Little evidence for cell fusion between recipient and donor-derived cells

Contribution of circulating vascular progenitors in lesion formation and vascular healing: lessons from animal models

PURPOSE OF REVIEW

It is a widely accepted view that vascular repair results from migration and proliferation of adjacent cells in animal models. On the contrary, accumulating evidence suggests that bone marrow can give rise to endothelial-like cells and smooth muscle like cells that potentially contribute to vascular healing, remodeling, and lesion formation under physiological and pathological conditions. The aim of this article is to review recent findings obtained from animal models of vascular diseases regarding bone marrow derived progenitor cells.

RECENT FINDINGS

Studies using chimeric animals revealed that bone marrow derived cells exist at the sites of vascular healing and lesion formation after injury. High-resolution histological analyses revealed that those bone marrow derived cells do express some markers for endothelial cells or smooth muscle cells. Peripheral mononuclear cells could differentiate into endothelial-like cells or smooth muscle like cells in vitro according to the culture conditions.

SUMMARY

Circulating progenitors significantly contribute to vascular repair and lesion formation. These findings provide the basis for the development of new therapeutic strategies that involve targeting the mobilization, homing, differentiation, and proliferation of bone marrow- derived vascular progenitor cells.

Regulation of cardiac regeneration by ACE inhibition following donor heart myocardial infarction after heterotopic transplantation in Tg mice

BACKGROUND

Experimental and clinical evidence have recently shown that pluripotent stem cells can be mobilized using granulocyte-colony stimulating factor (GCSF) and may enhance myocardial regeneration after acute myocardial infarction (MI). The present study investigated the pharmacological role of angiotensin-converting enzyme inhibition on cardiac regeneration after MI using a mouse model of heterotopic cardiac transplantation and coronary ligation.

METHODS AND RESULTS

Isogenic heterotopic cardiac transplantations and simultaneous coronary ligations were performed in green fluorescent protein (GFP) mice to produce MI in the donor heart. Five mice in the ligation group were treated with oral perindopril (PE) after the operation. Three mice in the ligation group were treated with subcutaneous GCSF and 4 angiotensin II type1a receptor knockout (AT1aRKO) mice were used as well. At 60 days after the operation, the maximum GFP-positive cell counts in the GCSF group were significantly higher than in the other 4 groups. The maximum GFP-positive cell counts in both the AT1aRKO and ligation & PE groups were significantly higher than in the sham and ligation groups.

CONCLUSIONS

Pharmacological modification for cardiac regeneration may provide an alternative treatment for subsequent cardiac remodeling in the late phase of MI.

The Angiotensin II Type 1 Receptor Blocker Candesartan Attenuates Graft Vasculopathy

OBJECTIVE

Transplant arteriosclerosis remains the major cause of graft failure after cardiac transplantation, although recent progress in immunosuppressive therapy has dramatically improved short-term survival of recipient. We investigated the effects of the angiotensin II type 1 receptor (AT(1)R) blocker candesartan on the development of transplant arteriosclerosis in a murine model of cardiac transplantation.

MATERIALS AND METHODS

Hearts from DBA/2 (H-2(d)) mice were heterotopically transplanted into B10.D2 (H-2(d)) mice. Recipients were treated with oral administration of candesartan (1 mg/kg per day) or vehicle. Allografts were analyzed at 14 or 30 days after transplantation.

RESULTS

Candesartan significantly reduced the development of coronary arteriosclerosis (intima/media ratio: 0.86 +/- 0.09 versus 0.57 +/- 0.10, P < 0.05), without affecting the degree of parenchymal rejection at 30 days. There was no significant difference in the expression of adhesion molecules and cytokines at 14 days. Candesartan significantly reduced the number of peripheral mononuclear cells that differentiated into smooth muscle-like cells in the presence of basic fibroblast growth factor and platelet-derived growth factor BB (27.1 +/- 3.1 versus 17.3 +/- 1.8 cells/HPF, P < 0.05).

CONCLUSIONS

Angiotensin II may play a role in the pathogenesis of transplant arteriosclerosis. Blockade of AT(1)R might be effective as a prophylactic therapy for transplant arteriosclerosis along with conventional immunosuppressive drugs.

The role of circulating precursors in vascular repair and lesion formation

The accumulation of smooth muscle cells (SMCs) plays a principal role in atherogenesis, post-angioplasty restenosis and transplantation-associated vasculopathy. Therefore, much effort has been expended in targeting the migration and proliferation of medial smooth muscle cells to prevent occlusive vascular remodeling. Recent evidence suggests that bone marrow-derived circulating precursors can also give rise to endothelial cells and smooth muscle cells that contribute to vascular repair, remodeling, and lesion formation under physiological and pathological conditions. This article overviews recent findings on circulating vascular progenitor cells and describes potential therapeutic strategies that target these cells to treat occlusive vascular diseases.

