Optogenetic Activation Of The Cortical Glutamatergic Neurons Promotes White Matter Recovery Following Chronic Cerebral Hypoperfusion

Subcortical ischemic vascular dementia caused by chronic cerebral hypoperfusion develops with progressive white matter and cognitive impairments,yet effective treatments are still not available,so it is urgent to search new drug target and effective treatment or strategy.The white matter damage following chronic cerebral hypoperfusion refers to loss of oligodendrocyte,progressive demyelination along with limited remyelination.Glutamate released from glutamatergic neurons can activate oligodendrocyte precursor cells(OPCs)and affect myelination during development.So,we explored the effect of activating the glutamatergic neurons-corpus callosum projection by optogenetic approach on OPCs proliferation and white matter damage following chronic cerebral hypoperfusion via right unilateral common carotid arteries occlusion(rUCCAO)in mice.We found that the corpus callosum,which is easily impaired after cerebral hypoperfusion,exists the glutamatergic projections from motor cortex and somatosensory cortex by reverse axon tracking.Optogenetic activation of the ChR2 expressing glutamatergic neurons in somatosensory(or motor)cortex remarkably promoted the OPCs proliferation and rescued the significant loss of OPCs in the corpus callosum at the early phase after rUCCAO.However,optogenetic activation of glutamatergic neurons in the motor cortex often induced seizures,but activation of the sensory cortex did not cause seizures or sensory dysfunction,suggesting sensory cortex may serve as an ideal target.Furthermore,we found that an appropriate light stimulus intensity is required to promote OPCs proliferation.At the same time,optogenetic activation of glutamatergic neurons in sensory cortex have the similar effects on promoting OPCs proliferation no matter it was performed in the early phase or middle phase after rUCCAO.It indicates that optogenetic activation has a wide time window for promoting oligodendrocyte proliferation following chronic cerebral hypoperfusion.Next,we traced the projections of the glutamatergic neurons in somatosensory cortex and found that the corpus callosum area exists more projecting fibers from the upper-layer cortex(II-III sublayer)of glutamatergic neurons.The proliferation of OPCs was increased by optogenetic activation of the upper-layer glutamatergic neurons or their projecting fibers in corpus callosum at the early stage following chronic cerebral hypoperfusion.However,axonal fibers from the deep cortical layers(V and VI sublayers)of glutamatergic neurons were rarely found and activation of these neurons had no effect on the proliferation of OPCs.We also observed the formation of neuro-oligodendrocyte synaptic connections in the corpus callosum after optogenetic activation of the upper-layer glutamatergic neurons.In addition,we generated the OPCs expressing ChR2 mice.When the OPCs in corpus callosum are optogenetically activated at the early stage in these mice,the proliferation OPCs was significantly increased,and then remyelination was improved at the late phase.We also observed that the newly generated OPCs after optogenetic activation of the glutamatergic neurons in somatosensory cortex,successfully differentiate into mature oligodendrocyte.It contributes to remyelination with increasing of myelin basic protein(MBP)expression and the percentage of myelinated axons,and functional recovery in novel object recognition test and Morris water maze test at the later phase after rUCCAO.Overall,our results demonstrated that optogenetic activation of the upper-layer cortical glutamatergic neurons-corpus callosum projection promoted OPCs proliferation following chronic cerebral hypoperfusion through the formation of neuro-oligodendrocyte synaptic connections,which may contribute to the recovery of white matter damage and cognitive impairments.This action relies on light intensity,brain area and has a wide window.Our study suggests that the glutamatergic neurons-corpus callosum projection is a potential circuit for oligodendrogenesis and may provide novel effective approaches or strategies for the clinical treatment of white matter damage induced by chronic cerebral hypoperfusion.