Enzyme replacement therapy for Fabry disease: proving the clinical benefit.

Abstract

Gender differences in the renal excretion of p-aminohippurate (PAH) and other organic anions are well established. The organic anion transporter OAT1, a member of the OAT family that plays a major role in secretion of various organic anions, has been immunolocalized in human and rat kidneys to the basolateral membrane (BLM) of the S2 proximal tubule segment. In rats, the expression of OAT1 protein was found to be stronger in males (M) than in females (F), whereas the existence of gender differences at the level of mRNA is still controversial. Hormones responsible for the observed gender differences in renal OAT1 have not been established. By using immunofluorescence cytochemistry in cryosections of fixed renal tissue as well as immunoblotting of isolated renal cortical BLM and total cell membranes, we studied localization and the abundance of OAT1 in adult and prepubertal M and F rats, as well as an effect of gonadectomy and steroid hormone replacement therapy in gonadectomized adult animals. The predominant localization of the OAT1 protein in the BLM of the S2 segment, and gender differences in its expression in adult rats (M > F) were confirmed. As found by immunocytochemistry, cells along the proximal tubule S3 segments also exhibited a limited expression of OAT1 both in the BLM and intracellularly. Two weeks following castration, the abundance of OAT1 in cortical total cell membranes of adult M decreased by 45%, whereas daily treatment of castrated M with testosterone, estradiol, or progesterone (each: 2.5 mg/kg b.m., s.c. for 8 days) resulted in a complete restitution, further depression (by 88%), or overexpression (by 22%) of the protein, respectively. In adult F rats, ovariectomy had no effect, whereas the treatment of ovariectomized animals with estradiol caused a strong decrease (by 73%) of OAT1 abundance in renal cortical membranes. The observations by immunocytochemistry in renal cortical tissues from sham-operated, gonadectomized and hormone-treated rats completely matched the findings in immunoblotting experiments. In prepubertal (4 week-old) rats, the abundance of OAT1 protein in cortical membranes, and the intensity of immunostaining in tissue cryosections were low, exhibiting no gender differences. Our data indicate that gender differences in renal OAT1 (M > F) appear after puberty and are determined by both a stimulatory effect of androgens and progesterone, and an inhibitory effect of estrogens.