Does endogenous testosterone mediate the lower preconditioning threshold in males?

Sex steroids and stem cell function

Gender dimorphisms exist in the pathogenesis of a variety of cardiovascular, cardiopulmonary, neurodegenerative, and endocrine disorders. Estrogens exert immense influence on myocardial remodeling following ischemic insult, partially through paracrine growth hormone production by bone marrow mesenchymal stem cells (MSCs) and endothelial progenitor cells. Estrogens also facilitate the mobilization of endothelial progenitor cells to the ischemic myocardium and enhance neovascularization at the ischemic border zone. Moreover, estrogens limit pathological myocardial remodeling through the inhibitory effects on the proliferation of the cardiac fibroblasts. Androgens also may stimulate endothelial progenitor cell migration from the bone marrow, yet the larger role of androgens in disease pathogenesis is not well characterized. The beneficial effects of sex steroids include alteration of lipid metabolism in preadipocytes, modulation of bone metabolism and skeletal maturation, and prevention of osteoporosis through their effects on osteogenic precursors. In an example of sex steroid-specific effects, neural stem cells exhibit enhanced proliferation in response to estrogens, whereas androgens mediate inhibitory effects on their proliferation. Although stem cells can offer significant therapeutic benefits in various cardiovascular, neurodegenerative, endocrine disorders, and disorders of bone metabolism, a greater understanding of sex hormones on diverse stem cell populations is required to improve their ultimate clinical efficacy. In this review, we focus on the effects of estrogen and testosterone on various stem and progenitor cell types, and their relevant intracellular mechanisms.

Stem Cells Improve Right Ventricular Functional Recovery After Acute Pressure Overload and Ischemia Reperfusion Injury

BACKGROUND

In many clinical scenarios, a relatively untrained right ventricle may be subjected to acute elevations in pulmonary artery and right ventricular pressures. The right and left heart are distinctly different in this regard and there is currently no in vivo model to study right ventricular ischemia in the setting of acute pressure overload. In acute injury, cardiomyocytes produce tumor necrosis factor, which mediates a proinflammatory pathway, eventually leading to myocardial dysfunction. Stem cells have been shown to reduce the production of proinflammatory mediators by the ischemic myocardium and protect the myocardium. Pretreatment with stem cells has been shown to protect the left ventricle. The effect of acute pressure overload to the untrained right ventricle is still not well understood. Furthermore, it is unclear whether pretreatment with stem cells would protect the right ventricle when it is subjected to acute pressure overload and concomitant ischemia reperfusion injury. The purpose of this study was (1) to create a simple model of acute pressure overload for the study of concomitant right ventricular ischemia and reperfusion, and (2) to evaluate the effect of pretreatment with stem cells prior to ischemia reperfusion injury.

MATERIALS AND METHODS

Isolated rat hearts were perfused with the modified Langendorff technique with the latex balloon in the right ventricle instead of the left, with a pressure-transduced balloon being used to create an acute elevation in right ventricular pressure before ischemia. In the first of a two-series experiment, there were two experimental groups (N = 8 per group): one with right ventricular balloon end-diastolic pressure (EDP) of 5 mmHg (physiological), and the other with an EDP of 40 mmHg (pathologic). In the second series, the hearts with the higher balloon pressure (EDP 40 mmHg) were divided into two experimental groups (N = 5 per group). The control group was not pretreated. One group was pretreated with human mesenchymal stem cells 5 min immediately prior to ischemia reperfusion injury. Right ventricular developed pressure (RVDP), contractility (+dP/dt), and compliance (-dP/dt) were continuously assessed. Additionally, mesenchymal stem cells (MSCs) in culture were stressed by hypoxia and activation was determined by measuring vascular endothelial growth factor-A (VEGF) and hepatocyte growth factor (HGF) production by enzyme-linked immunosorbent assay.

RESULTS

Recovery of RVDP, +dP/dt, and -dP/dt was significantly higher (P < 0.001) in the group with lower EDP compared to the group with the higher EDP [RVDP: 79.53 +/- 6.34 versus 54.28 +/- 10.76%; +dP/dt: 76.54 +/- 8.79 versus 38.75 +/- 19.74%; -dP/dt: 72.29 +/- 7.02 versus 30.54 +/- 12.44%]. In the higher EDP groups, pretreatment with human mesenchymal stem cells significantly improved myocardial function recovery (P < 0.01) when compared to controls [RVDP: 75.76 +/- 7.97 versus 59.10 +/- 11.18%; +dP/dt: 71.78 +/- 10.36 versus 54.93 +/- 12.64%; -dP/dt: 77.38 +/- 11.09 versus 59.30 +/- 15.20%]. Further, hypoxic MSCs demonstrated significantly greater VEGF and HGF release than controls.

CONCLUSION

This compounded injury model allowed the study of right ventricular dysfunction in the setting of acute pressure overload and ischemia. Additionally, we have also demonstrated that pretreatment with stem cells of an acutely pressure overloaded right ventricle prior to ischemia reperfusion injury improves functional recovery. This is the first report of a modified Langendorff technique to study right ventricular function in the setting of acute pressure overload and ischemia and the effect of pretreatment with stem cells.