Albumin overload induces adaptive responses in human proximal tubular cells through oxidative stress but not via angiotensin II type 1 receptor

Activation of G protein-coupled estrogen receptor 1 ameliorates proximal tubular injury and proteinuria in Dahl salt-sensitive female rats

Recent evidence indicates a crucial role for G protein-coupled estrogen receptor 1 (GPER1) in the maintenance of cardiovascular and kidney health in females. The current study tested whether GPER1 activation ameliorates hypertension and kidney damage in female Dahl salt-sensitive (SS) rats fed a high-salt (HS) diet. Adult female rats were implanted with telemetry transmitters for monitoring blood pressure and osmotic minipumps releasing G1 (selective GPER1 agonist, 400 μg/kg/day ip) or vehicle. Two weeks after pump implantation, rats were shifted from a normal-salt (NS) diet (0.4% NaCl) to a matched HS diet (4.0% NaCl) for 2 wk. Twenty-four hour urine samples were collected during both diet periods and urinary markers of kidney injury were assessed. Histological assessment of kidney injury was conducted after the 2-wk HS diet period. Compared with values during the NS diet, 24-h mean arterial pressure markedly increased in response to HS, reaching similar values in vehicle-treated and G1-treated rats. HS also significantly increased urinary excretion of protein, albumin, nephrin (podocyte damage marker), and KIM-1 (proximal tubule injury marker) in vehicle-treated rats. Importantly, G1 treatment prevented the HS-induced proteinuria, albuminuria, and increase in KIM-1 excretion but not nephrinuria. Histological analysis revealed that HS-induced glomerular damage did not differ between groups. However, G1 treatment preserved proximal tubule brush-border integrity in HS-fed rats. Collectively, our data suggest that GPER1 activation protects against HS-induced proteinuria and albuminuria in female Dahl SS rats by preserving proximal tubule brush-border integrity in a blood pressure-independent manner.

Cardioprotective Effects of Curcumin-Nisin Based Poly Lactic Acid Nanoparticle on Myocardial Infarction in Guinea Pigs

Myocardial infarction (MI) is the most prevalent cause of cardiovascular death. A possible way of preventing MI maybe by dietary supplements. The present study was thus designed to ascertain the cardio-protective effect of a formulated curcumin and nisin based poly lactic acid nanoparticle (CurNisNp) on isoproterenol (ISO) induced MI in guinea pigs. Animals were pretreated for 7 days as follows; Groups A and B animals were given 0.5 mL/kg of normal saline, group C metoprolol (2 mg/kg), groups D and E CurNisNp 10 and 21 mg/kg respectively (n = 5). MI was induced on the 7^th day in groups B-E animals. On the 9^th day electrocardiogram (ECG) was recorded, blood samples and tissue biopsies were collected for analyses. Toxicity studies on CurNisNp were carried out. MI induction caused atrial fibrillation which was prevented by pretreatment of metoprolol or CurNisNp. MI induction was also associated with increased expressions of cardiac troponin I (CTnI) and kidney injury molecule-1 (KIM-1) which were significantly reduced in guinea pig's pretreated with metoprolol or CurNisNp (P < 0.05). The LC₅₀ of CurNisNp was 3258.2 μg/mL. This study demonstrated that the formulated curcumin-nisin based nanoparticle confers a significant level of cardio-protection in the guinea pig and is nontoxic.

