Abstract
Blood-brain barrier (BBB) dysfunction is associated with an accumulation of neurotoxic molecules and increased infiltration of peripheral cells within the brain parenchyma. Accruing evidence suggests that microglia and astrocytes play a crucial role in the recovery of BBB integrity and the corralling of infiltrating cells into clusters after brain damage, but the mechanisms involved remain unclear. Intriguingly, the results of flow cytometry and immunofluorescence analyses have shown that BBB permeability to peripheral cells is substantially enhanced during normal aging at 12 months in mice. Thus, we used the SMART-seq2 method to perform RNA sequencing of microglia and astrocytes at five time points before and immediately after the BBB permeability change. Our comprehensive analyses revealed that microglia are characterized by marked alterations in the negative regulation of protein phosphorylation and phagocytic vesicles, whereas astrocytes show elevated enzyme or peptidase-inhibitor activity in the recovery of BBB function. Moreover, we identified a cassette of key genes that might ameliorate the insults of pathophysiological events in aging and neurodegenerative disease.
Highlights
Aging and neurological/psychiatric disorders are known to be associated with defective blood-brain barrier (BBB) function.[1,2,1] BBB breakdown facilitates entry into the brain of neurotoxic blood-derived products and pathogens and has been linked to inflammatory and immune responses that can induce neuronal injury, synaptic dysfunction, and loss of neuronal connectivity
Elevated levels of lymphocytes and macrophages in brain To confirm that aging causes a decrease in BBB integrity, we quantified the percentage of CD45High CD11b– lymphocytes at five time points by using fluorescence-activated cell sorting (FACS) analyses with an appropriate gating strategy (Figure 1A)
To identify the potential BBB regulatory genes that are significant altered when BBB permeability is compromised, we conducted Venn analysis of the core gene set enrichment analysis (GSEA) genes and core differentially expressed genes (DEGs), and our results identified 8 age-upregulated candidate genes (Figure 5A) including Pcsk1n, which encodes a protein that functions as an inhibitor of prohormone convertase 1; Ppp1r14a, which encodes an inhibitor of smooth muscle myosin phosphatase that enhances smooth muscle contraction;[20,21,22] and C4b, which encodes a component of the complement cascade involved in endopeptidase inhibitor activity that reduces the invasion and adhesion of peripheral pathogens to endothelial cells.[23,24]
Summary
Aging and neurological/psychiatric disorders are known to be associated with defective blood-brain barrier (BBB) function.[1,2,1] BBB breakdown facilitates entry into the brain of neurotoxic blood-derived products and pathogens and has been linked to inflammatory and immune responses that can induce neuronal injury, synaptic dysfunction, and loss of neuronal connectivity. The neurovascular unit, which comprises brain endothelial cells, pericytes, astrocytes, and microglia, primarily confers the low paracellular permeability of the BBB.[1,3,4] The tight cell-to-cell contacts that these cell types establish with each other restrict the entry of red blood cells, leukocytes, and plasma components into the brain parenchyma and ensure the export of potentially neurotoxic molecules from the brain to the blood.[5,6] The site of the anatomical BBB is composed of a continuous monolayer of endothelial cells that are connected by tight junctions (TJs) and adherens junctions (containing proteins such as claudin, occludin, and zonula occludens [ZO] 1, ZO2, ZO3, and other isoforms).[7,8] The interactions among the endothelial cells, pericytes, and glial cells are crucial for the formation and maintenance of the highly regulated CNS internal milieu.[5,9,10]
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