Role of nerve growth factor on cognitive impairment in Alzheimer's disease patients carrying apolipoprotein E ε4

doi:10.21203/rs.3.rs-2615238/v1

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Research Article

Role of nerve growth factor on cognitive impairment in Alzheimer's disease patients carrying apolipoprotein E ε4

https://doi.org/10.21203/rs.3.rs-2615238/v1

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published 19 Dec, 2023

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Background

Apolipoprotein E (APOE) ε4 and neurotrophic factors are related to Alzheimer’s disease (AD). This study aimed to investigate roles of neurotrophic factors on cognition in AD patients carrying APOE ε4.

Methods

173 AD patients were divided into the APOE ε4 carrier and the APOE ε4 non-carrier groups. Demographics, cognition, and neurotrophic factors in CSF were compared between two groups. Correlations among APOE ε4, neurotrophic factors, and cognition were analysed.

Results

55 AD patients carried APOE ε4. Global cognition and multiple domains were impaired in the APOE ε4 carrier group. Nerve growth factor (NGF) in CSF from the APOE ε4 carrier group were decreased. NGF correlated with global cognition and multiple domains. NGF mediated associations between APOE ε4 and language, attention/executive function. All P < 0.05.

Conclusion

In AD, APOE ε4 is associated with cognitive impairment and patients carrying APOE ε4 have decreased NGF in CSF. Declined NGF correlates with compromised cognition. NGF mediates APOE ε4-related cognitive impairment.

Alzheimer’s disease

nerve growth factor

Apolipoprotein E

cognitive impairment

Alzheimer's disease (AD) is the most common cognitive disorder in the elderly. Typical AD patients firstly showed episodic memory decline, and gradually developed overall cognitive impairment, neuropsychitric symptoms, and impaired activities of daily living.¹

Apolipoprotein E (APOE), encoding the indispensable lipid transporter APOE protein in brain, includes three alleles of ε2, ε3 and ε4, of which APOE ε4 is the strongest risk gene of developing sporadic AD.²APOE ε4 carriers have an earlier age of onset, a faster rate of cognitive decline, and poorer cognitive outcome.^2,3 Previous studies found that APOE ε4 mediated synaptic dysfunction and aggravated cognitive impairment by promoting depositions of neuropathological proteins of AD^4,5 and eliciting neuroinflammation.⁶ However, the role of APOE ε4 on neurotrophic state of the brain is still unclear.

Neurotrophic factors are a family of proteins, which mainly include brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), and nerve growth factor (NGF). It was found that neurotrophic factors played crucial roles in the neuronal survive, growth and differentiation of neurons during development.⁷ The levels of BDNF and its precursor were decreased in several brain regions and peripheral blood of AD patients.⁸ GDNF levels were elevated in CSF from patients at early stage of AD, whereas, were decreased in the middle temporal gyrus and serum of AD patients.⁹ Besides, proNGF levels in cerebral cortex and CSF from AD patients were increased, however, NGF mRNA was not changed in the cerebral cortex of AD patients.^10–12 It came to the limelight that abnormal secretions of those neurotrophic factors were correlated with progression of neuropathology and cognitive impairment of AD patients.^13,14 However, correlations of neurotrophic factors in CSF with APOE ε4 and functions of different cognitive domains are unknown.

In this study, we hypothesized that APOE ε4 and neurotrophic factors might be related to cognitive impairment, APOE ε4 might be associated with the decreased neurotrophic factors in CSF, and the declined neurotrophic factors in CSF might play a pivotal role on mediating APOE ε4-associated cognitive impairment. Based on this hypothesis, AD patients were divided into APOE ε4 carrier group and APOE ε4 non-carrier group. Demographic variables were collected, overall cognitive function and multiple cognitive domains were assessed by a series of rating scales, and the levels of neurotrophic factors, including BDNF, GDNF and NGF in CSF were measured by ELISA with aims to figure out the roles of neurotrophic factors on cognitive impairment in AD patients carrying APOE ε4.

