Review for 10.1186/1471-230X-6-40 (2006)

Reviewer's report 
 Urokinase-type plasminogen activator supports liver repair independent of binding to its cellular Title: 
receptor 
 1  29 July 2006 Version: Date: 
 Wendy Mars Reviewer: 
Reviewer's report: 
General: 
This paper describes the differential effects of injecting carbon tetrachloride on hepatic repair in mice 
lacking u-PA, u-PAR, or a double knockout combining u-PAR and t-PA deficiencies. The present study is an 
extension of previous work by the senior author, published in 2001 in the Am J Path. In the previous 
publication, the authors utilized the same strategy (carbon tetrachloride injections to induce hepatic damage) in u-PA, t-PA and u-PA/t-PA double knockouts. The original study concluded that plasminogen, one of the well known downstream targets of both t-PA and u-PA, is important for assuring efficient hepatic 
repair via its abilities to remove fibrin (after plasminogen is converted to plasmin) and that u-PA is a far more 
important molecule than t-PA with regards to generating plasmin from plasminogen. As u-PAR localizes 
u-PA activity to the cell surface in many injury models, the current study was undertaken to investigate 
whether or not the loss of u-PAR would invoke the same phenotype as seen with u-PA deficiency. The data 
presented herein indicates that u-PAR is, in fact, not critical for localizing u-PA to cell surfaces in order to 
ensure the clearance of fibrin. Instead, the authors note that the loss of u-PAR leads to a consistent, yet 
transient, down-regulation of hepatocyte proliferation that was not seen with the loss of either u-PA or t-PA alone and which is the most interesting aspect of this manuscript. 
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Major Compulsory Revisions (that the author must respond to before a decision on publication can be 
reached) 1. Statistics need to be calculated for Figure 1. The authors gloss over the values but it appears as though the u-PA KO mice have an inherently lower value for ALT at days 7 and 14, in direct contrast to the 
morphological changes they describe. Why is that? It also appears as though the double KO has an 
inherently higher ALT value at day 2, indicating these animals may in fact have a slightly higher degree of 
hepatic damage. Even if the data is not statistically significant, the statistical analyses need to be made and 
it needs to be commented on. 
2. The decrease in proliferative index for the hepatocytes when using the u-PAR KO mice is interesting and 
readily explained by less migration of immune cells into these livers. Immune cells are an important 
regulator of hepatocellular proliferation as well as a known bi-product of carbon tetrachloride poisoning. Furthermore, u-PAR is known to affect migration of immune cells. Minimally, the number of CD11b+ cells 
should be assayed in these animals to see whether this could be the reason for the difference that they 
note. 
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Minor Essential Revisions (such as missing labels on figures, or the wrong use of a term, which the author 
can be trusted to correct) 
1. In the introduction, the authors note that the loss of u-PA in their model does not lead to a deficiency in hepatocyte proliferation despite the fact that in work by Roselli et al, a deficiency in proliferation was noted 
when using a partial hepatectomy model with the u-PA knockout mice. Unfortunately, the authors do not 
offer any explanation for why this might be so in the introduction, potentially leading a reader unfamiliar with 
the field to think that this presents an unacceptable discrepancy. Furthermore, there is a Jo1 antibody study 
that backs up the findings by Roselli et al. Hence, the authors need to clarify the differences in these 
models. Unlike the model they have chosen, there is no overt inflammation with subsequent fibrin 
deposition when using the partial hepatectomy and Jo1 models. 
2. On page 9 the authors state that uPAR KOs have spontaneous deposition of fibrin in their livers and cite a 
PNAS publication by one of the authors (Degen). In fact, spontaneous deposition of fibrin was rarely found 
in the u-PAR KOs and the paper is essentially about the LACK of a need for u-PAR in order to effect fibrin 
clearance in liver. This needs to be corrected. 
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Discretionary Revisions (which the author can choose to ignore) 
None. 
 Unable to decide on acceptance or rejection until the authors have responded to the major What next?: 
compulsory revisions 
 An article of importance in its field Level of interest: 
 Acceptable Quality of written English: 
 No Statistical review: 
Declaration of competing interests: 
No competing interests financially. I happen to work on u-PA- and t-PA-mediated activation of HGF, another 
ligand that is known to be utilized by u-PA during other models of liver regeneration (t-PA is used for that 
purpose in models of kidney regeneration).