The muscular dystrophies target muscle groups differentially. In mouse models of muscular dystrophy, notably the mdx model of Duchenne Muscular Dystrophy, the diaphragm muscle shows marked fibrosis and at an earlier age than other muscle groups, more reflective of the histopathology seen in human muscular dystrophy.
Using a mouse model of limb girdle muscular dystrophy, the Sgcg mouse, we compared muscle pathology across different muscle groups and heart. A cohort of nearly 200 Sgcg mice were studied using multiple measures of pathology including echocardiography, Evans blue dye uptake and hydroxyproline content in multiple muscle groups. Spearman rank correlations were determined among echocardiographic and pathological parameters.
The abdominal muscles were found to have more fibrosis than other muscle groups, including the diaphragm muscle. The abdominal muscles also had more Evans blue dye uptake than other muscle groups. The amount of diaphragm fibrosis was found to correlate positively with fibrosis in the left ventricle, and abdominal muscle fibrosis correlated with impaired left ventricular function. Fibrosis in the abdominal muscles negatively correlated with fibrosis in the diaphragm and right ventricles. Together these data reflect the recruitment of abdominal muscles as respiratory muscles in muscular dystrophy, a finding consistent with data from human patients.
muscular dystrophy; heart; abdominal muscle; diaphragm muscle; fibrosis; membrane damage
To describe a novel surgical method for sutureless placement of amniotic membrane on the bulbar and palpebral conjunctiva in the setting of ocular-involving acute Stevens-Johnson syndrome.
Six days into an acute Stevens-Johnson episode, a 27-year-old male developed early symblepharon, despite aggressive lubrication and topical steroid therapy. He underwent symblepharon lysis and placement of an amniotic membrane wrapped around a symblepharon ring.
The patient maintained 20/20 vision in each eye with no recurrent symblepharon formation except for the temporal canthus (which was not covered with amniotic membrane).
Amniotic-membrane-wrapped symblepharon rings provide a sutureless way to fixate amniotic membrane to the bulbar and palpebral conjunctiva with very good anatomic and functional outcomes in an acute Stevens-Johnson patient. Future research could be directed towards development of a symblepharon ring able to better protect the far temporal conjunctiva.
Stevens-Johnson syndrome; amniotic membrane; bulbar conjunctiva; palpebral conjunctiva; Lamotrigine
Honokiol (HKL) is a natural biphenolic compound derived from the bark of
magnolia trees with anti-inflammatory, anti-oxidative, anti-tumor and
neuroprotective properties. Here we show that HKL blocks agonist-induced and
pressure overload-mediated, cardiac hypertrophic responses, and ameliorates
pre-existing cardiac hypertrophy, in mice. Our data suggest that the
anti-hypertrophic effects of HKL depend on activation of the deacetylase SIRT3.
We demonstrate that HKL is present in mitochondria, enhances SIRT3 expression
nearly two-fold and suggest that HKL may bind to SIRT3 to further increase its
activity. Increased SIRT3 activity is associated with reduced acetylation of
mitochondrial SIRT3 substrates, MnSOD and OSCP. HKL-treatment increases
mitochondrial rate of oxygen consumption and reduces ROS synthesis in wild-type,
but not in SIRT3-KO cells. Moreover, HKL-treatment blocks cardiac fibroblast
proliferation and differentiation to myofibroblasts in SIRT3-dependent manner.
These results suggest that HKL is a pharmacological activator of SIRT3 capable
of blocking, and even reversing, the cardiac hypertrophic response.
MicroRNAs (miRNAs) are now recognized as critical regulators of diverse physiological and pathological processes; however, studies of miRNAs and arrhythmogenesis remain sparse. Connexin43 (Cx43), a major cardiac gap junction protein, has elicited great interest in its role in arrhythmias. Additionally, Cx43 was a potential target for miR-130a as predicted by several computational algorithms. This study investigates the effect of miR-130a overexpression in the adult heart and its effect on cardiac rhythm.
