Sage Journals: Discover world-class research

Abstract

Triggering receptor expressed on myeloid cells 2 (TREM2) is upregulated in activated microglia and may be related to cognitive decline in patients with Alzheimer’s disease (AD). There is conflicting evidence regarding the association of peripheral TREM2 mRNA expression/soluble TREM2 (the extracellular domain of TREM2) with cognitive function/neuroinflammation in patients with AD. Herein, we studied the TREM2 and TREM2_alt mRNA expression and their association with the cognitive performance in subjects with mild dementia due to AD and healthy controls. In a subgroup of patients with AD, magnetic resonance spectroscopy was used to measure the myo-inositol level in the posterior cingulate cortex, a surrogate marker for neuroinflammation. The results showed that increased TREM2 and TREM2_alt mRNA expression is associated with AD pathogenesis at the mild dementia stage, thereby serving as a potential biomarker for early symptomatic stage of AD. TREM2 may exert protective effects on both cognition and central neuroinflammation.

Keywords

TREM2 soluble TREM2 alternatively spliced isoform Alzheimer’s disease dementia cognition

Significance Statement

• The peripheral blood TREM2 and TREM2_alt mRNA expression levels were higher in patients with mild AD than in the control group.

• TREM2 and TREM2_alt mRNA expression levels were positively associated with MMSE score in patients with mild AD. TREM2 might exert a protective function in cognition in the early symptomatic stages of AD.

• TREM2 and TREM2_alt mRNA expression levels were negatively associated with mI levels at the PCC on MRS, a surrogate marker for neuroinflammation, in patients with AD but not in controls.

Introduction

Alzheimer’s disease (AD), the most common neurodegenerative disease and dementia syndrome, involves amyloid-β (Aβ) deposition, tau aggregation, mitochondrial dysfunction, and cerebral vascular injury.¹ Recent evidence suggests that neuroinflammation contributes to its pathogenesis.^1-5 Neuroinflammation in AD can be modulated by microglial activation in response to Aβ pathology. Microglia may exhibit neuroprotective or neurotoxic effects that signify the course of disease.^6,7 Triggering receptor expressed on myeloid cells 2 (TREM2), a transmembrane glycoprotein expressed on the surface of microglia, promotes the association between microglia and Aβ plaques. This interaction facilitates the uptake and degradation of Aβ by microglia and appears to exhibit disease progression-dependent effects.^8,9 Several rare variants of TREM2 have been shown to increase AD risk by 2-4-fold, which is similar to the effect of a single copy of apolipoprotein E (APOE) ɛ4.^10,11

Due to the ectodomain shedding of TREM2, its extracellular domain, soluble TREM2 (sTREM2), can be detected in both the cerebrospinal fluid (CSF) and plasma. However, the relative levels of TREM2 or sTREM2 in the CSF or peripheral blood between healthy controls and patients with AD have been conflicting in previous studies.^12-18 In addition, the association between peripheral TREM2 mRNA expression and cognitive status in patients with AD also varied between studies. However, most studies reported a negative correlation between the both the CSF and peripheral TREM2 expression level as well as mini-mental state examination (MMSE) score in patients with AD and patients with amnestic mild cognitive impairment.^12-14,19 Finally, the correlation between peripheral TREM2 mRNA expression and central neuroinflammation is uncertain. Previous studies have shown that the level of neuroinflammation can be measured by brain magnetic resonance spectroscopy (MRS), a non-invasive method to measure metabolic, neurodegenerative changes, gliosis, and microgliosis by quantifying N-acetyl-aspartate and myo-inositol (mI).^20-22 Elevated levels of mI could be a surrogate of neuroinflammation, an organic glial marker with selective expression of mRNA for sodium-dependent mI transporters in astrocytes.^20,21,23,24

A recent study conducted by Moutinho and colleagues have presented experimental findings demonstrating that in the human brain, TREM2 alternatively spliced isoforms (TREM2_alt) are translated and secreted as sTREM2.²⁵ In accordance with these findings, we compared the peripheral expression of all TREM2 mRNA isoforms and TREM2_alt, which encodes sTREM2,²⁶ at the same time in patients with mild AD to healthy controls to examine the clinical significance of different mRNA isoforms in this study. MRS was used to investigate the association between peripheral TREM2 expression and central neuroinflammation. Based on previous studies,^12,14,19 we proposed that peripheral TREM2 or TREM2_alt expression might be higher in patients with mild AD than in healthy controls and is associated with cognitive function and central neuroinflammation.

Materials & Methods

Participants

We recruited patients with mild AD (clinical dementia rating (CDR)²⁷ = .5 or 1) and healthy controls at the outpatient clinics of 2 teaching hospitals in Taiwan. According to the National Institute on Aging-Alzheimer’s Association clinical criteria for probable AD, an AD diagnosis was made during a multidisciplinary consensus meeting.²⁸ The age at onset of the disease needed to be 65 years or older, and a caregiver who could provide a collateral history was required to be present. Patients with AD received a standardized evaluation that included clinical interviews, neuropsychological assessments, laboratory tests, and magnetic resonance imaging (MRI).