Patients

Patients who were diagnosed with AD according to the National Institute of Aging and Alzheimer’s Association (NIA-AA) criteria^15,16 were consecutively enrolled in this cross-sectional study from the Center for Cognitive Neurology, Department of Neurology, Beijing Tiantan Hospital, Capital Medical University. The exclusion criteria were as follows: (1) Patients with a history of diseases that might affect cognitive function besides AD, including frontotemporal dementia, dementia with Lewy bodies, corticobasal degeneration, primary progressive aphasia, Parkinson’s disease, multiple sclerosis, epilepsy, and substance abuse, etc. (2) Patients with severe systematic diseases, active infections, chronic wasting disease, autoimmune diseases, hematological system diseases, and malignant tumor. (3) Patients suffered traumatic brain injury and major surgery recently. (4) Patients were being treated with steroids. (5) Patients were unable to cooperate with all the examination for various reasons.

Collection Of Demographic Variables

Demographic variables, including gender, age, age of onset, education level, drinking, smoking, and body mass index (BMI), were collected. Additionally, history of hypertension, hyperlipidemia, myocardial infarction, atrial fibrillation, diabetes mellitus, et al. were also collected.

Assessment Of Cognitive Function

Overall cognitive function of enrolled AD patients was assessed by the Mini-Mental State Examination (MMSE)¹⁷ and the Montreal Cognitive Assessment (MoCA).¹⁸ In the multiple cognitive domains, verbal memory was evaluated by the Auditory Verbal Learning Test (AVLT), and visual delayed memory was evaluated by the Rey-Osterreithm Complex Figure Test (RCFT)-delayed recall.^19,20 Language was evaluated by the Verbal Fluency Test (VFT) and the Boston Naming Test (BNT).^21,22 Attention was evaluated by the Symbol Digit Modalities Test (SDMT),²³ the Trail Making Test (TMT)-A,²⁴ as well as the Stroop Color-Word Test (SCWT)-A and SCWT-B.²⁵ Visuospatial ability was evaluated by RFT. Executive function was evaluated by the SCWT-C and the TMT-B. The detailed descriptions of these scales were provided in the Supplementary material.

Detection of APOE genotypes

The venous blood samples of enrolled patients were collected from the median elbow under fasting condition the next morning after admission, and then sent to the clinical laboratory of our hospital.

Genotyping for APOE single nucleotide variants (rs429358 C/T and rs7412C/T), which define the APOE 𝜀2, 𝜀3, and 𝜀4, was performed using real-time fluorescence quantitative polymerase chain reaction by using nucleic acid detection reagents (Youzhiyou company, Wuhan, China).²⁶

Collections Of Csf Samples

Patients were requested to withdraw anti-cognitive impairment drugs for at least 12–14 hours before lumbar puncture if their condition allowed. CSF samples were collected under fasting condition through lumbar puncture, followed by being immediately centrifuged at 4°C with 3000 r/min for 10 minutes. Each CSF sample was then allocated into separate Nunc cryotubes (Beijing JingkeHongda Biotechnology Co., Ltd, Beijing, China) and frozen for 0.5 ml per tube at -80℃ until the assay.²⁷

Measurements Of Neurotrophic Factors In Csf

Neurotrophic factors, including BDNF (ProcartaPlex™ Multiplex Immunoassay Kit, Invitrogen, USA), GDNF (ProcartaPlex™ Multiplex Immunoassay Kit, Invitrogen, USA), and NGF (Human NGF DuoSet ELISA Kit, R&D Systems, USA) were detected by ELISA.

Statistical analysis

Statistical analyses were performed by SPSS Statistics 25.0 (IBM Corporation, New York, USA). Statistical significance was defined as a two-sided P < 0.05.

Data were tested for normal distribution using the Kolmogorov-Smirnov test. Demographic variables, cognitive function, and neurotrophic factors in CSF between the APOE ε4 carrier and non-carrier groups were compared. Continuous variables conforming to normal distribution were presented as means ± standard deviations (SD) and compared by two-tailed t test, while non-normal distributed measurement variables were presented as median (quartile) and compared by nonparametric test, and categorical variables were presented as number (percentage) and compared by Chi-Squared test. Multiple linear regression analyses were performed to evaluate the correlations among APOE ε4, neurotrophic factors, and cognitive function of AD patients. Mediation analyese was conducted to evaluate the sequential associations among APOE ε4, NGF, and cognitive function.

Demographic Variables In Ad Patients

A total of 173 patients were enrolled in this study, among which 55 cases (31.79%) carried APOE ε4, 34 cases (61.83%) were female, the mean age was 65.49 ± 9.00 years, and the median disease duration was 24.00 (12.00, 48.00) years in the APOE ε4 carrier group. Demographic variables including gender, age, age of onset, disease duration, education level, smoking, drinking, BMI, etc, were not significantly different between the two groups (Table 1).

