Altered Ovarian Sterol Carrier Protein Expression in the Pregnant Streptozotocin-Treated Diabetic Rat1

Abstract

Reproductive dysfunction in the diabetic female rat is associated with impaired folliculogenesis, reduced corpus luteum progesterone output, and spontaneous abortion. The underlying mechanism for reduced steroid production remains unresolved. In this study we examined whether or not diabetes alters levels of P450 side-chain cleavage enzyme (P450scc), 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), or the cholesterol transport proteins, steroidogenic acute regulatory (StAR) protein and sterol carrier protein-2 (SCP2), leading to lower progesterone levels and pregnancy loss. Rats (Day 3 pregnant) received an injection of streptozotocin (STZ, 60 mg/kg; i.v.) to induce a diabetic state; P450scc, 3 beta-HSD, and SCP2 were examined by Western and Northern blot analysis in ovarian tissue 12 days after injection of STZ (diabetic rats, n = 12) or vehicle (nondiabetic rats, n = 12). Serum progesterone, triglyceride, and beta-hydroxybutyrate (beta-HBA) levels were also examined. Results indicate that diabetic rats that aborted (diabetic-fetus [Ft], n = 6) had significantly lower progesterone levels (7.04 +/- 2.6 ng/ml; p < 0.004) than nondiabetic animals (108.6 +/- 5.15 ng/ml) and diabetic +Ft animals (74.3 +/- 8.9 ng/ml, n = 6). Western blot analysis of ovarian P450scc and 3 beta-HSD in the nondiabetic rats and the diabetic rats with fetuses indicated no significant difference. In contrast, ovaries from diabetic animals without fetuses had significantly lower SCP2 levels (p < 0.017) compared to controls. Concomitant with the reduction in SCP2, a 58-kDa SCP2-immunoreactive protein, referred to as sterol carrier protein-X (SCPx), increased significantly (p < 0.001). The C-terminal sequence of SCPx is identical to SCP2, while its N-terminal region is homologous with 3-oxoacyl coenzyme A thiolase, an enzyme involved in fatty acid metabolism. Increased SCPx expression coincided with increased serum triglyceride and beta-HBA levels, suggesting that the enhanced SCPx level may coincide with an ovarian shift to fatty acid metabolism. When SCPx steady-state mRNA levels were measured using an SCPx-specific riboprobe (280-bp protected fragment) in a ribonuclease protection assay, ovarian SCPx mRNA levels in the diabetic animals were increased 4.2-fold compared to control SCPx mRNA levels. Ovarian StAR mRNA levels were increased slightly in the diabetic animals, and ovarian P450scc and 3 beta-HSD mRNA levels were increased 3-fold in the diabetic animals that aborted relative to the nondiabetic animals and the +Ft diabetic animals. Results of this study confirm that SCPx mRNA levels are elevated following diabetes onset and that StAR, P450scc, and 3 beta-HSD mRNA levels do not correspond with the reduced steroid hormone profile associated with diabetes. These results are concordant with the possibility that reduced steroid levels in the diabetic animals reflect a loss of SCP2-mediated cholesterol transport capacity as SCPx/3-oxoacyl coenzyme A thiolase expression is enhanced.

Effects of high levels of glucose on the steroidogenesis and the expression of adiponectin receptors in rat ovarian cells

“…In the present study, no decrease in the amounts of 3βHSD and p450 aromatase was observed whereas the levels of StAR and p450scc proteins were increased in the ovaries of STZ-treated animals. These data are in a good agreement with other studies that report no alteration to p450scc or 3βHSD [ 47 ]. Possibly, the activity of these key steroidogenesis enzymes is decreased in STZ-treated rats and this could explain the decline in steroid production in these animals.…”

Neonatally Induced Mild Diabetes in Rats and Its Effect on Maternal, Placental, and Fetal Parameters

“…As a result, the morphometric alteration of the decidua is directly related to the reduced number of implantations and the increased rate of embryonic losses in the group with mild diabetes observed in our study. The disorders in reproduction in diabetic rats have been associated to dysfunctions in the hypothalamic-hypophysis-gonadal axis [48], and severe diabetic dams presented reduced progesterone levels (approximately 35%) even presenting at term fetuses compared to nondiabetic dams [49]. …”

Sterol carrier protein-2: structure reveals function

“…SCP-2 levels are altered in a number of diseases where lipid metabolism is abnormal, including diabetes, Zellweger, Niemann Pick C (NPC), and atherosclerosis. Streptozotocin-induced diabetes in rats decreased liver levels of 13-kDa SCP-2 by 60 -90 % [39], and ovarian levels by 60 % [40]. Reduced 13-kDa SCP-2 expression in the pregnant, diabetic rat was associated with pregnancy loss [41].…”