Person:

Bonventre, Joseph

Premature infants are frequently exposed to aminoglycoside antibiotics. Novel urinary biomarkers may provide a non-invasive means for the early identification of aminoglycoside-related proximal tubule renal toxicity, to enable adjustment of treatment and identification of infants at risk of long-term renal impairment. In this proof-of-concept study, urine samples were collected from 41 premature neonates (≤32 weeks gestation) at least once per week, and daily during courses of gentamicin, and for 3 days afterwards. Significant increases were observed in the three urinary biomarkers measured (Kidney Injury Molecule-1 (KIM-1), Neutrophil Gelatinase-associated Lipocalin (NGAL), and N-acetyl-β-D-glucosaminidase (NAG)) during treatment with multiple courses of gentamicin. When adjusted for potential confounders, the treatment effect of gentamicin remained significant only for KIM-1 (mean difference from not treated, 1.35 ng/mg urinary creatinine; 95% CI 0.05–2.65). Our study shows that (a) it is possible to collect serial urine samples from premature neonates, and that (b) proximal tubule specific urinary biomarkers can act as indicators of aminoglycoside-associated nephrotoxicity in this age group. Further studies to investigate the clinical utility of novel urinary biomarkers in comparison to serum creatinine need to be undertaken.

Kim-1/Tim-1 is an apoptotic-cell phagocytosis and scavenger receptor that is most highly upregulated in proximal tubular epithelium in acute and chronic kidney injury. While Kim-1/Tim-1 has been proposed to be a costimulatory molecule for immune cells, its potential immunological role has been controversial. In the presence of very high epithelial cell expression understanding the influence of immune cell Kim-1/Tim-1 expression in kidney injury relies on a better definition of its functional significance in immune cells and better characterization of antibodies used to probe function.

Pre-renal acute kidney injury (AKI) is assumed to represent a physiological response to underperfusion. Its diagnosis is retrospective after a transient rise in plasma creatinine, usually associated with evidence of altered tubular transport, particularly that of sodium. In order to test whether pre-renal AKI is reversible because injury is less severe than that of sustained AKI, we measured urinary biomarkers of injury (cystatin C, neutrophil gelatinase-associated lipocalin (NGAL), (\gamma)-glutamyl transpeptidase, IL-18, and kidney injury molecule-1 (KIM-1)) at 0, 12, and 24 h following ICU admission. A total of 529 patients were stratified into groups having no AKI, AKI with recovery by 24 h, recovery by 48 h, or the composite of AKI greater than 48 h or dialysis. Pre-renal AKI was identified in 61 patients as acute injury with recovery within 48 h and a fractional sodium excretion <1%. Biomarker concentrations significantly and progressively increased with the duration of AKI. After restricting the AKI recovery within the 48 h cohort to pre-renal AKI, this increase remained significant. The median concentration of KIM-1, cystatin C, and IL-18 were significantly greater in pre-renal AKI compared with no-AKI, while NGAL and (\gamma)-glutamyl transpeptidase concentrations were not significant. The median concentration of at least one biomarker was increased in all but three patients with pre-renal AKI. Thus, the reason why some but not all biomarkers were increased requires further study. The results suggest that pre-renal AKI represents a milder form of injury.

