Evidence of endoplasmic reticulum (ER) stress has been found in lungs of patients with familial and sporadic idiopathic pulmonary fibrosis. We tested whether ER stress causes or exacerbates lung ...fibrosis by (i) conditional expression of a mutant form of surfactant protein C (L188Q SFTPC) found in familial interstitial pneumonia and (ii) intratracheal treatment with the protein misfolding agent tunicamycin. We developed transgenic mice expressing L188Q SFTPC exclusively in type II alveolar epithelium by using the Tet-On system. Expression of L188Q SFTPC induced ER stress, as determined by increased expression of heavy-chain Ig binding protein (BiP) and splicing of X-box binding protein 1 (XBP1) mRNA, but no lung fibrosis was identified in the absence of a second profibrotic stimulus. After intratracheal bleomycin, L188Q SFTPC-expressing mice developed exaggerated lung fibrosis and reduced static lung compliance compared with controls. Bleomycin-treated L188Q SFTPC mice also demonstrated increased apoptosis of alveolar epithelial cells and greater numbers of fibroblasts in the lungs. With a complementary model, intratracheal tunicamycin treatment failed to induce lung remodeling yet resulted in augmentation of bleomycin-induced fibrosis. These data support the concept that ER stress produces a dysfunctional epithelial cell phenotype that facilitates fibrotic remodeling. ER stress pathways may serve as important therapeutic targets in idiopathic pulmonary fibrosis.
Recent evidence suggests that dysfunctional type II alveolar epithelial cells (AECs) contribute to the pathogenesis of idiopathic pulmonary fibrosis (IPF). Based on the hypothesis that ...disease-causing mutations in surfactant protein C (SFTPC) provide an important paradigm for studying IPF, we investigated a potential mechanism of AEC dysfunction suggested to result from mutant SFTPC expression: induction of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). We evaluated biopsies from 23 IPF patients (including 3 family members with L188Q SFTPC mutations, 10 individuals with familial interstitial pneumonia without SFTPC mutations, and 10 individuals with sporadic IPF) and sections from 10 control lungs. After demonstrating UPR activation in cultured A549 cells expressing mutant SFTPC, we identified prominent expression of UPR markers in AECs in the lungs of patients with SFTPC mutation-associated fibrosis. In individuals with familial interstitial pneumonia without SFTPC mutations and patients with sporadic IPF, we also found UPR activation selectively in AECs lining areas of fibrotic remodeling. Because herpesviruses are found frequently in IPF lungs and can induce ER stress, we investigated expression of viral proteins in lung biopsies. Herpesvirus protein expression was found in AECs from 15/23 IPF patients and colocalized with UPR markers in AECs from these patients. ER stress and UPR activation are found in the alveolar epithelium in patients with IPF and could contribute to disease progression. Activation of these pathways may result from altered surfactant protein processing or chronic herpesvirus infection.
Studies in multiple organ systems have shown cross-talk between signaling through the bone morphogenetic protein receptor type 2 (BMPR2) and estrogen pathways. In humans, pulmonary arterial ...hypertension (PAH) has a female predominance, and is associated with decreased BMPR2 expression. The goal of this study was to determine if estrogens suppress BMPR2 expression.
A variety of techniques were utilized across several model platforms to evaluate the relationship between estrogens and BMPR2 gene expression. We used quantitative RT-PCR, gel mobility shift, and luciferase activity assays in human samples, live mice, and cell culture.
BMPR2 expression is reduced in lymphocytes from female patients compared with male patients, and in whole lungs from female mice compared with male mice. There is an evolutionarily conserved estrogen receptor binding site in the BMPR2 promoter, which binds estrogen receptor by gel-shift assay. Increased exogenous estrogen decreases BMPR2 expression in cell culture, particularly when induced to proliferate. Transfection of increasing quantities of estrogen receptor alpha correlates strongly with decreasing expression of BMPR2.
BMPR2 gene expression is reduced in females compared to males in live humans and in mice, likely through direct estrogen receptor alpha binding to the BMPR2 promoter. This reduced BMPR2 expression may contribute to the increased prevalence of PAH in females.
The heritable form of pulmonary arterial hypertension (PAH) is typically caused by a mutation in bone morphogenic protein receptor type 2 (BMPR2), and mice expressing Bmpr2 mutations develop PAH with ...features similar to human disease. BMPR2 is known to interact with the cytoskeleton, and human array studies in PAH patients confirm alterations in cytoskeletal pathways. The goal of this study was to evaluate cytoskeletal defects in BMPR2-associated PAH. Expression arrays on our Bmpr2 mutant mouse lungs revealed cytoskeletal defects as a prominent molecular consequence of universal expression of a Bmpr2 mutation (Rosa26-Bmpr2(R899X)). Pulmonary microvascular endothelial cells cultured from these mice have histological and functional cytoskeletal defects. Stable transfection of different BMPR2 mutations into pulmonary microvascular endothelial cells revealed that cytoskeletal defects are common to multiple BMPR2 mutations and are associated with activation of the Rho GTPase, Rac1. Rac1 defects are corrected in cell culture and in vivo through administration of exogenous recombinant human angiotensin-converting enzyme 2 (rhACE2). rhACE2 reverses 77% of gene expression changes in Rosa26-Bmpr2(R899X) transgenic mice, in particular, correcting defects in cytoskeletal function. Administration of rhACE2 to Rosa26-Bmpr2(R899X) mice with established PAH normalizes pulmonary pressures. Together, these findings suggest that cytoskeletal function is central to the development of BMPR2-associated PAH and that intervention against cytoskeletal defects may reverse established disease.
