Mechanisms Involved in Pathological Succinate-Mediated Signaling

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review systematically discusses the pathological signaling roles of succinate in disease, with a particular focus on extracellular succinate, SUCNR1 receptor-mediated signaling, ischemia - reperfusion injury, inflammatory responses, and the underlying mechanisms in organs such as the heart, kidney, and brain, while also summarizing the potential application of succinate as a biomarker. Although the manuscript is relatively comprehensive, some revisions are still needed, and the specific comments are as follows:

 

Major Comments

1. As a review article, the manuscript should clearly describe the literature search strategy, including the databases consulted, search terms, time span covered, inclusion and exclusion criteria, whether primary studies and review articles were treated differently, and whether any assessment of evidence quality was performed. Without this information, it is difficult to evaluate the comprehensiveness, reproducibility, and potential selectivity of the literature coverage. At minimum, a dedicated “Review Methodology” section should be added.
2. The manuscript reviews the role of succinate and SUCNR1 across multiple organs and disease settings, including the heart, kidney, brain, and several chronic inflammatory conditions. To improve readability and help readers extract the key information efficiently, the authors should consider adding a comparative table summarizing, for each organ or condition, the trigger or pathological context, the major responding cell types, the principal signaling pathways involved, and the functional or pathological outcomes.
3. At Line 170 - 172, the discussion moves from intracellular succinate accumulation to extracellular succinate signaling, but the connection between these two levels remains underdeveloped. A short transition paragraph would improve the logic of the review by clarifying when intracellular mechanisms predominate, when extracellular signaling through SUCNR1 becomes more relevant, and how these two processes interact under different pathological conditions.
4. At Line 206, SUCNR1 is described as a “Gi-coupled receptor,” whereas Lines 218 - 223 discuss recent evidence indicating that different succinate concentrations may stabilize different receptor conformations and preferentially engage distinct G-protein pathways. These statements are not fully aligned. The receptor should therefore be defined more precisely, with terminology that reflects context-dependent or concentration-dependent signaling behavior, so as to avoid ambiguity.
5. At Line 406 - 455, The authors propose that succinate may serve as a biomarker in trauma, diabetes remission, transplantation, and cancer, which is a valuable perspective. However, the section lacks a comparative analysis of sensitivity, specificity, sample type, time window, detection methods, and clinical feasibility.
6. At Lines 447 - 454, the conclusion emphasizes that succinate can both promote injury and mediate protective adaptation, but the summary of the determinants underlying this “bidirectional” effect remains rather general. It is recommended that the conclusion explicitly incorporate the key variables discussed in the main text, such as succinate concentration, cell type, and receptor localization.
7. The current title, particularly the phrase “in disease,” is very broad. In practice, the review is centered mainly on extracellular succinate, SUCNR1-mediated signaling, inflammatory responses, ischemia - reperfusion injury, and selected organ systems. A more focused title could be considered, for example, one that emphasizes “extracellular succinate/SUCNR1 signaling across inflammatory and ischemic disorders.”
8. The manuscript cites in vitro experiments, animal models, patient serum observations, and review articles in parallel. It is recommended that, for each key conclusion, the authors specify which findings are derived from cell-based studies, which have been validated in animal models, and which are supported by clinical association evidence.

 

Minor Comments

1. At Line 473, HIF-1α is expanded as “Hydroxylating hypoxia-inducible factor 1 alpha,” which is inaccurate. The term “hydroxylating” refers to an upstream regulatory process, not to the name of HIF-1α itself. This should be corrected. More broadly, the authors are encouraged to verify that all abbreviations are consistent with their first appearance in the main text.
2. Professional terminology should be used consistently throughout the manuscript. In the abbreviation list (Line 473), MCT1 is defined as “Monocarboxylate carrier 1,” whereas in the legend of Figure 1 (Line 139), it is described as “Monocarboxylate transporter 1.” In addition, “hyprophobic” in Line 238 should be corrected to “hydrophobic,” and “MTC1” in Line 155 should be corrected to “MCT1.” The authors are advised to carefully proofread the entire manuscript and check for similar errors throughout.
3. At Line 518, reference [21] is missing author information. The authors should verify the full bibliographic details, including author names, article title, journal format, volume, issue, page range, and DOI presentation, to ensure that the reference list is complete and professionally formatted. In addition, Reference [22] at Line 520 and reference [65] at Line 614 appear to cite the same article. The reference list should be checked carefully for additional duplicate entries.

