Prenatal exposure to maternal disadvantage-related inflammatory biomarkers: Associations with neonatal white matter connectivity

doi:10.21203/rs.3.rs-2635951/v1

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Prenatal exposure to maternal disadvantage-related inflammatory biomarkers: Associations with neonatal white matter connectivity

https://doi.org/10.21203/rs.3.rs-2635951/v1

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published 02 Feb, 2024

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Prenatal exposure to heightened maternal inflammation has been associated with adverse neurodevelopmental outcomes, including atypical brain maturation and psychiatric illness. In mothers experiencing socioeconomic disadvantage, immune activation can be a product of the chronic stress inherent to such environmental hardship. While growing preclinical and clinical evidence has shown links between altered neonatal brain development and increased inflammatory states in utero, the potential mechanism by which socioeconomic disadvantage differentially impacts neural-immune crosstalk remains unclear. In the current study, we investigated the relationships among socioeconomic disadvantage, gestational inflammation, and neonatal white matter connectivity in 320 mother-infant dyads over-sampled for poverty. We analyzed maternal serum levels of four cytokines (IL-6, IL-8, IL-10, and TNF-α) over the course of pregnancy in relation to offspring white matter connectivity and socioeconomic disadvantage. Higher average maternal IL-6 was associated with very low socioeconomic status (SES; INR < 200% poverty line) and lower neonatal corticospinal and uncinate FA and, in most tracts, lower AD. Higher average maternal IL-10 was associated with lower FA but higher RD in corticospinal and inferior cingulum tracts. Family SES moderated the relationship between average maternal TNF-α levels during gestation and neonatal white matter diffusivity, such that the association was significant and positive in the lower-to-higher SES (INR ≥ 200% poverty line) neonates for superior cingulum MD, but significant and negative in the very low SES neonates for inferior cingulum and fornix AD. Taken together, these findings suggest that the relationship between prenatal cytokine exposure and white matter development differs as a function of SES. This raises important public health questions regarding how biological mechanisms diverge depending upon foundational resources in utero.

Biological sciences/Neuroscience

Health sciences/Biomarkers/Predictive markers

During intrauterine life, there are sensitive periods of development that contribute to fetal programming. The plastic fetal brain is highly sensitive to its environment, as its exposure to a variety of these factors guide development to prepare the fetus for life after birth ^{1, 2}. This environmental sensitivity, part of a “predictive adaptive response”, is generally advantageous in that prenatal environmental cues prepare the fetus for the postnatal environment ^{3, 4}. Specifically, transmission of maternal biological signals across the placenta during gestation is thought to cue the developing fetus about aspects of extrauterine life that reflect the environment into which they will be born ^5–7. In addition to glucocorticoid hormones, these signals might include inflammatory cytokines, which coordinate immune responses to wounding and injury ^8–10. Assuming the precipitating adverse stimulus (e.g., infection, trauma, disease) is eliminated, inflammatory responses are typically acute and controlled by regulatory signals. However, stressors like maternal social disadvantage and racial discrimination can interfere with these regulatory processes, leading to excess inflammatory activity in the placenta’s chorionic villous layer, which functions as the maternal-fetal interface ^11–14. This “non-resolving” inflammation is hypothesized to affect structural and functional development of multiple fetal organ systems, including the brain ^15–17. Maternal inflammation during pregnancy has, therefore, garnered substantial attention in the investigation of fetal neurodevelopment.

The maternal inflammatory response plays multiple and shifting roles over the course of pregnancy, which include protecting against infection, shaping the intrauterine environment, promoting fetal development, and facilitating childbirth. The formation of neural tissue heavily relies on the fine-tuned cellular signaling of each gestational stage. Consequently, aberrations in these rhythms brought on by adverse maternal environmental exposures or dysregulated inflammatory cytokine profiles can alter the neural developmental pathways and ultimately result in subtle, but impactful, structural differences in the fetal brain ^{18, 19}. Both preclinical and clinical research has shown that maternal immune activation during pregnancy alters the development of white matter microstructure in offspring ^{8, 20, 21}. Furthermore, multiple studies have revealed an association between cytokine biomarkers of maternal inflammation and subsequent brain disorders in childhood and beyond, including cerebral palsy, autism spectrum disorder, and schizophrenia ^22–24. There is also emerging evidence for increased risk of future depression and cognitive impairment in offspring ^{25, 26}. Related to these findings, high levels of maternal pro-inflammatory cytokines, specifically interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-ɑ, have been shown to induce downstream neuromodulatory effects consistent with these neuropsychiatric disorders ^27–29. In contrast, increased expression of anti-inflammatory cytokines by macrophages has been shown to be neuroprotective and neuromodulatory (e.g., influencing receptor behaviors and neuron activity) in the absence of a counteractive inflammatory response.

