XB-ART-55811Dev Growth Differ April 1, 2019; 61 (3): 212-227.
Recovery of the Xenopus laevis heart from ROS-induced stress utilizes conserved pathways of cardiac regeneration.
Urodele amphibians and some fish are capable of regenerating up to a quarter of their heart tissue after cardiac injury. While many anuran amphibians like Xenopus laevis are not capable of such feats, they are able to repair lesser levels of cardiac damage, such as that caused by oxidative stress, to a far greater degree than mammals. Using an optogenetic stress induction model that utilizes the protein KillerRed, we have investigated the extent to which mechanisms of cardiac regeneration are conserved during the restoration of normal heart morphology post oxidative stress in X. laevis tadpoles. We focused particularly on the processes of cardiomyocyte proliferation and dedifferentiation, as well as the pathways that facilitate the regulation of these processes. The cardiac response to KillerRed-induced injury in X. laevis tadpole hearts consists of a phase dominated by indicators of cardiac stress, followed by a repair-like phase with characteristics similar to mechanisms of cardiac regeneration in urodeles and fish. In the latter phase, we found markers associated with partial dedifferentiation and cardiomyocyte proliferation in the injured tadpole heart, which, unlike in regenerating hearts, are not dependent on Notch or retinoic acid signaling. Ultimately, the X. laevis cardiac response to KillerRed-induced oxidative stress shares characteristics with both mammalian and urodele/fish repair mechanisms, but is nonetheless a unique form of recovery, occupying an intermediate place on the spectrum of cardiac regenerative ability. An understanding of how Xenopus repairs cardiac damage can help bridge the gap between mammals and urodeles and contribute to new methods of treating heart disease.
PubMed ID: 30924142
Article link: Dev Growth Differ
Genes referenced: aldh1a2 dct gata4 hes1 hey1 hsp70 hspd1 notch1
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|FIGURE 3 Expression of heat shock protein genes is highly modulated early in the damage response. (a) Hsp70 is upregulated 15‐fold in KillerRed and light‐treated hearts over uninjected controls at 3‐hr post‐light exposure (*p < 0.05, Kruskal–Wallis test). Changes in Hsp70 expression were measured relative to Eef1aexpression as an endogenous control. Error bars indicate SEM of dCt values. n = 5–10 tadpoles per replicate, N = 3 replicates. (b) Hsp60 is downregulated in KillerRed and light‐treated hearts to 70% of expression levels in uninjected controls at 3‐hr post‐light exposure (*p < 0.05, Kruskal–Wallis test). Changes in Hsp60expression were measured relative to Eef1a expression as an endogenous control. Error bars indicate SEM of dCt values. n = 5–10 tadpoles per replicate, N = 3 replicates|
|Figure 5. Notch targets are unchanged during the cardiac oxidative stress response. Expression of (a) Hey1 and (b) Hes1, basic helix‐loop‐helix (bHLH) proteins downstream of Notch signaling, does not change significantly in KillerRed‐expressing and light‐treated tadpole hearts relative to uninjected controls over the first week after light activation (p > 0.05, Kruskal–Wallis test). Gene expression was measured relative to uninjected control hearts, using Eef1a as an endogenous control. Points indicate mean fold change at each time point, and vertical bars indicate range. n = 10 tadpoles per replicate, N = 2 replicates|
|Figure 6. Epicardial activation is not part of the Xenopus laevis oxidative damage response. (a) Retinaldehyde dehydrogenase (Raldh2) expression, a marker of epicardial activation in cardiac regeneration, does not change significantly in KillerRed‐expressing and light‐treated tadpole hearts relative to uninjected controls over the first week after light activation (p > 0.05, Kruskal–Wallis test). Raldh2 expression was measured relative to uninjected control hearts, using Eef1a as an endogenous control. Points indicate mean fold change at each time point, and vertical bars indicate range. n = 10 tadpoles per replicate, N = 2 replicates. (b) (i) Schematic of coronal heart sections. Plane of section is in red; X. laevis tadpole drawing modified from Nieuwkoop and Faber (1967). Inset: Outline of heart section; ventricle (V) and outflow tract (OFT) are labeled. (ii) Epicardial morphology and expression of epicardial genes do not change in response to light activation of KillerRed. Immunohistochemistry for Integrin β1 (Itgβ1), a marker of the developing epicardium, and cardiac troponin T, a marker of myocardium, was performed on 10 μm sections|
|Figure 7. Xenopus laevis cardiac repair shares elements of the mammalian stress response and the urodele/fish regenerative response. (a) The cardiac response of X. laevis tadpoles to oxidative stress shares elements with the stereotyped cardiac regeneration response, but each pathway also contains unique mechanisms not shared by the other. (b) The X. laevis cardiac repair response can be divided into two phases, a stress phase dominated by ventricular hypertrophy and upregulation of Hsp70, and a repair‐like phase dominated by re‐expression of cardiac development genes and cardiomyocyte proliferation|