Author Response

Response to the reviewers

Reviewer 1

We would like to point out that according to the suggestion of this reviewer, the article was carefully checked  by a native-english speaker with scientific background.  We carefully revised final versión and think that the English has been sustantially improved and the ideas are clearly expressed

Comments and Suggestions for Authors

This review systematically discusses the pathological signaling roles of succinate in disease, with a particular focus on extracellular succinate, SUCNR1 receptor-mediated signaling, ischemia - reperfusion injury, inflammatory responses, and the underlying mechanisms in organs such as the heart, kidney, and brain, while also summarizing the potential application of succinate as a biomarker. Although the manuscript is relatively comprehensive, some revisions are still needed, and the specific comments are as follows:

Major Comments

1. As a review article, the manuscript should clearly describe the literature search strategy, including the databases consulted, search terms, time span covered, inclusion and exclusion criteria, whether primary studies and review articles were treated differently, and whether any assessment of evidence quality was performed. Without this information, it is difficult to evaluate the comprehensiveness, reproducibility, and potential selectivity of the literature coverage. At minimum, a dedicated “Review Methodology” section should be added.

Our response: Thank you for your comment. We agree that providing the review methodology is essential to obtain robust and reproducible search results.  We describe the literature search strategy in a new header in the manuscript (2. Review Methodology), as follows: 

Databases Consulted: The main database consulted was PUBMED/Medline as a subject-specific database. 

Search terms: Those included core concepts, subject headings and keywords, such as “mitochondrial DAMPS”, “succinate receptor signaling”, succinylation in physiopatology” and “succinate metabolism in health and disease”. 

Time span covered: We include most recent literature ranging between 5-10 years to guarantee relevance and currency.  Some classical concepts described in the text, have earlier references.

Inclusion and Exclusion criteria: We included mainly experimental reports, but also small-case clinical report (Reference 62) and large clinical studies (Reference 61) were incorporated.  We did not include Editorials nor conference abstracts.

2. The manuscript reviews the role of succinate and SUCNR1 across multiple organs and disease settings, including the heart, kidney, brain, and several chronic inflammatory conditions. To improve readability and help readers extract the key information efficiently, the authors should consider adding a comparative table summarizing, for each organ or condition, the trigger or pathological context, the major responding cell types, the principal signaling pathways involved, and the functional or pathological outcomes.

Our response: Thank you for your valuable comment. In response to your suggestion, we have incorporated a comparative table into the manuscript that describes the signaling pathways triggered by the interaction of succinate with its receptor across different tissues (Table 1). This table also specifies the experimental conditions under which these pathways were identified, as well as their associated functional outcomes.

3. At Line 170 - 172, the discussion moves from intracellular succinate accumulation to extracellular succinate signaling, but the connection between these two levels remains underdeveloped. A short transition paragraph would improve the logic of the review by clarifying when intracellular mechanisms predominate, when extracellular signaling through SUCNR1 becomes more relevant, and how these two processes interact under different pathological conditions.

Our response: We have incorporated a transition paragraph that explicitly links intracellular succinate accumulation with its extracellular signaling role. This addition clarifies the conditions under which intracellular mechanisms, including metabolic alterations and post-translational modifications, predominate, as well as when extracellular signaling through SUCNR1 becomes more relevant, improving the overall coherence and logical flow of the review.

4. At Line 206, SUCNR1 is described as a “Gi-coupled receptor,” whereas Lines 218 - 223 discuss recent evidence indicating that different succinate concentrations may stabilize different receptor conformations and preferentially engage distinct G-protein pathways. These statements are not fully aligned. The receptor should therefore be defined more precisely, with terminology that reflects context-dependent or concentration-dependent signaling behavior, so as to avoid ambiguity.

 

Our response: The discrepancy in the description of the succinate receptor has been corrected, and a more detailed explanation has been incorporated to clarify how variations in succinate levels modulate receptor activity, resulting in extracellular succinate concentration–dependent signaling.  

5. At Line 406 - 455, The authors propose that succinate may serve as a biomarker in trauma, diabetes remission, transplantation, and cancer, which is a valuable perspective. However, the section lacks a comparative analysis of sensitivity, specificity, sample type, time window, detection methods, and clinical feasibility.

 

Our response: We have incorporated a concluding paragraph, based on the reported evidence, for considering extracellular succinate as a potential biomarker. This section describes the proposed sampling approach (blood-based measurements), the analytical methods employed for its detection (e.g., quantitative mass spectrometry–based metabolomics), and key considerations for future studies aimed at establishing its clinical relevance.

