How the muscle proteome changes as time goes by
osin forms, the researchers performed additional analyses. Myosins consist of two heavy chains coiled around As we age, we often find it difficult to do each other; small light chains bind to the things we used to do. Even if we stay moderately active, our muscles still unthe necks of the heavy chains and moddergo many changes, including a loss ulate their contraction velocity and of total mass. Many studies have been the rate of force development. The republished, but the details of age-related searchers investigated the distribution alterations are contradictory. Some reof MHCs in the two groups by running ports suggest that fast-twitching musthe samples on quantitative 1DE gels. cle fibers, which are responsible for On average, the elderly subjects had an quick movements, decrease in almost complete loss of MHC 2X number as we age. Other studproteins and a reduction of MHC ies suggest that the fiber types 2A proteins, which are both characteristic of fast-twitching musdo not change or even that the number of slow-twitching ficles, compared with the young bers, which contract slowly adult subjects. for extended periods of time, By running the samples on decreases. narrow-range 2DE gels and perTo gain a better underforming immunoblots, the restanding of age-related mussearchers also found that phoscle changes, Cecilia Gelfi and phorylated regulatory MLCs, colleagues at Consiglio Naziwhich are characteristic of fastonale delle Ricerche, the Unitwitching muscles, were almost versity of Milan, the Univerabsent in the elderly group. Gelsity of Pavia (all in Italy), and fi says that this study is the first Imperial College London have to demonstrate in humans that taken a proteomics approach. a decrease in fast MHC forms In this issue of JPR (pp 1344– is correlated with a decrease in 1353), the researchers comphosphorylated fast MLC forms. pared the muscle proteomes of This finding suggests that phosmoderately active elderly and phorylated MLCs modulate the young men by 2D difference activity of the MHCs. With this in-gel electrophoresis (DIGE) kind of proteomics approach, reand 1DE. Several proteins, insearchers can observe “changes Powerhouse. Muscle changes in composition as humans age. cluding myosin light chains in fiber type distribution, as well In particular, researchers have found that the number of myosin (MLCs) and myosin heavy as changes in muscle function— types characteristic of fast-twitching fibers decreases in older chains (MHCs), were differvelocity and rate of contraction,” subjects. entially expressed in the two she says. populations. Interestingly, when the reGelfi says that the hardest part probOxidative metabolic enzymes were searchers plotted the MHC composition ably was just getting started. “The most up-regulated in elderly subjects, wherefor each subject, they found that the difficult things were to find people who as anaerobic and glycolytic enzymes plots of the young adult MHCs were alwould consent to be biopsied and [to were up-regulated in young adults. For most identical to each other. The MHC obtain authorization from] the ethics example, creatine kinase, an enzyme plots for the older population, howevcommittees,” she explains. All of the involved in anaerobic metabolism, was er, were much more variable. Gelfi and subjects were healthy, and people are less abundant in elderly subjects. Crecolleagues say that this result could be often reluctant to undergo invasive atine kinase phosphorylates creatine; due to the larger variation in exercise procedures when they feel fine. The rethis process increases the amount of patterns in the elderly group. searchers didn’t have to perform extenATP available to muscles. “When you The researchers plan to expand this sive surgery to obtain samples, howev have a change in muscle fiber-type diswork in two directions in the future. Acer. She says that they removed ~15 mg tribution, also the metabolism must cording to Gelfi, they will analyze musof tissue from the vastus lateralis muschange,” explains Gelfi. Contractile pro cle tissue from female subjects to detercle in each patient’s thigh by performteins were also differentially expressed. mine whether sex-specific hormones ing needle biopsies, which are much For example, a-actin was up-regulated make a difference in the levels of proless painful and involve a much shorter and an MHC fragment was down-reguteins that are expressed as people age. recovery time than surgical biopsies. lated in elderly subjects. Fast and slow In addition, they plan to investigate the Eventually, they obtained samples from MLCs also showed differences in abunmuscle proteomes of people who are 6 active young adult and 6 active elderly dance between the two groups. immobilized. (75-year-old) males. Intrigued by the differences in my—Katie Cottingham PHOTODISC
Once the specimens were in hand, the researchers solubilized the t issue and extracted proteins by standard methods. The proteins were quantitatively analyzed by the 2D DIGE technique. Each sample was run on the same gel with an internal standard consisting of a pool of all of the samples. Of the 52 spots that were differentially expressed, 39 contained proteins that were identified by MS/MS.
Journal of Proteome Research • Vol. 5, No. 6, 2006 1297