Table 1

Demographic variables of the *APOE* ε4- and *APOE* ε4 + groups
	APOE ε4- group (n = 118)	APOE ε4 + group (n = 55)	p
Female [n (%)]	68.00 (57.63)	34.00 (61.82)	0.602
Age (years, mean ± SD)	62.71 ± 9.05	65.49 ± 9.00	0.062
Age of onset [years, median (quartile)]	59.00 (53.00, 64.75)	64.00 (53.50, 70.00)	0.075
Disease duration	25.00 (13.50, 49.00)	24.00 (12.00, 48.00)	0.460
Education level			0.311
Primary school and below [n (%)]	25 (21.19)	11 (20.00)
Middle and high school [n (%)]	55 (46.61)	21 (38.18)
Bachelor’s degree and above [n (%)]	38 (32.20)	13 (23.64)
Smoking [n (%)]	31 (26.27)	15 (27.27)	0.853
Drinking [n (%)]	28 (23.73)	14 (25.45)	0.832
BMI [median (quartile)]	23.89 (21.91, 25.87)	23.10 (21.60, 25.16)	0.252
History
Hypertension [n (%)]	39 (33.05)	13 (23.63)	0.215
Hyperlipidemia [n (%)]	15 (12.71)	13 (23.63)	0.142
Myocardial infarction [n (%)]	2 (1.69)	0 (0.00)	1.000
Atrial fibrillation [n (%)]	0 (0.00)	1 (1.82)	0.308
Diabetes mellitus [n (%)]	15 (12.71)	6 (10.91)	0.769
Hyperhomocysteinemia [n (%)]	3 (2.54)	0 (0.00)	0.553
Cerebrovascular disease [n (%)]	17 (14.41)	5 (9.10)	0.357
Thyroid disease [n (%)]	8 (6.78)	4 (7.27)	0.968
Chronic obstructive pulmonary disease [n (%)]	2 (1.69)	0 (0.00)	1.000
Asthma [n (%)]	3 (2.54)	2 (3.64)	0.411
Insomnia [n (%)]	16 (13.56)	3 (5.45)	0.074
Sleep apnea syndrome [n (%)]	4 (4.24)	1 (1.82)	0.588
Depression [n (%)]	8 (6.78)	3 (5.45)	0.564
Other mental disorder [n (%)]	3 (2.54)	0 (0.00)	0.223
Notes: Data were presented as number (percentage), means ± SD, or median (quartile). APOE ε4-, the APOE ε4 non-carriers; APOE ε4+, the APOE ε4 carriers. Abbreviation: APOE, apolipoprotein E; SD: standard deviation; BMI: body mass index.

Association ofAPOEε4 with cognitive function

Cognitive function was compared between the APOE ε4 carrier and the APOE ε4 non-carrier groups in Table 2. Multiple linear regression analyses further illustrated the association between APOE ε4 and cognitive function after adjusting for age, gender, age of onset, disease duration and education level (Supplementary Table 1). In terms of global cognitive function, APOE ε4 predicted lower score of MoCA scale [β, -2.31; 95% CI (-4.58, -0.05); P = 0.046]. Additionally, APOE ε4 was also associated with multiple cognitive domains. As far as memory, APOE ε4 was associated with lower scores of AVLT N1-3 [β, -2.35; 95% CI (-4.51, -0.18); P = 0.034], AVLT N1-5 [β, -4.20; 95% CI (-8.14, -0.25); P = 0.037], AVLT N6 [β, -1.01; 95% CI (-1.94, -0.08); P = 0.034] and AVLT N7 [β, -2.62; 95% CI (-5.02, -0.21); P = 0.033]. In terms of language, APOE ε4 was correlated with lower score of AFT [β, -2.06; 95% CI (-4.04, -0.09); P = 0.040]. With regard to attention/executive function, the APOE ε4 carrier group spend longer time on TMT-A [β, 0.45; 95% CI (0.21, 0.88); P = 0.040]. There was no association between APOE ε4 and language and visuospatial ability.