Oxidative stress increases megalin expression in the renal proximal tubules during the normoalbuminuric stage of diabetes mellitus

Megalin, an endocytic receptor expressed in proximal tubule cells, plays a critical role in renal tubular protein reabsorption and is associated with the albuminuria observed in diabetic nephropathy. We have previously reported increased oxidant production in the renal cortex during the normoalbuminuric stage of diabetes mellitus (DM); however, the relationship between oxidative stress and renal megalin expression during the normoalbuminuric stage of DM remains unclear. In the present study, we evaluated whether oxidative stress affects megalin expression in the normoalbuminuric stage of DM in a streptozotocin-induced diabetic rat model and in immortalized human proximal tubular cells (HK-2). We demonstrated that increased expression of renal megalin accompanies oxidative stress during the early stage of DM, before albuminuria development. Telmisartan treatment prevented the diabetes-induced elevation in megalin level, possibly through an oxidative stress-dependent mechanism. In HK-2 cells, hydrogen peroxide significantly increased megalin levels in a dose- and time-dependent manner; however, the elevation in megalin expression was decreased following prolonged exposure to severe oxidative stress induced by 0.4 mmol/l hydrogen peroxide. High-glucose treatment also significantly increased megalin expression in HK-2 cells. Concurrent administration of the antioxidant N-acetyl-cysteine blocked the effects of high glucose on megalin expression. Furthermore, the hydrogen peroxide-induced increase in megalin expression was blocked by treatment with phosphatidylinositol 3-kinase and Akt inhibitors. Increase of phosphorylated Akt expression was also seen in the renal cortex of diabetic rats. Taken together, our results indicate that mild oxidative stress increases renal megalin expression through the phosphatidylinositol 3-kinase-Akt pathway in the normoalbuminuric stage of DM.

Hypoxia inducible factor-1α mediates the profibrotic effect of albumin in renal tubular cells

Proteinuria is closely associated with the progression of chronic kidney diseases (CKD) by producing renal tubulointerstitial fibrosis. Over-activation of hypoxia inducible factor (HIF)-1α has been implicated in the progression of CKD. The present study tested the hypothesis that HIF-1α mediates albumin-induced profibrotic effect in cultured renal proximal tubular cells. Incubation of the cells with albumin (40 μg/ml) for 72 hrs significantly increased the protein levels of HIF-1α, tissue inhibitor of metalloproteinase (TIMP)-1 and collagen-I, which were blocked by HIF-1α shRNA. Albumin also stimulated an epithelial-mesenchymal transition (EMT) as indicated by the decrease in epithelial marker E-cadherin, and the increase in mesenchymal markers α-smooth muscle actin and fibroblast-specific protein 1. HIF-1α shRNA blocked albumin-induced changes in these EMT markers as well. Furthermore, albumin reduced the level of hydroxylated HIF-1α, indicating an inhibition of the activity of prolyl-hydroxylases, enzymes promoting the degradation of HIF-1α. An anti-oxidant ascorbate reversed albumin-induced inhibition of prolyl-hydroxylase activity. Overexpression of prolyl-hydroxylase 2 (PHD2) transgene, a predominant isoform of PHDs in renal tubules, to reduce HIF-1α level significantly attenuated albumin-induced increases in TIMP-1 and collagen-I levels. These results suggest that albumin-induced oxidative stress inhibits PHD activity to accumulate HIF-1α, which mediates albumin-induced profibrotic effects in renal tubular cells.

Fatty Acids in Nephrotic Syndrome and Chronic Kidney Disease

The role of fatty acids (FAs) in inflammation and in the related chronic diseases has been demonstrated. However, there is a lack of consistent and agreed knowledge about the role of FA profile and renal physiology and pathology, most articles focusing on the effect of polyunsaturated FAs supplementation, without considering the impact of basal FA metabolism on the efficacy of the supplementation. Here, we have summarized the specific literature concerning the assessment of circulating FA in 2 renal diseases, namely nephrotic syndrome and chronic kidney disease, also under hemodialytic treatment, and have received the most significant contributions in the last years. The effects of changes of FA profile and metabolism and the possible involvement of polyunsaturated FA metabolites in raising and modulating inflammation are discussed.

