1 | Introduction
Aortic aneurysm is a fatal vascular disease, lack of effective drug
treatment, surgery is the only choice. Most aortic aneurysms are
asymptomatic before catastrophic complications such as dissection or
rupture occur. Although surgery can stabilize large aneurysms, the
recurrence rate and mortality rate are still high. Therefore, it is
urgent to clarify the molecular mechanism of the occurrence and
development of aortic aneurysm and determine the target of intervention.
Smooth muscle cells (SMCs) located in the media of aorta are key to the
vascular remodeling of aortic aneurysm. Most SMCs are in the state of
differentiation under physiological conditions to maintain the
elasticity and tensile strength of the vascular wall. However, SMCs have
significant phenotypic plasticity and can quickly adapt to environmental
fluctuation signals. The transition of SMCs from a differentiated state
to a dedifferentiated state is called phenotypic modulation,
characterized by enhanced proliferation, migration, and expression of
fibrotic and inflammatory proteins, which is the key cellular basis of
aortic aneurysm (Ailawadi et al., 2009). Myocardin (MYOCD) is a
differentiation marker of SMCs, and its deletion in SMCs causes severe
aortic aneurysm (Tang et al., 2008). Matrix cytokine osteopontin
(OPN) is a marker of dedifferentiation of SMCs, and its serum level
predicts the progression of aortic aneurysm (Golledge et al., 2007).
Collagen type I and type III (Col I , Col III ) correlate
well with the size of aortic aneurysm, and they are also SMC
dedifferentiation markers (Meng et al., 2014; Wang et al., 2012a) .MMP2 degrades elastin and collagen (mainly Col IV in basal
laminae), destroys vascular integrity, critical in angiotensin
II-induced aortic aneurysm (Wang et al., 2012b). NF-κB is a
transcriptional factor and its activation favors its nuclear
translocation to up-regulate the gene expression of MMP2, vascular
cell adhesion molecule 1 (VCAM1) and intercellular adhesion
molecule 1 (ICAM1) , promotes SMC proliferation, migration, and
inflammation (de Winther et al., 2005; Monaco et al., 2004; Tsai et al.,
2017). NF-κB is up-regulated in the aortic aneurysm wall, and inhibition
of NF-κB decreases the size of aortic aneurysm (Miyake et al., 2007).
Sarco/endoplasmic reticulum calcium ATPase (SERCA) is a key
enzyme to maintain calcium homeostasis by taking up
Ca2+ from cytosol to sarcoplasmic reticulum and
endoplasmic reticulum. SERCA2 is the main subtype of SERCA in the
vasculature, and the S -glutathiolation of the amino acid residue
Cys674 (C674) is key to increase the activity of
SERCA2 under physiological conditions (Adachi et al., 2004; Tong et al.,
2008), but this post-translational protein modification is prevented by
the irreversible oxidation of C674 thiol in pathological situations
characterised by high levels of ROS, such as aging, diabetes mellitus,
atherosclerosis, and hypertension (Adachi et al., 2004; Liu et al.,
2020; Qin et al., 2013; Ying et al., 2008), which are risk factors for
aortic aneurysm. We have reported that the irreversible oxidation of
C674 occurred broadly in mouse and human aortic aneurysms (Que et al.,
2020). We used heterozygous SERCA2 C674S knock-in (SKI) mice, where half
of C674 was substituted by serine, to represent partial irreversible
oxidative inactivation of C674 under pathological conditions. The
inactivation of C674 by causing the accumulation of intracellular
Ca2+ to activate Ca2+-dependent
calcineurin that promoted the nuclear translocation of nuclear factor of
activated T-lymphocytes (NFAT) and NF-κB, therefore down-regulated the
expression of MYOCD, while up-regulated the expression of OPN, MMP2, Col
I, Col III, and VCAM1, accelerated SMC proliferation, migration and
macrophage adhesion to SMCs, and exacerbated angiotensin II-induced
aortic aneurysm (Que et al., 2020). We hypothesize that inactivation of
SERCA2 C674 not only activates NFAT/NF-κB, but also inhibits the
protective factors that restrict the phenotypic modulation of SMCs, thus
accelerating the occurrence of aortic aneurysm. This study was designed
to elucidate the downstream targets of C674 in regulating SMC phenotypic
modulation and aortic aneurysm.