The Role of Collagen Composition and Orientation in
Lateral Force Transmission with Aging
Jed Keenan Obra, Henning T. Langer, Agata A Mossakowski, Usha Sinha, Shantanu Sinha, and Keith Baar
University of California Davis
University of California San Diego
Collagen is the most abundant protein in the body and functions to provide the mechanical strength of connective tissues. In muscle, collagen fibrils function both to hold muscle fibers together and transmit force laterally between fibers. With aging, muscle mass is reduced, but there is a disproportionately larger loss of muscle strength associated with age, termed dynapenia, that is not accounted for completely by neural and muscle contractility origins. How changes to specific collagen isoforms and the extracellular matrix (ECM) orientation contribute to force loss is currently unclear. The purpose of this study is to compare lateral force transmission in young and old people by analyzing changes in specific collagen proteins and the ECM. To study this comparison, cross-sections of the gastrocnemius muscle were taken to determine specific collagen content, composition, and fiber cross-sectional area (CSA), whereas longitudinal sections were stained with picrosirius red to determine matrix orientation. As expected, fiber CSA tended (p = 0.1) to decrease in the old subjects. Picrosirius red staining showed that the collagen matrix is oriented at a 22.3±3.1% angle to the fibers in young and 30.2±8.7% in old subjects. By establishing the role of specific collagen proteins during aging, we hope to better understand the relationship between the extracellular matrix and force transmission in muscle and how this relationship changes with age. Characterization of this relationship allows for a more comprehensive understanding to the causes of dynapenia which will further enhance rehabilitation paradigms aimed at promoting strength, mobility, and longevity.
Keywords: muscle strength, aging, collagen