Hypertonic Stress Activates Glycogen Synthase Kinase 3β-mediated Apoptosis of Renal Medullary Interstitial Cells, Suppressing an NFκB-driven Cyclooxygenase-2-dependent Survival Pathway

Abstract

The survival of renal medullary interstitial cells (RMICs) requires their adaptation to rapid shifts in ambient tonicity normally occurring in the renal medulla. Previous studies determined that cyclooxygenase-2 (COX 2) activation is critical for this adaptation. The present studies find that these adaptive mechanisms are dampened by the simultaneous activation of an apoptotic pathway linked to a glycogen synthase kinase 3␤ (GSK 3␤). Inhibition of GSK 3 by LiCl or specific small molecule GSK inhibitors increased RMIC survival following hypertonic stress, and transduction of RMICs with a constitutively active GSK 3␤ (AdGSK 3␤A9) significantly increased apoptosis, consistent with a proapoptotic role of GSK 3␤. Following GSK 3␤ inhibition, increased survival was accompanied by increased COX 2 expression and COX 2 reporter activity. In contrast, GSK 3␤ overexpression reduced COX 2 reporter activity. Importantly, enhanced RMIC survival produced by GSK 3␤ inhibition was completely dependent on COX 2 because it was abolished by a COX 2-specific inhibitor, SC58236. The signaling pathway by which GSK 3␤ suppresses COX 2 expression was then explored. GSK 3␤ inhibition increased both NFB and ␤-catenin activity associated with decreased IB and increased ␤-catenin levels. The increase in COX 2 following GSK 3␤ inhibition was entirely blocked by NFB inhibition using mutant IB adenovirus. However, adenoviral overexpression of ␤-catenin did not increase COX 2 levels. These findings suggest that GSK 3␤ negatively regulates COX 2 expression and that GSK 3␤ inhibitors protect RMICs from hypertonic stress via induction of NFB-COX 2-dependent pathway.To survive and function normally, renal medullary cells rely on a unique ability to withstand the rapidly shifting osmotic environment present in the renal medulla (2). Failure to adapt to the harsh environment in the renal medulla contributes to the development of papillary necrosis, observed following nonsteroidal anti-inflammatory drug use, pregnancy, and diabetes mellitus (3). Hypertonic stress activates two opposing cellular signaling cascades that either lead to cell death or promote cell survival. The balance between these two pathways determines cell fate. Several mechanisms have been proposed to contribute to the ability of renal medullary cells to survive hypertonic stress, including accumulation of organic osmolytes (4, 5) and induction of heat shock proteins (6, 7). In addition, recent studies demonstrate that renal medullary interstitial cells (RMICs) 1 depend on robust COX 2 activity to adapt to hypertonic stress, both in vitro and in vivo (2,8,9). Conversely, the mechanisms contributing to hypertonic stress-induced RMIC cell death are less clearly defined.GSK 3␤ signaling has been implicated in a variety of biological processes associated with altered cell survival and differentiation, including Wnt-associated developmental patterning and ␤-catenin-driven tumorigenesis (10, 11). Recent studies demonstrate that the GSK 3␤ inhibitor lithium protects neurons from stress-indu...

Deregulation of the Phosphatidylinositol-3 Kinase Signaling Cascade Is Associated with Neurodegeneration in Npc1−/− Mouse Brain

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AMPK Potentiates Hypertonicity-induced Apoptosis by Suppressing NFκB/COX-2 in Medullary Interstitial Cells

“…RMICs were transfected with a NFB 3ϫ-luc reporter 52 or a mouse COX-2 promoter (Ϫ815)-luc reporter 53 with Lipofectamine 2000 (Invitrogen) under conditions recommended by the manufacturer. A ␤-galactosidase reporter gene (Promega) was cotransfected for normalization.…”

Severe toxicity and cyclooxygenase (COX)-2 mRNA increase by lithium in the neonatal mouse kidney

“…To this end, we selected a lithium compound as a test chemical by the following reasons. First, lithium has been reported to induce COX-2 in vivo (Rao et al, 2005;Kim et al, 2008) and in vitro (Rao et al, 2004), but no detailed analysis has been performed on the pathogenesis of hydronephrosis. Second, lithium is an important therapeutic drug for treatment of mood disorder and Alzheimer's disease (Eldar-Finkelman, 2002;Luna-Medina et al, 2005;Woodgett, 2001) and has been routinely prescribed in a clinical practice.…”