Early Impairment of Lung Mechanics in a Murine Model of Marfan Syndrome

Abstract

Early morbidity and mortality in patients with Marfan syndrome (MFS) -a connective tissue disease caused by mutations in fibrillin-1 gene- are mainly caused by aorta aneurysm and rupture. However, the increase in the life expectancy of MFS patients recently achieved by reparatory surgery promotes clinical manifestations in other organs. Although some studies have reported respiratory alterations in MFS, our knowledge of how this connective tissue disease modifies lung mechanics is scarce. Hence, we assessed whether the stiffness of the whole lung and of its extracellular matrix (ECM) is affected in a well-characterized MFS mouse model (FBN1C1039G/+). The stiffness of the whole lung and of its ECM were measured by conventional mechanical ventilation and atomic force microscopy, respectively. We studied 5-week and 9-month old mice, whose ages are representative of early and late stages of the disease. At both ages, the lungs of MFS mice were significantly more compliant than in wild type (WT) mice. By contrast, no significant differences were found in local lung ECM stiffness. Moreover, histopathological lung evaluation showed a clear emphysematous-like pattern in MFS mice since alveolar space enlargement was significantly increased compared with WT mice. These data suggest that the mechanism explaining the increased lung compliance in MFS is not a direct consequence of reduced ECM stiffness, but an emphysema-like alteration in the 3D structural organization of the lung. Since lung alterations in MFS are almost fully manifested at an early age, it is suggested that respiratory monitoring could provide early biomarkers for diagnosis and/or follow-up of patients with the Marfan syndrome.

Elastic properties of hydrogels and decellularized tissue sections used in mechanobiology studies probed by atomic force microscopy

“…Using pyramidal tips with k = 0.1 N/m we found that 7‐μm‐thick slices of acellular lung parenchyma ECM from rats exhibited heterogeneous E values, yet elastic measurements could clearly distinguish alveolar walls ( E ∼20 kPa) from the pleura ( E ∼50 kPa) (Luque et al, ). Slightly higher values were obtained in 12‐μm‐thick slices of acellular pulmonary tissue from mice (Figure A), which remained fairly constant with the age of the animal as shown in Figure B (Uriarte et al, ). Of note, AFM measurements revealed that elastin‐rich tissue structures such as the tunica media were 4‐fold stiffer than alveolar structures, and that this difference was maintained during aging (Figure A‐B), thereby illustrating the existence of homeostatic mechanisms that maintain physiologic tissue elasticities.…”

Losartan Attenuates Degradation of Aorta and Lung Tissue Micromechanics in a Mouse Model of Severe Marfan Syndrome

“…Interestingly, AFM measurements of ECM scaffolds from decellularized thin sections of MFS lung revealed similar stiffness as WT. 48 We suspect the 3D organization of cellular and ECM components both contribute to the disruption of micromechanics in the MFS lung. Our results indicated that the apparent elastic modulus of the lung tissue, E lung , decreased dramatically with disease progression in MFS mice, consistent with the symptoms of obstructive lung disease.…”

“…Similar softening effects were recently reported in excised whole lungs from a mouse model of mild MFS, indicating a lower elastance in diseased mice accompanied by emphysema-like structure similar to our findings. 48 A mouse model of emphysema showed similar changes in the mechanics of the diseased lung, including a loss of elastin, increased hysteresis and non-linearity, and decreased load-bearing capacity. 22 Lung inflation testing has been performed to obtain a pressure-volume relationship that reflects the lung mechanical properties, using sequential images of lung inflation to assess micro- or macro-strain of the parenchyma tissue.…”

“…47, 48, 53 In MFS mice, early lung tissue defects have been observed in neonates, and have been linked to the dysregulation of TGF-β activation in the developing lungs, with subsequent inhibition of cellular activities such as proliferation, and stimulation of apoptosis. 33 Correspondingly, we measured consistently lower area fraction of lung tissue in untreated MFS mice, with more severe disruption as the disease progressed, compared to age-matched WT mice.…”

Measured pulmonary arterial tissue stiffness is highly sensitive to AFM indenter dimensions

“…Recent expansion of AFM application to lung tissue has included several new studies on the mechanical properties of normal and decellularized lung tissue by AFM micro-indentation (Booth et al, 2012; Brown et al, 2013; Liu et al, 2010; Liu and Tschumperlin, 2011; Liu et al, 2016; Melo et al, 2014a; Meng et al, 2015; Shkumatov et al, 2015; Uriarte et al, 2016). Importantly, these new studies have begun to investigate anatomical variations in tissue mechanical properties, including comparisons of airways, vessels, pleura and parenchyma, but have also introduced substantial variation in tissue preparation (such as tissue decellularization), section thickness (10 to 1000 μm), and use of AFM tips with widely varying geometry and size.…”