Patients with significant neurological diseases other than AD that affect cognition, medical history of chronic inflammatory conditions, and anti-inflammatory or immunosuppressive medication use were excluded from the study. This study was approved by the institutional review boards of the 2 hospitals. Informed consent was obtained from all the patients and their caregivers before participating in the study.

Clinical Evaluation and Procedures

During recruitment, cognitive function was assessed using standard procedures. The MMSE²⁹ was used to assess global cognition. The CDR was administered to determine the severity of dementia. The 12-item memory test,³⁰ modified 15-item Boston naming test,³¹ category verbal fluency test,³² trail making test A,³³ and forward and backward digit span tests were used to assess short-term memory, language, executive function, attention, and working memory, respectively. Depression was evaluated using the short form of the geriatric depression scale.³⁴

TREM2 mRNA Measurement

Total ribonucleic acid (RNA) was extracted from the whole extraction of total RNA according to the standard protocol of the Tempus^TM Blood RNA Systems (P/N4342792; P/N4380204, Applied Biosystems, CA, USA). The concentration and purity of the extracted total RNA were measured using a NanoDrop® ND-1000 spectrophotometer (Thermo Fisher Scientific). To quantitatively estimate TREM2 mRNA levels, complementary deoxyribonucleic acid (cDNA) was synthesized from 1 μg of total RNA using a High Capacity cDNA Reverse Transcription Kit (P/N4368814, Applied Biosystems, CA, USA) in accordance with the manufacturer’s instructions.

Preamplification was performed using the TagMan® PreAmp Master Mix Kit (P/N4391128; Applied Biosystems, CA, USA). Following the manufacturer’s protocol, the pooled assay mixtures contained TagMan® Gene Expression Assays (P/N4331182, Applied Biosystems, CA, USA) and endogenous control, and Tris-ethylenediaminetetraacetic acid (EDTA) buffer was used to dilute the pooled assays to a final concentration (Assay ID: Hs00219132_m1 to capture all TREM2 transcripts; AI89K96 to capture TREM2_alt transcript; glyceraldehyde 3-phosphate dehydrogenase, Hs99999905_m1). The preamplification reaction, including the TagMan® PreAmp Master Mix, pooled assay mix, and cDNA sample, was incubated for 10 min at 95°C, followed by 14 cycles of 95°C for 15 s and 60°C for 4 min, and held at 4°C in an Applied Biosystems Thermocycler (9700). The preamplification product was further diluted with Tris-EDTA buffer to serve as a template for real-time polymerase chain reaction (PCR) analysis.

For quantitative estimation of TREM2 and TREM2_alt mRNA levels, the StepOnePlus^TM Real-Time PCR System (Applied Biosystems, CA, USA) was used in triplicate for each sample. The final reaction volume was 10 μL using the TaqMan Universal Master Mix with UNG (P/N4440044, Applied Biosystems, CA, USA). Relative mRNA levels were calculated using the 2-ΔΔCT method using StepOne software 2.3 (Applied Biosystems, CA, USA).³⁵ The median level of healthy controls was used for calibration in all experiments to correct for any observational errors.

DNA Analysis

Genomic DNA was isolated from whole blood using the Gentra Puregene kit, according to the manufacturer’s protocol (Qiagen, Hilden, Germany). The presence of the ε2, ε3, and ε4 alleles of the APOE gene was determined by genotyping the single nucleotide polymorphisms rs429358 and rs7412. An APOE ε4 carrier was defined as having at least one ε4 allele (including ε2/ε4, ε3ε4, and ε4/ε4). Genotyping of rs429358 and rs7412 was performed using the TaqMan genotyping assay (Applied Biosystems, Foster City, CA, USA). PCRs were performed in 96-well microplates using an ABI StepOnePlus^TM real-time PCR machine (Applied Biosystems). Allele discrimination was achieved by detecting fluorescence using StepOne software 2.3 (Applied Biosystems, CA, USA).

Magnetic resonance spectroscopy

The second half of the study involved brain MRS in 25 consecutive patients consecutively. Brain MRI studies were performed using a GE Discovery 3 Tesla MRI. A 3D T1 FSPGR image series (TR = 6.8 ms, TE = 2.5 ms, 24 cm² FOV; 1 mm³ isotropic voxels) was used for the localization of posterior cingulate cortex (PCC) (volume of interest = 2 × 2 × 2 cm³ in the midsagittal PCC region), which is commonly known the site of initial neuropathological changes in AD and has been investigated in many previous studies.^36,37 Proton MR spectra were acquired using the PRESS localization sequence with TR = 2000 ms, TE = 35 ms, and 8 and 160 total numbers of scans for each acquisition. Brain MRI and proton MR spectra quality were visually assessed by an expert neuroradiologist (Lirng JF) blinded to the clinical condition. Peak areas of creatine (Cr) + phosphocreatine (PCr) and mI were calculated using LCModel. The glial marker for neuroinflammation was measured using the mI relative to Cr + PCr at the PCC.

