Yung-Hsiung Lai

Role of receptor for advanced glycation end-product (RAGE) and the JAK/STAT-signaling pathway in AGE-induced collagen production in NRK-49F cells

Advanced glycation end‐product (AGE) is important in the pathogenesis of diabetic nephropathy (DN), and captopril (an angiotensin converting enzyme inhibitor) is effective in treating this disorder. We have shown that the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) cascade is responsible for AGE‐induced mitogenesis in NRK‐49F (normal rat kidney fibroblast) cells, but its role in renal fibrosis in DN remains unknown. Therefore, we have sought to determine whether JAK/STAT is involved in AGE‐regulated collagen production in NRK‐49F cells. We found that AGE time (1–7 days) and dose (10–200u2009μg/ml)‐dependently increased collagen production in these cells. Additionally, AGE increased RAGE (receptor for AGE) protein expression. AGE‐induced RAGE expression was dose‐dependently inhibited by antisense RAGE oligodeoxynucleotide (ODN) and captopril. AGE‐induced type I collagen production and JAK2‐STAT1/STAT3 activation were decreased by AG‐490 (a specific JAK2 inhibitor), antisense RAGE ODN and captopril. Meanwhile, STAT1 and STAT3 decoy ODNs also suppressed the induction of collagen by AGE. We concluded that RAGE and the JAK2‐STAT1/STAT3 pathway were involved in AGE‐induced collagen production in NRK‐49F cells. Furthermore, captopril was found to reverse AGE‐induced collagen production, probably by attenuating RAGE expression and JAK2‐STAT1/STAT3 activities. J. Cell. Biochem. 81:102–113, 2001.

Altering expression of α3β1 integrin on podocytes of human and rats with diabetes

Abstract The adhesion molecule integrin α3β1 is the major receptor of podocyte to the glomerular capillary basement membrane (GBM). Since progressive alteration of the glomerular extracellular matrix (ECM) compartment leading to GBM thickening is common in diabetic nephropathy, we investigated the cellular distribution of α3β1 integrin in podocytes of patients with diabetic nephropathy and streptozotocin-induced diabetic rats, and we evaluated the effects of high glucose on the cultured rat podocytes. Both human and rat kidneys were stained using the immunoelectron microscopy and immunoperoxidase technique with mouse monoclonal antibodies to human integrin α3 subunit. The results showed that both the number of immunogold particles and the staining of integrin α3 subunit on podocytes were weaker in patients with diabetic nephropathy than those of control kidneys. The staining of α3 on podocytes in the poorly-controlled diabetic rats was also weaker after one and three months of hyperglycemia. However, the staining was identical to controls in rats with only one week of hyperglycemia. High glucose (25 mM) but not streptozotocin in vitro suppressed the α3 expression of cultured rat podocytes. Our results demonstrated that the expression of integrin α3β1 on podocytes was suppressed in both human and rats with diabetes, possibly due to the effects of hyperglycemia, and the suppression became more severe with the duration of diabetes.

Fatal outcome after ingestion of star fruit (Averrhoa carambola) in uremic patients

Clinical outcome of dialysis patients after eating star fruit (Averrhoa carambola) varies, but it may be fatal. In the past 10 years, 20 such patients were treated in our hospital when they developed clinical symptoms after eating the fruit or drinking star fruit juice. Their initial presentations included sudden-onset limb numbness, muscle weakness, intractable hiccups, consciousness disturbance of various degrees, and seizure. No other major events that might be responsible for these symptoms could be identified. Eight patients died, including one patient with a serum creatinine level of 6.4 mg/dL who had not yet begun dialysis. The clinical manifestations of the survivors were similar to those who died except for consciousness disturbance and seizure. Death occurred within 5 days despite emergent hemodialysis and intensive medical care. The survivors symptoms usually became less severe after supportive treatment, and these patients subsequently recovered without obvious sequelae. The purpose of this article is to report that patients with renal failure who ingest star fruit may develop neurological symptoms and also run the risk for death in severe cases. Mortality may also occur in patients with chronic renal failure not yet undergoing dialysis.

