Human amniotic fluid-derived stem cells are rejected after transplantation in the myocardium of normal, ischemic, immuno-suppressed or immuno-deficient rat.

Human amniotic fluid-derived stem (AFS) cells, similarly to embryonic stem cells, could possess privileged immunological characteristics suitable for a successful transplantation even in a discordant xenograft system. We investigated whether AFS cells could be fruitfully used in a rat model of myocardial infarction. c-kit immunomagnetic-sorted AFS cells were characterized by flow cytometric analysis and cytospins as well as reverse-transcription polymerase chain reaction, Western blotting and immunocytochemistry for cardiovascular differentiation markers. In vitro, AFS cell phenotypic conversion was assayed by cardiovascular-specific induction media or co-cultured with rat neonatal cardiomyocytes. AFS cells showed mRNAs and/or protein for endothelial (angiopoietin, CD146) and smooth muscle (smoothelin) cells, and cardiomyocyte (Nkx2.5, MLC-2v, GATA-4, beta-MyHC) markers. Acquisition of a cardiomyocyte-like phenotype in rare AFS cells could be seen only in co-cultures with rat neonatal cells. In vivo, AFS cells xenotransplantated in a rat model of myocardial infarction, with or without cyclosporine treatment, or in intact heart from immuno-competent or immuno-deficient animals were acutely rejected due to the different recruitment of recipient CD4(+), CD8(+) T and B lymphocytes, NK cells and macrophages. This reaction is most likely to be linked to expression of B7 co-stimulatory molecules CD80 and CD86 as well as macrophage marker CD68 on AFS cells. Xenotransplanted AFS cells gave also rise in some animals to cell masses in the subendocardium and myocardium suggestive of a process of chondro-osteogenic differentiation. Despite AFS cells in vitro can differentiate to some extent to cells of cardiovascular lineages, their in vivo use in xenotransplantation for cell therapy of myocardial infarction is hampered by their peculiar immunogenic properties and phenotypic instability.

Amniotic fluid and bone marrow derived mesenchymal stem cells can be converted to smooth muscle cells in the cryo-injured rat bladder and prevent compensatory hypertrophy of surviving smooth muscle cells.

PURPOSE: Wound healing of the cryo-injured bladder can bring about organ remodeling because of incomplete reconstitution of depleted smooth muscle cells. Stem cell transplantation could be beneficial to improve smooth muscle cell regeneration and/or modulate the remodeling process. The repair of bladder injury using adult-type stem cells would be useful for adult urological patients but unsuited for neonatal patients, in whom major benefits are likely to derive from fetal-type stem cells. MATERIALS AND METHODS: The smooth muscle cell differentiation potential of fetal-type vs adult-type stem cells was evaluated by injecting green fluorescent protein labeled mesenchymal stem cells from rat amniotic fluid or bone marrow, respectively, in cryo-injured rat bladder walls. RESULTS: At 30 days after transplantation only a few fetal-type or adult-type mesenchymal stem cells gave rise to enteric or vascular smooth muscle cells, whereas most mesenchymal stem cells appeared incapable of specific differentiation. In vitro co-culture experiments of smooth muscle cells with fetal-type or adult-type mesenchymal stem cells selectively labeled with distinct fluorochromes showed the presence of hybrid cells, suggesting that some mesenchymal stem cells can undergo cell fusion. Surprisingly the major effect of rat bone marrow or amniotic fluid mesenchymal stem cell transplantation seemed to be preventing cryo-injury induced hypertrophy of surviving smooth muscle cells. CONCLUSIONS: In this model stem cell transplantation has a limited effect on smooth muscle cell regeneration. Instead it can regulate post-injury bladder remodeling, possibly via a paracrine mechanism.

Role of platelet activation in catheter-induced vascular wall injury.

PURPOSE: To investigate the role of smooth muscle cell (SMC) response and platelet activation in peripheral venous catheterization using a model of catheter injury associated with thrombocytopenic treatment. METHODS: Silicon elastic catheters were inserted into New Zealand White rabbit external jugular veins from 24 hours to 60 days. Immunocytochemical procedures with antibodies to differentiation markers specific for SMCs, myofibroblasts, and endothelial cells were used to ascertain the phenotypic features of injured venous SMCs and the tissue sleeve formed around the catheter. Thrombocytopenia was induced in rabbits by busulfan treatment and the effect on catheter injury development examined after 15 days. The putative direct effect of this drug on the venous SMC proliferation, migration, and differentiation was assayed in vitro for 48 hours. RESULTS: Catheter injury is characterized by the progressive formation of (1) a neointima, containing differentiating SMCs, which are derived from the media and adventitial layer, and (2) by the organizing thrombus formed around the catheter, which contains myofibroblasts. In busulfan-treated thrombocytopenic animals, there was no evidence for either neointimal development or thrombus formation. A direct role of this drug in the unresponsiveness of vascular wall can be excluded by the unchanged proliferation and migration pattern of cultured venous SMCs treated with busulfan compared to control cultures. CONCLUSIONS: In our model, accumulation of differentiated SMCs in the neointima and myofibroblast appearance in the thrombus are linked, although distinct, events regulated by platelet activation, which is able to furnish the appropriate microenvironment for vascular SMC recruitment from the media/adventitial layer.