Challenges of Primate Embryonic Stem Cell Research

Balancing animal welfare and assisted reproduction: ethics of preclinical animal research for testing new reproductive technologies

In the field of medically assisted reproduction (MAR), there is a growing emphasis on the importance of introducing new assisted reproductive technologies (ARTs) only after thorough preclinical safety research, including the use of animal models. At the same time, there is international support for the three R's (replace, reduce, refine), and the European Union even aims at the full replacement of animals for research. The apparent tension between these two trends underlines the urgency of an explicit justification of the use of animals for the development and preclinical testing of new ARTs. Considering that the use of animals remains necessary for specific forms of ART research and taking account of different views on the moral importance of helping people to have a genetically related child, we argue that, in principle, the importance of safety research as part of responsible innovation outweighs the limited infringement of animal wellbeing involved in ART research.

Protocol for serial cultivation of epithelial cells without enzymes or chemical compounds

Deriving keratinocytes from epidermis or oral mucosa is a critical first step in the construction of cell-based tissue engineering and regenerative medicine applications. It would be advantageous to develop a methodology to grow adult somatic cells with maximum plasticity in a rapid fashion and in large numbers with minimal manipulation. With routine methods, keratinocytes are cultured in standard amount of medium and passaged with enzymes, and the confluence of the monolayer induces differentiation and eventual cell death. A protocol to expand keratinocytes in culture by growing keratinocyte in large numbers using a technique in which keratinocytes are released into the overlaying medium, effectively "popping-up" into suspension from the cell monolayer, is described in this chapter. This technique does not require the use of enzymes or chemical compounds for serial cultivation. The cells possess the ability of active cell proliferation at 100 % confluence over 1-2 months' time. Based on previous characterization reports, these are untransformed, normal keratinocytes that appear to be highly suitable for clinical applications.

Characterization of cultured epithelial cells using a novel technique not requiring enzymatic digestion for subculturing

Our laboratory had developed a methodology to expand epithelial cells in culture by growing keratinocyte monolayers, under large volumes of medium that produces large numbers of keratinocytes that leave the monolayer and move into suspension. The cells have been defined as epithelial Pop Up Keratinocytes or ePUKs cells and appear to be highly suitable for clinical applications. In this publication we extend the characterization of the cells with a detailed analysis of the capabilities of the monolayer of a single culture flask to produce, over time, ePUK cells. The cells were characterized using standard epithelial markers for proliferation and differentiation. Analysis of morphology of the monolayer formed and total number of cells produced is presented for a variety of human epithelial cell strains. These keratinocytes provide an additional controlled human cell system for investigation of the mechanisms regulating epithelia cell growth and differentiation and since they are produced in large numbers, they are highly suitable for use in epithelial cell banking.

Characterization of a unique technique for culturing primary adult human epithelial progenitor/"stem cells"

Background

Primary keratinocytes derived from epidermis, oral mucosa, and urothelium are used in construction of cell based wound healing devices and in regenerative medicine. This study presents in vitro technology that rapidly expands keratinocytes in culture by growing monolayers under large volumes of serum-free, essential fatty acid free, low calcium medium that is replaced every 24 hrs.

Methods

Primary cell cultures were produced from epidermal skin, oral mucosa and ureter by trypsinization of tissue. Cells were grown using Epilife medium with growth factors under high medium volumes. Once densely confluent, the keratinocyte monolayer produced cells in suspension in the overlying medium that can be harvested every 24 hrs. over a 7–10 day period. The cell suspension (approximately 8 X 10⁵ cells/ml) is poured into a new flask to form another confluent monolayer over 2–4 days. This new culture, in turn produced additional cell suspensions that when serially passed expand the cell strain over 2–3 months, without the use of enzymes to split the cultures. The cell suspension, called epithelial Pop Up Keratinocytes (ePUKs) were analyzed for culture expansion, cell size and glucose utilization, attachment to carrier beads, micro-spheroid formation, induction of keratinocyte differentiation, and characterized by immunohistochemistry.

