ASK1 is involved in cognitive impairment caused by long-term high-fat diet feeding in mice

Adiponectin and resistin modulate the progression of Alzheimer´s disease in a metabolic syndrome model

Metabolic syndrome (MetS), a cluster of metabolic conditions that include obesity, hyperlipidemia, and insulin resistance, increases the risk of several aging-related brain diseases, including Alzheimer's disease (AD). However, the underlying mechanism explaining the link between MetS and brain function is poorly understood. Among the possible mediators are several adipose-derived secreted molecules called adipokines, including adiponectin (ApN) and resistin, which have been shown to regulate brain function by modulating several metabolic processes. To investigate the impact of adipokines on MetS, we employed a diet-induced model to induce the various complications associated with MetS. For this purpose, we administered a high-fat diet (HFD) to both WT and APP/PSN1 mice at a pre-symptomatic disease stage. Our data showed that MetS causes a fast decline in cognitive performance and stimulates Aβ42 production in the brain. Interestingly, ApN treatment restored glucose metabolism and improved cognitive functions by 50% while decreasing the Aβ42/40 ratio by approximately 65%. In contrast, resistin exacerbated Aβ pathology, increased oxidative stress, and strongly reduced glucose metabolism. Together, our data demonstrate that ApN and resistin alterations could further contribute to AD pathology.

Gene Expression Profile in Different Age Groups and Its Association with Cognitive Function in Healthy Malay Adults in Malaysia

The mechanism of cognitive aging at the molecular level is complex and not well understood. Growing evidence suggests that cognitive differences might also be caused by ethnicity. Thus, this study aims to determine the gene expression changes associated with age-related cognitive decline among Malay adults in Malaysia. A cross-sectional study was conducted on 160 healthy Malay subjects, aged between 28 and 79, and recruited around Selangor and Klang Valley, Malaysia. Gene expression analysis was performed using a HumanHT-12v4.0 Expression BeadChip microarray kit. The top 20 differentially expressed genes at p < 0.05 and fold change (FC) = 1.2 showed that PAFAH1B3, HIST1H1E, KCNA3, TM7SF2, RGS1, and TGFBRAP1 were regulated with increased age. The gene set analysis suggests that the Malay adult's susceptibility to developing age-related cognitive decline might be due to the changes in gene expression patterns associated with inflammation, signal transduction, and metabolic pathway in the genetic network. It may, perhaps, have important implications for finding a biomarker for cognitive decline and offer molecular targets to achieve successful aging, mainly in the Malay population in Malaysia.

Obesity-like metabolic effects of high-carbohydrate or high-fat diets consumption in metabolic and renal functions

Present study investigated which diet, high-carbohydrate (HCD) or high-fat (HFD), most effectively induces classical characteristics of obesity in mice. Mice were fed commercial chow (control), an HCD, or an HFD for 12 weeks. HFD and HCD increased body weight, fat mass, and glycaemia, whereas the HFD augmented insulinemia. In the kidney, the HFD caused albuminuria, and reductions in fractional Na⁺ excretion, Thromboxane B2 (TXB2) excretion, and urinary flow, whereas the HCD reduced glomerular filtration, plasma osmolality, and TXB2 and Prostaglandin E2 excretion. The consumption of HFD and HCD modified parameters that indicate histopathological changes, such as proliferation (proliferating-cell-nuclear antigen), inflammation (c-Jun N-terminal-protein), and epithelial-mesenchymal transition (vimentin, and desmin) in renal tissue, but the HCD group presents fewer signals of glomerular hypertrophy or tubule degeneration. In summary, the HCD generated the metabolic and renal changes required for an obesity model, but with a delay in the development of these modifications concerning the HFD.

