Q&A Report: Functional Recovery of the Musculoskeletal System Following Injury – Leveraging the Large Animal Model

Sarah Greising, PhD
Associate Professor
Kinesiology
University of Minnesota

There is not strong data on location of the injury, but it will of course impact the severity of functional loss. I suspect that injuries located at the immediate insertion of the terminal nerve would be more severe than others. Similarly, injuries near the myotendinous junction could also be more impactful, even if the volume lost is similar.

Vascularity and blood flow is one area that our group has not specifically evaluated. That said, it is expected that any approach to support regeneration of muscle fibers would require adequate regeneration of the vascular network.

It is possible that initial loading is exacerbating the over-development of fibrosis, as the muscle needs to support loading for movement. In the model we use to the PT muscle, the duty cycle during standing and ambulation is low, so while the loading or movement after injury could be contributing to fibrosis it is unclear how significant this is to the overall development.

We have not evaluated loading, so I can not say for sure. That said, over the initial recovery period pigs are continually enticed to ambulate by both bout our research staff and the veterinary staff.

The key aspects of our work that are informative to other conditions, like muscular dystrophy, is how to understand limited regeneration of the muscle. For example, understanding mechanisms related to lack of metabolic improves after treatments could provide insight into how to improve metabolism in dystrophic muscle.

To date, we have not evaluated aged animals (rodents or pigs). Dr. Jeffrey Wolchok’s group has done some work with the aged rodents in the context of volumetric muscle loss (VML). For the ability to obtained aged pigs, I don’t have a clear suggestion on this but would warn about the growing size of pig over their aging trajectory.

In our work mitochondrial dysfunction has been evaluated in a number of situations, including permeabilized muscle fibers and in vivo whole body metabolism.

Our work has primarily focused on physiology during development (e.g. PMID: 33782573) or trauma. That said there are other examples of functional assessments using this same platform (see the Aurora library at https://aurorascientific.com/resources/publications/).

The pigs in our studies have all utilized the standard IACUC/USDA space allotment. The animals do have space for ambulation about the housing.

Absolutely, a number of groups have used cellular approaches in isolation or loaded into biomaterials. I like the idea of cells from a younger or developing donor as those should provide additional regenerative potential for recovery and regeneration.

Our findings that provide mechanistic insight into the plasticity of the muscle remaining after VML could support interventions in the aged population as well.

To date, we have worked with clinical colleges primarily in orthopedics and transplant surgery to share results. We also commonly interface with military physicians-scientists to share our work. As we continue to progress this work presenting at more clinical organization (e.g. Orthopedic Trauma Association) will continue to be imperative.

At this point we are needing to evaluate the function of individual NMJs (patch clamping for example) to understand if release kinetics or something similar is not adapting along with innervation. It could also be possible there is an over-activity of the muscle activity that is impacting function as recovery occurs.

In collaborative work, we have evaluated sequencing profiles of the muscle remaining after injury and overwhelmingly there is an excessive increase in many myogenic signaling pathways. Significant work in this area is being done in the lab of Dr. Carlos Aguliar.

Yes, to date we have treated at the time of injury or the immediate day after. I think our data across rodent and large animals supports that starting treatment any time over the first two weeks could be beneficial. These delayed approaches are a current focus for our work.

At this point it is possible but not well evaluated in our group specifically. In a recent systematic-review and meta-analysis (PMID: 31578930) of various treatments for VML a pairwise sub-group analysis did not indicate a difference in treatment efficacy to promote functional recovery between male and female animals (mice, rats, pigs).

The cellular therapies we have used are an endogenous minced muscle graft, to date. I know that immunohistochemistry can be challenging in the pig, please do reach out directly (grei0064@umn.edu) and I would be happy to talk through some options we have used recently.

Our work would suggest that first improving metabolic function is necessary, then (or in parallel) mechanical loading is needed to drive hypertrophic improvements.