RhoE Fine-Tunes Inflammatory Response in Myocardial Infarction.

BACKGROUND: Inflammatory response after myocardial infarction (MI) is essential for cardiac healing, whereas excessive and prolonged inflammation extends the infarction and promotes adverse cardiac remodeling. Understanding the mechanistic insight of these tightly controlled inflammatory processes has a significant impact on post-MI recovery and therapy. Here, we uncover the critical role of small GTPase RhoE in post-MI recovery and its clinical implication. METHODS: Three genetic mouse lines are used: global RhoE knockout, cardiomyocyte-specific RhoE heterozygous, and cardiomyocyte-specific RhoE overexpression mice. A set of molecular signaling experiments, including bimolecular fluorescence complementation, immunoprecipitation, electrophoretic mobility shift assay, and mRNA microarray analysis, were conducted. Permanent ligation of the left anterior descending artery was performed, followed by the assessments of cardiac function, inflammation, and survival in the first week after MI. Finally, we examined the correlation of the expression levels of RhoE in MI patient heart and patient prognosis. RESULTS: RhoE deficiency turns on a group of proinflammatory gene expressions in mouse heart. Mice with cardiomyocyte-specific haploinsufficiency exhibit excessive inflammatory response with deleterious cardiac function after MI. A profound increase in nuclear factor-κB activity is detected in the mutant heart and the isolated cardiomyocytes. We further find that the expression of RhoE is upregulated in response to MI. Mechanistically, RhoE interacts with p65 and p50 individually in cytosol and blocks their nuclear translocation. RhoE also occupies the dimerization domain of p65 and subsequently disrupts the heterodimerization between p65 and p50. Cardiac RhoE overexpression inhibits nuclear factor-κB activity, restrains post-MI inflammation, and improves cardiac function and survival. Consistently, we find that the expression level of RhoE is elevated in the heart of patients with MI and that the patients with a higher expression level of RhoE exhibit a better prognosis in cardiac function recovery. CONCLUSIONS: The study uncovers RhoE as a new fine-tuning factor modulating MI-induced inflammation and promoting injured heart recovery. RhoE may serve as a new potential biomarker for the assessment of MI patient prognosis. Manipulation of RhoE could be as a potential therapeutic approach for MI and other inflammatory diseases.

Histone methyltransferase Setd2 is critical for the proliferation and differentiation of myoblasts.

Skeletal muscle cell proliferation and differentiation are tightly regulated. Epigenetic regulation is a major component of the regulatory mechanism governing these processes. Histone modification is part of the epigenetic code used for transcriptional regulation of chromatin through the establishment of an active or repressive state for genes involved in myogenesis in a temporal manner. Here, we uncovered the function of SET domain containing 2 (Setd2), an essential histone 3 lysine 36 trimethyltransferase, in regulating the proliferation and differentiation of myoblasts. Setd2 was silenced in the skeletal muscle myoblast cell line, C2C12, using the CRISPR/CAS9 system. The mutant cells exhibited defect in myotube formation. The myotube formation marker, myosin heavy chain (MHC), was downregulated earlier in Setd2 silenced cells compared to wild-type myoblasts during differentiation. The deficiency in Setd2 also resulted in repression of Myogenin (MyoG) expression, a key myogenic regulator during differentiation. In addition to the myoblast differentiation defect, decreased proliferation rate with significantly reduced levels of histone 3 phosphorylation, indicative of cell proliferation defect, were observed in the Setd2 silenced cells; suggesting an impaired proliferation phenotype. Furthermore, compromised G1/S- and G2/M-phase transition and decreased expression levels of major regulators of cell cycle G1/S checkpoints, cyclin D1, CDK4, CDK6, and cyclin E2 were detected in Setd2 silenced cells. Consistent with the cell cycle arrested phenotype, cyclin-dependent kinase inhibitor p21 was upregulated in Setd2 silenced cells. Together, this study demonstrates an essential role of Setd2 in myoblast proliferation and differentiation, and uncovers Setd2-mediated molecular mechanism through regulating MyoG and p21.

Rnd3/RhoE Modulates Hypoxia-Inducible Factor 1α/Vascular Endothelial Growth Factor Signaling by Stabilizing Hypoxia-Inducible Factor 1α and Regulates Responsive Cardiac Angiogenesis.

The insufficiency of compensatory angiogenesis in the heart of patients with hypertension contributes to heart failure transition. The hypoxia-inducible factor 1α-vascular endothelial growth factor (HIF1α-VEGF) signaling cascade controls responsive angiogenesis. One of the challenges in reprograming the insufficient angiogenesis is to achieve a sustainable tissue exposure to the proangiogenic factors, such as HIF1α stabilization. In this study, we identified Rnd3, a small Rho GTPase, as a proangiogenic factor participating in the regulation of the HIF1α-VEGF signaling cascade. Rnd3 physically interacted with and stabilized HIF1α, and consequently promoted VEGFA expression and endothelial cell tube formation. To demonstrate this proangiogenic role of Rnd3 in vivo, we generated Rnd3 knockout mice. Rnd3 haploinsufficient (Rnd3(+/-)) mice were viable, yet developed dilated cardiomyopathy with heart failure after transverse aortic constriction stress. The poststress Rnd3(+/-) hearts showed significantly impaired angiogenesis and decreased HIF1α and VEGFA expression. The angiogenesis defect and heart failure phenotype were partially rescued by cobalt chloride treatment, a HIF1α stabilizer, confirming a critical role of Rnd3 in stress-responsive angiogenesis. Furthermore, we generated Rnd3 transgenic mice and demonstrated that Rnd3 overexpression in heart had a cardioprotective effect through reserved cardiac function and preserved responsive angiogenesis after pressure overload. Finally, we assessed the expression levels of Rnd3 in the human heart and detected significant downregulation of Rnd3 in patients with end-stage heart failure. We concluded that Rnd3 acted as a novel proangiogenic factor involved in cardiac responsive angiogenesis through HIF1α-VEGFA signaling promotion. Rnd3 downregulation observed in patients with heart failure may explain the insufficient compensatory angiogenesis involved in the transition to heart failure.

