Subcutaneous transplantation of bovine and human adrenocortical cells in collagen gel in scid mice

In Vivo Formation of Adrenal Organoids in a Novel Porcine Model of Adrenocortical Cell Transplantation

Recognizing the limitations of current therapies for Addison's disease, novel treatments that replicate dynamic physiologic corticosteroid secretion, under control of ACTH, are required. The aim of these experiments was to evaluate the feasibility of adrenocortical cell transplantation (ACT) in a large animal model, adapting methods successfully used for intracutaneous pancreatic islet cell transplantation, using a fully biodegradable temporizing matrix. Autologous porcine ACT was undertaken by bilateral adrenalectomy, cell isolation, culture, and intracutaneous injection into a skin site preprepared using a biodegradable temporizing matrix (BTM) foam. Hydrocortisone support was provided during adrenocortical cell engraftment and weaned as tolerated. Blood adrenocortical hormone concentrations were monitored, and the transplant site was examined at endpoint. Outcome measures included cellular histochemistry, systemic hormone production, and hydrocortisone independence. Transplanted adrenocortical cells showed a capability to survive and proliferate within the intracutaneous site and an ability to self-organize into discrete tissue organoids with features of the normal adrenal histologic architecture. Interpretation of systemic hormone levels was confounded by the identification of accessory adrenals and regenerative cortical tissue within the adrenal bed postmortem. Corticosteroids were unable to be completely ceased. ACT in a large animal model has not previously been attempted, yet it is an important step toward clinical translation. These results demonstrate rhe potential for ACT based on the development of adrenal organoids at the BTM site. However, the inability to achieve clinically relevant systemic hormone production suggests insufficient function, likely attributable to insufficient cells through delivered dose and subsequent proliferation.

Recent advances in endocrine organoids for therapeutic application

The endocrine system, consisting of the hypothalamus, pituitary, endocrine glands, and hormones, plays a critical role in hormone metabolic interactions. The complexity of the endocrine system is a significant obstacle to understanding and treating endocrine disorders. Notably, advances in endocrine organoid generation allow a deeper understanding of the endocrine system by providing better comprehension of molecular mechanisms of pathogenesis. Here, we highlight recent advances in endocrine organoids for a wide range of therapeutic applications, from cell transplantation therapy to drug toxicity screening, combined with development in stem cell differentiation and gene editing technologies. In particular, we provide insights into the transplantation of endocrine organoids to reverse endocrine dysfunctions and progress in developing strategies for better engraftments. We also discuss the gap between preclinical and clinical research. Finally, we provide future perspectives for research on endocrine organoids for the development of more effective treatments for endocrine disorders.

Future directions for adrenal insufficiency: cellular transplantation and genetic therapies

Primary adrenal insufficiency occurs in 1 in 5-7000 adults. Leading aetiologies are autoimmune adrenalitis in adults and congenital adrenal hyperplasia (CAH) in children. Oral replacement of cortisol is lifesaving, but poor quality of life, repeated adrenal crises and dosing uncertainty related to lack of a validated biomarker for glucocorticoid sufficiency, persists. Adrenocortical cell therapy and gene therapy may obviate many of the shortcomings of adrenal hormone replacement. Physiological cortisol secretion regulated by pituitary adrenocorticotropin, could be achieved through allogeneic adrenocortical cell transplantation, production of adrenal-like steroidogenic cells from either stem cells or lineage conversion of differentiated cells, or for CAH, gene therapy to replace or repair a defective gene. The adrenal cortex is a high turnover organ and thus failure to incorporate progenitor cells within a transplant will ultimately result in graft exhaustion. Identification of adrenocortical progenitor cells is equally important in gene therapy where new genetic material must be specifically integrated into the genome of progenitors to ensure a durable effect. Delivery of gene editing machinery and a donor template, allowing targeted correction of the 21-hydroxylase gene, has the potential to achieve this. This review describes advances in adrenal cell transplants and gene therapy that may allow physiological cortisol production for children and adults with primary adrenal insufficiency.

