Parathyroid hormone-related peptide (hPTHrP) and parathyroid hormone-related peptide receptor type 1 (PTHR1) expression in human thymus.

Parathyroid hormone-related peptide (hPTHrP) is expressed in human tissues and regulates cellular proliferation, differentiation, and apoptosis by an autocrine/paracrine loop. In rodent thymus, both parathormone and parathyroid hormone-related peptide (PTHrP) are expressed by thymic epithelial cells (TECs). The present study demonstrated by RT-PCR and immunohistochemistry that hPTHrP and parathyroid hormone-related peptide receptor type 1 (PTHR1) were expressed in human thymus at both RNA and protein levels. hPTHrP was expressed mainly in the thymic medulla by epithelial (cytokeratin-positive), mature dendritic (CD40+/86+) and plasmacytoid interleukin (IL)-3Ralpha1 cells. This protein was also present in some cells forming Hassall's bodies and a few subcapsular and cortical TECs. PTHR1 was expressed by scattered subcapsular and cortical TECs and by rare TECs in the medulla. Thymocytes did not express either hPTHrP or PTHR1. Primary cultures of human TECs revealed the presence of both hPTHrP and PTHR1 mRNAs, confirming the capacity of TECs to synthesize both peptides. Moreover, synthetic (1-39) hPTHrP peptide administered on cultured TECs induced the expression of IL-6 mRNA, suggesting that hPTHrP can regulate thymic functions by inducing in TECs the expression of IL-6, which is involved in the development and maturation of thymocytes.