Loss of MURC/Cavin-4 induces JNK and MMP-9 activity enhancement in vascular smooth muscle cells and exacerbates abdominal aortic aneurysm.

Abdominal aortic aneurysm (AAA) is relatively common in elderly patients with atherosclerosis. MURC (muscle-restricted coiled-coil protein)/Cavin-4 modulating the caveolae function of muscle cells is expressed in cardiomyocytes, skeletal muscle cells and smooth muscle cells. Here, we show a novel functional role of MURC/Cavin-4 in vascular smooth muscle cells (VSMCs) and AAA development. Both wild-type (WT) and MURC/Cavin-4 knockout (MURC-/-) mice subjected to periaortic application of CaCl2 developed AAAs. Six weeks after CaCl2 treatment, internal and external aortic diameters were significantly increased in MURC-/- AAAs compared with WT AAAs, which were accompanied by advanced fibrosis in the tunica media of MURC-/- AAAs. The activity of JNK and matrix metalloproteinase (MMP) -2 and -9 were increased in MURC-/- AAAs compared with WT AAAs at 5 days after CaCl2 treatment. At 6 weeks after CaCl2 treatment, MURC-/- AAAs exhibited attenuated JNK activity compared with WT AAAs. There was no difference in the activity of MMP-2 or -9 between saline and CaCl2 treatments. In MURC/Cavin-4-knockdown VSMCs, TNFα-induced activity of JNK and MMP-9 was enhanced compared with control VSMCs. Furthermore, WT, MURC-/-, apolipoprotein E-/- (ApoE-/-), and MURC/Cavin-4 and ApoE double-knockout (MURC-/-ApoE-/-) mice were subjected to angiotensin II (Ang II) infusion. In both ApoE-/- and MURC-/-ApoE-/- mice infused for 4 weeks with Ang II, AAAs were promoted. The internal aortic diameter was significantly increased in Ang II-infused MURC-/-ApoE-/- mice compared with Ang II-infused ApoE-/- mice. In MURC/Cavin-4-knockdown VSMCs, Ang II-induced activity of JNK and MMP-9 was enhanced compared with control VSMCs. Our results suggest that MURC/Cavin-4 in VSMCs modulates AAA progression at the early stage via the activation of JNK and MMP-9. MURC/Cavin-4 is a potential therapeutic target against AAA progression.

MURC/Cavin-4 facilitates recruitment of ERK to caveolae and concentric cardiac hypertrophy induced by α1-adrenergic receptors.

The actions of catecholamines on adrenergic receptors (ARs) induce sympathetic responses, and sustained activation of the sympathetic nervous system results in disrupted circulatory homeostasis. In cardiomyocytes, α1-ARs localize to flask-shaped membrane microdomains known as "caveolae." Caveolae require both caveolin and cavin proteins for their biogenesis and function. However, the functional roles and molecular interactions of caveolar components in cardiomyocytes are poorly understood. Here, we showed that muscle-restricted coiled-coil protein (MURC)/Cavin-4 regulated α1-AR-induced cardiomyocyte hypertrophy through enhancement of ERK1/2 activation in caveolae. MURC/Cavin-4 was expressed in the caveolae and T tubules of cardiomyocytes. MURC/Cavin-4 overexpression distended the caveolae, whereas MURC/Cavin-4 was not essential for their formation. MURC/Cavin-4 deficiency attenuated cardiac hypertrophy induced by α1-AR stimulation in the presence of caveolae. Interestingly, MURC/Cavin-4 bound to α1A- and α1B-ARs as well as ERK1/2 in caveolae, and spatiotemporally modulated MEK/ERK signaling in response to α1-AR stimulation. Thus, MURC/Cavin-4 facilitates ERK1/2 recruitment to caveolae and efficient α1-AR signaling mediated by caveolae in cardiomyocytes, which provides a unique insight into the molecular mechanisms underlying caveola-mediated signaling in cardiac hypertrophy.

The coiled-coil domain of MURC/cavin-4 is involved in membrane trafficking of caveolin-3 in cardiomyocytes.