Table 2

Cognitive function of the *APOE* ε4- and *APOE* ε4 + groups
	APOE ε4- group (n = 118)	APOE ε4 + group (n = 55)	p
Cognitive function
Global cognitive function
MMSE [points, median (quartile)]	20.50 (13.00, 25.00)	18.00 (10.00, 22.00)	0.042*
MoCA (points, mean ± SD)	14.44 ± 6.53	11.69 ± 6.32	0.015*
Individual cognitive domain function
Memory
AVLT N1-3 (points, mean ± SD)	10.55 ± 5.84	8.86 ± 5.93	0.012*
AVLT N4 [points, median (quartile)]	0.00 (0.00, 3.00)	0.00 (0.00, 1.00)	0.027*
AVLT N5 [points, median (quartile)]	0.00 (0.00, 4.00)	0.00 (0.00, 1.00)	0.073
AVLT N1-5 [points, median (quartile)]	12.00 (8.00, 20.00)	8.50 (3.00, 14.25)	0.003**
AVLT N6 [points, median (quartile)]	0.00 (0.00, 3.00)	0.00 (0.00, 0.75)	0.013*
AVLT N7 [points, median (quartile)]	9.00 (6.00, 12.00)	8.00 (0.25, 10.75)	0.074
RCFT-delayed [points, median (quartile)]	0.00 (0.00, 10.00)	0.00 (0.00, 5.00)	0.467
Language
AFT (points, mean ± SD)	11.79 ± 5.81	9.73 ± 6.10	0.011*
VFT-H [points, median (quartile)]	9.00 (6.00, 15.00)	8.50 (5.00, 12.00)	0.044*
VFT-alternating fluency (points, mean ± SD)	7.59 ± 5.34	6.38 ± 5.15	0.046*
BNT [points, median (quartile)]	21.00 (18.00, 26.00)	21.00 (15.00, 24.00)	0.209
Visuospatial ability
RCFT-imitation [points, median (quartile)]	26.00 (1.00, 33.00)	20.25 (0.00, 32.25)	0.622
Attention / Executive function
TMT-A [points, median (quartile)]	25.00 (22.00, 25.00)	25.00 (20.25, 25.00)	0.683
TMT-A (time) [minutes, median (quartile)]	1.88 (1.05, 3.70)	2.55 (1.45, 4.00)	0.034*
TMT-B [points, median (quartile)]	21.00 (5.50, 25.00)	15.00 (6.00, 24.00)	0.184
TMT-B (time) [minutes, median (quartile)]	2.99 (1.18, 4.00)	4.00 (2.90, 4.00)	0.023*
SCWT-A [points, median (quartile)]	50.00 (49.00, 50.00)	50.00 (48.00, 50.00)	0.262
SCWT-A (time) [minutes, median (quartile)]	0.67 (0.48, 0.94)	0.79 (0.50, 1.06)	0.263
SCWT-B [points, median (quartile)]	50.00 (47.25, 50.00)	50.00 (46.00, 50.00)	0.523
SCWT-B (time) [minutes, median (quartile)]	0.88 (0.62, 1.20)	0.93 (0.74, 1.51)	0.461
SCWT-C [points, median (quartile)]	47.00 (37.00, 49.00)	43.00 (26.00, 47.50)	0.177
SCWT-C (time) [minutes, median (quartile)]	1.55 (0.91, 2.11)	1.74 (0.98, 2.52)	0.515
SDMT [points, median (quartile)]	20.00 (0.75, 31.75)	15.00 (0.00, 26.50)	0.318
Notes: Data were presented as means ± SD or median (quartile). p < 0.05, p < 0.01. APOE* ε4-, the APOE ε4 non-carriers; APOE ε4+, the APOE ε4 carriers. Abbreviation: APOE, apolipoprotein E; MMSE, Mini-Mental State Examination; MoCA, Montreal Cognitive Assessment; AVLT, Animal Fluency Test, AFT; Auditory Verbal Learning Test; VFT, Verbal Fluency Test; BNT, Boston Naming Test; RCFT, Rey-Osterrieth Complex Figure Test; TMT, Trail Making Test; SCWT, Stroop Color and Word Test; SDMT, Symbol Digit Modalities Test.

Association of APOE ε4 with the levels of neurotrophic factors in CSF

The levels of neurotrophic factors in CSF between the APOE ε4 carrier and non-carrier groups were compared (Fig. 1). NGF level in the APOE ε4 carrier group was significantly lower than that in the APOE ε4 non-carrier group (P = 0.016).