Results

The ePUKs expanded greatly in culture, attached to carrier beads, did not form micro-spheroids, used approximately 50% of medium glucose over 24 hrs., contained a greater portion of smaller diameter cells (8–10 microns), reverted to classical appearing cultures when returned to routine feeding schedules (48 hrs. and 15 ml/T-75 flask) and can be differentiated by either adding 1.2 mM medium calcium, or essential fatty acids. The ePUK cells are identified as cycling (Ki67 expressing) basal cells (p63, K14 expressing).

Conclusions

Using this primary culture technique, large quantities of epithelial cells can be generated without the use of the enzyme trypsin to split the cultures. The cells are small in diameter and have basal cell progenitor/”stem” (P/SC) cell characteristics induced by daily feeding with larger than normal medium volumes. The ePUK epithelial cells have the potential to be used in regenerative medicine and for basic studies of epithelia P/SC phenotype.

Separate and combined effects of caffeine and dbcAMP on olive baboon (Papio anubis) sperm

BACKGROUND

Improvement of baboon sperm capacitation is necessary for achieving high in vitro fertilization (IVF) rates in baboons. In this study, we evaluated separate and combined effects of caffeine and dbcAMP on baboon sperm capacitation.

METHODS

Sixteen male baboons (n = 16) were electroejaculated. Each sperm sample was divided into two aliquots: one for chemical activation and the other untreated control. Group 1: dbcAMP (n = 6); Group 2: caffeine (n = 6) and Group 3: combination of caffeine and dbcAMP (n = 4). In each aliquot, sperm motility after 30 minutes of incubation was evaluated as well as zona pellucida (ZP) binding ability after overnight incubation with 4-5 ZP from unfertilized human oocytes.

RESULTS

Sperm motility and ZP binding ability in all chemically activated groups increased significantly as compared to their respective controls (P < 0.05).

CONCLUSION

Combined and separate effects of caffeine and dbcAMP increases baboon sperm motility and ZP binding ability and may improve baboon IVF.

Mitochondria in stem cells

The current status of knowledge about mitochondrial properties in mouse, monkey and human embryonic, adult and precursor stem cells is discussed. Topics include mitochondrial localization patterns, oxygen consumption and ATP content in cells as they relate to the maintenance of stem cell properties and subsequent differentiation of stem cells into specific cell types. The significance of the perinuclear arrangement of mitochondria, which may be a characteristic feature of stem cells, as well as the expression of mitochondrial DNA regulatory proteins and mutations in the mitochondrial stem cell genome is also discussed.

Male-to-male differences in post-thaw motility of rhesus spermatozoa after cryopreservation of replicate ejaculates

BACKGROUND

The efficiency of controlled propagation to produce rhesus monkeys of particular genotypes can be maximized by use of cryopreserved spermatozoa collected from specific males to inseminate appropriate females. But this assumes that semen from males with different genotypes can be cryopreserved with equal effectiveness.

METHODS

To investigate whether spermatozoa from different Macaca mulatta males can be effectively cryopreserved when frozen under identical conditions, we collected and froze semen specimens from 13 adult, fertile males maintained at three primate research centers.

RESULTS

Survival, based on post-thaw motility normalized to the pre-freeze value, was assayed within 30 minutes after thawing; it varied from 50% to 70% but declined thereafter. To examine the response of semen from individual males, we collected and froze three to six ejaculates per male from each of seven males.

CONCLUSIONS

In general, semen from a given male responded reproducibly to freezing, but there were significant differences among males. The cause of these differences among M. mulatta males in post-thaw sperm survival remains unidentified.