Downregulation of RND3/RhoE in glioblastoma patients promotes tumorigenesis through augmentation of notch transcriptional complex activity.

Activation of Notch signaling contributes to glioblastoma multiform (GBM) tumorigenesis. However, the molecular mechanism that promotes the Notch signaling augmentation during GBM genesis remains largely unknown. Identification of new factors that regulate Notch signaling is critical for tumor treatment. The expression levels of RND3 and its clinical implication were analyzed in GBM patients. Identification of RND3 as a novel factor in GBM genesis was demonstrated in vitro by cell experiments and in vivo by a GBM xenograft model. We found that RND3 expression was significantly decreased in human glioblastoma. The levels of RND3 expression were inversely correlated with Notch activity, tumor size, and tumor cell proliferation, and positively correlated with patient survival time. We demonstrated that RND3 functioned as an endogenous repressor of the Notch transcriptional complex. RND3 physically interacted with NICD, CSL, and MAML1, the Notch transcriptional complex factors, promoted NICD ubiquitination, and facilitated the degradation of these cofactor proteins. We further revealed that RND3 facilitated the binding of NICD to FBW7, a ubiquitin ligase, and consequently enhanced NICD protein degradation. Therefore, Notch transcriptional activity was inhibited. Forced expression of RND3 repressed Notch signaling, which led to the inhibition of glioblastoma cell proliferation in vitro and tumor growth in the xenograft mice in vivo. Downregulation of RND3, however, enhanced Notch signaling activity, and subsequently promoted glioma cell proliferation. Inhibition of Notch activity abolished RND3 deficiency-mediated GBM cell proliferation. We conclude that downregulation of RND3 is responsible for the enhancement of Notch activity that promotes glioblastoma genesis.

Pathophysiological Functions of Rnd3/RhoE.

Rnd3, also known as RhoE, belongs to the Rnd subclass of the Rho family of small guanosine triphosphate (GTP)-binding proteins. Rnd proteins are unique due to their inability to switch from a GTP-bound to GDP-bound conformation. Even though studies of the biological function of Rnd3 are far from being concluded, information is available regarding its expression pattern, cellular localization, and its activity, which can be altered depending on the conditions. The compiled data from these studies implies that Rnd3 may not be a traditional small GTPase. The basic role of Rnd3 is to report as an endogenous antagonist of RhoA signaling-mediated actin cytoskeleton dynamics, which specifically contributes to cell migration and neuron polarity. In addition, Rnd3 also plays a critical role in arresting cell cycle distribution, inhibiting cell growth, and inducing apoptosis and differentiation. Increasing data have shown that aberrant Rnd3 expression may be the leading cause of some systemic diseases; particularly highlighted in apoptotic cardiomyopathy, developmental arrhythmogenesis and heart failure, hydrocephalus, as well as tumor metastasis and chemotherapy resistance. Therefore, a better understanding of the function of Rnd3 under different physiological and pathological conditions, through the use of suitable models, would provide a novel insight into the origin and treatment of multiple human diseases.

The LIM homeodomain transcription factor LHX6: a transcriptional repressor that interacts with pituitary homeobox 2 (PITX2) to regulate odontogenesis.

LHX6 is a LIM-homeobox transcription factor expressed during embryogenesis; however, the molecular mechanisms regulating LHX6 transcriptional activities are unknown. LHX6 and the PITX2 homeodomain transcription factor have overlapping expression patterns during tooth and craniofacial development, and in this report, we demonstrate new transcriptional mechanisms for these factors. PITX2 and LHX6 are co-expressed in the oral and dental epithelium and epithelial cell lines. Lhx6 expression is increased in Pitx2c transgenic mice and decreased in Pitx2 null mice. PITX2 activates endogenous Lhx6 expression and the Lhx6 promoter, whereas LHX6 represses its promoter activity. Chromatin immunoprecipitation experiments reveal endogenous PITX2 binding to the Lhx6 promoter. LHX6 directly interacts with PITX2 to inhibit PITX2 transcriptional activities and activation of multiple promoters. Bimolecular fluorescence complementation assays reveal an LHX6·PITX2 nuclear interaction in living cells. LHX6 has a dominant repressive effect on the PITX2 synergistic activation with LEF-1 and ß-catenin co-factors. Thus, LHX6 acts as a transcriptional repressor and represses the expression of several genes involved in odontogenesis. We have identified specific defects in incisor, molar, mandible, bone, and root development and late stage enamel formation in Lhx6 null mice. Amelogenin and ameloblastin expression is reduced and/or delayed in the Lhx6 null mice, potentially resulting from defects in dentin deposition and ameloblast differentiation. Our results demonstrate that LHX6 regulates cell proliferation in the cervical loop and promotes cell differentiation in the anterior region of the incisor. We demonstrate new molecular mechanisms for LHX6 and an interaction with PITX2 for normal craniofacial and tooth development.