Senescence marker protein-30/gluconolactonase expression in the mouse ovary during gestation

Senescence marker protein-30 (SMP30) was first described as a physiologic entity that decreases in the rat liver and kidney with aging. Previously, we established that SMP30 is the lactone-hydrolyzing enzyme gluconolactonase (GNL), which is involved in ascorbic acid (AA) biosynthesis. In the present study, we found SMP30/GNL mRNA expressed in the mouse ovary. To ascertain the reason for ovarian SMP30/GNL expression, we examined mice during gestation. SMP30/GNL mRNA expression was evident at the start of gestation, increased for the next eight days then decreased rapidly. Moreover, L-gulono-γ-lactone oxidase (Gulo) mRNA, which catalyzes the last step of AA, was found in the ovaries of these mice. The variations of these genes' expression showed an inverse pattern to that of Cyp19a1 (aromatase) mRNA expression. Therefore, the SMP30/GNL and Gulo mRNA expression might be regulated by estrogen levels in the ovary. Since the presence of both SMP30/GNL and Gulo mRNAs could indicate that AA synthesis occurs in the ovary, we quantified AA levels in mouse ovaries during gestation. However, no correlation was found between changes of AA content and SMP30/GNL or Gulo mRNAs expression at this site. Moreover, we compared the changes of AA content during gestation between wild-type and SMP30/GNL knockout mice, which cannot synthesize AA, and found no significant differences between them. These results indicated that, although AA synthesis might occur in the ovaries, the amount of AA which is synthesized in ovaries must be quite low and insufficient to influence the AA content in ovary.