We live in a world where looks have become the center of our attention. Previously, this idea of maintaining youth was something seen in older populations however, now it can be seen across the younger generations too. We know moisturizing is vital to maintaining the liveliness of our skin. Many products advertise to increase collagen production. We also know that telomere degradation plays a part in the way organisms age but there is a lot more to be investigated on this topic. In order to investigate this, scientist have created a concept called mitoribo-tag and throughout this article I will discuss why this technique is gaining popularity and why it’s relevant to things outside of aging.
Staring in high school biology we are taught that mitochondria is the powerhouse of the cell and while that is true, it is an immense understatement to the importance of mitochondria. Oxidative phosphorylation is a cellular process that occurs in the inner mitochondrial matrix of eukaryotes. It is responsible for producing ATP to be pumped into the outer cellular matrix and creates a proton gradient while doing so. Understanding this process is important to the process of aging because as eukaryotic organisms age the rate of which they are able to oxidatively phosphorylate significantly decreases. Secondary to a slowed rate, the cell is subject to more toxic materials which is shown outwardly through the things we recognize as aging (Lesnefsky, 2006). In humans, these are things like wrinkles, joint pain, gray hair and so forth. Apart from vanity purposes, based on an article put out by researchers at Karolinska Institute in Sweden, the efficient functioning of mitochondria is key in order to prevent mitochondrial disorders. They argue that in order to better prevent these disorders in humans, scientist must better understand the mechanisms occurring inside mitochondria. In order to investigate this, a group performed intensive research on the processes of mitochondria and a report on their findings was published by Cell Reports titled “MitoRibo Tag Mice Provide a Tool for in vivo Studies or Mitochondrial Composition”. The term mitoribo is in reference to specialized ribosomes necessary for the key membrane proteins of oxidative phosphorylation in the inner mitochondrial matrix (Busch, 2019). This experiment is so groundbreaking because in the past scientist have mostly studied bacterial ribosomes and this was an experiment done with mammalian ribosomes, and at the conclusion of the study they discovered 36 organelle specific proteins not found in bacterial ribosomes. In general, being able to study mitoribosomes is important to the future of medicine because the regulation of mitoribosomes is a vital factor in biogenesis due to mitochondria having such a long list of responsibilities. These responsibilities include but are not limited to, cell vitality, growth, and cell differentiation. A real-life example demonstrating the importance of mitochondria functioning normal is a disorder called Lethal Infantile Cardiomyopathy, but better known as Barth’s Syndrome. It is indicated by weakening heart muscle starting soon after birth, a short stature, and unusually high cheek bones. This disorder is X linked recessive and is caused by an anomaly in the TAZ gene that causes it to produce taffazin with little ability to function normally. Taffazin is involved in keeping the inner mitochondrial matrix functions as it should and without this protein to ensure its proper function cardiolipin, cannot be produced which leads to a weakened heart muscle. Cardiolipin helps maintain the shape of the inner mitochondrial matrix. As we learned in biochemistry, the function of a protein is determined by the shape. So, when the shape is altered the function is as well, so the protein synthesis, energy production and transport systems are all altered in this disorder because of the lack of proper coding for the mitochondria (NIH, 2019).
To carry out their experiment they used wild-type mice and mice tagged with Flag-Tag. Flag Tag is a protein tag this is added to the DNA of a organisms using recombinant DNA technology. This allows the protein to be investigated with an antibody (Wikipedia, 2019). The mitochondria they investigated are biochemically and physically different from normal eukaryotic ribosomes because they are composed to two subunits that are smaller in size than normal. The small subunit is 28s and the large subunit is 39s which come together to make a 55s complete ribosomal unit. In order to confirm the flag techniques don’t affect the normal functions of mitochondria they analyzed the mitochondrial DNA from the liver, heart, and kidneys of mice using a technique called sucrose density gradient centrifugation. This technique is used to analyze different sedimentation rate measurements. The different sedimentation rates analyzed were 28S, 39S and 55S. This study is also unique in the fact they compared many of the cultured observations to their in vivo observations. One thing specifically noted in their report is 55S complexes are more common in vivo and 28S and 39S are more prominent in cultured cells. They had a wild type (+/+), a heterozygous (+/T), and homozygous(T/T) mitoribo-tag mice for each type of tissues mentioned previously. When the gel later processed under light it was found that the homozygous mice had well defined bands at the same place the wild type mice did. This allowed them to conclude that the flagged mitochondria didn’t lose any of their normal functions after the flagging process.
