miR-127-3p as a candidate biomarker for preeclampsia: what is missing for clinical use?

Preeclampsia (PE) is a complex hypertensive disorder of pregnancy characterized by abnormal placentation, systemic endothelial dysfunction, and chronic inflammation.1-3 By definition, PE involves new-onset hypertension after 20 weeks of gestation (SBP ≥140 mmHg and/or DBP ≥90 mmHg on 2 occasions ≥4 hours apart) accompanied by proteinuria or maternal end-organ dysfunction. It affects 2%–8% of pregnancies worldwide and is a leading cause of maternal and perinatal morbidity and mortality,4 accounting for ∼46,000 maternal and 500,000 fetal/neonatal deaths annually.5 Maternal complications include cerebrovascular hemorrhage, retinal detachment, HELLP (hemolysis, elevated liver-enzyme levels, and low platelet count) syndrome, eclamptic seizures, acute renal failure, pulmonary edema, placental abruption, and cardiopulmonary arrest. Fetal and neonatal complications include intrauterine growth restriction, oligohydramnios, placental abruption, stillbirth, neonatal death, and neurodevelopmental disability.5 Earlier diagnosis and risk stratification can facilitate prediction of maternal and fetal outcomes and support evidence-based management, including antihypertensive therapy for blood pressure control and magnesium sulfate for seizure prophylaxis in patients with severe features.6 When the diagnosis is uncertain, angiogenic biomarkers provide valuable adjuncts. The proangiogenic VEGF-family member placental growth factor (PlGF) decreases, whereas the antiangiogenic factor soluble fms-like tyrosine kinase-1 (sFlt-1) increases weeks before the clinical onset of PE. These biomarkers are particularly useful for short-term rule-out, with high negative predictive value.7 However, rule-in performance is limited at commonly used thresholds (eg, sFlt-1/PlGF >38), with only modest and setting-dependent positive predictive value.8,9 In terms of early detection before clinical onset, circulating microRNAs offer several potential advantages as biomarkers for PE. Circulating miRNAs are differentially expressed weeks to months before the onset of clinical symptoms and have shown promising diagnostic performance for early risk stratification.1,2,10 Additionally, combining miRNA biomarkers with the sFlt-1/PlGF ratio has been reported to improve diagnostic performance beyond either biomarker class alone.11 However, no miRNA-based test has received regulatory approval for routine clinical use in PE diagnosis or prediction. MicroRNAs (miRNAs) are small, evolutionarily conserved non-coding RNAs (∼22 nucleotides in length) that post-transcriptionally regulate gene expression via mRNA degradation and/or translational repression.12 Through these mechanisms, miRNAs are key regulators of cellular differentiation, proliferation, and stress responses. During pregnancy, they regulate trophoblast invasion, vascular remodeling, and immune tolerance at the maternal–fetal interface, thereby contributing to appropriate placental development.1 Their stability in circulation, relative tissue enrichment, and compatibility with standardized PCR-based quantification make miRNAs feasible candidates for non-invasive biomarker development.12,13 Among the most well-characterized miRNAs, miR-210 is markedly upregulated in PE placentas under hypoxic conditions via HIF-1α activation and has been implicated in impaired trophoblast invasion and mitochondrial function, contributing to placental oxidative stress.2 By contrast, miR-155 downregulates the proangiogenic factor CYR61, promoting endothelial inflammation and vascular dysfunction.13 Other miRNAs, including miR-21, miR-125b, and miR-200b, have been associated with impaired trophoblast differentiation and defective spiral artery remodeling.1,14 Collectively, these alterations support miRNAs as both effectors and indicators of the molecular cascades driving placental maladaptation in PE.1,2,14 However, the translational value of miRNA profiling remains limited by variability in analytical methods, small cohort sizes, and a lack of longitudinal validation.13,14 Consequently, rigorous evaluation of individual miRNA candidates in large, well-phenotyped clinical cohorts, coupled with mechanistic studies, is essential. Within this evolving field, miR-127-3p has gained attention as a biomarker candidate and a potential mediator in PE. In this issue of the American Journal of Hypertension, Maocheng Xiong, Lin Yang, and Peng Hou15 investigated the clinical and mechanistic relevance of miR-127-3p in PE. To address this question, the authors analyzed samples from 113 patients with PE and 93 healthy controls, including mild and severe PE subgroups. To extend the clinical observations, in vitro experiments were performed in the human chorionic trophoblast cell line HTR8/SVneo. Key findings included reduced miR-127-3p levels in PE placenta and maternal serum, with lower expression associated with greater disease severity and poorer pregnancy outcomes, potentially through effects on placental development and function. Receiver operating characteristic (ROC) analyses indicated strong diagnostic performance for miR-127-3p in serum (AUC 0.928; sensitivity 80.53%; specificity 89.25%) and placenta (AUC 0.915; sensitivity 85.84%; specificity 83.87%), supporting its potential as a clinically useful biomarker. Consistent with these observations, miR-127-3p overexpression in a hypoxia/reoxygenation (H/R)-treated HTR8/SVneo model enhanced trophoblast proliferation and invasion and attenuated the inflammatory response. Finally, the authors identified KIF3B as a direct miR-127-3p target (Figure 1). KIF3B is a microtubule-based