Microglia are immune cells in the central nervous system (CNS) and essential for homeostasis that are important for both neuroprotection and neurotoxicity, and are activated in a variety of CNS diseases. Microglia aggravate cognitive impairment induced by chronic cerebral hypoperfusion, but their precise roles under these conditions remain unknown. Here, we used PLX3397, a colony-stimulating factor 1 receptor inhibitor, to deplete microglia in mice with chronic cerebral hypoperfusion induced by bilateral common carotid artery stenosis (BCAS). Cognitive impairment induced 28 days after BCAS was significantly improved in mice fed a diet containing PLX3397. In PLX3397-fed mice, microglia were depleted and white matter injury induced by BCAS was suppressed. In addition, the expression of proinflammatory cytokines, interleukin 6 and tumor necrosis factor alpha, was suppressed in PLX3397-fed mice. Taken together, these findings suggest that microglia play destructive roles in the development of cognitive impairment and white matter injury induced by chronic cerebral hypoperfusion. Thus, microglia represent a potential therapeutic target for chronic cerebral hypoperfusion-related diseases.

Aging causes various functional changes, including cognitive impairment and inflammatory responses in the brain. Transient receptor potential melastatin 2 (TRPM2), a Ca 2+-permeable channel expressed abundantly in immune cells, exacerbates inflammatory responses. Previously, we reported that TRPM2 on resident microglia plays a critical role in exacerbating inflammation, white matter injury, and cognitive impairment during chronic cerebral hypoperfusion; however, the physiological or pathophysiological role of TRPM2 during age-associated inflammatory responses remains unclear. Therefore, we examined the effects of TRPM2 deletion in young (2-3 months) and older (12-24 months) mice. Compared with young wild-type (WT) mice, middle-aged (12-16 months) WT mice showed working and cognitive memory dysfunction and aged (20-24 months) WT mice exhibited impaired spatial memory. However, these characteristics were not seen in TRPM2 knockout (TRPM2-KO) mice. Consistent with the finding of cognitive impairment, aged WT mice exhibited white matter injury and hippocampal damage and an increase in the number of Iba1-positive cells and amounts of pro-inflammatory cytokines in the brain; these characteristics were not seen in TRPM2-KO mice. These findings suggest that TRPM2 plays a critical role in exacerbating inflammatory responses and cognitive dysfunction during aging.

Vascular cognitive impairment (VCI) refers to cognitive alterations caused by vascular disease, which is associated with various types of dementia. Because chronic cerebral hypoperfusion (CCH) induces VCI, we used bilateral common carotid artery stenosis (BCAS) mice as a CCH-induced VCI model. Transient receptor potential ankyrin 1 (TRPA1), the most redox-sensitive TRP channel, is functionally expressed in the brain. Here, we investigated the pathophysiological role of TRPA1 in CCH-induced VCI. During early-stage CCH, cognitive impairment and white matter injury were induced by BCAS in TRPA1-knockout but not wild-type mice. TRPA1 stimulation with cinnamaldehyde ameliorated BCAS-induced outcomes. RNA sequencing analysis revealed that BCAS increased leukemia inhibitory factor (LIF) in astrocytes. Moreover, hydrogen peroxide–treated TRPA1-stimulated primary astrocyte cultures expressed LIF, and culture medium derived from these cells promoted oligodendrocyte precursor cell myelination. Overall, TRPA1 in astrocytes prevents CCH-induced VCI through LIF production. Therefore, TRPA1 stimulation may be a promising therapeutic approach for VCI.

Vascular cognitive impairment (VCI) is a syndrome defined as cognitive decline caused by vascular disease, which is associated with Alzheimer's disease and vascular dementia. Since chronic cerebral hypoperfusion (CCH) is commonly present in various types of dementia and induces VCI, we used bilateral common carotid artery stenosis (BCAS) mice as a CCH-induced VCI model. Transient receptor potential ankyrin 1 (TRPA1), the most redox-sensitive TRP channel, is functionally expressed in the brain and seems to function as a polymodal sensor in vascular disease. To clarify the involvement of TRPA1 in CCH-induced VCI, we used genetically engineered mice: TRPA1-knockout (TRPA1-KO) and cell-specific conditional TRPA1-KO mice. We showed that TRPA1 deficiency exacerbated BCASinduced cognitive impairment and white matter injury during early-stage CCH. TRPA1 stimulation with cinnamaldehyde ameliorated BCAS-induced outcomes. We also revealed that BCAS increased a cytokine in astrocytes. Moreover, TRPA1-stimulated primary astrocyte cultures expressed the cytokine, and culture medium derived from these TRPA1-stimulated cells promoted oligodendrocyte precursor cell myelination. Overall, TRPA1 stimulation in astrocytes plays a protective role in CCH-induced VCI through the cytokine production.