How To Maintain Muscle Mass And Strength As You Age

(Posted on Monday, December 18, 2023)

This article is part of a broad series on recent advances in the science and medicine of longevity and aging. The series covers a range of topics, including musculoskeletal health. Expect more articles on bone and muscle regeneration to follow.

There are a number of everyday activities that are easy to take for granted: getting up from a chair, walking up a flight of stairs, twisting a lid off a jar, carrying bags of groceries, and the list goes on. But as we age, workaday movements of this type may become increasingly difficult. Why? Loss of muscle mass and strength, or “sarcopenia” in technical speak. A study by researchers at the Tokyo Metropolitan University provides new insights into the growth and repair of muscle tissue. Their work, available online at ScienceDirect, homes in on a protein called platelet-derived growth factor subunit B (PDGF-B), which they discovered to be intimately linked to muscle growth. The findings may eventually help stave off age-related muscle loss. 

Understanding Sarcopenia

Starting at age 30, we begin to lose roughly three to five percent of our muscle mass every decade. This decline in muscle mass comes hand-in-hand with a decline in strength. If left unchecked, sarcopenia can lead to impaired mobility, and by extension, reduced activity. Soon enough, a negative feedback loop develops: muscular weakness makes exercise difficult, causing people to exercise less, which in turn leads to even more muscular weakness. This downward spiral can be difficult to break out of, and while a commitment to strength training and a protein-rich diet helps, these are often time-consuming and resource-intensive. A pharmaceutical intervention that helps older adults maintain their muscle mass would be a game changer. 

The Three ‘M’s of Muscle: Myoblasts, Myotubes, and Myokines

Muscles are complex biological “machines”. As with all machines, they have a variety of different components — the building blocks that make up the final product. Three crucial components of muscle tissue are myoblasts, myotubes, and myokines. 

Myoblasts are progenitor cells. All other parts of the muscle build on this elementary cell. Not only are they involved in the initial formation of muscle mass —called myogenesis— but they are also critical to muscle regeneration after injury or following exercise. In both cases, a bunch of myoblasts fuse together to form a larger structure called a myotube. Myotubes, in turn, can also fuse together, producing mature muscle fibers. When a muscle is injured, myoblasts and myotubes can fuse to the site of injury to replace damaged cells. This is also how muscle grows: small, manageable injury, such as happens during exercise, prompts the addition of new myoblasts and myotubes. 

Where do myokines fit into the picture? Myokines are signaling proteins that play a crucial role in crosstalk between muscles and other organs or tissues in the body. Because of this, they are intimately involved in modulating metabolism, inflammation, energy expenditure, and overall health. For example, a myokine called irisin has been implicated in cognitive function and may explain the link between exercise and brain health. And this is just one of roughly 600 myokines that have been discovered so far; unlike irisin, the exact functions of most of these remain unknown. 

PDGF-B Stimulates Muscle Growth and Improves Strength 

Platelet-derived growth factor subunit B (PDGF-B) is a protein produced in a wide array of cells. Generally, it helps regulate cellular processes including cell migration, differentiation, and importantly, cell proliferation. PDGF-B is one member of the larger platelet-derived growth factor family — there are four members in total. All of them are secreted in muscle tissue. Despite this, the role PDGF-B plays in muscle health is poorly understood. 

To find out, the researchers first confirmed that PDGF-B is, indeed, generated by both myoblasts and myotubes. Curiously, they noticed that the production of the myokine seemed independent of muscle contractions; its levels did not change following an hour of electrically stimulated muscle activity. This suggests that it is expressed “constitutively”, or without external stimuli. 

Next, the researchers directly exposed myoblasts and myotubes to PDGF-B. In the case of myoblasts, the addition of the protein led to noticeably increased cell proliferation. And treated myotubes matured quicker than their untreated counterparts, leading to increased thickness when seen under a microscope. Exposure to PDGF-B also led the myotubes to express more myosin heavy chain (MHC), which is a motor protein vital for muscle contraction. 

Increases in myotube diameter and myosin heavy chain expression were mirrored by an overall strength boost, as confirmed by experiments using electrical impulses to measure the force of myotube contraction. 

Takeaways

Age-related muscle loss is a serious concern for older adults, often leading to a decrease in quality of life. Currently, lifestyle changes are the main way of dealing with the issue: increased exercise and protein-rich diets. But such changes are not possible for some populations, especially those dealing with pain and reduced mobility. Here, an in-between step would be needed to get them to a place where they can exercise in the first place. This new study moves us one step closer in that direction. The findings show that platelet-derived growth factor subunit B can help stimulate muscle growth and boost contractile strength. Future research should aim to uncover how these benefits might be harnessed towards the development of novel therapeutics. 

This article was originally published on Forbes and can be read online here.