Identification of Small Proline-Rich Repeat Protein 3 as a Novel Atheroprotective Factor That Promotes Adaptive Akt Signaling in Vascular Smooth Muscle Cells

Abstract

Objective Atherosclerosis is the primary driver of cardiovascular disease, the leading cause of death worldwide. Identification of naturally occurring atheroprotective genes has become a major goal for development of interventions that will limit atheroma progression and associated adverse events. To this end, we have identified SPRR3 (small proline-rich repeat protein 3) as selectively upregulated in vascular smooth muscle cells (VSMCs) of atheroma-bearing arterial tissue versus healthy arterial tissue. In this study, we sought to determine the role of SPRR3 in atheroma pathophysiology. Approach and Results We found that atheroprone ApoE-null mice lacking SPRR3 developed significantly greater atheroma burden. To determine the cellular driver(s) of this increase, we evaluated SPRR3-dependent changes in bone-marrow-derived cells, endothelial cells (ECs), and VSMCs. Bone marrow transplant of SPRR3-expressing cells into SPRR3−/− ApoE−/− recipients failed to rescue atheroma burden. Similarly, ECs did not exhibit a response to SPRR3 loss. However, atheromas from SPRR3-deficient mice exhibited increased TUNEL-positive VSMCs compared with control. Cell death in SPRR3-deficient VSMCs was significantly increased in vitro. Conversely, SPRR3-overexpressing VSMCs exhibited reduced apoptosis compared with control. We also observed a PI3K/Akt-dependent positive association between SPRR3 expression and levels of active Akt in VSMCs. The survival advantage seen in SPRR3-overexpressing VSMCs was abrogated following the addition of a PI3K/Akt pathway inhibitor. Conclusions These results indicate that SPRR3 protects the lesion from VSMC loss by promoting survival signaling in plaque VSMCs, thereby significantly decreasing atherosclerosis progression. As the first identified atheroma-specific VSMC pro-survival factor, SPRR3 represents a potential target for lesion-specific modulation of VSMC survival.

Small proline‐rich repeat 3 is a novel coordinator of PDGFRβ and integrin β1 crosstalk to augment proliferation and matrix synthesis by cardiac fibroblasts

“…We previously reported that regulation of type I collagen transcript levels by Sprr3 may be PI3K/Akt dependent 20,21 . Other studies have also shown that Akt signaling can modulate type I collagen levels in various cell types 28‐30 .…”

“…Nonepithelial expression of several members, such as SPRR3 and SPRR2a, have been recently reported, yet their cellular and mechanistic roles are unclear 22,23 . Our group discovered high expression of SPRR3 in atheromatous plaques of larger arteries where its expression is restricted to vascular smooth muscle cells 20,21 . In response to mechanical stress, SPRR3 upregulates type I collagen expression in VSMCs, augments proliferation, and enhances basal phosphorylation of Akt and p38 19,20 .…”

“…We previously reported that Sprr3 regulates both type I collagen transcript and protein levels in vascular smooth muscle cells 21 . To determine if the increased numbers of cardiac fibroblasts in wild‐type mice vs Sprr3 −/− mice were elicited by increased proliferation vs survival, we performed proliferation and apoptosis assays on primary cardiac fibroblasts.…”

“…All procedures were carried out in accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health and Vanderbilt Institutional Animal Care and Use Committee (Protocol number: V/17/004). Sprr3 −/− mice were generated and maintained by PPY on a C57Bl/6J background as previously reported 21 . C57Bl/6J mice were purchased from the Jackson Laboratory (Bar Harbor, ME).…”

Atherosclerosis

“…93 Genetic deficiency of SPRR3 augmented atherosclerosis in apoE −/− mice, which were attributed to regulation of Akt signaling in SMCs. 94 Therefore, roles of SMC survival and apoptosis in the development of atherosclerosis through Akt signaling pathway have not been consistent in the literature.…”