
==== Front
Chin Med J (Engl)
Chin Med J (Engl)
CM9
Chinese Medical Journal
0366-6999
2542-5641
Lippincott Williams & Wilkins Hagerstown, MD

CMJ-2023-618
10.1097/CM9.0000000000003188
00018
3
Correspondence
White matter microstructure mediates the pairwise relationship between childhood maltreatment, microRNA-9, and the severity of major depressive disorder
Liu Xinyi 1
He Cancan 2
Bai Ying 3
Fan Dandan 1 2
Zang Feifei 1 2
Zhang Hongxing 4 5
Zhang Haisan 6
Yao Honghong 3 7
Zhang Zhijun 1 2 7
Xie Chunming 1 2 7
Wei Peifang
1 Department of Neurology, Affiliated ZhongDa Hospital, School of Medicine, Southeast University, Nanjing, Jiangsu 210009, China
2 Neuropsychiatric Research Institute, School of Medicine, Southeast University, Nanjing, Jiangsu 210009, China
3 Department of Pharmacology, School of Medicine, Southeast University, Nanjing, Jiangsu 210009, China
4 Henan Key Laboratory of Psychology and Behavior, Xinxiang Medical University, Xinxiang, Henan 453000, China
5 Psychology School of Xinxiang Medical University, Xinxiang, Henan 453003, China
6 Department of Radiology, Henan Provincial Mental Hospital, Xinxiang Medical University, Xinxiang, Henan 453000, China
7 Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu 210009, China
Correspondence to: Chunming Xie, Department of Neurology, Affiliated ZhongDa Hospital, School of Medicine, Southeast University, No. 87 Dingjiaqiao Road, Nanjing, Jiangsu 210009, China E-Mail: chmxie@163.com
08 8 2024
05 9 2024
137 17 21402142
15 1 2024
Copyright © 2024 The Chinese Medical Association, produced by Wolters Kluwer, Inc. under the CC-BY-NC-ND license.
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc-nd/4.0

OPEN-ACCESSTRUE
SDCT
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pmcTo the Editor: Major depressive disorder (MDD) affects over 300 million individuals globally, impairing daily life and leading to severe cases of suicide. Child maltreatment (CM), encompassing various types of mistreatment to children under 18 years, is a predisposing factor for MDD, with approximately 46% of MDD patients having experienced CM.[1] Understanding the biological mechanisms linking CM to MDD may reveal prevention and management strategies.

MicroRNAs (miRNAs), small non-coding RNAs regulated by gene transcription, are transported via exosomes, facilitating intercellular communication by entering blood or cerebrospinal fluid. Recent studies emphasize the role of microRNA-9 (miR-9) in brain development and its association with MDD.[2] miR-9 is also linked to white matter (WM) development, myelination, synaptic plasticity, and the potential effects of CM on mental health.

To describe the gene–behavioral–brain relationship, diffusion tensor imaging (DTI) was used to quantitatively assess WM, offering information about axonal size, myelination, and orientation. Many DTI studies have reported WM abnormalities in MDDs, mostly finding specific brain region alterations, while few have explored CM subjects. The effect of miRNAs on WM integrity in MDDs, and the association between vulnerable brain regions, CM, miR-9, and MDD severity need further investigation.

A previous study indicated that CM affects miR-9 levels, potentially affecting MDD. miR-9 alterations in stress models affect MDD symptoms. Therefore, this study proposes a two-step mediation model, testing the effects of interest.[3] It hypothesized that WM microstructure mediates the relationships between CM severity and miR-9 levels, and between miR-9 levels and depression severity. This approach avoids model-based constraints. If WM microstructure explains CM and miR-9, miR-9 and depression severity, and CM and depression severity relations, it suggests WM pathology, and explains adverse childhood events’ effect on epigenetic molecular alterations, further clarifying their respective effects on MDD symptoms.

This study consecutively enrolled 107 participants from June 2018 to June 2019, including 57 MDD patients and 50 healthy controls (HCs). MDD patients were hospitalized at the Second Affiliated Hospital of Xinxiang Medical University. HCs were recruited through local community posting and media advertising. The inclusion and exclusion criteria for the subjects are detailed in the Supplementary Material, http://links.lww.com/CM9/C61. The human subject protocol was approved by the Ethics Committee of the Second Affiliated Hospital of Xinxiang Medical University (No. 2017–08). Written informed consent was obtained from all subjects before the study. Scale assessments included the 17-item Hamilton Rating Scale for Depression (HAMD-17) for depression severity, the Hamilton Anxiety Scale (HAMA) for anxiety severity, and the Childhood Trauma Questionnaire (CTQ) to evaluate CM experience. Peripheral blood samples were collected from all participants and processed for miRNA extraction. Reverse transcription of miRNA was performed, and polymerase chain reaction (PCR) results were normalized using U6 as a reference, with relative expression levels determined using the 2−∆∆ct method. DTI was acquired using a 3.0 T scanner and preprocessed using FMRIB Software Library (FSL, Oxford, United Kingdom). Tract-based spatial statistics (TBSS) was employed for voxelwise statistical analysis of DTI data, involving registration, skeletonization, and projection onto the WM skeleton to analyze fractional anisotropy (FA).