Statistical Analysis

The demographic and neuropsychiatric data of the AD and control groups were compared using the chi-square test or Mann-Whitney U test when appropriate. The skewness values of TREM2 and TREM2_alt mRNA expression exceeded one. Thus, we log-transformed TREM2 and TREM2_alt mRNA expression values for further analysis.³⁸ Differences in TREM2 and TREM2_alt mRNA expression levels between the 2 groups were examined using a one-way analysis of covariance after adjusting for age, sex, and APOE ɛ4 carrier status. In addition, the linear regression stratified by sex was also performed. The associations between MMSE and TREM2 and TREM2_alt in patients with AD were examined using Spearman’s correlation and linear regression after adjusting for age, sex, years of education, and APOE ɛ4 carrier status. To further evaluate the association between TREM2 expression and mI level (mI relative to Cr + PCr) on MRS, Spearman’s correlation and linear regression analyses were performed after adjusting for age, sex, and APOE ɛ4 carrier status.

Results

Subjects and Demographics

In total, 61 patients with AD (36 males/25 females; mean age = 75.5 ± 6.4 years; mean education = 9.6 ± 5.0 years; mean MMSE = 22.5 ± 2.4) and 51 controls (20 males/31 females; mean age = 72.2 ± 6.2 years; mean education = 11.9 ± 4.3 years; mean MMSE = 28.6 ± 1.3) were recruited for this study. Table 1 shows the demographic and neuropsychiatric data of all participants. There were no differences in the sex ratio (P = .058) and depression scale score (P = .948) between patients with AD and controls. However, patients with AD had fewer years of education (P = .011) and were older (P = .004) than controls. Patients with AD were found to have lower scores in all cognitive assessments compared to the controls.

Table 1.

Clinical Characteristics and Neuropsychological Data of all Participants.

	Controls (n = 51)	Patients with AD (n = 61)	P-Value
Female, n (%)	31 (60.8)	25 (41.0)	.058
Age (years, mean ± SD)	72.2 ± 6.2	75.5 ± 6.4	.004
Education (years, mean ± SD)	11.9 ± 4.3	9.6 ± 5.0	.011
APOE ɛ4 carrier no. (%)	9 (17.6)	21 (34.4)	.075
MMSE (mean ± SD)	28.6 ± 1.3	22.3 ± 2.4	<.001
12-item delayed recall (mean ± SD)	8.8 ± 2.2	2.6 ± 2.7	<.001
Forward digit span (mean ± SD)	11.2 ± 2.1	9.3 ± 2.5	<.001
Backward digit span (mean ± SD)	7.8 ± 2.6	4.9 ± 2.2	<.001
Category verbal fluency (mean ± SD)	12.9 ± 3.0	8.0 ± 2.4	<.001
Modified Boston naming test (mean ± SD)	14.2 ± 1.1	12.8 ± 1.8	<.001
Trail making A (seconds, mean ± SD)	55.0 ± 24.3	122.9 ± 88.9	<.001
Geriatric depression scale (mean ± SD)	2.7 ± 2.3	3.0 ± 3.2	.948

P-values represent the comparison between groups using a chi-square or Mann-Whitney U test.

Abbreviations: AD, Alzheimer’s disease; APOE, apolipoprotein E; MMSE, mini-mental state examination.

TREM2 and TREM2_alt mRNA Expression Levels

After log-transforming the TREM2 and TREM2_alt mRNA expression values, patients with AD showed a significantly higher expression of TREM2 mRNA than the control group (1.28 ± .46 vs 1.05 ± .44, P = .013). Patients with AD also showed significantly higher expression of TREM2_alt mRNA compared to the control group (1.52 ± .77 vs 1.03 ± .48, P = .001) (Figure 1).

Figure 1.

Comparison of the peripheral TREM2 and TREM2_alt mRNA expression levels between patients with AD and controls. The expression of TREM2 and TREM2_alt mRNA showed significant differences between patients with AD and controls (TREM2, P = .013; TREM2_alt, P = .001).

Associations Between MMSE and TREM2, as Well as TREM2_alt mRNA Expression in Patients with AD

After log-transforming the TREM2 and TREM2_alt mRNA expression values, there were significant positive correlations between the MMSE score and TREM2 mRNA expression (rs = .305, P = .017) and TREM2_alt mRNA expression (rs = .302, P = .018) in patients with AD (Figure 2), but not in controls. After adjusting for covariates, linear regression also showed that TREM2 and TREM2_alt mRNA expression were independent predictors of the MMSE scores in patients with AD (TREM2, P = .001; TREM2_alt, P = .009) (Table 2). Furthermore, in the linear regression stratified by sex, there was still a significant correlation between TREM2 mRNA expression and MMSE in both male and female AD patients, although this correlation was less pronounced for TREM2_alt mRNA expression (Supplemental Tables 1 and 2).

