Hair cells vital for hearing are cultured in humans
Cochlear cells isolated from human fetuses have the capacity to differentiate to form inner ear cells important for hearing, leading researchers to hope that cell therapies might be possible for patients with hearing impairment.
This is the first identified source of sensory hair cells and associated neurons. Several causes of deafness involve loss of these cell types, and cell therapy would appear to be a good approach to treatment.
The authors isolated the cells from 9- to 10-week-old fetal cochlea and cultured them in vitro for up to a year, with the growth rate comparable to adult stem cell populations, around 30 population doublings. The cultured cells showed the same electrophysiological characteristics but not the ‘bundle‘ organization of hair cells in vivo.
“The results are the first in vitro renewable stem cell system derived from the human auditory organ and have the potential for a variety of applications, such as studying the development of human cochlear neurons and hair cells, as models for drug screening and helping to develop cell-based therapies for deafness,” commented the authors, who go on to state: “Although considerable information has been obtained about the embryology of the ear using animal models, the lack of a human system has impaired the validation of such information.”
Source: Chen W, Johnson SL, Marcotti W, Andrews PW, Moore HD, Rivolta MN: Human fetal auditory stem cells (hFASCs) can be expanded in vitro and differentiate into functional auditory neurons and hair cell-like cells (p N/A). Stem Cells DOI: 10.1002/stem.62 (2009) (Epub ahead of print).
Stem cells can regenerate the stroke-damaged rat brain
Laying the groundwork for future studies in treating the stroke-damaged brain, researchers from King‘s College London, UK, have proved that stem cells can replace areas of brain tissue destroyed by stroke in a rat model.
Guided by MRI, the researchers injected neural stem cells along with a biodegradable polymer into the damaged areas, in order to support the cells and prevent them from migrating. Previous studies have injected the cells alone, which tend to migrate to the healthy tissue and fail to fill the void left by damaged tissue.
Study author Michael Modo explained “We would expect to see a much better improvement in the outcome after a stroke if we can fully replace the lost brain tissue, and that is what we have been able to do with our technique.”
“This works really well because the stem cell-loaded PLGA particles can be injected through a very fine needle and then adopt the precise shape of the cavity. In this process the cells fill the cavity and can make connections with other cells, which helps to establish the tissue”, Dr Modo continued. “Over a few days we can see cells migrating along the scaffold particles and forming a primitive brain tissue that interacts with the host brain. Gradually the particles biodegrade, leaving more gaps and conduits for tissue, fibres and blood vessels to move into.”
The team plan future studies in which the cells will be injected not only with the polymer, but also with VEGF, with the aim of encouraging angiogenesis in the damaged areas.
Biotechnology and Biological Sciences Research Council Chief Executive Douglas Krell commented: “Stroke is a leading cause of disability in industrialized countries. It is reassuring to know that the technology for treating stroke by repairing brain damage is getting ever closer to translation into the clinic. This crucial groundwork by Dr Modo and his colleagues will surely be a solid foundation of basic research for much better treatments in the future.”
Source: Bible E, Chau DY, Alexander MR, Price J, Shakesheff KM, Modo M: The support of neural stem cells transplanted into stroke-induced brain cavities by PLGA particles. Biomaterials 30(16), 2985–2994 (2009).
A case of mistaken identity: “retinal stem cells“ may not be what they seem
The goal of isolating retinal stem cells may not have been achieved after all, according to new research conducted at St Jude Children‘s Research Hospital (TN, USA), which suggests that the previously identified ‘stem cells‘ are in fact normal epithelial cells.
The cells, isolated from ciliary epithelial cells lining the eye, were first identified as retinal stem cells in 2000, and the news was met with enthusiasm from researchers hopeful of developing cell therapies for blindness. The cells were thought to be stem cells as they form self-replicating spheres in culture and cultured cells showed gene markers of adult retinal cells.
However, the new study, led by Michael Dyer, reveals strong evidence that the cells are normal adult cells. “The first clue that these cells were not stem cells was that they were pigmented,” Dr Dyer explained. “Neural stem cells, in general, and retinal progenitor cells, in particular, are not pigmented. Nevertheless, the previous finding was met with a tremendous amount of enthusiasm because of the promise of introducing these cells into the eye to regenerate photoreceptors lost to blindness.”
Microscopy showed the sphere-forming cells to have many features of ciliary epithelial cells and few features in common with stem or progenitor cells. Culturing the cells in stem-cell medium caused them to express several factors associated with stem cells, but they remain adult cells morphologically.
The authors believe that hopes for cell therapy to treat blindness now lie with reprogramming induced pluripotent stem cells: “This approach would solve many problems of developing cell-based therapy for blindness,” Dyer commented. “First, these cells are immortal, so they can be grown indefinitely to produce large amounts of cells for treatment. And secondly, they would be immunologically matched to the patient, so there would be no danger of rejection. And thanks to some excellent research during the past 15 years, we know a lot about how to reprogram such stem cells to make them into photoreceptors.”
