Astrocyte Ca2+ dysregulation and neurovascular coupling deficits in a diet‐based mouse model of small cerebral vessel disease

Abstract

AbstractBackgroundMice exposed to a diet deficient in B6/B12 vitamins and enriched in methionine exhibit hyperhomocysteinemia (HHcy) concomitant with many pathologic features of vascular cognitive impairment and dementia: a very common Alzheimer’s disease related dementia. Here, we evaluated the impact of astrocyte Ca2+ dysregulation and astrocytic Ca2+ signaling pathways in the context of functional hyperemia in fully awake mice exposed to HHcy diet.MethodAdult C57/BL6 mice were fed for 15 weeks with control chow, or chow deficient in vitamins B6/B12 and enriched in methionine (HHcy diet). Spontaneous and evoked (via air puff whisker stimulation) Ca2+ transients in astrocytes of fully awake mice were investigated in barrel cortex using the Ca2+ sensor GCaMP6f (expressed specifically in astrocytes using AAV) and two‐photon imaging. In other experiments, mice were treated with AAV‐Gfa2‐VIVIT to inhibit the Ca2+‐sensitive calcineurin/NFAT pathway in astrocytes, which regulates reactive astrocyte phenotypes. Two‐photon imaging was then used to assess diet and VIVIT effects on functional hyperemia in barrel cortex of fully awake mice.ResultCa2+ transients in individual barrel cortex astrocytes were significantly augmented (greater in amplitude, with faster rise/decay kinetics) in mice treated with HHcy diet. However, the functional connectivity in astrocyte networks of HHcy mice was significantly impaired, particularly during engagement of brain activity with whisker stimulation. Compared to control diet mice, HHcy mice also showed impaired functional hyperemia during whisker stimulation characterized by impaired arteriole dilations and reduced red blood cell velocity in nearby capillaries. Inhibition of reactive astrocyte signaling in HHcy diet mice with VIVIT significantly ameliorated these neurovascular coupling deficits.ConclusionThe results show that astrocyte Ca2+ dysregulation is a major feature of HHcy and contributes to cerebrovascular dysfunction through hyperactivation of the astrocytic CN/NFAT pathway.