Figure 2.

Correlation between the MMSE score and TREM2 and TREM2_alt mRNA expression in patients with AD. Significant correlations between the MMSE score and TREM2 mRNA expression (rs = .305, P = .017) and TREM2_alt mRNA expression (rs = .302, P = .018).

Table 2.

Results of Linear Regression Showing That TREM2 and TREM2_alt mRNA Expression are Independent Predictors for the MMSE in Patients With AD.

	B	SE	β	P-Value
Model 1
Age	−.093	.041	−.250	.028
Sex	−1.007	.562	−.208	.079
APOE ɛ4 carrier status	−.978	.563	−.196	.088
Years of education	.151	.057	2.647	.011
TREM2 mRNA expression	6.288	1.789	.384	.001
Model 2
Age	−.074	.043	−.198	.093
Sex	−.700	.587	−.145	.238
APOE ɛ4 carrier status	−.820	.597	−.164	.173
Years of education	.162	.060	.336	.009
TREM2_alt mRNA expression	3.474	1.274	.319	.009

MMSE as the dependent variable. R² = .357.

MMSE as the dependent variable. R² = .306.

Abbreviation: AD, Alzheimer’s disease; APOE, apolipoprotein E; MMSE, mini-mental state examination; TREM2, triggering receptor expressed on myeloid cells 2; TREM2_alt, alternatively spliced TREM2.

Associations Between mI Level at PCC on MRS and TREM2 as Well as TREM2_alt mRNA Expression in Patients with AD

In total, 25 patients underwent MRS. There were no differences in the sex ratio (P = .51), age (P = .82), years of education (P = .96), the prevalence of APOE ɛ4 carriers (P = 1.00), and MMSE score (P = .72) between this subgroup and the subgroup without MRS. After log-transforming the TREM2 and TREM2_alt mRNA expression values, there were significant negative correlations between mI levels at the PCC on MRS and TREM2 mRNA expression (rs = −.426, P = .034) and TREM2_alt mRNA expression (rs = −.447, P = .025) in patients with AD (Figure 3), but not in controls. After adjusting for covariates, linear regression also showed that TREM2 and TREM2_alt mRNA expression were independent predictors of mI levels at the PCC on MRS in patients with AD (TREM2, P = .032; TREM2_alt, P = .028) (Table 3).

Figure 3.

Correlation between the MRS-measured mI level (mI/Cr + PCr) at PCC and TREM2 and TREM2_alt mRNA expression in patients with AD (n = 25). Significant correlations between the MMSE score and TREM2 mRNA expression (rs = −.426, P = .034) and TREM2_alt mRNA expression (rs = −.447, P = .025).

Table 3.

Results of Linear Regression Showing That TREM2 and TREM2_alt mRNA Expression Are Independent Predictors for the mI Level at PCC on MRS in Patients With AD.

	B	SE	β	P -Value
Model 1
Age	.001	.002	.02	.920
Sex	.059	.027	.470	.041
APOE ɛ4 carrier status	.008	.027	.059	.779
TREM2 mRNA expression	−.193	.084	−2.307	.032
Model 2
Age	−.001	.002	−.092	.646
Sex	.044	.026	.354	.105
APOE ɛ4 carrier status	−.003	.027	−.025	.903
TREM2_alt mRNA expression	−.149	.063	−.451	.028

mI/Cr + PCr as the dependent variable. R² = .306.

mI/Cr + PCr as the dependent variable. R² = .314.

Abbreviation: AD, Alzheimer’s disease; APOE, apolipoprotein E; Cr, creatine; mI, myo-inositol; MRS, magnetic resonance spectroscopy; PCC, posterior cingulate cortex; PCr, phosphocreatine; TREM2, triggering receptor expressed on myeloid cells 2; TREM2_alt, alternatively spliced TREM2.

Discussion

The present study showed higher peripheral blood TREM2 and TREM2_alt mRNA expression levels in patients with mild AD than in the control group. In addition, TREM2 and TREM2_alt mRNA expression were positively associated with cognitive status and negatively associated with the marker of central neuroinflammation. These findings suggest a protective function of peripheral TREM2 in cognition and neuroinflammation in the early symptomatic stages of AD. Furthermore, we observed increased peripheral TREM2 and TREM2_alt mRNA expression levels in patients with mild AD. The results provide additional evidence of changes in TREM2 expression during the early symptomatic stage of AD. They indicate that peripheral TREM2 and TREM2_alt mRNA levels could be potential biomarkers associated with neuroinflammation in the early stage of AD dementia.

