The Role of Transcription Factor PPAR-γ in the Pathogenesis of Psoriasis, Skin Cells, and Immune Cells
, Ekaterina Tchepourina 1, Irina M. Korsunskaya 1, Natalia A. Geppe 2, Svetlana N. Chebysheva 2, Anna G. Soboleva 1,3 and Alexandre Mezentsev 1,*
Round 1
Reviewer 1 Report
This is a comprehensive review on PPAR gamma, for its biology, and the roles in various physiological and pathological situation. The manuscript is very-well written, with several figures for readers’ understanding.
The followings are some concerns.
1) One of the main themes of this article is the pathogenesis of psoriasis in relation to PPAR gamma. It would be better to demonstrate psoriasis pathogenesis with the mode of action of PPAR gamma in the figure to quickly understand the mechanism of action of PPAR gamma by looking at the figure.
2) RXR also has subtypes, alpha, beta, gamma. The authors had better briefly mention which subtype make heterodimers with PPAR gamma.
3) There are some bald letters in the text, but I do not see any necessity for the bald letters.
Author Response
Dear Editor,
On behalf of my colleagues, I would like to thank reviewer #1 for the time devoted to our manuscript. We would also acknowledge that comments made by reviewer #1 significantly helped us in preparing the revised version of the manuscript.
Briefly, the reviewer wanted us include a figure that would demonstrate how PPAR-γ contributes to the pathogenesis of psoriasis (Comment #1), mention which subtype of RXR prevails in heterodimers with PPAR-γ in the skin (Comment #2) and remove unnecessary bold letters (Comment #3).
To comply with the reviewer's request made in Comment #1, we prepared a new figure (Figure 6). This figure explains how PPAR-γ may influence the pathogenesis of psoriasis. For your convenience, please, find Figure 6, on page 38 of the revised manuscript.
To address the reviewer's suggestion made in Comment #2, we mentioned the existence of three different RAXRs (RXR-α, -β, and -γ) in the text of the revised manuscript (lines 219-225). We also noticed that 90% of active PPRE elements in the skin cells bind heterodimers of PPAR-γ and RXR-α.
To address the reviewer's concern made in Comment #3, we carefully verified the text and removed excessive formatting elements, including the bold letters.
Reviewer 2 Report
I think a review about PPARgamma role in skin, immune cells, and psoriasis can be very interesting for the readers.
However, I believe this review will benefit from a revision of English (starting from the title which I think can be improved). Moreover, I believe the style is sometimes redundant and make the text hard to read. I suggest a style and English revision.
Moreover, it would be beneficial to the readers to insert a table summarizing the function of PPARgamma in each immune cell.
Author Response
Dear Editor,
On behalf of my colleagues, I would like to thank Reviewer #2 for the time devoted to our manuscript. The comments and suggestions made by Reviewer #2 helped us to improve the paper.
Briefly, the reviewer wanted us to edit the text of the manuscript and improve our writing style (Comment #1). The reviewer also suggested us to make the title of our manuscript more informative. In addition, the reviewer asked us to prepare a table summarizing the role of PPAR-γ (Comment #2).
To comply with the reviewer's request made in Comment #1, we edited the text correcting our writing style and occasional errors. We are also agreed on a new title of the manuscript, which is the following: "The role of transcription factor PPAR-γ in the pathogenesis of psoriasis, skin and immune cells".
To address the reviewer's suggestion made in Comment #2, we introduced Table 1 entitled "The role of PPAR-γ in immune cells" (lines 893-894).
Reviewer 3 Report
Authors review the role of Peroxisome proliferator-activated receptor PPAR-γ in the skin and in the immune cells ofpsoriasis. They also evaluate possible usage of the agonists of PPAR-γ for treatment of psoriatic skin. This reviewer has some comments.
Comment
1. Line 385-386. In general, phosphorylation of some amino acid residues inhibits the transcriptional activity ofPPAR-γ. The cases of the opposite are unknown.: Does this sentence indicate that phosphorylation of PPAR-γ alwayssuppresses of PPAR-γ activity?
