Altered MicroRNA processing in heritable pulmonary arterial hypertension: an important role for Smad-8

Am J Respir Crit Care Med. 2011 Dec 15;184(12):1400-8. doi: 10.1164/rccm.201106-1130OC. Epub 2011 Sep 15.

Abstract

Rationale: Heritable pulmonary arterial hypertension (HPAH) is primarily caused by mutations of the bone morphogenetic protein (BMP) type-II receptor (BMPR2). Recent identification of mutations in the downstream mediator Smad-8 (gene, SMAD9) was surprising, because loss of Smad-8 function in canonical BMP signaling is largely compensated by Smad-1 and -5. We therefore hypothesized that noncanonical pathways may play an important role in PAH.

Objectives: To determine whether HPAH mutations disrupt noncanonical Smad-mediated microRNA (miR) processing.

Methods: Expression of miR-21, miR-27a, and miR-100 was studied in pulmonary artery endothelial (PAEC) and pulmonary artery smooth muscle cells (PASMC) from explant lungs of patients with PAH.

Measurements and main results: SMAD9 mutation completely abrogated miR induction, whereas canonical signaling was only reduced by one-third. miR-21 levels actually decreased, suggesting that residual canonical signaling uses up or degrades existing miR-21. BMPR2 mutations also led to loss of miR induction in two of three cases. HPAH cells proliferated faster than other PAH or controls. miR-21 and miR-27a each showed antiproliferative effects in PAEC and PASMC, and PAEC growth rate after BMP treatment correlated strongly with miR-21 fold-change. Overexpression of SMAD9 corrected miR processing and reversed the hyperproliferative phenotype.

Conclusions: HPAH-associated mutations engender a primary defect in noncanonical miR processing, whereas canonical BMP signaling is partially maintained. Smad-8 is essential for this miR pathway and its loss was not complemented by Smad-1 and -5; this may represent the first nonredundant role for Smad-8. Induction of miR-21 and miR-27a may be a critical component of BMP-induced growth suppression, loss of which likely contributes to vascular cell proliferation in HPAH.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Bone Morphogenetic Protein Receptors, Type II / genetics*
  • Bone Morphogenetic Protein Receptors, Type II / metabolism
  • Cell Proliferation
  • Cells, Cultured
  • Endothelium, Vascular / pathology*
  • Familial Primary Pulmonary Hypertension
  • Female
  • Gene Expression Profiling
  • Humans
  • Hypertension, Pulmonary / genetics*
  • Male
  • MicroRNAs / metabolism*
  • Middle Aged
  • Muscle, Smooth, Vascular / pathology*
  • Mutation / genetics*
  • Pulmonary Artery / pathology
  • Signal Transduction / genetics
  • Smad8 Protein / genetics*
  • Smad8 Protein / metabolism

Substances

  • MIRN100 microRNA, human
  • MIRN21 microRNA, human
  • MIRN27 microRNA, human
  • MicroRNAs
  • Smad8 Protein
  • BMPR2 protein, human
  • Bone Morphogenetic Protein Receptors, Type II