Association between Donor Age and Osteogenic Potential of Human Adipose Stem Cells in Bone Tissue Engineering

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper entitled Association between Donor Age and Osteogenic Potential of Human
Adipose Stem Cells in Bone Tissue Engineering is presented.  The review is potentially interesting and well-presented.

 

There are some possible issues

In general, the discussion on the cellular  and molecular mechanistic insights of of Human Adipose Stem Cells in Bone Tissue Engineering is limited. For instance, the process of bone tissue regeneration is regulated by intramembranous and endochondral ossification as previously reported (for example, PMID: 33385019). It would be informative to discuss the cellular mechanism of Adipose Stem Cells on bone tissue regeneration.

Previous studies (for example PMID: 22465238) have shown that bone tissues contain many cell types such as macrophages, osteoclasts, osteoblasts, bone lining cells, osteomacs, and vascular endothelial cells, etc. It would be informative to discuss how Adipose Stem Cells might regulate these cell types in the bone local environment, which could facilitate bone tissue regeneration.  

Author Response

In general, the discussion on the cellular and molecular mechanistic insights of Human Adipose Stem Cells in Bone Tissue Engineering is limited. For instance, the process of bone tissue regeneration is regulated by intramembranous and endochondral ossification as previously reported (for example, PMID: 33385019). It would be informative to discuss the cellular mechanism of Adipose Stem Cells on bone tissue regeneration.

 

- We appreciate the comment of this reviewer and agree that some information on the cellular and molecular mechanisms of ASCs for bone tissue engineering was missing. Therefore, we added further sections on t the difference between the natural bone remodeling and bone repair process –highlighting the first is a lifelong process that takes place in every healthy individual, and the latter is a natural bone healing process in the case of mechanical injury.

In lines 24-50, we have described the 4-step mechanism of the natural bone healing process with an illustration on page 2 (Figure 1). We reviewed more papers on this topic (including one the referee mentioned) and outlined the cellular and molecular mechanism of fracture healing and the role of MSCs in this regard.

 

Previous studies (for example PMID: 22465238) have shown that bone tissues contain many cell types such as macrophages, osteoclasts, osteoblasts, bone lining cells, osteomacs, and vascular endothelial cells, etc. It would be informative to discuss how Adipose Stem Cells might regulate these cell types in the bone local environment, which could facilitate bone tissue regeneration.

 

- We thank this reviewer for raising this interesting point. To explain the ASC interaction with other cells, e.g. deriving from the immune system, we added further information on the role of ASCs in fracture healing (lines 122-136 on page 4). Admittedly, the mechanism by which ASCs influence the natural bone healing process is rather vague, however, a prevailing argument is that ASCs influence this process by their paracrine activity.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript summarizes recent updates regarding the age effects on human adipose stem cells’ (ASCs) osteogenic potential. Overall, the manuscript is well-written. However, minor revisions are recommended to address the issues outlined below.

 

1. There are several typos in the article. Thus, thorough proofreading is necessary.
2. As the authors have noted, estrogen level is crucial for bone regeneration and development. It might be more informative to conduct a sub-catalog analysis that separates studies including both genders from those conducted solely on female donors. 
3. The accurate definition of MSC, specifically ASCs, remains an open question (PMID: 34766140). Particularly, adult ASCs comprise at least two sub-populations (PMID: 21861688). While there may not be extensive research investigating the impact of age on them, the heterogeneity of ASCs could be a contributing factor to the conflicting results observed in the involved studies. This topic warrants discussion. 
4. One of the current hot topics regarding MSCs is their mechanism of action in tissue regeneration. A prevailing argument is that their therapeutic effects, at least in the long term, rely on their bioactive soluble factor production and secretion rather than direct cellular differentiation (PMID: 27612948, PMID: 28757877, PMID: 20412005, PMID: 34766140, et al.). It is also an issue that should be discussed, at least briefly. 

Comments on the Quality of English Language

1. There are several typos in the article. Thus, thorough proofreading is necessary.

Author Response

Comments and Suggestions for Authors:

As the authors have noted, estrogen level is crucial for bone regeneration and development. It might be more informative to conduct a sub-catalog analysis that separates studies including both genders from those conducted solely on female donors.

 

- We appreciate this reviewer`s comment and added further information on the inclusion of female-only vs. both-gender studies analyzed in our review. Among 15 included studies, six studies recruited female-only donors, this information was added to page 5, lines 159-161. Among six studies that isolated ASCs from female donors only, three studies considered the age range for perimenopause when estrogen level changes rapidly, and revealed declined osteogenic potential during the peri-menopausal period (40s). This information was added to lines 291-301. A comparison between the studies that included both genders and studies that included females only was not feasible because not all studies that included females only considered the age range related to perimenopause.

 

The accurate definition of MSC, specifically ASCs, remains an open question (PMID: 34766140). Particularly, adult ASCs comprise at least two sub-populations (PMID: 21861688). While there may not be extensive research investigating the impact of age on them, the heterogeneity of ASCs could be a contributing factor to the conflicting results observed in the involved studies. This topic warrants discussion.

 

- We thank this reviewer for raising this point; we totally agree and the controversy regarding the ASC definition has been added to lines 109-120. We cited the paper by Bourin et at (2013) who described specific characteristics of ASCs both in SVF and in culture, and how to differentiate ASCs from bmMSCs, as defined by the International Federation for Adipose Therapeutics and Science (IFATS) and the International Society for Cell and Gene Therapy ((ISCT).

