Osteoblasts-derived Exosomes as Novel Communicators in Particle Induced Periprosthetic Osteolysis

BackgroundThe inflammatory response to titanium implant-derived wear particles is considered as the hallmark of periprosthetic osteolysis, an event that cause pain, reduce patient motility, ultimately leading to the need of a revision surgery. Although macrophages are major cell players, other cell types such as bone cells can indirectly contribute to periprosthetic osteolysis, however the mechanisms are not fully understood. Exosomes (Exos) has been related with several bone pathologies, with growing body of literature recognizing them as actively shuttle molecules through the body, with their cargo being completely dependent of external stimuli (e.g. chemicals and metals ions and particles). Till the moment, the role of wear debris on osteoblasts exosomes biogenesis is absent and the possible contribution of Exos to osteoimmune communication and periprosthetic osteolysis is still in its infancy. Taking that in consideration, in this work we investigate the effect of wear debris on Exo biogenesis, where two bone cell models were exposed to titanium dioxide nanoparticles (TiO2 NPs) similar in size and composition to wear debris associated with prosthetic implants. The contribution of Exos to periprosthetic osteolysis was evaluated performing functional tests stimulating primary human macrophages with bone-derived Exos.ResultsFor the first time, we report that TiO2 NPs enter in multivesicular bodies, the nascent of Exos and altered osteoblasts derived exosomes secretion and cargo. No significant differences were observed in Exos morphology and size, however mass spectrometry analysis identified urokinase-type plasminogen activator (uPA), specifically enriched in Exos derived from bone cells pre-incubated with TiO2 NPs. Functional tests confirmed the activation of human macrophages towards a mixed phenotype with consequent secretion of pro and anti-inflammatory cytokines. ConclusionsThe external stimuli of osteoblasts to TiO2 NPs induced a dose dependent secretion of Exos, suggesting alterations in their biogenesis as well as in their cargo. Functional tests reveal that enriched uPA exosomal cargo is stimulating macrophages towards a mixed M1 and M2 phenotype inducing the release of pro-and anti-inflammatory signals that are characteristic of periprosthetic osteolysis. Interestingly, uPA may be proposed, in the future, as a possible candidate biomarker to early diagnose particle induced periprosthetic osteolysis, since uPA was also detected in the pseudocapsular interface around implants of patients with loosening of total hip prosthesis and joint replacement surgery, suggesting their active role in disease progression.