The Interaction between female sex hormone receptors and osteopontin in a rat hyperoxaluric model.

It is well known that the incidence of urinary stones is higher in men than women. Although it is believed that the lower incidence of urinary stones in women is due to a protective effect of estrogen, the mechanisms remain unclear. To clarify the relation between female sex hormones and stone matrix protein, we examined the interaction of estrogen receptor-α (ERα), estrogen receptor-related receptor-α (ERRα), and stone matrix protein osteopontin (OPN) in a rat hyperoxaluric model and in primary cultured rat kidney cells. Adult female Wistar rats were divided into 6 groups. Groups 1 and 4 consisted of normal females, Groups 2 and 5 consisted of ovariectomized females, and Groups 3 and 6 consisted of ovariectomized females receiving female sex hormone supplements. Groups 1-3 were administered distilled water, while groups 4-6 were administered 0.5% ethyleneglycol (EG). Moreover, rat kidney primary cultured cells were examined after treatment with female sex hormones under various conditions. The expressions of ERα, ERRα and OPN-mRNA in whole kidney and primary cultured cells were examined using Real-Time PCR. The expressions of OPN and ERRα-mRNA were suppressed by ovariectomy. Supplementation with female sex hormones increased the expression of OPN and ERRα-mRNA. In contrast, the expression of ERα-mRNA was increased by ovariectomy and suppressed by supplementation with female sex hormones. The results of the mRNA expression in primary cultured cells matched those in the hyperoxaluric model rats. Although the reason for the difference in expression between ERα and ERRα-mRNA is unclear, estrogen may regulates OPN expression through ERα and/or ERRα, either independently or in combination. Moreover, the decrease of OPN induced by removal of estrogen may increase urinary stones in postmenopausal women.