Two-pore channels regulate endomembrane tension to enable remodeling and resolution of phagolysosomes.

Phagocytes promptly resolve ingested targets to replenish lysosomes and maintain their responsiveness. The resolution process requires that degradative hydrolases, solute transporters, and proteins involved in lipid traffic are delivered and made active in phagolysosomes. It also involves extensive membrane remodeling. We report that cation channels that localize to phagolysosomes were essential for resolution. Specifically, the conductance of Na+ by two-pore channels (TPCs) and the presence of a Na+ gradient between the phagolysosome lumen and the cytosol were critical for the controlled release of membrane tension that permits deformation of the limiting phagolysosome membrane. In turn, membrane deformation was a necessary step to efficiently transport the cholesterol extracted from cellular targets, permeabilizing them to hydrolases. These results place TPCs as regulators of endomembrane remodeling events that precede target degradation in cases when the target is bound by a cholesterol-containing membrane. The findings may help to explain lipid metabolism dysfunction and autophagic flux impairment reported in TPC KO mice and establish stepwise regulation to the resolution process that begins with lysis of the target.

The spectrin cytoskeleton integrates endothelial mechanoresponses.

Physiological blood flow induces the secretion of vasoactive compounds, notably nitric oxide, and promotes endothelial cell elongation and reorientation parallel to the direction of applied shear. How shear is sensed and relayed to intracellular effectors is incompletely understood. Here, we demonstrate that an apical spectrin network is essential to convey the force imposed by shear to endothelial mechanosensors. By anchoring CD44, spectrins modulate the cell surface density of hyaluronan and sense and translate shear into changes in plasma membrane tension. Spectrins also regulate the stability of apical caveolae, where the mechanosensitive PIEZO1 channels are thought to reside. Accordingly, shear-induced PIEZO1 activation and the associated calcium influx were absent in spectrin-deficient cells. As a result, cell realignment and flow-induced endothelial nitric oxide synthase stimulation were similarly dependent on spectrin. We conclude that the apical spectrin network is not only required for shear sensing but also transmits and distributes the resulting tensile forces to mechanosensors that elicit protective and vasoactive responses.

The neurorepellent, Slit2, prevents macrophage lipid loading by inhibiting CD36-dependent binding and internalization of oxidized low-density lipoprotein.

Atherosclerosis is characterized by retention of modified lipoproteins, especially oxidized low density lipoprotein (oxLDL) within the sub-endothelial space of affected blood vessels. Recruited monocyte-derived and tissue-resident macrophages subsequently ingest oxLDL by binding and internalizing oxLDL via scavenger receptors, particularly CD36. The secreted neurorepellent, Slit2, acting through its transmembrane receptor, Roundabout-1 (Robo-1), was previously shown to inhibit recruitment of monocytes into nascent atherosclerotic lesions. The effects of Slit2 on oxLDL uptake by macrophages have not been explored. We report here that Slit2 inhibits uptake of oxLDL by human and murine macrophages, and the resulting formation of foam cells, in a Rac1-dependent and CD36-dependent manner. Exposure of macrophages to Slit2 prevented binding of oxLDL to the surface of cells. Using super-resolution microscopy, we observed that exposure of macrophages to Slit2 induced profound cytoskeletal remodeling with formation of a thick ring of cortical actin within which clusters of CD36 could not aggregate, thereby attenuating binding of oxLDL to the surface of cells. By inhibiting recruitment of monocytes into early atherosclerotic lesions, and the subsequent binding and internalization of oxLDL by macrophages, Slit2 could represent a potent new tool to combat individual steps that collectively result in progression of atherosclerosis.

Long-term risk of mortality and other adverse outcomes after acute kidney injury: a systematic review and meta-analysis.

BACKGROUND: Acute kidney injury (AKI) is common in hospitalized patients. The impact of AKI on long-term outcomes is controversial. STUDY DESIGN: Systematic review and meta-analysis. SETTING & PARTICIPANTS: Persons with AKI. SELECTION CRITERIA FOR STUDIES: MEDLINE and EMBASE databases were searched from 1985 through October 2007. Original studies describing outcomes of AKI for patients who survived hospital discharge were included. Studies were excluded from review when participants were followed up for less than 6 months. PREDICTOR: AKI, defined as acute changes in serum creatinine level or acute need for renal replacement therapy. OUTCOMES: Chronic kidney disease (CKD), cardiovascular disease, and mortality. RESULTS: 48 studies that contained a total of 47,017 participants were reviewed; 15 studies reported long-term data for patients without AKI. The incidence rate of mortality was 8.9 deaths/100 person-years in survivors of AKI and 4.3 deaths/100 patient-years in survivors without AKI (rate ratio [RR], 2.59; 95% confidence interval, 1.97 to 3.42). AKI was associated independently with mortality risk in 6 of 6 studies that performed multivariate adjustment (adjusted RR, 1.6 to 3.9) and with myocardial infarction in 2 of 2 studies (RR, 2.05; 95% confidence interval, 1.61 to 2.61). The incidence rate of CKD after an episode of AKI was 7.8 events/100 patient-years, and the rate of end-stage renal disease was 4.9 events/100 patient-years. LIMITATIONS: The relative risk for CKD and end-stage renal disease after AKI was unattainable because of lack of follow-up of appropriate controls without AKI. CONCLUSIONS: The development of AKI, defined as acute changes in serum creatinine level, characterizes hospitalized patients at increased risk of long-term adverse outcomes.

Hypocalcemia in a dialysis patient treated with deferasirox for iron overload.

Deferasirox is a new iron chelator approved recently for chelation therapy in iron-overloaded patients. It is considered safe and efficacious in most patients, but has not been tested formally in patients with end-stage renal disease. We report a case of a patient with end-stage renal disease secondary to sickle cell nephropathy who developed recurrent symptomatic hypocalcemia while on therapy and later reexposure with this medication for iron overload from long-term blood transfusions. This is the first case report of this complication with deferasirox therapy in a patient with end-stage renal disease.