Pravastatin suppress superoxide and fibronectin production of glomerular mesangial cells induced by oxidized-LDL and high glucose

Pravastatin is a potent inhibitor of HMG-CoA reductase and is effective in lowering serum lipid levels. Recent studies have shown that pravastatin also reduces oxidative modification of LDL and decreases albuminuria in patients with diabetes. To determine the possible benefit of pravastatin on the diabetic kidney, we have measured the effects of pravastatin on the proliferation and the production of superoxide and fibronectin, and the expression of fibronectin mRNA of glomerular mesangial cells stimulated by oxidized-LDL and high glucose. Our results demonstrated that the [(3)H]-labeled thymidine uptake of mesangial cells decreased after oxidized-LDL stimulation (50 microg/ml, 6 h) and increased after high glucose stimulation (25 mM, 48 h). The production of superoxide and fibronectin and the expression of fibronectin mRNA of glomerular mesangial cells were all significantly increased after stimulation with either oxidized-LDL or high glucose, or the combination of oxidized-LDL and high glucose. Pravastatin (100 microM, 48 h) alone had no effect on unstimulated cells. However, pravastatin significantly reversed thymidine uptake, inhibited the production of superoxide and fibronectin, and inhibited the expression of fibronectin mRNA of glomerular mesangial cells after stimulation with either oxidized-LDL or high glucose. Our results indicate that pravastatin may effect as an antioxidant and may suppress fibronectin synthesis of glomerular mesangial cells in diabetic patients with hyperlipidemia.

Leptin and connective tissue growth factor in advanced glycation end-product-induced effects in NRK-49F cells.

Previously, we showed that Janus kinase 2 (JAK2) is important in advanced glycation end‐product (AGE)‐induced effects in renal interstitial (NRK‐49F) fibroblasts. Leptin is a JAK2‐activating cytokine via the long form leptin receptor (Ob‐Rb). Leptin and connective tissue growth factor (CTGF) may be involved in renal fibrosis. However, the relationship between leptin and CTGF in terms of AGE‐induced effects remains unknown. Thus, the effects of AGE (150 μg/ml) and leptin on mitogenesis, CTGF and collagen expression in NRK‐49F cells were determined. We found that leptin and AGE increased mitogenesis and type I collagen protein expression at 3 and 7 days, respectively. AGE increased leptin mRNA and protein expression at 2–3 days. AGE increased CTGF mRNA and protein expression at 3–5 days. AG‐490 (JAK2 inhibitor) abrogated AGE‐induced leptin mRNA and protein expression at 2–3 days. AG‐490 and Ob‐Rb anti‐sense oligodeoxynucleotides (ODN) abrogated AGE‐induced CTGF mRNA and protein expression at 3–5 days. AG‐490 and CTGF anti‐sense ODN abrogated AGE‐induced mitogenesis and collagen protein expression at 7 days. Additionally, leptin dose (0.2–1 μg/ml) and time (1–2 days)‐dependently increased CTGF protein expression. AG‐490 abrogated leptin (1 μg/ml)‐induced CTGF protein expression at 2 days. AG‐490 and CTGF anti‐sense ODN abrogated leptin‐induced mitogenesis and collagen protein expression at 3 days. We concluded that AGE induced JAK2 to increase leptin while leptin induced JAK2 to increase CTGF‐induced mitogenesis and type I collagen protein expression in NRK‐49F cells. Additionally, AGE‐induced mitogenesis and type I collagen protein expression were dependent on leptin‐induced CTGF.

Effects of Pravastatin on Superoxide and Fibronectin Production of Mesangial Cells Induced by Low-Density Lipoprotein

Pravastatin is a potent inhibitor of HMG-CoA reductase and is effective in lowering serum lipid levels. Recent studies have shown that pravastatin also reduces the oxidative modification of low-density lipoprotein (LDL). To determine whether pravastatin has a direct effect on glomerular mesangial cells, we have measured the effects of pravastatin on the production of superoxide and fibronectin of glomerular mesangial cells stimulated by LDL. Our results demonstrated that the superoxide production of mesangial cells increased after LDL stimulation (100 µg/ml for 4 h) and that the superoxide production was significantly suppressed by either superoxide dismutase (SOD; 500 U/ml for 36 h; p < 0.01) or pravastatin (80 µM for 36 h; p < 0.05). The production of fibronectin was also increased after LDL stimulation which was also significantly suppressed by either SOD (p < 0.01) or pravastatin (p < 0.01). SOD or pravastatin alone had no effect on the unstimulated cells. Our results indicate that pravastatin may have a direct effect as an antioxidant and suppresses the fibronectin synthesis of glomerular mesangial cells independent of its hypolipidemic effect.