The Reciprocal Causation of the ASK1-JNK1/2 Pathway and Endoplasmic Reticulum Stress in Diabetes-Induced Cognitive Decline

Diabetes significantly induces cognitive dysfunction. Neuronal apoptosis is the main cause of diabetes-induced cognitive decline (DICD). Apoptosis signal-regulating kinase 1 (ASK1) and endoplasmic reticulum (ER) stress are remarkably activated by diabetes. The role and relationship of ASK1-JNK1/2 signaling and ER stress in DICD have not yet been elucidated. In this study, we used db/db mice as the DICD animal model and confirmed that db/db mice displayed cognitive decline with inferior learning and memory function. Diabetes significantly induced morphological and structural changes, excessive neuronal apoptosis, Aβ_{1 - 42} large deposition, and synaptic dysfunction in the hippocampus. Mechanistic studies found that diabetes significantly triggered ASK1-JNK1/2 signaling activation and increased ER stress in the hippocampus. Moreover, diabetes enhanced the formation of the IRE1α-TRAF2-ASK1 complex, which promotes the crosstalk of ER stress and the ASK1-JNK1/2 pathway during DICD. Furthermore, 4-PBA treatment blocked high glucose (HG)-induced ASK1-JNK1/2 signaling activation, and excessive apoptosis in vitro. Inhibiting ASK1 via siRNA remarkably ameliorated the HG-induced increase in p-IRE1α and associated apoptosis in SH-SY5Y cells, suggesting that ASK1 is essential for the assembly and function of the proapoptotic kinase activity of the IRE1α signalosome. In summary, ER stress and ASK1-JNK1/2 signaling play causal roles in DICD development, which has crosstalk through the formation of the IRE1α-TRAF2-ASK1 complex.

ASK1 inhibition: a therapeutic strategy with multi-system benefits

p38 mitogen-activated protein kinases (P38α and β) and c-Jun N-terminal kinases (JNK1, 2, and 3) are key mediators of the cellular stress response. However, prolonged P38 and JNK signalling is associated with damaging inflammatory responses, reactive oxygen species-induced cell death, and fibrosis in multiple tissues, such as the kidney, liver, central nervous system, and cardiopulmonary systems. These responses are associated with many human diseases, including arthritis, dementia, and multiple organ dysfunctions. Attempts to prevent P38- and JNK-mediated disease using small molecule inhibitors of P38 or JNK have generally been unsuccessful. However, apoptosis signal-regulating kinase 1 (ASK1), an upstream regulator of P38 and JNK, has emerged as an alternative drug target for limiting P38- and JNK-mediated disease. Within this review, we compile the evidence that ASK1 mediates damaging cellular responses via prolonged P38 or JNK activation. We discuss the potential benefits of ASK1 inhibition as a therapeutic and summarise the studies that have tested the effects of ASK1 inhibition in cell and animal disease models, in addition to human clinical trials for a variety of disorders.

Role of Hippocampal Lipocalin-2 in Experimental Diabetic Encephalopathy

Diabetic encephalopathy is a severe diabetes-related complication in the central nervous system (CNS) that is characterized by degenerative neurochemical and structural changes leading to impaired cognitive function. While the exact pathophysiology of diabetic encephalopathy is not well-understood, it is likely that neuroinflammation is one of the key pathogenic mechanisms that cause this complication. Lipocalin-2 (LCN2) is an acute phase protein known to promote neuroinflammation via the recruitment and activation of immune cells and glia, particularly microglia and astrocytes, thereby inducing proinflammatory mediators in a range of neurological disorders. In this study, we investigated the role of LCN2 in multiple aspects of diabetic encephalopathy in mouse models of diabetes. Here, we show that induction of diabetes increased the expression of both Lcn2 mRNA and protein in the hippocampus. Genetic deficiency of Lcn2 significantly reduced gliosis, recruitment of macrophages, and production of inflammatory cytokines in the diabetic mice. Further, diabetes-induced hippocampal toxicity and cognitive decline were both lower in Lcn2 knockout mice than in the wild-type animals. Taken together, our findings highlight the critical role of LCN2 in the pathogenesis of diabetic encephalopathy.

Omega-3 fatty acids revert high-fat diet-induced neuroinflammation but not recognition memory impairment in rats