Methods and Results
Using a cardiac-specific inducible system, transgenic mice demonstrated both atrial and ventricular arrhythmias. We performed ventricular-programmed electrical stimulation and found that the αMHC-miR130a mice developed sustained ventricular tachycardia beginning 6 weeks after overexpression. Western blot analysis demonstrated a steady decline in Cx43 after 2 weeks of overexpression with over a 90% reduction in Cx43 levels by 10 weeks. Immunofluorescent staining confirmed a near complete loss of Cx43 throughout the heart. To validate Cx43 as a direct target of miR-130a, we performed in vitro target assays in 3T3 fibroblasts and HL-1 cardiomyocytes, both known to endogenously express miR-130a. Using a luciferase reporter fused to the 3’UTR of Cx43, we found a 52.9% reduction in luciferase activity in 3T3 cells (p<0.0001) and a 47.6% reduction in HL-1 cells (p=0.0056) compared to controls. Addition of an antisense miR-130a inhibitor resulted in a loss of inhibitory activity of the Cx43 3’UTR reporter.
We have identified an unappreciated role for miR-130a as a direct regulator of Cx43. Overexpression of miR-130a may contribute importantly to gap junction remodeling and to the pathogenesis of atrial and ventricular arrhythmias.
MicroRNA; Ventricular Arrhythmia; Atrial Arrhythmia; Connexin43
Abnormal activation of insulin-like growth factor (IGF)-Akt signaling is implicated in the development of various diseases, including heart failure. However, the molecular mechanisms that regulate activation of this signaling pathway are not completely understood. Here we show that sirtuin 6 (SIRT6), a nuclear histone deacetylase, functions at the level of chromatin to directly attenuate IGF-Akt signaling. SIRT6-deficient mice developed cardiac hypertrophy and heart failure, whereas SIRT6 transgenic mice were protected from hypertrophic stimuli, indicating that SIRT6 acts as a negative regulator of cardiac hypertrophy. SIRT6-deficient mouse hearts showed hyperactivation of IGF signaling–related genes and their downstream targets. Mechanistically, SIRT6 binds to and suppresses the promoter of IGF signaling–related genes by interacting with c-Jun and deacetylating histone 3 at Lys9 (H3K9). We also found reduced SIRT6 expression in human failing hearts. These findings disclose a new link between SIRT6 and IGF-Akt signaling and implicate SIRT6 in the development of cardiac hypertrophy and failure.
Transgenic mice displaying abnormalities in cardiac development and function represent a powerful tool for the understanding the molecular mechanisms underlying both normal cardiovascular function and the pathophysiological basis of human cardiovascular disease. Fetal and perinatal death is a common feature when studying genetic alterations affecting cardiac development (1–3). In order to study the role of genetic or pharmacologic alterations in the early development of cardiac function, ultrasound imaging of the live fetus has become an important tool for early recognition of abnormalities and longitudinal follow-up. Noninvasive ultrasound imaging is an ideal method for detecting and studying congenital malformations and the impact on cardiac function prior to death (4). It allows early recognition of abnormalities in the living fetus and the progression of disease can be followed in utero with longitudinal studies (5, 6). Until recently, imaging of fetal mouse hearts frequently involved invasive methods. The fetus had to be sacrificed to perform magnetic resonance microscopy and electron microscopy or surgically delivered for transillumination microscopy. An application of high-frequency probes with conventional 2-D and pulsed-wave Doppler imaging has been shown to provide measurements of cardiac contraction and heart rates during embryonic development with databases of normal developmental changes now available (6–10). M-mode imaging further provides important functional data, although, the proper imaging planes are often difficult to obtain. High-frequency ultrasound imaging of the fetus has improved 2-D resolution and can provide excellent information on the early development of cardiac structures (11).
echocardiography; cardiac development; pulse Doppler; non-invasive imaging
Significance: The term epigenetics refers to the changes in the phenotype and gene expression that occur without alterations in the DNA sequence. There is a rapidly growing body of evidence that epigenetic modifications are involved in the pathological mechanisms of many cardiovascular diseases (CVDs), which intersect with many of the pathways involved in oxidative stress. Recent Advances: Most studies relating epigenetics and human pathologies have focused on cancer. There has been a limited study of epigenetic mechanisms in CVDs. Although CVDs have multiple established genetic and environmental risk factors, these explain only a portion of the total CVD risk. The epigenetic perspective is beginning to shed new light on how the environment influences gene expression and disease susceptibility in CVDs. Known epigenetic changes contributing to CVD include hypomethylation in proliferating vascular smooth muscle cells in atherosclerosis, changes in estrogen receptor-α (ER-α) and ER-β methylation in vascular disease, decreased superoxide dismutase 2 expression in pulmonary hypertension (PH), as well as trimethylation of histones H3K4 and H3K9 in congestive heart failure. Critical Issues: In this review, we discuss the epigenetic modifications in CVDs, including atherosclerosis, congestive heart failure, hypertension, and PH, with a focus on altered redox signaling. Future Directions: As advances in both the methodology and technology accelerate the study of epigenetic modifications, the critical role they play in CVD is beginning to emerge. A fundamental question in the field of epigenetics is to understand the biochemical mechanisms underlying reactive oxygen species-dependent regulation of epigenetic modification. Antioxid. Redox Signal. 18, 1920–1936.
