Telomere shortening and regenerative capacity after acute kidney injury

Comparison of the relative telomere length measured in leukocytes and eleven different human tissues

The relative length of telomeres measured in peripheral blood leukocytes is a commonly used system marker for biological aging and can also be used as a biomarker of cardiovascular aging. However, to what extent the telomere length in peripheral leukocytes reflects telomere length in different organ tissues is still unclear. Therefore, we have measured relative telomere length (rTL) in twelve different human tissues (peripheral blood leukocytes, liver, kidney, heart, spleen, brain, skin, triceps, tongue mucosa, intercostal skeletal muscle, subcutaneous fat, and abdominal fat) from twelve cadavers (age range of 29 week of gestation to 88 years old). The highest rTL variability was observed in peripheral leukocytes, and the lowest variability was found in brain. We found a significant linear correlation between leukocyte rTL and both intercostal muscle (R=0.68, P<0.02) and liver rTL (R=0.60, P<0.05) only. High rTL variability was observed between different organs from one individual. Furthermore, we have shown that even slight DNA degradation (modeled by sonication of genomic DNA) leads to false rTL shortening. We conclude that the rTL in peripheral leukocytes is not strongly correlated with the rTL in different organs.

Characterization and fate of telomerase-expressing epithelia during kidney repair

After acute kidney injury, mice with short telomeres develop increased damage with reduced proliferative capacity, which suggests an important role for telomere length in kidney repair. The enzyme telomerase reverse transcriptase (mTert) regulates telomere length; embryonic stem cells and certain adult stem cells express mTert, but whether cells in the adult kidney express mTert and whether these cells play a role in renal repair are unknown. Here, we found that telomerase protein and mRNA were highly enriched in renal papilla, a proposed niche of kidney stem cells. Using mTert-GFP reporter mice, we detected mTert in a subset of papillary epithelial cells comprising the collecting duct predominantly but also the loop of Henle. Approximately 5% of mTert-GFP(+) cells were label retaining, a characteristic of stem cells. mTert mRNA levels increased in renal papilla after ischemia-reperfusion injury, but genetically labeled mTert-expressing papillary cells neither divided nor migrated out of the renal papilla during kidney repair. In summary, these data suggest that cells expressing telomerase reverse transcriptase are not a progenitor-cell population, and they do not play a direct role in kidney repair.

Assessment of kidney organ quality and prediction of outcome at time of transplantation

The critical importance of donor organ quality, i.e., number of surviving nephrons, ability to withstand injury, and capacity for repair in determining short- and long-term outcomes is becoming increasingly clear. This review provides an overview of studies to assess donor kidney quality and subsequent transplant outcomes based on clinical pathology and transcriptome-based variables available at time of transplantation. Prediction scores using clinical variables function when applied to large data sets but perform poorly for the individual patient. Histopathology findings in pre-implantation or post-reperfusion biopsies help to assess structural integrity of the donor kidney, provide information on pre-existing donor disease, and can serve as a baseline for tracking changes over time. However, more validated approaches of analysis and prospective studies are needed to reduce the number of discarded organs, improve allocation, and allow prediction of outcomes. Molecular profiling detects changes not seen by morphology or captured by clinical markers. In particular, molecular profiles provide a quantitative measurement of inflammatory burden or immune activation and reflect coordinated changes in pathways associated with injury and repair. However, description of transcriptome patterns is not an end in itself. The identification of predictive gene sets and the application to an individualized patient management needs the integration of clinical and pathology-based variables, as well as more objective reference markers of transplant function, post-transplant events, and long-term outcomes.

Mechanisms of tubulointerstitial fibrosis

The pathologic paradigm for renal progression is advancing tubulointerstitial fibrosis. Whereas mechanisms underlying fibrogenesis have grown in scope and understanding in recent decades, effective human treatment to directly halt or even reverse fibrosis remains elusive. Here, we examine key features mediating the molecular and cellular basis of tubulointerstitial fibrosis and highlight new insights that may lead to novel therapies. How to prevent chronic kidney disease from progressing to renal failure awaits even deeper biochemical understanding.