Maternal stress and social disadvantage are increasingly recognized as risk factors for aberrant fetal neurodevelopment, including white matter development. Neonates exposed to prenatal stress have been found to have increased mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) in the uncinate fasciculus ³⁰ and decreased fractional anisotropy (FA) in white matter tracts including the angular gyrus, uncinate, and posterior cingulate ³¹. Both decreased FA and increased MD have also been found in amygdala-frontal white matter connections and the cingulum ³². Other work has shown increased MD, RD, and AD in right frontal areas ³³ in neonates prenatally exposed to maternal stress. Taken together, these findings may reflect slower white matter myelination in neonates born to mothers experiencing heightened stress during pregnancy. However, in a sample of healthy term-born neonates from the same study sample reported here, Lean et al. ³⁴ found that social disadvantage, a latent construct composed of income-to-needs ratio (INR), area deprivation, insurance status, parental education, and an index of healthy eating, was linked with lower MD in the inferior cingulum, uncinate, and fornix, as well as lower MD and higher FA in the dorsal cingulum. These findings potentially reflect faster white matter myelination in neonates exposed to social disadvantage in utero^34–36.

While growing evidence suggests that early exposure to chronic stress alters neurodevelopment, the mediating pathway by which this association occurs remains poorly understood. To elucidate this mechanism, Nusslock and Miller ³⁷ proposed a neuroimmune network hypothesis. This hypothesis suggests that severe chronic stress in childhood leads to excessive immune-brain crosstalk, involving elevated inflammatory activity and altered neural circuits involved in threat and reward processing. Indeed, several recent studies have observed strong relationships between inflammatory biomarkers and neural reactivity to threats and rewards among children facing chronic stressors relative to unexposed youth ^{11, 38, 39}. However, these existing studies have focused on children and adolescents. The question of whether these associations operate even earlier in life, for example during highly plastic prenatal development when stress exposure might affect neural-immune communication, remains unknown.

The current study aims to fill this gap in the literature. In a sample of 320 mother-infant dyads over-sampled for exposure to poverty, we consider the relationships among socioeconomic disadvantage, gestational inflammation, and neonatal white matter connectivity. Our first hypothesis was that socioeconomic disadvantage would be associated with higher concentrations of inflammatory cytokines across pregnancy. Second, we hypothesized that disadvantage would be associated with variations in newborn white matter connectivity, as reflected in lower tract MD and higher FA values reflecting altered maturation. Third, we hypothesized that mothers with higher cytokine concentrations during pregnancy would have newborns with significantly different white matter tract connectivity compared to those born to mothers with lower cytokine levels. Specifically, we expected higher maternal cytokine concentrations to be associated with higher MD and lower FA in white matter tracts overall, reflecting aberrant microstructural development. Lastly, we hypothesized that family SES would moderate the association between maternal cytokine levels and neonatal white matter connectivity. Namely, there would be a stronger relationship between maternal cytokine concentration and white matter connectivity in neonates from very low SES relative to lower-to-higher SES families, reflecting the excessive brain-immune crosstalk implied by the neuroimmune network hypothesis.

Sample

The current study included 320 mother-infant dyads who participated in the Early Life Adversity, Biological Embedding, and Risk for Developmental Precursors of Mental Disorders (eLABE) study. Pregnant women were recruited from the March of Dimes Prematurity Research Center at Washington University in St. Louis from 2017–2020. Women facing social disadvantage were over-sampled by increased recruitment from a clinic serving low-income women. All study procedures were approved by the Washington University School of Medicine Institutional Review Board. eLABE exclusion criteria spanned multiple gestations, infections known to cause congenital disease (e.g., syphilis), and maternal alcohol or drug use other than tobacco and cannabis. A total of 395 pregnant women and their 399 singleton offspring were recruited for participation in eLABE (n = 4 mothers with 2 singleton births during recruitment). During each trimester and after birth, mothers completed detailed surveys and provided blood samples. Neonatal brain imaging was performed within the first month of life on 385 non-sedated neonates. Of these, diffusion MRI (dMRI) data was deemed unusable for n = 20 (no dMRI collected n = 3, required frames not collected n = 4, sequence collected in one direction n = 8, artifact n = 5). Seventeen neonates were excluded for the presence of high-grade brain injury. An additional n = 28 neonates were removed from analyses because of maternal conditions and/or treatments that may affect immune or inflammatory activity (i.e., diagnosis of hepatitis C, human immunodeficiency virus, syphilis, lupus, or currently taking oral or intravenous steroids). Of the 320 neonates retained for final analyses, infants born preterm (< 37 weeks’ gestation; n = 45) or admitted to the Neonatal Intensive Care Unit > 7 days (n = 28) were included, but these indications were controlled for as outlined in the Statistical Analysis section. Further, sensitivity analyses excluding neonates born < 34 weeks’ gestation and born weighing < 2,000g are included in the Supplemental Information section.

