Impaired amyloid-β clearance from the brain is a core pathological event in Alzheimer's disease. The therapeutic effect of current pharmacotherapies is unsatisfactory, and some treatments cause severe side effects. The meningeal lymphatic vessels might be a new route for amyloid-β clearance. This study investigated whether promoting dural lymphangiogenesis facilitated the clearance of amyloid-β from the brain. First, human lymphatic endothelial cells were treated with 100 ng/mL recombinant human vascular endothelial growth factor-C (rhVEGF-C) protein. Light microscopy verified that rhVEGF-C, a specific ligand for vascular endothelial growth factor receptor-3 (VEGFR-3), significantly promoted tube formation of human lymphatic endothelial cells in vitro. In an in vivo study, 200 μg/mL rhVEGF-C was injected into the cisterna magna of APP/PS1 transgenic mice, once every 2 days, four times in total. Immunofluorescence staining demonstrated high levels of dural lymphangiogenesis in Alzheimer's disease mice. One week after rhVEGF-C administration, enzyme-linked immunosorbent assay results showed that levels of soluble amyloid-β were decreased in cerebrospinal fluid and brain. The Morris water maze test demonstrated that spatial cognition was restored. These results indicate that the upregulation of dural lymphangiogenesis facilities amyloid-β clearance from the brain of APP/PS1 mice, suggesting the potential of the VEGF-C/VEGFR-3 signaling pathway as a therapeutic target for Alzheimer's disease.

The spatial learning abilities of developing mice benefit from extrinsic cues, such as an enriched environment, with concomitant enhancement in cognitive functions. Interestingly, such enhancements can be further increased through intrinsic Bacillus Calmette-Guérin (BCG) vaccination. Here, we first report that combined neonatal BCG vaccination and exposure to an enriched environment (Enr) induced combined neurobeneficial effects, including hippocampal long-term potentiation, and increased neurogenesis and spatial learning and memory, in mice exposed to the Enr and vaccinated with BCG relative to those in the Enr that did not receive BCG vaccination. Neonatal BCG vaccination markedly induced anti-inflammatory meningeal macrophage polarization both in regular and Enr breeding mice. The meninges are composed of the pia mater, dura mater, and choroid plexus. Alternatively, this anti-inflammatory activity of the meninges occurred simultaneously with increased expression of the neurotrophic factors BDNF/IGF-1 and the M2 microglial phenotype in the hippocampus. Our results reveal a critical role for BCG vaccination in the regulation of neurogenesis and spatial cognition through meningeal macrophage M2 polarization and neurotrophic factor expression; these effects were completely or partially prevented by minocycline or anti-IL-10 antibody treatment, respectively. Together, we first claim that immunological factor and environmental factor induce a combined effect on neurogenesis and cognition via a common pathway-meningeal macrophage M2 polarization. We also present a novel functional association between peripheral T lymphocytes and meningeal macrophages after evoking adaptive immune responses in the periphery whereby T lymphocytes are recruited to the meninges in response to systemic IFN-γ signaling. This leads to meningeal macrophage M2 polarization, subsequent to microglial M2 activation and neurotrophic factor expression, and eventually promotes a positive behavior.

Prenatal infection is a substantial risk factor for neurodevelopmental disorders such as autism in offspring. We have previously reported that influenza vaccination (VAC) during early pregnancy contributes to neurogenesis and behavioral function in offspring. Here, we probe the efficacy of VAC pretreatment on autism-like behaviors in a lipopolysaccharide (LPS)-induced maternal immune activation (MIA) mouse model. We show that VAC improves abnormal fetal brain cytoarchitecture and lamination, an effect associated with promotion of intermediate progenitor cell differentiation in MIA fetal brain. These beneficial effects are sufficient to prevent social deficits in adult MIA offspring. Furthermore, whole-genome analysis suggests a strong interaction between Ikzf1 (IKAROS family zinc-finger 1) and neuronal differentiation. Intriguingly, VAC rescues excessive microglial Ikzf1 expression and attenuates microglial inflammatory responses in the MIA fetal brain. Our study implies that a preprocessed influenza vaccination prevents maternal bacterial infection from causing neocortical lamination impairments and autism-related behaviors in offspring.