Involvement of bone marrow-derived cells in healing of experimental colitis in rats

Bone marrow is reported to contain hematopoietic stem cells and other adult somatic stem cells that have phenotypes of cells composing tissues other than bone marrow. To explore the implication of bone marrow-derived cells in the treatment of inflammatory bowel diseases, experimental colitis was induced in wild-type rats after transplantation of bone marrow from transgenic rats expressing green fluorescence protein (GFP). Chronic colitis was induced 21 days later using 30 mg 2,4,6-trinitrobenzenesulfonic acid (TNBS). Control rats received saline. At 28, 56, and 224 days after TNBS administration, rats were euthanized, and tissues were removed and processed for paraffin-embedded sections. Cells derived from bone marrow were identified by immunohistochemistry using anti-GFP antibody. To identify the phenotypes of the cells expressing GFP, we conducted serial-section analysis and double-staining analysis using antibodies against cytokeratin (epithelial cells) or vimentin (interstitial cells). In the present study, GFP-positive, bone marrow-derived cells occupied 37.6% and 4.25% of the colonic epithelium at 28 days and 56 days after the induction of TNBS-colitis, respectively. Also, significant amounts of mucosal and submucosal interstitial cells were derived from the bone marrow. These findings showed that a large amount of bone marrow-derived cells were involved in regeneration of the colon after experimental colitis in rats.

Efficiency of bone marrow-derived cells in regeneration of the stomach after induction of ethanol-induced ulcers in rats

BACKGROUND

Bone marrow contains hematopoietic stem cells, nonhematopoietic mesenchymal stem cells, and several precursor cells for osteoblasts, chondrocytes, adipocytes, myocytes, hepatocytes, and even neural cells. Research findings indicate that multipotent stem cells in the adult body may be used to recover the lost functions of damaged tissues. This study examined the involvement of bone marrow-derived cells in the regeneration of the stomach after experimental gastric ulcers were produced in rats.

METHODS

We transplanted the bone marrow of transgenic rats that expressed green fluorescence protein (GFP) throughout the body. Twenty-one days after the bone marrow transplantation (BMT), gastric ulceration was induced, using absolute ethanol. Control animals received saline. After various observation periods, rats harboring GFP-positive bone marrow-derived cells were killed, and the tissues were removed and processed to prepare paraffin-embedded sections. Cells expressing GFP were identified by conventional immunohistochemistry, using anti-GFP antibody. To identify whether cells expressing GFP were epithelial cells or interstitial cells such as fibroblasts, serial sections were examined with anti-cytokeratin antibody or anti-vimentin antibody, respectively. Furthermore, to confirm that cells expressing GFP were epithelial cells or interstitial cells, we used double-staining analysis with anti-GFP antibody or anti-cytokeratin antibody, respectively.

RESULTS

GFP-positive, bone marrow-derived cells were found in the cytokeratin-positive gastrointestinal epithelium, as well as among vimentin-positive interstitial cells. Interestingly, the proportions of GFP-positive, cytokeratin-positive epithelial cells and vimentin-positive interstitial cells were significantly greater in the ethanol-treated damaged stomachs than in the saline-treated controls.

CONCLUSIONS

The present study clearly demonstrates that bone marrow-derived cells are involved in the regeneration of the stomach after ethanol-induced ulcers in rats.

Molecular strategies to treat vascular diseases: circulating vascular progenitor cell as a potential target for prophylactic treatment of atherosclerosis

Atherosclerosis is responsible for more than half of all deaths in Western countries. Numerous studies have reported that accumulation of smooth muscle cells (SMCs) plays a principal role in atherogenesis, post-angioplasty restenosis and transplantation-associated vasculopathy. Although much effort has been devoted to targeting the migration and proliferation of medial SMCs, effective therapy to prevent occlusive vascular remodeling has not been established. Recently, it was suggested that bone marrow-derived precursors can give rise to vascular cells that contribute to the repair, remodeling, and lesion formation of the arterial wall under certain circumstances. This review highlights the recent findings on circulating vascular precursors and describes the potential therapeutic strategies for vascular diseases, targeting mobilization, homing, differentiation and proliferation of circulating progenitor cells.

Lost in transdifferentiation

What are the true origins of the smooth muscle cells (SMCs) present in the intimal lesions of transplant arteriosclerosis? A new study in the JCI shows that Sca-1(+) cells purified from the mouse aortic root can migrate through an irradiated vein graft to the neointima of the vessel and transdifferentiate to express the early SMC differentiation marker gene SM22. Do Sca-1(+) cells transdifferentiate into SMC-like cells, or is activation of SMC marker genes a consequence of fusion of these cells with preexisting SMCs, a possibility raised by results of studies of adult stem cells in animal models of liver regeneration ? Or could this be bona fide transdifferentiation that recapitulates the pathologic processes in humans?