Intravital imaging of the kidney in a rat model of salt-sensitive hypertension

Hypertension is one of the most prevalent diseases worldwide and a major risk factor for renal failure and cardiovascular disease. The role of albuminuria, a common feature of hypertension and robust predictor of cardiorenal disorders, remains incompletely understood. The goal of this study was to investigate the mechanisms leading to albuminuria in the kidney of a rat model of hypertension, the Dahl salt-sensitive (SS) rat. To determine the relative contributions of the glomerulus and proximal tubule (PT) to albuminuria, we applied intravital two-photon-based imaging to investigate the complex renal physiological changes that occur during salt-induced hypertension. Following a high-salt diet, SS rats exhibited elevated blood pressure, increased glomerular sieving of albumin (GSC_alb = 0.0686), relative permeability to albumin (+Δ16%), and impaired volume hemodynamics (-Δ14%). Serum albumin but not serum globulins or creatinine concentration was decreased (-0.54 g/dl), which was concomitant with increased filtration of albumin (3.7 vs. 0.8 g/day normal diet). Pathologically, hypertensive animals had significant tubular damage, as indicated by increased prevalence of granular casts, expansion and necrosis of PT epithelial cells (+Δ2.20 score/image), progressive augmentation of red blood cell velocity (+Δ269 µm/s) and micro vessel diameter (+Δ4.3 µm), and increased vascular injury (+Δ0.61 leakage/image). Therefore, development of salt-induced hypertension can be triggered by fast and progressive pathogenic remodeling of PT epithelia, which can be associated with changes in albumin handling. Collectively, these results indicate that both the glomerulus and the PT contribute to albuminuria, and dual treatment of glomerular filtration and albumin reabsorption may represent an effective treatment of salt-sensitive hypertension.

Oxidant Mechanisms in Renal Injury and Disease

SIGNIFICANCE

A common link between all forms of acute and chronic kidney injuries, regardless of species, is enhanced generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) during injury/disease progression. While low levels of ROS and RNS are required for prosurvival signaling, cell proliferation and growth, and vasoreactivity regulation, an imbalance of ROS and RNS generation and elimination leads to inflammation, cell death, tissue damage, and disease/injury progression.

RECENT ADVANCES

Many aspects of renal oxidative stress still require investigation, including clarification of the mechanisms which prompt ROS/RNS generation and subsequent renal damage. However, we currently have a basic understanding of the major features of oxidative stress pathology and its link to kidney injury/disease, which this review summarizes.

CRITICAL ISSUES

The review summarizes the critical sources of oxidative stress in the kidney during injury/disease, including generation of ROS and RNS from mitochondria, NADPH oxidase, and inducible nitric oxide synthase. The review next summarizes the renal antioxidant systems that protect against oxidative stress, including superoxide dismutase and catalase, the glutathione and thioredoxin systems, and others. Next, we describe how oxidative stress affects kidney function and promotes damage in every nephron segment, including the renal vessels, glomeruli, and tubules.

FUTURE DIRECTIONS

Despite the limited success associated with the application of antioxidants for treatment of kidney injury/disease thus far, preventing the generation and accumulation of ROS and RNS provides an ideal target for potential therapeutic treatments. The review discusses the shortcomings of antioxidant treatments previously used and the potential promise of new ones. Antioxid. Redox Signal. 25, 119-146.

Albumin contributes to kidney disease progression in Alport syndrome

Alport syndrome is a familial kidney disease caused by defects in the collagen type IV network of the glomerular basement membrane. Lack of collagen-α3α4α5(IV) changes the glomerular basement membrane morphologically and functionally, rendering it leaky to albumin and other plasma proteins. Filtered albumin has been suggested to be a cause of the glomerular and tubular injuries observed at advanced stages of Alport syndrome. To directly investigate the role that albumin plays in the progression of disease in Alport syndrome, we generated albumin knockout (Alb(-/-)) mice to use as a tool for removing albuminuria as a component of kidney disease. Mice lacking albumin were healthy and indistinguishable from control littermates, although they developed hypertriglyceridemia. Dyslipidemia was observed in Alb(+/-) mice, which displayed half the normal plasma albumin concentration. Alb mutant mice were bred to collagen-α3(IV) knockout (Col4a3(-/-)) mice, which are a model for human Alport syndrome. Lack of circulating and filtered albumin in Col4a3(-/-);Alb(-/-) mice resulted in dramatically improved kidney disease outcomes, as these mice lived 64% longer than did Col4a3(-/-);Alb(+/+) and Col4a3(-/-);Alb(+/-) mice, despite similar blood pressures and serum triglyceride levels. Further investigations showed that the absence of albumin correlated with reduced transforming growth factor-β1 signaling as well as reduced tubulointerstitial, glomerular, and podocyte pathology. We conclude that filtered albumin is injurious to kidney cells in Alport syndrome and perhaps in other proteinuric kidney diseases, including diabetic nephropathy.

