Supercooling to preserve a renal proximal tubule cell line

This study examines the role of the actin cytoskeleton and integrin expression in the recovery of cell adhesion in the proximal tubule cell line JTC-12 after peroxide injury. The cells were exposed to 10, 20, or 50 mM hydrogen peroxide for 10 min and then allowed to recover. Viability measurements by trypan blue exclusion confirmed that the injury was largely nonlethal with 85% viability at 1 h even at 50 mM peroxide. ATP levels fell immediately after the peroxide incubation in all groups to approximately 10% of normal, but already showed some recovery by 1 h and full recovery in the 10 and 20 mM groups by 24 h. Cell adhesion to extracellular matrix immediately after injury was depressed at 20 and 50 mM peroxide, but by 12 h was abnormal only at 50 mM peroxide and at 24 h was essentially normal at all peroxide concentrations. Immediately after exposure to 10 mM peroxide, there were subtle abnormalities in the actin cytoskeleton (thickening of fibrils) as assessed by phalloidin staining, with more pronounced effects at 20 and 50 mM. At 1 h, many cells showed collapse of the actin cytoskeleton to the periphery. There was some recovery at 4 h; by 12 h, the actin cytoskeleton showed further recovery, although was still abnormal (coarsened microfilaments), especially at 20 and 50 mM peroxide. By 24 h, the actin cytoskeleton showed only subtle coarsening. Integrin surface expression was assessed by flow cytometry. The alpha6 subunit on cells exposed to 20 mM peroxide was unchanged at 1 h and 4 h, but by 12 h had increased to 118.5+/-4.5% and by 24 h to 146+/-13.4% of control levels. The expression of the beta1 and alphaVbeta3 integrins remained unchanged. Thus, despite coarsening of the actin cytoskeleton and depressed ATP levels, cell adhesion recovered from oxidant stress. Abnormal cell adhesion after injury was not a consequence of a decrease in integrin expression, and recovery of cell adhesion was not a consequence of the modest and selective increase in integrin expression.

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ER stress contributes to renal proximal tubule injury by increasing SREBP-2-mediated lipid accumulation and apoptotic cell death

AJP Renal Physiology ◽

10.1152/ajprenal.00482.2011 ◽

2012 ◽

Vol 303 (2) ◽

pp. F266-F278 ◽

Cited By ~ 45

Author(s):

Šárka Lhoták ◽

Sudesh Sood ◽

Elise Brimble ◽

Rachel E. Carlisle ◽

Stephen M. Colgan ◽

...

Keyword(s):

Er Stress ◽

Proximal Tubule ◽

Lipid Accumulation ◽

Cell Injury ◽

Apoptotic Cell ◽

Renal Proximal Tubule ◽

Proximal Tubule Cell ◽

Tubule Cell ◽

Proximal Tubule Cells ◽

Tubule Cells

Renal proximal tubule injury is induced by agents/conditions known to cause endoplasmic reticulum (ER) stress, including cyclosporine A (CsA), an immunosuppressant drug with nephrotoxic effects. However, the underlying mechanism by which ER stress contributes to proximal tubule cell injury is not well understood. In this study, we report lipid accumulation, sterol regulatory element-binding protein-2 (SREBP-2) expression, and ER stress in proximal tubules of kidneys from mice treated with the classic ER stressor tunicamycin (Tm) or in human renal biopsy specimens showing CsA-induced nephrotoxicity. Colocalization of ER stress markers [78-kDa glucose regulated protein (GRP78), CHOP] with SREBP-2 expression and lipid accumulation was prominent within the proximal tubule cells exposed to Tm or CsA. Prolonged ER stress resulted in increased apoptotic cell death of lipid-enriched proximal tubule cells with colocalization of GRP78, SREBP-2, and Ca2+-independent phospholipase A2 (iPLA2β), an SREBP-2 inducible gene with proapoptotic characteristics. In cultured HK-2 human proximal tubule cells, CsA- and Tm-induced ER stress caused lipid accumulation and SREBP-2 activation. Furthermore, overexpression of SREBP-2 or activation of endogenous SREBP-2 in HK-2 cells stimulated apoptosis. Inhibition of SREBP-2 activation with the site-1-serine protease inhibitor AEBSF prevented ER stress-induced lipid accumulation and apoptosis. Overexpression of the ER-resident chaperone GRP78 attenuated ER stress and inhibited CsA-induced SREBP-2 expression and lipid accumulation. In summary, our findings suggest that ER stress-induced SREBP-2 activation contributes to renal proximal tubule cell injury by dysregulating lipid homeostasis.

