Maternal Gestational Hypertension Is Associated with Reduced TSG-6 in Human Milk: Potential Implications for Neonatal Immunological Support

Tumor necrosis factor alpha-stimulated protein 6 (TSG-6) is a potent anti-inflammatory mediator secreted by mesenchymal stem cells (MSCs). In human milk (HM), these cells (human milk mesenchymal stem cells, HM-MSCs) contribute to postnatal programming of the neonatal gastrointestinal immune axis. This study assessed how maternal gestational hypertension and maternal age affect the cytoprotective TSG-6 pool and its associated immunomodulatory microRNA signature in early milk. Early colostrum, 2–4 days postpartum, from healthy mothers and hypertensive patients was analyzed. TSG-6 gene expression in the heterogeneous milk cellular fraction containing HM-MSCs and TSG-6 protein concentration in whole milk were determined using quantitative polymerase chain reaction (qPCR) and Enzyme-Linked Immunosorbent Assay (ELISA), respectively. Comprehensive multivariable General Linear Models (GLMs) were used to adjust for potential confounding variables, including pre-pregnancy Body Mass Index (BMI), gestational age (GA), and gestational diabetes. Additionally, TSG-6 levels were correlated with fetal cord blood gas parameters and previously profiled microRNAs in the cellular fraction. GLM analysis revealed that gestational hypertension remained significantly associated with reduced TSG-6 gene expression in the cellular fraction and total TSG-6 protein concentration in whole milk, regardless of pre-pregnancy BMI or metabolic comorbidities. In healthy pregnancies, exploratory analyses suggested that TSG-6 levels correlated positively with optimal fetal metabolic status (cord blood pH). Importantly, TSG-6 expression showed a strong positive correlation with a signature of immunomodulatory microRNAs (miR) (miR-155-5p, miR-21-3p, miR-126-3p). These microRNAs were concurrently downregulated in the hypertensive group; however, because all hypertensive participants received methyldopa, the independent contributions of hypertension and antihypertensive treatment to these changes cannot be distinguished. Gestational hypertension independently reduces the anti-inflammatory TSG-6 in early breast milk. The concomitant reduction in TSG-6 and its correlated microRNA co-expression pattern indicates an altered immunomodulatory profile within the mammary gland during lactation. We hypothesize that these changes might alter the local immunomodulatory properties of milk in the neonatal gastrointestinal tract. However, because no functional in vitro or in vivo assays were performed, this remains a purely theoretical implication that requires future experimental validation.