Muscular Swedish mutant APP-to-Brain axis in the development of Alzheimer's disease

Sarcopenia is a predictor for Alzheimer's continuum and related clinical outcomes

Low body mass index is closely related to a high risk of Alzheimer's disease (AD) and related biomarkers including amyloid-β (Aβ) deposition. However, the association between sarcopenia and Aβ-confirmed AD remains controversial. Therefore, we investigated the relationship between sarcopenia and the AD continuum. We explored sarcopenia's association with clinical implications of participants on the AD continuum. We prospectively enrolled 142 participants on the AD continuum (19 with preclinical AD, 96 with mild cognitive impairment due to AD, and 28 with AD dementia) and 58 Aβ-negative cognitively unimpaired participants. Sarcopenia, assessed using dual-energy X-ray absorptiometry and hand grip measurements, was considered a predictor. AD continuum, defined by Aβ deposition on positron emission tomography served as an outcome. Clinical severity in participants on the AD continuum assessed using hippocampal volume, Mini-Mental State Examination (MMSE), Seoul Verbal Learning Test (SVLT), and Clinical Dementia Rating Scale Sum of Boxes Scores (CDR-SOB) were also considered an outcome. Sarcopenia (odds ratio = 4.99, p = 0.004) was associated independently with the AD continuum after controlling for potential confounders. Moreover, sarcopenia was associated with poor downstream imaging markers (decreased hippocampal volume, β = - 0.206, p = 0.020) and clinical outcomes (low MMSE, β = - 1.364, p = 0.025; low SVLT, β = - 1.077, p = 0.025; and high CDR-SOB scores, β = 0.783, p = 0.022) in participants on the AD continuum. Sarcopenia was associated with the AD continuum and poor clinical outcome in individuals with AD continuum. Therefore, our results provide evidence for future studies to confirm whether proper management of sarcopenia can effective strategies are required for sarcopenia management to prevent the AD continuum and its clinical implications.

Long-term intake of thermo-induced oxidized oil results in anxiety-like and depression-like behaviors: involvement of microglia and astrocytes

Frequent consumption of fried foods has been strongly associated with a higher risk of anxiety and depression, particularly among young individuals. The existing evidence has indicated that acrylamide produced from starchy foods at high temperatures can induce anxious behavior. However, there is limited research on the nerve damage caused by thermo-induced oxidized oil (TIOO). In this study, we conducted behavioral tests on mice and found that prolonged consumption of TIOO led to significant anxiety behavior and a tendency toward depression. TIOO primarily induced these two emotional disorders by affecting the differentiation of microglia, the level of inflammatory factors, the activation of astrocytes, and glutamate circulation in brain tissue. By promoting the over-differentiation of microglia into M1 microglia, TIOO disrupted their differentiation balance, resulting in an up-regulation of inflammatory factors (IL-1β, IL-6, TNF-α, NOS2) in M1 microglia and a down-regulation of neuroprotective factors IL-4/IL-10 in M2 microglia, leading to nerve damage. Moreover, TIOO activated astrocytes, accelerating their proliferation and causing GFAP precipitation, which damaged astrocytes. Meanwhile, TIOO stimulates the secretion of the BDNF and reduces the level of the glutamate receptor GLT-1 in astrocytes, leading to a disorder in the glutamate-glutamine cycle, further exacerbating nerve damage. In conclusion, this study suggests that long-term intake of thermo-induced oxidized oil can trigger symptoms of anxiety and depression.

Targeted brain-specific tauopathy compromises peripheral skeletal muscle integrity and function

Tauopathies are neurodegenerative disorders in which the pathological intracellular aggregation of the protein tau causes cognitive deficits. Additionally, clinical studies report muscle weakness in populations with tauopathy. However, whether neuronal pathological tau species confer muscle weakness, and whether skeletal muscle maintains contractile capacity in primary tauopathy remains unknown. Here, we identified skeletal muscle abnormalities in a mouse model of primary tauopathy, expressing human mutant P301L-tau using adeno-associated virus serotype 8 (AAV8). AAV8-P301L mice showed grip strength deficits, hyperactivity, and abnormal histological features of skeletal muscle. Additionally, spatially resolved gene expression of muscle cross sections were altered in AAV8-P301L myofibers. Transcriptional changes showed alterations of genes encoding sarcomeric proteins, proposing a weakness phenotype. Strikingly, specific force of the soleus muscle was blunted in AAV8-P301L tau male mice. Our findings suggest tauopathy has peripheral consequences in skeletal muscle that contribute to weakness in tauopathy.

Targeted brain-specific tauopathy compromises peripheral skeletal muscle integrity and function

Tauopathies are neurodegenerative disorders in which the pathological intracellular aggregation of the protein tau causes cognitive deficits. Additionally, clinical studies report muscle weakness in populations with tauopathy. However, whether neuronal pathological tau species confer muscle weakness, and whether skeletal muscle maintains contractile capacity in primary tauopathy remains unknown. Here, we identified skeletal muscle abnormalities in a mouse model of primary tauopathy, expressing human mutant P301L-tau using adeno-associated virus serotype 8 (AAV8). AAV8-P301L mice showed grip strength deficits, hyperactivity, and abnormal histological features of skeletal muscle. Additionally, spatially resolved gene expression of muscle cross sections were altered in AAV8-P301L myofibers. Transcriptional changes showed alterations of genes encoding sarcomeric proteins, proposing a weakness phenotype. Strikingly, specific force of the soleus muscle was blunted in AAV8-P301L tau male mice. Our findings suggest tauopathy has peripheral consequences in skeletal muscle that contribute to weakness in tauopathy.

APP in the Neuromuscular Junction for the Development of Sarcopenia and Alzheimer's Disease

Sarcopenia, an illness condition usually characterized by a loss of skeletal muscle mass and muscle strength or function, is often associated with neurodegenerative diseases, such as Alzheimer's disease (AD), a common type of dementia, leading to memory loss and other cognitive impairment. However, the underlying mechanisms for their associations and relationships are less well understood. The App, a Mendelian gene for early-onset AD, encodes amyloid precursor protein (APP), a transmembrane protein enriched at both the neuromuscular junction (NMJ) and synapses in the central nervous system (CNS). Here, in this review, we highlight APP and its family members' physiological functions and Swedish mutant APP (APP_swe)'s pathological roles in muscles and NMJ. Understanding APP's pathophysiological functions in muscles and NMJ is likely to uncover insights not only into neuromuscular diseases but also AD. We summarize key findings from the burgeoning literature, which may open new avenues to investigate the link between muscle cells and brain cells in the development and progression of AD and sarcopenia.