GSK3β Promotes Apoptosis after Renal Ischemic Injury

Abstract

The mechanism by which the serine-threonine kinase glycogen synthase kinase-3␤ (GSK3␤) affects survival of renal epithelial cells after acute stress is unknown. Using in vitro and in vivo models, we tested the hypothesis that GSK3␤ promotes Bax-mediated apoptosis, contributing to tubular injury and organ dysfunction after acute renal ischemia. Exposure of renal epithelial cells to metabolic stress activated GSK3␤, Bax, and caspase 3 and induced apoptosis. Expression of a constitutively active GSK3␤ mutant activated Bax and decreased cell survival after metabolic stress. In contrast, pharmacologic inhibition (4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione [TDZD-8]) or RNA interference-mediated knockdown of GSK3␤ promoted cell survival. Furthermore, RNA interference-mediated knockdown of Bax abrogated the cell death induced by constitutively active GSK3␤. In a cell-free assay, TDZD-8 inhibited the phosphorylation of a peptide containing the Bax serine 163 site targeted by stress-activated GSK3␤. In rats, TDZD-8 inhibited ischemia-induced activation of GSK3␤, Bax, and caspase 3; ameliorated tubular and epithelial cell damage; and significantly protected renal function. Taken together, GSK3␤-mediated Bax activation induces apoptosis and tubular damage that contribute to acute ischemic kidney injury.

Conditional Knockout of Proximal Tubule Mitofusin 2 Accelerates Recovery and Improves Survival after Renal Ischemia

“…Twenty-four and forty-eight hours after 28 minutes of bilateral renal pedicle clamping, renal function was assessed in surviving Kap2-Cre/Mfn2 ff mice with conditional KO of PT (cKO-PT) Mfn2. The mean serum BUN level (a reliable estimate of renal function in this ischemia model that parallels measures of serum creatinine in this model [19][20][21] ) was significantly lower in mice with cKO-PT Mfn2 (P,0.04) at both time points (Figure 2A). Importantly, BUN was measured in only 9 of 18 of the surviving control animals, likely underestimating the severity of AKI in this group.…”

Lithium in the Kidney: Friend and Foe?

“…99,100 Different GSK3 inhibitors, including lithium, prevent ROS-induced apoptosis of mesangial cells and renal proximal epithelial cells. 87,[101][102][103] Although the molecular mechanism by which GSK3 inhibition prevents renal oxidative damage has not been investigated, studies on extrarenal tissues show that ROSinduced GSK3 activation induces the opening of the mitochondrial permeability transition pore, eventually resulting in cell death. 104,105 Active GSK3a/b induces permeability transition pore opening by activating Bax and BIM in the cytosol and cyclophilin-D in the mitochondrion (Figure 2, right panel).…”

Lithium in Kidney Diseases

“…After 24-hour reperfusion, serum creatinine was significantly increased and the high level of serum creatinine was maintained at 48 hours, suggesting that kidney injury, and not repair or recovery, still predominated. 10 Therefore, the protective effects of lithium on renal function and tubular damage could be the result of suppressing cell death, as suggested by other studies, [6][7][8][9] and not the result of promoting cell proliferation and regeneration. The effect of lithium on renal recovery in ischemic AKI should be better observed within a reperfusion period.48 hours to ensure that the recovery does occur.…”

“…5 In stark contrast, if used briefly and at low doses, lithium can be renoprotective. In this regard, recent studies have shown the protective effects of lithium in experimental models of AKI induced by renal ischemia-reperfusion, 6,7 nephrotoxin, 8 and endotoxin. 9 In this issue of JASN, Bao et al report that a single dose of lithium given after AKI promotes the recovery and repair of kidneys, whereas de Groot and colleagues show that lithium induces G2 cell cycle arrest in the principal cells of the collecting ducts, which may contribute to the development of NDI.…”

“…10 It is noteworthy that lithium was given during the recovery phase of AKI in this study, and, therefore, the observed effect is distinct from those shown for lithium given before or during AKI. [6][7][8][9] To further understand how lithium promotes renal recovery after AKI, Bao et al went on to examine glycogen synthase kinase-3b (GSK3b), a direct and relatively specific target of lithium. 10 Not surprisingly, cisplatin led to activation of GSK3b both in kidneys and in cultured renal tubular cells, which was inhibited by postinjury lithium treatment.…”