The CB1 receptor: unraveling its dysregulation by endocrine disruptions in human osteoblasts and its physiological role in sperm cells

The endocannabinoid system (ECS) is a conserved regulatory network involved in the maintenance of cellular homeostasis, including that of bone and male reproductive system. Although its role in skeletal biology remains not completely defined, increasing evidence suggests that ECS components, particularly the endocannabinoid receptor (CB1) receptor, contribute to osteoblast differentiation, extracellular matrix (ECM) remodeling and bone metabolism. On the other hand, endocrine disrupting chemicals (EDCs) such as bisphenol A (BPA) and perfluorooctanoic acid (PFOA) interfere with osteogenic and oxidative pathways and have been shown to affect ECS signaling, though the mechanisms remain unclear. In the first part of the PhD thesis, we examined how acute and chronic exposure to PFOA and BPA, alone or combined, affect osteoblast homeostasis with a focus on CB1 regulation. Using 2D and 3D hFOB1.19 models, the studies demonstrated that these contaminants alter spheroids morphology, ECM deposition and mineralization, and modulate antioxidant and osteogenic markers. Specifically, acute exposure to PFOA induced a transient CB1-related response linked to collagen remodeling, whereas chronic exposure disrupted ECM deposition and mineralization, independently of CB1 regulation, both after single and combined exposure to PFOA and BPA. Regarding the reproductive system, CB1 localization and function were explored in spermatozoa. High-resolution imaging revealed previously unrecognized intracellular CB1 localization extending to the sperm nuclei, which is conserved across mammalian species and persists after the acrosome reaction. Functionally, CB1 activation through selective agonist restored histone H4K12 acetylation in asthenozoospermic samples, demonstrating its involvement in human sperm chromatin remodeling. The nuclear localization of CB1 in sperm was also confirmed in somatic cells, such as osteoblast and astrocytes, further suggesting potential transcriptional and /or epigenetic functions in these cells as well. Overall, the results here obtained uncover novel mechanistic roles of CB1 in bone and sperm biology and also demonstrate its susceptibility to environmental contaminants such as BPA and PFOA.