Repression of Osmr and Fgfr1 by miR-1/133a prevents cardiomyocyte dedifferentiation and cell cycle entry in the adult heart

Targeting cardiomyocyte cell cycle regulation in heart failure

Heart failure continues to be a significant global health concern, causing substantial morbidity and mortality. The limited ability of the adult heart to regenerate has posed challenges in finding effective treatments for cardiac pathologies. While various medications and surgical interventions have been used to improve cardiac function, they are not able to address the extensive loss of functioning cardiomyocytes that occurs during cardiac injury. As a result, there is growing interest in understanding how the cell cycle is regulated and exploring the potential for stimulating cardiomyocyte proliferation as a means of promoting heart regeneration. This review aims to provide an overview of current knowledge on cell cycle regulation and mechanisms underlying cardiomyocyte proliferation in cases of heart failure, while also highlighting established and novel therapeutic strategies targeting this area for treatment purposes.

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.

Evidence of Histone H2A.Z Deacetylation and Cardiomyocyte Dedifferentiation in Infarcted/Tip60-depleted Hearts

Myocardial infarction (MI) in the human heart causes death of billions of cardiomyocytes (CMs), resulting in cardiac dysfunction that is incompatible with life or lifestyle. In order to re-muscularize injured myocardium, replacement CMs must be generated via renewed proliferation of surviving CMs. Approaches designed to induce proliferation of CMs after injury have been insufficient. Toward this end, we are targeting the Tip60 acetyltransferase, based on the rationale that its pleiotropic functions conspire to block the CM cell-cycle at several checkpoints. We previously reported that genetic depletion of Tip60 in a mouse model after MI reduces scarring, retains cardiac function, and activates the CM cell-cycle, although it is unclear whether this culminates in the generation of daughter CMs. For pre-existing CMs in the adult heart to resume proliferation, it is becoming widely accepted that they must first dedifferentiate, a process highlighted by loss of maturity, epithelial to mesenchymal transitioning (EMT), and reversion from fatty acid oxidation to glycolytic metabolism, accompanied by softening of the myocardial extracellular matrix. Findings in hematopoietic stem cells, and more recently in neural progenitor cells, have shown that Tip60 induces and maintains the differentiated state via site-specific acetylation of the histone variant H2A.Z. Here, we report that genetic depletion of Tip60 from naïve or infarcted hearts results in the near-complete absence of acetylated H2A.Z in CM nuclei, and that this is accordingly accompanied by altered gene expressions indicative of EMT induction, ECM softening, decreased fatty acid oxidation, and depressed expression of genes that regulate the TCA cycle. These findings, combined with our previous work, support the notion that because Tip60 has multiple targets that combinatorially maintain the differentiated state and inhibit proliferation, its transient therapeutic targeting to ameliorate the effects of cardiac injury should be considered.

MiR-431 promotes cardiomyocyte proliferation by targeting FBXO32 expression

BACKGROUND

The induction of cardiomyocyte (CM) proliferation is a promising approach for cardiac regeneration following myocardial injury. MicroRNAs (miRNAs) have been reported to regulate CM proliferation. In particular, miR-431 expression decreases during cardiac development, according to Gene Expression Omnibus (GEO) microarray data. However, whether miR-431 regulates CM proliferation has not been thoroughly investigated.

METHODS

We used integrated bioinformatics analysis of GEO datasets to identify the most significantly differentially expressed miRNAs. Real-time quantitative PCR and fluorescence in situ hybridization were performed to determine the miRNA expression patterns in hearts. Gain- and loss-of-function assays were conducted to detect the role of miRNA in CM proliferation. Additionally, we detected whether miR-431 affected CM proliferation in a myocardial infarction model. The TargetScan, miRDB and miRWalk online databases were used to predict the potential target genes of miRNAs. Luciferase reporter assays were used to study miRNA interactions with the targeting mRNA.

RESULTS

First, we found a significant reduction in miR-431 levels during cardiac development. Then, by overexpression and inhibition of miR-431, we demonstrated that miR-431 promotes CM proliferation in vitro and in vivo, as determined by immunofluorescence assays of 5-ethynyl-2'-deoxyuridine (EdU), pH3, Aurora B and CM count, whereas miR-431 inhibition suppresses CM proliferation. Then, we found that miR-431 improved cardiac function post-myocardial infarction. In addition, we identified FBXO32 as a direct target gene of miR-431, with FBXO32 mRNA and protein expression being suppressed by miR-431. FBXO32 inhibited CM proliferation. Overexpression of FBXO32 blocks the enhanced effect of miR-431 on CM proliferation, suggesting that FBXO32 is a functional target of miR-431 during CM proliferation.

CONCLUSION

In summary, miR-431 promotes CM proliferation by targeting FBXO32, providing a potential molecular target for preventing myocardial injury.