Background: Dominantly inherited missense mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson's disease, but its normal physiological function remains unclear. We previously reported that loss of LRRK2 causes impairment of protein degradation pathways as well as increases of apoptotic cell death and inflammatory responses in the kidney of aged mice. Results: Our analysis of LRRK2-/- kidneys at multiple ages, such as 1, 4, 7, and 20 months, revealed unique age-dependent development of a variety of molecular, cellular, and ultrastructural changes. Gross morphological abnormalities of the kidney, including altered size, weight, texture, and color, are evident in LRRK2-/- mice at 3-4 months of age, along with increased accumulation of autofluorescent granules in proximal renal tubules. The ratio of kidney/body weight in LRRK2-/- mice is increased at 1, 4, and 7 months of age (( \sim 10 %) at 1 month, and (( \sim20%) at 4 and 7 months), whereas the ratio is drastically decreased at 20 months of age (( \sim50%)). While kidney filtration function evaluated by levels of blood urea nitrogen and serum creatinine is not significantly affected in LRRK2-/- mice at 12-14 months of age, expression of kidney injury molecule-1, a sensitive and specific biomarker for epithelial cell injury of proximal renal tubules, is up-regulated (( \sim 10-fold)). Surprisingly, loss of LRRK2 causes age-dependent bi-phasic alterations of the autophagic activity in LRRK2-/- kidneys, which is unchanged at 1 month of age, enhanced at 7 months but reduced at 20 months, as evidenced by corresponding changes in the levels of LC3-I/II, a reliable autophagy marker, and p62, an autophagy substrate. Levels of α-synuclein and protein carbonyls, a general oxidative damage marker, are also decreased in LRRK2-/- kidneys at 7 months of age but increased at 20 months. Interestingly, the age-dependent bi-phasic alterations in autophagic activity in LRRK2-/- kidneys is accompanied by increased levels of lysosomal proteins and proteases at 1, 7, and 20 months of age as well as progressive accumulation of autolysosomes and lipofuscin granules at 4, 7-10, and 20 months of age. Conclusions: LRRK2 is important for the dynamic regulation of autophagy function in vivo.

Three decades have passed since a series of studies indicated that the aging kidney was characterized by increased susceptibility to nephrotoxic injury. Data from these experimental models is strengthened by clinical data demonstrating that the aging population has an increased incidence and severity of acute kidney injury (AKI). Since then a number of studies have focused on age-dependent alterations in pathways that predispose the kidney to acute insult. This review will focus on the mechanisms that are altered by aging in the kidney that may increase susceptibility to injury, including hemodynamics, oxidative stress, apoptosis, autophagy, inflammation and decreased repair.

Acute kidney injury in the context of acetaminophen (APAP; paracetamol)-induced liver injury is an important predictor of the requirement for urgent liver transplantation (LT) to avoid death. However, the prognostic biomarker used to report kidney dysfunction (serum creatinine concentration) has suboptimal sensitivity and specificity. Kidney injury molecule 1 (KIM-1) can be quantified in plasma as a sensitive and specific biomarker of kidney injury in both clinical and preclinical studies. Therefore, plasma KIM-1 has potential as a sensitive prognostic biomarker of patient outcome post-APAP overdose. In a cohort of APAP overdose patients (N = 74) with and without established liver injury, we quantified plasma KIM-1 by immunoassay on the first day of admission to a LT unit and assessed its diagnostic performance to predict outcome compared with serum creatinine concentration. Day 1 plasma KIM-1 was significantly elevated in patients that died or required LT, compared to spontaneous survivors (1,182 ± 251 vs. 214 ± 45 pg/mL; P < 0.005). Receiver operator characteristic analysis demonstrated the superiority of KIM-1 (area under the curve [AUC]: 0.87; 95% confidence interval [CI]: 0.78-0.95; 0.56 sensitivity at 0.95 specificity), compared with serum creatinine (AUC, 0.76; 95% CI: 0.64-0.87; 0.08 sensitivity at 0.95 specificity) and other current prognostic indicators, when measured on the first day of enrollment into the study. Furthermore, KIM-1 was found to be a statistically significant independent predictor of outcome at the 5% level (P < 0.0386) in a multivariable logistic regression model that considered all measured factors (pseudo-R^2 = 0.895). Conclusion:: Early measurement of plasma KIM-1 represents a more sensitive predictor of patient outcome than serum creatinine concentration post-APAP overdose. With further development, plasma KIM-1 could significantly improve prognostic stratification. (Hepatology 2015;62:591–599

Human-pluripotent-stem-cell-derived kidney cells (hPSC-KCs) have important potential for disease modelling and regeneration. Whether the hPSC-KCs can reconstitute tissue-specific phenotypes is currently unknown. Here we show that hPSC-KCs self-organize into kidney organoids that functionally recapitulate tissue-specific epithelial physiology, including disease phenotypes after genome editing. In three-dimensional cultures, epiblast-stage hPSCs form spheroids surrounding hollow, amniotic-like cavities. GSK3β inhibition differentiates spheroids into segmented, nephron-like kidney organoids containing cell populations with characteristics of proximal tubules, podocytes and endothelium. Tubules accumulate dextran and methotrexate transport cargoes, and express kidney injury molecule-1 after nephrotoxic chemical injury. CRISPR/Cas9 knockout of podocalyxin causes junctional organization defects in podocyte-like cells. Knockout of the polycystic kidney disease genes PKD1 or PKD2 induces cyst formation from kidney tubules. All of these functional phenotypes are distinct from effects in epiblast spheroids, indicating that they are tissue specific. Our findings establish a reproducible, versatile three-dimensional framework for human epithelial disease modelling and regenerative medicine applications.

