Disruption of actin dynamics regulated by Rho effector mDia1 attenuates pressure overload-induced cardiac hypertrophic responses and exacerbates dysfunction

Untangling the role of RhoA in the heart: protective effect and mechanism

RhoA (ras homolog family member A) is a small G-protein that transduces intracellular signaling to regulate a broad range of cellular functions such as cell growth, proliferation, migration, and survival. RhoA serves as a proximal downstream effector of numerous G protein-coupled receptors (GPCRs) and is also responsive to various stresses in the heart. Upon its activation, RhoA engages multiple downstream signaling pathways. Rho-associated coiled-coil-containing protein kinase (ROCK) is the first discovered and best characterized effector or RhoA, playing a major role in cytoskeletal arrangement. Many other RhoA effectors have been identified, including myocardin-related transcription factor A (MRTF-A), Yes-associated Protein (YAP) and phospholipase Cε (PLCε) to regulate transcriptional and post-transcriptional processes. The role of RhoA signaling in the heart has been increasingly studied in last decades. It was initially suggested that RhoA signaling pathway is maladaptive in the heart, but more recent studies using cardiac-specific expression or deletion of RhoA have revealed that RhoA activation provides cardioprotection against stress through various mechanisms including the novel role of RhoA in mitochondrial quality control. This review summarizes recent advances in understanding the role of RhoA in the heart and its signaling pathways to prevent progression of heart disease.

Diaph1 knockout inhibits mouse primordial germ cell proliferation and affects gonadal development

BACKGROUND

Exploring the molecular mechanisms of primordial germ cell (PGC) migration and the involvement of gonadal somatic cells in gonad development is valuable for comprehending the origins and potential treatments of reproductive-related diseases.

METHODS

Diaphanous related formin 1 (Diaph1, also known as mDia1) was screened by analyzing publicly available datasets (ATAC-seq, DNase-seq, and RNA-seq). Subsequently, the CRISPR-Cas9 technology was used to construct Diaph1 knockout mice to investigate the role of Diaph1 in gonad development.

RESULTS

Based on data from public databases, a differentially expressed gene Diaph1, was identified in the migration of mouse PGC. Additionally, the number of PGCs was significantly reduced in Diaph1 knockout mice compared to wild type mice, and the expression levels of genes related to proliferation (Dicer1, Mcm9), adhesion (E-cadherin, Cdh1), and migration (Cxcr4, Hmgcr, Dazl) were significantly decreased. Diaph1 knockout also inhibited Leydig cell proliferation and induced apoptosis in the testis, as well as granulosa cell apoptosis in the ovary. Moreover, the sperm count in the epididymal region and the count of ovarian follicles were significantly reduced in Diaph1 knockout mice, resulting in decreased fertility, concomitant with lowered levels of serum testosterone and estradiol. Further research found that in Diaph1 knockout mice, the key enzymes involved in testosterone synthesis (CYP11A1, 3β-HSD) were decreased in Leydig cells, and the estradiol-associated factor (FSH receptor, AMH) in granulosa cells were also downregulated.

CONCLUSIONS

Overall, our findings indicate that the knockout of Diaph1 can disrupt the expression of factors that regulate sex hormone production, leading to impaired secretion of sex hormones, ultimately resulting in damage to reproductive function. These results provide a new perspective on the molecular mechanisms underlying PGC migration and gonadal development, and offer valuable insights for further research on the causes, diagnosis, and treatment of related diseases.

Association between interatrial septum adiposity and atrial fibrillation: transesophageal echocardiography imaging and autopsy study