2. Line 378-379, "To avoid misinterpretations, we provide the numbers of amino acid residues in murine PPAR-γ 2.": Describe numbers of phosphorylation sites of amino acid is common. This sentence is unnecessary.
3. Lines 178-181, “Some ligands (e.g. TZDs) exhibit both specific and non-specific effects. The specific effects of the ligands require their interaction with PPAR-γ. The non-specific effects do not. In other words, the molecular mechanisms underlying the non-specific effects do not even require a presence of functional PPAR-γ in the cell.”: These sentences would confuse readers. Authors may intend to write “Some chemicals, including TZDs not only serve as a PPAR ligand, but also have other biological activities via PPAR independent manner. Author should revise these sentences
4. Section "Tissue-specific expression": Authors introduce role of PPAR-γ in specific cells/tissues. Tissue specificexpression generally is interpreted that PPAR-γ is expressed in certain specific tissue/cells. This reviewer recommends change section title.
5. Line 506-507. The second part of their name tells us that these enhancers remain inactive in the presence ofrosiglitazone, i.e. their activation requires a ligand-free PPAR-γ.: Rosiglitazone is PPAR agonist. Why is this pathway ligand-independent? Why is Rosiglitazone not shown in Fig. 4?
6. Lines 149-151 “The other group of agonists known as selective modulators of PPAR activity (SPPARMs) consists of compounds interacting with a comparable affinity to either two or all three PPARs.”: Authors should clarify difference between modulator of PPAR and agonists/antagonists.
7. Line 539 " In the healthy epidermis, the prevalent form of PPAR is PPAR-β/δ (rev. in [101]).”: All PPARs identified in mammals are expressed in skin. Why is the prevalent form of PPAR is PPAR-β/δ”?
8. Line 711 - Dendritic cells: Langerhans cells should be included in this section.
9. Does only PPAR-γ play a pathological relevant role in skin diseases, including psoriasis?
10. Lines 833- Animal studies: This section is described about characterization of PPAR deficient mice. This reviewer recommends change section title that indicate content of this section.
11. Line 1060: Please check font size of NCT…and also change from bold to plain characters.
12. Line 1121: What does “(IRCT 16381, Iran) mean?
Author Response
Dear Editor,
We would like to thank Reviewer #3 for quick and gentle evaluation of our paper. We would also acknowledge that the comments made by Reviewer #3 helped us a lot in preparing the first revision of the manuscript.
In Comment #1 (lines 385-386), the reviewer wanted us to clarify whether the phosphorylation of PPAR-γ always suppresses its transcriptional activity.
Responding to the reviewer's comment would like to mention that the phosphorylation of Ser112, Ser273, and Tyr78 inhibits the transcriptional activity of PPAR-γ and we really do not know examples of how phosphorylation might produce the opposite effect on the transcriptional activity of wild type PPAR-γ (lines 414-416).
In Comment #2 (lines 378-379), the reviewer wanted us to remove the following sentences: "To avoid misinterpretations, we provide the numbers of amino acid residues in murine PPAR-γ 2".
We agreed with the reviewer, and complied with the reviewer's request.
In Comment #3 (lines 178-181), the reviewer wanted us to rephrase the following sentences:
“Some ligands (e.g. TZDs) exhibit both specific and non-specific effects. The specific effects of the ligands require their interaction with PPAR-γ. The non-specific effects do not. In other words, the molecular mechanisms underlying the non-specific effects do not even require a presence of functional PPAR-γ in the cell.”
We complied with the reviewer's suggestion, and replaced the mentioned text with the following sentence: "Some of them, including TZDs not only serve PPAR as ligands, but also have other PPAR independent biological activities" (lines 204-205).
In Comment #4 (line 332), the reviewer suggested us to rename the section "Tissue-specific expression" because the title of this section can be misinterpreted by the readers.
We addressed the reviewer's concern and renamed this section of the manuscript. We propose the new title, which is the following: "Tissue-specific regulation of PPAR-γ controlled genes".
In Comment #5 (lines 506-507), the reviewer wanted us to answer two questions.
