Expression and signaling of parathyroid hormone-related protein in cultured podocytes

Podocyte function appears to be regulated by vasoactive factors. In vivo po docytes express parathyroid hormone-related protein (PTHrP), the N-terminal fragment of which has vasoactive properties. Since the signaling pathway(s ) of PTHrP(1-36) are unknown in podocytes, differentiated cells of a condit ionally immortalized mouse podocyte cell line were studied. Gene expression of PTHrP and the PTH/PTHrP receptor was investigated by RT-PCR; protein di stribution of PTHrP was examined by immunofluorescence. Accumulation of cAM P was determined by an enzyme immunoassay; [Ca2+](i) was measured by fura-2 ratio imaging. PTHrP and PTH/PTHrP receptor mRNA was detected in different iated podocytes. Immunoreactive PTHrP exhibited a granular distribution in the cytoplasm of differentiated podocytes. With regard to the signaling pat hway(s) of PTHrP(1-36), a concentration-dependent increase of cAMP levels w ith an EC50 value of 4 +/- 2 nM was found. PTHrP(1-36) (1 muM) increased cA MP levels 5.5 +/- 1.1-fold above baseline as compared with a 25.4 +/- 4.2-f old increase in response to forskolin (10 muM). The PTH/PTHrP receptor anta gonist PTHrP(7-34) significantly diminished the PTHrP(1-36)induced cAMP inc rease. While superfusion of podocytes with bradykinin (100 nM) increased [C a2+](i), PTHrP(1-36) (100 nM) was without effect on [Ca2+](i). However, PTH rP(1-36) attenuated the bradykinin-induced increase in [Ca2+](i). Our resul ts suggest that PTHrP is an autocrine hormone in podocytes, which selective ly activates the cAMP pathway through the PTH/PTHrP receptor. Copyright (C) 2001 S. Karger AG, Basel.