Marfan syndrome decreases Ca2+ wave frequency and vasoconstriction in murine mesenteric resistance arteries without changing underlying mechanisms.

BACKGROUND/AIMS: Vascular smooth muscle in Marfan syndrome, a connective tissue disorder caused by mutations in FBN1 encoding fibrillin-1, is associated with decreased tonic contraction. As Ca(2+) waves are tightly associated with vasoconstriction, we hypothesized decreased tonic contraction in Marfan syndrome is due to aberrant Ca(2+) wave signaling. METHODS: Isometric force and intracellular Ca(2+) were measured from second-order mesenteric arteries from mice heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1(C1039G/+)). RESULTS: Phenylephrine concentration-dependently induced tonic contraction associated with sustained repetitive oscillations in intracellular [Ca(2+)] in both control and Marfan vessels, although Marfan vessels displayed significantly decreased Ca(2+) wave frequency and decreased number of cells exhibiting waves. Inhibition of sarcoplasmic reticulum Ca(2+) re-uptake by cyclopiazonic acid abolished Ca(2+) waves, dramatically decreasing tonic contraction. Nifedipine significantly reduced Ca(2+) wave frequency and tonic contraction, while the nifedipine-insensitive component was abolished by SKF-96365. Ca(2+) waves and tonic contraction were abolished by 2-aminoethoxydiphenylborate, but were unaffected by ryanodine or tetracaine. CONCLUSION: Phenylephrine-induced Ca(2+) waves underlie tonic contraction in resistance-sized mesenteric arteries and appear to be produced by repetitive cycles of regenerative Ca(2+) release from the sarcoplasmic reticulum. Decreased frequency of Ca(2+) waves in Marfan syndrome appears to be responsible for reduced tonic contraction.

Dysfunction of endothelial and smooth muscle cells in small arteries of a mouse model of Marfan syndrome.

BACKGROUND AND PURPOSE: Marfan syndrome, a connective tissue disorder caused by mutations in FBN1 encoding fibrillin-1, results in life-threatening complications in the aorta, but little is known about its effects in resistance vasculature. EXPERIMENTAL APPROACH: Second-order mesenteric arteries from mice at 3, 6 and 10 months of age (n= 30) heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1(C1039G/+)) were compared with those from age-matched control littermates. KEY RESULTS: Stress-strain curves indicated that arterial stiffness was increased at 6 and 10 months of age in Marfan vessels. Isometric force measurement revealed that contraction in response to potassium (60 mM)-induced membrane depolarization was decreased by at least 28% in Marfan vessels at all ages, while phenylephrine (3 microM)-induced contraction was reduced by at least 40% from 6 months. Acetylcholine-induced relaxation in Marfan vessels was reduced to 70% and 45% of control values, respectively, at 6 and 10 months. Sensitivity to sodium nitroprusside was reduced at 6 months (pEC(50)= 5.64 +/- 0.11, control pEC(50)= 7.34 +/- 0.04) and 10 months (pEC(50)= 5.99 +/- 0.07, control pEC(50)= 6.99 +/- 0.14). Pretreatment with N(omega)-Nitro-L-arginine methyl ester (200 microM) had no effect on acetylcholine-induced relaxation in Marfan vessels, but reduced vasorelaxation in control vessels to 57% of control values. Addition of indomethacin (10 microM) and catalase (1000 U.mL(-1)) further inhibited vasorelaxation in Marfan vessels to a greater degree compared with control vessels. CONCLUSIONS AND IMPLICATIONS: Pathogenesis of Marfan syndrome in resistance-sized arteries increases stiffness and impairs vasomotor function.

Imbalanced synthesis of cyclooxygenase-derived thromboxane A2 and prostacyclin compromises vasomotor function of the thoracic aorta in Marfan syndrome.

BACKGROUND AND PURPOSE: Thoracic aortic dissection is a life-threatening complication of Marfan syndrome, a connective tissue disorder caused by mutations in the gene encoding fibrillin-1. We have demonstrated that nitric oxide-mediated endothelial-dependent relaxation is impaired in the thoracic aorta in Marfan syndrome. In the present study, we determined whether the cyclooxygenase (COX)-pathway is involved in the compromised aortic vasomotor function. EXPERIMENTAL APPROACH: Thoracic aortae from mice at 3, 6 and 9 months of age, heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1 (C1039G/+), 'Marfan', n=35), were compared with those from age-matched controls (n=35). KEY RESULTS: Isometric force measurement revealed that preincubation with indomethacin, a non-specific COX inhibitor, but not valeryl salicylate, a specific COX-1 inhibitor, improved the phenylephrine-induced contractions (at 6 months, EC(50) and E(max) were increased 4.5-fold and by 45%, respectively) in Marfan aortae. Sensitivity to acetylcholine-induced relaxation was improved 10-fold. Blockade of the thromboxane-endoperoxide receptor by SQ-29548 did not affect phenylephrine-mediated contractions in Marfan aortae, although they did respond to the thromboxane analogue, U46619. From 6 months on, phenylephrine-induced secretion of prostacyclin and thromboxane A(2) in Marfan aortae was 200% and 40%, respectively, of those in controls. Reduced COX-1 expression was detected in Marfan aortae at 3 and 9 months, whilst COX-2 expression was increased from 3 months on. CONCLUSIONS AND IMPLICATIONS: The compromised vasomotor function in Marfan thoracic aortae is associated with an imbalanced synthesis of thromboxane A(2) and prostacyclin resulting from the differential protein expression of COX-1 and COX-2.

Endothelial dysfunction and compromised eNOS/Akt signaling in the thoracic aorta during the progression of Marfan syndrome.

BACKGROUND AND PURPOSE: Aortic complications account for the major mortality in Marfan syndrome (MFS), a connective tissue disorder caused by mutations in FBN1 encoding fibrillin-1. We hypothesized that MFS impaired endothelial function and nitric oxide (NO) production in the aorta. EXPERIMENTAL APPROACH: Mice (at 3, 6, 9 and 12 months of age) heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1 (C1039G/+), Marfan mice, n=75), the most common class of mutation in MFS, were compared with age-matched control littermates (n=75). Thoracic and abdominal aortas from the two groups were studied. KEY RESULTS: Isometric force measurements revealed that relaxation to ACh (but not to sodium nitroprusside) was diminished in the phenylephrine-precontracted Marfan thoracic aorta at 6 months of age (pEC(50)=6.12+/-0.22; maximal response, E(max)=52.7+/-6.8%; control: pEC(50)=7.34+/-0.19; E(max)=84.8+/-2.2%). At one year, both inhibition of NO production with N(omega)-nitro-L-arginine methyl ester, or denudation of endothelium increased the phenylephrine-stimulated contraction in the control thoracic aorta by 35%, but had no effect in the Marfan aorta, indicating a loss of basal NO production in the Marfan vessel. From 6 months, a reduced phosphorylation of endothelial NOS (eNOS)(Ser1177) and Akt(Thr308) detected by Western blotting was observed in the Marfan thoracic aorta, which was accompanied by decreased levels of cGMP. Expressions of Akt and eNOS in the abdominal aorta were not different between the two groups. CONCLUSIONS AND IMPLICATIONS: MFS impairs endothelial function and signaling of NO production in the thoracic aorta, suggesting the importance of NO in the age-related progression of thoracic aortic manifestations.