This publication by P. Gilbert et al.was summarized by Renee Cosme, with edits by Tom Ben Arye. The original paper can be accessed here.
Extracted from either a mammal’s inner mass cells (i.e. blastocysts) and/or organ tissues, stem cells possess regenerative abilities; That is, they are capable of making copies of themselves via cellular division (mitosis). Previous studies have shown that many stem cells such as muscle stem cells (MuSCs) can keep the ability to multiply even after they are transplanted into a body. However, this ability is usually lost during in-vitro cell culture which fails to properly mimic the muscle environment (aka niche). Maintaining a stem cell’s niche in vitro is important to ensure that biophysical/biochemical properties (i.e. matrix rigidity) that regulate stem cell division are maintained.
In this study, Glibert et al. (2010) tested the efficiency of their bioengineered cell culture substrate for MuSC regeneration, comprised of a thin polyethylene glycol (PEG) hydrogel (a polymer web that stores water) crosslinked with laminin (a protein found in MuSC niche). The research team developed several cell culture substrates that possessed different elasticities depending on the PEG concentration.
The authors observed that MuSCs plated on a surface that possesses a similar elasticity (~12 kilopascals) to muscle maintain their ability to multiply, even when they are transplanted into mice subjects. The study demonstrates the feasibility of producing MuSCs in vitro. Although the applicability of this study to cell-based therapies involving muscle-related illnesses was briefly described, it is also relevant to cultured meat research.
A lineage tracking algorithm was developed and was used to track individual cells in a microwell array (sample video). The team observed:
- MuSCs, maintained on ‘soft’ surfaces (~12 kilopascals or kPa), had slower movement (99 μm/hour) compared to MuSCs maintained on the standard ‘stiff’ (~106 kPa) surfaces (120 μm/hour)
- After 1 week, MuSCs maintained on soft surfaces produced twice as many cells compared to MuSCs maintained on stiff surfaces. This was attributed to the rapid cell death rates of cell death on the stiff surface, which offsets the cell division; Figure 1G.
- After 1 week, MuSCs maintained on the soft surface produce one-third more cells that express myogenin compared to MuSCs maintained on the stiff surface. Myogenin is a myogenic transcription factor that is present in differentiated MuSCs and is required for myogenesis (muscle generation).
When transplanted into immunodeficient mice, the fluorescent labeled MuSCs that were cultured on soft surface demonstrated the ability to retain their regeneration and could also express engraftment capabilities (i.e. the ability to travel into the host’s body and begin producing muscle cells), whereas to the MuSCs that were cultured on the stiff medium did not demonstrate such abilities, producing very low engraftment potential (Figure 2C), which was considered as a ‘loss’ of regenerative ability.
Conclusion & Relevance to Cultured Meat
The authors demonstrated that MuSCs exhibit regenerative and proliferation abilities in vitro as long as they are cultured on surface that maintains a tissue rigidity that mimics the natural niche of muscle. Otherwise, the aforementioned abilities can be ‘lost’ or greatly reduced. Thus, this study demonstrates the viability of culturing MuSCs, which may gradually result in applicability towards cell-based therapies for muscle degenerative-illnesses. Additionally, this study is applicable to the topic of cultured meat.
Although we’ve reached several milestones related to cultured meat, there are still important issues to tackle regarding its research and development. Cultured meat is currently synthesized via extraction of myosatellite cells (from a cow’s neck) and are cultured in vitro to ultimately produce muscle fibres called myotubes. Although we’ve achieved its synthesis, many still argue that cultured meat is an ‘okay’ tasting product, and needs to be improved for mass public appeal, in terms of its taste, texture, and appearance. Therefore, this implies that cultured meat needs to simulate conventional meat products as much as possible. Studies like Gilbert et al. (2010) provide insight regarding how muscle cells can efficiently be cultured in vitro.
The following resources include links that feature supplementary information from the article and articles that were used for this summary.