Defective degradation and clearance of amyloid-β as well as inflammation per se are crucial players in the pathology of Alzheimer's disease (AD). A defective transport across the blood-brain barrier is causative for amyloid-β (Aβ) accumulation in the brain, provoking amyloid plaque formation. Using primary porcine brain capillary endothelial cells and murine organotypic hippocampal slice cultures as in vitro models of AD, we investigated the effects of the antioxidant astaxanthin (ASX) on Aβ clearance and neuroinflammation. We report that ASX enhanced the clearance of misfolded proteins in primary porcine brain capillary endothelial cells by inducing autophagy and altered the Aβ processing pathway. We observed a reduction in the expression levels of intracellular and secreted amyloid precursor protein/Aβ accompanied by an increase in ABC transporters ABCA1, ABCG1 as well as low density lipoprotein receptor-related protein 1 mRNA levels. Furthermore, ASX treatment increased autophagic flux as evidenced by increased lipidation of LC3B-II as well as reduced protein expression of phosphorylated S6 ribosomal protein and mTOR. In LPS-stimulated brain slices, ASX exerted anti-inflammatory effects by reducing the secretion of inflammatory cytokines while shifting microglia polarization from M1 to M2 phenotype. Our data suggest ASX as potential therapeutic compound ameliorating AD-related blood brain barrier impairment and inflammation.
Abstract Background Accumulation of amyloid beta (Aβ) and tau proteins have for decades been thought to be central in the pathogenesis of Alzheimer’s disease (AD). More recently, a plethora of evidence emerged that links metabolic dysfunctions such as obesity, type 2 diabetes (T2D), and dyslipidemia with the pathophysiology of AD. In this study, we investigated the effects of streptozocin and high fat diet (HFD) induced T2D on lipid and amyloid beta metabolism in APPxhQC transgenic mice and their wild‐type littermates. Method APPxhQC mice were generated by crossbreeding APP SL with hQC mice. As controls wild‐type littermates were used. APP SL mice express human APP751 with the Swedish and the London mutation on a C57Bl/6RccHsd background. hQC mice express human glutaminyl cyclase (QC) enzyme on B6CBAF1/J background. Plasma lipids (triglycerides and cholesterol) and liver function enzymes (aspartate aminotransferase and alanine transaminase, ALT and ALT, respectively) were determined by ELISA. Brain concentrations of soluble and insoluble Aβ 1‐38 , 1‐40 and 1‐42 peptides were determined using an immunosorbent assay (Mesoscale discovery immunosorbent assay) while pGlu Aβ 1‐42 was measured by ELISA. Hepatic mRNA expression levels of genes involved in cholesterol efflux and lipid metabolism were determined by quantitative real time polymerase chain reaction (qRT‐PCR). Result T2D induced increased concentrations of plasma cholesterol as well as AST and ALT levels. The magnitudes, however, were dependent on sex and genotype and were statistically significant in female wild‐type mice, while a similar pattern was observed in APPxhQC transgenes. These increased plasma concentrations were accompanied by a down‐regulation of hepatic gene expression levels of LRP1, ABCA1, PPARα, PBC1β, and NEP that were statistically significant in female wild‐type mice, while a similarly pattern was observed in APPxhQC transgenic mice. More interestingly, T2D provoked a progressive shift of brain Aβ 1‐38 and 1‐40 from soluble to insoluble forms in male APPxhQC mice and a significant increase of pyroglutamate modified Aβ 1‐42 in female mice. Conclusion T2D in APPxhQC mice provokes a shift from soluble to large insoluble polymers of Aβ in the brain, corroborates the deteriorating role of T2D in the progression of AD
Brain capillary endothelial cells (BCECs) are integral components of both the blood-brain barrier (BBB) and the neurovascular unit (NVU). Transport across the BBB is an important mediator of beta-amyloid (Aβ) accumulation in the brain and a contributing factor in the pathogenesis of Alzheimer's disease (AD). One of the receptors responsible for the transport of Aβ through the BBB is the low-density lipoprotein receptor-related protein 1 (LRP1). In addition, the development of AD and diabetes share many pathophysiological features including defective insulin signalling, impaired glucose metabolism, and cognitive decline. LRP1 is known to modulate insulin signalling by forming a dimer with insulin receptor beta when stimulated using insulin. Furthermore, LRP1 expression at the BBB is reduced during normal aging and in AD. Hence, we hypothesize that LRP1 activity in BCEC can be modulated using astaxanthin to improve Aβ clearance and insulin-mediated signalling at the BBB.By using the established in vitro porcine brain capillary endothelial cell (pBCEC) model of the BBB, we analyzed the effects of astaxanthin on LRP1 expression, Aβ clearance, insulin-mediated signalling and other systemic dysfunctions associated with AD at the protein and mRNA level. We also examined the ultra-structures by electron microscopy.pBCECs showed enhanced expression of LRP1 when treated with astaxanthin. We further observed improved insulin sensitivity when cells pre-incubated with astaxanthin were treated with Aβ1-40 , Aβ1-42 and Aβ1-40 + Aβ1-42 and insulin and further stimulated with insulin (10 nM). Increased expression of LRP1, Aβ-degrading enzymes, as well as autophagy and insulin signalling markers were observed when pBCECs pre-incubated with astaxanthin were further treated with amyloid beta peptides.Our results suggest that increased LRP1 expression by astaxanthin enhances insulin sensitivity, autophagy induction and improves Aβ degradation. Astaxanthin could thus be a promising therapeutic candidate for Alzheimer's disease.
