Medical researchers at the University of Minnesota’s Lillehei Heart Institute may have established the groundwork for a viable stem cell therapy to treat an otherwise debilitating and pernicious disease, Duchenne Muscular Dystrophy (DMD).
Duchenne muscular dystrophy (DMD) is a form of muscular dystrophy associated with the rapid weakening of the musculoskeletal system. Over time mobility is hampered and the condition creates an increased onset of heart disease by the age of 20.
Symptoms can appear as early as infancy, or before the age of 6. They include fatigue, intellectual disabilities and difficulties, limited motor skills, weakness —beginning in the legs and arms — and over time losing the ability to walk by the age of 12 as the deterioration of muscle worsens.
DMD is caused by a defective gene which fails to code for the protein in muscles (dystrophin). Although classified as a hereditary disorder, DMD can manifest in people without a family history.
One out of every 3,600 male infants can be affected. Females can only be carriers. A son of a carrier mother has a 50 percent chance of developing the disease, and daughters the same odds of becoming carriers themselves.
The report, published in Nature Communications, explained how researchers managed to reprogram cells, generating stem cells capable of genetically repairing and stimulating muscle regeneration in a mouse model.
If successfully applied to humans, the gene technology could revert and repair the loss of the overall vital musculature in DMD sufferers.
The mice used in the study presented with mutations in the dystrophin and utrophin genes, causing them to develop muscular dystrophy.
In order to achieve the most optimal, effecting therapy possible, scientists first reprogrammed skin cells from the mice into pluripotent cells. In cellular biology, pluripotency refers to a stem cell that has the potential to differentiate into any of the three germ layers: endoderm, mesoderm, or ectoderm. In this case the focus would be on the mesoderm (muscle).
Second, a genetic correction tool developed by the University of Minnesota called the “Sleeping Beauty Transposon” was deployed. A transposon is a sequence of DNA that can move to new positions within the genome of a single cell. Researchers used Sleeping Beauty to deliver a gene called “micro-utrophin” into the stem cells as they attempted to differentiate, allowing the gene to jump into the sequence and be coded.
Micro-utrophin was used in lieu of supplementing dystrophin as the body’s immune system does not detect utrophin as an invader. Utrophin is abundantly present in DMD sufferers. DMD patients lack dystrophin, therefore adding it can provoke a negative immune response. Utrophin mimics dystrophin, as both can support muscle fiber strength and prevent muscle fiber injury.
The final stage utilized a method of producing skeletal muscle stem cells originally developed by Rita Perlingeiro PhD, using a protein called Pax3. The Pax3 protein impulses the pluripotent cells to become muscle stem cells, and allows them to proliferate exponentially.
Combined, all three stages created muscle-generating stem cells that would not be rejected by the body’s immune system, as cells must be histocompatible. Histocompatibility is the property of having the same, or mostly the same, genetic alleles which are compatible or acceptable to one another. If cells are not seen as compatible or “friendly,” the immune system responds and attacks.
The mouse model provides a future feasibility for combining stem cell technology and genetic correction into potential autologous (transfusion) cell-based therapies for human muscular dystrophy and other similar conditions.
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