The Mechanisms of Human Renal Epithelial Cell Modulation of Autologous Dendritic Cell Phenotype and Function

Proximal tubule epithelial cells (PTEC) of the kidney line the proximal tubule downstream of the glomerulus and play a major role in the re-absorption of small molecular weight proteins that may pass through the glomerular filtration process. In the perturbed disease state PTEC also contribute to the inflammatory disease process via both positive and negative mechanisms via the production of inflammatory cytokines which chemo-attract leukocytes and the subsequent down-modulation of these cells to prevent uncontrolled inflammatory responses. It is well established that dendritic cells are responsible for the initiation and direction of adaptive immune responses. Both resident and infiltrating dendritic cells are localised within the tubulointerstitium of the renal cortex, in close apposition to PTEC, in inflammatory disease states. We previously demonstrated that inflammatory PTEC are able to modulate autologous human dendritic cell phenotype and functional responses. Here we extend these findings to characterise the mechanisms of this PTEC immune-modulation using primary human PTEC and autologous monocyte-derived dendritic cells (MoDC) as the model system. We demonstrate that PTEC express three inhibitory molecules: (i) cell surface PD-L1 that induces MoDC expression of PD-L1; (ii) intracellular IDO that maintains the expression of MoDC CD14, drives the expression of CD80, PD-L1 and IL-10 by MoDC and inhibits T cell stimulatory capacity; and (iii) soluble HLA-G (sHLA-G) that inhibits HLA-DR and induces IL-10 expression by MoDC. Collectively the results demonstrate that primary human PTEC are able to modulate autologous DC phenotype and function via multiple complex pathways. Further dissection of these pathways is essential to target therapeutic strategies in the treatment of inflammatory kidney disorders.

The endocytic receptor megalin and its associated proteins in proximal tubule epithelial cells

Receptor-mediated endocytosis in renal proximal tubule epithelial cells (PTECs) is important for the reabsorption and metabolization of proteins and other substances, including carrier-bound vitamins and trace elements, in glomerular filtrates. Impairment of this endocytic process results in the loss of such substances and development of proteinuria, which is an important clinical indicator of kidney diseases and is also a risk marker for cardiovascular disease. Megalin, a member of the low-density lipoprotein receptor gene family, is a multiligand receptor expressed in the apical membrane of PTECs and plays a central role in the endocytic process. Megalin interacts with various intracellular adaptor proteins for intracellular trafficking and cooperatively functions with other membrane molecules, including the cubilin-amnionless complex. Evidence suggests that megalin and the cubilin-amnionless complex are involved in the uptake of toxic substances into PTECs, which leads to the development of kidney disease. Studies of megalin and its associated molecules will be useful for future development of novel strategies for the diagnosis and treatment of kidney diseases.

