Antagonistic regulation of cell-cycle and differentiation gene programs in neonatal cardiomyocytes by homologous MEF2 transcription factors

Abstract

Cardiomyocytes acquire their primary specialized function (contraction) before exiting the cell cycle. In this regard, proliferation and differentiation must be precisely coordinated for proper cardiac morphogenesis. Here, we have investigated the complex transcriptional mechanisms employed by cardiomyocytes to coordinate antagonistic cell-cycle and differentiation gene programs through the molecular dissection of the core cardiac transcription factor, MEF2. Knockdown of individual MEF2 proteins, MEF2A, -C, and -D, in primary neonatal cardiomyocytes resulted in radically distinct and opposite effects on cellular homeostasis and gene regulation. MEF2A and MEF2D were absolutely required for cardiomyocyte survival, whereas MEF2C, despite its major role in cardiac morphogenesis and direct reprogramming, was dispensable for this process. Inhibition of MEF2A or -D also resulted in the activation of cell-cycle genes and down-regulation of markers of terminal differentiation. In striking contrast, the regulation of cell-cycle and differentiation gene programs by MEF2C was antagonistic to that of MEF2A and -D. Computational analysis of regulatory regions from MEF2 isoform-dependent gene sets identified the Notch and Hedgehog signaling pathways as key determinants in coordinating MEF2 isoform-specific control of antagonistic gene programs. These results reveal that mammalian MEF2 family members have distinct transcriptional functions in cardiomyocytes and suggest that these differences are critical for proper development and maturation of the heart. Analysis of MEF2 isoform-specific function in neonatal cardiomyocytes has yielded insight into an unexpected transcriptional regulatory mechanism by which these specialized cells utilize homologous members of a core cardiac transcription factor to coordinate cell-cycle and differentiation gene programs.

Molecular Characterization, Spatial–Temporal Expression Profiles, and Injury‐responsive Regulation of Myocyte‐specific Enhancer Factor 2 Gene Family in the Ricefield Eel, Monopterus albus

“…However, MEF2C was relatively more expressed in the intestine than in the other tissues, which revealed that MEF2C was involved in energy production in mitochondria, while MEF2A and MEF2D were related to cellular growth and survival. Conversely, MEF2B was barely expressed in skeletal and cardiac muscles in mice and goats (Desjardins and Naya 2017) but was also largely detectable in skeletal muscle and intestine in our study, the conflicts perhaps caused by different species. Similarly, MEF2A expression is undetectable or weak in the mouse, chicken, and zebrafish (Edmondson et al 1994).…”

“…In addition, it was reported that MEF2A, –B, and ‐D were expressed ubiquitously after birth, while MEF2C was restricted to skeletal muscle, brain, and spleen (Breitbart et al ; McDermott et al ). Moreover, MEF2A is expressed ubiquitously at the level of messenger RNA (mRNA) in humans (Yu et al ) and also expressed in vascular smooth muscle cells of rats (Suzuki et al ), particularly highly expressed in neonatal rat ventricular myocytes, where mRNA levels of MEF2A were 22‐ to 25‐fold higher than MEF2C and ‐D and 350‐fold higher than MEF2B (Desjardins and Naya ).…”

Misoprostol Attenuates Cardiomyocyte Proliferation in the Neonatal Heart through Bnip3 and Perinuclear Calcium Signaling

“…The developmental switch from proliferation to hypertrophy is the result of large-scale shifts in gene expression and metabolism, where changes in the expression pattern of the myocyte enhancer factor-2 (MEF2) family appears to be a key event [12][13][14][15]. Genetic studies have shown that three MEF2 genes have non-redundant and potentially antagonistic roles.…”

“…Genetic studies have shown that three MEF2 genes have non-redundant and potentially antagonistic roles. For example, MEF2C has been shown to regulate cardiomyocyte proliferation during cardiac looping, MEF2A promotes cardiomyocyte differentiation and mitochondrial biogenesis, and MEF2D modulates postnatal maturation and remodelling [13][14][15][16][17].…”

“…Furthermore, MEF2C expression is governed by hypoxia signalling, where loss of the hypoxia-inducible factor-1ɑ (HIF1ɑ) prevents MEF2C expression, cardiac looping and embryo viability [18,19]. Myocardin is a transcriptional co-activator involved in the proliferation, differentiation and maturation of cardiomyocytes, and is a direct transcriptional target of MEF2C [13,16,17,19]. Myocardin's ability to regulate cardiomyocyte proliferation is directly linked to the expression of bone morphogenetic protein (BMP) 10, a growth factor associated with embryonic cardiomyocyte expansion [2,[20][21][22].…”