Sex Difference in General Cognition Associated with Coupling of Whole-brain Functional Connectivity Strength to Cerebral Blood Flow Changes During Alzheimer's Disease Progression

Sexual dimorphism in cerebrovascular dysfunction: The pivotal role of endothelial CD2AP in Alzheimer's disease

Why there is sex-biased susceptibility to cerebrovascular dysfunction remains enigmatic. Vandal et al.1 reveal a sex-specific vulnerability to endothelial deficiency in CD2AP, an Alzheimer's disease risk gene, with impaired cerebrovascular reactivity, compromised cerebrovascular function, and cognitive decline, highlighting sex as an important biological variable in Alzheimer's disease.

Loss of endothelial CD2AP causes sex-dependent cerebrovascular dysfunction

Polymorphisms in CD2-associated protein (CD2AP) predispose to Alzheimer's disease (AD), but the underlying mechanisms remain unknown. Here, we show that loss of CD2AP in cerebral blood vessels is associated with cognitive decline in AD subjects and that genetic downregulation of CD2AP in brain vascular endothelial cells impairs memory function in male mice. Animals with reduced brain endothelial CD2AP display altered blood flow regulation at rest and during neurovascular coupling, defects in mural cell activity, and an abnormal vascular sex-dependent response to Aβ. Antagonizing endothelin-1 receptor A signaling partly rescues the vascular impairments, but only in male mice. Treatment of CD2AP mutant mice with reelin glycoprotein that mitigates the effects of CD2AP loss function via ApoER2 increases resting cerebral blood flow and even protects male mice against the noxious effect of Aβ. Thus, endothelial CD2AP plays critical roles in cerebrovascular functions and represents a novel target for sex-specific treatment in AD.

Neurovascular coupling dysfunction associated with inflammatory factors in sudden sensorineural hearing loss

PURPOSE

The neuropathologic mechanisms of sudden sensorineural hearing loss (SSNHL) are unknown. The aim of this study was to investigate the alterations of neurovascular coupling (NVC) in patients with SSNHL and its association with hematologic inflammatory factors.

METHODS

The amplitude of low-frequency fluctuations (ALFF), fractional amplitude of low-frequency fluctuations (fALFF), regional homogeneity (ReHo), and degree centrality (DC) were calculated in 48 patients with SSNHL and 54 age-, gender-, and education-matched healthy control (HC), and also utilized the arterial spin labeling imaging (ASL) to calculate cerebral blood flow (CBF). Four indices of NVC (CBF-ALFF, CBF-fALFF, CBF-ReHo, and CBF-DC) in the whole brain gray matter as well as the NVC ratio were compared between two groups. In addition, correlation analyses were performed with inflammatory factors for the NVC indexes at the global level and regional level, respectively.

RESULTS

The NVC at global level was lower in SSNHL group than in HC, except for CBF-ALFF. At the regional level, most of the brain regions with abnormal NVC in SSNHL patients involved auditory and sensorimotor language centers and limbic system compared to HC. In addition, both at the global and regional levels, NVC metrics were shown to correlate with partial inflammatory factors or hematologic parameters, including platelet-lymphocyte ratio (PLR), neutrophil-lymphocyte ratio (NLR), systemic immunoinflammatory index (SII), blood platelet count (PLT), and lymphocyte count (Lym).

CONCLUSION

From the view of the NVC metrics, these findings provide new perspectives on the neuropathologic mechanisms and clinical treatment of SSNHL.

Periodontitis associated with brain function impairment in middle-aged and elderly individuals with normal cognition

BACKGROUND

The present study aimed to investigate changes in intranetwork functional connectivity (FC) and internetwork FC in middle-aged and elderly individuals with normal cognition (NC) and varying degrees of periodontitis to determine the effects of periodontitis on brain function.

METHODS

Periodontal findings and resting-state functional magnetic resonance imaging data were acquired from 51 subjects with NC. Independent component analysis and correlation analysis were used for the statistical analysis of the data.