[Gene and cell therapy of adrenal pathology: achievements and prospects]

Our current understanding of the molecular and cellular mechanisms in tissues and organs during normal and pathological conditions opens up substantial prospects for the development of novel approaches to treatment of various diseases. For instance, lifelong replacement therapy is no longer mandatory for the management of some monogenic hereditary diseases. Genome editing techniques that have emerged in the last decade are being actively investigated as tools for correcting mutations in affected organs. Furthermore, new protocols for obtaining various types of human and animal cells and cellular systems are evolving, increasingly reflecting the real structures in vivo. These methods, together with the accompanying gene and cell therapy, are being actively developed and several approaches are already undergoing clinical trials. Adrenal insufficiency caused by a variety of factors can potentially be the target of such therapeutic strategies. The adrenal gland is a highly organized organ, with multiple structural components interacting with each other via a complex network of endocrine and paracrine signals. This review summarizes the findings of studies in the field of structural organization and functioning of the adrenal gland at the molecular level, as well as the modern approaches to the treatment of adrenal pathologies.

Comparison between slow and rapid freezing for adrenal gland cryopreservation and xenotransplantation

The aim of our study was to examine whether slow or rapid cryopreservation of adrenal xenografts affected xenotransplant outcome. Adrenal xenografts were got from newborn piglets (<24 h after birth). Receptor rats were randomly divided into four groups: a bilateral adrenalectomy group, fresh xenotransplantation group, rapid cryopreservation xenotransplantation group, and a slow cryopreservation xenotransplantation group. 30 days after xenotransplantation, the survival rates of rats in the fresh xenotransplantation group, rapid cryopreservation xenotransplantation group and slow cryopreservation xenotransplantation group were 80 %, 60 % and 60 %, respectively, which were significantly higher than 40 % of the bilateral adrenalectomy group. In addition, the survival rate of rats in the slow cryopreservation group was consistently significantly higher than that in the rapid cryopreservation group at 29 days after xenotransplantation. Morphological observation showed that there were a few medulla cells existed in the adrenal glands in the slow cryopreservation group after 30 days of xenotransplantation, but no medulla cells were found in the rapid cryopreservation group. The plasma cortisol level of rats in the fresh xenotransplantation group and the slow xenotransplantation group 30 days after xenotransplantation was significantly higher than that of the rapid cryopreservation group and bilateral adrenalectomy group (P < 0.05). The levels of liver glycogen and cholesterol in the xenotransplantation rats were increased relative to those of the bilateral adrenalectomy rats, and close to normal level. In conclusion, compared with rapidly frozen preserved grafts, slowly frozen preserved grafts not only ensure the structural integrity of adrenal tissues, but also have corresponding physiological functions, which provid a basic research opportunities for the preservation of xenografts and the treatment of adrenal corticosteroid deficiency. Moreover, these findings can provide evidence for xenotransplantation in the treatment of Addison's disease (adrenal cortex hormone deficiency).

Towards novel treatments for adrenal diseases: Cell- and gene therapy-based approaches

Adrenal insufficiency, the inability to produce adequate levels of corticosteroids, is a multi-causal disease that requires lifelong daily hormone replacement. Nevertheless, this cannot replace the physiological demand for steroids which are secreted following a circadian rhythm and vary in periods of stress; the consequences of under- or over-replacement include adrenal crisis and metabolic disturbances, respectively. Although clinical research has focused on enhancing the effectiveness/reducing side effects of current treatment modalities, only small improvements are deemed possible; thus, alternative solutions are urgently needed. Gene and cell therapy strategies have opened new possibilities for the cure of many diseases in a way that has never been possible before and could offer a viable option for the cure of adrenal diseases. The current state of cell- and gene-based approaches to restore adrenocortical function is discussed in this review.

Extension of Survival in Bilaterally Adrenalectomized Mice by Implantation of SF-1/Ad4BP-Induced Steroidogenic Cells

