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T95 nucleophosmin phosphorylation as a novel mediator and marker of regulated cell death in acute kidney injury.

ABSTRACT: The function of site-specific phosphorylation of nucleophosmin (NPM), an essential Bax chaperone, in stress-induced cell death is unknown. We hypothesized that NPM threonine 95 (T95) phosphorylation both signals and promotes cell death. In resting cells, NPM exclusively resides in the nucleus and T95 is nonphosphorylated. In contrast, phosphorylated T95 NPM (pNPM T95) accumulates in the cytosol after metabolic stress, in multiple human cancer cell lines following γ-radiation, and in postischemic human kidney tissue. Based on the T95 phosphorylation consensus sequence, we hypothesized that glycogen synthase kinase-3β (GSK-3β) regulates cytosolic NPM translocation by phosphorylating T95 NPM. In a cell-free system, GSK-3β phosphorylated a synthetic NPM peptide containing T95. In vitro, bidirectional manipulation of GSK-3β activity substantially altered T95 phosphorylation, cytosolic NPM translocation, and cell survival during stress, mechanistically linking these lethal events. Furthermore, GSK-3β inhibition in vivo decreased cytosolic pNPM T95 accumulation in kidney tissue after experimental ischemia. In patients with acute kidney injury, both cytosolic NPM accumulation in proximal tubule cells and NPM-rich intratubular casts were detected in frozen renal biopsy tissue. These observations show, for the first time, that GSK-3β promotes cell death partly by phosphorylating NPM at T95, to promote cytosolic NPM accumulation. T95 NPM is also a rational therapeutic target to ameliorate ischemic renal cell injury and may be a universal injury marker in mammalian cells.

SUBMITTER: Wang Z

PROVIDER: S-EPMC7509286 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background: Despite the term acute kidney injury (AKI), clinical biomarkers for AKI reflect function rather than injury and independent markers of injury are needed. Tubular cell death, including necroptotic cell death, is a key feature of AKI. Cyclophilin A (CypA) is an intracellular protein that has been reported to be released during necroptosis. We have now explored CypA as a potential marker for kidney injury in cultured tubular cells and in clinical settings of ischemia-reperfusion injury (IRI), characterized by limitations of current diagnostic criteria for AKI. Methods: CypA was analyzed in cultured human and murine proximal tubular epithelial cells exposed to chemical hypoxia, hypoxia/reoxygenation (H/R) or other cell death (apoptosis, necroptosis, ferroptosis) inducers. Urinary levels of CypA (uCypA) were analyzed in patients after nephron sparing surgery (NSS) in which the contralateral kidney is not disturbed and kidney grafts with initial function. Results: Intracellular CypA remained unchanged while supernatant CypA increased in parallel to cell death induction. uCypA levels were higher in NSS patients with renal artery clamping (that is, with NSS-IRI) than in no clamping (NSS-no IRI), and in kidney transplantation (KT) recipients (KT-IRI) even in the presence of preserved or improving kidney function, while this was not the case for urinary Neutrophil gelatinase-associated lipocalin (NGAL). Furthermore, higher uCypA levels in NSS patients were associated with longer surgery duration and the incidence of AKI increased from 10% when using serum creatinine (sCr) or urinary output criteria to 36% when using high uCypA levels in NNS clamping patients. Conclusions: CypA is released by kidney tubular cells during different forms of cell death, and uCypA increased during IRI-induced clinical kidney injury independently from kidney function parameters. Thus, uCypA is a potential biomarker of kidney injury, which is independent from decreased kidney function.

Project description:We evaluated urine NGAL as a marker of acute kidney injury in patients undergoing partial nephrectomy. We sought to identify the preoperative clinical features and surgical factors during partial nephrectomy that are associated with renal injury, as measured by increased urine NGAL vs controls.Using patients treated with radical nephrectomy or thoracic surgery as controls, we prospectively collected and analyzed urine and serum samples from patients treated with partial or radical nephrectomy, or thoracic surgery between April 2010 and April 2012. Urine was collected preoperatively and at multiple time points postoperatively. Differences in urine NGAL levels were analyzed among the 3 surgical groups using a generalized estimating equation model. The partial nephrectomy group was subdivided based on a preoperative estimated glomerular filtration rate of less than 60, or 60 ml/minute/1.73 m(2) or greater.Of 162 patients included in final analysis more than 65% had cardiovascular disease. The median estimated glomerular filtration rate was greater than 60 ml/minute/1.73 m(2) in the radical and partial nephrectomy, and thoracic surgery groups (61, 78 and 84.5 ml/minute/1.73 m(2), respectively). Preoperatively, a 10 unit increase in the estimated glomerular filtration rate was associated with a 4 unit decrease in urine NGAL in the partial nephrectomy group. Postoperatively, urine NGAL in the partial nephrectomy group was not higher than in controls and did not correlate with ischemia time. Patients with partial nephrectomy with a preoperative estimated glomerular filtration rate of less than 60 ml/minute/1.73 m(2) had higher urine NGAL postoperatively than those with a higher preoperative estimated rate.Urine NGAL does not appear to be a useful marker for detecting renal injury in healthy patients treated with partial nephrectomy. However, patients with poorer preoperative renal function have higher baseline urine levels and appear more susceptible to acute kidney injury, as detected by urine levels and Acute Kidney Injury Network criteria, than those with a normal estimated glomerular filtration rate.

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T95 nucleophosmin phosphorylation as a novel mediator and marker of regulated cell death in acute kidney injury.

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