Na Guan

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.

Key molecular events in puromycin aminonucleoside nephrosis rats

Nephrin, podocin and α‐actinin are all involved in proteinuria, but it is unclear which molecular event plays a crucial role during the development of proteinuria. Immunofluorescence staining and real‐time quantitative polymerase chain reaction were used to study the glomerular expression of these molecules in puromycin aminonucleoside (PAN) nephrosis. Morphometric methods were applied to evaluate the podocyte foot process (FP) morphology. Two days after PAN injection, nephrin and podocin staining became discontinuous, podocin intensity decreased and FP swelled. Nephrin protein and mRNA decreased at day 5. Both podocin and nephrin intensity decreased dramatically when heavy proteinuria occurred, but nephrin mRNA was regained. When proteinuria disappeared, podocin recovered whereas nephrin did not (P = 0.02); α‐actinin intensity increased (P = 0.009) and the distribution changed. The podocyte FP volume density correlated negatively with nephrin (r = −0.78, P = 0.0001) and podocin immunofluorescence intensity (r = −0.76, P = 0.0001). We conclude that, before the onset of proteinuria, the first response was the nephrin and podocin distribution change, podocin protein decrease and swollen FP; the podocin quantitative change was earlier than nephrin. Podocin and nephrin distribution and the protein level was associated with proteinuria more closely than their mRNA level. The delayed α‐actinin induction might be a reparative response.

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.

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 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.

Protective role of cyclosporine A and minocycline on mitochondrial disequilibrium-related podocyte injury and proteinuria occurrence induced by adriamycin

BACKGROUND Dysfunction of mitochondria is involved in podocyte injury in some kidney diseases, but the relationship between abnormal mitochondrial morphology and podocyte injury as well as the underlying mechanism is still unclear. This study aims to investigate dynamic changes of mitochondrial morphology and the potential molecular events in an adriamycin (ADR)-induced podocyte injury model. METHODS Podocyte apoptosis was evaluated by annexin V assay. Podocyte mitochondrial membrane potential (MMP) was measured with MitoCapture kit. Double staining was used to show the distribution changes of mitochondria and actin filament as well as mitofusin proteins and podocin. Mitochondrial shape descriptors were obtained using analySIS Image system. Effects of cyclosporine A (CsA) or minocycline (Mcy) on mitochondrial morphology were explored in ADR-induced nephropathy rats. RESULTS ADR caused podocyte damage displaying as induction of cellular apoptosis and increase of activated caspase 3 and cytochrome c. The MMP level was decreased remarkably in ADR-treated podocytes. Mitochondrial morphological changes induced by ADR occurred rapidly from large and ellipsoid shape to the small, long and irregular. ADR significantly decreased surface area, perimeter and circularity, while increasing aspect ratio of mitochondria. In addition, mitochondria number transiently increased at 6 h following ADR application. Mitochondria intensity was increased along with punctate mitochondria formation, which co-localized with polymerized actin cytoskeleton in ADR podocytes. In ADR-induced nephropathy rats, 24-h proteinuria was decreased significantly by CsA or Mcy. ADR-induced abnormal changes of mitochondrial morphology were restored by CsA or Mcy. The induction of mitofusin proteins and the reduction of podocin in ADR rat glomeruli were rescued by CsA or Mcy. CONCLUSIONS Mitochondrial dysfunction may be an early event in ADR-induced podocyte damage, and the protective role of CsA or Mcy may be mediated partially by improving mitochondrial function through inhibiting the induction of mitofusin proteins.

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.

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.

Antigen retrieval with protease digestion applied in immunohistochemical diagnosis of Alport syndrome

BACKGROUND Immunofluorescence (IF) staining of type IV collagen alpha chains on fresh frozen renal tissue is a convenient and accurate diagnosis technique for Alport syndrome (AS), which is restricted in the application with a non-frozen section. An alternative method for a paraffin-embedded section is needed in order to extend the application in various specimens. In this study, immunohistochemical staining of type IV collagen alpha chains on paraffin-embedded renal sections was investigated. METHODS Three antigen retrieval methods including autoclave heating, pepsin digestion and protease digestion were tried on paraffin-embedded renal sections from two X-linked male AS patients, two X-linked female AS patients and two autosomal recessive AS patients. Two patients with isolated haematuria were also involved. Normal portions of nephrectomized kidneys from two patients with renal tumours were used as controls. The immunohistochemical staining pattern of type IV collagen was compared with that of IF staining. RESULTS The results showed that both the autoclave heating method and protease digestion can be used for antigen retrieval for type IV collagen alpha chains. Compared to autoclave heating, protease digestion had the advantage of being less time consuming, with less renal sections being lost from the slides; it was the most optimal antigen retrieval method in this study. After protease digestion for 40 min, type IV collagen alpha3 and alpha5 chains showed a clear and proper distribution pattern in AS patients, haematuria patients and controls, which is the same as that of IF staining. CONCLUSIONS Compared to the autoclave heating method, protease antigen retrieval is more convenient and effective and can be used to restore type IV collagen alpha chains on paraffin-embedded renal sections for the diagnosis of AS.

IP 3 R-Grp75-VDAC1-MCU calcium regulation axis antagonists protect podocytes from apoptosis and decrease proteinuria in an Adriamycin nephropathy rat model

BackgroundThe mechanism of podocyte apoptosis is not fully understood. In addition, the role of the inositol 1,4,5-triphosphate receptor (IP3R)/glucose-regulated protein 75 (Grp75)/voltage-dependent anion channel 1 (VDAC1)/mitochondrial calcium uniporter (MCU) calcium regulation axis, which is located at sites of endoplasmic reticulum (ER) mitochondria coupling, in the mechanism of podocyte apoptosis is unclear. This study aimed to understand the roles of this axis in podocyte apoptosis and explore potential targets for podocyte protection.MethodsThe expression of IP3R, Grp75, VDAC1, and MCU and mitochondrial Ca2+ were analyzed during Adriamycin- or angiotensin II-induced apoptosis in cultured mouse podocytes. The interaction between IP3R, Grp75, and VDAC1 was investigated using co-immunoprecipitation experiments. The effects of IP3R, Grp75, and MCU agonists and antagonists on mitochondrial Ca2+ and apoptosis were investigated in cultured podocytes. The podocyte-protective effects of an MCU inhibitor were further investigated in rats with Adriamycin-induced nephropathy.ResultsIncreased expression of IP3R, Grp75, VDAC1 and MCU, enhanced interaction among the IP3R-Grp75-VDAC1 complex, mitochondrial Ca2+ overload, and increased active caspase-3 levels were confirmed during Adriamycin- or angiotensin II-induced mouse podocyte apoptosis. Agonists of this axis facilitated mitochondrial Ca2+ overload and podocyte apoptosis, whereas specific antagonists against IP3R, Grp75, or MCU prevented mitochondrial Ca2+ overload and podocyte apoptosis. A specific MCU inhibitor prevented Adriamycin-induced proteinuria and podocyte foot process effacement in rats.ConclusionsThis study identified a novel pathway in which the IP3R-Grp75-VDAC1-MCU calcium regulation axis mediated podocyte apoptosis by facilitating mitochondrial Ca2+ overload. Antagonists that inhibit Ca2+ transfer from ER to mitochondria protected mouse podocytes from apoptosis. An MCU inhibitor protected podocytes and decreased proteinuria in rats with Adriamycin-induced nephropathy. Therefore, antagonists to this pathway have promise as novel podocyte-protective drugs.