Alice M. Sheridan

Cell biology and molecular mechanisms of injury in ischemic acute renal failure.

The pathogenesis of acute renal failure has been attributed to persistent vasoconstriction and leukocyte-endothelial interactions, resulting in inflammation and compromise of local blood flow to the outer medulla, the loss of tubular epithelial cell polarity with multiple functional sequelae, necrosis or apoptosis of epithelial cells, and the de-differentiation, migration and proliferation of surviving cells. In this paper, the authors present their views of pathophysiology of ischemic acute renal failure.

Pathophysiology of Ischemic Acute Renal Failure

Acute renal failure (ARF) is a syndrome characterized by an abrupt and reversible kidney dysfunction. The spectrum of inciting factors is broad: from ischemic and nephrotoxic agents to a variety of endotoxemic states and syndrome of multiple organ failure. The pathophysiology of ARF includes vascular, glomerular and tubular dysfunction which, depending on the actual offending stimulus, vary in the severity and time of appearance. Hemodynamic compromise prevails in cases when noxious stimuli are related to hypotension and septicemia, leading to renal hypoperfusion with secondary tubular changes (described in Chapter 13). Nephrotoxic offenders usually result in primary tubular epithelial cell injury, though endothelial cell dysfunction can also occur, leading to the eventual cessation of glomerular filtration. This latter effect is a consequence of the combined action of tubular obstruction and activation of tubuloglomerular feedback mechanism. In the following pages we shall review the existing concepts on the phenomenology of ARF including the mechanisms of decreased renal perfusion and failure of glomerular filtration, vasoconstriction of renal arterioles, how formed elements gain access to the renal parenchyma, and what the sequelae are of such an invasion by primed leukocytes. Michael S. Goligorsky Wilfred Lieberthal

PLIP, a novel splice variant of Tip60, interacts with group IV cytosolic phospholipase A(2), induces apoptosis, and potentiates prostaglandin production.

ABSTRACT The group IV cytosolic phospholipase A2(cPLA2) has been localized to the nucleus (M. R. Sierra-Honigmann, J. R. Bradley, and J. S. Pober, Lab. Investig. 74:684–695, 1996) and is known to translocate from the cytosolic compartment to the nuclear membrane (S. Glover, M. S. de Carvalho, T. Bayburt, M. Jonas, E. Chi, C. C. Leslie, and M. H. Gelb, J. Biol. Chem. 270:15359–15367, 1995; A. R. Schievella, M. K. Regier, W. L. Smith, and L. L. Lin, J. Biol. Chem. 270:30749–30754, 1995). We hypothesized that nuclear proteins interact with cPLA2 and participate in the functional effects of this translocation. We have identified a nuclear protein, cPLA2-interacting protein (PLIP), a splice variant of human Tip60, which interacts with the amino terminal region of cPLA2. Like Tip60, PLIP cDNA includes the MYST domain containing a C2HC zinc finger and well-conserved similarities to acetyltransferases. Both PLIP and Tip60 coimmunoprecipitate and colocalize with cPLA2 within the nuclei of transfected COS cells. A polyclonal antibody raised to PLIP recognizes both PLIP and Tip60. Endogenous Tip60 and/or PLIP in rat mesangial cells is localized to the nucleus in response to serum deprivation. Nuclear localization coincides temporally with apoptosis. PLIP expression, mediated by adenoviral gene transfer, potentiates serum deprivation-induced prostaglandin E2 (PGE2) production and apoptosis in mouse mesangial cells from cPLA2 +/+ mice but not in mesangial cells derived from cPLA2 −/− mice. Thus PLIP, a splice variant of Tip60, interacts with cPLA2 and potentiates cPLA2-mediated PGE2 production and apoptosis.

