Differential regenerative capacity of neonatal mouse hearts after cryoinjury.

Neonatal mouse hearts fully regenerate after ventricular resection similar to adult zebrafish. We established cryoinjury models to determine if different types and varying degrees of severity in cardiac injuries trigger different responses in neonatal mouse hearts. In contrast to ventricular resection, neonatal mouse hearts fail to regenerate and show severe impairment of cardiac function post transmural cryoinjury. However, neonatal hearts fully recover after non-transmural cryoinjury. Interestingly, cardiomyocyte proliferation does not significantly increase in neonatal mouse hearts after cryoinjuries. Epicardial activation and new coronary vessel formation occur after cryoinjury. The profibrotic marker PAI-1 is highly expressed after transmural but not non-transmural cryoinjuries, which may contribute to the differential scarring. Our results suggest that regenerative medicine strategies for heart injuries should vary depending on the nature of the injury.

Estrogen receptor ESR1 controls cell migration by repressing chemokine receptor CXCR4 in the zebrafish posterior lateral line system.

The primordium that generates the embryonic posterior lateral line of zebrafish migrates from the head to the tip of the tail along a trail of SDF1-producing cells. This migration critically depends on the presence of the SDF1 receptor CXCR4 in the leading region of the primordium and on the presence of a second SDF1 receptor, CXCR7, in the trailing region of the primordium. Here we show that inactivation of the estrogen receptor ESR1 results in ectopic expression of cxcr4b throughout the primordium, whereas ESR1 overexpression results in a reciprocal reduction in the domain of cxcr4b expression, suggesting that ESR1 acts as a repressor of cxcr4b. This finding could explain why estrogens significantly decrease the metastatic ability of ESR-positive breast cancer cells. ESR1 inactivation also leads to extinction of cxcr7b expression in the trailing cells of the migrating primordium; this effect is indirect, however, and due to the down-regulation of cxcr7b by ectopic SDF1/CXCR4 signaling in the trailing region. Both ESR1 inactivation and overexpression result in aborted migration, confirming the importance of this receptor in the control of SDF1-dependent migration.

The regenerative response of cardiac interstitial cells.

Understanding how certain animals are capable of regenerating their hearts will provide much needed insights into how this process can be induced in humans in order to reverse the damage caused by myocardial infarction. Currently, it is becoming increasingly evident that cardiac interstitial cells play crucial roles during cardiac regeneration. To understand how interstitial cells behave during this process, we performed single-cell RNA sequencing of regenerating zebrafish hearts. Using a combination of immunohistochemistry, chemical inhibition, and novel transgenic animals, we were able to investigate the role of cell type-specific mechanisms during cardiac regeneration. This approach allowed us to identify a number of important regenerative processes within the interstitial cell populations. Here, we provide detailed insight into how interstitial cells behave during cardiac regeneration, which will serve to increase our understanding of how this process could eventually be induced in humans.

Lef1 controls patterning and proliferation in the posterior lateral line system of zebrafish.

The embryonic development of the posterior lateral line of zebrafish involves the migration from head to tail of a primordium comprising approximately 100 cells, and the deposition at regular intervals of presumptive mechanosensory organs (neuromasts). Migration depends on the presence of chemokine SDF1 along the pathway, and on the asymmetrical distribution of chemokine receptors CXCR4 and CXCR7 in the primordium. Primordium polarization depends on Wnt signaling in the leading region. Here, we examine the role of a major effector of Wnt signaling, lef1, in this system. We show that, although its inactivation has no overt effect on the expression of cxcr4b and cxcr7b, lef1 contributes to their control. We also show that cell proliferation, which ensures constant primordium size despite successive rounds of cell deposition, is reduced upon lef1 inactivation. Because of this defect, the primordium runs short of cells and vanishes before the line has been completed. We conclude that lef1-mediated Wnt signaling is involved in various aspects of primordium migration, although part of this implication is masked by a high level of developmental redundancy.

Evaluating ZNF217 mRNA Expression Levels as a Predictor of Response to Endocrine Therapy in ER+ Breast Cancer.

ZNF217 is a candidate oncogene with a wide variety of deleterious functions in breast cancer. Here, we aimed at investigating in a pilot prospective study the association between ZNF217 mRNA expression levels and the clinical response to neoadjuvant endocrine therapy (ET) in postmenopausal ER-positive (ER+) breast cancer patients. Core surgical biopsy samples before treatment initiation and post-treatment were obtained from 68 patients, and Ki-67 values measured by immunohistochemistry (IHC) were used to identify responders (n = 59) and non-responders (n = 9) after 4 months of ET. We report for the first time that high ZNF217 mRNA expression level measured by RT-qPCR in the initial tumor samples (pre-treatment) is associated with poor response to neoadjuvant ET. Indeed, the clinical positive response rate in patients with low ZNF217 expression levels was significantly higher than that in those with high ZNF217 expression levels (P = 0.027). Additionally, a retrospective analysis evaluating ZNF217 expression levels in primary breast tumor of ER+/HER2-/LN0 breast cancer patients treated with adjuvant ET enabled the identification of poorer responders prone to earlier relapse (P = 0.013), while ZNF217 did not retain any prognostic value in the ER+/HER2-/LN0 breast cancer patients who did not receive any treatment. Altogether, these data suggest that ZNF217 expression might be predictive of clinical response to ET.

Collagenolytic Activity Is Associated with Scar Resolution in Zebrafish Hearts after Cryoinjury.

Myocardial infarction is the major cause of cardiac injury in western countries and can result in a massive loss of heart cells, leading eventually to heart failure. A fibrotic collagen-rich scar may prevent ventricular wall rupture, but also may result in heart failure because of its stiffness. In zebrafish, cardiac cryoinjury triggers a fibrotic response and scarring. Unlike with mammals, zebrafish heart has the striking ability to regenerate and to resolve the scar. Thus, understanding the mechanisms of scar resolution in zebrafish heart might facilitate the design of new therapeutic approaches to improve the recovery of patients. To visualize the collagenolytic activity within the zebrafish heart following cryoinjury, we used an in situ collagen zymography assay. We detected expression of mmp2 and mmp14a and these matrix metalloproteinases might contribute to the collagenase activity. Collagenolytic activity was present in the wound area, but decreased as the myocardium regenerated. Comparison with neonatal mouse hearts that failed to regenerate after transmural cryoinjury revealed a similar collagenolytic activity in the scar. These findings suggest that collagenolytic activity may be key to how the zebrafish heart resolves its scar; however, it is not sufficient in mouse hearts that lack efficient myocardial regeneration.

Cardiac regeneration in model organisms.

OPINION STATEMENT: Myocardial infarction is the most common cause of cardiac injury in humans and results in acute loss of large numbers of myocardial cells. Unfortunately, the mammalian heart is unable to replenish the cells that are lost following a myocardial infarction and an eventual progression to heart failure can often occur as a result. Regenerative medicine based approaches are actively being developed; however, a complete blueprint on how mammalian hearts can regenerate is still missing. Knowledge gained from studying animal models, such as zebrafish, newt, and neonatal mice, that can naturally regenerate their hearts after injury have provided an understanding of the molecular mechanisms involved in heart repair and regeneration. This research offers novel strategies to overcome the limited regenerative response observed in human patients.