Platelet derived growth factor (PDGF) contained in Platelet Rich Plasma (PRP) stimulates migration of osteoblasts by reorganizing actin cytoskeleton.

Platelet-rich plasma (PRP) is a platelet concentrate in a small volume of plasma. It is highly enriched in growth factors able to stimulate the migration and growth of bone-forming cells. PRP is often used in clinical applications, as dental surgery and fracture healing. Platelet derived growth factor (PDGF), is highly concentrated in PRP and it was shown in our previous studies to provide the chemotactic stimulus to SaOS-2 osteoblasts to move in a microchemotaxis assay. Aim of the present studies is to analyze the effects of a PRP pretreatment (short time course: 30-150 min) of SaOS-2 cells with PRP on the organization of actin cytoskeleton, the main effector of cell mobility. The results indicate that a pretreatment with PRP increases chemokinesis and chemotaxis and concomitantly induces the organization of actin microfilaments, visualized by immunocytochemistry, in a directionally elongated phenotype, which is characteristic of the cells able to move. PRP also produces a transient increase in the expression of PGDF α receptor. This reorganization is blocked by the immunoneutralization of PDGF demonstrating the responsibility of this growth factor in triggering the mechanisms responsible for cellular movements.

The nervous structures of anterior cruciate ligament of human knee, healthy and lesioned, studied with confocal scanning laser microscopy.

The presence of nervous structures with proprioceptive function in the human knee ligaments is by now well known. Therefore a lesion of the anterior cruciate ligament (ACL), beyond a loss of mechanical stability, causes the interruption of proprioceptive signals. In the present study, the Authors verified the presence of nervous structures in lesioned ligaments, using bioptic samples taken from the distal portion of residual stumps of ACL, during surgical intervention of the ACL reconstruction. Their examination with conventional light microscopy, after silver impregnations and/or PGP 9.5 immunofluorescence, revealed that not all the nervous structures of injured ACL are completely lost after the trauma, but that some of them can maintain their morphology even many months far from the offending event. However most of them undergoes more or less marked alterations, as demonstrated the confocal laser scanning microscopy. The orthopaedic surgeons have to pay attention to the reconstruction of injured cruciate ligaments, even far from the injury, with different techniques which success may also depend on the number of lost proprioreceptors, interrupted reflex circuits or non re-educated propriocetive signals.

Polymorphonuclear leukocyte-myocyte interaction: an early event in collar-induced rabbit carotid intimal thickening.

The importance of mononuclear leukocyte (MO) adhesion to dysfunctional endothelium and migration to the subendothelial space in the early phases of atherogenesis is well established. Few studies have addressed the relevance of polymorphonuclear leukocytes (PMNs) in the context of evolving lesions, and nothing is known about PMN interaction with vascular smooth muscle cells (SMCs). In this study, we investigated leukocyte/SMC interactions in a model of rabbit carotid injury induced by placement of a silastic collar. This procedure leads to the development of intimal thickening characterized by SMC accumulation preceded by an abundant leukocyte infiltration. By transmission electron microscopy and immunocytochemistry, we demonstrated the occurrence of PMN infiltration starting at 6 h and ceasing within 72 h after collar placement. A previously unknown extensive interaction between medial myocytes and PMNs was detected, referring to emperipolesis, an active phenomenon of cells engulfing other cells in a process other than phagocytosis. PMNs, but not MOs, were internalized by SMCs, which showed ultrastructural features intermediate between the true contractile and the fully synthetic phenotype without exhibiting any sign of injury. Emperipolesis preceded any detectable cell proliferation in the vessel wall and disappeared within 72 h, following the kinetic of PMN infiltration in the vessel wall. In summary, our findings show the occurrence of an active and selective interaction between PMNs and SMCs via emperipolesis during the early phases of intimal thickening after perivascular collaring. However, the overall etiology of the phenomena described in the present study and their pathophysiological significance should be further investigated.