Recent clinical evidence has suggested that interatrial septal (IAS) adiposity contributes to atrial fibrillation (AF). The present study aimed to confirm the usefulness of transesophageal echocardiography (TEE) to estimate IAS adiposity in patients with AF. The histological IAS analysis based on autopsy samples sought to clarify characteristics that underlie the contribution of IAS adiposity to AF. The imaging study analyzed the TEE results in patients with AF (n = 184) in comparison with transthoracic echocardiography (TTE) and computed tomography (CT) results. The autopsy study histologically analyzed IAS in subjects with (n = 5) and without (n = 5) history of AF. In the imaging study, the ratio of interatrial septum adipose tissue (IAS-AT) volume per epicardial adipose tissue (EpAT) volume was greater in patients with persistent AF compared (PerAF) to those with paroxysmal AF (PAF). Multivariable analysis revealed that both TEE-assessed IAS thickness and TTE-assessed left atrial dimension were predicted by CT-assessed IAS-AT volume. In the autopsy study, the histologically-assessed IAS section thickness was greater in the AF group than that in the non-AF group and was positively correlated with the IAS-AT area percentage. In addition, the size of adipocytes in IAS-AT was smaller, compared to EpAT and subcutaneous adipose tissue (SAT). IAS-AT infiltrated into the IAS myocardium, as if adipose tissue split the myocardium (designated as myocardial splitting by IAS-AT). The number of island-like myocardium pieces as a result of myocardial splitting by IAS-AT was greater in the AF group than in the non-AF group and was positively correlated with the IAS-AT area percentage. The present imaging study confirmed the usefulness of TEE to estimate IAS adiposity in patients with AF without radiation exposure. The autopsy study suggested that the myocardial splitting by IAS-AT may contribute to atrial cardiomyopathy leading to AF.

Cell response to mechanical microenvironment cues via Rho signaling: From mechanobiology to mechanomedicine

Mechanical cues in the cell microenvironment such as those from extracellular matrix properties, stretching, compression and shear stress, play a critical role in maintaining homeostasis. Upon sensing mechanical stimuli, cells can translate these external forces into intracellular biochemical signals to regulate their cellular behaviors, but the specific mechanisms of mechanotransduction at the molecular level remain elusive. As a subfamily of the Ras superfamily, Rho GTPases have been recognized as key intracellular mechanotransduction mediators that can regulate multiple cell activities such as proliferation, migration and differentiation as well as biological processes such as cytoskeletal dynamics, metabolism, and organ development. However, the upstream mechanosensors for Rho proteins and downstream effectors that respond to Rho signal activation have not been well illustrated. Moreover, Rho-mediated mechanical signals in previous studies are highly context-dependent. In this review, we systematically summarize the types of mechanical cues in the cell microenvironment and provide recent advances on the roles of the Rho-based mechanotransduction in various cell activities, physiological processes and diseases. Comprehensive insights into the mechanical roles of Rho GTPase partners would open a new paradigm of mechanomedicine for a variety of diseases. STATEMENT OF SIGNIFICANCE: In this review, we highlight the critical role of Rho GTPases as signal mediators to respond to physical cues in microenvironment. This article will add a distinct contribution to this set of knowledge by intensively addressing the relationship between Rho signaling and mechanobiology/mechanotransduction/mechanomedcine. This topic has not been discussed by the journal, nor has it yet been developed by the field. The comprehensive picture that will develop, from molecular mechanisms and engineering methods to disease treatment strategies, represents an important and distinct contribution to the field. We hope that this review would help researchers in various fields, especially clinicians, oncologists and bioengineers, who study Rho signal pathway and mechanobiology/mechanotransduction, understand the critical role of Rho GTPase in mechanotransduction.

RhoA rescues cardiac senescence by regulating Parkin-mediated mitophagy

Heart failure is one of the leading causes of death worldwide. RhoA, a small GTPase, governs actin dynamics in various tissue and cell types, including cardiomyocytes; however, its involvement in cardiac function has not been fully elucidated. Here, we generated cardiomyocyte-specific RhoA conditional knockout (cKO) mice, which demonstrated a significantly shorter lifespan with left ventricular dilation and severely impaired ejection fraction. We found that the cardiac tissues of the cKO mice exhibited structural disorganization with fibrosis and also exhibited enhanced senescence compared with control mice. In addition, we show that cardiomyocyte mitochondria were structurally abnormal in the aged cKO hearts. Clearance of damaged mitochondria by mitophagy was remarkably inhibited in both cKO cardiomyocytes and RhoA-knockdown HL-1 cultured cardiomyocytes. In RhoA-depleted cardiomyocytes, we reveal that the expression of Parkin, an E3 ubiquitin ligase that plays a crucial role in mitophagy, was reduced, and expression of N-Myc, a negative regulator of Parkin, was increased. We further reveal that the RhoA-Rho kinase axis induced N-Myc phosphorylation, which led to N-Myc degradation and Parkin upregulation. Re-expression of Parkin in RhoA-depleted cardiomyocytes restored mitophagy, reduced mitochondrial damage, attenuated cardiomyocyte senescence, and rescued cardiac function both in vitro and in vivo. Finally, we found that patients with idiopathic dilated cardiomyopathy without causal mutations for dilated cardiomyopathy showed reduced cardiac expression of RhoA and Parkin. These results suggest that RhoA promotes Parkin-mediated mitophagy as an indispensable mechanism contributing to cardioprotection in the aging heart.