RESULTS

Differences in intranetwork FC were observed among groups in the anterior default-mode network (aDMN), dorsal attention network and dorsal sensorimotor network (dSMN). Compared with the nonperiodontitis (NP) group or the mild-periodontitis group, the analysis of internetwork FC showed increased FC between the auditory network and the ventral attention network (VAN), between the aDMN and the salience network (SN), and between the SN and the VAN and decreased FC between the posterior default-mode network and the right frontoparietal network in the moderate-to-severe periodontitis group. Additionally, internetwork FC between the dSMN and the VAN was also increased in the moderate-to-severe periodontitis group compared to the NP group. The altered intra- and internetwork FC were significantly correlated with the periodontal clinical index.

CONCLUSION

Our results confirmed that periodontitis was associated with both intra- and internetwork FC changes even in NC. The present study indicates that periodontitis might be a potential risk factor for brain damage and provides a theoretical clue and a new treatment target for the early prevention of Alzheimer disease.

PLAIN LANGUAGE SUMMARY

Recent research has proposed that periodontitis is a potential risk factor for Alzheimer disease (AD). However, the relationship between periodontitis and the brain function of middle-aged and elderly individuals with normal cognition (NC) remains unclear. Analyzing the effect of periodontitis on brain function in the NC stage can provide clues to AD development and help achieve early prevention of dementia. The present study aimed to investigate changes in brain functional connectivity (FC) in NC with different severity of periodontitis to determine the effects of periodontitis on brain function. Both changed intranetwork FC and internetwork FC were found in the moderate-to-severe periodontitis group, and periodontitis was associated with brain network function impairment in NC. The present study indicates that periodontitis might be a potential risk factor for brain damage even in NC stage, and provides a theoretical clue and a new treatment target for the early prevention of AD.

Neuroimaging meets neurophysiology: vascular endothelial growth factor and regional cerebral blood flow in early Alzheimer's disease

Angiogenesis may play an important role in the pathophysiology of Alzheimer's disease (AD). Previous in vitro and in vivo studies suggest a link between angiogenesis and cerebral blood flow (CBF) in AD; however, this has never been studied clinically. In this sample of study participants with early AD (n = 15), serum vascular endothelial growth factor (VEGF), an angiogenesis biomarker, was negatively associated with regional CBF (rCBF) in the angular gyrus even after bootstrapping at a repetition of 5,000 and controlling for age, sex, and diagnosis (β = -0.015, SE = 0.006, P = 0.02, f2 = 0.27, Pbootstrapped = 0.049). Sex-stratified subgroup analyses showed a strong negative correlation between rCBF in the angular gyrus and log-VEGF in males (n = 7; r = -0.78, P = 0.04), but not in females (n = 8; r = -0.16, P = 0.7). These results support an association between angiogenesis and CBF in early AD that should be further investigated in longitudinal studies and may have relevance for future therapeutic interventions in AD.NEW & NOTEWORTHY This manuscript supports the findings from previous in vitro and in vivo Alzheimer's disease (AD) studies where angiogenesis was associated with cerebral blood flow (CBF) changes. Using both neuroimaging and neurophysiology measures, this study showed the association between CBF and blood vascular endothelial growth factor (VEGF) in people with early AD, suggesting further investigation into angiogenesis and CBF as potential therapeutic targets for AD.

