Graduate Student University of Toronto Toronto, Ontario, Canada
Background: Stem cell antigen-1 (Sca-1) marks progenitor cells that contribute to vessel remodeling by differentiating into vascular smooth muscle cells (VSMC) and related myofibroblasts. However, the function of Sca-1 expression in vessel remodeling has not been shown. Here, we assessed the requirement for Sca-1 in a mouse model of experimental hypertension (HTN).
METHODS AND RESULTS: Male and female mice homozygous for GFP knock-in/Sca-1 knockout (Sca1KI-/-), heterozygous littermates (Sca1KI+/-), and control GFP-labeled Sca-1 reporter mice (Sca1GFP), age 12-14-wk, were subjected to angiotensin II-induced HTN (Ang-II 1-μg/kg/min) by osmotic mini-pump for 28d, or vehicle (0.9% saline). GFP+CD31-CD45- cells from Sca1KI-/-, Sca1KI+/-, and Sca1GFP represent progenitor cells with no-, partial-, or normal Sca-1 expression, respectively. Partial- or total loss of Sca-1 expression exacerbated aortic GFP+CD31-CD45- cell expansion, compared to Sca1GFP [Sca1KI-/- 32±7-fold change of vehicle vs. Sca1KI+/- 39±9 vs. Sca1GFP 5±1; n=11-13/group; p< 0.0001], suggesting disinhibited progenitor responses. Interestingly, Sca1KI-/- mice manifest blunted HTN in response to Ang-II [Sca1KI-/- 130±9 mmHg vs. Sca1KI+/- 159±8 vs. Sca1GFP 160±10; n=6-7/group; p< 0.01]. Partial- or total loss of Sca-1 worsened aortic dilation [Sca1KI-/- 1.25±0.06 mm vs. Sca1KI+/- 1.21±0.06 vs. Sca1GFP 1.04±0.05; n=6-7/group; p< 0.05], aortic wall thickness [Sca1KI-/- 105±9 μm vs. Sca1KI+/- 136±16 vs. Sca1GFP 82±5; n=6-7/group; p< 0.01], adventitial area [Sca1KI-/- 79±13 mm2 vs. Sca1KI+/- 178±46 vs. Sca1GFP 51±6; n=6-7/group; p< 0.01], and aortic aneurysm formation [Sca1KI-/- 6/17 vs. Sca1KI+/- 6/20 vs. Sca1GFP 2/18]. Mechanistically, in cultured progenitor cells subjected to TGFβ, profibrotic CD44 expression increased in Sca-1 deficient progenitors vs. wild-type [85±1% vs. 61±1; n=6-9/group]. Concomitantly, stem cell marker PDGFRα expression on these cultured progenitors was reduced [4±1% vs. 23±8; n=6-9/group], suggesting skewed differentiation of progenitors towards a pro-fibrotic lineage. Primary Sca-1 deficient VSMC similarly increased pro-fibrotic vimentin expression after TGFβ vs. wild-type, driven by 5-fold increased phosphorylated Smad2 signaling [n=3/group, p< 0.01].
Conclusion: Partial or complete loss of Sca-1 worsens aortic remodeling by promoting expansion and pro-fibrotic differentiation of progenitors and their VSMC progeny. These data highlight a critical role for vascular Sca-1 expression, which may inform a novel approach to preventing and treating HTN and associated aortic remodeling.
