Qingfeng Fan

Melamine-Contaminated Powdered Formula and Urolithiasis in Young Children

BACKGROUND A recent epidemic of melamine contamination of baby formula in China has been associated with the development of urinary tract stones, though the clinical manifestations and predisposing factors are incompletely delineated. METHODS We administered a questionnaire to the parents of children 36 months of age or younger who were being screened for a history of exposure to melamine and symptoms of, and possible predisposing factors for, urinary tract stones. In addition, we performed urinalysis, renal-function and liver-function tests, urinary tests for biochemical markers and the calcium:creatinine ratio, and ultrasonography. Powdered-milk infant formulas were classified as having a high melamine content (>500 ppm), a moderate melamine content (<150 ppm), or no melamine (0 ppm); no formulas contained between 150 and 500 ppm of melamine. RESULTS Contaminated formula was ingested by 421 of 589 children. Fifty had urinary stones, including 8 who had not received melamine-contaminated formula; 112 were suspected to have stones; and 427 had no stones. Among children with stones, 5.9% had hematuria and 2.9% had leukocyturia, percentages that did not differ significantly from those among children who were suspected to have stones or those who did not have stones. Serum creatinine, urea nitrogen, and alanine aminotransferase levels were normal in the 22 children with stones who were tested. Four of the 41 children (9.8%) who had stones and in whom urinary markers of glomerular function were measured had evidence of abnormalities; none had tubular dysfunction. Children exposed to high-melamine formula were 7.0 times as likely to have stones as those exposed to no-melamine formula. Preterm infants were 4.5 times as likely to have stones as term infants. CONCLUSIONS Prematurity and exposure to melamine-contaminated formula were associated with urinary stones. Affected children lacked typical signs and symptoms of urolithiasis.

RPC6 Up-Regulation in Ang II-Induced Podocyte Apoptosis Might Result from ERK Activation and NF-κB Translocation

Angiotensin II (Ang II) has been recognized as an apoptosis inducer in podocytes, but the mechanism of apoptosis induced by Ang II is unclear. Transient receptor potential cation channel 6 (TRPC6) is a calcium channel located in podocyte membrane. The present study evaluated the alteration of TRPC6 expression and the Ca2+ influx involved in Ang II-induced podocyte apoptosis. The possible pathways related to TRPC6 in Ang II-induced podocyte apoptosis were also investigated. The apoptosis of mouse podocytes (MPC5) was induced by Ang II. The protein level of TRPC6 was increased markedly in response to Ang II stimulation, and the intracellular Ca2+ concentration was elevated. By transfection with TRPC6 siRNA, Ang II-induced podocyte apoptosis and the transient Ca2+ influx were inhibited. Treated with extracellular signal-regulated kinase (ERK) pathway specific inhibitor U0126 or nuclear factor-κB (NF-κB) pathway specific inhibitor ammonium pyrrolidinedithiocarbamate (PDTC) and Ang II, respectively in podocytes, not only was the TRPC6 up-regulation reduced, but the podocyte apoptosis was also decreased. Moreover, the translocation of NF-κB in nucleus resulted from Ang II was reduced by treatment with U0126. In conclusion, the enhancement expression of TRPC6 as well as the increased Ca2+ influx mediated by TRPC6 channels contributed to the podocyte apoptosis. The activation of ERK pathway and subsequent translocation of NF-κB was possibly necessary for the up-regulation TRPC6 induced by Ang II.