Iron accumulation/overload and Alzheimer's disease risk factors in the precuneus region: A comprehensive narrative review

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by amyloid plaques, neurofibrillary tangles, and neuronal loss. Early cerebral and body iron dysregulation and accumulation interact with AD pathology, particularly in the precuneus, a crucial functional hub in cognitive functions. Quantitative susceptibility mapping (QSM), a novel post-processing approach, provides insights into tissue iron levels and cerebral oxygen metabolism and reveals abnormal iron accumulation early in AD. Increased iron deposition in the precuneus can lead to oxidative stress, neuroinflammation, and accelerated neurodegeneration. Metabolic disorders (diabetes, non-alcoholic fatty liver disease (NAFLD), and obesity), genetic factors, and small vessel pathology contribute to abnormal iron accumulation in the precuneus. Therefore, in line with the growing body of literature in the precuneus region of patients with AD, QSM as a neuroimaging method could serve as a non-invasive biomarker to track disease progression, complement other imaging modalities, and aid in early AD diagnosis and monitoring.

Sex differences in functional connectivity and the predictive role of the connectome-based predictive model in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline. Sex differences in the progression of AD exist, but the neural mechanisms are not well understood. The purpose of the current study was to explore sex differences in brain functional connectivity (FC) at different stages of AD and their predictive ability on Montreal Cognitive Assessment (MoCA) scores using connectome-based predictive modeling (CPM). Resting-state functional magnetic resonance imaging was collected from 81 AD patients (44 females), 78 amnestic mild cognitive impairment patients (44 females), and 92 healthy controls (50 females). The FC analysis was conducted and the interaction effect between sex and group was investigated using two-factor variance analysis. The CPM was used to predict MoCA scores. There were sex-by-group interaction effects on FC between the left dorsolateral superior frontal gyrus and left middle temporal gyrus, left precuneus and right calcarine fissure surrounding cortex, left precuneus and left middle occipital gyrus, left middle temporal gyrus and left precentral gyrus, and between the left middle temporal gyrus and right cuneus. In the CPM, the positive network predictive model significantly predicted MoCA scores in both males and females. There were significant sex-by-group interaction effects on FC between the left precuneus and left middle occipital gyrus, and between the left middle temporal gyrus and right cuneus could predict MoCA scores in female patients. Our results suggest that there are sex differences in FC at different stages of AD. The sex-specific FC can further predict MoCA scores at individual level.

Neurocognitive correlates of semantic memory navigation in Parkinson's disease

Cognitive studies on Parkinson's disease (PD) reveal abnormal semantic processing. Most research, however, fails to indicate which conceptual properties are most affected and capture patients' neurocognitive profiles. Here, we asked persons with PD, healthy controls, and individuals with behavioral variant frontotemporal dementia (bvFTD, as a disease control group) to read concepts (e.g., 'sun') and list their features (e.g., hot). Responses were analyzed in terms of ten word properties (including concreteness, imageability, and semantic variability), used for group-level comparisons, subject-level classification, and brain-behavior correlations. PD (but not bvFTD) patients produced more concrete and imageable words than controls, both patterns being associated with overall cognitive status. PD and bvFTD patients showed reduced semantic variability, an anomaly which predicted semantic inhibition outcomes. Word-property patterns robustly classified PD (but not bvFTD) patients and correlated with disease-specific hypoconnectivity along the sensorimotor and salience networks. Fine-grained semantic assessments, then, can reveal distinct neurocognitive signatures of PD.

Genome-wide association study of hippocampal blood-oxygen-level-dependent-cerebral blood flow correlation in Chinese Han population

Correlation between blood-oxygen-level-dependent (BOLD) and cerebral blood flow (CBF) has been used as an index of neurovascular coupling. Hippocampal BOLD-CBF correlation is associated with neurocognition, and the reduced correlation is associated with neuropsychiatric disorders. We conducted the first genome-wide association study of the hippocampal BOLD-CBF correlation in 4,832 Chinese Han subjects. The hippocampal BOLD-CBF correlation had an estimated heritability of 16.2-23.9% and showed reliable genome-wide significant association with a locus at 3q28, in which many variants have been linked to neuroimaging and cerebrospinal fluid markers of Alzheimer's disease. Gene-based association analyses showed four significant genes (GMNC, CRTC2, DENND4B, and GATAD2B) and revealed enrichment for mast cell calcium mobilization, microglial cell proliferation, and ubiquitin-related proteolysis pathways that regulate different cellular components of the neurovascular unit. This is the first unbiased identification of the association of hippocampal BOLD-CBF correlation, providing fresh insights into the genetic architecture of hippocampal neurovascular coupling.

