LINE-1 RNA Expression is Higher in Older Human Skeletal Muscle but Decreases With Endurance Exercise and Physical Activity

Abstract

INTRODUCTION: Long Interspersed Nuclear Element-1 (L1) has the autonomous ability to randomly move about the genome. As a result, L1 has been implicated with disease and aging. We sought to determine if skeletal muscle L1 is expressed differently between young and old humans, if acute cycling exercise alters L1 expression, and if L1 expression is related to daily physical activity. METHODS: DNA and RNA expression of L1 measured by PCR was determined on 15 young (23 ± 3 y/o) and 15 old participants (58 ± 8 y/o). Participants reported to the laboratory not having exercised for 48 h, under a 24 h standardized diet, and were 8 h fasted. Participants donated a skeletal muscle biopsy (PRE) directly prior to 1 h of cycling exercise at 71 ± 3% of heart rate reserve (young – 71 ± 4%, old – 71 ± 2%; p>0.05). A second (2 h) and third muscle biopsy (8 h) were donated 2 h and 8 h following exercise, respectively. Physical activity was measured via an accelerometer worn on the hip for 13 ± 4 days. RESULTS: PRE L1 DNA was not different between groups (young – 1.00 ± 0.05, old – 1.00 ± 0.05; p>0.050). L1 RNA demonstrated a time effect (p=0.034) and group effect (p=0.014). Old participants expressed more L1 RNA than young participants irrespective of exercise (young – 0.90 ± 0.39, old – 1.19 ± 0.48; p=0.014). Cycling lowered L1 RNA expression 2 h post-exercise regardless of group (PRE – 1.15 ± 0.53, 2 h – 0.89 ± 0.25; p=0.027). Lastly, higher levels of moderate to vigorous physical activity per day is related to lower PRE L1 RNA expression (r=-0.398, p=0.032). CONCLUSIONS: PRE L1 RNA expression is higher in older humans; however, expression is reduced with endurance exercise, and higher levels of physical activity are related to lower L1 RNA expression.