Extraneural CGRP Upregulates TGF-β1 through RAMP1 Signaling during Mechanical Stretch in Kidney Proximal Tubule Epithelial Cells

Abstract

Calcitonin gene-related peptide (CGRP) derived from sensory neurons contributes to the development of renal tubulointerstitial fibrosis during ureteral obstruction through upregulation of profibrotic factors. However, the mechanism by which CGRP upregulates the profibrotic factors in the ureteral obstructive setting in the kidney tubule epithelial cells is not defined. In the human kidney proximal tubule epithelial cell line, HK-2, treatment with 1 nM CGRP significantly enhanced transforming growth factor-β1 (TGF-β1) production, its release, and protein kinase C (PKC) activity. Furthermore, mechanical stretch for 6 and 24 hours significantly increased expressions of receptor activity modifying protein 1 (RAMP1) mRNA and protein among CGRP receptor components in HK-2 cells. In addition, a combination treatment with CGRP and mechanical stretch synergistically increased TGF-β1 upregulation and PKC activation. However, RAMP1 deficiency, induced by RAMP1 double nickase plasmid transfection, abolished CGRP-induced TGF-β1 upregulation and PKC activation in HK-2 cells with or without mechanical stretch. Finally, pharmacological inhibition of PKC markedly reduced TGF-β1 production and release after treatment of HK-2 cells with CGRP. Taken together, these data suggest that extraneural CGRP upregulates TGF-β1 through RAMP1-PKC axis during mechanical stretch in kidney proximal tubule epithelial cells.