Inhibition of the mitogen activated protein kinase ERK1/2 amplifies ochratoxin A toxicity in the proximal tubule of the kidney

Ochratoxin A (OTA) is a mycotoxin showing nephrotoxic properties. OTA activates the mitogen activated protein kinases ERK, JNK and p38 in renal epithelial cells. In brief, activation of ERK supports mitosis, growth and differentiation, whereas JNK and p38 are considered to induce the opposite effects. The balance of the mentioned key protein kinases decides the further fate of the cell. In renal disease, the proximal tubule of the nephron often is affected first. Thus, we investigated the effect of OTA incubation (24 or 48 hours) on proximal tubular OK cells (oppossum) and/or NRK-52E cells (rat) in presence of an inhibitor of ERK1/2 activation (U0126). U0126 (25 μM) completely abolished ERK1/2 activation induced by OTA. Parameters indicating necrosis, apoptosis, epithelial tightness, fibrosis, dedifferentiation and inflammation were determined. In presence of U0126, OTA led to a decrease of cell number as compared to OTA alone. U0126 in presence of OTA increased LDH release as compared to OTA alone. OTA alone did not change epithelial integrity, whereas OTA in presence of U0126 reduced epithelial tightness. 100 nM OTA alone did not increase apoptosis, while addition of U0126 to OTA induced apoptotis. U0126 stimulated the basolateral deposition of collagen induced by OTA. Furthermore, as investigated by RT-PCR, the effect of OTA on markers of inflammation (NF-κB) and dedifferentiation (α-smooth muscle actin) was also more pronounced when ERK1/2 was inhibited. ERK1/2 inhibition enhanced the effects of OTA. Thus, activation of ERK1/2 after OTA is a protective mechanism. We conclude that ERK1/2 not only acts anti-apoptotic but also is beneficial on cell viability, epithelial tightness, interstitial fibrosis, inflammation and trans-differentiation. We further conclude that ERK1/2 is a key protection factor in the proximal tubule. However, long term OTA exposition could lead to clonal selection of kidney cells overexpressing ERK1/2. As strong expression of ERK1/2 is found in various tumours not only of the kidney, we hypothesize that the mentioned clonal selection could be a mechanism inducing the cancerogenic action discussed for OTA. Presented at the 25^th Mykotoxin Workshop in Giessen, Germany, May 19–21, 2003     

The role of TGF-β and epithelial-to mesenchymal transition in diabetic nephropathy

Transforming Growth Factor-beta (TGF-β) is a pro-sclerotic cytokine widely associated with the development of fibrosis in diabetic nephropathy. Central to the underlying pathology of tubulointerstitial fibrosis is epithelial-to-mesenchymal transition (EMT), or the trans-differentiation of tubular epithelial cells into myofibroblasts. This process is accompanied by a number of key morphological and phenotypic changes culminating in detachment of cells from the tubular basement membrane and migration into the interstitium. Ultimately these cells reside as activated myofibroblasts and further exacerbate the state of fibrosis. A large body of evidence supports a role for TGF-β and downstream Smad signalling in the development and progression of renal fibrosis. Here we discuss a role for TGF-β as the principle effector in the development of renal fibrosis in diabetic nephropathy, focusing on the role of the TGF-β1 isoform and its downstream signalling intermediates, the Smad proteins. Specifically we review evidence for TGF-β1 induced EMT in both the proximal and distal regions of the nephron and describe potential therapeutic strategies that may target TGF-β1 activity.     