Measures

Income-to-Needs Ratio. Income-to-Needs Ratio (INR) was collected from mothers at each trimester. INR uses self-reported family income and household size compared to federal poverty thresholds, with a ratio of 1.0 being at the poverty line. The percent change in INR from the first through third trimesters was relatively small (i.e., 1.8%), and therefore, INR at the first trimester was used in the current analyses. INR was used to dichotomize the sample into very low and lower-to-higher family SES groups (defined as mean INR below or at/above 200% of the national poverty line threshold, respectively). This categorization is justified by its implementation in previous large-scale, prospective studies such as Fragile Families and the Child Wellbeing Study ^40–42. Analyses examining continuous INR are included in the Supplemental Information.

Cytokines. At each trimester, maternal antecubital blood samples were obtained during routine clinical lab visits. Samples were refrigerated at 4°C and centrifuged for 5 minutes at 1620 x g within 12 hours of collection. Aliquots of serum and plasma (1 mL) were stored at -80°C ⁴³. We measured serum levels of four inflammatory biomarkers: IL-6, IL-8, IL-10, and TNF-α. The cytokines were measured in triplicate using a multiplex immunoassay protocol on an automated microfluidic platform (Simple Plex, Protein Simple) ⁴⁴. Lower limits of detection range from 0.08 pg/mL (IL-8) to 0.28 pg/mL (TNF-α). Across runs, the average intra-assay coefficients of variation for triplicate samples were 3.6% (IL-6), 2.1% (IL-8), 2.4% (IL-10), and 3.8% (TNF-α). The corresponding inter-assay coefficients of variation were 3.6%, 3.2%, 4.5%, and 1.3%.

White Matter Microstructure. Non-sedated neonates (mean postmenstrual age [PMA] = 41 weeks, range = 37–45 weeks) underwent MRI scans on a Siemens Prisma 3T scanner (Siemens Healthineers Erlangen, Germany) using a 64-channel head coil. Neonates were fed, swaddled, and noise protection gear was applied. They were then positioned in a stabilizing vacuum fix wrap and placed in the head coil on foam padding to decrease motion. Neonatal dMRI scans were acquired as two 5-minute runs (multiband factor = MB4, TR/TE = 2500/79.4 ms, 1.75-mm isotropic voxels) with whole brain coverage (80 slices), 108 b values sampled on 3 shells b = 500–2500 s/mm² and 7 b = 0 images interspersed throughout each run with phase encoding directional reversal (anterior ◊ posterior and posterior ◊ anterior) for susceptibility- and eddy-current distortion correction ⁴⁵. dMRI parameters: FA, MD, AD, and RD, were extracted for the corpus callosum (CC) and eight bilateral (left and right) white matter tracts: superior cingulum bundle (CB), corticospinal tract (CST), optic radiation (OR), uncinate (UNCXL), inferior fronto-occipital fasciculus (IFOF), anterior limb of internal capsule (ALIC), inferior cingulum bundle (CBIF), and fornix (FX). Probabilistic tractography was completed in FSL Version 5.0.9 ⁴⁶. Anatomically landmarked seeds were placed by two highly trained raters (inter-rater coefficients: 0.80–0.98 for MD and 0.73–0.92 for FA).

Data Analysis

All analyses were conducted in R version 4.2.1 ⁴⁷. Data were examined for distributions and outliers, and extreme dMRI and cytokine outliers (> 3 SD from the mean) were removed from analysis. This included two FA values (1 CC, 1 CB), five MD values (3 CC, 1 CST, 1 FX), six AD values (4 CC, 1 OR, 1 ALIC), five RD values (2 CC, 2 CST, 1 FX), two IL-6 values, three IL-10 values, and three TNF-α values. Maternal cytokine data were normalized with log₁₀ transformations to account for skewed and kurtotic distributions and were labeled based on the estimated weeks of gestation at the time of blood draw (trimester 1: <14 weeks; trimester 2: ≥14 and < 27 weeks; trimester 3: ≥27 and ≤ 40 weeks). For each cytokine, we calculated the average concentration across gestational blood draws. For 32.8% of cases, values were available from blood draws in all three trimesters, and for the remaining 84.4% of the sample values were available from two trimesters. Trimester-specific effects were not analyzed as a primary aim of the study, given the variability in both blood collection by gestational age and sample size (trimester 1: 72% of sample, n = 231, SD = 2.98; trimester 2: 85% of sample, n = 272, SD = 4.03; trimester 3: 87% of sample, n = 279, SD = 3.13). However, these analyses are included in the Supplementary Information.

