Is later-life depression a risk factor for Alzheimer's disease or a prodromal symptom: a study using post-mortem human brain tissue?

Depression as a risk factor for Alzheimer's disease: A human post-mortem study

Depression is associated with persistent low mood. In mid to late life, it has been identified as a risk factor for Alzheimer's disease (AD) with evidence that depression might be an early manifestation of AD. Although the underlying mechanisms by which depression enhances AD development remain unknown, there are several features commonly seen in both diseases such as the presence of neuroinflammation. In this study, we aimed to identify whether neuroinflammation is increased in depression as observed in the early stages of AD by examining post-mortem human brain tissue. Post-mortem human brain tissue from 54 cases with depression and 37 controls without depression were retrieved from the Douglas Bell Canada Brain Bank. Sixteen early-stage AD cases defined as a Braak stage III-IV and 15 controls were sourced from the South West Dementia Brain Bank. Frozen tissue from the dorsal prefrontal cortex was obtained for all cases in order to measure inflammatory proteins (IFN-γ, IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, and TNF-α) and endothelial markers (ICAM-1, VCAM) using ELISA and MesoScale Multiplex Assays. In the depression group, increase of IL-6 and IL-10, and decrease of IL-1β were observed compared to controls, with no changes detected for the other cytokines and the endothelial markers. In early-stage AD cases, only increased ICAM-1 expression was found compared to controls, indicating endothelial activation as an early feature of AD. None of the cytokines measured showed alteration of their expression in early-stage AD cases. Depression, but not AD, was associated with evidence of neuroinflammation. Depression may increase AD risk through different mechanism(s) than inflammation.

Changes in dementia risk along with onset age of depression: a longitudinal cohort study of elderly depressed patients

BACKGROUND

Depression in late-life is linked to an increased risk of Alzheimer's dementia (AD), with the risk potentially varying according to the age at onset of depression. Previous studies have typically dichotomized depression onset ages between 55 and 65 years; however, the specific age at which depression onset increases AD risk in older adults remains unclear. In this study, we aimed to investigate the relationship between the age at onset of depression and AD risk, and compare the characteristics between different age groups.

METHODS

A longitudinal cohort of 251 older patients diagnosed with major depressive disorder was followed for up to 22 years. Participants were categorized into four groups based on depression onset age: ≤ 54 years, 55-64, 65-74, and ≥ 75 years. Annual cognitive assessments were conducted using the Korean Mini-Mental State Examination, with further neuropsychological testing when cognitive decline was suspected. Cox proportional hazards models were used to assess AD conversion risk across groups, adjusting for covariates.

RESULTS

During follow-up ranging from 1.0 to 22.9 years, 75 patients (29.88%) converted to AD. Depression onset after age 75 years was significantly associated with a higher risk of AD conversion (hazard ratio [HR], 8.95; 95% confidence interval [CI], 3.41-23.48; p < 0.0001) and a shorter time to conversion compared to onset before age 55 (40.93 vs. 83.40 months). After adjusting for covariates, depression onset after age 75 remained significantly associated with AD conversion (adjusted HR, 5.20; 95% CI, 1.04-25.93; p = 0.0431). This group also had milder depressive symptoms and a higher prevalence of hypertension and cerebrovascular disease than those with depression onset before 55 years of age.

CONCLUSIONS

The onset of depression after the age of 75 years was strongly associated with an increased risk of AD and a shorter time to dementia onset. Individuals with depression onset after age 75 appear more closely linked to vascular comorbidities, while those with depression onset before age 55 are characterized by severe and recurrent depressive episodes. The mechanisms underlying AD in individuals with depression may differ from those in individuals without prior depression.

The role of senescence-related genes in major depressive disorder: insights from machine learning and single cell analysis

BACKGROUND

Evidence indicates that patients with Major Depressive Disorder (MDD) exhibit a senescence phenotype or an increased susceptibility to premature senescence. However, the relationship between senescence-related genes (SRGs) and MDD remains underexplored.

METHODS

We analyzed 144 MDD samples and 72 healthy controls from the GEO database to compare SRGs expression. Using Random Forest (RF) and Support Vector Machine-Recursive Feature Elimination (SVM-RFE), we identified five hub SRGs to construct a logistic regression model. Consensus cluster analysis, based on SRGs expression patterns, identified subclusters of MDD patients. Weighted Gene Co-expression Network Analysis (WGCNA) identified gene modules strongly linked to each cluster. Single-cell RNA sequencing was used to analyze MDD SRGs functions.

RESULTS

The five hub SRGs: ALOX15B, TNFSF13, MARCH 15, UBTD1, and MAPK14 showed differential expression between MDD patients and controls. Diagnostics models based on these hub genes demonstrated high accuracy. The hub SRGs correlated positively with neutrophils and negatively with T lymphocytes. SRGs expression pattern revealed two distinct MDD subclusters. WGCNA identified significant gene modules within these subclusters. Additionally, individual endothelial cells with high senescence scores were found to interact with astrocytes via the Notch signaling pathway, suggesting a specific role in MDD pathogenesis.

CONCLUSION

This comprehensive study elucidates the significant role of SRGs in MDD, highlighting the importance of the Notch signaling pathway in mediating senescence effects.