Their study was able to show interesting things with two different proteins, PUSL1 and GTPBP10. They concluded that these two proteins are upregulated in mice with defective mitoribosomal assembly. One of these proteins is PUSL1 which is important to this experiment because it was confirmed that it is a protein that is found in the mitochondrial matrix. It was concluded that it behaves similar to known mitochondrial protein and when PUSL1 is washed from the outer mitochondrial matrix an immunofluorescence test came back negative for presence of PUSL1, which further supports the hypothesis that the enzyme is found in the outer mitochondrial membrane only. PUSL1 can function is mitochondria with or without GTPBP10. The psuedouridines involved with both of these complexes is can be variations of mitochondrial translation system and may be used to stabilize RNA confirmation. Due to these findings it is suspected that PUSL1 is involved in mitochondrial translation. The difference between the two nucleosides below is the pseudouridine is attached to the ribose sugar by the nitrogen and the Uridine is attached at the C4 carbon. They are structural isomers, and this changes the function of them comparatively. Understanding the important of pseudouridine is useful to the mouse model because it is able to be further confirmed that mitoribosomes are important and a new way to study RNA and mitochondria and the structures and mechanisms going on within them.
On first glance, their study sounds much more advanced than a sophomore cell biology class. However, this is not true, there is an application we can apply to our fundamental knowledge of cells. For a majority of our discussion in this post we discussed how mitochondria is important to prevent aging in cells and keep certain disorders from occurring. One function of mitochondria we haven’t discussed is its involvement in the regulated death of cells. A concept known as apoptosis is crucial for cells because it allows them to be programmed for death when, cell signals recognize the cell is not functioning properly. This is exactly the case in cancer cells. In cancer cells, they are able to reproduce at a rate that is abnormal and leads to rapid proliferation even in cases when the function of the cells is harmful to the organism. This is a situation where apoptosis would program the cell for death. In the case, with mitochondrial malfunctions, the cell cannot be programmed for death and instead the malfunctioning cells are allowed to grow further with no mechanism to regulate them. This role mitochondria plays in cell signaling was further investigated by in the 1990’s. It was previously known AKAP bind to the cAMP-dependent serine/threonine kinase PKA which collective come together to make a signaling area. These areas can then be used to target areas within a cell that also rely on PKA-phosphorylation. During this they discovered how a proapoptotic bcl2 binds to the outer mitochondrial membrane with a rather high affinity. This binding is what regulates glucose metabolism within mitochondria and allows mitochondria to respond in hypoxic environments (Chandel, 2014). Another portion of the article discusses how the outer mitochondria membrane is a scaffold for immunoregulating proteins. In this mechanism, interferons code for anti-viral proteins. As discussed this semester, interferons are heavily involved in immune responses within an organism and they work to prevent viruses, bacteria, or even cancer from progressing through the body. All of these specific cellular processes tie back to the most general functionality of mitochondria, which is to produce power for the cell. This is because during Krebs’s cycle 3 NADH molecules are created and 1 FADH2 is created. These electron donators can then give their electrons to the electron transport chain to be used by ATP Synthase to create ATP, ATP can then be used by various other cells to provide the energy for a copious amount of specific cellular functions.
As you can see, there is a lot of research being done on mitochondria because the importance it plays in various cellular functions is crucial. The better the understanding of mitochondria, the better treatments can be made for mitochondrial linked disorders.
References
“Barth Syndrome - Genetics Home Reference - NIH.” U.S. National Library of Medicine, National Institutes of Health, 10 Dec. 2019, https://ghr.nlm.nih.gov/condition/barth-syndrome#sourcesforpage.
Busch, Jakob D, et al. “MitoRibo-Tag Mice Provide a Tool for In Vivo Studies of Mitoribosome Composition.” Cell Reports, Science Direct, 26 Sept. 2019, https://www.cell.com/cell-reports/fulltext/S2211-1247(19)31284-7?_returnURL=https://linkinghub.elsevier.com/retrieve/pii/S2211124719312847?showall=true#articleInformation.
Chandel1, Navdeep S. “Mitochondria as Signaling Organelles.” BMC Biology, BioMed Central, 27 May 2014, https://bmcbiol.biomedcentral.com/articles/10.1186/1741-7007-12-34#citeas.
“FLAG-Tag.” Wikipedia, Wikimedia Foundation, 23 Sept. 2019, https://en.wikipedia.org/wiki/FLAG-tag.
Lesnefsky, Edward J., and Charles L. Hoppel. “Oxidative Phosphorylation and Aging.” Ageing Research Reviews, Elsevier, 10 July 2006, https://www.sciencedirect.com/science/article/pii/S1568163706000353.