Muscle-restricted coiled-coil protein (MURC), also referred to as cavin-4, is a member of the cavin family that works cooperatively with caveolins in caveola formation and function. Cavins are cytoplasmic proteins with coiled-coil domains and form heteromeric complexes, which are recruited to caveolae in cells expressing caveolins. Among caveolins, caveolin-3 (Cav3) is exclusively expressed in muscle cells, similar to MURC/cavin-4. In the heart, Cav3 overexpression contributes to cardiac protection, and its deficiency leads to progressive cardiomyopathy. Mutations in the MURC/cavin-4 gene have been identified in patients with dilated cardiomyopathy. In the present study, we show the role of MURC/cavin-4 as a caveolar component in the heart. In H9c2 cells, MURC/cavin-4 was localized at the plasma membrane, whereas a MURC/cavin-4 mutant lacking the coiled-coil domain (ΔCC) was primarily localized to the cytoplasm. ΔCC bound to Cav3 and impaired membrane localization of Cav3 in cardiomyocytes. Additionally, although ΔCC did not alter Cav3 mRNA expression, ΔCC decreased the Cav3 protein level. MURC/cavin-4 and ΔCC similarly induced cardiomyocyte hypertrophy; however, ΔCC showed higher hypertrophy-related fetal gene expression than MURC/cavin-4. ΔCC induced ERK activation in cardiomyocytes. Transgenic mice expressing ΔCC in the heart (ΔCC-Tg mice) showed impaired cardiac function accompanied by cardiomyocyte hypertrophy and marked interstitial fibrosis. Hearts from ΔCC-Tg mice showed a reduction of the Cav3 protein level and activation of ERK. These results suggest that MURC/cavin-4 requires its coiled-coil domain to target the plasma membrane and to stabilize Cav3 at the plasma membrane of cardiomyocytes and that MURC/cavin-4 functions as a crucial caveolar component to regulate cardiac function.

PTRF/Cavin-1 Deficiency Causes Cardiac Dysfunction Accompanied by Cardiomyocyte Hypertrophy and Cardiac Fibrosis.

Mutations in the PTRF/Cavin-1 gene cause congenital generalized lipodystrophy type 4 (CGL4) associated with myopathy. Additionally, long-QT syndrome and fatal cardiac arrhythmia are observed in patients with CGL4 who have homozygous PTRF/Cavin-1 mutations. PTRF/Cavin-1 deficiency shows reductions of caveolae and caveolin-3 (Cav3) protein expression in skeletal muscle, and Cav3 deficiency in the heart causes cardiac hypertrophy with loss of caveolae. However, it remains unknown how loss of PTRF/Cavin-1 affects cardiac morphology and function. Here, we present a characterization of the hearts of PTRF/Cavin-1-null (PTRF-/-) mice. Electron microscopy revealed the reduction of caveolae in cardiomyocytes of PTRF-/- mice. PTRF-/- mice at 16 weeks of age developed a progressive cardiomyopathic phenotype with wall thickening of left ventricles and reduced fractional shortening evaluated by echocardiography. Electrocardiography revealed that PTRF-/- mice at 24 weeks of age had low voltages and wide QRS complexes in limb leads. Histological analysis showed cardiomyocyte hypertrophy accompanied by progressive interstitial/perivascular fibrosis. Hypertrophy-related fetal gene expression was also induced in PTRF-/- hearts. Western blotting analysis and quantitative RT-PCR revealed that Cav3 expression was suppressed in PTRF-/- hearts compared with that in wild-type (WT) ones. ERK1/2 was activated in PTRF-/- hearts compared with that in WT ones. These results suggest that loss of PTRF/Cavin-1 protein expression is sufficient to induce a molecular program leading to cardiomyocyte hypertrophy and cardiomyopathy, which is partly attributable to Cav3 reduction in the heart.

MURC deficiency in smooth muscle attenuates pulmonary hypertension.

Emerging evidence suggests that caveolin-1 (Cav1) is associated with pulmonary arterial hypertension. MURC (also called Cavin-4) is a member of the cavin family, which regulates caveolar formation and functions together with caveolins. Here, we show that hypoxia increased Murc mRNA expression in the mouse lung, and that Murc-null mice exhibited attenuation of hypoxia-induced pulmonary hypertension (PH) accompanied by reduced ROCK activity in the lung. Conditional knockout mice lacking Murc in smooth muscle also resist hypoxia-induced PH. MURC regulates the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs) through Rho/ROCK signalling. Cav1 suppresses RhoA activity in PASMCs, which is reversed by MURC. MURC binds to Cav1 and inhibits the association of Cav1 with the active form of Gα13, resulting in the facilitated association of the active form of Gα13 with p115RhoGEF. These results reveal that MURC has a function in the development of PH through modulating Rho/ROCK signalling.