kinesin motor implicated in intracellular trafficking and linked to cell migration and proliferation, processes essential for trophoblast invasion,16 yet its causal role in PE requires further investigation. Despite these valuable insights, several limitations warrant further study. Notably, the single-center cohort and relatively modest sample size may limit generalizability to broader PE populations and may overestimate diagnostic performance. Although the authors stratified cases by disease severity, additional clinically relevant phenotypes (eg, early- vs late-onset PE and other endotype-defining features) were not examined and could influence circulating miR-127-3p levels and diagnostic performance. An additional limitation is the case-control design comparing PE cases exclusively with healthy pregnancies; therefore, diagnostic specificity across clinically relevant differential diagnoses remains uncertain. Future studies should include disease-control groups (eg, other obstetric/placental disorders) to determine whether miR-127-3p is PE-specific. In addition, medication exposure and clinical management may act as important confounders and should be carefully accounted for in future studies. An additional limitation is the absence of internal and external validation of the ROC analyses. Without internal validation (eg, bootstrapping or cross-validation) and confirmation in an independent cohort, the reported AUC values and selected cutoffs may be inflated, and their generalizability to broader PE populations remains uncertain. Performing external validation in an independent cohort would provide more rigorous evidence for the clinical utility of miR-127-3p as a diagnostic marker. A further limitation is that it remains unclear whether miR-127-3p provides incremental predictive value beyond established biomarkers used in clinical practice (eg, the sFlt-1/PlGF ratio). Additionally, the current data do not fully clarify the tissue and/or cellular origin of circulating miR-127-3p or its temporal dynamics across gestation; thus, the optimal time point(s) for clinical measurement remain undefined. Complementing the human data with in vivo validation in established animal models of PE would further support physiological relevance. Although KIF3B was identified as a key downstream target of miR-127-3p, the study did not include KIF3B-specific loss- or gain-of-function experiments; therefore, it remains uncertain whether KIF3B directly mediates the trophoblast phenotypes observed following miR-127-3p modulation (eg, proliferation, invasion, and inflammatory cytokine production). Incorporating KIF3B knockdown and overexpression experiments would help establish causality and strengthen the mechanistic basis of the proposed miR-127-3p-KIF3B axis. In addition, assessing KIF3B expression in maternal serum and/or placental tissues from patients with PE would further enhance the clinical relevance of this regulatory relationship. Moreover, because miRNAs typically regulate multiple targets,17 downstream effectors beyond KIF3B may contribute to the observed effects of miR-127-3p, and these alternative mechanisms warrant further investigation. Taken together, the study provides important clinical and biological evidence supporting miR-127-3p as a candidate biomarker in PE. A major strength is the parallel analysis of miR-127-3p in maternal serum and placental tissue, demonstrating consistent downregulation in PE.15 Notably, the association of miR-127-3p with disease severity supports its potential utility for risk stratification. The authors further integrate complementary clinical and in vitro approaches by combining serum-placenta profiling with functional validation in a hypoxia/reoxygenation trophoblast model and direct target identification. The findings of Xiong et al15 align with prior reports linking dysregulated placental and circulating miRNAs to impaired trophoblast function and placental hypoxia in PE.3,18 Moreover, the reported diagnostic performance of circulating miR-127-3p reinforces the concept that miRNAs may complement established angiogenic markers for PE diagnosis. Functionally, the study shows that miR-127-3p overexpression ameliorates hypoxia/reoxygenation-induced trophoblast dysfunction by enhancing proliferation and invasion while attenuating pro-inflammatory cytokine production. These processes are central to normal spiral artery remodeling and placental development, and their disruption is a hallmark of PE.1 The identification of KIF3B as a direct target of miR-127-3p strengthens the mechanistic framework of the study and implicates kinesin-mediated intracellular transport in trophoblast biology. To further strengthen translational relevance, future studies could adopt more physiologically relevant experimental approaches. The use of primary human trophoblasts and co-culture systems, including endothelial and/or immune cells, would better mimic the complex PE microenvironment. In addition, because single-marker strategies are vulnerable to confounding and inter-platform variability, miR-127-3p should be evaluated within multi-marker panels alongside established angiogenic factors such as the sFlt-1/PlGF ratio, which has established clinical utility for PE diagnosis and risk prediction.19,20 Overall, these findings provide a strong foundation for future research to delineate the miR-127-3p/KIF3B axis in trophoblast biology and placental inflammation. This work represents a promising step toward improving the molecular characterization of PE and advancing miRNA-based approaches for diagnosis and mechanistic insight, with potential to improve prediction and management of PE.