Pretreatment with an angiotensin II receptor blocker abolished ameliorating actions of adipose-derived stem cell sheets on cardiac dysfunction and remodeling after myocardial infarction

Abstract Introduction Cell sheets using myoblasts have been developed for the treatment of heart failure after myocardial infarction (MI) bridging to heart transplantation. Stem cells are supposed to be better than myoblasts as a source of cells, since they possess a potential to proliferate and differentiate into cardiomyocytes, and also have capacity to secrete angiogenic factors. Adipose- derived stemcells (ASCs) obtained from fat tissues are expected to be a new cell source for ASC sheet therapies. Administration of angiotensin IIreceptor blockers (ARBs) is a standard therapy for heart failure after MI. However, it is not known whether ARBs affect the cell sheet therapy. This study aimed to examine ameliorating effects of ASC sheets on heart failure and remodeling after MI, and how pretreatment with ARBs prior to the creation of MI and ASC sheet transplantation modifies the effects of ASC sheets. Methods ASCs were isolated from fat tissues of wild-type rats, and ASC sheets were engineered on temperature-responsive dishes. In in vitro studies using cultured cells, mRNA levels of vascular endothelial growth factor (VEGF) in ASCs were determined by RT-PCR in the presence of angiotensin IIand/or an ARB, irbesartan, under normoxia and hypoxia; mRNA and protein levels of angiotensin IIreceptor type 1a (AT1aR), type 1b (AT1bR) and type 2 (AT2R) were also determined by RT-PCR and western blotting. In in vivo studies using a rat MI model, effects of transplanted ASC sheets and/or irbesartanon cardiac functions and remodeling after MI were evaluated by echocardiography, histological analysis and molecular biological techniques. Results In the in vitro studies, ASCs expressed higher levels of VEGF mRNA under hypoxia. They also expressed mRNA and protein of AT1aR but not AT1bR or AT2R. Under normoxia, angiotensin IIincreased the level of VEGF mRNA in ASCs, which was abolished by irbesartan. Under hypoxia, irbesartanreduced the level of VEGF mRNA in ASCs regardless of whether angiotensin IIwas present or not. In the in vivo studies, ASC sheets improved cardiac functions after MI, leading to decreased interstitial fibrosis and increased capillary density in border zones. These effects of ASC sheets were abolished by oral administration of irbesartanbefore MI and their transplantation. Conclusions ASC sheets ameliorated cardiac dysfunctions and remodeling after MI via increasing VEGF expression, which was abolished by pretreatment with irbesartanbefore the creation of MI and transplantation.