Scientists have isolated human muscle stem cells and shown that the cells could repair damaged muscles, paving the way for potential treatments for severe muscle injury, paralysis or muscular dystrophy.

"We’ve shown definitively that these are bonafide stem cells that can self-renew, proliferate and respond to injury," said Jason Pomerantz, an assistant professor at University of California, San Francisco.

When muscles are badly damaged, they can lose the native populations of stem cells that are needed to heal.

This has posed a major roadblock for treating patients crippled by muscle injury and paralysis, particularly in the critical small muscles of the face, hand and eye, Pomerantz said.

Surgeons have shown remarkable success at restoring nerves in damaged muscles, but if the process takes too long the stem cell pool and capacity for regeneration is lost, these injured muscles fail to connect to the nerve tissue, causing their power to wither away.

So-called "satellite cells" dot the borders of muscle fibres and – at least in mice – were known to act as stem cells to contribute to muscle growth and repair.

Until now, however, it was not clear whether human satellite cells worked the same way or how to isolate them from human tissue samples and adapt them to help treat patients with muscle damage.

The researchers obtained surgical biopsies of muscles of the head, trunk and leg, and used antibody staining to show that human satellite cells can be identified by their co-expression of the transcription factor PAX7 with surface proteins CD56 and CD29.

This molecular signature enabled the research team to isolate populations of human satellite cells from the patient biopsies and graft them into mice with damaged muscles whose own muscle stem-cell populations had been depleted.

Within five weeks, the human cells successfully integrated into the mouse muscles and divided to produce families of daughter stem cells, replenishing the stem cell niche and repairing the damaged tissue.

This characterisation of human muscle stem cells and the ability to transplant them into injured muscles has wide-ranging implications for patients suffering from muscle paralysis, whose damaged muscles have lost the ability to regenerate.

"This gives us hope that we will be able to extract healthy stem cells from other muscles in the patient’s body and transplant them at the site of injury," Pomerantz said.

The study was published in the journal Stem Cell Reports.