Modulation of Intersectin-1s Lung Expression Induces Obliterative Remodeling and Severe Plexiform Arteriopathy in the Murine Pulmonary Vascular Bed

Abstract

Murine models of pulmonary arterial hypertension (PAH) that recapitulate the plexiform and obliterative arteriopathy seen in PAH patients and help in defining the molecular mechanisms involved are missing. Herein, we investigated whether intersectin-1s (ITSN) deficiency and prolonged lung expression of an ITSN fragment with endothelial cell (EC) proliferative potential (EH ITSN ), present in the lungs of PAH animal models and human patients, induce formation of plexiform/obliterative lesions and defined the molecular mechanisms involved. ITSN-deficient mice (knockout/heterozygous and knockdown) were subjected to targeted lung delivery of EH ITSN via liposomes for 20 days. Immunohistochemistry and histological and morphometric analyses revealed a twofold increase in proliferative ECs and a 1.35-fold increase in proliferative a-smooth muscle actinepositive cells in the lungs of ITSNdeficient mice, transduced with the EH ITSN relative to wild-type littermates. Treated mice developed severe medial wall hypertrophy, intima proliferation, and various forms of obliterative and plexiformlike lesions in pulmonary arteries, similar to PAH patients. Hemodynamic measurements indicated modest increases in the right ventricular systolic pressure and right ventricle hypertrophy. Transcriptional and protein assays of lung tissue indicated p38 MAPK -dependent activation of Elk-1 transcription factor and increased expression of c-Fos gene. This unique murine model of PAH-like plexiform/obliterative arteriopathy induced via a two-hit pathophysiological mechanism without hypoxia provides novel druggable targets to ameliorate and, perhaps, reverse the EC plexiform phenotype in severe human PAH. Pulmonary arterial hypertension (PAH) is a severe human disease characterized by narrowing of the small pulmonary arteries, leading to a progressive increase in pulmonary vascular resistance, which frequently leads to right-sided heart failure and death.1e3 A common histological finding in patients with severe PAH is the presence of plexiform lesions that obliterate the small to mid-sized pulmonary arterioles. 4,5 The plexiform pulmonary vascular lesions found at branching points in the small pulmonary arterioles are lumen-obliterating, glomeruloid-like vascular structures, predominantly composed of actively dividing and phenotypically abnormal apoptosis-resistant endothelial cells (ECs).6,7 The cellular and molecular mechanisms responsible for the development of plexiform lesions are poorly understood.Recent evidence suggests the involvement of inflammatory mechanisms in the development of PAH. 8 Studies have indicated that inflammation associated with human PAH Supported by NIH grants R01 HL089462 (S.P.) and R01 HL0127022 (S.P.).Disclosures: None declared.

Plexiform Arteriopathy in Rodent Models of Pulmonary Arterial Hypertension

“…50 Moreover, a plethora of EC-driven vascular arteriopathy is observed in this mouse model, including subtotal and complete concentric onion-skinelike intima thickening, eccentric intima proliferation, EC hobnail patterns, obliterative lesions with vascular slit-like channels, stalk-like lesions within the vessel lumen, peribronchial and subpleural lesions, and complex plexiform-like lesions. 50 Furthermore, this model also exhibits distal extension of smooth muscle into the small-to medium-sized pulmonary arteries, collagen deposition, and inflammatory cell infiltrates, characterized by a high nuclear/cytosol ratio. 50 Surprisingly, despite the extensive angio-obliterative remodeling present in the EH-KO ITSNþ/À mice, only a modest increase in RVSP and RVH was observed.…”

“…50 Surprisingly, despite the extensive angio-obliterative remodeling present in the EH-KO ITSNþ/À mice, only a modest increase in RVSP and RVH was observed. 50 However, the mice used in this study were all young female mice; it is generally accepted that older male mice exhibit a more severe hemodynamic phenotype. In addition, these mice underwent a 20-day treatment regimen, during which right ventricular adaptations occur after prolonged lung remodeling.…”

“…50 Furthermore, this model also exhibits distal extension of smooth muscle into the small-to medium-sized pulmonary arteries, collagen deposition, and inflammatory cell infiltrates, characterized by a high nuclear/cytosol ratio. 50 Surprisingly, despite the extensive angio-obliterative remodeling present in the EH-KO ITSNþ/À mice, only a modest increase in RVSP and RVH was observed. 50 However, the mice used in this study were all young female mice; it is generally accepted that older male mice exhibit a more severe hemodynamic phenotype.…”

“…Surprisingly, the EH ITSN proliferative potential was not just specific to ECs, and it induced smooth muscle cell proliferation. 50 Furthermore, fibroblast proliferation was evident, and led to adventitial thickening; in some cases, media-fibroproliferative structures were identified within the vessel wall and, therefore, led to significant increases in vessel wall thickness. 50 Moreover, a plethora of EC-driven vascular arteriopathy is observed in this mouse model, including subtotal and complete concentric onion-skinelike intima thickening, eccentric intima proliferation, EC hobnail patterns, obliterative lesions with vascular slit-like channels, stalk-like lesions within the vessel lumen, peribronchial and subpleural lesions, and complex plexiform-like lesions.…”

“…50 Furthermore, fibroblast proliferation was evident, and led to adventitial thickening; in some cases, media-fibroproliferative structures were identified within the vessel wall and, therefore, led to significant increases in vessel wall thickness. 50 Moreover, a plethora of EC-driven vascular arteriopathy is observed in this mouse model, including subtotal and complete concentric onion-skinelike intima thickening, eccentric intima proliferation, EC hobnail patterns, obliterative lesions with vascular slit-like channels, stalk-like lesions within the vessel lumen, peribronchial and subpleural lesions, and complex plexiform-like lesions. 50 Furthermore, this model also exhibits distal extension of smooth muscle into the small-to medium-sized pulmonary arteries, collagen deposition, and inflammatory cell infiltrates, characterized by a high nuclear/cytosol ratio.…”