CaMKIIα Expressing Neurons to Report Activity-Related Endogenous Hypoxia upon Motor-Cognitive Challenge

Abstract

We previously introduced the brain erythropoietin (EPO) circle as a model to explain the adaptive ‘brain hardware upgrade’ and enhanced performance. In this fundamental circle, brain cells, challenged by motor-cognitive tasks, experience functional hypoxia, triggering the expression of EPO among other genes. We attested hypoxic cells by a transgenic reporter approach under the ubiquitous CAG promoter, with Hif-1α oxygen-dependent degradation-domain (ODD) fused to CreERT2-recombinase. To specifically focus on the functional hypoxia of excitatory pyramidal neurons, here, we generated CaMKIIα-CreERT2-ODD::R26R-tdTomato mice. Behavioral challenges, light-sheet microscopy, immunohistochemistry, single-cell mRNA-seq, and neuronal cultures under normoxia or hypoxia served to portray these mice. Upon complex running wheel performance as the motor-cognitive task, a distinct increase in functional hypoxic neurons was assessed immunohistochemically and confirmed three-dimensionally. In contrast, fear conditioning as hippocampal stimulus was likely too short-lived to provoke neuronal hypoxia. Transcriptome data of hippocampus under normoxia versus inspiratory hypoxia revealed increases in CA1 CaMKIIα-neurons with an immature signature, characterized by the expression of Dcx, Tbr1, CaMKIIα, Tle4, and Zbtb20, and consistent with accelerated differentiation. The hypoxia reporter response was reproduced in vitro upon neuronal maturation. To conclude, task-associated activity triggers neuronal functional hypoxia as a local and brain-wide reaction mediating adaptive neuroplasticity. Hypoxia-induced genes such as EPO drive neuronal differentiation, brain maturation, and improved performance.

Introducing the brain erythropoietin circle to explain adaptive brain hardware upgrade and improved performance

“…Taken together, an intriguing novel model of neuroplasticity emerged, in which specific task-associated neuronal networks drift into transient functional hypoxia as a local as well as a brain-wide response comprising indirectly activated neurons and non-neuronal cells [ 77 , 80 ]. This in turn triggers neuronal EPO/EPOR expression to mediate neuroplasticity via adaptive transcript regulation in the behaving brain, leading to substantial ‘hardware upgrade’ (Fig.…”

Exploiting moderate hypoxia to benefit patients with brain disease: Molecular mechanisms and translational research in progress

“…Pilot data from our laboratories indicate that this will be essential to understand and exploit the underlying mechanisms. In preliminary work, using a transgenic reporter of transient hypoxia (CaMKIIα-CreERT2-ODD::R26R-tdTomato mice, expressing the HIF-1α oxygen-dependent degradation-domain, ODD, fused to CreERT2-recombinase 103 for persistent activation of a fluorescent reporter after hypoxia), we surprisingly found a mild increase in red-labeled (tdTo-mato+) neurons also after exposure to inspiratory hyperoxia (unpublished observations). It is unclear, however, whether this was due to the stabilization of CreERT2-ODD also at high O 2 concentration or to a rapidly sensed "relative hypoxia" after cessation of hyperoxia.…”