Dynamics of cardiomyocyte and muscle stem cell proliferation in pig

Retinoic acid signalling inhibits myogenesis by blocking MYOD translation in pig skeletal muscle cells

Vitamin A is an essential nutrient in animals, playing important roles in animal health. In the pig industry, proper supplementation of vitamin A in the feed can improve pork production performance, while deficiency or excessive intake can lead to growth retardation or disease. However, the specific molecular mechanisms through which vitamin A operates on pig skeletal muscle growth as well as muscle stem cell function remain unexplored. Therefore, in this study, we isolated the pig primary skeletal muscle stem cells (pMuSCs) and treated with retinoic acid (RA), the natural metabolite of vitamin A, and then examined the myogenic capacity of pMuSCs via immunostaining, real-time PCR, CCK8 and western-blot analysis. Unexpectedly, the RA caused a significant decrease in the proliferation and differentiation of pMuSCs. Mechanistically, the RA addition induced the activation of retinoic acid receptor gamma (RARγ), which inhibited the myogenesis through the blockage of protein translation of the master myogenic regulator myogenic differentiation 1 gene (MYOD). Specifically, RARγ inactivate AKT kinase (AKT) signalling and lead to dephosphorylation of eukaryotic translation initiation factor 4E binding protein 1 (eIF4EBP1), which in turn repress the eukaryotic translation initiation factor 4E (eIF4E) complex and block mRNA translation of MYOD. Inhibition of AKT could rescue the myogenic defects of RA-treated pMuSCs. Our findings revealed that retinoid acid signalling inhibits the skeletal muscle stem cell proliferation and differentiation in pigs. Therefore, the vitamin A supplement in the feedstuff should be cautiously optimized to avoid the potential adverse consequences on muscle development associated with the excessive levels of retinoic acid.

A PITX2-HTR1B pathway regulates the asymmetric development of female gonads in chickens

All female vertebrates develop a pair of ovaries except for birds, in which only the left gonad develops into an ovary, whereas the right gonad regresses. Previous studies found that the transcription factor Paired-Like Homeodomain 2 (PITX2), a key mediator for left/right morphogenesis in vertebrates, was also implicated in asymmetric gonadal development in chickens. In this study, we systematically screened and validated the signaling pathways that could be targeted by Pitx2 to control unilateral gonad development. Integrated chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) analyses indicated that Pitx2 directly binds to the promoters of genes encoding neurotransmitter receptors and leads to left-biased expression of both serotonin and dopamine receptors. Forcibly activating serotonin receptor 5-Hydroxytryptamine Receptor 1B (HTR1B) signaling could induce ovarian gene expression and cell proliferation to partially rescue the degeneration of the right gonad. In contrast, inhibiting serotonin signaling could block the development of the left gonad. These findings reveal a PITX2-HTR1B genetic pathway that guides the left-specific ovarian growth in chickens. We also provided new evidence showing neurotransmitters stimulate the growth of nonneuronal cells during the early development of reproductive organs well before innervation.

A change of heart: understanding the mechanisms regulating cardiac proliferation and metabolism before and after birth

Mammalian cardiomyocytes undergo major maturational changes in preparation for birth and postnatal life. Immature cardiomyocytes contribute to cardiac growth via proliferation and thus the heart has the capacity to regenerate. To prepare for postnatal life, structural and metabolic changes associated with increased cardiac output and function must occur. This includes exit from the cell cycle, hypertrophic growth, mitochondrial maturation and sarcomeric protein isoform switching. However, these changes come at a price: the loss of cardiac regenerative capacity such that damage to the heart in postnatal life is permanent. This is a significant barrier to the development of new treatments for cardiac repair and contributes to heart failure. The transitional period of cardiomyocyte growth is a complex and multifaceted event. In this review, we focus on studies that have investigated this critical transition period as well as novel factors that may regulate and drive this process. We also discuss the potential use of new biomarkers for the detection of myocardial infarction and, in the broader sense, cardiovascular disease.

Chenodeoxycholic Acid (CDCA) Promoted Intestinal Epithelial Cell Proliferation by Regulating Cell Cycle Progression and Mitochondrial Biogenesis in IPEC-J2 Cells

