Abstract
In the passive Heymann nephritis (PHN) model of membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury, proteinuria, and activation of cytosolic phospholipase A(2) (cPLA(2)). This study addresses the role of endoplasmic reticulum (ER) stress proteins (bip, grp94) in GEC injury. GEC that overexpress cPLA(2) (produced by transfection) and "neo" GEC (which expresses cPLA(2) at a lower level) were incubated with complement (40 min), and leakage of constitutively expressed bip and grp94 from ER into cytosol was measured to monitor ER injury. Greater leakage of bip and grp94 occurred in complement-treated GEC that overexpress cPLA(2), as compared with neo, implying that cPLA(2) activation perturbed ER membrane integrity. After chronic incubation (4-24 h), C5b-9 increased bip and grp94 mRNAs and proteins, and the increases were dependent on cPLA(2). Expression of bip-antisense mRNA reduced stimulated bip protein expression and enhanced complement-dependent GEC injury. Glomerular bip and grp94 proteins were up-regulated in proteinuric rats with PHN, as compared with normal control. Pretreatment of rats with tunicamycin or adriamycin, which increase ER stress protein expression, reduced proteinuria in PHN. Thus, C5b-9 injures the ER and enhances ER stress protein expression, in part, via activation of cPLA(2). ER stress protein induction is a novel mechanism of protection from complement attack.
Highlights
Activation of the complement cascade near a cell surface leads to assembly of terminal components, exposure of hydrophobic domains, and insertion of the C5b-9 membrane attack complex into the lipid bilayer of the plasma membrane [1, 2]
The activation of cytosolic phospholipase A2 (cPLA2) and release of arachidonic acid (AA) are compartmentalized to specific organelles, but it is presently unknown if hydrolysis of membrane phospholipids by cPLA2 leads to injury of these organelles in glomerular epithelial cell (GEC)
We show that cPLA2 activation in GEC was associated with leakage of luminal endoplasmic reticulum (ER) stress proteins into the cytosol (Fig. 1), suggesting that cPLA2-induced phospholipid hydrolysis resulted in impairment of ER membrane integrity
Summary
Activation of the complement cascade near a cell surface leads to assembly of terminal components, exposure of hydrophobic domains, and insertion of the C5b-9 membrane attack complex into the lipid bilayer of the plasma membrane [1, 2]. Based on studies in GEC culture and in vivo, C5b-9 assembly induces transactivation of receptor tyrosine kinases [15], an increase in cytosolic free Ca2ϩ concentration ([Ca2ϩ]i), and activation of protein kinase C, as well as cytosolic phospholipase A2-␣ (cPLA2) (16 –19). The activation of cPLA2 and release of AA are compartmentalized to specific organelles, but it is presently unknown if hydrolysis of membrane phospholipids by cPLA2 leads to injury of these organelles in GEC. Exposure of cells to mild stress, which induces ER stress proteins, may be protective to additional insults [33, 34], prolonged or more substantial ER stress may lead to cell death by apoptosis [35]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
