Loss-of-function thrombospondin-1 mutations in familial pulmonary hypertension

Abstract

Most patients with familial pulmonary arterial hypertension (FPAH) carry mutations in the bone morphogenic protein receptor 2 gene (BMPR2). Yet carriers have only a 20% risk of disease, suggesting that other factors influence penetrance. Thrombospondin-1 (TSP1) regulates activation of TGF-β and inhibits endothelial and smooth muscle cell proliferation, pathways coincidentally altered in pulmonary arterial hypertension (PAH). To determine whether a subset of FPAH patients also have mutations in the TSP1 gene (THBS1) we resequenced the type I repeats of THBS1 encoding the TGF-β regulation and cell growth inhibition domains in 60 FPAH probands, 70 nonfamilial PAH subjects, and in large control groups. We identified THBS1 mutations in three families: a novel missense mutation in two (Asp362Asn), and an intronic mutation in a third (IVS8+255 G/A). Neither mutation was detected in population controls. Mutant 362Asn TSP1 had less than half of the ability of wild-type TSP1 to activate TGF-β. Mutant 362Asn TSP1 also lost the ability to inhibit growth of pulmonary arterial smooth muscle cells and was over threefold less effective at inhibiting endothelial cell growth. The IVS8+255 G/A mutation decreased and/or eliminated local binding of the transcription factors SP1 and MAZ but did not affect RNA splicing. These novel mutations implicate THBS1 as a modifier gene in FPAH. These THBS1 mutations have implications in the genetic evaluation of FPAH patients. However, since FPAH is rare, these data are most relevant as evidence for the importance of TSP1 in pulmonary vascular homeostasis. Further examination of THBS1 in the pathogenesis of PAH is warranted.

Thrombospondin-1 and CD47 regulation of cardiac, pulmonary and vascular responses in health and disease

“…Two distinct TSP1 SNPs have been identified in familial PAH, which are hypothesized to alter transcription factor binding and/or modify pulmonary vascular smooth muscle and endothelial cell growth (Maloney et al 2012). Though rare in comparison to premature MI, these genetic variations in PAH implicate the importance of TSP1 in promoting pulmonary vascular pathology.…”

Invoking the power of thrombospondins: Regulation of thrombospondins expression

“…As a major activator of TGFβ1 (174), TSP-1 is often expressed in tissues producing TGFβ1, e.g., in cancers with high TGFβ1 levels (175) and in embryonic development (176). TSP-1 gene mutation was identified in a family with the familial pulmonary arterial hypertension (PAH)(177). The ability of the mutant Asp362Asn TSP-1 to activate TGFβ1 was reduced to ½ of the activity of the wild-type TSP-1.…”

Patients with systemic sclerosis-associated pulmonary arterial hypertension express a genomic signature distinct from patients with interstitial lung disease

“…In cell and animal models, hypoxia induces THBS1 expression in pulmonary artery smooth muscle cells, endothelial cells, and pulmonary fibroblasts in a hypoxia-inducible factor-2α (HIF-2α) –dependent manner; these changes are associated with destabilization of endothelial cell-cell interactions, suggesting that THBS1 regulates vascular remodeling (9). Furthermore, THBS1 expression was higher in tissue from patients with end-stage PAH compared to controls (9), and mutations in THBS1 have been reported in familial PAH patients (10). Taken together, these data suggest that THBS1 is important in pulmonary vascular homeostasis and remodeling; thus, it is plausible that THBS1 is important for the development of the SSc-PAH phenotype without restrictive ILD.…”