Question #1: Why the PPAR-γ-controlled polarization of macrophages is ligand-independent?
Question #2: Why is Rosiglitazone not shown in Fig. 4?
Our answers are the following:
Answer to Question 1: This pathway is ligand-independent because it requires direct interaction of PPAR-γ-RXR and STAT6. This interaction requires PPAR-γ to have a certain conformation. If PPAR-γ binds to a ligand, their binding causes conformational changes in PPAR-γ. Respectively, PPAR-γ will lose the ability to interact with STAT6.
Answer to Question 2: Rosiglitazone is not shown in Figure 4 because ligand-activated PPAR-γ does not interact with this type of enhancers. Otherwise, we would show the interaction of rosiglitazone and PPAR-γ in the same way as we did in Figures 2 and 3.
In Comment #6 (lines 149-151), the reviewer wanted us to clarify the difference between modulators of PPARs and their agonists/antagonists.
In response to the reviewer's comment, we would like to mention the following. The term "receptor modulator" is inclusive. It can be applied to receptor agonists, receptor antagonists, receptor partial agonists, inverse agonists, orthosteric and allosteric modulators. The term SPPARM (selective modulators of PPAR activity) applies to the compounds interacting with a comparable affinity to either two or all three PPARs. Based the definition of "receptor modulators", we see nothing wrong with calling pan-PPAR agonists either "receptor modulators" or SPPARMs.
To avoid confusion, we added a short clarifying statement to the revised manuscript:
"In this respect, we would acknowledge that the term "receptor modulators" is inclusive for all compounds capable of binding to the receptor and modulating its activity" (lines 174-176).
In Comment #7 (line 539), the reviewer wanted us to explain why PPAR-β/δ” is the prevalent form of PPAR in the epidermis?
In our best knowledge, prevalence of the isotype depends on the ability of the cell to activate the transcription of its specific mRNA(s). PPAR has three isotypes, namely PPAR-α, -β/δ and –γ. They are encoded by three different genes located on three different places of the genome. Each gene has own expression pattern. If we pick a tissue, the transcript(s) of a chosen gene prevail(s) if this gene is more frequently transcribed. Since the regulatory mechanisms are tissue specific, each isotype of PPAR may be prevalent in certain tissues. For instance, PPAR-β/δ prevails over PPAR-α, and –γ in the skin. For your convenience, please, see our short comment on the expression of PPAR–γ in various human tissues (lines 49-53).
In Comment #8, the reviewer wanted us to discuss the role of PPAR–γ in Langerhans cells.
We prepared a new section of the manuscript entitled: "Langerhans cells" (lines 785-797).
In Comment #9, the reviewer wanted to know whether other PPARs play a pathological relevant role in skin diseases, including psoriasis?
In our best knowledge, other PPARs also have a role in skin diseases. However, covering this subject would be out of scope of this study.
In Comment #10 (line 833), the reviewer wanted us to rename the section "Animal studies"
To satisfy the reviewer's request, the renamed this section and introduced the new title: " Genetic ablation of PPAR-γ in mice and its consequences ".
In Comment #11 (line 1,060, etc.), the reviewer wanted us to reduce the font size from 11 to 10 pt in some words.
We complied with the reviewer's suggestion and reduced the font size, respectively.
In Comment #12 (line 1,121), the reviewer wanted us to clarify the meaning of the phrase "IRCT 16381, Iran".
We complied with the reviewer's request and mentioned that "IRCT 16381, Iran" refers to the registration number of clinical study in Iran (line 1,157).
Reviewer 4 Report
Ms-IJMS-1844322 can be accepted. The authors have collected and investigated very well the information relating to the role of the PPAR-γ transcription factor in the target cells and tissues considered in the study. The introductory part, although reduced, is essential for the presentation of the subsequent parts of the review. The paragraph dedicated to PPAR ligands, both artificial and non-artificial agonists and antagonists is also useful. The figures inserted in the text are essential points of collection of the information reported by the studies taken into consideration for the drafting of this manuscript.