The majority of familial pulmonary arterial hypertension (PAH) cases are caused by mutations in the type 2 bone morphogenetic protein receptor (BMPR2). However, less than one-half of BMPR2 mutation ...carriers develop PAH, suggesting that the most important function of BMPR2 mutation is to cause susceptibility to a "second hit." There is substantial evidence from the literature implicating dysregulated inflammation, in particular the cytokine IL-6, in the development of PAH. We thus hypothesized that the BMP pathway regulates IL-6 in pulmonary tissues and conversely that IL-6 regulates the BMP pathway. We tested this in vivo using transgenic mice expressing an inducible dominant negative BMPR2 in smooth muscle, using mice injected with an IL-6-expressing virus, and in vitro using small interfering RNA (siRNA) to BMPR2 in human pulmonary artery smooth muscle cells (PA SMC). Consistent with our hypothesis, we found upregulation of IL-6 in both the transgenic mice and in cultured PA SMC with siRNA to BMPR2; this could be abolished with p38(MAPK) inhibitors. We also found that IL-6 in vivo caused a twofold increase in expression of the BMP signaling target Id1 and caused increased BMP activity in a luciferase-reporter assay in PA SMC. Thus we have shown both in vitro and in vivo a complete negative feedback loop between IL-6 and BMP, suggesting that an important consequence of BMPR2 mutations may be poor regulation of cytokines and thus vulnerability to an inflammatory second hit.
Most patients with primary pulmonary hypertension are thought to have sporadic, not inherited, disease. Because clinical disease develops in only 10 to 20 percent of persons carrying the gene for ...familial primary pulmonary hypertension, we hypothesized that many patients with apparently sporadic primary pulmonary hypertension may actually have familial primary pulmonary hypertension.
In a study conducted over 20 years, we developed a registry of 67 families affected by familial primary pulmonary hypertension. Through patient referrals, extensive family histories, and correlation of family pedigrees, we discovered shared ancestry among five subfamilies. We established the diagnosis of primary pulmonary hypertension by direct evaluation of patients and review of autopsy material and medical records. We assessed some family members for mutations in the gene encoding bone morphogenetic protein receptor II (BMPR2), which has recently been found to cause familial primary pulmonary hypertension.
We linked five separately identified subfamilies that included 394 known members spanning seven generations, which were traced back to a founding couple in the mid-1800s. Familial primary pulmonary hypertension has been diagnosed in 18 family members, 12 of whom were first thought to have sporadic disease. The conditions of 7 of the 18 were initially misdiagnosed as other cardiopulmonary diseases. Six members affected with familial primary pulmonary hypertension and 6 of 10 at risk for carriage have been undergone genotype analysis, and they have the same mutation in BMPR2, a transversion of thymine to guanine at position 354 in exon 3.
Many cases of apparently sporadic primary pulmonary hypertension may be familial. Failure to detect familial primary pulmonary hypertension results from incomplete expression within families, skipped generations, and incomplete family pedigrees. The recent discovery of mutations in BMPR2 should make it possible to identify those with susceptibility to disease.
Primary pulmonary hypertension (PPH), characterized by obstruction of pre-capillary
pulmonary arteries, leads to sustained elevation of pulmonary arterial pressure
(mean >25 mm Hg at rest or >30 mm ...Hg during exercise). The
aetiology is unknown, but the histological features reveal proliferation of
endothelial and smooth muscle cells with vascular remodelling
(Fig. 1). More than one affected relative has been identified
in at least 6% of cases (familial PPH, MIM 178600). Familial
PPH (FPPH) segregates as an autosomal dominant disorder with reduced penetrance
and has been mapped to a locus designated PPH1 on 2q33, with no evidence
of heterogeneity. We now show that FPPH is caused by
mutations in BMPR2, encoding a TGF-β type II receptor (BMPR-II).
Members of the TGF-β superfamily transduce signals by binding to heteromeric
complexes of type I and II receptors, which activates serine/threonine kinases,
leading to transcriptional regulation by phosphorylated Smads.
By comparison with in vitro studies, identified defects of BMPR-II
in FPPH are predicted to disrupt ligand binding, kinase activity and heteromeric
dimer formation. Our data demonstrate the molecular
basis of FPPH and underscore the importance in vivo of the TGF-β
signalling pathway in the maintenance of blood vessel integrity.†These authors contributed equally to this work.
