Gene-activation mechanisms in the regression of atherosclerosis, elimination of diabetes type 2, and prevention of dementia

Hepatopancreatic metabolic disorders and their implications in the development of Alzheimer's disease and vascular dementia

Dementia has been faced with significant public health challenges and economic burdens that urges the need to develop safe and effective interventions. In recent years, an increasing number of studies have focused on the relationship between dementia and liver and pancreatic metabolic disorders that result in diseases such as diabetes, obesity, hypertension and dyslipidemia. Previous reports have shown that there is a plausible correlation between pathologies caused by hepatopancreatic dysfunctions and dementia. Glucose, insulin and IGF-1 metabolized in the liver and pancreas probably have an important influence on the pathophysiology of the most common dementias: Alzheimer's and vascular dementia. This current review highlights recent studies aimed at identifying convergent mechanisms, such as insulin resistance and other diseases, linked to altered hepatic and pancreatic metabolism, which are capable of causing brain changes that ultimately lead to dementia.

DNA methylation dynamics in human carotid plaques after cerebrovascular events

OBJECTIVE

To understand whether cerebrovascular events, a major complication of atherosclerosis, are associated with any specific DNA methylation changes in the carotid plaque.

APPROACH AND RESULTS

We profiled the DNA methylomes of human symptomatic carotid plaques obtained from patients who had cerebrovascular events (n=19) and asymptomatic counterparts (n=19) with a high-density microarray (≈485 000 CpG sites, Illumina), and crossed DNA methylation data with RNAseq-based expression data from an independent symptomatic carotid plaque set (n=8). Few (30) CpGs showed a significant (P<0.05; absolute Delta-Beta, >0.20) differential methylation between the 2 groups. Within symptomatic carotid plaques, DNA methylation correlated significantly with postcerebrovascular event time (range, 3-45 days; r-value range, -0.926 to 0.857; P<0.05) for ≈45 000 CpGs, the vast majority of which became hypomethylated with increasing postcerebrovascular event time. Hypomethylation was not due to erasure of the gene-body and CG-poor region hypermethylation that accompany the progression of stable lesions, but rather targeted promoters and CpG islands. Noticeably, promoter hypomethylation and increased expression of genes involved in the inhibition of the inflammatory response, defense against oxidative stress, and active DNA demethylation were observed with increasing postcerebrovascular event time. Concomitantly, histological changes consistent with phagocyte-driven plaque healing were observed.

CONCLUSIONS

Weak changes in the DNA methylome distinguish symptomatic from asymptomatic plaques, but a widespread demethylation resulting in permissive transcriptional marks at atheroprotective gene promoters is established in plaques after a cerebrovascular event, thus mirroring previous observations that ruptured plaques tend to revert to a stable structure. The identified loci are candidate targets to accelerate the pace of carotid plaque stabilization.

New findings concerning vertebrate porin II--on the relevance of glycine motifs of type-1 VDAC

