Morphological and Molecular Characteristics of Choroid Plexus Epithelium in Aged Brains
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript addresses an important and timely topic and proposes a sequential degeneration model of the choroid plexus epithelium (CPE) that attempts to integrate barrier, metabolic/mitochondrial, and inflammatory remodeling across aging and neurodegenerative disease. The conceptual ambition is clear; however, in its current form the paper does not yet meet the level of methodological rigor, evidentiary discipline, and editorial precision expected for a high-impact journal. Substantial revision is required to strengthen scientific credibility, improve clarity, and ensure that the proposed sequence is presented as a rigorously constrained, testable framework rather than an extended interpretative narrative.
1) Evidence hierarchy and overstatement of mechanistic certainty
A central concern is the inconsistent separation between (i) mechanisms directly supported by choroid plexus–specific data, (ii) mechanisms inferred from related epithelial systems, and (iii) speculative links proposed to complete the sequential model. Several steps—particularly those involving epithelial extrusion dynamics, mitochondrial “collapse,” and downstream inflammatory remodeling—are phrased with a level of certainty that is not consistently justified by direct in vivo evidence in the CP. For a top-tier audience, the manuscript must adopt stricter evidentiary language and explicitly label each component of the model according to its evidence level. I strongly recommend adding a dedicated subsection (or a boxed summary) clearly stating: what is established, what is inferred, and what is proposed, alongside a concise list of falsifiable predictions. This would markedly improve scientific transparency and reduce the risk of perceived overreach.
2) Mechanistic precision and definitional rigor
The manuscript relies heavily on broad terms such as “degeneration,” “collapse,” “failure,” and “breakdown.” These are rhetorically compelling but mechanistically imprecise and can be interpreted as overstated. Each stage of the sequential model should be defined using concrete, measurable readouts (e.g., specific junctional proteins and polarity markers; transporter expression/function; mitochondrial abundance vs competence; oxidative stress markers; inflammasome/cytokine signatures; barrier permeability metrics). At present, causal chains are often implied rather than explicitly demonstrated, and the discussion would benefit from stricter phrasing that distinguishes correlation from causation. A high-impact manuscript should consistently answer: what exactly changes, by what molecular mediator(s), and how would it be measured in CP tissue or CSF?
3) Structure, redundancy, and narrative tightening
The organization is generally logical, but multiple sections repeatedly revisit similar concepts (junction disruption, metabolic stress, inflammation) with substantial overlap, which dilutes the argument and reduces readability. The mechanistic core would benefit from significant condensation and restructuring. In particular, Section 2 should be streamlined so that each subsection contributes a distinct mechanistic element and advances the model rather than reiterating previously stated points. High-tier reviews are typically sharply edited, with each paragraph delivering a unique concept, a clear evidence basis, and an explicit link to the next step in the sequence.
4) Stronger constraint of the “sequential” claim
The sequential framing is the manuscript’s defining feature, yet the temporal and causal ordering of stages is not consistently justified. The authors should more explicitly argue why stage A precedes stage B (what triggers the transition, what molecular switch governs it, what evidence supports directionality). Where true temporal evidence is lacking, the text should explicitly state that the ordering is a proposed framework rather than a proven sequence. Additionally, consider discussing whether multiple trajectories may exist (e.g., aging-dominant vs inflammation-dominant pathways), and whether disease-specific patterns might deviate from the proposed general sequence.
5) Disease specificity and heterogeneity
The manuscript sometimes intermixes aging-related changes and neurodegenerative disease-associated alterations without sufficiently delineating what is shared versus disease-specific. For example, the CP phenotype in Alzheimer’s disease, multiple sclerosis, vascular cognitive impairment, and hydrocephalus-related states may involve overlapping but non-identical mechanisms. A more rigorous review should explicitly separate (i) conserved aging-related epithelial remodeling, (ii) neuroinflammatory disease contexts, and (iii) vascular/CSF dynamics as potential confounders or parallel drivers. This would prevent overgeneralization and increase interpretative precision.