The role of oxidative stress in the ochratoxin A-mediated toxicity in proximal tubular cells

Balkan endemic nephropathy (BEN), a disease characterized by progressive renal fibrosis in human patients, has been associated with exposure to ochratoxin A (OTA). This mycotoxin is a frequent contaminant of human and animal food products, and is toxic to all animal species tested. OTA predominantly affects the kidney and is known to accumulate in the proximal tubule (PT). The induction of oxidative stress is implicated in the toxicity of this mycotoxin.In the present study, primary rat PT cells and LLC-PK(1) cells, which express characteristics of the PT, were used to investigate the OTA-mediated oxidative stress response. OTA exposure of these cells resulted in a concentration-dependent elevation of reactive oxygen species (ROS) levels, depletion of cellular glutathione (GSH) levels and an increase in the formation of 8-oxoguanine.The OTA-induced ROS response was significantly reduced following treatment with alpha-tocopherol (TOCO). However, this chain-braking anti-oxidant did not reduce the cytotoxicity of OTA and was unable to prevent the depletion of total GSH levels in OTA-exposed cells. In contrast, pre-incubation of the cell with N-acetyl-L-cysteine (NAC) completely prevented the OTA-induced increase in ROS levels as well as the formation of 8-oxoguanine and completely protected against the cytotoxicity of OTA. In addition, NAC treatment also limited the GSH depletion in OTA-exposed PT- and LLC-PK(1) cells.From these data, we conclude that oxidative stress contributes to the tubular toxicity of OTA. Subsequently, cellular GSH levels play a pivotal role in limiting the short-term toxicity of this mycotoxin in renal tubular cells.     

Evidence of apoptosis in human diabetic kidney

Diabetic nephropathy is characterized by an early period of renal growth with glomerular and tubular cell hypertrophy, but this is followed by progressive glomerulosclerosis and tubulointerstitial fibrosis, associated with loss of renal tissue. We studied whether apoptotic cell death occurs in human diabetic nephropathy. Percutaneous renal biopsy samples were obtained from five patients with diabetic nephropathy who were receiving insulin and/or angiotensin-converting enzyme inhibitor therapy. Apoptosis was determined by the presence of DNA fragmentation, detected by in situ TUNEL staining, and by characteristic features on electron microscopy, such as chromatin condensation. Apoptosis was present in all five biopsy specimens, either in epithelial cells of the proximal or distal tubules, or in endothelial cells or interstitial cells. No apoptosis was detected in cells of the glomeruli. The present study provides evidence for apoptosis in human diabetic kidney, and suggests a role for apoptosis in the gradual loss of renal mass.     

Adenine overload induces ferroptosis in human primary proximal tubular epithelial cells

The pathogenesis of crystal nephropathy involves deposition of intratubular crystals, tubular obstruction and cell death. The deposition of 8-dihydroxyadenine (DHA) crystals within kidney tubules, for instance, is caused by a hereditary deficiency of adenine phosphoribosyl transferase in humans or adenine overload in preclinical models. However, the downstream pathobiological patterns of tubular cell attrition in adenine/DHA-induced nephropathy remain poorly understood. In this study, we investigated: (i) the modes of adenine-induced tubular cell death in an experimental rat model and in human primary proximal tubular epithelial cells (PTEC); and (ii) the therapeutic effect of the flavonoid baicalein as a novel cell death inhibitor. In a rat model of adenine diet-induced crystal nephropathy, significantly elevated levels of tubular iron deposition and lipid peroxidation (4-hydroxynonenal; 4-HNE) were detected. This phenotype is indicative of ferroptosis, a novel form of regulated necrosis. In cultures of human primary PTEC, adenine overload-induced significantly increased mitochondrial superoxide levels, mitochondrial depolarisation, DNA damage and necrotic cell death compared with untreated PTEC. Molecular interrogation of adenine-stimulated PTEC revealed a significant reduction in the lipid repair enzyme glutathione peroxidase 4 (GPX4) and the significant increase in 4-HNE compared with untreated PTEC, supporting the concept of ferroptotic cell death. Moreover, baicalein treatment inhibited ferroptosis in adenine-stimulated PTEC by selectively modulating the mitochondrial antioxidant enzyme superoxide dismutase 2 (SOD2) and thus, suppressing mitochondrial superoxide production and DNA damage. These data identify ferroptosis as the primary pattern of PTEC necrosis in adenine-induced nephropathy and establish baicalein as a potential therapeutic tool for the clinical management of ferroptosis-associated crystal nephropathies (e.g., DHA nephropathy, oxalate nephropathy).Subject terms: Mechanisms of disease, Interstitial nephritis, Experimental models of disease