The increased peripheral TREM2 mRNA expression in patients with AD echoed most of the findings of previous studies.^12-14 However, the present study is the first to demonstrate that peripheral TREM2_alt mRNA expression is higher in patients with AD. TREM2_alt is responsible for encoding sTREM2, the extracellular domain of TREM2 due to ectodomain shedding. The CSF sTREM2 level serves as a surrogate measure of microglial activity and tauopathy.^39,40 While many studies demonstrate an elevation of CSF sTREM2 along the AD continuum, inconsistencies exist regarding disease stages,⁴¹ thereby reducing the discriminative power necessary for diagnostic purposes. A previous study showed that TREM2_alt mRNA expression was also higher in the temporal cortex of patients with AD, but this difference was not significant after adjusting for covariates.²⁶ Similarly, a recent research also demonstrated elevated levels of TREM2_alt mRNA and other isoforms in several AD brain regions.²⁵ One of the few studies addressing the implication of peripheral sTREM2 in AD demonstrated that plasma sTREM2 levels correlate with inflammatory activity in the peripheral circulation and vary across different stages of the disease.⁴² Therefore, the findings of the present study suggest that the measurement of TREM2_alt expression in the peripheral blood may reflect the activation of TREM2-related signaling and an altered peripheral immune activity in response to early-stage AD pathology.

Our study found a positive correlation between the MMSE score and TREM2 expression in patients with mild AD after adjusting for covariates, including APOE ɛ4 carrier status, but not in controls. In AD pathology, the continued activation of microglia and prolonged neuroinflammation may adversely affect brain function and contribute to neurodegeneration. The upregulation of TREM2 in peripheral blood mononuclear cells appears to offer protection against neuroinflammation by suppressing sustained microglial activation, enhancing phagocytosis, and facilitating the clearance of apoptotic neurons.⁴³ Hence, TREM2 might prove valuable as an early peripheral biomarker for AD development. Our discovery suggests possible alterations in systemic TREM2 function during the early stages of cognitive decline, highlighting its significance as a crucial player in a broader, potentially systemic immune response in AD.

The cognitive protective function of TREM2 was also supported by other studies, although indirectly. In vivo studies have shown that functional TREM2 plays a role in the phagocytic clearance of amyloid seeds during early amyloidogenesis⁴⁴ and that TREM2-deficient microglia exhibit strong cerebral metabolic defects and increased stress markers.⁴⁵ A recent study also showed that CSF sTREM2 expression was decreased in the earliest asymptomatic phase of AD with the presence of abnormal Aβ pathology but not tau pathology or neurodegeneration, and an increased sTREM2 level in the CSF in an early symptomatic stage of AD was associated with tau-related neurodegeneration instead of Aβ pathology.⁴⁶ Together, these findings suggest that CSF TREM2 expression might be a response to tau pathology in the early symptomatic phase of AD and that CSF TREM2 has a protective effect during the early stage. However, the results of studies examining the correlation between peripheral mRNA expression levels of TREM2 and MMSE were contradictory. One study showed a significant negative correlation between peripheral TREM2 expression and MMSE scores in patients with moderate to severe AD (MMSE: 0-16).¹² Another study reported that higher serum TREM2 levels were correlated with lower MMSE scores after correcting for APOE ɛ4 carrier status.¹³ Another study evaluating patients with AD and schizophrenia showed no correlation between peripheral TREM2 levels and MMSE scores.¹⁴ These conflicting findings suggest dynamic changes or a disease stage-dependent effect of peripheral TREM2 expression during the disease course of AD^18,47 and an interaction among cognitive status, APOE ɛ4 carrier status, and TREM2 expression.

Our study had several limitations. First, the diagnoses of AD were made based on clinical criteria without biomarker evidence of Aβ and tau, which may have influenced diagnostic accuracy. Second, we did not measure the corresponding peripheral TREM2 protein level at the same time because previous studies have shown similar results between the protein level and mRNA expression.¹² Third, while many pharmacological or metabolic factors may alter serum TREM2 mRNA expression levels in study participants, we only excluded subjects with infective or inflammatory conditions or anti-inflammatory or immunosuppressive medication use at the time of blood sampling. Fourth, the relatively small sample size may have limited the statistical power of our study. Another independent cohort study with more participants should be conducted in the future to confirm the results. Lastly, the carrier status of the TREM2 R47H variant, a risk mutation linked to AD, was unknown among the studied subjects. Consequently, we are unable to account for this variable in the study.

In conclusion, increased peripheral TREM2 and TREM2_alt mRNA expression are associated with AD pathogenesis in patients with mild dementia. The positive associations of both peripheral TREM2 and TREM2_alt mRNA expression with the MMSE score in mild AD suggested that TREM2 may exhibit protective effects on cognitive status. In contrast, the negative association of serum TREM2 mRNA levels with mI levels at the PCC in the subgroup of patients with AD might suggest the role of TREM2 in modulating central nervous system inflammation. Peripheral TREM2 and TREM2_alt mRNA levels may be potential biomarkers associated with neuroinflammation in the early symptomatic stages of AD.

