The term "cAMP" usually refers to the second messenger 3',5'-cyclic adenosine monophosphate. We serendipitously discovered that organ systems can produce (from mRNA degradation) and export to the extracellular compartment a positional isomer of 3',5'-cAMP, namely 2',3'-cAMP. We showed that organ systems convert extracellular 2',3'-cAMP to 2'-AMP + 3'-AMP and can metabolize 2'-AMP and 3'-AMP to adenosine. We refer to this pathway as the "2',3'-cAMP-adenosine pathway." We also showed that extracellular 2',3'-cAMP increases greatly post-traumatic brain injury (TBI) in brain in rodents and humans;and that when the pathway is impaired, TBI outcomes worsen in rodents. Intracellular 2',3'-cAMP opens mitochondrial permeability transition pores while extracellular adenosine is neuroprotective. Thus the "2',3'- cAMP-adenosine pathway" may be important in TBI because it eliminates an intracellular neurotoxin (export of 2',3'-cAMP) and generates an extracellular neuroprotectant (conversion of 2',3'-cAMP to adenosine). We also identified the enigmatic myelin protein 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase) to be the major enzyme that metabolizes extracellular 2',3'-cAMP to 2'-AMP (a key step toward conversion into adenosine). KO mice lacking CNPase produce less extracellular adenosine post-TBI, are more susceptible to injury and develop axonal degeneration with age despite no gross myelin abnormalities. Hypothesis: the "2',3'-cAMP- adenosine pathway" is an endogenous cytoprotective mechanism after TBI. We will elucidate which CNS cell types produce 2',3'-cAMP, what kinds of injury trigger 2',3'-cAMP production, how 2',3'-cAMP is transported out of cells, how downstream AMPs are converted to adenosine, and if manipulating the 2',3'-cAMP-adenosine pathway alters secondary damage.
Specific Aim 1 : To determine which CNS cell types produce 2',3'-cAMP after injury. Because in vivo TBI increases extracellular 2',3'-cAMP, it is important to determine which CNS cells produce 2',3'-cAMP and whether the effect is injury-type dependent.
Aim 1 will determine if metabolic stress, hypoxia or mechanical injury enhances 2',3'-cAMP production by astrocytes, microglia, neurons or oligodendrocytes.
Specific Aim 2 : To determine whether Multidrug Resistance Protein 4 (MRP4) mediates egress of 2',3'-cAMP. Because 2',3'-cAMP is an intracellular toxin, it is critical to elucidate how 2',3'-cAMP is extrude from CNS cells.
Aim 2 will test the hypothesis that MRP4 exports 2',3'-cAMP.
Specific Aim 3 : To determine if Tissue Alkaline Phosphatase (TAP) participates in the extracellular metabolism of 2'-AMP and 3'- AMP (downstream metabolites of 2',3'-cAMP) to adenosine. Because extracellular adenosine is neuroprotective it is essential to understand how extracellular 2'-AMP and 3'-AMP are converted to extracellular adenosine.
Specific Aim 4 : To test the hypothesis that the 2',3'-cAMP-adenosine pathway is an endogenous protective mechanism post-TBI.
Aim 4 will further test the hypothesis that the 2',3'-cAMP- adenosine pathway is cytoprotective by determining the effect of inhibiting or augmenting it on TBI outcomes.
The term cAMP usually refers to the second messenger 3',5'-cyclic adenosine monophosphate. We serendipitously discovered that brain can produce (from mRNA degradation) and export to the extracellular compartment a positional isomer of 3',5'-cAMP, namely 2',3'-cAMP. 2',3'-cAMP is neurotoxic but its metabolite adenosine is neuroprotective. This new 2',3'-cAMP-adenosine pathway thus has promise as a target for development of novel therapies for brain injury. In this proposal we will evaluate approaches to manipulate this novel pathway with the goal of developing a novel therapy for the important public health problem of traumatic brain injury.