AD patients were further divided into the APOE ε4-/-, APOE ε4+/- and APOE ε4+/+ groups, and found that NGF level in the APOE ε4+/- group was markedly lower than that in the APOE ε4-/- group (P = 0.042). Furthermore, NGF level in the APOE ε4+/+ group was lowest than that in other groups (Supplementary Fig. 1).

Multiple linear regression analyses illustrated that APOE ε4 was associated with lower NGF level in CSF after adjusting for age, gender, age of onset, disease duration, education level and BMI [β, -1.98; 95% CI (-3.78, -0.19); P = 0.031] (Table 3).

Table 3

Association between *APOE* ε4 and neurotrophic factors in CSF in AD patients
	Unadjusted		Adjusted
	β (95%CI)	p	β (95%CI)	p
BDNF (pg/ml)	-0.09 (-14.60, 14.43)	0.991	-7.25 (-24.56, 10.05)	0.408
GDNF (pg/ml)	2.28 (-2.65, 7.21)	0.363	3.38 (-3.36, 10.12)	0.322
NGF (pg/ml)	-1.87 (-3.39, -0.35)	0.016*	-1.98 (-3.78, -0.19)	0.031*
Notes: Age, gender, age of onset, disease duration, education level and BMI were adjusted. p < 0.05. Abbreviation: APOE, apolipoprotein E; APOE* ε4-, the APOE ε4 non-carriers; APOE ε4+, the APOE ε4 carriers; CSF, cerebrospinal fluid; AD, Alzheimer’s disease; GDNF, glial cell-derived neurotrophic factor; BDNF, brain-derived neurotrophic factor; NGF, nerve growth factor.

Association Between Ngf Level In Csf And Cognitive Function

Multiple linear regression analyses were conducted in order to explore the association of NGF level in CSF and cognitive function in AD patients (Fig. 2). In terms of overall cognitive function, NGF level was significantly and positively associated with score of MMSE scale [β, 0.33; 95% CI (0.01, 0.66); P = 0.046]. As far as the function of individual cognitive domain, NGF level was significantly and positively associated with scores of RCFT-delayed [β, 0.52; 95% CI (0.15, 0.89); P = 0.007], AFT [β, 0.35; 95% CI (0.107, 0.585); P = 0.005] and VFT-alternating fluency [β, 0.28; 95% CI (0.05, 0.52); P = 0.018], which reflected language function. Furthermore, NGF level was significantly and negatively associated with TMT-A (time) [β, -0.08; 95% CI (-0.14, -0.02); P = 0.008] and positively associated with SCWT-B score [β, 0.72; 95% CI (0.06, 1.37); P = 0.033], which reflected attention/executive function.

Association between NGF level in CSF and cognitive function was further conducted in patients carrying APOE ε4 (Supplementary Table 2). In individual cognitive domains, as far as memory, NGF level was significantly and positively associated with the scores of AVLT N1-3 [β, 0.50; 95% CI (0.11, 0.89); P = 0.015], AVLT N4 [β, 0.20; 95% CI (0.05, 0.34); P = 0.010], AVLT N1-5 [β, 0.63; 95% CI (0.03, 1.24); P = 0.042] and RCFT-delayed [β, 1.29; 95% CI (0.37, 2.22); P = 0.010]. With regard to language, NGF level was significantly and positively associated with the score of VFT-alternating fluency [β, 0.41; 95% CI (0.02, 0.79); P = 0.041]. NGF level was not associated with visuospatial ability, attention/executive function.

Mediation analyses among APOE ε4, NGF level and cognitive function

Mediation analyses were conducted to evaluate the sequential associations among APOE ε4, NGF level in CSF, and cognitive function in AD patients (Fig. 3). Results showed that NGF level in CSF significantly mediated the associations between APOE ε4 and AFT [β, -0.45; 95% CI (-0.96, -0.07); P < 0.001] (Fig. 3A) as well as TMT-A (time) [β, 0.15; 95% CI (0.01, 0.33); P < 0.001] (Fig. 3B). There was no marked mediation effect of NGF level in CSF on the associations between APOE ε4 and functions of other cognitive domains.

In this study, we investigated the associations among APOE ε4, neurotrophic factors in CSF, and cognitive function in AD patients, and found that: (1) APOE ε4 was significantly associated with poorer cognitive function; (2) APOE ε4 was associated with lower NGF level in CSF; (3) The decreased NGF level in CSF was significantly associated with cognitive impairment; (4) The decrease of NGF level in CSF mediated significant association between APOE ε4 and impairments of multiple cognitive domians.