*Micheala Aldred2, Christopher A. Brannon3, P. Michael Conneally4, Tatiana Foroud4, Neale Fretwell2, Radhika Gaddipati1, Daniel Koller4, Emily J. Loyd1, Neil Morgan2, John H. Newman1, Melissa A. Prince1, Carles Vilariño Güell2 & Lisa Wheeler1
1Vanderbilt University Medical Center, Nashville, Tennessee, USA.
2Division of Medical Genetics, Departments of Genetics and Medicine, University of Leicester, UK.
3Division of Human Genetics, Children's Hospital Medical Center, Cincinnati, Ohio, USA.
4Indiana University School of Medicine, Indianapolis, Indiana, USA.
Correspondence should be addressed to J.E.L. (e-mail: Jim.Loyd@mcmail.vanderbilt.edu), W.C.N. (e-mail: bill.nichols@chmcc.org) or R.C.T. (e-mail: rtrembat@hgmp.mrc.ac.uk).
Pulmonary arterial hypertension (PAH) is a disease of progressively increasing pulmonary vascular resistance, associated with mutations of the type 2 receptor for the BMP pathway, BMPR2. The ...canonical signaling pathway for BMPR2 is through the SMAD family of transcription factors. BMPR2 is expressed in every cell type, but the impact of BMPR2 mutations affecting SMAD signaling, such as Bmpr2delx4+, had only previously been investigated in smooth muscle and endothelium. In the present study, we created a mouse with universal doxycycline-inducible expression of Bmpr2delx4+ in order to determine if broader expression had an impact relevant to the development of PAH. We found that the most obvious phenotype was a dramatic, but patchy, increase in pulmonary inflammation. We crossed these double transgenic mice onto an NF-κB reporter strain, and by luciferase assays on live mice, individual organs and isolated macrophages, we narrowed down the origin of the inflammatory phenotype to constitutive activation of tissue macrophages. Study of bone marrow-derived macrophages from mutant and wild-type mice suggested a baseline difference in differentiation state in Bmpr2 mutants. When activated with LPS, both mutant and wild-type macrophages secrete BMP pathway inhibitors sufficient to suppress BMP pathway activity in smooth muscle cells (SMC) treated with conditioned media. Functionally, co-culture with macrophages results in a BMP signaling-dependent increase in scratch closure in cultured SMC. We conclude that SMAD signaling through BMP is responsible, in part, for preventing macrophage activation in both live animals and in cells in culture, and that activated macrophages secrete BMP inhibitors in sufficient quantity to cause paracrine effect on vascular smooth muscle.
Recent reports have linked mutations in the surfactant protein C gene (
SFTPC
) to familial forms of pulmonary fibrosis, but it is uncertain whether deficiency of mature SP-C contributes to disease ...pathogenesis. In this study, we evaluated bleomycin-induced lung fibrosis in mice with genetic deletion of
SFTPC
. Compared with wild-type (SFTPC+/+) controls, mice lacking surfactant protein C (SFTPC−/−) had greater lung neutrophil influx at 1 week after intratracheal bleomycin, greater weight loss during the first 2 weeks, and increased mortality. At 3 and 6 weeks after bleomycin, lungs from SFTPC−/− mice had increased fibroblast numbers, augmented collagen accumulation, and greater parenchymal distortion. Furthermore, resolution of fibrosis was delayed. Although remodeling was near complete in SFTPC+/+ mice by 6 weeks, SFTPC−/− mice did not return to baseline until 9 weeks after bleomycin. By terminal dUTP nick-end labeling staining, widespread cell injury was observed in SFTPC−/− and SFTPC+/+ mice 1 week after bleomycin; however, ongoing apoptosis of epithelial and interstitial cells occurred in lungs of SFTPC−/− mice, but not SFTPC+/+ mice, 6 weeks after bleomycin. Thus, SP-C functions to limit lung inflammation, inhibit collagen accumulation, and restore normal lung structure after bleomycin.
Bone morphogenetic peptides (BMPs), a family of cytokines critical to normal development, were recently implicated in the pathogenesis of familial pulmonary arterial hypertension. The type-II ...receptor (BMPRII) is required for recognition of all BMPs, and targeted deletion of BMPRII in mice results in fetal lethality before gastrulation. To overcome this limitation and study the role of BMP signaling in postnatal vascular disease, we constructed a smooth muscle-specific transgenic mouse expressing a dominant-negative BMPRII under control of the tetracycline gene switch (SM22-tet-BMPRII(delx4+) mice). When the mutation was activated after birth, mice developed increased pulmonary artery pressure, RV/LV+S ratio, and pulmonary arterial muscularization with no increase in systemic arterial pressure. Studies with SM22-tet-BMPRII(delx4+) mice support the hypothesis that loss of BMPRII signaling in smooth muscle is sufficient to produce the pulmonary hypertensive phenotype.
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