ABSTRACT Mechanisms regulating serotonin (5-HT) homeostasis at the maternal-fetal interface are important for proper placental functioning and fetal (neuro)development. Here we studied 5-HT uptake mechanisms in human primary trophoblasts, feto-placental endothelial cells and cord blood platelets, all isolated directly after birth. Trophoblasts and cord blood platelets demonstrated high-affinity 5-HT uptake with similar Michaelis constant ( Km ) values (0.60±0.27 and 0.65±0.18 μM, respectively). In contrast, feto-placental endothelial cells displayed saturation kinetics only over the low-affinity range of 5-HT concentrations ( Km =782±218 μM). 5-HT uptake into trophoblasts was inhibited by various psychotropic drugs targeting high-affinity serotonin transporter (SERT), and into feto-placental endothelial cells by an inhibitor of low-affinity transporters. SERT mRNAs were abundant in trophoblasts, but sparse in feto-placental endothelial cells; the opposite was found for transcripts of the low-affinity plasma membrane monoamine transporter (PMAT). These results show for the first time the presence of functional 5-HT uptake systems in feto-placental endothelial cells and fetal platelets, cells in direct contact with the fetal blood plasma. Data also emphasize sensitivity of 5-HT transport into trophoblasts, cells facing maternal blood, to various psychotropic drugs. The multiple, high- and low-affinity, systems present for cellular 5-HT uptake highlight the importance of maintaining 5-HT homeostasis at the maternal-fetal interface.
Helicobacter pylori infection in stomach leads to gastric cancer, gastric ulcer, and duodenal ulcer. More than 1 million people die each year due to these diseases, but why most H. pylori-infected individuals remain asymptomatic while a certain proportion develops such severe gastric diseases remained an enigma. Several studies indicated that gastric and intestinal microbiota may play a critical role in the development of the H. pylori-associated diseases. However, no specific microbe in the gastric or intestinal microbiota has been clearly linked to H. pylori infection and related gastric diseases. Here, we studied H. pylori infection, its virulence genes, the intestinal microbiota, and the clinical status of Trivandrum residents (N = 375) in southwestern India by standard H. pylori culture, PCR genotype, Sanger sequencing, and microbiome analyses using Illumina Miseq and Nanopore GridION. Our analyses revealed that gastric colonization by virulent H. pylori strains (vacAs1i1m1cagA+) is necessary but not sufficient for developing these diseases. Conversely, distinct microbial pools exist in the lower gut of the H. pylori-infected vs. H. pylori-non-infected individuals. Bifidobacterium (belonging to the phylum Actinobacteria) and Bacteroides (belonging to the phylum Bacteroidetes) were present in lower relative abundance for the H. pylori+ group than the H. pylori- group (p < 0.05). On the contrary, for the H. pylori+ group, genus Dialister (bacteria belonging to the phylum Firmicutes) and genus Prevotella (bacteria belonging to the phylum Bacteroidetes) were present in higher abundance compared to the H. pylori- group (p < 0.05). Notably, those who carried H. pylori in the stomach and had developed aggressive gastric diseases also had extremely low relative abundance (p < 0.05) of several Bifidobacterium species (e.g., B. adolescentis, B. longum) in the lower gut suggesting a protective role of Bifidobacterium. Our results show the link between lower gastrointestinal microbes and upper gastrointestinal diseases. Moreover, the results are important for developing effective probiotic and early prognosis of severe gastric diseases.