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Formate: A Critical Intermediate for Chloride Transport in the Proximal Tubule

Physiology ◽

10.1152/physiologyonline.1987.2.5.160 ◽

1987 ◽

Vol 2 (5) ◽

pp. 160-164

Author(s):

LP Karniski ◽

PS Aronson

Keyword(s):

Formic Acid ◽

Proximal Tubule ◽

Cell Membranes ◽

Chloride Transport ◽

Critical Role ◽

Renal Proximal Tubule ◽

Proximal Tubule Cell ◽

Tubule Cell ◽

Active Uptake

Recent experiments unexpectedly suggest that formate plays a critical role in chloride transport across cell membranes. In particular, active uptake of chloride in the renal proximal tubule cell occurs by chloride-formate exchange. Formate recycles from lumen to cell via nonionic diffusion of uncharged formic acid. In this manner, small amounts of formate can facilitate resorption of large quantities of chloride.

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Nitric oxide activates PKCα and inhibits Na+-K+-ATPase in opossum kidney cells

AJP Renal Physiology ◽

10.1152/ajprenal.1999.277.6.f859 ◽

1999 ◽

Vol 277 (6) ◽

pp. F859-F865 ◽

Cited By ~ 15

Author(s):

Mingyu Liang ◽

Franklyn G. Knox

Keyword(s):

Nitric Oxide ◽

Protein Kinase ◽

Proximal Tubule ◽

Cell Line ◽

Soluble Guanylate Cyclase ◽

Inhibitory Effect ◽

Proximal Tubule Cell ◽

Tubule Cell ◽

Opossum Kidney ◽

Ok Cells

Nitric oxide (NO) reduces the molecular activity of Na+-K+-ATPase in opossum kidney (OK) cells, a proximal tubule cell line. In the present study, we investigated the cellular mechanisms for the inhibitory effect of NO on Na+-K+-ATPase. Sodium nitroprusside (SNP), a NO donor, inhibited Na+-K+-ATPase in OK cells, but not in LLC-PK1cells, another proximal tubule cell line. Similarly, phorbol 12-myristate 13-acetate, a protein kinase C (PKC) activator, inhibited Na+-K+-ATPase in OK, but not in LLC-PK1, cells. PKC inhibitors staurosporine or calphostin C, but not the protein kinase G inhibitor KT-5823, abolished the inhibitory effect of NO on Na+-K+-ATPase in OK cells. Immunoblotting demonstrated that treatment with NO donors caused significant translocation of PKCα from cytosolic to particulate fractions in OK, but not in LLC-PK1, cells. Furthermore, the translocation of PKCα in OK cells was attenuated by either the phospholipase C inhibitor U-73122 or the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one. U-73122 also blunted the inhibitory effect of SNP on Na+-K+-ATPase in OK cells. The phospholipase A2inhibitor AACOCF3 did not blunt the inhibitory effect of SNP on Na+-K+-ATPase in OK cells. AACOCF3 alone, however, also decreased Na+-K+-ATPase activity in OK cells. In conclusion, our results demonstrate that NO activates PKCα in OK, but not in LLC-PK1, cells. The activation of PKCα in OK cells by NO is associated with inhibition of Na+-K+-ATPase.

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