Associations of metabolic syndrome, its severity with cognitive impairment among hemodialysis patients

BACKGROUND

In the general population, metabolic syndrome (MetS) is associated with increased risk of cognitive impairment, including global and specific cognitive domains. These associations are not well studied in patients undergoing hemodialysis and were the focus of the current investigation.

METHODS

In this multicenter cross-sectional study, 5492 adult hemodialysis patients (3351 men; mean age: 54.4 ± 15.2 years) treated in twenty-two dialysis centers of Guizhou, China were included. The Mini-Mental State Examination (MMSE) was utilized to assess mild cognitive impairment (MCI). MetS was diagnosed with abdominal obesity, hypertension, hyperglycemia, and dyslipidemia. Multivariate logistic and linear regression models were used to examine the associations of MetS, its components, and metabolic scores with the risk of MCI. Restricted cubic spline analyses were performed to explore the dose-response associations.

RESULTS

Hemodialysis patients had a high prevalence of MetS (62.3%) and MCI (34.3%). MetS was positively associated with MCI risk with adjusted ORs of 1.22 [95% confidence interval (CI) 1.08-1.37, P = 0.001]. Compared to no MetS, adjusted ORs for MCI were 2.03 (95% CI 1.04-3.98) for 22.51 (95% CI 1.28-4.90) for 3, 2.35 (95% CI 1.20-4.62) for 4, and 2.94 (95% CI 1.48-5.84) for 5 components. Metabolic syndrome score, cardiometabolic index, and metabolic syndrome severity score were associated with increased risk of MCI. Further analysis showed that MetS was negatively associated with MMSE score, orientation, registration, recall and language (P < 0.05). Significant interaction effect of sex (P for interaction = 0.012) on the MetS-MCI was observed.

CONCLUSION

Metabolic syndrome was associated with MCI in hemodialysis patients in a positive dose-response effect.

Decoupling of Regional Cerebral Blood Flow and Brain Function Along the Alzheimer's Disease Continuum

BACKGROUND

Alzheimer's disease (AD) is accompanied with impaired neurovascular coupling. However, its early alteration remains elusive along the AD continuum.

OBJECTIVE

This study aimed to investigate the early disruption of neurovascular coupling in cognitively normal (CN) and mild cognitive impairment (MCI) elderly and its association with cognition and AD pathologies.

METHODS

We included 43 amyloid-β-negative CN participants and 38 amyloid-β-positive individuals (18 CN and 20 MCI) from the Alzheimer's Disease Neuroimaging Initiative dataset. Regional homogeneity (ReHo) map was used to represent neuronal activity and cerebral blood flow (CBF) map was used to represent cerebral blood perfusion. Neurovascular coupling was assessed by CBF/ReHo ratio at the voxel level. Analyses of covariance to detect the between-group differences and to further investigate the relations between CBF/ReHo ratio and AD biomarkers or cognition. In addition, the correlation of cerebral small vessel disease (SVD) burden and neurovascular coupling was assessed as well.

RESULTS

Related to amyloid-β-negative CN group, amyloid-β-positive groups showed decreased CBF/ReHo ratio mainly in the left medial and inferior temporal gyrus. Furthermore, lower CBF/ReHo ratio was associated with a lower Mini-Mental State Examination score as well as higher AD pathological burden. No association between CBF/ReHo ratio and SVD burden was observed.

CONCLUSION

AD pathology is a major correlate of the disturbed neurovascular coupling along the AD continuum, independent of SVD pathology. The CBF/ReHo ratio may be an index for detecting neurovascular coupling abnormalities, which could be used for early diagnosis in the future.