitric oxide (NO) and superoxide (O2), is formed in an immune response by activated monocytes but can also be elaborated by a number of different cell types including endothelial cells, neurons, etc. An extremely reactive molecule, ONOO- can kill invading pathogens, transformed, and normal cells through a variety of mechanisms. These interactions can modify cell signaling, protein function, and induce apoptosis or necrosis. Despite the fact that ONOO- is elaborated in most immune reactions, the physiological contributions of this molecule to immunity are poorly understood. One reason is that humans have high serum levels of a natural scavenger of ONOO-, the end product of purine metabolism uric acid. Uric acid is a highly efficient inactivator of ONOO- that is present throughout the human body with the exception of the central nervous system (CNS). Thus it is not surprising that we and other investigators have demonstrated evidence of ONOO- toxicity in autoimmune and inflammatory CNS disorders such as multiple sclerosis (MS).

Most immunological studies are conducted in mice which, like most lower animals from fish to rhesus macaques, do not have substantial levels of uric acid. One of our projects is to determine how circulating uric acid level differences between humans and mice may influence immunity. For instance, ONOO- -mediated pathological mechanisms are involved in the immune destruction of certain tumor types in mice but do the uric acid levels found in humans compromise the ability to kill tumor cells with ONOO-? There is suggestive evidence that uric acid may have a prophylactic role in ONOO- -dependent CNS autoimmunity in humans. For example, women have uric acid levels which are on average 20% less than those of men and are more susceptible to MS and certain other autoimmune diseases.

The pathogenesis of neurodegenerative disease
The laboratory is funded by the National Multiple Sclerosis Society to investigate pathological processes mediated by ONOO- and to determine how uric acid may be used therapeutically. We have demonstrated that ONOO- plays a major role in the pathogenesis of MS and its related animal model experimental allergic encephalomyelitis (EAE). Evidence of ONOO- -mediated damage can be demonstrated in nervous tissue in both diseases that can be prevented in the models by uric acid treatment. A variety of neuropathological processes evidently involve ONOO-. We are collaborating in the study of several of these including neurotrophic virus infection, spinal cord injury, carbon monoxide poisoning, and models of inherited neurodegenerative disease. The objective of these studies is to elucidate the pathways and cellular targets of ONOO- -mediated pathology that are likely to be shared between these diseases.

Effect of peroxynitrite on vascular and blood-brain barrier function
We have recently published evidence that ONOO- produced in the CNS vasculature causes enhanced blood-CNS barrier permeability which promotes CNS inflammation and ONOO- -mediated pathological changes in the CNS. A major question for us is whether this is a physiological or pathological process. It seems unlikely that leakage of inflammatory cells into CNS and other tissues is the result of vascular endothelial cell death as opposed to a signaling processpotentially mediated perhaps by tyrosine nitration. Cell culture studies have revealed that ONOO- can induce changes in vascular endothelial cell function without killing the cells. Uncovering the signaling mechanisms involved is a major initiative inthe laboratory because of their importance to immunity, from the perspectives of both protective reactions and immunopathology.

Neuroviral immunity
The objective of our studies in this area is to elucidate the interactions between humoral, cellular,and inflammatory immune mechanisms in neurotropic virus infection and study the contribution of ONOO- to the various protective and pathological outcomes of viral infections of the CNS. To study protective and pathological immune responses to neurotropic viruses we employ rabies virus and Borna disease virus (BDV). We have recently demonstrated that the immune elimination of BDV from the infected rat brain, at the expense of significant immune-mediated damage, is dependent upon ONOO- opening the blood-brain barrier and inducing CNS inflammation. We have also shown that the nature of immune response to rabies virus as early as 48 hours after infection dictates the outcome of the infection and have evidence that de novo synthesized viral proteins are being recognized rather than input or newly produced intact virus. Our current investigations are focussed on how viral antigen produced in neurons can be recognized this rapidly and whether ONOO- -dependent mechanisms are responsible for providing accessto the site of infection.