INSIGHTS OF THE MOLECULAR PATHWAYS INVOLVED IN CHRONIC ALLOGRAFT NEPHROPATHY.

Valeria Mas, PhD1, Daniel Maluf, MD1, Kellie Archer, PhD2, Kenneth Yanek, MS1, Eric Gibney, MD1, Anne King, MD1, Adrian Cotterell, MD1, Robert Fisher, MD1 and Marc Posner, MD1. 1Surgery, Hume-Lee Transplant Center, VCUHS, Richmond, VA, United States and 2Biostatistics, VCUHS, Richmond, VA, United States.

Body: Loss of kidney graft function with tubular atrophy (TA) and interstitial fibrosis (IF), a set of findings termed chronic allograft nephropathy (CAN), causes most kidney allograft losses. The pathogenesis of CAN involves many cell types making difficult to predict which gene products are reliable markers of CAN. We aimed to identify the molecular signature involved in CAN.

Patients and Methods. Tissue from normal kidneys (NK) (N=26), normal allografts (NA) (N=8), and CAN (N=20) were analyzed using high-density oligonucletide microarray. All biopsies were evaluated using Banff criteria. The robust-multiarray average method was used to estimate probe set expression summaries. Class comparisons among groups were performed using the modified F-test within the Significance Analysis of Microarray method framework to permit estimation of the false discovery rate (FDR). Microarray results were confirmed using TaqMan.

Results. Biopsies were performed between 1558 m after (KT). CAN biopsies were graded 2 or 3 per Banff classification. In an unsupervised hierarchical clustering analysis all the CAN samples clustered together. We did not observe associations between specific histopathologic features of CAN and gene expression profiles. From the analysis of the gene expression profiles among the different study groups we observed an important number of differentially expressed genes (DEG). Gene ontology classified the DEG as related with immune response, inflammation, cell cycle regulation, and matrix deposition. Chemokines (CX) and CX receptor (i.e., CCL5, CXCL9, CXCR4), interleukins (ILs) and IL-receptors (i.e., IL-8, IL-16, IL10RA, IL2RA) genes were over expressed in CAN samples. Apoptosis genes were over expressed in CAN samples (i.e., CASP4, CASP10, CASP5, BCL2L13, FAF1). Genes related to angiogenesis were down regulated in CAN (i.e., ANGPTL3, ANGPT2, VEGF, EGF) but up regulated in NA when compared to NK. Gene expression of TGF-1 was up regulated in CAN samples while FGF and AGT were down regulated. Matrix deposition and production genes were over expressed in CAN samples (i.e., MMP12, MMP9, FCN1).

Conclusions. A distinctive gene expression pattern was observed in CAN samples. The high homogeneity in the profiles among CAN biopsies indicates that the signature may in fact be reflecting the final injury mechanism independently of the initial triggers.