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I am computational guy and hence apologies if the question is silly.

Can the same miRNA show upregulation and downregulation in the same disease? (Not in the same experiment, though). For e.g. can there be a instance of miRNA hsa-miR-21 being upregulated in a disease glioblastoma in 1 study and in another study there is an occurrence of hsa-miR-21 being down-regulated in glioblastoma. Is this possible?

As an example, I found: hsa-miR-345 -> overexpression in pancreatic cancer (PMID: 16966691) and, hsa-miR-345 -> downregulation in pancreatic cancer (PMID: 17149698)

Any pointers would be appreciated.

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  • $\begingroup$ Glioblastoma multiforme? miR-21 is usually upregulated in some cancers. Sometimes there is no real change but I haven't come across a case when it is downregulated. Pancreatic cancer is an even broader term than glioblastoma (glioblastoma usually refers to GBM but there can be others); there are many cells in pancreas and any of these cells could become cancerous. Some of these cells may overexpress miR-21 whereas others may not. But there should not be a downregulation, as far as I know. $\endgroup$ – WYSIWYG Aug 6 '16 at 8:46
  • $\begingroup$ Thanks. But as to the notion - 'that a certain miRNA documented as to be shown as upregulated and downregulated in a disease', do you think there is a biological basis for it? There are scientific databases (for e.g. miR2Disease) which have reported these and hence I'm curious. $\endgroup$ – Benny Aug 8 '16 at 16:07
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    $\begingroup$ In the same disease? In that case I would say that the particular miRNA is not a reliable marker for that disease. Usually, these datasets do not have enough replicates to calculate statistical significance. Moreover, the way upregulation/downregulation is usually calculated (fold changes) is not a good idea when the actual concentrations are too low. To attribute a biological significance, a more detailed and precise study is necessary. $\endgroup$ – WYSIWYG Aug 8 '16 at 19:26
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Since diseases are frequently complex, it is not surprising to find specific genes (both miRNA coding genes or protein coding genes) being deferentially regulated when different studies of similar-sounding-diseases are compared. In other words, things like glioblastoma or Pacreatic Cancer should be treated as labels describing grossly similar disease states (i.e. excessive proliferation of glia and pancreatic cells, respectively), rather than as labels of specific cellular state associated with a particular gene expression pattern.

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