Thymosin β4 and prothymosin α promote cardiac regeneration post-ischaemic injury in mice

Transient induction of actin cytoskeletal remodeling associated with dedifferentiation, proliferation, and redifferentiation stimulates cardiac regeneration

The formation of new and functional cardiomyocytes requires a 3-step process: dedifferentiation, proliferation, and redifferentiation, but the critical genes required for efficient dedifferentiation, proliferation, and redifferentiation remain unknown. In our study, a circular trajectory using single-nucleus RNA sequencing of the pericentriolar material 1 positive (PCM1+) cardiomyocyte nuclei from hearts 1 and 3 days after surgery-induced myocardial infarction (MI) on postnatal Day 1 was reconstructed and demonstrated that actin remodeling contributed to the dedifferentiation, proliferation, and redifferentiation of cardiomyocytes after injury. We identified four top actin-remodeling regulators, namely Tmsb4x, Tmsb10, Dmd, and Ctnna3, which we collectively referred to as 2D2P. Transiently expressed changes of 2D2P, using a polycistronic non-integrating lentivirus driven by Tnnt2 (cardiac-specific troponin T) promoters (Tnnt2-2D2P-NIL), efficiently induced transiently proliferative activation and actin remodeling in postnatal Day 7 cardiomyocytes and adult hearts. Furthermore, the intramyocardial delivery of Tnnt2-2D2P-NIL resulted in a sustained improvement in cardiac function without ventricular dilatation, thickened septum, or fatal arrhythmia for at least 4 months. In conclusion, this study highlights the importance of actin remodeling in cardiac regeneration and provides a foundation for new gene-cocktail-therapy approaches to improve cardiac repair and treat heart failure using a novel transient and cardiomyocyte-specific viral construct.

Alternative polyadenylation and dynamic 3' UTR length is associated with polysome recruitment throughout the cardiomyogenic differentiation of hESCs

Alternative polyadenylation (APA) increases transcript diversity through the generation of isoforms with varying 3' untranslated region (3' UTR) lengths. As the 3' UTR harbors regulatory element target sites, such as miRNAs or RNA-binding proteins, changes in this region can impact post-transcriptional regulation and translation. Moreover, the APA landscape can change based on the cell type, cell state, or condition. Given that APA events can impact protein expression, investigating translational control is crucial for comprehending the overall cellular regulation process. Revisiting data from polysome profiling followed by RNA sequencing, we investigated the cardiomyogenic differentiation of pluripotent stem cells by identifying the transcripts that show dynamic 3' UTR lengthening or shortening, which are being actively recruited to ribosome complexes. Our findings indicate that dynamic 3' UTR lengthening is not exclusively associated with differential expression during cardiomyogenesis but rather with recruitment to polysomes. We confirm that the differentiated state of cardiomyocytes shows a preference for shorter 3' UTR in comparison to the pluripotent stage although preferences vary during the days of the differentiation process. The most distinct regulatory changes are seen in day 4 of differentiation, which is the mesoderm commitment time point of cardiomyogenesis. After identifying the miRNAs that would target specifically the alternative 3' UTR region of the isoforms, we constructed a gene regulatory network for the cardiomyogenesis process, in which genes related to the cell cycle were identified. Altogether, our work sheds light on the regulation and dynamic 3' UTR changes of polysome-recruited transcripts that take place during the cardiomyogenic differentiation of pluripotent stem cells.

Critical Role of miR-130b-5p in Cardiomyocyte Proliferation and Cardiac Repair in Mice After Myocardial Infarction

Poor proliferative capacity of adult cardiomyocytes is the primary cause of heart failure after myocardial infarction (MI), thus exploring the molecules and mechanisms that promote the proliferation of adult cardiomyocytes is crucially useful for cardiac repair after MI. Here, we found that miR-130b-5p was highly expressed in mouse embryonic and neonatal hearts and able to promote cardiomyocyte proliferation both in vitro and in vivo. Mechanistic studies revealed that miR-130b-5p mainly promoted the cardiomyocyte proliferation through the MAPK-ERK signaling pathway, and the dual-specific phosphatase 6 (Dusp6), a negative regulator of the MAPK-ERK signaling, was the direct target of miR-130b-5p. Moreover, we found that overexpression of miR-130b-5p could promote the proliferation of cardiomyocytes and improve cardiac function in mice after MI. These studies thus revealed the critical role of miR-130b-5p and its targeted MAPK-ERK signaling in the cardiomyocyte proliferation of adult hearts and proved that miR-130b-5p could be a potential target for cardiac repair after MI.

Cardiomyocyte proliferation is suppressed by ARID1A-mediated YAP inhibition during cardiac maturation

The inability of adult human cardiomyocytes to proliferate is an obstacle to efficient cardiac regeneration after injury. Understanding the mechanisms that drive postnatal cardiomyocytes to switch to a non-regenerative state is therefore of great significance. Here we show that Arid1a, a subunit of the switching defective/sucrose non-fermenting (SWI/SNF) chromatin remodeling complex, suppresses postnatal cardiomyocyte proliferation while enhancing maturation. Genome-wide transcriptome and epigenome analyses revealed that Arid1a is required for the activation of a cardiomyocyte maturation gene program by promoting DNA access to transcription factors that drive cardiomyocyte maturation. Furthermore, we show that ARID1A directly binds and inhibits the proliferation-promoting transcriptional coactivators YAP and TAZ, indicating ARID1A sequesters YAP/TAZ from their DNA-binding partner TEAD. In ischemic heart disease, Arid1a expression is enhanced in cardiomyocytes of the border zone region. Inactivation of Arid1a after ischemic injury enhanced proliferation of border zone cardiomyocytes. Our study illuminates the pivotal role of Arid1a in cardiomyocyte maturation, and uncovers Arid1a as a crucial suppressor of cardiomyocyte proliferation.