     

HNRNPA1-mediated exosomal sorting of miR-483-5p out of renal tubular epithelial cells promotes the progression of diabetic nephropathy-induced renal interstitial fibrosis

Diabetic nephropathy (DN) is a serious complication in type 1 and type 2 diabetes, and renal interstitial fibrosis plays a key role in DN progression. Here, we aimed to probe into the role and potential mechanism of miR-483-5p in DN-induced renal interstitial fibrosis. In this study, we corroborated that miR-483-5p expression was lessened in type 1 and type 2 diabetic mice kidney tissues and high glucose (HG)-stimulated tubular epithelial cells (TECs), and raised in the exosomes derived from renal tissues in type 1 and type 2 diabetic mice. miR-483-5p restrained the expressions of fibrosis-related genes in vitro and renal interstitial fibrosis in vivo. Mechanistically, miR-483-5p bound both TIMP2 and MAPK1, and TIMP2 and MAPK1 were bound up with the regulation of miR-483-5p on renal TECs under HG conditions. Importantly, HNRNPA1-mediated exosomal sorting transported cellular miR-483-5p out of TECs into the urine. Our results expounded that HNRNPA1-mediated exosomal sorting transported cellular miR-483-5p out of TECs into the urine, thus lessening the restraint of cellular miR-483-5p on MAPK1 and TIMP2 mRNAs, and ultimately boosting extracellular matrix deposition and the progression of DN-induced renal interstitial fibrosis.Subject terms: Cell biology, Molecular biology     

Epithelial-fibroblast cross talk aggravates the impact of the nephrotoxin ochratoxin A

BackgroundChronic nephropathies result from different pathogenic agents, including nutritional factors triggering vicious pathophysiological cycles. Ochratoxin A (OTA) is a globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. The underlying mechanisms are not sufficiently understood, compromising risk assessment. Because crosstalk of proximal tubule cells with fibroblasts is crucial for tubulointerstitial damage, we investigated the effects of OTA in co-culture of these two cell types.MethodsRat renal proximal tubule cells (NRK-52E) and renal fibroblasts (NRK-49F) were exposed to nanomolar OTA concentrations under mono- and/or co-culture conditions for up to 48 h. We determined the impact on inflammation-, EMT- and fibrosis-associated proteins as well as microRNAs by western blot or qPCR, respectively. Alterations in cell morphology were quantitatively assessed. The roles of miRs, COX-2 and ERK1/2 in OTA-induced effects were investigated by specific inhibition.FindingsOnly under co-culture condition, OTA caused an increase of vimentin, fibronectin and miR-21 and a decrease of collagen III, E-cadherin, COX-2 and WISP1 mRNA abundance in NRK-52E cells. In NRK-49F cells, OTA induced an increase of N-cadherin, COX-2, WISP1 in co-culture only. The OTA-induced increase of fibronectin in NRK-52E cells was prevented by simultaneous inhibition of miR-21 and -200a, COX-2 or ERK1/2. The OTA-induced increase of COX-2 in NRK-49F cells was prevented by inhibition of miR-21 and -200a or ERK1/2.InterpretationOur results show that the complete nephropathic potential of nanomolar OTA, leading to EMT, is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential is underestimated.Research in contextChronic nephropathies are a severe health burden and the result of different pathogenic mechanisms, including nutritional factors that trigger vicious pathophysiological cycles. Ochratoxin A (OTA) is a ubiquitous, globally occurring nephrotoxic mycotoxin detectable in a variety of foodstuff and suspected to cause tubulointerstitial damage. Because underlying pathomechanisms are unclear, risk assessment is problematic. Crosstalk of proximal tubule cells (the main target of OTA) with fibroblasts is crucial for the development of tubulointerstitial damage. We show that during co-culture of proximal tubule cells and fibroblasts, OTA-induced effects (e.g. epithelial-mesenchymal transition (EMT)) change significantly as compared to monoculture. Our results show that the complete nephropathic potential of OTA is unveiled when cellular crosstalk is possible. In monoculture, the nephropathic potential of OTA is underestimated.     

