Human Non-Hypertrophic Nonunion Tissue Contains Osteoblast Lineage Cells and E-BMP-2 Activates Osteogenic and Chondrogenic Differentiation

Round 1

Reviewer 1 Report

This is an interesting study whereby the authors have investigated the effect of E-BMP-2 ability to activate osteoblast cells from Human Non-hypertrophic Nonunion tissue towards an osteogenic and chondrogenic lineage. The manuscript is well written with a concise hypothesis and clear methods and analysis. The conclusion is good, and the authors have cited the limitations to the study

There are a couple of points that the authors need to address and comment on.

The non-hypertrophic non-union tissue isolated from the patients which gave rise to the cells the authors used in the studies, were they a homogenous set of cells or would they contain numerous cell types such as fibroblasts, macrophages etc?

One of the reasons for non-unions is the lack of vascularisation of the fracture. Could the authors comment on this in relation to their findings with E-BMP-2 on the NHNCs.

Did the authors test the differentiation profile of normal human bone marrow mesenchymal stem cells. This would have been interesting to note how well the E-BMP-2 is effective in these differing populations of cells. The authors did refer to a reference whereby the normal BMSC had an increased level of proliferation compared to cells isolated from atrophic fracture non-union.

BMSC can be differentiated down the three lineages. Did the authors run any experiments with these NHNCs /E-BMP-2 and examine the adipogenic potential?

It is interesting in the discussion that E-BMP-2 induced chondrogenic differentiation as well in these NHNCs. Would this happen with normal BMSC?

In the Non-hypertrophic Non-union tissue do the authors think that the lack of BMP-2 is the cause of this problem or is it the other cell types, ECM and microenvironment adding to the problem.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors, I have read with interest the manuscript. First of all I have to congratulate for the topic selected and the conclusions obtained.
Prior to consider this paper for publication authors should answer some questions and solve some issues not clear in the manuscript:

In the research are included 5 patients, 4 patients with a lower extremity fracture and 1 patient with an upper extremity fracture, but with a bone with different embryological ossification mechanism. Recent publications focused in differences between bone activity according to the ossification origin. How this difference may affect outcomes.

When we review images from patients, there are huge differences between patients. How this heterogeneity may affect outcomes? Why are differences so huge between samples?

Author Response

Please see the attachment.

Author Response File: Author Response.docx