Rahmat Ali

Tgfbr2 disruption in postnatal smooth muscle impairs aortic wall homeostasis

TGF-β is essential for vascular development; however, excess TGF-β signaling promotes thoracic aortic aneurysm and dissection in multiple disorders, including Marfan syndrome. Since the pathology of TGF-β overactivity manifests primarily within the arterial media, it is widely assumed that suppression of TGF-β signaling in vascular smooth muscle cells will ameliorate aortic disease. We tested this hypothesis by conditional inactivation of Tgfbr2, which encodes the TGF-β type II receptor, in smooth muscle cells of postweanling mice. Surprisingly, the thoracic aorta rapidly thickened, dilated, and dissected in these animals. Tgfbr2 disruption predictably decreased canonical Smad signaling, but unexpectedly increased MAPK signaling. Type II receptor-independent effects of TGF-β and pathological responses by nonrecombined smooth muscle cells were excluded by serologic neutralization. Aortic disease was caused by a perturbed contractile apparatus in medial cells and growth factor production by adventitial cells, both of which resulted in maladaptive paracrine interactions between the vessel wall compartments. Treatment with rapamycin restored a quiescent smooth muscle phenotype and prevented dissection. Tgfbr2 disruption in smooth muscle cells also accelerated aneurysm growth in a murine model of Marfan syndrome. Our data indicate that basal TGF-β signaling in smooth muscle promotes postnatal aortic wall homeostasis and impedes disease progression.

Modulation of Transforming Growth Factor-β Signaling and Extracellular Matrix Production in Myxomatous Mitral Valves by Angiotensin II Receptor Blockers

Background— Little is known about the pathophysiology of myxomatous degeneration of the mitral valve, the pathological hallmark of mitral valve prolapse, associated with symptomatic mitral regurgitation, heart failure, and death. Excess transforming growth factor (TGF)-&bgr; signaling is known to cause mitral valve degeneration and regurgitation in a mouse model of Marfan syndrome. We examined if TGF-&bgr; signaling is dysregulated in clinical specimens of sporadic mitral valve prolapse compared with explanted nondiseased mitral valves and we tested the effects of angiotensin II receptor blockers on TGF-&bgr; signaling in cultured human mitral valve cells. Methods and Results— Operative specimens, cultured valve tissues, and cultured valvular interstitial cells were obtained from patients with mitral valve prolapse undergoing mitral valve repair or from organ donors without mitral valve disease. Increased extracellular matrix in diseased valve tissue correlated with an upregulation of TGF-&bgr; expression and signaling as evidenced by SMAD2/3 phosphorylation. Both TGF-&bgr; ligand and signaling mediators colocalized primarily to valvular interstitial cells suggesting autocrine/paracrine activation. In cultured valve tissue, exogenous TGF-&bgr; increased basal extracellular matrix production, whereas serological neutralization of TGF-&bgr; inhibited disease-driven extracellular matrix overproduction. TGF-&bgr;-induced extracellular matrix production in cultured valvular interstitial cells was dependent on SMAD2/3 and p38 signaling and was inhibited by angiotensin II receptor blockers. Conclusions— TGF-&bgr; has a profibrotic role in the pathogenesis of sporadic mitral valve prolapse. Attenuation of TGF-&bgr; signaling by angiotensin II receptor blockers may represent a mechanistically based strategy to modulate the pathological progression of mitral valve prolapse in patients.

miR-1 mediated suppression of Sorcin regulates myocardial contractility through modulation of Ca2+ signaling.

MicroRNAs are negative gene regulators and play important roles in cardiac development and disease. As evident by cardiomyopathy following cardiac-specific Dicer knockdown they also are required for maintaining normal cardiac contractile function but the specific role of miR-1 in the process is poorly understood. To characterize the role of miR-1 in particular and to identify its specific targets we created a tamoxifen-inducible, cardiac-specific Dicer knockdown mouse and demonstrated that Dicer downregulation results in a dramatic and rapid decline in cardiac function concurrent with significantly reduced levels of miR-1. The importance of miR-1 was established by miR-1 antagomir treatment of wild-type mice, which replicated the cardiac-specific Dicer knockdown phenotype. Down-regulation of miR-1 was associated with up-regulation of its predicted target Sorcin, an established modulator of calcium signaling and excitation-contraction coupling, subsequently verified as a miR-1 target with luciferase constructs. siRNA-mediated knockdown of Sorcin effectively rescued the cardiac phenotypes after Dicer or miR-1 knockdown affirming Sorcin as a critical mediator of the acute cardiomyopathy observed. The regulatory relationship between miR-1 and Sorcin was further confirmed in cultured mouse cardiomyocytes where modulation of miR-1 was associated with discordant Sorcin levels and dysregulation of calcium signaling. Pathological relevance of our findings included decreased miR-1 and increased Sorcin expression in end-stage cardiomyopathy. These findings demonstrate the importance of miR-1 in cardiac function and in the pathogenesis of heart failure via Sorcin-dependent calcium homeostasis.

