Exploring the potential relationship between collagen cross-linking and impaired myocardial relaxation in Marfan syndrome: An observational study using serum biomarkers.

BACKGROUND: Increased collagen cross-linking (CCL) has been described in hypertensive cardiomyopathy by means of reduced serum ratio of serum carboxyterminal telopeptide of collagen type I (CITP) to matrix metalloproteinase-1 (MMP1). Previous studies have demonstrated the existence of primary impaired diastole in patients with Marfan syndrome (MFS), but little is known about the pathophysiology of this condition. METHODS: 60 MFS patients (without previous cardiovascular surgery or significant valvular regurgitation) and 24 healthy controls (age and sex-matched) were enrolled. All participants underwent a comprehensive transthoracic echocardiographic study, including left atrial and left ventricular speckle-tracking strain analysis. CITP and MMP1 were measured in peripheral blood. RESULTS: All participants had normal diastolic function according to guidelines. Peak left atrial strain in the reservoir phase (LASr) was significantly reduced in the MFS cohort compared to controls (32.2 ± 9.4 vs 43.9 ± 7.0%; p < 0.001). Serum CITP and CITP:MMP1 ratio were lower among MFS patients, showing significant correlations with LASr (R = 0.311; p = 0.020 and R = 0.437; p = 0.001, respectively). The MFS cohort was divided into quartiles of LASr. MFS patients in the lowest quartile of LASr (<26%) had significantly lower values of CITP:MMP1 ratio compared to the other quartiles. CONCLUSIONS: The analysis of serum biomarkers revealed the presence of increased CCL in association with reduced LASr in the MFS cohort. Our results suggest that excessive CCL may play a role in the development of primary myocardial impairment in these patients. Future studies are needed to confirm our findings and evaluate the prognostic role of CCL markers in the MFS population.

Extracellular Tuning of Mitochondrial Respiration Leads to Aortic Aneurysm.

BACKGROUND: Marfan syndrome (MFS) is an autosomal dominant disorder of the connective tissue caused by mutations in the FBN1 (fibrillin-1) gene encoding a large glycoprotein in the extracellular matrix called fibrillin-1. The major complication of this connective disorder is the risk to develop thoracic aortic aneurysm. To date, no effective pharmacologic therapies have been identified for the management of thoracic aortic disease and the only options capable of preventing aneurysm rupture are endovascular repair or open surgery. Here, we have studied the role of mitochondrial dysfunction in the progression of thoracic aortic aneurysm and mitochondrial boosting strategies as a potential treatment to managing aortic aneurysms. METHODS: Combining transcriptomics and metabolic analysis of aortas from an MFS mouse model (Fbn1c1039g/+) and MFS patients, we have identified mitochondrial dysfunction alongside with mtDNA depletion as a new hallmark of aortic aneurysm disease in MFS. To demonstrate the importance of mitochondrial decline in the development of aneurysms, we generated a conditional mouse model with mitochondrial dysfunction specifically in vascular smooth muscle cells (VSMC) by conditional depleting Tfam (mitochondrial transcription factor A; Myh11-CreERT2Tfamflox/flox mice). We used a mouse model of MFS to test for drugs that can revert aortic disease by enhancing Tfam levels and mitochondrial respiration. RESULTS: The main canonical pathways highlighted in the transcriptomic analysis in aortas from Fbn1c1039g/+ mice were those related to metabolic function, such as mitochondrial dysfunction. Mitochondrial complexes, whose transcription depends on Tfam and mitochondrial DNA content, were reduced in aortas from young Fbn1c1039g/+ mice. In vitro experiments in Fbn1-silenced VSMCs presented increased lactate production and decreased oxygen consumption. Similar results were found in MFS patients. VSMCs seeded in matrices produced by Fbn1-deficient VSMCs undergo mitochondrial dysfunction. Conditional Tfam-deficient VSMC mice lose their contractile capacity, showed aortic aneurysms, and died prematurely. Restoring mitochondrial metabolism with the NAD precursor nicotinamide riboside rapidly reverses aortic aneurysm in Fbn1c1039g/+ mice. CONCLUSIONS: Mitochondrial function of VSMCs is controlled by the extracellular matrix and drives the development of aortic aneurysm in Marfan syndrome. Targeting vascular metabolism is a new available therapeutic strategy for managing aortic aneurysms associated with genetic disorders.