6) Translational claims and imaging biomarkers require a more critical treatment
The discussion of CP enlargement on imaging as a biomarker is interesting but currently somewhat interpretative. A high-impact venue would require a more critical appraisal of confounding variables and alternative explanations (e.g., vascular congestion, systemic inflammation, medication effects, ventricular size/CSF pressure dynamics, scanner/segmentation variability). The authors should specify what their model uniquely predicts at the imaging level beyond volumetry (e.g., permeability measures, contrast enhancement patterns, diffusion metrics, perfusion changes), and what would distinguish compensatory hypertrophy from degenerative remodeling. This section should be strengthened with clearer evidence-based reasoning and explicit limitations.
7) Figures: strengthen evidence annotation and conceptual transparency
The schematic figures are useful, but they currently read as broad conceptual summaries. For a rigorous readership, each figure should more explicitly indicate which elements are directly supported by CP-specific data versus extrapolated versus proposed. An “evidence-coded” schematic (even using simple notation within captions) would substantially improve transparency. Captions should be expanded to include key references supporting each major arrow/transition, thereby allowing readers to quickly evaluate evidentiary strength.
8) References: ensure primary mechanistic coverage and avoid inaccessible citation practices
The bibliography appears broadly appropriate, but the manuscript would benefit from more consistent citation of primary mechanistic studies (rather than relying heavily on secondary summaries) at each major claim. Additionally, claims that rely on “manuscript under review” or non-public findings should be minimized or framed very cautiously, as they weaken verifiability. A high-impact review should be anchored in accessible, peer-reviewed primary evidence wherever possible.
9) English language and editorial polishing are essential
The English requires substantial refinement to meet high-tier editorial standards. Long, multi-clause sentences, repeated phrasing, and occasional awkward constructions obscure key mechanistic points and contribute to a lack of concision. A professional-level language edit is strongly recommended. Beyond grammar, the manuscript should be revised for sharper topic sentences, tighter paragraph construction, clearer transitions, and more disciplined terminology (consistent use of abbreviations and mechanistic vocabulary). This will significantly improve readability and perceived rigor.
The manuscript has potential and addresses a meaningful gap by attempting to integrate disparate findings into a coherent epithelial-centric framework. However, major revision is required to ensure the work is scientifically constrained, mechanistically precise, and editorially polished at a level appropriate for a prestigious journal. If the authors rigorously separate evidence from hypothesis, substantially tighten redundancy, strengthen disease-specific nuance, and present the sequential model as a set of clearly articulated, falsifiable predictions supported by primary literature, the manuscript could become a valuable and credible contribution.
The manuscript is generally understandable, but the English does not yet meet the level of clarity and concision expected for a high-impact journal. Several sections contain long, multi-clause sentences, repetitive phrasing, and occasional awkward constructions that obscure key mechanistic points and weaken the logical flow. A thorough professional-level language edit is strongly recommended, focusing not only on grammar, but also on tightening sentence structure, improving transitions between paragraphs, reducing redundancy, and standardizing terminology and abbreviations throughout.
Author Response
To Reviewer 1
The manuscript addresses an important and timely topic and proposes a sequential degeneration model of the choroid plexus epithelium (CPE) that attempts to integrate barrier, metabolic/mitochondrial, and inflammatory remodeling across aging and neurodegenerative disease. The conceptual ambition is clear; however, in its current form the paper does not yet meet the level of methodological rigor, evidentiary discipline, and editorial precision expected for a high-impact journal. Substantial revision is required to strengthen scientific credibility, improve clarity, and ensure that the proposed sequence is presented as a rigorously constrained, testable framework rather than an extended interpretative narrative.
(Comment 1) Evidence hierarchy and overstatement of mechanistic certainty
A central concern is the inconsistent separation between (i) mechanisms directly supported by choroid plexus–specific data, (ii) mechanisms inferred from related epithelial systems, and (iii) speculative links proposed to complete the sequential model. Several steps—particularly those involving epithelial extrusion dynamics, mitochondrial “collapse,” and downstream inflammatory remodeling—are phrased with a level of certainty that is not consistently justified by direct in vivo evidence in the CP. For a top-tier audience, the manuscript must adopt stricter evidentiary language and explicitly label each component of the model according to its evidence level. I strongly recommend adding a dedicated subsection (or a boxed summary) clearly stating: what is established, what is inferred, and what is proposed, alongside a concise list of falsifiable predictions. This would markedly improve scientific transparency and reduce the risk of perceived overreach.
