Short-term high fat diet impairs memory, exacerbates the neuroimmune response, and evokes synaptic degradation via a complement-dependent mechanism in a mouse model of Alzheimer's disease.

Alzheimer's Disease (AD) is a neurodegenerative disease characterized by profound memory impairments, synaptic loss, neuroinflammation, and hallmark pathological markers. High-fat diet (HFD) consumption increases the risk of developing AD even after controlling for metabolic syndrome, pointing to a role of the diet itself in increasing risk. In AD, the complement system, an arm of the immune system which normally tags redundant or damaged synapses for pruning, becomes pathologically overactivated leading to tagging of healthy synapses. While the unhealthy diet to AD link is strong, the underlying mechanisms are not well understood in part due to confounding variables associated with long-term HFD which can independently influence the brain. Therefore, we experimented with a short-term diet regimen to isolate the diet's impact on brain function without causing obesity. This project investigated the effect of short-term HFD on 1) memory, 2) neuroinflammation including complement, 3) AD pathology markers, 4) synaptic markers, and 5) in vitro microglial synaptic phagocytosis in the 3xTg-AD mouse model. Following the consumption of either standard chow or HFD, 3xTg-AD and non-Tg mice were tested for memory impairments. In a separate cohort of mice, levels of hippocampal inflammatory markers, complement proteins, AD pathology markers, and synaptic markers were measured. For the last set of experiments, BV2 microglial phagocytosis of synapses was evaluated. Synaptoneurosomes isolated from the hippocampus of 3xTg-AD mice fed chow or HFD were incubated with equal numbers of BV2 microglia. The number of BV2 microglia that phagocytosed synaptoneurosomes was tracked over time with a live-cell imaging assay. Finally, we incubated BV2 microglia with a complement receptor inhibitor (NIF) and repeated the assay. Behavioral analysis showed 3xTg-AD mice had significantly impaired long-term contextual and cued fear memory compared to non-Tg mice that was further impaired by HFD. HFD significantly increased inflammatory markers and complement expression while decreasing synaptic marker expression only in 3xTg-AD mice, without altering AD pathology markers. Synaptoneurosomes from HFD-fed 3xTg-AD mice were phagocytosed at a significantly higher rate than those from chow-fed mice, suggesting the synapses were altered by HFD. The complement receptor inhibitor blocked this effect in a dose-dependent manner, demonstrating the HFD-mediated increase in phagocytosis was complement dependent. This study indicates HFD consumption increases neuroinflammation and over-activates the complement cascade in 3xTg-AD mice, resulting in poorer memory. The in vitro data point to complement as a potential mechanistic culprit and therapeutic target underlying HFD's influence in increasing cognitive vulnerability to AD.

Novel life cycle stages of Colpodella sp. (Apicomplexa) identified using Sam-Yellowe's trichrome stains and confocal and electron microscopy.

Colpodella spp. are free-living flagellates closely related to the apicomplexans. Human infections by Colpodella sp. have been reported. A biflagellated trophozoite and cyst stage comprise the known life cycle stages of Colpodella sp. However, the process of encystation and excystation within the life cycle is unclear. Life cycle stages initiating human infections are unknown. We performed a detailed investigation of the life cycle of Colpodella sp. (ATCC 50594) in culture using Sam-Yellowe's trichrome stains and differential interference contrast (DIC) for light microscopy and fluorescence microscopy of Congo red-stained cells and investigated ultrastructure using transmission electron microscopy (TEM). We report previously undocumented stages of Colpodella sp. Asymmetric and asynchronous division was detected inside cysts by trichrome staining and by TEM. Odd-numbered juveniles and cysts containing more than four juvenile trophozoites were identified. Live imaging of active cultures captured the excystation and egress of juvenile trophozoites and confirmed the presence of multinucleate cysts. The ultrastructure of the multinucleate cyst is reminiscent of apicomplexan schizonts. Insights gained from the life cycle stages observed in culture allowed the construction of the life cycle of Colpodella sp. Knowledge of the life cycle will aid biochemical and molecular characterization of Colpodella sp. and help identify stages in human infections.