Differential requirements for hematopoietic commitment between human and rhesus embryonic stem cells

Progress toward clinical application of ESC-derived hematopoietic cellular transplantation will require rigorous evaluation in a large animal allogeneic model. However, in contrast to human ESCs (hESCs), efforts to induce conclusive hematopoietic differentiation from rhesus macaque ESCs (rESCs) have been unsuccessful. Characterizing these poorly understood functional differences will facilitate progress in this area and likely clarify the critical steps involved in the hematopoietic differentiation of ESCs. To accomplish this goal, we compared the hematopoietic differentiation of hESCs with that of rESCs in both EB culture and stroma coculture. Initially, undifferentiated rESCs and hESCs were adapted to growth on Matrigel without a change in their phenotype or karyotype. Subsequent differentiation of rESCs in OP9 stroma led to the development of CD34(+)CD45(-) cells that gave rise to endothelial cell networks in methylcellulose culture. In the same conditions, hESCs exhibited convincing hematopoietic differentiation. In cytokine-supplemented EB culture, rESCs demonstrated improved hematopoietic differentiation with higher levels of CD34(+) and detectable levels of CD45(+) cells. However, these levels remained dramatically lower than those for hESCs in identical culture conditions. Subsequent plating of cytokine-supplemented rhesus EBs in methylcellulose culture led to the formation of mixed colonies of erythroid, myeloid, and endothelial cells, confirming the existence of bipotential hematoendothelial progenitors in the cytokine-supplemented EB cultures. Evaluation of four different rESC lines confirmed the validity of these disparities. Although rESCs have the potential for hematopoietic differentiation, they exhibit a pause at the hemangioblast stage of hematopoietic development in culture conditions developed for hESCs.

Anti-apoptotic effect of retinoic acid on retinal progenitor cells mediated by a protein kinase A-dependent mechanism

Retinal progenitor cells (RPCs) are neural stem cells able to differentiate into any normal adult retinal cell type, except for pigment epithelial cells. Retinoic acid (RA) is a powerful growth/differentiation factor that generally causes growth inhibition, differentiation and/or apoptosis. In this study, we demonstrate that RA not only affects mouse RPC differentiation but also improves cell survival by reducing spontaneous apoptotic rate without affecting RPC proliferation. The enhanced cell survival was accompanied by a significant upregulation of the expression of protein kinase A (PKA) and several protein kinase C (PKC) isoforms. Treatment of cells grown in RA-free media with 8-bromoadenosine3',5'-cyclic monophosphate, a known activator of PKA, resulted in an anti-apoptotic effect similar to that caused by RA; whereas the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride led to a significant ( approximately 32%) increase in apoptosis. In contrast, treatment of RPCs with any of two PKC selective inhibitors, 2,2',3,3',4,4'-hexahydroxy-1,1'-biphenyl-6,6'-dimethanol dimethyl ether and bisindolylmaleimide XI, led to diminished apoptosis; while a PKC activator, phorbol 12-myristate 13-acetate, increased apoptosis. These and other data suggest that the effect of RA on RPC survival is mostly due to the increased anti-apoptotic activity elicited by PKA, which might in turn be antagonized by PKC. Such a mechanism is a new example of tight regulation of important biological processes triggered by RA. Although the detailed mechanisms remain to be elucidated, we provide evidence that the pro-survival effect of RA on RPCs is not mediated by changed expression of p53 or bcl-2, and appears to be independent of beta-amyloid, Fas ligand, TNF-alpha, ganglioside GM1 and ceramide C16-induced apoptotic pathways.

Impact of Assisted Reproductive Technologies: A Mitochondrial Perspective of Cytoplasmic Transplantation

Many of the assisted reproductive techniques associated with maternal aging, disease states, or implantation failure aim to correct poor developmental capacity. These techniques are highly invasive and require the exchange of nuclear or cytoplasmic material from a donor oocyte to compensate for deficiencies inherent in the affected individual. These techniques are based on the assumption that the cytoplasm of the donor oocyte can effectively substitute the necessary component(s) to enable development to proceed. Several studies have attempted to inject cytoplasm from "normal" (young) donors, into aged eggs, again assuming that beneficial components of the cytoplasm are transferred to restore developmental capacity. These invasive assisted reproduction technology (ART) procedures aim to eliminate chromosomal abnormalities, improve the quality of oocytes deficient in some important cytoplasmic factors necessary for maturation and/or subsequent development, and eliminate maternally inherited diseases (particularly mitochondrial myopathies). However, in order to develop such ART, understanding the processes involving mitochondrial DNA replication and transcription is imperative, as asynchrony between mitochondrial and nuclear genomes may cause problems in mitochondrial function, localization, and biogenesis.