Actin-Binding Proteins in Cardiac Hypertrophy

The heart reacts to a large number of pathological stimuli through cardiac hypertrophy, which finally can lead to heart failure. However, the molecular mechanisms of cardiac hypertrophy remain elusive. Actin participates in the formation of highly differentiated myofibrils under the regulation of actin-binding proteins (ABPs), which provides a structural basis for the contractile function and morphological change in cardiomyocytes. Previous studies have shown that the functional abnormality of ABPs can contribute to cardiac hypertrophy. Here, we review the function of various actin-binding proteins associated with the development of cardiac hypertrophy, which provides more references for the prevention and treatment of cardiomyopathy.

Detection of fibrotic remodeling of epicardial adipose tissue in patients with atrial fibrillation: Imaging approach based on histological observation

Background

Fibrotic remodeling of epicardial adipose tissue (EAT) is crucial for proinflammatory atrial myocardial fibrosis, which leads to atrial fibrillation (AF).

Objectives

We tested the hypothesis that the ratio of central to marginal adipocyte diameter in EAT represents its fibrotic remodeling. Based on a similar concept, we also tested whether the percent (%) change in EAT fat attenuation determined using computed tomographic (CT) images can detect this remodeling.

Methods

Left atrial appendages were obtained from 76 consecutive AF patients during cardiovascular surgery. EAT in the central area (central EAT: C-EAT) and that adjacent to the atrial myocardium (Marginal EAT: M-EAT) were evaluated histologically. CT images for all of the 76 patients were also analyzed.

Results

The adipocyte diameter was smaller, fibrotic remodeling of EAT (EAT fibrosis) was more severe, and infiltration of macrophages and myofibroblasts was more extensive in M-EAT than in C-EAT. EAT fibrosis was positively correlated with adipocyte diameter in C-EAT and negatively correlated in M-EAT, resulting in a positive correlation between EAT fibrosis and the ratio of central to marginal adipocyte diameter (C/M diameter ratio; r = 0.73, P < .01). The C/M diameter ratio was greater in patients with persistent AF than in those with paroxysmal AF. CT images demonstrated that the %change in EAT fat attenuation was positively correlated with EAT fibrosis.

Conclusion

Our results suggest that the central-to-marginal adipocyte diameter ratio is tightly associated with fibrotic remodeling of EAT. In addition, the %change in EAT fat attenuation determined using CT imaging can detect remodeling noninvasively.

Cutoff value for hypertrophic heart weight in the Japanese population

BACKGROUND

Cardiac hypertrophy is a clinical risk factor for cardiovascular death (CVD) frequently recorded in autopsy reports, but the diagnostic criteria for the condition have not been clearly-established for autopsy. This study aimed to estimate the cutoff value for hypertrophic heart weight that can efficiently assist the postmortem diagnosis of CVD.

METHODS

We analyzed accumulated autopsy data from 3534 individuals aged 0-101 years.

RESULTS

We found that heart weight increased linearly with a person's age until 20 years, after which it remained stable. The mean heart weight in CVD cases was 473 g in men and 379 g in women. The mean heart weight in non-CVD cases was 385 g in men and 320 g in women. Receiver operating characteristic curve analysis for CVD assessment revealed that the cutoff value of heart weight was 407 g (odds ratio of 4.2) in men and 327 g (2.6) in women, and that of heart weight/body height was 2.38 g/cm (4.0) in men and 2.15 g/cm (2.6) in women, respectively. Overall, heart weight was a more useful predictor of CVD in men than in women. In logistic regression analysis, the predictive power of heart weight for CVD was higher than that of body mass index in both sexes.

CONCLUSION

Thus, the criteria for hypertrophic heart weight are practical and useful for autopsy recordings, and it can be helpful for postmortem diagnosis of CVD. Our report is the first to reveal the cutoff value for hypertrophic heart weight in the Japanese population.