Rapamycin Inhibits Smooth Muscle Cell Proliferation and Obstructive Arteriopathy Attributable to Elastin Deficiency

Objective—Patients with elastin deficiency attributable to gene mutation (supravalvular aortic stenosis) or chromosomal microdeletion (Williams syndrome) are characterized by obstructive arteriopathy resulting from excessive smooth muscle cell (SMC) proliferation, mural expansion, and inadequate vessel size. We investigated whether rapamycin, an inhibitor of the cell growth regulator mammalian target of rapamycin (mTOR) and effective against other SMC proliferative disorders, is of therapeutic benefit in experimental models of elastin deficiency. Approach and Results—As previously reported, Eln−/− mice demonstrated SMC hyperplasia and severe stenosis of the aorta, whereas Eln+/− mice exhibited a smaller diameter aorta with more numerous but thinner elastic lamellae. Increased mTOR signaling was detected in elastin-deficient aortas of newborn pups that was inhibited by maternal administration of rapamycin. mTOR inhibition reduced SMC proliferation and aortic obstruction in Eln−/− pups and prevented medial hyperlamellation in Eln+/− weanlings without compromising aortic size. However, rapamycin did not prolong the survival of Eln−/− pups, and it retarded the somatic growth of juvenile Eln+/− and Eln+/+ mice. In cell cultures, rapamycin inhibited prolonged mTOR activation and enhanced proliferation of SMC derived from patients with supravalvular aortic stenosis and with Williams syndrome. Conclusions—mTOR inhibition may represent a pharmacological strategy to treat diffuse arteriopathy resulting from elastin deficiency.

Characteristics of patients with injury secondary to smoking on home oxygen therapy transferred intubated to a burn center.

BACKGROUND The aim of this study was to compare outcomes of patients who sustained burn and ostensible inhalation injuries while on home oxygen therapy with those suffering equivalent injuries via other mechanisms. STUDY DESIGN Between December 2002 and January 2006, 109 burn patients were transferred to our center intubated. Their charts were retrospectively reviewed. Patients who sustained injuries while on home oxygen therapy were age and total body surface area matched to patients with inhalation and burn injuries secondary to other mechanisms. RESULTS Fourteen of 109 patients were injured while smoking on home oxygen therapy (15.26%). All 14 had COPD. Mean age was 63 years (range 53 to 77 years) and average total body surface area burned was 4% (range 0% to 10%). Charges for the 14 hospitalizations totaled

mTOR (Mechanistic Target of Rapamycin) Inhibition Decreases Mechanosignaling, Collagen Accumulation, and Stiffening of the Thoracic Aorta in Elastin-Deficient Mice

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Interferon-γ-mediated allograft rejection exacerbates cardiovascular disease of hyperlipidemic murine transplant recipients.

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Circulating interferon-γ-inducible Cys-X-Cys chemokine receptor 3 ligands are elevated in humans with aortic aneurysms and Cys-X-Cys chemokine receptor 3 is necessary for aneurysm formation in mice.

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Abstract 219: IFN-γ Plays an Essential Role in Accelerating Cardiovascular Disease of Recipients With MHC Class II-mismatched Allografts.

78,418 per admission). Average time to extubation was 5.7 ± 10.2 days and average length of stay was 11.4 ± 15.2 days. No significant differences in the average time to extubation, length of stay, cost of hospitalization, or clinical signs of inhalation injury (ie, soot and edema in the pharynx) were noted between our series and the control group. CONCLUSIONS Injury secondary to smoking on home oxygen therapy is a perennial problem, and guidelines for prescribing home oxygen therapy for smokers should be reassessed. Despite underlying lung disease, patients in our series did as well as patients without COPD who sustained similar injuries.

Abstract 155: Sustained CD4+ T-Cell Activation Promotes Transplant-Associated Recipient Cardiovascular Disease

Objective— Elastin deficiency because of heterozygous loss of an ELN allele in Williams syndrome causes obstructive aortopathy characterized by medial thickening and fibrosis and consequent aortic stiffening. Previous work in Eln-null mice with a severe arterial phenotype showed that inhibition of mTOR (mechanistic target of rapamycin), a key regulator of cell growth, lessened the aortic obstruction but did not prevent early postnatal death. We investigated the effects of mTOR inhibition in Eln-null mice partially rescued by human ELN that manifest a less severe arterial phenotype and survive long term. Approach and Results— Thoracic aortas of neonatal and juvenile mice with graded elastin deficiency exhibited increased signaling through both mTOR complex 1 and 2. Despite lower predicted wall stress, there was increased phosphorylation of focal adhesion kinase, suggestive of greater integrin activation, and increased transforming growth factor-&bgr;–signaling mediators, associated with increased collagen expression. Pharmacological blockade of mTOR by rapalogs did not improve luminal stenosis but reduced mechanosignaling (in delayed fashion after mTOR complex 1 inhibition), medial collagen accumulation, and stiffening of the aorta. Rapalog administration also retarded somatic growth, however, and precipitated neonatal deaths. Complementary, less-toxic strategies to inhibit mTOR via altered growth factor and nutrient responses were not effective. Conclusions— In addition to previously demonstrated therapeutic benefits of rapalogs decreasing smooth muscle cell proliferation in the absence of elastin, we find that rapalogs also prevent aortic fibrosis and stiffening attributable to partial elastin deficiency. Our findings suggest that mTOR-sensitive perturbation of smooth muscle cell mechanosensing contributes to elastin aortopathy.