Furthermore, the considerations made on the interactions with other transcription factors mentioned in the paragraph dealing with "silencing transcription", open up numerous points of possible study, for researchers in the field, in particular on the effects combined with STAT6, on the inhibition of PPAR-γ via phosphorylation. and the suppression of PPAR-γ via SUMOylation, ubiquitination, and acetylation.
In the part of the review dedicated to the role of PPAR in the skin and cells of the immune system as well as in the pathologies related to them, the authors reported in an orderly and in my opinion complete manner, a series of relevant and useful information for experts in the sector. No less relevant are the data relating to psoriasis and the therapies used to date as well as orienting research on aspects related to the action of PPAR-γ for the development of new dermatological therapeutic approaches.
The bibliography is well structured and complete with the references given in the text.
Author Response
Dear Editor,
On behalf of my colleagues, I would like to thank Reviewer #4 for detailed evaluation of our study. We appreciate the reviewer’s remarks and highlight the improvements made by us in the revised version of the manuscript. We proposed a new title of the manuscript: "The role of transcription factor PPAR-γ in the pathogenesis of psoriasis, skin and immune cells". We believe that the new title is more relevant the contents of the manuscript and will be appreciated by the readers. To summarize the role of PPAR-γ in immune cell, we prepared Table 1. We also introduced two new sections. One of them describes the role of PPAR-γ in Langerhans cells. Another reflects our view of future perspective for PPAR-γ agonists in clinical practice. We also added Figure 6 to explain the role of PPAR-γ in the pathogenesis of psoriasis.
Reviewer 5 Report
Thank you for giving me the opportunity to review this manuscript, which deals with the role of PPARgamma and its agonists in the development and treatment of psoriasis. In general, I think this is an interesting topic.
However, to make it even more interesting and easier to follow, I have a few suggestions.</p>
- My main point is that the authors might try to structure their manuscript more clearly with respect to their topic:
For instance, they should move the paragraph on PPARgamma and psoriasis much more towards the beginning, since they to refer to psoriasis in earlier paragraphs, but don't actually actually explain what psoriasis is up to page 22.
This would also make it easier to relate the different basic research findings they address to processes that are known to be important in psoriasis - which I would also highly recommend.</p>
Moreover, I think some of the provided detail could maybe omitted in order to highlight the important points of the manuscript.
- The forest plots that the authors provide are largely redundant with a meta-analysis of Chen et al. 2020, PubMed ID 32769894, that is not yet included in the manuscript (unless I have overlooked it), and that the authors may not yet know of. They should probably include the study in their manuscript and at least refer to it.</p>
<p>- Again referring to these forest plots: I'm not a meta-analysis specialist, but does it make sense to divide the pioglitazone trials into these many groups, so that some of them only contain one trial, and then provide an "average" of that one study?
- I like the idea to provide summaries for individual topics. I would suggest to include more of them, especially when the data provided in those paragraphs is controversial.
- Some of the adverse effects of the PPARgamma agonists appear to be class effects and not off target effects. Therefore, in the opinion of the authors, will it really be possible to design safe PPARgamma agonists as potential treatments for psoriasis? What strategy could be pursued to achieve this?</p>
- Minor point: Maybe you could show the manuscript to a native speaker to enhance the clarity of the presentation some more.
Author Response
Dear Editor,
We would like to thank Reviewer #5 for detailed evaluation of our manuscript. We would also acknowledge that comments and suggestions made by the reviewer were very helpful in our work at the revised version of the manuscript.
To address the reviewer’s concern about structural integrity of our paper we moved the section entitled "The role of PPAR-γ in psoriasis" to page 1 and reintroduced it as a part of new "Introduction". We are agreed with the reviewer that re-structuring the manuscript will make it easier to link various findings of basic research to certain aspects of clinical practice and highlight their role in the pathogenesis of psoriasis.