HIV-1 gp120-induced tubular epithelial cell apoptosis is mediated through p38-MAPK phosphorylation

BACKGROUND: HIV-associated nephropathy is accompanied by significant tubular alterations in the form of tubular cell proliferation, apoptosis, and microcystic dilatation. In the present study we evaluated the role of CD4 receptors in HIV-1-induced tubular cell injury. METHODS: To confirm the presence of CD4 receptors in tubular cells, immunocytochemical, Western and Northern blot studies were carried out. To determine the downstream effect of CD4 and gp120 interaction, we evaluated the effect of gp120 on tubular cell p38 mitogen-activated protein kinase (MAPK) activity and phosphorylation. To establish causal relationships between gp120, CD4, and p38 MAPK pathways, we studied the effect of anti-CD4 antibody and SB 202190 (an inhibitor of p38 MAPK) on gp120-induced tubular cell apoptosis. RESULTS: Proximal tubular cells in culture as well as in intact tissue showed expression of CD4 (immunocytochemical and Western blot studies). Cultured tubular cells also showed mRNA expression for CD4 (Northern blot studies). Gp120, at concentrations of 10-100 ng/ ml, triggered tubular cell apoptosis; however, this effect of gp120 was inhibited by anti-CD4 antibody. SB 202190 also inhibited gp120-induced tubular cell apoptosis. In addition, gp120 promoted tubular cell p38 MAPK phosphorylation in a time- and dose- dependent manner. CONCLUSION: Gp120 through interaction with CD4 triggers tubular cell apoptosis. This effect of gp120 on tubular cells is mediated through phosphorylation of p38 MAPK.     

Hypochlorite modified albumins promote cell death in the tubule interstitium in rats via mitochondrial damage in obstructive nephropathy and the protective effects of antioxidant peptides

A major feature of the injury sustained by the kidney during obstructive nephropathy is a profound induction of apoptosis in the tubular epithelium. In this study, we explored the central roles of mitochondria and the mechanism of the protective effect of the mitochondrial targeted peptides in tubular cell apoptosis and interstitial fibrosis during obstructive nephropathy. Unilateral ureter obstruction (UUO) was performed on rats, and the animals were randomly assigned to intravenous treatment with normal saline, rat serum albumin (RSA), or HOCl-rat serum albumin (HOCl-RSA) in the presence or absence of SS-31. A sham-operation control group was set up by left ureteral dissociation but not ligation. Compared with the control group, UUO animals displayed fibrotic abnormalities, accompanied by increased expression of collagen-I, fibronectin, α-SMA protein and mRNA in the renal interstitium. They also displayed oxidative stress, as evidenced by increased levels of HOCl-alb, TBARS, and mitochondrial reactive oxygen species (ROS) and a decrease in MnSOD activity in the renal homogenate. Damage to mitochondrial structure and functions was observed, as evidenced by a decrease in the mitochondrial membrane potential (MMP), ATP production, mtDNA copy number alterations and release of cytochrome C (cyto C) from the mitochondria to the cytoplasm. These changes were accompanied by activation of caspase-3, caspase-7, caspase-9, and PARP-1 and increased apoptotic cells in the proximal tubules. HOCl-RSA challenge further exacerbated the above biological effects in UUO animals, but these effects were prevented by administration of SS-31. These data suggested that accumulation of HOCl-alb may promote tubular cell apoptosis and interstitial fibrosis, probably related to mitochondrial oxidative stress and damage, and that SS-31 might contribute to apoptotic pathway suppression via scavenging of ROS in the mitochondria.     

