Acute exercise and brain BACE1 protein content: a time course study

Low-Dose Lithium Supplementation Influences GSK3β Activity in a Brain Region Specific Manner in C57BL6 Male Mice

BACKGROUND

Lithium, a commonly used treatment for bipolar disorder, has been shown to have neuroprotective effects for other conditions including Alzheimer's disease via the inhibition of the enzyme glycogen synthase kinase-3 (GSK3). However, dose-dependent adverse effects of lithium are well-documented, highlighting the need to determine if low doses of lithium can reliably reduce GSK3 activity.

OBJECTIVE

The purpose of this study was to evaluate the effects of a low-dose lithium supplementation on GSK3 activity in the brain of an early, diet-induced Alzheimer's disease model.

METHODS

Male C57BL/6J mice were divided into either a 6-week or 12-week study. In the 6-week study, mice were fed a chow diet or a chow diet with lithium-supplemented drinking water (10 mg/kg/day) for 6 weeks. Alternatively, in the 12-week study, mice were fed a chow diet, a high-fat diet (HFD), or a HFD with lithium-supplemented drinking water for 12 weeks. Prefrontal cortex and hippocampal tissues were collected for analysis.

RESULTS

Results demonstrated reduced GSK3 activity in the prefrontal cortex as early as 6 weeks of lithium supplementation, in the absence of inhibitory phosphorylation changes. Further, lithium supplementation in an obese model reduced prefrontal cortex GSK3 activity as well as improved insulin sensitivity.

CONCLUSION

Collectively, these data provide evidence for low-dose lithium supplementation to inhibit GSK3 activity in the brain. Moreover, these results indicate that GSK3 activity can be inhibited despite any changes in phosphorylation. These findings contribute to an overall greater understanding of low-dose lithium's ability to influence GSK3 activity in the brain and its potential as an Alzheimer's disease prophylactic.

APP Processing: A Biochemical Competition Influenced by Exercise-Induced Signaling Mediators?

Neurodegenerative diseases, such as Alzheimer's disease (AD), are becoming more common in aging our society. One specific neuropathological hallmark of this disease is excessive accumulation of amyloid-β (Aβ) peptides, which can aggregate to form the plaques commonly associated with this disease. These plaques are often observed well before clinical diagnosis of AD. At the cellular level, both production and aggregation of Aβ peptides in the brain is detrimental to neuronal cell production, survival, and function, as well as often resulting in neuronal dysfunction and death. Exercise and physical activity have been shown to improve overall health, including brain health, and in the last several years there has been evidence to support that exercise may be able to regulate Aβ peptide production in the brain. Exercise promotes the release of a wide array of signaling mediators from various metabolically active tissues and organs in the body. These exercise-induced signaling mediators could be the driving force behind some of the beneficial effects observed in brain with exercise. This review will aim to discuss potential exercise-induced signaling mediators with the capacity to influence various proteins involved in the formation of Aβ peptide production in the brain.

Post-Exercise Serum from Humans Influences the Biological Tug of War of APP Processing in Human Neuronal Cells

Neurodegenerative diseases such as Alzheimer's disease (AD) are becoming more prevalent in our aging society. One specific neuropathological hallmark of this disease is the accumulation of amyloid-β (Aβ) peptides, which aggregate to form extra-neuronal plaques. Increased Aβ peptides are often observed well before symptoms of AD develop, highlighting the importance of targeting Aβ producing pathways early on in disease progression. Evidence indicates that exercise has the capacity to reduce Aβ peptide production in the brain however the mechanisms remain unknown. Exercise-induced signaling mediators could be the driving force behind some of the beneficial effects observed in the brain with exercise. The purpose of this study was to examine if post-exercise serum and the factors it contains can alter neuronal APP processing. Human SH-SY5Y neuronal cells were differentiated with retinoic acid for 5 days and treated with 10% pre- or post-exercise serum from humans for 30 minutes. Cells were collected for analysis of acute (30 minutes; n=6) or adaptive (24 hours post-treatment; n=6) responses. There were no statistical differences in ADAM10 and BACE1 mRNA or protein expression with post-exercise serum treatment at either time point. However, there was an increase in the ratio of sAPPa to sAPPβ protein content (p=0.05) after 30 minutes of post-exercise serum treatment. Additionally, 30 minutes of post-exercise serum treatment increased ADAM10 (p=0.01) and BACE1 (p=0.02) activity. These findings suggest that post-exercise serum modulates important enzymes involved in APP processing, pushing the cascade towards the non-amyloidogenic arm.

