Response to Sadek et al. and Kotlikoff et al.

In our recent publication in Stem Cell Reports (Andersen et al., 2014Andersen D.C. Ganesalingam S. Jensen C.H. Sheikh S.P. Stem Cell Reports. 2014; 2: 406-413Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar), we resected neonatal mouse hearts and examined their ability to regenerate. As described previously (Porrello et al., 2011Porrello E.R. Mahmoud A.I. Simpson E. Hill J.A. Richardson J.A. Olson E.N. Sadek H.A. Science. 2011; 331: 1078-1080Crossref PubMed Scopus (1709) Google Scholar), we found that all hearts healed but, unexpectedly, this was accompanied with profound scarring of the apex, much like in damaged adult hearts, and little neomyogenesis. In their letter to the editor, Kotlikoff et al., 2014Kotlikoff M.I. Hesse M. Fleischmann B.K. Stem Cell Reports. 2014; 3 (this issue): 2Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar, emphasize the importance of distinguishing between regeneration and neomyogenesis. As we mentioned in our paper, normal postnatal cardiac development may actually replenish some of the cardiomyocytes removed by resection. Kotlikoff et al. provided evidence for such a scenario in their recent study (Jesty et al., 2012Jesty S.A. Steffey M.A. Lee F.K. Breitbach M. Hesse M. Reining S. Lee J.C. Doran R.M. Nikitin A.Y. Fleischmann B.K. Kotlikoff M.I. Proc. Natl. Acad. Sci. USA. 2012; 109: 13380-13385Crossref PubMed Scopus (178) Google Scholar) on cryoinjured neonatal mouse hearts in which they observed incomplete “repair or regeneration.” Overall, our results (Andersen et al., 2014Andersen D.C. Ganesalingam S. Jensen C.H. Sheikh S.P. Stem Cell Reports. 2014; 2: 406-413Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar) suggest that neomyogenesis as a repair mechanism is limited following apex resection, and complete regeneration of the resected apex did not occur in our hands. The discrepancies between our study (Andersen et al., 2014Andersen D.C. Ganesalingam S. Jensen C.H. Sheikh S.P. Stem Cell Reports. 2014; 2: 406-413Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar) and that of Sadek and colleagues (Porrello et al., 2011Porrello E.R. Mahmoud A.I. Simpson E. Hill J.A. Richardson J.A. Olson E.N. Sadek H.A. Science. 2011; 331: 1078-1080Crossref PubMed Scopus (1709) Google Scholar) regarding the apex resection model raise several issues that will be interesting to pursue, because they may help to identify factors and mechanisms that lead to complete versus incomplete heart regeneration. In their letter to the editor, Dr. Sadek and others not associated with the original study (Sadek et al., 2014Sadek H.A. Martin J.F. Takeuchi J.K. Leor J. Nei Y. Giacca M. Lee R.T. Stem Cell Reports. 2014; 3 (this issue): 1Abstract Full Text Full Text PDF PubMed Scopus (38) Google Scholar) suggest that either surgical technicalities or assessment procedures may vary between the two studies. We carefully examined their original surgery protocol (Porrello et al., 2011Porrello E.R. Mahmoud A.I. Simpson E. Hill J.A. Richardson J.A. Olson E.N. Sadek H.A. Science. 2011; 331: 1078-1080Crossref PubMed Scopus (1709) Google Scholar) and failed to identify any major differences between the procedures. Particularly, we took great care to resect identical tissue amounts based on heart-to-body weight. In their letter, Sadek et al. refer to other studies showing robust and reproducible regeneration. However, none of the studies published to date (Haubner et al., 2012Haubner B.J. Adamowicz-Brice M. Khadayate S. Tiefenthaler V. Metzler B. Aitman T. Penninger J.M. Aging. 2012; 4: 966-977Crossref PubMed Scopus (165) Google Scholar, Heallen et al., 2013Heallen T. Morikawa Y. Leach J. Tao G. Willerson J.T. Johnson R.L. Martin J.F. Development. 2013; 140: 4683-4690Crossref PubMed Scopus (308) Google Scholar, Jesty et al., 2012Jesty S.A. Steffey M.A. Lee F.K. Breitbach M. Hesse M. Reining S. Lee J.C. Doran R.M. Nikitin A.Y. Fleischmann B.K. Kotlikoff M.I. Proc. Natl. Acad. Sci. USA. 2012; 109: 13380-13385Crossref PubMed Scopus (178) Google Scholar, Naqvi et al., 2014Naqvi N. Li M. Calvert J.W. Tejada T. Lambert J.P. Wu J. Kesteven S.H. Holman S.R. Matsuda T. Lovelock J.D. et al.Cell. 2014; 157: 795-807Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar, Strungs et al., 2013Strungs E.G. Ongstad E.L. O’Quinn M.P. Palatinus J.A. Jourdan L.J. Gourdie R.G. Methods Mol. Biol. 2013; 1037: 343-353Crossref PubMed Scopus (47) Google Scholar) actually performed apex resection on postnatal day 1 mice. As we have already stated in our paper (Andersen et al., 2014Andersen D.C. Ganesalingam S. Jensen C.H. Sheikh S.P. Stem Cell Reports. 