<To comment 1>
According to comment 1, we revised abstract almost totally. In Fig. 3, we distinguished specific data, mechanisms inferred from data, and speculative links proposed to complete the sequential model and described. Specific data were circled by solid lines, whereas inferred descriptions were circled by dotted lines.
(Comment 2) Mechanistic precision and definitional rigor
The manuscript relies heavily on broad terms such as “degeneration,” “collapse,” “failure,” and “breakdown.” These are rhetorically compelling but mechanistically imprecise and can be interpreted as overstated. Each stage of the sequential model should be defined using concrete, measurable readouts (e.g., specific junctional proteins and polarity markers; transporter expression/function; mitochondrial abundance vs competence; oxidative stress markers; inflammasome/cytokine signatures; barrier permeability metrics). At present, causal chains are often implied rather than explicitly demonstrated, and the discussion would benefit from stricter phrasing that distinguishes correlation from causation. A high-impact manuscript should consistently answer: what exactly changes, by what molecular mediator(s), and how would it be measured in CP tissue or CSF?
<To comment 2>
According to comments 2 as well as 1, we revised abstract almost totally. In Fig. 3, we revised our manuscript by differentiating inferred mechanisms from published data.
(Comment 3) Structure, redundancy, and narrative tightening
The organization is generally logical, but multiple sections repeatedly revisit similar concepts (junction disruption, metabolic stress, inflammation) with substantial overlap, which dilutes the argument and reduces readability. The mechanistic core would benefit from significant condensation and restructuring. In particular, Section 2 should be streamlined so that each subsection contributes a distinct mechanistic element and advances the model rather than reiterating previously stated points. High-tier reviews are typically sharply edited, with each paragraph delivering a unique concept, a clear evidence basis, and an explicit link to the next step in the sequence.
<To comment 3>
According to comment 3, one section “2.1” was changed to “Structure of the choroid plexus epithelium-formation of blood-cerebrospinal fluid barrier-“. Another subsection “2.2” was changed to “Functional characteristics of the choroid plexus epithelium”. In addition, one subsection “2.3. Age-related and disease-associated vulnerability of the choroid plexus” was moved to new one subsection “3.4”.
One sentence in “2.1” was deleted. First paragraph in “3.3” was changed, whereas second paragraph in “3.3” was deleted. Three paragraphs in “5.4” were combined into one.
Two sentences in “6.3” were added to examine a role of CSF flow dynamics in neurodegeneration.
In addition, 6th sentence in “7” was deleted to avoid overlapping.
(Comment 4) Stronger constraint of the “sequential” claim
The sequential framing is the manuscript’s defining feature, yet the temporal and causal ordering of stages is not consistently justified. The authors should more explicitly argue why stage A precedes stage B (what triggers the transition, what molecular switch governs it, what evidence supports directionality). Where true temporal evidence is lacking, the text should explicitly state that the ordering is a proposed framework rather than a proven sequence. Additionally, consider discussing whether multiple trajectories may exist (e.g., aging-dominant vs inflammation-dominant pathways), and whether disease-specific patterns might deviate from the proposed general sequence.
<To comment 4>
According to comment 4, we distinguished specific data, mechanisms inferred from data, and speculative links proposed to complete the sequential model and described in Fig. 3. Specific data were circled by solid lines, whereas inferred descriptions were circled by dotted lines. Multiple trajectories were not observed in CP epithelial cells. At present, disease-specific patterns also remained to be clarified.
(Comment 5) Disease specificity and heterogeneity
The manuscript sometimes intermixes aging-related changes and neurodegenerative disease-associated alterations without sufficiently delineating what is shared versus disease-specific. For example, the CP phenotype in Alzheimer’s disease, multiple sclerosis, vascular cognitive impairment, and hydrocephalus-related states may involve overlapping but non-identical mechanisms. A more rigorous review should explicitly separate (i) conserved aging-related epithelial remodeling, (ii) neuroinflammatory disease contexts, and (iii) vascular/CSF dynamics as potential confounders or parallel drivers. This would prevent overgeneralization and increase interpretative precision.
