Glymphatic system alteration in an animal model of metabolic syndrome

Metabolic syndrome (MetS) is a clustering of metabolic and cardiovascular factors responsible for an increased risk of developing cardiovascular diseases and type 2 diabetes. MetS is also characterized by a chronic low-grade inflammatory status that could contribute to neuroinflammation and neurodegeneration, but the underlying mechanism is still unclear. Recently, an association between MetS, glymphatic dysfunction, and cognitive decline has been described. In the brain, metabolic waste removal is performed by the glymphatic system involving the astroglia water-channel protein aquaporin-4 (AQP4). Here, we evaluated glymphatic dysfunction associated with MetS-induced neuroinflammation using a high-fat diet (HFD) rabbit model of MetS and focusing on the hypothalamus, a brain area crucially regulating energy homeostasis and metabolism. Using immunohistochemical analysis, we confirmed the onset of hypothalamic inflammation in HFD rabbits, as demonstrated by the activation of resident immune cells (microglia) and astrocytes, as well as by the presence of RAM11-positive macrophage infiltrate and the significant induction of pro-inflammatory genes (COX2, IL-6, and CD68). Interestingly, immunohistochemistry analysis showed that AQP4 expression was significantly increased in HFD hypothalamic sections compared to controls, also showing increased colocalization at the astrocytic endfeet surrounding blood vessels. Accordingly, AQP4 vascular polarization was observed in the hypothalamus of the HFD group compared to controls. By ex vivo magnetic resonance imaging (MRI), we also analyzed structural morphological changes in the brains of HFD rabbits. Preliminary data showed no significant differences in total brain structure measurements. Overall, our data demonstrate an increase in glymphatic activity during Mets-induced neuroinflammation into the hypothalamus, suggesting a prior neuroprotective mechanism to maintain brain homeostasis. The lack of significant morphological and structural changes in brain areas suggests a precocious stage of MetS-related neuroinflammation not yet associated with neurodegenerative consequences. This work was supported by #NEXTGENERATIONEU (NGEU) and funded by the Ministry of University and Research (MUR), National Recovery and Resilience Plan (NRRP), project MNESYS (PE0000006) – A Multiscale integrated approach to the study of the nervous system in health and disease (DR. 1553 11.10.2022).