MicroRNAs are now recognized as important regulators of cardiovascular genes with critical roles in normal development and physiology, as well as disease development. MicroRNAs (miRNAs) are small non-coding RNAs approximately 22 nucleotides in length that regulate expression of target genes through sequence-specific hybridization to the 3′ untranslated region of messenger RNAs and either block translation or direct degradation of their target messenger RNA. They have been shown to participate in cardiovascular disease pathogenesis including atherosclerosis, coronary artery disease, myocardial infarction, heart failure and cardiac arrhythmias. Broadly defined, cardiac arrhythmias are a variation from the normal heart rate or rhythm. Arrhythmias are common and result in significant morbidity and mortality. Ventricular arrhythmias constitute a major cause for cardiac death, particularly sudden cardiac death in the setting of myocardial infarction and heart failure. As advances in pharmacologic, device, and ablative therapy continue to evolve, the molecular insights into the basis of arrhythmia is growing with the ambition of providing additional therapeutic options. Electrical remodeling and structural remodeling are identified mechanisms underlying arrhythmia generation; however, published studies focusing on miRNAs and cardiac conduction are sparse. Recent studies have highlighted the role of microRNAs in cardiac rhythm through regulation of key ion channels, transporters, and cellular proteins in arrhythmogenic conditions. This article aims to review the studies linking miRNAs to cardiac excitability and other processes pertinent to arrhythmia.
microRNAs; cardiovascular; arrhythmia; atrial fibrillation; conduction; ventricular fibrillation; ventricular tachycardia; electrical remodeling
There is an emerging widespread interest in the role of damage-associated molecular pattern molecules (DAMP) S100A8, S100A9 and S100A12 in cardiovascular and other diseases. In this study we tested the efficacy of ABR-215757, a S100 protein binding immuno-modulatory compound to stabilize atherosclerosis in transgenic ApoE null mice that express the human pro-inflammatory S100A12 protein within the smooth muscle cell (SM22α-S100A12).
Twelve-week old S100A12 transgenic/ApoE-/- and WT/ApoE-/- mice were treated with ABR-21575 for 5 weeks and were analyzed 4 month later.
Surface plasmon resonance analysis demonstrated that S100A12 interacts with ABR-215757 in a zinc dependent manner in vitro. In vivo, ABR-215757 administration reduced features of advanced plaque morphology resulting in smaller necrotic cores, diminished intimal and medial vascular calcification, and reduced amount of infiltrating inflammatory cells. ABR-215757 normalized aortic expression of RAGE protein and normalized experimentally-induced delayed hypersensitivity. The effect of ABR-215757 was more prominent in ApoE-/- mice expressing S100A12 than in ApoE-/- animals lacking expression of human S100A12 protein.
Our data suggest that S100A12 is important for progression of atherosclerosis and can be targeted by the small molecule ABR-215757. The specific binding of quinoline-3-carboxamides to S100A12 attenuates S100A12-mediated features of accelerated murine atherosclerosis.
atherosclerosis; S100 proteins; RAGE; Quinoline-3-carboxamides
To describe a previously unreported presentation of a conjunctival dermoid.
An 8-year-old girl presented with a progressively enlarging mass in the right conjunctival fornix composed of normal appearing eyelashes. The patient had a history of aberrant conjunctival eyelash growth that had caused recurrent conjunctivitis in her right eye over the past few years. The mass was surgically removed and the pathology report revealed it to be a conjunctival dermoid. The patient had an excellent surgical result with normal cosmetic appearance.
Mature hair follicle growth from the conjunctiva is another possible presentation of a conjunctival dermoid that can be cured by simple surgical excision.
