Role of CCN5 and CYTL1 in the heart

Abstract

Heart failure (HF) remains a significant public health problem with an unacceptably high morbidity and mortality affecting about three persons per thousand per year in the worldwide. Heart disease remains the predominant cause of mortality in the United States, accounting for nearly 800000 deaths per year. Furthermore, it presents a considerable economic burden, with estimated direct and indirect costs in 2011 of ≈$320 billion and predictions suggesting that costs will rise to ≈$918 billion by 2030. Heart failure is characterized by a progressive loss in contractility and ejection fraction, ventricular chamber dilation, and ventricular wall thinning or a devastating disorder characterized by interstitial fibrosis. Cardiac fibrosis is associated with increased ventricular stiffness and diastolic dysfunction, and is an independent predictor for the long-term clinical outcomes of patients with heart failure. Inhibiting cardiac fibrosis from progressing is critical to prevent heart failure. However, there is no efficient therapeutic approach currently available. In our lab we work on 2 proteins that related to cardiac fibrosis, one is an anti-fibrotic molecule named as CCN5 and another is pro-fibrotic molecule named as Cytokine-like 1 (CYTL1). In this study, I focused on the role of two molecules in the heart. This study splits into 2 parts. In the first part, the mechanism of CCN5 on cardiac fibrosis will be described. Second part will work on the role of CYTL1 that lead to cardiac fibrosis in the heart. CCN5 is a member of the CCN (Cysteine-rich 61/Connective tissue growth factor/Nephroblastoma overexpressed) family and identified as anti-hypertrophic, anti-fibrotic, and reverses established cardiac fibrosis in the heart. Overexpression of matricellular protein CCN5 in the heart by adenoviral deliver significantly improved cardiac fibrosis in severe heart failure. In our lab, we previously showed that the matricellular protein CCN5 reverses established cardiac fibrosis (CF) through inducing apoptosis in myofibroblasts (MyoFBs) but not in cardiomyocytes or fibroblasts (FBs). In this study, I set out to elucidate the molecular mechanisms underlying CCN5-mediated selective apoptosis of MyoFBs. I first observed that the apoptotic protein p53 and the anti-apoptotic protein NFB are simultaneously induced in MyoFBs. When the expression level of p53 was suppressed using a siRNA, CCN5 did not induce apoptosis in MyoFBs. By contrast, when NFB signaling was inhibited using IKK VII, an IB inhibitor, MyoFBs underwent apoptosis even in the absence of CCN5. SMAD7 is one of the downstream targets of CCN5 and it was previously shown to potentiate apoptosis in epithelial cells through inhibition of NFB. In accordance with these reports, when the expression of SMAD7 was suppressed using a siRNA, NFB signaling was enhanced, and CCN5 did not induce apoptosis. Lastly, we used a luciferase reporter construct to show that CCN5 positively regulated SMAD7 expression at the transcriptional level. Collectively, these data suggest that a delicate balance between the two mutually antagonistic proteins p53 and NFB is maintained for MyoFBs to survive, and CCN5 tips the balance in favor of the apoptotic protein p53. This study provides insight into the anti-fibrotic activity of CCN5 during the regression of CF. Otherwise, Cytokine like-1 protein (Cytl1) is a secreted protein that involved in diverse biological processes. Cytl1 was reported that it plays a role in the development and metastasis of neuroblastoma cells. A comparative modeling study indicated that CYTL1 is structurally and functionally similar to monocyte chemoattractant protein 1 (MCP-1). As MCP-1 plays an important role in cardiac fibrosis (CF) and heart failure (HF). Therefore, Cytl1 might be functionally related to MCP-1 that is known to be involved in pathogenesis of CF. Cytl1 was reported that it can lead to CF via the regulation of TGF-β-SMAD signaling. Cytl1 acts directly on endothelial cells and FBs, triggering the EndMT and trans-differentiation of FBs to MyoFBs, the two critical processes that occurs during CF. The question here is that Cytl1 is known as a secreted protein and what will be its receptor for Cytl1 binding and induce CF. In this study can provides the potential receptor by which Cytl1 may play the role of a pro-fibrotic molecule.