Hypoxic preconditioning (HPC) as an endogenous mechanism
can resist
hypoxia/ischemia injury and exhibit protective effects on neurological
function including learning and memory. Although underlying molecular
mechanisms remain unclear, HPC probably regulates the expression of
protective molecules by modulating DNA methylation. Brain-derived
neurotrophic factor (BDNF) activates its signaling upon binding to
the tropomyosin-related kinase B (TrkB) receptor, which is involved
in neuronal growth, differentiation, and synaptic plasticity. Therefore,
this study focused on the mechanism by which HPC regulates BDNF and
BDNF/TrkB signaling through DNA methylation to influence learning
and memory. Initially, the HPC model was established by hypoxia stimulations
on ICR mice. We found that HPC downregulated the expression of DNA
methyltransferase (DNMT) 3A and DNMT3B. Then, the upregulation of
BDNF expression in HPC mice was generated from a decrease in DNA methylation
of the BDNF gene promoter detected by pyrophosphate
sequencing. Subsequently, upregulation of BDNF activated BDNF/TrkB
signaling and ultimately improved learning and spatial memory in HPC
mice. Moreover, after mice were intracerebroventricularly injected
with the DNMT inhibitor, the restraint of DNA methylation accompanied
by an increase of BDNF and BDNF/TrkB signaling was also discovered.
Finally, we observed that the inhibitor of BDNF/TrkB signaling prevented
HPC from ameliorating learning and memory in mice. However, the DNMT
inhibitor promoted spatial cognition in mice. Thus, we suggest that
HPC may upregulate BDNF by inhibiting DNMTs and decreasing DNA methylation
of the BDNF gene and then activate BDNF/TrkB signaling
to improve learning and memory in mice. This may provide theoretical
guidance for the clinical treatment of cognitive dysfunction caused
by ischemia/hypoxia disease.