Nicotinamide reduces renal interstitial fibrosis by suppressing tubular injury and inflammation

Renal interstitial fibrosis is a common pathological feature in progressive kidney diseases currently lacking effective treatment. Nicotinamide (NAM), a member of water‐soluble vitamin B family, was recently suggested to have a therapeutic potential for acute kidney injury (AKI) in mice and humans. The effect of NAM on chronic kidney pathologies, including renal fibrosis, is unknown. Here we have tested the effects of NAM on renal interstitial fibrosis using in vivo and in vitro models. In vivo, unilateral urethral obstruction (UUO) induced renal interstitial fibrosis as indicated Masson trichrome staining and expression of pro‐fibrotic proteins, which was inhibited by NAM. In UUO, NAM suppressed tubular atrophy and apoptosis. In addition, NAM suppressed UUO‐associated T cell and macrophage infiltration and induction of pro‐inflammatory cytokines, such as TNF‐α and IL‐1β. In cultured mouse proximal tubule cells, NAM blocked TGF–β‐induced expression of fibrotic proteins, while it marginally suppressed the morphological changes induced by TGF‐β. NAM also suppressed the expression of pro‐inflammatory cytokines (eg MCP‐1 and IL‐1β) during TGF‐β treatment of these cells. Collectively, the results demonstrate an anti‐fibrotic effect of NAM in kidneys, which may involve the suppression of tubular injury and inflammation.     

Legumain/asparaginyl endopeptidase controls extracellular matrix remodeling through the degradation of fibronectin in mouse renal proximal tubular cells

Legumain/asparaginyl endopeptidase (EC 3.4.22.34) is a novel cysteine protease that is abundantly expressed in the late endosomes and lysosomes of renal proximal tubular cells. Recently, emerging evidence has indicated that legumain might play an important role in control of extracellular matrix turnover in various pathological conditions such as tumor growth/metastasis and progression of atherosclerosis. We initially found that purified legumain can directly degrade fibronectin, one of the main components of the extracellular matrix, in vitro. Therefore, we examined the effect of legumain on fibronectin degradation in cultured mouse renal proximal tubular cells. Fibronectin processing can be inhibited by chloroquine, an inhibitor of lysosomal degradation, and can be enhanced by the overexpression of legumain, indicating that fibronectin degradation occurs in the presence of legumain in lysosomes from renal proximal tubular cells. Furthermore, in legumain-deficient mice, unilateral ureteral obstruction (UUO)-induced renal interstitial protein accumulation of fibronectin and renal interstitial fibrosis were markedly enhanced. These findings indicate that legumain might have an important role in extracellular matrix remodeling via the degradation of fibronectin in renal proximal tubular cells.     

Proximal tubular atrophy: Qualitative and quantitative structural changes in chronic obstructive nephropathy in the pig

Summary Kidneys of pigs with various degrees of induced chronic obstructive nephropathy were studied by light- and electron microscopy to assess the structural changes of proximal convoluted tubules with increasing degrees of atrophy. A particular aim was to evaluate the quantitative relationship between proximal tubular and interstitial changes in early tubular atrophy. The kidneys were subjected to varying degrees of ureteral obstruction and were fixed by in vivo vascular perfusion. Quantitative (morphometric) analyses were carried out on montages of electron micrographs representing randomly selected cortical areas and cross sections of individual proximal convoluted tubules. The results demonstrated that ureteral obstruction was followed by significant reductions in proximal tubular epithelium, in volume of proximal tubular mitochondria and in surface area of proximal tubular basolateral membranes. These changes were present even in the absence of any demonstrable increase in cortical interstitium or alterations in the relationships between proximal tubules and peritubular capillaries. With increase in the volume of cortical interstitium the proximal tubules were further simplified in ultra-structure with a reduced number of interdigitating lateral cell processes. Concomitantly there were significant quantitative changes in the spatial associations between tubules and capillaries due to increase in tubulo-capillary distances. The present study shows that ultrastructural changes in proximal tubules during early atrophy precede the volume increase in cortical interstitium associated with chronic obstructive nephropathy. It is suggested that the early tubular changes are due to decreased functional loads, whereas the further progression of tubular atrophy may be a result of impaired nourishment of the tubular cells due to increased interstitial tissue and altered relationships between tubules and capillaries.This work was supported by grant no 12-0727 from the Danish Medical Research Council     