<To comment 5>
We also think that this comment perfectly captures the point. In Fig. 3, specific data were circled by solid lines, whereas inferred descriptions were circled by dotted lines. Oxidative stress is associated with inflammation, whereas cell hypertrophy is associated with aging. In addition, BCSFB breakdown is associated with CSF dynamics dysfunction, whereas CP enlargement detected by MRI is associated with aging and neurodegeneration. These descriptions were added to figure legend of Fig. 3.
(Comment 6) Translational claims and imaging biomarkers require a more critical treatment
The discussion of CP enlargement on imaging as a biomarker is interesting but currently somewhat interpretative. A high-impact venue would require a more critical appraisal of confounding variables and alternative explanations (e.g., vascular congestion, systemic inflammation, medication effects, ventricular size/CSF pressure dynamics, scanner/segmentation variability). The authors should specify what their model uniquely predicts at the imaging level beyond volumetry (e.g., permeability measures, contrast enhancement patterns, diffusion metrics, perfusion changes), and what would distinguish compensatory hypertrophy from degenerative remodeling. This section should be strengthened with clearer evidence-based reasoning and explicit limitations.
<To comment 6>
It is very important to clarify what their model uniquely predicts at the imaging level beyond volumetry (e.g., permeability measures, contrast enhancement patterns, diffusion metrics, perfusion changes). However, at present, it is difficult to show clear evidence on it. The focus in this review paper was on clarifying morphological and molecular characteristics of CP epithelium in aged brains, as shown in new title. At present, it remains to be clarified what are the differences among CP volumes in neurodegenerative diseases, whereas CP volume was demonstrated to increase commonly in aged peoples and patients suffered from several kinds of neurodegenerative diseases.
7) Figures: strengthen evidence annotation and conceptual transparency
The schematic figures are useful, but they currently read as broad conceptual summaries. For a rigorous readership, each figure should more explicitly indicate which elements are directly supported by CP-specific data versus extrapolated versus proposed. An “evidence-coded” schematic (even using simple notation within captions) would substantially improve transparency. Captions should be expanded to include key references supporting each major arrow/transition, thereby allowing readers to quickly evaluate evidentiary strength.
<To comment 7>
According to comment 7, we added descriptions on CP-specific data or inferences from other cells with references in Fig. 2. In the legend of Fig. 3, we added descriptions on recent published data or inferences drawn from other data and on what is associated with inflammation, aging, or CSF dynamics disorder.
8) References: ensure primary mechanistic coverage and avoid inaccessible citation practices
The bibliography appears broadly appropriate, but the manuscript would benefit from more consistent citation of primary mechanistic studies (rather than relying heavily on secondary summaries) at each major claim. Additionally, claims that rely on “manuscript under review” or non-public findings should be minimized or framed very cautiously, as they weaken verifiability. A high-impact review should be anchored in accessible, peer-reviewed primary evidence wherever possible.
<To comment 8>
Our recent paper, which was under review at the first submission [14], was accepted for publication in Neuropathology. Accordingly, we revised descriptions of this paper [15]. We added 9 new papers for reference. We have narrowed down the cited literature to key papers throughout the paper.
9) English language and editorial polishing are essential
The English requires substantial refinement to meet high-tier editorial standards. Long, multi-clause sentences, repeated phrasing, and occasional awkward constructions obscure key mechanistic points and contribute to a lack of concision. A professional-level language edit is strongly recommended. Beyond grammar, the manuscript should be revised for sharper topic sentences, tighter paragraph construction, clearer transitions, and more disciplined terminology (consistent use of abbreviations and mechanistic vocabulary). This will significantly improve readability and perceived rigor.
<To comment 9>
We improved our English writing.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe review manuscript by Murakami and Ueno with a title “A Sequential Degeneration Model of the Choroid Plexus Epithelium” summarizes the current literature on the choroid plexus (CP) and its role in aging and neurodegenerative diseases, with a focus on epithelial cells of CP. While the topic is interesting, the review itself lacks focus and does not delve into specific aspects in detail.
