Reactive oxygen species (ROS) contribute to atherogenesis. An unusual mechanism that increases cellular ROS levels and oxidative stress involves 4 ubiquitously expressed noncoding small nucleolar RNAs (snoRNAs) from introns of the ribosomal protein L13a (
Rpl13a
) locus:
U32a
,
U33
,
U34
, and
U35a
. We tested the hypothesis that these snoRNAs promote aortic smooth muscle cell (SMC) activation and vascular inflammation, by using “snoKO” mice with targeted deletion of the 4 snoRNAs (but not
Rpl13a
). Compared with congenic WT SMCs, snoKO SMCs showed 40±20% lower ROS levels, assessed by DCF fluorescence (
p
<0.02). Congruently, ROS levels were 35±5% lower in snoKO than WT aorta and carotid frozen sections (
p
<0.01), assessed by CellROX Orange fluorescence. Proliferation and migration evoked by FBS and PDGF-BB, respectively, were each 30±10% less in snoKO than WT SMCs (
p
<0.01 for each). To assess SMC migration and proliferation in vivo, we performed carotid artery endothelial denudation. Before injury, snoKO and WT carotid arteries were morphologically equivalent. Four wk after injury, carotid neointimal hyperplasia was 57±9% less and luminal area was 40±20 % more in snoKO than in WT mice (
p
<0.01). WT and snoKO mice had equivalent heart rates and systolic blood pressures by tail-cuff plethysmography: 480±20 vs 420±80 beats/min; 133±5, 132±7 mm Hg, respectively (n=5/group). To test whether snoRNAs affect atherosclerosis, we orthotopically transplanted carotid arteries from WT and snoKO mice into congenic
Apoe
-/-
mice. Six wk post-op, atherosclerotic neointima was 70±10% smaller in snoKO than in WT carotids (
p
<0.01). To assess SMC-to-foam-cell transdifferentiation, which is ROS-dependent, carotid cross-sections were stained for apoE to identify graft-derived cells and for cholesteryl ester with BODIPY. BODIPY
+
foam cells comprised 21±3% and 11±7% of neointimal area in WT and snoKO carotids, respectively (
p
<0.05). Confocal co-localization of apoE and BODIPY (optical slice thickness 1 μm) showed that graft-derived foam cells were 2.0±0.6-fold more prevalent in WT than in snoKO carotids (
p
<0.01). We conclude that
Rpl13a
snoRNAs promote SMC ROS levels, proliferation and migration in vitro and in vivo, and that these snoRNAs augment atherosclerosis.
Site-Specific Pseudouridine Formation in Preribosomal RNA Is Guided by Small Nucleolar RNAs