Derivation of embryonic stem cells for therapy: new technologies

Embryonic stem cells are currently derived from the inner cell mass of human blastocysts, generated from spare embryos donated for research. To overcome ethical concerns raised by destruction of the embryo, two groups of workers have attempted to derive these cells from isolated blastomeres of 8- to 10-cell stage embryos using the embryo biopsy method akin to that used in preimplantation diagnosis. This paper briefly discusses these two techniques in relation to the routine derivation of stem cells from blastocysts. Some embryological aspects of using the inner cell mass of blastocysts in preference to early embryonic cells are presented. The paper also considers some pitfalls in therapeutic cloning, especially in non-human primates, since legislation to allow this procedure for stem cell research is currently being passed in Australia.

Genetic modification of somatic cells for producing animal models and for cellular transplantation

Great progress has been made in two technologies related to biomedical research: (1) manipulating the genomes of cells; and (2) inducing stem cells in culture to differentiate into potentially useful cell types. These technologies can be used to create animal models of human disease and to provide cells for transplantation to ameliorate human disease. Both embryonic stem cells and adult stem cells have been studied for these purposes. Genetically modified somatic cells provide another source of cells for creating animal models and for cellular transplantation.

Mouse retinal progenitor cell (RPC) cocultivation with retinal pigment epithelial cell culture affects features of RPC differentiation

We provide evidence that coculturing of retinal progenitor cells (RPC) with retinal pigment epithelial cells significantly biases the standard in vitro RPC differentiation patterns. In particular, in cocultivation experiments RPCs lost the ability to differentiate spontaneously and displayed approximately 2.1-2.4-fold increase in immunoreactivity to the neural stem cell marker nestin and approximately 1.6-1.7-fold increase in rod photoreceptor cell rhodopsin marker immunoreactivity. The data suggest the influence of the intercellular interaction networks on RPC differentiation.

Mitochondrial DNA deletions in primate embryonic and adult stem cells

Mitochondrial DNA (mtDNA) mutations occur naturally in skeletal muscle fibers from aged rhesus macaques. In addition, mtDNA mutations have been observed in germinal vesicle oocytes from fertile monkeys. The goal of this study was to determine whether the rhesus macaque mitochondrial common deletion was present in oocytes and embryos generated by in-vitro embryo production (IVP), as well as in rhesus adult and embryonic stem cell lines. The rhesus common deletion was detected in IVP-generated embryos, three IVP-derived embryonic stem cell lines (ORMES 1, 2 and 7), one in-vivo-derived embryonic stem cell line (R4) and multiple passages of an adult bone marrow stromal cell (BMSC) line. Mitochondrial DNA from an adult adipose stromal cell (ATSC) line was compared with mtDNA from an immortalized line transfected with a retroviral vector expressing telomerase, ATSC-TERT. Multiple passages of the ATSC line harboured a dramatically higher level of the rhesus common deletion than the immortalized ATSC-TERT line. Accumulation of mtDNA mutations in oocytes, embryos and subsequent embryonic stem cell lines, as well as adult stem cell lines, may contribute to mitochondrial dysfunction, and thereby impair ATP production. The authors believe this information establishes a compelling argument for the parallel development of embryonic stem cell technology in non-human primates and humans.