Conjunctival Dermoid; Choristoma; Eyelash and Hair
P311 is an 8-kDa intracellular protein that is highly conserved across species and is expressed in the nervous system as well as in vascular and visceral smooth muscle cells. P311-null (P311–/–) mice display learning and memory defects, but alterations in their vasculature have not been previously described. Here we report that P311–/– mice are markedly hypotensive with accompanying defects in vascular tone and VSMC contractility. Functional abnormalities in P311–/– mice resulted from decreased total and active levels of TGF-β1, TGF-β2, and TGF-β3 that arise as a specific consequence of decreased translation. Vascular hypofunctionality was fully rescued in vitro and in vivo by exogenous TGF-β1–TGF-β3. Conversely, P311-transgenic (P311TG) mice had elevated levels of TGF-β1–TGF-β3 and subsequent hypertension. Consistent with findings attained in mouse models, arteries recovered from hypertensive human patients displayed increased P311 expression. Thus, we identified P311 as the first protein known to modulate TGF-β translation and the first pan-regulator of TGF-β expression under steady-state conditions. Together, our findings point to P311 as a critical blood pressure regulator and establish a potential link between P311 expression and the development of hypertensive disease.
Mice from the MRL or “superhealing” strain have enhanced repair after acute injury to the skin, cornea, and heart. We now tested an admixture of the MRL genome and found that it altered the course of muscle pathology and cardiac function in a chronic disease model of skeletal and cardiac muscle. Mice lacking γ-sarcoglycan (Sgcg), a dystrophin-associated protein, develop muscular dystrophy and cardiomyopathy similar to their human counterparts with limb girdle muscular dystrophy. With disruption of the dystrophin complex, the muscle plasma membrane becomes leaky and muscles develop increased fibrosis.
MRL/MpJ mice were bred with Sgcg mice, and cardiac function was measured. Muscles were assessed for fibrosis and membrane leak using measurements of hydroxyproline and Evans blue dye. Quantitative trait locus mapping was conducted using single nucleotide polymorphisms distinct between the two parental strains.
Introduction of the MRL genome reduced fibrosis but did not alter membrane leak in skeletal muscle of the Sgcg model. The MRL genome was also associated with improved cardiac function with reversal of depressed fractional shortening and the left ventricular ejection fraction. We conducted a genome-wide analysis of genetic modifiers and found that a region on chromosome 2 was associated with cardiac, diaphragm muscle and abdominal muscle fibrosis.
These data are consistent with a model where the MRL genome acts in a dominant manner to suppress fibrosis in this chronic disease setting of heart and muscle disease.
Cardiomyopathy; Fibrosis; MRL; Muscular dystrophy
Epidermolysis bullosa acquisita (EBA) is a rare and acquired autoimmune subepidermal bullous disease of the skin and mucosa. EBA includes various distinct clinical manifestations resembling Bullous Pemphigus, Brunsting-Perry pemphigoid, or cicatricial pemphigoid. These patients have autoantibodies against type VII collagen, an integral component of anchoring fibrils, which are responsible for attaching the dermis to the epidermis. Destruction or perturbation of the normally functioning anchoring fibrils clinically results in skin fragility, blisters, erosions, scars, milia and nail loss, all features reminiscent of genetic dystrophic epidermolysis bullosa. These anti-type VII collagen antibodies are “pathogenic” because when injected into a mouse, the mouse develops an EBA-like blistering disease. Currently treatment is often unsatisfactory, however some success has been achieved with colchichine, dapsone, photopheresis, plasmaphresis, infliximab, rituximab and IVIG.
Cardiac conduction system (CCS) disease, which results in disrupted conduction and impaired cardiac rhythm, is common with significant morbidity and mortality. Current treatment options are limited, and rational efforts to develop cell-based and regenerative therapies require knowledge of the molecular networks that establish and maintain CCS function. Recent genome-wide association studies (GWAS) have identified numerous loci associated with adult human CCS function, including TBX5 and SCN5A. We hypothesized that TBX5, a critical developmental transcription factor, regulates transcriptional networks required for mature CCS function. We found that deletion of Tbx5 from the mature murine ventricular conduction system (VCS), including the AV bundle and bundle branches, resulted in severe VCS functional consequences, including loss of fast conduction, arrhythmias, and sudden death. Ventricular contractile function and the VCS fate map remained unchanged in VCS-specific Tbx5 knockouts. However, key mediators of fast conduction, including Nav1.5, which is encoded by Scn5a, and connexin 40 (Cx40), demonstrated Tbx5-dependent expression in the VCS. We identified a TBX5-responsive enhancer downstream of Scn5a sufficient to drive VCS expression in vivo, dependent on canonical T-box binding sites. Our results establish a direct molecular link between Tbx5 and Scn5a and elucidate a hierarchy between human GWAS loci that affects function of the mature VCS, establishing a paradigm for understanding the molecular pathology of CCS disease.