The information on how included studies defined ASCs and how this could contribute to the conflicting findings have been added to lines 340-350.

 

One of the current hot topics regarding MSCs is their mechanism of action in tissue regeneration. A prevailing argument is that their therapeutic effects, at least in the long term, rely on their bioactive soluble factor production and secretion rather than direct cellular differentiation (PMID: 27612948, PMID: 28757877, PMID: 20412005, PMID: 34766140, et al.). It is also an issue that should be discussed, at least briefly.

 

- This is an excellent point raised by this reviewer. Indeed, the regenerative potential of MSCs (including ASCs) is generally defined by their capacity for proliferation, multipotency for differentiation, and their release of soluble factors. However, we agree with this reviewer that under natural conditions (not artificial bone tissue engineering) the secretory activity of ASCs has a stronger impact on tissue regeneration than their differentiation abilities. Thus, we have included the proposed mechanism of how ASCs could influence the bone repair process in lines 122-136.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

I commend your manuscript as an intriguing compilation of knowledge and literature that explores significant achievements in the field of medical research on Mesenchymal Stem Cells (ASCs). Mesenchymal stem cells (ASCs), derived from adipose tissue, hold great promise for regenerative therapies due to their versatility in differentiating into various cell types, immunomodulatory properties, and their ability to regulate repair processes through paracrine signaling. The added benefit of their easy retrieval without causing harm to the donor further underscores their potential.

Your acknowledgment of these attributes is apt, and your commitment to conducting a comprehensive review of scientific literature, including experimental studies in this domain, is commendable. Your manuscript systematically consolidates the current state of knowledge regarding the impact of age on the therapeutic potential of osteogenic human adipose-derived stem cells (hASCs). Your notable focus on evaluating the outcomes of numerous studies conducted between 2005 and 2021, scrutinizing conflicting results related to the osteogenic potential of hASCs based on the donor's age, significantly strengthens your review.

The thoughtful approach you have taken in critically analyzing the literature enhances the overall robustness of the review. However, the unresolved aspect concerning the utility of cells obtained from elderly donors for therapeutic purposes introduces a layer of complexity to the discussion.

Best regards,

Author Response

We would like to thank the reviewer for his/her appreciation and for taking the time to review our manuscript.

Reviewer 4 Report

Comments and Suggestions for Authors

Summary of the Manuscript: This study investigates the influence of donor age on the osteogenic potential of human adipose stem cells in bone tissue engineering. It involves a systematic review of existing literature and presents findings that highlight variations in stem cell efficacy based on donor age.

 

Strengths and Weaknesses: 

Strengths: 

• Relevant and timely topic in regenerative medicine.
• Comprehensive literature review.
• Clear presentation of results.
• Weaknesses:
• Lack of detailed methodology.
• Limited comparative analysis with existing studies.
• Conclusions need more emphasis on clinical implications.

• Recommendations for Improvement:

• Methodology: Provide a more thorough description of the selection criteria and data analysis methods.
• Comparative Analysis: Include a detailed comparison of the findings with existing studies to contextualize the results.
• Discussion: Expand the discussion to include potential clinical applications and future research directions.
• References: Update and broaden the reference list to include recent and pivotal studies.
• Figures/Tables: Ensure all figures and tables are clearly labeled, referenced in the text, and their relevance is explained.
• Clarity and Structure: Enhance the overall structure and clarity of the manuscript, particularly in the methodology and discussion sections.
•  

Author Response

Methodology: Provide a more thorough description of the selection criteria and data analysis methods.

- Done. As suggested by this reviewer we included the literature search method and selection criteria of literature In lines 156-166, with a flow chart. Since it is a narrative review rather than a systematic review, including detailed selection criteria should not be necessary.

 

Comparative Analysis: Include a detailed comparison of the findings with existing studies to contextualize the results.

Done. As suggested by this reviewer, we have summarized the results of 15 original studies in Table 1, and described the result in Section 2 (Review of previous studies).

Discussion: Expand the discussion to include potential clinical applications and future research directions.

Done. As suggested by this reviewer, section 3 (Discussion) now involves a discussion of the findings of our selected studies. Examples of the therapeutic potential and clinical application of ASCs have been added to lines 104-107

References: Update and broaden the reference list to include recent and pivotal studies. Figures/Tables: Ensure all figures and tables are clearly labeled, and referenced in the text, and their relevance is explained.

- Done. As suggested by this reviewer, the reference list was updated with more recent publications on the topic. Tables and figures are clearly labeled.

Clarity and Structure: Enhance the overall structure and clarity of the manuscript, particularly in the methodology and discussion sections.

- Done. As suggested by this reviewer we have thoroughly revised the manuscript and improved structure and clarity accordingly.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

 

I've reviewed the article titled "Association between donor age and osteogenic potential of human adipose stem cells in bone tissue engineering." The article provides a comprehensive review of existing data on the impact of donor age on the osteogenic potential of human adipose stem cells (ASCs). It addresses the inconsistent findings in previous studies and attempts to explain the reasons behind these discrepancies. The article discusses how donor-related factors such as age, gender, lifestyle, health, and metabolic state can influence the osteogenic potential of ASCs. Additionally, it suggests that future studies should consider various experimental factors in in-vitro conditions, such as passaging, cryopreservation, culture conditions, differentiation protocols, and readout methods.

Overall, the article appears to be well-structured and thorough in its approach, providing a critical analysis of the current understanding of ASCs' osteogenic potential and its relation to donor age. This suggests an improvement in clarity and depth compared to previous versions of the article.