Mesenchymal stroma/stem cells (MSCs) exist in adult tissues, such as adipose tissue and bone marrow, and differentiate into cells of multiple lineages. In previous studies, we found that MSCs differentiate into steroidogenic cells by forced expression of steroidogenic factor 1 (SF-1)/adrenal 4 binding protein (Ad4BP), the master regulator of steroidogenesis and differentiation of pituitary gonadotrophs, adrenal glands, and gonads. In this study, SF-1/Ad4BP-induced steroidogenic cells derived from mouse adipose tissue-derived MSCs (ADSCs) were implanted under the kidney capsule of bilateral adrenalectomized (bAdx) mice. bAdx mice did not survive after 7 days. However, 4 of 9 bAdx mice implanted with SF-1/Ad4BP-induced steroidogenic cells, 1 of 10 bAdx mice transplanted with control ADSCs, and bAdx mice transplanted with an adrenal gland survived for 30 days. Plasma corticosterone levels in bAdx mice implanted with SF-1/Ad4BP-induced steroidogenic cells and control ADSCs were 5.41 ± 2.26 ng/mL (mean ± SEM) and undetectable at 7 days after implantation, respectively. After removal of the kidney bearing the graft from the surviving mice at 30 days after implantation, plasma corticosterone was not detected in any of the samples. Immunohistochemical staining revealed SF-1/Ad4BP-positive cells under the capsule of the kidney. Although we performed an adrenocorticotropin (ACTH) loading test on bAdx mice implanted with SF-1/Ad4BP-induced steroidogenic cells, ACTH responsiveness was not observed. Implantation of steroidogenic cells derived from ADSCs into bAdx mice increased the basal plasma corticosterone level and extended the survival of bAdx mice, suggesting the capability of restoring steroidogenic cells by cell transplantation therapy for adrenal insufficiency.

Intradermal Cell Transplantation in Soluble Collagen

Intradermal, as opposed to subcutaneous, cell transplantation was previously shown to be advantageous for tumor cell growth, but this site has not been used for transplantation of normal nonneoplastic cells. In preliminary experiments we found that it was difficult to control the size and shape of transplants when we injected dissociated cells intradermally. This problem was solved by placing cells in nongelled, pepsin-solubilized collagen prior to injection. This technique permitted the successful transplantation of normal bovine adrenocortical cells and of neoplastic cells (3T3 cells secreting FGF) in scid mice. Primary bovine adrenocortical cells formed functional vascularized tissue and the transplants rescued the animals from the lethal effects of adrenalectomy. The histological structure of transplant tissues resembled that previously observed when cells were transplanted in the subrenal capsule space. We also used a line of 3T3 cells that has been genetically modified to secrete a form of acidic FGF. When transplanted intradermally in collagen, they formed rapidly enlarging masses of cells that could easily be palpated beneath the skin of the animal. Intradermal injection of cells in pepsin-solubilized collagen is a simple and reliable technique for transplanting normal primary cells and preneoplastic cells. The ability to grow both types of cells in an easily accessible site allows less invasive monitoring of growth, angiogenesis, and other features of the transplant.

Resistance to experimental tumorigenesis in cells of a long-lived mammal, the naked mole-rat (Heterocephalus glaber)

The naked mole-rat (NMR, Heterocephalus glaber) is a long-lived mammal in which spontaneous cancer has not been observed. To investigate possible mechanisms for cancer resistance in this species, we studied the properties of skin fibroblasts from the NMR following transduction with oncogenes that cause cells of other mammalian species to form malignant tumors. Naked mole-rat fibroblasts were transduced with a retrovirus encoding SV40 large T antigen and oncogenic Ras(G12V). Following transplantation of transduced cells into immunodeficient mice, cells rapidly entered crisis, as evidenced by the presence of anaphase bridges, giant cells with enlarged nuclei, multinucleated cells, and cells with large number of chromosomes or abnormal chromatin material. In contrast, similarly transduced mouse and rat fibroblasts formed tumors that grew rapidly without crisis. Crisis was also observed after > 40 population doublings in SV40 TAg/Ras-expressing NMR cells in culture. Crisis in culture was prevented by additional infection of the cells with a retrovirus encoding hTERT (telomerase reverse transcriptase). SV40 TAg/Ras/hTERT-expressing NMR cells formed tumors that grew rapidly in immunodeficient mice without evidence of crisis. Crisis could also be induced in SV40 TAg/Ras-expressing NMR cells by loss of anchorage, but after hTERT transduction, cells were able to proliferate normally following loss of anchorage. Thus, rapid crisis is a response of oncogene-expressing NMR cells to growth in an in vivo environment, which requires anchorage independence, and hTERT permits cells to avoid crisis and to achieve malignant tumor growth. The unique reaction of NMR cells to oncogene expression may form part of the cancer resistance of this species.

