Adamtsl2 deletion results in bronchial fibrillin microfibril accumulation and bronchial epithelial dysplasia – a novel mouse model providing insights into geleophysic dysplasia

Abstract

Mutations in the secreted glycoprotein ADAMTSL2 cause recessive geleophysic dysplasia (GD) in humans and Musladin–Lueke syndrome (MLS) in dogs. GD is a severe, often lethal, condition presenting with short stature, brachydactyly, stiff skin, joint contractures, tracheal-bronchial stenosis and cardiac valve anomalies, whereas MLS is non-lethal and characterized by short stature and severe skin fibrosis. Although most mutations in fibrillin-1 (FBN1) cause Marfan syndrome (MFS), a microfibril disorder leading to transforming growth factor-β (TGFβ) dysregulation, domain-specific FBN1 mutations result in dominant GD. ADAMTSL2 has been previously shown to bind FBN1 and latent TGFβ-binding protein-1 (LTBP1). Here, we investigated mice with targeted Adamtsl2 inactivation as a new model for GD (Adamtsl2−/− mice). An intragenic lacZ reporter in these mice showed that ADAMTSL2 was produced exclusively by bronchial smooth muscle cells during embryonic lung development. Adamtsl2−/− mice, which died at birth, had severe bronchial epithelial dysplasia with abnormal glycogen-rich inclusions in bronchial epithelium resembling the cellular anomalies described previously in GD. An increase in microfibrils in the bronchial wall was associated with increased FBN2 and microfibril-associated glycoprotein-1 (MAGP1) staining, whereas LTBP1 staining was increased in bronchial epithelium. ADAMTSL2 was shown to bind directly to FBN2 with an affinity comparable to FBN1. The observed extracellular matrix (ECM) alterations were associated with increased bronchial epithelial TGFβ signaling at 17.5 days of gestation; however, treatment with TGFβ-neutralizing antibody did not correct the epithelial dysplasia. These investigations reveal a new function of ADAMTSL2 in modulating microfibril formation, and a previously unsuspected association with FBN2. Our studies suggest that the bronchial epithelial dysplasia accompanying microfibril dysregulation in Adamtsl2−/− mice cannot be reversed by TGFβ neutralization, and thus might be mediated by other mechanisms.

ADAMTS proteins as modulators of microfibril formation and function

“…Interestingly, fibroblasts from patients with geleophysic dysplasia caused by FBN1 mutations were reported to have a reduced amount of microfibrils and a disorganized microfibril network [19]. In the ADAMTSL2 knock-out mouse lung, we observed considerably enhanced FBN2 staining in bronchial microfibrils [75], suggesting that one mechanism by which ADAMTSL2 may work is by regulating the ratio of FBN1 and FBN2 incorporated into microfibrils.…”

“…Although MLS resembles geleophysic dysplasia in these respects, pulmonary or cardiac abnormalities are absent and a normal lifespan is reported, in contrast to a significant proportion of affected humans. Adamtsl2 null mice die shortly after birth with severe lung anomalies [75]. Furthermore, Adamts10 inactivation in mice did not precisely phenocopy WMS1; although Adamts10 null mice are slightly smaller in size, they lacked specific skeletal and cardiac anomalies and did not develop ectopia lentis (Wang, Kutz, Apte, manuscript in preparation).…”

“…In addition, recombinant ADAMTSL2 protein interacts directly with FBN1, FBN2, and LTBP1 [19,69,75]. Although it is not known if these proteins form a tri-molecular complex or compete with each other in the binding, ADAMTSL2 seems to sit squarely within a context relevant to TGFβ regulation.…”

Fell‐Muir Lecture: Fibrillin microfibrils: structural tensometers of elastic tissues?

“…Homozygous ADAMTSL2 null mice have severe bronchial epithelial dysplasia (Hubmacher et al . ), whilst ADAMTLS4 mice with a non‐sense mutation have de‐differentiated retinal pigment epithelium defects (Collin et al . ).…”

Mutations inLTBP3cause acromicric dysplasia and geleophysic dysplasia

“…For example, latent transforming growth factor β (TGF-β)-binding protein-1 (LTBP1) interacts with ADAMTSL2,2 both of which also interact with FBN11 17 18 and fibrillin-2 (FBN2) 1 2 19 20…”