- Academic Editor
Background: The cerebellum is an area of the brain that is prone to
damage in individuals with Alzheimer’s disease (AD). As a non-pharmacological
intervention for AD, exercise training has shown an ameliorating effect on AD
pathology; however, the target regions have mostly been the cerebral cortex and
hippocampus. The main aim of this study was to explore the influence of 12 weeks
of treadmill running on the accumulation of AD-related proteins, dysfunction of
mitochondria, and subsequent neuronal cell death in the cerebellum of triple
transgenic (3xTg-AD) mice. Methods: Four-month-old 3xTg-AD mice were
allocated into two groups: an AD control group (AD, n = 10) and an AD exercise
group (AD-Exe, n = 10). The AD-Exe mice underwent training on a motorized animal
treadmill 5 days a week for 12 weeks. After sacrifice, the cerebellum was
collected and biochemically analyzed. Results: The AD-Exe mice expressed
reduced levels of extracellular
Alzheimer’s disease (AD), the most prevalent type of dementia, is clinically
characterized by a progressive deterioration in intellectual facilities,
difficulty in performing basic tasks, and cognitive impairment [1]. These
symptoms result from neuroinflammation and neurodegeneration potentially arising
from the buildup of extracellular
The cerebellum is as vulnerable as the hippocampus in AD patients, and recent
research has demonstrated A
Cerebellar dysfunction involves deficiencies in synaptic plasticity,
transmission, and motor performance [4]. The presence of toxic proteins can
interfere with mitochondrial structure and function, including mitochondrial
dynamics and biogenesis, leading to processes such as mitophagy or neuronal death
through apoptosis [11, 12]. In the presence of dysfunctional or damaged
mitochondria, there is a downregulation of mitochondrial fusion proteins,
including optic atrophy-1 (OPA1), phosphorylated dynamin-related protein 1 (Drp1)
and Mitofusin 1 (Mfn1). Additionally, there is an increase in the expression of
mitochondrial fission proteins, namely Drp1 and Fission Protein 1 (Fis1), as well
as biogenesis-related proteins such as peroxisome proliferator-activated receptor
gamma coactivator 1-alpha (PGC1), AMP-activated protein kinase (AMPK),
mitochondrial transcription factor A (TFAM), and nuclear respiratory factor
(NRF). Changes in morphology and increased mitochondrial biogenesis contribute to
the development of mitochondrial permeability transition pores (PTP) by
upregulating the expression of the voltage-dependent anion channel (VDAC),
adenine nucleotide translocase (ANT), and Cyclophilin D (CypD). This process
leads to the release of Cytochrome C through the pore, ultimately triggering
mitophagy and apoptosis [13, 14, 15, 16]. Exercise training, as a non-pharmacological
intervention and modifiable risk factor for individuals with AD, has indicated
beneficial effects in slowing down the progression of AD neuropathology [17].
Furthermore, considering physical inactivity is closely related to AD
development, exercise training could be a promising treatment for AD [18].
Extensive research has demonstrated the preventive effects of exercise in AD.
Exercise training ameliorates AD neuropathology by reducing A
Ten male wild-type (C57BL/6) mice, aged 4 months, were obtained from Orient Bio
(Seongnam, Korea) and 3xTg-AD (B6; 129-Tg (APPSwe, tauP301L) 1Lfa
Psen1
At four months of age, 3xTg-AD mice were allocated into two groups: an AD
control group (AD, n = 10) and an AD exercise group (AD-Exe, n = 10). C57BL/6
mice were employed as wild-type control mice (Con; Fig. 1). The exercise group
was given access to a motorized animal treadmill (Columbus Instruments, Inc.,
Columbus, OH, USA) for running for 40 min per session. The exercise training
duration consisted of 5 days per week for a total period of 12 weeks. Prior to
the training, the mice were acclimated to the treadmill for 2 days, starting with
a 10-min session at a speed of 5 m/min on the first day and increasing to 8 m/min
on the second day. Each treadmill session began with a warm-up period for 5 min
at a speed of 5 m/min, which was increased to 8 m/min (40–50% VO
Study design. Con, control; AD, Alzheimer’s disease; Exe, exercise; 3xTg, triple transgenic.
The half cerebellum was homogenized and protein extracts were prepared. After
centrifugation, the resulting supernatants were gathered from the homogenates.
