Contracting Human Muscle Tissue Created

On January 9, 2015 eLife published a paper “Bioengineered human myobundles mimic clinical responses of skeletal muscle to drugs” about creating contracting human muscle tissue in a dish for the first time. We have asked one of the authors of this research, Prof. Nenad Bursac from Duke University, to comment on this work.

The Study

We are the first group that succesfully generated contracting muscle microtissues using human muscle cells. We achieved that by carefully optimizing culture conditions including methods to expand and then to culture cells in a three-dimensional hydrogel protein matrix. By doing so, we made the first human skeletla muscle microtissue model that in response to electrical stimulation generates classical muscle contractile responses (twitch and tetanus). We have also shown that these miniature engineered muscles (that we call “myobundles”) contract in response to acetylcholine, a chemical that is naturally secreted by neurons in our body to activate muscles and induce motion, for example. We demonstrated reproducibility and robustness of the approach by generating functional myobundles with similar properties from 10 independent donor muscle samples. We further went to show that myobundles have intact signaling characteristic of native muscle and respond to a diverse set of drugs in similar fashion to how human muscles do in clinics.

This progress finally enables researchers in the field to study human muscle physiology and drug responses in a dish rather than only being able to look in biochemical outputs (gene and protein expression). As we can get more than 1,000 myobundles from a single small needle muscle biopsy we now have a platform to study beneficial (or toxic) effects of multiple drugs on the muscle from the same patient, opening doors to novel drug development studies and design of personalized therapeutics. This is exactly what “precision medicine” is all about. For example, with clinicians from Duke University we have started obtaining muscle biopsies from patients with a specific muscle disease. We are generating myobundles from these biopsies and are now working to validate that the results seen in clinics are the same to those we see in the lab – importantly, on a patient-per-patient basis.

Background

The field of skeletal muscle tissue engineering has almost 20 years of history. Over the last 2 decades, researchers have done large number of experiments to establish methods by which isolated muscle cells from rodent (rat and mouse) muscles can be coaxed in 3-dimensional cell cultures to obtain contracting skeletal muscle microtissues. These methodologies to create muscle microtissues included embedding of cells inside protein hydrogels (made of collagen or fibrinogen) or porous polymer meshes. Few trials to generate human contractile muscle using cells isolated from human muscle biopsies have failed. My group has had a long-standing interest in engineering of functional heart muscle, which beside skeletal muscle is another striated muscle in our body. About 10 years ago we have started working on skeletal muscle engineering and have first focused our efforts to improve contractile function of rodent muscle microtissues by systematically optimizing cell isolation and culture techniques. That enabled us to eventually create rat muscle microtissues with contractile strength that was more than 10-fold higher than previously achieved. These rat muscle microtissues also contain a functional pool of muscle stem cells called satelite cells which, similar to native muscle, enable muscle microtissue to self-regenerate in response to injury. More than 2 years ago, based on the success with rat cells, we started to apply similar methods to human cells isolated from muscle biopsies. It took us about year to optimize and validate the protocol that finally worked. There is a number of details how this protocol differs from those that were previously tried by others without success, of which purity of muscle cells, their density inside hydrogel, and hydrogel type and its protein concentration, we believe, played the most important roles in obtaining electrically responsive contractile human muscle.

Future Direction

Future research in this field will be geared towards modeling of human muscle disease in a dish and combining multiple human microtissue systems (e.g. muscle, heart, liver, gut, fat, etc) into a single platform, called “body-on-a-chip” that would hopefully be more predictive then animals are when testing the drug safety and efficacy. As I previously mentioned, such platforms will be made using cells from a single patient, thus allowing precision medicine applications and drug treatments tailored to single individuals (i.e., “you-on-a-chip” application) rather than average populations, as has been the long-standing practice.