Optimizing orthotopic cell transplantation in the mouse adrenal gland

Orthotopic cell transplantation models are important for a complete understanding of cell-cell interactions as well as tumor biology. In published studies of orthotopic transplantation in the mouse adrenal gland, human neuroblastoma cells have been shown to invade and occupy the adrenal, but in these investigations a true orthotopic model was not established. Here we show an orthotopic model in which transplanted cells are retained within the adrenal gland by formation of a fibrin clot. To establish an appropriate technique, we used brightly fluorescent 10 microm polystyrene microspheres injected into the mouse adrenal gland. In the absence of fibrinogen/thrombin for clot formation, much of the injected material was extruded to the outside of the gland. When the microspheres were injected in a fibrinogen/thrombin mixture, fluorescence was confined to the adrenal gland. As a model neoplastic cell originating from the cortex of the gland, we used a tumorigenic bovine adrenocortical cell line. When 3 x 10(5) cells were implanted orthotopically, by 16 days the cell mass had expanded and had invaded the cortex, whereas when 1 x 10(5) cells were used, tumor masses were much smaller. We therefore subsequently used 3 x 10(5) cells. When mice were sacrificed at different time points, we found that tumor growth resulting was progressive and that by 26 days cells there was extensive invasion into the cortex or almost complete replacement of the cortex with tumor cells. As a model neoplastic cell of neural crest origin, we used SK-N-AS human neuroblastoma cells. Orthotopic transplantation of 3 x 10(5) cells resulted in extensive invasion and destruction of the gland by 26 days. In summary, the present orthotopic model for intra-adrenal cell transplantation is valuable for investigation of growth of neoplastic cells of both cortical and medullary origin and should be useful for future studies of cortex-medulla interactions.

New methods for investigating experimental human adrenal tumorigenesis

Adenomas and nodules of the human adrenal cortex are common, whereas adrenocortical carcinomas are rare. Genes such as IGF2 have been suggested to be important in human adrenocortical tumorigenesis but their role has not been directly investigated. We describe here elements of a system in which hypotheses concerning the molecular basis for the formation of benign and malignant adrenocortical lesions can be experimentally tested. Various viral vectors have been employed in the study of adrenocortical cell biology. Because of the low proliferative rate of primary human adrenocortical (pHAC) cells, a lentiviral system is ideal for transducing these cells with genes that may alter their characteristics or cause them to acquire benign or malignant tumorigenicity. Cultures of pHAC cells were highly infectible with lentiviruses and showed a higher proliferative potential when transduced with a lentivirus encoding IGF2. For tumorigenesis studies of genetically modified adrenocortical cells, we use RAG2(-/-), gammac(-/-) mice. Using this immunodeficient mouse model, we established an orthotopic intra-adrenal cell transplantation technique for adrenocortical cells that should be of value for future studies of the experimental conversion of human adrenocortical cells to a benign or malignant tumorigenic state.

Senescent human fibroblasts increase the early growth of xenograft tumors via matrix metalloproteinase secretion

Although cellular senescence is believed to have a tumor suppressor function, senescent cells have been shown to increase the potential for growth of adjacent cancer cells in animal models. Replicatively senescent human fibroblasts increase the growth of cotransplanted cancer cells in vivo, but the role of cells that have undergone damage-mediated stress-induced premature senescence (SIPS) has not been studied in mouse transplant models. Here, we show that human fibroblasts that have undergone SIPS by exposure to the DNA-damaging agent bleomycin increase the growth of cotransplanted cancer cells (MDA-MB-231) in immunodeficient mice. Xenografts containing SIPS fibroblasts (SIPSF) exhibited early tissue damage as evidenced by fluid accumulation (edema). Cancer cells adjacent to the fluid showed increased DNA synthesis. Fluid accumulation, increased xenograft size, and increased cell proliferation were all reduced by the matrix metalloproteinase (MMP) inhibitor GM6001. MMPs and other genes characteristic of inflammation/tissue injury were overexpressed in SIPSF. Inhibition of MMP activity did not affect SIPSF stimulation of cancer cell proliferation in culture. However, another overexpressed product (hepatocyte growth factor) did have a direct mitogenic action on cancer cells. Based on the present results, we propose that senescent cells may promote cancer growth both by a direct mitogenic effect and by an indirect effect via tissue damage. Senescent stromal cells may cause an MMP-mediated increase in permeability of adjacent capillaries, thereby exposing incipient cancer cells to increased levels of mitogens, cytokines, and other plasma products. This exposure may increase cancer cell proliferation and result in promotion of preneoplastic cells.

