BACKGROUND. Kidney function decreases with age. A potential mechanistic explanation for kidney and allograft half-life has evolved through the realization that linear reduction in glomerular podocyte density could drive progressive glomerulosclerosis to impact both native kidney and allograft half-lives.
METHODS. Predictions from podometrics (quantitation of podocyte parameters) were tested using independent pathologic, functional, and outcome data for native kidneys and allografts derived from published reports and large registries.
RESULTS. With age, native kidneys exponentially develop glomerulosclerosis, reduced renal function, and end-stage kidney disease, projecting a finite average kidney life span. The slope of allograft failure rate versus age parallels that of reduction in podocyte density versus age. Quantitative modeling projects allograft half-life at any donor age, and rate of podocyte detachment parallels the observed allograft loss rate.
CONCLUSION. Native kidneys are designed to have a limited average life span of about 100–140 years. Allografts undergo an accelerated aging-like process that accounts for their unexpectedly short half-life (about 15 years), the observation that older donor age is associated with shorter allograft half-life, and the fact that long-term allograft survival has not substantially improved. Podometrics provides potential readouts for these processes, thereby offering new approaches for monitoring and intervention.
FUNDING: National Institutes of Health.
Abhijit S. Naik, Farsad Afshinnia, Diane Cibrik, Jeffrey B. Hodgin, Fan Wu, Min Zhang, Masao Kikuchi, Larysa Wickman, Milagros Samaniego, Markus Bitzer, Jocelyn E. Wiggins, Akinlolu Ojo, Yi Li, Roger C. Wiggins
Renal tubular atrophy and interstitial fibrosis are common hallmarks of etiologically different progressive chronic kidney diseases (CKD) that eventually result in organ failure. Even though these pathological manifestations constitute a major public health problem, diagnostic tests, as well as therapeutic options, are currently limited. Members of the dickkopf (DKK) family, DKK1 and -2, have been associated with inhibition of Wnt signaling and organ fibrosis. Here, we identify DKK3 as a stress-induced, tubular epithelia–derived, secreted glycoprotein that mediates kidney fibrosis. Genetic as well as antibody-mediated abrogation of DKK3 led to reduced tubular atrophy and decreased interstitial matrix accumulation in two mouse models of renal fibrosis. This was facilitated by an amplified, antifibrogenic, inflammatory T cell response and diminished canonical Wnt/β-catenin signaling in stressed tubular epithelial cells. Moreover, in humans, urinary DKK3 levels specifically correlated with the extent of tubular atrophy and interstitial fibrosis in different glomerular and tubulointerstitial diseases. In summary, our data suggest that DKK3 constitutes an immunosuppressive and a profibrotic epithelial protein that might serve as a potential therapeutic target and diagnostic marker in renal fibrosis.
Giuseppina Federico, Michael Meister, Daniel Mathow, Gunnar H. Heine, Gerhard Moldenhauer, Zoran V. Popovic, Viola Nordström, Annette Kopp-Schneider, Thomas Hielscher, Peter J. Nelson, Franz Schaefer, Stefan Porubsky, Danilo Fliser, Bernd Arnold, Hermann-Josef Gröne
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
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