Investigation of uterine blood vessel development in heavy menstrual bleeding

Abstract

Heavy menstrual bleeding (HMB) affects 30% of women of reproductive age, accounting for two-thirds of all hysterectomies. 50% HMB cases are unexplained and current treatment options often compromise fertility. Understanding the mechanisms underlying HMB is therefore critical to delineate potential pathways for therapeutic intervention. Previous studies suggested structural and functional roles for endometrial blood vessels in the pathogenesis of HMB. Endothelial cells (ECs) are associated with growth and formation of blood vessels; extracellular matrix (ECM) provides the framework for maintaining vascular structure, while vascular smooth muscle cell (VSMC) differentiation regulates blood flow and pressure. Altered endometrial vascular maturation is seen in recurrent miscarriage in association with increased uterine natural killer (uNK) cell number and variation in endometrial angiogenic growth factor (AGF) expression, but these processes have not been extensively studied in HMB. This study aimed to assess vascular maturation and AGF expression in HMB and investigate some of their effects in vitro. A study of VSMC differentiation revealed reduced endometrial calponin expression, suggesting a dysfunctional vascular contraction mechanism in HMB. This was associated with increased osteopontin expression, supporting previous evidence of regulation of vascular calponin expression by osteopontin. Endometrial collagen IV expression was lower in HMB, reflecting weaker vascular structure and definition. An altered pattern of uNK cell density in HMB may reflect altered in situ differentiation and or proliferation, which could impact vascular development and/or endometrial preparation for menstruation. VSMCs showed decreased endometrial expression of PDGFRα and TGFβRI, highlighting altered state of VSMC differentiation and potentially dysregulated endometrial vascular development in HMB. Furthermore, preliminary results indicated that PDGFBB helped to maintain EC ‘honeycomb’ structures, while anti-PDGFBB or TGFβ1 treatment decreased their numbers in vitro. Collectively, this study has highlighted key alterations in blood vessels in HMB, and established an in vitro model for future functional studies of blood vessel development.