The relationships between family SES group (very low, lower-to-higher), maternal cytokine concentrations during pregnancy, and neonatal dMRI metrics (FA, MD, AD, and RD) were examined separately with multiple linear regression using the “lm” function in the R package “stats” ⁴⁷. Covariates for the SES group and maternal cytokine analysis included maternal age and maternal pre-pregnancy body mass index (BMI). Covariates for the SES group, neonatal dMRI, and maternal cytokine analyses included infant sex, NICU stay > 7 days, gestational age at delivery, and infant PMA at scan. Next, moderation analyses were conducted to investigate the interaction between maternal cytokine concentration and family SES group on neonatal white matter connectivity. Linear models were fit using the “lm” function in the R package “stats” ⁴⁷. Significant interactions were probed by calculating the estimated marginal means of dMRI metric at different levels of maternal cytokine concentration (-1 SD, mean, + 1 SD) by family SES group (very low, lower-to-higher) with simple slope analysis using the R function “emtrends” in the “emmeans” package ⁴⁸. Interactions were visualized with the “probe_interaction” function in the R package “interactions” ⁴⁹. Benjamini-Hochberg False Discovery Rate (FDR) procedures were used to correct for multiple comparisons by white matter tract (9 corrections) for each dMRI metric. Standardized coefficients (β), standard errors, uncorrected p-values, and FDR-corrected significance values (q) are reported.

Supplementary Information includes analyses using continuous INR and sensitivity analyses excluding neonates born < 34 weeks’ gestation and < 2,000 grams.

Sample characteristics are presented in Table 1. All trimester-specific effects are included in the Supplementary Information material.

Table 1
	N	Mean	SD	Range
Infant Characteristics
Gestational age, weeks	320	37.99	1.86	28–41
Birthweight, grams	320	3165.85	572.16	1310–4627
Sex assigned at birth, % (n)	320
Female		44 (140)
Male		56 (180)
Race, % (n)^a	320
Black/African American		61.6 (197)
White/Caucasian		23.9 (118)
Asian		1.9 (6)
Native Hawaiian/Pacific Islander		0.3 (1)
Other (Not defined)		0.6 (2)
Ethnicity, % (n)	320
Hispanic or Latino/a		2.5 (8)
Not Hispanic or Latino/a		96.9 (310)
Unspecified		0.6 (2)
Postmenstrual age at MRI scan, weeks	320	41.2	1.47	37–45
Maternal Characteristics
Age at delivery, years	320	29.27	5.29	19–42
Tobacco use during pregnancy, % (n)	320	11.6 (37)
Cannabis use during pregnancy and/or positive urine drug screen, % (n)	320	10.9 (35)
Income-to-needs ratio	311	2.80	2.97	0.32–12.48
Family SES group	311
Lower, % (n)		63 (196)
Higher, % (n)		37 (115)
^a More than one race reported for four infants (African American-Caucasian = 2; Caucasian-Asian = 2).

Socioeconomic status

Mothers in the very low SES group had significantly higher average IL-6 than mothers in the higher-to-lower SES group (β = 0.17; q = 0.02). There were no significant associations between family SES group and average maternal IL-8 (β = 0.01; q = 0.84), IL-10 (β = 0.03; q = 0.84), or TNF-α (β=-0.03; q = 0.84) concentrations during pregnancy. In relation to white matter microstructure, neonates in the very low SES group had significantly lower 1) CC AD; 2) CB MD and RD; 3) CST MD and AD; 4) OR MD, AD, and RD; 5) UNCXL MD, AD, and RD; 6) IFOF MD and AD; 7) ALIC MD and AD; 8) CBIF MD and AD; and 9) FX MD and RD. There were no significant associations between family SES group and FA of any white matter tracts (see Fig. 1 & Table 2).

