May 02, 2018

Meet Aging Gracefully

Virtual Derby FBAging Gracefully

  • Trainer: Stem C. Ell
  • Career earnings: $2,255,000
  • Running Style: Front Runner
  • Brief Interesting History: Straight from the geriatric ward, Aging Gracefully appears to have an impressive career, but this may be due in part to having accumulated 16 years’ worth of earnings. With special permission, she has been accepted to race against the youngsters for one last memorable time. Betters may find her in the back paddocks with her legs laced up in Back on Track ice boots, but that should fool no one. Old time trainers know this is the secret to curbing excess inflammation and ridding the body of the extra weight caused by inflamed tissue. Never mind her aching joints and declining longissimus muscle tone, experience is this girl’s secret weapon. Her past races highlight her famed strategy as a front-runner. Personal strength lies in her accumulation of Type II muscle fibers. Perfectly legal under Jockey Club rules, this firecracker snatches the whip from her rider and uses it as a cane to propel herself to the front of the pack right from the gates. Disregard the length of the Derby and thanks to all her glycolytic fast twitching, she is sure to surge into first place.

Interpretive SummaryHORSE SPECIES SYMPOSIUM: The aging horse: Effects of inflammation on muscle satellite cells

by Jackie Walling

An article published in the March 2015 Journal of Animal Science explores how satellite cells in muscles are affected by the unavoidable process of aging. Satellite cells are simply stem cells in the muscle responsible for hypertrophy and maintenance of muscle mass. Cell activity seems to be compromised by high concentrations of cytokines commonly associated with increasing age and continuing exercise. 

Improvement in breeding practices, veterinary medicine, and daily care has increased the working lifespan of the average equine. An “aged horse” is considered to be over 15 years of age. An accurate census of this demographic is difficult to count, but breed associations report increasing numbers of registered older horses still actively competing. Though horses remain in work longer, the level of intensity they endure usually decreases with age. 

Aged horses can typically be spotted due to visual muscle atrophy. One study analyzed reduction in muscle mass by measuring area and depth of the longissimus muscle (LM) in 61 horses. Ages of horses ranged from 1 to 21 years and each participated in exercise five days a week. Growing horses had an increased LM area up to ages 11-15 before beginning a reduction in size. The depth was found to increase up to ages 6-10 before starting to decline. Both results confirmed muscle loss does occur as horses age.

Aging is also associated with reduced aerobic capacity and muscle fiber changes. Two types of muscle fibers exist: Type I (oxidative slow-twitch) and Type II (glycolytic fast-twitch). Type I fibers typically dominate in young horses while older horses see a transition to Type II. Type II fatigue much quicker than Type I indicating a reduced aerobic capacity and inability to withstand high-intensity, prolonged exercise. Careful training programs can only help improve capacity.

Exercise naturally stresses and strains muscles. When stress occurs, immune cells begin sending out cytokines to repair damage. This study looked at three: tumor necrosis factor-α (TNFα), interleukin-1β (IL-1β) and interleukin-6 (IL-6). Older horses have a sensitive proinflammatory environment where stress causes increased concentrations of cytokines resulting in excessive inflammation. Continuous inflammation at high levels causes decreased muscle mass and interferes with proliferation and differentiation of satellite cells.
High concentrations of TNFα interfere with growth and differentiation of satellite cells causing muscle atrophy. Excessive numbers are harmful in old age, but young horses need a limited amount for their muscles to undergo natural repair mechanisms. 

Macrophages activate IL-1β which is a mediator of the inflammatory response. It inhibits satellite cell differentiation possibly controlled by the presence or absence of growth factors. Reversing negative effects is possible if conditions for an anti-inflammatory environment can be met. 

Interleukin-6 is secreted from myoblasts and myofibers and contributes to atrophy, protein degradation, and declining muscle mass when too much is present. However, satellite cells need a limited amount to proliferate so a balance must be found to properly assist in the function of satellite cells.

Overall, aging causes high concentrations of cytokines which interfere with the function of satellite cells. If satellite cells are inhibited, stress on the muscle cannot be repaired or maintained which leads to declining muscle mass. More research is needed to assess the extent of damage caused by cytokines, the effects of aging, and the role exercise has on satellite cells.
To read the full article, visit the Journal of Animal Science. Take a peek at the other contestants