Parathyroid hormone-related protein (PTHrP) is present in the kidney, where it modulates glomerular function, and also has a mitogenic effect. Both parathyroid hormone (PTH) and PTHrP bind to a common PTH/PTHrP receptor (PTH1R). In a previous study (Garrido et al. 2001) we have found renal PTHrP up-regulation in STZ-induced diabetic nephropathy (DN).
In the present study we analysed the expression of the PTH1R in STZ-induced DN in CD mice as well as the expression of PTHrP and PTH1R in human mesangial cells (HMC) and mice tubular cells (MTC) in the presence and in the absence of high glucose (450 mg dl-1) and/or insulin (10 mg ml-1). Moreover we performed immunohistochemistry for PTHrP and PTH1R in the renal biopsies of six patients with DN, including two patients with type 1 and four patient with type II diabetes mellitus (aged 43 ± 3 years, with 10 ± 3 years of diabetes mellitus). Statistical analysis was performed by Kruskall-Wallis or Mann-Whitney test as appropriate. P < 0.05 was considered significant. All the experimetal were previously approved by the local commitee for human and animal reseach and are in agreement with the Declaration of Helsinki. Animals were killed under ether anaesthesia.
In diabetic mice, we observed an increase (of 2.5-fold over the control, P < 0.05) PTH1R from the second to the seventh week after the diabetes induction (Western blot and immunohistochemistry). Both HMC and MCT cells cultured in high glucose showed a PTHrP up-regulation (4- and 3.5-fold over the control, respectively, P < 0.05). In addition, in the latter cells we also observed an up-regulation of PTH1R (2.5-fold over the control, P < 0.05). In MCT, but not in HMC, insulin treatment was able to prevent the up-regulation of PTHrP induced by high glucose (Western blot and RPA).
In normal human kidney, PTHrP and PTH1R staining was only observed at the tubular level. In contrast, a dramatic PTHrP staining was observed at the glomerular level in all patients studied. Glomerular PTH1R staining was observed in three of the six patients studied.
Our study demonstrates the renal up-regulation of PTHrP and PTH1R in both mice and human with DN. Moreover, in vitro findings indicate that PTHrP expression can be modulated by high glucose and/or insulin in these renal cells. Taken together these findings strongly suggest a role of PTHrP in the pathophysiology of diabetic nephropathy.
This work was supported by Spanish Ministerio de Educación y Cultura (PB98-0700.C02-01 and 02), Comunidad Autónoma de Madrid (CAM 08.6/0038./2000 and The Spanish Society of Nephrology.