Kidney injury molecule-1 expression in IgA nephropathy and its correlation with hypoxia and tubulointerstitial inflammation

Tubulointerstitial injury plays an important role in the development and progression of chronic kidney disease (CKD). Kidney injury molecule (KIM)-1 is induced in damaged proximal tubules in both acute renal injury and CKD. However, the dynamics of KIM-1 in CKD and effects of KIM-1 expression on disease progression are unknown. Here, we aimed to determine the associations between tubular KIM-1 expression levels, renal function, and inflammation in CKD. The relationships between levels of KIM-1 and clinicopathological parameters were analyzed in patients with progressive and nonprogressive IgA nephropathy. KIM-1 expression was increased in patients with IgA nephropathy, and its expression was significantly correlated with the decrease of renal function. KIM-1 was particularly evident at the site with reduced capillary density, and KIM-1-positive tubules were surrounded by infiltrates of inflammatory cells. Using in vitro cell models, we showed that cellular stressors, including hypoxia, induced KIM-1 expression. KIM-1-expressing cells produced more chemokines/cytokines when cultured under hypoxic conditions. Furthermore, we showed that tubular cells with KIM-1 expression can regulate the immune response of inflammatory cells through the secretion of chemotactic factors. These data suggest that KIM-1-expressing epithelial cells may play a role in the pathogenesis of tubulointerstitial inflammation during chronic renal injury through the secretion of chemokines/cytokines.

Albumin-bound fatty acids but not albumin itself alter redox balance in tubular epithelial cells and induce a peroxide-mediated redox-sensitive apoptosis

Albuminuria is associated with metabolic syndrome and diabetes. It correlates with the progression of chronic kidney disease, particularly with tubular atrophy. The fatty acid load on albumin significantly increases in obesity, presenting a proinflammatory environment to the proximal tubules. However, little is known about changes in the redox milieu during fatty acid overload and how redox-sensitive mechanisms mediate cell death. Here, we show that albumin with fatty acid impurities or conjugated with palmitate but not albumin itself compromised mitochondrial and cell viability, membrane potential and respiration. Fatty acid overload led to a redox imbalance which deactivated the antioxidant protein peroxiredoxin 2 and caused a peroxide-mediated apoptosis through the redox-sensitive pJNK/caspase-3 pathway. Transfection of tubular cells with peroxiredoxin 2 was protective and mitigated apoptosis. Mitochondrial fatty acid entry and ceramide synthesis modulators suggested that mitochondrial β oxidation but not ceramide synthesis may modulate lipotoxic effects on tubular cell survival. These results suggest that albumin overloaded with fatty acids but not albumin itself changes the redox environment in the tubules, inducing a peroxide-mediated redox-sensitive apoptosis. Thus, mitigating circulating fatty acid levels may be an important factor in both preserving redox balance and preventing tubular cell damage in proteinuric diseases.

Laser capture microdissection and multiplex-tandem PCR analysis of proximal tubular epithelial cell signaling in human kidney disease

Interstitial fibrosis, a histological process common to many kidney diseases, is the precursor state to end stage kidney disease, a devastating and costly outcome for the patient and the health system. Fibrosis is historically associated with chronic kidney disease (CKD) but emerging evidence is now linking many forms of acute kidney disease (AKD) with the development of CKD. Indeed, we and others have observed at least some degree of fibrosis in up to 50% of clinically defined cases of AKD. Epithelial cells of the proximal tubule (PTEC) are central in the development of kidney interstitial fibrosis. We combine the novel techniques of laser capture microdissection and multiplex-tandem PCR to identify and quantitate "real time" gene transcription profiles of purified PTEC isolated from human kidney biopsies that describe signaling pathways associated with this pathological fibrotic process. Our results: (i) confirm previous in-vitro and animal model studies; kidney injury molecule-1 is up-regulated in patients with acute tubular injury, inflammation, neutrophil infiltration and a range of chronic disease diagnoses, (ii) provide data to inform treatment; complement component 3 expression correlates with inflammation and acute tubular injury, (iii) identify potential new biomarkers; proline 4-hydroxylase transcription is down-regulated and vimentin is up-regulated across kidney diseases, (iv) describe previously unrecognized feedback mechanisms within PTEC; Smad-3 is down-regulated in many kidney diseases suggesting a possible negative feedback loop for TGF-β in the disease state, whilst tight junction protein-1 is up-regulated in many kidney diseases, suggesting feedback interactions with vimentin expression. These data demonstrate that the combined techniques of laser capture microdissection and multiplex-tandem PCR have the power to study molecular signaling within single cell populations derived from clinically sourced tissue.