Table 2
	FA				MD				AD				RD
	β	SE	p	q	β	SE	p	q	β	SE	p	q	β	SE	p	q
Corpus Callosum
SES Group	0.096	0.003	0.05	0.20	-0.006	0.003	0.90	0.89	0.146	0.003	0.01	0.01	-0.050	0.004	0.29	0.29
Sex	-0.102	0.003	0.04	0.20	-0.006	0.003	0.90	0.90	-0.087	0.003	0.12	0.14	0.049	0.004	0.29	0.66
NICU stay	-0.106	0.007	0.08	0.35	0.001	0.007	0.98	0.98	-0.007	0.007	0.92	0.96	0.033	0.010	0.58	0.77
GA at delivery	0.001	0.001	0.99	0.99	0.016	0.001	0.81	0.87	0.105	0.001	0.17	0.41	-0.010	0.002	0.88	0.93
PMA at scan	0.462	0.001	< 0.001	< 0.001	-0.584	0.001	< 0.001	< 0.001	-0.229	0.001	< 0.001	< 0.001	-0.566	0.002	< 0.001	< 0.001
Superior Cingulum Bundle
SES Group	-0.147	0.003	0.01	0.06	0.147	0.004	< 0.001	0.01	0.047	0.005	0.38	0.38	0.170	0.005	0.001	0.003
Sex	-0.104	0.003	0.05	0.20	-0.027	0.004	0.58	0.65	-0.119	0.005	0.02	0.05	0.018	0.005	0.72	0.86
NICU stay	-0.057	0.006	0.39	0.51	0.075	0.009	0.22	0.78	0.037	0.011	0.57	0.96	0.079	0.011	0.20	0.57
GA at delivery	0.045	0.001	0.53	0.85	0.055	0.002	0.40	0.87	0.089	0.002	0.22	0.41	0.029	0.002	0.66	0.93
PMA at scan	0.354	0.001	< 0.001	< 0.001	-0.541	0.002	< 0.001	< 0.001	-0.417	0.002	< 0.001	< 0.001	-0.520	0.002	< 0.001	< 0.001
Corticospinal Tract
SES Group	0.056	0.003	0.25	0.44	0.102	0.004	0.01	0.02	0.222	0.003	< 0.001	< 0.001	0.055	0.005	0.20	0.23
Sex	0.003	0.003	0.96	0.98	-0.047	0.004	0.25	0.52	-0.071	0.003	0.10	0.14	-0.033	0.005	0.44	0.79
NICU stay	-0.031	0.006	0.61	0.68	0.020	0.009	0.69	0.78	0.027	0.007	0.62	0.96	0.020	0.011	0.70	0.79
GA at delivery	0.020	0.001	0.76	0.85	-0.009	0.001	0.87	0.87	0.022	0.001	0.71	0.78	0.006	0.002	0.91	0.93
PMA at scan	0.544	0.001	< 0.001	< 0.001	-0.710	0.001	< 0.001	< 0.001	-0.646	0.001	< 0.001	< 0.001	-0.688	0.002	< 0.001	< 0.001
Optic Radiation
SES Group	0.080	0.003	0.09	0.20	0.162	0.005	< 0.001	0.001	0.291	0.005	< 0.001	< 0.001	0.102	0.006	0.02	0.04
Sex	-0.013	0.003	0.78	0.98	-0.125	0.005	0.00	0.04	-0.204	0.005	< 0.001	< 0.001	-0.088	0.005	0.04	0.24
NICU stay	-0.161	0.007	0.01	0.05	0.094	0.010	0.09	0.78	-0.003	0.010	0.96	0.96	0.122	0.012	0.02	0.21
GA at delivery	-0.025	0.001	0.69	0.85	-0.065	0.002	0.27	0.87	-0.091	0.002	0.19	0.41	-0.046	0.002	0.43	0.93
PMA at scan	0.544	0.001	< 0.001	< 0.001	-0.587	0.002	< 0.001	< 0.001	-0.324	0.002	< 0.001	< 0.001	-0.618	0.002	< 0.001	< 0.001
Uncinate Fasciculus
SES Group	-0.017	0.003	0.72	0.72	0.141	0.004	0.00	0.01	0.144	0.005	0.01	0.01	0.116	0.004	0.01	0.03
Sex	-0.083	0.002	0.08	0.20	-0.051	0.004	0.29	0.52	-0.120	0.005	0.03	0.05	-0.014	0.004	0.76	0.86
NICU stay	-0.057	0.005	0.33	0.50	-0.035	0.009	0.56	0.78	-0.087	0.011	0.21	0.96	-0.004	0.009	0.94	0.94
GA at delivery	0.092	0.001	0.15	0.34	0.050	0.001	0.44	0.87	0.125	0.002	0.09	0.41	0.005	0.002	0.93	0.93
PMA at scan	0.511	0.001	< 0.001	< 0.001	-0.583	0.001	< 0.001	< 0.001	-0.294	0.002	< 0.001	< 0.001	-0.632	0.002	< 0.001	< 0.001
