Organ transplantation in mice: current status and future prospects

Whole bone subcutaneous transplantation as a strategy to study precisely the bone marrow niche

Hematopoietic stem cells are maintained in a specialized microenvironment, known as the 'niche', within the bone marrow. Understanding the contribution of cellular and molecular components within the bone marrow niche for the maintenance of hematopoietic stem cells is crucial for the success of therapeutic applications. So far, the roles of crucial mechanisms within the bone marrow niche have been explored in transgenic animals in which genetic modifications are ubiquitously introduced in the whole body. The lack of precise tools to explore genetic alterations exclusively within the bone marrow prevents our determination of whether the observed outcomes result from confounding effects from other organs. Here, we developed a new method - 'whole bone subcutaneous transplantation'- to study the bone marrow niche in transgenic animals precisely. Using immunolabeling of CD45.1 (donor) vs. CD45.2 (recipient) hematopoeitic stem cells, we demonstrated that hematopoeitic stem cells from the host animals colonize the subcutaneously transplanted femurs after transplantation, while the hematopoietic stem cells from the donor disappear. Strikinlgy, the bone marrow niche of these subcutaneously transplanted femurs remain from the donor mice, enabling us to study specifically cells of the bone marrow niche using this model. We also showed that genetic ablation of peri-arteriolar cells specifically in donor femurs reduced the numbers of hematopoietic stem cells in these bones. This supports the use of this strategy as a model, in combination with genetic tools, to evaluate how bone marrow niche specific modifications may impact non-modified hematopoietic stem cells. Thus, this approach can be utilized for genetic manipulation in vivo of specific cell types only within the bone marrow. The combination of whole bone subcutaneous transplantation with rodent transgenic models will facilitate a more precise, complex and comprehensive understanding of existing problems in the study of the hematopoietic stem cell bone marrow niche.

Orthotopic aortic transplantation in mice for the study of vascular disease

Vascular procedures involving anastomoses in the mouse are generally thought to be difficult and highly dependent on the skill of the individual surgeon. This is largely true, but there are a number of important principles that can reduce the difficulty of these procedures and enhance reproducibility. Orthotopic aortic transplantation is an excellent procedure in which to learn these principles because it involves only two end-to-end anastomoses, but requires good suturing technique and handling of the vessels for consistent success. This procedure begins with the procurement of a length of abdominal aorta from a donor animal, followed by division of the native aorta in the recipient. The procured aorta is then placed between the divided ends of the recipient aorta and sutured into place using end-to-end anastomoses. To accomplish this objective successfully requires a high degree of concentration, good tools, a steady hand, and an appreciation of how easily the vasculature of a mouse can be damaged, resulting in thrombosis. Learning these important principles is what occupies most of the beginner's time when learning microsurgery in small rodents. Throughout this protocol, we refer to these important points. This model can be used to study vascular disease in a variety of different experimental systems(1-8). In the context shown here, it is most often used for the study of post-transplant vascular disease, a common long-term complication of solid organ transplantation in which intimal hyperplasia occurs within the allograft. The primary advantage of the model is that it facilitates quantitative morphometric analyses and the transplanted vessel lies contiguous to the endogenous vessel, which can serve as an additional control(9). The technique shown here is most often used for mice weighing 18-25 grams. We have accumulated most of our experience using the C57BL/6J, BALB/cJ, and C3H/HeJ strains.

Importância da microcirurgia experimental para transplantes de órgãos

A microcirurgia experimental é uma área relativamente nova e seu desenvolvimento foi um marco importante para o desenvolvimento da pesquisa imunológica e de técnicas cirúrgicas de transplante, pois permitiu a utilização de modelos animais de pequeno porte; mais apropriados para pesquisa, e com menor custo. A microcirurgia exige bastante habilidade técnica e treinamento continuo. Além disso contribui para formação do cirurgião de transplantes na medida que promove o desenvolvimento de habilidade manual, interesse científico e cooperação interdisciplinar. Esse artigo relata alguns aspectos históricos, a importância e as vantagens e limitações da microcirurgia experimental.

Development of mouse cremaster transplantation model for intravital microscopic evaluation

OBJECTIVE

In this study, we investigated the possibility of transplanting cremaster muscle in mice. After transplantation, we measured the microcirculatory parameters and compared with the cremaster-control values with no transplantation.

METHODS

In group 1 (n = 10, C57BL/6N), normal cremaster microcirculation parameters were measured without transplantation. In group 2 (n = 6), isograft transplantations were performed between C57BL/6N mice. After transplantation, standard microcirculatory parameters were measured for 3 hours in both groups.

RESULTS

The procedure was performed with a 95% success rate and 75 minutes of ischemia time. Functional capillary perfusion, diameters, and red blood cell velocities of the first-, second-, and third-order arterioles and veins showed significant decreases in the isograft group within the first 2 hours (p < 0.05) but returned to normal values at the third hour. The number of rolling, adhering, and transmigrating leukocytes and lymphocytes also showed an increase in the isograft group within the first and second hours (p < 0.05, compared to cremaster control).

CONCLUSIONS

Leukocyte/endothelial interaction and hemodynamic parameters of muscle flap circulation displayed the effects of ischemia in the isograft group. The cremaster muscle transplantation in mice was found to be a reliable and reproducible model offering the unique possibility of observing and studying the leukocyte-endothelial interaction during ischemia/reperfusion injury and allograft rejection using intravital microscopy.