Amending the injured heart by in vivo reprogramming

Ischemic heart injury causes death of cardiomyocyte (CM), formation of a fibrotic scar, and often adverse cardiac remodeling, resulting in chronic heart failure. Therapeutic interventions have lowered myocardial damage and improved heart function, but pharmacological treatment of heart failure has only shown limited progress in recent years. Over the past two decades, different approaches have been pursued to regenerate the heart, by transplantation of newly generated CMs derived from pluripotent stem cells, generation of new CMs by reprogramming of cardiac fibroblasts, or by activating proliferation of preexisting CMs. Here, we summarize recent progress in the development of strategies for in situ generation of new CMs, review recent advances in understanding the underlying mechanisms, and discuss the challenges and future directions of the field.

OSMR deficiency aggravates pressure overload-induced cardiac hypertrophy by modulating macrophages and OSM/LIFR/STAT3 signalling

BACKGROUND

Oncostatin M (OSM) is a secreted cytokine of the interleukin (IL)-6 family that induces biological effects by activating functional receptor complexes of the common signal transducing component glycoprotein 130 (gp130) and OSM receptor β (OSMR) or leukaemia inhibitory factor receptor (LIFR), which are mainly involved in chronic inflammatory and cardiovascular diseases. The effect and underlying mechanism of OSM/OSMR/LIFR on the development of cardiac hypertrophy remains unclear.

METHODS AND RESULTS

OSMR-knockout (OSMR-KO) mice were subjected to aortic banding (AB) surgery to establish a model of pressure overload-induced cardiac hypertrophy. Echocardiographic, histological, biochemical and immunological analyses of the myocardium and the adoptive transfer of bone marrow-derived macrophages (BMDMs) were conducted for in vivo studies. BMDMs were isolated and stimulated with lipopolysaccharide (LPS) for the in vitro study. OSMR deficiency aggravated cardiac hypertrophy, fibrotic remodelling and cardiac dysfunction after AB surgery in mice. Mechanistically, the loss of OSMR activated OSM/LIFR/STAT3 signalling and promoted a proresolving macrophage phenotype that exacerbated inflammation and impaired cardiac repair during remodelling. In addition, adoptive transfer of OSMR-KO BMDMs to WT mice after AB surgery resulted in a consistent hypertrophic phenotype. Moreover, knockdown of LIFR in myocardial tissue with Ad-shLIFR ameliorated the effects of OSMR deletion on the phenotype and STAT3 activation.

CONCLUSIONS

OSMR deficiency aggravated pressure overload-induced cardiac hypertrophy by modulating macrophages and OSM/LIFR/STAT3 signalling, which provided evidence that OSMR might be an attractive target for treating pathological cardiac hypertrophy and heart failure.

Real-ambient particulate matter exposure-induced FGFR1 methylation contributes to cardiac dysfunction via lipid metabolism disruption

Particulate matter (PM)-induced cardiometabolic disorder contributes to the progression of cardiac diseases, but its epigenetic mechanisms are largely unknown. This study used bioinformatic analysis, in vivo and in vitro multiple models to investigate the role of PM-induced cardiac fibroblast growth factor 1 (FGFR1) methylation and its impact on cardiomyocyte lipid metabolic disruption. Bioinformatic analysis revealed that FGFR1 was associated with cardiac pathologies, mitochondrial function and metabolism, supporting the possibility that FGFR1 may play regulatory roles in PM-induced cardiac functional impairment and lipid metabolism disorders. Individually ventilated cage (IVC)-based real-ambient PM exposure system mouse models were used to expose C57/BL6 mice for six and fifteen weeks. The results showed that PM induced cardiac lipid metabolism disorder, DNA nucleotide methyltransferases (DNMTs) alterations and FGFR1 expression declines in mouse heart. Lipidomics analysis revealed that carnitines, phosphoglycerides and lysophosphoglycerides were most significantly affected by PM exposure. At the cellular level, AC16 cells treated with FGFR1 inhibitor (PD173074) led to impaired mitochondrial and metabolic functions in cardiomyocytes. Inhibition of DNA methylation in cells by 5-AZA partially restored the FGFR1 expression, ameliorated cardiomyocyte injury and mitochondrial functions. These changes involved alterations in AMP-activated protein kinase (AMPK)-peroxisome proliferator activated receptors gamma, coactivator 1 alpha (PGC1α) pathways. Bisulfite sequencing PCR (BSP) and DNA methylation specific PCR (MSP) confirmed that PM exposure induced FGFR1 gene promoter region methylation. These results suggested that, by inducing FGFR1 methylation, PM exposure would affect cardiac injury and deranged lipid metabolism. Overexpression of FGFR1 in mouse heart using adeno-associated virus 9 (AAV9) effectively alleviated PM-induced cardiac impairment and metabolic disorder. Our findings identified that FGFR1 methylation might be one of the potential indicators for PM-induced cardiac mitochondrial and metabolic dysfunction, providing novel insights into underlying PM-related cardiotoxic mechanisms.

