When people become sick with dermatomyositis (DM) they have an inflammatory skin rash and inflammation of the voluntary muscles. The patients experience muscle weakness which gets worse.
The DM most often starts with a speedy, severe onset of symptoms. Patients eventually become so weak they have trouble with daily routine activities such as standing up after sitting down, climbing stairs or lifting objects. Other organs such as the lungs may also become diseased.
The symptoms are often treated with prednisone which is a corticosteroid drug used to decrease the inflammation. Other corticosteroid drugs can be used but that family of drugs suppresses the body’s disease protection abilities. When the cells that are supposed to protect the body start to attack the body by mistake it is called an auto-immune reaction.
The part of the disease affecting the muscles has been studied a lot more than the DM skin rash. Researchers at Stanford University wanted to understand what causes the DM skin rash. They decided to compare the information from the genes observed in DM patients’ skin to genes in healthy skin. Biological scientists have developed a strategy for studying genes called microarray data analysis. Genes hold a huge amount of data that could not be easily managed without modern technology.
Why do the research?
DM skin inflammation has not been studied enough to understand whether or not the cause of the skin rash is related to the cause of the muscle inflammation. Some researchers have speculated that the disease is due to the body mistakenly attacking the blood vessels in an auto-immune reaction; this means that the immune system is not working properly by attacking the body it should be protecting. There are some observable similarities between the rash and the diseased muscles. For example the small blood vessels become diseased, cells are damaged and there are recognizable gene products produced. The damaged skin cells and the diseased muscle are close enough on the body to share a connecting membrane.
Differences between DM skin and DM muscle tissues have also been observed. The products produced by the genes in the DM skin tissues may attract genes attached to T cells. The T cells can cause inflammation and kill the basal cells. Our skin is mostly made up of basal cells.
Another important difference between the skin disease and the muscle disease has been determined. The muscle tissue samples contain B-cells which make antibodies but the skin tissue samples do not.
The researchers shared three points which motivated the research on DM skin tissue samples: (a) there are similarities between the DM skin tissues and DM muscle tissues (b) there are differencences between the DM skin tissues and DM muscle tissues, and (c) the medications commonly used for the DM skin disease do not always help the patient, in fact skin cells may continue to die even when the patient is using the prescribed medication.
The researchers hypothesized that the cause of DM for the two parts of the body affected by DM, the skin and the muscles, may not be the same. According to Wong (et al., 2012) the basic purpose of the research study was “to understand the molecular characteristics of DM” (p. E29161). The researchers decided that by studying the DM skin rash at a molecular level they might gain useful information.
Methodology
Each body of every human being has its own personal set of instructions called a genome. Genomes are the heredity instructions for how our bodies work. In order to provide clinicians with new and useful information the researchers proposed to study skin genomes; they would study microscopic pieces of DNA and RNA to better understand how the genes are sequenced in the diseased skin tissues. Scientists call that looking for a genetic marker. DNA molecules hold double strands of genetically coded information whereas RNA molecules hold a single strand.
The diseased tissues were compared to the healthy tissues in order to identify interferon (IFN) proteins that only showed up in the DM tissues. IFNs are proteins which are released when cells need to tell the immune system to fight off invaders like viruses or bacteria. A statistical analysis was done with information about interferon (IFN) from previous research to make sure that data corresponded with the new research data.
Skin samples from healthy volunteers and from DM patients were studied. This is a necessary experimental strategy so the researchers can compare the DM skin sample results to the normal baseline results. Biopsies, the preserved tissues, from the study participants were isolated and a (nucleotide) probe was used to get the genetic data. Nucleotides are the molecules that make up the DNA (and RNA) when the molecules are formed together in chains. Just as importantly the nucleotide can ‘communicate’ or give cellular signals. That is why they are good to use as probes.
Biopsies were taken from 16 DM patients and from 10 healthy patients. Twelve technical replicates were analyzed as a check for the use of high quality scientific techniques. If scientific technique is not good then the results will not be acceptable; when that happens, the laboratory measurements have to be redone.
The researchers used microarray technology. This means that samples are put on to the microscope’s glass slide in a particular way so that the data does not get confused; it is put on the slide in an orderly array. Samples look like tiny spots on the slide but they hold a lot of information. For an idea of the amount of information, Babu (2012) explains that “A microarray may contain thousands of spots and each spot may contain a few million copies of identical DNA molecules (or RNA molecules) that uniquely correspond to a gene” (p. 225).
The information from a picture of the microarray is used to make gene maps. Gene maps help researchers gain more information about the cell tissue genes. The samples on the microscope’s slide are “activated” or scanned with light rays at a certain wavelength so that they show up as either green or red when a picture is taken of them. Green cells are uploaded (producing) and red cells are downloaded (isolated).
The researchers also used data that was available from other studies in order to learn more about inflammatory disease gene expressions. A gene expression can be thought of as a translation of the DNA code; like an interpreter translates a foreign language.
The researchers thought about the questions other scientists might ask to test whether or not their research gives valuable information. The researchers considered that someone might challenge them by suggesting that their research had not shown anything new, it only demonstrated that all inflammatory diseases show the same gene expression.
So they looked at the whole spectrum of inflammatory skin diseases. They compared inflammatory skin diseases data. They found that “not all gene expression patterns are found uniformly across all skin inflammations diseases” and they gave examples (Wong et al., 2012, pp. e29161-e29162).
Results
The researchers were able to confirm that certain IFN proteins can only be identified in the tissues of patients with DM or lupus. This part of the experiment confirmed earlier research that identified the IFN proteins in DM skin tissues. That is another example of scientific method: one study can confirm or disprove the results of earlier studies; research is built upon the previous research.
The researchers successfully found a particular gene expression signature that only DM and lupus have in common. When they looked for the same gene expression signature in the other types of inflammatory diseased tissue samples, the same gene expression signature was not found.
Plus they found more useful information inside the gene expression signature. They found a code which showed them that a particular INF that is found in DM and lupus is related to a classification of inflammatory diseases that also have the auto-immune mechanism. This finding supports the theory that t-cells are killing the skin basal cells. The t-cell disease mechanism is not the same mechanism which has been identified in DM muscle tissues.
The researchers were successful in adding more knowledge and helpful information about DM for clinicians and other researchers to use. We now know that there is a difference between how the disease attacks the skin and how it attacks the muscles.
Works Cited
Babu, M. Madan.. An Introduction to Microarray Data Analysis. Chapter 11. In Computational Genomics: Theory and Application R. Grant, ed. Norwich, U.K: Horizon Scientific Press. 2004. pp. 225-295 (pdf) n.d. Web. 19 March 2012.
Wong, D., Kea, B., Peisch, R., Higgs, B. W., Zhu, W., Brown, P. Yao, Y. & Florentino, D. Interferon and biologic signatures in Dermatomyositis Skin: specificity and heterogeneity across diseases. PLoS ONE. www.plosone.org. 7(1): (2012 Jan.) pp. e29161-e29162.