The neural basis of neuropsychiatric symptoms in Alzheimer's disease

Neuropsychiatric symptoms (NPS) such as depression, anxiety, apathy and aggression affect up to 90% of Alzheimer's disease (AD) patients. These symptoms significantly increase caregiver stress and institutionalization rates, and more importantly they are correlated with faster cognitive decline. However, the neuronal basis of NPS in AD remains largely unknown. Here, we review current understanding of NPS and related pathology in studies of AD patients and AD mouse models. Clinical studies indicate that NPS prevalence and severity vary across different AD stages and types. Neuroimaging and postmortem studies have suggested that pathological changes in the anterior cingulate cortex, hippocampus, prefrontal cortex, and amygdala are linked to NPS, although the precise mechanisms remain unclear. Studies of AD mouse models have indicated that amyloid-beta and tau-related neurodegeneration in the hippocampus, prefrontal cortex, and anterior cingulate cortex are correlated with NPS-like behavioral deficits. A better understanding of the NPS phenotypes and related pathological changes will pave the way for developing a better management strategy for NPS in AD patients.

Association of modifiable risk factors with progression to dementia in relation to amyloid and tau pathology

BACKGROUND

Dementia preventive interventions targeting multiple modifiable risk factors are a promising approach. However, the impact of modifiable risk factors in the presence of beta-amyloid or phosphorylated-tau (p-tau) pathology is unclear.

METHODS

The objective of the study was to examine the role of modifiable risk factors (vascular factors, depression, and smoking) in the progression to mild cognitive impairment (MCI) or dementia among 434 cognitively unimpaired (CU) and 611 individuals with MCI from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Vascular risk factors were summarized with the Cardiovascular Risk Factors, Aging, and Dementia (CAIDE) score, dichotomized into higher versus lower risk. Depression and smoking (yes/no) were categorised according to medical history or current symptoms. Analyses were stratified by beta-amyloid negative (A-) and positive (A +), p-tau negative (T-) and positive (T +), or beta-amyloid and p-tau negative (A-T-) and positive (A + T +) biomarker status. Cox proportional hazard models were adjusted for age, sex, education, baseline MMSE score, baseline hippocampal volume and ApoE4 carrier status.

RESULTS

Higher CAIDE score was associated with increased risk of progression to all-cause dementia in most MCI subgroups: adjusted hazard ratios (aHR) [95% CI] were 3.1 [1.43; 6.53] in the A- subgroup, 1.7 [1.20-2.27] in T + , 2.6 [1.06-6.59] in A-T-, and 1.6 [1.15-2.22] in the A + T + subgroup. Smoking (yes/no) was associated with increased dementia aHR in the A + MCI subgroup: 1.6 [1.07-2.34]. Depression increased dementia aHR in the T + MCI subgroup: 1.5 [1.06-2.02]. No significant associations were found in the CU biomarker subgroups.

CONCLUSION

Addressing modifiable risk factors carries an important potential for reducing the risk of dementia even after the onset of Alzheimer's pathology. Knowledge of biomarker status can further optimize prevention strategies.

Amyloid deposition and its association with depressive symptoms and cognitive functions in late-life depression: a longitudinal study using amyloid-β PET images and neuropsychological measurements

BACKGROUND

Although depression is linked to an increased risk of dementia, the association between late-onset depression (LOD) and amyloid burden remains unclear. This study aimed to determine amyloid deposition in patients with LOD compared to healthy controls (HC) using amyloid-beta (Aβ) positron emission tomography (PET) images and neuropsychological assessments.

METHODS

Forty patients first diagnosed with major depressive disorder after the age of 60 (LOD) and twenty-one healthy volunteers (HC) were enrolled. Depression and anxiety were evaluated using the 17-item Hamilton Depression Scale, Hamilton Anxiety Rating Scale, and Clinical Global Impression Scale. Cognitive function was assessed using the Korean versions of the Mini-Mental Status Examination, Montreal Cognitive Assessment, and Seoul Neuropsychological Screening Battery at baseline and 3-month follow-up. 18F-florbetapir PET images were co-registered with T1-weighted magnetic resonance images.

RESULTS

There was no significant difference in Aβ deposition between LOD and HC groups. No significant correlation between Aβ burden and depressive symptom severity was found in LOD patients. Higher somatic anxiety was correlated with lower Aβ burden in multiple brain regions, including the left inferior frontal lobe (p = 0.009), right anterior cingulate (p = 0.003), and right superior frontal lobe (p = 0.009). Despite cognitive recovery in areas such as attention (Digit Span Forward, p = 0.026), memory (Auditory Verbal Learning Test Recall Total, p = 0.010; Rey Complex Figure Test Delayed Recall, p = 0.039), and frontal executive function (Contrasting Program, p = 0.033) after three months of antidepressant treatment, cognitive improvement showed no association with amyloid deposition.

CONCLUSIONS

These findings suggest distinct mechanisms may underlie amyloid deposition in neurodegenerative changes associated with depression. While amyloid burden in specific brain regions negatively correlated with somatic anxiety, it showed no significant correlation with the severity of depression or overall cognitive function.

The flavonoid fisetin reduces multiple physiological risk factors for dementia

Dementia is a growing problem around the globe as the world's population continues to age. Multiple studies have identified potentially modifiable risk factors for the development of dementia suggesting that addressing some or all of these risk factors might have a significant impact on the aging population worldwide. However, this is not always as straightforward as it seems since many of these risk factors are currently treated with drugs specific to the risk factor. Moreover, since people can have multiple risk factors, addressing each of them individually could be highly problematic as it would likely lead to negative outcomes associated with polypharmacy and, in the long term, could do significant harm. A potential alternative is to identify compounds that have shown efficacy against a number of these different risk factors. As discussed in this review, there is strong evidence that the flavonol fisetin is one such compound. In animal studies it has shown efficacy against many of the risk factors that have been associated with an increased risk of developing dementia and also exhibits direct neuroprotective effects. Thus, further human research on fisetin in the context of dementia risk factors is clearly warranted.