Voluntary wheel running alters markers of amyloid-beta precursor protein processing in an ovarian hormone depleted model

INTRODUCTION

Aberrant cleavage of the transmembrane protein, amyloid-beta precursor protein (ABPP), results in the overproduction of amyloid-beta (AB) peptides which can form senile plaques in the brain. These plaques can get lodged within synapses and disrupt neuronal communication ultimately leading to rampant neuron death. The rate-limiting enzyme in AB production is beta-site ABPP cleaving enzyme 1 (BACE1). In females, estrogen loss is associated with increases in AB and BACE1 content and activity. Exercise is known to have anti-amyloidogenic effects and may be able to alter BACE1 in cases of ovarian hormone depletion. This study aimed to examine the effects of physical activity on BACE1 in intact and ovariectomized female mice.

METHODS

Female C57BL/6 mice (24 weeks old) underwent bilateral ovariectomy (OVX; n=20) or SHAM surgery (SHAM; n=20). Mice were assigned to one of four groups (n=10/group) for 8 weeks: (1) sham (SHAM), (2) sham with a wheel (SHAM VWR), (3) ovariectomized (OVX), or (4) ovariectomized with a wheel (OVX VWR).

RESULTS

Novel object recognition testing demonstrated that OVX mice had a lower percentage of novel object investigation time compared to SHAM. OVX mice also had higher prefrontal cortex BACE1 activity compared to SHAM (p<0.0001), while the OVX+VWR activity was not different from SHAM.

DISCUSSIONS

Our results demonstrate that voluntary wheel running in an ovariectomized model prevented increases in BACE1 activity, maintained memory recall, and may provide a method of slowing the progression of Alzheimer's disease.

Wheel running leads to sex-specific effects on Western diet-associated glucose homeostasis and brain insulin signaling without altering food-related impulsive choice

OBJECTIVES

There is a clear association between obesity and impulsivity. While exercise can suppress weight gain and decrease impulsive choice (IC), the relationship between impulsivity, the consumption of palatable, energy dense diets, and exercise is unclear. We examined IC before and after Western diet (WD) exposure in rats of both sexes and whether exercise would rescue any diet-mediated increases in IC. Our hypotheses were twofold: first, increased impulsivity would be associated with higher WD preference in a positive feedback loop and second, increased WD consumption would impair both peripheral and central insulin signaling, both of which exercise would attenuate.

METHODS

Following baseline assessment of IC through a delay discounting task, rats were divided into naïve, sedentary (Sed), or wheel running (WR) groups for a 5-week WR and two-diet choice period after which rats underwent an oral glucose (OGTT) and insulin tolerance test (ITT) in addition to a re-test of IC. Insulin induced Akt-GSK3β signaling in the brain was examined using western blot.

RESULTS

All Sed rats preferred the WD diet, and all WR rats initially avoided the WD but subsequently reversed their avoidance to preference with females reversing earlier than males. Exercise suppressed weight gain and adiposity to a greater extent in males than females. Only WR males showed improved glucose clearance during OGTT, but both male and female WR rats had a faster recovery of hypoglycemia during ITT. Furthermore, WR rescued WD-induced deficits in hypothalamic Akt-GSK3β signaling in males but not females. In the prefrontal cortex, however, WD and WR both reduced Akt-GSK3β signaling in males but not females. There were no sex differences in IC at baseline, and all rats made more impulsive choices during the re-test independent of diet, sex, or exercise.

