A single bout of moderate-intensity aerobic exercise improves motor learning in premanifest and early Huntington's disease

Causal associations of physical activity and leisure sedentary behaviors with age at onset of Huntington's disease: A mendelian randomization study

BACKGROUND

Huntington's disease (HD) is a neurodegenerative disorder for which effective therapies are currently lacking. Studies suggest that increasing physical activity (PA) and reducing leisure sedentary behavior (LSB) mitigate the progression of HD, but their causal relationship with the age at onset (AAO) of HD remains uncertain. To investigate this, we conducted the Two-sample Mendelian Randomization (MR).

METHODS

Exposure were retrieved from the UK BioBank's (UKB) Genome-Wide Association Study (GWAS). PA included accelerometer-based average PA, vigorous PA, self-reported moderate-to-vigorous PA (MVPA), and light do-it-yourself activity. LSB included television (TV) time, computer time, and driving time. Outcome came from the GWAS of the GEM-HD Consortium. We applied several MR methods such as inverse variance weighted (IVW), MR-Egger regression, weighted median (WM) for sensitivity analysis.

RESULTS

Increases in light PA (β = 8.53 years, 95 % CI = 10.64 to 44.09, P = 0.001) and accelerometer-based vigorous PA (β = 5.18, 95 % CI = 0.92 to 9.43, P = 0.017) delayed AAO of HD, while longer TV time was associated with earlier AAO of HD (β = -2.88 years, 95 % CI = -4.99 to -0.77, P = 0.007). However, other PA and LSB phenotypes did not significantly affect AAO of HD.

CONCLUSION

The study revealed a unidirectional causality between PA, LSB and the AAO of HD. Increasing PA and reducing TV time delay HD onset. Therefore, we recommend increasing physical activity and reducing sedentary behavior to delay the occurrence of motor symptoms for premanifest HD individuals.

Dopamine D2 Receptor Modulates Exercise Related Effect on Cortical Excitation/Inhibition and Motor Skill Acquisition

Exercise is known to benefit motor skill learning in health and neurological disease. Evidence from brain stimulation, genotyping, and Parkinson's disease studies converge to suggest that the dopamine D2 receptor, and shifts in the cortical excitation and inhibition (E:I) balance, are prime candidates for the drivers of exercise-enhanced motor learning. However, causal evidence using experimental pharmacological challenge is lacking. We hypothesized that the modulatory effect of the dopamine D2 receptor on exercise-induced changes in the E:I balance would determine the magnitude of motor skill acquisition. To test this, we measured exercise-induced changes in excitation and inhibition using paired-pulse transcranial magnetic stimulation (TMS) in 22 healthy female and male humans, and then had participants learn a novel motor skill-the sequential visual isometric pinch task (SVIPT). We examined the effect of D2 receptor blockade (800 mg sulpiride) on these measures within a randomized, double-blind, placebo-controlled design. Our key result was that motor skill acquisition was driven by an interaction between the D2 receptor and E:I balance. Specifically, poorer skill learning was related to an attenuated shift in the E:I balance in the sulpiride condition, whereas this interaction was not evident in placebo. Our results demonstrate that exercise-primed motor skill acquisition is causally influenced by D2 receptor activity on motor cortical circuits.

Brain-Periphery Interactions in Huntington's Disease: Mediators and Lifestyle Interventions

Prominent pathological features of Huntington's disease (HD) are aggregations of mutated Huntingtin protein (mHtt) in the brain and neurodegeneration, which causes characteristic motor (such as chorea and dystonia) and non-motor symptoms. However, the numerous systemic and peripheral deficits in HD have gained increasing attention recently, since those factors likely modulate disease progression, including brain pathology. While whole-body metabolic abnormalities and organ-specific pathologies in HD have been relatively well described, the potential mediators of compromised inter-organ communication in HD have been insufficiently characterized. Therefore, we applied an exploratory literature search to identify such mediators. Unsurprisingly, dysregulation of inflammatory factors, circulating mHtt, and many other messenger molecules (hormones, lipids, RNAs) were found that suggest impaired inter-organ communication, including of the gut-brain and muscle-brain axis. Based on these findings, we aimed to assess the risks and potentials of lifestyle interventions that are thought to improve communication across these axes: dietary strategies and exercise. We conclude that appropriate lifestyle interventions have great potential to reduce symptoms and potentially modify disease progression (possibly via improving inter-organ signaling) in HD. However, impaired systemic metabolism and peripheral symptoms warrant particular care in the design of dietary and exercise programs for people with HD.

High-intensity acute exercise impacts motor learning in healthy older adults

Healthy aging is associated with changes in motor sequence learning, with some studies indicating decline in motor skill learning in older age. Acute cardiorespiratory exercise has emerged as a potential intervention to improve motor learning, however research in healthy older adults is limited. The current study investigated the impact of high-intensity interval exercise (HIIT) on a subsequent sequential motor learning task. Twenty-four older adults (aged 55-75 years) completed either 20-minutes of cycling, or an equivalent period of active rest before practicing a sequential force grip task. Skill learning was assessed during acquisition and at a 6-hour retention test. In contrast to expectation, exercise was associated with reduced accuracy during skill acquisition compared to rest, particularly for the oldest participants. However, improvements in motor skill were retained in the exercise condition, while a reduction in skill was observed following rest. Our findings indicate that high-intensity exercise conducted immediately prior to learning a novel motor skill may have a negative impact on motor performance during learning in older adults. We also demonstrated that exercise may facilitate early offline consolidation of a motor skill within this population, which has implications for motor rehabilitation.