For statistical data, Shapiro–Wilkes test was used to test for the normality distribution of each group. Independent-samples t-test, Mann–Whitney U test (for non-Gaussian distribution), or chi-squared tests were used for between-group comparisons. MiR-9 data followed a normal distribution, therefore, a two-sample t-test was applied to compare miR-9 levels between MDD patients and HCs. To explore the main effects of CTQ, miR-9, and HAMD on WM integrity, multivariate linear regression analyses were applied across voxels to the FA skeleton using permutation tests (N = 5000). Multiple comparisons were corrected by threshold-free cluster enhancement (TFCE) method and family wise error (FWE) at P <0.05. Conjunction analysis identified overlapping regions among each pair of main effects.

Mediation analysis tests whether the effect of the independent variable (X) on the dependent variable (Y) could be partially explained by a mediating variable (M). Three mediation models were constructed using 25.0 PROCESS macro (Andrew F. Hayes®, http://www.processmacro.org/index.html) for SPSS (SPSS Inc., Chicago, Illinois, USA)[4]: (1) CTQ score as X, miR-9 as Y, and CTQ × miR-9 interaction on the FA as M; (2) miR-9 as X, HAMD as Y, and miR-9 × HAMD interaction on the FA as M; (3) CTQ as X, HAMD as Y, and CTQ × HAMD interaction on the FA as M. The three steps of the mediation model were as follows: (1) M = aX + e2; (2) Y = cX + e1; (3) Y = c′X + bM + e3. The direct effect (path c′) represents the effect of X on Y controlling for M, and the indirect effect was the effect of X on Y through M (a*b) calculated using a bias-corrected bootstrap confidence interval (CI) estimated from 10,000 bootstrap samples. If the bootstrapped 95% CI did not include zero, it indicated significant mediation. The same procedures were repeated in the HC group to determine whether these mediating effects in MDD patients also exist in HCs. Additionally, the above steps were repeated to assess the mediation models for each subscale of CM and the severity of anxiety in MDD patients.

Demographic and neuropsychological data are listed in Supplementary Table 1, http://links.lww.com/CM9/C61. miR-9 expression was significantly elevated in MDD patients (P <0.001) [Supplementary Figure 1, http://links.lww.com/CM9/C61]. There was a significant correlation between miR-9 levels and CTQ scores (R2 = 0.07, P = 0.03), and between miR-9 levels and HAMD-17 scores (R2 = 0.07, P = 0.03) in MDD patients. CTQ scores were positively correlated with the severity of depression in MDD patients (R2 = 0.09, P = 0.02).

Using the three models, 13 mediation analyses (13 overlapping brain regions) were conducted, identifying 6 clusters with mediating effects [Supplementary Figure 2, http://links.lww.com/CM9/C61]. Firstly, through multiple linear regression analysis, the main effect of CM on brain networks was determined [Supplementary Figure 2A, http://links.lww.com/CM9/C61]. In addition, we similarly investigated the main effect of miR-9 levels on brain networks [Supplementary Figure 2B, http://links.lww.com/CM9/C61]. Likewise, the main effect of HAMD on brain networks is depicted in Supplementary Figure 2C, http://links.lww.com/CM9/C61. Subsequently, overlapping regions (dot product between brain regions) were identified through a conjunction analysis of the neural correlations between CTQ scores and miR-9 levels, miR-9 levels and HAMD scores as well as CTQ and HAMD scores on brain networks [Supplementary Figure 2D–F, http://links.lww.com/CM9/C61]. Bilateral anterior thalamic radiation (ATR) mediate the effect of the CM on miR-9 (indirect effect(ATR.L), β = −0.0115, 95% CI: [−0.0186, −0.0017]; indirect effect(ATR.R), β = −0.0107, 95% CI: [−0.0202, −0.0030]). Left sagittal stratum (SS.L) and left superior longitudinal fasciculus (SLF.L) negatively mediated the effects of miR-9 levels on HAMD scores (indirect effect(SS.L), β = −2.4115, 95% CI: [−3.5966, −0.7797]; indirect effect(SLF.L2), β = −1.3861, 95% CI: [−2.3678, −0.0004]). Right forceps major (FM.R) and ATR.R positively mediated the effects of CTQ scores on HAMD scores (indirect effect(FM.R), β = 0.1079, 95% CI: [0.0022, 0.1637]; indirect effect(ATR.R), β = 0.1176, 95% CI: [0.0097, 0.1505]). In the HCs, no miR-9-related brain regions were found. The overlapping brain regions between CM and HAMD scores were in right anterior corona radiata (ACR.R), which positively mediated the effects of CTQ scores on HAMD scores (indirect effect, β = 0.1472, 95% CI: [0.0773, 0.4300]) [Supplementary Figure 3, http://links.lww.com/CM9/C61]. Correlation pattern maps may vary between subscales and total scales. Left anterior limb of internal capsule (ALIC.L) had a mediating effect between CTQ-physical abuse (PA) and HAMD-diurnal variation factor (D), and right superior longitudinal fasciculus (SLF.R) had a mediating effect between CTQ-emotional neglect (EN) and HAMD-D [Supplementary Figures 4–5, http://links.lww.com/CM9/C61]. After removing the covariates of the HAMA score, the overlapping brain regions from the main effects of CM and HAMD included the left retrolenticular part of the internal capsule (RLIC.L), and no overlapping brain regions between miR-9 and CM/HAMD were found [Supplementary Figures 6, http://links.lww.com/CM9/C61].