Multiple metabolic hits converge on CD36 as novel mediator of tubular epithelial apoptosis in diabetic nephropathy

Background

Diabetic nephropathy (DNP) is a common complication of type 1 and type 2 diabetes mellitus and the most common cause of kidney failure. While DNP manifests with albuminuria and diabetic glomerulopathy, its progression correlates best with tubular epithelial degeneration (TED) and interstitial fibrosis. However, mechanisms leading to TED in DNP remain poorly understood.

Methods and Findings

We found that expression of scavenger receptor CD36 coincided with proximal tubular epithelial cell (PTEC) apoptosis and TED specifically in human DNP. High glucose stimulated cell surface expression of CD36 in PTECs. CD36 expression was necessary and sufficient to mediate PTEC apoptosis induced by glycated albumins (AGE-BSA and CML-BSA) and free fatty acid palmitate through sequential activation of src kinase, and proapoptotic p38 MAPK and caspase 3. In contrast, paucity of expression of CD36 in PTECs in diabetic mice with diabetic glomerulopathy was associated with normal tubular epithelium and the absence of tubular apoptosis. Mouse PTECs lacked CD36 and were resistant to AGE-BSA-induced apoptosis. Recombinant expression of CD36 in mouse PTECs conferred susceptibility to AGE-BSA-induced apoptosis.

Conclusion

Our findings suggest a novel role for CD36 as an essential mediator of proximal tubular apoptosis in human DNP. Because CD36 expression was induced by glucose in PTECs, and because increased CD36 mediated AGE-BSA-, CML-BSA-, and palmitate-induced PTEC apoptosis, we propose a two-step metabolic hit model for TED, a hallmark of progression in DNP.     

Persistent activation of autophagy in kidney tubular cells promotes renal interstitial fibrosis during unilateral ureteral obstruction

Renal fibrosis is the final, common pathway of end-stage renal disease. Whether and how autophagy contributes to renal fibrosis remains unclear. Here we first detected persistent autophagy in kidney proximal tubules in the renal fibrosis model of unilateral ureteral obstruction (UUO) in mice. UUO-associated fibrosis was suppressed by pharmacological inhibitors of autophagy and also by kidney proximal tubule-specific knockout of autophagy-related 7 (PT-Atg7 KO). Consistently, proliferation and activation of fibroblasts, as indicated by the expression of ACTA2/α-smooth muscle actin and VIM (vimentin), was inhibited in PT-Atg7 KO mice, so was the accumulation of extracellular matrix components including FN1 (fibronectin 1) and collagen fibrils. Tubular atrophy, apoptosis, nephron loss, and interstitial macrophage infiltration were all inhibited in these mice. Moreover, these mice showed a specific suppression of the expression of a profibrotic factor FGF2 (fibroblast growth factor 2). In vitro, TGFB1 (transforming growth factor β 1) induced autophagy, apoptosis, and FN1 accumulation in primary proximal tubular cells. Inhibition of autophagy suppressed FN1 accumulation and apoptosis, while enhancement of autophagy increased TGFB1-induced-cell death. These results suggest that persistent activation of autophagy in kidney proximal tubules promotes renal interstitial fibrosis during UUO. The profibrotic function of autophagy is related to the regulation on tubular cell death, interstitial inflammation, and the production of profibrotic factors.     

