Cardioprotection mediated by exosomes is impaired in the setting of type II diabetes but can be rescued by the use of non-diabetic exosomes in vitro.

Many patients with ischaemic heart disease also have diabetes. As myocardial infarction is a major cause of mortality and morbidity in these patients, treatments that increase cell survival in response to ischaemia and reperfusion are needed. Exosomes-nano-sized, lipid vesicles released from cells-can protect the hearts of non-diabetic rats. We previously showed that exosomal HSP70 activates a cardioprotective signalling pathway in cardiomyocytes culminating in ERK1/2 and HSP27 phosphorylation. Here, we investigated whether the exosomal cardioprotective pathway remains intact in the setting of type II diabetes. Exosomes were isolated by differential centrifugation from non-diabetic and type II diabetic patients, from non-diabetic and Goto Kakizaki type II diabetic rats, and from normoglycaemic and hyperglycaemic endothelial cells. Exosome size and number were not significantly altered by diabetes. CD81 and HSP70 exosome markers were increased in diabetic rat exosomes. However, exosomes from diabetic rats no longer activated the ERK1/2 and HSP27 cardioprotective pathway and were no longer protective in a primary rat cardiomyocytes model of hypoxia and reoxygenation injury. Hyperglycaemic culture conditions were sufficient to impair protection by endothelial exosomes. Importantly, however, exosomes from non-diabetic rats retained the ability to protect cardiomyocytes from diabetic rats. Exosomes from diabetic plasma have lost the ability to protect cardiomyocytes, but protection can be restored with exosomes from non-diabetic plasma. These results support the concept that exosomes may be used to protect cardiomyocytes against ischaemia and reperfusion injury, even in the setting of type II diabetes.

Plasma exosomes protect the myocardium from ischemia-reperfusion injury.

BACKGROUND: Exosomes are nanometer-sized vesicles released from cells into the blood, where they can transmit signals throughout the body. Shown to act on the heart, exosomes' composition and the signaling pathways they activate have not been explored. We hypothesized that endogenous plasma exosomes can communicate signals to the heart and provide protection against ischemia and reperfusion injury. OBJECTIVES: This study sought to isolate and characterize exosomes from rats and healthy volunteers, evaluate their cardioprotective actions, and identify the molecular mechanisms involved. METHODS: The exosome-rich fraction was isolated from the blood of adult rats and human volunteers and was analyzed by protein marker expression, transmission electron microscopy, and nanoparticle tracking analysis. This was then used in ex vivo, in vivo, and in vitro settings of ischemia-reperfusion, with the protective signaling pathways activated on cardiomyocytes identified using Western blot analyses and chemical inhibitors. RESULTS: Exosomes exhibited the expected size and expressed marker proteins CD63, CD81, and heat shock protein (HSP) 70. The exosome-rich fraction was powerfully cardioprotective in all tested models of cardiac ischemia-reperfusion injury. We identified a pro-survival signaling pathway activated in cardiomyocytes involving toll-like receptor (TLR) 4 and various kinases, leading to activation of the cardioprotective HSP27. Cardioprotection was prevented by a neutralizing antibody against a conserved HSP70 epitope expressed on the exosome surface and by blocking TLR4 in cardiomyocytes, identifying the HSP70/TLR4 communication axis as a critical component in exosome-mediated cardioprotection. CONCLUSIONS: Exosomes deliver endogenous protective signals to the myocardium by a pathway involving TLR4 and classic cardioprotective HSPs.

Remote ischaemic preconditioning involves signalling through the SDF-1α/CXCR4 signalling axis.

Ischaemic preconditioning is one of the most potent experimental modalities known to decrease infarct size after ischaemia and reperfusion. Much interest has been stimulated by the phenomenon of remote ischaemic conditioning (RIC), in which the preconditioning stimulus is applied to a limb remote from the heart to stimulate cardioprotection via an unidentified humoral factor, believed to be a protein between 3.5 and 15 kDa. Stromal cell-derived factor-1 (SDF-1α or CXCL12) is a chemokine of 10 kDa that is induced by hypoxia and recruits stem cells, but also exerts direct, acute, cardioprotection via its receptor, CXCR4. The serum dipeptidase DPPIV cleaves and inactivates SDF-1α. We measured SDF-1α in rat plasma and found it was significantly increased by RIC. DPPIV activity was unchanged after RIC, suggesting that increased synthesis or release or SDF-1α caused the increase in plasma levels. AMD3100, a highly specific inhibitor of CXCR4, was used to investigate the hypothesis that SDF-1α is involved in RIC. RIC in rats, which decreased infarct size from 53 ± 3 % to 27 ± 3 % (n = 6, P < 0.05), was blocked in rats treated with AMD3100 (40 ± 4 %). RIC also improved functional recovery of cardiac papillary muscle, and this, too, was blocked by AMD3100. Direct application of SDF-1α was confirmed to be protective in this model and was blocked by AMD3100. RIC stimulates SDF-1α release, and this 10-kDa peptide appears to be required for the mechanism of RIC.