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and EGFR expression in the initiation of parathyroid hyperplasia in experimental kidney disease
1Renal Division, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri; and 2Renal Division, San Paolo Hospital, Milan, Italy
Submitted 20 April 2005 ; accepted in final form 29 June 2005
The parathyroid hyperplasia secondary to kidney disease is associated with enhanced expression of the growth promoter transforming growth factor-
(TGF-
). TGF-
stimulates growth through activation of its receptor, the epidermal growth factor receptor (EGFR), normally expressed in the parathyroid glands. Because enhanced coexpression of TGF-
and EGFR causes aggressive cellular growth, these studies utilized highly specific inhibitors of EGFR tyrosine kinase, a step mandatory for TGF-
-induced EGFR activation, to assess the contribution of growth signals from enhanced expression of TGF-
exclusively or both TGF-
and EGFR to the rapid parathyroid growth induced by kidney disease and exacerbated by high-phosphorus (P) and low-calcium (Ca) diets in rats. The enhancement in parathyroid gland weight and proliferating activity (proliferating cell nuclear antigen/Ki67) induced by kidney disease and aggravated by either high P or low Ca intake, within the first week after 5/6 nephrectomy, in rats, coincided with simultaneous increases (2- to 3-fold) in TGF-
and EGFR content. Conversely, prevention of the increases in both TGF-
and EGFR paralleled the efficacy of either P restriction or high-Ca intake in ameliorating uremia-induced parathyroid hyperplasia. More importantly, suppression of TGF-
/EGFR signaling, through prophylactic administration of potent and highly selective inhibitors of ligand-induced EGFR activation, completely prevented both high-P- and low-Ca-induced parathyroid hyperplasia as well as TGF-
self-upregulation. Thus enhanced parathyroid TGF-
/EGFR expression, self-upregulation, and growth signals occur early in kidney disease, are aggravated by low-Ca and high-P intake, and constitute the main pathogenic mechanism of the severity of parathyroid hyperplasia.
secondary hyperparathyroidism; growth arrest; epidermal growth factor receptor; tyrosine kinase inhibitor; renal failure
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