Effect of the knockdown of podocin mRNA on nephrin and α-actinin in mouse podocyte

Recently, the novel podocyte proteins podocin, nephrin, and α-actinin-4 have been identified in three congenital/family nephrotic syndromes, respectively. Further studies showed that these podocyte proteins were involved in some acquired nephrotic syndromes and various experimental models of proteinuria. However, the molecular interactions among these podocyte proteins remain unclear. In this study, to investigate the molecular interactions among podocin, nephrin, and α-actinin-4, we reconstructed the RNA interference (RNAI) expression vector, pSilencer 2.1-U6, specifically targeting podocin mRNA, and it was transfected into the mouse podocyte clone (MPC5). Immunofluorescence staining, double-immunolabeling, confocal microscopy, semiquantitative reverse transcription polymerase chain reaction (RT-PCR), and Western blotting were used to detect the distribution and expression of podocin, nephrin, α-actinin-4, and glyseraldehyde-3-phosphate dehydrogenase (GAPDH)/β-actin. The fluorescence intensity of podocin and nephrin decreased obviously, along with the evident distribution change from the cell membrane surface to the nucleus circumference in podocyte. In relation to GAPDH, the mRNA reductions of podocin and nephrin were observed by about 65% and 70%, respectively. The expression of podocin protein was too low to be detected in the interference group. In relation to β-actin, the protein level of nephrin decreased by about 78%. The distribution and the mRNA and protein level of α-actinin showed no appreciable change. Alpha-actinin localized mainly in the cytoplasm and also extended to the processes. Thus, the significant decreased expression of nephrin along with the redistribution were detected with the knockdown of podocin mRNA, whereas the expression and distribution of α-actinin-4 showed no change. These results suggest that podocin may interact directly with nephrin, but not with α-actinin.

Over-expressing transient receptor potential cation channel 6 in podocytes induces cytoskeleton rearrangement through increases of intracellular Ca2+ and RhoA activation:

Transient receptor potential cation channel 6 (TRPC6) is one of the key molecules for filtration barrier function of podocytes. Over-expression of TRPC6 in podocytes is frequently found in acquired or inherited proteinuric kidney diseases, and animal model over-expression of TRPC6 may lead to proteinuria. To investigate the impact of TRPC6 over-expression in podocytes on its function and its relation to proteinuria in kidney diseases, we over-expressed TRPC6 in mouse podocytes by transient transfection of TRPC6 cDNA plasmid, and observed their changes in foot processes, intracellular F-actin distribution, nephrin and synaptopodin expression, electrophysiology, RhoA activity and intracellular Ca2+ . In podocytes over-expressing TRPC6, cell processes were reduced remarkably in association with the derangement of cytoskeleton demonstrated by the abnormal distribution of intracellular F-actin. These cells also displayed a higher increase of intracellular Ca2+ ion to the TRPC6 agonist 1-oleoyl-acetyl-sn-glycerol and a higher current in the patch-clamp experiment, down-regulation of nephrin and synaptopodin expression and increase of activated RhoA. These changes could be rescued by the treatment of the cells with U73122 to block TRPC6 channel or BAPTA-AM to chelate intracellular Ca2+ ion. Additionally, the podocytes over-expressing TRPC6 treated with RhoA inhibitor Y-27632 showed an improvement in F-actin arrangement in the cells and increase of nephrin and synaptopodin expression. From these results, we therefore propose that over-expression of TRPC6 in podocytes may be one of the fundamental changes relating to the dysfunction of the slit diaphragm and proteinuria. Podocytes over-expressing TRPC6 may lead to higher intracellular Ca2+ ion concentration in the presence of stimuli. The increase of intracellular Ca2+ down-regulates the expression of two important molecules, nephrin on slit diaphragm and synaptopodin in cytoskeleton, and stimulates RhoA activity, which in turn causes F-actin derangement and the decrease of foot processes.

Diversities of podocyte molecular changes induced by different antiproteinuria drugs.

