On 2020-10-24 16:39:52, user Johnathan Lyon wrote:
Hi Hannah, et al.,
Thank you for making this preprint available. I’m very glad to see more people continuing to advance the signaling understanding of electrotaxis. You actually cite my paper (Lyon, et al Sci Rep), and your work kind of mirrors the approach I used, so I was really happy to read this and see what you found! I also wanted to provide some detailed, critical feedback to help you make this paper stronger, and more accurate. Overall, it’s clear you have strong evidence that PPAR agonism impacts electrotaxis across these cells, so nothing I found would ultimately block you from publication of this novel result. I look forward to seeing any future updates/work.
all the best,<br />
Johnathan Lyon
Pioglitazone has some weak off-target effect on PPARa, and GW9662 will also inhibit PPARa. You may need to clarify this limitation in your discussion if you think it will have any impact on your findings. T0070907 (CAS No. 313516-66-4) would be an improved alternate antagonist that has superior selectivity.
Side note: I too was unable to get U87MG cells to electrotax in 2D, but in 3D they were cathodally-directed. I didn’t know about the contention over U87MG origins until my studies were near completion though (https://stm.sciencemag.org/... and there may be discrepancies due to sourcing.
You need higher-res figures (or try png instead of jpg to make the small text less garbled).
How do you deal with the differences in media? Does this help to explain the difference in migration preference? Having or lacking competing extracellular ligands and growth factors may change the way these cells are responding directionally. FBS is rich in a variety of factors that could change the complex interplay of signals at the cell surface. One of the hypotheses from my paper is that chemical gradients are modified by the DC fields (all molecules have an isoelectric point) and that gradients of different factors mapped onto the particular spectrum of receptors on a particular cell can dictate the electrotactic response.
Did you look at proliferation differences at all? Some hypotheses claim that cells migration and proliferation are mutually-exclusive. As the PPAR pathway has downstream effects on proliferation, this may be work a deeper look.
I think it would be helpful to discuss the differences in effects across your cell types. From the discussion you make it sound like PPAR agonism was overall effective, however you had varying efficacy. E.g, HROG02-diff had a weak, but distinguishable effect, compared to HROG05, where it completely obliterated directionality. The fact that in most cases you’re getting no change in velocity is important (it tells me that your effect alters directionality, but not migration overall), though for HROG05-diff this may not be the case, as it seems like a loss of velocity is consistent with a loss of persistent directionality. Overall, I think it seems to impact your GSC cells more so, which could actually be attributed to the differences in media (i.e., FBS in your Diff cells may be competing).
You should really consider using boxplots w/ replicate dots or violin plots instead of bar graphs; more and more journals are shying away from allowing bar graphs because they hide the true distribution and are harder to interpret.
Can you please clarify why you think this “may not be clinically feasible based on the requirements for medical screening tests”? Also, it’s not clear why you mention Optune here. Are you trying to point out existing electrotherapies for cancer? You may need to look into some of Marom Bikson’s work to see if externally applied tDCS can generate sufficient fields; otherwise DBS or penetrating electrodes may be a more apt medical intervention to point to clinical feasibility.
Please clarify when you say PI3K what isoforms you actually mean, they are all fairly distinct in their signaling effects. This is a fairly common oversight, and typically people equate PI3K to PI3K alpha, beta, and delta (class IA), however PI3K-gamma (class IB) is relevant in this case. PI3K-gamma is the culprit for the cathodal migration I observed in U87MG spheroids (this is corroborated by an earlier paper that Dr. McCaig was part of: https://pubmed.ncbi.nlm.nih.... For anodal electrotaxis in DAOY, pan-PI3K inhibitors were not sufficient to stop electrotaxis. Also point of clarification, I did not use ROCK1/2 inhibition on the U87MG cells; this was an additional study I tried on just the DAOY cells to see if their anodal preference was due to a chemo-repulsive stimulus.
Your claim “PI3K does not appear to be an efficient target to prevent…” is inaccurate based on the preceding evidence: Huang, et al., used LY294002 (PI3K a/b/d inhbitor) to decrease directed migration; I used differentiated U87MG cells and found that PI3Kg inhibition completely removed any electrotactic bias in direction (DAOY cells were not impacted, but their directionality and mechanism were different). I think you would have to show more wide-spread consensus that the effect of inhibition of each particular isoform is generalizable before you can make this claim.
“This provides early evidence that inhibition of GBM directed cell migration reliant on electrotaxis may be targeted with drug therapies.“ Please change “early” to “additional”; my paper, the Huang paper, Fei Li’s paper, and a recent Tsai paper (https://aip.scitation.org/d..., all use pharmacological intervention to manipulate electrotaxis. You can maybe clarify this to lead to your next point: that you have shown something novel impacting electrotaxis across the differentiation spectrum.
Two of your last discussion paragraphs (starting “Physiological EFs have been…” and “The generation of a pathological…”) feel a little disconnected from your study and feel like an extended background. Maybe pull some of this into the introduction instead, and tighten your claim about generation of a electrochemical gradient. You could alternatively connect with a pathologist/oncologist, and look at post-mortem tissue to see whether GSCs tend to be core or satellite-resident in the tumors (although, then again this could be obfuscated by heterogeneity and not knowing where the GSCs are generated/originating).
I think your discussion is lacking two major commentaries: 1) What, mechanistically, links differentiation to differences in directionality? Is it merely the media constituents, or is there literary evidence that indicates this (i think there’s some of this at least embedded in the Huang paper on BTICs); and 2) an expanded discussion on why is PPAR relevant to electrotaxis, specifically? I.e., what are the outputs of PPAR signaling and how are changes in those relevant to directional migration? (you have pepperings of this, but it’d be great to see it more concretely linked to existing work or new hypotheses).
It may be useful to look at this review by Michael Levin (https://pubmed.ncbi.nlm.nih... and consider whether you can connect PPAR and its impact on lipid biosynthesis, to changes in maybe mobility or expression of cell-surface-laden molecules that can alter resting membrane potential (would be interesting to see if this is different, in your diff vs. non-diff cells). This may somehow correlate to ‘metastatic potential’.
Some of your reference links may be wrong. E.g., the Fei Li paper’s pubmed link doesn’t lead me to the right place.