In vivo and in vitro studies on pathogenic mechanisms linking cigarette smoking to cardiovascular disease : what are the effects of human mesenchymal stem cells?

Abstract

Cardiovascular disease (CVD) is the leading cause of death worldwide. Smoking, a well-established major risk factor, accounts for one in every three deaths from CVD. However, the question of how smoking or secondhand smoke (SHS) exposure affects the cardiovascular system remains unclear. Using animal and cell line models, this thesis aims at studying the mechanisms underlying the pathogenesis of cigarette smoke (CS)-induced cardiac injury. Moreover, mesenchymal stem cells (MSCs) are regarded as a promising candidate for cell-based therapy for cardiac repair and regeneration. The therapeutic potential of bone marrow-derived MSCs (BM-MSCs) and induced pluripotent stem cell-derived MSCs (iPSC-MSCs) were also investigated in this study.

Both in vivo and in intro models were firstly established to determine the pathogenic role of CS. In the CS-exposed rat model, cardiac dysfunction was observed due to remodelling processes characterized by myocardial hypertrophy and interstitial and perivascular fibrosis in myocardium. CS induced cardiac oxidative stress characterized by suppression of the total antioxidant capacity such as reduction in anti-oxidant enzyme activities; cardiac inflammatory responses characterized by increased pro-inflammatory mediators and decreased anti-inflammatory mediators; and apoptosis in myocardium. Furthermore, CS caused abnormalities of systemic and cardiac lipid profile via dysregulation of cholesterol and fatty acid metabolism in the heart tissue through the regulation of AMPK signalling pathway. In the AC16 cardiomyocyte cell line model, cigarette smoke medium (CSM) resulted in increased ROS production and suppressed anti-oxidants activities, increased levels of pro-inflammatory chemokine IL-8 release, and accelerated cell apoptosis via the activation of NF-κB and p38 MAPK and inhibition of AMPK signalling pathways. The CSM-induced apoptosis is regulated through the intrinsic apoptotic pathway with the involvement of Bcl-2 family proteins accompanied by mitochondria dysfunction in the AC16 cells.

In addition, the effects of BM-MSCs and iPSC-MSCs on CS-induced cardiac injury were investigated in the CS-exposed rat model. Treatment with iPSC-MSCs was found to be more effective than BM-MSCs in attenuating both CS-induced cardiac remodelling and dysfunction, as well possessed potent anti-oxidative, anti-inflammatory, and anti-apoptotic effects in myocardium. In addition, the iPSC- MSCs were more effective in restoring the altered cardiac lipid profiles caused by CS exposure via the restoration of AMPK signalling pathway.

In the CSM-exposed cardiomyocytes, conditioned media (CdM) from iPSC-MSCs was found to be superior in reducing ROS generation and reversing antioxidant enzyme activities, suggesting the presence of paracrine effects. The anti-inflammatory action of CdM from iPSC-MSCs was due to the prevention of CSM-induced NF-κB and p38 MAPK activation and the restoration of CSM-induced inhibition of AMPK activation. Nevertheless, CdM from iPSC-MSCs also reduced CSM-induced apoptosis and rescued CSM-induced mitochondrial damage in the AC16 cells.

Taken together, the findings support that the cross-regulation of oxidative stress, inflammation and apoptosis as well as lipid profiles may play an important role in the pathogenesis of CVD associated with smoking. The use of iPSC-MSCs and their CdM may be promising for the development of cell-based therapy in smoking-related CVD.