A new scaffold material based on a biocompatible silk-alginate hydrogel, which can be made soft or stiff, could provide the just right environment to culture stem cells for regenerative medicine, say researchers.

Stem cells could provide powerful new treatments for intractable autoimmune diseases, cancer, and other conditions. But the use of stem cells in the clinic requires a robust and reliable culture system that mimics the natural microenvironment of the cell. This microenvironment provides crucial direction to the function and viability of stem cells but is tricky to recreate artificially.

The complex make-up of the microenvironment, which includes a network of proteins like collagen or elastins forming an extracellular matrix (ECM), decides the fate of stem cells through a number of different, complementary mechanisms. For example, the stiffness of the matrix, determined by the orientation and elasticity of the fibers making up the ECM, as well as its fluid handling properties, the presence of signaling molecules and the creation of cytokine gradients all have a profound effect on the growing stem cells.

The new silk-alginate biocomposite developed by researchers at Stanford University and Queens University in Canada could provide a simple solution to tackle these complex problems. The hydrogel is formed from a mixture of alginate and silk in solution, which rapidly gels when immersed in CaCl2 [Ziv, et al., Biomaterials 35 (2014) 3736-3743, http://dx.doi.org/10.1016/j.biomaterials.2014.01.029%5D. But crucially, the stable hydrogel can be made soft and flexible or stiff by controlling the silk-alginate ratio and the concentration of crosslinking ions. Varying the silk-alginate ratio during fabrication changes the elasticity of the hydrogel, which can determine the yield of a particular differentiation path. The elasticity can be further fine-tuned in vitro by varying the CaCl2 concentration. Being able to modify the stiffness of the scaffold material to such a degree gives researchers a powerful means of guiding stem cell survival and differentiation.

The ability to change the elasticity [of the silk-alginate hydrogel] helps mimic the natural process that is happening in the stem cell niche and improves the stem cell commitment into desired differentiation paths, explains first author Keren Ziv, of the Molecular Imaging Program at Stanford.

Using the protein laminin to enhance cell adhesion and promote cell growth, the researchers cultured mouse embryonic stem cells in the new scaffold material and transplanted samples into live mice. The silk-alginate hydrogel appears to be better at maintaining the survival of stem cells once transplanted than the best current alternative, matrigel.

But there is a long way to go until the new scaffold material could be used in the clinic for stem cell applications, cautions Ziv. Ideally, such applications would require the injection of the hydrogel in liquid form followed by gelation but this is currently unfeasible in vivo. The long-term stability of the hydrogel also needs to be scrutinized, along with its effect on other cell types. These issues are tractable, however, say the researchers, and are the focus of on-going efforts.

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Adjustable scaffold tunes stem cell growth

March 24, 2014

Image Caption: Muscle cells are stained green in this micrograph of cells grown from embryonic stem cells in the lab of Masatoshi Suzuki at the University of Wisconsin -- Madison. Cell nuclei are stained blue; the muscle fibers contain multiple nuclei. Nuclei outside the green fibers are from non-muscle cells. Suzuki has developed a new method of growing stem cells into muscle cells that could be more suitable for treating disease. Suzuki hopes to experiment next with animals that model muscular dystrophy and amyotrophic lateral sclerosis. Credit: Masatoshi Suzuki

David Tenenbaum, University of Wisconsin-Madison

As stem cells continue their gradual transition from the lab to the clinic, a research group at the University of Wisconsin-Madison has discovered a new way to make large concentrations of skeletal muscle cells and muscle progenitors from human stem cells.

The new method, described in the journal Stem Cells Translational Medicine, could be used to generate large numbers of muscle cells and muscle progenitors directly from human pluripotent stem cells. These stem cells, such as embryonic (ES) or induced pluripotent stem (iPS) cells, can be made into virtually any adult cell in the body.

Adapting a method previously used to make brain cells, Masatoshi Suzuki, an assistant professor of comparative biosciences in the School of Veterinary Medicine, has directed those universal stem cells to become both adult muscle cells and muscle progenitors.

Importantly, the new technique grows the pluripotent stem cells as floating spheres in high concentrations of two growth factors, fibroblast growth factor-2 and epidermal growth factor. These growth factors urge the stem cells to become muscle cells.

Researchers have been looking for an easy way to efficiently differentiate stem cells into muscle cells that would be allowable in the clinic, says Suzuki. The novelty of this technique is that it generates a larger number of muscle stem cells without using genetic modification, which is required by existing methods for making muscle cells.

Many other protocols have been used to enhance the number of cells that go to a muscle fate, says co-author Jonathan Van Dyke, a post-doctoral fellow in Suzukis laboratory. But whats exciting about the new protocol is that we avoid some techniques that would prohibit clinical applications. We think this new method has great promise for alleviating human suffering.

