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Aims: Interventions to inhibit oxidative stress and apoptosis, important pathogenic contributors toward the progression of chronic kidney disease (CKD), are not well established. Here, we investigated the role of a transforming growth factor beta (TGFβ) superfamily neutralizing protein, follistatin (FST), in the regulation of apoptosis and oxidative stress in glomerular mesangial cells (MCs) and in the progression of CKD. Results: The endoplasmic reticulum (ER) stress inducer thapsigargin (Tg), known to cause MC apoptosis, led to a post-translational increase in the expression of FST. Recombinant FST protected, whereas FST downregulation augmented, Tg-induced apoptosis without affecting Ca 2+ release or ER stress induction. Although activins are the primary ligands neutralized by FST, their inhibition with neutralizing antibodies did not affect Tg-induced apoptosis. Instead, FST protected against Tg-induced apoptosis through neutralization of reactive oxygen species (ROS) independently of its ability to neutralize activins. Importantly, administration of FST to mice with CKD protected against renal cell apoptosis and oxidative stress. This was associated with improved kidney function, reduced albuminuria, and attenuation of fibrosis. Innovation and Conclusion: Independent of its activin neutralizing ability, FST protected against Tg-induced apoptosis through neutralization of ROS and consequent suppression of oxidative stress, seen both in vitro and in vivo . Importantly, FST also ameliorated fibrosis and improved kidney function in CKD. FST is, thus, a novel potential therapeutic agent for delaying the progression of CKD. Antioxid. Redox Signal . 31, 551-571.

Increased intraglomerular pressure leads to kidney fibrosis, and can be modeled by exposing glomerular mesangial cells (MC) to mechanical strain. We previously showed that RhoA mediates strain-induced matrix production. Here we investigate whether reactive oxygen species (ROS) are required for RhoA activation. Maximal RhoA activation (1 min) was inhibited by ROS scavenge or NADPH oxidase inhibition. Strain activated NADPH oxidase, with Rac1, p47(phox), and p67(phox) membrane translocation, and Rac1 activation, observed within 30 sec. Epidermal growth factor receptor (EGFR) inhibition blocked RhoA and Rac1 activation, p67(phox) membrane translocation, and ROS generation. However, EGFR activation was unaffected by ROS inhibitors, placing it upstream of ROS generation. We previously showed, using chemical disruption, that caveolae mediate strain-induced EGFR and RhoA activation. In MC from caveolin-1 knockout mice, which lack caveolae, RhoA and Rac1 activation, p67(phox) membrane translocation, and ROS generation were absent. These were rescued by caveolin-1 re-expression. ROS generation, Rac1 activation, and p67(phox) membrane translocation were also prevented by Src inhibition. They were absent in MC stably infected with caveolin-1 Y14A, a mutant resistant to Src phosphorylation. In MC, caveolae are thus important mediators of strain-induced ROS generation through NADPH oxidase, mediating a signaling cascade which results in RhoA activation.

The accumulation of unfolded proteins in the endoplasmic reticulum (ER), leading to ER stress, is caused by a wide range of physiologic and pathologic conditions. Cells respond to ER stress by activating a series of integrative stress pathways termed the unfolded protein response (UPR). This either may be adaptive and promote cell survival, or if the ER stress is chronic or excessive, may lead to cell death. The role of ER stress in the pathophysiology of both acute and chronic kidney diseases has been gaining increasing interest. This review highlights the current knowledge of ER stress in renal disease, with emphasis on more recent advances. Potential therapeutic options targeting ER stress are discussed.