DISCUSSION

The results suggest that while exercise may have a greater efficacy at attenuating diet-mediated metabolic dysregulation in males, it has some beneficial effects for females and highlights the need to develop sex-specific interventions for restoring energy balance.

New Horizon: Exercise and a Focus on Tissue-Brain Crosstalk

The world population is aging, leading to increased rates of neurodegenerative disorders. Exercise has countless health benefits and has consistently been shown to improve brain health and cognitive function. The purpose of this review is to provide an overview of exercise-induced adaptations in the brain with a focus on crosstalk between peripheral tissues and the brain. We highlight recent investigations into exercise-induced circulating factors, or exerkines, including irisin, cathepsin B, GPLD1, and ketones and the mechanisms mediating their effects in the brain.

Exercise and estrogen: common pathways in Alzheimer's disease pathology

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by progressive declines in cognitive function. Current epidemiological data indicate significant sex-linked disparities, where females have a higher risk of developing AD compared with male counterparts. This disparity necessitates further investigations to uncover the pathological and molecular factors influencing these sex differences. Although the underlying pathways behind this observed disparity remain elusive, recent research points to menopausal estrogen loss as a potential factor. Estrogen holds a significant role in amyloid precursor protein (APP) processing and overall neuronal health through the regulation of brain-derived neurotrophic factor (BDNF), a factor that is also reduced in postmenopausal women. BDNF is a known contributor to neuronal health and its reduced expression is typically linked to AD disorders. Exercise is known to increase BDNF and may provide an accessible activity for postmenopausal women to reduce their risk of AD. This review aims to discuss the relationship between estrogen, exercise, and BDNF in AD pathology.

Examination of BDNF Treatment on BACE1 Activity and Acute Exercise on Brain BDNF Signaling

Perturbations in metabolism results in the accumulation of beta-amyloid peptides, which is a pathological feature of Alzheimer’s disease. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the rate limiting enzyme responsible for beta-amyloid production. Obesogenic diets increase BACE1 while exercise reduces BACE1 activity, although the mechanisms are unknown. Brain-derived neurotropic factor (BDNF) is an exercise inducible neurotrophic factor, however, it is unknown if BDNF is related to the effects of exercise on BACE1. The purpose of this study was to determine the direct effect of BDNF on BACE1 activity and to examine neuronal pathways induced by exercise. C57BL/6J male mice were assigned to either a low (n = 36) or high fat diet (n = 36) for 10 weeks. To determine the direct effect of BDNF on BACE1, a subset of mice (low fat diet = 12 and high fat diet n = 12) were used for an explant experiment where the brain tissue was directly treated with BDNF (100 ng/ml) for 30 min. To examine neuronal pathways activated with exercise, mice remained sedentary (n = 12) or underwent an acute bout of treadmill running at 15 m/min with a 5% incline for 120 min (n = 12). The prefrontal cortex and hippocampus were collected 2-h post-exercise. Direct treatment with BDNF resulted in reductions in BACE1 activity in the prefrontal cortex (p < 0.05), but not the hippocampus. The high fat diet reduced BDNF content in the hippocampus; however, the acute bout of exercise increased BDNF in the prefrontal cortex (p < 0.05). These novel findings demonstrate the region specific differences in exercise induced BDNF in lean and obese mice and show that BDNF can reduce BACE1 activity, independent of other exercise-induced alterations. This work demonstrates a previously unknown link between BDNF and BACE1 regulation.