Source: Cicero SA, Johnson D, Reyntjens S et al.: Cells previously identified as retinal stem cells are pigmented ciliary epithelial cells. Proc. Natl Acad. Sci. USA (2009) (Epub ahead of print).
Microcirculatory beds used as bioscaffolds for tissue engineering
In a rat model, researchers from Stanford University (CA, USA) have successfully used autologous microcirculatory beds as a means of culturing adult stem cells outside the body. The beds were removed from the rat and attached to a bioreactor, to form a “life support system for tissue”. The bioreactor provided oxygen and nutrients, keeping the tissue alive and allowing successful transplantation into a genetically identical animal for up to 24 h. Stem cells could be added to the bioreactor, and migrated to colonize the tissue.
The researchers hope that the tissue could be seeded with cells producing insulin or blood clotting factors, or even differentiated to form a replacement organ. “This is an incredible opportunity to bulk-deliver cells that don‘t just die,” commented lead author Geoffrey Gurtner. “Conceivably, we could use this technique at least to supply the synthetic function of an organ by stimulating the cells to form insulin-producing pancreas cells or albumin-producing liver cells.”
Source: Chang EI, Bonillas RG, El-ftesi S et al.: Tissue engineering using autologous microcirculatory beds as vascularized bioscaffolds. FASEB J. 23(3), 906–915 (2009).
A step closer to the clinic for iPS cells?
New methods for creating pluripotent stem cells without disrupting the genome have opened the possibility of using the cells for clinical applications.
Three recent studies have revealed novel methods of creating pluripotent stem cells from adult cells without the viral integration which has, until now, made induced pluripotent stem (iPS)-derived cells unsuitable for therapeutic applications.
To date, iPSCs have been produced by integrating pluripotency factors into the cell genome by viral transduction. The viral integration is random and can cause damage to the genome and consequent tumor formation in vivo.
Two of the studies used methods that involved insertion followed by removal of genes from the host cell genome, while a third method used a plasmid vector, avoiding the need for integration into the host genome altogether.
Andras Nagy and Keisuke Kaji published two complimentary papers in Nature, describing a method for integrating the relevant factors by electroporation, followed by removal. The genes were integrated using the piggyBac transposon, which can be entirely removed from the genome once the cells have been reprogrammed. In an interview with Regenerative Medicine (pages 351–352), Nagy explained: “The transfection efficiency of the piggyBac transposon is comparable to that achieved by the viral transduction – this caught my eye and I thought we could possibly use this to transfect cells as efficiently as viruses. Much to our surprise, it worked immediately, so we were able to very quickly come out with two publications showing how to induce these cells without viruses.” More importantly, he stated, the factors could be removed without leaving any trace.
A study by Whitehead Institute researchers kept the viral integration method used previously to induce skin cells from Parkinson‘s disease patients to become pluripotent, but removed the transfected elements using the Cre–Lox system. The researchers went on to induce the cells to become dopamine-producing neurons. “Until this point, it was not completely clear that when you take out the reprogramming genes from human cells, the reprogrammed cells would actually maintain the iPS state and be self-perpetuating,” commented Frank Soldner, coauthor of the article.
Just weeks later, a study was published from the lab of one of the pioneers of human embryonic stem cell and iPS cell derivation, James Thomson, using a plasmid-based system to generate iPS cells from newborn foreskin fibroblasts with no integration into the host cell genome. “We believe this is the first time human-induced pluripotent stem cells have been created that are completely free of vector and transgene sequences,” commented Thomson. The plasmid DNA does replicate with the cells, but does so inefficiently, leading to a gradual loss of the plasmid in cell culture and yielding reprogrammed cells with no foreign genetic material, highly desirable from a safety point of view. However, reprogramming rates were low and stable clones were not always formed.
“Given the rapid pace of the field, it won‘t be surprising if there are several alternative methods for producing vector and transgene free cells very soon,” Thomson predicted. “However, it will be essential to determine which of these methods most consistently produces induced pluripotent stem cells with the fewest genetic abnormalities. Any problems would impact research, drug development and possible transplantation therapies.”
Sources: Woltjen K, Michael IP, Mohseni P et al.: piggyBac transposition reprograms fibroblasts to induced pluripotent stem cells. Nature 458(7239), 766–770 (2009); Kaji K, Norrby K, Paca A, Mileikovsky M, Mohseni P, Woltjen K: Virus-free induction of pluripotency and subsequent excision of reprogramming factors. Nature 458(7239), 771–775 (2009); Soldner F, Hockemeyer D, Beard C et al.: Parkinson‘s disease patient-derived induced pluripotent stem cells free of viral reprogramming factors. Cell 136(5), 964–977 (2009); Yu J, Hu K, Smuga-Otto K et al.: Human induced pluripotent stem cells free of vector and transgene sequences. Science (2009) (Epub ahead of print).