Influence of ovarian steroid hormones or platelet-activating factor on mRNA of platelet-activating factor receptor in endometrial explant perfusion cultures from ovariectomized bovine

Bridging the gap between traditional cell cultures and bioreactors applied in regenerative medicine: practical experiences with the MINUSHEET perfusion culture system

To meet specific requirements of developing tissues urgently needed in tissue engineering, biomaterial research and drug toxicity testing, a versatile perfusion culture system was developed. First an individual biomaterial is selected and then mounted in a MINUSHEET(®) tissue carrier. After sterilization the assembly is transferred by fine forceps to a 24 well culture plate for seeding cells or mounting tissue on it. To support spatial (3D) development a carrier can be placed in various types of perfusion culture containers. In the basic version a constant flow of culture medium provides contained tissue with always fresh nutrition and respiratory gas. For example, epithelia can be transferred to a gradient container, where they are exposed to different fluids at the luminal and basal side. To observe development of tissue under the microscope, in a different type of container a transparent lid and base are integrated. Finally, stem/progenitor cells are incubated in a container filled by an artificial interstitium to support spatial development. In the past years the described system was applied in numerous own and external investigations. To present an actual overview of resulting experimental data, the present paper was written.

Paf receptor expression in the marsupial embryo and endometrium during embryonic diapause

The control of reactivation from embryonic diapause in the tammar wallaby (Macropus eugenii) involves sequential activation of the corpus luteum, secretion of progesterone that stimulates endometrial secretion and subsequent changes in the uterine environment that activate the embryo. However, the precise signals between the endometrium and the blastocyst are currently unknown. In eutherians, both the phospholipid Paf and its receptor, platelet-activating factor receptor (PTAFR), are present in the embryo and the endometrium. In the tammar, endometrial Paf releasein vitroincreases around the time of the early progesterone pulse that occurs around the time of reactivation, but whether Paf can reactivate the blastocyst is unknown. We cloned and characterised the expression of PTAFR in the tammar embryo and endometrium at entry into embryonic diapause, during its maintenance and after reactivation. Tammar PTAFR sequence and protein were highly conserved with mammalian orthologues. In the endometrium, PTAFR was expressed at a constant level in the glandular epithelium across all stages and in the luminal epithelium during both diapause and reactivation. Thus, the presence of the receptor appears not to be a limiting factor for Paf actions in the endometrium. However, the low levels of PTAFR in the embryo during diapause, together with its up-regulation and subsequent internalisation at reactivation, supports earlier results suggesting that endometrial Paf could be involved in reactivation of the tammar blastocyst from embryonic diapause.

Supportive development of functional tissues for biomedical research using the MINUSHEET® perfusion system

Functional tissues generated under in vitro conditions are urgently needed in biomedical research. However, the engineering of tissues is rather difficult, since their development is influenced by numerous parameters. In consequence, a versatile culture system was developed to respond the unmet needs.

Optimal adhesion for cells in this system is reached by the selection of individual biomaterials. To protect cells during handling and culture, the biomaterial is mounted onto a MINUSHEET® tissue carrier. While adherence of cells takes place in the static environment of a 24 well culture plate, generation of tissues is accomplished in one of several available perfusion culture containers. In the basic version a continuous flow of always fresh culture medium is provided to the developing tissue. In a gradient perfusion culture container epithelia are exposed to different fluids at the luminal and basal sides. Another special container with a transparent lid and base enables microscopic visualization of ongoing tissue development. A further container exhibits a flexible silicone lid to apply force onto the developing tissue thereby mimicking mechanical load that is required for developing connective and muscular tissue. Finally, stem/progenitor cells are kept at the interface of an artificial polyester interstitium within a perfusion culture container offering for example an optimal environment for the spatial development of renal tubules.

The system presented here was evaluated by various research groups. As a result a variety of publications including most interesting applications were published. In the present paper these data were reviewed and analyzed. All of the results point out that the cell biological profile of engineered tissues can be strongly improved, when the introduced perfusion culture technique is applied in combination with specific biomaterials supporting primary adhesion of cells.

The role of platelet-activating factor in the mammalian female reproductive tract

Platelet-activating factor (PAF) is a potent lipid mediator produced by various cell types of mammals and is involved in an inflammatory-like process with increased vascular permeability. Platelet-activating factor exerts its actions through the activation of specific PAF receptors (PAF-R) found in cells and tissues of the female reproductive tract. The aim of this article was summarized briefly in the current research on the role of PAF in female reproductive functions. Platelet-activating factor has been implicated in processes of ovulation, implantation and parturition because of its angiogenic and growth factor properties. This factor is influenced by ovarian steroid hormones in bringing about changes in the uterus and is a candidate molecule for initial embryo-maternal dialogue. Tissue concentrations of PAF are regulated by the equilibrium between biosynthesis and degradation by PAF-acetylhydrolase (PAF-AH). Antagonists of PAF interfere with ovulation and implantation. Platelet-activating factor, its receptor, and PAF-AH activity play an important role in the maintenance of pregnancy.

Role of the platelet-activating factor and its receptor in the proliferative regulation of bovine ovarian granulosa cells

Proliferation of granulosa cells and their withdrawal from the cell cycle may regulate follicular ovulation. Antagonists of platelet-activating factor (PAF) and its receptor (PAFr) inhibit follicle rupture.

OBJECTIVES

Thus, PAF and PAFr may be involved in proliferative regulation of granulosa cells; however, expression of PAFr in these cells is unknown.

MATERIALS AND METHODS

The aim of this study was to investigate the presence of PAFr and the effect of PAF on proliferation of cultured bovine granulosa cells using real-time polymerase chain reaction to assay steady-state level of mRNA, immunocytochemistry to quantify PAFr protein and proliferating cell nuclear antigen protein by flow cytometry.

RESULTS

We found that granulosa cells express PAFr transcripts and protein. PAF presence did not change the concentration of PAFr mRNA or PAFr protein. Granulosa cells responded to PAF doses of 10 and 50 nm with increasing proportions of cells entering G0/G1 phase, as well as a significant expansion of total cell numbers. Rise in G0/G1-phase cells was accompanied by a decline in proliferating cell nuclear antigen protein expression, and these effects could be suspended by simultaneous PAFr blockage. The results provide clear evidence for expression of PAFr in bovine granulosa cells and its functional involvement in PAF/PAFr-mediated stimulation of cell recruitment.

CONCLUSIONS

PAF antagonists are suggested to disturb this regulative activity of PAF and to contribute in this way to blockage of ovulation.