Perturbed astrocyte Ca2+ signaling in a diet‐based mouse model of small cerebral vessel disease

Abstract

AbstractBackgroundThe hyperhomocysteinemia (HHcy) diet model of small cerebral vessel disease exhibits vascular inflammation, cerebral hypoperfusion, impaired neurovascular coupling, synapse dysfunction, and cognitive decline. Pathological changes in astrocyte structural features have also been noted, but functional astrocyte phenotypes have not been characterized. Here, we assessed Ca2+ signaling in individual astrocytes and astrocyte networks in barrel cortex of mice, pretreated with control or HHcy diet. Investigations were performed in fully awake mice to avoid confounding interactions between anesthetics, neural circuit activity, and vasoactive factors.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). At week 11‐12, mice were injected with AAV‐Gfa104‐lck‐GCaMP6f into barrel cortex, followed by craniotomies and installation of a glass cranial windows with headmounts. Three weeks later, fully awake mice were head‐mounted under a two photon microscope to assess GCaMP6/Ca2+ transient activity in barrel cortex astrocytes during a 10 minute baseline (spontaneous activity) and also before, during, and air puff stimulation of contralateral whiskers (10Hz, 10 sec) . Mean Ca2+ transient amplitudes, transient rise/decay times, and number of transients per region of interest (ROI) were measured and averaged across the field of view (FOV). Functional relationships between multiple ROIs within the FOV were assessed to evaluate astrocyte network activityResultSpontaneous Ca2+ transients were comparable in amplitude and rise/decay kinetics across diet conditions. However, the number of transients per ROI was reduced in HHcy diet mice. Whisker stimulation evoked a primary Ca2+ elevation per ROI followed 10‐15 seconds later by a smaller amplitude Ca2+‐“aftershock”. Evoked Ca2+ signals were highly coordinated across ROIs within the FOV. However, the number of active ROIs and the functional connectivity between ROIs were significantly reduced in HHcy vs. control diet mice. Despite these network deficits, evoked Ca2+ transient amplitudes and aftershocks in individual ROIs were significantly larger with faster activation/decay kinetics in HHcy mice.ConclusionThe results suggest that altered astrocyte Ca2+ signaling, as a result of vascular pathology, may play an important role in the dynamic interplay between cerebral blood flow and neuronal activity, leading to overall neural dysfunction and cognitive impairment.