Concordance of Intrinsic Brain Connectivity Measures Is Disrupted in Alzheimer's Disease

Ferroptosis and its implications in treating cognitive impairment caused by aging: A study on the mechanism of repetitive transcranial magnetic stimulation

OBJECTIVE

Ferroptosis has been recognized as being closely associated with cognitive impairment. Research has established that Alzheimer's disease (AD)-associated proteins, such as amyloid precursor protein (APP) and phosphorylated tau, are involved in brain iron metabolism. These proteins are found in high concentrations within senile plaques and neurofibrillary tangles. Repetitive transcranial magnetic stimulation (rTMS) offers a non-pharmacological approach to AD treatment. This study aims to explore the potential therapeutic effects of rTMS on cognitive impairment through the modulation of the ferroptosis pathway, thereby laying both a theoretical and experimental groundwork for the application of rTMS in treating Alzheimer's disease.

METHODS

The study utilized senescence-accelerated mouse prone 8 (SAMP8) mice to model brain aging-related cognitive impairment, with senescence-accelerated-mouse resistant 1 (SAMR1) mice acting as controls. The SAMP8 mice were subjected to high-frequency rTMS at 25 Hz for durations of 14 and 28 days. Cognitive function was evaluated using behavioral tests. Resting-state functional magnetic resonance imaging (rs-fMRI) assessed alterations in cerebral activity by measuring the fractional amplitude of low-frequency fluctuations (fALFF) of the blood oxygen level-dependent signal. Neuronal recovery post-rTMS in the SAMP8 model was examined via HE and Nissl staining. Immunohistochemistry was employed to detect the expression of APP and Phospho-Tau (Thr231). Oxidative stress markers were quantified using biochemical assay kits. ELISA methods were utilized to measure hippocampal levels of Fe2+ and Aβ1-42. Finally, the expression of proteins related to the ferroptosis pathway was determined through western blot analysis.

RESULTS

The findings indicate that 25 Hz rTMS enhances cognitive function and augments cerebral activity in SAMP8 model mice. Treatment with rTMS in these mice resulted in diminished oxidative stress and safeguarded neurons against damage. Additionally, iron accumulation was mitigated, and the expression of ferroptosis pathway proteins Gpx4, system Xc-, and Nrf2 was elevated.

CONCLUSIONS

The Tau/APP-Fe-GPX4/system Xc-/Nrf2 pathway is implicated in the remedial effects of rTMS on cognitive dysfunction, offering a theoretical and experimental basis for employing rTMS in AD treatment.

MRI and Clinical Biomarkers Overlap between Glaucoma and Alzheimer's Disease

Glaucoma is the leading cause of blindness worldwide. It is classically associated with structural and functional changes in the optic nerve head and retinal nerve fiber layer, but the damage is not limited to the eye. The involvement of the central visual pathways and disruption of brain network organization have been reported using advanced neuroimaging techniques. The brain structural changes at the level of the areas implied in processing visual information could justify the discrepancy between signs and symptoms and underlie the analogy of this disease with neurodegenerative dementias, such as Alzheimer's disease, and with the complex group of pathologies commonly referred to as "disconnection syndromes." This review aims to summarize the current state of the art on the use of advanced neuroimaging techniques in glaucoma and Alzheimer's disease, highlighting the emerging biomarkers shared by both diseases.

Aberrant Volume-Wise and Voxel-Wise Concordance Among Dynamic Intrinsic Brain Activity Indices in Parkinson’s Disease: A Resting-State fMRI Study

Researches using resting-state functional magnetic resonance imaging (rs-fMRI) have applied different regional measurements to study the intrinsic brain activity (IBA) of patients with Parkinson’s disease (PD). Most previous studies have only examined the static characteristics of IBA in patients with PD, neglecting the dynamic features. We sought to explore the concordance between the dynamics of different rs-fMRI regional indices. This study included 31 healthy controls (HCs) and 57 PD patients to calculate the volume-wise (across voxels) and voxel-wise (across periods) concordance using a sliding time window approach. This allowed us to compare the concordance of dynamic alterations in frequently used metrics such as degree centrality (DC), global signal connectivity (GSC), voxel-mirrored heterotopic connectivity (VMHC), the amplitude of low-frequency fluctuations (ALFF), and regional homogeneity (ReHo). We analyzed the changes of concordance indices in the PD patients and investigated the relationship between aberrant concordance values and clinical/neuropsychological assessments in the PD patients. We found that, compared with the HCs, the PD patients had lower volume concordance in the whole brain and lower voxel-wise concordance in the posterior cerebellar lobe, cerebellar tonsils, superior temporal gyrus, and supplementary motor region. We also found negative correlations between these concordance alterations and patients’ age. The exploratory results contribute to a better understanding of IBA alterations and pathophysiological mechanisms in PD.