Adiponectin Stimulates Exosome Release to Enhance Mesenchymal Stem-Cell-Driven Therapy of Heart Failure in Mice.

Mesenchymal stem/stromal cells (MSCs) are cultured adult stem cells that originally reside in virtually all tissues, and the gain of MSCs by transplantation has become the leading form of cell therapy in various diseases. However, there is limited knowledge on the alteration of its efficacy by factors in recipients. Here, we report that the cardioprotective properties of intravenously injected MSCs in a mouse model of pressure-overload heart failure largely depend on circulating adiponectin, an adipocyte-secreted factor. The injected MSCs exert their function through exosomes, extracellular vesicles of endosome origin. Adiponectin stimulated exosome biogenesis and secretion through binding to T-cadherin, a unique glycosylphosphatidylinositol-anchored cadherin, on MSCs. A pharmacological or adenovirus-mediated genetic increase in plasma adiponectin enhanced the therapeutic efficacy of MSCs. Our findings provide novel insights into the importance of adiponectin in mesenchymal-progenitor-mediated organ protections.

Loss of Endogenous HMGB2 Promotes Cardiac Dysfunction and Pressure Overload-Induced Heart Failure in Mice.

BACKGROUND: The rapid increase in the number of heart failure (HF) patients in parallel with the increase in the number of older people is receiving attention worldwide. HF not only increases mortality but decreases quality of life, creating medical and social problems. Thus, it is necessary to define molecular mechanisms underlying HF development and progression. HMGB2 is a member of the high-mobility group superfamily characterized as nuclear proteins that bind DNA to stabilize nucleosomes and promote transcription. A recent in vitro study revealed that HMGB2 loss in cardiomyocytes causes hypertrophy and increases HF-associated gene expression. However, it's in vivo function in the heart has not been assessed. Methods and Results: Western blotting analysis revealed increased HMGB2 expression in heart tissues undergoing pressure overload by transverse aorta constriction (TAC) in mice. Hmgb2 homozygous knockout (Hmgb2-/-) mice showed cardiac dysfunction due to AKT inactivation and decreased sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2a activity. Compared to wild-type mice, Hmgb2-/- mice had worsened cardiac dysfunction after TAC surgery, predisposing mice to HF development and progression. CONCLUSIONS: This study demonstrates that upregulation of cardiac HMGB2 is an adaptive response to cardiac stress, and that loss of this response could accelerate cardiac dysfunction, suggesting that HMGB2 plays a cardioprotective role.

Circulating ANGPTL2 Levels Increase in Humans and Mice Exhibiting Cardiac Dysfunction.

BACKGROUND: Recently, it was reported that angiopoietin-like protein 2 (ANGPTL2) secreted from a pathologically stressed heart accelerates cardiac dysfunction in an autocrine/paracrine manner, and that suppression of ANGPTL2 production in the heart restored cardiac function and myocardial energy metabolism, thereby blocking heart failure (HF) development. Interestingly, circulating ANGPTL2 concentrations reportedly increase in HF patients, suggesting a possible endocrine effect on cardiac dysfunction. However, it remains unclear why circulating ANGPTL2 increases in those subjects and whether circulating ANGPTL2 alters cardiac function in an endocrine manner.Methods and Results:It was found that circulating ANGPTL2 levels are positively correlated with left atrial diameter and pulmonary capillary wedge pressure, and are inversely proportional to the percent of ejection fraction in patients with dilated cardiomyopathy. Furthermore, in mice, circulating ANGPTL2 concentrations increased as HF developed following transverse aorta constriction (TAC), and were inversely correlated with the percent of fractional shortening. Interestingly, although circulating ANGPTL2 concentrations significantly increased in transgenic mice overexpressing keratinocyte-derived ANGPTL2, no pathological cardiac remodeling was seen. Furthermore, it was observed that there was no difference in HF development between transgenic mice and controls following TAC surgery. CONCLUSIONS: Circulating ANGPTL2 levels increase in subjects experiencing cardiac dysfunction. However, circulating ANGPTL2 does not promote cardiac dysfunction in an endocrine manner, and increased levels of circulating ANGPTL2 seen during HF are a secondary effect of increased ANGPTL2 secretion from stressed hearts in HF pathologies.

Macrophages activate iNOS signaling in adventitial fibroblasts and contribute to adventitia fibrosis.

A large amount of NO is generated through the inducible nitric oxide synthase (iNOS) pathway from the vascular adventitia in various vascular diseases. However, it is currently not fully understood how the iNOS signaling pathway is activated. In the present study, this question was addressed in the context of adventitial cellular interactions. A rat model of acute hypertension in the contralateral carotid arteries was established through transverse aortic constriction (TAC) surgery. In this model, activated macrophages were found surrounded by a large quantity of iNOS-expressing adventitial fibroblasts (AFs), suggesting a possible causal relationship between macrophages and iNOS activation of the neighboring AFs. In an in vitro model, a macrophage-like cell line RAW 264.7 was first activated by LPS treatment. The supernatant was then harvested and applied to treat primary rat AFs. iNOS in AFs was activated robustly by the supernatant treatment but not by LPS itself. Treating AFs with interleukin-1ß (IL-1ß) also activated iNOS signaling, suggesting that the IL-1ß pathway might be a possible mediator. As a consequence of the iNOS activation, total protein nitration and S-nitrosylation significantly increased in those AFs. Additionally, increased deposition of type I and type III collagens was observed in both in vitro and in vivo models. The collagen deposition was partially restored by an iNOS inhibitor, 1400 W. These findings highlight the importance of iNOS signaling during vascular inflammation, and advance our understanding of its activation through a cellular interaction perspective.