Altered NPTX2 dynamics associated with impaired cognitive aging

Changes in synaptic integrity and neural activity homeostasis are hallmarks of brain aging and are closely tied to cognitive outcomes. Yet, defining their relationship across the continuum from normal aging to neurodegenerative disease has proven challenging. Recent research investigating the dynamic changes of neuronal pentraxin 2 (NPTX2, or Narp, neuronal activity-related pentraxin) in cerebrospinal fluid (CSF) of Alzheimers disease (AD) subjects supports its promise as a prognostic marker of disease progression, possibly as an expression of synaptic damage related to cognitive impairment. However, studies in human subjects are unable to clearly differentiate age-related and disease-related processes. Here we took advantage of a well-characterized rat model that displays substantial individual differences in hippocampal memory during aging, uncontaminated by slowly progressive, spontaneous neurodegenerative disease. Through this approach, we aimed to interrogate the underlying neural substrates that mediate aging as a uniquely permissive condition and the primary risk for neurodegeneration. We found that successful cognitive aging is associated with an elevation of NPTX2 levels above that found in young or cognitively impaired subjects. Pharmacological engagement of neural activity was sufficient to increase NPTX2 levels in all subjects, but cognitively-impaired aged subjects failed to recruit NPTX2 in response to a hippocampus-dependent memory task. Together the findings demonstrate that changes in NPTX2 are coupled to differential cognitive outcomes of aging, and that successful neurocognitive aging is associated with adaptive upregulation of NPTX2, not simply the persistence of youthful synaptic dynamics. Significance StatementAlthough aging is the most prominent risk factor for Alzheimer Disease (AD), the age-dependent processes that disrupt neurophysiological homeostasis leading to neurodegenerative disease remain poorly defined. Alterations in NPTX2, a synaptic protein biomarker for AD, may elucidate aging processes underlying pathological trajectories. We examined NPTX2 in an aging context and identified circuit specific alterations of NPTX2 that are coupled with distinct memory outcomes in aging in the absence of potential confounds of neurodegenerative disease. Greater NPTX2, associated with successful cognitive aging, may reflect coordinated molecular and circuit-level adaptations that sustain memory-relevant hippocampal activity. Development of targets and interventions that promote neuroadaptive network homeostasis, bending the trajectory of aging away from neurodegeneration, are a potentially valuable alternative to current therapeutic strategies.