Last year, Suzuki demonstrated that transplants of another type of human stem cells somewhat improved survival and muscle function in rats that model amyotrophic lateral sclerosis (ALS). Also known as Lou Gehrigs disease, ALS destroys nerves and causes a loss of muscle control. The muscle progenitors generated with Suzukis new method could potentially play a similar role but with enhanced effect.

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New Method Makes Muscle Cells From Human Stem Cells

As stem cells continue their gradual transition from the lab to the clinic, a research group at the University of Wisconsin-Madison has discovered a new way to make large concentrations of skeletal muscle cells and muscle progenitors from human stem cells.

The new method, described in the journal Stem Cells Translational Medicine, could be used to generate large numbers of muscle cells and muscle progenitors directly from human pluripotent stem cells. These stem cells, such as embryonic (ES) or induced pluripotent stem (iPS) cells, can be made into virtually any adult cell in the body.

Adapting a method previously used to make brain cells, Masatoshi Suzuki, an assistant professor of comparative biosciences in the School of Veterinary Medicine, has directed those universal stem cells to become both adult muscle cells and muscle progenitors.

Importantly, the new technique grows the pluripotent stem cells as floating spheres in high concentrations of two growth factors, fibroblast growth factor-2 and epidermal growth factor. These growth factors "urge" the stem cells to become muscle cells.

"Researchers have been looking for an easy way to efficiently differentiate stem cells into muscle cells that would be allowable in the clinic," says Suzuki. The novelty of this technique is that it generates a larger number of muscle stem cells without using genetic modification, which is required by existing methods for making muscle cells.

"Many other protocols have been used to enhance the number of cells that go to a muscle fate," says co-author Jonathan Van Dyke, a post-doctoral fellow in Suzukis laboratory. "But what's exciting about the new protocol is that we avoid some techniques that would prohibit clinical applications. We think this new method has great promise for alleviating human suffering."

Last year, Suzuki demonstrated that transplants of another type of human stem cells somewhat improved survival and muscle function in rats that model amyotrophic lateral sclerosis (ALS). Also known as Lou Gehrig's disease, ALS destroys nerves and causes a loss of muscle control. The muscle progenitors generated with Suzukis new method could potentially play a similar role but with enhanced effect.

The new technique can also be used to grow muscle cells from iPS cells from patients with neuromuscular diseases like ALS, spinal muscular atrophy and muscular dystrophy. Thus, the technique could produce adult muscle cells in a dish that carry genetic diseases. These cells could then be used as a tool for studying these diseases and screening potential drug compounds, says Suzuki. "Our protocol can work in multiple ways and so we hope to provide a resource for people who are exploring specific neuromuscular diseases in the laboratory."

The new protocol incorporates a number of advantages. First, the cells are grown in defined supplements without animal products such as bovine serum, enhancing the clinical safety for the muscle stem cells. Second, when grown as spheres, the cells grow faster than with previous techniques. Third, 40 to 60 percent of the cells grown using the process are either muscle cells or muscle progenitors, a high proportion compared to traditional non-genetic techniques of generating muscle cells from human ES and iPS cells.

Suzuki and his group hope that by further manipulating the chemical environment of the spheres of stem cells, they may increase that number, further easing the path toward human treatment.

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New way to make muscle cells from human stem cells

Researchers at the University of Wisconsin-Madison discovered a new method for generating muscle cells from stem cells, according to a Friday news release.

The new procedure is unique in its ability to yield large quantities of muscle cells, as well as muscle progenitors, directly from pluripotent stem cells without the use of genetic modification, according to the release. Pluripotent stem cells have yet to undergo differentiation and can develop effectively into any adult cell in the body.

Masatoshi Suzuki, UW-Madison assistant professor of comparative biosciences and co-author of the research project, pioneered the discovery. His method calls for the placement of stem cells in high concentrations of growth factors that influence growth and cell differentiation.

Last year, Suzuki showed that transplanting another type of human stem cell to rats suffering from Lou Gehrigs disease improved longevity and muscle function. He said in the release muscle progenitors, which serve as prototype for the formation of muscles, could have a similar but heightened effect.

While various methods have been used to increase the number of stem cells that become muscles, Suzukis co-author Jonathan Van Dyke explained in the release these often cannot be worked within a clinical setting.

What's exciting about the new protocol is that we avoid some techniques that would prohibit clinical applications, Van Dyke said in the release. We think this new method has great promise for alleviating human suffering.

Additionally, the new technique could advance disease and drug research by allowing cells infected with certain genetic diseases to be grown in a dish.

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UW-Madison researchers discover new way to turn stem cells into muscle cells