MicroRNA in the Diagnosis and Treatment of Doxorubicin-Induced Cardiotoxicity

Doxorubicin (DOX), a broad-spectrum chemotherapy drug, is widely applied to the treatment of cancer; however, DOX-induced cardiotoxicity (DIC) limits its clinical therapeutic utility. However, it is difficult to monitor and detect DIC at an early stage using conventional detection methods. Thus, sensitive, accurate, and specific methods of diagnosis and treatment are important in clinical practice. MicroRNAs (miRNAs) belong to non-coding RNAs (ncRNAs) and are stable and easy to detect. Moreover, miRNAs are expected to become biomarkers and therapeutic targets for DIC; thus, there are currently many studies focusing on the role of miRNAs in DIC. In this review, we list the prominent studies on the diagnosis and treatment of miRNAs in DIC, explore the feasibility and difficulties of using miRNAs as diagnostic biomarkers and therapeutic targets, and provide recommendations for future research.

Cardiomyocyte hyperplasia and immaturity but not hypertrophy are characteristic features of patients with RASopathies

AIMS

RASopathies are caused by mutations in genes that alter the MAP kinase pathway and are marked by several malformations with cardiovascular disorders as the predominant cause of mortality. Mechanistic insights in the underlying pathogenesis in affected cardiac tissue are rare. The aim of the study was to assess the impact of RASopathy causing mutations on the human heart.

METHODS AND RESULTS

Using single cell approaches and histopathology we analyzed cardiac tissue from children with different RASopathy-associated mutations compared to age-matched dilated cardiomyopathy (DCM) and control hearts. The volume of cardiomyocytes was reduced in RASopathy conditions compared to controls and DCM patients, and the estimated number of cardiomyocytes per heart was ~4-10 times higher. Single nuclei RNA sequencing of a 13-year-old RASopathy patient (carrying a PTPN11 c.1528C > G mutation) revealed that myocardial cell composition and transcriptional patterns were similar to <1 year old DCM hearts. Additionally, immaturity of cardiomyocytes is shown by an increased MYH6/MYH7 expression ratio and reduced expression of genes associated with fatty acid metabolism. In the patient with the PTPN11 mutation activation of the MAP kinase pathway was not evident in cardiomyocytes, whereas increased phosphorylation of PDK1 and its downstream kinase Akt was detected.

CONCLUSION

In conclusion, an immature cardiomyocyte differentiation status appears to be preserved in juvenile RASopathy patients. The increased mass of the heart in such patients is due to an increase in cardiomyocyte number (hyperplasia) but not an enlargement of individual cardiomyocytes (hypertrophy).

A coalition to heal-the impact of the cardiac microenvironment

Heart regenerative medicine has been gradually evolving from a view of the heart as a nonregenerative organ with terminally differentiated cardiac muscle cells. Understanding the biology of the heart during homeostasis and in response to injuries has led to the realization that cellular communication between all cardiac cell types holds great promise for treatments. Indeed, recent studies highlight new disease-reversion concepts in addition to cardiomyocyte renewal, such as matrix- and vascular-targeted therapies, and immunotherapy with a focus on inflammation and fibrosis. In this review, we will discuss the cross-talk within the cardiac microenvironment and how specific therapies aim to target the hostile cardiac milieu under pathological conditions.

Control of CRK-RAC1 activity by the miR-1/206/133 miRNA family is essential for neuromuscular junction function

Formation and maintenance of neuromuscular junctions (NMJs) are essential for skeletal muscle function, allowing voluntary movements and maintenance of the muscle tone, thereby preventing atrophy. Generation of NMJs depends on the interaction of motor neurons with skeletal muscle fibers, which initiates a cascade of regulatory events that is essential for patterning of acetylcholine receptor (AChR) clusters at specific sites of the sarcolemma. Here, we show that muscle-specific miRNAs of the miR-1/206/133 family are crucial regulators of a signaling cascade comprising DOK7-CRK-RAC1, which is critical for stabilization and anchoring of postsynaptic AChRs during NMJ development and maintenance. We describe that posttranscriptional repression of CRK by miR-1/206/133 is essential for balanced activation of RAC1. Failure to adjust RAC1 activity severely compromises NMJ function, causing respiratory failure in neonates and neuromuscular symptoms in adult mice. We conclude that miR-1/206/133 serve a specific function for NMJs but are dispensable for skeletal muscle development.

The miR-1/133/206 gene family codes for the most abundant microRNAs in striated muscles. Here, Klockner et al show that inactivation of all family members in skeletal muscle prevents formation of normal neuromuscular junctions due to increased expression of the adaptor protein CRK.