Neuroinflammation is a consequence of overeating and may predispose to the development of cognitive decline and neurological disorders. This study aimed to evaluate the impact of omega-3 supplementation on memory and neuroinflammatory markers in rats fed a high-fat diet. Male Wistar rats were divided into four groups: standard diet (SD); standard diet + omega-3 (SD + O); high fat diet (HFD); and high fat diet + omega-3 (HFD + O). Diet administration was performed for 20 weeks and omega-3 supplementation started at the 16th week. HFD significantly increased body weight, while omega-3 supplementation did not modify the total weight gain. However, animals from the HFD + O group showed a lower level of visceral fat along with an improvement in insulin sensitivity following HFD. Thus, our results demonstrate a beneficial metabolic role of omega-3 following HFD. On the other hand, HFD animals presented an impairment in object recognition memory, which was not recovered by omega-3. In addition, there was an increase in GFAP-positive cells in the cerebral cortex of the HFD group, showing that omega-3 supplementation can be effective to decrease astrogliosis. However, no differences in GFAP number of cells were found in the hippocampus. We also demonstrated a significant increase in gene expression of pro-inflammatory cytokines IL-6 and TNF-α in cerebral cortex of the HFD group, reinforcing the anti-inflammatory role of this family of fatty acids. In summary, omega-3 supplementation was not sufficient to reverse the memory deficit caused by HFD, although it played an important role in reducing the neuroinflammatory profile. Therefore, omega-3 fatty acids may play an important role in the central nervous system, preventing the progression of neuroinflammation in obesity.

Detrimental Effects of Centrally Administered Angiotensin II are Enhanced in a Mouse Model of Alzheimer Disease Independently of Blood Pressure

Background

The significance of brain angiotensin II in Alzheimer disease (AD) is unclear.

Methods and Results

To examine the role of brain angiotensin II in AD, intracerebroventricular angiotensin II infusion was performed on 5XFAD mice, a mouse model of AD, and wild‐type mice, and the detrimental effects of brain angiotensin II was compared between the 2 strains of mice. Intracerebroventricular angiotensin II infusion significantly impaired cognitive function in 5XFAD mice but not in wild‐type mice. This vulnerability of 5XFAD mice to brain angiotensin II was associated with enhancement of hippocampal inflammation and oxidative stress and with increased cerebrovascular amyloid β deposition. We also compared the effect of brain angiotensin II on the heart and skeletal muscle between the 2 strains because AD is associated with heart failure and sarcopenia. We found that cardiac compensatory response of 5XFAD mice to brain angiotensin II–induced hypertension was less than that of wild‐type mice. Brain angiotensin II caused skeletal muscle atrophy and injury in 5XFAD mice more than in wild‐type mice.

Conclusions

Brain angiotensin II seems to be involved in cognitive impairment and brain injury in AD, which is associated with oxidative stress, inflammation, and cerebral amyloid angiopathy. Further, brain angiotensin II may participate in cardiac disease and sarcopenia observed in AD.

Cholesterol contributes to dopamine-neuronal loss in MPTP mouse model of Parkinson's disease: Involvement of mitochondrial dysfunctions and oxidative stress

Hypercholesterolemia is a known contributor to the pathogenesis of Alzheimer’s disease while its role in the occurrence of Parkinson’s disease (PD) is only conjecture and far from conclusive. Altered antioxidant homeostasis and mitochondrial functions are the key mechanisms in loss of dopaminergic neurons in the substantia nigra (SN) region of the midbrain in PD. Hypercholesterolemia is reported to cause oxidative stress and mitochondrial dysfunctions in the cortex and hippocampus regions of the brain in rodents. However, the impact of hypercholesterolemia on the midbrain dopaminergic neurons in animal models of PD remains elusive. We tested the hypothesis that hypercholesterolemia in MPTP model of PD would potentiate dopaminergic neuron loss in SN by disrupting mitochondrial functions and antioxidant homeostasis. It is evident from the present study that hypercholesterolemia in naïve animals caused dopamine neuronal loss in SN with subsequent reduction in striatal dopamine levels producing motor impairment. Moreover, in the MPTP model of PD, hypercholesterolemia exacerbated MPTP-induced reduction of striatal dopamine as well as dopaminergic neurons in SN with motor behavioral depreciation. Activity of mitochondrial complexes, mainly complex-I and III, was impaired severely in the nigrostriatal pathway of hypercholesterolemic animals treated with MPTP. Hypercholesterolemia caused oxidative stress in the nigrostriatal pathway with increased generation of hydroxyl radicals and enhanced activity of antioxidant enzymes, which were further aggravated in the hypercholesterolemic mice with Parkinsonism. In conclusion, our findings provide evidence of increased vulnerability of the midbrain dopaminergic neurons in PD with hypercholesterolemia.