Tubular injury has a major etiological role in fibrosis. For many years, this relationship has been dominated by the perception that epithelial cells are transformed into myofibroblasts that proliferate and generate fibrotic matrix—the so-called epithelial-to-mesenchymal transition. Here we focus on mechanisms by which injury to the tubule results in fibrosis because of paracrine mechanisms. Specific injury to the proximal tubule results in inflammation, reversible injury, and adaptive repair if the insult is mild, self-limited in time, and occurs in a background of a normal kidney. Repeated injury, in contrast, leads to maladaptive repair with sustained tubule injury, chronic inflammation, proliferation of interstitial myofibroblasts, vascular rarefaction, interstitial fibrosis, and glomerular sclerosis. During the maladaptive repair process after the renal insult, many tubular cells become arrested in the G2/M phase of the cell cycle. This results in activation of the DNA repair response with the resultant synthesis and secretion of pro-fibrotic factors. Pharmacologic interventions that enhance the movement through G2/M or facilitate apoptosis of cells that otherwise would be blocked in G2/M may reduce the development of fibrosis after kidney injury and reduce the progression of chronic kidney disease.

Here we studied plasma metabolomic profiles as determinants of progression to ESRD in patients with Type 2 diabetes (T2D). This nested case-control study evaluated 40 cases who progressed to ESRD during 8-12 years of follow-up and 40 controls who remained alive without ESRD from the Joslin Kidney Study cohort. Controls were matched with cases for baseline clinical characteristics; although controls had slightly higher eGFR and lower levels of urinary albumin excretion than T2D cases. Plasma metabolites at baseline were measured by mass spectrometry-based global metabolomic profiling. Of the named metabolites in the library, 262 were detected in at least 80% of the study patients. The metabolomic platform recognized 78 metabolites previously reported to be elevated in ESRD (uremic solutes). Sixteen were already elevated in the baseline plasma of our cases years before ESRD developed. Other uremic solutes were either not different or not commonly detectable. Essential amino acids and their derivatives were significantly depleted in the cases, whereas certain amino acid-derived acylcarnitines were increased. All findings remained statistically significant after adjustment for differences between study groups in albumin excretion rate, eGFR or HbA1c. Uremic solute differences were confirmed by quantitative measurements. Thus, abnormal plasma concentrations of putative uremic solutes and essential amino acids either contribute to progression to ESRD or are a manifestation of an early stage(s) of the disease process that leads to ESRD in T2D.

Chronic kidney disease (CKD) remains one of the leading causes of death in the developed world and acute kidney injury (AKI) is now recognized as a major risk factor in its development. Understanding the factors leading to CKD after acute injury are limited by current animal models of AKI which concurrently target various kidney cell types such as epithelial, endothelial and inflammatory cells. Here we developed a mouse model of kidney injury using the Six2-Cre-LoxP technology to selectively activate expression of the simian diphtheria toxin receptor in renal epithelia derived from the metanephric mesenchyme. By adjusting the timing and dose of diphtheria toxin a highly selective model of tubular injury was created to define the acute and chronic consequences of isolated epithelial injury. The diphtheria toxin-induced sublethal tubular epithelial injury was confined to the S1 and S2 segments of the proximal tubule rather than being widespread in the metanephric mesenchyme derived epithelial lineage. Acute injury was promptly followed by inflammatory cell infiltration and robust tubular cell proliferation leading to complete recovery after a single toxin insult. In striking contrast, three insults to renal epithelial cells at one week intervals resulted in maladaptive repair with interstitial capillary loss, fibrosis and glomerulosclerosis which was highly correlated with the degree of interstitial fibrosis. Thus, selective epithelial injury can drive the formation of interstitial fibrosis, capillary rarefaction and potentially glomerulosclerosis, substantiating a direct role for damaged tubule epithelium in the pathogenesis of CKD.