Improving cell therapy--experiments using transplanted telomerase-immortalized cells in immunodeficient mice

Cell therapy is the use of stem cells and other types of cells in various therapies for age-related diseases. Two issues that must be addressed before cell therapy could be used routinely in medicine are improved efficacy of the transplanted cells and demonstrated long-term safety. Desirable genetic modifications that could be made to cells to be used for cell therapy include immortalization with human telomerase reverse transcriptase (hTERT). We have used a model for cell therapy in which transplantation of adrenocortical cells restores glucocorticoid and mineralocorticoid hormone levels in adrenalectomized immunodeficient mice. In this model, clones of cells that had been immortalized with hTERT were shown to be able to replace the function of the animals' adrenal glands by forming vascularized tissue structures when cells were transplanted beneath the capsule of the kidney. hTERT-modified cells showed no tendency for neoplastic changes. Moreover, a series of experiments showed that hTERT does not cooperate with known oncoproteins in tumorigenesis either in adrenocortical cells or in human fibroblasts. Nevertheless, hTERT was required for tumorigenesis when cells were implanted subcutaneously rather than in the subrenal capsule space. Changes in gene expression make hTERT-modified cells more robust. Understanding these changes is important so as to be able to separately control immortalization and other desirable properties of cells that could be used in cell therapy. Alternatively, desirable properties of transplants might be provided by co-transplanted mesenchymal cells: mesenchymal cell-assisted cell therapy. For both hTERT modification and mesenchymal cell-assisted cell therapy, genomics approaches will be needed to define what genetic modifications are desirable and safe in cells used in cell therapy.

Differentiation and regeneration of adrenal tissues: An initial step toward regeneration therapy for steroid insufficiency

In animal experiments, adrenal cortical tissue has been successfully regenerated through xenotransplantation of cloned adrenocortical cells, suggesting that the intraadrenal stem cells required for such tissue formation may be present in the adrenal cortex. Stable expression of Ad4BP/SF-1, a key factor for adrenal and gonadal development and steroidogenesis, has been shown to direct embryonic stem cells toward the steroidogenic lineage. However, this steroidogenic capacity was very limited since progesterone was only produced in the presence of an exogenous substrate. Bone marrow mesenchymal cells are thought to contain pluripotent progenitor cells, which differentiate into multiple lineages. We have demonstrated that adenovirus-mediated forced expression of SF-1 in long-term cultured bone marrow cells can produce steroidogenic cells with the capacity for de novo synthesis of various steroid hormones in response to ACTH. This discovery may represent the first step in autologous cell transplantation therapy for patients with steroid hormone deficiency.

Telomerase is not required for experimental tumorigenesis of human and bovine adrenocortical cells

Telomerase has often been thought to be essential for tumorigenesis of human cells. Adrenocortical cancers, like other cancers, typically have telomerase activity. We reinvestigated the requirement for telomerase in the conversion of normal human and bovine adrenocortical cells to cancer cells. When primary adrenocortical cells were transduced with retroviruses encoding SV40 large T antigen and Ha-RasG12V and immediately transplanted into immunodeficient mice they produced invasive and metastatic tumors. Cells had negligible telomerase activity before transplantation and after recovery from tumors. However, these tumors were not immortal and cells entered crisis, limiting further growth of the tumor as well as invasion and metastasis. Infection of these tumor cells with a retrovirus encoding hTERT restored growth in culture and restored the malignant properties of the cells in immunodeficient animals. These experiments differ from previous studies in which telomerase was found to be essential for tumorigenicity: 1) we used tissue reconstruction techniques for introduction of cells into host animals and 2) we infected primary cells with retroviruses and immediately transplanted them without drug selection.