Nephrin, podocin, CD2AP, and α-actinin-4 are important podocyte proteins that help maintain the integrity of the slit diaphragm and prevent proteinuria. Studies have shown that angiotensin-converting enzyme inhibitors, glucocorticoids, and all-trans retinoic acid (ATRA) have antiproteinuric effects. However, it is still unclear whether these drugs, with different pharmacological mechanisms, lead to a reduction in proteinuria by changing the expression and distribution of these important podocyte proteins. In this study, changes in the expression and distribution of nephrin, podocin, CD2AP, and α-actinin-4 were dynamically detected in Adriamycin-induced nephrotic (ADR) rats treated with three different drugs: lisinopril, prednisone, and ATRA. Nephropathy was induced by an intravenous injection of Adriamycin. After Adriamycin injection, rats received lisinopril, prednisone, and ATRA treatment, respectively. Renal tissues were collected at Days 3, 7, 14, and 28. The distribution and the expression of messenger RNA and protein of nephrin, podocin, CD2AP, and a-actinin-4 were detected by indirect immunofluorescence, real-time polymerase chain reaction, and Western blotting, respectively. With the intervention of lisinopril, prednisone, and ATRA, changes in the expression of nephrin, podocin, and CD2AP were diverse, which was different from that detected in ADR rats. After lisinopril and prednisone intervention, podocin exhibited prominent earlier changes compared with those of nephrin and CD2AP, whereas CD2AP showed more prominent changes after ATRA intervention. There was no change in the expression of α-actinin-4 molecule. In summary, we conclude that the antiproteinuric effects of lisinopril, prednisone, and ATRA were achieved by changes in the expression and distribution of the important podocyte molecules nephrin, podocin, CD2AP, and α-actinin-4. The pattern in the change of podocyte molecules after lisinopril and prednisone intervention was similar, but the pattern in the change of podocyte molecules after ATRA intervention was different from that of lisinopril or prednisone intervention.

The activation of extracellular signal-regulated kinase is responsible for podocyte injury.

Podocyte and its slit diaphragm play an important role in maintaining normal glomerular filtration barrier function and structure. Podocyte apoptosis and slit diaphragm injury leads to proteinuria and glomerulosclerosis. However, the molecular mechanism of podocyte injury remains poorly understood. The family of mitogen-activated protein kinases including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase, and p38 signal pathways, are implicated in the progression of various glomerulopathies. However, the role of the activated signal pathway(s) in podocyte injury is elusive. This study examined phosphorylation of ERK in rat puromycin aminonucleoside (PAN) nephropathy as well as conditionally immortalized mouse podocyte treated with PAN in vitro. The effect of treatment with U0126, an inhibitor of ERK, was also investigated. In PAN nephropathy, the phosphorylation of ERK was marked. In podocyte injury, the marked and sustained activation of ERK pathway was also observed before the appearance of significant podocyte apoptosis. Pretreatment with U0126 to podocyte completely inhibited ERK activation, with complete suppression podocyte apoptosis and ameliorated nephrin protein expression along with the phosphorylation of nephrin in podocyte injury. In cultured podocyte, PAN induced actin recorganition, and U0126 inhibited such change. However, U0126 did not recovery the phosphorylation change of neph1 in podocyte injury. We concluded that the sustained activation of ERK along with the phosphorylation of neph1 might be necessary for podocyte injury. The study here suggested that ERK might become a potential target for therapeutic intervention to prevent podocytes from injury which will result in proteinuria.

The first Chinese Pierson syndrome with novel mutations in LAMB2

BACKGROUND Pierson syndrome is typically manifested with congenital nephrotic syndrome (CNS) and peculiar ocular changes. LAMB2 was the causative gene. METHODS A 3.25-year-old girl presenting with childhood-onset heavy proteinuria, bilateral myosis and nystagmus was detected on mutations of LAMB2 gene by PCR direct sequencing. RESULTS Two novel mutations were identified, C757fsX767 and P1413fsX1451, which predicted truncated proteins and were confirmed in the paternal and maternal origins, respectively. CONCLUSIONS This is the first Chinese case of Pierson syndrome diagnosed by clinical manifestations and LAMB2 gene mutations. The phenotype may be different in different ethics.

