Urinary proteins induce lysosomal membrane permeabilization and lysosomal dysfunction in renal tubular epithelial cells

Abstract

Lysosomal membrane permeabilization (LMP) has been shown to cause the release of cathepsins and other hydrolases from the lysosomal lumen to the cytosol and initiate a cell death pathway. Whether proteinuria triggers LMP in renal tubular epithelial cells (TECs) to accelerate the progression of renal tubulointerstitial injury remains unclear. In the present study, we evaluated TEC injury as well as changes in lysosomal number, volume, activity, and membrane integrity after urinary protein overload in vivo and in vitro. Our results revealed that neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels were significantly increased in the urine of patients with minimal change nephrotic syndrome (MCNS) and the culture supernatant of HK-2 cells treated by urinary proteins extracted from MCNS patients. Urinary protein overload also induced apoptotic cell death in HK-2 cells. Importantly, we found that lysosomal volume and number were markedly increased in TECs of patients with MCNS and HK-2 cells overloaded with urinary proteins. However, lysosome function, as assessed by proteolytic degradation of DQ-ovalbumin and cathepsin-B and cathepsin-L activities, was decreased in HK-2 cells overloaded with urinary proteins. Furthermore, urinary protein overload led to a diffuse cytoplasmic immunostaining pattern of cathepsin-B and irregular immunostaining of lysosome-associated membrane protein-1, accompanying a reduction in intracellular acidic components, which could be improved by pretreatment with antioxidant. Taken together, our results indicate that overloading of urinary proteins caused LMP and lysosomal dysfunction at least partly via oxidative stress in TECs.

Chloroquine Autophagic Inhibition Rebalances Th17/Treg-Mediated Immunity and Ameliorates Systemic Lupus Erythematosus

“…Autophagy is a degradative process whereby cytoplasmic content is engulfed by lysosomes and destroyed [31]. It is well known that microtubule-associated protein 1 light chain 3 (LC3)-II and p62 are key markers used to monitor autophagic flux [26,32]. An increase in LC3-II indicates a buildup of autophagic vacuoles, reflecting either increased formation or decreased clearance.…”

Knockdown of RTN1A attenuates ER stress and kidney injury in albumin overload-induced nephropathy

“…It has been recognized that excessive protein in urine is not merely a marker of the kidney injury but has intrinsic cell toxicity that contributes to tubular injury and fibrosis (28). The protein droplets seen in the cytoplasm of proximal tubular cells are associated with an acceleration of tubulointerstitial damage via the proinflammatory response (13,27) and oxidative stress (15,18) in proximal tubules, which, in turn, leads to the excretion of chemokines and cytokines, resulting in inflammation, transformation of interstitial fibroblasts, and fibrosis (6). Therefore, tubular epithelial cells play a central role in orchestrating the progression of proteinuria-induced renal injury and fibrosis.…”

Megalin/Cubulin-Lysosome-mediated Albumin Reabsorption Is Involved in the Tubular Cell Activation of NLRP3 Inflammasome and Tubulointerstitial Inflammation

“…We recently reported that mitochondrial dysfunction and mitochondrial reactive oxygen species are also involved in albumin-induced inflammasomes, but whether lysosomal dysfunction is related with oxidative stress is not known. Another recent study suggested that oxidative stress was involved in the lysosomal dysfunction induced by urinary proteins (18).…”

“…Reactive oxygen species (13), mitochondrial translocation (14), potassium efflux (15), and the cytosolic release of lysosomal cathepsins (16) were identified as possible intermediate cellular signals (17). Several recent reports further demonstrated that the overloading of urinary proteins caused albumin accumulation in lysosomes, lysosomal membrane permeabilization and decreased lysosomal degradation in TECs (18,19). However, whether lysomoal dysfunction affected inflammasome activation in proteinuria-induced renal injury is the subject of intensive research.…”