Testing for High-Risk APOL1 Alleles in Potential Living Kidney Donors

Accurate risk assessment is critical when evaluating potential living kidney donors. High-risk kidney APOL1 variants have been associated with end-stage renal disease of multiple causes among African Americans, though the predictive power of these variants in population-based studies is small. No studies have looked at the effect of high-risk APOL1 alleles on donor outcomes, though few transplantation centers in the United States offer screening for APOL1 among African American donors. Screening all African Americans for high-risk APOL1 alleles may result in the exclusion of many potential donors (∼13% of African Americans). Such an exclusion may have a large effect on the availability of transplants for African Americans, who are already less likely to undergo transplantation. Nephrologists should be prepared to discuss with potential African American donors the relative increase in risk that is likely conferred by carrying 2 high-risk APOL1 alleles and how additional factors such as environmental exposures (eg, viral infections) and/or other genetic susceptibilities may be required for developing kidney disease. In this Perspective, we review the use of APOL1 testing for risk stratification of potential African American kidney donors.

Group IVA Cytosolic Phospholipase A2 Regulates the G2-to-M Transition by Modulating the Activity of Tumor Suppressor SIRT2.

ABSTRACT The G2-to-M transition (or prophase) checkpoint of the cell cycle is a critical regulator of mitotic entry. SIRT2, a tumor suppressor gene, contributes to the control of this checkpoint by blocking mitotic entry under cellular stress. However, the mechanism underlying both SIRT2 activation and regulation of the G2-to-M transition remains largely unknown. Here, we report the formation of a multiprotein complex at the G2-to-M transition in vitro and in vivo. Group IVA cytosolic phospholipase A2 (cPLA2α) acts as a bridge in this complex to promote binding of SIRT2 to cyclin A-Cdk2. Cyclin A-Cdk2 then phosphorylates SIRT2 at Ser331. This phosphorylation reduces SIRT2 catalytic activity and its binding affinity to centrosomes and mitotic spindles, promoting G2-to-M transition. We show that the inhibitory effect of cPLA2α on SIRT2 activity impacts various cellular processes, including cellular levels of histone H4 acetylated at K16 (Ac-H4K16) and Ac-α-tubulin. This regulatory effect of cPLA2α on SIRT2 defines a novel function of cPLA2α independent of its phospholipase activity and may have implications for the impact of SIRT2-related effects on tumorigenesis and age-related diseases.

Fatty acid-induced cytotoxicity: Differences in susceptibility between mdck cells and primary cultures of proximal tubular cells

We have compared the cytotoxicity of exogenously added fatty acid (oleic acid) and that of endogenous free fatty acids released from cell membranes by phospholipase A2 in primary cultures of mouse proximal tubular (MPT) cells and in Madine-Darby canine kidney (MDCK) cells. Exposure of MPT cell monolayers to oleic acid (125 mmol/L) for 2 hours resulted in severe irreversible injury to 70% +/- 4% of MPT cells. In striking contrast, only 8% +/- 3% of MDCK cells were killed by the same insult. This striking difference in the response to exogenous oleate by MPT and MDCK cells was associated with modest and comparable reductions in cell adenosine triphosphate (ATP) content in both cell types. Chemical anoxia induced by cyanide plus deoxyglucose (CN-DOG) in the absence of glucose was associated with greater injury in MPT cells (45% +/- 6% killed) than in MDCK cells (16% +/- 5% cells killed) despite severe and comparable depletion of cell ATP content in both MPT cells (96.0% +/- 0.6% reduction) and MDCK cells (96.0% +/- 0.5% reduction). The release of endogenous fatty acids by the exposure of cells to exogenous phospholipase A2 caused mild injury in both cell types that was more severe in MPT cells than in MDCK cells. The combined insult of phospholipase A2 and chemical anoxia for 2 hours caused substantially greater cell injury in both MPT and MDCK cells than either intervention alone, but the combined insult was still more damaging to MPT cells (73% +/- 4% killed) than to MDCK cells (30% +/- 4% killed). We conclude that the cell membrane in MDCK cells is intrinsically more resistant to fatty acid-induced injury than the lipid membrane in MPT cells.