The reviewer also suggested us to omit some details in our manuscript to highlight the key achievements of basic and clinical research in the field. In this regard, I would like to notice that we could not comply because three other required us exactly to include more data to the paper. To be precise, Reviewer #1 suggested us to include a new figure that would illustrate how PPAR-γ influences the pathogenesis of psoriasis. Reviewer #2 wanted us to prepare a table that would summarize the role of PPAR-γ in immune cells. Reviewer #3, asked us to add a new section describing the role of PPAR-γ in Langerhans cells. With all my respect to the reviewer’s opinion, I do not know how we could shorten the manuscript at these circumstances. I and my colleagues sincerely apologize to Reviewer #5 for inconvenience.
In the next comment, the reviewer suggested us to cite Chen’s paper, PubMed ID 32769894. The reviewer also wanted us to rearrange the cited clinical studies into larger groups. To address the reviewer’s concern, we cited Chen’s paper. However, we would also highlight differences between our study and theirs. First, Chen’s analysis is missing Abidi study, which was published in 2020 (PubMed ID 25209868). Second, we analyzed each combination of drugs separately because the influence of two drugs on each other does not have to be the same. For instance, a combination of drugs may target the same signaling pathway or type of cells. Alternatively, they may work on different pathways and cells. Respectively, a value of synergistic effect may significantly varry for different combinations of drugs.
The reviewer encouraged us to include more summaries into the paper, especially when the data provided in those paragraphs is controversial. To comply with the reviewer’s suggestion, we made sure that any major section of the manuscript is accompanied by a summary.
In addition, the reviewer asked us to share an opinion about a creation of safe PPAR-γ agonist as potential treatments for psoriasis and strategy that could be pursued to get one.
To respond the reviewer’s comment, we included a new section entitled "Future perspectives of PPAR-γ agonists in psoriasis" where we reviewed the available data on some experimental drugs. For your convenience, please, find it before "Conclusions"
Round 2
Reviewer 3 Report
Authors revised manuscript in response to reviewers’ comment. This reviewer has additional comments to improve manuscript. Details are below.
Comment
1. Related to prior comment #7 “Line539"In the healthy epidermis, the prevalent form of PPAR is PPAR-β/δ (rev. in [101]). AllPPARs identified in mammals are expressed in skin. Why is the prevalent form of PPAR is PPAR-β/δ?”:
Does Rev 101 indicate the prevalent form of PPAR is PPAR-β/δ?
2. Related to prior comment #9 “Does only PPAR-γplay apathologicalrelevantroleinskindiseases,including psoriasis?: This reviewer understands that authors focus on psoriasis in manuscript. But this reviewer recommends add a brief description about involvement of PPARs, including PPAR-γ in other skin diseases and refers other review articles. Because some readers may misunderstand that PPAR-γ is only relevant in psoriasis.
3. Line787, “Similar to macrophages”: Similar to other immune cells should be appropriate, because authors wrote that PPAR-γ is involved in modulation of lipid metabolism of Langerhans cells and monocytes in manuscript.
4. Figure 2, Legend: Please include explanation of DR1 and DR2.
5. Line 1259, Reference [252], does this prior study show anti-inflammatory activities? Reference [252] is a commentary on others including [251]. Authors should cite [251] and other prior studies.
Author Response
Dear Editor,
We would like to thank reviewer #3 for working with us to make our manuscript better. We value all suggestions and remain open to further comments.
In Comment #1 (line 539) the reviewer wanted us to explain the prevalence of PPAR-β/δ in the epidermis (part A) and comment on Ref 101 that had to prove it (part B).
Responding to part A, we added a short statement to the manuscript (lines 572-576).
The prevalence of PPARs in tissues depends on their role in the metabolism of resident cells. In healthy epidermis, the prevalent form of PPAR is PPAR-β/δ since PPAR-β/δ plays a significant role in the maintenance of the skin permeability barrier and the biogenesis of lipids. The epidermal keratinocytes also express some PPAR-α and even fewer PPAR-γ [107].
Responding to part B, we replaced the reference mentioned by the reviewer. The substitute paper proves that PPAR-β/δ is the prevalent form of PPARs in the epidermis.
In Comment #2, the reviewer wanted us to add a summary on the role of PPARs in other skin diseases.