Relationship between APOE ε4 and cognitive impairment in AD patients

It is well known that APOE ε4 was the strongest risk gene for sporadic AD.² Previous studies demonstrated that AD patients with APOE ε4 had poorer cognitive function.^28–30 However, the relationships between APOE ε4 and functions of cognitive domains were still unclear. In this study, we comprehensively evaluated multiple cognitive domains by a body of rating scales, and found that AD patients carrying APOE ε4 had particularly more severe memory impairment, which might be due to the close association of APOE ε4 with the atrophy of temporal lobe (especially hippocampus) and dysfunction of default mode network.^28–30 In additon to memory, we firstly observed that APOE ε4 was significantly associated with the impaired cognitive domains of language and attention/executive function, which might be attributed to the faster rate of cognitive decline and poorer cognitive function that APOE ε4 carriers had.^2,3

Relationship between APOE ε4 and the levels of neurotrophic factors in CSF in AD patients

In this study, in a variety of neurotrophic factors measured, NGF level in CSF from AD patients carrying APOE ε4 was significantly declined compared with those carrying no APOE ε4. APOE, the most important lipid transport protein in the brain, is mainly secreted by astrocytes and to a lesser extent by microglia. APOE binds with two major metabolic receptors, the low-density lipoprotein receptor and lipoprotein receptor-related protein, to promote lipid transport between cells, redistribute intracellular lipids and maintain lipid balance in the brain.³¹ Compared with other APOE isoforms, APOE4 encoded by APOE ε4 has the weakest effect on lipid transport.³² Cholesterol homeostasis is essential for the brain. Insufficient cholesterol led to abnormal nutrition and energy metabolism of cells, while excessive accumulation damaged synaptic plasticity and induced neuronal apoptosis.³³ However, there is a lack of studies directly targeting the relationship between APOE ε4 or APOE4 and NGF. Base on the results from this investigation, we speculate that the impaired cellular nutrient and energy metabolism due to the weaker lipid transport capacity of APOE4 may account for the declined NGF level in CSF of AD patients.

Relationship Between Ngf Level In Csf And Cognitive Impairment In Ad Patients

In this exploration, we found the close relationship between NGF level in CSF and cognitive function of AD patients. Forebrain cholinergic neurons are the main source of acetylcholine in hippocampus and cerebral cortex, which dysfunction or degeneration is the prominent cause of decreased acetylcholine level and impaired cognitive function in AD patients.¹ NGF, a member of neurotrophin family, supplies the forebrain cholinergic neurons to maintain their cholinergic phenotype. Degeneration of the cholinergic system is associated with dysregulation of NGF metabolic pathway, which controls the maturation and degradation of NGF.³⁴ Previous studies found that regulation disorders of NGF pathway, including impaired maturation and increased degradation of NGF, existed in AD, even in the preclinical stage of disease.^35,36 NGF deprivation was associated with poorer cognitive function, and treatment with NGF ameliorated neuropathology and thereafter inhibited memory decline in AD animal models.^10,37 However, the relationships between NGF and functions of different cognitive domains in AD remains are still unclear. In this study, we first found that the decreased NGF level in CSF was highly correlated with the impairments of global cognitive function and multiple cognitive domains of memory, language, attention and executive function. In addition, the decrease of NGF level was particularly and fairly associated with dysfunctions of memory and language in AD patients carrying APOE ε4. In the early stage of AD, the compromised cognitive domains include memory and language, which may be specifically vulnerable to the decrease of NGF in AD patients carrying APOE ε4 based on the results form this study. The detailed mechanism underlying their association needs further investigation in the future.

APOE ε4 may impair cognitive function in AD patients through NGF

Previous studies found that APOE ε4 aggravated cognitive impairment by promoting depositions of neuropathological proteins of AD, and facilliated neuroinflammation by activating microglia and astrocytes.^4–6 However, the effects of neurotrophic factors on APOE ε4 and related cognitive impairment are unclear. In the current study, we for the first time found that the declined NGF in CSF played an important role on mediating APOE ε4-associated cognitive impairment, particularly language and attention/executive function. It is well known that APOE4 has poor lipid transport capacity than other APOE isoforms, and consequently lead to lipid instability in cells. Accordingly, we speculate that APOE4 may be responsible for the declined of NGF in brain, and NGF deficiency may further accelerated degeneration of cholinergic system, eventually propagating impairment of cognitive function in AD patients. The potential mechanisms illustrating the mediating role of NGF on APOE ε4-relevent impairments of language and executive function remains to be elucidated.