6. At Lines 447 - 454, the conclusion emphasizes that succinate can both promote injury and mediate protective adaptation, but the summary of the determinants underlying this “bidirectional” effect remains rather general. It is recommended that the conclusion explicitly incorporate the key variables discussed in the main text, such as succinate concentration, cell type, and receptor localization.

 

Our response: We thank the reviewer for this valuable comment. In response, we have incorporated a more comprehensive concluding section that provides a mechanistic explanation for the duality of SUCNR1 signaling. This addition also emphasizes that such signaling exerts diverse and context-dependent effects across different tissues, thereby offering a more integrated perspective.

 

7. The current title, particularly the phrase “in disease,” is very broad. In practice, the review is centered mainly on extracellular succinate, SUCNR1-mediated signaling, inflammatory responses, ischemia - reperfusion injury, and selected organ systems. A more focused title could be considered, for example, one that emphasizes “extracellular succinate/SUCNR1 signaling across inflammatory and ischemic disorders.”

 

Our response: We appreciate the reviewer’s observation and agree with this point. Accordingly, we have changed the section title to “Mechanisms Involved in Pathological Succinate-Mediated Signaling,” as the previous wording was redundant by combining “pathological” with “in disease.” This modification improves clarity and avoids unnecessary repetition.

 

8. The manuscript cites in vitro experiments, animal models, patient serum observations, and review articles in parallel. It is recommended that, for each key conclusion, the authors specify which findings are derived from cell-based studies, which have been validated in animal models, and which are supported by clinical association evidence.

 

Our response: Taking the reviewer’s comment into consideration, in the comparative table we added a section indicating the type of experimental model used for each organ and condition, allowing for a more precise comparison of the reported studies.

Minor Comments

1. At Line 473, HIF-1α is expanded as “Hydroxylating hypoxia-inducible factor 1 alpha,” which is inaccurate. The term “hydroxylating” refers to an upstream regulatory process, not to the name of HIF-1α This should be corrected. More broadly, the authors are encouraged to verify that all abbreviations are consistent with their first appearance in the main text.

Our response: Thank you for your comment. The error has been corrected, and all abbreviations have been carefully reviewed.

2. Professional terminology should be used consistently throughout the manuscript. In the abbreviation list (Line 473), MCT1 is defined as “Monocarboxylate carrier 1,” whereas in the legend of Figure 1 (Line 139), it is described as “Monocarboxylate transporter 1.” In addition, “hyprophobic” in Line 238 should be corrected to “hydrophobic,” and “MTC1” in Line 155 should be corrected to “MCT1.” The authors are advised to carefully proofread the entire manuscript and check for similar errors throughout.

Our response: Thank you for your comment. The noted errors have been corrected, and a thorough review was conducted to identify and address any similar issues throughout the manuscript.

3. At Line 518, reference [21] is missing author information. The authors should verify the full bibliographic details, including author names, article title, journal format, volume, issue, page range, and DOI presentation, to ensure that the reference list is complete and professionally formatted. In addition, Reference [22] at Line 520 and reference [65] at Line 614 appear to cite the same article. The reference list should be checked carefully for additional duplicate entries.

Our response: The reference list was thoroughly reviewed using Zotero to identify and remove duplicate entries, and to ensure that all references contain complete information so that citations are presented accurately and consistently.

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

The submitted review manuscript aims to provide an “extensive discussion” of signaling pathways activated by extracellular succinate via SUCNR1 across tissues and diseases, and to comment on the therapeutic/biomarker potential of succinate regulation.

The topic is timely and important since succinate has well-established roles beyond metabolism, and SUCNR1 biology is increasingly recognized as context-dependent, with tissue-, cell type-, and concentration-dependent consequences. The manuscript contains several strengths such as clear high-level section structure; inclusion of recent mechanistic work on ligand binding and signaling bias; coverage of ischemia–reperfusion succinate biology; two helpful pathway figures. However, there are several important issues to be fixed in the major revision:

1. Surely, under certain conditions, succinate can be regarded as a DAMP, though it is not a classic DAMP, but rather a metabolic danger signal (metabolic DAMP / metabokine). I do not think that succinate is a classical DAMP. Please, discuss this issue.
2. Duplicated references and mis-numbered/mismatched citations. Perform a full citation audit.
3. Missing key primary/defining papers, given the manuscript’s broad framing, including:

1. Identification of SUCNR1/GPR91 as a receptor for succinate (2004 Nature paper).
2. Work demonstrating macrophage succinate release and SUCNR1-dependent amplification in inflammatory arthritis (feed-forward loop concept).
3. Recent structural works (e.g., cryo-EM structures and activation mechanisms) that directly underpin claims about binding sites and signaling bias.

