INTRODUCTION
The Cellular Communication Network Factor 2 (CCN2), previously known as connective tissue growth factor (CTGF), belongs to the CCN family (Perbal et al., 2018; Chaqour, 2020), composed also by CCN1/Cyr61 (cysteine rich protein), CCN3/Nov (nephroblastoma overexpressed protein) and other three secreted proteins (CCN4-6). These matricellular proteins share a structural tetramodular organization and are important extracellular matrix (ECM) components involved in the regulation of different cellular functions (Perbal, 2004; Leask and Abraham, 2006; Perbal et al., 2018).
CCN2 exerts multiple context-dependent biological functions, including regulation of cell growth, differentiation, development, adhesion, inflammation and ECM remodeling (Perbal, 2004). Regarding the cardiovascular system, CCN2 is highly expressed during development in heart, branchial arches, and in endothelium and vascular smooth muscle cells (VSMCs) of major blood vessel\souts (Ivkovic et al., 2003; Ponticos, 2013) and it is overexpressed in experimental and human cardiovascular diseases, like heart failure, pulmonary hypertension, restenosis and atherosclerosis (Perbal, 2004; Hall-Glenn et al., 2012; Ponticos, 2013; Rodrigues-Diez et al., 2015). CCN2 plays a relevant role in fibrogenesis, is a well-established marker of fibrosis and has been considered the key downstream profibrotic mediator of Transforming Growth Factor (TGF)-β and of other important factors involved in cardiovascular diseases, such as Angiotensin II (Ang II) (Leask and Abraham, 2006; Ruiz-Ortega et al., 2007a). Based on those studies, CCN2 was proposed as a growth factor and cytokine, but a recent review suggested also the potential relevance of CCN2 in maintaining optimal vascular stiffness, encouraging to further decrypt its contribution to mechanical homeostasis in blood vessels (Chaqour, 2020).
Preclinical studies suggest that CCN2 blockade could be a potential therapeutic option for fibrotic diseases, due to the promising results in experimental liver, lung and renal fibrosis (Luo et al., 2008; Ponticos et al., 2009; Phanish et al., 2010; Hao et al., 2014; Huang et al., 2016) as well as in pulmonary vascular remodeling and heart failure (Wang et al., 2011; Szabó et al., 2014). However, other studies demonstrated that CCN2 upregulation can also exert beneficial effects. Thus, specific CCN2 overexpression in cardiomyocytes protects against the deleterious changes in the heart caused by Ang II-induced pressure overload (Panek et al., 2009) or by ischemia-reperfusion injury (Shakil Ahmed et al., 2011). Accordingly, CCN2 overexpression attenuated myocardial hypertrophy, cardiac dysfunction and left ventricular remodeling in experimental pressure overload and stroke (Gravning et al., 2013). More recently, post-ischemic administration of recombinant CCN2 reduced infarct size and improved cardiac function recovery following ischemia-reperfusion injury (Moe et al., 2016). Due CCN2-KO mice complete embryonic development but die shortly after birth because of respiratory failure (Ivkovic et al., 2003), a conditional CCN2-KO mice have been developed. In this mice, CCN2 deletion ameliorates experimental renal fibrosis (Rayego-Mateos et al., 2018), but does not improve cardiac fibrosis and hypertrophy following transverse aortic constriction (Fontes et al., 2015). High circulating CCN2 levels have been proposed as a potential risk biomarker for cardiac dysfunction in patients with chronic heart failure and myocardial fibrosis (Koitabashi et al., 2008). Moreover, CCN2 mRNA expression was increased in human VSMCs from aneurysms and atherosclerotic plaques (Branchetti et al., 2013; Ponticos, 2013). Nevertheless, scarce information is available about the impact of CCN2 expression modulation in these vascular diseases. OK
Our aim was to further characterize the role of CCN2 in the regulation of vascular responses under normal and pathological conditions, using a conditional CCN2 deficient mouse strain (CCN2flox/floxROSA26-ERT/Cre; henceforth named CCN2-KO), and the well-known model of vascular damage induced by systemic Ang II administration (Daugherty et al., 2000) which, in turn, is associated with aortic CCN2 upregulation (Rupérez et al., 2003; Rodrigues-Díez et al., 2013).