Abstract
Purpose :
Aging is a significant risk factor for neurovascular injury in diseases such as diabetic retinopathy. This is in part attributable to declined function of progenitor cells to repair and replenish damaged endothelium resulting in sustained damage and loss of blood vessels. Herein, we investigated the role of NADPH oxidase 4 (Nox4), a key regulator of redox homeostasis, in endothelial progenitor function and senescence associated with retinal changes during aging.
Methods :
Bone marrow-derived endothelial outgrowth cells (EOCs) were isolated and cultured from Tie2-specific human Nox4 overexpression (Nox4-Tg) mice or Nox4 KO mice at ages 5, 8, 12, and 24 months. EOC cell proliferation, migration, senescence, apoptosis, ROS generation were determined. Gene expression of signaling pathways underlying the cellular events were examined.
Results :
The mRNA and protein levels of Nox4 were markedly increased, accompanied by enhanced ROS levels, in EOCs from mice of age 12 months, and to a signigicantly greater extent in EOCs from 24 month-old mice, when compared to young adults. Substantial increase of Nox4 and ROS were confirmed in EOCs from Nox4 Tg mice and reduction in Nox4 KO EOCs. Age or overexpression of NOX4 showed no effect on cell proliferation, but led to a significant increase in apoptosis and senescence of EOCs. Nox4 deletion significantly attenuated apoptosis, reduced pro-apoptotic gene CHOP expression, and inhibited caspase-3 activation in aging EOCs. Nox4 deletion also significantly decreased p53 and p21 expression, and demonstrated a trend in reducing senescence of aging EOCs. In addition, knockout Nox4 markedly improved the basal level and stromal derived factor-1 (SDF-1)-stimulated EOC migration through upregulation of CXCR4. Consistent with the changes in EOCs, Nox4 Tg mice demonstrated significantly increased acellular capillary formation in the retina compared to age-matched wild type.
Conclusions :
Our results suggest that Nox4-derived ROS is implicated in age-related endothelial progenitor cell apoptosis and senescence. Approaches that manipulate Nox4 and ROS production may improve the function of endothelial progenitor cells thus reducing the risk of vascular damage in retinal diseases.
This is a 2021 ARVO Annual Meeting abstract.