Serotonin (5-HT) plays an extensive role during pregnancy in regulating both the placental physiology and embryonic/fetal development. The uptake of 5-HT into cells is central to the control of local concentrations of 5-HT near its molecular targets. Here, we investigated the mechanisms of 5-HT uptake into human primary placental cells and cord blood platelets, all isolated immediately after birth. Trophoblasts and cord blood platelets showed 5-HT uptake with similar Michaelis constant (Km) values (~0.6 μM), typical of the high-affinity serotonin transporter (SERT). The uptake of 5-HT into trophoblasts was efficiently inhibited by various SERT-targeting drugs. In contrast, the uptake of 5-HT into feto-placental endothelial cells was not inhibited by a SERT blocker and showed a Km value (~782 μM) in the low-affinity range. Consistent with this, SERT mRNAs were abundant in term trophoblasts but sparse in feto-placental endothelial cells, whereas the opposite was found for the low-affinity plasma membrane monoamine transporter (PMAT) mRNAs. Organic cation transporter (OCT) 1, 2, and 3 mRNAs were absent or sparse in both cell types. In summary, the results demonstrate, for the first time, the presence of functional 5-HT uptake systems in feto-placental endothelial cells and fetal platelets, cells that are in direct contact with fetal blood plasma. The data also highlight the sensitivity to various psychotropic drugs of 5-HT transport into trophoblasts facing the maternal blood. The multiple, high-, and low-affinity systems present for the cellular uptake of 5-HT underscore the importance of 5-HT homeostasis at the maternal-fetal interface.
Oxysterols are oxidized cholesterol derivatives whose systemic levels are found elevated in pregnancy disorders such as gestational diabetes mellitus (GDM). Oxysterols act through various cellular receptors and serve as a key metabolic signal, coordinating inflammation. GDM is a condition of low-grade chronic inflammation accompanied by altered inflammatory profiles in the mother, placenta and fetus. Higher levels of two oxysterols, namely 7-ketocholesterol (7-ketoC) and 7β-hydroxycholesterol (7β-OHC), were observed in fetoplacental endothelial cells (fpEC) and cord blood of GDM offspring. In this study, we tested the effects of 7-ketoC and 7β-OHC on inflammation and investigated the underlying mechanisms involved. Primary fpEC in culture treated with 7-ketoC or 7β-OHC, induced the activation of mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NFκB) signaling, which resulted in the expression of pro-inflammatory cytokines (IL-6, IL-8) and intercellular cell adhesion molecule-1 (ICAM-1). Liver-X receptor (LXR) activation is known to repress inflammation. Treatment with LXR synthetic agonist T0901317 dampened oxysterol-induced inflammatory responses. Probucol, an inhibitor of LXR target gene ATP-binding cassette transporter A-1 (ABCA-1), antagonized the protective effects of T0901317, suggesting a potential involvement of ABCA-1 in LXR-mediated repression of inflammatory signaling in fpEC. TLR-4 inhibitor Tak-242 attenuated pro-inflammatory signaling induced by oxysterols downstream of the TLR-4 inflammatory signaling cascade. Taken together, our findings suggest that 7-ketoC and 7β-OHC contribute to placental inflammation through the activation of TLR-4. Pharmacologic activation of LXR in fpEC decelerates its shift to a pro-inflammatory phenotype in the presence of oxysterols.
As opposed to adults, high-density lipoprotein (HDL) is the main cholesterol carrying lipoprotein in fetal circulation. The major HDL receptor, scavenger receptor class B type I (SR-BI), contributes to local cholesterol homeostasis. Arterial endothelial cells (ECA) from human placenta are enriched with cholesterol compared to venous endothelial cells (ECV). Moreover, umbilical venous and arterial plasma cholesterol levels differ markedly. We tested the hypothesis that the uptake of HDL-cholesteryl esters differs between ECA and ECV because of the differential expression of SR-BI. We aimed to identify the key regulators underlying these differences and the functional consequences. Immunohistochemistry was used for visualization of SR-BI in situ. ECA and ECV were isolated from the chorionic plate of human placenta and used for RT-qPCR, Western Blot, and HDL uptake assays with 3H- and 125I-labeled HDL. DNA was extracted for the methylation profiling of the SR-BI promoter. SR-BI regulation was studied by exposing ECA and ECV to differential oxygen concentrations or shear stress. Our results show elevated SR-BI expression and protein abundance in ECA compared to ECV in situ and in vitro. Immunohistochemistry demonstrated that SR-BI is mainly expressed on the apical side of placental endothelial cells in situ, allowing interaction with mature HDL circulating in the fetal blood. This was functionally linked to a higher increase of selective cholesterol ester uptake from fetal HDL in ECA than in ECV, and resulted in increased cholesterol availability in ECA. SR-BI expression on ECV tended to decrease with shear stress, which, together with heterogeneous immunostaining, suggests that SR-BI expression is locally regulated in the placental vasculature. In addition, hypomethylation of several CpG sites within the SR-BI promoter region might contribute to differential expression of SR-BI between chorionic arteries and veins. Therefore, SR-BI contributes to a local cholesterol homeostasis in ECA and ECV of the human feto-placental vasculature.