Progressive loss of malignant behavior in telomerase-negative tumorigenic adrenocortical cells and restoration of tumorigenicity by human telomerase reverse transcriptase

Replicative senescence/crisis is thought to act as a tumor suppressor mechanism. Although recent data indicate that normal human cells cannot be converted into cancer cells without telomerase, the original concept of senescence as a tumor suppressor mechanism is that senescence/crisis would act to limit the growth of telomerase-negative tumors. We show here that this concept is valid when oncogene-expressing human and bovine cells are introduced into immunodeficient mice using tissue reconstruction techniques, as opposed to conventional subcutaneous injection. Primary human and bovine adrenocortical cells were transduced with retroviruses encoding Ha-Ras(G12V) and SV40 large T antigen and transplanted in immunodeficient mice using tissue reconstruction techniques. Transduced cells were fully malignant (invasive and metastatic) in this model. They had negligible telomerase activity both before transplantation and when recovered from tumors. When serially transplanted, tumors showed progressively slower growth, decreased invasion and metastasis, shortened telomeres, and morphological features of crisis. Whereas telomerase was not essential for malignant behavior, expression of human telomerase reverse transcriptase enabled cells from serially transplanted tumors that had ceased growth to reacquire tumorigenicity. Moreover, telomerase-negative oncogene-expressing cells were tumorigenic only when transplanted using tissue reconstruction techniques; human telomerase reverse transcriptase was required for cells to form tumors when cells were injected subcutaneously. This work provides a new model to study crisis in an in vivo setting and its effects on malignancy; despite having invasive and metastatic properties, cells are eventually driven into crisis by proliferation in the absence of a telomere maintenance mechanism.

EXPRESSION OF VASCULAR ENDOTHELIAL GROWTH FACTOR AND ITS RECEPTORS FLK-1 AND FLT-1 DURING THE REGENERATION OF AUTOTRANSPLANTED ADRENAL CORTEX IN THE ADRENALECTOMIZED RAT

PURPOSE

Autotransplantation of the adrenal cortex may be a therapeutic alternative in the future. For successful adrenal transplantation revascularization is necessary. It is possible that vascular endothelial growth factor (VEGF), which is a potent angiogenic peptide, may have some roles in adrenal transplantation through 2 its receptors, kinase insert domain-containing region (Flk-1) and fms-like tyrosine kinase (Flt-1). Therefore, we studied sequential changes in expression of VEGF, Flk-1 and Flt-1 in regenerated adrenal.

MATERIALS AND METHODS

Eight to 9-week-old male Wistar rats underwent bilateral adrenalectomy and immediate adrenal capsular autotransplantation. The expression of VEGF, Flk-1 and Flt-1 was analyzed by immunohistochemistry and reverse-transcriptase-polymerase chain reaction.

RESULTS

Angiogenesis was observed in the remodeling of adrenal sinusoidal endothelium during adrenal regeneration. Reverse transcriptase-polymerase chain reaction and immunohistochemistry showed that VEGF expression increased in grafted tissue with time after transplantation and its Flk-1 receptor, which localized to endothelial cells, increased transiently during the regeneration process. Immunostaining for Flt-1 receptor was identified in adrenocortical cells and its intensity gradually increased during adrenal regeneration.

CONCLUSIONS

During adrenal gland regeneration VEGF and its receptors Flk-1 and Flt-1 are thought to be involved in neovascularization.

Adrenocortical cell transplantation in scid mice: the role of the host animals' adrenal glands

Adrenocortical cell transplantation is a powerful technique for the investigation of the regulation of adrenocortical structure and function. Some classical organ and tissue transplantation experiments suggest that the success of transplantation depends on the activity of the pituitary gland and other endocrine systems, and is therefore influenced by the host animals' own adrenal glands. For this reason, our experiments have usually been performed on adrenalectomized animals. However, we show here that cell transplantation experiments, involving the introduction of bovine adrenocortical cells into scid mice, do produce transplant tissues in the presence of the host animals' adrenal glands. However, the tissue that forms is small and its cells also smaller than usual. When the adrenals of such animals are removed in a second surgical procedure, the transplants show a rapid increase in steroidogenic function and a slower increase in size, over several weeks. We conclude that the initial process by which transplanted adrenocortical cells organize into a tissue structure is not affected by the presence of the host animals' adrenal glands, but the growth of the transplants is limited until the adrenal glands are removed.