Supplemental Material

Supplemental Material - Different Splice Isoforms of Peripheral Triggering Receptor Expressed on Myeloid Cells 2 mRNA Expressions are Associated With Cognitive Decline in Mild Dementia Due to Alzheimer’s Disease and Reflect Central Neuroinflammation

Supplemental Material for Different Splice Isoforms of Peripheral TREM2 mRNA Expressions are Associated With Cognitive Decline in Mild Dementia Due to Alzheimer’s Disease and Reflect Central Neuroinflammation by Yi-Kuan Chiang, Yung-Shuan Lin, Chun-Yu Chen, Jiing-Feng Lirng, Yu-Hsiu Yang, Wei-Ju Lee, and Jong-Ling Fuh in American Journal of Alzheimer’s Disease & Other Dementias®

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is supported by grants from the Academia Sinica of Taiwan (AS-BD-108-2; AS-KPQ-111-KNT), National Health Research Institutes, Taiwan (PH-112-GP-08, NHRI-11A1-CG-CO-05-2225-1), the Ministry of Science and Technology, Taiwan (NSTC 111-2321-B-001-010-, 111-2314-B-075 -069 -, 111-2321-B-A49-011-, 111-2634-F-A49-014-, 112-2314-B-075 -036 -MY2, 112-2321-B-001 -008 -). Taipei Veterans General Hospital (V111C-216, V112C-016), Taichung Veterans General Hospital (TCVGH-1093402C, TCVGH-1103401C, TCVGH-1103401D, TCVGH-113401D), and the Brain Research Center, National Yang Ming Chiao Tung University from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan.

Ethical Statement

ORCID iDs

Yi-Kuan Chiang

Wei-Ju Lee

Jong-Ling Fuh

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Supplemental Material

Supplemental material for this article is available online

Abbreviations

References

Scheltens

Blennow

Breteler

, et al. Alzheimer’s disease. Lancet. 2016;388(10043):505-517. doi:10.1016/s0140-6736(15)01124-1

Jonsson

Stefansson

Steinberg

, et al. Variant of TREM2 associated with the risk of Alzheimer’s disease. N Engl J Med. 2013;368(2):107-116. doi:10.1056/NEJMoa1211103

Sims

van der Lee

Naj

, et al. Rare coding variants in PLCG2, ABI3, and TREM2 implicate microglial-mediated innate immunity in Alzheimer’s disease. Nat Genet. 2017;49(9):1373-1384. doi:10.1038/ng.3916

Sastre

Richardson

Gentleman

Brooks

. Inflammatory risk factors and pathologies associated with Alzheimer’s disease. Curr Alzheimer Res. 2011;8(2):132-141.

Calsolaro

Edison

. Neuroinflammation in Alzheimer’s disease: current evidence and future directions. Alzheimer’s Dement. 2016;12(6):719-732. doi:10.1016/j.jalz.2016.02.010

Polazzi

Contestabile

. Reciprocal interactions between microglia and neurons: from survival to neuropathology. Rev Neurosci. 2002;13(3):221-242.

Simard

Soulet

Gowing

Julien

Rivest

. Bone marrow-derived microglia play a critical role in restricting senile plaque formation in Alzheimer’s disease. Neuron. 2006;49(4):489-502. doi:10.1016/j.neuron.2006.01.022

Yeh

Wang

Tom

Gonzalez

Sheng

. TREM2 binds to apolipoproteins, including APOE and CLU/APOJ, and thereby facilitates uptake of amyloid-beta by microglia. Neuron. 2016;91(2):328-340. doi:10.1016/j.neuron.2016.06.015

Jay

Hirsch

Broihier

, et al. Disease progression-dependent effects of TREM2 deficiency in a mouse model of Alzheimer’s disease. J Neurosci. 2017;37(3):637-647. doi:10.1523/JNEUROSCI.2110-16.2016

10.

Gratuze

Leyns

CEG

Holtzman

. New insights into the role of TREM2 in Alzheimer’s disease. Mol Neurodegener. 2018;13(1):66. doi:10.1186/s13024-018-0298-9

11.

Guerreiro

Wojtas

Bras

, et al. TREM2 variants in Alzheimer’s disease. N Engl J Med. 2013;368(2):117-127. doi:10.1056/NEJMoa1211851

12.

Tan

, et al. Increased expression of TREM2 in peripheral blood of Alzheimer’s disease patients. J Alzheim Dis. 2014;38(3):497-501. doi:10.3233/jad-130854

13.

Tan

ASL

Vipin

, et al. Higher peripheral TREM2 mRNA levels relate to cognitive deficits and hippocampal atrophy in Alzheimer’s disease and amnestic mild cognitive impairment. J Alzheim Dis: JAD. 2017;58(2):413-423. doi:10.3233/jad-161277

14.

Mori

Yoshino

Ochi

, et al. TREM2 mRNA expression in leukocytes is increased in Alzheimer’s disease and schizophrenia. PLoS One. 2015;10(9):e0136835. doi:10.1371/journal.pone.0136835

15.

