Predicting Lifespan and "Healthspan"
As humans have begun to live longer it has become clear that the quality of our lives is equally as important as the duration. In the lab, a dramatic extension of lifespan isn’t difficult to achieve. In previous experiments using several types of mutated Caenorhabditis elegans roundworms (C. elegans), researchers were able to significantly extend the worm’s lifespan. The lengthened life that the worms experienced was not necessarily a good one, as many of the mutated varieties were less healthy than wild-type worms, especially during the segment of life that was extended beyond normal. Instead of focusing on drawing out the length of life, South Korea’s IBS Center for Plant Aging Research and the research group led by Coleen Murphy, a professor at Princeton University have created a tool that can be used for accurately predicting lifespan as well as assessing the current health state, and discovered the regulatory mechanism that extends “healthspan”, the time in which an organism is at its optimal health.
The scientists created their own health assessment for C. elegans, modeled after the Short Physical Performance Battery (SPPB), one of the most widely used tests of physical performance in elderly humans, which can accurately predict their future health. Among other things, the SPPB measures walking speed which was the inspiration for the C. elegans version of the test. The scientists recorded the maximum velocity (MV) of wild-type C. elegans worms during timed 30 second sessions for a life time. In the experiment, the worms all showed a decrease in MV from day 6 and onwards just as the movement ability of humans starts to decline at some point of our later life and onwards. Additionally, they found that at day 9 (midlife), the median lifespan of worms in the high MV group (23 ± 3.2 days) was 35.3% longer than that of the worms in the low MV group (17 ± 3.6 days). They concluded that MV of wild-type worms at day 9 of adulthood is a reliable predictor of longevity. Another factor they observed was the state of C. elegans mitochondria. Elderly humans have weaker muscles and less strength resulted from mitochondrial defects which occur later in life. C. elegans with lower MV exhibit similar defects by midlife but there are far fewer defects in worms with higher MV at the same age. These observations indicate that MV correlates with mitochondrial health expression, suggesting that MV can be a reliable indicator of the actual physical state. The findings show that MV of C. elegans is a reliable indicator of age-related physical decline, accurately reports movement ability and if measured in mid-adulthood, is predictive of future longevity.