Resveratrol, Metabolic Dysregulation, and Alzheimer's Disease: Considerations for Neurogenerative Disease

Alzheimer’s disease (AD) has traditionally been discussed as a disease where serious cognitive decline is a result of Aβ-plaque accumulation, tau tangle formation, and neurodegeneration. Recently, it has been shown that metabolic dysregulation observed with insulin resistance and type-2 diabetes actively contributes to the progression of AD. One of the pathologies linking metabolic disease to AD is the release of inflammatory cytokines that contribute to the development of brain neuroinflammation and mitochondrial dysfunction, ultimately resulting in amyloid-beta peptide production and accumulation. Improving these metabolic impairments has been shown to be effective at reducing AD progression and improving cognitive function. The polyphenol resveratrol (RSV) improves peripheral metabolic disorders and may provide similar benefits centrally in the brain. RSV reduces inflammatory cytokine release, improves mitochondrial energetic function, and improves Aβ-peptide clearance by activating SIRT1 and AMPK. RSV has also been linked to improved cognitive function; however, the mechanisms of action are less defined. However, there is evidence to suggest that chronic RSV-driven AMPK activation may be detrimental to synaptic function and growth, which would directly impact cognition. This review will discuss the benefits and adverse effects of RSV on the brain, highlighting the major signaling pathways and some of the gaps surrounding the use of RSV as a treatment for AD.

Resveratrol confers neuroprotection against high-fat diet in a mouse model of Alzheimer's disease via modulation of proteolytic mechanisms

Cumulative evidence indicates that excessive consumption of calories from saturated fat contributes to the development of Alzheimer's disease (AD). Here, we assess the triggering and progression of AD pathology induced by a high-fat diet (HFD), and the effects of resveratrol, a polyphenol found in common dietary sources with pleiotropic neuroprotective activities. Over 16 weeks, male wild type (WT) and AD transgenic 5XFAD mice were fed a control diet, HFD (60% kcal from fat), or HFD supplemented with 0.1% resveratrol. Resveratrol protected against HFD-induced memory loss in WT mice and prevented memory loss in 5XFAD mice. Resveratrol also reduced the amyloid burden aggravated by HFD in 5XFAD, and protected against HFD-induced tau pathology in both WT and 5XFAD strains. At the mechanistic level, resveratrol inhibited the HFD-increased amyloidogenic processing of the amyloid precursor protein in both strains; it also restored abnormal high levels in the proteolytic activity of the ubiquitin-proteasome system induced by HFD, suggesting the presence of a compensatory mechanism to counteract the accumulation of aberrant proteins. Thus, our data suggest that resveratrol can correct the harmful effects of HFD in the brain and may be a potential therapeutic agent against obesity-related disorders and AD pathology.

Healthy brain, healthy life: a review of diet and exercise interventions to promote brain health and reduce Alzheimer's disease risk

With the world's population aging at a rapid rate, the prevalence of Alzheimer's disease (AD) has significantly increased. These statistics are alarming given recent evidence that a third of dementia cases may be preventable. The role of lifestyle factors, such as diet and exercise, can directly alter the risk of disease development. However, an understanding of the effectiveness of dietary patterns and exercise strategies to reduce AD risk or improve brain function is not fully understood. The aim of this review is to discuss the effects of diet and exercise on AD risk. Key components of the Western and Mediterranean diets are discussed in relation to AD progression, as well as how physical activity promotes brain health. Components of the Western diet (saturated fatty acids and simple carbohydrates) are detrimental to the brain, impair cognition, and increase AD pathologies. While components of the Mediterranean diet (polyunsaturated fatty acids, polyphenols, and antioxidants) are considered to be neuroprotective. Exercise can significantly reduce the risk of AD; however, specific exercise recommendations for older adults are limited and optimal intensity, duration, and type remains unknown. This review highlights important modifiable risk factors for AD and points out potential avenues for future research. Novelty Diet and exercise are modifiable factors that can improve brain health and reduce the risk of AD. Polyunsaturated fatty acids, polyphenols, and antioxidants are neuroprotective. Exercise reduces neuroinflammation, improves brain insulin sensitivity, and increases brain derived neurotrophic factor.