Heslegrave

Heywood

Paterson

, et al. Increased cerebrospinal fluid soluble TREM2 concentration in Alzheimer’s disease. Mol Neurodegener. 2016;11:3. doi:10.1186/s13024-016-0071-x

16.

Kleinberger

Yamanishi

Suarez-Calvet

, et al. TREM2 mutations implicated in neurodegeneration impair cell surface transport and phagocytosis. Sci Transl Med. 2014;6(243):243ra86. doi:10.1126/scitranslmed.3009093

17.

Henjum

Almdahl

Arskog

, et al. Cerebrospinal fluid soluble TREM2 in aging and Alzheimer’s disease. Alzheimer’s Res Ther. 2016;8(1):17. doi:10.1186/s13195-016-0182-1

18.

Liu

Cao

Zhao

, et al. Soluble TREM2 changes during the clinical course of Alzheimer’s disease: a meta-analysis. Neurosci Lett. 2018;686:10-16. doi:10.1016/j.neulet.2018.08.038

19.

Morenas-Rodriguez

Nuscher

, et al. Soluble TREM2 in CSF and its association with other biomarkers and cognition in autosomal-dominant Alzheimer’s disease: a longitudinal observational study. Lancet Neurol. 2022;21(4):329-341. doi:10.1016/S1474-4422(22)00027-8

20.

Quarantelli

. MRI/MRS in neuroinflammation: methodology and applications. Clin Transl Imaging. 2015;3(6):475-489. doi:10.1007/s40336-015-0142-y

21.

Brand

Richter-Landsberg

Leibfritz

. Multinuclear NMR studies on the energy metabolism of glial and neuronal cells. Dev Neurosci. 1993;15(3-5):289-298. doi:10.1159/000111347

22.

Fernando

McLean

Chard

, et al. Elevated white matter myo-inositol in clinically isolated syndromes suggestive of multiple sclerosis. Brain. 2004;127(Pt 6):1361-1369. doi:10.1093/brain/awh153

23.

Chang

Munsaka

Kraft-Terry

Ernst

. Magnetic resonance spectroscopy to assess neuroinflammation and neuropathic pain. J Neuroimmune Pharmacol. 2013;8(3):576-593. doi:10.1007/s11481-013-9460-x

24.

Oenarto

Gorg

Moos

Bidmon

Haussinger

. Expression of organic osmolyte transporters in cultured rat astrocytes and rat and human cerebral cortex. Arch Biochem Biophys. 2014;560:59-72. doi:10.1016/j.abb.2014.06.024

25.

Moutinho

Coronel

Tsai

, et al. TREM2 splice isoforms generate soluble TREM2 species that disrupt long-term potentiation. Genome Med. 2023;15(1):11. doi:10.1186/s13073-023-01160-z

26.

Allen

Sakae

, et al. Expression and processing analyses of wild type and p.R47H TREM2 variant in Alzheimer’s disease brains. Mol Neurodegener. 2016;11(1):72. doi:10.1186/s13024-016-0137-9

27.

Morris

. The clinical dementia rating (CDR): current version and scoring rules. Neurology. 1993;43(11):2412-2414.

28.

McKhann

Knopman

Chertkow

, et al. The diagnosis of dementia due to Alzheimer’s disease: recommendations from the National Institute on Aging-Alzheimer’s Association workgroups on diagnostic guidelines for Alzheimer’s disease. Alzheimer’s Dement. 2011;7(3):263-269. doi:10.1016/j.jalz.2011.03.005

29.

Folstein

McHugh

. “Mini-mental state”. A practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res. 1975;12(3):189-198.

30.

O'Connell

Tuokko

. The 12-item Buschke memory test: appropriate for use across levels of impairment. Appl Neuropsychol. 2002;9(4):226-233. doi:10.1207/S15324826AN0904_5

31.

Mack

Freed

Williams

Henderson

. Boston naming test: shortened versions for use in Alzheimer’s disease. J Gerontol. 1992;47(3):P154-P158. doi:10.1093/geronj/47.3.p154

32.

Strauss

Sherman

EMS

Spreen

. A Compendium of Neuropsychological Tests: Administration, Norms, and Commentary. 3rd ed. New York: Oxford University Press; 2006:xvii, 1216.

33.

Tombaugh

. Trail making Test A and B: normative data stratified by age and education. Arch Clin Neuropsychol. 2004;19(2):203-214. doi:10.1016/S0887-6177(03)00039-8

34.

Yesavage

Sheikh

. 9/Geriatric depression scale (GDS). Clin Gerontol. 1986;5(1-2):165-173. doi:10.1300/J018v05n01_09

35.

Livak

Schmittgen

. Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) method. Methods. 2001;25(4):402-408. doi:10.1006/meth.2001.1262

36.

