Global Existence and Uniform Energy Decay Rates for the Semilinear Parabolic Equation with a Memory Term and Mixed Boundary Condition

This work is concerned with a mixed boundary value problem for the semilinear parabolic equation with a memory term and generalized Lewis functions which depends on both spacial variable and time. Under suitable conditions, we prove the existence and uniqueness of global solutions and the energy functional decaying exponentially or polynomially to zero as the time goes to infinity by introducing brief Lyapunov function and precise priori estimates

Endocytosis of Albumin by Podocytes Elicits an Inflammatory Response and Induces Apoptotic Cell Death

<div><p>The presence of albuminuria is strongly associated with progression of chronic kidney disease. While albuminuria has been shown to injure renal proximal tubular cells, the effects of albumin on podocytes have been less well studied. We have addressed the hypothesis that exposure of podocytes to albumin initiates an injury response. We studied transformed human-urine derived podocytes-like epithelial cells (HUPECS, or podocytes). Upon differentiation, these cells retain certain characteristics of differentiated podocytes, including expression of synaptopodin, CD2AP, and nestin. We exposed podocytes to recombinant human albumin, which lacks lipids and proteins that bind serum albumin; this reagent allowed a direct examination of the effects of albumin. Podocytes endocytosed fluoresceinated albumin and this process was inhibited at 4°C, suggesting an energy-dependent process. Exposure to albumin at concentrations of 5 and 10 mg/ml was associated with increased cell death in a dose-dependent manner. The mechanism of cell death may involve apoptosis, as caspase 3/7 were activated and the pan-caspase inhibitor z-VAD reduced cell death. Albumin exposure also increased nuclear factor (NF)-κB activation and increased transcription and release of interleukin (IL-) 1β, tumor necrosis factor (TNF), and IL-6. We extended these findings to an <em>in vivo</em> model. Glomeruli isolated from mice with nephrotic syndrome also had increased expression of IL-1β and TNF RNA. These data suggest that while podocyte injury begets albuminuria, albumin in the glomerular ultrafiltrate may also beget podocyte injury. Thus, an additional mechanism by which anti-proteinuric therapies are beneficial in the treatment of glomerular diseases may be a reduction in injury to the podocyte by albumin.</p> </div

Albumin exposure activates NFκB.

<p><i>A</i>, Confocal images of cultured human podocytes without treatment (top panel), and treated with 5 mg/ml dextran (middle panel) or 5 mg/ml recombinant human albumin (bottom panel) for 8 hrs. Cells were stained with an antibody against NFκB and with DAPI for nuclear localization. Albumin treatment, but not dextran treatment, was associated with translocation of NFκB to the cell nucleus. <i>B</i>, Albumin exposure leads to IκB degradation in podocytes. Western blot of lysate from podocytes treated with 5 mg/ml recombinant human albumin (A) or dextran (D) for 1 hr, 3 hrs or 6 hrs and probed with an antibody to IκB. Albumin treatment causes an initial degradation of IκB which is required for NFκB activation. α-tubulin is shown as a loading control. Graph to the right of the Western shows densitometric quantitation of the IκB band normalized to α-tubulin. * denotes P = 0.03 compared to dextran treated control cells.</p

Cultured human podocytes endocytose albumin.

<p><i>A</i>, Confocal image of cultured human podocytes placed at 4°C (inhibits endocytosis) or 37°C (promotes endocytosis) and treated with 1.5 mg/ml human FITC-albumin. Bright green vesicles seen in the podocytes at 37°C are FITC-albumin containing endosomes. <i>B,</i> Podocytes were treated with 1.5 mg/ml FITC-albumin at 4°C or 37°C for 2 hrs. There is a significant increase in the amount of albumin taken up by podocytes at 37°C compared to those at 4°C. * denotes P = 0.01 compared to albumin uptake at 4°C.</p

Albumin exposure upregulates pro-apoptotic pathways in podocytes.

<p><i>A</i>, Activated caspase 3/7 activity normalized to total cellular protein in podocytes treated with 5 mg/ml albumin (closed bars) or 5 mg/ml dextran (open bars) as an oncotic control for the indicated amounts of time. * denotes P<0.0001 compared to corresponding dextran treated control. <i>B</i>, TUNEL staining of cultured podocytes treated with 5 mg/ml dextran (Dex) or 5 mg/ml albumin (Alb). Nuclei are stained blue with DAPI. TUNEL-positive nuclei are green. <i>C,</i> Caspase 3/7 activity normalized to total cellular protein in podocytes treated with 5 mg/ml albumin or 5 mg/ml albumin +50 µM z-VAD, a pan-caspase inhibitor. z-VAD largely abrogated caspase activity (*, P = 0.01 versus albumin+z-VAD). <i>D</i>, Percentage of dead cells measured using the trypan blue assay in podocytes treated with 5 mg/ml albumin alone (open bar) or 5 mg/ml albumin +50 µM z-VAD (closed bar) for 24 hrs or 5 mg/ml albumin alone (horizontal hatched bar) or 5 mg/ml albumin +50 µM z-VAD for 48 hrs (vertical hatched bar). * denotes P = 0.001 compared to albumin+z-VAD at 48 hrs.</p

Albumin exposure modulates pro-inflammatory cytokine expression and release in human podocytes.

<p><i>A</i>, Time course of IL-1β RNA levels in podocytes treated with 5 mg/ml recombinant low endotoxin human albumin (closed bars) or 5 mg/ml dextran (open bars). * denotes P = 0.0002 compared to dextran controls. <i>B</i>, Time course of TNF RNA expression in podocytes treated with 5 mg/ml human albumin (closed bars) or 5 mg/ml dextran (open bars). * denotes P = 0.01 compared to dextran control. <i>C</i>, IL-6 RNA levels in podocytes treated with 5 mg/ml human albumin (closed bars) or 5 mg/ml dextran (open bars). * denotes P = 0.008 compared to dextran control. D, Amount of IL-1β normalized to total cellular protein released into the medium after treatment of podocytes with 5 mg/ml recombinant human albumin (closed bars) or 5 mg/ml dextran (open bars) for varying amounts of time. * denotes P = 0.005 compared to dextran treated controls. <i>E</i>, Amount of TNF normalized to total cellular protein released into the medium by podocytes after treatment with albumin (closed bars) or dextran (open bars) for varying amounts of time. * denotes P = 0.003 compared to dextran treated control cells. <i>F</i>, Levels of IL-6 normalized to total cellular protein released into the medium by podocytes treated with albumin (closed bars) or dextran (open bars) for varying amounts of time. * denotes P<0.0001 compared to dextran treated controls.</p

Albumin overload induces proteinuria and upregulates pro-inflammatory cytokine expression in isolated mouse glomeruli.

<p><i>A</i>, Urinary protein normalized to urinary creatinine in mice injected with saline (open bar) or low endotoxin bovine serum albumin (BSA; closed bar; n = 4 animals per group). * denotes P = 0.004 compared to saline injected controls. <i>B</i>, IL-1β expression in isolated glomeruli from mice injected with saline (open bar) or BSA (closed bar; n = 4 animals per group). * denotes P = 0.02 compared to controls. <i>C</i>, TNF expression in isolated glomeruli from mice injected with saline (open bar) or BSA (closed bar; n = 4 animals per group). * denotes P = 0.02 compared to controls. <i>D</i>, IL-6 expression in isolated glomeruli from mice injected with saline (open bar) or BSA (closed bar; n = 4 animals per group).</p