Usefulness of multidetector computed tomography for diagnosis and surgical treatment of large coronary artery fistula.

BACKGROUND: Coronary angiography (CAG) has been the mainstay of diagnostic image analysis for coronary artery fistula (CAF). However, it is difficult to fully delineate this complex vessel structure including coronary trees, particularly in cases with large CAF, by this method. CASE REPORTS: In the present 3 cases with large CAF, contrast-enhanced multidetector computed tomography (MDCT) was performed to examine the whole coronary vessel structure including CAF. Selective CAG was also undertaken. In all 3 cases, based on the echocardiographic findings and the characteristic heart murmur, presence of CAF was suspected. However, transthoracic echocardiography as well as CAG alone could not define the whole abnormal vessel structure precisely. Moreover, CAG could not obtain clear images of the coronary artery with large CAF, because of contrast-steal. In contrast, MDCT could not only define CAF in detail but also depict coronary artery adjacent to CAF. On the basis of the MDCT findings, in cases 1 and 3, surgical exclusions were undertaken without and with coronary artery bypass grafting, respectively. CONCLUSIONS: Contrast-enhanced MDCT might be useful for the diagnosis of large CAF and for the estimation of the coronary artery adjacent to CAF, which is absolutely indispensable for surgical treatment.

Intermediate fixed coronary artery stenosis at the site of ergonovine-provoked spasm as a predictor of long-term major adverse cardiac events of patients with coronary spastic angina.

BACKGROUND: Organic coronary artery stenosis is a significant prognostic factor in patients with coronary spastic angina (CSA), so the present study was focused on assessing the impact of intermediate fixed stenosis at sites of provoked spasm on the long-term outcomes of CSA patients. METHODS AND RESULTS: CSA patients diagnosed on the basis of ergonovine-provoked spasm were enrolled and the clinical background and long-term prognosis of CSA patients with intermediate fixed stenosis at the site of provoked spasm (with-fixed-stenosis group, n=37) and those without fixed stenosis (without-fixed-stenosis group, n=126) were retrospectively compared. During the follow-up period (average 4.01 years for with-fixed-stenosis, 4.47 years for without-fixed-stenosis), the with-fixed-stenosis group had a significantly lower event-free survival rate, as well as a higher frequency of admission for unstable angina and percutaneous coronary intervention than the without-fixed-stenosis group, whereas the survival rate did not differ significantly between the 2 groups. In the multivariate analysis, intermediate fixed stenosis at the site of provoked spasm was a predictor of long-term major adverse cardiac events (MACE). CONCLUSIONS: Intermediate fixed stenosis at the site of ergonovine-provoked spasm is an independent risk factor for MACE during the long-term period in CSA patients.

Usefulness of ultrasonography in carotid arteries and combined positron emission tomography/ computed tomography for diagnosis of Takayasu arteritis with unusual presentation as acute myocardial infarction: a case report.

This unusual case of Takayasu arteritis presenting as acute myocardial infarction could be defined by ultrasonography and 18-fluorodeoxyglucose positron emission tomography (18F-FDG PET) coregistered with computed tomography (CT). A 55-year-old male was admitted to our hospital with continuous chest pain and left-side neck pain. After primary percutaneous coronary intervention, elevation of inflammatory markers persisted and dull pain in the left side of the neck continued. Ultrasonography revealed characteristic wall thickening of the left common carotid artery and subsequent 18F-FDG PET with CT depicted positive uptake in the left common carotid artery and the vessel wall of the ascending aorta, confirming the diagnosis of Takayasu arteritis. Three months after angioplasty, follow-up cardiac catheterization was performed. Coronary angiography showed no restenosis. During the catheterization, angiography confirmed the mild stenosis in the long segment of the left common carotid artery and the left subclavian artery as well as the focal narrowing and the dilation of the abdominal aorta. This case shows that ultrasonography in the cervical region and combined 18F-FDG PET with CT may be useful in the diagnosis and evaluation of Takayasu arteritis. In addition, we should pay attention to underlying disease even in middle-aged or older male patients with acute myocardial infarction.