Limitations

This study had limitations. First, measurement of variables in CSF is one of the most objective ways to reflect the changes in brain. However, it is very tough to obtain CSF from the elderly, particularly from people with normal cognition. We will collect CSF samples from more AD patients and cognitively normal controls. Second, in contrast to a randomized controlled design, this cross-sectional study may have introduced selection bias.

APOE ε4 is associated with the significantly compromised cognitive function of AD patients. AD patients carrying APOE ε4 have prominently decreased NGF level in CSF. The declined NGF level in CSF is markedly correlated with drastically impaired overall cognition and multiple cognitive domains of memory, language and attention/executive function. More importantly, NGF plays a pivotal role in mediating remarkably compromised cognitive function associated with APOE ε4. The novel findings from this study are helpful for understanding the pivotal role of NGF deficiency on cognitive impairment of AD patients carrying APOE ε4, and replenishing NGF may be an effective therapy for slowing down cognitive impairment for AD patients carrying APOE ε4.

Ethics statement

The study protocol was approved by the Ethical Review Board of Beijing Tiantan Hospital. Written informed consents were obtained from patients and their caregivers. All procedures were conducted in accordance with the guidelines and regulations of ethical principles for medical research involving human subjects of the Declaration of Helsinki.

Consent for publication

Not applicable.

Availability of data and materials

The data that support the fndings of this study are available from the first author or the corresponding author upon reasonable request.

Competing interests

The authors report no competing interests.

Funding

This research was supported by the National Key R&D Program of China-European Commission Horizon 2020 (2017YFE0118800-779238), the National Key Research and Development Program of China (2016YFC1306300, 2016YFC1306000), the National Natural Science Foundation of China (81970992, 81571229, 81071015, 30770745，82201639), the Capital’s Funds for Health Improvement and Research (CFH) (2022-2-2048), the Key Technology R&D Program of Beijing Municipal Education Commission (kz201610025030), the Key Project of Natural Science Foundation of Beijing, China (4161004), the Natural Science Foundation of Beijing, China (7082032), the Project of Scientific and Technological Development of Traditional Chinese Medicine in Beijing (JJ2018-48), the Capital Clinical Characteristic Application Research (Z121107001012161), the High Level Technical Personnel Training Project of Beijing Health System, China (2009-3-26), the Project of Beijing Institute for Brain Disorders (BIBD-PXM2013_014226_07_000084), the Excellent Personnel Training Project of Beijing, China (20071D0300400076), the Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges Under Beijing Municipality (IDHT20140514), the Beijing Healthcare Research Project, China (JING-15-2), the Basic-Clinical Research Cooperation Funding of Capital Medical University, China (2015-JL-PT-X04, 10JL49, 14JL15), the Natural Science Foundation of Capital Medical University, Beijing, China (PYZ2018077) and the Youth Research Funding, Beijing Tiantan Hospital, Capital Medical University, China (2015-YQN-14, 2015-YQN-15, 2015-YQN-17).

Authors’ contributions and acknowledgements

We would like to thank Mingyue He contributed to the conception, design and data statistics of the study and paper writing; thank Tenghong Lian, Peng Guo, Wenjing Zhang, Weijiao Zhang, Jinghui Li, Huiying Guan, Weijia Zhang, Dongmei Luo, Jing Qi, Hao Yue and Zhan Liu contributed to the acquisition and collation of data; thank Yue Huang, Yanan Zhang, Gaifen Liu and Xiaomin Wang contributed to directing paper writing and data statistics; thank Wei Zhang contributed to the conception and design of the study and the supervision of paper writing.

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No competing interests reported.

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Role of nerve growth factor on cognitive impairment in Alzheimer's disease patients carrying apolipoprotein E ε4

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Introduction

Materials And Methods

Patients

Collection Of Demographic Variables

Assessment Of Cognitive Function

Collections Of Csf Samples

Measurements Of Neurotrophic Factors In Csf

Statistical analysis

Results

Discussion

Conclusion

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