2014; 2: 406-413Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar), we cannot exclude that cardiac regeneration may occur following other types of damage, such as myocardial infarction or cryoinjury (Haubner et al., 2012Haubner B.J. Adamowicz-Brice M. Khadayate S. Tiefenthaler V. Metzler B. Aitman T. Penninger J.M. Aging. 2012; 4: 966-977Crossref PubMed Scopus (165) Google Scholar, Jesty et al., 2012Jesty S.A. Steffey M.A. Lee F.K. Breitbach M. Hesse M. Reining S. Lee J.C. Doran R.M. Nikitin A.Y. Fleischmann B.K. Kotlikoff M.I. Proc. Natl. Acad. Sci. USA. 2012; 109: 13380-13385Crossref PubMed Scopus (178) Google Scholar, Naqvi et al., 2014Naqvi N. Li M. Calvert J.W. Tejada T. Lambert J.P. Wu J. Kesteven S.H. Holman S.R. Matsuda T. Lovelock J.D. et al.Cell. 2014; 157: 795-807Abstract Full Text Full Text PDF PubMed Scopus (200) Google Scholar, Strungs et al., 2013Strungs E.G. Ongstad E.L. O’Quinn M.P. Palatinus J.A. Jourdan L.J. Gourdie R.G. Methods Mol. Biol. 2013; 1037: 343-353Crossref PubMed Scopus (47) Google Scholar), that could leave a matrix beneficial for the repair process. Although it is possible that other surgery-related procedures not described in the published apex resection studies (Andersen et al., 2014Andersen D.C. Ganesalingam S. Jensen C.H. Sheikh S.P. Stem Cell Reports. 2014; 2: 406-413Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar, Mahmoud et al., 2014Mahmoud A.I. Porrello E.R. Kimura W. Olson E.N. Sadek H.A. Nat. Protoc. 2014; 9: 305-311Crossref PubMed Scopus (113) Google Scholar, Porrello et al., 2011Porrello E.R. Mahmoud A.I. Simpson E. Hill J.A. Richardson J.A. Olson E.N. Sadek H.A. Science. 2011; 331: 1078-1080Crossref PubMed Scopus (1709) Google Scholar) may actually diverge, we believe that the differences could be explained by how the amount of myocardium/fibrosis is assessed or interpreted. At P21, we observed that the scar in the heart located either posteriorly or anteriorly but seldom throughout the apex, which is in contrast to day 1–7 post surgery. We examindd more than 800 sections per heart and noted scarring in only 19.5%; hence, the damaged area could have been overlooked in other studies, including that of Porrello et al., 2011Porrello E.R. Mahmoud A.I. Simpson E. Hill J.A. Richardson J.A. Olson E.N. Sadek H.A. Science. 2011; 331: 1078-1080Crossref PubMed Scopus (1709) Google Scholar, where 140 sections per heart were examined (we apologize for stating “one heart” instead of “per heart” erroneously in our article [Andersen et al., 2014Andersen D.C. Ganesalingam S. Jensen C.H. Sheikh S.P. Stem Cell Reports. 2014; 2: 406-413Abstract Full Text Full Text PDF PubMed Scopus (92) Google Scholar]). In conclusion, we would very much like to examine and discuss these issues in a collaborative manner with the Sadek group. We look forward to seeing the apex resection results from other ongoing studies, so that we may pursue approaches that could release the heart from its inert state of repair. The work was supported by the Novo Nordisk Foundation, the Danish National Research Council (#09-073648), the Lundbeck Foundation (#R48-A4785), and the Department of Clinical Biochemistry and Pharmacology, Odense University Hospital. Comment on “Do Neonatal Mouse Hearts Regenerate following Heart Apex Resection”?Kotlikoff et al.Stem Cell ReportsJuly 08, 2014In BriefThe recent article by Andersen et al. (2014) reports that following resection of the neonatal heart, “complete regeneration” does not occur, and contrasts these results with those of Porrello et al. (2011), who used a similar lesion model. The authors cite our work in support of the fact that complete regeneration does not occur within the neonatal mouse, as we reported that infarction of the neonatal mouse heart is accompanied by inflammatory repair, including CD45+ cell influx, fibrosis, and vascularization of the ablated region of the neonatal myocardium (Jesty et al., 2012). Full-Text PDF Open AccessMulti-Investigator Letter on Reproducibility of Neonatal Heart Regeneration following Apical ResectionSadek et al.Stem Cell ReportsJuly 08, 2014In BriefWe appreciate the interest that Andersen et al. (2014) have shown in our work on neonatal cardiac regeneration. Their recent paper relates directly to resection methodology first presented by Porrello et al. (2011) and describes a failure to reproduce the observations made in that study regarding regeneration after resection. We are puzzled by the results and conclusion because in the hands of the seven different groups who authored this letter, this methodology has proved robust and reproducible and has been used in several ongoing studies across our different laboratories that are in various stages of completion (Heallen et al., [2013], as well as studies by the Lee, Takeuchi, and Nei groups that are currently under review).