STATus and Context within the Mammalian Nervous System.

Effective manipulation of human disease processes may be achieved by understanding transcriptional, posttranscriptional and epigenetic events that orchestrate cellular events. The levels of activation of specific molecules, spatial distribution and concentrations of relevant networks of signaling molecules along with the receptiveness of the chromatin to these signals are some of the parameters which dictate context. Effects elicited by the transcription factor signal transducers and activator of transcription 3 (Stat3) are discussed with respect to the context within which Stat3-mediated effects are elicited within the developing and adult mammalian nervous system. Stat3 signals are pivotal to the proliferation and differentiation of neural stem cells. They also participate in neuronal regeneration and cancers of the nervous system. An analysis of the context in which Stat3 activation occurs in these processes provides a potential predictive paradigm with which novel methods for intervention may be designed.

BMPs signal alternately through a SMAD or FRAP-STAT pathway to regulate fate choice in CNS stem cells.

The ability of stem cells to generate distinct fates is critical for the generation of cellular diversity during development. Central nervous system (CNS) stem cells respond to bone morphogenetic protein (BMP) 4 by differentiating into a wide variety of dorsal CNS and neural crest cell types. We show that distinct mechanisms are responsible for the generation of two of these cell types, smooth muscle and glia. Smooth muscle differentiation requires BMP-mediated Smad1/5/8 activation and predominates where local cell density is low. In contrast, glial differentiation predominates at high local densities in response to BMP4 and is specifically blocked by a dominant-negative mutant Stat3. Upon BMP4 treatment, the serine-threonine kinase FKBP12/rapamycin-associated protein (FRAP), mammalian target of rapamycin (mTOR), associates with Stat3 and facilitates STAT activation. Inhibition of FRAP prevents STAT activation and glial differentiation. Thus, glial differentiation by BMP4 occurs by a novel pathway mediated by FRAP and STAT proteins. These results suggest that a single ligand can regulate cell fate by activating distinct cytoplasmic signals.

Neural stem cells and their manipulation.

Extracellular signals dictate the biological processes of neural stem cells (NSCs) both in vivo and in vitro. The intracellular response elicited by these signals is dependent on the context in which the signal is received, which in turn is decided by previous and concurrent signals impinging on the cell. A synthesis of signaling pathways that control proliferation, survival, and differentiation of NSCs in vivo and in vitro will lead to a better understanding of their biology, and will also permit more precise and reproducible manipulation of these cells to particular end points. In this review we summarize the known signals that cause proliferation, survival, and differentiation in mammalian NSCs.

Establishment of a Brazilian line of human embryonic stem cells in defined medium: implications for cell therapy in an ethnically diverse population.

Pluripotent human embryonic stem (hES) cells are an important experimental tool for basic and applied research, and a potential source of different tissues for transplantation. However, one important challenge for the clinical use of these cells is the issue of immunocompatibility, which may be dealt with by the establishment of hES cell banks to attend different populations. Here we describe the derivation and characterization of a line of hES cells from the Brazilian population, named BR-1, in commercial defined medium. In contrast to the other hES cell lines established in defined medium, BR-1 maintained a stable normal karyotype as determined by genomic array analysis after 6 months in continuous culture (passage 29). To our knowledge, this is the first reported line of hES cells derived in South America. We have determined its genomic ancestry and compared the HLA-profile of BR-1 and another 22 hES cell lines established elsewhere with those of the Brazilian population, finding they would match only 0.011% of those individuals. Our results highlight the challenges involved in hES cell banking for populations with a high degree of ethnic admixture.

A novel composition for the culture of human adipose stem cells which includes complement C3.

Adipose tissue is an easily accessible and abundant source of stem cells. Adipose stem cells (ASCs) are currently being researched as treatment options for repair and regeneration of damaged tissues. The standard culture conditions used for expansion of ASCs contain fetal bovine serum (FBS) which is undefined, could transmit known and unknown adventitious agents, and may cause adverse immune reactions. We have described a novel culture condition which excludes the use of FBS and characterised the resulting culture. Human ASCs were cultured in the novel culture medium, which included complement protein C3. These cultures, called C-ASCs, were compared with ASCs cultured in medium supplemented with FBS. Analysis of ASCs for surface marker profile, proliferation characteristics and differentiation potential indicated that the C-ASCs were similar to ASCs cultured in medium containing FBS. Using a specific inhibitor, we show that C3 is required for the survival of C-ASCs. This novel composition lends itself to being developed into a defined condition for the routine culture of ASCs for basic and clinical applications.

Targeting cancer stem cells in cancer prevention and therapy.

The cancer stem cell hypothesis is an attractive framework within which one may think about cancer initiation, recurrence, and metastasis, and methods to devise treatment strategies for cancers. Although all cancers do not appear to sustain themselves with cancer stem cells, but also through a dominant cell population, creating strategies for cancer treatment which include cancer stem cells as targets seems reasonable. In this perspective we discuss possible strategies for controlling the viability and tumorigenecity of cancer stem cells, and extend our discussion to strategies approaching the prevention of cancer.

Stem cells as in vitro models of disease.

Although the use of stem cells in cell-replacement therapies by transplantation is obvious, another equally important and interesting application of stem cells is to use them in disease modeling. Disease models serve as a platform to dissect the biochemical mechanisms of normal phenotypes and the processes which go awry during disease conditions. Particularly in complex, multigenic diseases, molecular studies lead to a greater understanding of the disease, and perhaps more targeted approaches for therapies. Stem cells provide an ideal in vitro system in which to study events related to development at the molecular and cellular level. Neural stem cells have been used as excellent models to study the mechanisms of differentiation of cells of the central nervous system. These studies may be particularly relevant to diseases of complex etiology such as psychiatric illnesses, neurodegenerative diseases and brain tumors. Stem cell-derived systems are also being developed to create models of cardiovascular disease. The application of stem cells to the study of cardiovascular illnesses, and vertebrate heart development, is discussed.