Using cell transplantation to investigate genes involved in aging

Cell transplantation provides a way to study genes that may be important in human tissue aging. Studies on gene action in human cells are usually restricted to cell culture investigations and clinical observations. Differences in human and rodent cellular biology, particularly with respect to telomere dynamics, show the need for new systems for investigating aging that use human cells or cells of other large, long-lived mammals, such as bovine cells. The system we describe uses human and bovine adrenocortical cells transplanted into scid (severe combined immunodeficiency) mice. They form a vascularized tissue structure that can replace the essential functions of the animals' own adrenal glands. The cells may be genetically modified before introduction into the animal. Using hTERT (telomerase reverse transcriptase) and oncoproteins, we show the potential for investigating gene action in genetically modified tissues created by cell transplantation.

Adrenocortical cell proliferation in a cell transplantation model: the role of SV40 T antigen

Bovine adrenocortical cells immortalized by human telomerase reverse transcriptase (hTERT) are capable of forming functional vascularized tissue structures when transplanted in immunodeficient mice. These tissues maintain the life of adrenalectomized animals, show normal cell proliferation rates, and maintain a constant tissue size. These experiments were performed by co-transfection of an hTERT-encoding plasmid with an SV40 T antigen-encoding plasmid, but in tissues formed from clones derived in this way SV40 T Ag was not expressed. However, when tissues were formed from nonclonal heterogeneous populations of transfected cells, nodules of SV40 TAg-expressing cells arose that showed a high proliferation rate. These structures resembled nodules formed from transplanted bovine adrenocortical cells in which SV40 TAg was introduced by retroviral transduction rather than transfection. The reasons for these phenomena are discussed; in a nonclonal mixed population of cells, some may have much higher levels of SV40 TAg, which perturbs the normal histology and behavior of tissues formed from hTERT-immortalized adrenocortical cells.

Human adrenocortical cell xenotransplantation: model of cotransplantation of human adrenocortical cells and 3T3 cells in scid mice to form vascularized functional tissue and prevent adrenal insufficiency

To establish an experimental model for replacement of endocrine organ function by xenotransplantation, human adrenocortical cells from postnatal donors were transplanted beneath the kidney capsule of adrenalectomized scidmice together with mitomycin C-treated 3T3 cells that secrete FGF. Adrenocortical cells from seven donors, male and female, ranging from 6-50 years of age, were used. 12 of 13 animals survived > 16 days following surgery. After 50 days they were sacrified to allow assessment of the histology and ultrastructure of tissue formed from the transplanted cells. Only 1 of 23 adrenalectomized sham-operated animals survived > 16 days. In all surviving animals, vascularized adrenocortical tissue formed at the site of transplantation. Cortisol, the normal human glucocorticoid, was present in the plasma of these animals, replacing corticosterone, the mouse glucocorticoid. Some animals, but not most, had measurable aldosterone. The tissue formed from the transplanted cells showed histological and ultrastructural features of normal adrenal cortex. Mitochondria had tubulo-vesicular cristae and there were prominent microvilli between cells. Tissues had a well-developed vasculature, sometimes with large sinusoidal vessels. Proliferation in the transplant tissues was very low. These results show that tissue formed from transplanted human adrenocortical cells is able to replace the essential functions of the adrenal gland in scid mice. This demonstrates that transplanted human endocrine cells can functionally replace a surgically removed endocrine organ in a host animal.

A novel use of alginate hydrogel as Schwann cell matrix

The use of bioresorbable conduits supplemented with Schwann cells (SCs) is a promising tissue engineering technique to replace nerve grafting. Alginate hydrogel (AH), as a SC tissue engineering matrix, has many advantages over previously used matrices but has not been evaluated for this purpose. In this study, the viability and proliferation of SCs together with SC function in AH was evaluated in vitro. AlamarBlue cell assay was used to monitor the viability of SCs in AH and compared to SC viability in collagen gel, fibrin glue, hyaluronic acid, Matrigel, and standard culture plate over 5 days in culture. The results showed that the viability and growth of SCs in different matrices over the culture period did not significantly differ to culture plate culture. SC function when suspended in AH was monitored using chick embryo dorsal root ganglia (CDRG) growth assay. Growth of CDRG in AH with or without SCs was compared to CDRG growth without AH matrix. After 3 days in culture, the mean length of neurite sprouting was measured. The results showed that there was neurite growth in AH but was reduced to 43% of control. The neurite growth in AH was, however, enhanced by 170% when SCs were suspended in the gel. In conclusion, AH supported SC viability and function in vitro and may be useful in peripheral nerve tissue engineering in reconstructive procedures.