Inhibition of 4E-BP1 phosphorylation promotes tubular cell escaping from G2/M arrest and ameliorates kidney fibrosis

Upon occurrence of kidney injury, tubular cells arrested in G2/M stage may promote interstitial fibroblast activation and kidney fibrosis through producing large amounts of pro-fibrotic cytokines. MTORC1 signaling is essential for controlling cell growth, however, the role and mechanisms for mTORC1 in regulating tubular cell cycle progression during kidney fibrosis are not clear. Here we reported that p-S6 abundance was increased at 15 min, reached peak at 1 h and declined from 3 h to 24 h, while the abundance of p-4E-BP1 and p-Histone H3 was increased from 15 min to 24 h in tubular epithelial cells at the similar pattern after serum stimulation. The phosphorylation of 4E-BP1 was prohibited in NRK-52E cells by the transfection of 4E-BP1 plasmid with four phospho-sites mutation (4E-BP1A4). 4E-BP1A4 transfection led to less G2/M cell arrest as well as the production of pro-fibrotic cytokine and extracellular matrix in NRK-52E cells. In addition, aristolochic acid (AA)-induced tubular cell G2/M arrest induced by treatment was also largely attenuated in NRK-52E cells transfected with 4E-BP1A4. In mouse kidneys with UUO nephropathy, p-4E-BP1 abundance was markedly elevated in the mitotic tubular cells. Therefore, these data indicates that suppressing 4E-BP1 phosphorylation may inhibit tubular cell G2/M-arrest and kidney fibrosis.     

TLR4 Activation Promotes Podocyte Injury and Interstitial Fibrosis in Diabetic Nephropathy

Toll like receptor (TLR) 4 has been reported to promote inflammation in diabetic nephropathy. However the role of TLR4 in the complicated pathophysiology of diabetic nephropathy is not understood. In this study, we report elevated expression of TLR4, its endogenous ligands and downstream cytokines, chemokines and fibrogenic genes in diabetic nephropathy in WT mice with streptozotocin (STZ) diabetes. Subsequently, we demonstrated that TLR4^−/− mice were protected against the development of diabetic nephropathy, exhibiting less albuminuria, inflammation, glomerular hypertrophy and hypercellularity, podocyte and tubular injury as compared to diabetic wild-type controls. Marked reductions in interstitial collagen deposition, myofibroblast activation (α-SMA) and expression of fibrogenic genes (TGF-β and fibronectin) were also evident in TLR4 deficient mice. Consistent with our in vivo results, high glucose directly promoted TLR4 activation in podocytes and tubular epithelial cells in vitro, resulting in NF-κB activation and consequent inflammatory and fibrogenic responses. Our data indicate that TLR4 activation may promote inflammation, podocyte and tubular epithelial cell injury and interstitial fibrosis, suggesting TLR4 is a potential therapeutic target for diabetic nephropathy.     

Kidney atrophy vs hypertrophy in diabetes: which cells are involved?

One of the first structural changes in diabetic nephropathy (DN) is the renal enlargement. These changes resulted in renal hypertrophy in both glomerular and tubular cells. Shrink in the kidney size, which described as kidney atrophy resulted from the loss of nephrons or abnormal nephron function and lead to loss of the kidney function. On the other hand, increase in kidney size, which described as hypertrophy resulted from increase in proximal tubular epithelial and glomerular cells size. However overtime, tubular atrophy and tubulointerstitial fibrosis occurs as subsequent changes in tubular cell hypertrophy, which is associated with the infiltration of fibroblast cells into the tubulointerstitial space. The rate of deterioration of kidney function shows a strong correlation with the degree of tubulointerstitial fibrosis. A consequence of long-standing diabetes/hyperglycemia may lead to major changes in renal structure that occur but not specific only to nephropathy. Identifying type of cells that involves in renal atrophy and hypertrophy may help to find a therapeutic target to treat diabetic nephropathy. In summary, the early changes in diabetic kidney are mainly includes the increase in tubular basement membrane thickening which lead to renal hypertrophy. On the other hand, only renal tubule is subjected to apoptosis, which is one of the characteristic morphologic changes in diabetic kidney to form tubular atrophy at the late stage of diabetes.