Inferior Fronto-Occipital Fasciculus
SES Group	0.016	0.003	0.70	0.72	0.114	0.005	0.01	0.01	0.229	0.004	< 0.001	< 0.001	0.077	0.006	0.07	0.10
Sex	0.001	0.003	0.98	0.98	-0.101	0.004	0.02	0.05	-0.167	0.003	0.001	< 0.001	-0.070	0.005	0.09	0.26
NICU stay	-0.072	0.006	0.18	0.40	0.051	0.010	0.34	0.78	0.026	0.008	0.68	0.96	0.059	0.012	0.25	0.57
GA at delivery	0.085	0.001	0.14	0.34	-0.032	0.002	0.57	0.87	0.075	0.001	0.27	0.41	-0.054	0.002	0.34	0.93
PMA at scan	0.617	0.001	< 0.001	< 0.001	-0.664	0.002	< 0.001	< 0.001	-0.469	0.001	< 0.001	< 0.001	-0.668	0.002	< 0.001	< 0.001
Anterior Limb of Internal Capsule
SES Group	0.022	0.003	0.61	0.72	0.100	0.006	0.03	0.03	0.154	0.005	0.004	0.01	0.075	0.006	0.09	0.12
Sex	-0.031	0.002	0.47	0.84	-0.034	0.005	0.46	0.64	-0.055	0.005	0.28	0.28	-0.021	0.006	0.63	0.86
NICU stay	-0.056	0.005	0.29	0.50	0.053	0.012	0.36	0.78	0.032	0.010	0.62	0.96	0.059	0.014	0.29	0.77
GA at delivery	0.121	0.001	0.04	0.33	-0.017	0.002	0.78	0.87	0.083	0.002	0.24	0.41	-0.044	0.002	0.46	0.93
PMA at scan	0.597	0.001	< 0.001	< 0.001	-0.602	0.002	< 0.001	< 0.001	-0.460	0.002	< 0.001	< 0.001	-0.621	0.002	< 0.001	< 0.001
Inferior Cingulum Bundle
SES Group	-0.033	0.002	0.53	0.72	0.215	0.003	0.00	0.00	0.196	0.003	< 0.001	0.001	0.171	0.003	< 0.001	0.002
Sex	-0.025	0.002	0.63	0.94	-0.111	0.002	0.01	0.05	-0.121	0.003	0.02	0.05	-0.086	0.003	0.05	0.24
NICU stay	-0.104	0.005	0.12	0.35	0.032	0.005	0.57	0.78	-0.036	0.007	0.59	0.96	0.076	0.006	0.17	0.24
GA at delivery	-0.115	0.001	0.11	0.34	0.069	0.001	0.26	0.87	-0.020	0.001	0.78	0.78	0.110	0.001	0.07	0.61
PMA at scan	0.441	0.001	< 0.001	< 0.001	-0.633	0.001	< 0.001	< 0.001	-0.332	0.001	< 0.001	< 0.001	-0.658	0.001	< 0.001	< 0.001
Fornix
SES Group	-0.096	0.002	0.07	0.20	0.113	0.003	0.01	0.02	0.076	0.004	0.14	0.15	0.124	0.003	0.01	0.02
Sex	-0.091	0.002	0.09	0.20	-0.030	0.003	0.49	0.64	-0.078	0.004	0.12	0.14	0.003	0.003	0.94	0.94
NICU stay	-0.016	0.004	0.81	0.81	0.024	0.006	0.67	0.78	0.011	0.008	0.87	0.96	0.029	0.006	0.60	0.77
GA at delivery	0.031	0.001	0.67	0.85	0.020	0.001	0.74	0.87	0.041	0.001	0.55	0.71	0.008	0.001	0.90	0.93
PMA at scan	0.363	0.001	< 0.001	< 0.001	-0.647	0.001	< 0.001	< 0.001	-0.503	0.001	< 0.001	< 0.001	-0.653	0.001	< 0.001	< 0.001
Multiple linear regression results of the association between family socioeconomic status group and neonatal dMRI parameters. Bolded values represent statistical significance after FDR correction for multiple comparisons. β, standardized beta coefficient; SE, standard error; q, FDR-corrected p-value; FA, fractional anisotropy; MD, mean diffusivity; AD, axial diffusivity; RD, radial diffusivity; GA, gestational age; PMA, infant postmenstrual age; Sex, child sex. Bolded values indicate significant association after FDR correction for multiple comparisons.