The proinflammatory cytokine S100A12 is associated with coronary atherosclerotic plaque rupture. We previously generated transgenic mice with vascular smooth muscle–targeted expression of human S100A12 and found that these mice developed aortic aneurysmal dilation of the thoracic aorta. In the current study, we tested the hypothesis that S100A12 expressed in vascular smooth muscle in atherosclerosis-prone apolipoprotein E (ApoE)–null mice would accelerate atherosclerosis.
Methods and Results
ApoE-null mice with or without the S100A12 transgene were analyzed. We found a 1.4-fold increase in atherosclerotic plaque size and more specifically a large increase in calcified plaque area (45% versus 7% of innominate artery plaques and 18% versus 10% of aortic root plaques) in S100A12/ApoE-null mice compared with wild-type/ApoE-null littermates. Expression of bone morphogenic protein and other osteoblastic genes was increased in aorta and cultured vascular smooth muscle, and importantly, these changes in gene expression preceded the development of vascular calcification in S100A12/ApoE-null mice. Accelerated atherosclerosis and vascular calcification were mediated, at least in part, by oxidative stress because inhibition of NADPH oxidase attenuated S100A12-mediated osteogenesis in cultured vascular smooth muscle cells. S100A12 transgenic mice in the wild-type background (ApoE+/+) showed minimal vascular calcification, suggesting that S100A12 requires a proinflammatory/proatherosclerotic environment to induce osteoblastic differentiation and vascular calcification.
Vascular smooth muscle S100A12 accelerates atherosclerosis and augments atherosclerosis-triggered osteogenesis, reminiscent of features associated with plaque instability.
calcification; coronary artery disease; genetically altered mice; vascular biology
The proinflammatory cytokine S100A12 (also known as EN-RAGE) is associated with cardiovascular morbidity and mortality in hemodialysis patients. In the cur- rent study, we tested the hypothesis that S100A12 expressed in vascular smooth muscle in nonatherosclerosis-prone C57BL/6J mice on normal rodent chow diet, but exposed to the metabolic changes of chronic kidney disease (CKD), would develop vascular disease resembling that observed in patients with CKD.
CKD was induced in S100A12 transgenic mice and wild-type littermate mice not expressing human S100A12 by surgical ligation of the ureters. The aorta was analyzed after 7 weeks of elevated BUN (blood urea nitrogen), and cultured aortic smooth muscle cells were studied.
We found enhanced vascular medial calcification in S100A12tg mice subjected to CKD. Vascular calcification was mediated, at least in part, by activation of the receptor for S100A12, RAGE (receptor for advanced glycation endproducts), and by enhanced oxidative stress, since inhibition of NADPH-oxidase Nox1 and limited access of S100A12 to RAGE attenuated the calcification and gene expression of osteoblastic genes in cultured vascular smooth muscle cells.
S100A12 augments CKD-triggered osteogenesis in murine vasculature, reminiscent of features associated with enhanced vascular calcification in patients with chronic and end-stage kidney disease.
Chronic kidney disease; Blood urea nitrogen; Receptor for advanced glycation endproducts
Epigenetics refers to changes in phenotype and gene expression that occur without alterations in DNA sequence. Epigenetic modifications of the genome can be acquired de novo and are potentially heritable. This review focuses on the emerging recognition of a role for epigenetics in the development of pulmonary arterial hypertension (PAH). Lessons learned from the epigenetics in cancer and neurodevelopmental diseases, such as Prader-Willi syndrome, can be applied to PAH. These syndromes suggest that there is substantial genetic and epigenetic cross-talk such that a single phenotype can result from a genetic cause, an epigenetic cause, or a combined abnormality. There are three major mechanisms of epigenetic regulation, including methylation of CpG islands, mediated by DNA methyltransferases, modification of histone proteins, and microRNAs. There is substantial interaction between these epigenetic mechanisms. Recently, it was discovered that there may be an epigenetic component to PAH. In PAH there is downregulation of superoxide dismutase 2 (SOD2) and normoxic activation of hypoxia inducible factor (HIF-1α). This decrease in SOD2 results from methylation of CpG islands in SOD2 by lung DNA methyltransferases. The partial silencing of SOD2 alters redox signaling, activates HIF-1α) and leads to excessive cell proliferation. The same hyperproliferative epigenetic abnormality occurs in cancer. These epigenetic abnormalities can be therapeutically reversed. Epigenetic mechanisms may mediate gene-environment interactions in PAH and explain the great variability in susceptibility to stimuli such as anorexigens, virus, and shunts. Epigenetics may be relevant to the female predisposition to PAH and the incomplete penetrance of BMPR2 mutations in familial PAH.