We complied with this suggestion and added a short statement to the manuscript (lines 985-990).
Due to their role in lipid metabolism, cell proliferation, differentiation, and inflammatory response, PPARs directly participate in the pathogenesis of other skin disorders. Anti-proliferative, anti-inflammatory, and pro-differentiation activities make them drugs of interest in atopic dermatitis and skin cancer. They can be alternative treatment options for pigmentary diseases, scleroderma, and acne vulgaris (rev. in [219]).
In Comment #3, the reviewer wanted us to replace the phrase "Similar to macrophages" with "Similar to other immune cells" (line 787).
We agreed with the reviewer and corrected the text accordingly (line 800).
In Comment #4, the reviewer wanted us to explain the terms "DR1" and "DR2" in the legend of Figure 2.
In response to the reviewer’s comment, we changed the legend of Figure 2 accordingly (lines 234-235).
In Comment #5, the reviewer pointed to our attention that reference 252 was not the first paper that proved the anti-inflammatory role of amorfrutins.
We replaced the former reference 252 with the new reference 251. The substitute paper was published three years earlier than the former paper 252 (line 1266).
Reviewer 5 Report
Thank you for your point-by-point response and your revsions of the manuscript.
I think that the new paragraph on potential new drugs trargeting PPARgamma is very interesting. On little comment, though: Maybe you could replace some of the "will" in the first paragraph by "ought to" or alternatively write something like "several compounds that are currently being investigated retain the ability to... but cause less...?
That you didn't shorten the manuscript for the sake of clarity as I suggested is compensated by the addition of the table and the new figure, which also serve to highlight important aspects, so I'm fine with that.
Thank you for moving the psoriasis section to the first part of the manuscript, I think this is really helpful. Also, thanks for citing the Chen paper, which I think is necessary because of the similarity of the topic. However, this way of citing the manuscript could also mean that the contents are different, but you used their methodology, right? Maybe you could rephrase that a bit to clarify that the content of your studies is also related? Thank you.
I'm still not sure whether it makes sense to show a "total" effect when there is only one study in the section, though, but since none of the other reviewers seem to have voiced concerns in this direction, that is probably not a major point.
In summary, I think the manuscript has improved substantially through the revision, and I have only a few minor remaining points that could be addressed easily. Other than that, I think the manuscipt will be interesting for the readers of the journal.
Author Response
Dear Editor,
We would thank the reviewer for the detailed evaluation of our paper. We would also thank Reviewer #5 for all suggestions and comments.
In comment 1, the reviewer wanted us to correct the first paragraph in the section entitled "Future perspectives of PPAR-γ agonists in psoriasis" (lines 1259-1270).
To comply with the reviewer's request, we corrected the text accordingly.
The new generations of PPAR-γ agonists OUGHT TO preserve the beneficial characteristics of TZDs. They SHOULD enhance insulin sensitivity and decrease fatty acid oxidation. Moreover, they SHOULD cause less fluid retention and weight gain. We also anticipate them to exhibit potent anti-inflammatory and antiproliferative effects on keratinocytes. Compared to TZDs, the new drugs HAVE TO be less mutagenic and cytotoxic. Expectedly, some of these drugs CAN originate from natural sources. In this regard, we would mention amorfrutins from edible parts of Glycyrrhiza foetida and Amorpha fruticosa [251]. Activating PPAR-γ, amorfrutins significantly improve various metabolic parameters, such as the resistance to insulin [252]. Similar to other agonists of PPAR-γ, amorfrutins exhibit anti-inflammatory activities [251]. However, they do not cause unwanted side effects, like increased fat storage and genotoxicity [253].
In comment 2, the reviewer wanted us to rephrase our remark on Chen's paper (Ref. 230). The reviewer also questioned the applicability of the term meta-analysis to a single study.
We agreed with the reviewer that some readers might misinterpret our comment on Chen's paper. We also agreed with the reviewer on the statement that meta-analysis of clinical data shall include the results of two or more clinical studies.
To comply with the reviewer's request, we removed former Figure 5 from the manuscript and adjusted the text accordingly.
