Local medial microenvironment directs phenotypic modulation of smooth muscle cells after experimental renal transplantation.

Smooth muscle cells (SMCs) play a key role in the pathogenesis of occlusive vascular diseases, including transplant vasculopathy. Neointimal SMCs in experimental renal transplant vasculopathy are graft-derived. We propose that neointimal SMCs in renal allografts are derived from the vascular media resulting from a transplantation-induced phenotypic switch. We examined the molecular changes in the medial microenvironment that lead to phenotypic modulation of SMCs in rat renal allograft arteries with neointimal lesions. Dark Agouti donor kidneys were transplanted into Wistar Furth recipients and recovered at day 56. Neointimal and medial layers were isolated using laser microdissection. Gene expression was analyzed using low-density arrays and confirmed by immunostaining. In allografts, neointimal SMCs expressed increased levels of Tgf ß1 and Pdgfb. In medial allograft SMCs, gene expression of Ctgf, Tgf ß1 and Pdgfrb was upregulated. Gene expression of Klf4 was upregulated as well, while expression of Sm22α was downregulated. Finally, PDGF-BB-stimulated phenotypically modulated SMCs, as evidenced by reduced contractile function in vitro which was accompanied by increased Klf4 and Col1α1, and reduced α-Sma and Sm22α expression. In transplant vasculopathy, neointimal PDGF-BB induces phenotypic modulation of medial SMCs, through upregulation of KLF4 in the media to contribute to (further) expansion of the neointima.

Donor and recipient origin of mesenchymal and endothelial cells in chronic renal allograft remodeling.

Chronic transplant dysfunction (CTD) is the leading cause for limited kidney graft survival. Renal CTD is characterized by interstitial and vascular remodeling leading to interstitial fibrosis, tubular atrophy and transplant vasculopathy (TV). The origin of cells and pathogenesis of interstitial and vascular remodeling are still unknown. To study graft-versus-recipient origin of interstitial myofibroblasts, vascular smooth muscle cells (SMCs) and endothelial cells (ECs), we here describe a new rat model for renal CTD using Dark Agouti kidney donors and R26 human placental alkaline phosphatase transgenic Fischer344 recipients. This model showed the development of CTD within 12 weeks after transplantation. In interstitial remodeling, both graft- and recipient-derived cells contributed to a similar extent to the accumulation of myofibroblasts. In arteries with TV, we observed graft origin of neointimal SMCs and ECs, whereas in peritubular and glomerular capillaries, we detected recipient EC chimerism. These data indicate that, within the interstitial and vascular compartments of the transplanted kidney, myofibroblasts, SMCs and ECs involved in chronic remodeling are derived from different sources and suggest distinct pathogenetic mechanisms within the renal compartments.