4. Scope gaps. The text doesn't talk enough about the retina, blood vessel growth, AMD, mast-cell biology, and other immune-related topics. These topics are underdeveloped relative to the disease breadth implied by title/abstract.

Author Response

Reviewer 2

 

Comments and Suggestions for Authors

The submitted review manuscript aims to provide an “extensive discussion” of signaling pathways activated by extracellular succinate via SUCNR1 across tissues and diseases, and to comment on the therapeutic/biomarker potential of succinate regulation.

The topic is timely and important since succinate has well-established roles beyond metabolism, and SUCNR1 biology is increasingly recognized as context-dependent, with tissue-, cell type-, and concentration-dependent consequences. The manuscript contains several strengths such as clear high-level section structure; inclusion of recent mechanistic work on ligand binding and signaling bias; coverage of ischemia–reperfusion succinate biology; two helpful pathway figures. However, there are several important issues to be fixed in the major revision:

1. Surely, under certain conditions, succinate can be regarded as a DAMP, though it is not a classic DAMP, but rather a metabolic danger signal (metabolic DAMP / metabokine). I do not think that succinate is a classical DAMP. Please, discuss this issue.

Our response: We agree that succinate does not fit the definition of a classical damage-associated molecular pattern (DAMP), which typically includes structurally conserved intracellular molecules released upon cell damage. Instead, succinate is more appropriately classified as a metabolic danger signal, often referred to as a metabolic DAMP or metabokine. Under conditions of cellular stress or injury, the accumulation and extracellular release of succinate can activate signaling pathways—primarily through its receptor SUCNR1. In this context, succinate shares functional similarities with DAMPs, although its origin and mode of action are metabolically driven rather than structurally predefined.

 

2. Duplicated references and mis-numbered/mismatched citations. Perform a full citation audit.

Our response: Thank you for your observation. A thorough review of the reference list and in-text citations has been conducted, and all duplicated, misnumbered, and mismatched citations have been corrected accordingly.

 

3. Missing key primary/defining papers, given the manuscript’s broad framing, including:

a. Identification of SUCNR1/GPR91 as a receptor for succinate (2004 Nature paper).

b. Work demonstrating macrophage succinate release and SUCNR1-dependent amplification in inflammatory arthritis (feed-forward loop concept).

c. Recent structural works (e.g., cryo-EM structures and activation mechanisms) that directly underpin claims about binding sites and signaling bias.

Our response: Thank you for your comment. We have addressed this point and incorporated the suggested references into the revised manuscript to ensure the content aligns with the recommended scope.

He et al., “Citric acid cycle intermediates as ligands for orphan G-protein-coupled receptors,” Nature, vol. 429, no. 6988, pp. 188–193, May 2004, doi: 10.1038/nature02488

Li et al., “Succinate induces synovial angiogenesis in rheumatoid arthritis through metabolic remodeling and HIF-1α/VEGF axis,” Free Radical Biology and Medicine, vol. 126, pp. 1–14, Oct. 2018, doi: 10.1016/j.freeradbiomed.2018.07.009.

Huang et al., “Cellular succinate metabolism and signaling in inflammation: implications for therapeutic intervention,” Front. Immunol., vol. 15, p. 1404441, Jun. 2024, doi: 10.3389/fimmu.2024.1404441.

Liu et al., “Succinate dehydrogenase mediated ROS production contributes to ASIC1a-induced chondrocyte pyroptosis in rheumatoid arthritis,” Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, vol. 1871, no. 3, p. 167585, Mar. 2025, doi: 10.1016/j.bbadis.2024.167585.

Liu, Y. Liu, W. Zhang, and R. D. Ye, “Structural insights into ligand recognition and activation of the succinate receptor SUCNR1,” Cell Reports, vol. 43, no. 7, p. 114381, Jul. 2024, doi: 10.1016/j.celrep.2024.114381.

 

4. Scope gaps. The text doesn’t talk enough about the retina, blood vessel growth, AMD, mast-cell biology, and other immune-related topics. These topics are underdeveloped relative to the disease breadth implied by title/abstract.

Our response: We apologize for not addressing these aspects in greater depth. This limitation is primarily due to the scarcity of experimental evidence regarding the interaction between succinate and its receptor in these specific contexts. While notable advances have been reported in these pathologies, the available data remain insufficient to support a more detailed discussion. Accordingly, we have chosen to avoid overinterpretation until further evidence becomes available.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have made all the required revisions to the manuscript. The article can now be accepted.

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript is clearly improved and now approaches publishable quality.