Maternal cytokine concentration and neonatal dMRI parameters

Average maternal IL-6 concentration was negatively associated with 1) CST FA and AD; 2) UNCXL FA and AD; and 3) OR, IFOF, ALIC, and CBIF AD. Average maternal IL-10 concentration was 1) negatively associated with CST, IFOF, and CBIF FA and 2) positively associated with CST MD and RD and CBIF RD. There were no significant associations between average maternal IL-8 or TNF-α concentrations and neonatal dMRI measures (see Fig. 2 & Table 3).

Moderating effect of socioeconomic status in the relationship between maternal inflammation and neonatal white matter microstructure

There were significant interactions between family SES group and average maternal TNF-α concentration during pregnancy on neonatal CB MD (β = 0.18; q = 0.04), CBIF AD (β = 0.22; q = 0.01), and FX AD (β = 0.18; q = 0.02). Simple slopes analyses revealed similar patterns for CBIF AD and FX AD. As Fig. 3 shows, TNF-α and AD values were positively and significantly associated among the very low SES group (for CBIF AD: t=-3.24; p < 0.01; SE = 0.00 and for FX AD: t=-2.91; p < 0.01; SE = 0.00). However, these associations were not significant among the lower-to-higher SES group. By contrast, simple slopes analyses of CB MD indicated that its association with TNF-α was significant and positive in the lower-to-higher SES group (t = 2.20; p = 0.03; SE = 0.00) but negative and approaching significance in the very low SES group (t=-1.86; p = 0.06; SE = 0.00). Family SES group did not interact with average maternal IL-6, IL-8, or IL-10 concentration for any neonatal white matter tract measures (see Supplementary Table 1).

In this study, we capitalized on a cohort of mother-infant dyads oversampled for poverty to investigate early white matter development as a function of disadvantage-related prenatal inflammation. Consistent with our hypotheses, we found that family SES was associated with maternal cytokine concentrations during pregnancy and neonatal white matter microstructure. Very low SES was associated with higher average maternal IL-6 and lower diffusivity across multiple tracts in neonates. Additionally, higher maternal cytokine concentrations were associated with alterations in neonatal white matter microstructure. Furthermore, these associations varied across cytokines. Higher average maternal IL-6 was associated with lower tract FA and AD, whereas higher average maternal IL-10 was associated with lower tract FA but higher RD. An intriguing finding was that family SES moderated the relationship between average maternal TNF-α levels during gestation and neonatal white matter diffusivity, such that the association was significant and positive in the lower-to-higher SES neonates for superior cingulum MD, but significant and negative in the very low SES neonates for inferior cingulum and fornix AD. This suggests differential relationships of the effects of cytokines on white matter development depending upon SES context and raises questions about the divergence of biological mechanisms depending upon foundational resources/SES in utero.

The developing fetus’s expected extrauterine environment is communicated via maternal biological mediators that cross the placental barrier. Less favorable socioeconomic conditions impart unique mental, physical, and social challenges that, once born, a neonate must successfully interact with to facilitate survival. Fetal developmental trajectories are, therefore, malleable to environmental conditions. In the current study, we found that family SES was inversely related to maternal IL-6 levels during pregnancy. Chronic stress associated with economic disadvantage is hypothesized to result in a low-grade inflammatory phenotype, which is ultimately resistant to the dampening effects of glucocorticoids ^{16, 17}. Socioeconomic disadvantage has also been linked with aberrant neonatal white matter microstructure, whereby exposure to greater familial disadvantage early in life is associated with lower MD and RD in many major tracts ³⁴. Similarly, we found a positive relationship between family SES and neonatal white matter diffusivity in all tracts except the corpus callosum. Within the range of PMA studied herein, some tracts are myelinated while others are not. Our results suggest that economic disadvantage may modify white matter microstructure regardless of tract myelination timing. Consistent with findings from Lean et al. ³⁴ in this sample, this indicates that chronic exposure to maternally mediated stressors in utero may alter white matter maturation, particularly in the context of low SES (see Supplementary Information for a more in-depth discussion).