This study examined relationships between CM, miR-9 level, WM integrity, and depression severity in MDD patients. It showed that the overlapping effects of CM, miR-9, and depression severity on the integrity of WM in MDD patients are mainly located in the “cortico-limbic-striato-pallido-thalamic” circuit. Bilateral ATR may mediate the link between CM and miR-9, while SLF.L and SS.L may act as a mediator between miR-9 and depression severity. Additionally, FM.R and ATR.R may have a role in mediating the interaction between CM and depression severity.

miR-9 may be more related to mild CM. Stress generally impacts myelination and selective pruning. miR-9 is released in the primary axons of developing brain neurons in the cortex. Based on this reasoning, CM may lead to synaptic integrity disruption, which affects the transmisson of visual and emotional information for emotional integration and modulation, thus affecting miR-9 expression levels. Furthermore, miR-9 levels depend on the individual’s state. Myelination is a crucial process during critical periods of brain development, and any disruption may lead to faulty brain circuitry, potentially causing depressive symptoms. Bilateral SLF.L and SS.L may be as crucial substrates for effect of miR-9 levels on depression severity. Aberrant miR-9 may affect WM integrity, especially for the myelination, leading to impaired processing and integration of emotional visual stimuli, consequently exacerbating depression.

Mediation analysis involves adding a third variable to the X → Y relation, where X causes the mediator M, and M causes Y (i.e., X → M → Y).[5] This method helps explain the mechanism of how a third variable affects the relation between two variables. When constructing the model, it is crucial to distinguish the mediator M from other variables, such as confounders or covariates. However, this design has limitations that need to be addressed, and future research should carefully consider collecting and controlling data on confounding variables related to such mediation outcomes. Moreover, it is reasonable to allow flexibility in the model for primary effects of interest, as model constraints can introduce bias in parameter estimates (e.g., forcing the genuine direct effect to be zero would bias the indirect effect estimates).

Some limitations should be noted. First, it was a cross-sectional study. According to Sobel, mediation analysis in cross-sectional design can only provide partial causality, not full causality. Caution must be exercised in interpreting the findings. Second, a larger study cohort is required for validation. Third, the whole-brain structural connections were not measured for extended topology properties, so further more DTI measures for WM microstructure should be explored.

In conclusion, miR-9 dysregulation may play a key role in the pathogenesis of MDD, possibly triggered by CM. The gene–brain–behavior relationship can be modulated by regional WM.

Funding

This work was funded by the Science and Technology Innovation 2030 Major Projects (No. 2022ZD0211600), the National Natural Science Foundation of China (Nos. 82071204 and 82271574 to XCM, and 82201237 to CCH), and the Key Project of Jiangsu Commission of Health (No. ZDB2020008).

Conflicts of interest

None.

Supplementary Material

SUPPLEMENTARY MATERIAL

Xinyi Liu and Cancan He contributed equally to this work.

How to cite this article: Liu XY, He CC, Bai Y, Fan DD, Zang FF, Zhang HX, Zhang HS, Yao HH, Zhang ZJ, Xie CM. White matter microstructure mediates the pairwise relationship between childhood maltreatment, microRNA-9, and the severity of major depressive disorder. Chin Med J 2024;137:2140–2142. doi: 10.1097/CM9.0000000000003188
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