Differential Effects of Circulating IgA Isolated from Patients with IgA Nephropathy on Superoxide and Fibronectin Production of Mesangial Cells

Background: IgA nephropathy (IgAN) is characterized by predominant deposition of IgA in the glomerular mesangium. Serum IgA is often elevated in patients with IgAN, and it has been postulated that it is responsible for the mesangial lesions. However, the direct effect of circulating IgA on mesangial cells is not clear. Methods: We investigated the effects of sera and IgA which were isolated from patients with IgAN on thymidine uptake, superoxide and fibronectin production and fibronectin mRNA expression of cultured rat mesangial cells, and we compared the findings to the effects of IgA isolated from patients with non-IgA mesangial proliferative glomerulonephritis (MsPGN) and normal controls. IgA was isolated with affinity chromatography using cyanogen bromide activated Sepharose 4B coupled to sheep antihuman IgA antiserum. Results: Our results demonstrated that both sera and IgA from patients with IgAN dose-dependently increased mitogenesis of mesangial cells as measured by 3H-labeled thymidine uptake. The thymidine uptake by sera and IgA isolated from patients with IgAN was significantly higher than that of sera and IgA isolated from patients with MsPGN and normal controls. Sera and IgA from patients with IgAN significantly enhanced superoxide and fibronectin production and fibronectin mRNA expression of mesangial cells. The superoxide and fibronectin production was also significantly higher as compared with patients with MsPGN and normal controls. Conclusions: Our results indicate that circulating IgA isolated from patients with IgAN is different from that of patients with MsPGN and normal controls and may potentially induce oxidative injury and production of extracellular matrix of glomerular mesangial cells in IgAN.

Plasma Atrial Natriuretic Peptide and Natriuretic Response to Water Immersion in Patients with Nephrotic Syndrome

Eight nonnatriuretic (daily Na excretion less than 50 mEq), 4 natriuretic (daily Na excretion greater than 50 mEq), and 4 steroid-responsive nephrotic patients, and 12 normal controls were studied with a 4-hour water immersion with measurements of electrolytes, plasma atrial natriuretic peptide (ANP), plasma renin activity (PRA), and plasma aldosterone (PA) [corrected]. Four nonnatriuretic patients further received 25 g albumin infusion, with a subsequent 2-hour water immersion study. The results are as follows: (1) In the nonnatriuretic patients, the extremely low basal Na excretion rate, high PRA, and PA levels indicated a state of active Na retention. In spite of the water-immersion induced suppression of PRA and PA and a comparable magnitude of plasma ANP increment, the natriuretic response to water immersion was blunted in the nonnatriuretic patients. (2) In the natriuretic patients, water immersion resulted in a similar magnitude of natriuresis but a higher degree of plasma ANP increment in comparison to the normal controls. (3) Natriuretic and plasma ANP responses to water immersion were not different between the steroid-responsive patients and normal controls. (4) The increase in plasma ANP and the suppression of PRA and PA after 25 g albumin infusion did not result in natriuresis until the further suppression of PRA and PA and the further stimulation of plasma ANP by subsequent water immersion. The above results indicate that the natriuretic and plasma ANP responses to water immersion are related to the basal Na status in nephrotic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of High Glucose Culture on EGF Effects and EGF Receptors in the LLC-PK1 Cells

We have shown that epidermal growth factor (EGF) may be important in diabetic renal hypertrophy. Since EGF is the most potent mitogen for the proximal tubule, it may be relevant to the cellular hyperplasia component in diabetic nephropathy. In order to further clarify the possible alterations of mitogenic effects of EGF on cultured renal cells in hyperglycemic states, the effects of high glucose culture on EGF-induced events and EGF receptors were studied in LLC-PK1 cells with equimolar mannitol being used as an osmotic control. The results showed that high glucose dose-dependently decreased mitogenesis while increasing cellular hypertrophy in LLC-PK1 cells. The dose-response curve of EGF-induced mitogenesis was similar in both normal (11 mM) and high (27.5 mM) glucose cultures. Meanwhile, EGF receptor number and affinity were not changed by high glucose in these cells. Furthermore, mannitol mimicked the growth-suppressive (but not hypertrophic) effects of high glucose cultures. Based upon these findings, we conclude that high glucose did not alter the mitogenic effects of EGF on the LLC-PK1 cells. This was associated with unchanged EGF receptor characteristics. Thus, concurrent with our previous studies, we speculate that it is the increased local EGF level, rather than an increased renal sensitivity to it, which is associated with hyperglycemic tubulopathy.

HCV infection complicated with nephrotic syndrome, immune complex crescentic glomerulonephritis and acute renal failure: a case report.

There is ample evidence suggesting that hepatitis C virus (HCV)‐associated autoimmunity plays a role in a broad spectrum of autoimmune diseases, which are usually overlooked. We report on a case of nephrotic syndrome, palpable purpura, cryoglobulinemia, hypocomplementemia, and acute renal failure complicated by immune complex glomerulonephritis (GN). The patient is a 64‐year‐old man with HCV infection, who was initially considered to present only an HCV‐associated cryoglobulinemic GN. However, renal biopsy revealed a “full house” immune complex crescentic GN, which led to our subsequent investigation. The attending clinicians faced what is a common dilemma, where an HCV‐associated autoimmune disease inevitably switches to a lupus‐like GN. Hence, we also discuss treatment.