Mutations in the intellectual disability gene Ube2a cause neuronal dysfunction and impair parkin-dependent mitophagy

The prevalence of intellectual disability is around 3%; however, the etiology of the disease remains unclear in most cases. We identified a series of patients with X-linked intellectual disability presenting mutations in the Rad6a (Ube2a) gene, which encodes for an E2 ubiquitin-conjugating enzyme. Drosophila deficient for dRad6 display defective synaptic function as a consequence of mitochondrial failure. Similarly, mouse mRad6a (Ube2a) knockout and patient-derived hRad6a (Ube2a) mutant cells show defective mitochondria. Using in vitro and in vivo ubiquitination assays, we show that RAD6A acts as an E2 ubiquitin-conjugating enzyme that, in combination with an E3 ubiquitin ligase such as Parkin, ubiquitinates mitochondrial proteins to facilitate the clearance of dysfunctional mitochondria in cells. Hence, we identify RAD6A as a regulator of Parkin-dependent mitophagy and establish a critical role for RAD6A in maintaining neuronal function.

Albumin overload induces expression of hypoxia-inducible factor 1α and its target genes in HK-2 human renal proximal tubular cell line

The aim of this study was to investigate the effect of human serum albumin (HSA) overload on the expression of the transcription factor hypoxia-inducible factor-1α (HIF-1α) in human renal proximal tubular cell line HK-2. First, the cell viability and cytotoxic activity were examined to assess the cellular conditions in HK-2 cells with HSA treatment employed in this study. HSA treatment for 48h decreased the cell viability and increased the leakage of lactate dehydrogenase (LDH) into the medium in a concentration-dependent manner, but the toxicity was relatively mild. Western Blot analysis revealed that HSA treatment induced the expression of HIF-1α protein in a concentration-dependent manner without a change in β-actin protein expression. Confocal microscopy analysis revealed that HIF-1α protein was predominantly localized in the nucleus but was also observed in the cytoplasm. The HIF-1 target gene mRNAs, glucose transporter 1 and glyceraldehyde 3-phosphate dehydrogenase, were up-regulated by HSA treatment, leading to the increases in the protein expression levels. In addition, the mRNA of HIF-1α was increased by HSA treatment. In conclusion, albumin loading induces HIF-1α in HK-2 cells, resulting in the increases in the expression of proteins of its target genes.

Increased tubular proliferation as an adaptive response to glomerular albuminuria

Renal tubular atrophy accompanies many proteinuric renal diseases, suggesting that glomerular proteinuria injures the tubules. However, local or systemic inflammation and filtration of abnormal proteins known to directly injure tubules are also present in many of these diseases and animal models; therefore, whether glomerular proteinuria directly causes tubular injury is unknown. Here, we examined the renal response to proteinuria induced by selective podocyte loss. We generated mice that express the diphtheria toxin receptor exclusively in podocytes, allowing reproducible dose-dependent, specific ablation of podocytes by administering diphtheria toxin. Ablation of <20% of podocytes resulted in profound albuminuria that resolved over 1-2 weeks after the re-establishment of normal podocyte morphology. Immediately after the onset of albuminuria, proximal tubule cells underwent a transient burst of proliferation without evidence of tubular damage or increased apoptosis, resulting in an increase in total tubular cell numbers. The proliferative response coincided with detection of the growth factor Gas6 in the urine and phosphorylation of the Gas6 receptor Axl in the apical membrane of renal tubular cells. In contrast, ablation of >40% of podocytes led to progressive glomerulosclerosis, profound tubular injury, and renal failure. These data suggest that glomerular proteinuria in the absence of severe structural glomerular injury activates tubular proliferation, potentially as an adaptive response to minimize the loss of filtered proteins.

