Matrix Metalloproteinase-9 and its Role in Skeletal Muscle Tissue.

 During my time as an undergraduate research assistant, I was responsible for creating histology slides stained through immunohistochemistry  to monitor the activity of matrix metalloproteinase 9 (MMP-9) in mouse skeletal muscle tissue. Immunohistochemistry is the technique in which fluorescent dyes are created to “tag” specific proteins of interest and reflect a fluorescent pigment when exposed under the black light of a microscope. Matrix metalloproteinases are a group of enzymes that are often involved in the degradation of the extracellular matrix in normal physiological processes such as embryonic development, wound healing, and bone development. As these processes typically require the deconstruction of damaged or developing tissue before continuing cellular development can occur, matrix metalloproteinases aim to degrade extracellular proteins such as collagen and gelatin to allow for these development processes to occur.

Through my work under guide of Ryan Mehan, the graduate student at the time, we noticed that MMP-9 in particular was highly active in mouse skeletal muscle tissue, especially after the mice were exercised for prolonged periods of time. We could tell that this was the case since its upregulation could be visualized by increases in reflective light intensity of the MMP-9-specific dye under the microscope’s black light. This was done after both wildtype and knockout mice null in the MMP-9 gene had gone through controlled exercise bouts and after we created immunohistochemically stained histology slides of the mice’s hindlimb muscles one, three, and  seven days post-exercise.

By comparing the results of wildtype and knockout mice, the research personnel noticed that, through cross-sectional analysis, there were decreases in primary skeletal muscle fiber type (i.e. type I in the soleus, type IIb in the tibialis anterior, and type IId in the gastrocnemius muscle) in exercised mice null in MMP-9. However, oddly enough, Dr. Mehan noticed that the average force generated by the null mice during the exercise trials was not significantly different than that of the wildtype mice; the extracellular concentrations of both collagen and gelatin were not significantly altered between the two control groups either. This may suggest that there are other compensatory mechanism by which the knockout mice’s physiology could overcome any deficits in skeletal muscle maintenance and development.

Mehan, R.S., Grebeck, B.J., Emmons, K., Byrnes, W.C., Allen, D.L. (2011). Matrix metalloproteinase-9 deficiency results in decreased fiber cross-sectional area and alters fiber type distribution in mouse hindlimb skeletal muscle. Cells, Tissues, Organs, 194(6): 510-520. https://www.ncbi.nlm.nih.gov/pubmed/21389674