Activation of the hypoxia response protects mice from amyloid-ß accumulation.

Alzheimer's disease (AD) is the most common cause of dementia with limited treatment options affecting millions of people and the prevalence increasing with the aging population. The current knowledge on the role of the hypoxia/hypoxia-inducible factor (HIF) in the AD pathology is restricted and controversial. We hypothesized based on benefits of the genetic long-term inactivation of HIF prolyl 4-hydroxylase-2 (HIF-P4H-2) on metabolism, vasculature and inflammatory response that prolonged moderate activation of the hypoxia response could hinder AD pathology. We used an aging model to study potential spontaneous accumulation of amyloid-ß (Aß) in HIF-P4H-2-deficient mice and a transgenic APP/PSEN1 mouse model subjected to prolonged sustained environmental hypoxia (15% O2 for 6 weeks) at two different time points of the disease; at age of 4 and 10 months. In both settings, activation of the hypoxia response reduced brain protein aggregate levels and this associated with higher vascularity. In the senescent HIF-P4H-2-deficient mice metabolic reprogramming also contributed to less protein aggregates while in APP/PSEN1 mice lesser Aß associated additionally with hypoxia-mediated favorable responses to neuroinflammation and amyloid precursor protein processing. In conclusion, continuous, non-full-scale activation of the HIF pathway appears to mediate protection against neurodegeneration via several mechanisms and should be studied as a treatment option for AD.

Impaired Mitochondrial Fatty Acid Synthesis Leads to Neurodegeneration in Mice.

There has been a growing interest toward mitochondrial fatty acid synthesis (mtFAS) since the recent discovery of a neurodegenerative human disorder termed MEPAN (mitochondrial enoyl reductase protein associated neurodegeneration), which is caused by mutations in the mitochondrial enoyl-CoA/ACP (acyl carrier protein) reductase (MECR) carrying out the last step of mtFAS. We show here that MECR protein is highly expressed in mouse Purkinje cells (PCs). To elucidate mtFAS function in neural tissue, here, we generated a mouse line with a PC-specific knock-out (KO) of Mecr, leading to inactivation of mtFAS confined to this cell type. Both sexes were studied. The mitochondria in KO PCs displayed abnormal morphology, loss of protein lipoylation, and reduced respiratory chain enzymatic activities by the time these mice were 6 months of age, followed by nearly complete loss of PCs by 9 months of age. These animals exhibited balancing difficulties ∼7 months of age and ataxic symptoms were evident from 8-9 months of age on. Our data show that impairment of mtFAS results in functional and ultrastructural changes in mitochondria followed by death of PCs, mimicking aspects of the clinical phenotype. This KO mouse represents a new model for impaired mitochondrial lipid metabolism and cerebellar ataxia with a distinct and well trackable cellular phenotype. This mouse model will allow the future investigation of the feasibility of metabolite supplementation approaches toward the prevention of neurodegeneration due to dysfunctional mtFAS.SIGNIFICANCE STATEMENT We have recently reported a novel neurodegenerative disorder in humans termed MEPAN (mitochondrial enoyl reductase protein associated neurodegeneration) (Heimer et al., 2016). The cause of neuron degeneration in MEPAN patients is the dysfunction of the highly conserved mitochondrial fatty acid synthesis (mtFAS) pathway due to mutations in MECR, encoding mitochondrial 2-enoyl-CoA/ACP reductase. The report presented here describes the analysis of the first mouse model suffering from mtFAS-defect-induced neurodegenerative changes due to specific disruption of the Mecr gene in Purkinje cells. Our work sheds a light on the mechanisms of neurodegeneration caused by mtFAS deficiency and provides a test bed for future treatment approaches.

Contribution of genetic and dietary insulin resistance to Alzheimer phenotype in APP/PS1 transgenic mice.

According to epidemiological studies, type-2 diabetes increases the risk of Alzheimer's disease. Here, we induced hyperglycaemia in mice overexpressing mutant amyloid precursor protein and presenilin-1 (APdE9) either by cross-breeding them with pancreatic insulin-like growth factor 2 (IGF-2) overexpressing mice or by feeding them with high-fat diet. Glucose and insulin tolerance tests revealed significant hyperglycaemia in mice overexpressing IGF-2, which was exacerbated by high-fat diet. However, sustained hyperinsulinaemia and insulin resistance were observed only in mice co-expressing IGF-2 and APdE9 without correlation to insulin levels in brain. In behavioural tests in aged mice, APdE9 was associated with poor spatial learning and the combination of IGF-2 and high-fat diet further impaired learning. Neither high-fat diet nor IGF-2 increased ß-amyloid burden in the brain. In male mice, IGF-2 increased ß-amyloid 42/40 ratio, which correlated with poor spatial learning. In contrast, inhibitory phosphorylation of glycogen synthase kinase 3ß, which correlated with good spatial learning, was increased in APdE9 and IGF-2 female mice on standard diet, but not on high-fat diet. Interestingly, high-fat diet altered τ isoform expression and increased phosphorylation of τ at Ser202 site in female mice regardless of genotype. These findings provide evidence for new regulatory mechanisms that link type-2 diabetes and Alzheimer pathology.

Functional cholinergic damage develops with amyloid accumulation in young adult APPswe/PS1dE9 transgenic mice.

