Ablation of steroidogenic superoxide dismutase 2 increases oxidative stress and diminishes steroid hormone production.

Abstract

Mitochondria are a major source of reactive oxygen species, such as superoxide anion (O2●─), contain the enzyme complexes of the electron transport chain and, in steroidogenic tissues, steroid hormone synthesizing P450 enzymes. Superoxide dismutase 2 (SOD2) is the main antioxidant enzyme localized in mitochondria for protection from oxidative insult by enzymatically converting O2●─ into H2O2, which is further degraded into H2O and O2. Although expressed at high levels in steroidogenic tissues and transcriptionally regulated by trophic hormones, SOD2's role in the regulation of steroid hormone production is not fully explored. To address its role in regulating steroidogenesis, we generated adrenal, ovary and testis tissue specific SOD2-deficient mice. Adrenal/testis and adrenal/ovary SOD2-deficient mice exhibited a marked reduction in hormone stimulated corticosterone/testosterone and corticosterone/progesterone secretion in vivo, and hormone- or hormone + high density lipoprotein-stimulated steroid production by steroidogenic tissues in vitro, respectively. RT-qPCR measurements demonstrated dramatic reduction in mRNA levels of steroidogenic P450 enzymes and cholesterol transport protein, StAR. Small, but significant, declines in mRNA levels of certain hydroxysteroid dehydrogenases were also noted. Cellular levels of key biomarkers of oxidative stress revealed that mice with steroidogenic SOD2-deficiency exhibit high oxidative stress. Steroidogenic MLTC-1 cell lines stably overexpressing pairs of mitochondrial antioxidant enzymes, Sod2-catalase, Sod2-glutathione peroxidase-1 or Sod2-glutathione peroxidase-4, showed complete protection against oxidant-mediated suppression of steroidogenesis. These results led us to conclude that SOD2 plays an essential role in the regulation of steroidogenesis and that SOD2-deficiency-induced excessive oxidative stress adversely affects steroid production in mouse adrenal glands, ovary, and testis.