This web page was produced as an assignment for an undergraduate course at Davidson College
quantitative mass spectrometry-based proteome analysis of skeletal muscle biopsies from a variety of ages highlights an underrepresentation in mitochondrial proteins and an overrepresentation in inflammatory proteins.
Image from Google Images, Creative Common License Public Domain
As the world’s population continues to age , the percentage of people that will have difficulties accomplishing the activities of daily living is also increasing. Approximately 810 million people are currently 60 years or older and it is estimated that 2 billion people will also be of that age in 2050 (Tieland et al. 2018). Examples of physical limitations as a result of aging are an increase of falls, inability to maintain personal hygiene routines, and co-morbidity. A significant contributor to these physical limitations is age-related loss of skeletal muscle mass and function. Previous literature has suggested the decline of skeletal muscle strength is responsible for the loss of mobility and impairment of motor coordination (Cesari et al. 2015).
Moreover, there is an overall lack of understanding the mechanisms that drive the decline in muscle strength due to aging. Ubaida-Mohien et al decided to investigate the changes in the protein make-up of skeletal muscles as humans grow older with the hopes to identify new targets of intervention. The researchers used quantitative proteomic analysis to examine a large number of the different proteins in the skeletal muscle tissue. A proteomic approach allowed Ubaida-Mohien et al to study the proteins that are responsible for the maintenance and function of the skeletal muscle. In doing so, this can possibly provide insight to reversing or delaying the deterioration of human tissue as it ages.
Ubaida-Mohien et al began their investigation with the collection of skeletal muscle biopsies from 58 participants distributed between an age range of 20-87. They performed a quantitative mass spectrometry-based proteome analysis with Tandem Mass Tags (TMT) labeling on the muscle biopsies. Quantitative mass spectrometry-based proteome analysis is a laboratory method that allowed the researchers to label multiple peptides from the biopsy samples with an isobaric chemical tag like TMT (Bantscheff et al. 2007). Once peptide samples are labeled they can be recognized by their mass and quantified by the respective signal intensities they produce.
As a result, the researchers were able to identify and quantify 4380 proteins from their samples. The quantified proteins were categorized according to their biological mechanisms. Proteins involved in providing the cell with energy had a 70% decline due to aging. Processes such as muscle contraction, muscle architecture, mitochondria metabolism, and ribosome function are regulated by these specific proteins. Nevertheless, proteins related to the maintenance of existing proteinshad a 30% increase. Transcriptional regulation, splicing, neuromuscular junction, proteostasis, and immune function are examples of some of the processes that increased with age. To be concise, these results capture the underrepresentation in mitochondrial proteins and the overrepresentation of inflammatory proteins.
Now that the proteins have been categorized and their expressions have been analyzed, what is their correlation with aging? One of the mitochondrial proteins identified was MYBPH. This protein maintains the structural integrity of the skeletal muscle. According to previous literature, a decrease in expression has been associated with muscle weakness due to aging (Hundley et al. 2006) In addition, a specific inflammatory protein identified was TIMP3. This protein is known for regulating the adipogenic differentiation of fibro/adipogenic progenitors in skeletal muscle. An overrepresentation results in fat infiltration in aging muscle (Kopinke et al. 2017).
Because the newly found data was suggesting a significant change in the make up of the proteins in the skeletal muscle was occurring due to aging, this peaked the researchers interest into investigating possible changes in RNA processing. Ubaida-Mohien et al then decided to investigate the production of alternative transcripts. Alternative transcripts are when different forms of mature mRNAs are generated from the same gene. The more alternative transcripts there are in an aged biopsy versus a young one would confirm the the change in the protein make up. Moreover, the authors extracted the RNA from their participants’ muscles and compared them. Their results revealed that RNA in older people had more alternative transcripts. Therefore, the change in protein levels has downstream effects as the skeletal muscle ages.
Ubaida-Mohien et al’s results are consistent with those reported in model organisms(Pugh et al. 2013). Their findings suggests that aging skeletal muscles are characterized by profound changes in structural integrity and fat infiltration. Because proteomic analysis can only provide protein concentration at one point in time, further steps could include investigating other parameters such as sub-cellular localization or post-translational modification. Additional analysis of the skeletal muscle biopsies from a variety of ages could prove to be useful in discovering how to manipulate the expression of certain proteins to delay the decline in strength and function.
Oscar Lacayo is an undergraduate Biology major from Davidson College. Contact him at oslacayo@davidson.edu
RESOURCES
Bantscheff M., M. Schirle, G. Sweetman, J. Rick, and B. Kuster, 2007 Quantitative mass spectrometry in proteomics: a critical review. Anal Bioanal Chem 389: 1017–1031. https://doi.org/10.1007/s00216-007-1486-6
Cesari M., Y. Rolland, G. Abellan Van Kan, S. Bandinelli, B. Vellas, et al., 2015 Sarcopenia-Related Parameters and Incident Disability in Older Persons: Results From the “Invecchiare in Chianti” Study. J Gerontol A Biol Sci Med Sci 70: 457–463. https://doi.org/10.1093/gerona/glu181
Hundley A. F., L. Yuan, and A. G. Visco, 2006 Skeletal muscle heavy-chain polypeptide 3 and myosin binding protein H in the pubococcygeus muscle in patients with and without pelvic organ prolapse. American Journal of Obstetrics and Gynecology 194: 1404–1410. https://doi.org/10.1016/j.ajog.2006.01.049
Kopinke D., E. C. Roberson, and J. F. Reiter, 2017 Ciliary Hedgehog signaling restricts injury-induced adipogenesis. Cell 170: 340-351.e12. https://doi.org/10.1016/j.cell.2017.06.035
Pugh T. D., M. W. Conklin, T. D. Evans, M. A. Polewski, H. J. Barbian, et al., 2013 A shift in energy metabolism anticipates the onset of sarcopenia in rhesus monkeys. Aging Cell 12: 672–681. https://doi.org/10.1111/acel.12091
Tieland M., I. Trouwborst, and B. C. Clark, 2018 Skeletal muscle performance and ageing. J Cachexia Sarcopenia Muscle 9: 3–19. https://doi.org/10.1002/jcsm.12238
Ubaida-Mohien C., A. Lyashkov, M. Gonzalez-Freire, R. Tharakan, M. Shardell, et al., 2019 Discovery proteomics in aging human skeletal muscle finds change in spliceosome, immunity, proteostasis and mitochondria, (M. Kaeberlein, C. J. Rosen, M. Kaeberlein, and R. Anderson, Eds.). eLife 8: e49874. https://doi.org/10.7554/eLife.49874
