Endothelial HIFα/PDGF-B to smooth muscle Beclin1 signaling sustains pathological muscularization in pulmonary hypertension
Fatima Z. Saddouk, Andrew Kuzemczak, Junichi Saito, Daniel M. Greif
Fatima Z. Saddouk, Andrew Kuzemczak, Junichi Saito, Daniel M. Greif
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Research Article Pulmonology Vascular biology

Endothelial HIFα/PDGF-B to smooth muscle Beclin1 signaling sustains pathological muscularization in pulmonary hypertension

Abstract

Mechanisms underlying maintenance of pathological vascular hypermuscularization are poorly delineated. Herein, we investigated retention of smooth muscle cells (SMCs) coating normally unmuscularized distal pulmonary arterioles in pulmonary hypertension (PH) mediated by chronic hypoxia with or without Sugen 5416, and reversal of this pathology. With hypoxia in mice or culture, lung endothelial cells (ECs) upregulated hypoxia-inducible factor 1α (HIF1-α) and HIF2-α, which induce platelet-derived growth factor B (PDGF-B), and these factors were reduced to normoxic levels with re-normoxia. Re-normoxia reversed hypoxia-induced pulmonary vascular remodeling, but with EC HIFα overexpression during re-normoxia, pathological changes persisted. Conversely, after establishment of distal muscularization and PH, EC-specific deletion of Hif1a, Hif2a, or Pdgfb induced reversal. In human idiopathic pulmonary artery hypertension, HIF1-α, HIF2-α, PDGF-B, and autophagy-mediating gene products, including Beclin1, were upregulated in pulmonary artery SMCs and/or lung lysates. Furthermore, in mice, hypoxia-induced EC-derived PDGF-B upregulated Beclin1 in distal arteriole SMCs, and after distal muscularization was established, re-normoxia, EC Pdgfb deletion, or treatment with STI571 (which inhibits PDGF receptors) downregulated SMC Beclin1 and other autophagy products. Finally, SMC-specific Becn1 deletion induced apoptosis, reversing distal muscularization and PH mediated by hypoxia with or without Sugen 5416. Thus, chronic hypoxia induction of the HIFα/PDGF-B axis in ECs is required for non–cell-autonomous Beclin1-mediated survival of pathological distal arteriole SMCs.

Authors

Fatima Z. Saddouk, Andrew Kuzemczak, Junichi Saito, Daniel M. Greif

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Figure 1

Reversal of distal arteriole muscularization with re-normoxia following hypoxia.

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Reversal of distal arteriole muscularization with re-normoxia following ...
(A) Experimental strategy for B–E. (B–E) Wild-type mice were maintained in normoxia or were exposed to hypoxia for 21 days and either analyzed at that point or following re-exposure to normoxia for 7–42 days as indicated. (B) Vibratome lung sections were stained for SMA and the EC marker MECA-32. M and D, middle and distal arterioles are indicated, respectively. (C) Percentage of distal arterioles covered by SMCs. (D) RVSP (equivalent to PA systolic pressure). (E) The RV weight ratio (weight of the RV divided by the sum of left ventricle [LV] and septum [S] weight) were measured. n = 5–6 mice (3 males, 2–3 females) per experimental group and 3 arterioles per mouse. nd, not detected. ****P < 0.0001 vs. hypoxia by multifactor ANOVA with Tukey’s multiple-comparison test. (F) Experimental strategy for G–J. (G–J) Wild-type mice were exposed to (i) normoxia, (ii) hypoxia for 21 days, (iii) hypoxia for 21 days followed by normoxia for 42 days, or (iv) hypoxia for 21 days, normoxia for 42 days, and hypoxia again for 21 days. (G) Vibratome lung sections were stained for SMA and MECA-32. (H–J) Percentages of distal arteriole covered by SMCs, RVSP, and RV/(LV + S) were measured. n = 3 mice (1 male, 2 females). Significance evaluated by multifactor ANOVA with Tukey’s multiple-comparison test. nd, not detected. Scale bars: 20 μm.