Oxiracetam can improve cognitive impairment after chronic cerebral hypoperfusion in rats

Chronic cerebral hypoperfusion (CCH) induces cognitive deficits. Although CCH can be improved, cognitive impairment is not improved accordingly. To date, many studies have focused on investigating the pathophysiological mechanisms of CCH; however, the treatment of the induced cognitive impairment remains ineffective. Thus, the mechanisms underlying cognitive impairment after CCH and potential agents for treating this impairment need to be explored further. Oxiracetam is a nootropic drug that improves clinical outcomes for some central nervous system (CNS) disorders. Whether it can improve cognitive impairment after CCH is unknown. In this study, we used behavioural methods, electrophysiology, biochemistry, histopathological staining and transmission electron microscope to investigate rat's cognitive impairment by CCH, and found that Oxiracetam could improve CCH-induced cognitive impairment and prevent deficits of neural plasticity, white matter lesions, and synaptic ultrastructure. These results suggest that Oxiracetam may be effective as a potential agent against CCH-induced cognitive impairment.

High-Fat-Diet Intake Enhances Cerebral Amyloid Angiopathy and Cognitive Impairment in a Mouse Model of Alzheimer's Disease, Independently of Metabolic Disorders

Background

The high‐fat Western diet is postulated to be associated with the onset and progression of Alzheimer's disease (AD). However, the role of high‐fat‐diet consumption in AD pathology is unknown. This study was undertaken to examine the role of high‐fat‐diet intake in AD.

Methods and Results

5XFAD mice, a useful mouse model of AD, and control wild‐type mice were fed (1) high‐fat diet or (2) control diet for 10 weeks. The effects on cerebral AD pathology, cognitive function, and metabolic parameters were compared between each group of mice. High‐fat diet significantly enhanced cerebrovascular β‐amyloid (Aβ) deposition (P<0.05) and impaired cognitive function (P<0.05) in 5XFAD mice, but not in wild‐type mice. High‐fat diet enhanced hippocampal oxidative stress (P<0.05) and NADPH oxidase subunits, gp91^phox (P<0.01) and p22^phox (P<0.01) in 5XFAD mice, but not in wild‐type mice. Furthermore, high‐fat diet reduced cerebral occludin (P<0.05) in 5XFAD mice, but not in wild‐type mice. Thus, 5XFAD mice exhibited greater susceptibility to high‐fat diet than wild‐type mice regarding cerebrovascular injury and cognitive impairment. On the other hand, 5XFAD mice fed high‐fat diet exhibited much less increase in body weight, white adipose tissue weight, and adipocyte size than their wild‐type counterparts. High‐fat diet significantly impaired glucose tolerance in wild‐type mice but not in 5XFAD mice. Thus, 5XFAD mice had much less susceptibility to high‐fat‐diet‐induced metabolic disorders than wild‐type mice.

Conclusions

High‐fat diet, independently of metabolic disorders, significantly promotes the progression of AD‐like pathology through enhancement of cerebral amyloid angiopathy and oxidative stress.

Voluntary wheel-running attenuates insulin and weight gain and affects anxiety-like behaviors in C57BL6/J mice exposed to a high-fat diet

It is widely accepted that lifestyle plays a crucial role on the quality of life in individuals, particularly in western societies where poor diet is correlated to alterations in behavior and the increased possibility of developing type-2 diabetes. While exercising is known to produce improvements to overall health, there is conflicting evidence on how much of an effect exercise has staving off the development of type-2 diabetes or counteracting the effects of diet on anxiety. Thus, this study investigated the effects of voluntary wheel-running access on the progression of diabetes-like symptoms and open field and light-dark box behaviors in C57BL/6J mice fed a high-fat diet. C57BL/6J mice were placed into either running-wheel cages or cages without a running-wheel, given either regular chow or a high-fat diet, and their body mass, food consumption, glucose tolerance, insulin and c-peptide levels were measured. Mice were also exposed to the open field and light-dark box tests for anxiety-like behaviors. Access to a running-wheel partially attenuated the obesity and hyperinsulinemia associated with high-fat diet consumption in these mice, but did not affect glucose tolerance or c-peptide levels. Wheel-running strongly increased anxiety-like and decreased explorative-like behaviors in the open field and light-dark box, while high-fat diet consumption produced smaller increases in anxiety. These results suggest that voluntary wheel-running can assuage some, but not all, of the physiological problems associated with high-fat diet consumption, and can modify anxiety-like behaviors regardless of diet consumed.