Deficits in participation-level performance of specific cognitive tasks are one of the primary cognitive impairments reported after a mild TBI.3 There are no FDA-approved preventive or curative interventions. Mitochondrial dysfunction4-10 and neuroinflammation11-15 in the central nervous system (CNS) are postulated as underlying causes of cognitive impairment. Our preliminary data suggests that dysregulation of adenosine metabolism and loss of signaling at the A3 adenosine receptor (AR) subtype (A3AR) is key to these processes. Extracellular adenosine is regulated by ectonucleotidases and adenosine kinase and preliminary results in a mouse model of mild-TBI (close head weight drop)2,16 revealed that TBI altered the expression of these enzymes in the prefrontal cortex (PFC) and hippocampus. This was associated with time dependent development of memory and learning deficits [Novel Object/Place Recognition (NOPRT) and T-maze tests]. Supplementing adenosine signaling with highly selective, orally bioavailable, CNS penetrant A3AR agonists given therapeutically significantly attenuated TBI-induced memory and learning deficits 4 weeks after injury without any confounding influence on locomotor activity. Moreover, pilot data now links A3AR agonism to the inhibition of TBI-induced oxidative/nitrative stress (nitroxidative stress), neuroinflammation and activation of nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome. Our findings are very exciting since A3AR agonists (e.g., IB-MECA) are already in advanced clinical trials for other indications with a good safety profile.17,18 Two Specific Aims will test our hypothesis: dysregulation of adenosinergic signaling in the brain contributes to TBI-induced cognitive impairment; restoring adenosinergic signaling with highly selective A3AR agonists is an effective strategy for therapeutic intervention. A multidisciplinary approach is used in male and female mice. Pharmacological and genetic studies as well as time course and dose responses with selective A3AR agonists are proposed. Studies will also include A3AR antagonists and A3AR knockout mice to confirm selectivity of response.
In Aim 1, we will examine whether a decrease in adenosine signaling at the A3AR contributes to TBI-induced cognitive deficits.
In Aim 2, we will 1) examine whether restoring A3AR signaling with A3AR agonists ameliorates TBI-induced cognitive deficits, 2) validate A3AR as a target for therapeutic intervention with selective A3AR agonists and 3) investigate their mechanism of action by examining their impact on the mitochondrial dysfunction and neuroinflammatory processes that are intimately linked to the development of cognitive deficits. Our multidisciplinary research plan is anticipated to provide evidence for the applicability of highly selective A3AR agonists to preserve cognitive function following TBI while investigating their underlying protective mechanism(s).
Long-term cognitive impairment is a common problem following a traumatic brain injury (TBI), affecting an estimated 50% of patients following a mild injury. The mechanisms are largely unknown and there are no proven strategies to prevent or treat it. Our findings provide the first evidence that implicates dysregulation of adenosine signaling at the A3 adenosine receptor (A3AR) as a central event in the development of cognitive impairment following a TBI and a novel therapeutic approach to mitigate cognitive impairment with A3AR agonists.