Contrasting roles of p57(KIP2) and p21(WAF1/CIP1/SDI1) in transplanted human and bovine adrenocortical cells

Cell transplantation provides a way to compare the regulation of cell proliferation in the same cell type in cell culture and in a vascularized tissue structure in a host animal. The cyclin-dependent kinase inhibitors p57(KIP2), p21(WAF1/CIP1/SDI1) and p27(KIP1) have been extensively studied in cell culture but their role in growth control in tissues is less well understood. In the present experiments we compared the behavior of cell cycle inhibitors in human and bovine adrenocortical cells in culture and following cell transplantation in scid mice. p57 was expressed in the majority of cells in the intact human adrenal cortex. However, double immunofluorescence showed that cells that are in the cell cycle are p57(-) adrenocortical cells, p57 and p27 levels were not affected by inhibition of growth at high cell density, whereas p21 was higher in dividing than growth-inhibited cells. However, p21 was also high in senescent adrenocortical cells. After transplantation of human adrenocortical cells in scid mice, p57 and p27 were observed in most cells in the transplant tissue. Over time the number of p21(+) cells decreased greatly in human adrenocortical cells, but not in bovine adrenocortical cells. This difference correlated with lower levels of cell division (assessed by Ki-67 or incorporation of bromodeoxyuridine) in the human cells in transplant tissues in comparison to bovine cells. The differences between human and bovine cells were observed both when cells were transplanted beneath the kidney capsule and when cells were injected subcutaneously in collagen gel. We conclude that the behavior of p57, but not p21, is consistent with a role as a physiological mediator of proliferative quiescence in the adrenal cortex. The high level of p21 in dividing adrenocortical cells in culture, and in bovine adrenocortical cells in transplant tissues, may be a response to conflicting positive and negative growth influences. Cells may enter the cell cycle under the influence of a strong positive mitogenic signal, but coexisting negative growth stimuli trigger a p21-dependent block to further progression through the cell cycle. This model suggests that bovine adrenocortical cells respond to positive growth stimuli in transplant tissues but human cells lack this response.

Transplantation of normal and genetically modified adrenocortical cells

Cell transplantation techniques have been applied to the study of the biology of the adrenal cortex and to adrenocortical cell proliferation, differentiation, and senescence. Primary bovine adrenocortical cells, primary human adrenocortical cells and genetically modified bovine adrenocortical cells have been transplanted. Successful methods include transplantation of cells beneath the kidney capsule and several subcutaneous cell transplantation procedures. In successful transplants the cells form a functional vascularized tissue structure that allows the host animals to survive adrenalectomy. We show here that subcutaneous cell transplantation does not depend on embedding cells in collagen gel before introduction into the host animal. Subcutaneous transplants secrete both cortisol and aldosterone. However, the variability of plasma aldosterone levels indicates that the factors that determine glomerulosa-type and fasciculata-type cell function in transplant tissues are not well understood.

Cutaneous window for in vivo observations of organs and angiogenesis

BACKGROUND AND OBJECTIVE

The continuous observation in experimental animals of internal organs and processes, such as wound healing and angiogenesis, has been achieved using a variety of transparent windows and chambers. Our objective was to develop procedures for these observations using disposable material for the window and simple surgical techniques.

METHODS

For observation of wound healing in the mouse kidney, the kidney was externalized and a wedge was excised. An oval window of polyvinyl chloride film was sutured in place in the skin over the wound. The progress of healing of the wound was observed through the window over 10 days. For observation of angiogenesis, adrenocortical cells were transplanted beneath fascia and muscle and a window was sewn into the skin above the site of transplantation.

RESULTS

Clear observations could be made using these cutaneous windows over the period of the experiments. Healing of a wound in the kidney was photographed and measured. The growth of new blood vessels over the site of adrenocortical cell transplantation was observed.

CONCLUSIONS

Continuous in vivo observations of organs such as the kidney and processes such as angiogenesis can be made in experimental animals using this simple technique.