CpG islands; DNA methyl transferases; histone acetylation; small inhibitor RNA; superoxide dismutase 2
Excessive proliferation and impaired apoptosis of pulmonary artery smooth muscle cells (PASMC) contributes to vascular obstruction in patients and fawn-hooded rats (FHR) with pulmonary arterial hypertension (PAH). Expression and activity of mitochondrial superoxide dismutase-2 (SOD2), the major generator of H2O2, is known to be reduced in PAH; however, the mechanism and therapeutic relevance of this is unknown.
Methods and Results
SOD2 expression in PASMC is decreased in PAH patients and FHR with PAH. FHR PASMC have higher proliferation and lower apoptosis rates than Sprague-Dawley PASMC. Moreover, FHR PASMC have hyperpolarized mitochondria, low H2O2 production and a reduced cytoplasmic and mitochondrial redox state. Administration of SOD2 siRNA to normal PASMC recapitulates the FHR-PAH phenotype, hyperpolarizing mitochondria, decreasing H2O2 and inhibiting caspase activity. Conversely, SOD2 over-expression in FHR PASMC, or therapy with the SOD-mimetic MnTBAP, reverses the hyperproliferative PAH phenotype. Importantly, SOD-mimetic therapy regresses PAH in vivo. Investigation of the SOD2 gene revealed no mutation, suggesting a possible epigenetic dysregulation. Genomic bisulfite sequencing demonstrates selective hypermethylation of a CpG island in an enhancer region of intron 2 and another in the promoter. Differential methylation occurs selectively in PA versus aortic SMC and is reversed by the DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine, restoring both SOD2 expression and the proliferation/apoptosis ratio. The expression of the enzymes that mediate gene methylation, DNA methyltransferases 1 and 3B, is upregulated in FHR lungs.
Tissue-specific, epigenetic SOD2 deficiency initiates and sustains a heritable form of PAH by impairing redox signaling and creating a proliferative, apoptosis-resistant PASMC. SOD augmentation regresses experimental PAH. The discovery of an epigenetic component to PAH may offer new therapeutic targets.
Pulmonary arterial hypertension; Voltage-gated potassium channels (Kv1.5); Hypoxia-inducible factor-1α (HIF-1α); Epigenetic gene methylation; DNA methyltransferase
Mutations in LMNA, the gene encoding the nuclear membrane proteins, lamins A and C, produce cardiac and muscle disease. In the heart, these autosomal dominant LMNA mutations lead to cardiomyopathy frequently associated with cardiac conduction system disease. Herein, we describe a patient with the R374H missense variant in nesprin-1α, a protein that binds lamin A/C. This individual developed dilated cardiomyopathy requiring cardiac transplantation. Fibroblasts from this individual had increased expression of nesprin-1α and lamins A and C, indicating changes in the nuclear membrane complex. We characterized mice lacking the carboxy-terminus of nesprin-1 since this model expresses nesprin-1 without its carboxy-terminal KASH domain. These Δ/Δ KASH mice have a normally assembled but dysfunctional nuclear membrane complex and provide a model for nesprin-1 mutations. We found that Δ/Δ KASH mice develop cardiomyopathy with associated cardiac conduction system disease. Older mutant animals were found to have elongated P wave duration, elevated atrial and ventricular effective refractory periods indicating conduction defects in the myocardium, and reduced fractional shortening. Cardiomyocyte nuclei were found to be elongated with reduced heterochromatin in the Δ/Δ KASH hearts. These findings mirror what has been described from lamin A/C gene mutations and reinforce the importance of an intact nuclear membrane complex for a normally functioning heart.
cardiomyopathy; nuclear membrane; lamin A/C; nesprin
S100A12 is a small calcium binding protein that is a ligand of the Receptor for Advanced Glycation End products (RAGE). RAGE has been extensively implicated in inflammatory states such as atherosclerosis, but the role of S100A12 as its ligand is less clear.