New findings concerning vertebrate porin part I was published in 1997, then summarizing early data and reflections regarding the molecular structure of vertebrate voltage-dependent anion-selective channels, VDAC/eukaryotic porin, and the extra-mitochondrial expression pattern of human type-1 VDAC. Meanwhile, endeavors of different laboratories confirmed and widened this beginning by encircling the function of the channels. Regarding the function of mitochondrial outer membrane-standing VDACs the channels are established parts of the intrinsic apoptotic pathway and thus therapeutic targets in studies on several diseases: cancer, Alzheimer's disease, Down Syndrome, Parkinson's disease, Amyotrophic Lateral Sclerosis, cystic fibrosis and malaria. Regarding cell membrane-integrated type-1 VDAC it has been documented by different approaches that this porin channel is engaged in cell volume regulation, trans-membrane electron transport and apoptosis. Furthermore, new data insinuate a bridging of extrinsic and intrinsic apoptotic pathways, putatively gaining relevance in Alzheimer research. Mammalian type-1 VDAC, a β-barrel, is basically built up by nineteen β-sheets connected by peptide stretches of varying lengths. The molecule also comprises an N-terminal stretch of some twenty amino acids which, according to biochemical data, traverses the channel lumen towards the cytosolic surface of outer mitochondrial membranes or the plasma lemma, respectively and works as voltage sensor in channel gating. In artificial lipid bilayers VDACs figure as anion or cation-channels, as VDACs are permeable to both cations and anions, with voltage shifts changing the relative permeability. Type-1 VDAC carries several motifs where glycine residues are in critical positions. Motifs of this type, on the on hand, are established nucleotide binding sites. On the other hand, the GxxxG motifs are also discussed as relevant peptide dimerization/aggregation/membrane perturbation motifs. Finally, GxxxG motifs bind cholesterol. Type-1 VDAC shows one such GxxxG motif at the proximal end of its N-terminal voltage sensor while amyloid Aβ peptides include three of them in series. Noteworthy, two additional may be modified versions, GxxxGxG and GxxGxxxG, are found on β-sheet 19 or 9, respectively. Recent data have allowed speculating that amyloid Aβ induces apoptosis via opening type-1 VDAC in cell membranes of hypo-metabolic neurons, a process most likely running over life time--as leaves fall from trees in the tropics--and ending in Alzheimer's disease whenever critical brain regions are affected. The expression of GxxxG motifs on either reactant under consideration is in line with this model of Alzheimer's disease pathogenesis, which clearly differs from the amyloid Aβ cascade theory, and which can, furthermore, be understood as a basic model for apoptosis induction. However, to assume randomly distributed interactions of body wide found amyloid Aβ peptides with the N-terminal voltage sensors of ubiquitously expressed cell membrane-standing human type-1 VDAC opens up a new view on Alzheimer's disease, which might even include a clue on systemic aspects of the disease. While elaborating this concept, my focus was at first only on the GxxxG motif at the proximal end of the N-terminal voltage sensor of type-1 VDAC. Here, I include a corresponding sequence stretch on the channel's β-sheet 19, too.

Why cancer survivors have a lower risk of Alzheimer disease

Tying up two recent lines of experimental evidence may help explain this vital issue. On the one hand, data indicate that cancerous transformations of cells include changes in expression level and/or the functionality of multidrug resistance modulators which then disturb chemotherapy. On the other hand, studies have shown that some of the ABC transporters--at the blood-brain barrier--work as effective efflux pumps for amyloid Aβ peptides. Amyloid Aβ peptides, cut from the amyloid precursor protein of neurons can be assumed to induce brain wide neuronal apoptosis via opening plasma lemma-standing type-1 VDAC/porin channels as shown by in vitro experiments using established neuronal cell lines. However, extrusion of apoptosis inductive Aβ by increased ABC transporter activity at the blood-brain barrier from the brain of cancer survivors might abolish this effect. The hypothesis presented can be read as a clue on what in recent literature is referred to as the inverse association of cancer and Alzheimer disease.

Alterations of LXRα and LXRβ expression in the hypothalamus of glucose-intolerant rats

Liver X receptor (LXR) α and β are nuclear receptors that are crucial for the regulation of carbohydrate and lipid metabolism. Activation of LXRs in the brain facilitates cholesterol clearance and improves cognitive deficits, thus they are considered as promising drug targets to treat diseases such as atherosclerosis and Alzheimer's disease. Nevertheless, little is known about the function and localization of LXRs in the brain. Here, we studied the expression of LXR in the brains of rats that received free access to 10% (w/v) fructose group (FG) in their beverages or water control drinks (control group (CG)). After 6 weeks rats in the FG presented with hypertriglyceridemia, hyperinsulinemia, and became glucose intolerant, suggesting a progression toward type 2 diabetes. We found that hypothalamic LXR expression was altered in fructose-fed rats. Rats in the FG presented with a decrease in LXRβ levels while showing an increase in LXRα expression in the hypothalamus but not in the hippocampus, cerebellum, or neocortex. Moreover, both LXRα and β expression correlated negatively with insulin and triglyceride levels. Interestingly, LXRβ showed a negative correlation with the area under the curve during the glucose tolerance test in the CG and a positive correlation in the FG. Immunocytochemistry revealed that the paraventricular and ventromedial nuclei express mainly LXRα whereas the arcuate nucleus expresses LXRβ. Both LXR immunosignals were found in the median preoptic area. This is the first study showing a relationship between glucose and lipid homeostasis and the expression of LXRs in the hypothalamus, suggesting that LXRs may trigger neurochemical and neurophysiological responses for the control of food intake and energy expenditure through these receptors.