Chenodeoxycholic acid (CDCA), a primary bile acid (BA), has been demonstrated to play an important role as a signaling molecule in various physiological functions. However, the role of CDCA in regulating intestinal epithelial cell (IEC) function remains largely unknown. Herein, porcine intestinal epithelial cells (IPEC-J2) were used as an in vitro model to investigate the effects of CDCA on IEC proliferation and explore the underlying mechanisms. IPEC-J2 cells were treated with CDCA, and flow cytometry and transcriptome analysis were adopted to investigate the effects and potential molecular mechanisms of CDCA on the proliferation of IECs. Our results indicated that adding 50 μmol/L of CDCA in the media significantly increased the proliferation of IPEC-J2 cells. In addition, CDCA treatment also hindered cell apoptosis, increased the proportion of G0/G1 phase cells in the cell cycle progression, reduced intracellular ROS, and MDA levels, and increased mitochondrial membrane potential, antioxidation enzyme activity (T-AOC and CAT), and intracellular ATP level (p < 0.05). RNA-seq results showed that CDCA significantly upregulated the expression of genes related to cell cycle progression (Cyclin-dependent kinase 1 (CDK1), cyclin G2 (CCNG2), cell-cycle progression gene 1 (CCPG1), Bcl-2 interacting protein 5 (BNIP5), etc.) and downregulated the expression of genes related to mitochondrial biogenesis (ND1, ND2, COX3, ATP6, etc.). Further KEGG pathway enrichment analysis showed that CDCA significantly enriched the signaling pathways of DNA replication, cell cycle, and p53. Collectively, this study demonstrated that CDCA could promote IPEC-J2 proliferation by regulating cell cycle progression and mitochondrial function. These findings provide a new strategy for promoting the intestinal health of pigs by regulating intestinal BA metabolism.

Disturbance of calcium homeostasis and myogenesis caused by TET2 deletion in muscle stem cells

Skeletal muscle myogenesis is a sophisticated process controlled by genetic and epigenetic regulators. In animals, one of the key enzymes for the DNA demethylation of 5-methylcytosine is TET2. Although TET2 is essential for muscle development, the mechanisms by which TET2 regulates myogenesis, particularly the implication for muscle stem cells, remains unclear. In the present study, we employed the TET2 knockout mouse model to investigate the function of TET2 in muscle development and regeneration. We observed that TET2 deficiency caused impaired muscle stem cell proliferation and differentiation, resulting in the reduction in both myofiber number and muscle tissue size. Specifically, TET2 maintains calcium homeostasis in muscle stem cells by controlling the DNA methylation levels of the calcium pathway genes. Forced expression of the sodium/calcium exchanger protein SLC8A3 could rescue the myogenic defects in TET2 knockout cells. Our data not only illustrated the vital function of TET2 during myogenesis but also identified novel targets that contribute to calcium homeostasis for enhancing muscle function.

H3K27ac chromatin acetylation and gene expression analysis reveal sex- and situs-related differences in developing chicken gonads

BACKGROUND

Birds exhibit a unique asymmetry in terms of gonad development. The female left gonad generates a functional ovary, whereas the right gonad regresses. In males, both left and right gonads would develop into testes. How is this left/right asymmetry established only in females but not in males remains unknown. The epigenetic regulation of gonadal developmental genes may contribute to this sex disparity. The modification of histone tails such as H3K27ac is tightly coupled to chromatin activation and gene expression. To explore whether H3K27ac marked chromatin activation is involved in the asymmetric development of avian gonads, we probed genome-wide H3K27ac occupancy in left and right gonads from both sexes and related chromatin activity profile to the expression of gonadal genes. Furthermore, we validated the effect of chromatin activity on asymmetric gonadal development by manipulating the chromatin histone acetylation levels.

METHODS

The undifferentiated gonads from both sides of each sex were collected and subjected to RNA-Seq and H3K27ac ChIP-Seq experiments. Integrated analysis of gene expression and active chromatin regions were performed to identify the sex- and situs-specific regulation and expression of gonadal genes. The histone deacetylase inhibitor trichostatin A (TSA) was applied to the undifferentiated female right gonads to assess the effect of chromatin activation on gonadal gene expression and cell proliferation.

RESULTS

Even before sex differentiation, the gonads already show divergent gene expression between different sexes and between left/right sides in females. The sex-specific H3K27ac chromatin distributions coincide with the higher expression of male/female specification genes in each sex. Unexpectedly, the H3K27ac marked chromatin activation show a dramatic difference between left and right gonads in both sexes, although the left/right asymmetric gonadal development was observed only in females but not in males. In females, the side-specific H3K27ac occupancy instructs the differential expression of developmental genes between the pair of gonads and contributes to the development of left but not right gonad. However, in males, the left/right discrepancy of H3K27ac chromatin distribution does not drive the side-biased gene expression or gonad development. The TSA-induced retention of chromatin acetylation causes up-regulation of ovarian developmental genes and increases cell proliferation in the female right gonad.

CONCLUSIONS

We revealed that left/right asymmetry in H3K27ac marked chromatin activation exists in both sexes, but this discrepancy gives rise to asymmetric gonadal development only in females. Other mechanisms overriding the chromatin activation would control the symmetric development of male gonads in chicken.