The KISS1/KISS1R Axis in Human Placentation: Molecular Mechanisms and Implications for Foetal Growth Restriction and...

Pre-eclampsia and foetal growth restriction (FGR) are major pregnancy complications primarily driven by placental dysfunction, and remain leading causes of maternal and perinatal morbidity. Ultrasound imaging, Doppler studies, and angiogenic biomarkers like placental growth factor (PlGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) constitute the main diagnostic modalities; however, these predominantly reflect established disease rather than early molecular disturbances underlying placentation. The identification of biomarkers directly associated with trophoblast signalling pathways has the potential to improve early risk stratification and enable mechanistic classifications. Kisspeptin signalling via its receptor (KISS1R) regulates trophoblast invasion, extracellular matrix remodelling, ERK1/2 activation, and angiogenic balance, thereby modulating spiral artery transformation. Kisspeptin-10 (KP-10), the minimal bioactive fragment of KISS1, is highly expressed in placental syncytiotrophoblasts and exerts its effects through the G-protein-coupled receptor KISS1R. Core features of early-onset FGR and pre-eclampsia (PE)-including defective placentation, maternal vascular malperfusion, and angiogenic imbalance-have been linked to dysregulation of this pathway. During normal gestation, maternal circulating kisspeptin concentrations rise exponentially. In contrast, pregnancies subsequently complicated by FGR or PE, particularly in the early gestation, are associated with reduced levels. However, the comparability of existing studies and their translational applicability are limited by a substantial methodological heterogeneity, including assay variability, gestational age dependence, and inadequate adjustment for maternal confounders. These limitations hinder robust conclusions regarding the role of kisspeptin in placental pathology. This review critically integrates molecular, pathophysiological, and clinical evidence relating to the role of KP-10 in placental dysfunction. The key question is whether KP-10 represents a mechanistic biomarker of trophoblast signalling dysfunction or merely a secondary marker of reduced placental mass; resolving this distinction is essential.