We investigated the functional characteristics of pre- and postsynaptic cholinergic transmission in APPswe/PS1dE9 double transgenic mice at a young age (7-10 weeks) before the onset of amyloid plaque formation and at adult age (5-6 months) at its onset. We compared brain slices from cerebral cortex and hippocampus with amyloid deposits to slices from striatum with no amyloid plaques by 6 months of age. In young transgenic mice we found no impairments of preformed and newly synthesized [(3)H]-ACh release, indicating intact releasing machinery and release turnover, respectively. Adult transgenic mice displayed a significant increase in preformed [(3)H]-ACh release in cortex but a decrease in hippocampus and striatum. The extent of presynaptic muscarinic autoregulation was unchanged. Evoked release of newly synthesized [(3)H]-ACh was significantly reduced in the cortex and hippocampus but unchanged in the striatum. Carbachol-induced G-protein activation in cortical membranes displayed decreased potency but normal efficacy in adult animals and no changes in young animals. These results indicate that functional pre- and postsynaptic cholinergic deficits are not present in APPswe/PS1dE9 transgenic mice before 10 weeks of age, but develop along with beta-amyloid accumulation in the brain.

Cerebral dopamine neurotrophic factor improves long-term memory in APP/PS1 transgenic mice modeling Alzheimer's disease as well as in wild-type mice.

Cerebral dopamine neurotrophic factor (CDNF) protects and repairs dopamine neurons in animal models of Parkinson's disease, which motivated us to investigate its therapeutic effect in an animal model of Alzheimer's disease (AD). We employed an established APP/PS1 mouse model of AD and gave intrahippocampal injections of CDNF protein or CDNF transgene in an AAV2 viral vector to 1-year-old animals. We performed a behavioral test battery 2 weeks after the injections and collected tissue samples after the 3-week test period. Intrahippocampal CDNF-therapy improved long-term memory in both APP/PS1 mice and wild-type controls, but did not affect spontaneous exploration, object neophobia or early stages of spatial learning. The memory improvement was not associated with decreased brain amyloid load or enhanced hippocampal neurogenesis. Intracranial CDNF treatment has beneficial effects on long-term memory and is well tolerated. The CDNF molecular mechanisms of action on memory await further studies.

High-fat diet increases tau expression in the brain of T2DM and AD mice independently of peripheral metabolic status.

Alzheimer's disease and type 2 diabetes mellitus are risk factors for each other. To investigate the effects of both genetic and high-fat-induced diabetic phenotype on the expression and exon 10 splicing of tau, we used the Alzheimer's disease mouse model (APdE9) cross-bred with the type 2 diabetes mouse model over-expressing insulin-like growth factor 2 in the pancreas. High-fat diet, regardless of the genotype, significantly induced the expression of four repeat tau mRNA and protein in the temporal cortex of female mice. The mRNA levels of three repeat tau were also significantly increased by high-fat diet in the temporal cortex, although three repeat tau expression was considerably lower as compared to four repeat tau. Moreover, high-fat diet significantly increased the mRNA ratio of four repeat tau vs. three repeat tau in the temporal cortex of these mice. All of these effects were independent of the peripheral hyperglycemia, hyperinsulinemia and insulin resistance. Increased four repeat tau and three repeat tau levels significantly associated with impaired memory and reduced rearing in the female mice. High-fat diet did not affect neuroinflammation, Akt/GSK3ß signaling pathway or the expression of tau exon 10 splicing enhancers in the temporal cortex. Our study suggests that the high-fat diet independently of type 2 diabetes or Alzheimer's disease background induces the expression and exon 10 inclusion of tau in the brain of female mice.

Anthocyanin-enriched bilberry and blackcurrant extracts modulate amyloid precursor protein processing and alleviate behavioral abnormalities in the APP/PS1 mouse model of Alzheimer's disease.

A growing body of epidemiological evidence suggests that fruit and vegetable juices containing various phenolic compounds can reduce the risk of Alzheimer's disease (AD). As the altered amyloid precursor protein (APP) processing leading to increased ß-amyloid (Aß) production is a key pathogenic feature of AD, we elucidated the effects of different polyphenols on neuroprotection and APP processing under different in vitro stress conditions. The effects of these compounds were also investigated in transgenic AD mice (APdE9). Free radical toxicity and apoptosis were induced in human SH-SY5Y neuroblastoma cells overexpressing APP751. Menadione-induced production of reactive oxygen species was significantly decreased upon treatment with myricetin, quercetin or anthocyanin-rich extracts in a dose-dependent manner. However, these extracts did not affect caspase-3 activation, APP processing or Aß levels upon staurosporine-induced apoptosis. APdE9 mice fed with anthocyanin-rich bilberry or blackcurrant extracts showed decreased APP C-terminal fragment levels in the cerebral cortex as compared to APdE9 mice on the control diet. Soluble Aß40 and Aß42 levels were significantly decreased in bilberry-fed mice as compared to blackcurrant-fed mice. Conversely, the ratio of insoluble Aß42/40 was significantly decreased in blackcurrant-fed mice relative to bilberry-fed mice. Both berry diets alleviated the spatial working memory deficit of aged APdE9 mice as compared to mice on the control diet. There were no changes in the expression or phosphorylation status of tau in APdE9 mice with respect to diet. These data suggest that anthocyanin-rich bilberry and blackcurrant diets favorably modulate APP processing and alleviate behavioral abnormalities in a mouse model of AD.