New in vitro model to study high glucose-dependent endothelial dysfunctions

Short-term hyperglycaemia causes non-reversible changes in arterial gene expression in a fully 'switchable' in vivo mouse model of diabetes

AIMS/HYPOTHESIS

Irreversible arterial damage due to early effects of hypo- or hyperglycaemia could account for the limited success of glucose-lowering treatments in preventing cardiovascular disease (CVD) events. We hypothesised that even brief hypo- or hyperglycaemia could adversely affect arterial gene expression and that these changes, moreover, might not be fully reversible.

METHODS

By controlled activation of a 'switchable' c-Myc transgene in beta cells, adult pIns-c-MycER(TAM) mice were rendered transiently hypo- and then hyperglycaemic, after which they were allowed to recover for up to 3 months. Immediate and sequential changes in aortic global gene expression from normal glycaemia through hypo- and hyperglycaemia to recovery were assessed.

RESULTS

Gene expression was compared with that of normoglycaemic transgenic and tamoxifen-treated wild-type controls. Overall, expression of 95 genes was significantly affected by moderate hypoglycaemia (glucose down to 2.5 mmol/l), whereas over 769 genes were affected by hyperglycaemia. Genes and pathways activated included several involved in atherogenic processes, such as inflammation and arterial calcification. Although expression of many genes recovered to initial pre-exposure levels when hyperglycaemia was corrected (74.9%), in one in four genes this did not occur. Quantitative reverse transcriptase PCR and immunohistochemistry verified the gene expression patterns of key molecules, as shown by global gene arrays.

CONCLUSIONS/INTERPRETATION

Short-term exposure to hyperglycaemia can cause deleterious and persistent changes in arterial gene expression in vivo. Brief hypoglycaemia also adversely affects gene expression, although less substantially. Together, these results suggest that early correction of hyperglycaemia and avoidance of hypoglycaemia may both be necessary to avoid excess CVD risk in diabetes.

Hyperglycemia attenuates angiogenic capability of survivin in endothelial cells

Survivin, an anti-apoptotic protein, can be induced by hypoxia and contributes to angiogenic activity in endothelial cells. To determine the potential mechanism of survivin in endothelial dysfunction caused by hyperglycemia in diabetes, we evaluated the role of survivin in hyperglycemia and its effect on endothelial homeostasis. We demonstrated that an increase of D-glucose was sufficient to down-regulate survivin expression, impacting survivin's angiogenic role in endothelial cells. We additionally showed that survivin expression was increased in response to hypoxia yet this reaction was mitigated when the endothelial cells were in hyperglycemic conditions prior to hypoxia. Hyperglycemia also affected survivin-related proliferation and migration of endothelial cells and increased the number of apoptotic cells. In the ischemic porcine myocardium, the expression of survivin was induced. Moreover, survivin expression in the aorta, myocardium, and isolated endothelial cells was attenuated in a porcine model of diabetes in comparison to non-diabetes, which correlated negatively with the levels of fasting blood sugars and positively with territory perfusion. These results demonstrate that hyperglycemia critically alters survivin expression in vitro and in vivo, which leads to attenuation of angiogenic activity and impacts endothelial metabolism.

Direct isolation, culture and transplant of mouse skeletal muscle derived endothelial cells with angiogenic potential

BACKGROUND

Although diseases associated with microvascular endothelial dysfunction are among the most prevalent illnesses to date, currently no method exists to isolate pure endothelial cells (EC) from skeletal muscle for in vivo or in vitro study.

METHODOLOGY

By utilizing multicolor fluorescent-activated cell sorting (FACS), we have isolated a distinct population of Sca-1(+), CD31(+), CD34(dim) and CD45(- )cells from skeletal muscles of C57BL6 mice. Characterization of this population revealed these cells are functional EC that can be expanded several times in culture without losing their phenotype or capabilities to uptake acetylated low-density lipoprotein (ac-LDL), produce nitric oxide (NO) and form vascular tubes. When transplanted subcutaneously or intramuscularly into the tibialis anterior muscle, EC formed microvessels and integrated with existing vasculature.

CONCLUSION

This method, which is highly reproducible, can be used to study the biology and role of EC in diseases such as peripheral vascular disease. In addition this method allows us to isolate large quantities of skeletal muscle derived EC with potential for therapeutic angiogenic applications.