The protein concentration in the samples was quantified using the Bradford assay
(Bio-Rad, Hercules, CA, USA). A total of 20 µg of protein was boiled in
Laemmli sample buffer. The protein samples were then placed onto an
SDS/polyacrylamide gel with a concentration range of 7.5% to 15% for
electrophoresis. Following electrophoresis, the separated proteins were moved
onto a nitrocellulose membrane (Whatman, Dassel, Germany). The membranes were
treated with a blocking solution composed of 5% nonfat dry milk and 0.05% Tween
in Tris-buffered saline for a duration of 1 hour. The membranes were then
incubated with primary antibodies overnight at a temperature of 4 °C.
The following antibodies were used: rabbit anti-Amyloid Oligomer (1:1000; ab9234;
Merck Millipore, Darmstadt, Germany), mouse anti-Tau (Tau46) (1:1000; #4019;
Cell Signaling, Danvers, MA, USA), rabbit anti-Phospho-Tau pThr205 (1:1000;
PA5-35757; Thermo Fisher Scientific, Waltham, MA, USA), rabbit
anti-
The half cerebellum was cut into 40 µm thick sections using a microtome
(CM3050S; Leica Microsystems, Nussloch, Germany). These sections were then
preserved in a cryoprotection solution containing 20 mM KH
The recorded values are presented as means with standard deviation (SD). To
assess statistically significant disparities in the measurements among the groups
of mice, one-way analysis of variance (ANOVA) and post-hoc tests were performed.
All statistical analyses were performed using SPSS-PC software (version 21.0, IBM
Corp., Armonk, NY, USA). Statistical significance was set at p
To explore the effects of exercise training on AD neuropathology and subsequent
Purkinje cell death, levels of amyloid oligomer, p-tau and Purkinje cell markers
were assessed. AD mice had significantly elevated levels of amyloid oligomers
(p
Effect of treadmill exercise on AD-related pathology in
the cerebellum. Representative immunoblot images and quantification of Amyloid
oligomer, p-tau, and Total tau levels. Protein levels are expressed as means
Effect of treadmill exercise on Purkinje cell survival
in the cerebellar vermis. Immunofluorescence staining sections of the cerebellum
were imaged, and the count of Purkinje cells was performed. Values are expressed
as means
With respect to mitochondrial dynamics, AD mice showed significantly
downregulated expressions of OPA1 (p = 0.028) and Mfn1 (p
Effect of treadmill running on mitochondrial dynamics in the
cerebellum. Representative immunoblot images and quantification of OPA1, Mfn1,
p-Drp1, Drp1, and Fis1 levels. Protein levels are expressed as means
The mitochondrial PTP markers were assessed for neural apoptosis (Fig. 5). While
AD induced significantly enhanced expression levels of VDAC (p = 0.028),
ANT (p
Effect of treadmill running on apoptosis in the cerebellum.
Representative immunoblot images and quantification of VDAC, ANT, CypD, and
Cytochrome C levels. Protein levels are expressed as means
Alzheimer’s disease and exercise training showed no significant influence on the
expression of mitochondrial biogenesis (Fig. 6) or mitophagy (Fig. 7) markers.
Although exercise induced upregulation of AMPK (p
Effect of treadmill running on mitochondrial biogenesis in the
cerebellum. Representative immunoblot images and quantification of AMPK, p-AMPK,
PGC1, NRF1, NRF2, and TFAM levels. Protein levels are expressed as means
Effect of treadmill exercise on mitophagy in the
cerebellum. Representative immunoblot images and quantification of Parkin, PINK1
and p62 levels. Protein levels are expressed as means
We investigated whether 12 weeks of treadmill running alleviated AD
neuropathology and mitochondrial damage that could arise from the accumulation of
A
Our findings align with previous studies that provide evidence for accumulated
A
In addition, exercise training has been reported to reduce A
In our study, no significant decrease in p-tau protein was demonstrated in
AD-Exe mice (Fig. 2). This finding corresponds with that of Kim et al.