The title is not justified by the article’s content. Please increase the focus of the review.
The authors mention TOM20 and SPINT1 as important proteins for introducing various aspects. More comprehensive background information on these two proteins would be desirable.
The need for clinical translation is not addressed.
The authors cite numerous review articles. More original articles should be included. Please also use more recent literature where possible.
The authors repeatedly cite up to 14 different references in a sentence without summarizing their content in more detail. Are all these references truly necessary for a single sentence? Please add further information from the cited articles to the text (e.g. page 3, line 109; page 4, line 120; page 5, line 171; page 5, line 182; page 6, line 230 and 242; page 7, line 251 and 277; page 8, line 297, 310 and 320; page 9, line 347, 358, 369).
Minor
Please use abbreviations consistently, e.g. “BCSFB” -page 4, line 141; page 7, line 265; page 8, line 314; page 9, line 338- BCSFB is explained in the introduction (page 1, line 35), therefore please use abbreviations after the first use. Please correct all the other terms and their abbreviations: choroid plexus, aquaporin-1, SPINT1
Reference 14 – manuscripts that are under review should not be cited
Figure 1- only one mitochondrion per cell is shown, but “the cytoplasm of these cells is densely packed with mitochondria”. More mitochondria could be drawn into the cytoplasm.
Author Response
(Reviewer 2)
The review manuscript by Murakami and Ueno with a title “A Sequential Degeneration Model of the Choroid Plexus Epithelium” summarizes the current literature on the choroid plexus (CP) and its role in aging and neurodegenerative diseases, with a focus on epithelial cells of CP. While the topic is interesting, the review itself lacks focus and does not delve into specific aspects in detail.
(1)The title is not justified by the article’s content. Please increase the focus of the review.
<To comment 1>
We changed the title to “Morphological and molecular characteristics of choroid plexus epithelium in aged brains” to increase the focus of our review paper.
(2)The authors mention TOM20 and SPINT1 as important proteins for introducing various aspects. More comprehensive background information on these two proteins would be desirable.
<To comment 2>
We added descriptions on Tom20 in one subsection “5.1” and on SPINT1 in one subsection “4.3”.
(3)The need for clinical translation is not addressed.
<To comment 3>
We added descriptions on clinical translation in the last paragraph of “9”.
(4)The authors cite numerous review articles. More original articles should be included. Please also use more recent literature where possible.
<To comment 4>
We added 9 new papers for reference including more recent literature.
(5)The authors repeatedly cite up to 14 different references in a sentence without summarizing their content in more detail. Are all these references truly necessary for a single sentence? Please add further information from the cited articles to the text (e.g. page 3, line 109; page 4, line 120; page 5, line 171; page 5, line 182; page 6, line 230 and 242; page 7, line 251 and 277; page 8, line 297, 310 and 320; page 9, line 347, 358, 369).
<To comment 4>
We have narrowed down the cited literature to key papers throughout the paper.
Minor
(1)Please use abbreviations consistently, e.g. “BCSFB” -page 4, line 141; page 7, line 265; page 8, line 314; page 9, line 338- BCSFB is explained in the introduction (page 1, line 35), therefore please use abbreviations after the first use. Please correct all the other terms and their abbreviations: choroid plexus, aquaporin-1, SPINT1
<To minor comment 1>
We revised usage of abbreviations such as BCSFB, CP (choroid plexus), AQP1 (aquaporin-1), and SPINT1 throughout the paper.
(2)Reference 14 – manuscripts that are under review should not be cited
<To minor comment 2>
Our recent paper, which was under review at the first submission [14], was accepted for publication in Neuropathology. Accordingly, we revised descriptions of this paper [15].
(3)Figure 1- only one mitochondrion per cell is shown, but “the cytoplasm of these cells is densely packed with mitochondria”. More mitochondria could be drawn into the cytoplasm.
<To minor comment 3>
We revised Figure 1, as edited to show more mitochondria into the cytoplasm
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have revised the manuscript according to the reviewers’ comments. I have no further concerns.