Maternal inflammatory biomarkers during pregnancy were also associated with variations in white matter microstructure. Higher maternal average IL-6 levels during pregnancy were related to lower AD in offspring with effects found for both both early and later developing white matter tracts, as well as lower FA in both the corticospinal tract and uncinate. Chronically elevated IL-6 may have deleterious effects on cell survival, synaptogenesis, and axonal growth ⁵⁰. Our results support the notion that heightened inflammatory cytokine exposure may alter the course of axonal maturation, as indicated by AD. In terms of tract FA, a study by Rasmussen et al. ⁵¹ similarly found that elevated maternal IL-6 was associated with lower uncinate FA in newborns. The uncinate plays a key role in communication between regions involved in emotion regulation and higher-order cognition, and its integrity is associated with socioemotional development. Our results in conjunction with those of Rasmussen et al. suggest that the uncinate in a developing fetus may be uniquely sensitive to maternal inflammation during pregnancy. In addition, we found that higher average maternal IL-10 concentration was associated higher MD and RD in the corticospinal tract, higher RD in the inferior cingulum bundle, and lower FA in the corticospinal tract, inferior fronto-occipital fasciculus, and inferior cingulum bundle in neonates. IL-10, a key anti-inflammatory cytokine, can suppress inflammatory cytokine production. However, chronically elevated IL-10 concentrations have been implicated in behavioral abnormalities ⁵² and demyelination of white matter ⁵³ in animal models. Taken together, elevated maternal cytokine concentrations during gestation may have implications for myelination disturbances of major projection, limbic, and association fibers.

Notably, the relationship between maternal TNF-α during pregnancy and neonatal white matter diffusivity was moderated by the SES context of the dyad. Specifically, higher concentrations of maternal TNF-α interacted with family SES to predict superior and inferior cingulum and fornix diffusivity. This association suggested that higher prenatal TNF-α exposure related to reduced axonal integrity in these fronto-limbic tracts specifically in neonates from very low SES families. Interestingly, the opposite pattern was observed in lower-to-higher SES neonates, with neonates born to mothers experiencing less disadvantage showing higher superior cingulum MD in relation to elevated TNF-α exposure in utero. These findings are consistent with a critical and central facet of the neuroimmune network hypothesis: the early environmental context differentially impacts crosstalk between neural circuitry and the immune system ³⁷. Low SES environments may amplify brain-immune bidirectional communication whereby the chronicity of stress-induced inflammation promotes a positive feedback circuit between peripheral cytokines and brain systems ¹⁵. While we cannot make specific inferences about the neurobiological source of alterations to diffusion parameters, this pattern suggests that sustained exposure to elevated TNF-α during gestation may alter fronto-limbic axonal development via aberrant pruning or reduced fiber branching among neonates from very low SES environments. Enhanced brain-immune crosstalk characterized by stress-induced inflammatory phenotypes may also function to prematurely prompt fetal brain development in preparation for a harsh extrauterine environment. While potentially advantageous for immediate survival, atypical maturation could hinder experience-dependent synaptic plasticity that prolonged, more typical maturation affords. Given that the white matter projections implicated here are critical for social and emotional development and typically continue to myelinate into the postnatal period, their aberrant maturation may have detrimental consequences for healthy socioemotional development. These findings raise important questions regarding how prenatal disadvantage may alter the course of brain development.

This study had several limitations. First, the current analyses are cross-sectional in design, precluding from the ability to make specific mechanistic inferences regarding how maternal inflammatory biomarkers during pregnancy and their association with economic disadvantage might impact brain maturation. However, the eLABE study is longitudinal in nature, and we will be able to investigate how these factors relate to trajectories of brain development into the second year of life and beyond. Second, our measure of brain-immune interaction is indirect, as methodology to better assess this is still being explored ^{11, 54}. Lastly, there was some variability in blood collection time by trimester as well as unequal sample sizes by trimester. Therefore, we averaged maternal cytokine concentrations over the course of pregnancy for the main analyses but include results by trimester in the Supplemental Information.

In summary, our results provide unique information about the relationships between SES and maternal inflammatory biomarkers, and in turn, how these factors interact in unique ways that are context dependent, to impact the developing fetus. We found that while average pregnancy levels of maternal IL-6 and IL-10 were associated with variations in neonatal white matter microstructure, average pregnancy levels of maternal TNF-α uniquely interacted with family SES to predict fronto-limbic white matter tract diffusivity. These findings suggest that neonates from very low SES families experience altered white matter tract maturation under high inflammatory conditions. Future studies that further interrogate these unique context-dependent trajectories in utero are indicated.

Conflict of Interest Statement: The authors have no real or perceived competing interesting to disclose.

Study Funding: This study was supported by the National Institute of Mental Health (R01 MH113883, T32 MH100019), March of Dimes Prematurity Research Center at Washington University, Washington University Intellectual and Developmental Disability Research Center (P50 HD103525), Children’s Discovery Institute, and the McDonnell Center for Systems Neuroscience.

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Table 3 is available in the Supplementary Files section.

The authors have declared there is NO conflict of interest to disclose

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Prenatal exposure to maternal disadvantage-related inflammatory biomarkers: Associations with neonatal white matter connectivity

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Socioeconomic status

Maternal cytokine concentration and neonatal dMRI parameters

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