Effect of red wine on urinary protein, 8-hydroxydeoxyguanosine, and liver-type fatty acid-binding protein excretion in patients with diabetic nephropathy

The aim of the present study was to determine whether red or white wine affects urinary protein, 8-hydroxydeoxyguanosine (8-OHdG), and liver-type fatty acid-binding protein (L-FABP) excretion in type 2 diabetic nephropathy patients. Twenty-four type 2 diabetes mellitus patients with nephropathy were randomly allocated to drink a 118-mL (4-oz) glass of red wine (n = 12, group A) or white wine (n = 12, group B) daily for 6 months. Twelve type 2 diabetes mellitus patients with nephropathy who did not drink any wines served as control subjects (group C). Serum creatinine, 24-hour creatinine clearance, hemoglobin A(1c), urinary protein, urinary 8-OHdG, and urinary L-FABP were measured before and 3 and 6 months after the start of the study. In groups A, B, and C, serum creatinine, 24-hour creatinine clearance, and hemoglobin A(1c) changed little during the experimental period. However, urinary protein, 8-OHdG, and L-FABP excretions were significantly decreased at 3 (P < .05) and 6 months (P < .01) compared with the baseline values in group A. In contrast, these markers changed little during the experimental period in groups B and C. Thus, these urinary markers were significantly lower in group A than in groups B and C at 3 and 6 months. These results suggest that red wine is renoprotective whereas white wine has no such effect in type 2 diabetes mellitus patients with nephropathy. The renoprotective effect of red wine may be due in part to its ability to reduce oxidative stress.

Effect of BSA-induced ER stress on SGLT protein expression levels and α-MG uptake in renal proximal tubule cells

Recent studies demonstrated that endoplasmic reticulum (ER) stress regulates glucose homeostasis and that ER stress preconditioning which induces an adaptive, protective unfolded protein response (UPR) offers cytoprotection against nephrotoxins. Thus the aim of the present study was to use renal proximal tubule cells (PTCs) to further elucidate the link between the BSA-induced ER stress and α-methyl-d-glucopyranoside (α-MG) uptake and to identify related signaling pathways. Among ER stress inducers such as high glucose, BSA, H2O2, or tumicamycin, BSA pretreatment ameliorated the reduction of Na+-glucose cotransporter (SGLT) expression and α-MG uptake by gentamicin or cyclosporine A. Immunofluorescence studies revealed that BSA (10 mg/ml) stimulated the expression of glucose-regulated protein 78 (GRP78), an ER stress biomarker. In addition, BSA increased levels of GRP78 protein expression and eukaryotic initiation factor 2α (eIF2α) phosphorylation in a time-dependent manner. Furthermore, transfection with a GRP78-specific small interfering RNA (siRNA) inhibited BSA-stimulated SGLT expression and α-MG uptake. In experiments designed to unravel the mechanisms underlying BSA-induced ER stress, BSA stimulated the production of cellular reactive oxygen species (ROS), and antioxidants such as ascorbic acid or N-acetylcysteine (NAC) blocked BSA-induced increases in GRP78 activation, eIF2α phosphorylation, SGLT expression, and α-MG uptake. Moreover, the cells upregulated peroxisome proliferator-activated receptor-γ (PPARγ) mRNA levels in response to BSA or troglitazone (a PPARγ agonist), but BSA was ineffective in the presence of GW9662 (a PPARγ antagonist). In addition, both BSA and troglitazone stimulated GRP78 and eIF2α activation, SGLT expression, and α-MG uptake, whereas GW9662 inhibited the effects of BSA. BSA also stimulated phosphorylation of JNK and NF-κB, and GW9662 or GRP78 siRNA attenuated this response. Moreover, SP600125 or SN50 effectively blocked SGLT expression and α-MG uptake in BSA- or PPARγ agonists (troglitazone or PGJ2)-treated PTCs. We conclude that BSA induces ER stress through ROS production and PPARγ activation, which subsequently activates JNK/NF-κB signaling to enhance glucose uptake in renal PTCs.