Fate Tracing of Isl1+Cells in Adult Mouse Hearts under Physiological and Exercise Conditions

Abstract

Myocardial damage due to dysfunctional myocardium has been increasing, and the prognosis of pharmacological and device-based therapies remain poor. Isl1-expressing cells were thought to be progenitor cells for cardiomyocyte proliferation after specific stimuli. However, the true origin of the proliferating myocardiac cells and the role of Isl1 in adult mammals remain unresolved. In this study, Isl1-CreERT2 knock-in mouse model was constructed using CRISPR/Cas9 technology. Using tamoxifen-inducible Isl1-CreERT/Rosa26R-LacZ system, Isl1+cells and their progeny were permanently marked by lacZ-expression. X-gal staining, immunostaining, and quantitative PCR were then used to reveal the fate of Isl1+cells under physiological and exercise conditions in mouse hearts from embryonic stage to adulthood. Isl1+cells were found to localize to the sinoatrial node, atrioventricular node, cardiac ganglia, aortic arch, and pulmonary roots in adult mice heart. However, they did not act as cardiac progenitor cells under physiological and exercise conditions. Although Isl1+cells showed progenitor cell properties in early mouse embryos (E7.5), this ability was lost by E9.5. Furthermore, although the proliferation and regeneration of heart cell was observed in response to exercise, the cells associated were not Isl1 positive.

Advances and Prospects in Understanding Vertebrate Cardiac Conduction System, Pacemaker Cell, and Cardiac Muscle Development: Toward Novel Biological Therapies

“…ISL1, a transcription factor, fulfills diverse roles across multiple organs during embryonic development, and, within cardiac development, it serves as a marker for second heart field progenitors [65]. Its expression is detectable as early as E7 in mouse heart development, and its pattern shifts as development progresses, with the expression being observed in the SAN from postnatal stages through to adulthood [66]. In zebrafish, Isl1 is a marker for pacemaker cells located at the junction of the sinus venosus and atrium, where it is necessary for normal pacemaker function and development [67].…”

Spotlight on Isl1: A Key Player in Cardiovascular Development and Diseases

“…By E14.5, Isl1 expression only persists in a subset of cells in the heart, including subdomains within the OFT, RV, venous valves, aorta, pulmonary artery, atrial septum, and in regions of sinoatrial node (SAN), atrioventricular node (AVN), and in clusters of cells of cardiac ganglia ( Sun et al, 2007b ). From postnatal stage to adulthood, Isl1 expression is still observed in several cell types of the heart, which are localized in the SAN, very few if any in the AVN, at the base of the aorta and pulmonary artery and in cardiac ganglia ( Moretti et al, 2006 ; Sun et al, 2007b ; Weinberger et al, 2012 ; Zhou et al, 2019 ).…”

“…In addition, a number of studies have produced clear evidence that, in accordance with its expression profile, Isl1 marks the SHF progenitors during cardiogenesis ( Cai et al, 2003 ; Moretti et al, 2006 ; Bu et al, 2009 ; Gao et al, 2019 ), even though Isl1 was found to be transiently detected in a small number of cells in the FHF ( Ma et al, 2008 ). Interestingly, there have been reports of small numbers of Isl1 + cells being detected in the hearts of adult mice ( Genead et al, 2010a ; Khattar et al, 2011 ; Weinberger et al, 2012 ; Zhou et al, 2019 ), but there is growing evidence to suggest that these cells may not be functioning as CPCs ( Weinberger et al, 2012 ; Zhou et al, 2019 ).…”