BACKGROUND. Kidney transplant biopsies offer an opportunity to understand the pathogenesis of organ fibrosis. We studied the relationships between the time of biopsy after transplant (TxBx), histologic fibrosis, diseases, and transcript expression.
METHODS. Expression microarrays from 681 kidney transplant indication biopsies taken either early (
RESULTS. Fibrosis was absent at transplantation but was present in some early biopsies by 4 months after transplant, apparently as a self-limited response to donation implantation injury not associated with progression to failure. The molecular phenotype of early biopsies represented the time sequence of the response to wounding: immediate expression of acute kidney injury transcripts, followed by fibrillar collagen transcripts after several weeks, then by the appearance of immunoglobulin and mast cell transcripts after several months as fibrosis appeared. Fibrosis in late biopsies correlated with injury, fibrillar collagen, immunoglobulin, and mast cell transcripts, but these were independent of time. Pathway analysis revealed epithelial response-to-wounding pathways such as Wnt/β-catenin.
CONCLUSION. Fibrosis in late biopsies had different associations because many kidneys had potentially progressive diseases and subsequently failed. Molecular correlations with fibrosis in late biopsies were independent of time, probably because ongoing injury obscured the response-to-wounding time sequence. The results indicate that fibrosis in kidney transplants is driven by nephron injury and that progression to failure reflects continuing injury, not autonomous fibrogenesis.
TRIAL REGISTRATION. INTERCOM study (www.clinicalTrials.gov; NCT01299168).
FUNDING. Canada Foundation for Innovation and Genome Canada.
Jeffery M. Venner, Konrad S. Famulski, Jeff Reeve, Jessica Chang, Philip F. Halloran
Relationship between the histologic scores for fibrosis and time after transplant to biopsy.
Distribution of fibrosis lesions (ci scores) in time intervals after transplant. The block height represents the number of biopsies with each ci score in each time interval. d, days after transplant; mo, months after transplant; yr, years after transplant; N, number of biopsies in each time interval; and %ci>1, percentage of biopsies with ci score >1 in each time interval.