Differentiation-related changes in mitochondrial properties as indicators of stem cell competence

Several methods may be used to assess stem cell competence, including the expression of cell surface markers and telomerase activity. We hypothesized that mitochondrial characteristics might be an additional and reliable way to verify stem cell competence. In a multipotent, adult monkey stromal stem cell line, previously shown to differentiate into adipocytes, chondrocytes, and osteocytes, we found that several mitochondrial properties change with increasing passage number in culture. Cells from the earliest passage (P11) versus those from a later passage (P17) are characterized by: (a) a much higher percentage of cells (85% vs. 18%) with a perinuclear arrangement of mitochondria; (b) a much lower percentage of cells (1% vs. 57%) with an aggregated mitochondrial arrangement, in which mitochondria appear to coalesce into large clumps; (c) a much lower percentage of cells with lipid droplets (1% vs. 36%), suggesting less differentiation into adipocytes; (d) a 5.6-fold lower ATP content per cell (0.45 vs. 2.51 pmoles ATP/cell; and (e) a 10-fold higher rate of oxygen consumption (37.8 vs. 3.8 nmoles O2/min/10(3) cells), indicating a higher metabolic activity. Collectively, these data indicate that the perinuclear arrangement of mitochondria, accompanied by a low ATP/cell content and a high rate of oxygen consumption, may be valid indicators of stem cell differentiation competence, while departures from this profile indicate that cells are differentiating or perhaps becoming senescent. These results represent the first characterization of mitochondrial properties reported for a primate stem cell line.

Isolation and characterization of novel rhesus monkey embryonic stem cell lines

ESCs are important as research subjects since the mechanisms underlying cellular differentiation, expansion, and self-renewal can be studied along with differentiated tissue development and regeneration in vitro. Furthermore, human ESCs hold promise for cell and tissue replacement approaches to treating human diseases. The rhesus monkey is a clinically relevant primate model that will likely be required to bring these clinical applications to fruition. Monkey ESCs share a number of properties with human ESCs, and their derivation and use are not affected by bioethical concerns. Here, we summarize our experience in the establishment of 18 ESC lines from rhesus monkey preimplantation embryos generated by the application of the assisted reproductive technologies. The newly derived monkey ESC lines were maintained in vitro without losing their chromosomal integrity, and they expressed markers previously reported present in human and monkey ESCs. We also describe initial efforts to compare the pluripotency of ESC lines by expression profiling, chimeric embryo formation, and in vitro-directed differentiation into endodermal, mesodermal, and ectodermal lineages.

From teratocarcinomas to embryonic stem cells and beyond: a history of embryonic stem cell research

We are currently facing an unprecedented level of public interest in research on embryonic stem cells, an area of biomedical research that until recently was small, highly specialized and of limited interest to anyone but experts in the field. Real and imagined possibilities for the treatment of degenerative and other diseases are of special interest to our rapidly ageing population; real and imagined associations of stem cells to cloning, embryos and reproduction stir deeply held beliefs and prejudices. The conjunction of these factors could explain the recent sudden interest in embryonic stem cells but we ought to remember that this research has a long and convoluted history, and that the findings described today in the scientific and popular press are firmly grounded in research that has been going on for several decades. Here I briefly recapitulate this fascinating history.

The mitochondrial contribution to stem cell biology

The distribution and functions of mitochondria in stem cells have not been examined, yet the contributions of these organelles to stem cell viability and differentiation must be vitally important in view of their critical roles in all other cell types. A key role for mitochondria in stem cells is indicated by reports that they translocate in the oocyte during fertilisation to cluster around the pronuclei and can remain in a perinuclear pattern during embryo development. This clustering appears to be essential for normal embryonic development. Because embryonic stem cells are derived from fertilised oocytes, and eventually can differentiate into ‘adult’ stem cells, it was hypothesised that mitochondrial perinuclear clustering persists through preimplantation embryo development into the stem cells, and that this localisation is indicative of stem cell pluripotency. Further, it was predicted that mitochondrial activity, as measured by respiration and adenosine triphosphate (ATP) content, would correlate with the degree of perinuclear clustering. It was also predicted that these morphological and metabolic measurements could serve as indicators of ‘stemness.’ This article reviews the distribution and metabolism of mitochondria in a model stem cell line and how this information is related to passage number, differentiation and/or senescence. In addition, it describes mitochondrial DNA deletions in oocytes and embryos that could adversely affect stem cell performance.