Griffith

den Hollander

Stewart

, et al. Elevated brain scyllo-inositol concentrations in patients with Alzheimer’s disease. NMR Biomed. 2007;20(8):709-716. doi:10.1002/nbm.1132

37.

Mitolo

Stanzani-Maserati

Capellari

, et al. Predicting conversion from mild cognitive impairment to Alzheimer’s disease using brain (1)H-MRS and volumetric changes: a two- year retrospective follow-up study. Neuroimage Clin. 2019;23:101843. doi:10.1016/j.nicl.2019.101843

38.

Sundmacher

Gotz

Vogt

. Statistische Methoden der kleinraumigen Versorgungsforschung [Statistical methods for research on regional health-care services]. Bundesgesundheitsblatt - Gesundheitsforsch - Gesundheitsschutz. 2014;57(2):174-179. doi:10.1007/s00103-013-1887-y

39.

Wunderlich

Glebov

Kemmerling

Tien

Neumann

Walter

. Sequential proteolytic processing of the triggering receptor expressed on myeloid cells-2 (TREM2) protein by ectodomain shedding and γ-secretase-dependent intramembranous cleavage. J Biol Chem. 2013;288(46):33027-33036. doi:10.1074/jbc.M113.517540

40.

Piccio

Buonsanti

Cella

, et al. Identification of soluble TREM-2 in the cerebrospinal fluid and its association with multiple sclerosis and CNS inflammation. Brain. 2008;131(11):3081-3091. doi:10.1093/brain/awn217

41.

Carmona

Zahs

Dakin

Bras

Guerreiro

. The role of TREM2 in Alzheimer’s disease and other neurodegenerative disorders. Lancet Neurol. 2018;17(8):721-730. doi:10.1016/S1474-4422(18)30232-1

42.

Weber

Khrestian

Tuason

, et al. Peripheral sTREM2-related inflammatory activity alterations in early-stage Alzheimer’s disease. J Immunol. 2022;208(10):2283-2299. doi:10.4049/jimmunol.2100771

43.

Casati

Ferri

Gussago

, et al. Increased expression of TREM2 in peripheral cells from mild cognitive impairment patients who progress into Alzheimer’s disease. Eur J Neurol. 2018;25(6):805-810. doi:10.1111/ene.13583

44.

Parhizkar

Arzberger

Brendel

, et al. Loss of TREM2 function increases amyloid seeding but reduces plaque-associated ApoE. Nat Neurosci. 2019;22:191. doi:10.1038/s41593-018-0296-9

45.

Ulland

Song

Huang

, et al. TREM2 maintains microglial metabolic fitness in Alzheimer’s disease. Cell. 2017;170(4):649-663.e13. doi:10.1016/j.cell.2017.07.023

46.

Suarez-Calvet

Morenas-Rodriguez

Kleinberger

, et al. Early increase of CSF sTREM2 in Alzheimer’s disease is associated with tau related-neurodegeneration but not with amyloid-beta pathology. Mol Neurodegener. 2019;14(1):1. doi:10.1186/s13024-018-0301-5

47.

Shi

Holtzman

. Interplay between innate immunity and Alzheimer disease: APOE and TREM2 in the spotlight. Nat Rev Immunol. 2018;18(12):759-772. doi:10.1038/s41577-018-0051-1

Supplementary Material

Please find the following supplemental material available below.

For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.

For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.

0.00 MB

0.24 MB

Different Splice Isoforms of Peripheral Triggering Receptor Expressed on Myeloid Cells 2 mRNA Expressions are Associated With Cognitive Decline in Mild Dementia Due to Alzheimer’s Disease and Reflect Central Neuroinflammation

Abstract

Keywords

Significance Statement

Introduction

Materials & Methods

Participants

Clinical Evaluation and Procedures

TREM2 mRNA Measurement

DNA Analysis

Magnetic resonance spectroscopy

Statistical Analysis

Results

Subjects and Demographics

TREM2 and TREM2alt mRNA Expression Levels

Associations Between MMSE and TREM2, as Well as TREM2alt mRNA Expression in Patients with AD

Associations Between mI Level at PCC on MRS and TREM2 as Well as TREM2alt mRNA Expression in Patients with AD

Discussion

Supplemental Material

Supplemental Material - Different Splice Isoforms of Peripheral Triggering Receptor Expressed on Myeloid Cells 2 mRNA Expressions are Associated With Cognitive Decline in Mild Dementia Due to Alzheimer’s Disease and Reflect Central Neuroinflammation

Footnotes

Declaration of Conflicting Interests

Funding

Ethical Statement

ORCID iDs

Data Availability Statement

Supplemental Material

Abbreviations

References

Supplementary Material

TREM2 and TREM2_alt mRNA Expression Levels

Associations Between MMSE and TREM2, as Well as TREM2_alt mRNA Expression in Patients with AD

Associations Between mI Level at PCC on MRS and TREM2 as Well as TREM2_alt mRNA Expression in Patients with AD