Reduction in VEGF Protein and Phosphorylated Nephrin Associated with Proteinuria in Adriamycin Nephropathy Rats

Background/Aims: The relationship between vascular endothelial growth factor (VEGF) and the phosphorylated critical podocyte slit diaphragm molecule nephrin is not fully clarified. This study investigated the dynamic changes in VEGF expression and nephrin phosphorylation, and the effects of the antiproteinuric drugs prednisone and lisinopril on them in Adriamycin nephropathy rats. Methods: Renal tissues from Adriamycin rats were collected at days 3, 7, 14, and 28. Distribution and expression of VEGF was revealed by immunohistochemistry, real-time PCR and Western blot. Phosphorylated nephrin was evaluated by immunoprecipitation. Results: A discontinuous redistribution of VEGF was displayed at day 3, followed by significant protein reduction at day 7 with persistent downregulation to day 28. Phosphorylated nephrin decreased evidently at day 14 and persisted to day 28. The reduction in VEGF and phosphorylated nephrin was not a result of podocyte loss. The intervention of prednisone and lisinopril evidently reduced proteinuria, effectively attenuated the severe lesions of podocyte foot processes, and restored the reduction in VEGF and nephrin phosphorylation. At day 28, the reduction in VEGF and phosphorylated nephrin was negatively correlated with proteinuria, whereas the phosphorylated nephrin was positively correlated with VEGF protein from day 7 to day 28. Conclusion: The reduction in VEGF protein and nephrin phosphorylation was possibly involved in the proteinuria in Adriamycin rats, and there might be some relationship between VEGF and nephrin phosphorylation. The antiproteinuric effects of lisinopril and prednisone were achieved at least partially by restoring VEGF protein and nephrin phosphorylation.

WT1 gene mutations in Chinese children with early onset nephrotic syndrome.

In Chinese children with steroid-resistant nephrotic syndrome (SRNS), it was reported that NPHS2 mutation was detected in 4.3%, which was lower than that in Caucasians (10–30%). However, there were no data on WT1 mutation in nephrotic syndrome (NS), especially in early-onset NS of Chinese children. Thus, a study, which enrolled 36 Chinese children with early-onset (before 3 y old) NS and steroid resistance if failing steroid therapy (early-group), was conducted. As control, 35 children with SRNS and with disease onset age after 3 y old were also analyzed (control-group). WT1 gene was examined by PCR and direct sequencing. The result showed that in the early-group 6/36 (16.7%) were detected with WT1 mutations. Further analysis according to different onset age revealed that the mutation detection rates of WT1 were 26.3% (5/19), 6.3% (1/16), and 0 (0/1) in children younger than 1 y, 1–2 y, and 2–3 y, respectively. In control-group, no WT1 (0/35) mutation was detected. WT1 mutation combined with NPHS2 variant was detected in a girl. In conclusion, WT1 mutations seemed more common in Chinese children with early-onset NS.

R168H and V165X mutant podocin might induce different degrees of podocyte injury via different molecular mechanisms

A lot of mutations of podocin, a key protein of podocyte slit diaphragm (SD), have been found both in hereditary and sporadic focal segmental glomeruloscleorosis (FSGS). Nevertheless, the mechanisms of podocyte injury induced by mutant podocins are still unclear. A compound heterozygous podocin mutation was identified in our FSGS patient, leading to a truncated (podocin V165X) and a missense mutant protein (podocin R168H), respectively. Here, it was explored whether and how both mutant podocins induce podocyte injury in the in vitro cultured podocyte cell line. Our results showed that podocin R168H induced more significant podocyte apoptosis and expression changes in more podocyte molecules than podocin V165X. Podocyte injury caused by the normal localized podocinV165X was effectively inhibited by TRPC6 knockdown. The abnormal retention of podocinR168H in endoplasmic reticulum (ER) resulted in the mis‐localizations of other critical SD molecules nephrin, CD2AP and TRPC6, and significantly up‐regulated ER stress markers Bip/grp78, p‐PERK and caspase‐12. These results implicated that podocin R168H and podocin V165X induced different degrees of podocyte injury, which might be resulted from different molecular mechanisms. Our findings provided some possible clues for further exploring the pharmacological targets to the proteinuria induced by different mutant podocins.