Hypoxia-induced apoptosis in cultured glomerular endothelial cells: involvement of mitochondrial pathways

Glomerular endothelial cells (GENs) play a key role in the preservation and reconstruction of the glomerular capillary network following injury, thus maintaining the tissue oxygenation. Accumulating evidence has shown that failure to maintain the microcirculation leads to irreversible glomerular injury and glomerular sclerosis. In this regard, the behavior of endothelial cells in a hypoxic milieu is of interest.

We exposed cultured GENs to hypoxia and observed apoptosis by annexin V assay. We examined mitochondrial signaling, focusing on Bcl2 and Bax by real-time polymerase chain reaction (PCR), immunocytochemistry, and immunoprecipitation. Furthermore, we examined the response to hypoxia in an overexpression model of Bcl2.

Hypoxic treatment induced apoptosis in 12.8%+/- 1.1% of GENs at 24 hours, and in 19.8%+/- 0.9% at 24 hours followed by 8 hours of reoxygenation. The expression of Bcl2 mRNA decreased to 0.45- +/- 0.15-fold at 24 hours, whereas that of Bax increased to 7.3- +/- 1.2-fold 1 hour after reoxygenation, accompanied by translocation from the cytosol to mitochondria. These changes were associated with a decrease in mitochondrial membrane potentials and an increase in caspase-9 activity. Both overexpression of Bcl2 and inhibition of Bax protected GENs from hypoxic injury.

We conclude that changes of quantity and localization of Bcl2 and Bax contribute to hypoxia-mediated apoptosis of GENs in vitro. Further investigation into glomerular endothelial cell injury and intracellular signaling in a hypoxic milieu is required to better understand and ultimately prevent progression of chronic kidney disease.