This is the first of my paper reviews and today I will be explaining the paper “Regulator of Calcineurin-1 (RCAN1) facilitates neuronal apoptosis through caspase 3 activation” that is fresh off the pages of the JBC.
I know that the title is a mouthful, but I will try to simplify the work that was done and explain the inherent beauty of it all.
At the outset, please remember that Alzheimer’s disease is a neurodegenerative disorder (it kills brain cells, basically, and in doing so impairs brain function), this of course is a product of various pathogenic factors, the most famous of which is a protein that is called Beta-amyloid, the formation of plaques of which is a defining feature of the disease, the disease leads to neurons becoming sticky, getting all tangled up, and dying, if one were to stick to the very basics.
Scientific breakthroughs, in my opinion, often entail the application of insights that are drawn from other works of research into testing hypotheses, and in this case the insight came from a well documented facet of observational reality, that patients with Down’s syndrome (with three copies of Chromosome 21, a condition known as trisomy 21) inevitably suffer from Alzheimer’s disease while only being middle-aged.
This led the authors to hypothesize that genes that are overexpressed in Down’s syndrome may have something to do with it, and the candidate gene they studied,and its protein output, of course, and have reported here in the paper, happens to be a gene called RCAN1 (Regulator of Calcineurin 1).
They found there is a version of RCAN1 with a unique regulatory region, which is called a promoter, and promoters basically control how active a gene is, they determined that RCAN1 is upregulated by one or two other substances firstly, confirming that this was part of a signalling cascade (a signalling cascade consists of proteins working like Dominoes, if a laymen’s analogy were to be used) , thus indicating that the involvement of this particular gene and its protein in the pathogenesis of Alzheimer’s may have something to do with its regulation.
The next step was to verify if RCAN1 is indeed upregulated, and the evidence that they present in the paper suggested it is the case, not only are levels of RCAN1 mRNA elevated, as per previous studies they quote) but the protein product is also elevated in patients with Down’s Syndrome + Alzheimer’s.
The next bit of their work, dealing with the actual relationship between RCAN1 and caspase activation, involved an ingenious bit of work. They had noticed that dexamethasone, a chemical, triggers cell death (apoptosis) in cell cultures, and if caspase inhibitors were concurrently used, this would not happen. Now the question to be answered is “Is RCAN1 a mediator in the pathway between dexamethasone and caspase activity?”
If RCAN1 was essential for dexamethasone to cause apoptosis, knocking it out would result in Dexamethasone activity not being able to cause apoptosis, and they verified if that was true using antisense oligomers (which can be used to silence a gene) to turn RCAN1 off , the results confirmed the integral role of RCAN1 in apoptosis since Dexamethasone couldn’t trigger apoptosis with RCAN1 switched off.
Now we have Dexamethasone ——-> RCAN1 ———->Apoptosis, and
Dexamethasone ——-> Caspase ———> Apoptosis
The next question to ask would obviously be if the correct pathway was RCAN1 ——>Caspase —–>Apoptosis.
But wait! There are many caspases, and caspase 3 is perhaps the most important of them, going by this line of reasoning, the authors reformulated their question as , to paraphrase “Does RCAN1 cause apoptosis through Caspase 3?”
They first identified a correlation by seeing what happens to Caspase 3 levels when RCAN1 was overexpressed, they found that these levels shoot up, indicating that the two are related statistically, next question, was there a causal relationship?
To check this out, they used a test system that used mutant cells without Caspase 3, and found that RCAN1 couldn’t cause apoptosis in this case, thus establishing that Caspase 3 was also essential for RCAN1 to cause apoptosis. Great work so far.
There are again three upstream activators of Caspase 3 (that is, these have to be activated first before they carry out the activation of caspase 3) namely caspase 9,10 and 8, to identify the correct upstream activator, they again used the correlation approach, seeing which of the two candidate caspases would be expressed more if an excess of RCAN1 was present, the results pointed towards Caspase 9.
They also wanted to see if the activation of Caspase 9 was specific, or whether other caspase families were also activated in some kind of broad effect, they used levels of Caspase-11 as a measure for this and found that the activation involved was indeed specific to the caspase-9 pathway.
The authors note, from previous literature, that Beta amyloid can increase RCAN1 expression and also that Caspase 3 can increase Beta amyloid expression, combine this with the fact that RCAN1 expression can increase Caspase 3 expression, we have a tirumvirate for Alzheimer’s
They also noted that an ortholog of RCAN1 in Drosophila, called Nebula, could be associated with severe memory impairment in that subject species if it is not regulated properly.
The work is significant because breaking the circle could lead to better therapeutic strategies against what is a very devastating disease.
The paper itself, for the discerning reader, can be found here at
More useful information may be obtained by means of the following links.
I hope you enjoy this and do not doze off.