[36], indicating no change in p-tau but A
We further investigated the potential protective effects of exercise training on mitochondrial dynamics and biogenesis in the AD cerebellum. Our findings indicate that AD mice exhibited reduced levels of the mitochondrial fusion proteins Mfn1, OPA1, and p-Drp1, while the expression levels of the fission proteins Fis1 and Drp1 were increased. In contrast, AD-Exe mice exhibited reversed patterns of expression for mitochondrial fusion and fission proteins, suggesting that exercise training induces mitochondrial fusion. This finding aligns with previous research that demonstrated exercise-induced mitochondrial fusion. Yan et al. [41] reported that 12 weeks of treadmill exercise improved memory and learning in APP/PS1 mice by increasing the expression of mitochondrial fusion proteins, and balancing mitochondrial fusion and fission in the hippocampus. Marques-Aleixo et al. [42] also showed that both treadmill and free-wheel voluntary running improved mitochondrial dynamics and biogenesis in the cortex and cerebellum of Sprague–Dawley rats. However, unlike these findings, we observed significant increases only in AMPK and NRF2 expression in AD-Exe mice, suggesting that exercise had no significant effect on mitochondrial biogenesis (Fig. 6). Possible explanations for this disparity include the AD-induced upregulation of p-tau (Fig. 2) and downregulation of OPA1 (Fig. 4) observed in this study, which did not show significant changes in AD-Exe mice. Jara et al. [12] demonstrated that genetic deletion of tau improved mitochondrial biogenesis and brain function, and Caffin et al. [43] showed that Opa1+/– mice displayed a defect in mitochondrial biogenesis. Therefore, increased p-tau levels and decreased OPA1 expression may contribute to mitochondrial dysfunction.
Considering the increased levels of mitochondrial fission proteins in AD mice (Fig. 4), mitochondrial fragmentation aligned with Cytochrome C, and fusion protein OPA1 release led to mitophagy and neural apoptosis [44]. Therefore, we investigated the mitochondrial PTP and mitophagy markers in the cerebellum of 3xTg mice. The current findings revealed a significant increase in the expression levels of PTP proteins in AD mice, indicating mitochondrial dysfunction. In contrast, protein expression levels in AD-Exe mice were significantly reduced (Fig. 5). This finding suggests an exercise-induced reduction in apoptosis in the cerebellum of 3xTg mice, which is in accordance with previous studies reporting the regulatory effect of exercise training on PTP formation. Koo et al. [45] demonstrated that the brains of transgenic (NSE/APPsw) AD mice subjected to 16 weeks of treadmill exercise showed improved mitochondrial biogenesis and reduced neural apoptosis by suppressing the formation of PTP. Marques-Aleixo et al. [42] also showed that both voluntary wheel and treadmill running enhanced resistance to PTP formation and apoptosis with intensified mitochondrial respiratory activity in the brain of Sprague-Dawley rats. With respect to mitophagy, we found a significant increase in the levels of mitophagy activator proteins parkin and PINK1 in AD mice, indicating dysfunctional mitophagy. This has been well documented in previous studies [46, 47]. However, exercise training did not affect expression of mitophagy markers, as observed in AD-Exe mice, and there was no significant change in p62 levels among the groups. These findings correspond to those of Kim et al. [36] that showed no significant alterations in exercise-induced mitophagy in both the hippocampus and cortex. Marques-Aleixo et al. [42] also found no exercise-induced alteration of p62 in the cortex and cerebellum. This feature may have resulted from the toxicity of p-tau [12], which showed no significant change after exercise training in our study, as also reported by Kim et al. [36].
Our study had some limitations. First, we did not use the same strains of mice in each group. Thus, it is possible that the diverse phenotypes of the mice may have impacted the results. Second, we did not include a positive control. Hence, the general effect of exercise on mitochondrial activities remains to be verified. Previous research has suggested that muscle contraction stimulates the release of myokines, such as lipids, mRNA, microRNAs, and mtDNA. These molecules are transported to various brain regions through exosomes, subsequently regulating the expression of mitochondrial proteins involved in various mitochondrial activities [48]; hence, third, due to the absence of a behavioral test, we were unable to demonstrate potential behavioral changes that could arise from Purkinje cell survival and mitochondrial dysfunction. Fourth, of the various types of p-tau antibodies available, we used only a single type. It is worth noting that the use of different types of p-tau antibodies could have yielded different results [49]. Last, the utility of the microscopic images we used was limited; future studies that provide visual representation of the protein expression levels related to mitochondrial biogenesis, dynamics, apoptosis, and mitophagy in the cerebellum of AD mice are required.
Our study provided evidence that treadmill running resulted in improved survival
of Purkinje cells and alleviated the buildup of A
AD, Alzheimer’s disease; 3xTg-AD mice, triple transgenic Alzheimer’s disease
mice; PTP, permeability transition pores; Con, control; Exe, exercise;
A
The data and supportive information are available within the article.
YJ designed the research study and analyzed the data. TWanK and TWoonK performed the research. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.
This study was reviewed and approved by the Sungkyunkwan University School of Medicine Institutional Animal Care and Use Committee in accordance with the AAALAC International Guidelines for animal experiments (SKKUIACUC2021-04-41-3).
We would like to extend our appreciation to everyone who assisted us throughout the process of composing this manuscript.
This work was supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea (NRF-2018R1D1A1B07051291).
The authors declare no conflict of interest.
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