A new mouse model for myotonic dystrophy – the most common form of adult-onset muscular dystrophy – helped Baylor College of Medicine researchers show that levels of CUGBP1, a protein that binds and controls the activity of the genetic material RNA, increase early in affected cells of the animals with the disease. This means CUGBP1 plays a key role in the disorder.
?We wanted to find out if this is a primary event associated with the disorder or if it is a secondary response to tissue injury,? said Dr. Thomas A. Cooper, professor of pathology at BCM and senior author of the report that appears today in the Journal of Clinical Investigation.
Myotonic dystrophy type 1 is associated with hundreds and even thousands of repeats of the nucleotides CTG within a gene called DM kinase protein gene or DMPK. [Cytosine (C), thymine (T), guanine (G) and adenine (A) are all nucleotides that make up DNA. C, G, A, and uracil (U) make up RNA.] In the mouse that Cooper and his colleagues specially bred, the repeats in the gene can be turned on in heart, skeletal muscle and brain tissue at any age.
The researchers found that within three hours of turning on the repeats, another RNA-binding protein called muscleblind like (MBNL) began to bind the genetic material in the nucleus of the cell. That mean the RNA was trapped in the nucleus and unable to take the genetic message about which proteins to make to the protein manufacturing areas in the cytoplasm of the cell.
Within six hours, levels of CUGBP1 begin to increase. The increased in CUGBP1 then alters how a number of other genes are regulated. At that point, the cascade of events that affect the heart starts.
?The heart doesn?t even ?know? that it is sick yet,? said Cooper. This finding shows that the increase levels of CUGBP1 is an early event and plays an important role in the development of the disease.
Others who took part in this research include Drs. Guey-Shin Wang, Debra L. Kearney, Mariella De Biasi and George Taffet, all of BCM. Funding for this research came from the National Institutes of Health and the Muscular Dystrophy Association.Note to reporters:The article will be available at http://www.jci.org/ when the embargo lifts.