To test the role of S100A12 in vascular inflammation, we generated and analyzed mice expressing human S100A12 in vascular smooth muscle under control of the SM22α promoter since S100A12 is not present in mice.
Methods and Results
Transgenic mice displayed pathologic vascular remodeling with aberrant thickening of the aortic media, disarray of elastic fibers, and increased collagen deposition, together with increased latent MMP-2 protein and reduction in smooth muscle stress fibers leading to a progressive dilatation of the aorta. In primary aortic smooth muscle cell cultures, we found that S100A12-mediates increased IL-6 production, activation of TGF β pathways and increased metabolic activity with enhanced oxidative stress. To correlate our findings to human aortic aneurysmal disease, we examined S100A12 expression in aortic tissue from patients with thoracic aortic aneurysm and found increased S100A12 expression in vascular smooth muscle cells.
S100A12 expression is sufficient to activate pathogenic pathways through the modulation of oxidative stress, inflammation and vascular remodeling in vivo.
S100A12; calgranulins; smooth muscle cell differentiation; RAGE; aortic aneurysms
Sirtuin 3 (SIRT3) is a member of the sirtuin family of proteins that promote longevity in many organisms. Increased expression of SIRT3 has been linked to an extended life span in humans. Here, we have shown that Sirt3 protects the mouse heart by blocking the cardiac hypertrophic response. Although Sirt3-deficient mice appeared to have normal activity, they showed signs of cardiac hypertrophy and interstitial fibrosis at 8 weeks of age. Application of hypertrophic stimuli to these mice produced a severe cardiac hypertrophic response, whereas Sirt3-expressing Tg mice were protected from similar stimuli. In primary cultures of cardiomyocytes, Sirt3 blocked cardiac hypertrophy by activating the forkhead box O3a–dependent (Foxo3a-dependent), antioxidant–encoding genes manganese superoxide dismutase (MnSOD) and catalase (Cat), thereby decreasing cellular levels of ROS. Reduced ROS levels suppressed Ras activation and downstream signaling through the MAPK/ERK and PI3K/Akt pathways. This resulted in repressed activity of transcription factors, specifically GATA4 and NFAT, and translation factors, specifically eukaryotic initiation factor 4E (elf4E) and S6 ribosomal protein (S6P), which are involved in the development of cardiac hypertrophy. These results demonstrate that SIRT3 is an endogenous negative regulator of cardiac hypertrophy, which protects hearts by suppressing cellular levels of ROS.
MicroRNAs are increasingly being recognized as regulators of embryonic development; however, relatively few microRNAs have been identified to regulate cardiac development. FOG-2 (also known as zfpm2) is a transcriptional co-factor that we have previously shown is critical for cardiac development. In this report, we demonstrate that FOG-2 expression is controlled at the translational level by microRNA-130a. We identified a conserved region in the FOG-2 3′ untranslated region predicted to be a target for miR-130a. To test the functional significance of this site, we generated an expression construct containing the luciferase coding region fused with the 3′ untranslated region of FOG-2 or a mutant version lacking this microRNA binding site. When these constructs were transfected into NIH 3T3 fibroblasts (which are known to express miR-130a), we observed a 3.3-fold increase in translational efficiency when the microRNA target site was disrupted. Moreover, knockdown of miR-130a in fibroblasts resulted in a 3.6-fold increase in translational efficiency. We also demonstrate that cardiomyocytes express miR-130a and can attenuate translation of mRNAs with a FOG-2 3′ untranslated region. Finally, we generated transgenic mice with cardiomyocyte over-expression of miR-130a. In the hearts of these mice, FOG-2 protein levels were reduced by as much as 80%. Histological analysis of transgenic embryos revealed ventricular wall hypoplasia and ventricular septal defects, similar to that seen in FOG-2 deficient hearts. These results demonstrate the importance of miR-130a for the regulation of FOG-2 protein expression and suggest that miR-130a may also play a role in the regulation of cardiac development.