Cooking with Stem Cells
On August 5, 2013, a “lab-grown,†5-ounce burger patty was taste tested in London, U.K. The patty had been grown from muscle stem cells that were isolated from cows. While this piece of “meat,†which was said to have tasted “close to meat,†represents significant progress in the field of making lab-grown food, the current approach needs to be improved before widespread use is feasible; the patty cost over $330,000 to make (not to mention probably significant culturing time in the lab to generate the 20,000 muscle strands used to make the patty). Luckily, there are many avenues that can be explored to optimize this technology. To understand them, it’s important to first understand the muscle stem cells themselves and how they’re cultured.
Origins of Muscle Stem Cells:
During development, the embryo has three different tissue types that, together with the germ cells, will make up the animal’s entire body. These are called the three germ layers. One of these tissue types, specifically the mesoderm, develops into skeletal muscle cells (along with other cell types, including cardiac muscle, kidney cells, red blood cells, and smooth muscle). Some stem cells that have been isolated from muscle appear to be mesenchymal stem cells. Mesenchymal stem cells (MSCs) got their name because they’re thought to primarily contain progenitors in the mesenchyme, which is a collection of cells mostly derived from mesoderm. (The majority of these cells later make up supportive structures throughout the body, such as bone, cartilage, connective tissue, muscle, adipose tissue, and the lymphatic and hematopoietic systems.) MSCs are typically multipotent, which means they can differentiate, or turn into, multiple different cell types. Specifically, MSCs are usually confirmed to be MSCs by showing that they can differentiate into three different, standard mesenchymal cell types: osteocytes (bone), chondrocytes (cartilage), and adipocytes (fat).
In muscle, there are two main groups of stem cells: satellite cells and muscle-derived stem cells (MDSCs) (Jankowski et al., 2002). Satellite cells were discovered decades ago (Mauro, 1961) and are commonly simply (and perhaps confusingly) referred to as muscle stem cells. It’s thought that these cells can regenerate damaged skeletal muscle and self-renew, but their ability to differentiate is rather limited; they can only make other types of muscle cells. (They’re basically unipotent.) MDSCs, on the other hand, are thought to be a type of multipotent mesenchymal stem cell and possibly a precursor of the satellite cells. But not only can the MDSCs differentiate into mesenchymal cell types, they have been found capable of becoming non-mesenchymal cell types as well. However, when picking the right stem cells to use for making lab-grown meat, the ability to differentiate into many different cell types is, for once, not an appealing trait.
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